Autoimmunity against INS-IGF2 Protein Expressed in Human Pancreatic Islets*

Background: Islet INS-IGF2 was examined as a possible autoantigen in type 1 diabetes. Results: INS-IGF2 expression was inversely related to donor HbA1c and glucose-stimulated insulin release. Autoantibodies doubly reactive with INS-IGF2 and insulin were more common in patients with type 1 diabetes than controls. Conclusion: INS-IGF2 is recognized by autoantibodies in type 1 diabetes. Significance: Autoantibodies doubly reactive with both INS-IGF2 and insulin may contribute to type 1 diabetes. Insulin is a major autoantigen in islet autoimmunity and progression to type 1 diabetes. It has been suggested that the insulin B-chain may be critical to insulin autoimmunity in type 1 diabetes. INS-IGF2 consists of the preproinsulin signal peptide, the insulin B-chain, and eight amino acids of the C-peptide in addition to 138 amino acids from the IGF2 gene. We aimed to determine the expression of INS-IGF2 in human pancreatic islets and autoantibodies in newly diagnosed children with type 1 diabetes and controls. INS-IGF2, expressed primarily in beta cells, showed higher levels of expression in islets from normal compared with donors with either type 2 diabetes ( p = 0.006) or high HbA1c levels ( p < 0.001). INS-IGF2 autoantibody levels were increased in newly diagnosed patients with type 1 diabetes ( n = 304) compared with healthy controls ( n = 355; p < 0.001). Displacement with cold insulin and INS-IGF2 revealed that more patients than controls had doubly reactive insulin-INS-IGF2 autoantibodies. These data suggest that INS-IGF2, which contains the preproinsulin signal peptide, the B-chain, and eight amino acids of the C-peptide may be an autoantigen in type 1 diabetes. INS-IGF2 and insulin may share autoantibody-binding sites, thus complicating the notion that insulin is the primary autoantigen in type 1 diabetes.