IL-4 bypasses the immune suppressive effect of cyclosporin A during the in vitro induction of murine cytotoxic T lymphocytes

We have analyzed at the clonal level the effect of IL-4 on the immune suppressive action of cyclosporin A (CsA) during the in vitro primary activation of anti-MHC alloantigen-reactive murine CD8+ CTL. Although neither IL-4 nor IL-2 alone were able to overcome the CsA-mediated suppression, the addition of IL-4 in the presence of IL-2 restored in a dose-dependent manner the induction of cytolytic activity. On the other hand, CsA greatly impaired proliferative responses of alloantigen-reactive CD8 T cells, thereby operationally dissecting proliferative responsiveness from acquisition of cytolytic activity during primary activation of alloantigen-reactive CD8+ T cells. The existence of a CsA-resistant induction pathway for Ag-specific CD8+ T cell-mediated cytolytic activity may be of relevance for experimental and clinical organ transplantation.