Sensitivity of long-standing xenografts of rat hearts to humoral antibodies

Long-standing rat skin xenografts on immunosuppressed mice are known to become insensitive to destruction by mouse anti-rat serum. The present experiments demonstrate that long-standing primary vascularized rat-to-mouse cardiac xenografts, unlike skin, remain fully sensitive to antiserum-mediated destruction, even in mice also bearing a long-standing skin graft that is resistant to antiserum. It appears that skin grafts become resistant to antiserum-mediated destruction because of extensive replacement of the endothelium by cells of host origin. The hearts remain sensitive to antiserum since such an extensive endothelial replacement would not occur as readily in these whole organ grafts.