Influenza and superantigen stimulation of CD4+ cytotoxic T cell effector functions

Engagement of the T cell receptor has the potential to elicit a myriad of effector functions, such as cytokine production, cytotoxicity, and proliferation, and display differential responses to different stimuli. We utilized influenza-specific, MHC restricted CD4+ cytotoxic T lymphocyte (CTL) clones to delineate distinct signaling events leading to specific effector functions by comparing responses elicited by antigen, influenza virus, with those elicited by a superantigen, Staphylococcus enterotoxin B (SEB). Here we show that SEB elicited proliferative responses and production of IFNgamma that were comparable to influenza. While Ag/MHC elicited both mechanisms of cytolysis, perforin/granzyme and FasL/Fas-mediated, SEB was unable to trigger the former. We previously reported that intracellular calcium mobilization events are qualitatively and quantitatively different in Ag/MHC vs. SEB stimulated CD8+ CTL clones. Here we show that for our CD4+ CTL clones the intracellular calcium mobilization events following stimulation with Ag/MHC or SEB were surprisingly similar. Thus the intracellular calcium mobilization while correlated with the ability of CD8+ CTL to mediate perforinlgranzyme cytolysis, appears to be necessary by not sufficient for perforinlgranzyme cytolysis by our CD4+ CTL clones. This suggests that the earliest difference in eliciting perforinlgranzyme and FasL/Fas-mediated cytolysis may occur after or parallel to calcium mobilization events.;We examined the requirements for protein kinase C (PKC) activation in eliciting perforinlgranzyme-mediated and FasL/Fas-mediated cytolysis, using cell permeable inhibitors of specific PKC isoforms. We report here that the inability of SEB to trigger perforin-mediated cytolysis may be the failure of SEB to activate the calcium dependent PKC isoforms. We investigated signaling molecules that have been implicated in early upstream events of calcium mobilization events and PKC activation, using wortmannin to investigate the role of phosphoinositide 3-kinase (PI3-K). We report here that, similar to CD8+ CTL, (PI3-K) activation was required for perforin-mediated cytolysis by our CD4+ CTL clones. Our findings suggest that perforin-mediated cytolysis occurs through a PI3-K, calcium dependent PKC pathway while FasL/Fas-mediated cytolysis proceeds through a (PI3-K). PKC independent pathway. Additionally, (PI3-K) is required for IFNgamma production elicited by Ag/MHC or SEB.