Induction of Hyperglycemia with Insulin Antibodies to B-Chain Determinants

Insulin antibodies measured by a radioimmune method (AB_R) are significantly better inducers of hyperglycemia than are insulin antibodies measured by an immune hemolysis method (AB_H) when injected intraperitoneally into mice. The ability to induce hyperglycemia by an insulin antiserum can be predicted by the titer of ABR measured. AB_R interact in vitro with determinants severely perturbed on nickel-insulin, partially perturbed on proinsulin and desasparaginedesalanine insulin, and unaffected on zinc-insulin or zinc-free monocomponent insulin. AB_H, on the other hand, interact in vitro with determinants severely perturbed on proinsulin and desasparagine-desalanine insulin but stabilized on nickel-insulin and zinc-insulin. Since the connecting peptide of proinsulin is probably in apposition to the A-chain residues on the solvent surface, the more effective reaction of proinsulin with AB_R than with AB_H is submitted as evidence that AB_R are directed toward residues on the B-chain surface of insulin. Because AB_R are more effective inducers of hyperglycemia than are AB_H, it is proposed that the degree of hyperglycemia induced by antibodies in vivo is a result of interactions with determinants on the B-chain surface of insulin. These results support the possibility that insulin in vivo is more accessible for interaction with antibodies directed to the B-chain of insulin. It is also possible that AB_R, which are directed to B-chain determinants, are of higher affinity than is the affinity between insulin and receptors or that the active site of insulin for maintaining euglycemia includes the B-chain surface residues.