Nonenzymatic Glycation of Immunoglobulins Leads to an Impairment of Immunoreactivity

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Abstract
Incubation of purified human and rabbit IgG with glucose leads to covalent incorporation of the sugar into the protein, depending on glucose concentration, incubation time and pH. The level of glycated IgG from normal and diabetic subjects was determined using the thiobarbituric acid reaction. The median for glycated IgG, expressed as mmol 5-hydroxymethylfurfural/mol IgG, obtained from 20 normal and 29 diabetic subjects was 62 and 107, respectively. Glucose incubation of IgG purified from rabbit antihuman-transferrin serum, from human antivaricella/zoster virus serum and from human anti-lues-spirochete serum, respectively, leads to a marked decrease in biological activity, as determined in a micro complement fixation test. Inactivation of specific antibody was dependent on incubation time and glucose concentration employed. Loss in complement-fixing activity was observed at glycation levels well comparable to those found in diabetics.