Potent inhibition of dendritic cell differentiation and maturation by vitamin D analogs

Rag-1-dependent cells are necessary for 1,25-dihydroxyvitamin D(3) prevention of experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is a demyelinating disease involving genetic and environmental risk factors. Geographic, genetic, and biological evidence suggests that one environmental risk factor may be lack of vitamin D. Here, we investigated how 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)) inhibits experimental autoimmune encephalomyelitis (EAE), an MS model. The experiments used adoptive transfer of TCR-transgenic (TCR1) cells specific for myelin basic protein (MBP) peptide into unprimed recipients. When unprimed TCR1 splenocytes were transferred, and the recipients were immunized with peptide, the mock-treated mice developed EAE, but the 1,25-(OH)(2)D(3)-treated recipients remained disease-free. Both groups had TCR1 T cells that proliferated in response to MBP Ac1-11 and produced IFN-gamma but not IL-4 in the lymph node. In the central nervous system (CNS), the mock-treated mice had activated TCR1 T cells that produced IFN-gamma but not IL-4, while the 1,25-(OH)(2)D(3)-treated mice had TCR1 T cells with a non-activated phenotype that did not produce IFN-gamma or IL-4. When activated TCR1 T cells producing IFN-gamma were transferred into unprimed mice, the mock-treated and the 1,25-(OH)(2)D(3)-treated recipients developed EAE. Likewise, the 1,25-(OH)(2)D(3) did not inhibit Th1 cell IFN-gamma production or promote Th2 cell genesis or IL-4 production in vitro. Finally, the 1,25-(OH)(2)D(3) inhibited EAE in MBP-specific TCR-transgenic mice that were Rag-1(+), but not in animals that were Rag-1-null. Together, these data refute the hypothesis that the hormone inhibits Th1 cell genesis or function directly or through an action on antigen-presenting cells, or promotes Th2 cell genesis or function. Instead, the evidence supports a model wherein the 1,25-(OH)(2)D(3) acts through a Rag-1-dependent cell to limit the occurrence of activated, autoreactive T cells in the CNS.

Regulatory T cells induced by 1 alpha,25-dihydroxyvitamin D3 and mycophenolate mofetil treatment mediate transplantation tolerance

1alpha,25-dihydroxyvitamin D3, the active form of vitamin D3, and mycophenolate mofetil, a selective inhibitor of T and B cell proliferation, modulate APC function and induce dendritic cells (DCs) with a tolerogenic phenotype. Here we show that a short treatment with these agents induces tolerance to fully mismatched mouse islet allografts that is stable to challenge with donor-type spleen cells and allows acceptance of donor-type vascularized heart grafts. Peritransplant macrophages and DCs from tolerant mice express down-regulated CD40, CD80, and CD86 costimulatory molecules. In addition, DCs from the graft area of tolerant mice secrete, upon stimulation with CD4+ cells, 10-fold lower levels of IL-12 compared with DCs from acutely rejecting mice, and induce a CD4+ T cell response characterized by selective abrogation of IFN-gamma production. CD4+ but not CD8+ or class II+ cells from tolerant mice, transferred into naive syngeneic recipients, prevent rejection of donor-type islet grafts. Graft acceptance is associated with impaired development of IFN-gamma-producing type 1 CD4+ and CD8+ cells and an increased percentage of CD4+CD25+ regulatory cells expressing CD152 in the spleen and in the transplant-draining lymph node. Transfer of CD4+CD25+ cells from tolerant but not naive mice protects 100% of the syngeneic recipients from islet allograft rejection. These results demonstrate that a short treatment with immunosuppressive agents, such as 1alpha,25-dihydroxyvitamin D3/mycophenolate mofetil, induces tolerance to islet allografts associated with an increased frequency of CD4+CD25+ regulatory cells that can adoptively transfer transplantation tolerance.

Aspirin inhibits in vitro maturation and in vivo immunostimulatory function of murine myeloid dendritic cells

Aspirin is the most commonly used analgesic and antiinflammatory agent. In this study, at physiological concentrations, it profoundly inhibited CD40, CD80, CD86, and MHC class II expression on murine, GM-CSF + IL-4 stimulated, bone marrow-derived myeloid dendritic cells (DC). CD11c and MHC class I expression were unaffected. The inhibitory action was dose dependent and was evident at concentrations higher than those necessary to inhibit PG synthesis. Experiments with indomethacin revealed that the effects of aspirin on DC maturation were cyclooxygenase independent. Nuclear extracts of purified, aspirin-treated DC revealed a decreased NF-kappaB DNA-binding activity, whereas Ab supershift analysis indicated that aspirin targeted primarily NF-kappaB p50. Unexpectedly, aspirin promoted the generation of CD11c+ DC, due to apparent suppression of granulocyte development. The morphological and ultrastructural appearance of aspirin-treated cells was consistent with immaturity. Aspirin-treated DC were highly efficient at Ag capture, via both mannose receptor-mediated endocytosis and macropinocytosis. By contrast, they were poor stimulators of naive allogeneic T cell proliferation and induced lower levels of IL-2 in responding T cells. They also exhibited impaired IL-12 expression and did not produce IL-10 after LPS stimulation. Assessment of the in vivo function of aspirin-treated DC, pulsed with the hapten trinitrobenzenesulfonic acid, revealed an inability to induce normal cell-mediated contact hypersensitivity, despite the ability of the cells to migrate to T cell areas of draining lymphoid tissue. These data provide new insight into the immunopharmacology of aspirin and suggest a novel approach to the manipulation of DC for therapeutic application.

Dendritic cell modulation by 1alpha,25 dihydroxyvitamin D3 and its analogs: a vitamin D receptor-dependent pathway that promotes a persistent state of immaturity in vitro and in vivo

Dendritic cells (DCs) play a central role in regulating immune activation and responses to self. DC maturation is central to the outcome of antigen presentation to T cells. Maturation of DCs is inhibited by physiological levels of 1alpha,25 dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)] and a related analog, 1alpha,25(OH)(2)-16-ene-23-yne-26,27-hexafluoro-19-nor-vitamin D(3) (D(3) analog). Conditioning of bone marrow cultures with 10(-10) M D(3) analog resulted in accumulation of immature DCs with reduced IL-12 secretion and without induction of transforming growth factor beta1. These DCs retained an immature phenotype after withdrawal of D(3) analog and exhibited blunted responses to maturing stimuli (CD40 ligation, macrophage products, or lipopolysaccharide). Resistance to maturation depended on the presence of the 1alpha,25(OH)(2)D(3) receptor (VDR). In an in vivo model of DC-mediated antigen-specific sensitization, D(3) analog-conditioned DCs failed to sensitize and, instead, promoted prolonged survival of subsequent skin grafts expressing the same antigen. To investigate the physiologic significance of 1alpha,25(OH)(2)D(3)/VDR-mediated modulation of DC maturity we analyzed DC populations from mice lacking VDR. Compared with wild-type animals, VDR-deficient mice had hypertrophy of subcutaneous lymph nodes and an increase in mature DCs in lymph nodes but not spleen. We conclude that 1alpha,25(OH)(2)D(3)/VDR mediates physiologically relevant inhibition of DC maturity that is resistant to maturational stimuli and modulates antigen-specific immune responses in vivo.

The role of heat shock protein 70 in vitamin D receptor function

We previously demonstrated that the 1alpha,25-dihydroxyvitamin D(3) receptor (VDR) interacts with the constitutive heat shock protein, hsc70 in vitro, and with DnaK (Biochem. Biophys. Res. Commun. 260, 446-452, 1999). The biological significance of VDR-heat shock protein interactions, however, is unknown. To examine the role of such interactions in eukaryotic cells, we heterologously expressed VDR and RXRalpha together with a vitamin D-responsive reporter system in Saccharomyces cerevisiae and examined the consequences of heat shock protein 70 gene (SSA) deletion in these cells. We show that heterologously expressed VDR associates with the yeast cytosolic hsp70 protein, Ssa1p. Deletion of the SSA2, SSA3, and SSA4 genes and reduction of Ssa1p activity, reduces the intracellular concentrations of the VDR and its heterodimeric partner, RXRalpha and reduces the activity of a vitamin D-dependent gene. Hsp70-like chaperone proteins play a role in controlling concentrations of the VDR within the cell.

Vitamin D(3) and its synthetic analogs inhibit the spontaneous in vitro immunoglobulin production by SLE-derived PBMC

The production of high-affinity pathogenic autoantibodies in systemic lupus erythematosus (SLE) may result from aberrant immune regulation. Since 1,25 dihydroxy vitamin D(3) (1,25 D(3)) has immunoregulatory activity, we examined effects of 1,25 D(3) and its analogs HM, V, MC1288, and KH1060 on autoantibody production and proliferation of SLE PBMC. We found, in SLE, a higher percentage of T, B, and NK expressing vitamin D(3) receptors (VDRs) (P = 0.034, 0.006, 0.012, respectively). Incubating SLE PBMC with 1,25 D(3) compounds significantly reduced proliferation, polyclonal and anti-dsDNA IgG production, and the percentages of CD3(+)/DR(+) T and B (CD19(+)) cells, while elevating NK (CD16(+)) cells (P < 0.001). 1,25 D(3) analogs were more potent than the natural compound: KH1060 up-regulated CD14 expression by SLE monocytes (P < 0.001), inhibited polyclonal and anti-dsDNA IgG production by SLE-derived B lymphoblasts, and induced apoptosis of activated B lymphoblasts. These data suggest that 1,25 D(3) compounds can offer novel approaches to the clinical management of SLE.