Anti-nuclear antibodies of primary biliary cirrhosis recognize 78-92-kD and 96-100-kD proteins of nuclear bodies

VI Brazilian consensus guidelines for detection of anti-cell autoantibodies on HEp-2 cells

BACKGROUND

The VI Brazilian Consensus on Autoantibodies against HEp-2 cells for determination of autoantibodies against cellular constituents on HEp-2 cells was held on September, 2019, in Fortaleza (CE, Brazil). The guidelines in this edition were formulated by the group of Brazilian experts discussing the classification of complex patterns, the classification of the nuclear discrete dots (few and multiple), the identification of the discrete fine speckled pattern (AC-4a) and improvements on the ANA report.

MAINBODY

Sixteen Brazilian researchers and experts from universities and clinical laboratories representing the various geographical regions of Brazil participated in the meeting. Four main topics were discussed: (1) How to classify patterns with fluorescence in more than one cell compartment considering three relevant categoris: composite patterns, mixed patterns and multiple patterns; (2) The splitting of the discrete nuclear dots pattern into the multiple discrete nuclear dots (AC-6) and few discrete nuclear dots (AC-7) patterns, respectively; (3) Inclusion of a novel nuclear pattern characterized by discrete fine speckled pattern highly associated with antibodies to SS-A/Ro60, classified as AC-4a. In addition, adjustments on the Brazilian Consensus nomenclature were implemented aiming to harmonize the designation of some patterns with the International Consensus on ANA Patterns (ICAP). Furthermore, the designations of the PCNA-like pattern (AC-13), CENP-F-like pattern (AC-14) and Topo I-like pattern (AC-29) were adjusted in accordance to ICAP. Finally, there was a recommendation for adjustment in the test report in order to address the status of nuclear envelope staining. For all topics, the aim was to establish specific guidelines for laboratories and clinicians. All recommendations were based on consensus among participants. All recommendations from the V Consensus were maintained and there was relevant progress in the BCA/HEp-2 guidelines and further harmonization with ICAP.

CONCLUSION

The VI BCA/HEp-2 edition was successful in establishing important recommendations regarding the classification of complex patterns, in supporting the identification of a novel pattern within the AC-4 group and in the harmonization process with the ICAP terminology.

Detection of anti-SP100 antibodies in primary biliary cirrhosis. Comparison of ELISA and immunofluorescence

Primary biliary cirrhosis (PBC) is, which a chronic, autoimmune liver disease. Some patients have antinuclear antibodies anti-Sp100, which are considered to be disease-specific. We compared an enzyme-linked immunosorbent assay (ELISA) and indirect immunofluorescence (IIF) for detection of anti-Sp100. The sensitivity of anti-Sp100 determined by ELISA and IIF was 44% and 34%, respectively. Specificity was 99% for ELISA and 98% for IIF, respectively. The positive and negative predictive value (PPV, NPV) for anti-Sp100 determined by ELISA were 98%, 60% and 95%, 56% for IIF respectively. IIF required substantial experience in interpreting subjective patterns, whereas ELISA was more sensitive, cheaper, less time consuming, and produced clear-cut quantitative results.

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.

Role of auto-antibodies for the diagnosis of chronic cholestatic liver diseases

Auto-antibodies are an integral part of the diagnostic armentarium in chronic cholestatic liver disorders, such as primary sclerosing cholangitis (PSC), primary biliary cirrhosis (PBC),auto-immune cholangitis, or overlap syndromes among these disorders. However, care should be taken not to overestimate the diagnostic specificity. Auto-antibodies to mitochondrial antigens(AMAs) with reactivity to the E2 subunit of the pyruvate dehydrogenase complex represent the hallmark antibody for the diagnosis of PBC, whereas antinuclear antibodies (ANAs)with low disease specificity are found in up to 50% of these sera. Antibodies that recognize nuclear envelope proteins exert a similarly high diagnostic specificity as AMA in PBC but occur at a rather low prevalence. The role of auto-antibodies is less well-studied for patients with PSC, but there is growing evidence that only antineutrophil cytoplasmic antibodies(ANCAs) are of relevant diagnostic significance. In contrast, auto-antibodies-particularlyAMAs-do not contribute to the diagnosis of auto-immune cholangitis, whereas ANCAs,ANAs, smooth muscle antibodies, and AMAs are of varying significance in PBC-auto-immune hepatitis (AIH) or PSC-AIH overlap syndromes. It has been widely accepted that the course of the auto-antibody serum end point titers are not suited for the clinical management of patients with chronic cholestatic liver disorders. Additionally, auto-antibodies in these disorders usually do not contribute to the immunopathogenesis of the disease.

Antinuclear antibodies specific for primary biliary cirrhosis

The serological hallmark of primary biliary cirrhosis (PBC) is the presence of antimitochondrial antibodies. However, antinuclear antibodies (ANA) are also detectable in approximately 50% of subjects with PBC. Most clinical laboratories use indirect immunofluorescence microscopy to detect ANA and two labeling patterns that predominate in PBC are 'punctate nuclear rim' and 'multiple nuclear dots.' Work over the past several years has shown that antibodies giving these patterns most often recognize nuclear pore membrane protein gp210 and nuclear body protein sp100, respectively. These ANA are highly specific for PBC and detected in approximately 25% of patients. Less frequently, ANA apparently unique to PBC recognize other proteins of the nuclear envelope and nuclear bodies. While antibodies against gp210, sp100 and some other nuclear proteins are very specific to PBC and may therefore be useful diagnostic markers, their connection to pathogenesis remains to be elucidated.

New autoantibodies and autoantigens in autoimmune hepatitis

The molecular characterization of the autoreactivities associated with autoimmune liver disease will improve their diagnosis and enhance understanding of their pathogenic mechanisms. Surprisingly, little is known about the nature of the major autoreactivities associated with type 1 AIH, including homogeneous ANA and antibodies to microfilaments [3]. Type 1 AIH is, however, the prototype of autoimmune liver disease [103].

Anti-multiple nuclear dots (anti-MND) and anti-SP100 antibodies in hepatic and rheumatological disorders

Multiple nuclear dots pattern has been described in primary biliary cirrhosis and, less often, in rheumatological disorders. Sp100 is the major antigen of multiple nuclear dots. We evaluated prevalence and diagnostic significance of multiple nuclear dots and anti-Sp100 reactivity both in hepatic and rheumatological diseases. A series of 283 consecutive liver patients (89 primary biliary cirrhosis, 12 primary sclerosing cholangitis, 85 autoimmune hepatitis, 97 hepatitis C virus-related chronic liver disease) and of 89 consecutive rheumatological cases were evaluated. Presence of multiple nuclear dots was assessed by indirect immunofluorescence on HEp-2 cells, anti-Sp100 reactivity by ELISA with recombinant protein. Multiple nuclear dots were detected in 20 patients (7%) with liver disease (of whom 15 with primary biliary cirrhosis), and in eight patients (9%) with rheumatological disorders. Anti-Sp100 was detected in 45 liver patients (16%), of whom 30 with primary biliary cirrhosis, but in only two with rheumatological disorders (2%) (P =0.0004). The concordance between multiple nuclear dots and anti-Sp100 in liver and rheumatological patients was 90% and 25% (P=0.0018), respectively. Among 89 consecutive patients with primary biliary cirrhosis, multiple nuclear dots and anti-Sp100 were present in 17% and 34%, respectively (P=0.0152). Anti-Sp100 positivity was associated with older age and higher gamma-globulin levels. Multiple nuclear dots are similarly observed in liver and rheumatological patients. In contrast, anti-Sp100 is more frequent in liver patients and is significantly more often detected in primary biliary cirrhosis, of which it can be regarded as a highly specific serological marker. The antigenic target of multiple nuclear dots in most rheumatological patients is other than Sp100.

Autoantigens in primary biliary cirrhosis

The automimmune liver disease primary biliary cirrhosis (PBC) is characterised by serum autoantibodies directed at mitochondrial and nuclear antigens (seen in most patients and a subset of patients, respectively). The antimitochondrial antibodies (AMA) characteristic of PBC are directed at members of the 2-oxoacid dehydrogenase components of multienzyme complexes; in particular, the E2 and E3 binding protein (E3BP) components of the pyruvate dehydrogenase complex (PDC). The presence of autoantibodies reactive with PDC-E2 and/or E3BP is strongly predictive of the presence of PBC. Therefore, the detection of these antibodies plays a very important role in the diagnosis of PBC. Originally demonstrated using immunofluorescence approaches, AMA can now be detected by the use of commercially available enzyme linked immunosorbent assays (ELISAs). Although the ELISA based approaches have advantages in terms of laboratory practicality, they are slightly less sensitive for the diagnosis of PBC than immunofluorescence (occasional patients with PBC show reactivity with PDC related antigens not present in the antigen preparations available for use with ELISA). Therefore, immunofluorescence should continue to be available as a complementary diagnostic test for use in occasional patients. In a subset of patients with PBC, autoantibodies are directed at increasingly well characterised nuclear antigens. Antinuclear antibody (ANA) positive patients are typically AMA negative. There are no significant differences in disease phenotype between AMA positive and AMA negative groups. At present, the clinical detection of ANA is mostly by Hep2 immunofluorescence, although ELISA kits for individual nuclear antigens are increasingly becoming available.

Auto-antibodies in hepatitis C

Hepatitis C virus (HCV) has been implicated in the development of a variety of autoimmune phenomena, some of which are well documented and include a panel of auto-antibodies shared with autoimmune hepatitis (AIH). Anti-nuclear (ANA) and smooth muscle (SMA) antibodies (markers of AIH type 1 [AIH-1]), have been demonstrated in 9-38% and 5-91% of cases respectively, whereas anti-liver/kidney microsomal type 1 (anti-LKM-1) and anti-liver cytosol type 1 antibodies (anti-LC1) (markers of AIH type 2 [AIH-2]), are definitely rarer, especially in adults. The presence of these auto-reactivities in chronic hepatitis C generates clinical overlaps and dilemmas in the correct classification and treatment of such patients. The immunopathological characterization of the auto-antibodies, anti-nuclear and smooth muscle antibodies in particular, combined with internationally defined criteria for the diagnosis of AIH is helpful in this clinical process. Thyroid auto-antibodies and cryoprecitable rheumatoid factors are also commonly detected in hepatitis C, while the occurrence of other auto-antibodies still awaits confirmation.

Nuclear domain 10, the site of DNA virus transcription and replication

Within the highly organized nuclear structure, specific nuclear domains (ND10) are defined by accumulations of proteins that can be interferon-upregulated, implicating ND10 as sites of a nuclear defense mechanism. Compatible with such a mechanism is the deposition of herpesvirus, adenovirus, and papovavirus genomes at the periphery of ND10. However, these DNA viruses begin their transcription at ND10 and consequently initiate replication at these sites, suggesting that viruses have evolved ways to circumvent this potential cellular defense and exploit it. Other ND10-associated proteins belong to ubiquitin-related pathways. These findings, together with the accumulation of various overexpressed cellular and viral proteins, suggest that ND10 function as nuclear dumps or as nuclear depots. Consistent with the recruitment or deposition of various proteins and viral genomes adjacent to ND10, ND10 themselves may only be protein accumulations at specific but as yet undefined nuclear deposition sites. The concept of specific nuclear deposition sites may explain the juxtaposition of various nuclear bodies and allows testable predictions about a potential supramolecular regulatory mechanism whereby proteins are selectively segregated or released by global changes induced in nuclear functions such as viral infections, stress, or hormonal induction.

Antinuclear antibodies and patterns of nuclear immunofluorescence in type 1 autoimmune hepatitis

To determine the significance of antinuclear antibodies and their patterns of indirect immunofluorescence in type 1 autoimmune hepatitis, sera from 99 patients were evaluated. Patients with antinuclear antibodies had a lower frequency of liver transplantation (6% vs 22%, P = 0.04) than seronegative patients. They were also more commonly HLA-DR4-positive than seronegative patients (56% vs 30%, P = 0.05) and normal subjects (56% vs 30%, P = 0.004). The 42 patients with antinuclear antibodies and a diffuse pattern of indirect immunofluorescence had higher serum titers of ANA (serum titers > or = 1:500, 71% vs 14%, P < 0.0001) and SMA (serum titers > or = 1:500, 69% vs 27%, P = 0.003) than the 22 patients with antinuclear antibodies and a speckled pattern. These patients, however, were otherwise not distinguished by clinical features and treatment response. Patients with a speckled pattern had A1-B8-DR3 more frequently than patients with a diffuse pattern (65% vs 23%, P = 0.005) and normal subjects (65% vs 13%, P < 0.0001), but they had no other salient features. We conclude that patients with antinuclear antibodies have a better long-term prognosis than seronegative patients, and they have HLA-DR4 more commonly. The patterns of indirect immunofluorescence associated with ANA positivity have no practical clinical implications.

PML-containing nuclear bodies: their spatial distribution in relation to other nuclear components

The PML protein is a human growth suppressor concentrated in 10 to 20 nuclear bodies per nucleus (PML bodies). Disruption of the PML gene has been shown to be related to acute promyelocytic leukaemia (APL). To obtain information about the function of PML bodies we have investigated the 3D-distribution of PML bodies in the nucleus of T24 cells and compared it with the spatial distribution of a variety of other nuclear components, using fluorescence dual-labeling immunocytochemistry and confocal microscopy. Results show that PML bodies are not enriched in nascent RNA, the splicing component U2-snRNP, or transcription factors (glucocorticoid receptor, TFIIH, and E2F). These results show that PML bodies are not prominent sites of RNA synthesis or RNA splicing. We found that a large fraction of PML bodies (50 to 80%) is closely associated with DNA replication domains during exclusively middle-late S-phase. Furthermore, in most cells that we analysed we found at least one PML body was tightly associated with a coiled body. In the APL cell line NB4, the PML gene is fused with the RAR alpha gene due to a chromosomal rearrangement. PML bodies have disappeared and the PML antigen, i.e., PML and the PML-RAR fusion protein, is dispersed in a punctated pattern throughout the nucleoplasm. We showed that in NB4 cells the sites that are rich in PML antigen significantly colocalize with sites at which nascent RNA accumulates. This suggests that, in contrast to non-APL cells, in NB4 cells the PML antigen is associated with sites of transcription. The implications of these findings for the function of PML bodies are consistent with the idea that PML bodies are associated with specific genomic loci.

The RNA 3' cleavage factors CstF 64 kDa and CPSF 100 kDa are concentrated in nuclear domains closely associated with coiled bodies and newly synthesized RNA

The cleavage stimulation factor (CstF), and the cleavage and polyadenylation specificity factor (CPSF) are necessary for 3'-terminal processing of polyadenylated mRNAs. To study the distribution of 3' cleavage factors in the nuclei of human T24 cells, monoclonal antibodies against the CstF 64 kDa subunit and against the CPSF 100 kDa subunit were used for immunofluorescent labelling. CstF 64 kDa and CPSF 100 kDa were distributed in a fibrogranular pattern in the nucleoplasm and, in addition, were concentrated in 1-4 bright foci. Double immunofluorescence labelling experiments revealed that the foci either overlapped with, or resided next to, a coiled body. Inhibition of transcription with alpha-amanitin or 5,6-dichloro-beta-D-ribofuranosyl-benzimidazole (DRB) resulted in the complete co-localization of coiled bodies and foci containing 3' cleavage factors. Electron microscopy on immunogold double-labelled cells revealed that the foci represent compact spherical fibrous structures, we named 'cleavage bodies', intimately associated with coiled bodies. We found that approximately 20% of the cleavage bodies contained a high concentration of newly synthesized RNA, whereas coiled bodies were devoid of nascent RNA. Our results suggest that the cleavage bodies that contain RNA are those that are adjacent to a coiled body. These findings reveal a dynamic and transcription-dependent interaction between different subnuclear domains, and suggest a relationship between coiled bodies and specific transcripts.

Nuclear domains and the nuclear matrix

This overview describes the spatial distribution of several enzymatic machineries and functions in the interphase nucleus. Three general observations can be made. First, many components of the different nuclear machineries are distributed in the nucleus in a characteristic way for each component. They are often found concentrated in specific domains. Second, nuclear machineries for the synthesis and processing of RNA and DNA are associated with an insoluble nuclear structure, called nuclear matrix. Evidently, handling of DNA and RNA is done by immobilized enzyme systems. Finally, the nucleus seems to be divided in two major compartments. One is occupied by compact chromosomes, the other compartment is the space between the chromosomes. In the latter, transcription takes place at the surface of chromosomal domains and it houses the splicing machinery. The relevance of nuclear organization for efficient gene expression is discussed.

Nuclear domain 10 (ND10) associated proteins are also present in nuclear bodies and redistribute to hundreds of nuclear sites after stress

The promyelocytic leukemia protein fused to the retinoic acid receptor alpha in t(15;17) acute promyelocytic leukemia, the primary biliary cirrhosis autoantigen, Sp100, as well as the incompletely characterized protein NDP55, are co-localized in specific immunohistochemically defined nuclear domains (ND10), which are potential equivalents of ultrastructurally defined nuclear bodies. We investigated whether the distribution of these proteins depends on environmental conditions and whether ND10 correlate with nuclear bodies. Certain nuclear bodies and ND10 react in a similar way and share antigens. Interferon exposure doubled the number of ND10 and increased the frequency of nuclear bodies, whereas herpes simplex virus infection or heat shock modify both. Redistribution of ND10-associated proteins to hundreds of small sites throughout the chromatin was inducible by stress in the form of heat shock and exposure to Cd++ ions. The change of distribution was rapid and independent of protein synthesis, and thus not part of the classical heat shock response. The very rapid redistribution of these proteins after heat shock, together with the development of ND10 upon interferon activation, raises the possibility that ND10 represent storage sites of certain matrix proteins readily accessible throughout the chromatin in response to stress or other effectors that induce global nuclear changes.

Mapping functional domains of the polycomb protein of Drosophila melanogaster

In Drosophila the Polycomb group (Pc-G) proteins are responsible for the stable and heritable silencing of genes. The Pc-G apparently uses heterochromatin-like mechanisms to transcriptionally inactivate developmental regulators such as the homeotic genes. The Polycomb (Pc) protein is part of a large multimeric complex composed of other members of the Pc-G. We have identified functionally relevant domains of the Pc protein by sequencing different Pc alleles. Additionally, using a Pc-beta gal fusion protein with deleted internal histidine repeats, we found that this mutant protein cannot bind to four particular target loci, but otherwise does not change the remaining overall binding pattern. We show that, in contrast to the dotted subnuclear localization of the wild-type protein, the nuclear distribution of mutant proteins becomes homogeneous. Surprisingly, in Pc mutants the polyhomeotic protein, another member of the Pc-G, is also redistributed in the nucleus. Our results indicate that the appropriate subnuclear localization of the two proteins is critical for the silencing function of the Pc-G complex.

Two nuclear dot-associated proteins, PML and Sp100, are often co-autoimmunogenic in patients with primary biliary cirrhosis

The nucleoproteins Sp100 and PML, the first an autoantigen predominant in patients with primary biliary cirrhosis (PBC) and the second a transformation and cell growth suppressing protein aberrantly expressed in promyelocytic leukaemia cells, were recently shown to colocalize in dot-like nuclear domains. Here we analysed whether PML, like Sp100, is also an autoantigen in patients with PBC and other autoimmune diseases, and wether both proteins interact directly. Testing sera from autoimmune patients using an immunoprecipitation assay with radiolabelled PML and an immunofluorescence assay based on a cell line overexpressing PML, autoantibodies (Aabs) against PML were found in the majority o anti-Sp100 Aab positive patients. Only very few patients with PBC or other autoimmune diseases contained anti-PML or anti-Sp100 Aabs exclusively. In contrast to Sp100, immunoreactivity of recombinant PML in immunoblots was only weak and was directed to one region. This suggests that anti-PML Aabs recognize fewer and preferentially conformation-dependent epitopes. In an immunoprecipitation assay using in vitro synthesized Sp100 and PML proteins and Abs to recombinant proteins, no direct interaction was observed. Taken together, these data indicate that Aabs against PML are as highly prevalent and specific for patients with PBC as those against Sp100. The colocalization of these autoantigens and the frequent co-occurrence of the corresponding Aabs might reflect an association of both proteins mediated by one or several other proteins.

High prevalence of antibodies to recombinant CENP-B in primary biliary cirrhosis: nuclear immunofluorescence patterns and ELISA reactivities

The purpose of the present study is to evaluate the centromeric pattern on human laryngeal tumour (HEp-2) cells by indirect immunofluorescent (IIF) test and to compare their reactivities with a newly developed recombinant centromere protein B enzyme linked immunosorbent assay (CENP-B ELISA) test using sera of antinuclear antibody (ANA)-reactive primary biliary cirrhosis (PBC) patients. Antimitochondrial antibody (AMA) subtypes (PDC-E2, BCOADC-E2, OGDC, protein X, and PDC-E1 alpha) by Western blot were also investigated to see whether they have any effect on the expression of CENP-B reactivities. A centromeric pattern (anticentromere antibody [ACA]) was detected in 11 of 25 (44%) PBC patients whereas CENP-B reactivity was found in 15 (60%) of them. There were some differences in IIF patterns and CENP-B reactivities. One PBC serum with indistinguishable ANA pattern reacted with CENP-B. Eight of 15 (53%) CENP-B reactive patients had other autoimmune-like disorders. Of 181 healthy sera, none was reactive for ACA either by IIF or by ELISA test. There was a correlation between ACA IIF and CENP-B ELISA titres (r = 0.824, P < 0.001). However, no correlation was observed between either CENP-B or AMA reactivities and/or between either autoantibodies or laboratory and histologic indices of PBC. These findings suggest that recombinant CENP-B ELISA appears to be more sensitive in identifying ACA than IIF, underlying its potential value as a screening test for the diagnosis of PBC complicated with other autoimmune-like disorders. The presence of multiple autoantibodies in PBC sera may reflect heterogeneous antigens recognition, and requires further study to identify target antigens at cellular and molecular levels.

Primary biliary cirrhosis is associated with specific changes in liver IgG-bearing cell subpopulations

BACKGROUND/AIMS

The density of total IgG-bearing cells and the distribution of their subclasses were studied in the liver of patients with primary biliary cirrhosis.

METHODS

Immunohistochemistry and computerized image analysis were used to compare liver specimens from 18 patients with primary biliary cirrhosis and 28 with chronic hepatitis of different etiology.

RESULTS

The density of total IgG-bearing cells was similar in the two groups. However, in patients with primary biliary cirrhosis the proportion of IgG3-positive cells was significantly higher than in patients with chronic hepatitis (53 +/- 7% vs. 7.5 +/- 2.4%) (p < 10(-8)). Conversely, IgG1-positive cells were significantly less prevalent in patients with primary biliary cirrhosis than in chronic hepatitis patients (27 +/- 6.9% vs. 68 +/- 7.2%, p < 10(-8)). Stratification of patients with primary biliary cirrhosis according to histology did not show any difference in the distribution of IgG subclasses associated with the progression of disease.

CONCLUSION

These data suggest a pathogenetic role of local IgG3-bearing cells in primary biliary cirrhosis.

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.

The t(15;17) translocation alters a nuclear body in a retinoic acid-reversible fashion

Nuclear bodies (NBs) are ultrastructurally defined granules predominantly found in dividing cells. Here we show that PML, a protein involved in the t(15;17) translocation of acute promyelocytic leukaemia (APL), is specifically bound to a NB. PML and several NB-associated proteins, found as auto-antigens in primary biliary cirrhosis (PBC), are co-localized and co-regulated. The APL-derived PML-RAR alpha fusion protein is shown to be predominantly localized in the cytoplasm, whereas a fraction is nuclear and delocalizes the NB antigens to multiple smaller nuclear clusters devoid of ultrastructural organization. RA administration (which in APL patients induces blast differentiation and consequently complete remissions) causes the re-aggregation of PML and PBC auto-antigens onto the NB, while PML-RAR alpha remains mainly cytoplasmic. Thus, PML-RAR alpha expression leads to a RA-reversible alteration of a nuclear domain. These results shed a new light on the pathogenesis of APL and provide a molecular link between NBs and oncogenesis.

Visualization of replication factories attached to nucleoskeleton

HeLa cells in early S phase were encapsulated in agarose microbeads, permeabilized, and incubated with biotin-11-dUTP in a "physiological" buffer. Sites of DNA synthesis were then immunolabeled. As others have found, approximately 150 focal sites of synthesis were visible in each nucleus by light microscopy; they also contained DNA polymerase alpha and proliferating cell nuclear antigen. Electron microscopy of thick resinless sections from which approximately 90% of the chromatin had been removed revealed a similar number of dense, morphologically discrete ovoid bodies strung along a nucleoskeleton. The ovoids remained morphologically and functionally intact despite the removal of most of the chromatin. After 2.5 min of incubation with biotin-11-dUTP, the incorporated analog was associated only with ovoids; after 5 min it began to spread into the adjacent chromatin, which became extensively labeled after 1 hr. This provides visual evidence for polymerization "factories" fixed to a skeleton, with replication occurring as the template moves through them.

Visualization of focal sites of transcription within human nuclei

HeLa cells were encapsulated in agarose microbeads, permeabilized and incubated with Br-UTP in a 'physiological' buffer; then sites of RNA synthesis were immunolabelled using an antibody that reacts with Br-RNA. After extending nascent RNA chains by < 400 nucleotides in vitro, approximately 300-500 focal synthetic sites can be seen in each nucleus by fluorescence microscopy. Most foci also contain a component of the splicing apparatus detected by an anti-Sm antibody. alpha-amanitin, an inhibitor of RNA polymerase II, prevents incorporation into these foci; then, using a slightly higher salt concentration, approximately 25 nucleolar foci became clearly visible. Both nucleolar and extra-nucleolar foci remain after nucleolytic removal of approximately 90% chromatin. An underlying structure probably organizes groups of transcription units into 'factories' where transcripts are both synthesized and processed.

Autoantibodies to the nuclear Sp100 protein in primary biliary cirrhosis and associated diseases: epitope specificity and immunoglobulin class distribution

Sp100, a protein with a dot-like intranuclear localization in immunofluorescence microscopy, is a major target for patient autoantibodies in primary biliary cirrhosis (PBC) and occasionally in rheumatic disorders. The human Sp100 cDNA has recently been cloned, and the deduced amino acid sequence was found to contain sequence similarities with an MHC class I domain and several transacting regulatory proteins, including HIV-1 nef proteins. In this study, recombinant Sp100 fusion proteins were used to differentiate the immunoglobulin isotypes and to map the epitopes involved in the anti-Sp100 autoimmune response. PBC patients developed IgG as well as IgM and/or IgA class anti-Sp100 autoantibodies whereas most patients with rheumatic diseases developed IgG class autoantibodies only. For epitope mapping, truncated versions of the Sp100 protein were probed for immunoreactivity in ELISA and immunoblotting. With 55 sera, 17 different reaction patterns were obtained, and at least three non-overlapping major autoantigenic domains were recognized by the majority of sera. One domain, which contains the sequence similarity with HIV nef proteins, was recognized by all anti-Sp100 sera and harbours multiple, in part discontinuous, epitopes. These data demonstrate a heterogeneous and patient-specific anti-Sp100 autoimmune response which is antigen-driven and, at least in terms of isotype composition, different in PBC and non-PBC patients.

Multiple nuclear dots antinuclear antibodies are not specific for primary biliary cirrhosis

Multiple nuclear dots antinuclear antibodies display a specific immunofluorescence pattern on HEp-2 cells. They have been reported to be strongly associated with primary biliary cirrhosis, especially when sicca syndrome was present. To determine whether multiple nuclear dots antinuclear antibodies are specific for primary biliary cirrhosis, we studied the clinical, biochemical, immunological and morphological features of 38 patients between December 1983 and September 1990 who had serum multiple nuclear dots antinuclear antibodies detected in an immunology laboratory of a large medical center. Sufficient information was reliable in 36 patients; the group included 31 women and 5 men (mean age = 57.6 +/- 14.5, range = 30 to 87). Fifteen patients (42%) had primary biliary cirrhosis, 5 patients (14%) had type 1 autoimmune chronic active hepatitis, 4 patients (11%) had liver disease of unknown cause and 12 patients (33%) had various immunological disorders but no liver disease. Two of the patients with primary biliary cirrhosis (13%) had clinical sicca syndrome. Our study demonstrates the following: (a) serum multiple nuclear dots antinuclear antibodies are not specific for liver disease because they can be observed in one third of patients with various immunological disorders without liver involvement, and (b) serum multiple nuclear dots antinuclear antibodies are not specific for PBC because they can also be observed in type 1 autoimmune chronic active hepatitis. Our results also suggest that patent sicca syndrome is abnormally present in patients with primary biliary cirrhosis and multiple nuclear dots antinuclear antibodies.

The nucleus: a black box being opened

Until recently our knowledge about the structural and functional organization of the cell nucleus was very limited. Recent technical developments in the field of ultrastructural analysis, combined with ongoing research on the properties of the nuclear matrix, give new insight into how the nucleus is structured. Two types of observations shape our ideas about nuclear organization. First, most nuclear functions (replication, transcription, RNA processing, and RNA transport) are highly localized within the nucleus, rather than diffusely distributed. Moreover, they are associated with the nuclear matrix. Second, chromatin is organized in discrete loops, bordered by nuclear matrix attachment sequences (MARs). Each loop may contain one or several genes. The arrangement of chromatin in loops has profound consequences for the regulation of gene expression.

Compartmentalization within the nucleus: discovery of a novel subnuclear region

Antibodies to a set of structurally related autoantigens (p23-25) bind to a previously uncharacterized, large structural domain in the nucleus of a variety of human cell types. This subnuclear domain is visible by phase contrast alone as a region of decreased density after several different fixation protocols. The morphology of this region changes dramatically during the cell cycle and we have given it the name PIKA (for polymorphic interphase karyosomal association) based on preliminary evidence that the PIKA proteins may be associated with chromatin. The function of the PIKA is not yet known, but our immunolocalization data indicate that it is unlikely to be associated with regions of ongoing DNA replication, heterogeneous nuclear RNA storage, or mRNA processing. The discovery of the PIKA provides evidence supporting an emerging model of nuclear structure. It now appears that the nucleus is organized into distinct domains which include not only the nucleolus, but also previously unidentified regions such as the PIKAs. Furthermore, structural rearrangements undergone by the nucleolus and the PIKAs may be indicative of a broad tendency for nuclear organization to change in a cell cycle-specific fashion.