Equilibrium binding studies of insulin antibodies in diabetic subjects.

Equilibrium binding of insulin to human insulin antibodies from diabetic subjects has been studied by two methods. Results obtained by using a nondissociating gel filtration assay differed from those obtained by a conventional competitive binding method. Both methods yield data consistent with two classes of insulin binding site, having association constants of approximately 10(9) and 10(7) liter/mol. The principal differences are the higher association constant and lower number of binding sites for the high-affinity binding component, observed with the gel filtration method. In the conventional competitive binding assay, damaged radioligand, dissociation of the binding complex, or limitations of ligand availability may be responsible for the erroneous results. Data from nine diabetic patients indicate that insulin resistance and stability of diabetes cannot be explained by the binding properties of insulin antibodies alone.