The targets of vitamin D depend on the differentiation and activation status of CD4 positive T cells

Vitamin D and chronic rhinitis

PURPOSE OF REVIEW

To discuss the role of vitamin D in chronic rhinitis and chronic rhinosinusitis (CRS).

RECENT FINDINGS

Vitamin D has been shown to have an immunomodulatory effect with a significant impact on immune function. Specifically, vitamin D regulates the mechanisms which suppress the inflammatory response and direct the differentiation fate of immune cells. Vitamin D has been shown to play an important role in asthma, and the concept of the unified airway model allows the extrapolation of vitamin D as a critical player in chronic rhinitis and rhinosinusitis.

SUMMARY

Recent findings on the function of vitamin D may explain aspects of the pathophysiology of chronic rhinitis and CRS, and may help direct future treatment of these diseases.

Adjudication of the alleged role of vitamin d in the antimicrobial pathway

Dynamic interactions between microorganism and host have evolved in such a way that while microbial pathogens are the cause of many human infections, a symbiotic relationship is also known to exist. Another important anomaly is that exposure to pathogenic organisms does not necessarily result in development of clinical disease. The latter conclusion infers that susceptibility to infectious disease can be modified by host-related factors. Arguably the two most prominent factors are genetic variability and immunologic status of the exposed individual. Because of the Human Genome and the HapMap projects, developments in genotyping technology have brought the possibility of identifying associations between specific genetic alterations and common diseases closer to reality. In addition, a growing body of evidence suggests vitamin D has an important contributory role in the antimicrobial pathway.

Low vitamin D status: definition, prevalence, consequences, and correction

Low vitamin D status is extremely common worldwide due to low dietary intake and low skin production. Suboptimal vitamin D status contributes to many conditions, including osteomalacia/rickets, osteoporosis, falls, and fractures. It is possible or even likely that low vitamin D status increases risk for a multitude of other conditions. Although consensus does not exist, it appears that circulating 25(OH)D concentrations greater than 30 to 32 ng/mL are needed for optimal health. To achieve this, daily intakes of at least 1000 IU of D3 daily are required, and it is probable that substantially higher amounts are required to achieve such values on a population basis. It seems premature to recommend widespread screening for 25(OH)D measurement. Targeted measurement in those at increased risk for vitamin D deficiency and those most likely to have a prompt positive response to supplementation is appropriate. Widespread optimization of vitamin D status likely will lead to prevention of many diseases with attendant reduction of morbidity, mortality, and expense.

Vitamin D deficiency exacerbates experimental stroke injury and dysregulates ischemia-induced inflammation in adult rats

Vitamin D deficiency (VDD) is widespread and considered a risk factor for cardiovascular disease and stroke. Low vitamin D levels are predictive for stroke and more fatal strokes in humans, whereas vitamin D supplements are associated with decreased risk of all-cause mortality. Because VDD occurs with other comorbid conditions that are also independent risk factors for stroke, this study examined the specific effect of VDD on stroke severity in rats. Adult female rats were fed control or VDD diet for 8 wk and were subject to middle cerebral artery occlusion thereafter. The VDD diet reduced circulating vitamin D levels to one fifth (22%) of that observed in rats fed control chow. Cortical and striatal infarct volumes in animals fed VDD diet were significantly larger, and sensorimotor behavioral testing indicated that VDD animals had more severe poststroke behavioral impairment than controls. VDD animals were also found to have significantly lower levels of the neuroprotective hormone IGF-I in plasma and the ischemic hemisphere. Cytokine analysis indicated that VDD significantly reduced IL-1α, IL-1β, IL-2, IL-4, IFN-γ, and IL-10 expression in ischemic brain tissue. However, ischemia-induced IL-6 up-regulation was significantly higher in VDD animals. In a separate experiment, the therapeutic potential of acute vitamin D treatments was evaluated, where animals received vitamin D injections 4 h after stroke and every 24 h thereafter. Acute vitamin D treatment did not improve infarct volume or behavioral performance. Our data indicate that VDD exacerbates stroke severity, involving both a dysregulation of the inflammatory response as well as suppression of known neuroprotectants such as IGF-I.

Management of inflammatory bowel disease with vitamin D: beyond bone health

A relationship between vitamin D and several disorders, including Crohn's disease (CD), has recently been proposed. Vitamin D appears to have several important actions beyond the maintenance of bone health, including various effects on the immune system. Vitamin D deficiency has been implicated in the development of CD, and its analogues may have a role in the treatment of CD. Current research also suggests a role for vitamin D in counteracting some IBD-specific complications, including osteopenia, colorectal neoplasia, and depression. There remains a need for prospective studies to further delineate these relationships. Given current evidence and the apparent safety of vitamin D supplementation, it appears reasonable to screen for and treat vitamin D deficiency in patients with IBD.

Different doses of supplemental vitamin D maintain interleukin-5 without altering skeletal muscle strength: a randomized, double-blind, placebo-controlled study in vitamin D sufficient adults

BACKGROUND

Supplemental vitamin D modulates inflammatory cytokines and skeletal muscle function, but results are inconsistent. It is unknown if these inconsistencies are dependent on the supplemental dose of vitamin D. Therefore, the purpose of this study was to identify the influence of different doses of supplemental vitamin D on inflammatory cytokines and muscular strength in young adults.

METHODS

Men (n = 15) and women (n = 15) received a daily placebo or vitamin D supplement (200 or 4000 IU) for 28-d during the winter. Serum 25-hydroxyvitamin D (25(OH)D), cytokine concentrations and muscular (leg) strength measurements were performed prior to and during supplementation. Statistical significance of data were assessed with a two-way (time, treatment) analysis of variance (ANOVA) with repeated measures, followed by a Tukey's Honestly Significant Difference to test multiple pairwise comparisons.

RESULTS

Upon enrollment, 63% of the subjects were vitamin D sufficient (serum 25(OH)D ≥ 30 ng/ml). Serum 25(OH)D and interleukin (IL)-5 decreased (P < 0.05) across time in the placebo group. Supplemental vitamin D at 200 IU maintained serum 25(OH)D concentrations and increased IL-5 (P < 0.05). Supplemental vitamin D at 4000 IU increased (P < 0.05) serum 25(OH)D without altering IL-5 concentrations. Although serum 25(OH)D concentrations correlated (P < 0.05) with muscle strength, muscle strength was not changed by supplemental vitamin D.

CONCLUSION

In young adults who were vitamin D sufficient prior to supplementation, we conclude that a low-daily dose of supplemental vitamin D prevents serum 25(OH)D and IL-5 concentration decreases, and that muscular strength does not parallel the 25(OH)D increase induced by a high-daily dose of supplemental vitamin D. Considering that IL-5 protects against viruses and bacterial infections, these findings could have a broad physiological importance regarding the ability of vitamin D sufficiency to mediate the immune systems protection against infection.

Vitamin D improves viral response in hepatitis C genotype 2-3 naïve patients

AIM: To examine whether vitamin D improved viral response and predicted treatment outcome in patients with hepatitis C virus (HCV) genotype 2-3.

METHODS: Fifty patients with chronic HCV genotype 2-3 were randomized consecutively into two groups: Treatment group [20 subjects, age 48 ± 14 years, body mass index (BMI) 30 ± 6, 65% male], who received 180 μg pegylated α-interferon-2a plus oral ribavirin 800 mg/d (Peg/RBV), together with oral vitamin D3 (Vitamidyne D drops; 2000 IU/d, 10 drops/d, normal serum level > 32 ng/mL) for 24 wk; and control group (30 subjects, age 45 ± 10 years, BMI 26 ± 3, 60% male), who received identical therapy without vitamin D. HCV RNA was assessed by reverse transcription polymerase chain reaction. Undetectable HCV RNA at 4, 12 and 24 wk after treatment was considered as rapid virological response, complete early virological response, and sustained virological response (SVR), respectively. Biomarkers of inflammation were measured.

RESULTS: The treatment group with vitamin D had higher BMI (30 ± 6 vs 26 ± 3, P < 0.02), and high viral load (> 400 000 IU/mL, 65% vs 40%, P < 0.01) than controls. Ninety-five percent of treated patients were HCV RNA negative at week 4 and 12. At 24 wk after treatment (SVR), 19/20 (95%) treated patients and 23/30 (77%) controls were HCV RNA negative (P < 0.001). Baseline serum vitamin D levels were lower at baseline (20 ± 8 ng/mL) and increased after 12 wk vitamin D treatment, to a mean level of (34 ± 11 ng/mL). Logistic regression analysis identified vitamin D supplement [odds ratio (OR) 3.0, 95% CI 2.0-4.9, P < 0.001], serum vitamin D levels (< 15 or > 15 ng/mL, OR 2.2, P < 0.01), and BMI (< 30 or > 30, OR 2.6, P < 0.01) as independent predictors of viral response. Adverse events were mild and typical of Peg/RBV.

CONCLUSION: Low vitamin D levels predicts negative treatment outcome, and adding vitamin D to conventional Peg/RBV therapy for patients with HCV genotype 2-3 significantly improves viral response.

The relationship between Th1/Th2 balance and 1α,25-dihydroxyvitamin D₃ in patients with nasal polyposis

We aimed to study Th1/Th2 cell balance by measuring the levels of cytokines IL-4, IL-10, and IFN-γ, which play an important role in the immune response of patients with allergic rhinitis and/or nasal polyps, and determine the correlation between Th1/Th2 cell balance and 1α,25-dihydroxyvitamin D(3), an active metabolite of vitamin D. The study subjects were 60 adult patients and 40 healthy volunteers. Subjects were separated into three groups: 30 patients diagnosed with nasal polyposis together with allergic rhinitis formed Group I, 30 patients with nasal polyposis but without allergic rhinitis constituted Group II, and 40 healthy volunteers without nasal polyp and/or allergic rhinitis were the control group, or Group III. IFN-γ, IL-4, IL-10, and total IgE levels were determined in the serum samples of all patients and vitamin D(3) in their plasma. A statistically significant difference was found between the Group I and the control group in their IgE, IL-4, IL-10, IFN-γ, and vitamin D levels (p < 0.05), while there were no such significant differences between Group II and the control group in these measurements (p > 0.05). Within Group I, vitamin D levels showed a negative correlation with IgE and IL-4 levels, and a positive correlation with IFN-γ (p < 0.05). Within Group II, IgE levels showed a positive correlation with IL-4 and IL-10 levels (p < 0.05) and a negative correlation with IFN-γ levels (p < 0.05). In this study, no significant relation was detected between vitamin D deficiency and nasal polyposis in the absence of allergic rhinitis. The study demonstrates that vitamin D is effective on Th1/Th2 balance in patients with allergic rhinitis and that there is a significant relation between vitamin D deficiency and allergy. These results are compatible with the possibility of an important role of vitamin D in the pathogenesis and degree of severity of allergic disease, and its capacity to control allergic disease.

Translating the role of vitamin D3 in infectious diseases

Vitamin D(3) affects both the innate as well as adaptive immune responses. Epidemiological studies have established that vitamin D(3) deficiency plays an important role in tuberculosis (TB) and viral influenza prevalence as well as susceptibility to active disease in TB. Vitamin D(3) status has been associated with the clinical course of HIV infection and drug interaction with anti-retroviral therapy. This article reviews the immunomodulatory capacity of vitamin D(3) and examines the impact of vitamin D(3) supplementation as a preventive or therapeutic intervention with the intent to uncover its potential therapeutic application in infectious diseases and to identify novel areas for future research. We present a review of randomized, controlled clinical studies conducted in humans which included assessment of the immune function or clinical outcome as study end points. Current data support vitamin D(3) supplementation as risk-modifying intervention in tuberculosis and viral respiratory tract infection, but the optimal dosage regimen remains to be determined. However, to date the knowledge on its role in fungal infection and sepsis is limited although a potential benefit could be harnessed from its ability to curtail the unrestrained pro-inflammatory response and therefore prevent excessive collateral tissue damage.

Fat-soluble vitamins and atopic disease: what is the evidence?

The prevalence of asthma and other atopic disorders continues to increase worldwide. Examination of the epidemiologic patterns has revealed that this rise has occurred primarily in western, industrialised countries and countries transitioning to this lifestyle. While many changes have occurred in human populations over the years, it has been hypothesised that some of the relevant changes that have led to the rise in asthma and atopic disorders have been the changes from a traditional diet to a more western diet consisting of decreased intake of fruits and vegetables (sources of antioxidant vitamins and carotenoids) leading to decreased intakes of vitamins E and A, and a decrease in sun exposure (e.g. greater time spent indoors and heavy use of sunscreen) leading to decreased circulating levels of vitamin D. This review will examine the evidence for an effect of fat-soluble vitamins (vitamins A, D and K) on the development and severity of asthma and allergies. While observational studies suggest that these vitamins may play a salutary role in asthma and allergies, large, well-designed clinical trials are lacking. Of the fat-soluble vitamins, vitamin D holds great promise as an agent for primary and secondary prevention of disease. Ongoing clinical trials will help determine whether results of observational studies can be applied to the clinical setting.

Seasonal variation in vitamin D₃ levels is paralleled by changes in the peripheral blood human T cell compartment

It is well-recognized that vitamin D₃ has immune-modulatory properties and that the variation in ultraviolet (UV) exposure affects vitamin D₃ status. Here, we investigated if and to what extent seasonality of vitamin D₃ levels are associated with changes in T cell numbers and phenotypes. Every three months during the course of the entire year, human PBMC and whole blood from 15 healthy subjects were sampled and analyzed using flow cytometry. We observed that elevated serum 25(OH)D₃ and 1,25(OH)₂D₃ levels in summer were associated with a higher number of peripheral CD4⁺ and CD8⁺ T cells. In addition, an increase in naïve CD4⁺CD45RA⁺ T cells with a reciprocal drop in memory CD4⁺CD45RO⁺ T cells was observed. The increase in CD4⁺CD45RA⁺ T cell count was a result of heightened proliferative capacity rather than recent thymic emigration of T cells. The percentage of Treg dropped in summer, but not the absolute Treg numbers. Notably, in the Treg population, the levels of forkhead box protein 3 (Foxp3) expression were increased in summer. Skin, gut and lymphoid tissue homing potential was increased during summer as well, exemplified by increased CCR4, CCR6, CLA, CCR9 and CCR7 levels. Also, in summer, CD4⁺ and CD8⁺ T cells revealed a reduced capacity to produce pro-inflammatory cytokines. In conclusion, seasonal variation in vitamin D₃ status in vivo throughout the year is associated with changes in the human peripheral T cell compartment and may as such explain some of the seasonal variation in immune status which has been observed previously. Given that the current observations are limited to healthy adult males, larger population-based studies would be useful to validate these findings.

1,25-Dihydroxyvitamin D3 inhibits proliferation but not the suppressive function of regulatory T cells in the absence of antigen-presenting cells

Vitamin D3 is known to induce regulatory T (Treg) cells by rendering antigen-presenting cells tolerogenic, its direct effect on human naturally occurring Treg cells is unclear. Here, we investigated if and how 1,25-dihydroxyvitamin D(3) [1,25(OH)2D3] can directly affect the proliferation and function of human naturally occurring Treg cells in vitro. First, we demonstrated that these Treg cells express vitamin D receptors that were up-regulated following anti-CD3/CD28-bead stimulation. 1,25(OH)2D3 inhibited proliferation of Treg cells even when exogenous interleukin-2 was provided. Treg cells were more susceptible to the inhibitory effect of 1,25(OH)2D3 than conventional T cells(.) 1,25(OH)2D3 neither affected the anergic state nor the suppressive function of Treg cells but induced a subtle increase in interleukin-10-secreting cells. The cell-division-inhibiting effect of 1,25(OH)2D3 on Treg cells was also demonstrated in vivo by supplementing vitamin D-deficient HIV-1-infected patients with 2000 IU cholecalciferol (vitamin D3). Increased serum 1,25(OH)2D3 levels were associated with a drop in the number and percentage of Treg cells, which may be attributed to a decrease in the proliferating Foxp3+ Treg cell population. In conclusion, 1,25(OH)2D3 directly affects Treg cell growth and promotes interleukin-10 production without apparent effects on activation status and suppressive phenotype whereas in vivo, high serum 1,25(OH)2D3 levels are associated with reduced Treg cell proliferation and a reduced number of Treg cells.

Vitamin D supplementation improves sustained virologic response in chronic hepatitis C (genotype 1)-naïve patients

AIM: To determine whether adding vitamin D, a potent immunomodulator, improves the hepatitis C virus (HCV) response to antiviral therapy.

METHODS: Seventy-two consecutive patients with chronic HCV genotype 1 were randomized into two groups: the treatment group (n = 36, 50% male, mean age 47 ± 11 years) received Peg-α-2b interferon (1.5 μg/kg per week) plus ribavirin (1000-1200 mg/d) together with vitamin D3 (2000 IU/d, target serum level > 32 ng/mL), and the control group (n = 36, 60% male, mean age 49 ± 7 years) received identical therapy without vitamin D. HCV-RNA was assessed by real-time polymerase chain reaction (sensitivity, 10 IU/mL). The sustained virologic response (SVR) was defined as undetectable HCV-RNA at 24 wk post-treatment.

RESULTS: Clinical characteristics were similar in both groups. The treatment group had a higher mean body mass index (27 ± 4 kg/m²vs 24 ± 3 kg/m²; P < 0.01), viral load (50% vs 42%, P < 0.01), and fibrosis score (> F2: 42% vs 19%, P < 0.001) than the controls. At week 4, 16 (44%) treated patients and 6 (17%) controls were HCV-RNA negative (P < 0.001). At week 12, 34 (94%) treated patients and 17 (48%) controls were HCV-RNA negative (P < 0.001). At 24 wk post-treatment (SVR), 31 (86%) treated patients and 15 (42%) controls were HCV-RNA negative (P < 0.001). Viral load, advanced fibrosis and vitamin D supplementation were strongly and independently associated with SVR (multivariate analysis). Adverse events were mild and typical of Peg-α-2b/ribavirin.

CONCLUSION: Adding vitamin D to conventional Peg-α-2b/ribavirin therapy for treatment-naïve patients with chronic HCV genotype 1 infection significantly improves the viral response.

Progesterone and vitamin d hormone as a biologic treatment of traumatic brain injury in the aged

There is growing recognition that traumatic brain injury is a highly variable and complex systemic disorder that is refractory to therapies that target individual mechanisms. It is even more complex in elderly persons, in whom frailty, previous comorbidities, altered metabolism, and a long history of medication use are likely to complicate the secondary effects of brain trauma. Progesterone, one of the few neuroprotective agents that has shown promise for the treatment of acute brain injury, is now in national and international phase 3 multicenter trials. New findings show that vitamin D hormone (VDH) and VDH deficiency in the aging process (and across the developmental spectrum) may interact with progesterone and treatment for traumatic brain injury. In this article we review the use of progesterone and VDH as biologics-based therapies along with recent studies demonstrating that the combination of progesterone and VDH may promote better functional outcomes than either treatment independently.

Vitamin D and diabetes: its importance for beta cell and immune function

Experimental evidence indicates that vitamin D may play a role in the defense against type 1 diabetes (T1D) as well as type 2 diabetes (T2D). Epidemiological data have established a link between vitamin D deficiency and an increased incidence of both T1D and T2D, whereas early and long-term vitamin D supplementation may decrease the risk of these disorders. The protective effects of vitamin D are mediated through the regulation of several components such as the immune system and calcium homeostasis. However, an increasing amount of evidence suggests that vitamin D also affects beta cells directly thereby rendering them more resistant to the types of cellular stress encountered during T1D and T2D. This review evaluates the role of vitamin D signaling in the pathogenesis of T1D and T2D with a special emphasis on the direct effects of vitamin D on pancreatic beta cells.

Vitamin D regulation of immune function in the gut: why do T cells have vitamin D receptors?

Low vitamin D status is associated with an increased risk of immune-mediated diseases like inflammatory bowel disease (IBD) in humans. Experimentally vitamin D status is a factor that shapes the immune response. Animals that are either vitamin D deficient or vitamin D receptor (VDR) deficient are prone to develop IBD. Conventional T cells develop normally in VDR knockout (KO) mice but over-produce IFN-γ and IL-17. Naturally occurring FoxP3+ regulatory T cells are present in normal numbers in VDR KO mice and function as well as wildtype T regs. Vitamin D and the VDR are required for the development and function of two regulatory populations of T cells that require non-classical MHC class 1 for development. The two vitamin D dependent cell types are the iNKT cells and CD4/CD8αα intraepithelial lymphocytes (IEL). Protective immune responses that depend on iNKT cells or CD8αα IEL are therefore impaired in the vitamin D or VDR deficient host and the mice are more susceptible to immune-mediated diseases in the gut.

Vitamin D3: a helpful immuno-modulator

The active metabolite of vitamin D, 1α, 25-dihydroxyvitamin D3 [1,25(OH)(2) D3], is involved in calcium and phosphate metabolism and exerts a large number of biological effects. Vitamin D3 inhibits parathyroid hormone secretion, adaptive immunity and cell proliferation, and at the same time promotes insulin secretion, innate immunity and stimulates cellular differentiation. The role of vitamin D3 in immunoregulation has led to the concept of a dual function as both as an important secosteroid hormone for the regulation of body calcium homeostasis and as an essential organic compound that has been shown to have a crucial effect on the immune responses. Altered levels of vitamin D3 have been associated, by recent observational studies, with a higher susceptibility of immune-mediated disorders and inflammatory diseases. This review reports the new developments with specific reference to the metabolic and signalling mechanisms associated with the complex immune-regulatory effects of vitamin D3 on immune cells.

Vitamin D and asthma

Vitamin D deficiency and asthma are common conditions that share risk factors such as African American ethnicity, inner-city residence, and obesity. This review provides a critical examination of current experimental and epidemiologic evidence of a causal association between vitamin D status and asthma or asthma morbidity, including potential protective mechanisms such as antiviral effects and enhanced steroid responsiveness. Because most published epidemiologic studies of vitamin D and asthma or asthma morbidity are observational, a recommendation for or against vitamin D supplementation as preventive or secondary treatment for asthma is not advisable and must await results of ongoing clinical trials. Should these trials confirm a beneficial effect of vitamin D, others will be needed to assess the role of vitamin D supplementation to prevent or treat asthma in different groups such as infants, children of school age, and ethnic minorities.

Vitamin D: immunomodulation of asthma, allergic rhinitis, and chronic rhinosinusitis

PURPOSE OF REVIEW

To discuss the role of vitamin D in asthma, allergic rhinitis, and chronic rhinosinusitis (CRS).

RECENT FINDINGS

Over the last several years, the role of vitamin D in immunomodulation has been studied and shown to have a significant impact on immune function. A causal relationship exists between vitamin D function and innate and adaptive immunity to infections. The mechanisms underlying vitamin D immune actions could be attributed to a paracrine feedback loop that reduces inflammation as well as influencing the differentiation fate of activated CD4 T cells, or the enhancement of suppressor T-cell function; indeed, a combination of these factors may underlie the actions of vitamin D.

SUMMARY

Recent findings on the function of vitamin D may explain aspects of the pathophysiology of allergic rhinitis and CRS and may help direct future interventions and treatment of these diseases.

Invariant NKT cell defects in vitamin D receptor knockout mice prevents experimental lung inflammation

Vitamin D receptor (VDR) deficiency (knockout [KO]) results in a failure of mice to generate an airway hyperreactivity (AHR) response on both the BALB/c and C57BL/6 background. The cause of the failed AHR response is the defective population of invariant NKT (iNKT) cells in the VDR KO mice because wild-type (WT) iNKT cells rescued the AHR response. VDR KO mice had significantly fewer iNKT cells and normal numbers of T cells in the spleen compared with WT mice. In BALB/c VDR KO mice, the reduced frequencies of iNKT cells were not apparent in the liver or thymus. VDR KO and WT Th2 cells produced similar levels of IFN-γ and IL-5. On the BALB/c background, Th2 cells from VDR KO mice produced less IL-13, whereas on the C57BL/6 background, Th2 cells from VDR KO mice produced less IL-4. Conversely, VDR KO iNKT cells were defective for the production of multiple cytokines (BALB/c: IL-4, IL-5, and IL-13; C57BL/6: IL-4 and IL-17). Despite relatively normal Th2 responses, BALB/c and C57BL/6 VDR KO mice failed to develop AHR responses. The defect in iNKT cells as a result of the VDR KO was more important than the highly susceptible Th2 background of the BALB/c mice. Defective iNKT cell responses in the absence of the VDR result in the failure to generate AHR responses in the lung. The implication of these mechanistic findings for human asthma requires further investigation.

Vitamin D3: a helpful immuno-modulator

The active metabolite of vitamin D, 1α, 25-dihydroxyvitamin D3 [1,25(OH)(2) D3], is involved in calcium and phosphate metabolism and exerts a large number of biological effects. Vitamin D3 inhibits parathyroid hormone secretion, adaptive immunity and cell proliferation, and at the same time promotes insulin secretion, innate immunity and stimulates cellular differentiation. The role of vitamin D3 in immunoregulation has led to the concept of a dual function as both as an important secosteroid hormone for the regulation of body calcium homeostasis and as an essential organic compound that has been shown to have a crucial effect on the immune responses. Altered levels of vitamin D3 have been associated, by recent observational studies, with a higher susceptibility of immune-mediated disorders and inflammatory diseases. This review reports the new developments with specific reference to the metabolic and signalling mechanisms associated with the complex immune-regulatory effects of vitamin D3 on immune cells.

Cholecalciferol plus calcium suppresses abnormal PBMC reactivity in patients with multiple sclerosis

CONTEXT

The active metabolite of vitamin D, 1,25-dihydroxyvitamin D [1,25(OH)(2)D], is a potent modulator of immune cells in vitro.

OBJECTIVE

Our objective was to determine whether the sun-dependent nutrient, cholecalciferol, can alter disease-associated cellular immune abnormalities in patients with multiple sclerosis (MS).

DESIGN

This was an open-label, 12-month, randomized controlled trial.

SETTING

Patients with MS were recruited from the MS Clinic at St. Michael's Hospital, Toronto.

PATIENTS

Forty-nine patients were matched (for age, sex, disease duration, disease-modifying drug, and disability) and enrolled (treated n = 25; control n = 24). Four patients were lost to follow-up (n = 2 from each group).

INTERVENTION

Treated patients received increasing doses of cholecalciferol (4,000-40,000 IU/d) plus calcium (1200 mg/d), followed by equilibration to a moderate, physiological intake (10,000 IU/d). Control patients did not receive supplements.

MAIN OUTCOME MEASURES

At enrollment and at 12 months, peripheral blood mononuclear cell (PBMC) proliferative responses to disease-associated, MS-relevant, and control antigens were measured, along with selected serum biochemical markers.

RESULTS

At 12 months, mean serum 25-hydroxyvitamin D [25(OH)D] concentrations were 83 ± 35 nmol/liter and 179 ± 76 nmol/liter in control and treated participants, respectively (paired t, P < 0.001). Serum 1,25(OH)(2)D did not differ between baseline and 1 yr. In treated patients, 12-month PBMC proliferative responses to neuron antigens myelin basic protein and exon-2 were suppressed (P = 0.002). In controls, there were no significant changes in disease-associated PBMC responsiveness. There were no significant differences between groups in levels of selected biomarkers.

INTERPRETATION

MS-associated, abnormal T cell reactivities were suppressed in vivo by cholecalciferol at serum 25(OH)D concentrations higher than 100 nmol/liter.

Vitamin D in autoimmune, infectious and allergic diseases: a vital player?

Vitamin D is a steroid hormone that is acquired via diet or synthesized in the skin upon UV exposure and needs subsequent hydroxylation steps to become activated as 1,25-dihydroxyvitamin D. While widely known for its role in maintaining bone health, vitamin D receptors have also been identified in different immune cell types. Many immune cells can also convert vitamin D into its bioactive form, thus enhancing the locally available concentrations to those required for the immunomodulatory effects of vitamin D. In this review, we summarize the genetic and epidemiologic data potentially linking vitamin D to autoimmune, infectious and allergic diseases. We also discuss how vitamin D influences the immune responses in each of those conditions based on the data generated using patient samples or preclinical models of each of these diseases.

Relative vitamin D insufficiency in Hashimoto's thyroiditis

BACKGROUND

Vitamin D insufficiency, defined as serum levels of 25-hydroxyvitamin D [25(OH)D3] lower than 30 ng/mL, has been reported to be prevalent in several autoimmune diseases such as multiple sclerosis and type 1 diabetes mellitus. The goal of the present study was to assess whether vitamin D insufficiency is also a feature of Hashimoto's thyroiditis (HT).

METHODS

We performed a prevalence case-control study that included 161 cases with HT and 162 healthy controls. Serum levels of 25(OH)D3, calcium, phosphorus, and parathyroid hormone were measured in all 323 subjects.

RESULTS

The prevalence of vitamin D insufficiency in HT cases (148 of 161, 92%) was significantly higher than that observed in healthy controls (102 of 162, 63%, p < 0.0001). Among HT cases, the prevalence rate of vitamin D insufficiency showed a trend to be higher in patients with overt hypothyroidism (47 of 50, 94%) or subclinical hypothyroidism (44 of 45, 98%) than in those with euthyroidism (57 of 66, 86%), but the differences were not significant (p = 0.083).

CONCLUSION

Vitamin D insufficiency is associated with HT. Further studies are needed to determine whether vitamin D insufficiency is a casual factor in the pathogenesis of HT or rather a consequence of the disease.

Low Vitamin D Impairs Strength Recovery After Anterior Cruciate Ligament Surgery

The purpose of this study was to identify strength gains after an anterior cruciate ligament injury and surgery and during inflammatory challenge in participants with disparate vitamin D levels. Plasma samples were obtained from those who had not previously experienced an anterior cruciate ligament injury and from injured patients 2 weeks before and 3 months after anterior cruciate ligament surgery. Plasma 25-hydroxyvitamin D and cytokine concentrations were measured in each blood sample. Single-leg peak isometric forces were measured 2 weeks presurgery and 3 months postsurgery. Compared with noninjured participants, inflammatory cytokines were elevated prior to and following anterior cruciate ligament reconstruction. During this inflammatory challenge, the peak isometric force increases after surgery were significantly lower in those with plasma 25-hydroxyvitamin D concentrations <30 ng/mL compared with those with concentrations ≥30 ng/mL. The authors conclude that low vitamin D appears to hinder strength recovery after anterior cruciate ligament surgery and during inflammatory insult.

Vitamin D deficiency and connective tissue disease

Recently, the evidence linking vitamin D status as a potential environmental factor affecting autoimmune disease prevalence continues to accumulate. Beyond that the traditional known metabolic activities, vitamin D has been shown to modulate the immune system and has anti-inflammatory properties. The immune-regulatory role of vitamin D affects both the innate and adaptive immune responses contributing to the immune-tolerance of self-structures. Vitamin D deficiency skews the immunologic response towards loss of tolerance. Serum levels of vitamin D have been found to be significantly lower in several autoimmune or immune-mediated diseases than in the healthy population. Experimental animal models and clinical studies show that 1,25-dihydroxyvitamin D3 or vitamin D receptor (VDR) agonists can either prevent or suppress symptoms of type 1 diabetes, experimental autoimmune encephalomyelitis, rheumatoid arthritis, systemic lupus erthyematosus and inflammatory bowel disease. The heading aims at reviewing the complex immune-regulatory role of vitamin D from the cellular and humoral level through animal models of autoimmune rheumatic diseases and representing the known contribution of vitamin D in the pathogenesis of connective tissue diseases. Increased vitamin D intakes might reduce the incidence and severity of autoimmune disorders besides reducing the rate of osteoporotic bone fracture.

Vitamin D-mediated immune regulation in multiple sclerosis

Although Vitamin D is best known as a modulator of calcium homeostasis, it also has immune modulating potential. A protective effect of Vitamin D on Multiple Sclerosis (MS) is supported by the reduced risk associated with sun exposure and use of Vitamin D supplements. Moreover, high circulating levels of Vitamin D have been associated with lower risk of MS. To gain more insight into putative regulatory mechanisms of Vitamin D in MS pathogenesis, we studied 132 Hispanic patients with clinically definite MS, 58 with relapsing remitting MS (RR MS) during remission, 34 RR MS patients during relapse, and 40 primary progressive MS cases (PP MS). Sixty healthy individuals matched with respect to place of residence, race/ethnicity, age and gender served as controls. Levels of 25(OH) Vitamin D and 1,25(OH)(2) Vitamin D, measured by ELISA were significantly lower in RR MS patients than in controls. In addition, levels in patients suffering relapses were lower than during remissions. By contrast, PP 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)(2) Vitamin D. Moreover, activated Vitamin D enhanced the development of IL-10 producing cells, and reduced the number of IL-6 and IL-17 secreting cells. Notably, VDR expression was induced by 1,25(OH)(2) Vitamin D in both activated and resting cells. Interestingly, T cells were able to metabolize 25(OH) Vitamin D into biologically active 1,25(OH)(2) Vitamin D, since T cells express 1α-hydroxylase constitutively. Finally, 1,25(OH)(2) Vitamin D also increased the expression and biological activity of IDO, triggering significant increase in the number of CD4+CD25+ T regulatory cells. Collectively, these findings suggest that 1,25(OH)(2) VitaminD plays an important role in T cell homeostasis during the course of MS, suggesting correction of its deficiency may be useful during treatment of the disease.

Vitamin D and chronic lung disease: a review of molecular mechanisms and clinical studies

Vitamin D is classically recognized for its role in calcium homeostasis and skeletal metabolism. Over the last few decades, vitamin D deficiency has increased in prevalence in adults and children. Potential extraskeletal effects of vitamin D have been under investigation for several diseases. Several cross-sectional studies have associated lower vitamin D status with decreased lung function. This finding has prompted investigators to examine the association of vitamin D deficiency with several chronic lung diseases. One major focus has been the link between maternal vitamin D status and childhood asthma. Vitamin D deficiency has also been associated with increased risk of respiratory infection from influenza A and Mycobacterium tuberculosis. Other chronic respiratory diseases associated with vitamin D deficiency include cystic fibrosis, interstitial lung disease, and chronic obstructive pulmonary disease. This review will examine the current clinical literature and potential mechanisms of vitamin D in various pulmonary diseases.

The impact of vitamin D on regulatory T cells

Epidemiologic studies highlight the increasing prevalence of vitamin D deficiency and insufficiency and its association with an increased risk of autoimmune diseases and poor respiratory function, including asthma. These and additional studies have raised interest in the immunomodulatory properties of vitamin D beyond its well-established role in calcium homeostasis and bone health. Vitamin D has been shown to influence the function of cells intrinsic to innate and adaptive immunity. This review discusses recent evidence that vitamin D promotes--both directly and indirectly--regulatory or suppressor T-cell populations with the capacity to inhibit inappropriate immune responses that cause disease, suggesting that this property may in part underpin the epidemiologic findings.

Role of vitamin D in immune responses and autoimmune diseases, with emphasis on its role in multiple sclerosis

Vitamin D is a seco-steroid involved in calcium and phosphorus metabolism, and bone formation and mineralization, through binding to a specific nuclear receptor, vitamin D receptor (VDR). Besides its well-established functions on bone health, multiple lines of evidence have indicated the immunomodulatory roles of vitamin D. Vitamin D can affect both innate and adaptive immunity, and prevent autoimmune responses efficiently. Vitamin D regulates the immune responses by suppressing T cell proliferation and modulating macrophage functions. Epidemiological studies have shown that vitamin D deficiency is associated with multiple diseases such as rickets and cancer. Moreover, associations between vitamin D and autoimmune diseases have been confirmed in multiple sclerosis (MS), rheumatoid arthritis (RA), etc. The present review mainly summarized the recent findings on the immunomodulatory role of vitamin D in various disorders, with special focus on its role in MS, an autoimmune disease of the nervous system.

Vitamin D and asthma

PURPOSE OF REVIEW

asthma is a disease that continues to carry a significant health burden on humanity. Vitamin D is thought to play a role in many chronic diseases as it may possess immunomodulatory properties. This article will review the role of vitamin D regulation on the immune system and its potential implication in the pathophysiology of asthma.

RECENT FINDINGS

vitamin D receptors are present on many cells in the body, specifically peripheral blood mononuclear cells. Vitamin D has been shown to regulate the balance of several pro-inflammatory and anti-inflammatory responses in the immune system. Studies have suggested that prenatal vitamin D intake has an effect on childhood wheezing and asthma. Additionally, vitamin D may play a role in asthma exacerbations, and recent evidence also suggests its importance in steroid resistant asthma.

SUMMARY

vitamin D has a complex role on the immune system and its regulation of various aspects of immunity has allowed speculation on its potential role in asthma. However, the net effect of vitamin D on the immune system and its role in asthma still remains unanswered. More research needs to address the diagnostic and therapeutic implications vitamin D may have in the future of asthma management.

Vitamin D: emerging roles in infection and immunity

In the preantibiotic era, TB of the skin was treated successfully with UV light. By the 1920s, pulmonary TB was being treated with regular sun exposure. During the last decade, basic laboratory research into the antimicrobial actions of vitamin D has provided new insights into these historical observations. Vitamin D has a critical role in the innate immune system through the production of antimicrobial peptides - particularly cathelicidin. Vitamin D would appear to have an important role in respiratory tract, skin and potentially gut health. A number of autoimmune diseases, including multiple sclerosis, Type I diabetes, systemic lupus erythematosus and rheumatoid arthritis, are associated with vitamin D deficiency. Vitamin D could have an important role in the prevention and possible treatment of these conditions; however, much of the current evidence relates to basic science and epidemiological research. In many situations, appropriate double-blind, randomized controlled trial data to guide clinicians treating infectious and autoimmune disease is still lacking.

Vitamin D in atopic dermatitis, asthma and allergic diseases

This review examines the scientific evidence behind the hypothesis that vitamin D plays a role in the pathogenesis of allergic diseases, along with a focus on emerging data regarding vitamin D and atopic dermatitis. Elucidated molecular interactions of vitamin D with components of the immune system and clinical data regarding vitamin D deficiency and atopic diseases are discussed. The rationale behind the sunshine hypothesis, laboratory evidence supporting links between vitamin D deficiency and allergic diseases, the clinical evidence for and against vitamin D playing a role in allergic diseases, and the emerging evidence regarding the potential use of vitamin D to augment the innate immune response in atopic dermatitis are reviewed.

Asthma and endocrine disorders: shared mechanisms and genetic pleiotropy

Asthma is a common inflammatory disease for which the cause is not yet known. Studies of the epidemiology and natural history of childhood asthma into adulthood demonstrate a change in gender prevalence with age. Hormones and inflammation may interact in asthma pathogenesis and determine its course. The same may be true for some endocrine disorders, including diabetes and obesity. Obesity plays a major role in the development of the metabolic syndrome and has been identified as an important risk factor for chronic diseases such as type 2 diabetes mellitus. The prevalence of asthma has paralleled the rise in obesity, suggesting that shared environmental factors could affect both conditions. In addition, endocrine diseases and asthma may share common genetic determinants. In the first part of this review we assess endocrine influences on asthma and overlaps between endocrine disorders and asthma while in the second part we explore the potential benefit of comparative genetic analyses between asthma and endocrine diseases.

Regulation of cytokine responses by seasonality of vitamin D status in healthy individuals

The immune modulating capacity of vitamin D(3) is well-recognized. Ultra-violet (UV) exposure determines production of vitamin D(3) in vivo and varies through the course of the year, especially in temperate regions. However, it is not known whether the human innate immune response differs due to seasonality. To validate the seasonal effects of vitamin D(3) , the effect of 1,25(OH)(2) D(3) on peripheral blood mononuclear cells (PBMC) cytokine response was first determined in vitro. 1,25(OH)(2) D(3) decreased interleukin (IL)-6 and tumour necrosis factor (TNF)-α release by PBMC stimulated with tripalmitoyl-S-glycerylcysteine (Pam3Cys) or lipopolysaccharide (LPS). Subsequently, ex-vivo stimulation studies were performed in 15 healthy volunteers through the course of the four seasons of the year. PBMC were isolated and stimulated with Toll-like receptor (TLR)-2 and TLR-4 ligands Pam3Cys and LPS, respectively. Circulating concentrations of 25(OH)D(3) and 1,25(OH)(2) D(3) were higher during summer (P<0·05) and a down-regulation of TLR-4-mediated IL-1β, IL-6, TNF-α, interferon (IFN)-γ and IL-10 production in summer was observed compared to winter (P<0·05). The variation in cytokine response upon TLR-2 (Pam3Cys) stimulation was moderate throughout the four seasons. The repressed cytokine production during the summer months could be explained partly by the reduced cell-membrane expression of TLRs. Physiological variation in vitamin D(3) status through the four seasons of the year can lead to alteration in the innate immune responses. Elevated vitamin D(3) level in vivo is associated with down-regulation of cytokine response through diminished surface expression of pattern recognition receptors.

Topical 1,25-dihydroxyvitamin D3 subverts the priming ability of draining lymph node dendritic cells

The active form of vitamin D, 1,25-hydroxyvitamin D(3) [1,25(OH)(2)D(3)] is produced in skin following exposure to sunlight. It is also used topically to control inflammatory skin diseases by stimulating keratinocyte differentiation and suppressing immune responses. Administration of 1,25(OH)(2)D(3) to the skin of mice increases the capacity of CD4(+) CD25(+) (Foxp3(+) ) regulatory T cells residing in the skin-draining lymph nodes (SDLN) to suppress immune responses. We hypothesized that dendritic cells (DC) may migrate from the skin to the lymph nodes to regulate T-cell function. Increased proportions of skin-derived DC (CD11c(+) ClassII(+) DEC-205(hi) CD8(lo)) cells were detected in the SDLN 18 hr after topical 1,25(OH(2) D(3) treatment of mouse skin. The capacity of DC from the SDLN to take up, process and present antigen to co-cultured T cells was not modified following topical 1,25(OH)(2)D(3). However, CD11c(+) cells from the SDLN of 1,25(OH)(2)D(3)-treated mice induced a significantly smaller ear-swelling response in a T helper type 1/17-mediated model of contact hypersensitivity. CD4(+) CD25(+) cells isolated from the ear-draining lymph nodes (EDLN) of mice that received ear injections of CD11c(+) cells from donor mice topically treated with 1,25(OH)(2)D(3) more potently suppressed effector cell proliferation. In addition, EDLN cells from recipients of CD11c(+) cells from 1,25(OH)(2)D(3)-treated mice produced increased interleukin-4 levels. The CD11c(+) cells from the SDLN of mice treated with topical 1,25(OH)(2)D(3) expressed increased levels of indoleamine 2,3-dioxygenase messenger RNA, a molecule by which topical 1,25(OH)(2)D(3) may enhance the ability of DC to control the suppressive function of CD4(+) CD25(+) cells.

Vitamin D: the iceberg nutrient

The understanding of vitamin D's role in human health has recently expanded. It is now recognized as more than a hormone activated in the kidney only for calcium homeostasis. It is metabolized and used by virtually every cell in the body. Patients with chronic kidney disease have a deficit in their kidney production of 1,25(OH)(2)D and have classically been treated with calcitriol or its active analogues. Despite often having lower systemic levels of 1,25(OH)(2)D, patients with chronic kidney disease retain the capability of extra renal production of 1,25(OH)(2)D. This has far reaching implications for their health. This review examines clinical trials and observations in 3 areas that impact chronic kidney disease patients. Cancer, cardiovascular disease and infections are responsible for much of the morbidity and mortality in this patient population. We will discuss vitamin D's role in these disease states with a focus on the chronic kidney disease patient.

Extraskeletal effects of vitamin D: facts, uncertainties, and controversies

Vitamin D was long viewed as a hormone acting chiefly to regulate calcium-phosphate metabolism and bone mineralization. Over the last decade, however, basic science and clinical researchers have produced a bewildering amount of information on the extraskeletal effects of vitamin D. This article is a review of the clinical and biological actions of vitamin D including effects on the immune system, auto-immune diseases, infections, cancer, metabolic syndrome, fall risk, cognitive function, and muscle function.

Vitamin D suppresses Th17 cytokine production by inducing C/EBP homologous protein (CHOP) expression

Vitamin D has been shown to have immunomodulatory function, but the molecular basis for it has not been well understood. In this study, we found that vitamin D receptor expression was induced in a CD4+ effector T cell lineage, Th17 cells, which required the transcription factors, RORα, RORγt, and STAT3. Treatment of mice with an active ligand of vitamin D receptor (VDR), 1,25-dihydroxyvitamin D(3) (1,25D3), ameliorated experimental autoimmune encephalomyelitis, accompanied with reduced IL-17 and IL-17F expression. In vitro, treatment of CD4+ T cells with the physiological doses of 1,25D3 preferentially inhibited cytokine production by Th17 cells, in a VDR-dependent manner, without affecting the expression of transcription factors or surface molecules. Moreover, at these concentrations, cytokine expression was suppressed only at protein but not at mRNA levels. Stimulation of Th17 cells with 1,25D3, in a concentration-dependent manner, induced the expression of C/EBP homologous protein (CHOP), a molecule involved in endoplasmic reticulum stress and translational inhibition. In addition, overexpression of CHOP in developing Th17 cells suppressed their cytokine production. Our results suggest a novel, post-transcriptional mechanism whereby Th17 cytokines are inhibited by VDR, which may underscore future therapeutic usage of vitamin D in treatment of autoimmune diseases.

The vitamin D analog, TX527, promotes a human CD4+CD25highCD127low regulatory T cell profile and induces a migratory signature specific for homing to sites of inflammation

The use of hypocalcemic vitamin D analogs is an appealing strategy to exploit the immunomodulatory actions of active vitamin D in vivo while circumventing its calcemic side effects. The functional modulation of dendritic cells by these molecules is regarded as the key mechanism underlying their ability to regulate T cell reactivity. In this article, we demonstrate the capacity of the vitamin D analog, TX527, to target T cells directly. Microarray analysis of purified human CD3(+) T cells, cultured in the presence of TX527, revealed differential expression of genes involved in T cell activation, proliferation, differentiation, and migratory capacity. Accordingly, functional analysis showed a TX527-mediated suppression of the T cell proliferative capacity and activation status, accompanied by decreased expression of effector cytokines (IFN-γ, IL-4, and IL-17). Furthermore, TX527 triggered the emergence of CD4(+)CD25(high)CD127(low) regulatory T cells featuring elevated levels of IL-10, CTLA-4, and OX40 and the functional capacity to suppress activation and proliferation of effector T cells. Moreover, the vitamin D analog profoundly altered the homing receptor profile of T cells and their migration toward chemokine ligands. Remarkably, TX527 not only modulated skin-homing receptors as illustrated for the parent compound, but also reduced the expression of lymphoid organ-homing receptors (CD62L, CCR7, and CXCR4) and uniquely promoted surface expression of inflammatory homing receptors (CCR5, CXCR3, and CXCR6) on T cells. We conclude that TX527 directly affects human T cell function, thereby inhibiting effector T cell reactivity while inducing regulatory T cell characteristics, and imprints them with a specific homing signature favoring migration to sites of inflammation.

Vitamin D3 treatment of Crohn's disease patients increases stimulated T cell IL-6 production and proliferation

BACKGROUND

Vitamin D3 has shown immune-modulating effects in CD4+ T cells from Crohn's disease patients in vitro.

AIM

To investigate the effects of in vivo vitamin D3 treatment on T cells in Crohn's disease patients.

METHODS

Peripheral blood mononuclear cells (PBMC) were isolated at week 0 and at week 26 from 10 vitamin D3- and 10 placebo-treated Crohn's disease patients participating in a randomized, placebo-controlled, clinical trial study. Monocyte-depleted PBMC were stimulated with anti-CD3 and anti-CD28, and cultured for 7, days, to investigate CD4+ T-cell proliferation and T-cell cytokine production.

RESULTS

In vitamin D3-treated patients, the median 25-hydroxyvitamin D3 levels increased 70 nmol/L compared with -5 nmol/L in the placebo group. Vitamin D3 treatment increased interleukin-6 production (delta = 188 pg/mL, range: -444 to 4071) compared with a decrease in the placebo group (delta = -896 pg/mL, range: -3841 to 1323) (P < 0.02, Wilcoxon rank sum test). Interestingly, vitamin D3 increased the amount of proliferating stimulated CD4+ T cells from median 41% (range: 10-75%) to 56% (range: 26-77%) (P = 0.02, Wilcoxon rank sum test).

CONCLUSIONS

Vitamin D3 treatment of Crohn's disease patients increased the IL-6 levels. Interestingly, vitamin D3 treatment enhanced the CD4+ T cell proliferation.

Why do T cells express the vitamin D receptor?

Vitamin D is an important regulator of immune function. T cells express the vitamin D receptor (VDR) and have been shown to be direct and indirect vitamin D targets. Why should T cells be responsive to vitamin D? The data suggest that expression of the VDR is required for the development of two cell types, NKT cells and CD8αα T cells, which inhibit autoimmunity. In addition, effector T cell cytokine production is regulated by vitamin D. Available evidence suggests that NKT and CD8αα T cells express the VDR as part of the selection process to protect against the generation of autoimmunity, particularly in the gut.

Vitamin D and inflammation

Calcitriol, or 1,25-dihydroxyvitamin D3 (1,25(OH)(2)D3) is a well-known endocrine regulator of calcium homeostasis. More recently, local calcitriol production by immune cells was shown to exert autocrine or paracrine immunomodulating effects. Immune cells that produce calcitriol also express the vitamin D receptor (VDR) and the enzymes needed to metabolize vitamin D3 (1α-, 25-, and 24-hydroxylases). Studies of animal models and cell cultures showed both direct and indirect immunomodulating effects involving the T cells, B cells, and antigen-presenting cells (dendritic cells and macrophages) and affecting both innate and adaptive immune responses. The overall effect is a switch from the Th1/Th17 response to the Th2/Treg profile. The immunomodulating effects of vitamin D may explain the reported epidemiological associations between vitamin D status and a large number of autoimmune and inflammatory diseases. Such associations have been suggested by observational studies not only in rheumatoid arthritis, lupus, inflammatory bowel disease, and type 1 diabetes; but also in infections, malignancies, transplant rejection, and cardiovascular disease. In animal models for these diseases, vitamin D supplementation has been found to produce therapeutic effects. Thus, vitamin D is a key focus for public health efforts and may hold promise for the treatment of dysimmune diseases.

Does vitamin D affect risk of developing autoimmune disease?: a systematic review

OBJECTIVES

We evaluated the epidemiologic evidence that vitamin D may be related to human autoimmune disease risk.

METHODS

PubMed, limited to English from inception through April 2010, was searched using keywords: "vitamin D," "autoimmune," and autoimmune disease names. We summarized in vitro, animal, and genetic association studies of vitamin D in autoimmune disease pathogenesis. We sorted epidemiologic studies by design and disease and performed a systematic review of (a) cross-sectional data concerning vitamin D level and autoimmune disease; (b) interventional data on vitamin D supplementation in autoimmune diseases; and (c) prospective data linking vitamin D level or intake to autoimmune disease risk.

RESULTS

Vitamin D has effects on innate and acquired immune systems, and vitamin D receptor polymorphisms have been associated with various autoimmune diseases. In experimental animal models, vitamin D supplementation can prevent or forestall autoimmune disease. Of 1446 studies identified and screened, 76 studies examined vitamin D levels in autoimmune disease patients, particularly with active disease, and compared with controls. Nineteen observational or interventional studies assessed the effect of vitamin D supplementation as therapy for various autoimmune diseases (excluding psoriasis and vitiligo) with a range of study approaches and results. The few prospective human studies performed conflict as to whether vitamin D level or intake is associated with autoimmune disease risk. No interventional trials have investigated whether vitamin D affects human autoimmune disease risk.

CONCLUSIONS

Cross-sectional data point to a potential role of vitamin D in autoimmune disease prevention, but prospective interventional evidence in humans is still lacking.

The seasonality of pandemic and non-pandemic influenzas: the roles of solar radiation and vitamin D

OBJECTIVES

Seasonal variations in ultraviolet B (UVB) radiation cause seasonal variations in vitamin D status. This may influence immune responses and play a role in the seasonality of influenza.

METHODS

Pandemic and non-pandemic influenzas in Sweden, Norway, the USA, Singapore, and Japan were studied. Weekly/monthly influenza incidence and death rates were evaluated in view of monthly UVB fluences.

RESULTS

Non-pandemic influenzas mostly occur in the winter season in temperate regions. UVB calculations show that at high latitudes very little, if any, vitamin D is produced in the skin during the winter. Even at 26°N (Okinawa) there is about four times more UVB during the summer than during the winter. In tropical regions there are two minor peaks in vitamin D photosynthesis, and practically no seasonality of influenza. Pandemics may start with a wave in an arbitrary season, while secondary waves often occur the following winter. Thus, it appears that a low vitamin D status may play a significant role in most influenzas.

CONCLUSIONS

In temperate latitudes even pandemic influenzas often show a clear seasonality. The data support the hypothesis that high fluences of UVB radiation (vitamin D level), as occur in the summer, act in a protective manner with respect to influenza.