Increased plasma levels of IgA-IgG immune complexes and anti-F(ab')2 antibodies in patients with type 2 (non insulin-dependent) diabetes mellitus and microangiopathy.

C3 fixing IgA immune complexes were found to be elevated in 25% of patients with type 2 (non insulin-dependent) diabetes mellitus as compared to healthy subjects (2%). Immune complexes containing both IgA and IgG were found in 42% of the diabetic population but not in controls. The presence of C3-IgA and/or IgA/IgG immune complexes correlated with the occurrence of antiglobulins antibodies of IgA class in particular with autoantibodies reactive with the Fab2 portion of IgG. These immunopathological findings were more frequent in patients that exhibited microvascular complications and in particular in patients with proliferative retinopathy. These and our previous results strongly suggest a role of IgA system abnormality in the pathogenesis of diabetic vascular complications.