Differential expression and regulation of MHC products in the endocrine and exocrine cells of the human pancreas.

Inappropriate expression of HLA Class II (D/DR) molecules has been detected in the target cells of most autoimmune diseases including Type I (insulin-dependent) diabetes. The possibility that this phenomenon is due to the action of lymphocytes or some of their products has been investigated by analysing in vitro the modulation of HLA products in Beta cells. Monolayer cultures from 25 human pancreatic glands were supplemented with alpha-interferon (IFN), beta-IFN or gamma-IFN, interleukin 2 (IL-2) and supernatants from activated lymphocytes. In addition, lectins and a variety of other hormones, biological products and chemicals were tested. Major histocompatibility complex (MHC) expression was assessed by double immunofluorescence technique using monoclonal antibodies to non-polymorphic determinants of Class I and Class II molecules and the pancreatic cells were identified by antibodies to islet hormones and other cytoplasmic antigens. gamma-IFN and lectins produced a parallel enhancement of HLA-A,B,C expression in islet, exocrine/ductal cells and fibroblasts. HLA-D/DR was inducible in all pancreatic cell types, except endocrine islet cells which did not produce Class II molecules in response to any of the stimuli including supernatants from activated lymphocytes. Exocrine/ductal cells from glands of patients with chronic pancreatitis spontaneously expressed Class II products, but islet cells were devoid of any detectable D/DR. These data are consistent with recent observations which have indicated that in the 'diabetic' pancreas inappropriate Class II expression in the Beta cells occurs independently of the presence of lymphocytes infiltrating the islets, and make it necessary to postulate that other factors are responsible for the Class II induction in Beta cells in human Type I diabetes.