Successful allogeneic transplantation of rat islets expressing cytokine-induced major histocompatibility complex class II antigen.

Cultured neonatal rat (F344, RT1(1v1)) islets that were devoid of MHC class II (OX6) antigen and antigen-presenting cells were treated with recombinant murine interferon (IFN-gamma) and/or recombinant murine tumor necrosis factor (TNF-alpha) in vitro. The IFN-gamma and TNF-alpha resulted in some disruption of the integrity of the islets by 7 days of culture, but the combination resulted in disaggregation of the islets within 7-8 days. Insulin release into the medium and secretion in response to glucose were adversely affected by the cytokines. The IFN-gamma resulted in expression of class II antigen on about 10% of the endocrine cells after 3-4 days in culture. This effect of IFN-gamma was potentiated by TNF-alpha resulting in 27% of the cells expressing class II antigen. Islets treated with IFN-gamma and TNF-alpha alone or in combination were not rejected in a subsequent transplant underneath the kidney capsule of WF rats (RT1u). We conclude that expression of class II antigen alone is not sufficient to initiate an allogeneic rejection response, but that cytokine-mediated destruction of endocrine cells could be the basis of immune-mediated islet-cell loss in islet-allograft rejection or autoimmune diabetes.