A novel microwell indirect immunofluorescence assay to detect antibodies against islet cell surface antigens in insulin-dependent diabetes mellitus.

End-point titers of islet cell surface antibodies (ICSA) were determined in 144 patients with newly diagnosed insulin-dependent diabetes mellitus (IDDM), 98 siblings to such patients, and 188 controls using a microwell indirect immunofluorescence assay with an insulin-producing cell line of Syrian hamster origin. The prevalence of ICSA of a titer equal to or greater than 1:4 was 33% (p less than 0.001) in IDDM patients and 15% (p less than 0.01) in siblings, compared to 5% among the controls. In patients under 15 years of age at clinical onset, the prevalence of ICSA was 43% (37/77), which was higher than the 30% (20/67) found in patients older than 15 years at onset (p less than 0.05). The ICSA titer at the time of diagnosis varied between 1:4 and 1:32; however, 43% (23/53) of ICSA positive IDDM patients had a titer equal to or greater than 1:8. Although gender did not affect ICSA prevalence, 56% (15/27) of the female IDDM patients had ICSA titers exceeding 1:8 which was higher than 30% (8/26) among male patients (p less than 0.05). These results confirm that IDDM patients have a high prevalence of ICSA and that this convenient, high capacity immunofluorescence assay allows studies of large numbers of serum samples. The cell-specific reaction following absorption should also allow the islet cell surface antigens to be characterized.