Porcine valves are reendothelialized by human recipient endothelium in vivo

The degeneration of human allogeneic and porcine xenogeneic heart valves has not been clearly understood. The question is whether the observed loss of function and calcification is primarily an immunologic process or a mechanical process or is influenced by both factors. In the current study, we looked at explanted xenogeneic heart valves for the presence of recipient endothelium. Explanted valves were shock frozen and stored at -80 degrees C before use. They were subsequently examined by immunohistochemical staining with a variety of monoclonal antibodies. Xenogeneic valves showed clearly positive results for the human major histocompatibility complex class I and class II antigens and morphologically showed a thin layer of viable endothelium restricted to the annular region of the valve. Additionally, they were also positive for intercellular adhesion molecule-1 and the H-Y antigen. Although the xenogeneic valves were significantly degenerated, the endothelium was clearly defined and could be identified immunohistochemically as being of recipient origin. The grafts remained negative for endothelial cell-leukocyte adhesion molecule-1 and factor VIII. These data allow speculation on whether reendothelialization of valvular grafts with recipient endothelium is a normal repair mechanism in vivo.