Titer and specificity of autoantibody to beta 2-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 beta 2-microglobulin (beta 2m) 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-beta 2m antibody in sera from those patients immunoprecipitated free beta 2m but not beta 2m in association with major histocompatibility complex class I antigen heavy chain. It was suggested that anti-beta 2m antibody in sera from either patients or healthy controls might be directed mainly against free beta 2m. The relationship between the anti-beta 2m antibody and anti-lymphocytotoxic antibody found in those patients is discussed.