ISLET-CELL ANTIBODIES - VARIABLE IMMUNOSTAINING OF PANCREATIC-ISLET CELLS AND CARCINOID TISSUE

Objectives. Islet cell antibodies (ICA) in sera of patients with autoi mmune diabetes mellitus generally stain not only the insulin-producing beta cells but also the non-beta cells of the islets of Langerhans, T he antibodies have been reported to react also with the chromaffin cel ls of carcinoid tissue, In the present study, we examined in detail th e reactivity of 10 ICA-positive sera of patients with new onset insuli n-dependent diabetes mellitus (IDDM) and two sera of patients with sti ff-man syndrome. Design. The sera were analysed by immunofluorescence and by immunoperoxidase staining of human islets as well as by immunop recipitations using S-35-methionine labelled rat islet lysates. In add ition, immunofluorescence analyses of carcinoid tissues were carried o ut. Results, Eight of the 10 IDDM-positive sera reacted with all islet endocrine cells, whereas two sera showed staining restricted to the b eta cells, as did the two sera of the patients with stiff-man syndrome . All beta cell 'selective' sera, but only 6 of 8 'whole' islet positi ve sera, immunoprecipitaied the 64 kDa glutamic acid decarboxylase (GA D) antigen. The staining of carcinoid tissue was variable and did not correlate with the 'whole' or 'selective' staining pattern of islets. Conclusion, The data underline a heterogeneity of ICA and indicate the presence of a separate, non-GAD antigen in islet cells. it is possibl e that in future studies, a resolution of ICA titres with respect to d ifferent types of islet cellular reactivity might provide insights int o the pathogenesis of IDDM and improve the prognostic implications of antibody determinations.