Vitamin D differentially regulates B7.1 and B7.2 expression on human peripheral blood monocytes

Effect of different 1, 25-(OH)2D3 doses on high mobility group box1 and toll-like receptors 4 expression in lung tissue of asthmatic mice

We established a mouse model of asthmatic airway remodeling. To investigate the effects of different doses of 1,2 5-(OH)2D3 on airway remodeling, expression of high mobility group box 1 (HMGB1) and Toll-like receptors 4 (TLR4) in asthmatic mice. The female mice (BALB/c) groups consisted of a control group, asthma group and 1,2 5-(OH)2D3 low, middle, high dose group. Each group contained 10 mice. An asthmatic mice model was induced by ovalbumin. The control group and asthma group used physiological saline instead. 1,2 5-(OH)2D3 low, middle and high dose group was given different doses of 1,2 5-(OH)2D3 respectively. Changes in mice airway structure were observed by hematoxylin-eosin (H&E). The expression of HMGB1 and TLR4 in molecular lever were monitored by RT-PCR. We used immunohistochemistry to test HMGB1 and TLR4 protein levels. Obvious changes were noted in the airway of OVA-induced asthma mice compared with the control group by HE. These changes were less pronounced in mice receiving the low and middle doses of 1,2 5-(OH)2D3, but were more pronounced in mice receiving the highest dose of 1,2 5-(OH)2D3. Immunohistochemistry showed that expression of HMGB1 and TLR4 in the asthma group was higher than the control group. And low and middle dose group was decreased compared with asthma group, while higher than the control group; high dose group had an increased expression compared with the asthma group. From RT-PCR we got the same results as immunohistochemistry. In the asthmatic airway remodeling animal model, the appropriate amount of 1,2 5-(OH)2D3 reduced airway remodeling in asthmatic mice, and decreased the expression of HMGB1 and TLR4 in the asthmatic mice. However, over dose might play detrimental effect.

Vitamin D regulation of OX40 ligand in immune responses to Aspergillus fumigatus

OX40 ligand (OX40L) is a costimulatory molecule involved in Th2 allergic responses. It has been shown that vitamin D deficiency is associated with increased OX40L expression in peripheral CD11c(+) cells and controls Th2 responses to Aspergillus fumigatus in vitro in cystic fibrosis (CF) patients with allergic bronchopulmonary aspergillosis (ABPA). To investigate if vitamin D deficiency regulated OX40L and Th2 responses in vivo, we examined the effect of nutritional vitamin D deficiency on costimulatory molecules in CD11c(+) cells and A. fumigatus-induced Th2 responses. Vitamin D-deficient mice showed increased expression of OX40L on lung CD11c(+) cells, and OX40L was critical for enhanced Th2 responses to A. fumigatus in vivo. In in vitro assays, vitamin D treatment led to vitamin D receptor (VDR) binding in the promoter region of OX40L and significantly decreased the promoter activity of the OX40L promoter. In addition, vitamin D altered NF-κB p50 binding in the OX40L promoter that may be responsible for repression of OX40L expression. These data show that vitamin D can act directly on OX40L, which impacts Th2 responses and supports the therapeutic use of vitamin D in diseases regulated by OX40L.

Light and ocular immunity

PURPOSE OF REVIEW

Current scientific evidence suggests that the systemic immune response is affected by exposure to light. During the past century man has been exposed for the first time in evolution to light at night, as well as increasing ultraviolet radiation through depletion of the ozone layer in our atmosphere. These ecological changes have enhanced the impact of light on our systemic immune response. We will review the effect of light on the systemic immune response with particular emphasis on ocular immunity.

RECENT FINDINGS

Visible light is now recognized to be important in the maintenance of immune privilege within the eye; however, little is known about the mechanism through which this effect occurs. Recent studies suggest that the generation of regulatory T cells involved in immune privilege within the eye is dependent on retinoic acid formation by retinal pigment epithelial cells. Light is also important in modulation of multiple pathways including adjustment of circadian rhythm and production of vitamin D.

SUMMARY

Light regulates our biologic systems in many different ways. Its effect on the systemic immune response suggests that it is important in maintaining health, as well as in the induction of disease. A better understanding of the interaction of light with our biologic systems may allow new preventive measures to avoid disease and novel forms of treatment.

Quantitative Association Tests of Immune Responses to Antigens ofMycobacterium Tuberculosis: A Study of Twins in West Africa

There is now considerable evidence that host genetic factors are important in determining the outcome of infection withMycobacterium tuberculosis(MTB). The aim of this study was to assess the role of several candidate genes in the variation observed in the immune responses to MTB antigens. In-vitro assays of T-cell proliferation, an in-vivo intradermal delayed hypersensitivity response; cytokine and antibody secretions to several mycobacterial peptide antigens were assessed in healthy, but exposed, West African twins. Candidate gene polymorphisms were typed in theNRAMP1,Vitamin D receptor,IL10,IL4,IL4 receptorandCTLA-4genes. Variants of the lociIL10(−1082 G/A),CTLA-4(49 A/G) and theIL4 receptor(128 A/G) showed significant associations with immune responses to several antigens. T-cell proliferative responses and antibody responses were reduced, TNF-α responses were increased for subjects with theCTLA-4G allele. The T-cell proliferative responses of subjects withIL10GA and GG genotypes differed significantly.IL4 receptorAG and GG genotypes also showed significant differences in their T-cell proliferative responses to MTB antigens. These results yield a greater understanding of the genetic mechanisms that underlie the immune responses in tuberculosis and have implications for the design of therapeutic interventions.

Types I and II interferons upregulate the costimulatory CD80 molecule in monocytes via interferon regulatory factor-1

CD80/B7.1 expressed on monocytes plays a prominent role in the activation of T cell-mediated immunity and its level is reduced in monocytes from cancer patients. Type I (alpha/beta) and type II (gamma) IFNs are widely administered as adjuvant therapy. We show here that both classes of IFNs upregulate CD80 mRNA and protein in primary monocytes ex vivo. The stimulatory action of IFN-alpha/beta on CD80 is accompanied by the activation of both interferon regulatory factors IRF-1 and IRF-7, whereas IFN-gamma stimulating effect is associated only with IRF-1 induction. IFNs concomitantly upregulate the transcription of CD40 costimulatory molecule whose activation is known to require IRF-1. In monocytic U937 cells, IRF-1 is activated by IFN-gamma but not by IFN-alpha/beta, whereas it is the reverse for IRF-7; in the latter cells, only IFN-gamma is capable of stimulating CD80 transcription emphasizing the essential role of IRF-1. Moreover, siRNA against IRF-1 prevents IFN-gamma-mediated CD80 activation. In AML cells, IFNs upregulate CD40, CD80 and IRF-1 in the FAB-M4/M5 subtypes but not in the less differentiated M1/M2 subtypes. Monitoring the expression of CD80 on AML cells and its modulation by IFNs could help to predict the patients more susceptible to benefit from therapeutic strategies aimed at eliciting specific T cell responses to leukemia-associated antigens.

1Alpha,25-dihydroxyvitamin D3 inhibits CD40L-induced pro-inflammatory and immunomodulatory activity in human monocytes

CD40 ligand (CD40L) stimulation induces proinflammatory and immunomodulatory activity in monocytes. Here, we report on the effects of the steroid hormone 1alpha,25-dihydroxyvitamin D3 (1,25D3) on human blood monocytes that have been stimulated with the CD40L ligand. Co-treatment of CD40L-stimulated monocytes with 1,25D3 resulted in reduced production and secretion of tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta, as well as in reduced expression of the surface co-stimulatory molecules CD80 and CD86. In addition, costimulation of CD4+ T lymphocytes by monocytes co-treated with CD40L and 1,25D3 resulted in reduced cell proliferation and diminished interferon (IFN)-gamma but enhanced IL-10 production by CD4+ T cells. Finally, 1,25D3 interfered with the ability of CD40L to rescue monocytes from apoptosis induced by serum withdrawal. These findings suggest that 1,25D3 may regulate the interaction of monocytes with T cells or other cell types that express CD40L, thus influencing the outcome of the immune or inflammatory response.

Archaeosomes as Self-adjuvanting Delivery Systems for Cancer Vaccines*

Archaeal ether glycerolipid vesicles (archaeosomes) efficiently deliver exogenous antigen for induction of humoral and cell-mediated immunity. Because induction of CD8 cytotoxic T cells is critical for protective vaccination against tumors, we compared the ability of various archaeosome lipid compositions to evoke a strong CD8 CTL response to entrapped antigen. Subcutaneous immunization of mice with ovalbumin (OVA) entrapped in all archaeosome lipid compositions evoked a primary (day 10) splenic CTL response indicating processing for MHC class I presentation. Interestingly, several polar lipid compositions from halophilic archaea were very potent to adjuvant this early CTL response. Despite this, the lytic units reduced substantially by weeks 6-7. More importantly, at >50 weeks, only Methanobrevibacter smithii and Thermoplasma acidophilum both rich in bipolar membrane-spanning caldarchaeols, demonstrated recall memory CTLs. Immunization of mice with OVA entrapped in M. smithii, Halobacterium salinarum or T. acidophilum vesicles provided prophylactic protection against challenge with OVA-expressing solid tumors at 6 weeks. Even a dose of 3 microg OVA in archaeosomes significantly delayed tumor growth. Tumor protection was also noted in a therapeutic design wherein OVA-archaeosomes were injected concurrent with the tumor challenge. Interestingly, antigen-free T. acidophilum but not antigen-free H. salinarum archaeosomes provided innate therapeutic protection. Vaccination with a CTL peptide epitope from the melanoma differentiation antigen, tyrosinase-related protein 2, in archaeosomes induced a protective CD8 response against B16OVA metastasis, indicating potential for targeting self, tumor antigens. Thus, lipid structural properties of archaea may differentially modulate primary, long-term and/or innate immunity, impacting adjuvant choice for vaccine design.

An overview of interactions between micronutrients and of micronutrients with drugs, genes and immune mechanisms

The objective of the present review is to examine critically the consequences of interactions that micronutrients undergo with nutrients and non-nutrients (mainly prescribed medicines) in diets and lifestyle factors (smoking, tea and alcohol consumption). In addition, the review describes recent work on interactions between nutrients and genes, the influence of gene polymorphisms on micronutrients, the impact of immune responses on micronutrients and specific interactions of antioxidant micronutrients in disease processes to minimise potential pro-oxidant damage.

Apoptosis of multiple myeloma cells induced by agonist monoclonal antibody against human CD28

CD28 is expressed abnormally on human multiple myeloma (MM) cells but the significance had not been identified until now. In this paper, we are suggesting that abnormal expression of CD28 might be a marker of tumour progression. We therefore took the approach of generating a hybridoma cell line capable of secreting agonist monoclonal antibody directed against human CD28 (agonist anti-CD28 mAb) and then determined the expression of CD28 molecules on the MM cell lines U266 and XG1. The biological effects of agonist anti-CD28 mAb on cell growth and proliferation of U266 and XG1 cell lines were then analysed. Our results showed that the expression of CD28 on U266 and XG1 was significantly higher than that of PBTC or Jurkat cells. We found that by adding the agonist anti-CD28 mAb to cultures of U266 and XG1 cells their rate of growth and proliferation was obviously inhibited. Further morphological and molecular analyses found that U266 and XG1 incubated with agonist anti-CD28 mAb showed signs of nuclear condensation, chromatin marginal changes, cells membrane breaking, and cytoplasmic shrinkage. Vacuoles and apoptotic bodies were also observed using a transmission electron microscope and the development of typical DNA laddering patterns were found by the use of electrophoresis assays, suggesting that U266 and XG1 cells were undergoing apoptosis induced by agonist anti-CD28 mAb in vitro.

Induction of regulatory dendritic cells by dexamethasone and 1α,25-Dihydroxyvitamin D3

Dendritic cells (DC) modulated to induce T cell hyporesponsiveness have promising potential in immunotherapy of autoimmune disorders and for the prevention of allograft rejection. While studying the effect of immunosuppressive agents on the maturation of DC we found that 1alpha,25-Dihydroxyvitamin D(3) the active form of Vitamin D(3) (D(3)) in combination with dexamethasone (Dex) has a synergistic effect on LPS-induced maturation of DC. Monocyte-derived DCs cultured with D(3) and Dex during LPS-induced maturation have a low stimulatory effect on allogeneic T cells comparable with that of immature DCs. But in contrast to immature DCs, D3/Dex exposed DCs secrete IL-10 and show upregulated transcription of mRNA encoding the Ig-like inhibitory receptor ILT4. D3/Dex exposed DCs also inhibit alloreactivity and slightly enhance the degree of apoptosis in mature DCs. Thus, D(3)/Dex is an effective immunosuppressive drug combination for the induction of DCs capable of inducing T cell hyporesponsiveness.

Treatment of experimental autoimmune encephalomyelitis in rat by 1,25-dihydroxyvitamin D3 leads to early effects within the central nervous system

We report here that curative treatment of the multiple sclerosis paradigm, chronic relapsing experimental autoimmune encephalomyelitis (EAE) of the Lewis rat, by 1,25-dihydroxyvitamin D(3 )(1,25-D3) leads to a rapid clinical improvement accompanied by an inhibition of CD4, MHC class II and type II nitric oxide synthase (NOS II) expression in the posterior areas of the central nervous system (CNS). In contrast, the hormone has no effect on transforming growth factor-beta1 transcripts. Computer analysis of the NOS II promoter, expressed by microglia and astrocytes, reveals consensus sequence for vitamin D receptor binding, emphasizing the idea that 1,25-D3 may regulate some aspects of EAE by acting directly on CNS constituent cells. We also demonstrate that vitamin D deprivation leads to minimal effects on the kinetic profile of EAE accompanied by a moderate exacerbation of the clinical symptoms. Interestingly, curative treatment of vitamin D-deprived rats with a non-toxic-1,25-D3 analogue (MC1288) strongly inhibited EAE symptoms, thus promulgating the potential interest of such compounds in the management of multiple sclerosis.

Vitamin D3 inhibits proinflammatory cytokines and nitric oxide production by the EOC13 microglial cell line

In recent years, a neuroimmunomodulatory role for 1,25-dihydroxyvitamine D(3) [1,25(OH)(2)D(3)] has emerged. Microglial cells present a potential target for the effects of this hormone in the brain. This study focuses on the effect of 1,25(OH)(2)D(3) on the expression and production of inflammatory cytokines and nitric oxide (NO) by the EOC13 microglial cell line. The presence of the vitamin D3 receptor in microglia was demonstrated by RT-PCR. 1,25(OH)(2)D(3) inhibited the production of tumor necrosis factor-alpha, interleukin-6, and NO by stimulated microglia in a concentration-related fashion. The production of transforming growth factor-beta1 (TGF-beta1), an anti-inflammatory cytokine, was not modified in the presence of 1,25(OH)(2)D(3), indicating that the effects of 1,25(OH)(2)D(3) may not involve TGF-beta1 regulation. These results show that 1,25(OH)(2)D(3) has direct anti-inflammatory properties on microglia. It further supports the hypothesis that 1,25(OH)(2)D(3) could be involved in the maintenance of the brain homeostasis and may have a therapeutic potential in inflammatory pathologies of the central nervous system.

Monocyte-derived IL12, CD86 (B7-2) and CD40L expression in relapsing and progressive multiple sclerosis

Multiple sclerosis has been postulated to be an autoimmune disease in which Th1 immune responses predominate. This response is associated with an increased production of IFNgamma and IL12 produced by T cells and by cells of the monocyte (MO) lineage, respectively. An increased expression of costimulatory molecules by T cells and antigen-presenting cells is also observed. We hypothesized that in relapsing-remitting MS (RRMS) (with or without of IFNbeta treatment) and in secondary progressive patients (SPMS) IL12 and costimulatory molecules (CD80 [B7-1], CD86 [B7-2], CD28, CD40, CD40L) would be differentially produced or expressed by MO or T cells. We performed cross-sectional and longitudinal flow cytometric studies (at monthly intervals) on peripheral blood mononuclear cells (PBMC) or on MO from SPMS or untreated and IFNbeta-treated patients with RRMS. We determined that CD86 and CD40L expression was highest on MO derived from SPMS patients compared to those from RRMS or from healthy controls (HC). In vitro culture of PBMC with recombinant human IL10, a cytokine that may be increased in response to treatment with IFNbeta and that down-regulates CD86 expression, reduced the expression of CD86 on MO derived from RRMS patients to a much higher degree compared to cells derived from SPMS or HC. In vitro secreted IL12 levels from freshly isolated MO from SPMS patients were more than 10-fold higher than either the treated or the untreated RRMS or HC. RRMS patients treated with IFNbeta demonstrated slightly lower levels of MO IL12 secretion. Our data suggest that a key mechanism in the pathogenesis of MS is the increased expression of CD86 and CD40L and the increased production of IL12 during disease progression. Part of the mechanism of action of IFNbeta may be to reduce MO CD86 and CD40L expression and IL12 secretion; failure to do so might signify either a lack of response or a transition to a more progressive phase of illness.

A novel immunosuppressive 1alpha,25-dihydroxyvitamin D3 analog with reduced hypercalcemic activity

1Alpha,25-dihydroxyvitamin D3, the biologically active form of vitamin D3, is a potent immunomodulatory molecule; however, its clinical use as an immunosuppressant is limited due to its strong effects on calcium homeostasis and the risk of associated side-effects. Here, we present a representative of a novel class of vitamin D analogs that exhibits potent immunosuppressive activity in a murine model of contact hypersensitivity when applied systemically and is efficacious also at nonhypercalcemic dosages. In vitro analysis revealed a binding affinity of ZK 191784 to the vitamin D receptor comparable with 1,25-dihydroxyvitamin D3. This compound inhibits lymphocyte proliferation and secretion of tumor necrosis factor alpha and interleukin-12 in monocytes in a concentration-dependent manner, but with reduced potency and efficacy than 1,25-dihydroxy-vitamin D3. Treatment of human monocytes with this analog significantly reduces expression of major histocompatibility complex class II, B7.1, and intercellular adhesion molecule-1 equipotent to 1,25-dihydroxyvitamin D3. Interestingly, the compound failed to induce vitamin D-induced differentiation of human promyelocytic leukemia cell line HL-60 to monocytes and was capable of antagonizing the action of 1,25-dihydroxyvitamin D3. In vivo, as analyzed in mice the compound potently inhibits the contact hypersensitivity when applied systemically. ZK 191784 has a clear therapeutic advantage over 1,25-dihydroxyvitamin D3 by inducing immunosuppressive effects also at concentrations that do not cause hypercalcemia. ZK 191784 is the first representative of a novel class of vitamin D analogs that might have therapeutic potential in T cell-mediated immune disorders.

Vitamin D as immunomodulatory therapy for kidney transplantation

Vitamin D (1alpha,25-dihydroxyvitamin D(3) [1alpha,25-(OH)(2)D(3)]) has been studied in the past for its immunosuppressive properties, and, in that context, it may also have potential utility as an immunomodulatory agent for transplantation. A number of studies have demonstrated that 1alpha,25-(OH)(2)D(3) or its analogs regulate immune cell proliferation, differentiation, and responsiveness. A burgeoning number of studies have also explored using 1alpha,25-(OH)(2)D(3) and its analogs directly as therapy in animal models of kidney transplantation with success in prolonging allograft function and preventing acute rejection. Some of these in vivo effects may well be caused by alterations in immune cell function, but it is also possible that exogenous 1alpha,25-(OH)(2)D(3) and its analogs are altering the intragraft milieu as well, specifically through changes in the TGF-beta signaling cascade. Such provocative data and the availability of newer 1alpha,25-(OH)(2)D(3) analogs that may limit side effects (e.g. hypercalcemia) have created interest in examining this secosteroid clinically in kidney transplantation.

Synergistic inhibitory effect of cyclosporin A and vitamin D derivatives on T-lymphocyte proliferation in active ulcerative colitis

OBJECTIVE

1,25-Dihydroxyvitamin D3 [1,25(OH)2D3], the hormonal active form of vitamin D3, could represent a potentially therapeutic agent in autoimmune diseases. Cyclosporin A (CsA) shows immunoregulatory properties, which, in many respects, seem to be similar to those of 1,25(OH)2D3. Our aim was to investigate the possible synergistic effect exerted by CsA in combination with 1,25(OH)2D3 or its nonhypercalcemic analogues, EB 1089 and KH 1060, on the proliferative response of T lymphocytes obtained from active ulcerative colitis patients.

METHODS

The T lymphocyte-enriched population was treated with phytohemagglutinin and CsA (doses from 1 ng to 1000 ng/ml) alone or in association with 1,25(OH)2D3 or EB 1089 or KH 1060 (0.1, 1, 10 nM final concentration). Cell proliferation was determined by [3H]thymidine incorporation and analyzed on day 5 of culture.

RESULTS

After incubation with CsA, T lymphocyte proliferation was significantly inhibited in comparison with the vehicle-treated cultures. However, T lymphocytes from ulcerative colitis patients were significantly more sensitive to CsA than those from healthy controls. The inhibition in T lymphocyte proliferation, after treatment of the cultures with CsA associated with either 1,25(OH)2D3 or EB 1089 or KH 1060, was synergistic at well-defined concentrations.

CONCLUSIONS

Taking into account the lowest CsA dose (1 ng/ml), the highest synergistic inhibition in the proliferation of T lymphocytes prepared from ulcerative colitis patients was found combining CsA and 10 nM of 1,25(OH)2D3 or 10 nM of EB 1089 or KH 1060 at the three concentrations. The results obtained, associating the lowest CsA dose and the lowest KH 1060 concentration, may suggest an alternative therapeutic approach in these patients, reducing the dose, and consequently the toxicity, of CsA.

Monocytes influence the fate of T cells challenged with oxidised low density lipoproteins towards apoptosis or MHC-restricted proliferation

Atherosclerosis has been implicated in myocardial infarction, stroke and a host of cardiovascular diseases. The presence of activated T lymphocytes and macrophages, and the increased expression of HLA-DR antigen are consistent with the notion of immune activity in the atherosclerotic plaque. The nature of the causative antigen has not been established although oxidised low density lipoproteins (oxLDL) that accumulate in atherosclerotic plaques could fulfil this role. Here, we report that monocytes play a key role in influencing the fate of purified peripheral human T lymphocytes from healthy donors when the cells are exposed to LDL oxidised under the controlled conditions of water radiolysis. Our data showed that oxLDL generated under these conditions were chemoattractants for T cells. However, they induced a state of apoptosis in T lymphocytes cultured in the absence of monocytes. The extent of apoptosis was related to the degree of oxidation of LDL and the time of T cell exposure to oxLDL. OxLDL-dependent apoptosis did not involve a scavenger-like receptor. CD4(+) cells were more sensitive to the apoptotic effect of oxLDL than CD8(+) cells. OxLDL-primed (12 h) autologous monocytes triggered a robust proliferation of T lymphocytes cultured in the absence of oxLDL. The strength of T cell stimulation was related to the degree of oxidation of the LDL used in priming. Heterologous monocytes exposed to oxLDL under similar conditions induced a response that was not different than monocytes exposed to untreated LDL (natLDL) which did not induce T cell proliferation. Fucoidan did not modify the oxLDL-, monocyte-dependent T cell response to proliferation, suggesting that a scavenger-like receptor was not involved. The expression of the HLA-DR marker and the B7.2 protein were up-regulated in monocytes exposed to oxLDL but not to natLDL. The levels of B7.1 were unchanged. Our data are consistent with the notion that monocytes are critical for T cell survival in the presence of oxLDL and MHC-restricted T cell proliferative response to oxLDL.

Association of primary biliary cirrhosis with vitamin D receptor BsmI genotype polymorphism in a Hungarian population

We sought to determine the distribution of vitamin D receptor genotypes defined by the BsmI polymorphism and to investigate their association with bone mineral density in patients with primary biliary cirrhosis. Vitamin D receptor genotype and bone mineral density at the lumbar spine was determined in 31 female Hungarian patients with primary biliary cirrhosis and 51 age-matched healthy female controls. The genotype frequency (BB: 45%, Bb: 32%, bb: 22%) of the patients was significantly different from the control group (P = 0.01) due to an overrepresentation of the BB genotype. There was an apparent trend, not reaching statistical significance, for a lower bone mineral density in both the patient and control groups carrying a B allele. In conclusion, we found a strikingly high frequency of the BB genotype in patients with primary biliary cirrhosis, which raises questions about hormonal influences on the development of primary biliary cirrhosis.

1,25-Dihydroxyvitamin D(3) inhibits dendritic cell differentiation and maturation in vitro

OBJECTIVE

Because of its potent immunosuppressive properties in vitro as well as in vivo, we studied the effect of 1,25-dihydroxyvitamin D(3) (calcitriol) on differentiation, maturation, and function of dendritic cells (DC).

MATERIALS AND METHODS

Monocyte-derived DCs were generated with GM-CSF plus IL-4, and maturation was induced by a 2-day exposure to TNFalpha. DCs were derived from CD34(+) progenitors using SCF plus GM-CSF plus TNFalpha. For differentiation studies, cells were exposed to calcitriol at concentrations of 10(-)(9)- 10(-7) M at days 0, 6, and 8, respectively. The obtained cell populations were evaluated by morphology, phenotype, and function.

RESULTS

When added at day 0, calcitriol blocked DC differentiation from monocytes and inhibited the generation of CD1a(+) cells from progenitor cells while increasing CD14(+) cells. Exposure of immature DCs to calcitriol at day 6 resulted in a loss of the DC-characteristic surface molecule CD1a, downregulation of the costimulatory molecules CD40 and CD80, and MHC class II expression, whereas the monocyte/macrophage marker CD14 was clearly reinduced. In addition, calcitriol hindered TNFalpha-induced DC maturation, which is usually accompanied with induction of CD83 expression and upregulation of costimulatory molecules. In contrast, the mature CD83(+) DCs remained CD1a(+)CD14(-) when exposed to calcitriol. The capacity of cytokine-treated cells to stimulate allogeneic and autologous T cells and to take up soluble antigen was inhibited by calcitriol.

CONCLUSION

The potent suppression of DC differentiation, the reversal of DC phenotype, and function in immature DCs, as well as the inhibition of DC maturation by calcitriol, may explain some of its immunosuppressive properties.

1 Alpha,25-dihydroxyvitamin D3 inhibits differentiation, maturation, activation, and survival of dendritic cells leading to impaired alloreactive T cell activation

1 Alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3), the active form of vitamin D3, is a potent immunomodulatory agent. Here we show that dendritic cells (DCs) are major targets of 1,25(OH)2D3-induced immunosuppressive activity. 1,25(OH)2D3 prevents the differentiation in immature DCs of human monocytes cultured with GM-CSF and IL-4. Addition of 1,25(OH)2D3 during LPS-induced maturation maintains the immature DC phenotype characterized by high mannose receptor and low CD83 expression and markedly inhibits up-regulation of the costimulatory molecules CD40, CD80, and CD86 and of class II MHC molecules. This is associated with a reduced capacity of DCs to activate alloreactive T cells, as determined by decreased proliferation and IFN-gamma secretion in mixed leukocyte cultures. 1, 25(OH)2D3 also affects maturing DCs, leading to inhibition of IL-12p75 and enhanced IL-10 secretion upon activation by CD40 ligation. In addition, 1,25(OH)2D3 promotes the spontaneous apoptosis of mature DCs. The modulation of phenotype and function of DCs matured in the presence of 1,25(OH)2D3 induces cocultured alloreactive CD4+ cells to secrete less IFN-gamma upon restimulation, up-regulate CD152, and down-regulate CD154 molecules. The inhibition of DC differentiation and maturation as well as modulation of their activation and survival leading to T cell hyporesponsiveness may explain the immunosuppressive activity of 1, 25(OH)2D3.