Combined analysis of islet cell antibodies which cross-react with mouse pancreas, antibodies to the M(r) 64,000 islet protein, and antibodies to glutamate decarboxylase in subjects at risk for IDDM.

With regard to progression to diabetes, ICA cross-reactive with mouse pancreas, antibodies to the M(r) 64,000 islet antigen (64K), antibodies immunotrapping brain GAD activity, and IAA were analysed in 53 ICA-positive first-degree relatives of IDDM patients and 18 ICA-positive schoolchildren without a family history of diabetes. Sera from 29 (55%) relatives did not bind to mouse pancreas, whereas 24 (45%) displayed cross-species reaction. ICA titres on human and mouse pancreas were weakly correlated in the overall population (p < 0.05) but more strongly (p < 0.01) in only those subjects who displayed antibodies on tissues from both species. GAD and 64K antibodies were detected in 31% and 35% of relatives. In schoolchildren, the frequencies of cross-species reactive ICA (22%), GAD antibodies (6%), 64K antibodies (22%), and IAA (6%), were lower (p < 0.05) than in relatives. A strong correlation (p < 0.0001) was observed between GAD and 64K antibodies. GAD or 64K antibodies were strongly correlated with ICA on human pancreas (p < 0.0001) but poorly with ICA on mouse pancreas (p = 0.05). After pre-incubation of sera with brain homogenate, ICA titres were unaffected on mouse pancreas but reduced on human pancreas. ICA-positive subjects who displayed neither cross-species reactive ICA nor GAD or 64K antibodies were more frequent (p < 0.05) among schoolchildren than relatives, whereas subjects who displayed all antibody specificities were more numerous (p < 0.04) in relatives. All relatives with ICA binding only to human pancreas, as well as all schoolchildren, permanently displayed an AIRG higher than the first control percentile and remained non-diabetic.(ABSTRACT TRUNCATED AT 250 WORDS)