Cyclosporine A and prednisolone inhibit lectin- and alloantigen-induced release of sCD8: correlation with proliferative responses.

It has been shown previously that there is a strong correlation between the in vitro release of soluble CD8 glycoprotein (sCD8) and CD8+ T lymphocyte activation. In the present study, the lectin stimulation of peripheral blood mononuclear cells (PBMC) induced a dose-dependent release of sCD8 which correlated with the magnitude of CD8 lymphocyte activation as measured by the expression of the interleukin 2 (IL-2) receptor and HLA-DR antigen and of the T cell proliferative responses. Both the proliferative responses and the release of sCD8 were inhibited by cyclosporine A (CyA) and prednisolone (PRED) in a concentration-dependent manner. When the immunosuppressants were present for only 60 min before the initiation of the cultures, an inhibitory effect was also seen, but this was maximal only when the agents were added at the initiation of the culture period; when the addition of CyA or PRED was delayed for either 24 or 48 hr after the initiation of the culture, the degree of inhibition of the proliferative response was greatly reduced. However, there was a significant inhibition of sCD8 release by CyA even when it was added 48 hr after the culture initiation. The addition of recombinant IL-2 did not affect the lectin-induced sCD8 release. The inhibition of the lectin-induced proliferative response and sCD8 release by PRED, but not that by CyA, was reversed by the recombinant IL-2. Alloantigen stimulation also induced sCD8 release and this release was inhibited both by CyA and by PRED. These data, together with the known effects of CyA on differentiation, clonal amplification, and activation of CD8 T lymphocytes, suggest that in vitro sCD8 release occurs during the early stages of activation of CD8+ cytotoxic T cells.