Decreased porcine valve antigenicity with in vitro culture.

Abstract

Porcine valvular prostheses may stimulate inflammation after implantation, with resultant accelerated structural degeneration. We investigated the expression of porcine major histocompatibility complex (MHC) class II molecules on valve leaflets and the possibility of decreasing valve antigenicity with in vitro culture. Aortic and pulmonary valves were harvested from domestic pigs under sterile conditions and cultured in vitro with either porcine or baboon serum for 4 days. Valves were harvested daily and fixed in Carnoy's or formalin solution. Microtome sections of valves were examined by hematoxylin and eosin, and by immunohistochemistry for porcine MHC class II proteins and an endothelial marker, alpha-N-acetylgalactosaminyl glycoprotein (alpha-GalNac). Porcine aortic and pulmonary valves constitutively express alpha-GalNac proteins and porcine MHC class II antigens. Porcine valves continue to express both alpha-GalNac and MHC class II after 48 hours of culture in porcine serum. After 48-hour culture in baboon serum, however, MHC class II antigens became undetectable on valvular leaflets, although alpha-GalNac molecules were still detected. Porcine valvular endothelial cells remain viable after 2 days of in vitro culture. Porcine valves cultured with primate serum show decreased MHC class II antigenic expression. In vitro culture before glutaraldehyde fixation may decrease inflammation associated with implantation.