TDP-43 prevents endogenous RNAs from triggering a lethal RIG-I-dependent interferon response

RIG-I-like receptors (RLRs) are involved in the discrimination of self versus non-self via the recognition of double-stranded RNA (dsRNA). Emerging evidence suggests that immunostimulatory dsRNAs are ubiquitously expressed but are disrupted or sequestered by cellular RNA binding proteins (RBPs). TDP-43 is an RBP associated with multiple neurological disorders and is essential for cell viability. Here, we demonstrate that TDP-43 regulates the accumulation of immunostimulatory dsRNA. The immunostimulatory RNA is identified as RNA polymerase III transcripts, including 7SL and Alu retrotransposons, and we demonstrate that the RNA-binding activity of TDP-43 is required to prevent immune stimulation. The dsRNAs activate a RIG-I-dependent interferon (IFN) response, which promotes necroptosis. Genetic inactivation of the RLR-pathway rescues the interferon-mediated cell death associated with loss of TDP-43. Collectively, our study describes a role for TDP-43 in preventing the accumulation of endogenous immunostimulatory dsRNAs and uncovers an intricate relationship between the control of cellular gene expression and IFN-mediated cell death.

Influenza A (H3N2) infection followed by anti-signal recognition particle antibody-positive necrotizing myopathy: A case report

A 60-year-old Japanese woman presented with subacute progressive muscle pain and weakness in her proximal extremities. She was diagnosed with influenza A (H3N2) infection a week before the onset of muscle pain. At the time of admission, she exhibited weakness in the proximal muscles of the upper and lower limbs, elevated serum liver enzymes and creatinine kinase, and myoglobinuria. She did not manifest renal failure and cardiac abnormalities, indicating myocarditis. Electromyography revealed myogenic changes, and magnetic resonance imaging of the upper limb showed abnormal signal intensities in the muscles, suggestive of myopathy. Muscle biopsy of the biceps revealed numerous necrotic regeneration fibers and mild inflammatory cell infiltration, suggesting immune-mediated necrotizing myopathy (IMNM). Necrotized muscle cells were positive for human influenza A (H3N2). Autoantibody analysis showed the presence of antibodies against the signal recognition particle (SRP), and the patient was diagnosed with anti-SRP-associated IMNM. She was resistant to intravenous methylprednisolone pulse therapy but recovered after administration of oral systemic corticosteroids and immunoglobulins. We speculate that the influenza A (H3N2) infection might have triggered her IMNM. Thus, IMNM should be considered as a differential diagnosis in patients with proximal muscle weakness that persists after viral infections.

Refractory Myositis Affecting the Intrinsic Muscles of the Hand

Myositis generally affects the proximal muscles. However, we herein report a case of a 48-year-old woman with intractable myositis affecting the intrinsic muscles of the hands. Her myositis, which developed in childhood, was refractory to treatment with steroids and several immunosuppressants, causing walking disability. After experiencing pain and swelling in the hands for six months, she was diagnosed with myositis of the intrinsic muscles of the hands and tested positive for the anti-signal recognition particle antibody. Intravenous immunoglobulin therapy improved the myositis of the hands. This case suggests that inflammation caused by intractable myositis can extend to the hands.

Interleukin-33/suppression of tumorigenicity 2 (IL-33/ST2) axis in idiopathic inflammatory myopathies and its association with laboratory and clinical parameters: a pilot study

Idiopathic inflammatory myopathies (IIM) are rare connective tissue diseases, which can lead to internal organ involvement. IL-33/ST2 pathway is involved in the pathogenesis of numerous diseases including autoimmune disorders. IL-33 fulfils cardioprotective function, while soluble ST2 (sST2) is a decoy receptor that reduces protective impact of IL-33. The aim of the study was to evaluate the concentrations of sST2 and IL-33 in sera of patients with IIM and evaluate its associations with the clinical course of the disease. Patients with IIM as well as age- and sex-matched healthy controls were recruited. Concentrations of sST2 and IL-33 were assessed with ELISA in sera of both patients and controls. Patients were asked to fill in the questionnaires concerning clinical symptoms and physical functioning. Concentrations of sST2 and IL-33 were correlated with the results of laboratory tests and clinical symptoms. Concentrations of sST2 were significantly higher in IIM group than in healthy subjects (median sST2 in IIM 26.51 vs in healthy controls 21.39; p = 0.03). In the majority of patients, IL-33 concentrations did not exceed the detection limit. Anti-SRP-positive patients presented significantly higher concentrations of sST2 as compared to anti-SRP-negative patients (p = 0.04). In patients with anti-Ro52 antibodies, sST2 concentrations were significantly lower than in anti-Ro52-negative patients (p = 0.02). Concentrations of sST2 correlated with the degree of disability evaluated with Health Assessment Questionnaire. sST2 is increased in patients with IIM and its concentration correlates with the degree of disability. In patients with anti-SRP antibodies, levels of sST2 are exceptionally high.

Coexistence of anti-Jo1 and anti-signal recognition particle antibodies in a polymyositis patient

Idiopathic inflammatory myopathies are a heterogeneous group of potentially treatable myopathies. They are classified, on the basis of clinical and histopathological features, into four subtypes: dermatomyositis, polymyositis, necrotizing autoimmune myositis and inclusion-body myositis. Myositis-associated antibodies and myositis-specific autoantibodies are frequently found in patients with idiopathic inflammatory myopathies, and are useful in the diagnosis and classification. Anti-histidyl transfer RNA synthetase antibody is the most widely prevalent and is highly specific for polymyositis. Signal recognition particle antibody is also a specific autoantibody for polymyositis, but it is infrequent and rarely found in patients having other myositis-specific autoantibodies. We present a man with polymyositis who had both antibodies in serum, which is considered an extremely rare clinical situation. Here we analyze the clinical course and findings, and examine the effect of the coexistence and possible interaction on prognosis.

Anti-signal Recognition Particle Antibody-positive Necrotizing Myopathy with Secondary Cardiomyopathy: The First Myocardial Biopsy- and Multimodal Imaging-proven Case

A 69-year-old Japanese woman was admitted to our hospital with progressive muscle weakness and dysphagia. She was taking pitavastatin for dyslipidemia. Her serum creatine kinase was 6,300 U/L. Pitavastatin was stopped, but her symptoms deteriorated, and cardiac congestion appeared. A muscle biopsy showed necrotizing myopathy (NM), and anti-signal recognition particle (SRP) antibody was positive. ¹⁸F-fluorodeoxyglucose-positron emission tomography showed an abnormal uptake, and magnetic resonance imaging showed abnormal gadolinium enhancement in the left ventricular wall. An endomyocardial biopsy revealed inflammatory cardiomyopathy. Steroid, tacrolimus, and intravenous immunoglobulins were effective against the symptoms. This is the first case of biopsy-proven secondary cardiomyopathy due to anti-SRP-positive NM.

Potential Pathogenic Role of Anti-Signal Recognition Protein and Anti-3-hydroxy-3-methylglutaryl-CoA Reductase Antibodies in Immune-Mediated Necrotizing Myopathies

PURPOSE OF REVIEW

This review provides an overview of the potential pathogenic roles of anti-SRP and anti-HMGCR in IMNM over the past 5 years.

RECENT FINDINGS

Idiopathic inflammatory myopathies (IIM) are a group of acquired autoimmune disorders that mainly affect the skeletal muscle tissue. Classification criteria of IIM are comprised of polymyositis, dermatomyositis, inclusion body myositis and immune-mediated necrotizing myopathies. One important hallmark of autoimmune diseases is the detection of autoantibodies in patient sera. The anti-SRP (signal recognition particle) and anti-HMGCR (3-hydroxy-3-methylglutaryl coenzyme A reductase) antibodies are specifically associated with IMNM patients, and their detection has been described as related to disease severity. The muscles of IMNM patients are characterized by necrosis, atrophy and regenerating fibres with sparse inflammatory infiltrates. Although an important correlation between autoantibody titres, creatine kinase levels and disease progression/severity has been described in the last few years, the potential pathogenic roles of these autoantibodies have only recently been described.

Proposed cut-off for reactivity of anti-HMGCR and anti-SRP antibodies in patients statin-exposed and statin-unexposed

The therapeutic approach with statins is widely used in the control of dyslipidemias. However, there is no laboratory evaluation to elect patients to make use of this class of therapeutic drugs.We analyzed the prevalence of anti-signal recognition particle (anti-SRP) and anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (anti-HMGCR) antibodies in a heterogeneous cohort of 85 patients in order to determine cutoff reference values for these antibodies.Serum samples from 85 patients were screened for the presence of anti-HMGCR and anti-SRP autoantibodies by enzyme-linked immunosorbent assay. The demographic, clinical, and morphological features were also correlated with anti-HMGCR and anti-SRP antibodies. The patients were divided in 2 groups: A, statin-exposed, and B, statin-unexposed.There was no significant association (P > .05) among anti-HMGCR and anti-SRP titers in relation to age, sex, statin exposure, and CK level. The concentrations of both antibodies were not correlated with symptoms, CK level, or statin exposure. Eleven (12.9%) patients had anti-HMGCR antibodies. We found a tendency (P = .051) toward greater anti-HMGCR positivity in women with no symptoms. Twelve (14.1%) patients had anti-SRP antibodies. There was no sex predominance, and only 1 patient had muscle complaints. Muscular symptoms were present in 31 (36.5%) patients, 4 (12.9%) were positive for anti-HMGCR antibodies, and 1 (3.2%) was positive for anti-SRP antibodies. A total of 54 (63.5%) patients had no muscle symptoms, 7 (13%) were anti-HMGCR positive, and 11 (20.4%) were anti-SRP positive. We found statistical significance for patients with anti-SRP antibodies when asymptomatic and symptomatic patients were compared (P = .029). In contrast, there was no statistically significant difference between symptoms and positivity for anti-HMG antibodies.One of the main aims of this study was to define a cutoff point in a heterogeneous population with different diagnoses. We also demonstrated that anti-HMGCR and anti-SRP antibodies are not 100% specific to immune-mediated necrotizing myopathy. We believe that these antibodies must be tested and interpreted within the specific context.

Development of Necrotizing Myopathy Following Interstitial Lung Disease with Anti-signal Recognition Particle Antibody

A 72-year-old man was admitted due to dyspnea on exertion with interstitial shadows and elevated serum creatinine kinase (CK). Despite a close examination, which included magnetic resonance imaging (MRI), we could not diagnose myopathy. Prednisolone was administered and gradually tapered. One year later, anti-signal recognition particle (SRP) antibody was confirmed and he was re-admitted for hypoxemia with elevated CK. MRI revealed muscle edema and a histopathological examination of a muscle biopsy specimen showed necrotizing myopathy. Prednisolone, cyclosporine, and intravenous immunoglobulin were administered. Physicians should carefully monitor muscle symptoms and serum CK levels in cases of interstitial lung disease with anti-SRP antibodies.

Dermatomyositis Complicated by Digital Ischemia and Lung Adenocarcinoma in a Patient with Positive Anti-signal Recognition Particle Antibodies

A 58-year-old Japanese woman was diagnosed with anti-signal recognition particle (SRP)-positive dermatomyositis associated with Sjögren's syndrome, rheumatoid arthritis and lung adenocarcinoma. She presented with cutaneous lesions, including ulceration of her right middle finger. Tissue specimens obtained from her right deltoid muscle were positive for CD4⁺ T-cell infiltration and the sarcolemma showed the upregulation of major histocompatibility complex (MHC) class I antigens. The present case suggests that overlapping autoimmune diseases or complications of malignancy may result in an atypical clinical presentations and histological findings in patients with anti-SRP antibody-positive dermatomyositis.

[Screening of autoantibodies associated with necrotizing myopathy among undiagnosed chronic myopathy]

We screened anti-signal recognition particle (SRP) and anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) antibodies among 42 patients who had undiagnosed chronic myopathy from six national hospitals. Anti-SRP and anti-HMGCR antibodies were determined by RNA immuneprecipitation and enzyme-linked immune-sorbent assay (ELISA), respectively. We identified two patients with anti-SRP antibodies (4.7%) and, two with anti-HMGCR antibodies (4.7%). Both of anti-SRP-positive patients showed dysphagia with a high level of creatine kinase. Anti-HMGCR antibodies were associated with mild muscle weakness with a relatively late disease onset. Our study suggests the importance of autoantibody testing among undiagnosed chronic myopathy.

Necrotising myopathy associated with anti-signal recognition particle (anti-SRP) antibody

OBJECTIVES

Prompted by the few studies available in the literature, we analysed patients with necrotising myopathy associated with anti-signal recognition particle (anti-SRP).

METHODS

We conducted a retrospective, single-centre cohort study involving 14 patients with anti-SRP antibody followed between 2001 and 2016.

RESULTS

Patients had a mean age at disease onset of 40.7 years and were predominantly female and of white ethnicity. At disease onset, all patients had limb muscle weakness with median serum of creatine phosphokinase level of 8080U/L, 64.3% had constitutional symptoms, 50% dysphagia, 42.9% myalgia, 21.4% and 14.3% pulmonary and articular involvement, respectively. There were no cases of cutaneous, neurological or cardiac involvements. Notably, 21.4% of patients had previous exposure to statins. Moreover, with the exception of one patient, all received methylprednisolone pulse therapy and/or human intravenous immunoglobulin (IVIg), as well as prednisone and different immunosuppressive drugs or rituximab. Relapse occurred in 64.3% of the cases. However, most patients had significant recovery of muscle strength, with half no longer using glucocorticoids and the remainder on a weaning regimen with low dose prednisone.

CONCLUSIONS

Unlike the cases described in the literature, there was a high frequency of extra-muscular symptoms in the patients studied. Moreover, one fifth of patients had previous exposure to statin use. There was a high relapse rates, but with good clinical and laboratory recovery, especially with pulse therapy regimen of methylprednisolone and/or IVIg.

Paraneoplastic Anti-3-hydroxy-3-methylglutary-coenzyme A Reductase Antibody-positive Immune-mediated Necrotizing Myopathy in a Patient with Uterine Cancer

We report the case of a 69-year-old woman with proximal limb muscle weakness, who received post-operative chemotherapy for uterine cancer. Her serum creatinine kinase level was high (10,779 mg/dL) and a muscle biopsy from her left biceps revealed various sizes of muscle fibers accompanied by necrotic and regenerating fibers. She was positive for anti-3 hydroxy-3-methylglutary-coenzyme A reductase (anti-HMGCR) antibodies, but negative for anti-signal recognition particle (anti-SRP) antibodies. She was diagnosed with immune-mediated necrotizing myopathy (IMNM) and treated with prednisolone. Our findings indicate that not only drug-induced myopathy but also paraneoplastic myopathy can be involved in the pathogenesis of IMNM.

Chronic Myopathy Associated With Anti-Signal Recognition Particle Antibodies Can Be Misdiagnosed As Facioscapulohumeral Muscular Dystrophy

OBJECTIVES

To report cases of chronic autoimmune necrotizing myopathy with anti-signal recognition particle antibodies (anti-SRP myopathy) initially misdiagnosed as muscular dystrophy, in particular, facioscapulohumeral muscular dystrophy (FSHD).

METHODS

Medical records of patients with anti-SRP myopathy in our institution were retrospectively reviewed.

RESULTS

All 6 patients were initially diagnosed with muscular dystrophy because of the long-term clinical course and lack of inflammation on biopsy; 5 were diagnosed with FSHD based on a winged scapula. However, the following features suggested an alternative diagnosis, leading to anti-SRP antibody measurement: (1) lack of family history, (2) lack of facial involvement and asymmetry, (3) prominent dysphagia, and (4) profuse spontaneous activities on needle electromyography. All patients showed improvement with immunomodulating therapy.

CONCLUSIONS

Anti-SRP antibody measurement should be considered in patients diagnosed with FSHD if they present with diagnostic hallmarks of anti-SRP myopathy listed above, to avoid oversight of this potentially treatable disorder.

Juvenile dermatomyositis with anti-signal recognition particle antibodies: a case report

Serologic investigation has been explored in inflammatory myopathies in order to define subgroups that can help us predict clinical course, treatment and prognosis. The level of similarity between juvenile and adult myopathies regarding the presence of myositis-specific autoantibodies has not been fully elucidated. We report the case of a 8-year-old girl who presented with a rapid progression of muscle weakness and cutaneous signs consistent with the diagnosis of juvenile dermatomyositis and whose serologic testing revealed the presence of anti-signal recognition particle (SRP) antibodies. So far these antibodies have been described mostly in adult subsets, frequently associated with poorer outcomes and rarely related to cutaneous manifestations. The knowledge of the degree of overlap between paediatric and adult SRP positive myopathies may improve the medical care we provide to these children.

Anti-synthetase syndrome associated with anti PL-12 and anti-Signal recognition particle antibodies and a necrotizing auto-immune myositis

We report a 37-year-old woman with a 2 month history of proximal muscle weakness and extremely high creatine kinase (21,808 U/L) due to necrotizing auto-immune myositis (NAM) in association with anti-synthetase syndrome. Myositis-specific auto-immune antibody panel was positive for anti-Signal recognition particle and anti-PL-12. CT scan of the chest confirmed interstitial lung disease. Prednisolone, intravenous immunoglobulin and cyclophosphamide therapy was given with gradual improvement. This patient is notable for the unusual combination of NAM and anti-synthetase syndrome with the rare finding of two myositis-specific autoantibodies, which directed testing for associated extramuscular features and management with more aggressive immunotherapy.

[Anti-signal recognition particle autoantibody positive myopathy]

Idiopathic inflammatory myopathies are systemic, autoimmune diseases characterized by proximal symmetrical muscle weakness. We review the myositis-associated and myositis-specific autoantibodies, among them the anti-SRP autoantibody. Among those autoimmune myopathy cases, that are associated with autoantibodies, we can detect anti-SRP autoantibody positive myositis cases. We describe the role of signal recognition particle, its structure and role in protein biosynthesis. We review how necrotizing autoimmune myopathy is identified, and the differences from classical polymyositis. The anti-SRP titer correlates with disease activity. We present some cases to show how the disease appears in childhood and also some rare cases from the literature. Finally we present a case to draw attention to the importance of this disease.

Complement-mediated muscle cell lysis: a possible mechanism of myonecrosis in anti-SRP associated necrotizing myopathy (ASANM)

The mechanism of necrotizing myopathy associated with antibodies to signal recognition particle (SRP) remains unclear. We investigated the effect of anti-SRP+serum and complement on cell viability in myoblast cultures. Cell viability was only slightly reduced by incubation with anti-SRP+serum compared with control serum. However, the addition of fresh complement resulted in a marked reduction in cell survival. Surface immunostaining for SRP, C3c and C5b-9 was demonstrated in cultures pre-incubated with anti-SRP+serum and complement, and in muscle biopsies from patients with myopathy. These findings provide further support for a complement-dependent antibody-mediated mechanism in anti-SRP associated myopathy.

[Head drop syndrome in a patient with immune-mediated necrotizing myopathy with anti-signal recognition particle antibody: a case report]

We report an 87-year-old female patient who presented a dropped head and progressive weakness in proximal muscles over five months. The value of serum creatine kinase was 2,708 IU/l and the antibody against signal recognition particle (SRP) was detected by means of immunoprecipitation. The computed tomography of skeletal muscles revealed atrophy and fatty degeneration preferentially in the neck extensors and paraspinal muscles. The biopsied specimen of the deltoid muscle showed necrotic fibers scattered in fascicles with marked myophagia. The mononuclear cells in necrotic fibers were positive against CD68, leading to the diagnosis of immune-mediated necrotizing myopathy. We hypothesize that a group of patients with necrotizing myopathy can present a preferential involvement in neck extensors resulting in dropped head syndrome.

Characterization of dermatomyositis with coexistence of anti-Jo-1 and anti-SRP antibodies

We describe a patient with dermatomyositis who presented with rapidly developing severe muscle weakness complicated by massive pleural effusion with interstitial lung disease. Myopathological analysis was suggestive of dermatomyositis. This patient showed both anti-Jo-1 and anti-SRP antibodies in serum. To our knowledge, the coexistence of these two myositis-specific autoantibodies (MSA) is considered extremely rare and is clearly an exception to the rule of having only one MSA. Our findings provide compelling evidence that the coexistence of these two MSAs may lead to more severe clinical symptoms, interacting in a complex fashion, thus expanding the clinical spectrum of idiopathic inflammatory myopathy.

[Myositis-specific autoantibodies and their clinical significance]

The idiopathic inflammatory myopathies polymyositis (PM) and dermatomyositis (DM) have historically been defined using broad clinical and pathological criteria. These conditions affect both adults and children with clinical features including muscle weakness, skin disease, internal organ involvement, and an association with cancer in adults. Using a clinical-serological approach, PM and DM can be defined into more homogeneous subsets. In recent years, myositis-specific autoantibodies (MSAs) have been better characterized and include autoantibodies to the signal-recognition particle and aminoacyl tRNA-synthetase enzymes. In addition, clinically significant novel autoantibodies -anti-p155/p140, anti-CADM-140, and others- have been described in the disease spectrum. MSAs are directed against cytoplasmic or nuclear components involved in key regulatory intracellular processes including protein synthesis, translocation, and transcription. The striking association between unique serological profiles and distinct clinical phenotypes suggests that target autoantigens may play a role in disease induction and propagation. This review reports recent progress in myositis-specific autoantigens, particularly their clinical significance.

Anti-signal recognition particle myopathy in the first decade of life

Autoantibodies to signal recognition particle have been associated with juvenile and adult-onset necrotizing myopathy. However, only a few teenage patients with anti-signal recognition particle myopathy have been reported, and to date, to our knowledge, no patient younger than 10 years has been documented. We describe 2 Japanese girls with anti-signal recognition particle myopathy who developed symptoms from the ages of 5 and 9 years, respectively. Both patients had progressive muscle weakness and atrophy without myalgia. Facioscapulohumeral muscular dystrophy was initially suspected because of asymmetric shoulder girdle muscle involvement in one patient, and limb girdle muscular dystrophy due to proximal limb muscle weakness in the other. There were no extramuscular manifestations, including fever or arthritis. Serum creatine kinase levels were elevated to 2,467-4,629 IU/L. Results of muscle biopsy revealed necrotizing myopathy with minimal to mild endomysial fibrosis but without inflammatory infiltrates. Immunosuppressive agents were not effective for muscle weakness, resulting in marked disability. Anti-signal recognition particle myopathy can occur in the first decade of life and should be included in the differential diagnosis for children with progressive limb girdle muscle weakness and high creatine kinase levels.

[How can we diagnose and better understand inflammatory myopathies? The usefulness of auto-antibodies]

The inflammatory myopathies are a group of quite proteiform, systemic auto-immune diseases which include polymyositis, dermatomyositis and inclusion body myopathies. To facilitate the diagnosis, classification criteria (Bohan and Peter, 1975) have been proposed, based essentially on clinical criteria. In addition, over the past fifteen years, auto-antibodies characterizing certain forms of inflammatory myopathy have been identified. One distinguishes schematically: auto-antibodies specific for myositis and auto-antibodies sometimes associated with myositis. Concerning the myositis specific auto-antibodies (MSA), schematically there are a dozen specificities which are classed according to the cellular distribution of the auto-antigen. The most characteristic are certainly the auto-antibodies directed against cytoplasmic antigens: the anti-tRNA synthetases (anti-Jo-1 (PL-1), anti-PL-7, PL-12, EJ, OJ, JS, KS, ZO, YRS), anti-SRP (signal recognition particle), anti-Mas and anti-KJ, anti-Fer (eEF1), anti-Wa and anti-CADM p140. Other auto-antibodies are directed against nuclear auto-antigens: the anti-Mi-2, anti-PMS (PMS1, PMS2) and related antibodies (MLH1, DNA PKcs…), anti-56 kDa, anti-MJ (NXP-2), anti-SAE and anti-p155/p140 (TIF-1γ). Concerning the auto-antibodies sometimes associated with myositis (myositis associated auto-antibodies or MAA), they can also be observed in other auto-immune diseases. These auto-antibodies are directed against nuclear or nucleolar auto-antigens: the anti-PM-Scl, anti-Ku, anti-RNP (U1 RNP and U2 RNP, U4/U6 RNP and U5 RNP), anti-Ro 52 kDa and more rarely, anti-Ro 60 kDa and anti-La. The auto-antibodies related to myositis are biological tools which are of interest in two main ways. They have allowed us to sort out the nosology of these inflammatory myopathies, in particular by defining anti-tRNA synthetase syndrome. It now remains to determine how they might be employed to complement the classical clinico-biological diagnostic criteria. In this perspective, it will be indispensable first of all to diffuse and standardize the methods of detection. The latter are at the moment very heterogeneous as they use techniques and above all antigenic preparations which are extremely diverse. These antibodies are also very interesting "physiopathological" tools to try to better understand myositis. The example of anti-tRNA synthetases is a particularly original model of auto-immunization, which allows one to establish a link between an initial, probably poorly specific muscular lesion and the appearance of auto-antibodies which maintain and aggravate the muscular disease.

[A case of interstitial pneumonia with anti-signal recognition particle (SRP) antibody without myopathy]

Interstitial pneumonia in a 54-year-old woman was diagnosed in April 2007, without symptoms. She was admitted to our hospital in February 2009 because chest radiography showed gradual worsening. On physical examination, she had fine crackles on chest auscultation and "mechanic's hands", without arthritis, myopathy, or Reynaud disease. On laboratory tests, antinuclear antibody (speckled and cytoplasmic pattern) and anti SS-A antibody were positive. Chest CT showed ground-glass opacities in both lower lobes with volume loss and she had a restrictive disorder on a pulmonary function test. Bronchoalveolar lavage was within almost normal limits. For a definitive diagnosis, video associated thracoscopic surgery was performed. The histopathological findings showed a fibrotic nonspecific interstitial (f-NSIP) pattern. Corticosteroid therapy (prednisolone, initially 40 mg/day) was started, and the chest radiography improved. Later, an RNA immunoprecipitation test was positive for anti-signal recognition particle (SRP) antibody. This is a rare case of interstitial pneumonia with anti-SRP antibody without myopathy.

Autoantibody to signal recognition particle in African American girls with juvenile polymyositis

Anti-signal recognition particle (anti-SRP) is a myositis-specific autoantibody that is linked to a severe polymyositis (PM) associated with interstitial lung disease (ILD) and esophageal dysmotility in adults. We describe 3 African American adolescent girls with anti-SRP juvenile PM. One child required aggressive treatment to control her disease and 2 were refractory to multiple immunosuppressants. Patient 1 developed ILD and cardiac disease; Patient 2 developed ILD; Patient 3 developed esophageal dysmotility and cardiac disease. Organ system involvement was comparable to that seen in adults. We conclude that testing for anti-SRP in children with PM may facilitate diagnosis and management.

Myopathy associated with anti-signal recognition peptide antibodies: clinical heterogeneity contrasts with stereotyped histopathology

We report three patients with anti-signal recognition particle antibodies who had different presenting clinical pictures, mimicking acute polymyositis, limb-girdle muscular dystrophy, and acute rhabdomyolysis. Muscle biopsies typically showed necrotizing myopathy with little or no inflammation and deposits of membrane attack complex (C5b-9) in endomysial capillaries. The clinical course was severe in two patients and mild in one. The combination of corticosteroid with either an immunosuppressive agent or intravenous immunoglobulins was required to improve the condition of these patients.

A fast and efficient procedure to produce scFvs specific for large macromolecular complexes

We have expanded the application of antibody phage display to a new type of antigen: ribonucleoprotein (RNP) complexes. We describe a simple and efficient method for screening antibodies specific for large intact RNPs and individual components. We also describe a fast and easy method to overcome the abundance of amber stop codons in the positive phage clones. The resulting antibodies have been used in ELISA and Western blot analysis.

Anti-signal recognition particle autoantibodies: marker of a necrotising myopathy

OBJECTIVE

To elucidate the clinical importance of the anti-signal recognition particle (SRP) autoantibody in patients with myositis.

METHODS

Retrospective systematic assessment of the clinical, laboratory and histological characteristics of 23 anti-SRP-positive patients from six European centres. Data were compared with a large group of anti-SRP-negative patients with myositis published previously.

RESULTS

Clinically, patients with anti-SRP autoantibodies often had a severe symmetric proximal muscle weakness resulting in marked disability, dysphagia and highly elevated levels of serum creatine kinase. Three patients had typical dermatomyositis rashes. The disease was associated with the occurrence of extramuscular signs and symptoms including interstitial lung disease. No association was found with an increased risk of cardiac involvement, and the disease carried a reasonably favourable prognosis with most patients responding to treatment. None of the patients had the typical histological features of myositis. Most muscle biopsy specimens showed the presence of necrotic muscle fibres and no inflammatory infiltrates.

CONCLUSIONS

Anti-SRP autoantibodies are associated with a syndrome of a necrotising myopathy in the spectrum of immune-mediated myopathies that differs from typical polymyositis. Further studies are needed to elucidate the pathogenesis and to clarify the role of the anti-SRP autoantibodies in this unique disease.

Marked efficacy of a therapeutic strategy associating prednisone and plasma exchange followed by rituximab in two patients with refractory myopathy associated with antibodies to the signal recognition particle (SRP)

We report two patients with myopathy associated with anti-signal recognition particle Ab, refractory to conventional therapy, who were treated with prednisone and plasma exchange, followed by rituximab. A marked response was observed in both patients, with partial to complete recovery of muscle strength, which was sustained.

Human autoantibodies against the 54 kDa protein of the signal recognition particle block function at multiple stages

The 54 kDa subunit of the signal recognition particle (SRP54) binds to the signal sequences of nascent secretory and membrane proteins and it contributes to the targeting of these precursors to the membrane of the endoplasmic reticulum (ER). At the ER membrane, the binding of the signal recognition particle (SRP) to its receptor triggers the release of SRP54 from its bound signal sequence and the nascent polypeptide is transferred to the Sec61 translocon for insertion into, or translocation across, the ER membrane. In the current article, we have characterized the specificity of anti-SRP54 autoantibodies, which are highly characteristic of polymyositis patients, and investigated the effect of these autoantibodies on the SRP function in vitro. We found that the anti-SRP54 autoantibodies had a pronounced and specific inhibitory effect upon the translocation of the secretory protein preprolactin when analysed using a cell-free system. Our mapping studies showed that the anti-SRP54 autoantibodies bind to the amino-terminal SRP54 N-domain and to the central SRP54 G-domain, but do not bind to the carboxy-terminal M-domain that is known to bind ER signal sequences. Nevertheless, anti-SRP54 autoantibodies interfere with signal-sequence binding to SRP54, most probably by steric hindrance. When the effect of anti-SRP autoantibodies on protein targeting the ER membrane was further investigated, we found that the autoantibodies prevent the SRP receptor-mediated release of ER signal sequences from the SRP54 subunit. This observation supports a model where the binding of the homologous GTPase domains of SRP54 and the alpha-subunit of the SRP receptor to each other regulates the release of ER signal sequences from the SRP54 M-domain.

Autoantibodies specifically detected in patients with polymyositis/dermatomyositis

Polymyositis/Dermatomyositis (PM/DM) is a chronic inflammatory disorder that culminates in injury to the skin and muscle and, sometimes, is accompanied by interstitial lung disease (ILD). A number of autoantibodies are associated with myositis, including those specific for aminoacyl-tRNA synthetase (anti-ARS), signal recognition particle (anti-SRP), and Mi-2. These autoantibodies have proven to be useful in the diagnosis and classification of the diseases and are predictive of prognosis. It has been known that certain patients may have typical DM skin manifestations without clinical evidence of myositis for at least 2 years (Clinically Amyopathic DM; C-ADM). Although classical myositis-related antibodies are well known, specificities related to C-ADM have not been examined in detail. Therefore, we have examined sera from 15 Japanese patients with C-ADM to identify additional autoantibodies associated with this disease. Eight sera of C-ADM patient recognized a polypeptide of approximately 140 kDa and we named this new antibody specificity anti-CADM-140. Anti-CADM-140 antibodies were detected in 8 of 42 patients with DM, but not in patients with other connective tissue diseases or idiopathic pulmonary fibrosis. It is noteworthy that DM patients with anti-CADM-140 had significantly more rapidly progressive ILD when compared to patients without anti-CADM-140 (50% vs 6%, P=0.008). Further studies of the pathogenicity of these autoantibodies specificity may provide insight into the pathogenic mechanisms of PM/DM accompanied by rapidly progressive ILD.

Novel autoantibodies against 7SL RNA in patients with polymyositis/dermatomyositis

OBJECTIVE

Autoantibodies against signal recognition particle (SRP) are detected in patients with polymyositis/dermatomyositis (PM/DM). The SRP consists of 7SL RNA and 6 protein components. We examined autoantibodies against deproteinized 7SL RNA in PM/DM patients with anti-SRP antibodies and evaluated the association of anti-7SL RNA antibodies with PM/DM clinically and serologically.

METHODS

Sera from 10 Japanese and 22 North American PM/DM patients with anti-SRP antibodies were tested for the presence of anti-7SL RNA antibodies, using the sera to immunoprecipitate deproteinized RNA extracts derived from HeLa cells.

RESULTS

The immunoprecipitation analysis indicated that 5 Japanese (50%) and one North American (5%) patient with anti-SRP antibodies had novel autoantibodies against deproteinized 7SL RNA. The frequency of anti-7SL RNA antibodies was significantly higher in Japanese than North American patients (p = 0.006). The presence of anti-7SL RNA antibodies appeared to be associated with DM (2 patients) and finger swelling (2 PM patients). The seasonal onset of the disease was different (p = 0.008) for Japanese PM/DM patients with anti-7SL RNA antibodies, who developed the disease between October and January (mean month November; p = 0.01) from that of patients without these antibodies, who developed it between June and August (mean month July; p = 0.01).

CONCLUSION

Novel autoantibodies against 7SL RNA were identified in patients with PM/DM, and the presence of these antibodies was correlated to ethnic background, clinical features, and season of disease onset. These findings indicated that autoantibodies against 7SL RNA are a novel serological marker for a subset of PM/DM cases.

Novel classification of idiopathic inflammatory myopathies based on overlap syndrome features and autoantibodies: analysis of 100 French Canadian patients

Our objective was to improve the currently imperfect classifications of idiopathic inflammatory myopathies (IIM). In clinical practice, overlap features are common in IIM. This provided a rationale for positioning overlap clinical features at the core of a new classification system. We conducted a longitudinal study of 100 consecutive adult French Canadian patients with IIM. Clinical and laboratory data were obtained by retrospective chart review. Sera were analyzed for autoantibodies (aAbs) by protein A-assisted immunoprecipitation and double immunodiffusion. Overlap aAbs encompassed aAbs to synthetases, systemic sclerosis-associated aAbs, anti-signal recognition particle (SRP) and anti-nucleoporins. Patients were classified both at IIM diagnosis, based on data at presentation, and at the end of follow-up, based on cumulative findings. Three classifications were used: 1) the Bohan and Peter original classification, 2) a new version of that classification as modified by us, and 3) a novel clinicoserologic classification. As investigators were blinded to aAb results, the modified classification is strictly a clinical classification. Its core concept is the attribution of diagnostic significance to the presence of overlap features, that is, their presence resulted in a diagnosis of overlap myositis (OM). This approach allowed direct comparison with the original Bohan and Peter classification. By integrating aAb results to the modified classification, we also defined the clinicoserologic classification, which allowed to examine the added value of aAbs to diagnostic, therapeutic and prognostic stratification. Whereas polymyositis (PM) was the most common IIM according to the original classification, accounting for 45% of the cohort at diagnosis, its frequency fell to 14% with the modified classification. Conversely, while the frequency of myositis associated with connective tissue disease was 24% according to the original classification, the frequency of OM was 60% when using the modified classification. At last follow-up, the frequency of PM fell further to only 9%, while the frequency of OM rose to 67%. Systemic sclerosis was the most common connective tissue disease associated with IIM, accounting for 42.6% of OM patients and 29% of the cohort. The frequencies of overlap aAbs in the cohort and in OM patients were 48% and 70.5% (n =48/68), respectively. The presence of overlap aAbs at IIM diagnosis identified additional OM patients unrecognized by the modified classification. The sensitivity of the modified classification for OM at diagnosis was 87%, suggesting that clinicians may rely on the modified classification for identification of most OM patients, while awaiting results of aAb assays. The new classifications predicted the response to prednisone and IIM course. Using stringent definitions, IIM was classified as responsive or refractory after an adequate initial corticosteroid therapy, and the disease course as monophasic or chronic after a single adequate trial of prednisone. PM was always chronic and was associated with the highest rate (50%) of refractoriness to initial corticosteroid treatment. Dermatomyositis was almost always chronic (92% rate); however, its responsiveness to initial corticosteroid treatment was high (87%). OM was almost always responsive to corticosteroids (89%-100% rates). When OM patients were divided according to aAb subsets, anti-synthetase, SRP, or nucleoporin aAbs were markers for chronic myositis, whereas aAbs to U1RNP, Pm-Scl, or Ku were markers for monophasic myositis. We conclude that the original Bohan and Peter classification should be abandoned as it leads to misclassification of patients. Much of IIM is composed of OM. The proposed modified and clinicoserologic classifications have diagnostic, prognostic, and therapeutic value.

Seasonal influence on the onset of idiopathic inflammatory myopathies in serologically defined groups

OBJECTIVE

To assess possible seasonal patterns in the onset of polymyositis (PM) and dermatomyositis (DM).

METHODS

The study group comprised 503 patients who met the criteria for probable or definite PM or DM and for whom detailed data on the time of myositis onset were available. Statistical analyses were performed using a Poisson model that assessed associations of ethnicity, sex, autoantibody presence, and month of onset of muscle weakness.

RESULTS

There were no significant seasonal patterns of disease onset in myositis patients as a whole or in the total PM or DM populations. Significant seasonal associations were present, however, in the serologically defined groups. In the 131 patients with antisynthetase autoantibodies who were categorized as non-black, myositis onset peaked in March-April (P = 0.03). Among the antisynthetase-positive patients, the association was predominantly in those with PM (n = 85; P = 0.05) and in men (n = 51; P = 0.042). Patients with anti-signal recognition particle autoantibodies, however, did not have a significant seasonal onset, which is in contrast to previous findings. Patients without myositis-specific autoantibodies showed a significant peak in summer, with myositis onset in June-July (n = 252; P = 0.03); this seasonal association was significant in women (n = 182; P = 0.005), whereas there was no seasonal pattern in men (P = 0.9).

CONCLUSION

These findings, in conjunction with other data, suggest that diverse environmental agents, acting upon different immunogenetic backgrounds, result in distinct immune responses and clinical syndromes in the idiopathic inflammatory myopathies. Our results emphasize the importance of considering more homogeneous disease groups, based on clinicopathologic features, immune responses, ethnicity, and sex, when attempting to decipher the pathogeneses of autoimmune disorders.

Anti-signal recognition particle autoantibody in patients with and patients without idiopathic inflammatory myopathy

OBJECTIVE

To determine the long-term outcome and associated clinical, serologic, and pathologic features in a cohort of patients with connective tissue disease (CTD) and the anti-signal recognition particle (anti-SRP) autoantibody.

METHODS

Sera and clinical data were collected prospectively from consecutive adult patients with polymyositis (PM; n = 134), dermatomyositis (n = 129), or other CTDs (predominantly systemic sclerosis [SSc; n = 790]). Patients were first evaluated during 1973-2001.

RESULTS

Nineteen patients with the anti-SRP autoantibody were identified, 16 (84%) of whom had pure PM and 3 (2 with SSc and 1 with antisynthetase syndrome) had yet to develop features of myositis after a mean followup of 4.5 years (range 2.5-6 years). More SRP-positive PM patients had severe proximal muscle weakness (50%) and muscle atrophy (67%) at initial presentation compared with antisynthetase-positive PM controls. Cardiac involvement occurred in only 2 of 16 SRP-positive PM patients (13%), and interstitial lung disease was noted in 3 of 13 SRP-positive PM patients (23%) and in the 3 SRP-positive nonmyositis patients. There was a relative lack of inflammation in muscle biopsy specimens from the SRP-positive PM cohort. Other autoantibodies in the SRP-positive patients included Ro/SSA (4 patients), Th/To (1 patient), and anti-PL-12 (1 patient). Survival in the SRP-positive PM patients was comparable with that seen in the cohort of SRP-negative PM patients.

CONCLUSION

The anti-SRP autoantibody is not specific for PM. Severe muscle weakness and atrophy were prominent features in PM patients with anti-SRP. Cardiac involvement was less common and survival was better in patients with anti-SRP than has previously been reported.

Myopathy with antibodies to the signal recognition particle: clinical and pathological features

OBJECTIVES

To study myopathies with serum antibodies to the signal recognition particle (SRP), an unusual, myositis specific antibody associated syndrome that has not been well characterised pathologically.

METHODS

Clinical, laboratory, and myopathological features were evaluated in seven consecutive patients with a myopathy and serum anti-SRP antibodies, identified over three years. The anti-SRP myopathy was compared with myopathology in other types of inflammatory and immune myopathies.

RESULTS

The patients with anti-SRP antibodies developed weakness at ages ranging from 32 to 70 years. Onset was seasonal (August to January). Weakness became severe and disability developed rapidly over a period of months. Muscle pain and fatigue were present in some patients. No patient had a dermatomyositis-like rash. Serum creatine kinase was very high (3000 to 25 000 IU/l). Muscle biopsies showed an active myopathy, including muscle fibre necrosis and regeneration. There was prominent endomysial fibrosis, but little or no inflammation. Endomysial capillaries were enlarged, reduced in number, and associated with deposits of the terminal components of complement (C5b-9, membrane attack complex). Strength improved in several patients after corticosteroid treatment.

CONCLUSIONS

Myopathies associated with anti-SRP antibodies may produce severe and rapidly progressive weakness and disability. Muscle biopsies show active myopathy with pathological changes in endomysial capillaries but little inflammation. Corticosteroid treatment early in the course of the illness is often followed by improvement in strength. In patients with rapidly progressive myopathies and a high serum creatine kinase but little inflammation on muscle biopsy, measurement of anti-SRP antibodies and pathological examination of muscle, including evaluation of endomysial capillaries, may provide useful information on diagnosis and treatment.

Myositis-specific autoantibodies: overview and recent developments

Myositis-specific autoantibodies (MSAs) are found in almost half the patients with an idiopathic inflammatory myopathy (IIM). Several clinical and epidemiological studies have suggested that MSAs are associated with specific clinical characteristics. Some of these associations are well-defined and are of clinical significance ( eg, anti-Jo-1 and the anti-synthetase syndrome), others are less well established and can cause unnecessary anxiety for both patients and physicians ( eg, anti-SRP and cardiac involvement). In this review, an overview is given of the various MSAs, their biochemical background, their clinical usefulness, and the promises they hold for a better understanding of IIM.

Heterodimer SRP9/14 is an integral part of the neural BC200 RNP in primate brain

BC200 RNA is a brain-specific, small non-messenger RNA with a somatodendritic localization in primate neurons and a constituent of a ribonucleoprotein (RNP) complex. The primary and secondary structure of the 5' domain of BC200 RNA resembles that of the Alu domain of 7SL RNA, which is an integral part of the signal recognition particle (SRP). This would predict that similar proteins bind to this defined domain of both RNA species in vitro and in vivo. The data presented in this paper reveal that a protein that binds BC200 RNA in vivo is immunoreactive with antibodies against SRP9. This further supports the notion that the 5' domain of the BC200 RNA can fold into structures similar to the SRP Alu domain and, as a result, bind identical or similar proteins in vivo. The SRP9 protein binds only as dimer with SRP14 protein to the Alu domain of 7SL RNA to form a subdomain that, in SRP, is functional in translation arrest. Therefore, our data also indicate that the neuronal BC200 RNP is a candidate for regulating decentralized protein biosynthesis in dendrites, possibly with a mechanism that resembles translation arrest of the SRP.

Identification of a region required for binding to presecretory protein in Bacillus subtilis Ffh, a homologue of the 54-kDa subunit of mammalian signal recognition particle

Bacillus subtilis Ffh protein is a homologue of the 54-kDa subunit of mammalian signal recognition particle (SRP54). It contains three highly hydrophobic regions (h1, h2, and h3) in the C-terminal methionine-rich domain (M-domain). Two of the hydrophobic regions, h2 and h3, are essential for small cytoplasmic RNA (scRNA) binding [Kurita, K., Honda, K., Suzuma, S., Takamatsu, H., Nakamura, K., & Yamane, K. (1996) J. Biol. Chem. 271, 13,140-13,146]. Using purified presecretory proteins and mutant Ffh proteins, we identified a region required for presecretory protein binding in B. subtilis Ffh. Deletion of this region, which consisted of residues Ser311-Gly362 of B. subtilis Ffh, including a hydrophobic sequence (h1), reduced precursor binding activity. In contrast, deletions of residues Leu121-Lys279, Lys364-Met446, or Leu338-Ser397 of B. subtilis Ffh did not. We also analyzed the mutant B. subtilis Ffh proteins, FfhQQQR and FfhQQQQ having wild-type residues 398-401 (Arg-Arg-Lys-Arg) replaced with Gln3Arg and Gln4, respectively. FfhQQQR bound to both scRNA and presecretory protein. Although the FfhQQQQ mutation prevented binding to scRNA, binding to the precursor was not affected. FfhQQQR restored the growth of B. subtilis DF46 strain in which ffh gene expression is regulated by an inducible promoter in the absence of an inducer, whereas FfhQQQQ did not. These results indicate that the region including h1 is required for B. subtilis Ffh to bind to presecretory protein. The results also suggest that scRNA is required for the complete function of the B. subtilis SRP-like particle in vivo, although this protein is intrinsically capable of binding a signal peptide free from scRNA.

Structures targeted by the immune system in myositis

Polymyositis and dermatomyositis are characterized by the production of a series of autoantibodies to various cellular constituents. Some of these autoantibodies are found specifically in patients with polymyositis or dermatomyositis or myositis overlap syndrome and predict clinical subgroups and prognosis. If we are to understand the etiology and pathogenic mechanisms of polymyositis and dermatomyositis, it will be particularly important to elucidate the structure and function of target autoantigens recognized by these myositis-specific autoantibodies. In recent years, many autoantigens and some epitopes have been identified using molecular biology approaches. During the 1-year period reviewed here, the nature and function of the Mi-2 and the Ku(p70/p80) antigens which are recognized by autoantibodies in patients with dermatomyositis and with the myositis overlap syndrome, respectively, have been elucidated. Several new autoantibodies that are not specific for but that are associated with myositis have also been described.