Immunologic and pathologic features of delayed xenograft rejection (DXR) of pig-to-monkey cardiac transplants after a high activity Y-CVF therapy
Introduction In this study we investigated the immunologic and pathologic features of delayed xenograft rejection (DXR) when HAR of pig-to-monkey cardic grafts was prevented with a high activity cobra venom factor (Y-CVF) isolated and purified from the venom of Naja kaouthia living in Yunnan, China.
Materials and methods Heterotopic xenogeneic heart transplantation in the abdominal cavity was performed using piglets as donors. Four monkeys (macaca mulatta) were used as recipients. Complete complement depletion was achieved in the recipients treated with repetitive doses of Y-CVF (0.05 mg/kg on day minus 3 and 2; 0.02 mg/kg 12 h before transplantation; 0.02 mg/kg at 36 h intervals until the graft rejection post-transplantation). The recipients were immunosuppressed with a combination of cyclosporine A, cyclophosphamide, and steroids. Sera were analyzed for C3, C4 levels and complement activity and anti-pig endotheliocyte xenoantibody. The grafts were examined histopathologically and immunohistochemically for C3, C4, C5b-9, IgG, and IgM.
Results The xenografts survived 8, 10, 13, 13 days, respectively, and all grafts occurred DXR. Venular thrombosis was outstanding feature within DXR xenografts, complicated with interstitial edema, local hemorrhage (3/4) and myocardial necrosis (2/4), without gross cellular infiltration. Complete complement depletion (C3 = 0, CH50 < 2.8 μ/ml) was achieved in all recipients treated with Y-CVF from preoperation to graft rejected. The C4 levels began to decrease 2-4 days before the xenografts losing their function. The anti-pig endotheliocyte xenoantibody also decreased after transplantation, and 3 of 4 monkeys slightly increased during DXR. All rejected xenorafts showed C3, C4 deposits in different degree, and C5b-9 deposit was showed in 50% (2/4). Deposition of IgG and IgM was also seen in all grafts with almost the same degree.
Conclusion (1) Venular thrombosis was the most marked histopathologic feature of DXR in this dicordant xenograft model. (2) Though C3 levels and complement activity almost decreased to 0 from the day of transplantation, four rejected xenografts still showed C3 deposits in different degree, and C5b-9 deposit was showed in 2 grafts. (3) C4 may involve in DXR. (4) Both IgG and IgM may play important role in DXR.