Cyclosporin A and prednisolone do not inhibit the expression of high-affinity receptors for interleukin 2

To elucidate the mechanisms of action of cyclosporin A (CyA) and prednisolone (pred), we investigated the effects of these immunosuppressive drugs on the expression of receptors for interleukin 2 (IL-2) as well as the effect of exogenous IL-2 on CyA-inhibited and pred-inhibited responses. Pred-induced inhibition of T cell proliferative responses could be reversed by addition of exogenous IL-2. In contrast, exogenous IL-2 could not overcome CyA-mediated inhibition of T cell proliferation. Receptors for IL-2, as measured by the expression of Tac antigen, were slightly decreased by CyA and pred. However, expression of the biologically active, high-affinity IL-2 receptors was not diminished. These data suggest that pred-mediated inhibition occurs at the level of the IL-2 system, whereas CyA affects the proliferative mechanism of the T cell itself.