Impaired immunoglobulin G Fc fragment function in diabetics is caused by a mechanism different from glycation.

Glycation and fluorescence at 440 nm (excitation at 370 nm) were found to be increased in immunoglobulin G (IgG) from diabetics, strongly indicating the presence of IgG-linked advanced glycosylation end products. In contrast, levels of IgG-linked advanced glycosylation end products were low or undetectable in both normal and diabetic subjects when an advanced glycosylation end products specific antibody was employed for immunological determination of advanced glycosylation end products. Furthermore, no correlation exists between IgG glycation, fluorescence and immunoreactivity. In diabetics, the Fc fragment of IgG showed decreased protein A binding and decreased fixation of complement. This impairment of biological activity was not correlated with the immunologically determined level of advanced glycosylation end products, whereas IgG-linked fluorescence was inversely related to complement fixing activity. These results indicate that mechanisms different from glycation or browning are responsible for changes in the functional properties of IgG.