EFFECT OF COMPLEMENT ACTIVATION IN HUMAN SERUM ON ISOLATED PORCINE ISLETS

We investigated the effect of the activation of complement in human se rum on isolated adult porcine islets using an in vitro model of pig-to -human islet transplantation. Pancreata were obtained from slaughterho use pigs (6-8 mo old). Islets were prepared by intraductal collagenase digestion followed by purification on Ficoll gradients. The purified islets were incubated with xenogeneic human serum with or without heat inactivation for 45 min. As control, islets were incubated with autol ogous porcine serum. After the incubation, the islets' responsiveness to an acute glucose stimulus (5.5 mM, static incubation) was evaluated by measurement of the insulin content of the medium. Islets exposed t o human serum showed significantly lower insulin secretory response th an the control (1.76 +/- 1.17 mu U/islet/120 min, without heat inactiv ation; 1.74 +/- 1.36 mu U/islet/120 min, with heat inactivation; 3.39 +/- 0.92 mu U/ islet/120 min, control). No difference in insulin secre tory response, however, was observed between islets exposed to human s erum with heat inactivation and without. Furthermore, we evaluated the cytotoxic activity of human serum on porcine islets by a complement-d ependent cytotoxicity using the MTT colorimetric assay, and found that the human serum had no complement-dependent cytotoxic activity agains t the islets. We concluded that the insulin secretion dysfunction of p orcine islets exposed to human serum was not due to the activation of complement and there was no evidence of hyperacute rejection mediated by complement activation in the in vitro model of pig-to-human islet t ransplantation.