Effects of concanavalin A on the in vitro responses of mouse spleen cells to T-dependent and T-independent antigens.

?The stimulatory and inhibitory effects of concanavalin A (Con A) on the in vitro primary immune responses to a T-dependent antigen, sheep erythrocytes (SRBC) and a T-independent antigen, TNP-lipopolysaccharide (TNP-LPS) have been studied. Inhibition of the response to both antigens was optimal when 2 mug Con A were added at the initiation of the culture period. The response to SRBC was considerably enhanced by the addition of Con A 24 hr later. In contrast, this late addition did not stimulate the TNP-LPS response and often inhibited it. Inhibition of the TNP-LPS response required the participation of T cells since it was not observed in cells from adult thymectomized irradiated bone marrow-reconstituted (ATXBM) mice. The response to TNP-LPS was somewhat enhanced in ATXBM cells, but the degree of enhancement was strikingly less than that observed for SRBC. LPS per se did not block the stimulatory effect of Con A on the SRBC response, and was observed to act synergistically with this lectin. None of the Con A effects observed required the participation of adherent cells. These observations are consistent with a model in which different subpopulations of T cells are responsible for the inhibitory and stimulatory effects. They further suggest that the Con A inhibitory activity acts via a T cell to inhibit directly the B cell response to antigen.