Passively acquired autoimmunity and the maternal fetal dyad in systemic lupus erythematosus

Neonatal lupus syndromes consist of transient cutaneous and hematologic abnormalities and permanent cardiac disorders all of which result from a common pathogenetic mechanism, the passive transfer of maternal autoantibodies. Detrimental antibodies such as SSA/Ro and SSB/La gain access to the fetal circulation via the normal active transport system of the trophoblast tissue which is operative after 20 weeks gestation. Despite functional maturation of the cardiac conduction system by 16 weeks gestation, fetal bradycardias are most often encountered after this time. Several lines of evidence are advanced in this review to support the role of myocarditis as the initial consequence of autoantibody attack on the fetal heart. The end result of this inflammatory insult is permanent fibrosis manifest as complete congenital heart block (CCHB). Despite the clearly demonstrated presence of SSA/Ro and SSB/La in fetal tissues as well as their fluctuation in quantity during the cell cycle, the precise accessibility of these antigens to their respective autoantibodies in unknown at the present time. However, ultraviolet light is reported to induce cell surface expression of SSA/Ro on cultured keratinocytes. The recognition of CCHB by fetal echocardiogram is presented. The rationale for the use of dexamethasone which crosses the placenta in an active form to treat fetal immune effector functions is discussed. Intense maternal plasmapheresis in an attempt to rapidly decrease maternal autoantibodies may provide another approach to the management of CCHB. Through increasing knowledge of this model of "passively acquired pure" systemic lupus erythematosus, insights into mechanisms of tissue injury and strategies for treatment will emerge.

[Antinuclear antibodies in Sjögren's disease and syndrome]

A study was made of the presence of antinuclear antibodies to Ro, La, nDNA, RNP and Sm in 18 patients with Sjögren's disease (SD) and in 13 patients with Sjögren's syndrome (SS). Anti-Ro and/or anti-La were revealed in 12 SD patients (67%) and in 3 SS patients (23%, P less than 0.05) only. Anti-nDNA and anti-RNP were detected in 39 and 15% of the SS patients respectively and were undetectable in the SD patients. Anti-Ro and/or anti-La were detected in all SD patients, III degree activity, and associated with the presence of Raynaud's syndrome, recurring nonerosive arthritis and the absence of adequate therapy. Anti-Ro only were detected in 44% of the SD patients only and in none of the SS patients. Higher values of ESR, RF and CIC were revealed in the SD patients with anti-La and especially anti-Ro.

Antibody class differences are detected in anti-nRNP and anti-Sm antibodies directed against distinct antigen subunits

Antibodies to nRNP, Sm and La were detected and characterised by immunoblot analysis. A comparison was made between IgG and IgM autoantibodies in 77 patients with systemic lupus erythematosus (SLE) and 50 normal subjects. No antibodies were detected in the normal subjects. In all 3 antigen specificity groups, a heterogeneity of antibody class was observed between patients. Antibodies to the 2 nRNP-specific polypeptides (33 and 67 kD) were approximately equally frequent. Although IgG antibodies to the 67 kD polypeptide were detected in 88% of patients with antibodies to this polypeptide, IgG antibodies to the 33 kD polypeptide were only detected in 43% of patients with antibodies to this polypeptide. This suggested either that anti-33 kD antibody is produced by a B cell which cannot mature to an IgG-secretor, or that anti-33 kD antibody production succeeds an initial immune response producing anti-67 kD. Reactivity with the 29 kD, Sm-specific polypeptide appeared to be the most frequent in anti-Sm sera compared with the 16 kD polypeptide suggesting that this polypeptide may be the primary immunogenic component of Sm.

Subclass restriction of anti-SS-B (La) autoantibodies

Antibodies to the SS-B (La) nuclear ribonucleoprotein particle are relatively specific for the diagnoses of Sjögren's syndrome or systemic lupus erythematosus. The formation of such autoantibodies is likely, then, to reflect the basic immunopathogenesis of these disorders. We have studied the isotype distribution of anti-SS-B antibodies as a clue to their immunoregulation. Using specific ELISA assays, we found that nearly all anti-SS-B antibodies in 39 patients were IgG, and, of these, only the IgG1 and, to a much lesser extent, IgG3 subclasses were represented. Both kappa and lambda light chain antibodies were found in most sera, and the overall kappa/lambda ratio approximated that of normal serum immunoglobulin. These results suggest that the formation of anti-SS-B antibodies is T-cell dependent and that the response is polyclonal in most patients.

Epitopes and structural domains of a RNA-binding nuclear protein, SS-B/La: similarities with adenovirus DNA-binding protein

SS-B/La is a conserved cellular phosphoprotein of 46/48 KD molecular weight which is the target antigen of autoantibodies in sera of patients with Sjögren's syndrome. Two relatively protease-resistant domains (X and Y) were defined in the SS-B antigen from HeLa cells. Human autoantibodies to SS-B were used as reagents. Domain X is a methionine-containing, non-phosphorylated 28 KD polypeptide and is resistant to partial digestion with six different proteases. Domain Y is a 23 KD polypeptide which contains little if any methionine, but all the detectable phosphorylated amino acids. These results demonstrate that there are at least two distinct antigenic epitopes on the 46/48 KD SS-B protein, each located on a separate structural domain. The asymmetric distribution of methionine and phosphorylated amino acid residues in SS-B show striking similarity to two reported domains of the adenovirus 72 KD DNA-binding protein, which also have separate methionine and phosphorylated amino acid distributions.

Molecular analysis of the RNA and protein components recognized by anti-La(SS-B) autoantibodies

The aim of this study was to determine whether sera with autoantibodies to the La(SS-B) nuclear antigen react with the same or different sets of cellular or viral ribonucleoproteins (RNPs) and whether patients with anti-La(SS-B) comprised a homogeneous group with respect to phenotypic and serological markers. The 34 anti-La(SS-B) sera studied were detected in the course of screening 2,000 sera referred from patients with suspected or defined multisystem autoimmune disease. Analysis of the molecular components of the small nuclear (sn) RNPs isolated from immune complexes developed in vitro between the IgG fractions of the anti-La(SS-B) sera and cell lines selected for their content of viral and cellular (non-viral) RNA showed that all 34 anti-La(SS-B) sera reacted with the same group of cellular RNAs and with two viral RNAs encoded by Epstein-Barr virus. The La(SS-B) RNPs contained one major 50,000 dalton antigenic polypeptide that resolved into 5-6 heterogeneously charged isospecies on two-dimensional immunoblots. In addition to anti-La(SS-B) reactivity, all 34 sera were shown to contain anti-Ro(SS-A) activity by counterimmunoelectrophoresis (CIEP); however, with three exceptions, the antigenic Ro(SS-A) polypeptide was not detectable by immunoblotting. The homogeneity of this group with anti-La(SS-B) was indicated by the findings that of the 34 cases 31 (88%) had hypergammaglobulinaemia, 33 (97%) had rheumatoid factor and 27 (of 30 tested, 90%) were HLA-B8. Thus all anti-La(SS-B) sera react with the same set of RNAs associated with an antigenic 50,000 dalton nucleoprotein, and the presence of anti-La(SS-B) autoantibodies identified a homogeneous group of patients with the serological and phenotypic features of primary Sjögren's syndrome.

Autoantibodies to ribonucleoproteins

Presently we recognize at least 12 different autoantibodies that involve ribonucleoproteins as antigens in patients with SLE and other rheumatic diseases. Such autoantibodies have a number of clinically useful diagnostic associations. Moreover, they have proved to be powerful tools for understanding the structure and function of a variety of cellular components that involve RNA molecules. In SLE, autoantibodies that recognize the U1 snRNP (i.e. anti-(U1)RNP and anti-Sm antibodies) and the Ro scRNPs (i.e. anti-Ro and anti-La antibodies) are especially prominent in terms of their high frequency and titre. These particles, along with the nucleosome (which is the principal focus of autoantibodies to chromatin) appear to have active roles in eliciting autoimmune responses in such patients. Future studies aimed at understanding how and when these particular structures interact with the immune system could provide important insights into the aetiology and pathogenesis of this disorder.

Antibodies to nRNP, Sm, Ro(SSA) and La(SSB) detected by ELISA: their specificity and inter-relations in connective tissue disease sera

The profile of autoantibodies to four soluble cellular ribonucleoproteins nRNP, Sm Ro(SSA) and La(SSB) was determined using ELISA with immuno-affinity-purified antigens in a connective tissue disease population. Compared with immunodiffusion, results using ELISA showed greater sensitivity but lower specificity and low titres of antibodies were frequently found in the sera of patients with connective tissue diseases other than systemic lupus erythematosus. This was true even for antibodies to Sm which have been considered highly specific for SLE. Antibodies to these antigens were predominantly of the IgG class and were capable of fixing complement irrespective of the clinical context. As previously demonstrated by immunodiffusion strong associations between anti-nRNP and anti-Sm and between anti-Ro(SSA) and anti-La(SSB) were detected by ELISA, while antibodies to nRNP and to Ro(SSA) identify distinctive serological groups. The observation that certain antibodies are closely linked suggests a relationship between the immune responses to particular antigens, and this might be explained by biological links between the antigens.

Immunohistochemical localization of La nuclear antigen in brain. Selective concentration of the La protein in neuronal nucleoli

We analyzed the subcellular distribution of La antigen in brain tissue using 5 La antisera regarded as monospecific on the basis of immunofluorescence, counterimmunoelectrophoresis and Western blot studies. Staining patterns of these sera on human, rat and guinea pig brain were assessed by indirect immunofluorescence and immunoperoxidase methods. There was an intense staining of the nucleolus in most neurons exposed to the La antisera in guinea pig brain. Human cerebral cortical neurons as well as a subset of neurons of rat brain also showed nucleolar staining with the La antisera. This staining could be inhibited by preincubation of La antisera with immunopurified La protein. One- and two-dimensional analysis of the La antigen from soluble and nuclear extracts suggested that the soluble and nucleolar La antigens are the same protein. The concentration of La in the nucleolus may be related to the proposed processing activity of this protein for the RNA polymerase III transcript, 5S RNA.

Association between the Ro and La antigenic determinants: immunodiffusion analysis of human spleen extract

The Ro (SS-A) and La (SS-B) antigenic determinants appear to be related to one another because of the frequent coincidence of spontaneous anti-Ro and anti-La in the same autoimmune sera, and because of a tendency of the Ro and La immunoprecipitin lines in double immunodiffusion analysis to fuse. We have developed an enzyme immunodiffusion staining (EIS) procedure that permitted us to identify the specific antigenic determinants found in an immunoprecipitin line. By using this technique with human spleen extract, we showed that the Ro and La particles are found together as a complex, as well as individually. The EIS technique insured that our results were not confounded by lack of monospecificity of our autoantibody and antigenic reagents. Ro-La antigenic complexes exist at physiologic pH, and are dissociated by high ionic strength. They may be formed in vivo either intracellularly or extracellularly. Such Ro-La complexes could be immunogenic, and thereby might account for the frequent coincidence of the anti-La and anti-Ro autoantibody specificities.

HLA and genetic predisposition to lupus erythematosus and other dermatologic disorders

Human leukocyte antigen (HLA) associations with different clinical and serologic subsets of lupus erythematosus are providing important clues to genetic predisposition and pathogenesis. The evolving complexity of the HLA-D region is described, and currently recognized HLA-region associations with systemic lupus erythematosus, subacute cutaneous lupus erythematosus, homozygous C2-deficient lupus, Sjögren's syndrome, and the neonatal lupus syndrome are reviewed. The striking relationship between the Ro/SSA-La/SSB antibody responses and HLA-DR2 and DR3 are emphasized. Other dermatologic conditions associated with HLA are also noted.

Immunologic and structural studies of the lupus/Sjögren's syndrome autoantigen, La/SSB, with a monoclonal antibody

La/SSB is a small nuclear RNA protein against which precipitating autoantibodies are made in many patients with systemic lupus erythematosus or Sjögren's syndrome. The recent purification of La/SSB has made structural and immunologic studies possible. Consequently, a mouse hybridoma antibody (La1) was raised, after immunization and fusion, that reacted with bovine La/SSB. Results of inhibition tests with tissue extracts and fluorescent antinuclear antibody tests demonstrated that La1 reacted with bovine extracts and cells, but not with those from human, mouse, or rabbit sources. La1 reacted in Western blot and in an adapted anti-La/SSB enzyme-linked immunosorbent assay with only the 41-kD bovine La/SSB peptide and not with the smaller 29-kD bovine La/SSB peptide. RNA gels showed that La1 bound the La/SSB particle that contained the predominant La/SSB RNA species near 90 nucleotides as well as the minor RNA species, both of which were bound by the human autoimmune anti-La/SSB serum. A solid-phase assay for human autoimmune anti-La/SSB antibody using La1 was more sensitive for the detection of human anti-La/SSB than was a comparable assay using purified La/SSB, and showed that anti-La/SSB is present in nearly all Ro/SSA precipitin-positive sera. Thus, this study demonstrates that monoclonal antibody can be raised against La/SSB; that the protein moiety of bovine La/SSB differs from human, mouse, and rabbit at an epitope on the 41-kD La/SSB peptide; that the RNA bound to the La1-reactive particle was as heterogeneous as that binding the anti-La/SSB autoimmune serum; and that anti-Ro/SSA and anti-La/SSB are closely associated.

Nucleoprotein autoantibodies in lupus erythematosus

Autoantibodies against deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) proteins are commonly detected in patients with lupus erythematosus (LE). Antibodies against native DNA are frequently detected in a subset of LE patients with a high prevalence of renal disease. Single-stranded DNA antibodies are also commonly detected in patients with systemic lupus erythematosus (SLE) but recent evidence indicates that approximately 25% of patients with benign, cutaneous (discoid) lupus also possess single-stranded DNA IgM autoantibodies. LE patients also frequently possess antibodies directed against a variety of ribonuclear proteins (RNP). These RNA protein autoantibodies are generally divided into two groups. One group is termed snRNPs (small nuclear ribonuclear protein); the other is termed scRNPs (small cytoplasmic ribonuclear protein). Anti-RNA protein autoantibodies occur as frequently in patients with SLE as do native DNA antibodies. Furthermore, in contradistinction to nDNA antibodies, lupus patients generally make large quantities (detected by gel precipitin techniques) of anti-RNP antibodies. The anti-RNP antibodies are directed against proteins that bind with specific RNA nucleotides. The best evidence at present indicates that these RNA proteins containing the specific RNA nucleotides are involved in RNA processing and post-translational activities such as protein synthesis. Furthermore, these SLE autoantibodies are now being employed, together with other autoantibody systems detected in other connective tissue diseases, to define the biological role of the respective RNA proteins.

Detection of autoantigens by immunoblotting using a peroxidase-anti-peroxidase complex

An immunoblotting procedure using a peroxidase-anti-peroxidase (PAP) complex was developed for the detection of autoantigens in crude mixtures by human autoimmune sera. Thymus proteins were transferred to a nitrocellulose sheet after electrophoresis in polyacrylamide gels and probed with a 1:100 dilution of serum. The location and extent of immunoglobulin G (IgG) binding was determined by sequential reaction with: rabbit anti-human IgG, goat anti-rabbit IgG and rabbit peroxidase-anti-peroxidase complex. The peroxidase was allowed to react with chloronaphthol and low levels of autoantigen/autoantibody complex were detectable with virtual absence of background colour. The inclusion of human IgG and its pepsin-generated fragment provided a means of controlling and calibrating the blotting procedure.

Fine specificities of autoantibodies directed against the Ro, La, Sm, RNP, and Jo-1 proteins defined by two-dimensional gel electrophoresis and immunoblotting

Although useful for specific purposes, immunofluorescence, precipitation in agarose gels, and the m.w. estimation of RNA or proteins immunoprecipitated from transformed cells often provide partial or ambiguous definition of autoantibody specificity. We have analyzed organ and cell extracts by one-and two-dimensional electrophoresis together with Western blotting to define the fine specificities of antibodies to the ribonucleoprotein (RNP) antigens Ro, La, Sm, RNP and Jo-1. One-dimensional analysis identified the Ro protein as a 57 kilodalton (kd) protein, although many anti-Ro sera also react with a 50 kd protein. La antisera react with 50 and 43 kd proteins. The 50 kd La protein readily breaks down into 43, 25, and smaller immunoreactive cleavage products. Partial proteolysis of Ro and La proteins in human spleen extracts produces similar immunoreactive products, providing evidence for a common structure. The major immunoreactive Sm antigens defined by human polyclonal antisera and a mouse monoclonal antiserum were doublets of 25/26 and 16/18 kd, whereas anti-RNP sera reacted with a protein of 68 kd. Most Sm-RNP antisera contained antibodies reactive with additional proteins, especially when whole cell extracts were used as a source of antigens. Two-dimensional analysis provided characteristic maps of the antigens. Ro and La were acidic, and La showed a unique set of acidic charge isomers at 50 and 43 kd. Anti-Sm antibodies reacted with discrete dots corresponding to both the acidic and basic regions of the first-dimension (charge) gels, whereas the RNP antigen showed a series of basic charge isomers of 68 kd. Many anti-Sm-RNP sera reacted with other closely spaced proteins of a similar charge and size to the Sm and RNP antigens, suggesting antibody cross-reactivity or reactivity with closely related functional proteins. Although Jo-1 had the same m.w. as the undegraded La antigen, the fingerprints were quite distinctive on two-dimensional electrophoresis. The results of this study indicate how the source and preparation of antigen extracts, as well as protein degradation, influence the m.w. determinations of soluble protein antigens. With these factors taken into account, two-dimensional fractionation with immunoblotting provides a highly discriminating, sensitive, and reproducible method of analysis of autoantibody specificity. This technique can be used to standardize reference antisera and to study protein antigens in normal and abnormal cell and tissue extracts, and could lead to new or more precise correlations with clinical disease.

Synthesis of small nuclear ribonucleoprotein particles by the malarial parasite Plasmodium falciparum

Sera from patients with autoimmune diseases have been used to identify small nuclear ribonucleoprotein particles (snRNPs) present in higher eukaryotic cells and also in dinoflagellates. Previously these sera have not detected crossreactive snRNP protein antigens of other lower eukaryotes such as yeast, Tetrahymena, or Dictyostelium. We report that anti-Sm, anti-U1-RNP, and anti-La/SS-B human antisera react with specific snRNP protein antigens synthesized by the protozoan Plasmodium falciparum, the human malarial parasite. These results suggest that the structure and antigenicity (and thus probably the function) of snRNPs have been widely conserved in eukaryote evolution.

Antinuclear antibodies in autoimmune disease. Significance and pathogenicity

A large number of antigen-antibody systems have been described in association with connective tissue diseases. However, with the exception of antibodies to dsDNA, none of them have yet been successfully implicated in the pathogenesis of autoimmune diseases. It is also unclear why specific ANA are associated just with certain diseases, for example, anti-Sm with systemic lupus erythematosus. Although many questions remain about what triggers ANA production and whether these antibodies are innocent bystanders or disease inducers or enhancers, ANA serology can still be very useful to the clinician.

Association of the lupus antigen La with a subset of U6 snRNA molecules

U6 snRNA is a component of the major class of small RNA-protein complexes, the Sm snRNPs, present in mammalian cell nuclei. Here we report that a substantial fraction (about 10%) of U6 RNA from human and mouse cells is associated with another lupus antigen, the 50 kd La protein. The La-bound U6 subpopulation is characterized by 3' end heterogeneity and partial undermethylation. These U6 molecules have U-rich 3' termini that could be responsible for their selective association with the La protein. The question of whether they are precursors to the major U6 RNAs found in Sm snRNPs is discussed.

Isolation and analysis of cDNA clones expressing human lupus La antigen

Several cDNA clones of the La antigen recognized by certain lupus autoantibodies were isolated from lambda gt11 expression libraries made from human liver. Recombinant clones were used to hybrid-select HeLa cell mRNA that was subsequently translated in vitro into a single protein species that comigrated with HeLa cell La protein. The in vitro translated protein was reactive with anti-La patient sera and was identical to the authentic La protein by peptide mapping. By analyzing overlapping cDNA clones, we mapped an antigenic site of La protein at the terminal 12% of the carboxyl end of the molecule. Within this region we identified a unique decapeptide of high hydrophilicity that may constitute a La antigenic determinant. We further demonstrated that the La antigen expressed from the recombinant clones can be used in a definitive enzyme-linked assay (ELISA) for the classification of sera from patients with systemic lupus erythematosus.

Characterization and purification of lupus antigen La, and RNA-binding protein

HeLa cell La antigen, an RNA-binding protein, was characterized by using two-dimensional gel electrophoresis. Eight isoelectric forms (pI 6 to 7) were observed, many containing phosphate. An in vitro translation product similar in size and antigenicity was identified. The HeLa cell protein purified by using an assay based on ribonucleoprotein reconstitution with adenovirus VA RNAI also comprised several isoelectric forms.

Effect of actinomycin D on the expression of nuclear antigen SS-B/La

The nuclear autoantigen SS-B/La, which is recognized by antibodies in certain autoimmune diseases, is complexed with distinct cellular RNAs and the complex of antigen-RNA profile remains constant throughout the cell cycle. This antigen is prominent in the nucleolus during G1/S phase of the cell cycle. Actinomycin D at a concentration of 0.0005 microgram/ml is capable of abolishing the appearance of SS-B/La in the nucleolus. The amount of immune-precipitable SS-B/La-associated RNAs is reduced by 0.005 microgram/ml actinomycin D treatment. The mechanism for these findings is suggested to be related to inhibition of the synthesis of messenger RNA coding for SS-B/La.

Monoclonal antibodies to the Sjögren's syndrome associated antigen SS-B (La)

The nuclear autoantigen SS-B (Sjögren's syndrome B antigen) was purified from rabbit thymus extract by immunoaffinity chromatography with human autoantibodies, and used to immunise BALB/c mice for production of monoclonal antibodies. Fusion of spleen cells from an immunised mouse with NS-1 myeloma cells resulted in the isolation of 3 clones secreting anti-SS-B antibody. Subclasses were shown to be IgG2b by immunodiffusion. Specificity of the monoclonal antibodies (MCA) was determined by ELISA and indirect immunofluorescence. By immunoblotting all 3 MCA identified a single 45 K immunoreactive polypeptide in rabbit thymus, identical with the major polypeptide recognised by human sera containing anti-SS-B. Affinity columns prepared from the 3 MCA all bound SS-B from rabbit thymus extract, without binding other nuclear antigens. Immunofluorescence studies on standard substrates showed that SS-B was located predominantly in the nucleoplasm but in cells transformed by EBV or phytohaemagglutinin more prominent nucleolar and cytoplasmic staining was seen.

Molecular characteristics of SS-B/La and SS-A/Ro cellular antigens

Anti-SS-B/La and anti-SS-A/Ro antibodies coexist in certain patients with connective tissue diseases such as systemic lupus erythematosus or Sjögren's syndrome. The respective antigenic structures with which these autoantibodies bind have not been fully characterized. The present study was conducted to better define these two different cellular antigens. WiL2 cell extracts were used to obtain partially purified SS-B/La and SS-A/Ro antigens. Both were found to be present in most fractions obtained after sequential purification with ammonium sulfate salt precipitation, G-200 gel filtration, DE-52 ion exchange chromatography, and preparative slab gel electrophoresis. However, SS-B/La antigenic activity was also found to be present in some fractions that did not contain detectable SS-A/Ro activity. These findings suggested the existence of two different forms of SS-B/La antigen: one containing the SS-B/La antigen only and the other containing both the SS-B/La and SS-A/Ro antigens. The RNA and protein components of these two ribonuclear protein particles were further defined by immunoprecipitation experiments using 32P-labeled WiL2 cell extract. The SS-B/La antigen was found to be associated with several RNAs while the SS-A/Ro antigen was associated with several other distinct RNAs. Both antibodies precipitated a common 43K molecular weight phosphoprotein. The antigenic peptides of these 2 antibodies were analyzed using an immunoblot system. The SS-B/La antigen was present on a 43K peptide which was unstable and could be degraded to several peptides of lower molecular weight (40K, 38K, 30K), while the SS-A/Ro antigen occurred on a peptide having a molecular weight of about 60K.

Regulation of a protein synthesis initiation factor by adenovirus virus-associated RNA

A small RNA accumulating late in adenovirus infection is required for efficient protein synthesis, although not specifically for the translation of viral proteins. This RNA maintains the activity of an initiation factor catalysing the earliest step of polypeptide chain initiation.

IgG antibodies to SS-B (La), RNP/Sm and DNA are produced by PWM-stimulated normal human lymphocytes in culture

Peripheral blood lymphocytes from five healthy subjects and three patients with Sjögrens syndrome and systemic lupus erythematosus were stimulated with pokeweed mitogen to examine the effects of polyclonal activation on the secretion of autoantibodies in health and disease. Antibodies to SS-B (La), RNP/Sm and DNA were detected in supernatants from cultures from healthy controls, in some cases approaching levels secreted by the patients. All secreted autoantibodies were of IgG class and the antigen specificity of the secreted anti-SS-B was proven by cross-adsorption experiments. Our results extend the range of defined specificities of autoreactive B cells in healthy individuals. These data argue against a case for physiological deletion of autoreactive B cell clones and support theories of their active recruitment in autoimmunity.

Dry eyes: autoimmunity and relationship to other systemic disease

Sjögren's syndrome is one of the more common connective tissue diseases, perhaps second in frequency only to rheumatoid arthritis. Autoimmunity in Sjögren's is suggested by its close clinical association with other connective tissue diseases and autoimmune disorders, the dense lymphocytic infiltration of the exocrine glands and the presence of circulating autoantibodies in the majority of cases. Antibodies to the cellular ribonucleoproteins, Ro(SSA) and La(SSB) appear to have clinical significance in this condition, since not only do they identify patients at risk of developing Sjögren's syndrome but also they may have a pathogenetic role in this disease, at least in some of the systemic manifestations.

Clinical relevance of PM-1 antibody and physiochemical characterization of PM-1 antigen

Using an improved immunodiffusion test with partially purified antigen, PM-1 antibody was identified in the serum of 18 patients. In 67% this system was associated with a polymyositis-scleroderma overlap, it occurred less frequently in polymyositis, dermatomyositis and scleroderma, and was not detected in other rheumatic diseases. The predominant clinical features of PM-1 positive patients were muscle weakness, sclerodactyly, Raynaud's phenomenon and pulmonary disease; widespread sclerodermatous features with infrequent. Characterization of the PM-1 antigen showed it to be a heat sensitive, trypsin sensitive acidic protein associated with the cell nucleus and possibly with nucleoli.

Antibodies to nonhistone nuclear antigens and antilymphocyte antibodies among children and adults with systemic lupus erythematosus and their relatives

Antibodies to nonhistone nuclear antigens are found with increased frequency in the serum of patients with systemic lupus erythematosus (SLE) and their first degree relatives. We measured the prevalence of ANA and antibodies against DNA, RNP, Sm, SSA, and SSB as well as antilymphocyte antibodies (ALA) in the serum of 24 patients with childhood onset SLE and 94 of their first degree relatives and compared the prevalence of these same antibodies in 8 patients with adult onset SLE and 33 of their first degree relatives. Antibodies against DNA, RNP, and Sm occurred more frequently in the serum of adult onset SLE patients. Among the first degree relatives ALA occurred more frequently in the sera of relatives of patients with childhood onset SLE, and parental antibodies to SSA were associated with the occurrence of childhood onset SLE in 3/24 cases. Since antibodies to SSA have been shown to be related to neonatal SLE their possible relationship to childhood SLE requires further study.

Characterization of the La (SS-B) antigen from several mammalian sources

The La or SS-B antigen is associated with rheumatic diseases, systemic lupus erythematosus, and Sjogren's syndrome, and is part of a larger ribonucleoprotein complex. Immunoaffinity chromatography allowed for the efficient separation of the La antigen from the bulk of the cellular proteins, with a minimum of protease exposure. Protein blot analysis of the affinity-isolated material indicated a major immunoreactive polypeptide of 50,000 m.w. A comparison of this antigen in a number of mammalian sources (human, rabbit, and rat) suggested strong conservation of the native polypeptide m.w. Likewise, in a direct comparison of this antigen from Epstein-Barr virus-infected cells in which there are distinct differences in the antigen-associated RNA species, the immunoreactive polypeptide species were of similar size. The La protein is readily susceptible to endogenous proteolysis, with the resulting generation of smaller, discrete polypeptides that still retain antigenicity. By using the La protein to monitor potential degradation, we have developed a simple two-step procedure to isolate the La-associated snRNP complex. The complexes thus isolated provide material suitable as a source of both the active antigen and of the functional ribonucleoprotein complex.

Autoantibodies reactive with small ribonucleoprotein antigens: a convergence of molecular biology and clinical immunology

Autoantibodies to nuclear antigens (ANA) occur in patients with systemic lupus erythematosus (SLE) and other multisystem autoimmune diseases. Although heterogeneous, there are 2 major groups, autoantibodies to DNA and autoantibodies to non-DNA antigens, the latter including ANAs to the soluble or "extractable nuclear antigens" (ENA). This review discusses those ENAs which are ribonucleoproteins (RNPs) consisting of small RNA molecules (80-400 nucleotides) attached to non-histone proteins: these are called small nuclear (sn) or small cytoplasmic (sc) ribonucleoproteins according to their location in the cell and at least some are known to play an important role in nuclear metabolism. ENAs can be immunoprecipitated from crude preparations of nuclei by sera from patients with multisystem autoimmune diseases and, after removal of the associated proteins, the RNA components can be analyzed by gel electrophoresis. This shows 3 main categories of small RNAs: the U group comprising U1-U6 snRNAs, the Ro group comprising small nucleocytoplasmic RNAs, and the La group comprising several species of cellular snRNAs as well as the Ro scRNAs. La, in addition, includes small RNAs encoded by adenovirus (VA I, VA II), Epstein-Barr virus (EBER 1, EBER 2) and vesicular stomatitis virus (leader RNA). In the case of each group, the RNAs themselves are not antigenic but become so when associated with proteins, most of which are uncharacterized. The U snRNAs, located in the nucleus, are transcribed by RNA polymerase II and appear to be involved in the splicing of introns from mRNA. Sera from patients with mixed connective tissue disease (MCTD) react with RNPs containing U1 RNA and sera from patients with SLE react with U RNPs containing U1, U2, U4, U5 and U6 RNAs, collectively known as the Sm antigen. The Ro RNAs are transcribed by RNA polymerase III and have no known function. Sera from patients with primary Sjögren's syndrome and some cases of SLE react with Ro scRNPs. The La RNAs are also transcribed by RNA polymerase III and are located mostly in the nucleus; functionally the protein associated with the La RNAs appears to be important in RNA polymerase III transcription. Sera from patients with primary Sjögren's syndrome react with the heterogeneous group of both cellular and viral RNAs which constitute the La RNP antigen. Sera of patients with SLE, scleroderma, polymyositis and dermatomyositis also react with RNPs relevant to nuclear metabolism and further definition of these RNPs is awaited. Many advances can be expected from the convergence of molecular biology and clinical immunology exemplified by the current studies on ENAs.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of antigenic polypeptides of the RNP, Sm and SS-B nuclear antigens from calf thymus

Antinuclear autoantibodies are a hallmark of autoimmune diseases. The RNP, Sm and SS-B nuclear antigens from calf thymus in whole tissue, nuclear extracts and fractions have been studied by using different techniques including immunodiffusion, counterimmunoelectrophoresis and protein blotting. Such studies were done in order to obtain a precise characterization of the polypeptide components of those antigens. From our results it can be established that: one 69.8 Kd polypeptide (for whole tissue and nuclei) and a number of well-defined 32-38-Kd polypeptides (for nuclear extracts and ammonium sulfate fractions) show an antigenic character against anti-RNP sera; anti-Sm sera from different patients show in all cases a variable component of antigenic polypeptides, including one 28.8, 29.7 Kd doublet and two singlets of 14.8 and 11.0 Kd; and a 52.0-Kd SS-B antigenic polypeptide is found for whole tissue, which is gradually degraded in nuclei and nuclear extracts to a more stable 47.1-Kd polypeptide.

Identification of the SS-A/Ro intracellular antigen with autoimmune sera

Autoantibodies to SS-A/Ro antigen have been described in the sera of certain patients with Sjögren's syndrome, systemic lupus erythematosus and in neonates with lupus and/or congenital heart block. SS-A/Ro is a trypsin-sensitive intracellular antigen which appears to be associated with another intracellular antigen SS-B/La in tissue extracts. This study describes a simple method of separation of SS-A/Ro and SS-B/La antigenic activity by differential salt elution in polybuffer ion exchange chromatography. The partially purified SS-A/Ro antigen was separated by polyacrylamide gel electrophoresis under non-denaturing conditions and identified by Western blot analysis as a single polypeptide of 61,000 Da. The pI of SS-A/Ro antigen was 4.67. The partially purified SS-A/Ro antigen derived from gel electrophoresis could be adapted to an enzyme linked immunosorbent assay (ELISA) for the detection of antibody.

Standardization of the immunofluorescence test for autoantibody to nuclear antigens (ANA): use of reference sera of defined antibody specificity

Standardization of the indirect immunofluorescence antinuclear antibody (IF-ANA) test can be improved for a given substrate with use of reference ANA sera, uniform assay conditions, and standardization of optical systems. To accomplish this, reference sera from the Arthritis Foundation with defined antibody specificities for nDNA, SS-B, RNP, Sm, nucleoli, and "speckled pattern" were reacted with commonly used IF-ANA substrates, mouse kidney sections, KB and HEp-2 tissue culture cells. Reagents and assay conditions used were those provided with the substrates in commercially available IF-ANA kits. A microscope slide with graded intensities of fluorescent beads was used to standardize microscope fluorescence intensity readings. The authors' fluorescence pattern and intensity results should be directly comparable to results obtained in other laboratories for the six antibodies for which reference sera are available. Although no defined sera are widely available for SS-A, Scl-70, PM-1, and centromere antibodies, the ability of each substrate to detect these antinuclear antibodies as well as mitochondrial, smooth muscle, ribosomal and microsomal antibodies also was tested. HEp-2 cells and KB cells were found to be superior to mouse kidney sections for detection of SS-A, Scl-70, PM-1 and centromere antinuclear antibodies. Mouse kidney sections were superior for screening of sera for the absence of ANA as well as for detection of smooth muscle and liver-kidney microsomal antibodies. Other antibodies were detected with equal sensitivity with all substrates and each of the three ANA kits used in the study performed satisfactorily. Use of reference sera as well as optical standardization is recommended for IF-ANA testing.

La antigen recognizes and binds to the 3'-oligouridylate tail of a small RNA

The La antigen is a cellular protein which interacts with many RNA species that are products of RNA polymerase III, including the adenovirus virus-associated (VA) RNAs. We demonstrate that the efficiency of antigen binding in vitro is determined by the number of U residues at the RNA 3' terminus. Forms of VA RNAI with more than two terminal U residues are fully bound, forms with two U residues are partially bound, and forms with fewer than two U residues are not bound at all. The antigen can be covalently linked to VA RNA by UV irradiation, and the site of cross-linking is shown to contain the 3' terminus of the RNA. We conclude that the antigen recognizes the U-rich 3' tail of VA RNA, and presumably that of other polymerase III products, and that it binds at or close to this site.

Nucleotide sequence and host La protein interactions of rabies virus leader RNA

Rabies virus leader RNA was detected in infected BHK-21 cell extracts by hybridization to end-labeled genomic RNA. Similar to the leader RNA of vesicular stomatitis virus, the leader RNA of rabies virus was also found to be associated with the La protein by specific immunoprecipitation with antisera from lupus patients. The 3' end of the genomic RNA of rabies virus was sequenced, and the size and termination site of leader RNA were determined. In addition, extension of the sequence into the nucleocapsid gene of rabies virus showed an open reading frame for at least 37 amino acid residues. Sequence relationships between rabies virus and vesicular stomatitis virus leader genes and the possible involvement of the La protein in rhabdovirus biology are discussed.

Partial immunochemical characterization of the Ro and La proteins using antibodies from patients with the sicca syndrome and lupus erythematosus

Ro and La are intracellular ribonucleoproteins that are frequent targets for autoantibodies in the sicca syndrome and in lupus erythematosus. We analyzed the m.w. of the protein (antigen) moieties of Ro and La in saline cell extracts of human spleen by SDS-PAGE and immunoblotting, gel filtration, and sucrose density ultracentrifugation with radioimmunoassay. pI values for Ro and La proteins were established by isoelectric focusing on thin layer agarose gels and immunoblotting on nitrocellulose transfers. The La protein had an m.w. of approximately 43 kd and was heterogeneous in charge, with pI values from 4.2 to 4.8. Composite two-dimensional maps developed by immunoblotting revealed a characteristic set of seven dots of m.w. 43 kd. Ro determinants were identified on polypeptides of 50 and/or 57 kd. Antigenic activity was also detected in the void volume of spleen extract fractionated by Sephadex G-200 and in 8 to 9S and greater than 19S regions of sucrose gradients, suggesting either aggregation of the Ro protein or participation in protein-protein complexes. pI values of 4.3 to 5.5 were obtained for the Ro antigen, and two-dimensional maps revealed that the 57 kd polypeptide had a similar charge heterogeneity to the La protein, whereas the 50 kd polypeptide had a different fingerprint. Immunoblotting of extracts from bovine, rabbit, and dog extracts showed that antibodies to Ro and La reacted with a limited number of polypeptides (m.w. 50 and/or 57 kd for anti-Ro and 43 or 50 kd for anti-La). These studies support the physical independence of the isolated Ro and La polypeptides, although a precursor product or functional relationship in vivo is possible. These studies also suggest that, in addition to Western blotting, techniques involving immunodeletion, isoelectric focusing with capillary immunoblotting, and 2D immunoblotting provide useful approaches to characterize saline-soluble cellular antigens.

Interactions of plus and minus strand leader RNAs of the New Jersey serotype of vesicular stomatitis virus with the cellular La protein

The New Jersey serotype of vesicular stomatitis virus (VSV-NJ) was found to synthesize a minus strand leader RNA of 44-46 bases long and a plus strand leader RNA of 47-50 bases long in infected cells. The minus strand leader RNA of VSV-NJ was found associated with the host cell La protein in infected cells by immunoprecipitation with antisera from patients with systemic lupus erythematosus. These results differ from those reported previously (J. Wilusz , M. G. Kurilla , and J. D. Keene (1983). Proc. Natl. Acad. Sci. USA 80, 5827-5831) for the similarly sized species of minus strand leader RNA made by the Indiana serotype of VSV (VSV-IND). Despite sequence differences between the 3' ends of the plus strand leader RNAs of the two serotypes, the plus strand leader RNA of VSV-NJ was found to have a pattern of La protein accumulation similar to that reported previously for the plus strand leader RNA of VSV-IND. These results provide additional support for a role for La protein in VSV replication and help further delineate the sequence requirements for La protein binding to VSV leader RNAs.

Cellular protein and RNA antigens in autoimmune disease

Antibodies directed against soluble cellular antigens are a distinctive feature of systemic autoimmune disease. We have examined 22 autoantibodies in sera from 1111 patients and present the disease associations together with a biochemical analysis of the antigens. The data emphasize the clinical specificity of the antibodies and the restricted number of cellular components that commonly elicit an immune response. In several instances, serological relationships between antibodies mirror biochemical relationships between the corresponding antigens. The antigens are mainly proteins and are often present in complexes with additional protein or nucleic acid molecules. In myositis the antibodies react chiefly with cytoplasmic antigens such as aminoacyl-tRNA synthetases, in contrast to the mainly antinuclear response in SLE. It is argued that both environmental stimuli and genetic factors govern autoantibody specificity, and that molecular characterization of the cellular antigens may yield clues to the aetiology of the disease and of the concomitant, specific autoimmune response.

Autoantibodies in the sicca syndrome (primary Sjögren's syndrome)

IgA and IgM rheumatoid factors as well as antibodies to Ro and La were measured in 37 patients with the sicca syndrome and 9 patients with Sjögren's syndrome secondary to rheumatoid arthritis. Positive results were found in 84% (IgA rheumatoid factor), 76% (IgM rheumatoid factor), 62% (Ro), and 50% (La) of patients with the sicca syndrome. There was no significant difference in the frequency of positive results in patients with glandular versus extraglandular disease. Antibodies to La invariably occurred in patients with antibodies to Ro. In addition, patients who were anti-Ro positive also had significantly higher IgA (p less than 0.05) and IgM (p less than 0.01) rheumatoid factor activity. Since 81% of the sicca patients were concordant for 3 of the 4 antibodies tested, production of these autoantibodies appears to be related.

Tissue uptake and catabolic studies of 125I SS-B (La) injected into mice

The radiolabeled soluble cellular antigen 125I SS-B (La) has a plasma half-life of 3 min following iv injection into BALB/C mice. Uptake by Kupffer cells (KC) and proximal renal tubular (PRT) cells was demonstrated by autoradiography (ARG). That trichloracetic acid (TCA)-soluble products of 125I SS-B appeared in plasma within 1 min of iv injection suggests rapid in vivo breakdown. Activated peritoneal macrophages (APM) degraded 125I SS-B in a time- and cell-dose-dependent fashion. These findings suggest that the plasma clearance and catabolism of 125I SS-B may be dependent on its interaction with phagocytic cells. This rapid antigen elimination may protect against harmful autoantibody responses.

The coexistence of systemic lupus erythematosus and psoriasis

Systemic and discoid lupus erythematosus (LE) have both been reported in association with psoriasis. Four additional patients who had systemic LE are reported. All of them had a high titer of antinuclear antibodies (ANAs) and were SS-A(Ro)-negative. Only one patient exhibited photosensitivity. SS-A(Ro) antibodies do not appear to be specific markers for the coexistence of LE and psoriasis, and screening for them in all psoriatics prior to ultraviolet B phototherapy is not recommended. Pitfalls in the management of patients with systemic LE and psoriasis are discussed.

Use of the Bio-Rad silver stain to identify gel purified RNA components of small nuclear ribonucleoprotein antigens

The ultrasensitive silver staining procedure developed for the detection of proteins in polyacrylamide gels has been used to identify the RNA component of small nuclear ribonucleoprotein antigens recognised by antinuclear antibodies. The technique described is a simple, safe and inexpensive procedure with a sensitivity comparable with that obtained by biosynthetic labelling of RNA with 32P.

Purified lupus antigen La recognizes an oligouridylate stretch common to the 3' termini of RNA polymerase III transcripts

The small ribonucleoproteins recognized by anti-La sera consist mainly of RNA polymerase III products complexed with an antigenic cellular protein of 50 kd. A biochemical procedure for purifying the La protein from HeLa cells is described. The interaction of the isolated protein with a collection of model tRNA precursors, generated by ligation of specific oligonucleotides to the 3' terminus of yeast tRNAPhe, was studied. The most stable complexes are formed with adducts possessing three or four terminal uridylate residues. Addition of a terminal phosphate, fragmentation of the RNA, or substitution of other nucleotides reduce the affinity for the La protein. The preferred terminal sequence recognized and bound by La protein is homologous to the transcriptional termination signal for RNA polymerase III.