In Vivo and in Vitro Properties of Intact and Pepsin-Digested Heterologous Anti-Mouse Thymus Antibodies

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Abstract
Summary: Rabbit anti-mouse thymus globulin (AMT-IgG) had a strong inhibitory effect of IgM antibody-forming spleen cells of mice when injected prior to the antigen. No effect was observed when AMT-IgG was injected after or simultaneously with the immunizing dose of sheep red cells. Pepsin-digested bivalent antibody did not inhibit formation of antibody-synthesizing spleen cells nor did it prolong survival of allogeneic skin grafts. AMT-IgG as well as the bivalent fragment F(ab')2 stimulated uridine incorporation of thymocytes in vitro. The F(ab) fragment, however, had no stimulatory effect though it protected the cells when exposed to complete cytotoxic antibodies in the presence of complement. The possible mechanism of immediate immunosuppression by which AMT-IgG acts in vivo is discussed. Biologic properties of the Fc fragment are implicated in this action.