Quantitative estimation of islet cell surface antibodies in sera of patients with diabetes mellitus, using BK virus-induced insulinoma, rat islet or fish islet cells and 125I-antihuman IgG antibody.

Using a radioligand assay with 125I-antihuman IgG antibody as well as an 125I-protein A binding assay, we quantitatively evaluated islet cell surface antibodies (ICSA) in the sera of diabetic patients already proven to contain antibodies by the immunofluorescence method (IF). It was possible to use not only rat islet but also BK virus-induced hamster insulinoma cells and yellow tail fish (Serolia quinqueradiata) islet cells as target cells in these radioassays. 7 out of 8 diabetic subjects, positive for ICSA by IF, showed levels of binding of 125I-antihuman IgG antibody greater than 2SD above the mean for normal controls. Additionally 3 diabetic subjects negative for ICSA by IF showed levels of binding of 125I-antihuman IgG antibody less than 2SD above the mean for normal controls, and 2 subjects negative for ICSA by IF had levels slightly higher than 2SD above the mean for normal controls. The quantitative ICSA radioligand assay reported here is both sensitive and specific in the detection of the IgG of ICSA. It is also more convenient to use than other methods, and may use any of several different kinds of target cells, each of which may be easily and reproducibly obtained. These radioimmunological methods for the detection of ICSA appear to be ideal for screening large numbers of patients for ICSA.