Flow cytometry was recently introduced for the detection of antibodies in human serum to a cultured insulin-secreting rat insulinoma cell line (RINm5F) to investigate humoral immune reactivity in newly diagnosed type I (insulin-dependent) diabetic patients. Fifty-three patients were observed for 6–20 mo after clinical onset of diabetes with a reported duration of symptoms of <6 wk. Human anti-RINm5F antibodies were detected in 28%, human anti-islet cell antibodies in 62%, and anti-insulin autoantibodies in 36% of patients before initiation of insulin therapy. Occurrence of human anti-RINm5F antibodies at this stage was correlated with human anti-insulin autoantibodies rather than with the formation of anti-islet cell antibodies. Incidence of anti-RINm5F antibodies in individuals with duration of diabetes >6 wk was 38%, whereas human anti-islet cell antibodies and anti-insulin antibodies became detectable in 72 and 61% of the patients, respectively. These findings are in line with previous reports of immunoprecipitation by human diabetic serums of a 64,000-Mr antigenic structure in freshly prepared rat islet cells. The results suggest a reactivity of distinct classes of antibodies in serums of patients with type I diabetes to disparate antigens on human islet cells and cloned rat insulinoma cells and, moreover, reactivity to insulin as the secreted product. Further characterization of the reacting RINmSF antigens and prospective studies in subjects at risk for diabetes are required to validate the application of RIN cells to the investigation of immune mechanisms involved in the pathogenesis of human type I diabetes.

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