Rheumatoid factors from patients with rheumatoid arthritis react with tryptophan 60 and 95, lysine 58, and arginine 97, on human β2-microglobulin

Objective. To define precise epitopes on human β₂-microglobulin (β₂m) reacting with polyclonal IgM rheumatoid factors (RF) from patients with rheumatoid arthritis (RA). Methods. Ten polyclonal RF were tested for their human β₂m epitope–binding specificities using the entire 99–amino acid sequence synthesized as overlapping 7-mers in an enzyme-linked immunosorbent assay. Glycine substitution for each residue within RF-reacting linear regions was employed to define major reactive sites. Results and Conclusion. Major β₂m residues contributing to RF reactivity were tryptophans at positions 60 and 95, lysine at 58, and arginine at position 97.