INTACT PIG PANCREATIC-ISLET FUNCTION IN THE PRESENCE OF HUMAN XENOREACTIVE NATURAL ANTIBODY-BINDING AND COMPLEMENT ACTIVATION

Background. The expression of xenogeneic epitopes and the activation o f human complement by adult pig islets after prolonged culture have hi therto not been described. Materials and Methods. Freshly isolated and cultured islets were analyzed by fluorescence-activated cell sorter a nalysis, fluorescence microscopy, and immunohistology for expression o f Gal(alpha 1,3)Gal epitopes, binding of human xenoreactive natural an tibodies (XNA), and complement deposition. Results. Freshly isolated a nd cultured islets showed detectable Gal(alpha 1,3)Gal expression and human XNA binding limited to intraislet capillary endothelial cells. N o significant modification in Gal(alpha 1,3)Gal expression and human X NA binding levels was detected in adult pig islets cultured for up to 4 days compared with freshly isolated islets. Incubation of pig islets with human serum demonstrated the deposition of C3, C4, and membrane attack complex, but not factor B with a similar pattern to XNA. Howeve r C3 and C4 showed a more widespread deposition. Despite complement ac tivation, no cytotoxic effect on islets was detected after 4 hr of inc ubation with human serum capable of killing porcine endothelial cells. Even after 4 days of culture in 50% intact human serum, pig islets re tained both their normal morphology and a normal insulin response to g lucose stimulation. Conclusions. Neither islet cell lysis nor, more im portantly, any alteration in beta cell function occurred, which sugges ts that adult pig islets may not be directly damaged by serum after xe notransplantation in humans. Nevertheless, complement activation in vi vo could trigger rapid cellular rejection mechanisms through islet cel l opsonization and release of bioactive fragments.