To investigate the association between glycosylation and immune complex formation in various disease groups.
Methods. Immune complexes and IgG were isolated from serum and their carbohydrate content evaluated in a dot-blot assay using specifically binding lectins.
Results. Significantly more N-acetylglucosamine was detected in complexes from patients with rheumatoid arthritis (RA) than in those from patients with systemic lupus erythematosus, Crohn's disease, or infectious endocarditis, or from normal controls (P < 0.001). The immune complex concentration in the circulation was strongly associated with N-acetylglucosamine levels (P < 0.001 by chi-square analysis).
Conclusion. The composition of immune complexes from RA patients is distinct in carbohydrate content from those found in other disease groups.
Glycosylation has marked effects on the activity of the immunoglobulin molecule (1). In 1976, Mullinax et a1 found that IgG carbohydrate composition differed between rheumatoid arthritis (RA) patients and normal individuals (2). These changes involved the lack of terminal galactose residues from the oligosaccharide located in the conserved glycosylation site on the C,2 domain of the Fc fragment at Asn 297 and resulted in oligosaccharides terminating in N-acetylglucosamine. It has been hypothesized that this agalactosyl IgG may be responsible for inducing rheumatoid factor production (3) and immune complex formation.