Exploratory Study: Vitamin D and COVID 19 – Evidence for Prevention and Treatment
This is an exploratory study based on the work that Professor Roger Seheult MD has shared through his Med Cram bulletin and Dr John Campbell. It can be viewed as an exercise in investigatory method and exploratory study exploring what underlying biochemical mechanisms might offer accounts of the therapeutic observations which Prof Seheult and Dr Cambell are discussing.
As an educational and learning perspective science and medicine is a part of common experience and knowledge commons which belongs to everyone. This stands in contrast to the perspective that only those with special status have the capability to engage in these fields of knowledge. In many ways it is important for individuals to become informed about their health and wellbeing taking time to understand the principles which underpin how we know what we think we know.
In this situation it relates to a public health bulletin offered from a well respected medical doctor and educator in relation to the Covid 19 pandemic. Professor Roger Seheult, MD is an Associate Professor at the University of California, Riverside School of Medicine and Assistant Prof. at Loma Linda University School of Medicine. Dr. Seheult is Quadruple Board Certified in the areas of Internal Medicine, Pulmonary Disease, Critical Care, and Sleep Medicine. He is the co-founder and lead professor at Medcram (https://www.medcram.com)
Prof Seheult Literature Review
In the video Professor Roger Seheult, MD explains the important role Vitamin D may have in the prevention and treatment of COVID-19. Dr. Seheult summarizes the best available data and clinical trials on vitamin D, and discusses vitamin D dosage recommendations. Along with the video he shares the sources of knowledge which he is reporting on:
- Klepeis, Neil & Nelson, William & Ott, Wayne & Robinson, John. (2001). The National Human Activity Pattern Survey (NHAPS): A Resource for Assessing Exposure to Environmental Pollutants: Download Link
- MacLaughlin J, Holick MF. Aging decreases the capacity of human skin to produce vitamin D3. J Clin Invest. 1985 Oct;76(4):1536-8. doi: 10.1172/JCI112134. PMID: 2997282; PMCID: PMC424123: Download Link
- Gutiérrez, O. M., Farwell, W. R., Kermah, D., & Taylor, E. N. (2011). Racial differences in the relationship between vitamin D, bone mineral density, and parathyroid hormone in the National Health and Nutrition Examination Survey. Osteoporosis international : a journal established as result of cooperation between the European Foundation for Osteoporosis and the National Osteoporosis Foundation of the USA, 22(6), 1745–1753: Download Link
- Jacobo Wortsman, Lois Y Matsuoka, Tai C Chen, Zhiren Lu, Michael F Holick, Decreased bioavailability of vitamin D in obesity, The American Journal of Clinical Nutrition, Volume 72, Issue 3, September 2000, Pages 690–693: Download Link
- Brenner H, Holleczek B, Schöttker B. Vitamin D Insufficiency and Deficiency and Mortality from Respiratory Diseases in a Cohort of Older Adults: Potential for Limiting the Death Toll during and beyond the COVID-19 Pandemic? Nutrients. 2020; 12(8):2488. Download Link
- Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data
- Urashima M, Segawa T, Okazaki M, Kurihara M, Wada Y, Ida H. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. Am J Clin Nutr. 2010 May;91(5):1255-60. doi: 10.3945/ajcn.2009.29094. Epub 2010 Mar 10. PMID: 20219962: Download Link
- McCartney, D.M., O’Shea, P.M., Faul, J.L. et al. Vitamin D and SARS-CoV-2 infection—evolution of evidence supporting clinical practice and policy development. Ir J Med Sci (2020). https://doi.org/10.1007/s11845-020-02427-9: Download Link
- Williamson, E.J., Walker, A.J., Bhaskaran, K. et al. Factors associated with COVID-19-related death using OpenSAFELY. Nature 584, 430–436 (2020). https://doi.org/10.1038/s41586-020-2521-4: Download Link
- Rhodes JM, Subramanian S, Laird E, Kenny RA. Editorial: low population mortality from COVID-19 in countries south of latitude 35 degrees North supports vitamin D as a factor determining severity. Aliment Pharmacol Ther. 2020 Jun;51(12):1434-1437. doi: 10.1111/apt.15777. Epub 2020 Apr 28. PMID: 32311755; PMCID: PMC7264531: Download Link
- Ilie, P. C., Stefanescu, S., & Smith, L. (2020). The role of vitamin D in the prevention of coronavirus disease 2019 infection and mortality. Aging clinical and experimental research, 32(7), 1195–1198. https://doi.org/10.1007/s40520-020-01570-8: Download Link
- D’Avolio A, Avataneo V, Manca A, Cusato J, De Nicolò A, Lucchini R, Keller F, Cantù M. 25-Hydroxyvitamin D Concentrations Are Lower in Patients with Positive PCR for SARS-CoV-2. Nutrients. 2020; 12(5):1359: Download Link
- Smolders, J., van den Ouweland, J., Geven, C., Pickkers, P., & Kox, M. (2021). Letter to the Editor: Vitamin D deficiency in COVID-19: Mixing up cause and consequence. Metabolism: clinical and experimental, 115, 154434. https://doi.org/10.1016/j.metabol.2020.154434: Download Link
- Merzon E, Tworowski D, Gorohovski A, Vinker S, Golan Cohen A, Green I, Frenkel-Morgenstern M. Low plasma 25(OH) vitamin D level is associated with increased risk of COVID-19 infection: an Israeli population-based study. FEBS J. 2020 Sep;287(17):3693-3702. doi: 10.1111/febs.15495. Epub 2020 Aug 28. PMID: 32700398; PMCID: PMC7404739: Download Link
- Israel, A., Cicurel, A., Feldhamer, I., Dror, Y., Giveon, S. M., Gillis, D., Strich, D., Lavie, G., The link between vitamin D deficiency and Covid-19 in a large population, MedRivXiv: Download Link
- Kaufman HW, Niles JK, Kroll MH, Bi C, Holick MF (2020) SARS-CoV-2 positivity rates associated with circulating 25-hydroxyvitamin D levels. PLoS ONE 15(9): e0239252: Download Link
- Baktash, V., Hosack, T., Patel, N., Shah, S., Kandiah, P., Van den Abbeele, K., Mandal, A., & Missouris, C. G. (2020). Vitamin D status and outcomes for hospitalised older patients with COVID-19. Postgraduate medical journal, postgradmedj-2020-138712. Advance online publication: Download Link
- Radujkovic A, Hippchen T, Tiwari-Heckler S, Dreher S, Boxberger M, Merle U. Vitamin D Deficiency and Outcome of COVID-19 Patients. Nutrients. 2020; 12(9):2757: Download Link
- Entrenas Castillo, M., Entrenas Costa, L. M., Vaquero Barrios, J. M., Alcalá Díaz, J. F., López Miranda, J., Bouillon, R., & Quesada Gomez, J. M. (2020). “Effect of calcifediol treatment and best available therapy versus best available therapy on intensive care unit admission and mortality among patients hospitalized for COVID-19: A pilot randomized clinical study”. The Journal of steroid biochemistry and molecular biology, 203, 105751: Download Link
- Annweiler, C., Hanotte, B., Grandin de l’Eprevier, C., Sabatier, J. M., Lafaie, L., & Célarier, T. (2020). Vitamin D and survival in COVID-19 patients: A quasi-experimental study. The Journal of steroid biochemistry and molecular biology, 204, 105771: Download Link
- Igor H. Murai, Alan L. Fernandes, Lucas P. Sales, Ana J. Pinto, Karla F. Goessler, Camila S. C. Duran, Carla B. R. Silva, André S. Franco, Marina B. Macedo, Henrique H. H. Dalmolin, Janaina Baggio, Guilherme G. M. Balbi, Bruna Z. Reis, Leila Antonangelo, Valeria F. Caparbo, Bruno Gualano, Rosa M. R. Pereira, Effect of Vitamin D3 Supplementation vs Placebo on Hospital Length of Stay in Patients with Severe COVID-19: A Multicenter, Double-blind, Randomized Controlled Trial, medRxiv 2020.11.16.20232397: Download Link
- Rastogi A, Bhansali A, Khare N, et al, Short term, high-dose vitamin D supplementation for COVID-19 disease: a randomised, placebo-controlled, study (SHADE study), Postgraduate Medical Journal Published Online First: 12 November 2020: Download Link
- Meltzer DO, Best TJ, Zhang H, Vokes T, Arora V, Solway J. Association of Vitamin D Status and Other Clinical Characteristics With COVID-19 Test Results. JAMA Netw Open. 2020;3(9):e2019722. doi:10.1001/jamanetworkopen.2020.19722: Download Link
- Michael F. Holick, Neil C. Binkley, Heike A. Bischoff-Ferrari, Catherine M. Gordon, David A. Hanley, Robert P. Heaney, M. Hassan Murad, Connie M. Weaver, Evaluation, Treatment, and Prevention of Vitamin D Deficiency: an Endocrine Society Clinical Practice Guideline, The Journal of Clinical Endocrinology & Metabolism, Volume 96, Issue 7, 1 July 2011, Pages 1911–1930: Download Link
- Itkonen, S. T., Erkkola, M., & Lamberg-Allardt, C. (2018). Vitamin D Fortification of Fluid Milk Products and Their Contribution to Vitamin D Intake and Vitamin D Status in Observational Studies-A Review. Nutrients, 10(8), 1054: Download Link
- Jain, A., Chaurasia, R., Sengar, N.S. et al. Analysis of vitamin D level among asymptomatic and critically ill COVID-19 patients and its correlation with inflammatory markers. Sci Rep 10, 20191 (2020): Download Link
Dr John Cambell Examines Correlations
In the video Dr John Campbell discusses some of the studies which have been done on vitamin D in relation to the covid 19 pandemic as a part of his regular Youtube tutorials exploring medical principles and emerging research. Along with the video he shares the sources of knowledge which he is reporting on along with edified notes:
- Hao Ma, Tao Zhou, Yoriko Heianza, Lu Qi, Habitual use of vitamin D supplements and risk of coronavirus disease 2019 (COVID-19) infection: a prospective study in UK Biobank, The American Journal of Clinical Nutrition, Volume 113, Issue 5, May 2021, Pages 1275–1281, https://doi.org/10.1093/ajcn/nqaa381
- Radujkovic, Aleksandar; Hippchen, Theresa; Tiwari-Heckler, Shilpa; Dreher, Saida; Boxberger, Monica; Merle, Uta. 2020. “Vitamin D Deficiency and Outcome of COVID-19 Patients” Nutrients 12, no. 9: 2757. https://doi.org/10.3390/nu12092757
The Politicisation of Knowledge vs Knowledge Building as a Shared Activity
As you can see in the videos above and from reviewing the papers which they have been scrutinizing, there is a significant body of evidence suggesting that vitamin D has an important role in improving health outcomes for people with regards to covid 19 viral infection. What I am particularly interestested in exploring is the forms of evidence which are available to test an idea (falsify a given hypothesis).
Falsification is the word used in the philosophy of science to refer to the process by which we establish how reliable a hypothesis is – in other words how reliable an idea about something is when it is tested. The philosophy of science examines the principles of ‘how do we know what we think we know ?’. How do we know the world is round or flat ? How do we test a ‘knowledge claim ‘ ? This is where we get into the process of testing for proofs.
Science is the search for increasingly reliable knowledge and is not special to any one person; doctors and scientists etc dont have magical powers – they are quite ordinary people. The processes of science are rooted in the way we encounter our everyday experience. How do I know that when I strike a match fire will be produced ? An account based on logical principles moves us from superstition and fantasies of magic to science – knowledge which is repeatably testable and which can be demonstrated in some practical way.
The skills of science are increasingly important in this information age in which media encourages fiction, opinion and disagreement as a source of revenue. Exercising the skills of testing truth claims (hypotheses) is important in a pecuniary age (relating to or consisting of money) and in a species which can be obsessed with social status. There are plenty of people in the world ready to sell you any old thing with the promise that it will do what you desire. Not only this but human beings also have a special talent for convincing themselves that the ideas they have are the correct ones, more correct than others and at the expense of finding the most appropriate responses.
Human interference with truer apprehension of the universe comes in many forms. The creation of prizes generates bizarre cultures which exceptionalise one individual over another, one group over another. There are countless examples where human beings have declared themselves paladins – special representatives who alone can understand what others cannot. This is a kind of cult thinking Prof Arthur Deikman suggests is a characteristic which runs through society and is bound up with attaining special status over others.
Medicine, because of its importance, attracts this kind of behaviour and medical knowledge often becomes politicised due to the affect it evokes. Ingroups and outgroups are formed drawing people into argumentation and away from the process of establishing the truth of a claim. Around big health issues pantomimes can take place, not necessarily because something cannot be understood but because people have become polarized against the idea of identifying with and relating to the group they feel outside of. This is a disaster in terms of science which equals the disaster of the effects on money on science.
Prof Arthur Deikman examines this kind of behaviour in his book ‘The Wrong Way Home; Uncovering The Patterns of cult Behavior in American Society‘. In this book (which has relevance to many more places than America) he identifies the following characteristics as defining cult behaviour:
Compliance with the Group
Dependence on a Leader
Devaluing the Outsider
These characteristics interface in an interesting way with the characteritics of pseudoskepticism which were laid out in a commentary by Prof Marcello Truzzi to describe ‘critics who take the negative rather than an agnostic position but still call themselves “skeptics”‘. The characteristics of peseudoskepticism Marcello wrote about were helpfully distilled into the following:
- Denying, when only doubt has been established
- Double standards in the application of criticism
- The tendency to discredit rather than investigate
- Presenting insufficient evidence or proof
- Assuming criticism requires no burden of proof
- Making unsubstantiated counter-claims
- Counter-claims based on plausibility rather than empirical evidence
- Suggesting that unconvincing evidence provides grounds for completely dismissing a claim
The shifting of the locus of understanding from a shared activity of building knowledge to a winning of opinion represents a politicisation of knowledge – the ends of the means has shifted from ‘coming to know’ to ‘success in argument’. The enterprise has become about holding sway over a public body, a group of people, rather than getting at what is actually true; as such the exercise which does this slips category to exercises of rhetoric, eristics and argumentation.
No matter what the argument or captivating charisma of a speaker or group, its staus or special claim, the human arts do not change the nature of the material universe, they only alter our thoughts about it. Having the opinion that diabetes mellitus is an ailment brought about by clog dancing does not make it so, despite the wilingness of someone attempting to compell an audience. If the audience believes it is so, it does not make it so, even if it is an audience the size of a country.
Getting Beyond Opinion
For our purposes here and now I am more interested in examining the tools we have available to us to get at and test obscure knowledge claims – ones which medicine often develops. When I say obscure, I mean not immediately visible; not apparent to the naked eye. For example, how do we know that cells divide using the mechanisms of deoxyribonucleic acid (DNA) ? We cannot see it with the naked eye. If you are interested in reading more about ideas associated with the philosophy of science you can find them HERE.
To paraphrase Richard Feynman said ‘Science is a system we have developed to keep us from fooling ourselves’. Large cultures have become organised over millenia to assist us in avoiding fooling ourselves which involve all manner of methods. Various forms of getting people to check each others work has been the backbone of how we collectively generally improve the quality of information we have available to us.
Certain methods like doing blind trials have been important at points to ensure that the outcome of tests and experiments are neutrally arrived at. Most significantly though is the research process of building up of a research base – that is, finding properly reported on evidence which supports or undermines a particular proposition. This can be done through cross-referencing published work or be done through cross-referencing physical tests of the idea.
Correlations with Biochemical Understandings
Here I am going to do a rudimentary examination of what is known about the biochemistry of vitamin D – a long known and profoundly well studied natural molecule which has distinct medical properties. The findings of the studies which Prof Seheult and Dr Cambell highlight in their discussions prompt the need to find a rationale of how it is working.
In the search for therapeutic substances there is typically the discussion about what the ‘mechanism of action’ is. The textbook Rang and Dale’s Pharmacology is well used in medicine for teaching and learning about substances used to treat illnesses and symptoms. Multiple editions have brought together a range of information which enables the learner to understand what a substance is, the effects it has on the body, how it is used and how it is working in the natural chemistry of the body tissues.
The Rang and Dale textbook is a good representation of the ongoing project of medicine and over time more information is added as new techniques and technology for studying biochemistry emerge, new substances become understood as being helpful in medicine, and as agreement forms over time. For the purposes of researching what the mechanism of action could be for vitamin D acting in the situation of covid 19 I am using the following textbook:
Vitamin D. Edited by Feldman, D., Pike, J. W., & In Bouillon, R. (2018). Elsevier Inc.
ISBN: 978-0-12-381978-9 Two Volume Set
In this analysis I am going to be taking some verbatim excerpts from the textbook which offer possible accounts for the mechanism of action of vitamin D supplementation in respect to covid 19. This is a knowledge exercise aimed to draw out conversation about the above respected scientists and physicians due to a seeming lack of focus on important findings which have a bearing on public wellbeing.
I have included the page number where the excerpt is found and expand many of the acronyms used for the sake of clarity as well as to interrupt the culture of abbreviation which I believe helps to obscure understanding. I use supplementary sense making notes in bold to give the reader a sense of how I am parsing the information. Each excerpt has been sectioned off to aid the digestion of the information stepwise.
Vitamin D Biochemistry
Page 33: Uptake of 25-hydroxyvitamin D3 bound to its blood carrier vitamin-D-binding protein (DBP), allows the cells to then manufacture 1a,25-dihydroxyvitamin D3, which in turn stimulates vitamin D receptor-mediated gene transcription of cathelicidin. Cathelicidin is an antimicrobial peptide, which specifically kills mycobacterium tuberculosis.
Vitamin D stimulates the body to make the antimicrobial peptide cathelidicin. Cathelicidin is capable of killing tubercolosis.
Page 595: The critical involvement of the innate immune system has been demonstrated in the role of myocbacterial tuberculosis infection in humans where toll-like receptor 2 (TLR2) could increase 1a,25-dihydroxyvitamin D3 production and, with 1a,25-dihydroxyvitamin D3, stimulate expression of the antibacterial protein cathelicidin , resulting in vitamin-D-promoted monocyte killing of mycobacterium tuberculosis . Thus, mechanistically, 1a,25-dihydroxyvitamin D3 can stimulate the innate immune system and strengthen the antimicrobial function of monocytes and macrophages, for example through enhanced expression of cathelicidin, eventually leading to better clearance of pathogenic microorganisms and thus to prevention of increased susceptibility to infections.
Vitamin D is critically involved in the innate immune system and has been demonstrated to play an active role in fighting tuberculosis infection. It does this by stimulating the production of antibacterial protein cathelicidin and strengthening the white blood cells (monocytes and macrophages) involved in clearing infections.
Page 880: In times gone by vitamin D was advocated in the treatment of a great variety of conditions, including tuberculosis (especially lupus vulgaris), sarcoidosis, rheumatoid arthritis, hay fever, chilblains, and asthma.
Historically vitamin D has been used in medicine to treat a variety of conditions
Page 1078: A very large number of genes involved in the immune system, from antigen-presenting cells to B cells and all subclasses of T cells express the vitamin D receptor at some stage of their development. Monocytes and macrophages also express (extra-renal) CYP27B1 when appropriately stimulated by several immune signals [86,87] so that they can locally produce the 1a,25-dihydroxyvitamin D3 hormone now functioning as an autocrine/paracrine immune regulator. Indeed, the immune cells are clear targets of 1a,25-dihydroxyvitamin D3 action with a different action on the native and acquired immune system.
A large number of genes involved in the immune system express the vitamin D receptor. Genes create proteins which perform specific functions in the body. Vitamin D stimulates the production of a wide range of proteins involved in immunity associated with antigen-presenting cells, B cells, and all subclasses of T cells.
Monocytes and macrophage white blood cells produce 1a,25-dihydroxyvitamin D3 on demand when stimulated by immune signals. Vitamin D acts to regulate immune activity. 1a,25-dihydroxyvitamin D3 has different actions on the native and the acquired immune system.
The native immune system and more specifically monocytes/macrophages are stimulated by 1a,25-dihydroxyvitamin D3 and display enhanced antibacterial activities such as phagocytosis and bacterial killing. This was already observed many decades ago [88,89] but has more recently been better understood by the 1a,25-dihydroxyvitamin D3 effects on the expression of bactericidal natural defensins [90,91] (Table 58.4). By contrast 1a,25-dihydroxyvitamin D3 downregulates the activation and action of T helper-1 cells and thus decreases autoimmune reactions. This is further demonstrated by similar inhibitory effects on Th17 cells and stimulatory effects on Treg cells which by nature suppress T helper cells.
Vitamin D causes white blood cells – monocytes and macrophages – to exhibit enhanced antibacterial activities like phagocytosis (engulf and digest immune threats) and bacterial killing.
Vitamin D stimulates the production of defensins, a class of antibacterial proteins.
Vitamin D downregulates the activation and action of T helper-1 cells and T helper-17 cells consequently decreasing autoimmune reactions.
The overall picture is thus one of tapering down the acquired immune system and thus the risk of autoimmune diseases. In several experimental settings this has been confirmed either by using 1a,25-dihydroxyvitamin D3 itself or even better by using less calcemic agonists. The effects include reduction of autoimmune diabetes, experimental allergic encephalitis (a model for multiple sclerosis), inflammatory bowel disease, autoimmune nephritis models, and autoimmune prostatitis [30,86,92].
In experimental settings vitamin D is found to reduce autoimmune diabetes, experimental allergic encephalitis (a model for multiple sclerosis), inflammatory bowel disease, autoimmune nephritis models, and autoimmune prostatitis
From these preclinical studies it is clear that a link between the vitamin D endocrine system and the immune system and immune disorders is highly likely. Indeed a poor vitamin D status is frequently observed in patients with active tuberculosis but also in patients with other infections such as otitis media, upper respiratory infections, or COPD [93,94]. Intervention studies are, however, yet equivocal as one study in Indian tuberculosis patients revealed an accelerated sputum clearance by vitamin D supplementation  whereas a US study could not demonstrate a beneficial effect of vitamin D supplementation on the evolution of tuberculosis . Several clinical trials are, however, registered on the NIH clinical trial register so that one can expect a better understanding of the role of vitamin D for the innate immune system within the foreseeable future.
Low vitamin D levels have been noted in patients with tuberculosis, infections like otitis media, upper respiratory infections, and chronic obstructive pulmonary disease (COPD)
Many patients with autoimmune diseases have a lower vitamin D status than their healthy controls (e.g., type 1 diabetic patients, patients with multiple sclerosis or inflammatory bowel disease, etc.). The largest nested control study in US army recruits demonstrated that a low vitamin D status (defined by 25(OH)D levels below 20 ng/ml) at the time of recruitment to the US army conveyed a nearly two-fold risk of later onset of multiple sclerosis compared to Caucasians with a better vitamin D baseline level  and the lowest risk in subjects with 25(OH)D levels above 40 ng/ml.
Low vitamin D levels have been associated with the risk of later onset multiple sclerosis
Studies in the Netherlands also suggest that a poor vitamin D status predisposes to more frequent or severe relapses of multiple sclerosis [98,99]. For type 1 diabetes there are several retrospective studies indicating that vitamin D supplementation during early life reduces the later risk of developing this disease later in life  but as these studies were not designed for that purpose the quality of the data are not optimal. The overall reduction in incidence of type 1 diabetes by such intervention was about 30%. The dose needed for this effect has not been clearly defined but in one study up to 2000 IU per day during the first year of life was most effective and this dose is markedly higher than the presently accepted or recommended dose for infants (200e400 IU/d).
Low vitamin D status has been associated with autoimmune diseases like type 1 diabetes. Supplementation studies suggested that vitamin D can reduce incidence by around 30%
Infants and young children with rickets are prone to an increased number and severity of infections [59,112]. Although the increase in respiratory infections may be explained on the thoracic cage abnormalities (softening of the ribs, the enlarged costochondral junctions and the decreased thoracic movement due to muscle weakness), other reasons for the increase in diarrheal disease must be sought. The now well documented role of 1,25(OH)2D in modulating immune function [113,114] may contribute to the observed increase in infections (cf. Section XI of this book Immunity, Inflammation, and Disease). Impaired phagocytosis  and neutrophil motility  have been described in children with vitamin D deficiency rickets and the lack of production of cathelicidin following the activation of Toll-like receptors may play a role in predisposing vitamin-D-deficient subjects to M. tuberculosis infection . [Page 1111]
The syndrome of vitamin D deficiency is called rickets. Children with rickets display an increased number and severity of infections. Although the increase in respiratory infections theoretically could be due to mechanical alterations of the thoracic cage, this does not offer an account for the increase in diarrhea associated diseases.
Vitamin D is well documented as modulating immune function and deficiency has been suggested as being involved in increased infection.
In vitamin D deficiency impaired phagocytosis, neutrophil motility and failure of production of cathelicidin antimicrobial peptide is observed.
Page 1291: Vitamin D potentiates the innate immune system, and protects against bacterial infections and tuberculosis . Monocytes and macrophages produce 1,25(OH)2D, which has intracellular antimicrobial effects and can also interact with and govern the cytokine profiles of activated T and B lymphocytes in the local environment . The ability of monocytes and macrophages to synthesize sufficient 1,25(OH)2D is dependent on availability of adequate serum concentrations of 25(OH)D and therefore increases in response to vitamin D supplementation . When there is insufficient 25(OH)D immunity may be impaired because local production of 1,25(OH)2D will decline. Subsequent decreased binding of 1,25(OH)2D to the macrophage vitamin D receptor (VDR) will result in reduced antimicrobial activity against ingested microbes . The anti-microbial actions of 1,25(OH)2D also occur in barrier epithelial cells of the skin [19,20], gut , and lungs , sites which may be of particular importance to transplant recipients. Infections with herpes simplex virus-1 and Candida albicans, two common opportunistic infections in transplant patients, were reduced in animals treated with calcitriol . In a population study, upper respiratory tract infections were more common in individuals with lower 25(OH)D .
Vitamin D augments the activity of the innate immune system protecting the body against bacterial infection and tuberculosis.
Monocytes and macrophages produce vitamin D which has intracellular antimicrobial effects.
Vitamin D interacts with and governs the production of cytokines by activated T and B lymphocytes.
The ability of white blood cells to make 1a,25-dihydroxyvitamin D3 (the active form of vitamin D) they need depends on the amount of 25-hydroxyvitamin D3 available in the blood serum. Supplementation of vitamin D supports immune function.
The antimicrobial effects of vitamin D also occur in the epithelial cells of the skin, gut and lungs.
Vitamin D supplementation (calcitriol) has been noted in animals to have an antiviral effect agains herpes simplex virus-1 and to reduce candida albicans infection.
Upper respiratory tract infections are more common in people with low vitamin D levels
Page 1777: Vitamin D was originally discovered for its critical role in calcium homeostasis. However, we now know that vitamin D has pleiotropic actions, and one of the more active areas of recent vitamin D research has focused on understanding its role as a modulator of immune system function. The immune system in vertebrates can be divided into innate and adaptive arms. The role of vitamin D in regulating adaptive immunity is covered by Dr. Luciano Adorini in the following chapter. Unlike the adaptive immune system, which is present only in vertebrates, innate immune responses are found in a wide variety of plant and animal life and provide front-line defenses to pathogenic challenge [1-3].
Vitamin D plays a role in modulating immune system function
The immune system is comprised of innate immunity and adaptive immunity
The innate immune system defends the host from infection in a non-specific manner but, unlike adaptive immunity, has no memory and does not confer long-lasting immunity against specific pathogens. Stimulation of the innate immune system leads to the production of cytokines and chemokines, which act to communicate with other components of the immune system, including cells essential for eventual adaptive responses. As developed further below, it also leads to the production of antimicrobial peptides (AMPs), which represent the first wave of defense against invading pathogens .
The innate immune system defends against infection in a non-specific manner but lacks the learning capacity of the adaptive immune system
Stimulation of the innate immune system results in producing cytokines and chemokines that coordinate other components of the immune system including cells that function in adaptive immunity
Stimulation of the innate immune system results in antimicrobial peptides being produced which act against invading pathogens
There are threads of evidence linking vitamin D to immune system function that extend back over millennia, and closely parallel the emergence of its role in calcium homeostasis. Vitamin D therapy can be traced back to Hippocrates, the father of medicine, who used heliotherapy, or exposure to sunlight, to treat phthisis (tuberculosis; TB) . Nutritional vitamin D therapy arose from the early medicinal use of cod liver oil, which was first described as an agent for treatment of chronic rheumatism in 1789.
Evidence connecting vitamin D to immune system function can be traced back to Hippocrates who used sunlight exposure to treat tuberculosis
Vitamin D supplementation via cod liver oil was described as a treatment for chronic rheumatism in 1789
Throughout the next century, the medical literature documented its effectiveness for treating a number of prevalent conditions such as gout and scrofula, a form of tuberculosis which infects the lymph nodes . The use of cod liver oil as an anti-rachitic agent dates from the 1820s [6,7]. By 1849, the list of conditions treatable with cod liver oil would grow to include TB infection [8,9]. Links between sun exposure, UV light and treatment of rickets date from the 1820s . Sun exposure became a popular therapy for treatment of TB in the mid-19th century with the emergence of sanitoria, and Niels Finsen won the 1903 Nobel prize for showing that UV light could be used to treat cutaneous TB (lupus vulgaris) – Hippocrates would surely have approved.
Niels Finsen won the 1903 Nobel prize for showing ultraviolet light treats cutaneous tuberculosis
Page 1778: There is a wealth of epidemiological data linking vitamin D deficiency to increased rates of a range of life-threatening diseases including digestive tract cancers and leukemias, as well as autoimmune and infectious diseases . US rates of bladder, breast, colon, ovary, and rectal cancer increase two-fold from south to north , and vitamin D deficiency is associated with autoimmune conditions such as rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis, and type 1 diabetes [20-23].
Epidemiological data links vitamin D deficiency to cancers and leukemias as well as autoimmune and infectious diseases
Vitamin D deficiency is associated with rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis and type 1 diabetes
Tuberculosis As documented above, there is a long history of links between vitamin D deficiency and elevated rates of tuberculosis through the therapeutic use of sun exposure or cod liver oil [5-7]. Associations between clinical vitamin D deficiency and tuberculosis susceptibility were made over 20 years ago [24,25], and evidence continues to accumulate (e.g., ). More importantly, we have known for over 20 years that hormonal 1,25(OH)2D3 inhibits the growth of M. tuberculosis in cultured human macrophages [27,28], thus providing evidence that 1,25(OH)2D3 directly enhances host innate immune responses to infection.
There are links between vitamin D deficiency and increased levels of tuberculosis which has been treated with sunlight exposure and cod liver oil
Vitamin D inhibits growth of tuberculosis in cultured human macrophages
Vitamin D enhances host innate immune responses to infection
Other Infectious Diseases Data are accumulating from several sources that maintaining vitamin D sufficiency may also be beneficial in combating a range of other infectious agents of bacterial or viral origin. One small but intriguing study worthy of follow-up found that elderly women undergoing longterm treatment with vitamin D as an anti-osteoporosis agent had a significantly lower rate of Helicobacter pylori infections than an untreated control group .
Vitamin D may be beneficial in combating a range of infectious illnesses of bacterial and viral origin
Vitamin D may be therapeutic in relation to Helicobacter pylori infections
A recently completed clinical trial showed that supplementation with 2000 versus 800 IU reduced the risk of hospital readmission significantly by 39% in elderly patients recovering from fractures. Remarkably, there was a 90% reduction in readmissions due to infections . There are also a number of studies examining the potential role of vitamin D in protection against upper and lower respiratory tract infections, which can be caused by a variety of etiological agents, many of them viral in origin [35-38].
A study showed 2000 IU of vitamin D reduced hospital readmission by 39% in elderly patients recovering from fractures; there was a 90% reduction in readmissions due to infections
Subclinical vitamin D deficiency was associated with severe lower respiratory tract infection in an Indian study , and clinical vitamin D deficiency was associated with a 13-fold increased risk of pneumonia in Ethiopian children . A Finnish study found an association between serum 25(OH)D concentrations of less than 40 nM (16 ng/ml) and a range of acute respiratory infections (sinusitis, tonsillitis, otitis, bronchitis, pneumonia, pharyngitis, and laryngitis) in young army recruits . There are also epidemiological data that cutaneous vitamin D production provides the “seasonal stimulus” associated with solar radiation that underlies the seasonality of epidemic influenza [42,43].
In one study subclinical vitamin D deficiency was associated with severe lower respiratory infection
A study found vitamin D deficiency was associated with a 13-fold increase of pneumonia in children
A study found that less than 40 nM (16 ng/ml) was associated with acute respiratory infections – sinusitis, tonsillitis, otitis, bronchitis, pneumonia, pharyngitis, and laryngitis
Epidemiological data suggests sunlight related vitamin D production correlates with seasonal influenza epidemics
Indeed, a recent randomized double-blind placebocontrolled trial  conducted between December 2008 and March 2009 found that vitamin D supplementation of school children (1200 IU/d) significantly reduced rates of influenza A (relative risk (RR) 0.58; 95% CI 0.34, 0.99; p ¼ 0.04). The effect of supplementation was even more pronounced in children not previously receiving vitamin D supplements (RR 0.36; 95% CI 0.17, 0.79; p ¼ 0.006). However, 12 weeks of treatment with 2000 IU/d of vitamin D3 had no effect on frequency of severity of upper respiratory tract infections in adults .
A study found that vitamin D supplementation of children significantly reduced rates of influenza A
A study found that 12 weeks supplementation of 2000 IU a day of vitamin D did not reduce the frequency of severity of upper respiratory tract infections in adults
Page 1779: Clinical and genetic evidence is also accumulating that vitamin D may play a role in modulating human immunodeficiency virus (HIV) infection. Vitamin D insufficiency or deficiency is widespread in urban European HIV patients (e.g., [46-48]). One study established positive correlation between vitamin D supplementation and CD4-positive T cell counts in seropositive individuals , whereas an analysis of 884 HIV-infected pregnant women in Tanzania did not reveal any association between vitamin D status and T cell counts . However, the authors did conclude that “vitamin D status had a protective association with HIV disease progression, all-cause mortality, and development of anemia during follow-up in HIV-infected women,” and encouraged confirmation of the results in randomized trials . Moreover, analysis of the same cohort showed that 347 of the women had a low vitamin D status and provided evidence that low maternal vitamin D levels were associated with enhanced risk of mother-to-child transmission of HIV .
Vitamin D may play a role in modulating human immunodeficiency virus (HIV) infection
Vitamin D deficiency is widespread in urban European HIV patients
One study suggests a positive correlation between vitamin D supplementation and CD4-positive T cell counts in seropositive individuals
Vitamin D status had a protective association with HIV disease progression, all-cause mortality, and development of anemia during follow-up in HIV-infected women
Low maternal vitamin D levels were associated with enhanced risk of mother-to-child transmission of HIV
Vitamin D Signaling in the Immune System: The vitamin D receptor is widely expressed in the immune system, including in T lymphocytes, neutrophils, and antigen presenting cells such as macrophages and dendritic cells [62-65]. In addition, cytochrome P450 family 27 subfamily B member 1 (CYP27B1), the enzyme that converts circulating the major circulating precursor 25(OH)D3 to hormonal 1,25(OH)2D3, is expressed in cells such as macrophages and dendritic cells [66-69]. Moreover, unlike the renal enzyme, CYP27B1 expression in the immune system is not regulated by Caþþ homeostatic signals, but primarily by immune inputs, rendering the immune system responsive to circulating levels of 25(OH)D3 upon appropriate stimulation.
The vitamin D receptor is widely expressed in the immune system, including in T lymphocytes, neutrophils, and antigen presenting cells such as macrophages and dendritic cells
Cytochrome P450 family 27 subfamily B member 1 (CYP27B1), the enzyme that creates vitamin D3 from its precursor is found in macrophages and dendritic cells
Page 1780: Consistent with previous findings [16,17], 25(OH)D levels serum from African-Americans used in the study were markedly lower than those of Caucasian Americans . These results provided a clear demonstration of the dependence of the magnitude of immune responses on circulating 25(OH)D levels, thus providing a molecular basis for the links between vitamin D deficiency and elevated rates of infectious diseases.
African-American populations demonstrated markedly lower levels of vitamin D than Caucasian American populations
In silico screening for vitamin D response elements (VDREs) revealed consensus response elements in two genes encoding antimicrobial peptides CAMP (cathelicidin antimicrobial peptide, hCAP18, LL37) and human b-defensin 2 (DEFB2, DEFB4, HBD2) contained promoter-proximal consensus DR3-type response elements  (Fig. 91.1). Antimicrobial Peptides (AMPs) are vanguards of innate immune responses against bacterial, fungal, and viral attack, and many act directly by disrupting the integrity of pathogen membranes [4,80-82]. Further analysis of the CAMP and DEFB2 VDREs showed that both elements bound the vitamin D receptor (VDR) in a 1,25(OH)2D3-dependent manner in vitro and in cells in culture, and functioned in reporter gene assays . Human b-defensin 2 (DEFB2) expression was modestly induced by 1a,25-dihydroxyvitamin D3 [1,25(OH)2D3] in cells of epithelial origin. In contrast, CAMP expression was strongly stimulated in all cell types examined (epithelial cells, macrophages/monocytes, and neutrophils). The strong induction of CAMP by 1,25D was subsequently observed by others in a range of cell types [29,83], including in 1,25(OH)2D3-treated or UVB-irradiated human skin biopsies , clearly indicating that 1,25(OH)2D3 is a primary inducer of the gene.
Vitamin D response elements include two genes responsible for antimicrobial peptides – cathelicidin antimicrobial peptide and human b-defensin 2
Antimicrobial Peptides (AMPs) are vanguards of innate immune responses against bacterial, fungal, and viral attack, and many act directly by disrupting the integrity of pathogen membranes
Human b-defensin 2 (DEFB2) was stimulated by 1a,25-dihydroxyvitamin D3 in epithelial cells
Cathelicidin antimicrobial peptide (CAMP) was stimulated in all cell types examined including epithelial cells, macrophages/monocytes, and neutrophils
Page 1781: 1,25(OH)2D3-induced CAMP colocalized with mycobacteria in infected macrophages , and subsequently knockdown of CAMP expression in TB-infected human THP-1 macrophage-like cells, confirmed that its induction is essential for 1,25(OH)2D3- stimulated anti-mycobacterial activity . 1,25(OH)2D3-induced CAMP expression has also been linked to enhancement of autophagy in mycobacterium tuberculosis infected macrophages , although it is not clear whether the stimulation was a direct effect of CAMP on autophagy itself or an indirect effect of reduced mycobacterial viability due to AMP activity. Autophagy is essential for capture and destruction of immature phagosomes that harbor M. tuberculosis in infected cells. In this regard, it is intriguing that many of the loci, including NOD2, associated with susceptibility to CD encode proteins implicated in autophagy [87,100], indicating that robust autophagic responses to phagocytosed pathogens are essential components of innate immunity.
Vitamin D stimulates anti-mycobacterial activity
Vitamin D stimulates Cathelicidin antimicrobial peptide (CAMP) production and is linked to enhanced autophagy in Mycobacterium tuberculosis infected macrophages
Autophagy is the natural destruction of the cell as a part of a process that removes unnecessary or dysfunctional components in the body
Autophagy is essential for capture and destruction of immature phagosomes that harbor Mycobacterium tuberculosis in infected cells
Robust autophagic responses to pathogens are important elements of innate immunity
Page 1782: In addition, DEFB2/HBD2 expression was induced in response to Helicobacter pylori infection in the gastric mucosa , and rhinovirus infection in airway epithelia . Finally, while the relationship between vitamin D signaling in controlling HIV infection remains to be clarified, it is noteworthy that human cathelicidin inhibited the replication of a number of HIV isolates , and that the human and porcine homologs reduced the infectivity of lentiviral vectors , suggesting that vitamin D signaling may indeed induce antiretroviral activity.
Human b-defensin 2 (DEFB2) is produced in response to Helicobacter pylori infection in the gastric mucosa and rhinovirus infection in airway epithelia
Helicobacter pylori, previously known as Campylobacter pylori, is a gram-negative, microaerophilic, spiral bacterium usually found in the stomach
The rhinovirus is a common viral infectious agent in humans and has been related as the cause of the common cold
Cathelicidin inhibited the replication of a number of HIV isolates and infectivity of lentiviral vectors
Lentivirus is a genus of retroviruses which cause diseases characterized by long incubation periods; human immunodeficiency virus is an example
Vitamin D signaling may induce antiretroviral activity
Page 1783: Initial work [79,83] showed that 1a,25-dihydroxyvitamin D3 [1,25(OH)2D3] induced CAMP expression strongly and in a wide variety of cell human types in vitro, suggesting that the regulation is widespread in vivo. This has since been borne out in studies performed in several tissues. CAMP expression in skin is of broad (patho)physiological significance. It has been speculated that regulation of CAMP transcription by 1,25(OH)2D3 was retained in primates and humans because of the importance of cutaneous ultraviolet light (UVB) induced vitamin D synthesis in these organisms . CAMP is strongly induced in human keratinocytes by UV light , and under conditions of epithelial wound healing [110-112], providing a molecular basis for the stimulatory role of vitamin D in the process.
1a,25-dihydroxyvitamin D3 stimulates cathelicidin antimicrobial peptide (CAMP) in a wide variety of cells in laboratory settings (in vitro)
Cathelicidin antimicrobial peptide (CAMP) production is stimulated by ultraviolet light in skin cells (keratinocytes) and in wound healing
AMP expression is decreased in atopic dermatitis (AD), leading to increased rates of infection of affected skin . However, elevated 1,25(OH)2D3 signaling in AD would not be beneficial because it would skew the T helper response towards a Th2 phenotype, due in part to the induction of thymic stromal lymphopoietin, which is a 1,25(OH)2D3 target gene in human and mouse [78,115]. In contrast, the persistent inflammatory skin disorder rosacea is characterized by elevated expression of CAMP, which is abnormally processed and contributes to inflammation . 1,25(OH)2D3-induced CAMP expression may contribute to aggravation of rosacea caused by exposure to UV light. It has been noted that azole antimycotics (ketoconazole, itraconazole, metronidazole), used in dermatology as antifungal agents in treatment of inflammatory conditions such as rosacea, also block cytochrome P450-driven vitamin D metabolism .
The persistent inflammatory skin disorder rosacea is characterized by elevated expression of Cathelicidin antimicrobial peptide (CAMP), which contributes to inflammation
Azole antimycotics (ketoconazole, itraconazole, metronidazole), used in dermatology as antifungal agents in treatment of inflammatory conditions such as rosacea, also block cytochrome P450-driven vitamin D metabolism
Drugs which use the cytochrome P450 enzyme system may damage the bodys capacity to create vitamin D
Intriguingly, expression of cathelicidin is also elevated in psoriasis, another inflammatory skin condition , where vitamin D analogs are therapeutically effective. 1,25(OH)2D3-dependent CAMP expression is enhanced by proinflammatory cytokine IL-17A produced by psoriatic lesional T cells . Moreover, CAMP triggers an autoimmune response in psoriasis by activating toll-like receptor (TLR) signaling in plasmatoid dendritic cells (pDCs) of the skin, which are specialized for sensing viral and certain microbial infections.
Cathelicidin antimicrobial peptide (CAMP) is elevated in psoriasis; vitamin D analogs are therapeutically effective in this context
Cathelicidin antimicrobial peptide (CAMP) triggers an autoimmune response in psoriasis by activating toll-like receptor (TLR signalling) in plasmatoid dendritic cells (pDCs) of the skin – cells specialized for sensing viral and certain microbial infections
Page 1789: The raison d’etre of the immune system is to control the biological integrity of the individual. This is accomplished by two layers of immune responses, innate and adaptive, which are tightly interconnected . Innate immune responses can be induced in virtually any cell, but they are primarily mediated by specialized cell types, such as dendritic cells (DCs), macrophages, neutrophils, and natural killer cells.
The immune system has two layers of immune responses – the innate and the adaptive immune responses which are closely bound with each other
Innate immune responses can be induced in most cells but are especially mediated by dendritic cells (DCs), macrophages, neutrophils and natural killer cells
Innate immunity is characterized by rapid, local responses, largely based on the production of pro-inflammatory mediators, in particular cytokines, chemokines, and reactive oxygen species. Production of these mediators is triggered by recognition of stereotyped patterns conserved in infectious microorganisms via toll-like receptors (TLRs), surface molecules able to recognize distinct structural components of pathogens . Thus, the innate immune system is genetically programmed to detect invariant features of invading microbes. Activation of signal transduction pathways by TLRs leads to upregulation of different genes that operate in host defense, including co-stimulatory molecules, cytokines and chemokines .
Innate immunity produces rapid, local responses which give rise to pro-inflammatory mediators such as cytokines, chemokines and reactive oxygen species
The production of the mediators is triggered by recognition of infectious microorganisms via toll-like receptors (TLRs)
Toll-like receptors are found on the surface of cells such as macrophages and dendritic cells and react to molecules found on microbes triggering a cascade of immune activity
Activation of toll-like receptors activates biochemical signals that stimulate different genes involved in defending the body and result in the production of cytokines and chemokines
Adaptive immune responses are primarily induced by cells specialized in antigen processing and presentation, in particular DCs, and are mediated by cells specialized in antigen recognition, namely T and B lymphocytes. Lymphocytes employ antigen receptors that are not encoded in the germ line but are generated de novo in each organism, rendering adaptive immune responses highly specific. Adaptive immune responses are primarily orchestrated by CD4+ T lymphocytes. Triggered by microbial pathogens, naieve CD4+ T cells orchestrate immune responses by differentiating into T helper (Th) cell populations that secrete distinct sets of cytokines .
An antigen is a molecule which is present on the outside of a pathogen; A pathogen is any organism that can produce disease (a germ or infectious agent)
Adaptive immune responses are primarily induced by cells which function in antigen processing and presentation
Adaptive immune responses are mediated by cells involved in antigen recognition – specifically T and B lymphocytes (white blood cells)
Lymphocytes use antigen receptors which are not coded in DNA but generated in the body in a sort of biological learning process based on what the immune system has already encountered
Adaptive immune responses are primarily organised by CD4+ T lymphocytes (T cells)
When triggered by pathogens CD4+ T cells change their form into T helper (Th) cell types which release different cytokines
Tailoring their responses to the character of the threat encountered, Th cells differentiate to provide help to B lymphocytes and CD8+ cytotoxic T cells, and to activate cells of the innate immune system. CD4+ T cells can be distinguished, based on their pattern of cytokine production, into three major effector cell types, Th1, Th2, and Th17 cells. Th1 cells are characterized by secretion of interferon-g (IFN-g), IL-2, and TNF-b, and they promote cell-mediated immunity able to eliminate intracellular pathogens. Th2 cells selectively produce IL-4, IL-5, and IL-13, and are involved in the development of humoral immunity protecting against parasites. Th17 cells, characterized by production of IL-17, IL-21, and IL-22, are involved in host defense against extracellular pathogens. All these effector T cell types can also mediate pathogenic immune responses, such as autoimmunity (Th1 and Th17) and allergy (Th2).
T helper cells tailor their responses to the specific needs of the immunological threat (pathogen)
T helper cells support B lymphocytes and CD8+ cytotoxic T cells as well as activate cells involved in innate immune responses
CD4+ T cells are known to transform into three main cell types – Th1, Th2 and Th17 cell types
Th1 cells secrete interferon-g (IFN-g), interleukin-2 (IL-2) and tumor necrosis factor beta (TNF-b) which eliminate intracellular pathogens
Th2 cells secrete interleukin 4 (IL-4), interleukin 5 (IL-5) and interleukin 13 (IL-13) which protect cells against parasites
Th17 cells secrete interleukin 17 (IL-17), interleukin 21 (IL-21) and interleukin 22 (IL-22) which protect against extracellular pathogens
All these T cell types are involved in mediating pathogenic immune responses such as autoimmunity and allergy
Peripheral naieve CD4+ T precursor cells can differentiate not only into the three main subsets of effector T cells but also into several subsets of regulatory T cells (Treg), including induced Treg cells (iTreg), Tr1 cells, and Th3 cells. Naturally occurring Treg cells (nTreg) are generated from CD4+ thymic T cell precursors. The differentiation of these subsets is governed by selective cytokines and transcription factors, but their differentiation into lineages with distinct effector functions is not necessarily an irreversible event and a great degree of flexibility in their differentiation options exists, with an exquisite plasticity characterizing iTreg and Th17 cells [5,6].
Naieve CD4+ T precursor cells can differentiate into three main subsets of effector T cells (Th1, Th2, Th17) but also further into subsets of regulatory T cells (Treg)
T regulatory cell types include ‘induced Treg cells’ (iTreg), Tr1 cells and Th3 cells
Cytokines and transcription factors orchestrate the differentiation of CD4+ T cells and their form can flexibly change to circumstance
Page 1790: 1,25(OH)2D3, the activated form of vitamin D, is a secosteroid hormone that regulates, in addition to calcium and bone metabolism, growth and differentiation of many cell types, and displays pronounced immunoregulatory properties [7-11]. The biological effects of 1,25(OH)2D3 are mediated by the vitamin D receptor (VDR), a member of the superfamily of nuclear hormone receptors . Ligand binding induces conformational changes in the VDR, which promote heterodimerization with the retinoid X receptor (RXR) and recruitment of a number of corepressor and coactivator proteins, including steroid receptor coactivator family members and a multimember coactivator complex, D receptor interacting proteins (DRIP).
1a,25-dihydroxyvitamin D3 [1,25(OH)2D3] – the biologically active form of vitamin D is a steroid hormone which regulates calcium and bone metabolism, growth and differentiation of various cell types and functions in regulating the immune system
The biological effects of 1a,25-dihydroxyvitamin D3 [1,25(OH)2D3] are mediated by the vitamin D receptor (VDR) which is a nuclear hormone receptor
Binding of vitamin D3 produces changes in the vitamin D receptor joining together with the retinoid X receptor involving a number of coactivating and corepressing proteins
These coactivators induce chromatin remodeling through intrinsic histone-modifying activities and direct recruitment of key transcription initiation components at regulated promoters. Thus, the VDR functions as a ligand activated transcription factor that binds to specific DNA sequence elements (vitamin D responsive elements, VDRE) in vitamin D responsive genes and ultimately influences the rate of RNA polymerase II mediated transcription . The discovery of VDR expression in most cell types of the immune system , in particular in antigen presenting cells (APCs) such as macrophages  and dendritic cells (DCs) , as well as in both CD4+ and CD8+ T lymphocytes (reviewed in ), prompted the investigation of VDR ligands as agents able to modulate T cell responses .
The coactivating proteins cause changes in chromatin – a complex of DNA and protein found in cells – by modifying histones (a type of protein abundant in the cell nucleus) and stimulates transcription initiation components which give rise to production of RNA that goes on to produce specific proteins
The vitamin D receptor acts as a transcription factor for vitamin D responsive genes and influences the rate of RNA polymerase II mediated production of proteins via transcription
Vitamin D receptors have been found in most cells involved in the immune system, in particular antigen presenting cells such as macrophages and dendritic cells, as well as CD4+ and CD8+ lymphocytes
Data accumulated in the last few years clearly demonstrate that the vitamin D endocrine system is involved in a variety of biological processes able to modulate immune responses, and plays an important role in the control of autoimmune diseases [10,18-20]. In addition to exerting direct modulatory effects on T and B cell function, VDR agonists shape phenotype and function of dendritic cells (DCs), promoting tolerogenic properties that favor the induction of regulatory rather than effector T cells . These intriguing actions of VDR agonists have been demonstrated in several experimental models and could be exploited, in principle, to treat a variety of autoimmune diseases and other immuno-mediated pathologies characterized by chronic inflammatory responses.
The vitamin D endocrine system is involved with a variety of biological processes capable of modulating immune responses and has been suggested as playing an important role in the control of autoimmune disease
Vitamin D has direct modulatory effects on the function of T and B cells
Substances that activate the vitamin D receptor influence the type and function of dendritic cells promoting immunological tolerance through favouring the production of regulatory rather than effector T cells
Equally important, accumulating data document the capacity of 1,25(OH)2D3, which is produced by macrophages [22,23], DCs [24,25], T , and B  cells, to physiologically contribute, via the VDR expressed in all these cell types, to regulate via autocrine and paracrine effects both innate and adaptive immune responses. The tight control of bioactive hormone production by cells of the immune system itself further supports the relevance of the vitamin D endocrine system in the modulation of immune responses in health and disease.
1a,25-dihydroxyvitamin D3 [1,25(OH)2D3], via the vitamin D receptor, regulates innate and adaptive immune responses through macrophages, dendritic cells and B cells
Cells of the immune system keep tight control over bioactive hormone production supporting the view that vitamin D plays a significant role in modulating immune responses
DCs, a highly specialized antigen-presenting cell system critical for the initiation of CD4+ T cell responses, are present, in different stages of maturation, in the circulation as well as in lymphoid and non-lymphoid organs. After antigen uptake, DCs migrate through the afferent lymph to T-dependent areas of secondary lymphoid organs where they can prime naıeve T cells. During migration to lymphoid organs, DCs mature into potent APCs by increasing their immunostimulatory properties while decreasing antigen-capturing capacity .
Dendritic cells represent a highly specialized antigen presenting system essential for starting CD4+ T cell responses
Dendritic cells exist in different stages of maturation in blood circulation as well as in lymphoid and non-lymphoid organs
Once dendritic cells have an antigen reaction they migrate through the lymphatic system to thymus dependent areas of secondary lymphoid organs where they informationally prime naieve T cells for appropriate differentiation
During migration to lymphoid organs, dendritic cells mature into potent antigen presenting cells by increasing their immunostimulatory properties whilst decreasing their antigen-capturing capacity
Page 1792: Only vitamin D receptor (VDR) agonists, among the agents tested, are able to enhance the secretion by DCs of IL-10, a cytokine favoring the induction of regulatory T cells . Several of these effects could be mediated by NF-kB, a signal transduction pathway crucially involved in the inflammatory response . The NF-kB family member RelB is required for myeloid DC differentiation, and antigen-pulsed DCs in which RelB function is inhibited can induce regulatory CD4+ T cells able to transfer tolerance to primed recipients in an IL-10- dependent fashion .
Substances which stimulate vitamin D receptors enhance the secretion of interleukin 10 (IL-10) by dendritic cells which chemically stimulates the production of regulatory T cells
Interestingly, both dexamethasone  and VDR agonists  upregulate the transcription of Nfkbia, which results in increased rate of IkBa synthesis and in reduced NF-kB translocation to the nucleus. The promoter of the Nfkbia gene encoding IkBa contains, as the Relb gene , several vitamin D responsive elements, suggesting a direct transcriptional regulation of IkBa by VDR agonists. The direct targeting of NF-kB components by VDR agonists exemplified by arrest of NF-kBp65 nuclear translocation in M-DCs  contributes to explain their capacity to induce tolerogenic DCs, as well as their inhibitory effects on pro-inflammatory cytokine and chemokine production by DCs. Thus, VDR agonists share with several immunomodulatory agents the capacity to target DCs, rendering them tolerogenic and fostering the induction of regulatory rather than effector T cells.
Both dexamethasone and vitamin D receptor agonists upregulate the transcription of Nfkbia which results in increased IkBa synthesis and in reduced NF-kB translocation to the nucleus
Vitamin D receptor agonists have the capacity to target dendritic cells causing them to become immunologically tolerant which resultantly fosters the production of regulatory rather than effector T cells
Multiple mechanisms contribute to induction of DC tolerogenicity by VDR agonists, from downregulation of costimulatory molecules, both membrane-bound as CD40, CD80, CD86, and secreted as IL-12, to upregulation of inhibitory molecules like ILT3 and IL-10, to modulation of chemokine secretion, enhancing the production of chemokines able to recruit Treg cells, and inhibiting production of chemokines recruiting pathogenic cells by the target organ in inflammatory conditions.
Vitamin D receptor agonists produce dendritic cell immunological tolerance via multiple mechanisms
APCs, and notably DCs, express the VDR and are key targets of VDR agonists, both in vitro and in vivo. A number of studies have clearly demonstrated that 1,25(OH)2D3 and its analogs markedly modulate DC phenotype and function . These studies have consistently shown that in vitro treatment of DCs with VDR agonists leads to downregulated expression of the costimulatory molecules CD40, CD80, CD86, and to decreased IL-12 and enhanced IL-10 production, resulting in decreased T-cell proliferation (Fig. 92.1).
Antigen presenting cells, notably dendritic cells express the vitamin D receptor and are key targets of vitamin D receptor agonists both in the laboratory and in living tissues
1a,25-dihydroxyvitamin D3 [1,25(OH)2D3] and structurally related substances play a role in determining which type dendritic cells differentiate into which ultimately determines the form the immunological reaction takes
In laboratory settings treatment of dendritic cells with vitamin D receptor agonists downregulates the expression of costimulatory molecules CD40, CD80, CD86 and decreases interleukin 12 (IL-12) whilst enhances interleukin 10 production which results in decreased T cell proliferation
Recent data indicate that exogenous or endogenously generated 1,25(OH)2D3 regulates in DCs a large set of target genes involved in tolerogenicity autonomously rather than via inhibition of differentiation and maturation, suggesting that the tolerogenic program initiated in DCs by VDR agonists is largely independent of their inhibitory effects on DC differentiation and maturation .
Exogenous or endogenously generated vitamin D3 regulates in dendritic cells a large set of genes involved in immunological tolerance independently of any action to inhibit differentiation and maturation
Page 1793: DCs are able to synthesize 1,25(OH)2D3 in vitro as a consequence of increased 1a-hydroxylase expression [24,25], and this could contribute to promote regulatory T cell induction. It is also possible that 1,25(OH)2D3 may contribute to the physiological control of immune responses, and possibly be also involved in maintaining tolerance to self antigens, as suggested by the enlarged lymph nodes containing a higher frequency of mature DCs in VDR-deficient mice . This intriguing concept has been recently highlighted by the observation that vitamin D3 induced by sunlight in the skin is hydroxylated by local DCs into the active hormone, which in turn upregulates on activated T cells expression of the epidermiotropic chemokine receptor CCR10, a primary VDR responsive gene, enabling them to migrate in response to the epidermal chemokine CCL27 . Thus, the autocrine production of 1,25(OH)2D3 by DCs can program the homing of skin-associated T cells, which could include regulatory T cells able to counteract the proinflammatory effects induced in the skin by sun exposure. Interestingly, B cells can also synthesize 1,25(OH)2D3  and can preferentially expand Foxp3+ Treg cells , suggesting that the tolerogenic potential of B cells could perhaps be associated with their capacity to produce 1,25(OH)2D3.
In the laboratory dendritic cells generate 1a,25-dihydroxyvitamin D3 via increased expression of the enzyme 1-alpha hydroxylase (also known as cytochrome p450 27B1 – CYP27B1)
It is suggested that the expression of the enzyme that generates vitamin D3 may contribute to regulatory T cell induction
Vitamin D3 may contribute to the physiological control of immune responses and be involved in maintaining tolerance to self antigens
Vitamin D3 production induced by sunlight in the skin is hydroxylated by local dendritic cells into the active hormone which in turn upregulates activated T cell expression of epidermiotropic chemokine receptor CCR10, a primary VDR responsive gene enabling them to migrate in response to epidermal chemokine CCL27
Autocrine production of 1a,25-dihydroxyvitamin D3 by dendritic cells can program the homing of skin associated T cells which cloud include regulatory T cells able to counteract the pro-inflammatory effects of sunlight to the skin
B cells can synthesize 1a,25-dihydroxyvitamin D3 and can preferentially differentiate Foxp3+ Treg cells suggesting that immunological tolerance generated by B cells may come from their capacity to create vitamin D hormone when needed
The prevention of DC differentiation and maturation as well as the modulation of their activation and survival leading to DCs with tolerogenic phenotype and function play an important role in the immunoregulatory activity of VDR agonists, and appear to be critical for the capacity of this hormone to induce CD4+CD25+ Treg cells that are able to control autoimmune responses and allograft rejection (Table 92.1). VDR agonists enhance CD4+CD25+ Treg cells and promote tolerance induction in transplantation and autoimmune disease models.
Substances which stimulate vitamin D receptors enhance CD4+CD25+ Treg cells and promote immunological tolerance in transplantation and autoimmune disease models
Page 1794: A combination of 1,25(OH)2D3 and dexamethasone has been shown to induce human and mouse naıeve CD4+ T cells to differentiate in vitro into T reg cells, even in the absence of APCs . These T reg cells produced IL-10, but no IL-5 nor IFN-g, thus distinguishing them from the previously described Tr1 cells . Upon transfer, the IL-10-producing Treg cells could prevent central nervous system inflammation, indicating their capacity to exert a suppressive function in vivo . Thus, although DCs appear to be primary targets for the immunomodulatory activities of VDR agonists, they can also act directly on T cells, as expected by VDR expression in both cell types and by the presence of common targets in their signal transduction pathways, such as the nuclear factor (NF)-kB that is downregulated in both APCs and T cells.
In the laboratory combination of 1a,25-dihydroxyvitamin D3 and dexamethasone induces naieve CD4+ T cells to differentiate into T reg cells even in the absence of antigen presenting cells
Although dendritic cells are primary targets for the immunomodulatory activities of vitamin D receptor agonists, they can also act directly on T cells
Page 1796: Analysis of immunomodulatory effects exerted by 1,25(OH)2D3 on human blood M-DCs and P-DCs demonstrates a differential capacity of this hormone to modulate cytokine and chemokine production in DC subsets, showing marked effects in M-DCs and negligible ones in P-DCs . In addition to CCL22 and CCL17, neither IFN-a, the signature cytokine produced by P-DCs, nor expression of MHC class II molecules or CCR7, a key regulator of DC migration to secondary lymphoid organs, are affected in P-DCs by 1,25(OH)2D3 treatment . Conversely, production of IL-12, the M-DC signature cytokine, as well as MHC class II and CCR7 expression are markedly inhibited by 1,25(OH)2D3 in M-DCs . All these molecules are controlled by NF-kB, a signal transduction pathway crucially involved in the inflammatory response .
The immunomodulatory effects of 1a,25-dihydroxyvitamin D3 on human blood myloid dendritic cells (M-DCs) and plasmacytoid dendritic cells (P-DCs) are different
1a,25-dihydroxyvitamin D3 modulates cytokine and chemokine production markedly in myloid dendritic cells but neglibly in plasmacytoid dendritic cells
1a,25-dihydroxyvitamin D3 inhibits interleukine 12, MHC (major histocompatibility complex) class II and CCR7 expression in myloid dendritic cells
Page 1798: 1,25(OH)2D3 is able to prevent and to partially reverse experimental autoimmune uveitis (EAU). This is accompanied by reduced production of IL-17 via two independent mechanisms, direct inhibition of IL-17 production by CD4+ T cells and indirect inhibition of IL-17 lineage commitment by downregulation of the ability of DCs to support priming of T cells towards the Th17 effector pathway . Lineage commitment, as judged by induction of the Th17 lineage-specific transcription factor RORgt, is not impaired by the direct inhibitory effect on T cells, but is downregulated by the indirect effect mediated by DCs, thus permitting to distinguish between these two effects. In addition, development of Th17 cells requires interferon-regulatory factor 4 (IRF- 4) , a transcription factor that is strongly inhibited by 1,25(OH)2D3 in DCs . Thus, 1,25(OH)2D3 may act at several levels to suppress the pro-inflammatory uveitogenic Th17 response by affecting functions of both DCs and CD4+ T cells. In conclusion, VDR agonists appear primarily to inhibit proinflammatory, pathogenic T cells like Th1 and Th17 cells and, under appropriate conditions, may favor a deviation to the Th2 pathway. These effects are partly due to direct T cell targeting, but modulation of DC function by VDR agonists plays an important role in directing T cell responses. Thus, VDR agonists can target T cells both directly and indirectly, selectively inhibiting T cell subsets able to mediate chronic inflammation and tissue damage.
1a,25-dihydroxyvitamin D3 is able to prevent and partially reverse experimental autoimmune uveitis (EAU) – a disease of the neural retina induced by immunization with retinal antigens and serves as a model of certain ocular inflammatory pathologies in human
1a,25-dihydroxyvitamin D3 may act at several levels to suppress the pro-inflammatory uveitogenic Th17 response by affecting functions of both dendritic cells and CD4+ T cells
Substances which act through the vitamin D receptors (VDR agonists) primarily inhibit proinflammatory pathogenic effector T cells like Th1 and Th17; and they may favour a deviation of cell differentiation to the Th2 pathway
VDR agonists can target T cells both directly and indirectly selectively inhibiting T cell subsets which mediate chronic inflammation and tissue damage
In the presence of 1,25(OH)2D3, cellular activation associated with stimulation of such a progression appears to be sufficient for the upregulation of VDR message and protein and necessary for the establishment of VDRE binding complexes. Furthermore, biologic functions are modulated, as 1,25(OH)2D3 inhibits proliferation in a subset of activated B cells. These observations suggest that reactivity to 1,25(OH)2D3 is tightly regulated in B lymphocytes, requiring specific signals for its initiation, but once activated B cells, like macrophages, DCs and T cells, express the VDR and can synthesize 1,25(OH)2D3 able to exert autocrine and paracrine regulatory actions .
1a,25-dihydroxyvitamin D3 inhibits proliferation in a subset of activated B cells
Page 1799: Potent direct effects of 1,25(OH)2D3 on B cell responses, inhibiting proliferation, generation of class switched memory B cells, plasma cell differentiation, and Ig production, were also observed by Chen and coworkers . In addition, the reduced levels of 1,25(OH)2D3 in systemic lupus patients, particularly in those with high disease activity scores and anti-nuclear antibodies, suggest that vitamin-D-dependent B cell regulation may play an important role in maintaining normal B cell homeostasis and that decreased levels of 1,25(OH)2D3 may contribute to B cell hyperactivity in systemic lupus patients .
Direct effects of 1a,25-dihydroxyvitamin D3 on B cell responses were reported as inhibition of proliferation, generation of class switched memory B cells, plasma cell differentiation, and immunoglobulin (Ig) production
Reduced levels of 1a,25-dihydroxyvitamin D3 were found in systemic lupus patients, especially thos with high disease activity scores and anti-nuclear antibodies
Research on the relation between vitamin D exposure and disease in population-based studies is increasing exponentially . Although there is no firm consensus on optimal serum levels of 25(OH)D3, the accepted biomarker of vitamin D status, vitamin D deficiency is usually defined by 25(OH)D3 levels below 20 ng/ml [147,148]. Mounting evidence indicates a high prevalence of vitamin D deficiency in the general population, and this has been linked to increased frequency of autoimmune diseases, in addition to bone diseases and cancer [149,150].
There is no firm consensus on optimal serum levels of 25-hydroxyvitamin D3 [25(OH)D3] the major circulating form of vitamin D and the accepted biomarker of vitamin D status
Vitamin D deficiency is usually defined by 25(OH)D3 levels below 20 ng/ml
Mounting evidence indicates a high prevalence of vitamin D deficiency in the general population
Vitamin D deficiency has been linked to increased frequency of autoimmune diseases, in addition to bone diseases and cancer
Epidemiologic analysis shows strong ecologic and case-control evidence that vitamin D reduces the risk of several autoimmune diseases, including multiple sclerosis (MS), type 1 diabetes (T1D), inflammatory bowel disease (IBD), rheumatoid arthritis (RA), osteoarthritis, and SLE . A large prospective study has confirmed that high circulating levels of 25(OH)D3 are associated with a lower risk of MS , suggesting that dietary vitamin D supplementation may help prevent the development of MS and may represent a useful addition to therapy in this indication [153,154].
There is evidence that vitamin D reduces the risk of several autoimmune diseases including multiple sclerosis (MS), type 1 diabetes (T1D), inflammatory bowel disease (IBD), rheumatoid arthritis (RA), osteoarthritis, and systemic lupus erythematosus (SLE)
High circulating levels of 25-hydroxyvitamin D3 are associated with lower risk of multiple sclerosis
Consistent with this possibility, vitamin D supplementation during infancy significantly reduced T1D incidence evaluated 30 years later , and was confirmed by a meta-analysis of data from case-control studies . In addition, vitamin D intake has been found to be inversely correlated with the risk of developing RA , and case-control studies have shown significantly lower 25(OH)D3 levels in SLE patients .
Vitamin D supplementation during infancy significantly reduced type 1 diabetes incidence evaluated 30 years later
Vitamin D intake has been found to be inversely correlated with the risk of developing rheumatoid arthritis
Case control studies have shown significantly lower 25-hydroxyvitamin D3 levels in systemic lupus erythematosus patients
Vitamin D deficiency has been reported to contribute to IBD development , and lower amounts of 1,25(OH)2D3 are synthesized from sunlight exposure in areas in which IBD occurs most often, such as North America and Northern Europe, a situation common to other autoimmune diseases .
Vitamin D deficiency has been reported to contribute to inflammatory bowel disease (IBD)
Lower amounts of 1a,25-dihydroxyvitamin D3 are made in people who have limited exposure to sunlight such as North America and Northern Europe
Greater incidence of inflammatory bowel disease and other autoimmune diseases are associated with geographies with limited sunlight exposure
Collectively, these data indicate vitamin D status as a key environmental factor affecting autoimmune disease prevalence. VDR polymorphisms have also been repeatedly correlated with increased frequency of autoimmune diseases, but so far no association has been described with functional phenotypes .
Vitamin D status may be a key environmental factor affecting autoimmune disease prevalence
Vitamin D receptor polymorphisms have been repeatedly correlated with increased frequency of autoimmune diseases
The immunoregulatory properties of VDR ligands have been studied in different models of autoimmune diseases (Table 92.3). The capacity of VDR agonists to inhibit autoimmune diseases has been studied in different experimental models, including collagen induced arthritis, Lyme arthritis, SLE in MRLlpr/lpr mice, T1D in non-obese diabetic (NOD) mice, experimental allergic encephalomyelitis (EAE), and colitis, reviewed in [10,18,19]. VDR agonists are able not only to prevent but also to treat ongoing autoimmune diseases, as demonstrated by their ability to inhibit T1D development in adult NOD mice, and to ameliorate established chronic-relapsing EAE .
Substances which act on the vitamin D receptor (VDR agonists) are able not only to prevent but also to treat ongoing autoimmune diseases
Vitamin D receptor agonists can inhibit type 1 diabetes development in adult non-obese diabetic (NOD) mice and can ameliorate established chronic-relapsing Experimental autoimmune encephalomyelitis (EAE)
Rheumatoid arthritis (RA) is an immune-mediated disease characterized by articular inflammation and subsequent tissue damage leading to severe disability and increased mortality. VDR agonists have been tested in two RA models, namely Lyme arthritis and collagen induced arthritis . Infection of mice with Borrelia burgdorferi, the causative agent of human Lyme arthritis, produces acute arthritic lesions with footpad and ankle swelling. Supplementation with 1,25(OH)2D3 to mice infected with B. burgdorferi minimized or prevented these symptoms, and the same treatment could also inhibit collagen-induced arthritis, preventing the progression to severe arthritis when given to mice with early symptoms . In a separate study, VDR agonists displayed a similar capacity to prevent and to suppress already established collagen-induced arthritis without inducing hypercalcemia .
Supplementation of 1a,25-dihydroxyvitamin D3 to mice infected with Borrelia burgdorferi (the causative agent of Lyme disease) minimized or prevented symptoms of experimental Lyme arthritis
Supplementation of 1a,25-dihydroxyvitamin D3 to mice inhibited collagen-induced arthritis preventing progression to severe arthritis when given at the stage of early symptoms
Vitamin D receptor agonists showed a capacity to prevent and suppress already established collagen induced arthritis without inducing hypercalcaemia
Page 1800: 1,25(OH)2D3 contributes to the regulation of MMPs and PGE2 production by human articular chondrocytes in osteoarthritic cartilage , suggesting immunomodulatory effects also in human RA. In addition, 1,25(OH)2D3 directly modulates human Th17 polarization, accompanied by suppression of IL-17A, IL-17F, TNF-a, and IL-22 production by memory T cells sorted by FACS from patients with early RA . VDR agonists show potential in RA treatment [167,168], as indicated by the beneficial effects of alpha-calcidiol in a 3-month open-label trial on 19 RA patients .
1a,25-dihydroxyvitamin D3 is involved in the regulation of matrix metalloproteinases (MMPs) and prostaglandin E2 (PGE2) production by human articular chondrocytes in osteoarthritic cartilage
1a,25-dihydroxyvitamin D3 directly modulates Th17 polarization, accompanied by suppression of interleukin 17A (IL-17A), interleukin 17F (IL-17F), tumor necrosis factor alpha (TNF-a) and interleukin 22 (IL-22) production by memory T cells from patients with early rheumatoid arthritis
Vitamin D receptor agonists have shown beneficial effects in trials with rheumatoid arthritis patients
Page 1801: Systemic lupus erythematosus (SLE) is a T-cell dependent antibody-mediated autoimmune disease, and the mouse strain MRLlpr/lpr spontaneously develops an SLE-like syndrome sharing many immunological features with human SLE . Administration of VDR agonists significantly prolonged the average lifespan of MRLlpr/lpr mice and induced a significant reduction in proteinuria, renal arteritis, granuloma formation, and knee joint arthritis [171,172]. In addition, dermatological lesions, like alopecia, necrosis of the ear, and scab formation, were also completely inhibited by 1,25(OH)2D3 therapy .
Systemic lupus erythematosus (SLE) is a T-cell dependent antibody-mediated autoimmune disease
Administration of vitamin D receptor agonists significantly prolonged the average lifespan of mice with the experimental animal model of systemic lupus erythematosus showing a reduction in proteinuria, renal arteritis, granuloma formation and knee joint arthritis
Dermatological lesions, like alopecia, necrosis of the ear, and scab formation, were also completely inhibited by 1a,25-dihydroxyvitamin D3 therapy
Preclinical models and epidemiological data suggest a beneficial role of VDR agonists in the treatment of human SLE . VDR agonists can significantly reduce cell proliferation and IgG production, both polyclonal and anti-dsDNA, while enhancing B cell apoptosis in lymphocytes from SLE patients . Vitamin D deficiency is a risk factor for SLE [158,175], and reduced levels of 1,25(OH)2D3 in SLE patients may contribute to B cell hyperactivity in this disease .
In human systemic lupus erythematosus, vitamin D receptor agonists significantly reduce cell proliferation, immunoglobulin G production (both polyclonal and anti-dsDNA), and enhance B cell apoptosis in lymphocytes
Vitamin D deficiency is a risk factor in systemic lupus erythematosus
Experimental allergic encephalomyelitis (EAE), an autoimmune disease resembling multiple sclerosis (MS) characterized by Th1 and Th17-type cells specific for myelin antigens , can be ameliorated by treatment with VDR agonists [19,183]. 1,25(OH)2D3 and the non-hypercalcemic analog Ro 63-2023 have been shown to be selective and potent inhibitors of Th1 development in vitro and in vivo . Administration of 1,25(OH)2D3 or its analog could prevent chronic-relapsing experimental allergic encephalomyelitis (CR-EAE) induced by the MOG peptide 35-55 in Biozzi AB/H mice, and this was associated with a profound reduction of MOG35-55-specific proliferation and Th1 cell development.
Experimental allergic encephalomyelitis (EAE), an autoimmune disease resembling multiple sclerosis (MS) characterized by Th1 and Th17-type cells specific for myelin antigens
Vitamin D receptor agonists ameliorate experimental allergic encephalomyelitis in animals
Page 1802: 1,25(OH)2D3 treatment significantly reduced clinical EAE severity within 3 days, preceded by sharp declines in chemokines, inducible iNOS, and CD11bþ monocyte recruitment into the central nervous system .
1a,25-dihydroxyvitamin D3 significantly reduced clinical experimental allergic encephalomyelitis
Levels of 25(OH)D3 and 1,25(OH)2D3 are significantly lower in relapsing-remitting MS patients than in controls . In addition, levels in patients suffering relapse are lower than during remissions. In contrast, primary progressive MS patients showed similar values to controls . Proliferation of both freshly isolated CD4+ T cells and MBP-specific T cells was significantly inhibited by 1,25(OH)2D3. Moreover, 1,25(OH)2D3 enhanced the development of IL-10 producing cells, and reduced the number of IL-6 and IL-17 secreting cells. 1,25(OH)2D3 also increased the expression and biological activity of indoleamine 2,3-dioxygenase (IDO), mediating significant increase in the number of CD4+CD25+ Treg cells . Collectively, these data suggest that 1,25(OH)2D3 plays an important role in T cell homeostasis during the course of MS, highlighting its potential in treatment of the disease .
Levels of 1a,25-dihydroxyvitamin D3 and 25-hydroxyvitamin D3 are significantly lower in relapsing-remitting multiple sclerosis patients
Levels of vitamin D are found to be lower during relapse than during remissions
Primary progressive multiple sclerosis patients showed similar vitamin D values to controls
1a,25-dihydroxyvitamin D3 significantly inhibited isolated CD4+ T cells and MBP-specific T cells
1a,25-dihydroxyvitamin D3 enhanced the interleukin 10 producing cells and reduced interleukin 6 and interleukin 7 secreting cells
1a,25-dihydroxyvitamin D3 increased the activity of indoleamine 2,3-dioxygenase (IDO), mediating significant increase in the number of CD4+CD25+ Treg cells
1a,25-dihydroxyvitamin D3 is suggested to play an important role in T cell homeostasis in multiple sclerosis and has been put forward as a potential treatment in the disease
Inflammatory bowel diseases (IBDs) are immune mediated diseases affecting the gastrointestinal tract. Two distinct forms of IBDs have been defined, ulcerative colitis and Crohn’s disease. These are chronic recurring illnesses most commonly involving inflammation of the terminal ileum and colon, although they can also affect many sites throughout the alimentary tract . In addition to genetic factors, including also VDR gene polymorphisms, the environment contributes to IBD development, and vitamin D may be an important environmental component in this respect. Epidemiological evidence supports a pathogenetic link between vitamin D deficiency and the risk of IBD .
Inflammatory bowel diseases (IBDs) are immune mediated diseases affecting the gastrointestinal tract
Two distinct forms of IBDs have been defined, ulcerative colitis and Crohn’s disease
Epidemiological evidence supports a pathogenetic link between vitamin D deficiency and the risk of inflammatory bowel diseases
Vitamin D deficiency may compromise the mucosal barrier, leading to increased susceptibility to mucosal damage and increased risk of IBD, as suggested by studies in VDR deficient mice indicating a critical role for the VDR in mucosal barrier homeostasis, by preserving the integrity of junction complexes and the healing capacity of the colonic epithelium [190,191]. In IBD models, the immune-mediated attack against the gastrointestinal tract has been shown to be mediated by Th1 and Th17 cells, and the production of Th1-type cytokines has also been found associated with human IBDs .
Vitamin D deficiency may compromise the mucosal barrier leading to increased susceptibility to mucosal damage and consequent increased risk of inflammatory bowel diseases
Studies in vitamin D receptor deficient mice indicate a critical role for the vitamin D receptor in mucosal barrier homeostasis
In inflammatory bowel disease models, the immune mediated attack against the gastrointestinal tract has been shown to be mediated by Th1 and Th17 cells
The produciton of Th1 type cytokines has been found associated with human inflammatory bowel diseases
Conclusion: Biochemistry Offers a Level of Information Corroboration
Having reviewed a selection of work on the biochemistry of vitamin D and its relation to immune function we come to ask the question – ‘has this body of work lent any strength to the work reviewed by Seheult and Campbell ?’. In terms of scientific method and process we are working through what Thomas Henry Huxley called the Agnostic position.
Huxley coined the term in 1869 saying “It simply means that a man shall not say he knows or believes that which he has no scientific grounds for professing to know or believe”. In the philosophy of science, a theory needs to be falsifiable by resort to experiments which produce observations which count towards refuting or affirming the theory. This process of experiment and observation, over time, helps us build pictures of increasingly reliable knowledge.
Karl Popper is famous for making contributions to defining how we can distinguish scientific knowledge from un-scientific knowledge. What I have done above involves a process of corroboration which compares work synthesised by medical doctors largely based on statistical inference with biochemical work which brings together seasoned texts documenting what we know about a substance – in this case vitamin D.
This process, in the absence of large laboratories and tremendous resources I argue is a valuable and important tool in scientific and medical research. There is a lot of discussion about how the randomised, double blind, placebo control trial is the gold standard of medical science testing but there are distinct problems with this – namely resourcing such cumbersome ways of going about affirmation. I still have not found a randomised, double blind, placebo control trial on whether water is an effective rehydrating agent for those who suffer from dehydration.
The fetishization of knowledge forms and the fetishization of status are two barriers to progress. A multiplicity of informational source is essential for the researcher to search for patterns in nature. Using library publications to falsify theories is an important mode of working in a time when so much information is available via the internet and libraries. What is important here is that knowledge building is done with sufficiently reliable information sources.
The internet and life in general is abound with opinion but opinion is largely empty calories in terms of science. Getting hold of papers and books which have gone through some sort of mutual checking process is the bread and butter of scientific and medical knowledge building. Communities of peer review are embodying the requirement of authors having their work critically thought about before it is published and this counts towards picking up on mistakes, misapprehensions and other problems in complex fields.
Building on picture which Seheult and Campbell have offered on vitamin D possibly being useful in terms of covid 19 I have set out to see if there is corroborating information about its mechanism of action. Taking a well researched textbook you can see that there is a body of evidence that vitamin D does indeed play critical roles in immunity. What has happened in this research process is that a series of possible mechanisms of action have arisen to explain why vitamin D is working to offer health benefits in terms of covid 19 infection.
The theory that vitamin D is therapeutic in this context has become increasingly reliable as opposed to decreasingly reliable. If there were no studies demonstrating that vitamin D causes repeatedly observable effects on human immune cells, I would have judged the work to be decreasingly reliable knowledge.
In particular the mechanism(s) of action seem to be:
The stimulation of production of antimicrobial peptides cathelicidin and defensins
The participation in and coordination of innate and adaptive immune responses
This is a part of a series of works where I am studying the administrative processes and methods available to organise scientific and medical knowledge. Above has been a loose demonstration of a forensic verbatim science methodology used to keep track of where and how positive statements of ‘fact’ are brought into conjunction with each other to produce a study of a medical and/or scientific phenomenon. You can see a more seasoned example in the study I did on atopic conditions HERE.
If you are interested in reading more about how scientific knowledge comes about you can read more in the article below. Please leave any thoughts and critiques in the comments section below, or, if you want any information about the bibliographies referenced in ‘Vitamin D. Edited by Feldman, D., Pike, J. W., & In Bouillon, R.’ get in touch and I can furnish you with them.
This article was written by Alex Dunedin