Recognition of islet-directed peripheral blood lymphocytes in vitro before rejection of allogeneic grafted islets

A co-culture of splenic lymphocytes with allogeneic pancreatic islets [i.e., mixed lymphocyte islet co-culture (MLIC)] for 96 hr leads to reduction of beta-cells and to an allospecific induction of major histocompatibility complex (MHC) class II antigens on beta-cells. The intent of our investigation was to determine whether peripheral blood lymphocytes (PBL) obtained from allogeneic islet-grafted BB/OK rats (=sensitization in vivo) cause similar alterations to donor-specific islet cells. PBL prepared before transplantation, before (at day 7) and after islet rejection were co-cultured for 24 hr with donor-specific islets. PBL obtained at any time before and after transplantation caused reduction of beta-cells and enhancement of intercellular adhesion molecule-1(+) beta-cells. Induction of MHC class II+ beta-cells was most pronounced with PBL obtained before rejection. Down-regulation of major histocompatibility complex class I+ beta-cells was caused by PBL that had been obtained from grafted animals only; it was most pronounced before islet rejection and has never been observed with lymphocytes from nongrafted normoglycemic rats. The 24-hr MLIC is capable of recognizing functionally active, donor-specific lymphocytes and is able to distinguish between the effects of sensitized and nonsensitized lymphocytes.