Antibodies to amyloid A protein in rheumatic diseases.

Circulating autoantibodies against amyloid A protein (AA) were demonstrated by enzyme immunoassay in 18/62 patients with rheumatoid arthritis (RA) and in 9/27 patients with systemic lupus erythematosus (SLE). In the subset of RA patients who had developed amyloid, the frequency of antibodies to AA was lower than in those without amyloid (P less than 0.05). The antibody levels showed some variation in serial serum samples during follow-up (1-4 years) of patients with amyloidosis or SLE, but did not correlate with disease activity. In contrast to the patients with rheumatic diseases, patients with inflammatory bowel disease and acute bacterial peritonitis had antibody levels within the range of the healthy control subjects. The results show that autoantibodies to protein AA may occur in rheumatic diseases; their occurrence does not, however, identify subjects with tissue amyloid deposits. Absorption experiments suggest that the antibodies may be directed to circulating amyloid A protein.