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

Cytolysis and interferon(IFN)-γ production are two independent effector functions of activated cytotoxic T (Tc) cells. We have used the Tc-cell response against the flavivirus, Murray Valley encephalitis virus (MVE), to investigate the requirements for inducing these two functions with regard to antigen-concentration and CD8 coreceptor involvement. Cognate peptide-pulsed target cells triggered cytolysis by primary ex vivo MVE-immune as well as in vitro peptide-restimulated splenocytes at lower peptide concentrations than IFNγ-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-γ by virus-infected target cells, although cytolysis occurred. This result raises the posibility that the levels of presentation of cognate antigen on virus-infected cells in vivo may be below the threshold required for the IFN-γ production.