Abstract
Sensitization of human recipients with transplantation antigens (leucocytes, skin, or kidney allografts) has resulted in the appearance of serum hemagglutinins directed against sheep, guinea pig, and rat erythrocytes. Such hemagglutinins have been identified as IgG and IgM antibodies. Their appearance was not related to AB0 erythrocyte group incompatibility between donors and recipients, and the antibodies were not of the Forssman or Paul-Bunnel type. The antibody responses appeared to be primarily directed against antigen(s) present on rat erythrocytes, but shared to varying extents by other species. The peak antibody titers occurred in association with allograft rejection. In this regard, they may be of interest as a possible early warning system for the diagnosis and prompt management of rejection crises in clinical organ transplantation.