Additive immunosuppressive effects of 1,25-dihydroxyvitamin D-3 and couticosteroids on T(H)1, but not T(H)2, responses

Background: The biologic role of the vitamin D analogue 1,25-dihydroxyvitam in D-3, such as antiinflammatory functions, reduction of cytokine productio n by T cells, and immunoglobulin production by B cells, has been reported, Such immunomodulatory effects may be potentially useful in dealing with aut oimmunity and transplantation. However, whether this hormone has an additiv e immunosuppressive effect when it is used with corticosteroids has not bee n investigated, although these agents are commonly used together Objective: Our purpose was to investigate the additive immunomodulatory eff ects of 1,25-dihydroxyvitamin D-3 on lymphocyte proliferation and cytokine production when used with corticosteroids. Methods: To investigate the additive effects of 1,25-dihydroxyvitamin D-3 a nd dexamethasone on suppression of lymphocyte proliferation, normal PBMCs w ere cultured in anti-CD3 with or without different concentrations of dexame thasone (0-10(-7) mol/L) plus or minus different concentrations of 1,25-dih ydroxyvitamin D-3 (0-10(-6) mol/L), After 3 days, lymphocyte proliferation was assessed by [H-3]-thymidine incorporation. To investigate the additive effects of 1,25-dihydroxyvitamin D, and dexamethasone on cytokine productio n, PBMCs were cultured for 3 days in the presence of anti-CD3 with or witho ut 10(-6) mol/L dexamethasone plus or minus 10(-6) mol/L, 1,25-dihydroxyvit amin D-3. IFN-gamma IL-5, and IL-13 production in supernatants were measure d by ELISA. Results: Our study demonstrated that, at concentrations of 10(-8), 10(-7), and 10(-6) mol/L, 1,25-dihydroxyvitamin D-3 significantly decreased lymphoc yte proliferation compared with an ethanol control (P <.05), The IC50 for d examethasone was 4 x 10(-9) mol/L in culture without 1,25-dihydroxyvitamin D-3. When 10(-9) mol/L of 1,25-dihydroxyvitamin D-3 was added to cultures w ith dexamethasone, IC50 became 2 x 10(-9) mol/L, Moreover, when 10(-6), 10( -7), and 10(-8) morn of 1,25-dihydroxyvitamin D-3 were added in culture wit h dexamethasone, IC50 became less than 1 x 10(-9) mol/L, IFN-<gamma> produc tion in culture with either dexamethasone or 1,25-dihydroxyvitamin D-3 was significantly decreased compared with media or ethanol control (P <.0001). Moreover, when both agents were added in the same culture, IFN-<gamma> prod uction was further decreased compared with either agent alone (P <.05), In contrast, 1,25-dihydroxyvitamin D, significantly (P <.0001) increased IL-5 and IL-13, whereas dexamethasone significantly decreased these 2 cytokines (P <.0005), When 1,25-dihydroxyvitamin D-3 was combined with dexamethasone, IL-5 and IL-13 production was increased compared with dexamethasone alone (P <.001). Conclusions: Our results demonstrate that 1,25-dihydroxyvitamin D-3 has sig nificant additive effects on dexamethasone-mediated inhibition of lymphocyt e proliferation. This hormone also has additive effects on inhibition of T( H)1 cytokine production when combined with dexamethasone. However, this hor mone upregulates T(H)2 cytokines and inhibits steroid-mediated suppression of cytokines, These findings demonstrate the potential use of 1,25-dihydrox yvitamin D-3 as an immunosuppressive agent when combined with corticosteroi ds in T(H)1, but not T(H)2, immune responses.