Alterations in the carbohydrate structures of an abnormal protein from sera of patients with rheumatoid arthritis.

G4-11, an abnormal immunoglobulin G4 (IgG4) glycoprotein, highly purified from the sera of patients with rheumatoid arthritis and from healthy individuals, contains two asparagine-linked sugar chains in one molecule. Comparative studies of the sugar chains released by hydrazinolysis revealed that the structures of the sugar chains of rheumatoid arthritis G4-11 are quite different from those of normal individuals. Although all G4-11 contained biantennary complex-type oligosaccharides like in the case of serum IgGs, samples from patients with rheumatoid arthritis had less galactosylated forms than those from normal individuals. These results indicated that this galactose deficiency of the sugar chains occurs in the abnormal IgG4 molecule of rheumatoid arthritis patients, just as was found in whole serum IgG.