Sera from patients with autoimmune disease recognize conformational determinants on the 60-kd Ro/SS-A protein

Antibodies to Both Ro52 and Ro60 for Identifying Sjögren's Syndrome Patients Best Suited for Clinical Trials of Disease-Modifying Therapies

OBJECTIVE

To assess anti-Ro52 and anti-Ro60 serologic profiles as markers of clinically relevant phenotypic subsets of patients with Sjögren's syndrome (SS).

METHODS

From a cohort of 839 consecutive patients with suspected or established SS seen in our multidisciplinary SS center, we compared the association of key phenotypic features in 390 patients who fulfilled SS classification criteria and in the parent cohort, stratifed by the presence of both anti-Ro60 and anti-Ro52, anti-Ro60 alone, and anti-Ro52 alone.

RESULTS

The SS cohort included 227 patients (58%) with both anti-Ro60 and anti-Ro52, 65 (17%) with anti-Ro60 alone, 58 (15%) with anti-Ro52 alone, and 40 (10%) with neither antibody. Those with both anti-Ro60 and anti-Ro52 had a significantly increased prevalence of abnormal ocular surface staining, focal lymphocytic sialadenitis with focus score ≥1, antinuclear antibody ≥1:320, anti-SSB/La, rheumatoid factor, and IgG ≥15.6 gm/liter (P < 0.0016 for all). The groups with isolated anti-Ro52 and anti-Ro60 were equivalent to each other in their phenotypic associations, except for rheumatoid factor, which was higher in the anti-Ro52 alone group. The associations of these Ro antibody serologic profiles were similar in the parent cohort, except for additional associations with salivary gland enlargement and parotid gland ultrasound score.

CONCLUSION

SS patients with both anti-Ro60 and anti-Ro52 antibodies are distinguished by a higher prevalence of markers of B-cell hyperactivity and glandular inflammation. Antibody reactivity to both Ro60 and Ro52 may thus serve as an important inclusion criterion for SS patients in clinical trials where the therapeutic agent targets pathways mediating these pathogenic abnormalities.

Discordant Predictions of Extraglandular Involvement in Primary Sjögren's Syndrome According to the Anti-SSA/Ro60 Antibodies Detection Assay in a Cohort Study

Electrophoresis-derived techniques for anti-SSA/Ro60 KDa (anti-SSA) antibodies detection have been progressively replaced by methods using non-native antigens. We aimed to compare the patients’ phenotypes and the occurrence of extraglandular manifestations in primary Sjögren’s syndrome according to the method used to detect anti-SSA antibodies. Sera from patients with a diagnosis of pSS according to ACR/EULAR 2016 criteria between 2008 and 2017 were tested for anti-SSA antibodies using methods with non-native antigens (magnetic bead multiplex assay; line immunoassays) and one with native antigens (counterimmunoelectrophoresis (CIE)). The population was split into three groups according to anti-SSA antibodies status: absence (SSA−), presence in any method except for CIE (SSA+CIE−), and presence in CIE (SSA+CIE+). The patients in the SSA+CIE+ group (n = 70, 42.7%) were ten years younger and presented more immunological activity compared with both the SSA− (n = 80, 48.8%) and SSA+CIE− groups (n = 14, 8.5%). The SSA− and SSA+CIE− groups were poorly distinct. The presence of anti-SSA antibodies solely in CIE was significantly associated with the occurrence of extraglandular manifestations of pSS (HR = 4.45 (2.35–8.42)). Contrary to CIE, methods using non-native antigens to detect anti-SSA antibodies were unable to predict the occurrence of systemic expression of pSS.

The Autoantigen Repertoire and the Microbial RNP World

Although autoimmunity and autoimmune disease (AID) are relatively common, the repertoire of autoantigens is paradoxically very limited. Highly enriched in this autoantigen repertoire are nucleic acids and their binding proteins, which together form large macromolecular structures. Most of these complexes are of ancient evolutionary origin, with homologs throughout multiple kingdoms of life. Why and if these nucleic acid-protein particles drive the development of autoimmunity remains unresolved. Recent advances in our understanding of the microbiome may provide clues about the origins of autoimmunity - and the particular puzzle of why the autoantigen repertoire is so particularly enriched in ribonucleoprotein particles (RNPs). We discuss the possibility that autoimmunity to some RNPs may arise from molecular mimicry to microbial orthologs.

Progress in the pathogenesis and treatment of cardiac manifestations of neonatal lupus

PURPOSE OF REVIEW

To provide new insights into pathogenesis, prevention and management of cardiac manifestations of neonatal lupus (cardiac neonatal lupus) and issues pertinent to all anti-SSA/Ro positive individuals of childbearing age.

RECENT FINDINGS

Antibody specificity with high risk for cardiac neonatal lupus remains elusive, but high titers of Ro60, Ro52 or Ro52p200 antibodies appear to be required. Varying antibody specificities to the p200 region of Ro52 can induce first-degree block in a rodent model. In consideration of the contribution of macrophages to inflammation and fibrosis in cardiac neonatal lupus, hydroxychloroquine (HCQ) is being considered as preventive therapy. Cord blood biomarkers support the association of fetal reactive inflammatory and fibrotic components with the development and morbidity of cardiac neonatal lupus. Data from U.S. and French registries do not provide evidence that the prompt use of fluorinated steroids in cases of isolated block significantly alters fetal/neonatal morbidity or mortality.

SUMMARY

The search for a high-risk cardiac neonatal lupus antibody profile remains, but high-titer antibodies to Ro60 and R052 are a consistent finding, and this may guide the need for fetal echocardiographic surveillance. The uniform use of fluorinated steroids to prevent progression of cardiac neonatal lupus or reduce mortality does not appear justified. HCQ, based on diminishing an inflammatory component of cardiac neonatal lupus, is under consideration as a potential preventive approach.

Next-Generation Autoantibody Testing by Combination of Screening and Confirmation-the CytoBead® Technology

Occurrence of autoantibodies (autoAbs) is a hallmark of autoimmune diseases, and the analysis thereof is an essential part in the diagnosis of organ-specific autoimmune and systemic autoimmune rheumatic diseases (SARD), especially connective tissue diseases (CTDs). Due to the appearance of autoAb profiles in SARD patients and the complexity of the corresponding serological diagnosis, different diagnostic strategies have been suggested for appropriate autoAb testing. Thus, evolving assay techniques and the continuous discovery of novel autoantigens have greatly influenced the development of these strategies. Antinuclear antibody (ANA) analysis by indirect immunofluorescence (IIF) on tissue and later cellular substrates was one of the first tests introduced into clinical routine and is still an indispensable tool for CTD serology. Thus, screening for ANA by IIF is recommended to be followed by confirmatory testing of positive findings employing different assay techniques. Given the continuous growth in the demand for autoAb testing, IIF has been challenged as the standard method for ANA and other autoAb analyses due to lacking automation, standardization, modern data management, and human bias in IIF pattern interpretation. To address these limitations of autoAb testing, the CytoBead® technique has been introduced recently which enables automated interpretation of cell-based IIF and quantitative autoAb multiplexing by addressable microbead immunoassays in one reaction environment. Thus, autoAb screening and confirmatory testing can be combined for the first time. The present review discusses the history of autoAb assay techniques in this context and gives an overview and outlook of the recent progress in emerging technologies.

IgV peptide mapping of native Ro60 autoantibody proteomes in primary Sjögren's syndrome reveals molecular markers of Ro/La diversification

We have used high-resolution mass spectrometry to sequence precipitating anti-Ro60 proteomes from sera of patients with primary Sjögren's syndrome and compare immunoglobulin variable-region (IgV) peptide signatures in Ro/La autoantibody subsets. Anti-Ro60 were purified by elution from native Ro60-coated ELISA plates and subjected to combined de novo amino acid sequencing and database matching. Monospecific anti-Ro60 Igs comprised dominant public and minor private sets of IgG1 kappa and lambda restricted heavy and light chains. Specific IgV amino acid substitutions stratified anti-Ro60 from anti-Ro60/La responses, providing a molecular fingerprint of Ro60/La determinant spreading and suggesting that different forms of Ro60 antigen drive these responses. Sequencing of linked anti-Ro52 proteomes from individual patients and comparison with their anti-Ro60 partners revealed sharing of a dominant IGHV3-23/IGKV3-20 paired clonotype but with divergent IgV mutational signatures. In summary, anti-Ro60 IgV peptide mapping provides insights into Ro/La autoantibody diversification and reveals serum-based molecular markers of humoral Ro60 autoimmunity.

Clinical and pathological roles of Ro/SSA autoantibody system

Anti-Ro/SSA antibodies are among the most frequently detected autoantibodies against extractable nuclear antigens and have been associated with systemic lupus erythematosus (SLE) and Sjögren's syndrome (SS). Although the presence of these autoantibodies is one of the criteria for the diagnosis and classification of SS, they are also sometimes seen in other systemic autoimmune diseases. In the last few decades, the knowledge of the prevalence of anti-Ro/SSA antibodies in various autoimmune diseases and symptoms has been expanded, and the clinical importance of these antibodies is increasing. Nonetheless, the pathological role of the antibodies is still poorly understood. In this paper, we summarize the milestones of the anti-Ro/SSA autoantibody system and provide new insights into the association between the autoantibodies and the pathogenesis of autoimmune diseases.

Reactivity with dichotomous determinants of Ro 60 stratifies autoantibody responses in lupus and primary Sjögren's syndrome

OBJECTIVE

Analysis of B cell determinants of Ro 60 exposed on the surface of apoptotic cells (apotopes) or intracellular epitopes provides insight into the structural forms of the autoantigen that break immune tolerance. This study was initiated to compare anti-Ro 60 responses in systemic lupus erythematosus (SLE) and primary Sjögren's syndrome (SS) against membrane-bound and intracellular forms of Ro 60.

METHODS

The reactivity of autoantibodies from patients with SLE and primary SS to Ro 60 apotopes and epitopes was assessed by multiparameter flow cytometry and solid-phase immunoassay. Anti-Ro 60 IgG was eluted from early apoptotic cells or recombinant Ro 60 immobilized on nitrocellulose, and binding to membrane-bound and intracellular forms of Ro 60 was quantitated by flow cytometry.

RESULTS

An immunodominant apotope, which was recognized by IgG from a subset of SLE patients with anti-Ro, but not anti-La, autoantibodies, was mapped to a region forming a helix-loop-helix at the apical tip of the Ro 60 molecule. Immobilization of this region to the solid phase exposed an epitope that was recognized by IgG from primary SS and SLE patients whose sera had both anti-Ro and anti-La autoantibodies. Autoantibodies eluted from either the surface of apoptotic cells or the Ro 60 epitope on the solid phase were non-cross-reactive and specifically recognized membrane-bound or cytoplasmic forms of Ro 60.

CONCLUSION

This is the first example of a dichotomy of human autoantibody responses against mutually exclusive determinants linked to a single domain of a systemic autoantigen and supports a model in which tolerance is broken by different immunogenic forms of Ro 60.

Antinuclear antibodies and their detection methods in diagnosis of connective tissue diseases: a journey revisited

It has been more than 50 years since antinuclear antibodies were first discovered and found to be associated with connective tissue diseases. Since then different methods have been described and used for their detection or confirmation. For many decades immunofluorescent antinuclear antibody test has been the "gold standard" in the diagnosis of these disorders. However to increase the sensitivity and specificity of antinuclear antibody detection further approaches were explored. Today a battery of newer techniques are available some of which are now considered better and are competing with the older methods. This article provides an overview on advancement in antinuclear antibody detection methods, their future prospects, advantages, disadvantages and guidelines for use of these tests.

Post-translational modifications of the major linear epitope 169-190aa of Ro60 kDa autoantigen alter the autoantibody binding

Ro60 kDa is a member of the Ro/LaRNP ribonucleoprotein complex and its major linear B cell epitope, corresponding to the region 169-190aa, has been found to be the initial target of the autoimmune response in patients with systemic lupus erythematosus. This sequence contains one serine and two arginine amino acid residues, which can potentially be modified post-translationally by phosphorylation or citrullination, respectively. The aim of this study was to develop an immunoassay for anti-Ro60 kDa epitope antibody detection and to investigate the changes in the antigenicity of the Ro60 kDa epitope when it is post-translationally modified, by either citrullination or phosphorylation. Peptide analogues corresponding to the unmodified form of the epitope, its phosphorylated form, and a form with both arginine residues citrullinated were synthesized. The peptide coating conditions were investigated and it was found that the use of highly hydrophilic surfaces increase the efficiency of the coating, as well as the sensitivity of the method for anti-peptide antibody detection. All peptides were tested by the optimized enzyme-linked immunosorbent assay (ELISA) against 119 sera from patients with primary Sjögren's syndrome, systemic lupus erythematosus and rheumatoid arthritis with anti-Ro/SSA reactivity, 20 sera from patients with systemic diseases without anti-Ro/SSA immune reactivity, as well as against 65 sera from normal individuals. A large proportion of the tested sera reacted against all three peptide analogues, although with a preference for the unmodified form of the epitope. In conclusion, post-translational modifications of the major Ro60 kDa B cell epitope can alter the autoantibody binding.

The Ro 60 kDa autoantigen comes into focus: interpreting epitope mapping experiments on the basis of structure

A conserved RNA-binding protein, the Ro 60 kDa (Ro60) autoantigen, is a major target of autoantibodies in patients suffering from the rheumatic diseases Sjogren's syndrome, systemic lupus erythematosus, subacute cutaneous lupus erythematosus and neonatal lupus erythematosus. In both mice and certain bacteria, Ro60 is important for cell survival following ultraviolet irradiation. Although the function of Ro60 was mysterious for many years, recent experiments have demonstrated that this protein binds misfolded noncoding RNAs in vertebrate cells and likely functions in a pathway by which defective RNAs are recognized and targeted for degradation. Recent structural studies have revealed that Ro60 is shaped like a doughnut with an inner hole. Noncoding RNAs called Y RNAs bind on the outer surface of the ring, while the single-stranded ends of misfolded RNAs likely bind within the hole. Comparison of the Ro60 structure with the results of epitope-mapping studies reveals that many of the currently identified epitopes recognized by patient sera overlap regions of Ro60 that function in RNA binding. Moreover, in some patients with anti-Ro60 antibodies, the initial antigenic epitope corresponds to a loop involved in binding single-stranded RNA in the central cavity.

Anti-Ro/SSA and La/SSB antibodies

The Ro/La system is considered as an heterogeneous antigenic complex, constituted by three different proteins (52 kDa Ro, 60 kDa Ro and La) and four small RNAs particles. Anti-Ro/SSA are the most prevalent specificity among many autoimmune diseases, such as systemic lupus erythematosus (SLE), SS/SLE overlap syndrome, subacute cutaneous LE (SCLE), neonatal lupus and primary biliary cirrhosis. In contrast, anti-La/SSB is more associated with Sjögren's syndrome (SS). The differences between 52 kDa, 60 kDa Ro and La could explain why different assays did not show equivalent performance in anti-Ro and anti-La autoantibodies detection. The RNA precipitation assay had the highest sensitivity and specificity, usually considered as the reference methods. CIE is considered the most reliable to detect anti-Ro/SSA antibodies in routine practice, performing better than immunoblotting (IB) and some ELISAs. It shows a high sensitivity (89%) and specificity (100%). ELISA is generally considered a safe, rapid, sensitive and specific tecnique. Therefore, its high sensitivity often corresponds to a very low clinical specificity and the assay can give false positive results. Therefore, it is very important to search anti-Ro and anti-La only in selected patients, using the assay with high specificity and good predictive value, in order to have clinically significant and true positive results.

Simultaneous identification of various antinuclear antibodies using an automated multiparameter line immunoassay system

The objective was to determine the sensitivity and specificity of an automated multiparameter line immunoassay system compared with other techniques for the identification of autoantibodies in rheumatic diseases. We studied sera from 90 patients. Anti-U1RNP, anti-Sm, anti-Ro/SS-A, anti-La/SS-B, anti-Jo 1 and anti-Scl 70 antibodies were identified by counterimmunoelectrophoresis (CIE) techniques, enzyme-linked immunosorbent assay (ELISA), immunoblotting (IB) using extracts of rabbit thymus and human placenta, and an automated multiparameter line immunoassay system (INNO-LIA ANA UPDATE K-1090) that detects nine different antibodies simultaneously (anti-U1RNP, anti-Sm, anti-Ro/SS-A, anti-La/SS-B, anti-Scl 70, anti-Jo 1, anticentromere, antihistone, and antiribosomal P protein). The line immunoassay system equaled or surpassed the other techniques in the identification of anti-Sm, anti-La/SS-B, anti-Jo 1 and anti-Scl 70 antibodies (sensitivity 100%, specificity 94-100%) and was similarly effective in the case of anti-U1RNP (sensitivity 87.5%, specificity 93.9%) and anti-Ro/SS-A (sensitivity 91.4%, specificity 87.2%) antibodies. In addition, this technique detected more 52 and 60 kD anti-Ro/SS-A sera than IB. Nine antibodies can be detected with this method at a cost of 25.38 Euros per serum sample. In five hours, 19 sera can be studied. The approximate cost of detecting these nine antibodies with an automated ELISA system would be 28.93 Euros, which allows 10 sera to be studied in four hours. In conclusion, the automated multiparameter line immunoassay system is a valid method for the detection of autoantibodies in rheumatic diseases. Its most notable advantages are automated simultaneous detection of several autoantibodies in the same serum and its lower cost compared with ELISA techniques.

The Ro 60 kDa autoantigen: insights into cellular function and role in autoimmunity

An RNA-binding protein, the Ro 60 kDa autoantigen, is a major target of the immune response in patients suffering from two systemic rheumatic diseases, systemic lupus erythematosus and Sjogren's syndrome. In lupus patients, anti-Ro antibodies are associated with photosensitive skin lesions and with neonatal lupus, a syndrome in which mothers with anti-Ro antibodies give birth to children with photosensitive skin lesions and a cardiac conduction defect, third degree heart block. In vertebrate cells, the Ro protein binds small RNAs of unknown function known as Y RNAs. Although the cellular function of Ro has long been mysterious, recent studies have implicated Ro in two distinct processes: small RNA quality control and the enhancement of cell survival following exposure to ultraviolet irradiation. Most interestingly, mice lacking the Ro protein develop an autoimmune syndrome that shares some features with systemic lupus erythematosus in patients, suggesting that the normal function of Ro may be important for the prevention of this autoimmune disease. In this review, we summarize recent progress towards understanding the role of the Ro 60 kDa protein and discuss whether the cellular function of Ro could be related to certain manifestations of lupus in patients.

Zinc Ion Dependent B-Cell Epitope, Associated with Primary Sjogren's Syndrome, Resides within the Putative Zinc Finger Domain of Ro60kD Autoantigen: Physical and Immunologic Properties

The Ro/La ribonucleoprotein (RNP) complex is composed of the proteins Ro60kD, Ro52kD, and La48kD that are in association with one small cytoplasmic RNA (YRNA). Specific protein-RNA and protein-protein interactions are thought to occur through the RNP and zinc-finger secondary structure elements of the Ro60kD protein. The aim of our study was to investigate the antigenic properties of the zinc finger domain of the Ro60KD autoantigen and its contribution to the formation of Ro/La RNP complex. It was found that the peptide VSLVCEKLCNEKLLKKARIHPFHILIA (Zif-1), which corresponds to the natural sequence of the zinc finger domain (301-327), and the peptide C(Acm)NEKLLKKARIC(Acm), analogous to the intermediate loop 310-319 (Zif-3) of the same domain of Ro60KD, are recognized by the majority of anti-Ro/SSA and anti-La/SSB positive sera (82.6% and 77.1%, respectively) in the absence of zinc ions. The same sera failed to react with Zif-1 peptide in the presence of Zn2+. In contrast, the addition of zinc ions was necessary for the binding of Zif-1 to recombinant Ro52KD as shown by direct binding experiments of the recombinant protein with synthetic peptides. Our data suggest the zinc finger domain of Ro60kD contains a B-cell epitope with high specificity for primary Sjogren's syndrome. Furthermore, depending on the presence of zinc ions, the zinc finger domain of the Ro60KD protein can exist in two different conformational states favoring either an interaction with the Ro52KD protein or binding with autoantibodies.

[Congenital heart block associated with maternal anti SSA/SSB antibodies :a report of four cases]

Congenital heart block (CHB) associated with maternal anti-SSA/SSB antibodies: a report of four cases. CHB detected in utero is strongly associated with maternal antibodies to SSA (Ro) and SSB (La). Their pathogenic role in the development of CHB has been established in several studies. The mothers of affected infants frequently had autoimmune disease (systemic lupus erythematosus, Sjögren's syndrome) or were entirely asymptomatic. It is very difficult to identify pregnant asymptomatic mothers carrying anti-SSA/SSB antibodies. We report four cases of infants born to asymptomatic mothers with anti-SSA/SSB antibodies, three of them developed isolated congenital cardiac heart block and one with no evidence of CHB. All three CHB are detected during pregnancy between 16 and 24 weeks of gestation. All maternal sera contained antibodies to SSA alone or the both SSA and SSB. Three of four subsequent pregnancies were complicated by heart block. One child affected died in utero. While the two other newborns with CHB required pacemaker insertion during the first 3 months of life. Although the association of anti-SSA/SSB with CHB is widely accepted, the precise mechanism by which these antibodies cause cardiac conduction abnormalities remains to be defined. Antibodies to SSA/SSB have been proposed to be a serologic marker for neonatal lupus syndrome and CHB. Fetal and neonatal diseases are presumed to be due to the transplacental passage of these IgG autoantibodies from the mother into the fetal circulation. Since these antibodies may have a pathogenic role in CHB, screening of infants with isolated CHB or neonatal lupus and their mothers for the presence of anti-SSA and anti-SSB is strongly recommended.

Calreticulin binds preferentially with B cell linear epitopes of Ro60 kD autoantigen, enhancing recognition by anti-Ro60 kD autoantibodies

Calreticulin is a molecular chaperone to newly synthesized polypeptides. Previous studies suggested that calreticulin is probably a protein member of the Ro/La RNP complex. The aims of this study were (a) to investigate whether linear B cell epitopes of the Ro/La RNP complex are bound to calreticulin and (b) if the complex peptide-calreticulin is recognized specifically by anti-Ro autoantibodies. Calreticulin was isolated from either human or pig spleen using a multi-step purification method and found to interact preferentially with biotinylated peptides derived from the sequence of the Ro60 kD 175-184aa(10p) and 216-232aa(17p). The interaction of the peptide-calreticulin complex was favoured by the combination of heat treatment, divalent cations and ATP. La/SSB epitopes did not react with calreticulin. Peptides corresponding to La/SSB epitopes as well as the common epitope of Sm did not interact with calreticulin. Thirty-eight anti-Ro60 KD positive and 23 anti-Ro60 kD negative sera of patients with systemic lupus erythematosus (SLE) and primary Sjögren's syndrome (pSS) were tested. All anti-Ro60 kD positive sera bound the complex calreticulin-17p, while 95% of the same sera had activity against the complex calreticulin - 10p. Tested individually, calreticulin, pep10p and pep17p presented very low reactivity (8%, 11% and 29%, respectively) against anti-Ro60 kD positive sera. Anti-Ro60 KD negative sera did not exhibit significant reactivity either with calreticulin, 10rho and 17rho or with the complexes calreticulin - 10p and calreticulin-17p (<5%). These results suggest that calreticulin can induce conformation-dependent recognition of the Ro60 kD epitopes, leading eventually to their recognition by autoantibodies. This is the first time that such a relationship is shown between a chaperone protein and fragments of an intracellular autoantigen. This work also provides insights into the understanding of mechanisms for autoantibody production. Furthermore, this association can be proved useful for the development of new sensitive assays for autoantibody detection.

Association of stress proteins with autoantigens: a possible mechanism for triggering autoimmunity?

Patterns of autoantibody production are diagnostic of many autoimmune disorders; the recent observation of additional autospecificities towards stress-induced proteins may also provide insight into the mechanisms by which such responses arise. Grp78 (also known as BiP) is a target of autoaggressive B and T cell responses in our murine model of anti-Ro (SS-A) autoimmunity and also in rheumatoid arthritis. In this report we demonstrate reciprocal intermolecular spreading occurs between Ro52 and Grp78 in immunized mice, reflecting physiological association of these molecules in vivo. Moreover, we provide direct biochemical evidence that Grp78 associates with the clinically relevant autoantigen, Ro52 (SS-A). Due to the discrete compartmentalization of Ro52 (nucleocytoplasmic) and Grp78 (endoplasmic reticulum; ER) we propose that association of these molecules occurs either in apoptotic cells, where they have been demonstrated indirectly to co-localize in discrete apoptotic bodies, or in B cells themselves where both Ro52 and Grp78 are known to bind to immunoglobulin heavy chains. Tagging of molecules by association with Grp78 may facilitate receptor mediated phagocytotsis of the complex; we show evidence that exogenous Grp78 can associate with cell surface receptors on a subpopulation of murine splenocytes. Given the likelihood that Grp78 will associate with viral glycoproteins in the ER it is possible that it may become a bystander target of the spreading antiviral immune response. Thus, we propose a model whereby immunity elicited towards Grp78 leads to the selection of responses towards the Ro polypeptides and the subsequent cascade of responses observed in human disease.

A new conformational epitope generated by the binding of recombinant 70-kd protein and U1 RNA to anti-U1 RNP autoantibodies in sera from patients with mixed connective tissue disease

OBJECTIVE

To establish an enzyme-linked immunosorbent assay (ELISA) using a complex of in vitro-transcribed U1 RNA and recombinant 70-kd, A, and C proteins (C-ELISA) to detect anti-U1 RNP antibodies reactive in double immunodiffusion (DID), but not in ELISA using the proteins alone (P-ELISA).

METHODS

Sera from 196 patients with mixed connective tissue disease were used to test reactivity in P- and C-ELISAs, and the specificity of the sera was also tested by DID and immunoprecipitation (IP).

RESULTS

In P-ELISA, 15 of 196 sera positive for anti-U1 RNP in DID did not react, while all sera reacted in C-ELISA. The reactivity of 15 sera to the U1 RNA was tested by IP and ELISA, and only 3 sera reacted with the U1 RNA. These results indicated that the increased reactivity in C-ELISA was not due to the U1 RNA itself. We confirmed that the 70-kd and A proteins were bound directly to the U1 RNA by IP using antibodies to His-tag, and we tested the reactivity of the sera to the U1 RNA-70-kd protein complex and the U1 RNA-A protein complex by IP. All sera reacted with the U1 RNA-70-kd protein complex, and 1 sample reacted with the U1 RNA-A protein complex.

CONCLUSION

These results suggest that some anti-U1 RNP-positive sera specifically recognize the conformational structure altered by the binding of U1 RNA to the proteins, and the ELISA using U1 RNA and recombinant proteins is as useful as the DID method for detecting anti-U1 RNP antibodies.

Specificity of autoantibodies to SS-A/Ro on a transfected and overexpressed human 60 kDa Ro autoantigen substrate

The objective of this study was to analyze apparently discrepant results that arose during the use of an indirect immunofluorescence (IIF) assay using transfected HEp-2 cells to detect anti-SS-A/Ro autoantibodies in human sera. Fourteen sera that had SS-A/Ro antibodies as detected on this commercial substrate, but did not have antibodies to SS-A/Ro as determined by double immunodiffusion (ID) or enzyme-linked immunosorbent assay (ELISA), were studied by immunoprecipitation (IP) of radiolabeled cell extracts and full-length recombinant SS-A/Ro. A multi-antigen strip immunoblotting (IB) assay containing both the 52- and 60-kDa antigens was included in the analysis. We confirmed that 12 of 14 of the sera under study had antibodies to SS-A/Ro protein antigens as determined by at least one other immunoassay. One serum had antibodies to hyRNA but no detectable reactivity with the 52- or 60-kDa antigens. One serum remained negative in all assays for SS-A/Ro autoantibodies.

Anti-Ki antibodies recognize an epitope homologous with SV40 nuclear localization signal: clinical significance and reactivities in various immunoassays

Abstract We studied the characteristics of anti-Ki antibodies that react with a synthetic peptide (KILT) which has homology with SV40 large T antigen nuclear localization signal (SV40 T NLS). Immunoreactivity of antibodies to KILT was tested by enzyme-linked immunosorbent assay (ELISA), and this reactivity was compared with results obtained by immunoblotting using purified Ki and ELISA using purified or recombinant Ki antigen. The clinical significance of anti-KILT antibodies in lupus patients was also studied. Twenty percent of anti-Ki sera reacted with KILT, and all sera that reacted with KILT recognized both purified and recombinant Ki antigen in all our assay systems. A significant correlation was observed between reactivities in ELISA using KILT and with these using purified and recombinant Ki. Some sera with low titers by double immunodiffusion (DID) reacted with KILT, whereas high-titer anti-Ki sera showed a tendency to react with Ki antigen in different assays. The prevalence of discoid rash and sicca complex was higher in the anti-KILT-positive group. The amino acid sequence homologous to SV40 T NLS is an immunologically active epitope on the Ki antigen; reactivity to this epitope is associated with characteristic clinical features allied with anti-Ki antibodies in lupus patients.

Guidelines for the laboratory use of autoantibody tests in the diagnosis and monitoring of autoimmune rheumatic diseases

The Italian Society of Laboratory Medicine Study Group on the Diagnosis of Autoimmune Diseases has generated a series of guidelines for the laboratory diagnosis and monitoring of systemic autoimmune rheumatic diseases intendedfor the use of clinical pathologists and laboratory physicians. These guidelines are based on a systematic review of published works and expert panel discussion and consist of 13 recommendations for antinuclear antibodies, anti-double-stranded native DNA, and antinuclear specific antibodies. To improve analytic performances and help select the most appropriate test for specific autoantibodies, as well as provide education and guidance in the use of these tests, special emphasis is placed on laboratory methods.

Antibodies to extractable nuclear antigens. Has technological drift affected clinical interpretation?

Precipitating antibodies to extractable nuclear antigens are important in the diagnosis of connective tissue diseases. Disease associations are defined using gel based techniques. Alternative technologies have been introduced, including passive haemagglutination, enzyme linked immunosorbent assay, and western blotting. This leader contains a review of the literature on the clinical usefulness of these assays, together with knowledge gained from personal experience. Using the example of systemic lupus erythematosus, the sensitivity, specificity, and positive predictive value of the assays for disease is discussed, as is their differences in performance. The conclusion drawn is that disease specificity is method dependent. Validation and audit of performance of the method selected by the investigation laboratory is essential.

Autoantibody to the leucine zipper region of 52 kDa Ro/SSA binds native 60 kDa Ro/SSA: identification of a tertiary epitope with components from 60 kDa Ro/SSA and 52 kDa Ro/SSA

Anti-Ro (or SSA) is found in the sera of patients with autoimmune rheumatic illnesses. All patients with anti-Ro defined by precipitation bind a 60 000 Da antigen (60 kDa Ro), whereas some patients also bind a 52 000 Da molecule (52 kDa Ro). In general, antibody binding is directed against native 60 kDa Ro and denatured 52 kDa Ro. The mechanism by which anti-52 kDa Ro arises in the setting of anti-60 kDa Ro is unknown. Conflicting data exist as to the existence of a physical interaction between the two proteins in cells and as to cross-reacting antibodies. Antibodies were affinity purified from a peptide within the leucine zipper region of 52 kDa Ro. These purified antibodies binding the 197-207 peptide from 52 kDa Ro (anti-52LZ) bound native 60 kDa Ro as well as denatured 52 kDa Ro. In addition, anti-52LZ also bound up to four regions from the sequence of 60 kDa Ro and a single conformational epitope of 60 kDa Ro. Thus, these primary sites represent components of the tertiary epitope. We hypothesized that if this was the case, these peptides making up a tertiary epitope would show molecular interaction. In fact, peptides from 60 kDa Ro have a molecular interaction with the 52 kDa Ro peptide as well as full-length 52 kDa Ro when assessed by surface plasmon resonance. The leucine-zipper region peptide from 52 kDa Ro bound three of the four peptides from 60 kDa Ro. These data suggest that these two molecular species, 60 and 52 kDa Ro, form a conformational epitope. This relationship may explain why anti-52 kDa Ro is found in association with anti-60 kDa Ro.

Can B cell epitopes of 60 kDa Ro distinguish systemic lupus erythematosus from Sjögren's syndrome?

Antibodies binding components of the Ro/La (or SSA/SSB) ribonucleoprotein particle are found in the sera of patients with systemic lupus erythematosus (SLE) and Sjögren's syndrome (SS) as well as mothers who give birth to babies with neonatal lupus. Anti-La occurs in a subset of sera that contain anti-Ro, and anti-La is found more commonly in sera of patients with SS than in sera from SLE patients. The fine specificity of autoantibodies binding 60 kDa has been studied extensively. Recent data have suggested that there are disease-specific epitopes which identify patients with either SLE or SS. Alternatively, other data suggest that the B cell epitopes of 60kDa Ro vary according to the presence of anti-La. The present study was undertaken to determine whether binding of putative disease-specific 60 kDa Ro epitopes is associated with the diagnosis of SLE vs SS, or instead associated with the presence of anti-La. Anti-60 kDa Ro positive sera from 24 SLE patients and 44 SS patients were studied for antibodies binding two epitopes of 60 kDa Ro. We find the epitope defined by residues 171-190 is associated with anti-60 kDa Ro without anti-La, regardless of diagnosis. Meanwhile, binding of the epitope defined by residues 215-232 is not commonly found in anti-60 kDa Ro sera, especially in those sera with both anti-60 kDa Ro and anti-La. Thus, the fine specificity of antibody binding to 60 kDa Ro varies according to the presence of anti-La, not to the diagnosis of either SLE or SS.

On the origin of surface proteinase 3 of nonmyeloid cells: evidence favoring an exogenous source

In Wegener's granulomatosis (WG), when the endogenous Proteinase 3 (PR3) of myeloid cells is translocated to the cell surface, a pathologically consequent interaction is believed to occur with classic anti-neutrophil cytoplasmic antibody (cANCA). In contrast, the exact origin of surface PR3 on cells of nonmyeloid origin is still debated. By various methods, PR3 mRNA and protein are easily demonstrated in myeloid cells but not in nonmyeloid cells. Exceptionally, the endothelial ECV304 cell line spontaneously produced PR3 mRNA but no PR3 protein. In the other nonmyeloid cells, we could not show cell surface PR3 either spontaneously or after TNFalpha stimulation. On the other hand, under serum-free conditions and using [(3)H]DFP-labeled HL-60 extract, a rapid, dose-dependent, saturable binding was demonstrated to both myeloid and nonmyeloid cells. That was reproduced with purified [(3)H]DFP-PR3. While we could not demonstrate cell surface PR3 on nonmyeloid cells after incubation with serum-containing supernatants of HL-60 cell cultures, we could do so after an overnight coculture period with HL-60 cell suspensions under the usual serum-containing culture conditions. Overall, our data would suggest that in vivo, the surface PR3 found on nonmyeloid cells is not endogenous but results from adsorption of PR3 extruded in their microenvironment by neighboring myeloid cells coming in close contact with them.

Analysis of the autoimmune epitopes on human testicular NASP using recombinant and synthetic peptides

The human nuclear autoantigenic sperm protein, NASP, is a testicular histone-binding protein of 787 amino acids to which most vasectomized men develop autoantibodies. In this study to define the boundaries of antigenic regions and epitope recognition pattern, recombinant deletion mutants spanning the entire protein coding sequence and a human NASP cDNA sublibrary were screened with vasectomy patients' sera. Employing panel sera from 21 vasectomy patients with anti-sperm antibodies, a heterogeneous pattern of autoantibody binding to the recombinant polypeptides was detected in ELISA and immunoblotting. The majority of sera (20/21) had antibodies to one or more of the NASP fusion proteins. Antigenic sites preferentially recognized by the individual patients' sera were located within aa 32-352 and aa 572-787. Using a patient's serum selected for its reactivity to the whole recombinant protein in Western blots, cDNA clones positive for the C-terminal domain of the molecule were identified. The number and location of linear epitopes in this region were determined by synthetic peptide mapping and inhibition studies. The epitope-containing segment was delimited to the sequence aa 619-692 and analysis of a series of 74 concurrent overlapping 9mer synthetic peptides encompassing this region revealed four linear epitopes: amino acid residues IREKIEDAK (aa 648-656), KESQRSGNV (aa 656-664), AELALKATL (aa 665-673) and GFTPGGGGS (aa 680-688). All individual patients' sera reacted with epitopes within the sequence IREellipsis.GGS (aa 648-688). The strongest reactivity was displayed by peptides corresponding to the sequence AELALKATL (aa 665-673). Thus, multiple continuous autoimmune epitopes in NASP involving sequences in the conserved C-terminal domain as well as in the less conserved testis-specific N-terminal region comprising the histone-binding sites, as predicted for an antigen-driven immune response, may be a target of autoantibodies in vasectomized men and may provide a relevant laboratory variable to describe more accurately the spectrum of autoantibody specificities associated with the clinical manifestation of vasectomy.

Immunological and clinical differences between juvenile and adult onset of systemic lupus erythematosus

INTRODUCTION

Systemic lupus erythematosus (SLE) in children usually follows a more severe course than in adults, but sometimes in the previous studies reported there are many confounding factors.

OBJECTIVE

To analyse the immunological and clinical characteristics of SLE juvenile onset and SLE adult onset.

METHODS

We studied 179 patients with SLE, 49 patients were aged 6-18 yrs at onset of disease. Anti-dsDNA antibodies were detected by radioimmunoassay and antibodies to extractable nuclear antigens (ENA): anti-nRNP, anti-Sm, anti-Ro/SS-A and anti-La/SS-B antibodies by ELISA, counterimmuno-electrophoresis and immunoblotting.

RESULTS

Juvenile-onset SLE shows a higher frequency of cutaneous vasculitis (44.8% vs 27.6%; P < 0.05), seizures (18.3% vs 7.6%; P < 0.05) nephropathy (67.3% vs 48.4%; P < 0.025), and discoid lupus erythematosus (26.5% vs 13.8%; P < 0.05). The incidence of articular manifestations is lower than in adults (85.7% vs 96.1%; P < 0.025). No significant differences were found between the two groups in relation with the prevalence of antinuclear antibodies.

CONCLUSIONS

Juvenile-onset SLE has more frequent neurological and renal manifestations than adult-onset SLE, but immunological markers are similar in both groups. These features suggest the most severe clinical manifestations in the juvenile-onset SLE group are not related with the presence of studied antibodies by different methods.

Analysis of B-cell epitopes of the Ro/SS-A autoantigen

Autoantibodies to the Ro and La ribonucleoprotein antigens are found in several rheumatoid diseases. The important epitopes have been studied using synthetic peptides and recombinant antigens to understand how they arise and their implication in disease. Here, we analyse the results of epitope mapping studies of Ro60 and Ro52 autoantigens and focus on the major findings to date.

Detecting anti-SSA and anti-SSB antibodies in routine analysis: a comparison between double immunodiffusion and immunoblotting

The aim of this study was to assess the performance of a commercially available procedure for detecting anti-Sjögren's syndrome A (anti-SSA) and anti-Sjögren's syndrome B (anti-SSB) antibodies by immunoblotting (IB) and compare it with double immunodiffusion (DID). We also studied the clinical significance of these profiles in a series of unselected anti-SSA positive patients. Serum samples from 534 patients that were positive on an immunofluorescent screening test using HEp-2 cells were analysed for anti-SSA and anti-SSB antibodies by DID and IB (Biolab Anablot System II), and the results on anti-SSA antibodies were confirmed by an enzyme-linked immunosorbent assay (ELISA). Fifty-five serum samples were found to be positive for anti-SSA antibodies. Among these, 24 were anti-SSA negative by IB but positive by DID and ELISA ('non-blotter sera'), whereas only three serum samples were anti-SSA negative by DID but positive by IB and ELISA. Of the 18 anti-SSB positive serum samples, eight were negative by DID. All the serum samples that were anti-SSB positive by DID were also positive by IB. Anti-SSB antibodies showed a significant association with eye dryness and leucopenia. Anti-52 kDa SSA antibodies were associated with anti-SSB antibodies but showed no significant association with sicca symptoms, while anti-60 kDa SSA antibodies were associated with lower rates of leucopenia. The 'non-blotter' profile showed no significant association with any clinical parameter. IB is less sensitive than DID for detecting anti-SSA antibodies but more sensitive than DID for detecting anti-SSB antibodies. The determination of anti-SSA immunoblotting profiles in patients positive for anti-SSA antibodies by DID does not significantly improve the clinical usefulness of this test. As expected, anti-SSB antibodies were associated with clinical features of Sjögren's disease. Non-blotting (probably conformational) anti-SSA antibodies did not show any further association with clinical parameters and seem to have no clinical relevance.

Fine specificity of the autoimmune response to the Ro/SSA and La/SSB ribonucleoproteins

The fine specificity of the Ro and La proteins has been studied by several techniques. In general, there is agreement in a qualitative sense that autoantibodies bind multiple epitopes. For some specific antibody binding, different studies agree quantitatively, for instance, the binding of the carboxyl terminus of 60-kd Ro as described by 2 studies using different techniques and the presence of an epitope within the leucine zipper of 52-kd Ro. In addition, there is general agreement about the location of a prominent epitope at the RRM motif region of the La molecule. On the other hand, the many specific epitope regions of the molecules differ among these studies. These discrepancies are likely the result of using different techniques, sera, and peptide constructs as well as a result of inherent advantages and disadvantages in the individual approaches. Several theories concerning the origin of not only the antibodies, but also the diseases themselves, have been generated from studies of the fine specificity of antibody binding. These include a theory of a primordial foreign antigen for anti-Ro autoimmunity, molecular mimicry with regard to La and CCHB, as well as the association of anti-Ro with HLA. These remain unproven, but are of continuing interest. An explanation for the association of anti-60-kd Ro and anti-52-kd Ro in the sera of patients has sprung from evaluating antibody binding. Data demonstrating multiple epitopes are part of a large body of evidence that strongly suggests an antigen-driven immune response. This means that the autoantigens are directly implicated in initiating and sustaining autoimmunity in their associated diseases. A number of studies have investigated the possibility of differences in the immune response to these antigens in SS and SLE sera. While several differences have been reported, none have been reproduced in a second cohort of patients. Furthermore, none of the reported differences may be sufficiently robust for clinical purposes, such as distinguishing between SS with systemic features and mild SLE, although some might be promising. For instance, in at least 3 groups of SLE patients, no binding of residues spanning amino acids 21-41 of 60-kd Ro has been found. Meanwhile, 1 of those studies found that 41% of sera from patients with primary SS bound the 60-kd Ro peptide 21-41. Perhaps future studies will elaborate a clinical role of such a difference among SS and SLE patients. Study of the epitopes of these autoantigens has, in part, led to a new animal model of anti-Ro and anti-La. Non-autoimmune-prone animals are immunized with proteins or peptides that make up the Ro/La RNP. Such animals develop an autoimmune response to the entire particle, not just the immunogen. This response has been hypothesized to arise from autoreactive B cells. In another, older animal model of disease, the MRL-lpr/lpr mouse, B cells have recently been shown to be required for the generation of abnormal, autoreactive T cells. Thus, there are now powerful data indicating that B cells that produce autoantibodies are directly involved in the pathogenesis of disease above and beyond the formation of immune complexes. Given that the autoreactive B cell is potentially critical to the underlying pathogenesis of disease, then studying these cells will be crucial to further understanding the origin of diseases associated with Ro and La autoimmunity. Hopefully, an increased understanding will eventually lead to improved treatment of patients. Progress in the area of treatment will almost surely be incremental, and studies of the fine specificity of autoantibody binding will be a part of the body of basic knowledge contributing to ultimate advancement. In the future, the animal models will need to be examined with regard to immunology and immunochemistry as well as genetics. The development of these autoantibodies has not been studied extensively because upon presentation to medical care, virtually all patients have a full-

Ro/SS-A- and La/SS-B-reactive B lymphocytes in peripheral blood of patients with Sjögren's syndrome

The aim of this study was to investigate the production of anti-Ro/SS-A and anti-La/SS-B antibodies in peripheral blood (PB) of patients with Sjögren's syndrome (SS). The ELISPOT method was performed to quantify the frequency of PB lymphocytes spontaneously secreting anti-Ro/SS-A and/or anti-La/SS-B antibodies. The total number of IgG-, IgA- and IgM-producing cells was also quantified. The recombinant Ro 52-kD, Ro 60-kD and La 48-kD proteins were used as target antigens. Three of 18 SS patients had PB lymphocytes secreting IgG antibodies against the recombinant Ro 52-kD protein. The same three patients had high serum titres of anti-Ro 52-kD antibodies. In addition, these patients were classified as having severe disease, and all three had focus scores of >/= 8 in biopsies of the labial salivary glands (LSG). The correlation between the number of PB cells producing IgG antibodies against the recombinant Ro 52-kD protein and the focus score was significant (P < 0.01). The results indicate that only SS patients with severe disease and high degree of local inflammation in LSG have B cells producing anti-Ro/SS-A antibodies in PB. Thus, most of the spontaneous autoantibody production must take place in other body compartments, e.g. in exocrine glands and probably also in the lymphoid organs and/or other mucosal sites.

B-cell epitope spreading in autoimmunity

How the immune response matures from recognizing a single or a few structures of the antigen to many is an obviously important process. Models of B-cell epitope spreading have been developed in a variety of systems. For example, immunization of animals with PPPGMRPP, one of the earliest B-cell epitopes in the anti-Sm response found in human lupus, leads to antispliceosomal autoimmunity and features of lupus. The humoral immune response spreads from PPPGMRPP to other structures of the spliceosome in an apparently reproducible sequence. B-cell epitope spreading has provided the experimental basis from which a relationship between lupus and Epstein-Barr virus was suspected. An understanding of B-cell epitope spreading is likely to lead to important principles in basic immunology and to answers to human disease problems.

Structural, molecular and immunological properties of linear B-cell epitopes of Ro60KD autoantigen

Antibodies to Ro60KD protein are found with high frequency in sera from patients with systemic lupus erythematosus (SLE) and primary Sjögren's syndrome (pSS). Two major epitopes of the Ro60KD antigen, the TKYKQRNGWSHKDLLRSHLKP (169-190) and the ELYKEKALSVETEKLLKYLEAV (211-232), were synthesized and their antigenic and structural properties were studied. Using a large panel of SLE and pSS patients' sera, it was found that the anti-Ro60KD reactivity of both Ro60KD epitopes is rather limited (approximately 45%), although they retain their original disease specificity. The epitope p.169-190 possessed sequence similarity with the peptide RPDAEYWNSQKDLLEQKRGR, shared in the beta-chain of different HLA-DR molecules, among them the HLA-DR3 (which is associated with anti-Ro/Sjögren's syndrome A (SSA) response in patients with SLE). The antigenicity of the HLA-DR3 RPDAEYWNSQKDLLEQKRGR peptide was found to be similar to the 169-190 homologous Ro60KD epitope, recognized mainly by SLE sera. Structural studies showed that the 211-232 Ro60KD epitope exhibits pronounced helical characteristics, while the 169-190 epitope and the HLA-DR3 homologous peptide possess a somewhat lower percentage of alpha-helix. A beta-folded structure was identified in the latter two peptides. Although the diagnostic value of the reported Ro60KD epitopes seems to be rather limited, correlations with other ribonucleoprotein epitopes (La/Sjögren's syndrome B, Ro52KD) may prove complementary to each other and valuable in clinical use. The ordered structure of the HLA-DR3 homologous peptide, exposed to the autoantibody binding, may offer an initiative in further investigation of the role of the HLA haplotypes, associated with the anti-Ro/SSA response, in the autoimmune stimulus.

Anti-Ro/SS-A positivity and heat shock protein antibodies in patients with normal-pressure glaucoma

PURPOSE

To describe the clinical and laboratory findings in 10 patients with normal-pressure glaucoma and anti-Ro/SS-A positivity by enzyme-linked immunosorbent assay (ELISA) and to determine whether that positivity may be related to an autoimmune mechanism for the optic neuropathy.

METHODS

In this prospective study, we evaluated ocular and systemic clinical findings of 10 patients with normal-pressure glaucoma and anti-Ro/SS-A positivity by ELISA, including sicca complex features. Oüchterlony immunodiffusion was performed to confirm the presence of antibodies for Ro/SS-A, and the presence of other serum antibodies and their possible cross-reactivities with Ro/SS-A were investigated.

RESULTS

None of the 10 patients with normal-pressure glaucoma and anti-Ro/SS-A positivity (by ELISA) had clinical or laboratory signs of Sjögren syndrome or other connective tissue diseases. Only one of 10 patients had evidence of anti-Ro/SS-A antibodies by Oüchterlony immunodiffusion. All patients demonstrated serum immunoreactivity to bacterial heat shock protein 60 (hsp60) by Western blotting. Cross-reactivity between bacterial hsp60 and Ro/SS-A was demonstrated by Western blotting. Immunoreactivity to bacterial hsp60 by ELISA was significantly elevated in the sera of patients with normal-pressure glaucoma. Furthermore, patients with either normal-pressure or primary open-angle glaucoma had increased serum immunoreactivity to human hsp60.

CONCLUSIONS

Anti-Ro/SS-A positivity by ELISA in 10 patients with normal-pressure glaucoma was associated with a high level of serum immunoreactivity to bacterial hsp60, which may indicate that their glaucomatous optic neuropathy involves an as yet unidentified autoimmune mechanism. The identification of autoantibodies that react with human hsp60 in patients with normal-pressure and primary open-angle glaucoma may signify a common finding associated with the glaucomatous optic neuropathy process in some patients and appears to be unrelated to intraocular pressure levels.

Ro/SS-A and La/SS-B antibody level variation in patients with Sjögren's syndrome and systemic lupus erythematosus

To examine both possible correlations between anti-Ro/SS-A and anti-La/SS-B levels and their correlation with clinical disease activity in patients with Sjögren's syndrome (SS) or systemic lupus erythematosus (SLE), an ELISA was developed using purified recombinant Ro 60 kDa, Ro 52 kDa and La antigens. The ELISA was used for testing sequential serum samples from 16 patients with either SS or SLE. The patients were followed for periods between 15 and 128 months, and 3-15 serum samples per patient were analysed and compared with clinically apparent disease activity at the time of sampling in 14 patients. A temporal correlation of antibody levels to Ro and La antigens was found, and antibodies to different epitopes of the Ro 60 kDa protein showed parallel variation in seven of eight patients tested. Co-variation of autoantibody levels and disease activity was found in 11 of 14 patients. In seven of these 11 patients the anti-Ro and anti-La levels were stable and changes in disease activity were minimal during the observation period. In the other four of these 11, changes in disease activity were noted, with an associated change in autoantibody levels. The results suggest that the serological response to Ro and La antigens, as well as to different epitopes of the Ro 60 kDa protein, is antigen driven and regulated by common mechanisms, and indicate a correlation of Ro and La antibodies with pathogenic events.

Antiribonucleoprotein antibodies in children with HIV infection: a comparative study with childhood-onset systemic lupus erythematosus

A number of clinical and laboratory features of HIV infection are found in systemic lupus erythematosus (SLE). The objective of this study was to analyze the presence of circulating antibodies to small nuclear ribonucleoproteins (snRNP) in both diseases. Sera from 44 HIV-infected children, from 22 patients with childhood-onset SLE, and from 50 healthy children were studied. Anti-snRNP antibodies were detected by ELISA using recombinant and affinity-purified nuclear antigens, by counterimmunoelectrophoresis (CIE), and by immunoblotting using extractable nuclear antigens. Results included the detection of anti-snRNP antibodies by ELISA in 30 HIV-infected patients (68.1%) and 19 SLE patients (86.3%). These antibodies were directed against U1-RNP (61.3% and 77.2%, respectively), Sm (29.5% and 54.5%, respectively), 60 kDa Ro/SS-A (47.7% and 50%, respectively), and La/SS-B proteins (18.1% and 9%, respectively). None of the HIV-infected children and 11 SLE patients (50%) showed anti-snRNP antibodies by CIE. None of the HIV-infected patients showed anti-70 kDa U1-RNP or anti-D-Sm antibodies by immunoblotting. No differences between the two groups were noted on the presence of nonprecipitating anti-snRNP antibodies. No such reactivities were observed among the normal sera tested. The authors concluded that nonprecipitating anti-snRNP antibodies in HIV-infected children are as frequent as in childhood-onset SLE. The significance of these antibodies is not clear at present. Although polyreactive and low-affinity antibodies and a mechanism of molecular mimicry may explain these results, a specific stimulation of B cells by nuclear antigens could not be excluded.

Clinical significances of antibodies to Ro/SS-A autoantigens and its subtypes in primary Sjögren's syndrome

OBJECTIVE

To evaluate the patterns of Ro autoantigen recognition in Korean patients with primary Sjögren's syndrome (SS) and to investigate its clinical significance in SS.

METHODS

Sera from primary SS (n = 51) and systemic lupus erythematosus (SLE) (n = 132) were tested by double immunodiffusion test and immunoblotting for reactivity with 60 kDa and 52 kDa Ro/SS-A proteins. Clinical manifestations were evaluated on the basis of the presence of anti-Ro/SS-A antibodies and anti-60 kDa/52 kDa proteins.

RESULTS

The prevalence of anti-Ro/SS-A antibodies in Korean patients with primary SS was 64.7%. In immunoblotting analysis, the incidence of anti-60 kDa without anti-52 kDa was lower in patients with SS(3.0% vs. 11.6%, p > 0.05), whereas anti-52 kDa without anti-60 kDa was more common in SS patients than in SLE patients(42.5% vs. 4.3%, p < 0.001). Patients with anti-Ro/SS-A antibody were significantly associated with the presence of vasculitis, hyperglobulinemia and rheumatoid factor in primary SS (p < 0.05).

CONCLUSION

The patterns of 52 kDa and 60 kDa Ro autoantigen recognition were quite different in the SLE and primary SS. Anti-52 kDa without anti-60 kDa antibody may be used as a diagnostic marker for primary SS. Although the presence of anti-Ro/SS-A antibody was closely associated with certain clinical features in SS, these clinical manifestations were not correlated with the presence of antibodies against each 52 kDa and 60 kDa proteins. Extended studies with a large population are required to determine the clinical correlation of autoantibodies against each peptides or epitopes of Ro/SS-A proteins.

Human anti-Ro autoantibodies bind multiple conformational epitopes of 60-kD Ro autoantigen

A gel filtration method was developed to estimate the number of conformational epitopes on the 60-kD Ro antigen. Anti-Ro Fab or Fab' was incubated with native Ro antigen at different ratios and the Stokes radius molecular weight of complexes was estimated by gel filtration. Binding was saturated at 9 to 11 Fab molecules per bovine Ro molecule. Two additional Fab or Fab' were bound if human Ro was used as the antigen. Isolated Ro antigen/anti-Ro Fab complexes were evaluated for the relative proportion of antigen to antibody at saturation of antigen with antibody and thus stoichiometry was determined. This provided data supporting there being between 7 and 11 binding sites, results similar to those with the gel filtration method. Experiments carried out with anti-Ro monoclonal antibodies showed one binding site per molecule of 60-kD Ro. Therefore, we have developed methods to count conformational epitopes on autoantigens and have applied it to the Ro/anti-Ro system. The data indicate that multiple conformational epitopes can be bound simultaneously by polyclonal anti-Ro sera from patients with systemic lupus erythematosus.

Characteristic epitope recognition pattern of autoantibodies against eukaryotic ribosomal protein L7 in systemic autoimmune diseases

OBJECTIVE

To define the epitope-recognition pattern and the fine specificity of the autoantibody response to protein L7 in patients with rheumatic diseases.

METHODS

The epitope-recognition pattern was studied by enzyme-linked immunosorbent assay utilizing overlapping fragments of L7. The fine specificity was examined by binding inhibition and isoelectric focusing.

RESULTS

We observed a disease-specific epitope-recognition pattern of anti-L7 autoantibodies. There was one immunodominant epitope that was recognized by all anti-L7-positive sera from patients with systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and systemic sclerosis (SSc). Additional recognition of minor epitopes was observed; it arises by intramolecular epitope spreading and was correlated with disease activity in SLE patients. SSc patients differed from SLE and RA patients in that their sera did not recognize certain minor epitopes. The major epitope was recognized by high-affinity autoantibodies of limited heterogeneity. Minor epitopes were recognized by heterogeneous low-affinity autoantibodies.

CONCLUSION

The anti-L7 autoantibody response is oligoclonal. Additional B cell clones are activated by antigen during active phases of disease.

Cardiac expression of 52beta, an alternative transcript of the congenital heart block-associated 52-kd SS-A/Ro autoantigen, is maximal during fetal development

OBJECTIVE

Congenital heart block (CHB), associated with antibodies to SS-A/Ro and SS-B/La, is most often detected between 18 and 24 weeks of gestation, yet the maternal heart is unaffected. We recently described an alternatively spliced 52-kd SS-A/Ro messenger RNA (mRNA) derived from the skipping of exon 4 which encodes a smaller protein, 52beta (MW 45 kd), recognized by CHB maternal antisera. This study was designed to identify whether cardiac expression of 52beta and full-length 52alpha relates to the development of CHB.

METHODS

Reverse transcriptase-polymerase chain reaction was performed using primers flanking exon 4 and mRNA from 22 human fetal hearts (age 11-25 weeks) and 3 adult hearts. The brain, kidney, liver, lung, and spleen were similarly evaluated in a 15-week, an 18-week, and a 24-week fetus.

RESULTS

Expression of 52beta was greatest and 52alpha lowest between 14 and 16 weeks of gestation. In fetal hearts ages 22-25 weeks and adult heart, the 52beta transcript was markedly diminished and 52alpha clearly dominated. The 52beta mRNA was observed in a 15-week brain, kidney, lung, and spleen; however, its expression relative to 52alpha was greatest in the heart.

CONCLUSION

Since expression of the alternative product 52beta is maximal at the time of cardiac ontogeny when maternal antibodies gain access to the fetal circulation, just prior to the clinical detection of bradyarrhythmia, a role for 52beta in the development of CHB is implicated. Although other fetal tissues express 52beta, there may be differences in accessibility of antigen or regenerative capacities.

Arrhythmogenicity of IgG and anti-52-kD SSA/Ro affinity-purified antibodies from mothers of children with congenital heart block

An important advance in the description and understanding of congenital heart block (CHB) came in the 1970s with the observation that mothers of affected infants frequently had autoimmune diseases and, in particular, that many maternal sera contained antibodies to SSA/Ro and SSB/La ribonucleoproteins. Although the molecular biology of the candidate antigens has been extensively defined, the arrhythmogenic and electrophysiological effects of their cognate antibodies on the human fetal heart are unknown. In the present study, we provide evidence that IgG-enriched fractions and anti-52-kD SSA/Ro antibodies affinity-purified from sera of mothers whose children have CHB induce complete atrioventricular (AV) block in the human fetal heart perfused by the Langendorff technique and inhibit L-type Ca2+ currents at the whole-cell and single-channel level. Immunization of female BALB/c mice with recombinant 52-kD SSA/Ro protein generated high-titer antibodies that crossed the placenta during pregnancy and were associated with varying degrees of AV conduction abnormalities, including complete AV block, in the pups. These findings strongly suggest that anti-52-kD SSA/Ro antibodies are causally related to the development of CHB.

Systemic lupus erythematosus: clinical expression and anti-Ro/SS--a response in patients with and without lesions of subacute cutaneous lupus erythematosus

Patients with subacute cutaneous lupus erythematosus (SCLE) have recurrent annular and/or psoriasiphorm skin lesions, with or without systemic disease.

OBJECTIVE

To analyse the clinical expression and the Ro/SS-A response associated with SCLE in patients with systemic lupus erythematosus (SLE).

METHODS

128 consecutive patients with SLE were studied. Anti-Ro/SS-A antibodies were detected by ELISA, (anti-60 kD Ro/SSA antibodies), immunoblotting (anti-60 kD and anti-52 kD Ro/SS-A antibodies) and counterimmunoelectrophoresis (CIE).

RESULTS

Seventeen patients (13.2%) showed SCLE lesions. Photosensitivity was more frequent in patients with SCLE (82%) than in patients without these cutaneous lesions (45%) (OR: 5.6). Arthritis (OR: 6.3), Raynaud's phenomenon (OR: 4.9), pleuritis (OR: 7.6), central nervous system disorder (OR: 6.4), renal disease (OR: 6.3), anemia (OR: 7.9), hypocomplementemia (OR: 6.1) and anti-dsDNA antibodies (OR: 12.7) were significantly more frequent in patients without SCLE. Anti-Ro/SS-A antibodies were detected in 15 (88.2%) patients with SCLE and 62 (55.8%) patients without SCLE by ELISA, in 10 (58.8%) and 34 (30.6%) patients by immunoblotting, and in 13 (76.4%) and 34 (30.6%) by CIE, respectively. Anti-60 kD-Ro/SS-A and anti-La antibodies, but not anti-52 kD-Ro/SS-A, were significantly more frequent in patients with SCLE than in patients without SCLE.

CONCLUSIONS

The presence of SCLE lesions in patients with SLE is associated with a more favourable prognosis. The major anti-Ro/SS-A response is directed against the native 60 kD Ro/SS-A protein.

A subpopulation of WIL-2 cell calreticulin molecules is associated with RO/SS-A ribonucleoprotein particles

A subpopulation of human calreticulin (CR) molecules that is reactive with human Ro/SS-A autoimmune sera was identified in a nucleic acid- enriched Wil-2 cell fraction derived by anion exchange column chromatography. Further resolution of this fraction by gel filtration size separation demonstrated that the appearance of CR (true mol. weight 46 kD) coincided with the emergence of Ro/SS-A ribonucleoprotein (mol. weight > 250 kD) antigenic activity and increasing 260 nm ultraviolet absorbance. This high nucleic acid fraction could be further partitioned into four small RNA-containing Ro/SS-A antigenic subfractions by a second passage over the anion exchange column. CR was enriched in one subfraction and present in the other three subfractions as well. No CR was found in the RNA-free fraction of the repartition eluate. These results represent the first direct demonstration that CR, a high-affinity calcium binding protein, exists in a form that is directly associated with all four varieties of native, human Ro/SS-A ribonucleoprotein particles (hY1-5).

Disparate locations of the 52- and 60-kDa Ro/SS-A antigens in cultured human keratinocytes

Anti-52- and anti-60-kDa Ro/SS-A (Ro) autoantibodies are produced by most patients with subacute cutaneous lupus erythematosus and neonatal lupus erythematosus and are thought to be pathogenic in these two disorders. To learn more about the epidermal antigens targeted by Ro autoantibodies, a panel of anti-52 and anti-60-kDa Ro antibodies was purified from human autoimmune sera and rabbit antisera and then used to: (i) determine the expression and location of the Ro antigens in human keratinocytes; (ii) clarify discrepancies in previous localization studies; and (iii) verify the existence of Ro autoantibodies that cross-react with the 52- and 60-kDa Ro antigens, as previously reported. By immunoblot analysis these antibodies demonstrate that 52- and 60-kDa Ro proteins are expressed in normal human skin and cultured keratinocytes. By indirect immunofluorescence studies with cultured human cells, the anti-52-kDa Ro antibodies produce fine granular cytoplasmic fluorescence and less intense nuclear fluorescence, with apparent nucleolar sparing. The anti-60-kDa Ro autoantibodies produce weak cytoplasmic fluorescence and intense coarse granular nuclear fluorescence with apparent nucleolar sparing. We found distinct differences in the intracellular localization of the 52- and 60-kDa Ro autoantigens. This difference suggests that the 52-and 60-kDa Ro antigens may have independent cellular functions. Finding 60-kDa Ro antigen predominantly in the nucleus challenges the notion that the majority of the intracellular 60-kDa Ro antigen is complexed with the cytoplasmic hY RNA. Additionally, our failure to find a cross-reactive epitope on these two proteins indicates that the 52-kDa Ro antigen is probably a true immunogen and not merely a protein that cross-reacts with anti-60-kDa Ro autoantibodies, as others have suggested.

Significance of the anti-Ro (SS-A) antibody in evaluation of patients with cutaneous manifestations of a connective tissue disease

The anti-Ro(SS-A) antibody is arguably the most important antibody determination except for antinuclear antibodies in evaluation of patients suspected of having lupus erythematosus. During the past 25 years, studies have established the importance of this antibody in the evaluation of patients with atypical lupus erythematosus, who have a photosensitive dermatitis as the presenting sign. The purpose of this review is to demonstrate the utility and the necessity of this antibody determination in the evaluation of all patients with cutaneous manifestations who are suspected of having a connective tissue disease.

Stability of immunoblot profile of anti-SSA/Ro-SSB/La antibodies over time in mothers whose children have neonatal lupus

Neonatal lupus is strongly associated with antibodies reactive with SSA/Ro-SSB/La proteins, independent of maternal disease activity or classification. We sought to determine whether the fine specificity of antibody profiles remains stable or evolves over time and whether these findings relate to clinical status. Sera from 23 mothers whose children had neonatal lupus (22 heart block, one skin) were evaluated by SDS-immunoblot. For each mother two samples were available at least 13 months apart; the mean duration of time between testing was 45 months +/- 27 S.D. (range 13-108 months). Twenty-two of the 23 initial profiles were identical to the results obtained in a later sample. The health status of seven (30%) of 23 mothers changed after the birth of the affected infant but the immunoblot specificity of the antibodies remained unchanged. SLE was the initial and final diagnosis in the only mother whose profiles differed, with development of weak reactivity to 48 kD SSB/La in addition to the 52kD SSA/Ro after 14 months. In conclusion, the fine specificity of anti-SSA/Ro-SSB/La antibodies as assessed by immunoblot is highly stable for years. Progression of clinical status was not associated with a concomitant change in antibody profile.