T-Cell response to proinsulin and insulin in type 1 and pretype 1 diabetes

Insulin-dependent diabetes mellitus (IDDM) results from the selective destr uction of pancreatic beta cells by a T cell-mediated autoimmune process. In sulin and proinsulin are the only known beta cell-specific autoantigens. Us ing short-term cultures of freshly isolated peripheral blood mononuclear ce lls, we evaluated T-cell responses to proinsulin and to insulin in IDDM pat ients and individuals at risk for IDDM. A proliferative T-cell response to proinsulin was observed in only of 16 recent-onset IDDM subjects and 2 of 1 2 long-standing IDDM subjects and was associated with a proliferative respo nse to insulin. In contrast, 5 of 13 islet cell autoantibody-positive first -degree relatives of IDDM patients showed a proliferative response to proin sulin alone, 3 of 13 to insulin alone, and 1 of 13 to both insulin and proi nsulin. Overall, 9 of 13 ICA-positive first-degree relatives responded to e ither proinsulin or insulin. We observed an inverse relationship between an tiinsulin antibodies and T-cell responses to insulin in ICA-positive first- degree relatives but not in long-standing IDDM patients. Our data indicate that proinsulin is a major antigen in IDDM and, further, illustrate the dif ference between the autoimmune response to insulin and the immune response to exogenous insulin.