SOLID VERSUS LIQUID-PHASE ASSAYS IN DETECTION OF INSULIN-ANTIBODIES INFLUENCE OF IODINATION SITE ON LABELED INSULIN BINDING

On type 1 newly diagnosed and on insulin treated diabetic patients, an ti-insulin autoantibodies (IAA) and antibodies (IA) having the same sp ecificity are respectively induced. Such immune response may be evalua ted either by radiobinding assay (RBA) or enzyme-linked immunosorbent assay (ELISA). Both methodologies have been compared at previous Inter national Workshops, which pointed out discrepancies in results. In thi s work, IAA/IA prevalence was assessed by displacement RBA and ELISA, in normal subjects, type 2 (treated with hypoglycaemic agents), insuli n treated and newly diagnosed type 1 diabetic patients. Results showed a lack of RBA-ELISA agreement. An attempt was then made to determine whether such results were, at least in part, attributable to iodinatio n site in Tyr-A(14). For this purpose parallel RBA assays were carried out by using radiolabelled insulin at A(14) and A(19) Tyr residues. C ontrol sera and samples from insulin treated and type 1 newly diagnose d diabetic patients were tested. Our results suggest that labelling po sition is not involved in artifactual binding of tracers, at least as a systematic phenomenon. In the majority of cases the variability in R BA-ELISA signal ratios are best explained in terms of differences in t he basic principles operating in both methods instead of artifacts due to tracer preparation.