Concanavalin A‐mediated in Vitro Activation of a Secondary Cytotoxic T‐Cell Response in Virus‐primed Splenocytes

In a recent report it was shown that what appeared to be secondary cytotoxic T cells could be obtained from lymphocytic choriomeningitis virus (LCMV)‐primed splenocytes after stimulation in vitro with the non‐specific T cell mitogen concanavalin A (Con A). The present experiments attempt to characterize further these effector cells and, in particular, to establish whether the Con A‐activated cytotoxic effectors are qualitatively different from the secondary cytotoxic T cells induced by restimulation with the homologous antigen. It was found that: (1) in vitro activation with Con A could be obtained with populations harvested between 13 days (the earliest tested) and at least 300 days after priming: (2) cytotoxicity was independent of the presence of carried‐over Con A in the cytotoxicity assay; (3) cytotoxicity was dependent on close association between activated T cells and target cells, since no evidence was found to indicate a role for other cell types or soluble (cytotoxic or arming) factors; (4) cytotoxicity was specific with regard to both virus and ‘self’. By comparison with previous data on LCMV‐induced cytotoxic T cells, it is concluded that Con A induces the generation of cytotoxic T cells from LCMV‐primed splenocytes, which, by the criteria used, are indistinguishable from virus‐induced secondary cytotoxic T cells. The implications of these findings are discussed.