Effector cytolotic funtion but not IFN-gamma production in cytotoxic T cells triggered by virus-infected target cells in vitro

Cytolysis and interferon(IFN)-gamma production are two independent effector functions of activated cytotoxic T (Tc) cells. We have used the Tc-cell re sponse against the flavivirus, Murray Valley encephalitis virus (MVE), to i nvestigate the requirements for inducing these two functions with regard to antigen-concentration and CD8 coreceptor involvement. Cognate peptide-puls ed target cells triggered cytolysis by primary ex vivo MVE-immune as well a s in vitro peptide-restimulated splenocytes at lower peptide concentrations than IFN-gamma -production (100-fold lower in the case of primary ex vivo effectors). Little difference was observed in CD8 dependency. Importantly, neither of the effector populations were triggered to produce IFN-gamma by virus-infected target cells, although cytolysis occurred. This result raise s the possibility that the levels of presentation of cognate antigen on vir us-infected cells in vivo may be below the threshold required for the IFN-g amma production.