Enhancement of cardiac allografts in rats. Comparison of host responses to different treatment protocols.

: Immunological responses to heterotopic (L X BN)F1 cardiac allografts placed in untreated L rats were compared with those grafts enhanced by different treatment regimens. Host pretreatment by antigen and antibody (Ag-Ab) 11 and 10 days before transplantation, respectively, was the most effective treatment regimen for prolongation of graft function; active or passive immunization alone increased survival only modestly. A late dose of antiserum administered to Ag-Ab-pretreated animals significantly shortened graft survival. Patterns of cellular responsiveness were measured serially by lymphocyte-mediated cytotoxicity; humoral immunity by Ab-lymphocyte-mediated cytotoxicity, capillary hemagglutination, and complement-dependent cytotoxicity. Allograft rejection in animals of all groups was heralded in vitro by increasing immunological activity. All cellular and humoral responses were depressed consistently in Ag-Ab-pretreated recipients. Cellular but not humoral responses were decreased in Ag-pretreated hosts, while humoral but not cellular responses were decreased in Ab-treated animals. The results suggest that the in vitro determinants of immunological activity used in this study generally followed clinical patterns of rejection or enhancement of cardiac allografts in the rat. Recipient pretreatment with Ag and Ab is more effective in graft prolongation than treatment with Ag or Ab alone, and in vitro data suggest an additive effect of these two regiments.