Structural changes in the oligosaccharide chains of IgG in autoimmune MRL/Mp-lpr/lpr mice

The structures of the asparagine-linked oligosaccharide chains of IgG from autoimmune arthritic MRL/Mp-lpr/lpr (MRL-lpr/lpr) mice and control MRL/Mp-+/+ (MRL-+/+) mice were investigated. Two subpopulations of IgG, Ml-I and Ml-II, were obtained from serum of MRL-lpr/lpr mice by column chromatography on protein A-Sepharose CL-4B. Although Ml-I did not bind to the column, its elution was retarded, whereas Ml-II was bound and was eluted in acidic buffer. IgG (Mn) from MRL-+/+ mice showed the same chromatographic behavior as Ml-II. The structures of oligosaccharide chains liberated quantitatively by hydrazinolysis from IgG samples Mn, Ml-I, Ml-II, and a pooled mixture (Ml) of Ml-I and Ml-II were determined by sequential exoglycosidase digestion, lectin (RCA120) affinity HPLC, and by methylation analysis. Their oligosaccharide structures were the same and shown to be biantennary complex-type chains ±Galβ1 → 4GlcNAcβ1 → 2Manα1 → 6(±Galβ1 → 4GlcNAcβ1 → 2Manα1 → 3)Manβ1 → 4GlcNAcβ1 → 4(±Fucα1 → G)GlcNAc. The proportion of each oligosaccharide in Mn and Ml-II was the same but differed from that in Ml-I where the degree of the galactosylation was significantly decreased which caused the change in the oligosaccharide pattern of total serum IgG (Ml) of autoimmune MRL-lpr/lpr mice. This phenomenon, which is also found in total serum IgG of patients with rheumatoid arthritis, suggests that alteration of oligosaccharides in IgG may be a common feature in animals which develop arthritis with the production of rheumatoid factor regardless of species.