Cytokine Secretion Depends on Galα(1,3)Gal Expression in a Pig-to-Human Whole Blood Model

Abstract

Transplants from α1,3-galactosyltransferase (Gal) gene-knockout pigs to nonhuman primates are largely protected from hyperacute but not acute humoral xenograft rejection. The present study investigates the role of Gal in cytokine responses using a novel pig-to-human whole blood in vitro model, developed for species-specific analysis of porcine and human cytokines. Porcine (n = 7) and human (n = 27) cytokines were measured using ELISA or multiplex technology, respectively. Porcine aortic endothelial cells from control (Gal+/+) and Gal-deficient (Gal−/−) pigs were incubated with human lepirudin anticoagulated whole blood from healthy donors. E-selectin expression was measured by flow cytometry. The C3 inhibitor compstatin and a C5aR antagonist were used to study the role of complement. Cytokine species specificity was documented, enabling detection of 2 of 7 porcine cytokines and 13 of 27 human cytokines in one single sample. Gal+/+ porcine aortic endothelial cells incubated with human whole blood showed a marked complement C5b-9 dependent up-regulation of E-selectin and secretion of porcine IL-6 and IL-8. In contrast, Gal−/− cells responded with E-selectin and cytokine expression which was so weak that the role of complement could not be determined. Human IL-6, IL-8, IFN-γ, MIP-1α, MIP-1β, eotaxin, and RANTES were detected in the Gal+/+ system, but virtually no responses were seen in the Gal−/− system (p = 0.03). The increase in human cytokine release was largely complement dependent and, in contrast to the porcine response, mediated through C5a. Species-specific analysis of cytokine release revealed a marked, complement-dependent response when Gal+/+ pig cells were incubated with human whole blood, compared with Gal−/− cells which induced virtually no cytokine release.