SPECIES-DIFFERENCES IN THE EXPRESSION OF MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-II ANTIGENS ON CORONARY-ARTERY ENDOTHELIUM - IMPLICATIONS FOR CELL-MEDIATED XENOREACTIVITY

Background. There is controversy in the Literature as to whether swine coronary endothelium expresses major histocompatibility complex (MHC) class LI antigens constitutively. Methods., Because this issue has im plications for cell-mediated human anti-swine xenogeneic responses, we stained tissue sections from human, pig, rat, and mouse hearts with t he anti-class II monoclonal antibody ISCR3, which has a similar specif icity and titer when binding to human, porcine, and rodent class II mo lecules. Results. Immunoperoxidase staining of human and porcine heart s with ISCR3 resulted in a dense reaction on the coronary endothelium of epicardial arteries, intramuscular arterioles, and capillaries. In contrast, the coronary endothelium of rat and mouse hearts did not sta in with ISCR3. When freshly harvested porcine aortic endothelial cells were placed in culture, class II MHC antigen expression was lost with in three to four passages. Conclusions. Thus, using a single antibody with cross-species reactivities, we demonstrate that swine coronary en dothelium, unlike rodent coronary arteries, expresses similar basal am ounts of class LI MHC antigens to human coronary vessels, The constitu tive expression of class II NMC antigens on swine coronary artery endo thelium may contribute to host T cell-mediated xenogeneic responses in clinical pig-to-human cardiac xenotransplantation and thus become a t arget for therapeutic intervention.