CD8(+) T cells are not necessary for 1 alpha,25-dihydroxyvitamin D(3) to suppress experimental autoimmune encephalomyelitis in mice

Effect of Vitamin D on Graft-versus-Host Disease

The different cell subsets of the immune system express the vitamin D receptor (VDR). Through the VDR, vitamin D exerts different functions that influence immune responses, as previously shown in different preclinical models. Based on this background, retrospective studies explored the impacts of vitamin D levels on the outcomes of patients undergoing allogeneic hematopoietic stem-cell transplantation, showing that vitamin D deficiency is related to an increased risk of complications, especially graft-versus-host disease. These results were confirmed in a prospective cohort trial, although further studies are required to confirm this data. In addition, the role of vitamin D on the treatment of hematologic malignancies was also explored. Considering this dual effect on both the immune systems and tumor cells of patients with hematologic malignancies, vitamin D might be useful in this setting to decrease both graft-versus-host disease and relapse rates.

Autoimmune disease and interconnections with vitamin D

Vitamin D has well-documented effects on calcium homeostasis and bone metabolism but recent studies suggest a much broader role for this secosteroid in human health. Key components of the vitamin D system, notably the vitamin D receptor (VDR) and the vitamin D-activating enzyme (1α-hydroxylase), are present in a wide array of tissues, notably macrophages, dendritic cells and T lymphocytes (T cells) from the immune system. Thus, serum 25-hydroxyvitamin D (25D) can be converted to hormonal 1,25-dihydroxyvitamin D (1,25D) within immune cells, and then interact with VDR and promote transcriptional and epigenomic responses in the same or neighbouring cells. These intracrine and paracrine effects of 1,25D have been shown to drive antibacterial or antiviral innate responses, as well as to attenuate inflammatory T cell adaptive immunity. Beyond these mechanistic observations, association studies have reported the correlation between low serum 25D levels and the risk and severity of human immune disorders including autoimmune diseases such as inflammatory bowel disease, multiple sclerosis, type 1 diabetes and rheumatoid arthritis. The proposed explanation for this is that decreased availability of 25D compromises immune cell synthesis of 1,25D leading to impaired innate immunity and over-exuberant inflammatory adaptive immunity. The aim of the current review is to explore the mechanistic basis for immunomodulatory effects of 25D and 1,25D in greater detail with specific emphasis on how vitamin D-deficiency (low serum levels of 25D) may lead to dysregulation of macrophage, dendritic cell and T cell function and increase the risk of inflammatory autoimmune disease.

Effect of micronutrient malnutrition on periodontal disease and periodontal therapy

Periodontitis is a complex chronic inflammatory noncommunicable disease, initiated by the development of a dysbiotic microbial plaque biofilm below the gingival margin. Whilst the pathogenic biofilm is a "necessary cause" of periodontitis, it is insufficient on its own to cause the disease, and a destructive immune-inflammatory response is a key to the translation of risk to destructive events. Other exposures or "component causes" include individual genetic predisposition, lifestyle (including smoking and nutrition), and environmental factors. Dietary nutrients are essential for life as they provide crucial energy sources in the form of macronutrients, as well as important cofactors in the form of micronutrients, which regulate the functionality of enzymes during the regulation of anabolic and catabolic processes in human cells. Moreover, micronutrients can regulate gene transcription factors, such as the proinflammatory nuclear factor kappa B and the anti-inflammatory nuclear factor (erythroid-derived 2)-like 2. This review focuses on the role of vitamins (vitamin A, carotenoids, the vitamin B complex, vitamins C, D, and E, and coenzyme Q10) and minerals (calcium, magnesium, iron, zinc, potassium, copper, manganese, and selenium) in human physiology and the impact of their deficiencies upon periodontal health and disease.

Vitamin D: Effect on Haematopoiesis and Immune System and Clinical Applications

Vitamin D is a steroid-like hormone which acts by binding to vitamin D receptor (VDR). It plays a main role in the calcium homeostasis and metabolism. In addition, vitamin D display other important effects called “non-classical actions.” Among them, vitamin D regulates immune cells function and hematopoietic cells differentiation and proliferation. Based on these effects, it is currently being evaluated for the treatment of hematologic malignancies. In addition, vitamin D levels have been correlated with patients’ outcome after allogeneic stem cell transplantation, where it might regulate immune response and, accordingly, might influence the risk of graft-versus-host disease. Here, we present recent advances regarding its clinical applications both in the treatment of hematologic malignancies and in the transplant setting.

Modulation of inflammatory and immune responses by vitamin D

Vitamin D (VitD) is a prohormone most noted for the regulation of calcium and phosphate levels in circulation, and thus of bone metabolism. Inflammatory and immune cells not only convert inactive VitD metabolites into calcitriol, the active form of VitD, but also express the nuclear receptor of VitD that modulates differentiation, activation and proliferation of these cells. In vitro, calcitriol upregulates different anti-inflammatory pathways and downregulates molecules that activate immune and inflammatory cells. Administration of VitD has beneficial effects in a number of experimental models of autoimmune disease. Epidemiologic studies have indicated that VitD insufficiency is frequently associated with immune disorders and infectious diseases, exacerbated by increasing evidence of suboptimal VitD status in populations worldwide. To date, however, most interventional studies in human inflammatory and immune diseases with VitD supplementation have proven to be inconclusive. One of the reasons could be that the main VitD metabolite measured in these studies was the 25-hydroxyVitD (25OHD) rather than its active form calcitriol. Although our knowledge of calcitriol as modulator of immune and inflammatory reactions has dramatically increased in the past decades, further in vivo and clinical studies are needed to confirm the potential benefits of VitD in the control of immune and inflammatory conditions.

Vitamin D in Autoimmunity: Molecular Mechanisms and Therapeutic Potential

Over the last three decades, it has become clear that the role of vitamin D goes beyond the regulation of calcium homeostasis and bone health. An important extraskeletal effect of vitamin D is the modulation of the immune system. In the context of autoimmune diseases, this is illustrated by correlations of vitamin D status and genetic polymorphisms in the vitamin D receptor with the incidence and severity of the disease. These correlations warrant investigation into the potential use of vitamin D in the treatment of patients with autoimmune diseases. In recent years, several clinical trials have been performed to investigate the therapeutic value of vitamin D in multiple sclerosis, rheumatoid arthritis, Crohn’s disease, type I diabetes, and systemic lupus erythematosus. Additionally, a second angle of investigation has focused on unraveling the molecular pathways used by vitamin D in order to find new potential therapeutic targets. This review will not only provide an overview of the clinical trials that have been performed but also discuss the current knowledge about the molecular mechanisms underlying the immunomodulatory effects of vitamin D and how these advances can be used in the treatment of autoimmune diseases.

Impact of vitamin D on immune function: lessons learned from genome-wide analysis

Immunomodulatory responses to the active form of vitamin D (1,25-dihydroxyvitamin D, 1,25D) have been recognized for many years, but it is only in the last 5 years that the potential role of this in normal human immune function has been recognized. Genome-wide analyses have played a pivotal role in redefining our perspective on vitamin D and immunity. The description of increased vitamin D receptor (VDR) and 1α-hydroxylase (CYP27B1) expression in macrophages following a pathogen challenge, has underlined the importance of intracrine vitamin D as key mediator of innate immune function. It is now clear that both macrophages and dendritic cells (DCs) are able to respond to 25-hydroxyvitamin D (25D), the major circulating vitamin D metabolite, thereby providing a link between the function of these cells and the variations in vitamin D status common to many humans. The identification of hundreds of primary 1,25D target genes in immune cells has also provided new insight into the role of vitamin D in the adaptive immune system, such as the modulation of antigen-presentation and T cells proliferation and phenotype, with the over-arching effects being to suppress inflammation and promote immune tolerance. In macrophages 1,25D promotes antimicrobial responses through the induction of antibacterial proteins, and stimulation of autophagy and autophagosome activity. In this way variations in 25D levels have the potential to influence both innate and adaptive immune responses. More recent genome-wide analyses have highlighted how cytokine signaling pathways can influence the intracrine vitamin D system and either enhance or abrogate responses to 25D. The current review will discuss the impact of intracrine vitamin D metabolism on both innate and adaptive immunity, whilst introducing the concept of disease-specific corruption of vitamin D metabolism and how this may alter the requirements for vitamin D in maintaining a healthy immune system in humans.

Fraction of IL-10+ and IL-17+ CD8 T cells is increased in MS patients in remission and during a relapse, but is not influenced by immune modulators

In the present study, circulating proportions of CD8(+) T (Tc) cell subsets, including IL-17 (Tc17) and IL-10 (Tc10) producing cells, were assessed in relapsing-remitting MS (RRMS) patients and a possible effect of beta interferon (IFN-β), glatiramer acetate (GA), and vitamin D (VitD) on these cell subsets was investigated. We show that both Tc17 and Tc10 cell fractions are elevated in the circulation of RRMS patients in remission compared to healthy subjects and that these Tc subsets remain unaffected by current immune modulating regimens.

Physiological insights from the vitamin D receptor knockout mouse

Identification of vitamin D as a potent antirachitic factor almost a century ago prompted investigations aimed at addressing its mechanism of action and key target tissues. Studies in vitamin D deficiency models and in kindreds with impaired hormone activation and function were critical in identifying key steps in the vitamin D signaling pathway. Studies in humans with vitamin D receptor (VDR) mutations provided a tremendous amount of information regarding the role of this receptor in calcium and skeletal homeostasis. The availability of mouse models of VDR ablation provided an important tool for detailed molecular analyses of the pathophysiologic basis for the skeletal, parathyroid and cutaneous phenotypes observed in mice and humans with impaired VDR function. These investigations revealed that a critical action of the liganded receptor is the promotion of intestinal calcium absorption. Bypassing this defect by dietary or transgenic rescue prevents the severe skeletal phenotype of the VDR ablated mice, as well as the development of hyperparathyroidism. In contrast, intestine specific ablation of the receptor results in marked skeletal pathology. Like their human counterparts, VDR knockout mice develop alopecia. Studies in these mice demonstrated that the actions of the VDR required for cyclical regeneration of the hair follicle and prevention of alopecia were shown independent of 1,25-dihydroxyvitamin D demonstrating that the unliganded receptor has an important role in the cutaneous homeostasis.

Pathogenesis of pediatric multiple sclerosis

Onset of multiple sclerosis in childhood occurs in 3-5% of patients. There is limited, but growing knowledge about the underlying pathobiology of pediatric MS. It is crucial to better understand this area in order to address central questions in the field: 1) Can pediatric multiple sclerosis inform us about factors related to disease initiation and propagation? 2) What are the biomarkers of disease course in pediatric multiple sclerosis; 3) Does pediatric multiple sclerosis pathogenesis differ from adult-onset multiple sclerosis; 4) How can we optimize treatment in pediatric demyelinating diseases? 5) Can pediatric multiple sclerosis provide insights into the environmental risk factors for multiple sclerosis in general? Here we review the current knowledge of the pathogenesis of multiple sclerosis in children, and address the five questions raised above.

Predictors of anaemia and iron deficiency in HIV-infected pregnant women in Tanzania: a potential role for vitamin D and parasitic infections

OBJECTIVE

Anaemia is common during pregnancy, and prenatal Fe supplementation is the standard of care. However, the persistence of anaemia despite Fe supplementation, particularly in HIV infection, suggests that its aetiology may be more complex and warrants further investigation. The present study was conducted to examine predictors of incident haematological outcomes in HIV-infected pregnant women in Tanzania.

DESIGN

Prospective cohort study. Cox proportional hazards and binomial regression models were used to identify predictors of incident haematological outcomes: anaemia (Hb < 110 g/l), severe anaemia (Hb < 85 g/l) and hypochromic microcytosis, during the follow-up period.

SETTING

Antenatal clinics in Dar es Salaam, Tanzania.

SUBJECTS

Participants were 904 HIV-infected pregnant women enrolled in a randomized trial of vitamins (1995-1997).

RESULTS

Malaria, pathogenic protozoan and hookworm infections at baseline were associated with a two-fold increase in the risk of anaemia and hypochromic microcytosis during follow-up. Higher baseline erythrocyte sedimentation rate and CD8 T-cell concentrations, and lower Hb concentrations and CD4 T-cell counts, were independent predictors of incident anaemia and Fe deficiency. Low baseline vitamin D (<32 ng/ml) concentrations predicted a 1.4 and 2.3 times greater risk of severe anaemia and hypochromic microcytosis, respectively, during the follow-up period.

CONCLUSIONS

Parasitic infections, vitamin D insufficiency, low CD4 T-cell count and high erythrocyte sedimentation rate were the main predictors of anaemia and Fe deficiency in pregnancy and the postpartum period in this population. A comprehensive approach to prevent and manage anaemia, including micronutrient supplementation and infectious disease control, is warranted in HIV-infected women in resource-limited settings - particularly during the pre- and postpartum periods.

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 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 immune function: an overview

Immunomodulatory actions of vitamin D have been recognised for over a quarter of a century, but it is only in the last few years that the significance of this to normal human physiology has become apparent. Two key factors have underpinned this revised perspective. Firstly, there are increasing data linking vitamin insufficiency with prevalent immune disorders. Improved awareness of low circulating levels of precursor 25-hydroxyvitamin D in populations across the globe has prompted epidemiological investigations of health problems associated with vitamin D insufficiency. Prominent among these are autoimmune diseases such as multiple sclerosis, type 1 diabetes and Crohn's disease, but more recent studies indicate that infections such as tuberculosis may also be linked to low 25-hydroxyvitamin D levels. The second factor expanding the link between vitamin D and the immune system is our improved knowledge of the mechanisms that facilitate this association. It is now clear that cells from the immune system contain all the machinery needed to convert 25-hydroxyvitamin D to active 1,25-dihydroxyvitamin D, and for subsequent responses to 1,25-dihydroxyvitamin D. Mechanisms such as this are important for promoting antimicrobial responses to pathogens in macrophages, and for regulating the maturation of antigen-presenting dendritic cells. The latter may be a key pathway by which vitamin D controls T-lymphocyte (T-cell) function. However, T-cells also exhibit direct responses to 1,25-dihydroxyvitamin D, notably the development of suppressor regulatory T-cells. Collectively these observations suggest that vitamin D is a key factor linking innate and adaptive immunity, and both of these functions may be compromised under conditions of vitamin D insufficiency.

Vitamin D deficiency diminishes the severity and delays onset of experimental autoimmune encephalomyelitis

Multiple sclerosis incidence is clearly inversely related to sun exposure. This observation led to the idea that vitamin D might be responsible for this relationship. Providing super-physiologic doses of the hormonal form of vitamin D, 1α,25-dihydroxyvitamin D₃, suppresses an animal model of multiple sclerosis, i.e. experimental autoimmune encephalomyelitis (EAE) but causes unwanted hypercalcemia. Further, dietary calcium is needed for this activity of 1α,25-dihydroxyvitamin D₃. B10PL mice were maintained on a vitamin D-deficient diet for two generations to produce frank vitamin D deficiency. These animals showed delayed onset and reduced severity of EAE compared to control animals on the same diet and given vitamin D₃ or provided a vitamin D-containing chow diet. Thus, vitamin D deficiency interferes with the development of this autoimmune disease rather than increasing susceptibility.

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.

1,25-Dihydroxyvitamin D3 acts directly on the T lymphocyte vitamin D receptor to inhibit experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is an incurable autoimmune neurodegenerative disease. Environmental factors may be key to MS prevention and treatment. MS prevalence and severity decrease with increasing sunlight exposure and vitamin D(3) supplies, supporting our hypothesis that the sunlight-dependent hormone, 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2) D(3) ), inhibits autoimmune T-cell responses in MS. Moreover, 1,25-(OH)(2) D(3) inhibits and reverses experimental autoimmune encephalomyelitis (EAE), an MS model. Here, we investigated whether 1,25-(OH)(2) D(3) inhibits EAE via the vitamin D receptor (VDR) in T lymphocytes. Using bone marrow chimeric mice with a disrupted VDR only in radio-sensitive hematopoietic cells or radio-resistant non-hematopoietic cells, we found that hematopoietic cell VDR function was necessary for 1,25-(OH)(2) D(3) to inhibit EAE. Furthermore, conditional targeting experiments showed that VDR function in T cells was necessary. Neither 1,25-(OH)(2) D(3) nor T-cell-specific VDR targeting influenced CD4(+) Foxp3(+) T-cell proportions in the periphery or the CNS in these studies. These data support a model wherein 1,25-(OH)(2) D(3) acts directly on pathogenic CD4(+) T cells to inhibit EAE.

Vitamin D as a T-cell modulator in multiple sclerosis

Vitamin D is a potent immune modulator, keeping the T-cell compartment in a more tolerogenic state. Multiple sclerosis (MS), a disease in which an autoreactive T-cell response contributes to inflammation in the central nervous system, has been associated with vitamin D deficiency. The effects of vitamin D on the immune system are believed to be an important driver of this association. In this chapter, we elaborate on vitamin D as a modulator of the T-cell response. This discussion will be placed in the perspective of MS as a T-cell-mediated disease and in the perspective of the numerous association studies on vitamin D deficiency and multiple health outcomes. We conclude that there is a firm experimental and epidemiological basis supporting the model of vitamin D as a physiological immune modulator, on which intervention studies assessing clinical and immunological outcome measures should be designed.

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 and the immune system: new perspectives on an old theme

Interaction with the immune system is one of the most well-established nonclassic effects of vitamin D. For many years this was considered to be a manifestation of granulomatous diseases such sarcoidosis, in which synthesis of active 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) is known to be dysregulated. However, recent reports have supported a role for 1,25(OH)(2)D(3) in mediating normal function of the innate and adaptive immune systems. Crucially, these effects seem to be mediated via localized autocrine or paracrine synthesis of 1,25(OH)(2)D(3) from precursor 25-hydroxyvitamin D(3), the main circulating metabolite of vitamin D. The ability of vitamin D to influence normal human immunity is highly dependent on the vitamin D status of individuals, and may lead to aberrant response to infection or autoimmunity in those who are lacking vitamin D. The potential health significance of this has been underlined by increasing awareness of impaired vitamin D status in populations across the globe. This article describes some of the recent developments with respect to vitamin D and the immune system, and possible clinical implications.

Perinatal outcomes, including mother-to-child transmission of HIV, and child mortality and their association with maternal vitamin D status in Tanzania

BACKGROUND

Vitamin D is a strong immunomodulator and may protect against adverse pregnancy outcomes, mother-to-child transmission (MTCT) of human immunodeficiency virus (HIV), and child mortality.

METHODS

A total of 884 HIV-infected pregnant women who were participating in a vitamin supplementation trial in Tanzania were monitored to assess pregnancy outcomes and child mortality. The association of these outcomes with maternal vitamin D status at enrollment was examined in an observational analysis.

RESULTS

No association was observed between maternal vitamin D status and adverse pregnancy outcomes, including low birth weight and preterm birth. In multivariate models, a low maternal vitamin D level (<32 ng/mL) was associated with a 50% higher risk (95% confidence interval [CI], 2%-120%) of MTCT of HIV at 6 weeks, a 2-fold higher risk of MTCT of HIV through breast-feeding among children who were HIV uninfected at 6 weeks (95% CI, 1.08-3.82), and a 46% higher overall risk of HIV infection (95% CI, 11%-91%). Children born to women with a low vitamin D level had a 61% higher risk of dying during follow-up (95% CI, 25%-107%).

CONCLUSIONS

If found to be efficacious in randomized trials, vitamin D supplementation could prove to be an inexpensive method of reducing the burden of HIV infection and death among children, particularly in resource-limited settings.

Multiple sclerosis, osteoporosis, and vitamin D

Multiple sclerosis (MS) is associated with reduced bone mass and higher frequency of osteoporosis. Although high-dose short-term intravenous glucocorticoid regimens cause a decrease in bone formation, this effect is usually reversible and osteoporosis in MS patients may be independent of the short-term corticosteroid treatment. Clinical evidence suggests an important role of vitamin D as a modifiable risk factor in MS. Low circulating levels of vitamin D have been found in MS patients, especially during relapses, suggesting that vitamin D could be involved in the regulation of the clinical disease activity. Vitamin D mediates its function through a single vitamin D receptor (VDR). Polymorphisms of the VDR have major effects on vitamin D function and metabolism, and some VDR genotypes have been linked to osteoporosis and MS. Because the safety of high doses of vitamin D has not been established yet, vitamin D hasn't been used in enough doses to increase the serum level to a desired therapeutic target. Future clinical trials should determine the upper limit of vitamin D intake in order to achieve therapeutic benefit in MS patients.

Clinical implications of a possible role of vitamin D in multiple sclerosis

Hypovitaminosis D is currently one of the most studied environmental risk factors for multiple sclerosis (MS) and is potentially the most promising in terms of new clinical implications. These practical consequences, which could be applied to MS patients without further delay, constitute the main purpose of this review. Vitamin D is involved in a number of important general actions, which were not even suspected until quite recently. In particular, this vitamin could play an immunomodulatory role in the central nervous system. Many and varied arguments support a significant role for vitamin D in MS. In animal studies, vitamin D prevents and improves experimental autoimmune encephalomyelitis. Epidemiologically, latitude, past exposure to sun and the serum level of vitamin D influence the risk of MS, with, furthermore, significant links existing between these different factors. Clinically, most MS patients have low serum levels of vitamin D and are in a state of insufficiency or even deficiency compared to the international norm, which has been established on a metabolic basis. Large therapeutic trials using vitamin D are still lacking but the first results of phase I/II studies are promising. In the meantime, while awaiting the results of future therapeutic trials, it can no longer be ignored that many MS patients have a lack of vitamin D, which could be detected by a serum titration and corrected using an appropriate vitamin D supplementation in order to restore their serum level to within the normal range. From a purely medical point of view, vitamin D supplementation appears in this light to be unavoidable in order to improve the general state of these patients. Furthermore, it cannot currently be ruled out that this supplementation could also be neurologically beneficial.

Immunomodulation by a novel, dissociated Vitamin D analogue

The biologically active metabolite of vitamin D3, 1alpha,25-dihydroxyvitamin D3, has potent immunomodulatory activity; however, its clinical use is limited because of its hypercalcaemic activity in anti-inflammatory active doses. Here, we present ZK203278, a novel, structurally different vitamin D3 analogue with profound immunomodulatory activities. It potently inhibits lymphocyte proliferation in the mixed lymphocyte reaction, and release of cytokines that are central in inflammation, such as TNFalpha and IL-12 in the low nanomolar range. Similarly, expression of cell-surface molecules involved in cell adhesion and antigen presentation, e.g. to T cells, is down-regulated on human monocytes by low nanomolar concentrations of ZK203278. Potent anti-inflammatory activity has been demonstrated also in vivo in rodent disease models. ZK203278 inhibited allergic contact dermatitis in rodents after oral administration in doses approximately two orders of magnitude below the hypercalcaemic threshold dose. Moreover, ZK203278 significantly prolonged skin allograft survival in rats in well-tolerated doses. Altogether ZK203278, in contrast to 1alpha,25-dihydroxyvitamin D3, exerts considerable immunomodulatory activity at non-hypercalcaemic dosages and may have therapeutic potential for immune disorders or transplant rejection.

Vitamin D and multiple sclerosis

Vitamin D is a principal regulator of calcium homeostasis. However, recent evidence has indicated that vitamin D can have numerous other physiological functions including inhibition of proliferation of a number of malignant cells including breast and prostate cancer cells and protection against certain immune mediated disorders including multiple sclerosis (MS). The geographic incidence of MS indicates an increase in MS with a decrease in sunlight exposure. Since vitamin D is produced in the skin by solar or UV irradiation and high serum levels of 25-hydroxyvitamin D (25(OH)D) have been reported to correlate with a reduced risk of MS, a protective role of vitamin D is suggested. Mechanisms whereby the active form of vitamin D, 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) may act to mediate this protective effect are reviewed. Due to its immunosuppressive actions, it has been suggested that 1,25(OH)(2)D(3) may prevent the induction of MS.

Vitamin D receptor signaling contributes to susceptibility to infection with Leishmania major

We have previously reported that 1alpha,25-dihydroxyvitamin D3 (1alpha,25(OH)2D3) can selectively suppress key functions of interferon-gamma (IFN-gamma) activated macrophages. To further explore this mechanism for its relevance in vivo, we investigated an infection model that crucially depends on the function of IFN-gamma activated macrophages, the infection with the intracellular protozoan Leishmania major. 1Alpha,25(OH)2D3 treatment of L. major infected macrophages demonstrated a vitamin D receptor (Vdr) dependent inhibition of macrophage killing activity. Further analysis showed that this was a result of decreased production of nitric oxide by 1alpha,25(OH)2D3-treated macrophages due to Vdr-dependent up-regulation of arginase 1 expression, which overrides NO production by Nos2. When analyzing the course of infection in vivo, we found that Vdr-knockout (Vdr-KO) mice were more resistant to L. major infection than their wild-type littermates. This result is in agreement with an inhibitory influence of 1alpha,25(OH)2D3 on the macrophage mediated host defense. Further investigation showed that Vdr-KO mice developed an unaltered T helper cell type 1 (Th1) response on infection as indicated by normal production of IFN-gamma by CD4+ and CD8+ T cells. Therefore, we propose that the absence of 1alpha,25(OH)2D3-mediated inhibition of macrophage microbicidal activity in Vdr-KO mice results in increased resistance to Leishmania infection.

IL-10 signaling is essential for 1,25-dihydroxyvitamin D3-mediated inhibition of experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) results from an aberrant, neuroantigen-specific, T cell-mediated autoimmune response. Because MS prevalence and severity decrease sharply with increasing sunlight exposure, and sunlight supports vitamin D(3) synthesis, we proposed that vitamin D(3) and 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)) may protect against MS. In support of this hypothesis, 1,25-(OH)(2)D(3) strongly inhibited experimental autoimmune encephalomyelitis (EAE). This inhibition required lymphocytes other than the encephalitogenic T cells. In this study, we tested the hypothesis that 1,25-(OH)(2)D(3) might inhibit EAE through the action of IL-10-producing regulatory lymphocytes. We report that vitamin D(3) and 1,25-(OH)(2)D(3) strongly inhibited myelin oligodendrocyte peptide (MOG(35-55))-induced EAE in C57BL/6 mice, but completely failed to inhibit EAE in mice with a disrupted IL-10 or IL-10R gene. Thus, a functional IL-10-IL-10R pathway was essential for 1,25-(OH)(2)D(3) to inhibit EAE. The 1,25-(OH)(2)D(3) also failed to inhibit EAE in reciprocal, mixed bone marrow chimeras constructed by transferring IL-10-deficient bone marrow into irradiated wild-type mice and vice versa. Thus, 1,25-(OH)(2)D(3) may be enhancing an anti-inflammatory loop involving hemopoietic cell-produced IL-10 acting on brain parenchymal cells and vice versa. If this interpretation is correct, and humans have a similar bidirectional IL-10-dependent loop, then an IL-10-IL-10R pathway defect could abrogate the anti-inflammatory and neuro-protective functions of sunlight and vitamin D(3). In this way, a genetic IL-10-IL-10R pathway defect could interact with an environmental risk factor, vitamin D(3) insufficiency, to increase MS risk and severity.

Experimental allergic encephalomyelitis in pituitary-grafted Lewis rats

Treatment of susceptible rats with dopaminergic agonists that reduce prolactin release decreases both severity and duration of clinical signs of experimental allergic encephalomyelitis (EAE). To assess to what extent the presence of an ectopic pituitary (that produces an increase in plasma prolactin levels mainly derived from the ectopic gland) affects EAE, 39 male Lewis rats were submitted to pituitary grafting from littermate donors. Another group of 38 rats was sham-operated by implanting a muscle fragment similar in size to the pituitary graft. All rats received subcutaneous (s.c.) injections of complete Freund's adjuvant (CFA) plus spinal cord homogenate (SCH) and were monitored daily for clinical signs of EAE. Animals were killed by decapitation on days 1, 4, 7, 11 or 15 after immunization and plasma was collected for prolactin RIA. In a second experiment, 48 rats were immunized by s.c. injection of a mixture of SCH and CFA, and then received daily s.c. injections of bromocriptine (1 mg/kg) or saline. Groups of 8 animals were killed on days 8, 11 or 15 after immunization and plasma prolactin was measured. Only sham-operated rats exhibited clinical signs of the disease when assessed on day 15 after immunization. A progressive decrease in plasma prolactin levels was observed in pituitary-grafted rats, attaining a minimum 15 days after immunization, whereas plasma prolactin levels were increased during the course of the disease in sham-operated rats. Plasma prolactin levels were higher in pituitary-grafted rats than in sham-operated rats 1 day after immunization, but lower on days 7, 11 and 15 after immunogen injection. Further supporting a correlation of suppressed prolactin levels with absence of clinical signs of EAE, rats that were administered the dopaminergic agonist bromocriptine showed very low plasma prolactin levels and did not exhibit any clinical sign of EAE. These results indicate that low circulating prolactin levels coincide with absence of clinical signs of EAE in Lewis rats.

Vitamin D3Confers Protection from Autoimmune Encephalomyelitis Only in Female Mice

The prevalence of multiple sclerosis (MS) increases significantly with decreasing UV B light exposure, possibly reflecting a protective effect of vitamin D(3). Consistent with this theory, previous research has shown a strong protective effect 1,25-dihydroxyvitamin D(3) in experimental autoimmune encephalomyelitis (EAE), an MS model. However, it is not known whether the hormone precursor, vitamin D(3), has protective effects in EAE. To address this question, B10.PL mice were fed a diet with or without vitamin D(3), immunized with myelin basic protein, and studied for signs of EAE and for metabolites and transcripts of the vitamin D(3) endocrine system. The intact, vitamin D(3)-fed female mice had significantly less clinical, histopathological, and immunological signs of EAE than ovariectomized females or intact or castrated males. Correlating with reduced EAE, the intact, vitamin D(3)-fed female mice had significantly more 1,25-dihydroxyvitamin D(3) and fewer CYP24A1 transcripts, encoding the 1,25-dihydroxyvitamin D(3)-inactivating enzyme, in the spinal cord than the other groups of mice. Thus, there was an unexpected synergy between vitamin D(3) and ovarian tissue with regard to EAE inhibition. We hypothesize that an ovarian hormone inhibited CYP24A1 gene expression in the spinal cord, so the locally-produced 1,25-dihydroxyvitamin D(3) accumulated and resolved the inflammation before severe EAE developed. If humans have a similar gender difference in vitamin D(3) metabolism in the CNS, then sunlight deprivation would increase the MS risk more significantly in women than in men, which may contribute to the unexplained higher MS incidence in women than in men.

Noncalcemic actions of vitamin D receptor ligands

1alpha,25-Dihydroxyvitamin D(3) [1,25-(OH)(2)D(3)], the active metabolite of vitamin D(3), is known for the maintenance of mineral homeostasis and normal skeletal architecture. However, apart from these traditional calcium-related actions, 1,25-(OH)(2)D(3) and its synthetic analogs are being increasingly recognized for their potent antiproliferative, prodifferentiative, and immunomodulatory activities. These actions of 1,25-(OH)(2)D(3) are mediated through vitamin D receptor (VDR), which belongs to the superfamily of steroid/thyroid hormone nuclear receptors. Physiological and pharmacological actions of 1,25-(OH)(2)D(3) in various systems, along with the detection of VDR in target cells, have indicated potential therapeutic applications of VDR ligands in inflammation (rheumatoid arthritis, psoriatic arthritis), dermatological indications (psoriasis, actinic keratosis, seborrheic dermatitis, photoaging), osteoporosis (postmenopausal and steroid-induced osteoporosis), cancers (prostate, colon, breast, myelodysplasia, leukemia, head and neck squamous cell carcinoma, and basal cell carcinoma), secondary hyperparathyroidism, and autoimmune diseases (systemic lupus erythematosus, type I diabetes, multiple sclerosis, and organ transplantation). As a result, VDR ligands have been developed for the treatment of psoriasis, osteoporosis, and secondary hyperparathyroidism. Furthermore, encouraging results have been obtained with VDR ligands in clinical trials of prostate cancer and hepatocellular carcinoma. This review deals with the molecular aspects of noncalcemic actions of vitamin D analogs that account for the efficacy of VDR ligands in the above-mentioned indications.

Flavonoids influence monocytic GTPase activity and are protective in experimental allergic encephalitis

In the chronic disabling disease multiple sclerosis (MS), migration of monocytes across the blood-brain barrier is a crucial step in the formation of new lesions in the central nervous system (CNS). Infiltrating monocyte-derived macrophages secrete inflammatory mediators such as oxygen radicals, which contribute to axonal demyelination and damage, resulting in neurological deficits. Flavonoids are compounds occurring naturally in food, which scavenge oxygen radicals and have antiinflammatory properties. To investigate whether they might suppress clinical symptoms in MS, we treated rats sensitized for acute and chronic experimental allergic encephalomyelitis, an experimental model of MS, with flavonoids. We demonstrated that the flavonoid luteolin substantially suppressed clinical symptoms and prevented relapse when administered either before or after disease onset. Luteolin treatment resulted in reduced inflammation and axonal damage in the CNS by preventing monocyte migration across the brain endothelium. Luteolin influenced migration by modulating the activity of Rho GTPases, signal transducers involved in transendothelial migration. Oral administration of luteolin also significantly reduced clinical symptoms.

Vitamin D and its analogs as regulators of immune activation and antigen presentation

It has been a little more than 20 years since the first appreciation that the biologically active hormonal form of the secosteroid vitamin D-classically categorized as a regulator of calcium/phosphorous metabolism and bone mineralization-can exert effects on cells of the immune system. Since then a substantial literature has accumulated to suggest that these effects are exerted on multiple immune cell types, are predominantly suppressive at pharmacologic levels, and are potent enough to have true therapeutic potential in the management or prevention of immune-mediated diseases. Less clear at present, however, are the physiological roles played by the vitamin D endocrine system in the regulation of normal and abnormal immune responses. In this review, an appraisal of the current understanding of vitamin D-mediated immune regulation is presented that emphasizes progress towards its clinical application as well as the manner in which emerging models of normal immune function may facilitate a more complete understanding of its physiologic significance.