COMBINED ANALYSIS OF ISLET-CELL ANTIBODIES THAT CROSS-REACT WITH MOUSE PANCREAS, ANTIBODIES TO THE M(R)-64,000 ISLET PROTEIN, AND ANTIBODIES TO GLUTAMATE-DECARBOXYLASE IN TYPE-I DIABETIC-PATIENTS

OBJECTIVE- A combined analysis of whether islet cell autoantibodies (I CAs) are cross-reactive with mouse pancreas, with glutamate decarboxyl ase (GAD) antibodies, and with 64K antibodies was performed in a large sample of recently diagnosed type I diabetic patients. The disappeara nce rates of these different autoantibodies were compared in some pati ents after onset of the disease. The aims were to determine patterns i n GAD/64K antibodies with regard to cross-species reaction of ICA and to assess whether GAD could contribute to ICA positivity in mouse and human pancreases and whether the simultaneous search for all the antib ody specificities enhances the detection of autoimmune stigma. RESEARC H DESIGN AND METHODS- ICA detected by immunofluorescence in human and mouse pancreases, antibodies immunoprecipitating the 64K rat islet ant igen, and antibodies immunotrapping brain GAD activity were quantified at diagnosis of diabetes in 95 patients and in sequential samples dur ing 1 year alter diagnosis in 13 patients. The contribution of GAD to ICA positivity in mouse and human pancreases was evaluated by the anal ysis of correlations between tests and by the ability of brain homogen ate to block ICA reactivity in pancreases from both species. RESULTS - ICAs were detected in human pancreases in sera from 63 (66%) patients , among which 61% bound also to a mouse pancreas. GAD and 64K antibodi es were strongly correlated (P < 0.0001) and were detected in 69 and 7 396 of the patients, respectively. All but two patients with ICA in hu man pancreas also displayed either ICA in mouse pancreas or GAD/64K an tibodies. Among 32 patients without ICA in human pancreas, 54% display ed either GAD/64K antibodies or ICA in mouse pancreas. Only 16% of the patients displayed neither ICA nor GAD/64K antibodies. A correlation (P < 0.005) was found between ICA in human and mouse pancreases. GAD o r 64K antibodies were strongly correlated with ICA in human pancreas ( P < 0.0001), but nor with ICA in mouse pancreas. After preincubation o f six sera with GAD-containing brain homogenate, ICA titers were unaff ected in mouse pancreas but reduced in human pancreas. ICA titers in m ouse pancreas were decreased after 3 months (P < 0.01) in diabetic pat ients, contrasting with the stability of ICA in human pancreas and GAD antibodies by 1 year after diagnosis. CONCLUSIONS- According to cross -species reaction, we confirm the heterogeneity of ICA in a large seri es of type I diabetic patients, ICAs that cross-reacted with mouse pan creas being more frequent than ICAs without cross-species reactivity. GAD and 64K antibodies were also present in a majority of patients. Th e simultaneous search for all the antibody specificities enhances the detection of autoimmune stigma so that only a few patients did not dis play any autoantibody at diagnosis. GAD is not the target of ICAs in m ouse pancreas, whereas GAD accounts for ICA positivity in human pancre as. The conclusion that ICAs in mouse pancreas are not GAD-reactive is reinforced by the fact that they are more transient after onset of di abetes than are GAD antibodies or the complex mixture of ICAs in human pancreas.