Background: The biologic role of the vitamin D analogue 1, 25-dihydroxyvitamin D(3), such as antiinflammatory functions, reduction of cytokine production by T cells, and immunoglobulin production by B cells, has been reported. Such immunomodulatory effects may be potentially useful in dealing with autoimmunity and transplantation. However, whether this hormone has an additive immunosuppressive effect when it is used with corticosteroids has not been investigated, although these agents are commonly used together.
Objective: Our purpose was to investigate the additive immunomodulatory effects 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) and dexamethasone on suppression of lymphocyte proliferation, normal PBMCs were cultured in anti-CD3 with or without different concentrations of dexamethasone (0-10(-7) mol/L) plus or minus different concentrations of 1, 25-dihydroxyvitamin D(3) (0-10(-6) mol/L). After 3 days, lymphocyte proliferation was assessed by [(3)H]-thymidine incorporation. To investigate the additive effects of 1,25-dihydroxyvitamin D(3) and dexamethasone on cytokine production, PBMCs were cultured for 3 days in the presence of anti-CD3 with or without 10(-6) mol/L dexamethasone plus or minus 10(-6) mol/L 1,25-dihydroxyvitamin D(3). IFN-gamma, IL-5, and IL-13 production in supernatants were measured 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 lymphocyte proliferation compared with an ethanol control (P <.05). The IC(50) for dexamethasone 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 with dexamethasone, IC(50) became 2 x 10(-9) mol/L. Moreover, when 10(-6), 10(-7), and 10(-8) mol/L of 1,25-dihydroxyvitamin D(3) were added in culture with dexamethasone, IC(50) became less than 1 x 10(-9) mol/L. IFN-gamma production 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 production was further decreased compared with either agent alone (P <.05). In contrast, 1,25-dihydroxyvitamin D(3) 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 significant additive effects on dexamethasone-mediated inhibition of lymphocyte proliferation. This hormone also has additive effects on inhibition of T(H)1 cytokine production when combined with dexamethasone. However, this hormone upregulates T(H)2 cytokines and inhibits steroid-mediated suppression of cytokines. These findings demonstrate the potential use of 1,25-dihydroxyvitamin D(3) as an immunosuppressive agent when combined with corticosteroids in T(H)1, but not T(H)2, immune responses.