The reliability of immunoassays to detect autoantibodies in patients with myositis is dependent on autoantibody specificity

273rd ENMC International workshop: Clinico-Sero-morphological classification of the Antisynthetase syndrome. Amsterdam, The Netherlands, 27-29 October 2023

Among the idiopathic inflammatory myopathies, patients harbouring an Antisynthetase syndrome exhibit a unique clinical picture, with characteristic signs such as myositis, interstitial lung disease, arthritis, rash, and/or fever. Characteristic morphological features on skeletal muscle biopsies differentiate Antisynthetase syndrome from other forms of myositis. Autoantibodies typically recognizing one of the members of the aminoacyl-tRNA synthetase family of proteins can be detected in the serum of such patients, with anti-Jo1 being most frequent. Until now, an international consensus definition of the Antisynthetase syndrome is lacking, hence this workshop has undertaken the task to inform about the clinical, morphological and autoantibody profiles of Antisynthetase syndrome. The authors also expand their aims by giving management and therapeutic strategies, and finally provide precise classification criteria for Antisynthetase syndrome.

Patient experiences of muscle biopsy in idiopathic inflammatory myopathies: a cross-sectional survey

INTRODUCTION

Muscle biopsy plays an important role in the diagnostic evaluation of individuals with suspected idiopathic inflammatory myopathies (IIM). However, variability in biopsy practices may result in a heterogenous patient experience. The existing literature offers limited insights into the experiences and perspectives of patients undergoing muscle biopsy.

METHODS

This study employed a 27-item online survey to comprehensively characterise the experience of muscle biopsy among Australian patients, including their concerns, beliefs about procedure utility, information sources, physical sensations, perceived complications and recovery.

RESULTS

A total of 111 Australian individuals who reported a diagnosis of IIM completed the survey, with data collected from March to June 2023. Most participants had inclusion body myositis (76/111, 68.5%) and had undergone one biopsy procedure (87/111, 78.4%) as part of their IIM work-up. Nine of the 111 respondents did not undergo a muscle biopsy. The procedure was well-tolerated by many respondents, however, a notable number of respondents experienced post-procedural pain lasting > 72 h (27/102, 26.5%), increasing weakness post-biopsy (13.7%), numbness at the biopsy site (18/102, 17.6%) and a recovery time beyond 3 days (36/102, 35.3%). A substantial minority (30/111, 27%) felt they were inadequately informed about the risks and benefits of the procedure.

CONCLUSIONS

This survey highlights that although muscle biopsy is often well-tolerated, there are considerable patient concerns that are often inadequately addressed. Our findings underscore the need for improved patient-doctor communication and support throughout the biopsy process.

Comparison of Lineblot and Immunoprecipitation Methods in the Detection of Myositis-Specific and Myositis-Associated Antibodies in Patients with Idiopathic Inflammatory Myopathies: Consistency with Clinical Diagnoses

Background: the reference method for detection of myositis-specific and myositis-associated antibodies (MSAs and MAAs) is considered immunoprecipitation (IP), but it is routinely replaced by semi-automated methods, like lineblot (LB). Few data are available on the consistency with clinical diagnoses; thus, we aim at analysing these aspects. Methods: sixty-nine patients with idiopathic inflammatory myopathies (IIM) were studied via LB (Myositis Antigens Profile 3 EUROLINE, Euroimmun) and IP (RNA and protein antigens). The degree of concordance between methods was calculated using Cohen's coefficient. Results: a substantial concordance was found for anti-Ku and anti-PM/Scl and a moderate concordance was found for anti-Jo1 and anti-Mi-2, while a fair concordance was found for anti-EJ, anti-SRP, and anti-Ro52 antibodies. The concordance could not be calculated for anti-OJ, anti-PL-7, anti-PL-12, anti-NXP2, anti-TIF1ɣ, and anti-MDA5, because they were only detected with one method. Multiple MSAs were found only with LB in 2/69 sera. Anti-MDA5, TIF1ɣ, NXP2 (detected via IP), and anti-Jo1 in anti-synthetase syndrome (both LB and IP) had the best concordance with clinical diagnosis. Conclusions: LB and IP show substantial concordance for PM/Scl and Ku, and moderate concordance for Jo1 and Mi-2, with a good concordance with clinical diagnoses. IP shows a high performance for DM-associated MSAs. LB seems to be more sensitive in detecting anti-Ro52 antibodies, but it identified multiple MSAs, unlike IP.

Myositis -specific and -associated antibodies in neurological disorders - A retrospective study of 727 patients

OBJECTIVE

Myositis-specific antibodies (MSAs) and myositis-associated antibodies (MAAs) are assessed in clinical neurology, serving as a non-invasive tool for the differential diagnosis of autoimmune myopathies. However, the presence of MSAs and MAAs in neurological disorders remains uncertain.

METHODS

Retrospective analysis was conducted on 878 serum samples from the neurological laboratory of the University Hospital Tübingen, Germany. The EUROLINE Myositis Profil 3 (IgG) Line Blot was used for antibody evaluation (anti-Mi2, -Ku, -PM-Scl100, -PM-Scl75, -Jo1, -SRP, -PL7, -PL12, -EJ, -OJ, and -Ro52). Samples were categorized into 19 disease groups, with consideration for myositis-linked and non-myositis-linked diseases. Then, the distribution of positive findings and the concurrent presence of more than one MAA/MSA were analyzed.

RESULTS

Among 727 included line blots, 84 could be assigned to myositis-linked diseases (thereof 44 positive for MAA/MSA). MAA and MSA taken together were more frequently positive for the main group of myositis-linked disease (52.4 %) compared to the non-myositis-linked group (14.6 %, overall specificity 85.4 %). However, individual antibodies were specific, ranging above 97.5 %. False positive antibody results can also occur in neurological differential diagnoses such as muscle dystrophy or cramp fasciculation syndrome. Furthermore, the concurrent presence of more than one MAA/MSA does not show a significant association with the presence of a myositis-linked disease for antibody-positive samples (p = 0.136).

DISCUSSION

Testing MSA and MAA simultaneously may not be suitable as a primary screening method for myositis-linked diseases in clinical neurological groups. However, MSAs and MAAs may offer valuable diagnostic support, particularly in cases where myositis is strongly considered.

Anti-aminoacyl tRNA synthetase antibodies showing the discrepancy between enzyme-linked immunosorbent assay and RNA-immunoprecipitation

Anti-aminoacyl-tRNA synthetase (ARS) antibodies are myositis-specific antibodies associated with anti-synthetase syndrome (ASSD). Some patients are positive for anti-ARS antibodies on enzyme-linked immunosorbent assay (ELISA) but negative on RNA-immunoprecipitation (RNA-IP) (the gold standard method). Whether these patients should be considered truly positive for anti-ARS antibodies remains unclear. Therefore, we investigated the clinical characteristics of these patients and verified the authenticity of their anti-ARS positivity. Patients who were positive for anti-ARS antibodies on ELISA were divided into the non-discrepant (positive on RNA-IP, n = 52) and discrepant (negative on RNA-IP, n = 8) groups. Patient clinical characteristics were compared between the groups. For each positive individual, the authenticity of anti-ARS antibody positivity on ELISA was cross-examined using protein-IP and western blotting. All patients in the discrepant group had lung involvement, including five (63%) with interstitial lung disease. The overall survival time was significantly lower in the discrepant group than in the non-discrepant group (p < 0.05). Validation tests confirmed the presence of anti-ARS antibodies in the sera of the discrepant group but indicated different reactivity from typical anti-ARS antibodies. In conclusion, some anti-ARS antibodies are detected by ELISA but not RNA-IP. Such anti-ARS antibody discrepancies need further elucidation to attain validation of the diagnostic process in ASSD.

Assessing the sensitivity and specificity of myositis-specific and associated autoantibodies: a sub-study from the MyoCite cohort

OBJECTIVES

Myositis-specific and associated autoantibodies are important biomarkers in routine clinical use. We assessed local testing performance for myositis autoantibodies by comparing line immunoassay (LIA) to protein radio-immunoprecipitation and identifying clinical characteristics associated with each myositis autoantibody in the MyoCite cohort.

METHODS

Serum samples from patients within the MyoCite cohort, a well-characterized retro-prospective dataset of adult and juvenile idiopathic inflammatory myopathy (IIM) patients in Lucknow, India (2017-2020), underwent LIA at Sanjay Gandhi Postgraduate Institute of Medical Science (SGPGIMS), Lucknow. Immunoprecipitation of 147 IIM patients' serum samples (125 adult-onset, 22 juvenile-onset) was conducted at the University of Bath, with researchers blind to LIA results. LIA performance was assessed against immunoprecipitation as the reference standard, measuring sensitivity, specificity and inter-rater agreement. Univariate and multivariate logistic regression determined clinical associations for specific myositis-specific autoantibodies.

RESULTS

Immunoprecipitation identified myositis autoantibodies in 56.5% (n = 83) of patient samples, with anti-Jo1 (n = 16; 10.9%) as the most common, followed by anti-MDA5 (n = 14, 9.5%). While LIA showed good agreement for anti-Jo1, anti-PL7 and anti-PL12 (Cohen's κ 0.79, 0.83 and 1, respectively), poor agreement was observed in other subgroups, notably anti-TIF1γ (Cohen's κ 0.21). Strongly positive samples, especially in myositis-specific autoantibodies, correlated more with immunoprecipitation results. Overall, 59 (40.1%) samples exhibited non-congruence on LIA and immunoprecipitation, and κ values for LIAs for anti-TIF1γ, anti-Ku, anti-PmScl, anti-Mi2 and anti-SAE ranged between 0.21 and 0.60.

CONCLUSION

While LIA reliably detected anti-Jo1, anti-PL7, anti-PL12, anti-MDA5 and anti-NXP-2, it also displayed false positives and negatives. Its effectiveness in detecting other autoantibodies, such as anti-TIF1γ, was poor.

Autoantibody testing in myositis: an update

PURPOSE OF REVIEW

This review aims to provide an update on myositis autoantibody testing strategies. We have focussed on the reliability and usefulness of different myositis autoantibody detection methods, including commonly used solid phase immunoassays and newer discovery techniques.

RECENT FINDINGS

Several studies have highlighted the limitations of currently available immunoassays, particularly when used in populations with low pretest probability and without supporting clinical evidence. While many autoantibodies, such as anti-Jo1, are detected with high sensitivity and specificity, the low incidence of myositis autoantibodies in tested populations reduces their positive predictive value. The low sensitivity of line immunoassays to detect key myositis autoantibodies, including anti-TIF1γ and rarer antisynthetase autoantibodies, is a concern.

SUMMARY

Myositis autoantibodies are widely accepted as important clinical tools, and hence, there is a significant demand for reliable, accessible, and affordable detection methods. False positives and negative results have the potential to impact on patient care, particularly for malignancy and lung disease associated autoantibodies. Increased availability of myositis autoantibody testing has led to a rise in requests from a broader range of clinicians. It is critically important that clinicians are aware of specific limitations of tests and interpret results in the context of clinical findings.

Anti-Ku + myositis: an acquired inflammatory protein-aggregate myopathy

Myositis with anti-Ku-autoantibodies is a rare inflammatory myopathy associated with various connective tissue diseases. Histopathological studies have identified inflammatory and necrotizing aspects, but a precise morphological analysis and pathomechanistic disease model are lacking. We therefore aimed to carry out an in-depth morpho-molecular analysis to uncover possible pathomechanisms. Muscle biopsy specimens from 26 patients with anti-Ku-antibodies and unequivocal myositis were analyzed by immunohistochemistry, immunofluorescence, transcriptomics, and proteomics and compared to biopsy specimens of non-disease controls, immune-mediated necrotizing myopathy (IMNM), and inclusion body myositis (IBM). Clinical findings and laboratory parameters were evaluated retrospectively and correlated with morphological and molecular features. Patients were mainly female (92%) with a median age of 56.5 years. Isolated myositis and overlap with systemic sclerosis were reported in 31%, respectively. Isolated myositis presented with higher creatine kinase levels and cardiac involvement (83%), whereas systemic sclerosis-overlap patients often had interstitial lung disease (57%). Histopathology showed a wide spectrum from mild to pronounced myositis with diffuse sarcolemmal MHC-class I (100%) and -II (69%) immunoreactivity, myofiber necrosis (88%), endomysial inflammation (85%), thickened capillaries (84%), and vacuoles (60%). Conspicuous sarcoplasmic protein aggregates were p62, BAG3, myotilin, or immunoproteasomal beta5i-positive. Proteomic and transcriptomic analysis identified prominent up-regulation of autophagy, proteasome, and hnRNP-related cell stress. To conclude, Ku + myositis is morphologically characterized by myofiber necrosis, MHC-class I and II positivity, variable endomysial inflammation, and distinct protein aggregation varying from IBM and IMNM, and it can be placed in the spectrum of scleromyositis and overlap myositis. It features characteristic sarcoplasmic protein aggregation on an acquired basis being functionally associated with altered chaperone, proteasome, and autophagy function indicating that Ku + myositis exhibit aspects of an acquired inflammatory protein-aggregate myopathy.

Severe finger necrosis in antisynthetase syndrome with positive anti-OJ antibodies

Key Clinical Message

In a patient with anti-aminoacyl tRNA synthetase antibody and anti-OJ antibody syndrome, interventions likes warming, prostaglandins, and antiplatelets failed. However, prednisolone pulse treatment rapidly halted disease progression. Patients with mild interstitial pneumonia, myositis, and extremity necrosis should be promptly considered for anti-synthetase syndrome and receive immunosuppression after ruling out other causes.

Abstract

Anti-aminoacyl tRNA synthetase (ARS) autoantibodies are myositis-specific, and patients who test positive for ARS and have common clinical features are usually diagnosed with antisynthetase antibody syndrome (antisynthetase syndrome). Anti-ARS antibodies include histidyl-tRNA synthetase-1 (Jo-1), anti-threonyl (PL-7), anti-alanyl (PL-12), anti-glycyl (EJ), anti-asparaginyl (KS), anti-tyrosyl (Ha), and anti-phenylalanyl (Zo) tRNA synthetases. Among these, anti-isoleucyl tRNA synthetase (OJ) autoantibodies are extremely rare, and patients with these are frequently complicated by interstitial pneumonia. We report the case of an older man with ARS antibody syndrome who tested positive for anti-OJ and anti-Sjögren's-syndrome-related antigen A (Ro-52) antibodies. He had muscle weakness due to myositis and unparalleled rapid and severe finger necrosis. Pulsed prednisolone effectively treated the myositis symptoms and terminated the progression of finger necrosis.

Updates on efficacy and safety janus kinase inhibitors in juvenile dermatomyositis

INTRODUCTION

Juvenile dermatomyositis (JDM) is a rare autoimmune disease most commonly with proximal weakness due to inflammation and characteristic skin rashes. Most patients have a chronic or polycyclic disease course on standard therapy so better treatments are needed. An interferon signature is well-established in key tissues of JDM. Janus kinase inhibitors (jakinibs), which can decrease IFN signaling, are therefore appealing as a targeted therapy.

AREAS COVERED

Herein is a review of the growing literature on JDM patients in jakinibs, including specifics of their jakinib exposure, summary of efficacy, disease features, and characteristics of patients treated, and safety parameters.

EXPERT OPINION

The vast majority of refractory JDM patients respond to jakinib therapy, though they have varied features, doses, and previous/concurrent medications, and data is largely retrospective. Jakinibs are an exciting and promising treatment in JDM. Evaluation with larger prospective controlled studies is needed to answer remaining questions about jakinibs in JDM regarding dosing, which JDM patients to treat with jakinibs, potential biomarkers to use, and how best to monitor safety risks in JDM.

The central helicase domain holds the major conformational epitopes of melanoma differentiation-associated gene 5 autoantibodies

OBJECTIVE

Autoantibodies against MDA5 (melanoma differentiation-associated protein 5) serve as a biomarker for DM (dermatomyositis) and indicate a risk factor for interstitial lung disease (ILD). MDA5 is a protein responsible for sensing RNA virus infection and activating signalling pathways against it. However, little is known about the antigen epitopes on MDA5 autoantibodies. We aimed to determine the interaction of the MDA5 autoantibody-antigen epitope.

METHODS

Cell-based assays (CBAs), immunoprecipitation-immunoblot assays, and various immunoblotting techniques were used in the study.

RESULTS

We demonstrated that DM patient autoantibodies recognize MDA5 epitopes in a native conformation-dependent manner. Furthermore, we identified the central helicase domain （3Hel） formed by Hel1, Hel2i, Hel2, and pincer as the major epitopes. As proof of principle, the purified 3Hel efficiently absorbed MDA5 autoantibodies from patient sera through immunoprecipitation-immunoblot assay.

CONCLUSION

Our study uncovered the nature of the antigen epitopes on MDA5 and can provide guidance for diagnosis and a targeted therapeutic approach development.

The Utility of Laboratory Investigations for the Assessment and Management of Rheumatic Immune Related Adverse Events

Immune checkpoint inhibitors (ICIs) have greatly improved survival of several cancers with historically very poor prognosis. ICIs act by stimulating the patient's own immune system to fight cancer. Simultaneously, this immune activation can lead to immune-related adverse events (irAEs), including rheumatic manifestations (Rh-irAEs). Rh-irAEs mimic primary rheumatic diseases including arthritis, polymyalgia rheumatica, myositis, vasculitis, sarcoidosis, and sicca. This article summarizes the latest evidence regarding the utility of laboratory investigations in Rh-irAEs.

Identification of connective tissue disease autoantibodies and a novel autoantibody anti-annexin A11 in patients with "idiopathic" interstitial lung disease

BACKGROUND

Autoantibodies are a hallmark feature of Connective Tissue Diseases (CTD). Their presence in patients with idiopathic interstitial lung disease (ILD) may suggest covert CTD. We aimed to determine the prevalence of CTD autoantibodies in patients diagnosed with idiopathic ILD.

METHODS

499 patient sera were analysed: 251 idiopathic pulmonary fibrosis (IPF), 206 idiopathic non-specific interstitial pneumonia (iNSIP) and 42 cryptogenic organising pneumonia (COP). Autoantibody status was determined by immunoprecipitation.

RESULTS

2.4% of IPF sera had a CTD-autoantibody compared to 10.2% of iNSIP and 7.3% of COP. 45% of autoantibodies were anti-synthetases. A novel autoantibody targeting an unknown 56 kDa protein was found in seven IPF patients (2.8%) and two NSIP (1%) patients. This was characterised as anti-annexin A11.

CONCLUSION

Specific guidance on autoantibody testing and interpretation in patients with ILD could improve diagnostic accuracy. Further work is required to determine the clinical significance of anti-annexin A11.

Autoantibody evaluation in idiopathic inflammatory myopathies

Idiopathic inflammatory myopathies (IIM), generally referred to as myositis is a heterogeneous group of diseases characterized by muscle inflammation and/or skin involvement, diverse extramuscular manifestations with variable risk for malignancy and response to treatment. Contemporary clinico-serologic categorization identifies 5 main clinical groups which can be further stratified based on age, specific clinical manifestations and/or risk for cancer. The serological biomarkers for this classification are generally known as myositis-specific (MSAs) and myositis-associated antibodies. Based on the use of these antibodies, IIM patients are classified into anti-synthetase syndrome, dermatomyositis, immune-mediated necrotizing myopathy, inclusion body myositis, and overlap myositis. The current classification criteria for IIM requires clinical findings, laboratory measurements, and histological findings of the muscles. However, the use MSAs and myositis-associated autoantibodies as an adjunct for disease evaluation is thought to provide a cost-effective personalized approach that may not only guide diagnosis but aid in stratification and/or prognosis of patients. This review provides a comprehensive overview of contemporary autoantibodies that are specific or associated myositis. In addition, it highlights possible pathways for the detection and interpretation of these antibodies with limitations for routine clinical use.

Diagnosis and subtyping of idiopathic inflammatory myopathies: caution required in the use of myositis autoantibodies

Detection of myositis autoantibodies (MAs) has utility in both the diagnosis and subtyping of idiopathic inflammatory myopathies (IIMs). Multiplex assays such as the Euroimmun line immunoassay (LIA) have significant limitations in rare diseases like IIM. A retrospective cohort study was performed on positive MA detected on LIA in 171 patients using the manufacturer's recommended cut-off. Only 16.7% were deemed true positive after clinical correlation. Autoantibody-specific cut-offs were created and applied to the original cohort, along with generically applied higher cut-offs. Positive predictive value (PPV) improved, but there was variable increase in false negatives. False positive MA results are common using LIA, but locally derived cut-offs can improve performance. Clinicians must be aware of the limitations of LIA, which is the commonest method for MA detection in Australasia.

Dermatomyositis: Practical Guidance and Unmet Needs

Dermatomyositis is a heterogeneous idiopathic inflammatory myopathy associated with various cutaneous manifestations and variable presence of myositis, interstitial lung disease, and other visceral organ involvement. An accurate diagnosis of dermatomyositis requires correlating clinical examination findings with serological and histological findings. Familiarity with pathognomonic and common cutaneous manifestations of dermatomyositis, which are highlighted here, can be especially helpful in making an accurate diagnosis. Additionally, evaluating patients for presence of myositis-specific autoantibodies can further support or refute a dermatomyositis diagnosis. When present, myositis-specific autoantibodies can also help guide workups for various dermatomyositis-associated manifestations, as each is associated with relatively distinct clinical characteristics. Evaluating patients for various systemic manifestations often relies on expert opinion recommendations; however, societal guideline statements concerning the evaluation of some manifestations have recently been described. Although malignancy-associated dermatomyositis is a well-accepted subtype, there is limited evidence to support extensive malignancy screening has a favorable benefit-risk ratio in most dermatomyositis patients. However, recent research has uncovered novel associations between dermatomyositis and malignancy, suggesting the possibility of identifying high-risk subsets of dermatomyositis patients in whom malignancy screening may have a high value. Treatment for dermatomyositis has remained largely unchanged over the past several decades. Although many dermatomyositis patients can be effectively treated with current options, either as monotherapy or with combination regimens, there is a need for more targeted and effective DM therapies, in general, and for MDA5(+) dermatomyositis-associated rapidly progressive interstitial lung disease. Fortunately, significant current and emerging research activities evaluating various novel medications for dermatomyositis provide hope for exciting future advances in patients with this intriguing immune-mediated disease.

Analytic and Clinical Validity of Myositis-Specific Antibodies by Line-Blot Immunoassay Is Essential

OBJECTIVES

This study assessed the concordance between line blot (LB) and immunoprecipitation (IP) assays for detecting myositis-specific antibodies (MSAs) in idiopathic inflammatory myopathies (IIMs) and their association with IIM subtypes.

METHODS

One hundred patients with IIM were enrolled, and MSA was detected using LB and IP. The IIM subtypes, including immune-mediated necrotizing myopathy-like, anti-tRNA synthetase syndrome-like, and clinically amyopathic dermatomyositis-like, were clinically diagnosed. The validity and reliability of the LB compared with the IP were evaluated. Optimal cutoff levels for LB were determined using various statistical methods including Cohen κ, Gwet's AC, diagnostic odds ratios, and receiver operating characteristic analysis.

RESULTS

Line blot exhibited lower specificity and accuracy than IP in predicting IIM subtypes. Some MSAs performed better at higher LB cutoff values. Anti-signal recognition particle antibodies showed poor performance in predicting the immune-mediated necrotizing myopathy-like subtype using LB. Raising the cutoffs improved the reliability of anti-threonyl-tRNA synthetase and anti-signal recognition particle antibodies. Anti-histidyl-tRNA synthetase antibodies performed well at lower positivity, whereas diagnostic odds ratios increased for anti-transcription intermediary factor 1γ and anti-nuclear matrix protein 2 with higher cutoffs.

CONCLUSIONS

Inconsistencies between LB and IP have been observed in patients with IIM. Individual optimal cutoffs for MSA by LB correlating with IP were determined. Rheumatologists should consider the differences between LB and IP results when classifying IIM subtypes.

IFN-γ: An overlooked cytokine in dermatomyositis with anti-MDA5 antibodies

Dermatomyositis with anti-melanoma differentiation-associated gene 5 antibody (anti-MDA5 DM) is a rare autoimmune disease, often complicated by life-threatening, rapidly progressive interstitial lung disease. Additional manifestations of the disease include skin lesions, vascular abnormalities, joints and muscles pain. Despite its clinical significance, the pathogenesis of anti-MDA5 DM remains largely unknown. Currently, the disease is perceived as driven by type I interferon (IFN) whose expression is increased in most of the patients. Importantly, the regulation of IFN-γ is also altered in anti-MDA5 DM as evidenced by the presence of IFN-γ positive histiocytes in the lungs of patients, and the identification of autoantibodies that directly stimulate the production of IFN-γ by mononuclear cells. This review critically examines the pathogenesis of the disease, shedding light on recent findings that emphasize a potential role of IFN-γ. A novel conceptual framework is proposed, which integrates the molecular mechanisms altering IFN-γ regulation in anti-MDA5 DM with the known functional effects of IFN-γ on key tissues affected during the disease, such as the lungs, skin, and vessels. Understanding the precise role and relevance of IFN-γ in the pathogenesis of the disease will not only enhance the selection of available therapies for anti-MDA5 DM patients but also pave the way for the development of new therapeutic approaches targeting the altered molecular pathways.

Distinct HLA associations with autoantibody-defined subgroups in idiopathic inflammatory myopathies

BACKGROUND

In patients with idiopathic inflammatory myopathies (IIM), autoantibodies are associated with specific clinical phenotypes suggesting a pathogenic role of adaptive immunity. We explored if autoantibody profiles are associated with specific HLA genetic variants and clinical manifestations in IIM.

METHODS

We included 1348 IIM patients and determined the occurrence of 14 myositis-specific or -associated autoantibodies. We used unsupervised cluster analysis to identify autoantibody-defined subgroups and logistic regression to estimate associations with clinical manifestations, HLA-DRB1, HLA-DQA1, HLA-DQB1 alleles, and amino acids imputed from genetic information of HLA class II and I molecules.

FINDINGS

We identified eight subgroups with the following dominant autoantibodies: anti-Ro52, -U1RNP, -PM/Scl, -Mi2, -Jo1, -Jo1/Ro52, -TIF1γ or negative for all analysed autoantibodies. Associations with HLA-DRB1∗11, HLA-DRB1∗15, HLA-DQA1∗03, and HLA-DQB1∗03 were present in the anti-U1RNP-dominated subgroup. HLA-DRB1∗03, HLA-DQA1∗05, and HLA-DQB1∗02 alleles were overrepresented in the anti-PM/Scl and anti-Jo1/Ro52-dominated subgroups. HLA-DRB1∗16, HLA-DRB1∗07 alleles were most frequent in anti-Mi2 and HLA-DRB1∗01 and HLA-DRB1∗07 alleles in the anti-TIF1γ subgroup. The HLA-DRB1∗13, HLA-DQA1∗01 and HLA-DQB1∗06 alleles were overrepresented in the negative subgroup. Significant signals from variations in class I molecules were detected in the subgroups dominated by anti-Mi2, anti-Jo1/Ro52, anti-TIF1γ, and the negative subgroup.

INTERPRETATION

Distinct HLA class II and I associations were observed for almost all autoantibody-defined subgroups. The associations support autoantibody profiles use for classifying IIM which would likely reflect underlying pathogenic mechanisms better than classifications based on clinical symptoms and/or histopathological features.

FUNDING

See a detailed list of funding bodies in the Acknowledgements section at the end of the manuscript.

The Autoantibody Array Assay: A Novel Autoantibody Detection Method

Systemic sclerosis (SSc) and dermatomyositis (DM) are autoimmune collagen diseases. Specific autoantibodies are known to be involved in their pathogeneses, each presenting with a different clinical manifestation. Although immunoprecipitation is the gold standard method for detecting autoantibodies, it is difficult to perform in all cases owing to the use of radioisotopes. In this study, we developed a new detection method for SSc and DM autoantibodies (A-cube) using cell-free protein synthesis and examined its validity. Proteins were synthesized using wheat germ cell-free protein synthesis. A total of 100 cases of SSc, 50 cases of DM, and 82 healthy controls were examined. The validity of the method was examined by a comparison with existing test results. Anti-centromere antibody, anti-topoisomerase I antibody, anti-RNA polymerase III antibody, anti-U1RNP anti-body, anti-Jo-1 antibody, anti-TIF1γ antibody, anti-Mi-2 antibody, and anti-ARS antibody were tested for. The results suggested that A-cube is comparable with existing testing methods or has a high sensitivity or specificity. In addition, there was a case in which the diagnosis was reconsidered using the A-cube. The quality of the A-cube was ensured, and its usefulness for a comprehensive analysis was demonstrated. The A-cube can therefore contribute to the clinical assessment and treatment of SSc and DM.

Clinical and Radiological Features of Korean Patients With Anti-HMGCR Myopathy

BACKGROUND AND PURPOSE

To understand the characteristics of Korean patients with anti-3-hydroxy-3-methylglutaryl-coenxyme A reductase (HMGCR) myopathy, we measured anti-HMGCR antibodies and analyzed the clinical, radiological, and pathological features of patients with anti-HMGCR myopathy.

METHODS

We measured titers of anti-HMGCR antibodies in the sera of 99 patients with inflammatory myopathy, 36 patients with genetic myopathy, and 63 healthy subjects using an enzyme-linked immunosorbent assay. We tested 16 myositis-specific autoantibodies (MSAs) in all patients with anti-HMGCR myopathy.

RESULTS

Positivity for the anti-HMGCR antibody was observed in 17 (4 males and 13 females) of 99 patients with inflammatory myopathy. The median age at symptom onset was 60 years. Ten (59%) of the patients with anti-HMGCR positivity had taken statins. The titer of anti-HMGCR antibodies was significantly higher in the statin-naïve group (median=230 U/mL, interquartile range=170-443 U/mL) than in the statin-exposed group (median=178 U/mL, interquartile range=105-210 U/mL, p=0.045). The most common symptom was proximal muscle weakness in 15 patients (88%), followed by myalgia in 9 (53%), neck weakness in 4 (24%), dysphagia in 3 (18%), and skin lesions in 2 (12%). The median titer of anti-HMGCR antibody was 202 U/mL. We found eight different MSAs in nine (53%) patients. The median disease duration from symptom onset to diagnosis was significantly shorter in the MSA-positive group than in the MSA-negative group (p=0.027).

CONCLUSIONS

Our study was the first to measure anti-HMGCR antibodies in inflammatory myopathy. It has provided new findings, including the suggestion of the coexistence of other MSAs in Korean patients.

Urine proteomics by mass spectrometry identifies proteins involved in key pathogenic pathways in patients with juvenile dermatomyositis

OBJECTIVES

To identify and validate biomarkers in JDM patients using a multiplexing tandem mass tag urine proteome profiling approach.

METHODS

First morning void urine samples were collected from JDM patients (n = 20) and healthy control subjects (n = 21) and processed for analysis using a standardized liquid chromatography-tandem mass spectrometry approach. Biomarkers with significantly altered levels were correlated with clinical measures of myositis disease activity and damage. A subset of candidate biomarkers was validated using commercially available ELISA kits.

RESULTS

In total, 2348 proteins were detected in the samples, with 275 proteins quantified across all samples. Among the differentially altered proteins, cathepsin D and galectin-3 binding protein were significantly increased in the urine of JDM patients (adjusted P < 0.05), supporting previous findings in myositis patients. These two candidate biomarkers were confirmed with ELISAs. Cathepsin D positively correlated with Myositis Damage Index (r = 0.57, P < 0.05) and negatively correlated with the Childhood Myositis Assessment Scale (r = -0.54, P < 0.05). We also identified novel JDM candidate biomarkers involved with key features of myositis, including extracellular matrix remodelling proteins.

CONCLUSION

This study confirmed the presence of several proteins in the urine of JDM patients that were previously found to be elevated in the blood of myositis patients and identified novel candidate biomarkers that require validation. These results support the use of urine as a source for biomarker development in JDM.

Comprehensive autoantibody profiling in systemic autoimmunity by a highly-sensitive multiplex protein array

Comprehensive autoantibody evaluation is essential for the management of autoimmune disorders. However, conventional methods suffer from poor sensitivity, low throughput, or limited availability. Here, using a proteome-wide human cDNA library, we developed a novel multiplex protein assay (autoantibody array assay; A-Cube) covering 65 antigens of 43 autoantibodies that are associated with systemic sclerosis (SSc) and polymyositis/dermatomyositis (PM/DM). The performance of A-Cube was validated against immunoprecipitation and established enzyme-linked immunosorbent assay. Further, through an evaluation of serum samples from 357 SSc and 172 PM/DM patients, A-Cube meticulously illustrated a diverse autoantibody landscape in these diseases. The wide coverage and high sensitivity of A-Cube also allowed the overlap and correlation analysis between multiple autoantibodies. Lastly, reviewing the cases with distinct autoantibody profiles by A-Cube underscored the importance of thorough autoantibody detection. Together, these data highlighted the utility of A-Cube as well as the clinical relevance of autoantibody profiles in SSc and PM/DM.

Lateral flow immunoassay for rapid and sensitive detection of dsRNA contaminants in in vitro-transcribed mRNA products

High purity is essential in mRNA-based therapeutic applications. A major contaminant of in vitro-transcribed (IVT) mRNA manufacturing is double-stranded RNA (dsRNA), which can induce severe anti-viral immune responses. Detection methods, such as agarose gel electrophoresis, ELISA, and dot-blot assay, are used to detect the existence of dsRNA in IVT mRNA products. However, these methods are either not sensitive enough or time-consuming. To overcome these challenges, we develop a rapid, sensitive, and easy-to-implement colloidal gold nanoparticle-based lateral flow strip assay (LFSA) with sandwich format for the detection of dsRNA from IVT process. dsRNA contaminant can be determined visually on the test strip or quantitatively with a portable optical detector. This method allows for a 15 min detection of N1-methyl-pseudouridine (m1Ψ)-containing dsRNA with a detection limit of 69.32 ng/mL. Furthermore, we establish the correlation between the LFSA test results and the immune response caused by dsRNA in mice. The LFSA platform allows the rapid, sensitive, and quantitative monitoring of purity in massive IVT mRNA products and aids for the prevention of immunogenicity by dsRNA impurities.

Juvenile idiopathic inflammatory myositis: an update on pathophysiology and clinical care

The childhood-onset or juvenile idiopathic inflammatory myopathies (JIIMs) are a heterogenous group of rare and serious autoimmune diseases of children and young people that predominantly affect the muscles and skin but can also involve other organs, including the lungs, gut, joints, heart and central nervous system. Different myositis-specific autoantibodies have been identified that are associated with different muscle biopsy features, as well as with different clinical characteristics, prognoses and treatment responses. Thus, myositis-specific autoantibodies can be used to subset JIIMs into sub-phenotypes; some of these sub-phenotypes parallel disease seen in adults, whereas others are distinct from adult-onset idiopathic inflammatory myopathies. Although treatments and management have much improved over the past decade, evidence is still lacking for many of the current treatments and few validated prognostic biomarkers are available with which to predict response to treatment, comorbidities (such as calcinosis) or outcome. Emerging data on the pathogenesis of the JIIMs are leading to proposals for new trials and tools for monitoring disease.

Subsets of Idiopathic Inflammatory Myositis Enriched for Contemporaneous Cancer Relative to the General Population

OBJECTIVE

This study investigates cancer risk in idiopathic inflammatory myopathy (IIM) relative to the general population.

METHODS

We conducted a single-center, retrospective cohort study of IIM patients and malignancy. Myositis-specific and -associated autoantibodies were determined by Euroimmun line blot, enzyme-linked immunosorbent assay, and immunoprecipitation. We calculated standardized prevalence ratios (SPRs) and adjusted for calendar year, age, sex, race, and ethnicity by comparing observed cancers in IIM patients versus expected cancers in the general population using the Surveillance, Epidemiology, and End Results registry.

RESULTS

Of 1,172 IIM patients, 203 (17%) patients with a cancer history were studied. Over a median follow-up of 5.2 years, the observed number of IIM patients diagnosed with cancer was increased 1.43-fold (SPR 1.43 [95% confidence interval (95% CI) 1.15-1.77]; P = 0.002). Within 3 years of IIM symptom onset, an increased SPR was observed for anti-transcription intermediary factor 1γ (anti-TIF1γ)-positive patients for ovarian and breast cancer (ovarian SPR 18.39 [95% CI 5.01-47.08], P < 0.001; breast SPR 3.84 [95% CI 1.99-6.71], P < 0.001). As expected, anti-TIF1γ positivity was associated with a significantly elevated SPR; however, only 55% (36 of 66) of all cancers within 3 years of dermatomyositis onset were observed in anti-TIF1γ-positive patients. Other myositis-specific autoantibodies, including anti-Mi-2, anti-small ubiquitin-like modifier activating enzyme (SAE), and anti-nuclear matrix protein 2 (NXP-2), accounted for 26% (17 of 66) of cancers diagnosed within 3 years of dermatomyositis onset. No cancer association, positive or negative, was observed for patients with antisynthetase, anti-melanoma differentiation-associated protein 5 (anti-MDA-5), or anti-hydroxymethylglutaryl-coenzyme A reductase (anti-HMGCR) antibodies.

CONCLUSION

In a tertiary referral center population, anti-TIF1γ was most strongly associated with breast and ovarian cancer. Patients with antisynthetase, anti-MDA-5, or anti-HMGCR antibodies had the same cancer risk as the general population.

Muscle pathology of antisynthetase syndrome according to antibody subtypes

Identification of antisynthetase syndrome (ASS) could be challenging due to inaccessibility and technical difficulty of the serology test for the less common non-Jo-1 antibodies. This study aimed to describe ASS antibody-specific myopathology and evaluate the diagnostic utility of myofiber HLA-DR expression. We reviewed 212 ASS muscle biopsies and compared myopathologic features among subtypes. Additionally, we compared their HLA-DR staining pattern with 602 non-ASS myositis and 140 genetically confirmed myopathies known to have an inflammatory component. We used t-test and Fisher's exact for comparisons and used sensitivity, specificity, positive and negative predictive values to assess the utility of HLA-DR expression for ASS diagnosis. RNAseq performed from a subset of myositis cases and histologically normal muscle biopsies was used to evaluate interferon (IFN)-signaling pathway-related genes. Anti-OJ ASS showed prominent myopathology with higher scores in muscle fiber (4.6 ± 2.0 vs. 2.8 ± 1.8, p = 0.001) and inflammatory domains (6.8 ± 3.2 vs. 4.5 ± 2.9, p  = 0.006) than non-OJ ASS. HLA-DR expression and IFN-γ-related genes upregulation were prominent in ASS and inclusion body myositis (IBM). When dermatomyositis and IBM were excluded, HLA-DR expression was 95.4% specific and 61.2% sensitive for ASS with a positive predictive value of 85.9% and a negative predictive value of 84.2%; perifascicular HLA-DR pattern is common in anti-Jo-1 ASS than non-Jo-1 ASS (63.1% vs. 5.1%, p < 0.0001). In the appropriate clinicopathological context, myofiber HLA-DR expression help support ASS diagnosis. The presence of HLA-DR expression suggests involvement of IFN-γ in the pathogenesis of ASS, though the detailed mechanisms have yet to be elucidated.

Overlap syndrome with antibodies against multiple transfer-RNA components presenting antisynthetase syndrome

Overlap syndrome is a clinical entity of myositis concomitant with one or more collagen diseases such as systemic lupus erythematosus, systemic sclerosis, and/or rheumatoid arthritis. It is not evident whether the myopathology of overlap syndrome is disease-specific or categorizes one of the four major subsets: inclusion body myositis, immune-mediated necrotizing myopathy, dermatomyositis, and antisynthetase syndrome. We report a patient with overlap syndrome who exhibited autoantibodies against multiple transfer-RNA components by RNA immunoprecipitation, suggesting antisynthetase syndrome. A 64-year-old woman developed systemic lupus erythematosus, systemic sclerosis, and myositis. Muscle biopsy showed perifascicular necrosis and perimysial alkaline phosphatase positivity, suggesting antisynthetase syndrome. Enzyme-linked immunosorbent assay was negative for autoantibodies to aminoacyl transfer-RNA synthetase, whereas RNA immunoprecipitation revealed a novel antibody to multiple transfer-RNA components. Although the myopathology of overlap syndrome may be diagnosed as any one of various subsets, this case suggests that the myopathological features of overlap syndrome may include antisynthetase syndrome.

Performance of cut-offs adjusted with positive control band intensity in line-blot assays for myositis-specific antibodies

The diagnostic performance of band intensity (BI) cut-offs, adjusted by a positive control band (PCB) in a line-blot assay (LBA) for myositis-related autoantibodies (MRAs) is investigated. Sera from 153 idiopathic inflammatory myositis (IIM) patients with available immunoprecipitation assay (IPA) data and 79 healthy controls were tested using the EUROLINE panel. Strips were evaluated for BI using the EUROLineScan software, and the coefficient of variation (CV) was calculated. Sensitivity and specificity, area under the curve (AUC), and the Youden's index (YI) were estimated at non-adjusted or PCB-adjusted cut-off values. Kappa statistics were calculated for IPA and LBA. Although inter-assay CV for PCB BI was 3.9%, CV was 12.9% in all samples, and a significant correlation was found between BIs of PCB and seven MRAs (all P < 0.05). At adjusted BI (aBI) > 10, the negative conversion rate of myositis-specific autoantibody (MSA)-positivity at BI > 10 was 11.5% in controls and 1.3% in patients. The specificity, AUC, and YI for MSAs at aBI > 10 or > 20 were higher than those at non-adjusted cut-off values. Additionally, AUC (0.720), YI (0.440), and the prevalence of MRAs with kappa > 0.60 (58.3%) were the highest at aBI > 20. The overall sensitivity and specificity for MSAs were 50.3% and 93.7% at aBI > 20, respectively, and 59.5% and 65.8% with BI > 10, respectively. The diagnostic performance of LBA can be improved using PCB-adjusted BIs. aBI > 20 is the optimal cut-off for IIM diagnosis using the EUROLINE LBA panel.

Myositis autoantibodies detected by line blot immunoassay: clinical associations and correlation with antibody signal intensity

The aim of this study is to assess the relationship between myositis specific (MSA) and myositis associated (MAA) antibodies and diagnosis (including idiopathic inflammatory myopathies [IIM] and other systemic autoimmune diseases [SAID]), and to explore the impact of antibody signal intensity in diagnostic accuracy. We retrospectively reviewed all the serum samples obtained from patients tested for MSA/MAA by line immunoassay (LIA) between 01/01/2018 and 31/12/2020 in Ramón y Cajal University Hospital (Spain). Clinical true positive (CTP) MSAs and MAAs were defined as those patients with IIM or SAID with phenotypes expected of that MSA/MAA. Patients who did not have a phenotype compatible with that antibody were classified as clinical false positive (CFP). One hundred and thirty positive samples were analysed. Forty-six patients (33.38%) were classified as IIM, forty-two (32.3%) as SAID and forty-two (32.3%) as non-IIM/SAID. Among these 130 patients, 164 MSA/MAA were detected. Eighty-five (51.8%) positive MSA/MAA were classified as CTP, and seventy-nine (48.2%) as CFP. Strongly positive antibodies were more frequently CTP (35/47, 74.5%) than weak positives (54/68, 36.8%), (p ˂ 0.001). Antibodies classified as CTP had a higher signal intensity than CFP (36.77 AU vs 20.00 AU, CI95% 7.79-22.09, p ˂ 0.001). The probability of a CFP was associated to negative ANA, low ANA titer, and multiple positive MSA/MAA (p ˂ 0.001). In this study, we confirmed that CFP results using LIA are frequent, and are associated with low signal intensity MSA/MAA, negative ANA, lower titer ANA, and with multiple positive samples.

Deciphering the Autoantibody Response to the OJ Antigenic Complex

(1) Background: Myositis specific antibodies (MSA) are important diagnostic biomarkers. Among the rarest and most challenging MSA are anti-OJ antibodies which are associated with anti-synthetase syndrome (ASS). In contrast to the other tRNA synthetases that are targets of ASS autoantibodies (e.g Jo-1, PL-7, PL-12, EJ, KS, Zo), OJ represents a macromolecular complex with several ribonucleoprotein subunits. Therefore, the choice of the antigen in autoantibody assays can be challenging. (2) Methods: We collected two independent cohorts with anti-OJ antibodies, one based on a commercial line immunoassay (LIA) (n = 39), the second based on protein immunoprecipitation (IP) (n = 15). Samples were tested using a particle-based multi-analyte technology (PMAT) system that allows for the simultaneous detection of antibodies to various autoantigens. For the detection of anti-OJ antibodies, two different antigens were deployed (KARS, IARS) on PMAT. The reactivity to the two antigens KARS and IARS was analyzed individually and combined in a score (sum of the median fluorescence intensities). (3) Results: In the cohort selection based on LIA, 3/39 (7.7%) samples were positive for anti-KARS and 7/39 (17.9%) for anti-IARS and 14/39 (35.9%) when the two antigens were combined. In contrast, in samples selected by IP the sensitivity of anti-KARS was higher: 6/15 (40.0%) samples were positive for anti-KARS, 4/15 (26.7%) for anti-IARS and 12/15 (80.0%) for the combination of the two antigens. 18/39 (46.2%) of the LIA samples generated a cytoplasmic IIF pattern (compatible with anti-synthetase antibodies), but there was no association with the antibody levels, neither with LIA nor with PMAT. (4) Conclusions: The combination of IARS and KARS might represent a promising approach for the detection of anti-OJ antibodies on a fully automated platform.

Autoantigenic properties of the aminoacyl tRNA synthetase family in idiopathic inflammatory myopathies

OBJECTIVES

Autoantibodies are thought to play a key role in the pathogenesis of idiopathic inflammatory myopathies (IIM). However, up to 40% of IIM patients, even those with clinical manifestations of anti-synthetase syndrome (ASSD), test seronegative to known myositis-specific autoantibodies. We hypothesized the existence of new potential autoantigens among human cytoplasmic aminoacyl tRNA synthetases (aaRS) in patients with IIM.

METHODS

Plasma samples from 217 patients with IIM according to 2017 EULAR/ACR criteria, including 50 patients with ASSD, 165 without, and two with unknown ASSD status were identified retrospectively, as well as age and gender-matched sera from 156 population controls, and 219 disease controls. Patients with previously documented ASSD had to test positive for at least one of the five most common anti-aaRS autoantibodies (anti-Jo1, -PL7, -PL12, -EJ, and -OJ) and present with one or more of the following clinical manifestations: interstitial lung disease, myositis, arthritis, Raynaud's phenomenon, fever, or mechanic's hands. Demographics, laboratory, and clinical data of the IIM cohort (ASSD and non-ASSD) were compared. Samples were screened using a multiplex bead array assay for presence of autoantibodies against a panel of 117 recombinant protein variants, representing 33 myositis-related proteins, including all nineteen cytoplasmic aaRS. Prospectively collected clinical data for the IIM cohort were retrieved and compared between groups within the IIM cohort and correlated with the results of the autoantibody screening. Principal component analysis was used to analyze clinical manifestations between ASSD, non-ASSD groups, and individuals with novel anti-aaRS autoantibodies.

RESULTS

We identified reactivity towards 16 aaRS in 72 of the 217 IIM patients. Twelve patients displayed reactivity against nine novel aaRS. The novel autoantibody specificities were detected in four previously seronegative patients for myositis-specific autoantibodies and eight with previously detected myositis-specific autoantibodies. IIM individuals with novel anti-aaRS autoantibodies (n = 12) all had signs of myositis, and they had either muscle weakness and/or muscle enzyme elevation, 2/12 had mechanic's hands, 3/12 had interstitial lung disease, and 2/12 had arthritis. The individuals with novel anti-aaRS and a pathological muscle biopsy all presented widespread up-regulation of major histocompatibility complex class I. The reactivities against novel aaRS could be confirmed in ELISA and western blot. Using the multiplex bead array assay, we could confirm previously known reactivities to four of the most common aaRS (Jo1, PL12, PL7, and EJ (n = 45)) and identified patients positive for anti-Zo, -KS, and -HA (n = 10) that were not previously tested. A low frequency of anti-aaRS autoantibodies was also detected in controls.

CONCLUSION

Our results suggest that most, if not all, cytoplasmic aaRS may become autoantigenic. Autoantibodies against new aaRS may be found in plasma of patients previously classified as seronegative with potential high clinical relevance.

Evaluation of the Performance of an Indirect Immunofluorescence Assay for the Detection of Anti-MDA5 Antibodies

Anti-melanoma differentiation-associated protein 5 (MDA5) antibody (Ab) positive dermatomyositis (anti-MDA5 DM) is a rare systemic autoimmune disease; further, its prognosis can be rapidly fatal due to pulmonary involvement. The identification and quantification of anti-MDA5 Abs, which serve as a highly specific biomarker of the disease, is a critical step for the establishing of both the diagnosis and monitoring of the disease's activity. The development of a simple, fast, low-cost, and specific detection system of anti-MDA5 Ab is therefore highly desirable for the purposes of routine laboratory diagnosis. Here, we developed a human cell line that stably expresses MDA5 and evaluated its analytical performance in order to detect anti-MDA5 Abs by the utilization of indirect immunofluorescence (IIF). Serum samples from 23 anti-MDA5 DM patients and 22 anti-MDA5 Abs negative myositis readings, which were obtained at time of diagnosis, were analyzed by IIF on MDA5-transfected cells. The results were compared with those obtained with specific semi-quantitative (immunodot) and quantitative (ELISA) assays. A specific cytoplasmic pattern was found solely with the sera of anti-MDA5 DM patients. The sensitivity and specificity of IIF on MDA5-transfected cells were 96% and 100%, respectively, compared with ELISA. The anti-MDA5 Abs titers that were determined by this approach were consistent with the quantitative results obtained by ELISA. Baseline concentrations of anti-MDA5 Abs, either by ELISA or IIF, were not significantly different between surviving and deceased patients; further, they did not differ significantly according to clinical phenotypes. Overall, an IIF cell-based assay constitutes a simple, fast, and low-cost approach to identify and quantify anti-MDA5 Abs; moreover, it is as efficient as ELISA.

Update on dermatomyositis

PURPOSE OF REVIEW

This review summarizes and comments on current knowledge in dermatomyositis.

RECENT FINDINGS

The 2018 European Neuromuscular Centre classification of dermatomyositis has been challenging by the discovery of clinicopathological features associated with dermatomyositis-specific antibody (DMSA) that were not incorporated in the original criteria. These features include but may not be limited to the presence of perifascicular necrosis in anti-Mi-2 dermatomyositis; presence of diffuse nonperifascicular sarcoplasmic myxovirus resistance protein A expression in anti-MDA5 dermatomyositis; and dermatomyositis sine dermatitis in anti-NXP-2 dermatomyositis. Variations and subclassifications within the same DMSA subtypes are observed: anti-MDA5 dermatomyositis is clinically subcategorized into good, intermediate, and poor prognostic subgroups; concurrent anti-CCAR1 and anti-TIF1-γ positivity identify anti-TIF1-γ-positive patient with a lower risk for cancer-associated myositis. Owing to distinct IFN1-signaling pathway activation in dermatomyositis, JAK-STAT inhibitor - the pathway-targeted therapy, have been studied with promising results in refractory dermatomyositis and some new-onset dermatomyositis. In addition, the potential serum biomarkers for IFN1 pathway activation are being investigated for their performance in monitoring the disease activity and the efficacy of the treatment.

SUMMARY

DMSA, evidence of prominent IFN1 pathway activation, and risk/severity-associated biomarkers would likely play major roles in future dermatomyositis classification, disease monitoring, and treatment decision.

A multidisciplinary approach to the diagnosis of antisynthetase syndrome

Antisynthetase syndrome is a subtype of idiopathic inflammatory myopathy, strongly associated with the presence of interstitial lung disease. Diagnosis is made by identifying myositis-specific antibodies directed against aminoacyl tRNA synthetase, and relevant clinical and radiologic features. Given the multisystem nature of the disease, diagnosis requires the careful synthesis of subtle clinical and radiological features with the interpretation of specialized autoimmune serological testing. This is provided in a multidisciplinary environment with input from rheumatologists, respiratory physicians, and radiologists. Differentiation from other idiopathic interstitial lung diseases is key; treatment and prognosis differ between patients with antisynthetase syndrome and idiopathic interstitial lung disease. In this review article, we look at the role of the multidisciplinary team and its individual members in the initial diagnosis of the antisynthetase syndrome, including the role of physicians, radiologists, and the wider team.

The use of ELISA is comparable to immunoprecipitation in the detection of selected myositis-specific autoantibodies in a European population

Background

The reliable detection of myositis-specific autoantibodies (MSA) provides valuable clinical information regarding prognosis, clinical progression and diagnostic confirmation.

Objectives

To evaluate the reliability of a commercial ELISA immunoassay in detecting myositis-specific autoantibodies in comparison to immunoprecipitation as the reference standard.

Methods

Serum samples were chosen from a biobank of more than 3000 samples. Samples with a confirmed MSA on Immunoprecipitation (n=116) were evaluated in duplicate by ELISA to detect Mi2, MDA5, Jo1, EJ, KS, PL-7 and PL-12 (Medical &amp; Biological Laboratories Co. Ltd, Nagoya, Aichi, Japan). Healthy control samples (n=246) confirmed autoantibody negative by immunoprecipitation were similarly assessed.

Results

There was a very good agreement between ELISA and immunoprecipitation for serum samples containing anti-Mi2, MDA5, Jo1, EJ, KS and PL-7 and PL-12 auto-antibodies. Cohen’s κ values ranged from 0.86-1 for the measured autoantibodies on ELISA.

Conclusion

ELISA was an accurate method for detecting anti-synthetase, anti-Mi2 and anti-MDA5 autoantibodies.

Anti-FHL1 autoantibodies in juvenile myositis are associated with anti-Ro52 autoantibodies but not with severe disease features

OBJECTIVES

Four-and-a-half LIM domains 1 (FHL1) is a muscle-specific protein. Autoantibodies against FHL1 were recently discovered in adults with idiopathic inflammatory myopathies (IIMs) and were found to be associated with clinical features and outcomes indicative of increased disease severity. Anti-FHL1 autoantibodies have not been described in children. Here, the prevalence and clinical features associated with anti-FHL1 autoantibodies were examined in a large North American cohort of juvenile patients with IIM.

METHODS

Sera from 338 juvenile IIM patients and 91 juvenile healthy controls were screened for anti-FHL1 autoantibodies by ELISA. Clinical characteristics and HLA alleles of those with and without anti-FHL1 autoantibodies were compared among those with juvenile IIM.

RESULTS

Anti-FHL1 autoantibodies were present in 10.9% of juvenile IIM patients and 1.1% of controls. The frequency of anti-FHL1 autoantibodies among clinical and serologic subgroups did not differ. A higher percentage of Asian patients had anti-FHL1 autoantibodies (11% vs 0.7%; P = 0.002). Myositis-associated autoantibodies (MAAs) [odds ratio (OR) 2.09 (CI 1.03, 4.32)], anti-Ro52 autoantibodies specifically [OR 4.17 (CI 1.83, 9.37)] and V-sign rash [OR 2.59 (CI 1.22, 5.40)] were associated with anti-FHL1 autoantibodies. There were no differences in other features or markers of disease severity. No HLA associations with anti-FHL1 autoantibodies in Caucasian myositis patients were identified.

CONCLUSION

Anti-FHL1 autoantibodies are present in ∼11% of juvenile IIM patients and commonly co-occur with MAAs, including anti-Ro52 autoantibodies. In contrast to adult IIM, anti-FHL1 autoantibodies in juvenile myositis are associated with V-sign rash but not with other distinctive clinical features or worse outcomes.

ELISA, protein immunoprecipitation and line blot assays for anti-TIF1-gamma autoantibody detection in cancer-associated dermatomyositis

OBJECTIVES

Anti-TIF1-gamma autoantibodies can be detected with immunoprecipitation (IP), line blot (LB) and ELISA. We compared assay performance in patients with DM and the potential of these assays to detect anti-TIF1-gamma positive cancer-associated DM (CADM).

METHODS

We included sera from 131 patients with DM followed at Karolinska University Hospital, Stockholm, Sweden and 82 healthy controls. Serum samples taken at DM diagnosis were tested for anti-TIF1-gamma autoantibodies with IP, two ELISAs (in-house and commercial) and LB. Cancer diagnosis and dates were obtained from the Swedish national cancer register. CADM was defined as a malignancy that developed within 3 years of DM diagnosis.

RESULTS

Anti-TIF1-gamma autoantibodies were detected in 19/101 (18.8%), 15/113 (13.2%), 34/131 (26%) and 45/131 (34.4%) of the patients with IP, LB, in-house and commercial ELISA, respectively. The anti-TIF1-gamma results from the in-house ELISA were confirmed with IP in 93 of 101 (92%) cases, κ = 0.76, with a commercial ELISA in 110 of 131 (84%) cases, κ = 0.63, and with LB in 101 of 113 (89.3%) cases, κ = 0.67. Anti-TIF1-gamma results with IP were confirmed with LB in 85 of 92 (92.4%) cases, κ = 0.73. For detecting CADM, the anti-TIF1-gamma in-house ELISA had a sensitivity of 58% and specificity of 86%, the commercial ELISA had a sensitivity of 63% and specificity of 82%, IP had a sensitivity of 52% and specificity of 92%, LB had a sensitivity of 40% and specificity of 96%.

CONCLUSION

The two anti-TIF1-gamma ELISA assays had advantages both for autoantibody detection and to identify anti-TIF1-gamma-positive CADM.

Performance of the 2017 EULAR/ACR classification criteria in anti-MDA5 associated idiopathic inflammatory myopathy

OBJECTIVE

To evaluate the performance of the 2017 EULAR/ACR classification criteria in a cohort of anti-MDA5 associated IIM patients.

METHODOLOGY

Consecutive adult patients with a clinical diagnosis of anti-MDA5 associated IIM from 10 hospitals in Hong Kong were recruited retrospectively. Clinical characteristics were collected by reviewing the electronic medical records. A commercial line-blot immunoassay was used to detect the myositis specific antibodies (MSA). Performance of the 2017 EULAR/ACR classification criteria was examined. Incorporation of the anti-MDA5 antibody in the EULAR/ACR criteria and the MSA-based criteria recently proposed by Casal-Dominguez et al. were also evaluated. Lastly, a new set of phenotypic-serological classification criteria specific for anti-MDA5 was proposed.

RESULTS

A hundred and twenty patients with anti-MDA5 associated IIM were recruited. The subgroups were exclusively DM (31.7%) and CADM (68.3%). Eight-six (71.7%) and 49 (40.8%) patients fulfilled the EULAR/ACR classification criteria and the Bohan/Peter criteria respectively. With the addition of Sontheimer's criteria for CADM, 76.7% the patients could be classified by the Bohan and Peter criteria. The sensitivity of the EULAR/ACR criteria could be improved to 98.3% if anti-MDA5 antibody was considered one of the criteria. The criteria by Casal-Dominguez et al. had 100% sensitivity in this cohort. Our newly proposed criteria for "anti-MDA5 syndrome" could also classify 97.5% of the patients.

CONCLUSIONS

Almost 30% of patients with clinical anti-MDA5 associated IIM could not be classified by the EULAR/ACR criteria. Modification of the existing criteria incorporating anti-MDA5 antibody or development of a new specific set of criteria for "anti-MDA5 syndrome" are suggested.