Determination of anti-actin antibodies by a solid-phase immunoenzymatic assay and by indirect immunofluorescence technique

Anti-actin IgA antibodies in severe coeliac disease

Anti-actin IgA antibodies have been found in sera of coeliacs. Our aim was to define the prevalence and clinical significance of anti-actin IgA in coeliacs before and after gluten withdrawal. One hundred and two biopsy-proven coeliacs, 95 disease controls and 50 blood donors were studied. Anti-actin IgA were evaluated by different methods: (a) antimicrofilament positivity on HEp-2 cells and on cultured fibroblasts by immunofluorescence; (b) anti-actin positivity by enzyme-linked immuosorbent assay (ELISA); and (c) presence of the tubular/glomerular pattern of anti-smooth muscle antibodies on rat kidney sections by immunofluorescence. Antimicrofilament IgA were present in 27% of coeliacs and in none of the controls. Antimicrofilament antibodies were found in 25 of 54 (46%) coeliacs with severe villous atrophy and in three of 48 (6%) with mild damage (P < 0.0001). In the 20 patients tested, antimicrofilaments IgA disappeared after gluten withdrawal in accordance with histological recovery. Our study shows a significant correlation between antimicrofilament IgA and the severity of intestinal damage in untreated coeliacs. The disappearance of antimicrofilament IgA after gluten withdrawal predicts the normalization of intestinal mucosa and could be considered a useful tool in the follow-up of severe coeliac disease.

Immunofluorescence evidence for cytoskeletal rearrangement accompanying pigment redistribution in goldfish xanthophores

Immunofluorescence and phase-contrast microscopic studies of goldfish xanthophores with aggregated or dispersed pigment show two unusual features. First, immunofluorescence studies with anti-actin show punctate structures instead of filaments. These punctate structures are unique for the xanthophores and are absent from both goldfish dermal non-pigment cells and a dedifferentiated cell line (GEM-81) derived from a goldfish xanthophore tumor. Comparison of immunofluorescence and phase-contrast microscopic images with electron microscopic images of thin sections and of Triton-insoluble cytoskeletons show that these punctate structures represent pterinosomes with radiating F-actin. The high local concentration of actin around the pterinosomes results in strong localized fluorescence such that, when the images have proper brightness for these structures, individual actin filaments elsewhere in the cell are too weak in their fluorescence to be visible in the micrographs. Second, whereas immunofluorescence images with anti-tubulin show typical patterns in xanthophores with either aggregated or dispersed pigment, namely, filaments radiating out from the microtubule organizing center, immunofluorescence images with anti-actin or with anti-intermediate filament proteins show different patterns in xanthophores with aggregated versus dispersed pigment. In cells with dispersed pigment, the punctate structures seen with anti-actin are relatively evenly distributed in the cytoplasm, and intermediate filaments appear usually as a dense perinuclear band and long filaments elsewhere in the cytoplasm. In cells with aggregated pigment, both intermediate filaments and pterinosomes with associated actin are largely excluded from the space occupied by the pigment aggregate, and the band of intermediate filaments surrounds not only the nucleus but also the pigment aggregate. The patterns of distribution of the different cytoskeleton components, together with previous results from this laboratory, indicate that formation of the pigment aggregate depends at least in part on the interaction between pigment organelles and microtubules. The possibility that intermediate filaments may play a role in the formation/stabilization of the pigment aggregate is discussed.

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.

Rabbit autoantibodies to actin induced by immunization with modified homologous actins

Actin is a major antigen involved in the reaction of smooth muscle antibody positive sera from patients with chronic active hepatitis. In the present study, actin extracted from rabbit skeletal muscle was denatured by sodium dodecyl sulfate and was immunized into the rabbit, a homologous animal for actin. The rabbits, thus immunized, produced antibodies reactive with actins of homologous and heterologous animals. In addition, the antibodies showed reactivity with autologous actin. It indicates that the denatured homologous actin is capable of terminating immunological tolerance to actin and induces formation of autoantibody to rabbit actin. This phenomenon may be implicated in the occurrence of anti-actin antibody in sera from patients with chronic liver disease and several other diseases.

Anti-actin antibodies of IgM and IgG class in chronic liver diseases detected by fluorometric immunoassay

Using a sensitive fluoroimmunoassay, anti-actin antibodies (AA) of the IgM and IgG classes were measured in 240 patients with various chronic liver diseases and in 211 patients with non-hepatic autoimmune muscle, heart, malignant and inflammatory bowel diseases. Thirty-two out of 40 patients (80%) with autoimmune chronic active hepatitis (CAH) had AA only of the IgG class (geom. mean X = 1.78, SEM +/- 0.07) and only three patients (8%) had both IgG and IgM AA, the latter in lower titres. In patients with primary biliary cirrhosis (PBC) and AMA-positive cholestatic CAH, AA of both IgM and IgG classes were equally represented (60% IgG and 64% IgM AA in PBC, 73% IgG and 51% IgM AA in cholestatic CAH) but the titres were very low (geom. mean IgG AA in PBC 1.035, SEM +/- 0.03, in cholestatic CAH 1.18, SEM +/- 0.02). In contrast to autoimmune (lupoid) CAH, AA were rare in HBsAg positive CAH (9/43, 21%) and only present in low titres. However, in six out of 21 patients with anti-HBs and anti-HBc-positive chronic active hepatitis, high AA of IgG class were found, suggesting the autoimmune type of liver disease. In NANB virus-induced chronic liver disease after blood transfusion, AA were only occasionally found (IgG antibodies 1/19, IgM antibodies 3/19) and none were found in the eight patients with sporadic NANB hepatitis. They were also rare in 30 patients with alcoholic liver disease (3/30, 10%).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Stress fibers in cells in situ: immunofluorescence visualization with antiactin, antimyosin, and anti-alpha-actinin

Stress fiber-like patterns are visualized by indirect immunofluorescence in scleroblasts (fibroblasts) in situ on the scale of the common goldfish, Carassius auratus, using an affinity-purified antiactin, antimyosin, and anti-alpha-actinin. These fibers demonstrate the classical convergent and parallel patterns exhibited by stress fibers in tissue culture cells. Because the dimensions, the composition, and the pattern of distribution of these cytoplasmic fibers correspond well with those of stress fibers in cultured cells, we will call these fibers stress fibers also. The staining patterns with anti-alpha-actinin and antimyosin along the stress fibers often reveal a periodicity of 1-2 microM, identical to that found in cells in vitro. The majority of scleroblasts do not exhibit stress fiber staining and they are specifically located in the central regions of the scale. Stress fibers are present in scleroblasts residing on or near the edges or radical ridges of the scale. They are consistently orientated perpendicular to these structures; however, unlike microtubules, stress fibers show no co-alignment with collagen fibers of the scale. The finding that stress fibers are located in regions of the scale more subject to shearing forces may indicate their role in increased cellular adhesion to the substratum.

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.

Tumor-associated antibodies in the serum of patients with ocular melanoma. IV. Correction for smooth muscle antibodies

Serum samples from patients with choroidal malignant melanoma, carcinoma metastatic to the choroid and "normal" controls containing tumor-associated antibodies (TAA) to tissue cultured melanoma cells were examined for the presence of smooth muscle antibody (SMA). Sera found to contain SMA were absorbed with actin or thrombosthenin and reassayed for TAA. With this modification, 72% (78% before absorption) of patients with uveal melanoma, 26% (78% before absorption) of patients with carcinoma metastatic to the choroid and 13% (24% before absorption) of "normal" controls were found to have tumor-associated antibodies in their serum.