Induction of specific anti-actin antibodies and their measurement by ELISA technique

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.

Western-blotting method for detecting antibodies against human muscle contractile proteins in myositis

Many investigators report anti-muscle antibodies using various kinds of methods. The Western-blotting method, however, has not previously been used for this purpose. We have detected antibodies to muscle contractile proteins in sera from patients with collagen disease and muscular dystrophy by this method. The antigens detected included myosin heavy and light chains, tropomyosin and troponin complex. Our method is a quick and sensitive way to determine which are the antigenic muscle contractile proteins.

Anti-actin antibodies. Chemical modification allows the selective production of antibodies to the N-terminal region

The specific properties of sera elicited by various native, unfolded or chemically modified actins were compared to provide a means of obtaining high titres of antibodies directed against the N-terminal (1-39) or the central regions of the actin sequence. The antigenic structure of the N-terminal region of actin was analyzed. It has at least 2 discrete epitopes, one of which appears to be species-specific and is composed of the hydrophilic N-terminal heptapeptide sequence.

Antibodies against the bovine brain glutamate binding protein

Antibodies against the purified bovine brain glutamate binding protein (GBP) were raised in rabbits. Both nonderivatized and dinitrobenzene-derivatized GBP produced strong immunological responses in rabbits. Using the enzyme-linked immunosorbent assay (ELISA), we have quantified the antibody production and determined the specificity of the antibodies. Bovine brain GBP and the analogous protein from rat brain interacted most strongly with the antibodies. A bacterial glutamate-aspartate binding protein, as well as the enzymes glutamate dehydrogenase (EC 1.4.1.3), glutamine synthetase (EC 6.3.1.2), and gamma-glutamyl transpeptidase (EC 2.3.2.2), showed little or no cross-reactivity with the anti-GBP antibodies. A crude bacterial glutamate decarboxylase (EC 4.1.1.15) preparation gave a small to moderate cross-reaction with the anti-GBP antibodies. The sensitivity of the ELISA assay and the specificity of the antibodies were such that GBP levels as low as 3-10 ng could be detected.

Studies on the antigenic sites of actin: a comparative study of the immunogenic crossreactivity of invertebrate actins

The structural homologies of invertebrate actins with cytoplasmic vertebrate actins have recently been substantiated by comparative sequence analyses. This suggests that cytoplasmic actin is the ancestral precursor of smooth and striated muscle actin in vertebrates. We have raised antibodies in rabbits against a number of invertebrate muscle actins and have characterized the antisera by means of the highly sensitive ELISA method, which allows quantitation of nanomolar amounts of actin. Despite the fact that the invertebrate actins examined are very similar in primary structure, our results indicate that antibodies raised against them clearly distinguish between only a few amino-acid substitutions, and that the immunoreactivities quantitatively reflect the genetic divergence of this ubiquitous conservative protein. Examination of several proteolytic fragments of scallop actin for immunoreactivity with the homologous antiserum suggests that the major antigenic sites of actin are located within the amino terminal region of the molecule, while a carboxy terminal fragment comprising residues 69-372 exhibits very weak crossreactivity. Immunoadsorption experiments further indicate that species-specific antibodies are directed to antigenic determinants in the N-terminal region. This finding is supported by an examination of the effects of chemical modifications to Tyr, His, Arg, and Cys residues on the immunoreactivity of actin. Interaction with DNAase I markedly decreases the immunoreactivity of actin. This is consonant with the finding that the amino terminal peptide comprising residues 1-207 inhibits DNAase I, whilst a tryptic fragment fails to bind to the enzyme. The interaction is abolished by EDTA and the removal of the tightly bound cation is accompanied by a conformational change, shown by shifts in circular dichroic spectra. The possible involvement of the amino terminal peptide of actin in cation binding is discussed.

An enzyme-linked immunosorbent assay for antistriational antibodies associated with myasthenia gravis and thymoma: comparison with indirect immunofluorescence

Autoantibodies to the striations of skeletal muscle (AStrA) detected by immunofluorescence are useful in the diagnosis of a thymoma associated with myasthenia gravis (MG). With the intention of developing a better method, an enzyme-linked immunosorbent assay (ELISA) has been evaluated in 147 MG patients and 200 healthy controls. An additional 107 patients with various autoimmune diseases and autoantibodies were also tested. With a crude actomyosin preparation, the ELISA gave similar results to immunofluorescence, viz. positives in 42% of MG patients, but in all with a histologically proven thymoma. Less than 1% of the healthy controls were positive but false positives were found in patients with liver disease and anti-smooth muscle antibodies. After treatment of rheumatoid arthritis with D-penicillamine the titre of AStrA may rise. The ELISA was shown to be sensitive and reproducible, but immunofluorescence is a more practical method of distinguishing between the different categories of anti-muscle antibodies. ELISA should prove particularly useful for quantitation and sequential monitoring.

Characterization of a beta-actinin-like protein in purified non-muscle cell membranes. Its activity on (Na+ + K+)-ATPase

Treatment by EDTA of purified plasma membranes from MF2S cells (a variant of the murine plasmacytoma MOPC 173) solubilized proteins and increased by a 1000-fold the sensitivity of (Na+ + K+)-ATPase to ouabain. When added back with Ca2+ to treated plasma membranes, these EDTA-solubilized proteins restored the initial sensitivity of the enzyme to its inhibitor. We report the purification of a protein of Mr 32000, isolated from the EDTA-treated membrane supernatant. This protein was purified by a one-step procedure involving a preparative polyacrylamide gel electrophoresis without detergent. In the presence of Ca2+ it was able to restore the original sensitivity to ouabain of (Na+ + K+)-ATPase from EDTA-treated membrane. This protein was shown to be similar to the beta-actinin described by Maruyama by the following criteria: (1) molecular weight and amino acid composition; (2) cross-reactivity with their respective antisera; (3) in the presence of Ca2+ the same quantitative biological activity on ouabain sensitivity of the (Na+ + K+)-ATPase. A possible interaction between beta-actinin, calmodulin and membrane-bound (Na+ + K+)-ATPase is discussed.

A radioimmunoassay for determination of anti-actin antibodies

The reaction of spontaneously occurring human anti-human antibodies and experimentally produced rabbit anti-actin antibodies was investigated in a solid-phase radioimmunoassay (RIA). Three structurally different in vitro forms of actin monomeric G-actin filamentous F-actin and aggregated denatured actin were used as antigens. Human anti-actin antibodies reacted with F- and G-actin but not with aggregated actin, while rabbit anti-actin antibodies gave a strong reaction with all 3 forms of actin indicating differences in antibody specificities. The results of the anti-actin RIA were compared with those obtained by indirect immunofluorescence (IFL) on cryostat sections of rat stomach. The anti-actin RIA discriminated between patients' sera and control sera in most cases, although the indirect IFL test gave more conclusive results. The seemingly low sensitivity of the anti-actin RIA compared with that of indirect IFL test for detection of human anti-actin antibodies is probably due to favourable antigen distribution in tissue, not available in the solid phase. The anti-actin RIA was able to detect anti-actin antibodies in 8 out of 8 immunized rabbits although only two produced antibodies detectable by indirect IFL. The differences in reactivity between the two methods may depend on the presence of aggregated denatured actin in the antigen preparation used for immunization and exposure of the corresponding antigenic determinants of actin on the solid phase.