Endothelial and smooth muscle cells in the heart allograft response: isolation procedure and immunocytochemical features.

Studies on mechanisms for allograft rejection are focused on recognition of major histocompatibility complex (MHC) antigens. In addition, there is evidence for non-MHC-mediated alloreactivity, possibly evoked by tissue-specific antigens. To measure cellular immune responses toward tissue-specific alloantigens, we isolated endothelial cells and smooth muscle cells from small pieces of human atrium at the time of transplantation. Endothelial cells were scraped off the endocardium after trypsin digestion and cultured in fibronectin-coated dishes. Smooth muscle cells were obtained by outgrowth of small pieces of atrium in a culture flask. Morphologic and immunologic characterization showed only minor differences between endothelial and smooth muscle cells cultured from atrium and cells cultured from umbilical vein (endothelial cells) and artery (smooth muscle cells). Furthermore, we studied the proliferative immune responses with endothelial and smooth muscle cells as stimulator cells, with and without induction of MHC class II antigens on these cells by addition of interferon-gamma to the culture. Peripheral blood mononuclear cells showed a proliferative response to donor human atrium endothelial cells, even without pre-incubation with interferon-gamma. Human atrium smooth muscle cells caused only a weak triggering of the mononuclear cells, irrespective of interferon-gamma pre-incubation. Immunofluorescence studies demonstrated HLA-DR expression on these endothelial and smooth muscle cells. These observations may indicate a role for non-MHC, probably tissue-specific, alloantigens expressed by endothelial cells in human cardiac allograft rejection.