Inhibition of T cell cytolytic potential by concanavalin A: a result of activation?

We investigated the effects of concanavalin A (Con A) on T cell-mediated lympholysis. Human cytotoxic T cell lines were generated from peripheral blood and these lines were shown to lyse lectin-coated K562 target cells. Addition of soluble Con A to the assay resulted in a dose-dependent inhibition of the cytolysis. Preincubation experiments demonstrated that this inhibitory effect was exerted at the effector cell level. F(ab')2 fragments of WT32, a monoclonal antibody against T3, blocked the cytolysis of Con A-preincubated K562 target cells to a large extent. We further showed that Con A strongly inhibited the cytolysis exerted by alloantigen-specific, major histocompatibility complex (MHC)-restricted cytotoxic T cell lines against their specific targets. On the other hand, Con A had no clear inhibitory effect on the cytotoxicity of freshly isolated peripheral blood mononuclear cells against K562 target cells. We hypothesize that Con A-induced inhibition of cytotoxicity may be explained by a direct triggering of the lytic potential of activated T cells.