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 beta 2-microglobulin (beta 2m) reacting with polyclonal IgM rheumatoid factors (RF) from patients with rheumatoid arthritis (RA). METHODS: Ten polyclonal RF were tested for their human beta 2m 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 beta 2m residues contributing to RF reactivity were tryptophans at positions 60 and 95, lysine at 58, and arginine at position 97.