Screening Monoclonal Islet Cell Surface Antibodies (ICSA) by Radioimmunoassay — Detection of Crossreactivity with ICSA from Insulin-Dependent (Type 1) Diabetic Patients1)

A radioimmunoassay for the detection of monoclonal islet cell antibodies was developed using rat insulinoma cells as antigen carriers and 125I-labeled affinity-chromatographically purified anti-mouse Ig antibodies for detecting cell-bound mouse Ig. Prior to the assay cells had been attached to glass tubes by poly-dimethyl-diallyl ammonium chloride thus allowing to perform the assay as easy as a solid-phase immunoassay. Incubation protocol and cell number were chosen to ensure a high sensitivity of the assay. Results compared well with immunofluorescence findings. Of seven monoclonal islet cell antibodies tested for crossreactivity only one was displaceable by islet cell surface antibodies from diabetic sera. This antibody was induced by immunization with human islets whereas all others were from mice which had been autoimmunized with streptozotocin and complete Freund's adjuvant.