Anti-rabbit thymus actin antibody inhibits proliferation of Epstein-Barr virus-transformed human B cell line LA350: augmentation by cyclic AMP

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 beta-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 micrograms ml-1) by immunofluorescence 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 micrograms ml-1 (range 2-20 micrograms 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 micrograms ml-1), 43 out of 64 (67%) patients with human immunodeficiency virus infection and AIDS (range 3-80 micrograms ml-1), and 17 out of 23 (74%) infants with Kawasaki Syndrome (range 7-138 micrograms 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.

Antibody to human lymphocyte actin regulates immunoglobulin secretion by an EBV-transformed human B-cell line

Antibody against actin isolated from a human EBV-transformed lymphoblastoid B-cell line exerted an inhibitory effect on in vitro IgM secretion by a different lymphoblastoid B-cell line, LA350. This effect was dose dependent showing from 24-40% inhibition at a dilution of 1:100 and 68-80% inhibition at a dilution of 1:50. This effect was noted in the absence of changes in either total cell count or [3H]-thymidine incorporation and was reversed by co-incubation with purified rabbit thymus actin (100 micrograms/ml) but not bovine serum albumin at the same concentration. These data demonstrate regulation of immunoglobulin synthesis by antibodies against human lymphocyte derived actin in a lymphoblastoid B-cell line.