Antibody to threonyl–transfer rna synthetase in myositis sera

The prevalence and clinical correlations of antithreonyl–transfer RNA synthetase (anti–PL-7), as well as the relationship of anti–PL-7 to anti–histidyl–transfer RNA synthetase (anti–Jo-1) were studied in 109 sera from patients with myositis. Inhibition of threonine aminoacylation was used to screen for anti–PL-7. Sera from 3 patients, 2 with polymyositis and 1 with polymyositis–overlap syndrome, and a fourth serum from a patient with dermatomyositis, which was previously found to contain anti–PL-7, inhibited >90% of activity (3.7% of 109 sera). All 4 sera reacted strongly in an enzyme-linked immunosorbent assay with enzyme that was either affinity purified with anti–PL-7 or was biochemically purified. There was no indication of cross-reactivity by aminoacylation inhibition or, for most sera, by enzyme-linked immunosorbent assay. Anti–PL-7 is an uncommon myositis-associated antibody that is independent of anti–Jo-1, but is directed at a functionally related enzyme.     

Antibodies to glycyl-transfer RNA synthetase in patients with myositis and interstitial lung disease.

OBJECTIVE. We have previously described anti-EJ antibodies, and provided evidence that these antibodies react with glycyl-transfer RNA (gly-tRNA) synthetase. The aim of the present study was to identify patients with anti-EJ antibodies and describe the clinical associations of the antibody, in particular, whether it is associated with the syndrome of myositis and interstitial lung disease (ILD) that has been previously associated with autoantibodies to the aminoacyl-tRNA synthetases for histidine, threonine, and alanine. METHODS. Sera from patients with suspected or proven polymyositis or dermatomyositis (DM), sera with anticytoplasmic patterns, and control sera were tested for anti-EJ antibodies by immunoprecipitation (IPP). Positive sera and controls were tested for the ability to inhibit gly-tRNA synthetase by preincubation of the enzyme source with the serum. RESULTS. Anti-EJ antibodies were demonstrated in the sera of 5 patients, by IPP of characteristic tRNAs and protein. Original serum EJ and each of the new sera significantly inhibited the enzymatic activity of gly-tRNA synthetase but not histidyl-tRNA synthetase. All 5 of the new patients had inflammatory myopathy, a typical DM rash, and ILD. One, who had an overlap syndrome with systemic lupus erythematosus, had anti-EJ at least 4 months before the development of clinical myositis. Arthritis and Raynaud's phenomenon, other features associated with antisynthetases, were also seen. CONCLUSION. Anti-EJ is associated with the syndrome of myositis and lung disease that is seen in association with other antisynthetases. The finding of specific inhibition of gly-tRNA synthetase by all anti-EJ-positive sera strongly supports the identification of EJ antigen as gly-tRNA synthetase.     

Multiplicity of antibodies in myositis sera

Serologic studies on 114 patients with polymyositis and dermatomyositis revealed that 89% had either a precipitating antibody to antigens in calf thymus extract or a positive immunofluorescent reaction on HEp-2 cells, a human tissue culture line. Previously, the greatest proportion of polymyositis sera demonstrating positive serologic results (i.e., the proportion of patients' sera forming precipitates with calf thymus extract) was reported to be 60%. Use of the HEp-2 cell as immunofluorescent substrate enabled the detection of antibody in 89 (78%) of the sera, providing the additional probe which demonstrated specific antibody. Nuclear, cytoplasmic, and nucleolar staining are the most common patterns of immunofluorescence. The immunofluorescent patterns and individual precipitin reactions are related to each other and to the clinical syndromes in which they appear.     

Autoantibodies to glycyl–transfer RNA synthetase in myositis. Association with dermatomyositis and immunologic heterogeneity

Objective. To elucidate the clinical significance and immunologic heterogeneity of anti–glycyl–transfer RNA (tRNA) synthetase antibodies in polymyositis/dermatomyositis (PM/DM). Methods. Sera from 345 patients with rheumatic diseases, including 91 with myositis, were examined using immunoprecipitation assays. Autoantibodies to aminoacyl-tRNA synthetases were further analyzed with 2-dimensional RNA fractionation and via inhibition of in vitro aminoacylation. Results. Serum from 1 patient with DM and interstitial lung disease immunoprecipitated glycyl-tRNA synthetase along with only 1 of 4 associated tRNAs, in comparison with control anti–glycyl-tRNA synthetase antibodies, which bound the enzyme along with all 4 associated tRNAs. Immunoblotting findings and a lack of in vitro inhibition aminoacylation of tRNA^gly by serum from this patient also suggested differences between the epitope specificity of this serum and that of other sera with anti–glycyl-tRNA synthetase antibodies. Conclusion. This identification of antibodies to glycyl-tRNA synthetase from a patient with DM underscores the association of this specificity with the disease. The finding that these antibodies bound an epitope outside the active site of the synthetase enzyme, in contrast to most anti–aminoacyl-tRNA synthetases, emphasizes the immunologic heterogeneity of these autoantibodies.     

Novel conformation of histidyl-transfer RNA synthetase in the lung: the target tissue in Jo-1 autoantibody-associated myositis

OBJECTIVE: We previously proposed that novel expression and/or conformation of autoantigens in the target tissue may play a role in generating phenotype-specific immune responses. The strong association of autoantibodies to histidyl-transfer RNA synthetase (HisRS, Jo-1) with interstitial lung disease in patients with myositis led us to study HisRS expression and conformation in the lung. METHODS: Normal human tissue specimens were probed with a novel anti-HisRS antibody recognizing its granzyme B-cleavable conformation by immunoblotting and immunohistochemistry. The HisRS granzyme B site was mapped using site-directed mutagenesis, and its relationship to the antibody recognition domain was evaluated in tandem immunoprecipitation/granzyme B cleavage studies. RESULTS: The HisRS alpha-helical coiled-coil N-terminal domain recognized by autoantibodies is bounded by a granzyme B cleavage site. In immunoprecipitation studies with patient sera, HisRS was found to exist in 2 conformations, defined by sensitivity to cleavage by granzyme B and modification by autoantibody binding. Despite similar global expression of HisRS in different tissue, expression of its granzyme B-cleavable form was enriched in the lung and localized to the alveolar epithelium. CONCLUSION: A proteolytically sensitive conformation of HisRS exists in the lung, the target tissue associated with this autoantibody response. We thus propose that autoimmunity to HisRS is initiated and propagated in the lung.     

HLA-D region genes associated with autoantibody responses to histidyl-transfer RNA synthetase (Jo-1) and other translation-related factors in myositis

Myositis has been associated with HLA-B8 and DR3, especially in white patients with polymyositis and serum anti-Jo-1 antibodies. Twenty-eight patients with myositis and serum translation-related autoantibodies anti-Jo-1, anti-PL-7, anti-PL-12, anti-KJ, and anti-SRP were studied for HLA class II specificities by Southern blotting with HLA-DR beta, DQ beta, and DQ alpha probes. The association of HLA-DR3 (DRw17) with anti-Jo-1 antibodies in white myositis patients was confirmed (P = 0.003, relative risk 8.9). However, HLA-DRw52 haplotypes, regardless of subtype, were present in all of the white and black patients with serum anti-Jo-1 and other translation-related autoantibodies. Moreover, one anti-Jo-1 positive patient had HLA-DRw8, an HLA-DRw52 haplotype on which the DR beta 3 gene has been partially deleted. No HLA-DQ specificity or allele was common to all patients. The HLA-DR3, DR5, DRw6, and DRw8 haplotypes, which bear the HLA-DRw52 specificity, share the most homology in the DR beta 1 first hypervariable region at amino acid positions 9-13. Thus, this DR beta 1 region appears to be the most likely candidate "epitope" for translation-related autoimmune responses in inflammatory myositis.     

Autoantibody profiles in the sera of European patients with myositis

OBJECTIVE: To determine the prevalence of myositis specific autoantibodies (MSAs) and several myositis associated autoantibodies (MAAs) in a large group of patients with myositis. METHODS: A total of 417 patients with myositis from 11 European countries (198 patients with polymyositis (PM), 181 with dermatomyositis (DM), and 38 with inclusion body myositis (IBM)) were serologically analysed by immunoblot, enzyme linked immunosorbent assay (ELISA) and/or immunoprecipitation. RESULTS: Autoantibodies were found in 232 sera (56%), including 157 samples (38%) which contained MSAs. The most commonly detected MSA was anti-Jo-1 (18%). Other anti-synthetase, anti-Mi-2, and anti-SRP autoantibodies were found in 3%, 14%, and 5% of the sera, respectively. A relatively high number of anti-Mi-2 positive PM sera were found (9% of PM sera). The most commonly detected MAA was anti-Ro52 (25%). Anti-PM/Scl-100, anti-PM/Scl-75, anti-Mas, anti-Ro60, anti-La, and anti-U1 snRNP autoantibodies were present in 6%, 3%, 2%, 4%, 5%, and 6% of the sera, respectively. Remarkable associations were noticed between anti-Ro52 and anti-Jo-1 autoantibodies and, in a few sera, also between anti-Jo-1 and anti-SRP or anti-Mi-2 autoantibodies. CONCLUSIONS: The incidence of most of the tested autoantibody activities in this large group of European patients is in agreement with similar studies of Japanese and American patients. The relatively high number of PM sera with anti-Mi-2 reactivity may be explained by the use of multiple recombinant fragments spanning the complete antigen. Furthermore, our data show that some sera may contain more than one type of MSA and confirm the strong association of anti-Ro52 with anti-Jo-1 reactivity.     

Antibodies to glycyl–transfer rna synthetase in patients with myositis and interstitial lung disease

Objective. We have previously described anti-EJ antibodies, and provided evidence that these antibodies react with glycyl–transfer RNA (gly-tRNA) synthetase. The aim of the present study was to identify patients with anti-EJ antibodies and describe the clinical associations of the antibody, in particular, whether it is associated with the syndrome of myositis and interstitial lung disease (ILD) that has been previously associated with autoantibodies to the aminoacyl-tRNA synthetases for histidine, threonine, and alanine. Methods. Sera from patients with suspected or proven polymyositis or dermatomyositis (DM), sera with anticytoplasmic patterns, and control sera were tested for anti-EJ antibodies by immunoprecipitation (IPP). Positive sera and controls were tested for the ability to inhibit gly-tRNA synthetase by preincubation of the enzyme source with the serum. Results. Anti-EJ antibodies were demonstrated in the sera of 5 patients, by IPP of characteristic tRNAs and protein. Original serum EJ and each of the new sera significantly inhibited the enzymatic activity of gly-tRNA synthetase but not histidyl-tRNA synthetase. All 5 of the new patients had inflammatory myopathy, a typical DM rash, and ILD. One, who had an overlap syndrome with systemic lupus erythematosus, had anti-EJ at least 4 months before the development of clinical myositis. Arthritis and Raynaud's phenomenon, other features associated with antisynthetases, were also seen. Conclusion. Anti-EJ is associated with the syndrome of myositis and lung disease that is seen in association with other antisynthetases. The finding of specific inhibition of gly-tRNA synthetase by all anti-EJ–positive sera strongly supports the identification of EJ antigen as gly-tRNA synthetase.     

A truncated aminoacyl-tRNA synthetase modifies RNA

Aminoacyl-tRNA synthetases are modular enzymes composed of a central active site domain to which additional functional domains were appended in the course of evolution. Analysis of bacterial genome sequences revealed the presence of many shorter aminoacyl-tRNA synthetase paralogs. Here we report the characterization of a well conserved glutamyl-tRNA synthetase (GluRS) paralog (YadB in Escherichia coli) that is present in the genomes of >40 species of proteobacteria, cyanobacteria, and actinobacteria. The E. coli yadB gene encodes a truncated GluRS that lacks the C-terminal third of the protein and, consequently, the anticodon binding domain. Generation of a yadB disruption showed the gene to be dispensable for E. coli growth in rich and minimal media. Unlike GluRS, the YadB protein was able to activate glutamate in presence of ATP in a tRNA-independent fashion and to transfer glutamate onto tRNA(Asp). Neither tRNA(Glu) nor tRNA(Gln) were substrates. In contrast to canonical aminoacyl-tRNA, glutamate was not esterified to the 3'-terminal adenosine of tRNA(Asp). Instead, it was attached to the 2-amino-5-(4,5-dihydroxy-2-cyclopenten-1-yl) moiety of queuosine, the modified nucleoside occupying the first anticodon position of tRNA(Asp). Glutamyl-queuosine, like canonical Glu-tRNA, was hydrolyzed by mild alkaline treatment. Analysis of tRNA isolated under acidic conditions showed that this novel modification is present in normal E. coli tRNA; presumably it previously escaped detection as the standard conditions of tRNA isolation include an alkaline deacylation step that also causes hydrolysis of glutamyl-queuosine. Thus, this aminoacyl-tRNA synthetase fragment contributes to standard nucleotide modification of tRNA.     

Antibody profiles of sera giving different nuclear staining patterns

Antibodies to three major antigens of the non-histone or saline-extractable nuclear antigen (ENA) complex were sought by counterimmunoelectrophoresis (CEP) in three groups of sera which gave different patterns in the immunofluorescence test for antinuclear antibodies (ANA). Precipitins, mainly anti RNP and anti SS-B, were found most commonly (61%) in 70 sera with a speckled ANA pattern but were less frequent (8%) in 61 sera with a homogeneous ANA pattern and exceptional (1%) in 72 sera which showed fibrillar ANA staining. Rim staining was an insensitive indicator of nDNA antibody. An enzyme immunoassay (EIA), specific for anti-SS-B was more sensitive than CEP and identified this antibody in 28 sera, compared with 18 for CEP.     

Role of innate immunity in a murine model of histidyl–transfer RNA synthetase (Jo‐1)–mediated myositis

Objective

Previous studies in humans and in animal models support a key role of histidyl–transfer RNA synthetase (HisRS; also known as Jo‐1) in the pathogenesis of idiopathic inflammatory myopathy. While most investigations have focused on the ability of HisRS to trigger adaptive immune responses, in vitro studies clearly indicate that HisRS possesses intrinsic chemokine‐like properties capable of activating the innate immune system. The purpose of this study was therefore to examine the ability of HisRS to direct innate immune responses in a murine model of myositis.

Methods

Following intramuscular immunization with soluble HisRS in the absence of exogenous adjuvant, selected strains of mice were evaluated at different time points for histopathologic evidence of myositis. Enzyme‐linked immunosorbent assay–based assessment of autoantibody formation and carboxyfluorescein succinimidyl ester proliferation studies provided complementary measures of B cell and T cell responses triggered by HisRS immunization.

Results

Compared to appropriate control proteins, a murine HisRS fusion protein induced robust, statistically significant muscle inflammation in multiple congenic strains of C57BL/6 and NOD mice. Time course experiments revealed that this inflammatory response occurred as early as 7 days postimmunization and persisted for up to 7 weeks. Parallel immunization strategies in DO11.10/RAG‐2^–/– and C3H/HeJ (TLR‐4^–/–) mice indicated that the ability of murine HisRS to drive muscle inflammation was not dependent on B cell receptor or T cell receptor recognition and did not require Toll‐like receptor 4 signaling.

Conclusion

Collectively, the findings of these experiments support a model in which HisRS can trigger both innate and adaptive immune responses that culminate in severe muscle inflammation that is the hallmark of idiopathic inflammatory myopathy.

     

Clinical and immunogenetic features of patients with autoantibodies to asparaginyl-transfer RNA synthetase

OBJECTIVE: We have previously described anti-KS autoantibodies and provided evidence that they are directed against asparaginyl-transfer RNA (tRNA) synthetase (AsnRS). The aim of the present study was to identify patients with anti-AsnRS autoantibodies and elucidate the clinical significance of this sixth antisynthetase antibody. In particular, we studied whether it was associated with the syndrome of myositis (polymyositis or dermatomyositis [DM]), interstitial lung disease (ILD), arthritis, and other features that had been previously associated with the 5 other anti-aminoacyl-tRNA synthetase autoantibodies. METHODS: More than 2,500 sera from patients with connective tissue disease (including myositis and ILD) and controls were examined for anti-AsnRS autoantibodies by immunoprecipitation (IP). Positive and control sera were tested for the ability to inhibit AsnRS by preincubation of the enzyme source with the serum. The HLA class II (DRB1, DQA1, DQB1, DPB1) alleles were identified from restriction fragment length polymorphism of polymerase chain reaction-amplified genomic DNA. RESULTS: Anti-AsnRS antibodies were identified in the sera of 8 patients (5 Japanese, 1 American, 1 German, and 1 Korean) by IP of the same distinctive set of tRNA and protein that differed from those precipitated by the other 5 antisynthetases, and these antibodies showed specific inhibition of AsnRS activity. Two of these patients had DM, but 7 of 8 (88%) had ILD. Four patients (50%) had arthritis, and 1 had Raynaud's phenomenon. This antisynthetase was very rare among myositis patients (present in 0% of Japanese myositis patients), but it was found in 3% of Japanese ILD patients. Thus, most patients with anti-AsnRS had chronic ILD with or without features of connective tissue disease. Interestingly, all 4 Japanese patients tested had DR2 (DRB1*1501/1502), compared with 33% of healthy controls. CONCLUSION: These results indicate that anti-AsnRS autoantibodies, like anti-alanyl-tRNA synthetase autoantibodies, have a stronger association with ILD than with myositis and may be associated with the DR2 phenotype.     

Antibody to the RNA-Dependent DNA Polymerase of Mammalian C-Type RNA Tumor Viruses

Sera from rats bearing transplantable tumors induced by murine C-type tumor viruses contain an inhibitor of the activity of the viral RNA-dependent DNA polymerase. The inhibitor is shown to be an immunoglobulin (IgG) directed against the enzyme. Antiserum made in rabbits against partially purified murine leukemia virus polymerase also inhibits the polymerases of other mammalian C-type RNA-containing tumor viruses. Thus, the polymerases from different mammalian tumor viruses are antigenically related.     

Resected RNA pseudoknots and their recognition by histidyl-tRNA synthetase

Duplexes constituted by closed or open RNA circles paired to single-stranded oligonucleotides terminating with 3′-CCA_OH form resected pseudoknots that are substrates of yeast histidyl-tRNA synthetase. Design of this RNA fold is linked to the mimicry of the pseudoknotted amino acid accepting branch of the tRNA-like domain from brome mosaic virus, known to be charged by tyrosyl-tRNA synthetases, with RNA minihelices recapitulating accepting branches of canonical tRNAs. Prediction of the histidylation function of the new family of minimalist tRNA-like structures relates to the geometry of resected pseudoknots that allows proper presentation to histidyl-tRNA synthetase of analogues of the histidine identity determinants N-1 and N73 present in tRNAs. This geometry is such that the analogue of the major N-1 histidine determinant in the RNA circles faces the analogue of the discriminator N73 nucleotide in the accepting oligonucleotides. The combination of identity elements found in tRNA^His species from archaea, eubacteria, and organelles (G-1/C73) is the most efficient for determining histidylation of the duplexes. The inverse combination (C-1/G73) leads to the worst histidine acceptors with charging efficiencies reduced by 2–3 orders of magnitude. Altogether, these findings open new perspectives for understanding evolution of tRNA identity and serendipitous RNA functions.