Anti-Ro60 and anti-Ro52/TRIM21: Two distinct autoantibodies in systemic autoimmune diseases

As iconic and important diagnostic autoantibodies, anti-Ro60 and anti-Ro52/tri-partite motif-containing 21 (TRIM21) make a common appearance in a number of systemic autoimmune disorders such as systemic lupus erythematosus (SLE). These autoantibodies often co-exist together; yet despite their close relationship, there is no evidence that they are physically linked and probably reflect a convergence of separate processes of failed immunological tolerance. Confusingly, they are sometimes classed together as the "SSA" or "Ro" autoantibody system without clear distinction between the two. In this Short Communication, we discuss the diagnostic merits for separate detection and reporting of these two autoantibodies, and discuss avenues for future research. Indeed, further insight into their fascinating origins and pathogenic roles in autoimmunity will surely shed light on how we can prevent and treat devastating autoimmune disorders.

Clinical manifestations in anti-Ro52/SS-A antibody-seropositive patients with Sjögren's syndrome

Background: The relationship between anti-Ro52/SS-A antibody (anti-Ro52) and the clinical manifestations of Sjögren's syndrome (SS) has not been fully clarified. We determined the clinical factors relevant to SS patients with anti-Ro52.Methods: We conducted a retrospective study of 149 subjects suspicious for SS and 50 healthy control subjects. We analyzed items of the American-European Consensus Group (AECG) criteria and the EULAR Sjögren's Syndrome Disease Activity Index (ESSDAI).Results: SS was documented in 115 subjects. Anti-Ro52 was observed in 70 SS patients. Anti-Ro52 positivity showed a significantly higher association with anti-Ro60 positivity than with anti-centromere antibody (ACA) positivity (p < 0.05). Regarding the difference in the anti-Ro52 concentration, we observed six significantly relevant components: two AECG components and four non-AECG components. The anti-Ro52 concentration well-discriminated three clinical factors (ROC AUC >0.75), i.e., ACA seropositivity, ESSDAI score ≥1, and RF, and it moderately discriminated high serum IgG, focus score ≥1, and anti-La/SS-B antibody seropositivity (ROC AUC >0.7). A linear relationship between the ESSDAI score and the anti-Ro52 concentration was observed.Conclusion: A significant association between clinical factors (including the ESSDAI) and the anti-Ro52 concentration were revealed. Anti-Ro52 was more highly associated with anti-Ro60 positivity than with ACA positivity.

Identification of a short form of a Caenorhabditis elegans Y RNA homolog Cel7 RNA

Cel7 RNA is a member of the Caenorhabditis elegans stem-bulge RNAs (sbRNAs) that are classified into the Y RNA family based on their structural similarity. We identified a 15-nucleotide-shorter form of Cel7 RNA and designated it Cel7s RNA. Both Cel7 and Cel7s RNAs increased during the development of worms from L1 to adult. Cel7s RNA was notably more abundant in embryos than in L1 to L3 larvae. Cel7 RNA in embryo was less than those in L2 to adult. The ratio of cellular level of Cel7 RNA to that of Cel7s RNA was higher in L1 to L4, but reversed in embryos and adults. In rop-1 mutants, in which the gene for the C. elegans Ro60 homolog, ROP-1, was disrupted, Cel7s RNA decreased similar to CeY RNA, another C. elegans Y RNA homolog. Surprisingly, Cel7 RNA, existed stably in the absence of ROP-1, unlike Cel7s and CeY RNAs. Gel-shift assays demonstrated that Cel7 and Cel7s RNAs bound to ROP-1 in a similar manner, which was much weaker than CeY RNA. The 5'-terminal 15-nt of Cel7 RNA could be folded into a short stem-loop structure, probably contributing to the stability of Cel7 RNA in vivo and the distinct expression patterns of the 2 RNAs.

Ro60 and Y RNAs: structure, functions, and roles in autoimmunity

Ro60, also known as SS-A or TROVE2, is an evolutionarily conserved RNA-binding protein that is found in most animal cells, approximately 5% of sequenced prokaryotic genomes and some archaea. Ro60 is present in cells as both a free protein and as a component of a ribonucleoprotein complex, where its best-known partners are members of a class of noncoding RNAs called Y RNAs. Structural and biochemical analyses have revealed that Ro60 is a ring-shaped protein that binds Y RNAs on its outer surface. In addition to Y RNAs, Ro60 binds misfolded and aberrant noncoding RNAs in some animal cell nuclei. Although the fate of these defective Ro60-bound noncoding RNAs in animal cells is not well-defined, a bacterial Ro60 ortholog functions with 3' to 5' exoribonucleases to assist structured RNA degradation. Studies of Y RNAs have revealed that these RNAs regulate the subcellular localization of Ro60, tether Ro60 to effector proteins and regulate the access of other RNAs to its central cavity. As both mammalian cells and bacteria lacking Ro60 are sensitized to ultraviolet irradiation, Ro60 function may be important during exposure to some environmental stressors. Here we summarize the current knowledge regarding the functions of Ro60 and Y RNAs in animal cells and bacteria. Because the Ro60 RNP is a clinically important target of autoantibodies in patients with rheumatic diseases such as Sjogren's syndrome, systemic lupus erythematosus, and neonatal lupus, we also discuss potential roles for Ro60 RNPs in the initiation and pathogenesis of systemic autoimmune rheumatic disease.

Detection of SSA and SSB Antibodies Associated with Primary Sjögren's Syndrome Using Enzyme-Linked Immunosorbent Assay

Antibodies to Ro52/Ro60 (SSA) and La (SSB) are strongly associated to the autoimmune disease primary Sjögren's syndrome and are important in the serologic diagnosis of the disease. Several methods for detection of these antibodies exist such as indirect immunofluorescence, commercial western blot kits, in-house assays, and numerous commercial enzyme-linked immunosorbent assays (ELISAs). Dependent on the type of assay, sensitivity and specificity may vary notably. Especially ELISAs, where the antibody reactivity to synthetic peptides, recombinant or native proteins are determined, are often applied. This chapter describes detection of SSA and SSB antibodies by ELISA.

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.

Characterization of continuous monoclonal antibody epitopes in the N-terminus of Ro60

One of the major targets of the autoimmune response in the rheumatic autoimmune diseases, Systemic Lupus Erythematosus and Sjögrens Syndrome, is the protein Ro60. Ro60 is known to associate with small misfolded RNAs, and is involved in RNA quality control and in enhancing cell survival during cellular stress, e.g. after ultaviolet irradiation. In this study, six monoclonal antibodies to Ro60 were analyzed in order to identify antigenic regions and the nature of these. Preliminary analyses revealed that two of the antibodies recognized continuous epitopes, while the remaining antibodies most likely recognized conformational epitopes. The continuous epitopes of Ro60 were characterised by modified immunoassays employing resin-bound peptides and free peptides. Peptide screenings located the epitopes to the N-terminus of Ro60, and further analyses indicated that the epitopes of the monoclonal antibodies TROVE2 and SSI-HYB 358-02 were located to amino acids 8-17 and 34-49, respectively. Moreover, charged amino acids were found to be especially important for antibody reactivity, although antibody reactivity of the monoclonal antibody TROVE2 primarily was found to be epitope backbone-dependent.

The detection of Ro52 and Ro60 according to the presence of SS-B/La, and ANA pattern and titer

Anti-Ro52 (Ro52) and anti-Ro60 (Ro60) antibodies are associated with different clinical entities. We investigated their relationship with the presence of anti-SS-B/La (SSB) antibody, the pattern and titer of antinuclear antibody (ANA), and the variations in antibody profiles related with anti-SS-A/Ro (SSA) positivity. Our aim was to develop a strategy to increase the efficiency of anti-extractable nuclear antigen (ENA) determinations. Statistical analyses were based on the Chi-squared test for categorical variables, the Mann-Whitney U test to compare profiles, and the odds ratio (OR) and 95% confidence interval (95% CI) to estimate the risk of variability. We analyzed 800 SSA-positive samples with Ro52 or Ro60 reactivity. The most frequent profiles were Ro52+Ro60+SSB (n=349, 43.6%); Ro52+Ro60 (n=126, 15.8%); Ro52 (n=121, 15.1%) and Ro60 (n=71, 8.9%). In samples positive only for SSA and an ANA titer ≤1:640, the most likely profile was positivity for either Ro52 or Ro60, whereas when the ANA titer was >1:640, positivity for both Ro52 and Ro60 simultaneously was more likely (p<0.001). In samples positive for both SSA and SSB, the most likely profile was Ro52+Ro60+SSB regardless of the ANA titer (p=0.001). When only SSA was positive and the ANA staining pattern was nucleolar, centromeric or cytoplasmic, Ro52 positivity was most likely (p<0.001). When both SSA and SSB were positive, both Ro52 and Ro60 were likely to be positive regardless of the ANA staining pattern. In 28.7% of the patients the profile was variable. Variability was significantly greater in those with the SSA profile (23/67) than with the SSA+SSB profile (15/105; OR=1.9, 95% CI=1.1-3.3; p=0.025), and the difference in variability was greatest between the Ro52+Ro60 profile (8/23) and the Ro52+Ro60+SSB profile (8/68; OR=4.2, 95% CI=1.9-9.5; p<0.001). We conclude that to increase efficiency in the immunology laboratory, positivity for Ro52 and Ro60 individually or simultaneously can be deduced from SSB status and the ANA pattern and titer. In general, for the most frequent anti-ENA findings, priority should be given to retesting autoantibodies not detected in the initial analysis.