Nonenzymatic glycosylation of immunoglobulin G impairs complement fixation.

Transient hyperglycemia in patients receiving total parenteral nutrition may be associated with impaired immune function. The effects of short-term hyperglycemia on one aspect of antimicrobial immune function, ie, the ability of IgG to fix complement, were investigated. Aliquots of anti-human albumin, anti-horse ferritin, and anti-alkaline phosphatase were incubated for 0, 8, 16, 24, 48, and 96 hr with either 0 or 240 mg of glucose per deciliter of buffer. All samples were analyzed for the degree of glycation using a thiobarbituric acid assay, and for complement fixation ability using a microcomplement fixation assay. Significant increases in glycation over control samples were observed after only 16 hr (31 vs 15 mmol 5-hydroxymethylfurfural/mol IgG, p less than 0.01). Complement fixation was significantly altered after 48 hr of incubation (76 +/- 5% vs 90 +/- 8% total serum complement fixed by albumin/anti-albumin complex, p less than 0.03) when four of the 84 (4.7%) IgG lysine residues were glycated. It is demonstrated that a significant reduction in complement fixation by immunoglobulin occurs with elevated glucose concentrations and that this may play a clinically significant role in transiently hyperglycemic patients.