IgM autoantibody to intermediate filaments in Mycoplasma pneumoniae infections

Protein citrullination as a source of cancer neoantigens

BACKGROUND

Citrulline post-translational modification of proteins is mediated by protein arginine deiminase (PADI) family members and has been associated with autoimmune diseases. The role of PADI-citrullinome in immune response in cancer has not been evaluated. We hypothesized that PADI-mediated citrullinome is a source of neoantigens in cancer that induces immune response.

METHODS

Protein expression of PADI family members was evaluated in 196 cancer cell lines by means of indepth proteomic profiling. Gene expression was assessed using messenger RNA data sets from The Cancer Genome Atlas. Immunohistochemical analysis of PADI2 and peptidyl-citrulline was performed using breast cancer tissue sections. Citrullinated 12-34-mer peptides in the putative Major Histocompatibility Complex-II (MHC-II) binding range were profiled in breast cancer cell lines to investigate the relationship between protein citrullination and antigen presentation. We further evaluated immunoglobulin-bound citrullinome by mass spectrometry using 156 patients with breast cancer and 113 cancer-free controls.

RESULTS

Proteomic and gene expression analyses revealed PADI2 to be highly expressed in several cancer types including breast cancer. Immunohistochemical analysis of 422 breast tumor tissues revealed increased expression of PADI2 in ER- tumors (p<0.0001); PADI2 protein expression was positively correlated (p<0.0001) with peptidyl-citrulline staining. PADI2 expression exhibited strong positive correlations with a B cell immune signature and with MHC-II-bound citrullinated peptides. Increased circulating citrullinated antigen-antibody complexes occurred among newly diagnosed breast cancer cases relative to controls (p=0.0012).

CONCLUSIONS

An immune response associated with citrullinome is a rich source of neoantigens in breast cancer with a potential for diagnostic and therapeutic applications.

Identification of a Specific Vimentin isoform that Induces an Antibody Response in Pancreatic Cancer

Pancreatic cancer has a poor prognosis, in part due to lack of early detection. The identification of circulating tumor antigens or their related autoantibodies provides a means for early cancer diagnosis. We have used a proteomic approach to identify proteins that commonly induce a humoral response in pancreatic cancer. Proteins from a pancreatic adenocarcinoma cell line (Panc-1) were subjected to two-dimensional PAGE, followed by Western blot analysis in which individual sera were tested for autoantibodies. Sera from 36 newly diagnosed patients with pancreatic cancer, 18 patients with chronic pancreatitis and 15 healthy subjects were analyzed. Autoantibodies were detected against a protein identified by mass spectrometry as vimentin, in sera from 16/36 patients with pancreatic cancer (44.4%). Only one of 18 chronic pancreatitis patients and none of the healthy controls exhibited reactivity against this vimentin isoform. Interestingly, none of several other isoforms of vimentin detectable in 2-D gels exhibited reactivity with patient sera. Vimentin protein expression levels were investigated by comparing the integrated intensity of spots visualized in 2-D PAGE gels of various cancers. Pancreatic tumor tissues showed greater than a 3-fold higher expression of total vimentin protein than did the lung, colon, and ovarian tumors that were analyzed. The specific antigenic isoform was found at 5–10 fold higher levels. The detection of autoantibodies to this specific isoform of vimentin may have utility for the early diagnosis of pancreatic cancer.

Relationship of Anti-vimentin antibodies to anti-endothelial antibodies

The intermediate filament protein vimentin is a potential target antigen for autoantibodies in some infectious and autoimmune diseases. Because endothelial cells contain an extensive interconnecting cytoplasmic network of vimentin, we examined the relationship between anti-vimentin and anti-endothelial cell antibodies (AECAs). We measured the level of anti-vimentin antibodies in patients with systemic autoimmune diseases (n=42), healthy blood donors (n=58), and patients with acute inflammation and showing anti-vimentin immunofluorescence (n=50). AECAs were detected by indirect immunofluorescence in human umbilical vein endothelial cells. Anti-vimentin antibodies were detected by indirect immunofluorescence in HEp-2 cells, and levels of anti-vimentin antibodies were measured using an enzyme-linked immunosorbent assay. We did not find significant differences in anti-vimentin levels between AECA-positive and-negative samples for any of the groups; however, serum anti-vimentin antibody levels were significantly higher in patients with acute non-autoimmune inflammatory diseases than in patients with systemic autoimmune diseases or healthy controls. There were no differences between the levels of anti-vimentin antibodies between patients with systemic autoimmune diseases and healthy individuals. The anti-vimentin antibodies levels also did not correlate with the AECA positivity.

High molecular weight vimentin complex is formed after proteolytic digestion of vimentin by caspase-3: detection by sera of patients with interstitial pneumonia

In a previous study, we demonstrated anti-vimentin antibodies in sera of patients with interstitial pneumonia. We hypothesized that antibodies in sera might detect vimentin fragments formed during the process of apoptosis. To prove this, recombinant human vimentin was digested by recombinant human caspase-3 or caspase-8. Then, Western blotting using several commercially available antibodies against human vimentin or patients' sera which had anti-vimentin autoantibodies, was performed. As a result, after recombinant human vimentin was digested by caspase-3 or caspase-8, several vimentin fragments were formed and detected by 2 kinds of monoclonal anti-vimentin antibodies (clone 3B4 and clone V9) as well as by polyclonal sheep anti-human vimentin antibody. It was demonstrated that high molecular weight vimentin was formed after the digestion of vimentin by caspase-3, which was only detected by patients' sera. The high molecular weight vimentin was not formed after digestion of vimentin by caspase-8. Our present results show that high molecular weight vimentin was formed after the digestion of vimentin by caspase-3. In addition, it is suggested that this high molecular weight vimentin acted as an autoantigen to form anti-vimentin autoantibody in vivo.

Detection of antivimentin antibody in sera of patients with idiopathic pulmonary fibrosis and non-specific interstitial pneumonia

It has been suggested that the humoral immune system plays a role in the pathogenesis of non-specific interstitial pneumonia (NSIP). Although some circulating autoantibodies to cytoskeletal protein(s) have been suggested, the antimyofibroblast antibody has not been investigated in patients with idiopathic pulmonary fibrosis (IPF) and NSIP. The purpose of this study is to evaluate the existence of antimyofibroblast antibody in the sera of patients with IPF and NSIP. The MRC5 cell line was used as a model of myofibroblast. The anti-MRC5 cell antibody was characterized in a patient with NSIP using Western blotting. Since we found that one of the anti-MRC5 antibodies was an antivimentin antibody, we established an enzyme-linked immunosorbent assay (ELISA) to measure the levels of antivimentin antibody in the sera of patients with IPF (n = 12) and NSIP (n = 23). Initially, two anti-MRC5 cell antibodies were detected in the sera of patients with NSIP, one of which was characterized as the antivimentin antibody by Western blotting. The other was characterized as an antivimentin fragment antibody. We established an ELISA to measure the antivimentin antibody and found significantly higher levels in patients with IPF and NSIP than in normal volunteers. One of the anti-MRC5 cell antibodies in the serum of a patient with NSIP was against vimentin. The serum levels of antivimentin antibody were increased in patients with IPF and NSIP compared with that of normal volunteers. These results suggest that the antivimentin antibody may be involved in the process of lung injury in IPF and NSIP.

Immunofluorescent localization of intermediate filaments (IFs) in helminths using anti-mammalian IFs monoclonal antibody

Intermediate filaments (IFs) make up the cytoskeleton of most eukaryotic cells. In vertebrates, a number of IF proteins have been identified, showing distributions unique to tissue or cell type. Information on helminth IFs is limited to some nematode species. To observe immunofluorescent localization of IFs in helminth tissues, we selected a murine hybridoma clone producing IgM antibody to multiple types of mammalian IF proteins and examined cross-reactivity to helminth proteins. The selected monoclonal antibody (HUSM-9) cross-reacted well with IFs from nematode species such as Toxocara canis, Dirofilaria immitis, Anisakis simplex, and Trichinella britovi; strong immunofluorescence on cryostat sections was detected in the hypodermis, cords, body muscle, smooth muscle of the uterus, and other epithelial structures. In platyhelminths, i.e., adult Schistosoma mansoni, larval Taenia taeniaeformis, adult Taenia crassiceps, and Echinococcus multilocularis protoscolex, the reactivity was weaker than in nematodes, and localized in the body wall muscle and subtegumental tissue. Western blotting of 8 M urea extracts of parasites with the antibody detected a pair of clear bands in nematodes but not in S. mansoni or the cestodes. These results might be explained by sparse distribution of IFs in platyhelminths, or low affinity of the used antibody to platyhelminth IF proteins, or both.

Anti-smooth muscle antibody in clinical human and experimental animal Mycoplasma pneumoniae infection

Autoantibody formation is possibly integral to the development of non-respiratory manifestations of acute Mycoplasma pneumoniae infection. We sought to confirm the occurrence of smooth muscle antibodies (SMA) in humans with acute Myc. pneumoniae respiratory infection and furthermore to assess whether similar autoantibodies would develop in a hamster model of respiratory infection. Paired sera from 21 patients with acute infection were assayed for SMA by immunofluorescence on mouse kidney/stomach substrates. The frequency of SMA was then determined for 52 paediatric patients with acute Myc. pneumoniae infection and 16 controls, and for sera from a hamster model of infection. Five of 21 paired sera had an increment in SMA between acute and convalescent specimens. At a screening dilution of 1:40, 18/52 infected and 0/16 controls had positive sera (P = 0.003); positive specimens demonstrated IgG rather than IgM SMA. In the hamster model of Myc. pneumoniae respiratory infection, significant IgG SMA increases occurred in 7/19 infections but not in 11 controls (P = 0.02). Immunoblotting did not identify actin as the substrate for SMA. Smooth muscle antibody increases are found in a significant minority of Myc. pneumoniae-infected humans and hamsters. A role for SMA in the pathogenesis of Myc. pneumoniae infection remains to be defined.

Anticentriolar autoantibodies in children with central nervous system manifestations of Mycoplasma pneumoniae infection

Serum samples from 49 children with acute Mycoplasma pneumoniae infection were screened for the presence of antibodies to mitotic spindle apparatus. None of these serum samples showed such antibodies at a screening dilution of 1:40, though anticentriolar antibodies at titres of 1:320 were observed in two children with acute cerebellar dysfunction. Anticentriolar antibodies may play a part in the pathogenesis of CNS disease associated with M pneumoniae infection.

Mycoplasma pneumoniae lacks immunologically-active eukaryotic actin-like antigens

Mycoplasma pneumoniae was tested for immunologically active eukaryotic actin-like antigens with the use of both polyclonal and monoclonal anti-actin antibodies. No reactivity was demonstrable. Monoclonal antibody OC2F5, which reacts with a M. pneumoniae antigen that co-migrates with actin in one-dimensional sodium dodecyl sulphate polyacrylamide electrophoresis, did not recognize actin. Organism-specific actin antigens are not likely to be responsible for the development of smooth muscle antibodies during acute M. pneumoniae infection.

Antibodies to cytoskeletal proteins in patients with Crohn's disease

The immunologic basis of inflammatory bowel disease has been the focus of interest of a series of studies on Crohn's disease and the process of immune sensitization at the gastrointestinal mucosal level is functionally poorly understood. To date only few contradictory reports concerning the incidence of autoantibodies in patients with this disease exist. The aim of this study was to investigate the sera drawn from 60 patients suffering from biopsy-proven Crohn's disease to evaluate the prevalence of autoantibodies against nuclear antigens and cytoskeletal proteins. Using standard methods, no anti-nuclear antibodies or antibodies to extractable nuclear antigens could be detected. All sera were also negative for antibodies to double-stranded DNA, anti-mitochondrial antibodies, and antibodies to gastric parietal cells. Using sensitive enzyme-linke immunosorbent assays with purified antigens and Western blotting with cytoskeletal proteins of human intestinal cells, the following antibodies could be demonstrated: cytokeratin 18 autoantibodies (IgG 20.0%; IgM 6.7%; IgA 13.3%), actin antibodies (IgG 36.7%; IgM 48.3%, IgA 26.7%), desmin antibodies (IgG 6.7%; IgM 15.08%; IgA 5.0%), vimentin antibodies (IgG 3.3%; IgM 16.7%; IgA 10.0%) and tropomyosin antibodies (IgG 3.3%; IgM 3.3%, IgA 5.0%). Statistically significant correlations could be found for levels of cytokeratin 18 antibodies (IgM-type) and the BEST index of activity, and for levels of desmin antibodies (IgM-type) and the van HEES index of activity. Highest levels could be measured for actin antibodies (IgG-type) in patients with isolated disease manifestation in the colon. The mechanism of induction of autoantibodies against cytoskeletal components in Crohn's disease still remains obscure. Unmasking of hidden antigens after cell injury during the inflammatory process of disease might lead to sensitization and antibody production. The pattern of antibodies in patients with Crohn's disease seems to be different compared with that of connective tissue diseases.

Relation of antivimentin antibodies to anticardiolipin antibodies in systemic lupus erythematosus

Tests for antivimentin antibodies (AVA) were performed on 50 systemic lupus erythematosus (SLE) and 63 control sera by indirect immunofluorescence and enzyme linked immunosorbent assay (ELISA). The prevalence was significantly raised in SLE (38% and 50% of sera positive for IgM-AVA and IgG-AVA, respectively, by immunofluorescence; 36% and 64% of sera positive for IgM-AVA and IgG-AVA, respectively, by ELISA) in comparison with the control sera. A significant correlation existed between IgM-AVA, on the one hand, and anticardiolipin antibodies (ACA) and anti-single-stranded DNA (ssDNA), on the other. A stepwise principal component analysis demonstrated that IgM-AVA and IgG-AVA accounted for 71% of the total variance in SLE (50 patients x 5 parameters = total variance). Twenty ACA positive serum samples from patients with syphilis were therefore tested for the presence of AVA, but hardly any were found to be positive. IgM-AVA from patients with SLE were inhibited by cardiolipin and absorbed with ssDNA. An association between AVA positivity and arthralgia was also shown in SLE.

A patient with lepromatous leprosy and anticytoskeletal antibodies

Sera from 34 patients with lepromatous leprosy were screened for the presence of autoantibodies by indirect immunofluorescence using two epithelial cell lines, PTK2 and HEp2, as substrates. Indirect immunofluorescence staining of both substrates with the serum of a patient with lepromatous leprosy revealed a cytoplasmic intermediate filament staining pattern. After exposure of PTK2 cells to colchicine, the filaments collapsed into thick perinuclear coils, confirming the presence of intermediate filament reactivity. Immunofluorescence of rat fibroblasts with the same serum also revealed an intermediate filamentous staining pattern. Human keratinocytes exposed to the patient's serum revealed a diffuse cytoplasmic staining pattern. Our study suggests the presence of autoantibodies to cytoskeletal intermediate filaments or to molecules associated with vimentin and possibly keratin subunit proteins in the serum of a patient with lepromatous leprosy.

Autoantibodies to the mitotic spindle apparatus in Mycoplasma pneumoniae disease

Antibodies to the mitotic spindle apparatus (MS) have been detected in only a very few patient sera studied for antinuclear antibodies by routine screening (G. A. McCarty, D. W. Velencia, and M. J. Fritzler, J. Rheumatol. 11:213-218, 1984). We found anti-MS antibodies to be quite common in sera from patients with Mycoplasma pneumoniae, especially in those who developed cold agglutinins (71%). Absorption experiments indicated that the formation of anti-MS antibodies is not triggered by epitopes on the M. pneumoniae surface. These antibodies were distinct from cold agglutinins, antibrain antibodies, and smooth-muscle antibodies. All patients previously reported to harbor anti-MS had clinical features compatible with a diagnosis of systemic lupus erythematosus, rheumatoid arthritis, or an evolving connective-tissue disorder. Such systemic disorders might develop in a small proportion of patients who have had M. pneumoniae illness.

Natural IgM and IgG autoantibodies to epidermal keratins in normal human sera. I: ELISA-titration, immunofluorescence study

This paper presents a study of autoantibodies (autoAB) to keratins and to epidermis by a double approach associating a specific immunoenzymatic technique and immunofluorescence. The existence of natural autoAB to keratins in all normal human sera was asserted and the heterogeneity of natural autoAB to the epidermis explored. By a sensitive enzyme-linked immunosorbent assay we detected natural IgM and IgG autoAB to keratin polypeptides extracted from human plantar stratum corneum (SC) in 60 randomly selected normal human sera. The interindividual variation factors of their titers were about 100X in IgM and 50X in IgG antikeratin (AK) autoAB. The IgM and IgG AK autoAB titers varied independently. By a semiquantitative indirect immunofluorescence assay we detected in these sera IgM and IgG autoAB that labeled normal epidermis according to various morphologic patterns. The IgG autoAB labeled SC and suprabasal layers (SBL) in 57.4% of sera, SC in 20.4% and SBL in 7.4%. The IgM autoAB labeled SC and SBL in 52% of sera, SC in 24%, SC and SBL plus basal layer (BL) in 18%, and SBL in 2%. Like the titers, the patterns of IgM and IgG autoAB to epidermis were found to be unrelated. The IgG AK autoAB titers were found to significantly correlate only with the IgG autoAB directed to SC + SBL; the IgM AK autoAB titers only with the IgM autoAB directed to SC + SBL + BL. This showed that these patterns of labeling are typical for AK autoAB and that autoAB to SC, which could not be related to AK autoAB, exist in some normal sera. Antikeratin and antiepidermis IgM autoAB titers were found to be strongly correlated to total amounts of IgM assayed by radial immunodiffusion, indicating that the synthesis of these natural IgM autoAB vary in the same way as that of general IgM synthesis. For the AK and antiepidermis IgG autoAB, however, the same correlation to total serum IgG was found to be much weaker.

Antibody to intermediate filaments of the cytoskeleton in patients with Behçet's disease

Antibodies to 10-nm intermediate filaments (anti-IF) were determined in the sera of 30 patients with Behçet's disease (BD), in addition to C-reactive protein and C9, and an attempt has been made to determine whether the presence of anti-IF indicate disease activity. The vimentin type of anti-IF was found to be positive in 14 out of 30 patients with BD (47%), whereas it was positive in 35% of the patients with rheumatoid arthritis (20 cases), 16% of the patients with systemic lupus erythematosus (19 cases) and in only 9% of the normal controls. The anti-IF were predominantly IgG class and the titers in BD were significantly higher than those in normal controls. Out of the 14 patients with anti-IF, 10 showed significantly increased levels of serum C9 and 8 showed increased levels of CRP activity. Only one patient showed increased C9, but was negative for anti-IF and CRP. The presence of anti-IF in the patients' sera was found to be a more sensitive indicator, though not specific, for the clinical assessment of disease activity.

Assay of measles virus IgM and IgG class antibodies by use of peroxidase-labelled viral antigens

Purified measles virions, nucleocapsid protein and crude lysate of measles infected cells were labelled with horseradish peroxidase, and used for the detection of IgM and IgG antibodies to measles virus by direct enzyme immunoassay. The assays consisted of three layers: anti-human IgM or IgG immunoglobulins on solid-phase, test serum specimen and enzyme labelled viral antigen. For the expression of the results, a standard curve was included in each test and the O.D. values were changed to arbitrary antibody units. Specificity and sensitivity of the assays were compared with indirect EIAs. The specificity studies included a collection of serum specimens containing either rheumatoid factor, antinuclear antibodies or IgM antibody specific for other viruses. The assays proved both reliable and simple to perform and sensitivity was slightly higher than that for indirect EIAs. However, specificity was dependent on the purity of the viral antigens. When crude infected cell lysate antigen was used, some nonspecific results were obtained, particularly with serum specimens containing antinuclear antibodies. When virion or nucleocapsid protein were used, no nonspecific reactions were obtained.

Anticytoskeletal autoantibodies in the connective tissue diseases

The sera of 103 patients with connective tissue diseases were studied for the presence of anticytoskeletal antibodies by using an indirect immunofluorescence method. PTK2 cells fixed with paraformaldehyde and digitonin were used as substrate. Antibodies to intermediate filaments were detected in sera of 85.7% of polymyositis/dermatomyositis (PM/DM), 62.8% of systemic sclerosis, 54.5% of rheumatoid arthritis, and 37.5% of systemic lupus erythematosus patients, and in 42.5% of normal sera. High titers of these antibodies, which were IgM, were present in 30% of patients' and 5% of normal sera. Antibodies to microfilaments were present in 11.6% of patients' sera and absent in all control sera. These antibodies were IgM or IgG. The switch from an IgM to an IgG antibody was observed in 1 patient. An IgG antibody to the spindle poles and midbody of mitotic cells was present in the serum of 1 patient with the CREST syndrome (calcinosis, Raynaud's phenomenon, esophageal dysmotility, sclerodactyly, telangiectasias). Antibodies to intermediate filaments and to microfilaments occur commonly in the connective tissue diseases, particularly in PM/DM, and are not detected with substrates or fixation methods used in routine antinuclear antibody testing.

Antigenic mimicry of mammalian intermediate filaments by mycoplasmas

A murine monoclonal antibody raised against Mycoplasma hyorhinis specifically reacted by indirect immunofluorescence with mammalian intermediate filaments. The antibody recognized a related epitope on a 74,000-molecular-weight protein of M. hyorhinis and on components of similar size from other pathogenic mycoplasmas. This defines a shared antigenic structure of interest in autoantibody development during mycoplasmal diseases.

Comparison of nonspecific reactivity in indirect and reverse immunoassays for measles and mumps immunoglobulin M antibodies

Serum specimens collected from patients convalescing from acute measles or mumps infections, other viral infections, or rheumatoid arthritis and from blood donors were tested in indirect and reverse assays for measles and mumps immunoglobulin M (IgM) antibodies. All the samples from patients convalescing from acute mumps and measles infections gave positive IgM results in both tests. However, 6% of sera from patients recovering from other viral infections, 68.4% of sera from patients with rheumatoid arthritis, and 5.6% of sera from normal blood donors gave false-positive results by the indirect measles IgM enzyme immunoassay (EIA). By the indirect mumps IgM EIA, 9% of sera from other viral infections, 70.1% of sera from patients with rheumatoid arthritis, and 5.6% of sera from normal blood donors gave false-positive reactions. The reverse test system for measles IgM gave false-positive results in 1.5% of sera from the group with other viral infections, and the reverse mumps EIA gave false-positive results in 0.9% of the patients. Other sera groups did not react in either measles or mumps reverse IgM assays. The results indicated that although nonspecific reactions are frequent in indirect IgM tests for viral antibodies, such reactions are rarely encountered when reverse IgM EIA tests are employed.

Immunofluorescent sites in vero cells infected with the flavivirus Kunjin

The sites of replication and of accumulation of viral macromolecules were examined using fluorescent antibodies to viral products and to cell organelles. Synthesis of envelope protein and its accumulation in a narrow rim around the nucleus were detected at 4 hours post infection; concurrently, a progressive change was observed in the rough endoplasmic reticulum from a fine to a coarse network emanating from around the nucleus. This change in the network was visible by light microscopy. The immunofluorescent sites of viral RNA synthesis, located by use of anti-double stranded RNA, extended from the perinuclear region in another fine network which included many small foci or vesicles; these sites were also visible by light microscopy late in infection. None of these changes were associated with any visible redistribution of actin, intermediate filaments or microtubules, and no nuclear involvement was detected. However, when microtubules were disrupted by vinblastine treatment of cells, the distribution of the immunofluorescent sites of viral RNA synthesis was modified and the virus yield was reduced by at least 10-fold. These results confirmed our biochemical studies showing separation of viral sites of RNA synthesis and translation, and the accumulation of envelope protein in nuclear-associated membranes. The relevance of these observations is discussed in relation to the reports of specific membrane structures induced in flavivirus-infected cells.

Detection of IgM antibodies to measles virus by enzyme-immunoassay

A method of solid-phase enzyme-immunoassay (EIA) with horseradish-peroxidase-conjugated anti-mu-globulin was used to determine IgM antibodies to measles virus in human sera. Antigens prepared from measles-infected and noninfected Vero cells passively adsorbed to polystyrene cuvettes were both important for the tests, because sera from many patients convalescing from viral infections and sera from rheumatoid arthritis patients were able to bind to control antigen. Sera from measles patients, patients with other viral infections, rheumatoid arthritis (RA) patients, and from blood donors were tested in a dilution of 1:200. Almost all of the acute-phase measles sera (37/38) were positive. The first measles-IgM-negative specimen was found 9 weeks after the onset of rash. Seven percent (15/213) of patients with other viral infections gave positive results in these IgM tests. False-positive reactions were also found in 33 of 51 (65%) sera from RA patients. This nonspecific binding could be abolished by absorptions with latex-IgG particles. This treatment did not have any effect on specific IgM. The IgM-EIA test developed for measles virus antibodies, which requires only a single serum specimen, appears to be a useful diagnostic method for routine virus laboratories.

Human monoclonal IgM with autoantibody activity against intermediate filaments

Monoclonal IgMs from two patients with Waldenström macroglobulinemia were found to react with intermediate filaments. This was shown by (a) immunostaining of various tissues and cultured cells and (b) immunological characterization of the reactive antigen after blotting of polypeptides separated from total cell extracts by gel electrophoresis or purified intermediate filaments on nitrocellulose sheets. One monoclonal IgM had an activity directed only against vimentin, whereas the other reacted with four different classes of intermediate filaments--vimentin, desmin, glial fibrillary protein, and keratins. All of the reactivity of the latter IgM was absorbed by purified vimentin, suggesting that different classes of proteins of intermediate filaments share common antigenic determinant(s). The significance of such autoantibody activity of human monoclonal IgM is discussed in the light of the startling frequency of IgM anti-intermediate filaments antibodies in various diseases.

Cytoskeletal elements in mycoplasmas and other prokaryotes

This paper reviews the relationship of mycoplasmas to eubacteria, the question of whether mycoplasmas and eubacteria have a cytoskeleton, and whether the unique ultrastructural features of certain mycoplasmas function as a mitotic-like apparatus. Although cytochalasins have inhibitory effects on some mycoplasmas and eubacteria, there are no data indicating that eubacteria have an actin-like protein or other cytoskeletal element. However, the situation for the mycoplasmas remain confusing. While mycoplasma may not contain actin, the data do suggest the presence of other cytoskeletal elements.