The hormone, 1,25-dihydroxyvitamin D3 (1,

A s bstract. Activated B and T lymphocytes from normal human subjects are known to have the specific high-affinity receptor for 1,25-dihydroxyvitamin D3 (1,25-(OH)2-D3 data demonstrate that 1,25-(OH)2-D3 is a potent inhibitor of human PBM Ig production in vitro and suggest that this action is mediated through the hormone's antiproliferative effect on Ig-producing B cells and/or helper T cells.

The active vitamin D metabolite 1,25-dihydroxyvitamin D3 [1,25-D3] is thought to promote many of its actions through interaction with a specific intracellular receptor. The discovery of such receptors in monocytes and activated lymphocytes has led investigators to evaluate the role of the hormone on the immune system. The sterol inhibits lymphocyte proliferation and immunoglobulin production in a dose-dependent fashion. At a molecular level, 1,25-D3 inhibits the accumulation of mRNA for IL-2, IFN-gamma, and GM-CSF. At a cellular level, the hormone interferes with T helper cell (Th) function, reducing Th-induction of immunoglobulin production by B cells and inhibiting the passive transfer of cellular immunity by Th-clones in vivo. The sterol promotes suppressor cell activity and inhibits the generation of cytotoxic and NK cells. Class II antigen expression on lymphocytes and monocytes is also affected by the hormone. When given in vivo, 1,25-D3 has been particularly effective in the prevention of autoimmune diseases such as experimental autoimmune encephalomyelitis and murine lupus but its efficacy has been limited by its hypercalcemic effect. Synthetic vitamin D3 analogues showing excellent 1,25-D3-receptor binding but less pronounced hypercalcemic effects in vivo have recently enhanced the immunosuppressive properties of the hormone in autoimmunity and transplantation.

No abstract

The murine strain MRL/l spontaneously develops a systemic lupus erythematosus (SLE)-like syndrome. An increased number of T cells and polyclonal T helper cell activity has been described in these mice suggesting a potential role for 1,25-dihydroxyvitamin-D3 [1,25-D3], an antiproliferative hormone selecting the T-helper lymphocyte subset. One month old MRL/l mice were submitted or not to 1,25-D3 0.1 microgram for 4 weeks, then 0.15 microgram given i.p. every other day for 18 weeks while maintained on a low calcium chow. Dermatologic lesions, i.e. alopecia, necrosis of the ear and scab formation, were completely inhibited by 1,25-D3 therapy. By 20 weeks, all mice had developed proteinuria. However, the degree of proteinuria was somewhat reduced in treated mice as assessed by urine protein/creatine ratios (less than 4 vs greater than 4 in treated vs untreated mice respectively). Moreover, a trend for a reduction in serum titers for anti-ssDNA antibodies was observed at 18 weeks. The active vitamin D metabolite had no effect on the development of the generalized lymphoid hyperplasia. Hypercalcemia developed when 1,25-D3 was increased to 0.15 microgram (2.62 +/- 0.12 vs 1.97 +/- 0.07 mmol/l, treated vs untreated mice respectively). These results suggest a beneficial role of 1,25-D3 in the prevention or attenuation of some manifestations of murine SLE, a model sharing many immunologic features with human SLE.