INHIBITION OF COMPLEMENT-MEDIATED XENOGENEIC INJURY BY THE MEMBRANE ATTACK COMPLEX IS SUFFICIENT TO ALLOW INDUCTION OF ACCOMMODATION IN THE HAMSTER-TO-RAT MODEL

Abstract

55 Accommodation is long-term graft survival in the presence of xenoreactive antibodies and complement. Accommodation can be obtained in the hamster-to-rat cardiac model by a combination of complement inactivation with cobra venom factor (CVF) and daily administration of cyclosporin A (CSA). Since CVF inactivates both C3 and subsequent components following C3, experiments with CVF suggest that several complement activation fragments, in addition to the membrane attack complex (MAC), may play a role in preventing accommodation in this model. To define which complement-mediated process needs to be inhibited to allow induction of accommodation, we investigated accommodation of a hamster heart xenograft in C6-deficient (C6D) PVG rats and in normocomplementemic PVG rats treated with antibodies against C6. Golden Syrian hamster hearts were transplanted heterotopically into normal or C6D rats. C6D rats had complete deficiency of C6 hemolytic activity; addition of purified C6 to the serum fully restored CH50 total complement activity, confirming that other complement components were intact. Graft survival in untreated rats was 3-4 days (n=4) and in untreated C6D rats was 5 days (n=5). Experimental groups received either CVF (60 U/Kg at day-1 pre-tx. and 20U/day × 9 days) or polyclonal goat anti-C6 antiserum (Cappel) (140 mg IgG/kg/day × 5 days) with or without CSA. The table shows the number of grafts performed in each group and grafts surviving >100 days. C6D rats bearing hamster hearts had no reconstitution of hemolytically active C6. Histopathologic examination was performed on rejected hearts (<100 day survivors) or after sacrifice (>100 day survivors).TableC6D rats treated with CSA or CSA and CVF had 90% long-term graft survival. Normal rats treated with CSA and CVF, or CSA and anti-C6 antibodies had >60% long-term graft survival. Histologically, rejected hearts had myofiber necrosis, interstitial hemorrhage, acute inflammation and vascular damage. In contrast, hearts from >100 day survivors lacked these findings and had preservation of normal architecture; however, a mononuclear cell infiltrate was present. These features are characteristic of accommodated hearts in the hamster-to-rat model. In conclusion, the finding that C6D rats and normal rats treated with anti-C6 antibodies develop accommodation without CVF treatment to inactivate C3 and C5 demonstrates that xenogeneic injury due to the MAC is responsible for preventing the development of accommodation in the hamster-to-rat model. Accommodation occurred in the face of unabated formation of fragments derived from C3 and C5.