Modulation of glucocorticoid inhibitory action on human lymphocyte mitogenesis: dependence on mitogen concentration and T-cell maturity.

The inhibitory effect of glucocorticoids on the mitogenesis of human T cells derived from thymus and peripheral blood compartments have been investigated. The capacity of dexamethasone (Dex) (10(-7) M) of inhibiting the peripheral blood lymphocyte (PBL) mitogenesis was inversely correlated with the phytohemagglutinin (PHA) concentration used. Conversely, Dex completely (greater than 90%) inhibited the thymocyte mitogenesis, irrespective of PHA concentrations. T cells purified from PBL (M phi less than or equal to 1%) behaved as thymocytes regarding the Dex inhibitory pattern. The addition of macrophages (M phi) or interleukin 1 (IL1) was effective in removing the Dex inhibitory effect on T cells purified from PBL, but not on thymocytes. The higher corticosensitivity of thymocyte mitogenesis in comparison to PBL mitogenesis cannot be explained by differences in the relative number of M phi, but seems an intrinsic property of these less mature T cells.