Islet cell surface antibodies have been detected in the sera of many patients with insulindependentdiabetes. Autoantibodies against the islet cell plasma membrane are detected mainly by indirect immunofluorescence and ¹²⁵I-protein A binding assays. We therefore compared these assay methods, using rat islet cells and a human islet cell line (JHPI-1) as antigenic cells.
In indirect immunofluorescence of both the rat cells and the JHPI-1 cells, there was a good correlation between fixed and living cells (p<0.05). After fixation with paraformaldehyde, some antigens on rat islet cells may have been damaged and no correlation was observed between the rat and JHPI-1 cells. In the ¹²⁵I-protein A binding assay, there was a good correlation between fixed and living cells of JHPI-1 (p<0.01).
In comparing the results of immunofluorescence and ¹²⁵I-protein A binding assays, a difference was observed in the islet cell surface antibody titers in the rat and JHPI-1 cells.
It is concluded that these assays of islet cell surface antibodies are limited to measuring the amount of autoantibodies.