Binding of Rheumatoid and Lupus Synovial Fluids and Sera-Derived Human IgG Rheumatoid Factor to Degalactosylated IgG

Altered glycosylation of immunoglobulin G (IgG) has been demonstrated in patients with rheumatoid arthritis (RA). Specificity of IgG rheumatoid factor (RF) in recognizing degalactosylated IgG (Fab)(2) and Fc was analyzed in the present study.(Fab)(2) and Fc fragments were prepared from IgG of normal healthy subjects. Enzymes, including peptide-N-glycosidase (PNGase), neuraminidase, and beta-1,4-galactosidase, were used to digest (Fab)(2) and Fc fragments. Binding capacity of IgG RF from patients with RA, systemic lupus erythematosus (SLE), and from healthy subjects to (Fab)(2) and Fc treated with glycosidase, was measured with immunoassay.Treating (Fab)(2) and Fc with PNGase significantly diminished their binding capacity to IgG RFs. Degalactosylated (Fab)(2) revealed higher affinity to IgG RF in all tested groups. Fc lacking terminal galactose on oligosaccharide chains showed elevated binding with synovial IgG RF of RA patients. However, lesser binding was observed in sera of patients with RA and SLE.Our data suggest that IgG molecules containing less terminal galactose on their oligosaccharide moieties are preferentially recognized by IgG RF. Furthermore, IgG RF display alternative binding specificity to degalactosylated (Fab)(2) and Fc in synovial fluids and sera of RA patients.