Improved detection of anti-Jo-1 antibody, a marker for myositis, using purified histidyl-tRNA synthetase

A narrative review of interstitial lung disease in anti-synthetase syndrome: a clinical approach

Anti-synthetase syndrome (AS) is a rare autoimmune disorder characterized by the presence of aminoacyl-transfer RNA synthetase antibodies in conjunction with clinical features such as interstitial lung disease (ILD), Raynaud's phenomenon, nonerosive arthritis, and myopathy. AS distinguishes itself from other inflammatory myopathies by its significant lung involvement and rapidly progressive interstitial lung disease (AS-ILD), therefore the management of AS-ILD requires careful clinical, serologic and radiologic assessment. Glucocorticoids are considered the mainstay of therapy; however, additional immunosuppressive agents are often required to achieve disease control. Patient prognosis is highly dependent on early diagnosis and symptom recognition as the antibody profile is thought to influence therapy response. Since progressive ILD is the leading cause of morbidity and mortality, this review will discuss the clinical approach to patient with suspected AS, with particular emphasis on diagnosis and management of AS-ILD.

Myositis-related interstitial lung disease and antisynthetase syndrome

In patients with myositis, the lung is commonly involved, and the presence of anti-aminoacyl-tRNA synthetase (anti-ARS) antibodies marks the presence or predicts the development of interstitial lung disease (ILD). A distinct clinical entity-antisynthetase syndrome-is characterized by the presence of anti-ARS antibodies, myositis, ILD, fever, arthritis, Raynaud's phenomenon, and mechanic's hands. The most common anti-ARS antibody is anti-Jo-1. More recently described anti-ARS antibodies might confer a phenotype that is distinct from that of anti-Jo-1-positive patients and is characterized by a lower incidence of myositis and a higher incidence of ILD. Among patients with antisynthetase syndrome-related ILD, the response to immunosuppressive medications is generally, but not universally, favorable.

The cutaneous pathology of lupus erythematosus: a review

The presentation of lupus erythematosus (LE) ranges from a skin rash unaccompanied by extracutaneous stigmata to a rapidly progressive lethal multiorgan disease. The diagnosis and subclassification is traditionally based on the correlation of serological and clinical findings. The latter include a photoinduced skin rash, arthralgia, arthritis, fever, Raynaud's phenomenon, anemia, leukopenia, serositis, nephritis and central nervous sysdtem disease. The conventional classification scheme includes systemic, subacute cutaneous and discoid LE. Recent advances in our understanding of the cutaneous histopathology which correlates with the traditional forms of LE, along with certain novel LE subtypes, are the focus of this review. In addition to the main subtypes of LE, we will discuss associated vasculopathic lesions and the contribution of immunofluorescence microscopy to the diagnosis of LE and related connective tissue disease syndromes. Consideration will be given to unusual variants of LE such as anti-Ro/SSA-positive systemic lupus erythematosus (SLE), bullous SLE, lymphomatoid LE, lupus erythematosus profundus, drug induced LE, linear cutaneous LE, chiblains LE and parvovirus B19-associated LE.

Histidyl-tRNA synthetase

Histidyl-tRNA synthetase (HisRS) is responsible for the synthesis of histidyl-transfer RNA, which is essential for the incorporation of histidine into proteins. This amino acid has uniquely moderate basic properties and is an important group in many catalytic functions of enzymes. A compilation of currently known primary structures of HisRS shows that the subunits of these homo-dimeric enzymes consist of 420-550 amino acid residues. This represents a relatively short chain length among aminoacyl-tRNA synthetases (aaRS), whose peptide chain sizes range from about 300 to 1100 amino acid residues. The crystal structures of HisRS from two organisms and their complexes with histidine, histidyl-adenylate and histidinol with ATP have been solved. HisRS from Escherichia coli and Thermus thermophilus are very similar dimeric enzymes consisting of three domains: the N-terminal catalytic domain containing the six-stranded antiparallel beta-sheet and the three motifs characteristic of class II aaRS, a HisRS-specific helical domain inserted between motifs 2 and 3 that may contact the acceptor stem of the tRNA, and a C-terminal alpha/beta domain that may be involved in the recognition of the anticodon stem and loop of tRNA(His). The aminoacylation reaction follows the standard two-step mechanism. HisRS also belongs to the group of aaRS that can rapidly synthesize diadenosine tetraphosphate, a compound that is suspected to be involved in several regulatory mechanisms of cell metabolism. Many analogs of histidine have been tested for their properties as substrates or inhibitors of HisRS, leading to the elucidation of structure-activity relationships concerning configuration, importance of the carboxy and amino group, and the nature of the side chain. HisRS has been found to act as a particularly important antigen in autoimmune diseases such as rheumatic arthritis or myositis. Successful attempts have been made to identify epitopes responsible for the complexation with such auto-antibodies.

The cutaneous pathology associated with seropositivity for antibodies to SSA (Ro): a clinicopathologic study of 23 adult patients without subacute cutaneous lupus erythematosus

Antibodies to Ro/SSA are found in patients with subacute cutaneous lupus erythematosus (SCLE), complement deficiency lupus erythematosus, systemic lupus erythematosus (SLE), neonatal lupus erythematosus, and Sjögren syndrome (SS). Most studies describing the cutaneous pathology associated with anti-Ro antibodies have been of patients with SCLE. Over a 42-month period, we encountered skin biopsy specimens from 23 anti-Ro-positive patients who did not have SCLE: 15 had SLE variably manifesting as SCLE-like rashes; malar erythema; a dermatomyositis-like rash; vascular disease involving cutaneous, cardiac, peripheral, and central nervous systems; restrictive pulmonary disease; periorbital edema; and myositis. Two patients had primary Sjögren syndrome, one had primary antiphospholipid antibody syndrome, and two had rheumatoid arthritis; all five had clinical evidence of cutaneous vasculopathy encompassing livedo, perniosis, and palpable purpura. Three additional patients presented with folliculocentric purpura without other stigmata to permit classification as a specific connective tissue disease. In the SLE patients, biopsy specimens of photodistributed eruptions showed an interface dermatitis accompanied by superficial vascular plexus density reduction. Vasculopathic reactions in patients with and without SLE comprised neutrophilic, lymphocytic, or pauciinflammatory thrombogenic subtypes. Although at times a marker of SCLE, the identification of anti-Ro antibodies may isolate a subset of patients at higher risk of multiorgan vasculopathy, myositis, and progressive pulmonary disease. We postulate that many of the features seen in these patients reflect the sequelae of antibody mediated endothelial cell injury.

The immunofluorescent profile of dermatomyositis: a comparative study with lupus erythematosus

We have demonstrated a role for microvascular injury mediated by the membrane attack complex of complement (C5b-9) in the genesis of cutaneous lesions of dermatomyositis (DM) (1). The purpose of this study is to revisit the immunofluorescent (IF) profile of DM, to further investigate the role of C5b-9 in the pathogenesis of cutaneous lesions, and to see if any features of the IF profile reliably distinguish DM from LE. Lesional skin biopsies from 24 patients with clinical findings characteristic of DM were received in formalin and in Michel's transport medium. Conventional light microscopy, and IF studies with antibodies monospecific for IgG, IgA, IgM, C3, fibrin and C5b-9 were performed. The control group comprised biopsies from 31 patients with well-documented LE. A positive lupus band test (LBT) correlated highly with a diagnosis of LE, with a sensitivity of 64.5% and a specificity of 95.6% (p=0.001). The LBT was most sensitive in the setting of DLE and SLE and was least sensitive in the setting of SCLE. The finding of vascular C5b-9 deposition correlated with a diagnosis of DM versus LE (p=0.001) although the false positive rate was 21.4%. The false negative rate was reduced when vascular C5b-9 was seen in the absence of antibodies to Ro, La, or RNP. While a negative LBT correlated with a diagnosis of DM (p=0.001), the specificity was only 64.5%. However, when it was seen in concert with C5b-9 along the DEJ, specificity was increased to 80.6% (p=0.001). The presence of C5b-9 in vessels and along the DEJ in concert with a negative LBT was predictive of DM (p=0.001) with a specificity of 93.5%, sensitivity of 78.3%, a false positive rate of 10% and a false negative rate of 14.7%. The combination of a negative LBT, vascular C5b-9 deposition and negative serology for Ro, La, and RNP was a predictor of DM versus LE with a sensitivity of 90.5%, a specificity of 96.8%, a false positive rate of 5% and a false negative rate of 6.2% (p=0.001). The IF profile of DM in lesional skin comprises a negative LBT, deposition of C5b-9 within vessels and along the DEJ, and variable keratinocyte decoration for IgG and C5b-9. The most statistically powerful predictor of DM is the combination of a negative LBT with vascular C5b-9 deposition and negative serology for antibodies to Ro, La, Sm, and RNP. Demonstration of a negative LBT in all but 1 case of DM suggests that the DEJ is not a primary site for antigen-antibody interaction. We postulate that the aforementioned IF findings reflect humorally mediated injury of endothelium and keratinocytes, effected by C5b-9.

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.

Recently characterised autoantibodies and their clinical significance

Multisystem autoimmune diseases such as systemic lupus erythematosus (SLE), primary Sjögren's syndrome (SS), scleroderma and polymyositis are characterised by the presence of antinuclear antibodies (ANAs). Immunoblotting and cDNA cloning studies reveal that the autoantigens of the multisystem autoimmune diseases are important proteins involved in nucleic acid metabolism, including tRNA charging, intron splicing, DNA uncoiling, and RNA polymerase co-factors. Each specific syndrome associates with a restricted variety of ANAs, e.g. anti-La with primary SS, anti-Sm with SLE, anti-synthetase enzymes with myositis, anti-topoisomerase 1 (Scl 70) with scleroderma, and anti-centromere with CREST. Precise characterisation of an ANA provides valuable diagnostic and prognostic information, and should be performed when an ANA is detected.

A flexible, efficient, checkerboard immunoblot system for the detection and semiquantitation of specific antinuclear antibodies

In this paper an uncomplicated method for the simultaneous detection and semiquantitation of 11 of the 12 commonly studied antinuclear antibodies (ANA) in a single run is described. This new application of checkerboard immunoblotting (CBIB) is based upon available technology and employs purified antigens which can be either purchased or produced in-house. CBIB requires no electronic instrument, can be formatted to meet the needs of the user, is rapidly performed, and has acceptable labor and materials costs. Data on the use of the method to examine available reference antisera is presented. CBIB has also proven practical for the clinical study of 18 sera, at two dilutions per membrane, for each set of specific antinuclear antibodies, also at two or more dilutions.

Antibody to signal recognition particle in polymyositis

Using immunoprecipitation, we identified 13 patients with antibodies to the signal recognition particle (SRP) from a collection of sera representing 265 polymyositis/dermatomyositis (PM/DM) patients. Antibody reactivity with SRP was confirmed by enzyme-linked immunosorbent assay and immunoprecipitation with isolated dog pancreas SRP. The antibody was present in the serum of 4% of PM/DM patients, and 18% of PM/DM patients with anticytoplasmic antibodies other than anti-Jo-1, but not in patients with other conditions who had anticytoplasmic antibodies. Anti-SRP was associated with classic adult PM, and some of these cases were unusually severe and/or of rapid onset; it was not found in patients with overlap syndromes or with DM involvement. Unlike patients with antibodies to aminoacyl-transfer RNA synthetases, patients with anti-SRP had a low frequency of pulmonary fibrosis, as well as of arthritis and Raynaud's phenomenon. Anti-SRP antibodies may serve as a marker for a second, distinct subgroup of adult PM.

Clinical manifestations in patients with antibody to PL-12 antigen (alanyl-tRNA synthetase)

PURPOSE

Anti-PL-12 antibody is directed at the enzyme alanyl-tRNA synthetase (ARS). Studies have clearly associated anti-Jo-1, also directed at an aminoacyl-tRNA synthetase (histidyl-tRNA synthetase), with a subgroup of myositis marked by a high frequency of interstitial lung disease (ILD) and arthritis. A similar syndrome has been reported in patients with antibodies to PL-12, but few patients have been studied. We describe the clinical manifestations in a new series of patients with antibody to PL-12.

PATIENTS AND METHODS

Sera from patients with polymyositis and sera found to contain anticytoplasmic antibodies were screened for antibody to PL-12 by testing for inhibition of ARS enzymatic activity by serum, and by immunoprecipitation.

RESULTS

Nine sera inhibited ARS. These nine plus two additional sera with anticytoplasmic antibodies immunoprecipitated an identical pattern of tRNAs and a polypeptide of 110 kd. Of the 10 patients that could be evaluated, eight had some evidence of myositis, including six that satisfied the criteria for myositis. Three of these six, all with dermatomyositis, had severe muscle involvement. Eight of the 10 patients had radiographic evidence of pulmonary fibrosis, and seven of the eight had clinical pulmonary impairment, including four with clinically severe ILD. Joint manifestations were found in five patients, and arthritis was the only clinical problem in one patient.

CONCLUSION

We conclude that anti-PL-12, like anti-Jo-1 and anti-PL-7, was frequently associated with the "Jo-1 syndrome" of myositis with ILD. ILD was a major clinical problem in this group of patients.

Dermatomyositis as a systemic disease

Dermatomyositis is a classic example of a disease that has both cutaneous and systemic manifestations. The skin and muscle disease are described as well as the possible systemic manifestations including overlap syndromes, joint symptoms, pulmonary disease, and other internal organ involvement. The association with pregnancy is also discussed.

Anti-KJ: a new antibody associated with the syndrome of polymyositis and interstitial lung disease

Antibodies to aminoacyl-tRNA synthetases (anti-Jo-1, anti-PL-7, anti-PL-12) have been found in the serum of some patients with polymyositis (PM). Patients with these antibodies have an unusually high rate of interstitial lung disease (ILD) in association with their PM. Two patients (K.J. and B.T.) with severe ILD and PM were found to have antibodies to a cytoplasmic antigen, but tests to determine whether the antigen was an aminoacyl-tRNA synthetase were negative, including tests of KJ serum for inhibitory effects on the 20 synthetases. KJ immunoprecipitates did not contain tRNA, in contrast to antisynthetase sera. When IgG samples were added to a reticulocyte in vitro translation system at a concentration of 0.3 mg/ml, KJ IgG inhibited globin mRNA translation by 98%, while anti-Jo-1 IgG inhibited 62% and normal IgG had little effect. Thus, both anti-KJ and the antisynthetases are directed at antigens that are involved in translation and protein synthesis, and both are associated with the syndrome of lung disease and PM. This syndrome may be associated with antibodies to translation-related proteins in general, which may have implications for the link of PM and enteroviruses, which are mRNA viruses.

Polymyositis-dermatomyositis: a clinical review

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Antibody to threonyl-transfer RNA synthetase in myositis sera

The prevalence and clinical correlations of anti-threonyl-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 greater than 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.

Interstitial lung disease as the presentation of anti-Jo-1 positive polymyositis

A patient presenting with interstitial lung disease was predicted to have underlying polymyositis when found to be anti-Jo-1 antibody positive. When myopathy developed later with elevated serum creatine phosphokinase and myoglobin levels, the electromyogram was nonmyopathic, and polymyositis was confirmed by muscle biopsy. The case illustrates the value of anti-Jo-1 as a 'marker' autoantibody for polymyositis, and the need for thorough investigation of patients with interstitial lung disease of uncertain etiology. This should include indirect immunofluorescence using a dividing cell substrate and tests for antibodies to extractable tissue antigens. The need to completely evaluate patients with dermatopolymyositis is also emphasised.

Purification of bovine liver histidyl-tRNA synthetase, the Jo-1 antigen of polymyositis: size of the whole enzyme and its characteristic proteolytic fragments

We have recently reported the marked increase in frequency which can be achieved in the detection of the anti-Jo-1 antibody of polymyositis in serum samples by replacing commercial mixtures of cytoplasmic and nuclear antigens with the purified antigen, histidyl-tRNA synthetase. The present paper describes a method for purifying this antigen and an investigation of its size. Molecular masses previously reported for the enzyme have varied from 85-154 kDa and subunit molecular masses varying from 40-77 kDa have been observed. Several of these fragments are of sizes similar to those of a number of other autoantigens commonly observed in connective tissue diseases. Since the clinical identification of these autoantigens often relies exclusively on size determination by Western blotting, we have characterized the commonly occurring fragments of histidyl-tRNA synthetase lest they confuse such identification. It is concluded that histidyl-tRNA synthetase, like many other aminoacyl-tRNA synthetases, is subject to severe proteolysis during extraction procedures. Several characteristic fragments (Mr = 80, 75, 61, 55, 50 and 45 kDa) result, a finding that provides a satisfactory explanation of the various values previously reported. The intact bovine enzyme is a dimer of molecular mass close to 160 kDa.