Effect of human natural xenoantibody depletion and complement inactivation on early pig kidney function

Preformed xenoreactive natural antibodies (XNA) and complement mediate hyperacute xenograft rejection (HXR) in pig-to-human discordant xenotransplantation. In a pig kidney-human blood xenoperfusion model, we investigated whether XNA depletion and/or human complement inactivation preserved early pig kidney function. Pig kidneys were perfused for 180 min with pig blood (AUTO group, n = 8), human blood (HETER group, n = 6), complement-inactivated human blood (COMi group, n = 5), XNA-depleted human blood (ABd group, n = 5) or complement-inactivated and XNA-depleted human blood (ABd&COMi group, n = 5). HETER kidneys were rejected after 15-30 min and showed vascular microthrombi and interstitial hemorrhages. XNA depletion and/or complement inactivation prevented HXR. The glomerular filtration rate in ABd, COMi and ABd&COMi groups was significantly lower than in the AUTO group. Also, beyond 60 min, the COMi group showed a significantly lower glomerular filtration rate than that observed in ABd and ABd&COMi groups. Kidneys from ABd, COMi and ABd&COMi groups displayed endothelial cell edema, as well as higher soluble P-selectin levels and a higher renal myeloperoxidase content than the AUTO group kidneys. COMi and ABd&COMi groups had a significantly lower renal myeloperoxidase level than the HETER group. Also, in contrast to HETER and ABd groups, these complement-inactivated groups failed to show a positive correlation between P-selectin and renal myeloperoxidase. We also investigated platelet-activating factor (PAF) as possible mediator for these functional and pathologic changes. We found that blood PAF levels were similar in HETER, ABd, COMi and ABd&COMi groups and significantly higher than in the AUTO group. Also, when PAF was added to porcine endothelial cell monolayers, morphological changes due to cytoskeleton contraction were observed, and these changes were prevented by preincubation with a PAF receptor antagonist. In conclusion, although depletion of XNA and/or complement inactivation prevent HXR, the pig kidney function is not preserved at the level of the autologous combination. The PAF overproduction observed in the xenogenic combination, which is independent of the presence of XNA and complement, may be, at least in part, responsible for early endothelial cell morphological changes still present when HXR is prevented.