Hyperacute rejection of guinea-pig to rat cardiac xenografts. I. Morphology

The morphological changes occurring in xenograft hyperacute rejection, using guinea-pig to rat cardiac transplants, have been studied. Ultrastructural evidence of platelet aggregation in myocardial capillaries and veins first occurred two minutes after revascularisation. Small amounts of fibrin, associated with platelet degranulation occurred at three minutes. From four minutes, platelet aggregates increased in number and endothelial damage first appeared in those vessels containing platelet aggregates. Rejection was complete by 12 minutes and platelet aggregates then filled many capillaries, veins, arterioles and arteries. Polymorphonuclear leucocyte infiltration was not seen.