Immunological status of mice with long-standing allogeneic or xenogeneic neonatal heart grafts

Adult mice were thymectomized and given 1 X 10(8) allogeneic or xenogeneic spleen cells i.v. On the day following cell injection, the mice were treated with 200 mg/kg cyclophosphamide (Cy) i.p. Of the CBA mice treated according to this protocol, 87% accepted heterotopically transplanted C57BL/6 neonatal heart grafts and 61% accepted August rat heart grafts. Electrical activity of the grafts could be recorded in the majority of recipients for more than 5 months. Graft acceptance in most cases was specific. Some recipients with long standing rat heart grafts produced antirat hemagglutinins, but were negative for lymphocytotoxins. The absence of xenoantibodies correlated with specific unresponsiveness in the mixed lymphocyte culture (MLC) response.