The effect of 1,25(OH)2-vitamin D3 on Langerhans cells and contact hypersensitivity in mice

Protection from Ultraviolet Damage and Photocarcinogenesis by Vitamin D Compounds

Exposure of skin cells to UV radiation results in DNA damage, which if inadequately repaired, may cause mutations. UV-induced DNA damage and reactive oxygen and nitrogen species also cause local and systemic suppression of the adaptive immune system. Together, these changes underpin the development of skin tumours. The hormone derived from vitamin D, calcitriol (1,25-dihydroxyvitamin D₃) and other related compounds, working via the vitamin D receptor and at least in part through endoplasmic reticulum protein 57 (ERp57), reduce cyclobutane pyrimidine dimers and oxidative DNA damage in keratinocytes and other skin cell types after UV. Calcitriol and related compounds enhance DNA repair in keratinocytes, in part through decreased reactive oxygen species, increased p53 expression and/or activation, increased repair proteins and increased energy availability in the cell when calcitriol is present after UV exposure. There is mitochondrial damage in keratinocytes after UV. In the presence of calcitriol, but not vehicle, glycolysis is increased after UV, along with increased energy-conserving autophagy and changes consistent with enhanced mitophagy. Reduced DNA damage and reduced ROS/RNS should help reduce UV-induced immune suppression. Reduced UV immune suppression is observed after topical treatment with calcitriol and related compounds in hairless mice. These protective effects of calcitriol and related compounds presumably contribute to the observed reduction in skin tumour formation in mice after chronic exposure to UV followed by topical post-irradiation treatment with calcitriol and some, though not all, related compounds.

Investigating the roles of regulatory T cells, mast cells and interleukin-9 in the control of skin inflammation by vitamin D

Topical application of biologically active vitamin D [1,25-dihydroxyvitamin D (1,25(OH)₂D)], or low-calcemic analogues, curb skin inflammation through mechanisms that involve migratory dendritic cells (DCs) and regulatory T (T_Reg) cells. 1,25(OH)₂D also promotes immunoregulation by mast cells, and inhibits the development of T helper type-9 (Th9) cells that secrete interleukin-9 (IL-9). Here, we investigated the ability of topical 1,25(OH)₂D to suppress contact dermatitis through an IL-9-dependent process, examining mast cells and IL-9-secreting T cells. Contact dermatitis was modelled in adult BALB/c female mice by initiating a "biphasic ear swelling response" following a single application of 2,4-dinitrofluorobenzene (DNFB). Topical 1,25(OH)₂D (125 ng) applied to ear pinnae prior to (but not after) DNFB sensitisation suppressed the efferent phase of the ear swelling response. This dose of 1,25(OH)₂D did not cause hypercalcemia. At the peak of the efferent ear swelling response, proportions of T_Reg (CD3 + Foxp3+) cells and numbers of mast cells were increased in ear skin of 1,25(OH)₂D-treated mice. Topical 1,25(OH)₂D increased the proportion of Foxp3 + IL-9 + T_Reg cells and the capacity of T_Reg cells to secrete IL-9 ex vivo. However, the proportion of the IL-9 + cells of the total T_Reg cell population was small (< 1%), and the amount of IL-9 secreted by T_Reg cells from mice treated with IL-9 was low (< 50 pg/ml). Furthermore, injection of anti-IL-9 neutralising antibody (100 µg, intraperitoneally) prior to sensitisation did not significantly reverse the suppressive effects of 1,25(OH)₂D. In conclusion, topically applied 1,25(OH)₂D suppressed the efferent phase of a biphasic cutaneous ear swelling response through mechanism(s) that may be dependent on mast cells and T_Reg cells; however, the role of IL-9 in mediating these responses is uncertain. More studies are needed to further characterise the mechanisms by which topical 1,25(OH)₂D modulates cell-mediated immune responses central to its suppressive effects upon contact dermatitis.

Mechanisms of vitamin D₃ metabolite repression of IgE-dependent mast cell activation

BACKGROUND

Mast cells have gained notoriety based on their detrimental contributions to IgE-mediated allergic disorders. Although mast cells express the vitamin D receptor (VDR), it is not clear to what extent 1α,25-dihydroxyvitamin D3 (1α,25[OH]2D3) or its predominant inactive precursor metabolite in the circulation, 25-hydroxyvitamin D3 (25OHD3), can influence IgE-mediated mast cell activation and passive cutaneous anaphylaxis (PCA) in vivo.

OBJECTIVE

We sought to assess whether the vitamin D3 metabolites 25OHD3 and 1α,25(OH)2D3 can repress IgE-dependent mast cell activation through mast cell-25-hydroxyvitamin D-1α-hydroxylase (CYP27B1) and mast cell-VDR activity.

METHODS

We measured the extent of vitamin D3 suppression of IgE-mediated mast cell degranulation and mediator production in vitro, as well as the vitamin D3-induced curtailment of PCA responses in WBB6F1-Kit(W/W-v) or C57BL/6J-Kit(W-sh/W-sh) mice engrafted with mast cells that did or did not express VDR or CYP27B1.

RESULTS

Here we show that mouse and human mast cells can convert 25OHD3 to 1α,25(OH)2D3 through CYP27B1 activity and that both of these vitamin D3 metabolites suppressed IgE-induced mast cell-derived proinflammatory and vasodilatory mediator production in a VDR-dependent manner in vitro. Furthermore, epicutaneously applied vitamin D3 metabolites significantly reduced the magnitude of skin swelling associated with IgE-mediated PCA reactions in vivo; a response that required functional mast cell-VDRs and mast cell-CYP27B1.

CONCLUSION

Taken together, our findings provide a mechanistic explanation for the anti-inflammatory effects of vitamin D3 on mast cell function by demonstrating that mast cells can actively metabolize 25OHD3 to dampen IgE-mediated mast cell activation in vitro and in vivo.

1,25-dihydroxyvitamin D exerts similar immunosuppressive effects as UVR but is dispensable for local UVR-induced immunosuppression

Low-dose UV radiation (UVR) inhibits the induction of contact hypersensitivity and induces regulatory T cells (Tregs), which because of their antigen specificity harbor therapeutic potential. Topical application of 1α,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) is known to induce Tregs as well, which implies that 1,25(OH)(2)D(3) might be involved in UVR-induced immunosuppression. It was the aim of this study to clarify this issue, to further characterize 1,25(OH)(2)D(3)-induced Tregs and to determine whether they differ from UVR-induced Tregs. Our data demonstrate that 1,25(OH)(2)D(3)-induced Tregs act in an antigen-specific manner and belong to the Foxp3-expressing subtype of Tregs as demonstrated by diphtheria toxin (DT)-mediated depletion of Foxp3(+) Tregs in DEREG (depletion of Tregs) mice. Using Langerin-DTR (DT receptor) knock-in mice, it was shown that Langerhans cells (LCs) are required for the induction of Tregs by 1,25(OH)(2)D(3), as depletion of LCs but not Langerin(+) dermal dendritic cells abrogated the induction of Tregs. Taken together, 1,25(OH)(2)D(3) affects the immune system in a similar manner as UVR, probably using the same pathways. However, vitamin D receptor knockout mice were equally susceptible to UVR-induced immunosupppression as wild-type controls. This indicates that 1,25(OH)(2)D(3) exerts similar immunosuppressive effects as UVR but is dispensable for local UVR-induced immunosuppression.

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.

Immune-modifying properties of topical vitamin D: Focus on dendritic cells and T cells

Topical creams containing the active form of vitamin D (1,25-dihydroxyvitamin D3; 1,25(OH)2D3) or analogues of this compound are currently used with some success to treat skin conditions including psoriasis and vitiligo. As well as targeting inflammatory processes in the skin, topical application of 1,25(OH)2D3 also affects the function of immune cells in the skin and draining lymph nodes. Topically applied 1,25(OH)2D3 reduces the number of dendritic cells in the skin, resulting in suppressed immunity and in particular reduced contact hypersensitivity (CHS) responses. Topical 1,25(OH)2D3 may also promote the migration of dendritic cells from the skin to the draining lymph nodes. Skin application of 1,25(OH)2D3 prevented the inflammatory effects of UVB irradiation on lymph node hypertrophy, when cell numbers were examined 4 days after skin treatment. In contrast, when 1,25(OH)2D3 was applied to UVB irradiated skin, there was no reversal in the suppression of CHS responses caused by UVB irradiation. Instead, 1,25(OH)2D3 had an additive effect with UVB to suppress CHS responses to a greater degree than UVB alone. In these studies, 1,25(OH)2D3 was applied to the treated skin of BALB/c mice immediately following UVB irradiation. Finally, topical 1,25(OH)2D3 also enhanced the number and suppressive activity of CD4+CD25+ regulatory T cells in the lymphatic tissue draining skin.

Gene regulation by 1,25-dihydroxyvitamin D3 in CD4+CD25+ cells is enabled by IL-2

Vitamin D may be responsible for reducing the development and severity of autoimmune and allergic diseases. Topically applied 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) enhances the immunoregulatory ability of CD4+CD25+ T cells residing in the skin-draining lymph nodes (SDLNs) of mice. The mechanisms responsible were investigated by examining the expression of 84 cytokine and cytokine-related genes in a 96-well gene array. CD4+CD25+ cells isolated from the SDLNs of BALB/c mice, 24 and 96  hours after topical treatment with 1,25(OH)(2)D(3), consistently expressed increased IL-2 mRNA levels and also secreted enhanced quantities of IL-2 after ex vivo stimulation with phorbol 12-myristate 13-acetate and ionomycin. CD4+CD25+ cells from the lymph nodes of naive mice constitutively express the vitamin D receptor, allowing direct modulation by 1,25(OH)(2)D(3). However, in vitro treatment with 1,25(OH)(2)D(3) did not modify the expression of 84 tested cytokine and cytokine-related mRNAs. It was only in the presence of IL-2 that 1,25(OH)(2)D(3) increased the expression of genes including IL-2 and TLR4. Further, 1,25(OH)(2)D(3) enhanced the ability of IL-2 to stimulate CD4+CD25+ cells to proliferate in vitro and also regulate contact hypersensitivity responses on adoptive transfer into naive mice. Therefore, 1,25(OH)(2)D(3) enabled by IL-2 can directly enhance the regulatory potential of CD4+CD25+ T cells to control immune disease.

Topically applied 1,25-dihydroxyvitamin D3 enhances the suppressive activity of CD4+CD25+ cells in the draining lymph nodes

The immunomodulatory effects of vitamin D have been described following chronic oral administration to mice or supplementation of cell cultures with 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), the active form of vitamin D. In this study, topically applied 1,25(OH)(2)D(3), enhanced the suppressive capacity of CD4(+)CD25(+) cells from the draining lymph nodes. The effects of topical 1,25(OH)(2)D(3) were compared with those of UVB irradiation, which is the environmental factor required for 1,25(OH)(2)D(3) production in skin. CD4(+) cells from the skin-draining lymph nodes (SDLN) of either 1,25(OH)(2)D(3)-treated or UVB-irradiated mice had reduced capacity to proliferate to Ags presented in vitro, and could suppress Ag-specific immune responses upon adoptive transfer into naive mice. This regulation was lost upon removal of CD4(+)CD25(+) cells. Furthermore, purified CD4(+)CD25(+) cells from the SDLN of 1,25(OH)(2)D(3)-treated or UVB-irradiated mice compared with equal numbers of CD4(+)CD25(+) cells from control mice had increased capacity to suppress immune responses in both in vitro and in vivo assay systems. Following the sensitization of recipient mice with OVA, the proportion of CD4(+)Foxp3(+) cells of donor origin significantly increased in recipients of CD4(+)CD25(+) cells from the SDLN of 1,25(OH)(2)D(3)-treated mice, indicating that these regulatory T cells can expand in vivo with antigenic stimulation. These studies suggest that 1,25(OH)(2)D(3) may be an important mediator by which UVB-irradiation exerts some of its immunomodulatory effects.

The direct action of 1α,25(OH)2-vitamin D3 on purified mouse Langerhans cells

The action of vitamin D(3) on Langerhans cells (LCs) is not well understood. Using highly purified murine LCs (>95%), we investigated the direct action of 1alpha,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) on their functions. 1,25(OH)(2)D(3) inhibited the expression of cell surface molecules including I-A(d), CD40, CD80, and CD86, leading to impaired ability of LCs to stimulate allogenic T cells in the mixed leukocyte reaction. Furthermore, this reagent inhibited chemotaxis of LCs to CCL21 and their survival. Interestingly, 1,25(OH)(2)D(3) reduced the IL-10 production by LCs, whereas the production of IL-6 and IL-12p40 upon activation by CD40 ligation was enhanced. With regard to inflammatory cytokines and chemokines, 1,25(OH)(2)D(3) upregulated the production of IL-1beta, CCL3, CCL4, and CCL5. The production of Th2-type chemokines, represented by CL17 and CCL22, was inhibited, whereas IFN-gamma-triggered production of Th1-type chemokines, represented by CXCL9, CXCL10, and CXCL11, was augmented. These data indicate that the mode of regulation of cytokine and chemokine production in association with 1,25(OH)(2)D(3) treatment seems to be another characteristic discriminating LCs from classical myeloid dendritic cells.

Ultraviolet Immunosuppression: Mechanisms and Consequences

It is well recognized that exposure to solar radiation has several detrimental consequences, both acute and chronic. The suppression of immune functions remains one of the most intriguing phenomena brought about by ultraviolet (UV) radiation. This concept has challenged experts from various disciplines including dermatology, immunology, and photobiology. Although controversies exist regarding the mechanisms involved, the consensus is that UV immune suppression contributes significantly to the growth of cutaneous malignancies--both melanoma and nonmelanoma skin cancer. It is therefore a critical issue to be addressed in the context of developing and using sun protection strategies.

Topical tacalcitol (1,24-(R)-dihydroxyvitamin D3) induces a transient increase in thymidine incorporation and calmodulin content in pig epidermis following tape stripping in vivo

Tape stripping induces transient increase in keratinocyte proliferation in vivo. The effects of tacalcitol (1,24-(R)-dihydroxyvitamin D3) ointment on the cell kinetics of pig epidermis after the tape stripping were investigated. The tacalcitol ointment (2 micrograms/g) was applied once to the back of pigs immediately after the tape stripping. The pig epidermal cell kinetics were analyzed at various times following the treatment. Tape stripping transiently increased thymidine incorporation of keratinocytes; the maximal effect was observed at 24 h. Tape stripping-induced increase in thymidine incorporation was markedly augmented by tacalcitol treatment. At 24 h following the tape stripping DNA-flow cytometry revealed an accelerated transition from G0/1 to S phase of cell cycle in tacalcitol treated epidermis. There was no significant difference, however, in mitotic counts and G2/M phase fractions between tape stripping-treated and tape stripping plus tacalcitol ointment-treated epidermis. We also measured calmodulin content of pig epidermis following the treatments. Although tape stripping slightly increased calmodulin content of pig epidermis, this was statistically not significant. Tape stripping plus tacalcitol ointment treatment resulted in a significant increase in calmodulin content at 24 h following the treatment. There was no significant difference in calmodulin content between tape stripping treated- and tape stripping plus tacalcitol-treated epidermis.