Galactose residues in chronic inflammatory disease

The changes in monosaccharide composition of immunoglobulin G in the course of rheumatoid arthritis

The objective of this study was to determine whether galactosylation of immunoglobulin G (IgG) in patients with rheumatoid arthritis (RA) correlates with severity and duration of illness. Serum IgG glycosylation from 50 patients with RA in comparison with 30 healthy controls was analyzed. IgG from sera was isolated and monosaccharide composition was determined by means of gas chromatography. Ratio of galactose to mannose content was calculated. Patients were divided into groups according to three different criteria: disease duration, severity of RA (disease activity score index), and radiological degree of advancement of illness according to Steinbrocker. In patients with RA, significant decrease (p<0,01) of galactose ratio was observed in comparison with healthy control. In patients with long duration of RA (more than 15 years), significant decrease of galactose (p<0.05) ratio in comparison with patients who have had arthritis for less then 5 years was observed. For the group of patients with severe RA, we found reduction of galactose (p<0.001) ratio vs the group of patients in remission. For those patients who had radiological stage IV according to Steinbrocker, IgG galactose (p<0.01) content per oligosaccharide chain were also more decreased than in those patients who had stage I RA. Decreased galactosylation and of IgG in RA was observed. The lack of this carbohydrate component of IgG correlates with severity and duration of RA and could be used in monitoring the progression in early arthritis.

Changes in the galactose content of IgG during humoral immune responses

The Fc region of IgG bears two oligosaccharides of variable composition. The serum level of one variant which lacks terminal galactose and sialic acid (agalactosyl IgG) is raised in a number of autoimmune diseases and animal models thereof. Here it is shown that such changes in IgG glycosylation occur during non-pathological humoral immune responses. It was found that if specific pathogen free (SPF) CBA/Ca mice are transferred from a sterile to a conventional environment, their levels of total serum IgG rise whereas the degree of IgG galactosylation falls. Next, mice were immunised with bovine serum albumin (BSA) in incomplete Freund's adjuvant. As anti-BSA titres rose the antibodies became less galactosylated and later, as the titres fell, the antibodies became more galactosylated. By contrast, there was little or no variation in the relative galactosylation of total IgG. It is considered that the galactosylation of IgG antibodies varies during an immune response.