[Immuno-hematologic aspects of xenotransplantation]

The main barrier to pig organ xenograft in humans, is the hyperacute rejection, which is provoked by the fixation of human xenoantibodies on the graft endothelial cells, and by complement activation. Because pig red blood cells and endothelial cells carry common xenogeneic epitopes, human anti-pig xenoantibodies can be detected and titered by pig red blood cells direct agglutination. Individuals of AB blood group have lower anti-pig hemagglutinins titers than those of other blood groups. Anti-A and anti-B alloantibodies do not agglutinate pig red blood cells. The anti-B (and not the anti-A) alloantibodies can be adsorbed on pig red blood cells. A linear B type 2 epitope recognized by human natural antibodies has been previously described on pig cells. If the role of xenoantibodies is prominent in the rejection of pig organ xenografts in humans, the role of alloantibodies remains to be precise.