Quantitative Estimation of Islet CellSurface Antibodies Using ¹²⁵I-antihuman IgG Antibody and Insulinoma Cells as Target Cells, and Its Clinical Application

Abstract

Using the radioimmunoassay for the detection of islet cell surface antibodies (ICSA) by an ¹²⁵Iantihuman IgG antibody (ICSA radioimmunoassay), the author detected the presence of ICSA in the sera of diabetic patients.
To determine whether the assay using ¹²⁵I-protein A and ICSA radioimmunoassay were equivalent, the author compared their binding of insulinoma cells previously exposed to sera of diabetic patients. The results of these two assays were highly correlated (r =O.806, p<0.001).
Since non-radioactive antihuman IgG antibody reduced the binding of ¹²⁵I-antihuman IgG antibody (¹²⁵I-anti-hIgG Ab) to islet cells in a dose-dependent manner, this assay detects the specific binding of human IgG on the surface of islet cells.
The binding of ¹²⁵I-anti-hIgG Ab to insulinoma cells exposed to sera from diabetic patients correlated with the binding of fish islet (r =0.936, p<O.001) and rat islet cells (r=0.943, p<0.001), Therefore, it was possible to use not only rat islet cells, but also BK-virus-induced insulinoma derived from hamster and yellow tail fish islet cells as target cells in this assay.
In the sera of 10 out of 44 patients with diabetes, the binding of ¹²⁵I-anti-hIgG Ab to cells exceeded the level of the mean plus 2SD of the normal control values. Seven of the 10 patients were insulin-treated patients and three were non-insulin-treated patients, two of which were associated with Hashimoto's thyroiditis and Graves' disease.
The author examined the relationship between insulin antibody and ICSA in insulin-treated patients. There was no correlation between them.
In conclusion, ICSA directed to determinants on the surface of islet cells can be quantitatively detected with high sensitivity by the ICSA radioimmunoassay. This method is both more specific and more convenient than all other methods. Though it may also be possible to use any one of three different kinds of target cells, insulinoma cells in particular, which may be maintained in tissue culture, assure a constant supply of target cells easily and reproducibly.