To test anti-Sa antibody in different autoimmune connective tissue diseases and analyze the relationship between Sa antibody and clinical manifestations and laboratory tests in rheumatoid arthritis.
Sa antigen was extracted from human placenta. Anti-Sa antibody was tested in 40 normal people and 478 connective tissue disease (CTD) patients using Western Blotting (WB).
Sa antigen was a protein with molecular weights of 50 kD and 55 kD. Anti-Sa antibody was positive in 31.9% (61/191) rheumatoid arthritis (RA), 3.0% (2/67) Sjögren's syndrome (SS), 4.3% (2/46) systemic lupus erythmatosus (SLE) and 0% (0/66) Behcet's disease, 0% (0/60) polymyositis/dermatomyositis (PM/DM), 0% (0/66) other CTD and 0% (0/40) normal controls. Anti-Sa antibody was different from other auto-antibodies in RA. In rheumatoid arthritis its sensitivity, specificity, positive prediction rate, negative prediction rate were 31.9%, 98.6%, 93.8% and 68.5% respectively. Anti-Sa antibody positive patients were significantly different from anti-Sa antibody negative patients in moming stiffness, ESR, ANA and X-ray grade.
Anti-Sa antibody was a new auto-antibody for the diagnosis of RA. Anti-Sa antibody positive patients seem to have more serious inflammation and more advanced disease process.