Co-culture of pancreatic islets and allogeneic lymphocytes: alterations of responder and stimulator cells.

Abstract

Mixed lymphocyte cultures have been used, e.g., in clinical transplantation, for donor-recipient selections. In experimental research, the mixed lymphocyte culture is valuable in studying several aspects of lymphocyte activation by allogeneic major histocompatibility complex (MHC) antigens and, therefore, in proving new strategies of interrupting lymphocyte activation and proliferation. However, this in vitro model is donor-specific but not antigen-specific. Therefore, we used islets of Langerhans, the donor tissue for grafting diabetic recipients, to stimulate allogeneic mononuclear cells prepared from spleens of healthy LEW.1A, LEW.1W, or WF rats and from diabetes-prone normoglycemic BB/OK rats. The considerable advantage of the mixed lymphocyte islet culture is not only the antigen specificity but also the possibility to separate lymphocytes from islets after the co-culture. In addition to lymphocyte activation, we investigated cytokine secretion and changes of antigen expression on the stimulatory islet cells. After allogeneic co-culture, lymphocyte activation was found by an increased release of the cytokines interferon-gamma, interleukin 2, and macrophage inflammatory protein 2, as well as by an enhanced expression of the interleukin 2 receptor on CD4+ T and CD8+ T cells. We also demonstrated changes in antigen expression on the surface of stimulatory islet cells after co-culture with allogeneic lymphocytes. These changes comprised not only the enhancement of MHC class I and intercellular adhesion molecule 1 but also the induction of MHC class II antigens on pancreatic beta cells. Activation of responding lymphocytes, cytokine secretion, and changes in islet cell antigen expression were time dependent. We did not find major differences in the effects induced by allogeneic lymphocytes obtained from the different donor rat strains. In a syngeneic control mixed lymphocyte islet culture, lymphocytes were not activated and no induction of MHC class II antigens on beta cells was observed. However, up-regulation of intercellular adhesion molecule 1 was found. The enhancement and induction of MHC antigens and an adhesion molecule improve the binding of effector and target cells supporting our hypothesis that the change of antigen expression on target cells induced by allogeneic lymphocytes might contribute to their destruction. Since lymphocytes obtained from healthy or diabetes-prone rats induce very similar effects, we conclude that the results described are of general importance.