Histologic and immunohistochemical responses after aortic valve allograftsin the rat

Background. Human aortic valve allografts elicit a cellular and humoral imm une response. It is not clear whether this is important in promoting valve damage. We investigated the changes in morphology, cell populations, and ma jor histocompatibility complex antigen distribution in the rat aortic valve allograft. Methods. Fresh heart valves from Lewis rats were transplanted into the abdo minal aorta of DA rats. Valves from allografted, isografted, and presensiti zed recipient rats were examined serially with standard morphologic and imm unohistochemical techniques. Results. In comparison with isografts, the allografts were infiltrated and thickened by increased numbers of CD4(+) and CD8(+) lymphocytes, macrophage s, and fibroblasts. Thickening of the valve wall and leaflet and the densit y of the cellular infiltrate was particularly evident after presensitizatio n. Endothelial cells were frequently absent in presensitized allografts whe reas isografts had intact endothelium. Cellular major histocompatibility co mplex class I and II antigens in the allograft were substantially increased . A long-term allograft showed dense fibrosis and disruption of the media w ith scattered persisting donor cells. Conclusions. The changes in these aortic valve allograft experiments are co nsistent with an allograft immune response and confirm that the response ca n damage aortic valve allograft tissue. (C) 1998 by The Society of Thoracic Surgeons.