Agalactosyl IgG in aggregates from the rheumatoid joint

Area of Science:

• Immunology
• Glycobiology
• Rheumatology

Background:

• Rheumatoid arthritis (RA) is characterized by joint inflammation.
• Self-associating agalactosyl immunoglobulin G (IgG) is hypothesized to contribute to RA pathology.
• Understanding IgG modifications in the rheumatoid joint is crucial for RA research.

Purpose of the Study:

• To investigate the presence and characteristics of agalactosyl IgG in synovial fluid (SF) from RA patients.
• To determine if agalactosyl IgG preferentially aggregates in the rheumatoid joint.
• To explore potential alterations in IgG glycosylation associated with pathological aggregates.

Main Methods:

• IgG was isolated from synovial fluid (SF) and polyethylene glycol (PEG) precipitates of 22 RA patients.
• Reduced IgG was purified using protein G to separate it from other glycosylated proteins.
• Galactose and N-acetylglucosamine (GlcNAc) levels on IgG were quantified using lectin binding assays (RCA120 and BS II).

Main Results:

• IgG from PEG precipitates showed proportionally less galactose compared to paired SF IgG (P = 0.001).
• Increased binding of RCA120 and BS II lectins was observed for IgG in PEG precipitates in many cases.
• These findings suggest preferential aggregation of agalactosyl IgG in RA SF PEG precipitates.

Conclusions:

• Agalactosyl IgG appears to preferentially occur in RA synovial fluid precipitates.
• This agalactosyl IgG may also exhibit increased glycosylation on its Fab region.
• The study supports the hypothesis of agalactosyl IgG's role in rheumatoid arthritis pathogenesis.