Generation and partial characterization of monoclonal antibodies reactive with islet cell antigens.

Islet cell antibodies have been detected in more than 60% of newly diagnosed type I diabetics. Their pathogenetic role is still unclear. We have generated monoclonal antibodies (mc-ab) reactive with islet cell antigens by fusing mouse myeloma cells with spleen cells from Balb/c mice immunized with pancreatic islet cells. Hybridomas producing islet cell surface antibodies (ICSA) were detected by indirect immunofluorescence on viable cells from rat islets or rat insulinoma. Cytoplasmic islet cell antibodies (ICA) were detected by indirect immunofluorescence on Bouin-fixed sections of mouse pancreas. The ICSA- and/or ICA-producing hybridomas were cloned twice by limiting dilution. This paper describes six different mc-ab. All hybrid cell lines obtained produced IgM antibodies. Four of them mediate complement-dependent cytotoxicity to viable rat islet cells. In the present study the heterogeneity of circulating ICSA is demonstrated. Also, a monoclonal beta cell surface autoantibody K56aF3 was produced by fusion of spleen cells from a mouse treated with sub-diabetogenic doses of streptozotocin in combination with complete Freund's adjuvant. It was cytotoxic against islet cells up to a dilution of 1:1,000 and it could inhibit the insulin secretion from neonatal rat islets cultured in RPMI 1640 as stimulated by glucose or by the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine common with glucose. The latter effect was reversible as indicated by the recovery of insulin secretion in a subsequent culture period without mc-ab. These results suggest that circulating ICSA in type I diabetics may alter beta cell function and thereby contribute to the pathogenesis of type I diabetes.