Differences in the fine specificity of anti-Ro (SS-A) in relation to the presence of other precipitating autoantibodies

Prevalence and clinical relevance of 52-kDa and 60-kDa Ro/SS-A autoantibodies in Japanese patients with systemic sclerosis

OBJECTIVE

To determine the prevalence of 52-Kda and 60-Kda Ro/SS-A autoantibodies in serum samples from Japanese patients with systemic sclerosis (SSc).

METHODS

Serum samples from 263 Japanese patients with SSc were examined by double immunodiffusion and enzyme linked immunosorbent assay (ELISA).

RESULTS

By double immunodiffusion, 29 serum samples from patients with SSc were found to possess anti-Ro/SS-A antibodies. By ELISA, 31 serum samples were positive for anti-Ro52 and/or anti-Ro60. Of 27 serum samples that were positive by both methods, 15 reacted with both Ro52 and Ro60, five with Ro52 alone, and seven with Ro60 alone. Eleven of 12 patients with both anti-Ro52 and anti-Ro60 and all five patients with anti-Ro52 alone had Sjögren's syndrome, while only one of six patients with anti-Ro60 alone had this disorder.

CONCLUSIONS

Anti-Ro52 may be a serological marker for the presence of Sjögren's syndrome in anti-Ro/SS-A-positive patients with SSc.

The ultrastructural localization of 60-kDa Ro protein and human cytoplasmic RNAs: association with novel electron-dense bodies

The 60-kDa Ro ribonucleoprotein is an important target of humoral autoimmune responses. However, the ultrastructural locations of the 60-kDa Ro protein and its associated small cytoplasmic RNAs (Y RNAs) have not been previously determined, and the functions of the Ro protein and RNAs are not known. In this study, the cellular locations of the 60-kDa Ro protein and the Ro Y1 and Y4 RNAs are determined by immunoelectron microscopy and in situ hybridization electron microscopy, respectively. Both Ro protein and Y RNAs are concentrated in discrete areas of the nucleoplasm, nucleolus, and cytoplasm of cultured cells and human skin sections. The 60-kDa Ro protein and Y RNAs are also present diffusely in the cytoplasm, where they occur in ribosome-rich regions, and in the nucleus. The presence of Ro ribonucleoprotein components in nucleoli and in ribosome-rich cytoplasmic areas suggests a potential for the involvement of Y RNAs and/or 60-kDa Ro protein in ribosome synthesis, assembly, or transport. Double labeling experiments show that Ro protein and Y RNAs colocalize in the nucleoplasm, nucleolus, and cytoplasm. In addition, aggregates of Y RNA occur unassociated with 60-kDa Ro protein, and aggregates of 60-kDa Ro protein occur unassociated with Y RNA. Aggregates of both Ro protein and Y RNAs label previously unreported nuclear and cytoplasmic electron-dense bodies. We propose that these distinctive Ro-associated electron-dense bodies may represent structure(s) important for cellular transport and/or Ro function.

Neonatal lupus syndromes

Congenital heart block is considered to be a model of passively acquired autoimmunity, whereby immune abnormalities in the mother lead to the production of autoantibodies that cross the placenta and presumably injure the otherwise normally developing fetus. The major targets of the maternal immune response are the SSA/Ro and SSB/La ribonucleoproteins. Other neonatal abnormalities affecting the skin, liver, and blood elements have also been reported to be associated with anti-SSA/Ro-SSB/La antibodies in the maternal and fetal circulation and are now grouped along with congenital heart block under the heading of the neonatal lupus syndromes. This review covers the histopathology, SSA/Ro-SSB/La antigen-antibody systems, immunogenetics, clinical manifestations, and diagnosis and management strategies of these syndromes.

Interaction between certain major histocompatibility complex class II and T-cell receptor V beta alleles promotes the antibody production to extractable nuclear antigen-related peptides

Our objective was to study the interaction between major histocompatibility complex (MHC) class II and T-cell receptor (TCR) alleles in the recognition of extractable nuclear antigen-derived peptides in 32 patients with systemic lupus erythematosus and 173 of their family members. MHC genes were analyzed using sequence specific oligonucleotides, and TCR beta-chain gene polymorphism using restriction fragment-length polymorphism. One dominant peptide (as defined by enzyme-linked immunosorbent assay autoantibody reactivity) was identified in each antigen studied: peptide 1-20 in Sm-D, peptide 35-58 in U1-RNP-A, and peptide 304-324 in the Ro/SSA 60 Kd protein. None of the MHC class II and TCR beta haplotypes was directly associated with any of the autoantibodies. Twenty-six subjects had antibodies to the peptide Sm-D1-20; nine of them were DRB1*0101/DQB1*0501. Among subjects with this haplotype, the number of responders was higher (p < 0.028, p corrected, pc = 0.336) in those with the 2-25-9 TCR beta haplotype than in the remainder. Conversely, the number of DRB1*04/DQB1*0302 responders was lower (p < 0.030, pc = 0.360) among subjects with the 23-20-9 TCR beta haplotype than in those without. The odds ratios (OR) were 4.23 and 0.21, respectively. Of the 54 subjects positive for anti-U1-RNP-A 35-38, 13 were DRB1*0101/DQB1*0501 and eight DRB1*04/DQB1*0302. The percentage of responders was higher (p < 0.041, pc = 0.492, OR = 3.48) in the former group of subjects with the 2-25-9 TCR beta haplotype, and lower (p < 0.02, pc = 0.024, OR = 0.09) in the latter with the 23-20-9 TCR beta haplotype. Three of the 12 anti Ro/SSA 60Kd 304-324-positive subjects were DRB1*0101/DQB1*0501. All had the 2-25-9 TCR beta haplotype (p < 0.046, pc = 0.552, OR = 6.29) and none the 23-20-9 (p < 0.031, pc = 0.372, OR = 0.10). The same combinations of genes were associated with high/low response toward the three peptides. These data provide evidence for an interplay of the MHC class II and TCR beta alleles in the control of specific autoantibody response to well-defined nuclear Ag peptides.

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.

The etiopathogenesis of Sjögren's syndrome

With increasing awareness and improved diagnostic tests, Sjögren's syndrome (SS) is becoming recognized as a common autoimmune disease, affecting as many as 3% of women over age 55 years. Apart from keratoconjunctivitis sicca, systemic features are common, leading to considerable morbidity and occasionally mortality. Predisposing factors for SS include HLA determinants that have been linked to DR3 and heterozygosity for DQ-1 and DQ-2. There is accumulating evidence that activated epithelial cells and their interaction with T cells play a central role in pathogenesis. Some restriction of T-cell receptor gene usage to V beta 6.7b and V beta 13.2 and a profile of cytokine production consistent with Th-1-type cells has been observed in affected tissues. Antibodies to Ro (SS-A) and La (SS-B) are found in about 50% of patients and are associated with more severe glandular and extraglandular manifestations. There is evidence that the antibodies are pathogenic, not only in patients, but in their infants born with congenital heart block. Studies of herpesviruses have led to conflicting results, and interest has recently focussed on retroviruses, based on the findings of the expression of retroviral elements in salivary glands of SS patients and antiretrovial antibodies in serum. Mice infected with or transgenic for retroviruses develop SS-like pathology and are currently being studied as animal models of the disease. In the last few years, considerable progress has been made in the understanding of the pathogenesis of SS, and the disease has become the prototype for the investigation of a viral etiology for autoimmune rheumatic disease. Study of its etiopathogenesis may be the key to understanding autoimmune disease in general.

Deforming arthropathy of the hands in systemic lupus erythematosus is associated with antibodies to SSA/Ro and to SSB/La

Thirteen patients with systemic lupus erythematosus and deforming arthropathy (DA) of the hands were compared with 111 patients with SLE without deforming arthropathy. Clinical features were comparable in the two groups. Patients fulfilling criteria for mixed connective tissue disease (MCTD) were not included in the present study. A higher prevalence of antibodies to SSA/Ro (P < 0.0125) and SSB/La (P < 0.004) were found in the SLE-DA group. The detection of antibodies to SSA/Ro and SSB/La was even more strictly associated with DA in SLE antibodies to SSA/Ro alone (P < 0.002). Regarding the fine specificity of anti-SSA/Ro, a prevalent response to the 52 kD protein of the Ro antigen was found. We conclude that patients with SLE developing deformities of the hands belong to a subset of patients with circulating antibodies to SSA/Ro, particularly to the 52 kD component, and to SSB/La.

A distinctive autoantibody profile in black female patients with lupus nephritis

OBJECTIVE

Lupus nephritis has often been associated with anti-DNA, but, based on the findings in eluate studies, it appears that other antigen-antibody reactions, such as those involving anti-Ro/SS-A, anti-nuclear RNP (anti-nRNP), and/or anti-Sm, may also contribute to the pathogenesis of nephritis. In the present investigation, we identified and further studied a distinctive precipitin profile present in black women with nephritis.

METHODS

Longitudinal clinical and serologic studies of a cohort of university-based systemic lupus erythematosus (SLE) patients (n = 120) were carried out over an 8-year period.

RESULTS

A subset of 20 black female patients was identified, of whom 8 had lupus nephritis (group I) and 12 did not (group II). Group I was characterized by a distinct precipitin profile consisting of anti-Ro/SS-A, anti-SM, and anti-nRNP, but no anti-La/SS-B. SLE disease duration at presentation was significantly shorter in group I than in group II (mean 1.94 years versus 5.21 years; P = 0.02). The distinctive precipitin profile of anti-Ro/SS-A, anti-Sm, and anti-nRNP occurred exclusively in group I patients (6 of 8, versus 0 of 12 in group II; P < 0.001). In white lupus nephritis patients, this precipitin profile was not seen.

CONCLUSION

While the mechanism responsible for the relationship of this distinctive serologic profile to the development of nephritis in black female lupus patients remains to be determined, its presence may be used as a marker for severe and progressive renal disease.

Sera from patients with rheumatic diseases recognize different epitope regions on the 52-kD Ro/SS-A protein

Patients suffering from systemic lupus erythematosus (SLE) or Sjögren's syndrome (SS) often contain autoantibodies directed to the Ro(SS-A) complex. In this study the antigenic determinants on two of the components of the Ro complex, i.e. the Ro60 and the Ro52 polypeptides, were investigated. Anti-Ro+ sera were selected by counter-immunoelectrophoresis. Depending on the detection method, 59-68% of the SLE patients produced anti-Ro but not anti-La antibody, while 72-81% of the SS patients produced both anti-Ro and anti-La antibody. Immunoprecipitation of recombinant Ro-proteins showed that 61 sera (87%) were reactive with both Ro proteins, seven sera with Ro60 only, one serum with Ro52 only, and one serum did not precipitate the proteins at all. The anti-Ro60 reactivity of human sera is strongly associated with the native form of Ro60, suggesting that conformational autoepitopes are an important feature of Ro60. In the case of Ro52, frequently the residues located between amino acids 216 and 292 were essential for reactivity with the antibodies. With 70% of the lupus sera tested this appeared to be the only region important for reactivity. The antibodies of SS patients generally recognized multiple B cell epitopes located between amino acids 55 and 292. The results of this study indicate that the antigenic determinants on Ro52 are different for autoantibodies produced by lupus patients compared with those of SS patients.

Identification of mothers at risk for congenital heart block and other neonatal lupus syndromes in their children. Comparison of enzyme-linked immunosorbent assay and immunoblot for measurement of anti-SS-A/Ro and anti-SS-B/La antibodies

OBJECTIVE

To identify the fine specificity patterns of maternal anti-SS-A/Ro and anti-SS-B/La antibodies that are associated with the birth of a child with transient or permanent manifestations of neonatal lupus syndromes, and to suggest a predictor algorithm for use in counseling.

METHODS

Sera were obtained from 4 groups of mothers: 57 whose children had congenital heart block, 12 whose children had transient dermatologic or hepatic manifestations of neonatal lupus but no detectable cardiac involvement, 152 with systemic lupus erythematosus and related autoimmune diseases, who gave birth to healthy infants, and 30 with autoimmune diseases whose pregnancy resulted in miscarriage, fetal death, or early postpartum death unrelated to neonatal lupus. Antibodies to SS-A/Ro and SS-B/La were assessed by enzyme-linked immunosorbent assay (ELISA) and by sodium dodecyl sulfate (SDS)-immunoblot.

RESULTS

Anti-SS-A/Ro antibodies were identified by ELISA in 100%, 91%, 47%, and 43% of the mothers of infants with heart block, with transient neonatal lupus, healthy infants, and fetal death, respectively. High titers of anti-SS-A/Ro antibodies were present more often in mothers of children with cardiac disease or transient neonatal lupus than in either of the other 2 groups. Maternal antibodies to SS-B/La were detected by ELISA in 76% of the heart block group, 73% of the cutaneous neonatal lupus group, 15% of the group with healthy children, and 7% of the fetal death group. On SDS-immunoblot, sera from 91% of the heart block group mothers who had antibodies to SS-A/Ro but not to SS-B/La recognized at least 1 SS-A/Ro antigen, with significantly greater reactivity against the 52-kd component. In contrast, only 62% of the anti-SS-A/Ro positive, anti-SS-B/La negative responders in the healthy group recognized the 52-kd and/or the 60-kd component. Although there was no profile of anti-SS-A/Ro response unique to the mothers of children with heart block or cutaneous manifestations of neonatal lupus, only 1% of the healthy infants were born to mothers with antibodies directed to both the 52-kd SS-A/Ro and 48-kd SS-B/La antigens and not to the 60-kd SS-A/Ro antigen.

CONCLUSION

Women with antibodies to both SS-A/Ro and SS-B/La have an increased risk of giving birth to children with neonatal lupus, especially if the anti-SS-A/Ro response identifies the 52-kd component on SDS-immunoblot. Women whose sera contain only anti-SS-A/Ro antibodies in low titer and only recognize determinants that are altered by conditions of SDS-immunoblot have a low risk for giving birth to a child with neonatal lupus. Specific antibody profiles do not distinguish among the manifestations of the neonatal lupus syndromes.

Presence of anti-La(SS-B) is associated with binding to the 13-kD carboxyl terminus of 60-kD Ro(SS-A) in systemic lupus erythematosus

In systemic lupus erythematosus (SLE) clinical manifestations, autoantibody production, and immunogenetics are inter-related. The ability to study parts of the autoimmune response may allow a more detailed understanding of these relationships. We undertook this study to determine whether the fine specificity of the autoimmune response to 60-kD Ro(SS-A) was related to the presence of other autoantibodies. We screened 74 patients with SLE for antibodies to the carboxyl 13-kD terminal of 60-kD Ro(SS-A) (13 kD). Twenty-five sera had such antibodies. This reactivity was distinguished by the presence of not only anti-Ro(SS-A) but also other antibodies. All nine sera with Ro(SS-A) and La(SS-B) Ouchterlony immunodiffusion precipitins bound 13-kD (p = 0.01), whereas 10 of 11 sera with both anti-Ro(SS-A) and anti-La(SS-B) as determined by immunosorbent assay bound 13-kD (p = 0.002). Inhibition studies demonstrated that antibodies binding the 13-kD fragment bound the 60-kD Ro(SS-A) protein but did not bind the La(SS-B) protein. Thus, anti-La(SS-B) was found in those sera that bound epitopes within the 13-kD carboxyl terminal of 60-kD Ro(SS-A). These data suggest a structural basis by which anti-Ro(SS-A) and anti-La(SS-B) are coupled in SLE.

Autoantibodies to the Ro/SSA antigen are conformation dependent. I: Anti-60 kD antibodies are mainly directed to the native protein; anti-52 kD antibodies are mainly directed to the denatured protein

Recent studies have shown that Ro/SSA autoantigen is heterogeneous and the autoanti-Ro/SSA response is correspondingly heterogeneous. There are two isoform families; the 60 kD forms and the 52 kD forms. We studied the antigenic difference between the native and denatured Ro/SSA isoforms and found that the autoanti-Ro/SSA response to the native 60 kD antigen is quite homogeneous. All anti-Ro/SSA sera recognize the native kD antigen regardless of the reactivities to the 60 kD band on the Western blot. Surprisingly, no anti-Ro/SSA sera without anti-La/SSB reacts with the native 52 kD Ro/SSA, although sera with both precipitating anti-Ro/SSA and anti-La/SSB can immunoprecipitate the native 52 kD antigen. Anti-Ro/SSA sera exist which react exclusively with the native 60 kD Ro/SSA protein (10/43, 23%) while no anti-Ro/SSA sera have been found which react exclusively with the denatured 52 kD Ro/SSA antigen. In sera with anti-Ro/SSA precipitins alone, only antibody to the denatured 52 kD Ro/SSA molecule is found! In sera with anti-Ro/SSA and anti-U1 RNP precipitins, no antibody to either native or denatured 52 kD Ro/SSA is found, while in sera with both anti-Ro/SSA and anti-La/SSB precipitins, antibodies to both the native and denatured forms of 52 kD Ro/SSA are present. These data suggest that the anti-Ro/SSA response to the 60 kD molecule is driven by the native 60 kD Ro/SSA molecule while the molecular identification of the antigen drive in the anti-52 kD Ro/SSA response is unknown.

Characterization of the liver cytosol antigen type 1 reacting with autoantibodies in chronic active hepatitis

An autoantibody to liver cytosol was previously described in childhood autoimmune chronic active hepatitis type 2. The antigen, liver cytosol antigen type 1, was for the first time partially purified using gel filtration and ion exchange chromatography, and it was characterized using immunodiffusion, immunoblot and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of the immunoprecipitate. Immunoblot detected a unique antigenic peptide at 62 kD from human cytosol and at 58 kD from rat cytosol. The same peptides were also detected when immunoprecipitates of liver cytosol antigen type 1 and autoantibodies to liver cytosol antigen were submitted to sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A polymeric structure, probably a tetramer, is suggested for native liver cytosol antigen type 1 because in gel filtration chromatography liver cytosol antigen type 1 was eluted as a protein of a molecular weight between 240 and 290 kD when human liver cytosol was fractionated and between 220 and 270 kD from rat liver cytosol. Liver cytosol antigen type 1 is probably poor in carbohydrates because it was not stained by periodic acid-Schiff stain. The autoantibodies to liver cytosol were frequently found in association with antiliver kidney microsomal autoantibodies type 1, which are directed against the cytochrome P-450 of the IID6 subfamily. Antiliver kidney microsomal autoantibodies type 1 but not antiliver cytosol autoantibodies were found in association with antibodies to hepatitis C virus. Autoantibodies to liver cytosol antigen type 1 seem to be a more specific marker for autoimmune hepatitis type 2 than antiliver kidney microsomal antibodies type 1 autoantibodies.

Identification of antigenic regions of the human Ro 60 kDa protein using recombinant antigen and synthetic peptides

Autoantibodies reacting with the human Ro 60 kDa protein are present in anti-Ro/SS-A positive sera from patients with several different connective tissue diseases including Sjögren's syndrome and systemic lupus erythematosus. To investigate the humoral immune response to this protein, the pattern of antibody recognition of recombinant Ro 60 kDa proteins encoded by both full-length and deletion clones was analysed by immunoblotting. An antigenic region recognized by nearly all anti-Ro 60 kDa positive sera was found to reside in the middle part of the protein. In addition, some sera reacted with two other antigenic regions located in the amino-terminal and carboxyl-terminal part of the protein. For further mapping, overlapping peptides covering the most frequently recognized region of the protein were synthesized by solid-phase methods and used as antigens in ELISA. Three major patterns of reactivity to Ro 60 kDa peptides were found. These results not only indicate the presence of an immunodominant region but also heterogeneity in the autoimmune human response to the Ro 60 kDa antigen.

Definition of a discontinuous immunodominant epitope at the NH2 terminus of the La/SS-B ribonucleoprotein autoantigen

High-titer IgG autoantibodies to the La/SS-B ribonucleoprotein (RNP) are a hallmark of patients with primary Sjogren's syndrome. Anti-La/SS-B-positive human sera bind to multiple epitopes on recombinant La/SS-B, although the initial response is against an immunodominant epitope within the first 107 NH2-terminal amino acids (aa). Sequence analysis has identified a striking homology between aa 88-101 in this NH2-terminal region of La/SS-B and a feline retroviral gag polypeptide suggesting the anti-La/SS-B response may be initiated by cross-reactivity with an exogenous agent. In the present study, detailed mapping of this NH2-terminal epitope, using recombinant La/SS-B purified from the expression of overlapping DNA fragments spanning aa 1-107, has shown that this immunodominant epitope is a complex conformational or discontinuous epitope dependent upon both aa 12-28 and 82-99 for expression, even though these regions share no homology with each other. This requirement questions the significance of the homology between La/SS-B and a retroviral gag polypeptide in the generation of the B cell response to La/SS-B and is in accord with the general concept that B cells recognize conformational epitopes on antigens rather than small linear peptide sequences. The finding also reinforces the notion that native autoantigen could be the initiator of the autoimmune response.

MHC associations of autoantibodies against recombinant Ro and La proteins in systemic lupus erythematosus. Results of a multicenter study. SLE Study Group

Antibodies against recombinant 52 kD-Ro, recombinant 60 kD-Ro and recombinant La protein were determined by ELISA in over 300 central European patients with systemic lupus erythematosus (SLE). A strong association with HLA-DR3 was found for antibodies against 52 kD-Ro and La, but not for recombinant 60 kD-Ro antibodies in the absence of antibodies against 52 kD-Ro or La. Ro/La negative SLE patients still showed an increased frequency of HLA-DR3 as compared to healthy controls. These results indicated that the preferential formation of Ro and La antibodies was not due to an unspecific stimulatory effect of HLA-DR3 but that the antibody response to certain defined proteins (52 kD-Ro and La) was influenced by MHC genes in SLE. Furthermore, the association of SLE with HLA-DR3 was independent of the effects of DR3 on the formation of 52 kD-Ro and La antibodies.

Antibodies to carbonic anhydrase in systemic lupus erythematosus and other rheumatic diseases

OBJECTIVE

Autoantibodies to CA were demonstrated in the sera of patients with systemic lupus erythematosus (SLE) and some other rheumatic diseases. This study was undertaken to define the isoform and species specificity of these reactions, as well as to develop a method for detecting immune complexes.

METHODS

Antibodies to CA were sought by enzyme-linked immunosorbent assay (ELISA) and by Western immunoblotting.

RESULTS

An increased prevalence of CA autoantibodies was detected, by both methods, in patients with SLE, scleroderma, and polymyositis, compared with controls. In SLE patients, CA autoantibodies occurred preferentially in those with anti-U1 RNP or anti-U1 RNP and Ro/SS-A. Some sera reacted with only the CA I or CA II isoform, while approximately 50% of sera that were CA positive reacted with both isoforms. The autoantibodies reacted preferentially with the human enzymes, rather than the bovine CA, both on Western blot and by ELISA: Selected IgG F(ab')2 fragments from anti-CA-containing sera specifically inhibited the enzyme activity of CA, and the CA inhibitor acetazolamide partially inhibited the binding of anti-CA to CA. Thus, at least a part of autoanti-CA is directed toward the active site of CA. Finally, CA molecules were detected as immune complexes in sera from selected anti-CA-positive patients.

CONCLUSION

Autoantibodies to CA represent a previously unrecognized autoantibody to an abundant intracellular protein of the human erythrocyte.

Detection and occurrence of the 60- and 52-kD Ro (SS-A) antigens and of autoantibodies against these proteins

The simultaneous detection of anti-La, anti-60-kD Ro and anti-52-kD Ro antibodies by immunoblotting is greatly improved by changing the crosslinking level in the gel to an acrylamide/bisacrylamide ratio of 19:1. Using this method for the analysis of a number of systemic lupus erythematosus (SLE) and Sjögren's syndrome patient sera it was observed that antibody to the 52-kD Ro protein without anti-60-kD Ro antibody was restricted to Sjögren's syndrome patients (9/26), whereas antibody to the 60-kD Ro protein without contaminating anti-52-kD Ro antibody was only found in SLE patients (8/38). Moreover, in Sjögren's syndrome patient sera anti-Ro antibody was found only in combination with anti-La antibody (20/26), whereas in SLE patient sera anti-Ro antibody could be found without detectable anti-La specificity (4/38). Double immunofluorescence microscopy revealed that the 52-kD Ro and the 60-kD Ro proteins co-localize in the cytoplasm as well as in the nucleus, whereas immunoprecipitation of [32P]-labelled HeLa cell extract with monospecific anti-52-kD Ro and anti-60-kD Ro sera showed that both proteins are associated with the Ro RNAs. These data suggest the presence of both the 52-kD and the 60-kD Ro proteins in the same ribonucleoprotein complexes. To study the evolutionary conservation of the 52-kD Ro, the 60-kD Ro and the La proteins, extracts of cell lines derived from various mammalian species were analysed on Western blots using monospecific human antibodies. In contrast to the 60-kD Ro and the La antigens which are well conserved in evolution, the 52-kD Ro antigen could be detected in primate cells only by this immunological approach.

Antinuclear antibodies to RNA-binding proteins in SLE

The presence of autoantibodies is a prominent feature of connective tissue disease (CTD). At first glance there is a wide range of antibody specificities, but in the individual patient the autoantibody profile is much more restricted. Thus, certain antinuclear antibodies are not only strongly associated with disease expression, but also identify distinctive serological subsets within the spectrum of CTD. In turn, these subsets are associated with particular patterns of disease expression. With increasing knowledge of the molecular nature of the autoantigen targets, the relationship between fine specificity of the antibody response and disease manifestations is being further defined.

Importance of detection of SS-A/Ro autoantibody in screening immunofluorescence tests for autoantibodies to nuclear antigens

SS-A/Ro autoantibodies are related to Sjögren's syndrome and to several clinical subsets of lupus erythematosus. The most widely used laboratory procedure for ANA screening is the indirect immunofluorescence test (IF-ANA); the laboratory detection of anti-SS-A/Ro requires implementation and adherence to several technical and quality assurance recommendations. Using appropriate substrate cells containing the SS-A/Ro antigen, many so-called "ANA-negative" lupus erythematosus patients will demonstrate a positive IF-ANA.

Organ distribution of the Ro (SS-A) antigen in the guinea pig

Using an anti-Ro (SS-A)-specific "sandwich" enzyme-linked immunosorbent assay (ELISA) and Western immunoblotting, we determined the Ro (SS-A) content (both quantitative and qualitative) in saline-perfused organs of the guinea pig. All tissue extracts contained substantial concentrations of Ro (SS-A) antigen and could be grouped into 3 categories based on quantitative reactivity in the sandwich ELISA. The 60-kd and 52-kd molecular forms of Ro (SS-A) present in tissue extracts were similar to those described in Wi-L2 extracts, and the 54-kd molecular form of Ro (SS-A) in guinea pig erythrocytes was similar to that found in human erythrocytes. The tissue distribution of the isoforms of Ro (SS-A) was shown by Western immunoblotting to vary in different tissues, and the reactivity to the 60-kd Ro (SS-A) was correlated with the activity seen in the ELISA. Both the 60-kd and 52-kd Ro (SS-A) bands in guinea pig liver extracts were very weak on Western immunoblots, in contrast to the high concentration of Ro (SS-A) antigen in the ELISA. Other data suggest the possible existence of a unique form of Ro (SS-A) in the liver. Guinea pig tissues have 4 Y RNA that are equivalent to the 4 human RNA--hY1, hY3, hY4, and hY5--present in HeLa cells, while guinea pig red blood cells have only one Y RNA, which is equivalent in size to human hY4.(ABSTRACT TRUNCATED AT 250 WORDS)

Heterogeneity of the Ro/SSA antigen and autoanti-Ro/SSA response: evidence of the four antigenically distinct forms

Precipitating antibodies to the Ro/SSA antigen occur in the sera of 40% of patients with systemic lupus erythematosus (SLE) and in 40-70% of the sera of patients with primary Sjögren's syndrome. Previous work has shown that lymphocyte extracts contain two Ro/SSA antigens with protein moieties of 60 kD and 52 kD and that erythrocyte haemolysate contain two analogous but antigenically distinct Ro/SSA molecules of 60 kD and 54 kD. Frequency analysis of the various specificities in 43 sera with precipitating anti-Ro/SSA and studies with affinity-eluted antibodies suggest that the lymphocyte 60 kD and erythrocyte 60 kD Ro/SSA molecules are related as are the lymphocyte 52 kD and erythrocyte 54 kD Ro/SSA proteins. Anti-Ro/SSA sera when accompanied by other precipitins (anti-La/SSB and anti-U1RNP) react preferentially with certain Ro/SSA isoforms. Evidence is also presented for a 45 kD form of Ro/SSA. These data suggest that the antigenic heterogeneity of the Ro/SSA antigen is immunologically relevant and that there are two families of Ro/SSA antigens; one comprising of the two 60-kD proteins in the erythrocyte and lymphocyte and the other the erythrocyte 54 kD and lymphocyte 52 kD Ro/SSA proteins, respectively.