Mechanisms underlying the protective effects of vitamin D and its analogs (alone or in combination with immunosuppressive agents) against recurrence of autoimmunity and graft failure in animal models of syngeneic islet transplantation. Abbreviations: CyA, cyclosporine A; IFN-β, interferon-beta; IFN-γ, interferon-gamma; IL-1, interleukin-1; IL-2, interleukin-2; IL-4, interleukin-4; IL-12, interleukin-12; NF-kB p65, nuclear factor kB p65; NOD mice, non-obese diabetic mice; STZ, streptozotocin; Th1, T-helper 1 cell; Th2, T-helper 2 cell; TNF-α, tumor necrosis factor-alpha; Tregs, regulatory T cells.