Antibodies to nuclear lamins in autoimmune liver disease

Primary biliary cirrhosis: What do autoantibodies tell us?

Primary biliary cirrhosis (PBC) is a chronic, progressive, cholestatic, organ-specific autoimmune disease of unknown etiology. It predominantly affects middle-aged women, and is characterized by autoimmune-mediated destruction of small- and medium-size intrahepatic bile ducts, portal inflammation and progressive scarring, which without proper treatment can ultimately lead to fibrosis and hepatic failure. Serum autoantibodies are crucial tools for differential diagnosis of PBC. While it is currently accepted that antimitochondrial antibodies are the most important serological markers of PBC, during the last five decades more than sixty autoantibodies have been explored in these patients, some of which had previously been thought to be specific for other autoimmune diseases.

Characterization of the antibodies to p62 nucleoporin in primary biliary cirrhosis using human recombinant antigen

Reactivity of sera from patients with primary biliary cirrhosis (PBC) with a 60 kDa component of nuclear pore complexes (NPCs), purified by affinity chromatography on wheat-germ agglutinin (WGA)-Sepharose, was previously detected. Recently, clinical significance of the anti-NPC antibodies in PBC became evident. In the light of recent reports, indicating the correlation of the anti-NPC antibodies with severity and progression of the disease, the characterization of the reactive antigens is becoming essential in the clinical management of patients with PBC. Since accurate autoantibody detection represents one of the fundamental requirements for a reliable testing, we have generated a human recombinant p62 protein and validated an immunoprecipitation assay for the detection of anti-p62. We also demonstrated that the generated human recombinant p62 nucleoporin was modified by N-acetylglucosamine residues. More than 50% of tested PBC sera precipitated (35)S-radioactively labeled p62 recombinant nucleoporin and 40% recognized this recombinant antigen by immunoblotting. We compared the reactivity of PBC sera with rat and human nucleoporin. The incidence of anti-p62 nucleoporin positive PBC sera increased by 15% when human recombinant antigen was used. The titer of autoantibodies in p62-positive PBC samples strongly varied. Preadsorption of the PBC sera with p62 recombinant protein completely abolished their reactivity with the antigen. In conclusion, this study unequivocally proves that autoantibodies reacting with the 60 kDa component of NPCs target p62 nucleoporin and, more importantly, provide a better antigen source for future evaluations of the clinical role of anti-p62 in PBC.

Autoimmune cytopenias associated with autoantibodies to nuclear envelope polypeptides

A subset of anti-nuclear autoantibodies (ANA) are directed against nuclear envelope (NE) polypeptides and display by indirect immunofluorescence (IIF) a ring-like fluorescent pattern. We report herein 19 patients with autoimmune cytopenias associated with antibodies (Abs) to NE polypeptides. Anti-NE specificity was determined by immunoblot, using NE preparations and purified lamina fractions. Eleven sera reacted with lamin B(1), and two reacted with both lamin B(1) and an unidentified 150-kDa protein (p150). One serum reacted with only p150. Four sera reacted with lamins A and C, and one reacted with and an unidentified 52-kDa NE polypeptide (p52). Autoimmune cytopenias included hemolytic anemia (7 cases), thrombocytopenia (13 cases), and neutropenia (6 cases). Five patients had 2 (3 cases) or 3 (2 cases) different cytopenias. Antiphospholipid antibodies (APLA) were detected in 14 patients, 2 of whom experienced thromboembolic events. A liver disorder was present in 7 patients. Systemic lupus erythematosus and lupus-like syndrome were diagnosed in 11 and 2 patients, respectively. Cytopenias responded to steroids alone (13 patients), or together with intravenous immunoglobulins (2 patients), or cyclophosphamide (2 patients). Two patients did not require treatment. Our results suggest that anti-NE Abs need to be sought for in patients with peripheral cytopenias, particularly when they are associated with APLA and/or liver disorders. Their detection strongly suggests an autoimmune process. Such cytopenias are often manifestations of a lupus or lupus-like disease and are responsive to steroids.

Anti-nuclear envelope antibodies: Clinical associations

OBJECTIVES

Characterization of the clinical associations and clinical implications of antibodies reacting with antigens of the nuclear envelope.

METHODS

Description of an illustrative case and a MEDLINE search-assisted literature review of relevant cases.

RESULTS

With indirect immunofluorescence, autoantibodies directed against various antigens of the nuclear envelope stain the nucleus in a ring-like (rim) pattern. Autoantibodies against 5 antigenic components of the nuclear envelope have been described: anti-gp210, p62, lamina, lamina-associated polypeptides, and lamin B receptor. Antibodies to antigens of the nuclear pore complex, such as gp210 and p62, are highly specific (> 95%) for primary biliary cirrhosis and may aid in the serologic diagnosis of this condition, especially in cases in which antimitochondrial antibodies are not detectable. In contrast, antilamin antibodies are not disease-specific but seem to be associated with lupus anticoagulant or anticardiolipin antibodies, antiphospholipid syndrome, thrombocytopenia, autoimmune liver diseases, and arthralgia. High-titered antilamin antibodies help to define a subset of lupus patients with antiphospholipid antibodies who are at a lower risk of developing thrombotic events. In addition, preliminary data suggest that the presence of antilamin antibodies may be helpful in the diagnosis of chronic fatigue syndrome.

CONCLUSIONS

Each of the antibodies reacting with nuclear membrane antigens has its own spectrum of disease associations.

RELEVANCE

Determination of anti-nuclear envelope antibody pattern by indirect immunofluorescence, with subsequent determination of the specific antibody, carries important diagnostic and prognostic implications in various autoimmune conditions.

"Atypical p-ANCA" in IBD and hepatobiliary disorders react with a 50-kilodalton nuclear envelope protein of neutrophils and myeloid cell lines

BACKGROUND & AIMS

Atypical "antineutrophil cytoplasmic antibodies" (ANCA) are present in patients with ulcerative colitis (UC), primary sclerosing cholangitis (PSC), and autoimmune hepatitis (AIH). Recently, we showed that atypical p-ANCA react with nuclear envelope proteins of neutrophils. Based on this observation, we aimed to characterize the nuclear antigen recognized by atypical p-ANCA.

METHODS

We prepared cytoplasmic and nuclear extracts of human neutrophils, human HL-60, and murine 32D myeloid cells. Proteins were resolved by 1- and 2-dimensional gel electrophoresis. Reactive proteins were detected by immunoblotting with sera from 118 individuals (UC, 25; PSC, 28; AIH, 35; disease and normal controls, 30). Atypical p-ANCA (n = 64) were affinity-purified against the reactive protein and investigated for their immunofluorescence pattern using confocal microscopy.

RESULTS

Immunoblotting showed reactivity to a myeloid-specific 50-kilodalton nuclear protein with an isoelectric point of pH 6.0 detected in 92% (59 of 64) of the patients with inflammatory bowel or hepatobiliary diseases and atypical p-ANCA. Affinity-purified antibodies against the 50-kilodalton protein gave a nuclear rim-like fluorescence on myeloid cells examined by immunofluorescence microscopy. Affinity-purified antibodies did not recognize antigens in nonmyeloid cells.

CONCLUSIONS

Atypical p-ANCA in UC, PSC, or AIH recognize a 50-kilodalton myeloid-specific nuclear envelope protein.

Review: nuclear lamins--structural proteins with fundamental functions

The nuclear lamina is located between the inner nuclear membrane and the peripheral chromatin. It is composed of both peripheral and integral membrane proteins, including lamins and lamina-associated proteins. Lamins can interact with one another, with lamina-associated proteins, with nuclear scaffold proteins, and with chromatin. Likewise, most of the lamina-associated proteins are likely to interact directly with chromatin. The nuclear lamina is required for proper cell cycle regulation, chromatin organization, DNA replication, cell differentiation, and apoptosis. Mutations in proteins of the nuclear lamina can disrupt these activities and cause genetic diseases. The structure and assembly of the nuclear lamina proteins and their roles in chromatin organization and cell cycle regulation were recently reviewed. In this review, we discuss the roles of the nuclear lamina in DNA replication and apoptosis and analyze how mutations in nuclear lamina proteins might cause genetic diseases.

Atypical antineutrophil cytoplasmic antibodies with perinuclear fluorescence in chronic inflammatory bowel diseases and hepatobiliary disorders colocalize with nuclear lamina proteins

Antineutrophil cytoplasmic antibodies (ANCA) are frequently associated with chronic inflammatory bowel diseases (IBD) and hepatobiliary disorders. However, their target antigens have not been identified yet. Recently, we observed an atypical perinuclear ANCA fluorescence (p-ANCA) together with an intranuclear staining using ANCA-positive sera from patients with IBD and hepatobiliary disorders. This observation suggests that the target antigens are localized within the nucleus of neutrophilic granulocytes. To further investigate this hypothesis, we examined sera from patients with ulcerative colitis, primary sclerosing cholangitis, autoimmune hepatitis or systemic vasculitis on ethanol or formaldehyde-fixed neutrophils using confocal laser scanning microscopy and immunoelectron microscopy. Counterstaining with propidium iodide, a DNA-specific dye, showed that ANCA-positive sera in IBD and heptobiliary disorders react with intranuclear antigens at the nuclear periphery of the neutrophils. Double immunolabeling techniques revealed that nuclear lamina proteins, lamins A, C and B1, and lamin B receptor were colocalized with the antigen(s) recognized by atypical p-ANCA. No colocalization was observed with classical p-ANCA and antibodies against histones (H1-H4). Our study showed that atypical p-ANCA are antinuclear antibodies reactive with granulocyte-specific antigens present in the nuclear lamina.

Acute hepatitis caused by alverine associated with anti-lamin A and C autoantibodies

We report the case of a 67-year-old woman in whom onset and regression of acute hepatitis were closely related to the time of administration and withdrawal of the smooth muscle relaxant alverine. Antinuclear antibodies were positive, and their titer followed the course of hepatitis. They presented a smooth rim-like nuclear immunofluorescence staining pattern. Immunoblot assay showed that they were directed against lamin A and lamin C. This suggests that alverine should be added to the list of drugs known to produce acute hepatitis, and that drug-induced liver injury is a possible cause of antinuclear antibodies specific for lamin A and lamin C.

Autoantibodies to nuclear envelope antigens in chronic fatigue syndrome

We have identified and partially characterized the autoantibodies in sera of 60 patients with chronic fatigue syndrome. Approximately 52% of the sera were found to react with nuclear envelope antigens. The combination of nuclear rim staining observed in immunofluorescence microscopy and immunoblot analysis of highly purified nuclear envelope proteins provided initial characterization of these autoantibodies. Further characterization showed that some sera immunoprecipitated the in vitro transcription and translation product of a human cDNA clone encoding the nuclear envelope protein lamin B1. The autoantibodies were of the IgG isotype. The occurrence of autoantibodies to a conserved intracellular protein like lamin B1 provides new laboratory evidence for an autoimmune component in chronic fatigue syndrome.

Clinical associations of anti-lamin autoantibodies

BACKGROUND

The clinical associations of anti-lamin autoantibodies were first described in 1973. Since then a number of individual case reports and two small series have been published. These have suggested an association with connective tissue disorders and autoimmune liver disease.

AIMS

To identify the clinical and laboratory associations of anti-lamin autoantibodies in an Australian population.

METHODS

Retrospective review of routine antinuclear antibody testing between 1990-1994 for characteristics linear staining of nuclear envelope on indirect immunofluorescence on HEp-2 cells with clinical status defined by retrospective review of case records.

RESULTS

Twenty-eight patients were identified and the clinical status of 27 patients defined. Eleven patients had associated IgG anti-cardiolipin antibodies; anti-phospholipid syndrome was present in nine. Seven further patients had liver disease; five had autoimmune liver disease, with associated autoantibodies. The remaining nine patients had a diverse group of diseases. There was no correlation between the titre of the autoantibody and clinical status. An association with anti-cardiolipin antibodies was found although the cause remains obscure.

CONCLUSION

Anti-lamin autoantibodies, as identified by indirect immunofluorescence, are associated with a diverse group of diseases but particularly with anti-phospholipid syndrome and liver disease. Testing for anti-phospholipid antibodies and more specific markers of systemic lupus erythematosus and autoimmune disease, for example anti-dsDNA antibodies, anti-smooth muscle antibodies and anti-mitochondrial antibodies should be pursued when anti-lamin autoantibodies are detected.

Autoantibodies in hepatitis delta

Hepatitis delta virus infection is associated with a wide range of different autoantibodies. The humoral immune response in chronic hepatitis D is directed against the cytoskeleton, the nucleus, the nuclear lamina and the endoplasmic reticulum. Smooth muscle antibodies (SMA), basal cell layer antibodies (BCLA), stellate epithelial cell antibodies (SECA), thymic reticular cell antibodies (TRA), perithymocytic cell antibodies (PTA), and anti-calmodulin antibodies are reactive with constituents of the cytoskeleton. Antinuclear antibodies (ANA) and anti-lamin C antibodies recognize antigens of the nucleus and the nuclear lamina, respectively. Autoantibodies directed against antigens of the endodoplasmic reticulum (LKM) are also common in chronic hepatitis D. Recently, the major molecular target of LKM-3 autoantibodies was described as an epitope on UDP-glucuronosyltransferases of family 1. In view of the important role of UGTs in drug metabolism, LKM-3 autoantibodies represent a new model to study virus induced autoimmunity in man. Future studies should focus on the role of the host immune response and the clinical relevance of these autoantibodies in chronic hepatitis D.

Patterns of nuclear immunofluorescence and reactivities to recombinant nuclear antigens in autoimmune hepatitis

BACKGROUND/AIMS

Antibodies to nuclear antigens have not been fully characterized in autoimmune hepatitis. The aims of this study were to determine the different patterns of immunofluorescence associated with antinuclear antibodies and to correlate these patterns with reactivities to recombinant nuclear antigens and clinical manifestations of autoimmune hepatitis.

METHODS

Sera from 65 patients were tested by indirect immunofluorescence and by enzyme immunoassay for antibodies to recombinant centromere, ribonucleoproteins, and ribonucleoprotein complexes.

RESULTS

Homogeneous and speckled patterns of immunofluorescence occurred with similar frequencies (34% vs. 38%) in the majority of patients (72%). Patients with speckled patterns were younger and had higher serum aspartate aminotransferase levels at presentation than counterparts with other patterns. Antibodies to centromere (42%) and 52K ribonucleoprotein complex (23%) were the most common reactivities. Of the 35 patients with antibodies, 16 (46%) had multiple specificities. Individual reactivities were not associated with specific immunofluorescent patterns, and they did not identify patients with distinctive features.

CONCLUSIONS

Antinuclear antibodies produce mainly homogeneous and speckled patterns of immunofluorescence in patients with autoimmune hepatitis. Speckled patterns are associated with a younger age and greater aminotransferase activity. Multiple autoantibodies are frequently associated with each immunofluorescent pattern. Antibodies to centromere and the 52K ribonucleoprotein complex have a previously unrecognized high frequency and uncertain significance.

Autoimmune hepatitis: classification, heterogeneity, and treatment

Autoimmune hepatitis, a chronic necroinflammatory disorder of unknown etiology, is characterized by immunologic and autoimmunologic features. It is more prevalent in women than in men, and genetic factors appear to play a major role in the disease. The classification of autoimmune hepatitis is based on circulating autoantibody status; however, heterogeneity is distinguished not only by autoantibodies, but by histologic differences, a variety of clinical features, immunogenetic status, and probably pathogenesis. Presentation extends from the asymptomatic to the severely ill patient. Although patients may present with or without evidence of circulating autoantibodies, hyperglobulinemia is a rather consistent laboratory feature. Because the disease is generally steroid-responsive, therapeutic remission rates of 60-80% have been achieved with prednisone or a combination of prednisone and azathioprine, and many patients can be maintained with these drugs alone or in combination. There are no firm guidelines for decisions regarding withdrawal or reduction of medication. When treatment failures occur, orthotopic liver transplantation may be required.

Contemporary concepts for the clinical and laboratory evaluation of systemic lupus erythematosus and "lupus-like" syndromes

Systemic lupus erythematosus (SLE) is a nonorgan-specific autoimmune disease which affects multiple organ systems and is multifactorial in etiology. SLE is the prototypic systemic rheumatic disease with immune dysregulation characterized by (1) polyclonal activation of B-cells and (2) production of a large spectrum of autoantibodies with a marked preference for nuclear and intracellular antigens. The clinical and laboratory manifestations and criteria for classification and diagnosis of systemic lupus erythematosus, lupus-like syndromes, and various subsets of systemic lupus erythematosus, are reviewed. The differential diagnosis of SLE and related diseases is described with correlation of specific intracellular autoantibodies.

Cell cycle-associated autoantibodies: markers for autoimmunity and probes for molecular cell biology

Antinuclear autoantibodies are useful diagnostic markers for systemic autoimmune diseases and as probes for the molecular cell biology of nuclear proteins. Here, we review a subset of autoantibodies to nuclear and cytoplasmic proteins involved in the cell cycle. We propose a classification of these autoantibodies into S-phase (DNA Synthesis) and M-phase (Mitosis) autoantibodies. S-phase autoantibodies are represented by autoantibodies to PCNA (Proliferating Cell Nuclear Antigen), the auxiliary protein of DNA polymerase delta. M-phase autoantibodies are represented by autoantibodies to mitotic spindle components viz. centrosomes, condensed chromosomes, centromeres, mitotic spindle proper and intercellular bridge. We have included autoantibodies to nuclear lamins as M-phase autoantibodies as lamins play a key role in reversible breakdown and reformation of nuclear membranes during mitosis. The usefulness of these autoantibodies as diagnostic markers in systemic autoimmune disease is tempered by their presence in patients with "atypical" autoimmune diseases and in normal individuals. However, as molecular probes, they have proven to be unique and invaluable tools for shedding new light on the workings of the cell cycle.

Autoantibodies against integral membrane proteins of the nuclear envelope in patients with primary biliary cirrhosis

BACKGROUND/AIMS

Autoantibodies against nuclear membrane proteins have been identified in patients with primary biliary cirrhosis (PBC). The aim of the present study was to determine the incidence of these autoantibodies in patients with PBC and examine their significance.

METHODS

An assay using recombinant polypeptides was designed to unequivocally detect autoantibodies against gp210 and the lamin B receptor, integral proteins of the nuclear membranes.

RESULTS

Autoantibodies against gp210 were detected in 15 of 159 patients with PBC and 0 of 46 controls. Autoantibodies against lamin B receptor were detected in 2 patients with PBC and 0 controls. The presence of these autoantibodies had a sensitivity of 11% and specificity of 100% for the diagnosis of PBC. Autoantibodies against gp210 were present in 4 of 19 (21%) patients with PBC who did not have detectable antimitochondrial antibodies. Patients with PBC and gp210 autoantibodies had a higher incidence of associated arthritis.

CONCLUSIONS

Autoantibodies against gp210 and the lamin B receptor are present in approximately 10% of patients with PBC. These autoantibodies are highly specific for the diagnosis of PBC and may be useful in diagnosing individuals without antimitochondrial antibodies and in identifying a subgroup of patients with an increased incidence of associated arthritis.

Autoantibodies from patients with primary biliary cirrhosis recognize a restricted region within the cytoplasmic tail of nuclear pore membrane glycoprotein Gp210

Patients with primary biliary cirrhosis (PBC) frequently have autoantibodies against a 210-kD integral glycoprotein of the nuclear envelope pore membrane. This protein, termed gp210, has a 1,783-amino acid amino-terminal domain located in the perinuclear space, a 20-amino acid transmembrane segment, and a 58-amino acid cytoplasmic carboxy-terminal tail. We now demonstrate that autoantibodies from 25 patients with PBC that recognize gp210 react with the cytoplasmic carboxy-terminal tail while none react with unmodified linear epitopes in the amino-terminal domain. The epitope(s) recognized by autoantibodies from all 25 patients is contained within a stretch of 15 amino acids. The recognized amino acid sequence is homologous to the protein products of the Escherichia coli mutY gene and Salmonella typhimurium mutB gene with an exact identity of six consecutive amino acids, suggesting that anti-gp210 antibodies may arise by molecular mimicry of bacterial antigenic determinants.

Recognition of multiple epitopes in the coiled-coil domain of lamin B by human autoantibodies

The nuclear lamina of mammalian cells consists of three major proteins, lamins A, B and C, which form a fibrous meshwork interposed between the inner nuclear membrane and the chromatin. Sera from certain patients with systemic lupus erythematosus (SLE) and autoimmune liver disease contain high titers of autoantibodies against lamin B. We have shown previously that anti-lamin B autoantibodies in SLE recognize epitopes highly specific for lamin B, even though lamin B and lamins A/C are highly homologous proteins. To further characterize the specificities of these autoantibodies, fusion proteins carrying fragments of lamins B and C were tested for reactivity with SLE sera by immunoblotting. Five distinct epitopes of lamin B were identified, at least four of which were located in the highly conserved coiled-coil rod domain. Epitopes located on amino acids (AA) 80-193 and 245-303 were recognized by 4/10 and 8/10 anti-lamin B positive sera, respectively. Affinity purified anti-lamin B autoantibodies reacted preferentially with lamin B, indicating that they recognized mainly portions of lamin B that differ from lamins A and C. On the contrary, most of the affinity-purified anti-lamin C autoantibodies from SLE sera cross-reacted with lamin B, suggesting that the anti-nuclear lamina immune response in these patients is directed primarily against lamin B. The preferential reactivity of these sera with multiple epitopes specific to lamin B, and the finding that the autoantibodies to lamins A and C present in some of these sera cross-react with lamin B suggest that autoantibodies to lamin B are generated in response to the authentic lamin B protein rather than a cross-reactive foreign protein.

Characterization of two human monoclonal IgM antibodies that recognize nuclear lamins

Using immunofluorescence and immunoblotting techniques, we have identified monoclonal IgM lambda from two patients that are specific for lamins A and C and lamin B, respectively. Lamins A, B, and C are peripheral membrane proteins of the nuclear envelope with structural similarities to cytoplasmic intermediate filament proteins. When studied by indirect immunofluorescence on rat tissues, the serum containing anti-lamin B IgM stained smooth and striated muscles in addition to nuclear envelopes. Lamin B antibodies affinity purified from this serum were able to label muscle cells, suggesting that lamin B shares an epitope(s) with an unidentified muscular component(s). Since in an enzyme-linked immunosorbent assay there was no reactivity with a panel of proteins which are frequent targets of "natural" antibodies, these monoclonal IgM appear to belong to the rare category of IgM that possess a restricted specificity.

Autoantibodies to major and minor nuclear lamins are not restricted to autoimmune diseases

Autoantibodies to lamins, the major polypeptide components of the nuclear lamina, have been reported in selected sera from patients with autoimmune diseases, including anti-lamin B in systemic lupus erythematosus (SLE) and anti-lamins AC in autoimmune chronic active hepatitis (CAH). We have studied the frequency, specificity, and isotypy of autoantibodies to major and minor lamins by immunoblotting on purified rat liver lamins in 190 sera from normal controls (n = 62), rheumatic disease controls (n = 42), and autoimmune disease patients (n = 86). The frequency of anti-lamin in normal controls was 85.5%, and ranged from 77 to 100% in the other groups. Anti-lamin frequency was not related to age, sex, or disease duration. Reactivity with lamin A or with minor lamins only was observed with 7 various sera and 2 normal sera, respectively. Between groups, the proportions of reactive sera were not different for lamins AC (18-47%) and for lamin B (22-36%). In particular, anti-lamin B and anti-lamins AC were not more common in SLE or CAH than in normal sera. The most frequent lamin specificity of SLE sera was anti-lamins ABC. Anti-lamin isotypes were IgG and/or IgM. Titers of IgM antibodies were not higher in any group. However, IgG anti-lamin titers were higher in CAH than in normal, ankylosing spondylitis, or SLE sera. The highest end point titers (greater than or equal to 1:3200) were observed with CAH, SLE, and rheumatoid arthritis (RA) sera with IgG anti-lamins AC, B, or ABC, or with IgM anti-lamins ABC. None of these SLE and RA patients had evidence of liver disease. Reactivity with minor lamins was more frequent in CAH. We conclude that anti-lamin autoantibodies are present in sera from most individuals and that the highest titers are found in sera from patients with autoimmune diseases.

Clinical manifestations in patients with autoantibodies specific for nuclear lamin proteins

IgG antibodies to nuclear lamin proteins have been found in serum samples from 31 patients using immunofluorescence on HEp-2 cells, Western blotting, and enzyme-linked immunosorbent assay, performed against a nuclear lamina preparation from Ehrlich ascites tumor cells. Antilamin antibodies were most prevalent among patients with nonerosive, seronegative polyarthritis, or patients showing serum antiphospholipid reactivity as well. It is possible that anti-lamin antibodies may thus be a marker for a subgroup of polyarthritis patients who have a different prognosis from that of those with seropositive rheumatoid arthritis. The mechanism for the combined occurrence of anti-lamin and antiphospholipid autoantibodies is obscure. Future studies will answer whether these two antibodies represent a distinct antibody profile in patients with antiphospholipid antibody syndrome.

Human autoantibodies to lamin B receptor are also anti-idiotypic to certain anti-lamin B antibodies

Autoantibodies reactive with nuclear envelope proteins are mainly detected in human sera from patients with liver diseases. Some of these antibodies are directed to lamin B, lamins A and C, or to the lamin B receptor (LBR). We show here that the latter one are anti-idiotypic to certain anti-lamin B antibodies. Using an enzyme-linked immunosorbent assay specific for lamins we found that serum M containing anti-LBR antibodies inhibited the binding to lamins of anti-lamin B autoantibodies from three of five sera tested. Similar results were obtained using patient's M purified IgG. The binding of monoclonal IgM, lambda anti-lamin B antibodies produced by a lymphoblastoid cell line derived from the patient's blood lymphocytes was also inhibited. Absorption of serum M with nuclei abolished the inhibitory activity. No inhibition was recorded with normal sera or sera containing other antinuclear specificities. Anti-LBR antibodies did not alter the binding to lamins of sera containing anti-lamins A and C antibodies. Altogether these findings demonstrate that anti-LBR antibodies are also combining site related anti-idiotypic antibodies (Ab2) to certain anti-lamin B antibodies, provide further evidence for discrete specificities among anti-lamin B antibodies and suggest that the occurrence of autoantibodies to nuclear envelope antigens may be under idiotypic regulation.

Diversity and origin of rheumatologic autoantibodies

A hallmark of sera from patients with systemic rheumatic diseases is the presence of circulating autoantibodies directed against nuclear antigens. The identification of the antigens binding to these antibodies has provided the cell biologist and the immunologist with important tools to study cell structure, cell function, and the processes underlying the immune response. Through the elucidation of autoantibody specificities, the clinician has been provided with a better appreciation of the diagnostic and prognostic significance of autoantibodies. Many autoantigens, including those directed against components in the nuclear matrix, chromosomes, Golgi apparatus, and other intracellular antigens, are not yet characterized nor is their clinical significance established. The mechanisms leading to the breakdown of tolerance and the appearance of autoantibodies are not fully understood. Molecular mimicry at an interspecies or an intracellular level may be involved in altering immune tolerance. On the other hand, studies of epitopes on human autoantigens has provided compelling evidence that most autoantibody responses seen in systemic rheumatic diseases are driven by endogenous antigen.

Onset and regulation of anti-lamin B autoantibody production is independent of the level of polyclonal activation

Anti-lamin B autoantibodies are associated with both systemic lupus erythematosus (SLE) and autoimmune liver disease. We examined the possibility that the underlying clinical feature in patients with anti-lamin B autoantibodies might be chronic autoimmune liver disease, and whether the hypergammaglobulinemia present in both disorders is involved in generating anti-lamin B autoantibodies. A lamin B fusion protein (MLB1), consisting of amino acids 77-533 of lamin B fused to TrpE, was used to screen sera from 84 patients with SLE for anti-lamin B autoantibodies. 3/4 prototype human lamin B antisera, 5/84 SLE sera (6%), and 0/30 sera from healthy individuals reacted with MLB1 on immunoblots at a 1:500 dilution. Of the 9 anti-lamin B autoantibody positive patients studied, all but 1 fulfilled at least four ARA criteria for SLE. None of the patients displayed evidence of chronic autoimmune liver disease, suggesting that autoimmune liver disease is not strongly associated with anti-lamin B antibodies in SLE. In SLE, as in "lupoid hepatitis", anti-lamin B autoantibodies are often produced transiently during periods of increased disease activity. Although polyclonal hypergammaglobulinemia is also associated with increased activity of both diseases, anti-lamin B autoantibody production in 2 patients was independent of total immunoglobulin levels, antibodies to irrelevant proteins, and production of some other autoantibodies. Thus, polyclonal activation is insufficient to explain either the initiation or regulation of anti-lamin B autoantibody production, supporting the hypothesis that antinuclear antibodies are antigen-selective.

Cellular intermediate filament networks and their derangement in alcoholic hepatitis

Intermediate filaments are major components of most eukaryotic cells that form from the polymerization of protein subunits that are expressed in tissue and development specific fashions. The interactions of intermediate filaments with a myriad of other cellular proteins and structures give rise to a complex overall cellular architecture that is likely responsible for cellular well-being. The mature 10-nm filaments are relatively stable cellular structures, but the intermediate filaments undergo major morphological and biochemical changes, especially during mitosis, differentiation, and in response to certain drugs. Evidence exists that hepatocyte intermediate filaments (keratin filaments) are deranged in alcoholic hepatitis, an inflammatory liver disease of alcoholics and heavy spree drinkers. The classical and characteristic pathological hepatocyte inclusion bodies of alcoholic hepatitis, Mallory bodies, are composed in part of normal keratins that likely derive from the pre-existing hepatocyte intermediate filament network. It is unclear if intermediate filament network derangement in alcoholic hepatitis is directly caused by the actions of ethanol or its metabolites on intermediate filaments or their associated structures, or whether alcohol causes a cellular insult or injury elsewhere and a subsequent response (e.g., immune) causes intermediate filament network derangement. The precise mechanisms responsible for intermediate filament derangement remain to be elucidated; however, experimental data exist that support and refute several hypotheses. Hopefully, further studies will help determine a better overall understanding of the abnormalities of intermediate filaments and their relationship to the pathophysiology of alcoholic hepatitis and other diseases.

Antibodies to nuclear lamin C in chronic hepatitis delta virus infection

Sera of patients with chronic hepatitis delta virus infection stained the nuclear periphery in indirect immunofluorescence. Using proteins of isolated nuclei, isolated nuclear matrices, the nuclear pore complex-lamina fraction and purified lamins A and C as antigen source in immunoblotting experiments, nuclear lamin C was identified as the reactive antigen. Most sera tested (8 of 10) recognized nuclear lamin C exclusively, but not the nuclear lamins A and B. Antibodies reacting with both nuclear lamins A and C, which share extensive sequence homologies, have been reported to occur in autoimmune hepatitis and primary biliary cirrhosis. The present findings suggest that the novel autoantibody associated with chronic hepatitis delta virus infection recognizes an epitope localized in the short carboxyterminal region of nuclear lamin C.

Identification and characterization of autoantibodies against the nuclear envelope lamin B receptor from patients with primary biliary cirrhosis

We have identified autoantibodies from two patients with primary biliary cirrhosis (PBC) that recognize the nuclear envelope of mammalian cells on indirect immunofluorescence microscopy. These antibodies bind to a 58-kD integral membrane protein (p58) of the turkey erythrocyte nuclear envelope, which has been previously identified as a membrane receptor for lamin B (Worman, H. J., J. Yuan, G. Blobel, and S. D. Georgatos. 1988. Proc. Natl. Acad. Sci. USA. 85:8531). The antibodies also bind to a 61-kD integral membrane protein (p61) of the rat liver nuclear envelope. Affinity-purified antibodies eluted from turkey p58 bind to rat p61, showing that the two proteins share an epitope(s) and that p61 is likely the rat liver lamin B receptor. In human nuclear envelopes, the antigen recognized has an apparent molecular mass close to that of avian protein. These findings, along with the previous discovery of autoantibodies against an integral membrane glycoprotein (gp210) of the nuclear pore membrane in patients with PBC, suggest that antibodies against integral membrane proteins of the nuclear envelope are characteristic of a subset of patients with PBC.

Autoantibodies to lamins A and C in sera of patients showing peripheral fluorescent antinuclear antibody pattern on HEP-2 cells

Lamins A, B, and C are the major proteins of a polymeric structure called nuclear lamina, which is intercalated between chromatin and the inner membrane of the nuclear envelope. Using immunofluorescence on HEp-2 cells, specific enzyme-linked immunosorbent assay, and Western blotting performed against nuclear lamina preparation from Ehrlich ascites tumor cells, we characterized three patients, whose sera contained antibodies to nuclear lamins. The reaction pattern observed in two of the patients may result from single or combined occurrence of anti-lamin A and C antibodies. The third patient had antibodies that probably recognized an epitope in the carboxy-terminal region of lamin C. The sera were donated by a heterogeneous group of patients, and no common clinical or laboratory signs seemed to link them together.

Autoantibodies against different histone H1 subtypes in systemic lupus erythematosus sera

The H1 histones represent the most heterogenous class of histone proteins. In this study, we analyzed the specificity of human antibodies against 6 H1 subtypes. H1 histones from rat organs were separated by reverse-phase high performance liquid chromatography and used as antigens in immunoblotting experiments. Sera containing anti-histone H1 antibodies were obtained from patients with systemic lupus erythematosus. Of the 9 sera tested, 2 reacted with only 1 H1 subtype. The other sera recognized different combinations of H1 subtypes. Only 1 serum reacted with all 6 H1 subtypes. Histones H1.5 and H1.1 were the subtypes most frequently recognized by the human autoantibodies. Our data indicate that human anti-H1 antibodies represent a heterogenous population, directed mainly against epitopes localized in the variable region of the H1 molecule.

Identification of the platelet glycoprotein IIb/IIIa complex as a target antigen in primary biliary cirrhosis-associated autoimmune thrombocytopenia. Evidence that platelet-reactive autoantibodies can also bind to the mitochondrial antigen M2

A 67-year-old woman with a 4-year history of primary biliary cirrhosis (PBC) unexpectedly developed autoimmune thrombocytopenia. The platelet-bound IgG antibody was eluted from the patient's platelets to determine the platelet target antigen. The autoantibodies were found to precipitate the platelet glycoprotein complex IIb/IIIa of autologous and allogeneic platelets. A further precipitate of 70 kDa was detectable under reducing conditions. In addition, platelet-reactive antibodies bound to the 70 kDa mitochondrial antigen M2. No cross-absorption studies were performed to confirm that a single antibody reacted with both antigens. Computer analysis of published peptide sequences of the mitochondrial protein and the platelet GPIIb/IIIa complex showed partial amino acid sequence homology suggesting the possibility of a common antibody binding site. These findings suggest a relationship between the development of autoimmune thrombocytopenia in PBC and the underlying liver disease.

Antinuclear antibodies directed to a 200-kilodalton polypeptide of the nuclear envelope in primary biliary cirrhosis. A clinical and immunological study of a series of 150 patients with primary biliary cirrhosis

Antinuclear antibodies giving a perinuclear fluorescence and directed to a 200-kilodalton polypeptide of the nuclear envelope have been described in primary biliary cirrhosis. The purpose of this study, based on a series of 150 patients with primary biliary cirrhosis, was to ascertain the prevalence of these antibodies and to compare patients with and without these antibodies. Antinuclear antibodies giving a perinuclear fluorescence were demonstrated in 43 of the 150 patients (29%); antibodies directed to the 200-kilodalton polypeptide of the nuclear envelope were found in 40 of these 43 patients. Asthenia, arthralgia, associated extrahepatic diseases, Raynaud's phenomenon, and other antinuclear specificities were significantly less common, and titers of antimitochondrial antibodies were significantly lower in patients with antibodies directed to the 200-kilodalton polypeptide of the nuclear envelope than in patients without these antibodies. Clinical outcome, liver tests, and histological lesions did not significantly differ in patients with and without these antibodies.

Autoantibodies to lamins in rheumatoid arthritis

The presence of autoantibodies reacting with lamins A and C was demonstrated in sera from 2 patients with rheumatoid arthritis (RA). One patient developed antilamin antibodies several years after being diagnosed as having RA; she was also found to have chronic active hepatitis. The second patient had severe nodular RA. We describe the other serologic findings in these 2 patients and discuss the relationships between antilamin antibodies and RA.

In vitro posttranslational modification of lamin B cloned from a human T-cell line

Autoimmune diseases are characterized by spontaneously occurring autoantibodies which have proven to be useful reagents for the characterization of specific nuclear proteins. Using a monoclonal autoantibody (72B9) derived from a murine lupus strain, we have cloned a cDNA from the human T-cell line MOLT-4, which encodes nuclear lamin B. The identity of the encoded protein as lamin B was established by both biochemical and immunological criteria. Inspection of the deduced amino acid sequence of lamin B revealed the presence in coil 1B of the alpha-helical domain of a leucine heptad repeat region. Analysis of mRNA in HL60 and MOLT-4 cells, which express only lamin B, or HeLa cells, which express all three major lamins (A, B, and C), together with the comigration of in vitro-translated product with isolated HeLa cell lamin B by two-dimensional gel electrophoresis, suggests that a single lamin B is expressed in mammalian somatic cells. In vitro translation with the cDNA clone revealed an EDTA-sensitive posttranslational modification which resulted in an increase in the apparent molecular weight to that equivalent to the native in vivo-synthesized lamin B protein. This in vitro modification included incorporation of a product of mevalonolactone and required an intact carboxy terminus.

In vitro posttranslational modification of lamin B cloned from a human T-cell line

Autoimmune diseases are characterized by spontaneously occurring autoantibodies which have proven to be useful reagents for the characterization of specific nuclear proteins. Using a monoclonal autoantibody (72B9) derived from a murine lupus strain, we have cloned a cDNA from the human T-cell line MOLT-4, which encodes nuclear lamin B. The identity of the encoded protein as lamin B was established by both biochemical and immunological criteria. Inspection of the deduced amino acid sequence of lamin B revealed the presence in coil 1B of the alpha-helical domain of a leucine heptad repeat region. Analysis of mRNA in HL60 and MOLT-4 cells, which express only lamin B, or HeLa cells, which express all three major lamins (A, B, and C), together with the comigration of in vitro-translated product with isolated HeLa cell lamin B by two-dimensional gel electrophoresis, suggests that a single lamin B is expressed in mammalian somatic cells. In vitro translation with the cDNA clone revealed an EDTA-sensitive posttranslational modification which resulted in an increase in the apparent molecular weight to that equivalent to the native in vivo-synthesized lamin B protein. This in vitro modification included incorporation of a product of mevalonolactone and required an intact carboxy terminus.

Auto-immune (lupoid) hepatitis: an entity in the spectrum of chronic active liver disease

The concept of auto-immune hepatitis as a disease entity evolved from the descriptions of 'chronic active hepatitis' (CAH) in the 1950s. Several types of CAH are distinguished by disease-specific features. The distinctive (but not exclusive) markers for auto-immune CAH include: a negative test for HBsAg; female; Northern European ethnic background; multisystem disease expression; histological CAH with large areas of periportal piecemeal necrosis and plasmacytosis; pronounced hypergammaglobulinaemia; serum auto-antibodies the HLA B8-DR3 phenotype; responsiveness to corticosteroid therapy; and rarity of supervening hepatocellular carcinoma. Much weight is attached to the serological marker auto-antibodies to nuclear or smooth muscle (actin) antigens (ANA, SMA). However, these auto-antibodies do not have an absolute association with auto-immune CAH: the serological reactions are not yet standardized; titres decrease with remission of disease; and other auto-antibodies mark variant forms of auto-immune hepatitis. A more confident acceptance of auto-immune hepatitis as an entity requires detection of a liver-specific antigen, a valid experimental disease model in animals, and a better understanding of immune-mediated damage to liver cells.