Tissue transplantation immunity in goldfish.

1. The survival times of successive sets of orthotopic scale (skin) homografts revealed that increasing systemic immunity develops rapidly in stepwise fashion. Moreover, a secondary immune response to homografts was obtained within a week after an initial exposure to homologous antigens. 2. Both lyophilized and heat-treated grafts failed to confer transplantation immunity toward subsequent living scale homografts. Such immunization with non-viable tissues also failed to prolong the survival of later normal scale grafts from the same donors. 3. A strong skin transplantation immunity developed in goldfish which had previously been immunized with whole blood by the subcutaneous-intramuscular route, whereas no secondary transplantation immunity was evident in the fish into which blood cells had previously been injected by the intraperitoneal route. 4. Isohaemagglutinin titres were determined before and after immunization with blood and/or scale homografts. No correlation was observed between the presence or concentration of serum antibodies and the degree of transplantation immunity. It is concluded that the haemagglutinating antibodies are distinct from the cell-bound antibodies presumed to participate in scale homograft breakdown in goldfish.