Bovine and human NPH insulins as T cell immunogens

Abstract

The aim of this study was to assess the immunocompetence of T cells from patients with poorly controlled diabetes with respect to Candida albicans antigen and to compare the relative immunogenicity of human insulin, bovine insulin and protamine at the T-cell level during 6 months treatment with human or bovine NPH insulins. T-cell proliferation was measured in vitro in response to C. albicans, bovine and human insulin, bovine and human NPH and protamine in 17 patients with newly-diagnosed type 1 (insulin-dependent) and 12 with poorly-controlled type 2 (non-insulin-dependent diabetes) before and after 0.5, 1, 3 and 6 months of treatment with either bovine or human NPH insulin. The following results were found: Baseline responses to C. albicans (as a recall antigen) were similar for patients and controls despite marked hyperglycaemia in the patients. No patient had a response greater than mean + 2 S.D. of controls to human or bovine insulin before starting treatment, or had insulin autoantibodies. Treatment with human NPH insulin did not induce T-cell responses to human or bovine insulin, but 3 13 (23%) patients treated with bovine NPH responded to bovine and human insulin after 6 months, of whom one responded exclusively to human. In contrast, 6 (46%) bovine and 3 (19%) human NPH-treated patients responded to protamine. It was concluded that there is no evidence of T-cell immunosuppression in poorly-controlled diabetes or of T-cell autoimmunity to insulin in newly-diagnosed type 1 diabetes. Treatment with bovine NPH insulin immunizes T cells to insulin, but human NPH does not. Regardless of insulin species the main immunogen in NPH insulins is protamine.