Radioimmunoassay for anti-actin antibody: application in viral and autoimmune diseases

The development of a non-competitive, solid-phase radioimmunoassay for quantitating anti-actin antibody is described. Anti-actin antibody was captured on BSA-coated microspheres of polystyrene to which a synthetic peptide representing the fifteen amino acid N-terminus of human β-actin was covalently attached. A rabbit antiserum against the actin peptide fragment was used as reference serum for the assay. Serums of 23 out of 28 (82%) patients with chronic active hepatitis, shown to have anti-actin antibodies (range 2–140 μg ml −1) by immunofluorescense and immunoblot assays, were used to validate the radioimmunoassay. Only 7 out of 130 (5%) control subjects exhibited anti-actin antibody serum concentrations above 14 μg ml −1 (range 2–20 μg ml −1), the 95% confidence interval. Anti-actin antibody serum concentrations were determined to be elevated in 28 out of 47 (60%) patients with juvenile rheumatoid arthritis (range 5–89 μg ml −1), 43 out of 64 (67%) patients with human immunodeficiency virus infection and AIDS (range 3–80 μg ml −1), and 17 out of 23 (74%) infants with Kawasaki Syndrome (range 7–138 μg ml −1). All of the differences observed between patient groups, either singly or collectively, and the control group are highly significant ( P less than 0·001) as judged by chi-square analysis. Since all of these disease states contain elements of viral infection and autoimmune disease, it is possible that viral infection in these diseases triggers the production of anti-actin antibody, possibly by means of molecular mimicry in response to viral oncogenes or to abnormal expression of actin in host tissue. This radioimmunoassay for anti-actin antibodies may prove to be a useful tool for the detection and monitoring of certain forms of autoimmune disease.