Suppression of a thymus dependent humoral response in mice by concanavalin A in vivo

Mice treated with Concanavalin A prior to immunization with sheep erthyrocytes exhibit a markedly reduced plaque forming spleen cell response. This immunosuppressive effect could be reversed by using higher doses of antigen or priming the animals with nonimmunizing doses of antigen prior to Concanavalin A injection designed to either by-pass or enhance thymus derived lymphocyte functions. It was also demonstrated that Concanavalin A in vivo activated the thymus derived lymphocyte subpopulation in the spleen, and this activation was dose dependent and correlated with the immunosuppression observed. Animals injected with Concanavalin A at various times prior to whole body lethal irradiation would not support the plaque forming cell response of adoptively transferred normal syngeneic spleen cells. This effect was shown to be time and dose of Concanavalin A dependent. It was also shown that the route of injection of Concanavalin A prior to irradiation determined the results observed, in that the intravenous route resulted in the suppression of transferred cells, while the intraperitoneal route showed no effect. It is suggested that Concanavalin A induced immunosuppression of the humoral, thymus dependent immune response in mice results for the activation of a subpopulation of thymus derived suppressors cells, and that the effect is short lived, radiation resistant, and dose of Concanavalin A and antigen dependent.