PERIPHERAL MONITORING OF DIRECT AND INDIRECT ALLOANTIGEN PRESENTATIONPATHWAYS IN CLINICAL HEART-TRANSPLANT RECIPIENTS

It has been reported that the response to alloantigens presented by th e direct and indirect pathway may be of differential relevance after h uman kidney transplantation. Accordingly, we monitored these routes in peripheral blood mononuclear cells (PBMC) of heart transplant patient s from before transplantation and up to 2 years thereafter in an attem pt to find a correlation with the clinical status of the patients. Bot h before and after transplantation, comparable proportions of PBMC sam ples reacted in mixed lymphocyte culture to nondepleted donor spleen c ells (direct route), but never to donor cells depleted for antigen-pre senting cells (indirect route). In contrast, the latter route could ea sily be activated by a nominal antigen and persisted after transplanta tion, although the proportion of PBMC samples responding was significa ntly suppressed, irrespective of the occurrence of rejection. Conseque ntly, complete removal of antigen-presenting cells from the stimulator population in a mixed lymphocyte culture with PBMC as responder is no t a suitable tool for measuring indirect presentation of alloantigens, and therefore not relevant for monitoring the immunological status of heart transplant recipients.