[Studies on the pathogenesis of type I diabetes mellitus--destruction of pancreatic beta cells by cytotoxic T lymphocytes in nonobese diabetic mice].

Proliferation of islet-associated leukocytes occurred when isolated islets from 20 week-old female Non-obese Diabetic (NOD) mice were cultured with 10 U/ml recombinant interleukin-2 (rIL-2) for 7 days. Co-culture of these lymphocytes with freshly-isolated islets from 6-8 week-old NOD donors in the presence of 1 U/ml rIL-2 produced islet structural deformation within 24 h and islet cytolysis within 48 h. Three lines of evidence suggest that leukocytes were cytotoxic T lymphocytes (CTL) specific for islet cells. First, these proliferating cells adhered to NOD islets at 6 h and specifically killed islets after 48 h of culture, but the cytoadherence of these cells to the other organs including thyroid, pancreatic exocrine glands and liver from NOD mice could not be observed and the shape of tissue clumps hardly deformed after culture for 48 h. The accumulated insulin release from NOD islets to the medium after 6 h of culture was significantly increased in the presence of islet-derived cells compared with the insulin release in the absence of cells. On the contrary, lactic dehydrogenase activity released from liver and amylase activity from pancreatic exocrine glands showed on difference between with and without these cells for 6h of culture. Second, a flow cytometric analysis showed that these cells consisted of 96%Thy1.2, 70%Lyt2, and 8%L3T4-positive cells. After treatment with monoclonal anti-Thy1.2 or Lyt2 antibody and complement, these cells lost their activity to destroy NOD islets. However, these cells still had a full killing activity after the depletion of L3T4-positive cells. Third, islets of NOD (H-2 genotype KdDb), B10.GD (H-2KdDb), BALB/cA (H-2d), and DBA/2N (H-2d) were susceptible to destructive activity of these cells, whereas islets of NON (H-2b), C57BL/6N (H-2b), C57BL/10J (H-2b), and C3H/He (H-2k) mice remained intact. Furthermore, anti-Kd monoclonal antibody could prevent islet-specific cytolysis of these cells. These results suggest that CTL expressing Thy1.2 and Lyt2 phenotypes appear to recognize islet cell antigen with restriction of major histocompatibility complex (MHC) class H-2Kd and then destroy pancreatic beta cells in NOD mice.