Inhibition of cytotoxic T lymphocyte activity by concanavalin A

Several lectins were tested for the ability to interfere with the recognition or lysis of target cells by cytotoxic T lymphocytes (CTL). Of those tested, concanavalin A (Con A) had the greatest effect: at 0.25 to 10 micrograms/ml, it profoundly blocked antigen-specific lysis of target cells by cloned and uncloned CTL in various allo- and syngeneic systems. Separate pretreatment of CTL and target cells showed that the effect of Con A is exercised predominantly on CTL. Various experimental results ruled out several possible explanations for the inhibitory effect of Con A, such as: CTL-CTL self-killing by nonspecific, lectin-dependent cytotoxicity, impairment of lateral mobility of CTL surface components, and cell agglutination, preventing recycling of CTL among target cells. The findings suggest that subagglutinating concentrations of Con A block CTL activity by binding to and interfering with CTL surface structures that have relatively high affinity for Con A and are critically involved in recognition or lysis of target cells.