IgA- and insulin-containing (C3-fixing) circulating immune complexes in diabetes mellitus.

Sera of patients with type 1 and type 2 diabetes were examined for IgA- and insulin-containing immune complexes (IgA-ICs, ICs-insulin) using a solid-phase anti-C3 enzyme immunoassay. IgM-ICs and IgG-ICs were also investigated. IgA-ICs were detected in 6 of 26 type 1 diabetics, in 9 of 25 insulin-treated type 2 diabetics, and in 8 of 34 type 2 diabetics on oral hypoglycemic agents, but only in 2 sex- and age-matched controls. ICs-insulin was detected in 9 of 25 type 1 diabetics and in 1 of 19 insulin-treated type 2 diabetics, irrespective of the time of insulin treatment. ICs-insulin did not appear to be related to the presence of microangiopathy. IgA-ICs were found to be associated with the presence of microangiopathy, suggesting that they may play a role in the pathogenesis of the late diabetic complications.