Titer and Specificity of Autoantibody to β2-Microglobulin in Sera from Patients with Rheumatic Disease

Sera from patients with rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and mixed connective tissue disease (MCTD) possessed higher titer of antibody to human β2-microglobulin (β2m) than those from healthy controls and patients with Behçet's disease in the enzyme-linked immunosorbent assay. It was also confirmed by the immunoprecipitation method. Anti-β2m antibody in sera from those patients immunoprecipitated free β2m but not β2m in association with major histocompatibility complex class I antigen heavy chain. It was suggested that anti-β2m antibody in sera from either patients or healthy controls might be directed mainly against free β2m. The relationship between the anti-β2m antibody and anti-lymphocytotoxic antibody found in those patients is discussed.