Complement-mediated vasoconstriction and graft rejection.

The hyperacute rejection of renal allografts has much in common with pigto-dog renal xenograft rejections. An analysis of the xenograft model revealed new functional aspects of graft rejection that appear to be an integral part of the humoral immune injury. Anaphylatoxin or C5a, a cleavage product of the fifth complement component was shown to play a major role in the rejection of isolated kidneys; it was generated in pig and dog serum by activation of the complement system and caused severe vasoconstriction in the renal vasculature. It is suggested that histocompatibility antibodies and complement may affect allograft survival via this potent mediator.