Effect of active vitamin D on expression of co-stimulatory molecules and HLA-DR in renal transplant recipients.

Objectives: Full activation of T cells requires 2 distinct but synergistic signals. The first is the T-cell antigen receptor, which is antigen specific, and the second is activation of co-stimulatory signals. Active vitamin D (1, 25-dihydroxyvitamin D3) decreases T-cell activation and proliferation, inhibits differentiation and maturation of dendritic cells, and induces tolerogenic dendritic cells.