Islet cell surface antibodies in diabetic children determined with 125I-labelled anti-IgG as tracer.

We have developed an assay for ICSA using fixed beta-cells as target cells and 125-I-Anti-IgG as tracer. Interassay variation was 9.5% and intraassay variation was 9.9%. For high titers of ICSA specificity was 100% but sensitivity then only 70%. Our technique enables a laboratory assistant to determine 200 samples in one week. Absorption of the samples with rat beta-cells as well as rat fibroblasts showed that ICSA are beta-cell specific and does not crossreact with rat fibroblasts. We found a significant difference in prevalence of high titer ICSA between healthy school children (4%) and newly diagnosed diabetic children (19%) (p < 0.001). That difference had disappeared after 18 months duration of IDDM when the B-cell mass and thus the amount of antigen had decreased. No difference was seen between healthy children and adult blood donors. There was no seasonal variation of ICSA titers in healthy children.