Autoantibodies in the Pathogenesis of Mixed Connective Tissue Disease

Childhood mixed connective tissue disease at disease onset: Evidence from a systematic review

OBJECTIVE

Childhood Mixed Connective Tissue Disease (cMCTD) is the rarest pediatric connective tissue disease that includes features of systemic lupus erythematosus, polymyositis/dermatomyositis, juvenile idiopathic arthritis, and systemic sclerosis, identified by Sharp in 1972 and whose diagnosis remains challenging. This systematic review aims to identify clinical features at the onset of cMCTD and manifestations not currently included into the available diagnostic criteria.

METHODS

A systematic literature review was performed in accordance with PRISMA guidelines 2020 using bibliographic databases: MEDLINE via PubMed and EMBASE.

ELIGIBILITY CRITERIA

patients diagnosed with MCTD with onset before 18 years.

STUDIES INCLUDED

registries, retrospective and prospective cohort studies, case series and reports with analysis of data on signs and symptoms of presentation.

RESULTS

39 articles were included (215 subjects, 82.5% female), mean age of 141 months (± 41 months DS, range 2.5-204). The most used criteria for the diagnosis of MCTD were the Kasukawa criteria (54.5%). The clinical manifestations described at onset were Raynaud's phenomenon (69.7%), arthritis (60.9%), muscular involvement (53.5%), dermatological signs (39.5%), swollen fingers or hands (29.3%), arthralgias (25.6%), fever (22.3%), lung involvement (14.4%), sclerodactily (13.5%), lymphadenopathy (10.7%) serositis (10.2%), esophageal involvement (6.9%), nervous system involvement (6.9%), xeroftalmia (3.7%), xerostomia (3.7%), hepatosplenomegaly (2.8%), cardiac involvement (2.8%), hepatitis (2.3%), parotiditis (2.3%), Hashimoto's thyroiditis (0.9%), ocular involvement (0.9%).

CONCLUSIONS

The data from this systematic review suggest great heterogeneity of the clinical presentation of cMCTD for which there are no validated diagnostic criteria that may suggest a new diagnostic approach to allow earlier or more accurate diagnosis in the future.

The diagnostic challenge of patients with anti-U1-RNP antibodies

Anti-U1-RNP antibodies are necessary for the diagnosis of mixed connective tissue disease (MCTD), but they are also prevalent in other connective tissue diseases, especially systemic lupus erythematosus (SLE), from which distinction remains challenging. We aimed to describe the presentation and outcome of patients with anti-U1-RNP antibodies and to identify factors to distinguish MCTD from SLE. We retrospectively applied the criteria sets for MCTD, SLE, systemic sclerosis (SSc) and rheumatoid arthritis (RA) to all patients displaying anti-U1-RNP antibodies in the hospital of Caen from 2000 to 2020. Thirty-six patients were included in the analysis. Eighteen patients (50%) satisfied at least one of the MCTD classifications, 11 of whom (61%) also met 2019 ACR/EULAR criteria for SLE. Twelve other patients only met SLE without MCTD criteria, and a total of 23 patients (64%) met SLE criteria. The most frequent manifestations included Raynaud's phenomenon (RP, 91%) and arthralgia (67%). We compared the characteristics of patients meeting only the MCTD (n = 7), SLE (n = 12), or both (n = 11) criteria. Patients meeting the MCTD criteria were more likely to display SSc features, including sclerodactyly (p < 0.01), swollen hands (p < 0.01), RP (p = 0.04) and esophageal reflux (p < 0.01). The presence of scleroderma features (swollen hands, sclerodactyly, gastro-oesophageal reflux), was significantly associated with the diagnosis of MCTD. Conversely, the absence of those manifestations suggested the diagnosis of another definite connective tissue disease, especially SLE.

The enigma of mixed connective tissue disease-challenges in routine care

OBJECTIVES

As a rare and heterogeneous disease, mixed connective tissue disease (MCTD) represents a challenge. Herein, we aimed to unravel potential pitfalls including correct referral diagnosis, distinction from other connective tissue diseases (CTD) and treatment modalities.

METHODS

We characterised the MCTD cohort at our tertiary referral centre. All patients were evaluated for fulfilment of classification criteria of various CTDs. SLEDAI-2 K and EUSTAR-AI were used in accordance with previous research to evaluate disease activity and treatment response.

RESULTS

Out of 85 patients initially referred as MCTD, only one-third (33/85, 39%) fulfilled the diagnostic MCTD criteria and the other patients had undifferentiated CTD (16/85, 19%), non-MCTD overlap syndromes (11/85, 13%) and other rheumatic diseases. In our final cohort of 33 MCTD patients, 16 (48%) also met the diagnostic criteria of systemic sclerosis, 13 (39%) these of systemic lupus erythematosus, 6 (18%) these of rheumatoid arthritis and 3 (9%) these of primary myositis. Management of MCTD required immunomodulating combination therapy in most cases (15/28, 54%), whereas monotherapy was less frequent (10/28, 36%), and only a few (3/28, 11%) remained without immune modulators until the end of the follow-up period. Treatment led to a significant decline in disease activity.

CONCLUSIONS

Our study showed a high risk for misdiagnosis for patients with MCTD. As a multi-organ disease, MCTD required prolonged immunomodulating therapy to achieve remission. The establishment of an international registry with longitudinal data from observational multi-centre cohorts might represent a first step to address the many unmet needs of MCTD.

Biomarkers for Inner Ear Disorders: Scoping Review on the Role of Biomarkers in Hearing and Balance Disorders

The diagnostics of inner ear diseases are primarily functional, but there is a growing interest in inner ear biomarkers. The present scoping review aimed to elucidate gaps in the literature regarding the definition, classification system, and an overview of the potential uses of inner ear biomarkers. Relevant biomarkers were categorized, and their possible benefits were evaluated. The databases OVID Medline, EMBASE, EBSCO COINAHL, CA PLUS, WOS BIOSIS, WOS Core Collection, Proquest Dissertations, Theses Global, PROSPERO, Cochrane Library, and BASE were searched using the keywords "biomarker" and "inner ear". Of the initially identified 1502 studies, 34 met the inclusion criteria. The identified biomarkers were classified into diagnostic, prognostic, therapeutic, and pathognomonic; many were detected only in the inner ear or temporal bone. The inner-ear-specific biomarkers detected in peripheral blood included otolin-1, prestin, and matrilin-1. Various serum antibodies correlated with inner ear diseases (e.g., anti-type II collagen, antinuclear antibodies, antibodies against cytomegalovirus). Further studies are advised to elucidate the clinical significance and diagnostic or prognostic usage of peripheral biomarkers for inner ear disorders, filling in the literature gaps with biomarkers pertinent to the otology clinical practice and integrating functional and molecular biomarkers. These may be the building blocks toward a well-structured guideline for diagnosing and managing some audio-vestibular disorders.

Mixed connective tissue disease: Not always an obvious diagnosis

Mixed connective tissue disease (MCTD) is characterized by a mixture of clinical features. The initial presentation is often incomplete, and the features of MCTD usually develop as the disease evolves. We present a 37‐year‐old female patient with overlapping symptoms. The most plausible diagnosis was MCTD.

Interferons (IFN-A/-B/-G) Genetic Variants in Patients with Mixed Connective Tissue Disease (MCTD)

Mixed connective tissue disease (MCTD) is a rare complex autoimmune disease in which autoantigens are recognized by endosomal TLRs. Their activation induces a higher secretion of the type I interferons, IFN-γ and the up-regulation of the INF-inducible genes. The present study aimed to investigate whether SNPs that are located in the IFN-A, IFN-B, and IFN-G genes are associated with MCTD. 145 MCTD patients and 281 healthy subjects were examined for IFN-A, IFN-B, and IFN-G genetic variants by TaqMan SNP genotyping assay. ELISA determined IFN-α/-β/-γ serum levels. Among the seven tested SNPs, four polymorphisms: IFN-A rs10757212, IFN-A rs3758236, IFN-G rs2069705, IFN-G rs2069718, as well as INF-G rs1861493A/rs2069705A/rs2069718G haplotype were significantly associated with a predisposition for MCTD. Raynaud's phenomenon, erosive arthritis, swollen hands and fingers, and sclerodactyly were significantly more frequently observed in MCTD patients with IFN-G rs2069718 G allele than in patients with IFN-G rs2069718 A allele. We also found that anti-U1-A autoantibodies most frequently occurred in MCTD patients with rs2069718 GA genotype, while the IFN-G rs2069705 AG and rs2069718 GA genotypes might be a marker of anti-Ro60 presence in MCTD patients. Our results indicate that IFN-G genetic variants may be potential genetic biomarkers for MCTD susceptibility and severity.

Massive Hemorrhagic Pericardial Effusion With Cardiac Tamponade as Initial Manifestation of Mixed Connective Tissue Disease

Mixed connective tissue disease (MCTD) is a distinct entity of connective tissue disorders characterized by overlapping clinical features of various autoimmune diseases along with the presence of antibodies to ribonucleoprotein (anti-RNP). The prevalence of cardiac involvement in MCTD varies from 13% to 65% and accounts for approximately 20% of MCTD related mortality. In this case, we describe an elderly female patient with multiple complaints without a clear etiology on presentation. Echocardiogram revealed severe rapidly accumulating pericardial effusion causing tamponade necessitating pericardial window. Laboratory investigations showed positive ribonucleoprotein antibodies. Biopsy of pericardial tissue revealed fibrinous pericarditis. While pericarditis is commonly associated with MCTD, pericardial tamponade on the other hand is rarely described. This case highlights a very rare complication of the disease. Early recognition, prompt treatment, and regular follow-up with serial echo are essential for treatment.

Facts and controversies in mixed connective tissue disease

Mixed connective tissue disease (MCTD) is a systemic autoimmune rheumatic disease (SARD) characterised by the combination of clinical manifestations of systemic lupus erythematosus (SLE), cutaneous systemic sclerosis (SSc) and polymyositis-dermatomyositis, in the presence of elevated titers of anti-U1-RNP antibodies. Main symptoms of the disease are polyarthritis, hand oedema, Raynaud's phenomenon, sclerodactyly, myositis and oesophageal hypomobility. Although widely discussed, most authors today accept MCTD as an independent entity. Others, however, suggest that these patients may belong to subgroups or early stages of certain definite connective diseases, such as SLE or SSc, or are, in fact, SARD overlap syndromes.

Systemic lupus erythematosus in a multiethnic US Cohort LUMINA XLVIII: factors predictive of pulmonary damage

The objective of this study was to determine the factors predictive of time to the occurrence of pulmonary damage in systemic lupus erythematosus (SLE). Six-hundred and twenty-six SLE patients from a multiethnic (Hispanics, African Americans and Caucasians) longitudinal study of outcome were studied. Pulmonary damage was defined as per the Systemic Lupus International Collaborating Clinics Damage Index. Socioeconomic-demographic, clinical, genetic, serological features, pharmacologic treatments, behavioural, psychological and disease activity [as per the Systemic Lupus Activity Measure-Revised (SLAM-R)] were examined. Factors associated with time to the occurrence of pulmonary damage were examined by Cox proportional hazards regressions. A Kaplan—Meier survival curve was also examined. Forty-six (7.3%) patients had pulmonary damage after a mean (SD) total disease duration of 5.3 (3.6) years. Among those patients, 25 had pulmonary fibrosis, 12 pulmonary hypertension, eight pleural fibrosis, four pulmonary infarction and four shrinking lung syndrome. Seven patients had more than one type of lung damage. Cumulative rates of pulmonary damage at five and 10 years were 7.6% and 11.6%, respectively. In the multivariable analyses, age (HR = 1.033, 95% CI 1.006—1.060; P = 0.0170), pneumonitis (HR = 2.307, 95% CI 1.123—4.739; P = 0.0229) and anti-RNP antibodies (HR = 2.344, 95% CI 1.190—4.618; P = 0.0138) were associated with a shorter time to the occurrence of pulmonary damage while photosensitivity (HR = 0.388, 95% CI 0.184—0.818; P = 0.0128) and oral ulcers (HR = 0.466, 95% CI 0.230—0.942; P = 0.0335) with a longer time. Pulmonary damage is relatively common in SLE. Age, pneumonitis and anti-RNP antibodies were associated with a shorter time to the development of permanent lung disease. Lupus (2007) 16, 410—417.

Role of autoantibody testing

Autoantibodies are the serological hallmark of autoimmune disease. Though their pathogenic role is debatable, they play an important role in the management of a patient with rheumatic disease. However, due to their presence in the general population as well as in multiple autoimmune diseases, the presence of an autoantibody alone does not make a diagnosis; the result has to be interpreted along with clinical findings. Similarly, the absence of autoantibody does not exclude a disease. The common autoantibodies used in clinical practice include rheumatoid factor, anti-CCP antibodies, antinuclear antibodies (ANAs), anti-neutrophil cytoplasmic antibodies (ANCA) and anti-phospholipid antibodies. Once an autoantibody to a broad antigen is detected in a patient, sub-specificity analysis can improve the utility of the antibody. Autoantibodies are detected in the serum using different assays and results of which can vary; thus, it is important for a clinician to know the method used, its sensitivity and specificity to help in the proper interpretation of the laboratory results. This review will address these issues.

U1-RNP and TLR receptors in the pathogenesis of mixed connective tissue diseasePart I. The U1-RNP complex and its biological significance in the pathogenesis of mixed connective tissue disease

Mixed connective tissue disease (MCTD) is a rare autoimmune syndrome, signified by complex interactions between disease-related phenomena, including inflammation, proliferative vascular arteriopathy, thrombotic events and humoral autoimmune processes. It is still controversial whether MCTD is a distinct clinical entity among systemic connective tissue diseases, although several authors consider that it is distinct and underline characteristic, distinct clinical, serological and immunogenetic features. The putative target of autoimmunity in MCTD is U1-RNP, which is a complex of U1-RNA and small nuclear RNP. Both the U1-RNA component and the specific proteins, particularly U1-70K, engage immune cells and their receptors in a complex network of interactions that ultimately lead to autoimmunity, inflammation, and tissue injury. U1-RNA is capable of inducing manifestations consistent with TLR activation. Stimulation of innate immunity by native RNA molecules with a double-stranded secondary structure may help explain the high prevalence of autoimmunity to RNA binding proteins.

Derailed B cell homeostasis in patients with mixed connective tissue disease

Mixed connective tissue disease (MCTD) is a systemic autoimmune disorder, characterized by the presence of antibodies to U1-RNP protein. We aimed to determine phenotypic abnormalities of peripheral B cell subsets in MCTD. Blood samples were obtained from 46 MCTD patients, and 20 controls. Using anti-CD19, anti-CD27, anti-IgD and anti-CD38 monoclonal antibodies, the following B cell subsets were identified by flow cytometry: (1) transitional B cells (CD19+CD27-IgD+CD38(high)); (2) naive B cells (CD19+CD27-IgD+CD38(low)); (3) non-switched memory B cells (CD19+CD27+IgD+); (4) switched memory B cells (CD19+CD27+IgD-); (5) double negative (DN) memory B cells (CD19+CD27-IgD-) and (6) plasma cells (CD19+CD27(high)IgD-). The proportion of transitional B cells, naive B cells and DN B lymphocytes was higher in MCTD than in controls. The DN B cells were positive for CD95 surface marker. This memory B cells population showed a close correlation with disease activity. The number of plasma cells was also increased, and there was an association between the number of plasma cells and the anti-U1RNP levels. Cyclophosphamide, methotrexate, and corticosteroid treatment decreased the number of DN and CD27(high) B cells. In conclusion, several abnormalities were found in the peripheral B-cell subsets in MCTD, which reinforces the role of derailed humoral autoimmune processes in the pathogenesis.

Characterization of TLR4-mediated auto-antibody production in a mouse model of histidyl-tRNA synthetase-induced myositis

We have previously shown that intramuscular immunization with a recombinant fragment of murine histidyl-tRNA synthetase (HRS) in the absence of exogenous adjuvant generates Ag-specific, IgG class switched Abs a murine model of myositis. Markedly diminished IgG anti-HRS auto-Ab responses in TLR4 signaling-deficient C3H/HeJ mice indicate that TLR4 is required for auto-Ab formation and/or class switching in this system. Comparative time course assessment of HRS-immunized C3H/HeOuJ (wild type) and C3H/HeJ (TLR4 mutant) mice shows here that despite significant impairment of class switched IgG anti-HRS responses in TLR4-deficient C3H/HeJ mice, production of IgM anti-HRS auto-Abs is relatively preserved-suggesting that TLR4-mediated signals modulate IgG class switching rather than auto-Ab formation in this genetic background. In C57BL/6-derived knockout mice lacking either MyD88 (B6.MyD88(-/-)) or TRIF (B6.TRIF(-/-)) adaptor molecules, immunization studies indicate that TRIF exerts a dominant role in the generation of HRS-specific IgG auto-Abs. Complementing these analyses, in vitro stimulation of unfractionated, as well as T cell-depleted, C3H/HeOuJ splenocytes with recombinant murine HRS reveals that TLR4-mediated generation of class switched auto-Abs can occur independently of T cell help. Overall, these findings support a broader role for TLR4 in the breakdown of immune tolerance and development of autoimmunity.

Serum antibodies against the 70k polypeptides of the U1 ribonucleoprotein complex are associated with psychiatric syndromes in systemic lupus erythematosus: a retrospective study

OBJECTIVES

We assessed the association between serum autoantibodies against the 70-kDa polypeptide of the U1-ribonucleoprotein (RNP) complex (U1-70k) and the central nervous system (CNS) syndromes in systemic lupus erythematosus (SLE) patients.

METHODS

We studied 106 hospitalized patients with active SLE, comparing those with (n = 32) and without (n = 74) CNS syndromes. CNS syndromes were further classified into neurologic (n = 21) and psychiatric (n = 15) disorders. Immunoglobulin G (IgG) anti-U1-70k antibodies were measured by enzyme-linked immunosorbent assay (ELISA) using recombinant antigens. IgG antibodies against whole U1-RNP were measured using commercial ELISA kits.

RESULTS

Although there was no significant difference in the levels of serum anti-U1-70k antibodies in SLE patients with or without CNS syndromes (p = 0.83), the levels were significantly elevated in SLE patients compared with patients without psychiatric syndromes (p = 0.030). In contrast, no significant difference was observed in the levels of serum anti-U1-RNP antibodies in SLE patients with or without psychiatric syndromes (p = 0.555).

CONCLUSIONS

These results indicate that serum anti-U1-70k antibodies are associated with psychiatric syndromes in SLE but that they are not associated with CNS syndromes as a whole or with neurologic syndromes. The anti-U1-70k antibodies might be involved in the pathological mechanisms of psychiatric syndromes in SLE.

Isolated central nervous system vasculitis associated with antiribonuclear protein antibody

We describe the case of a young woman who was referred to a tertiary care center with unexplained subacute progressive encephalopathy preceded by long-standing severe headaches. Her extensive workup was remarkable for abnormal intracranial angiography suggestive of small- and medium-vessel vasculitis, persistently elevated protein in the cerebrospinal fluid and persistently high titers of antiribonuclear protein antibody. The patient showed a modest response to intravenous high-dose steroids. We propose that the patient's neurologic disease is secondary to immune-mediated central nervous system vasculitis, possibly as an initial manifestation of mixed connective tissue disease.

Case history of mixed connective tissue disease

The literary review on mixed connective tissue disease is given according to modern international data. The case history of this pathology is described. The case has been observed in the rheumatological department of the Federal Research Clinical Center FMBA of Russia.

Sensorineural Hearing Loss in Patients with Mixed Connective Tissue Disease: Immunological Markers and Cytokine Levels

Objective.

To investigate the frequency of sensorineural hearing loss (SNHL) in patients with mixed connective tissue disease (MCTD).

Methods.

The study population consisted of 71 patients with MCTD (69 female; 2 male), with a mean age of 57.1 ± 7.9 years and a mean disease duration of 14.5 ± 8.0 years. All patients underwent audiological evaluation that included pure tone and speech audiometry. In addition, the systemic manifestations of the disease and drug therapy were recorded. All patients were tested for presence of autoantibodies. Fifty-one age-matched healthy subjects served as controls.

Results.

SNHL was found in 33 (46.4%) of the 71 patients with MCTD. There was no correlation between SNHL and age and disease duration. An association was found between Raynaud’s phenomenon (p < 0.03), secondary antiphospholipid syndrome (APS) (p < 0.05), and SNHL. MCTD patients with SNHL had higher serum levels of anti-U1RNP (p < 0.05), antiendothelial cell antibodies (p < 0.001), and IgG type anticardiolipin antibodies (p < 0.0001) than patients without SNHL. Serum levels of interferon-γ and tumor necrosis factor-α were increased in MCTD patients with SNHL compared to patients without SNHL. The absolute number of natural (CD4+CD25highFoxP+) regulatory T cells (Treg) was lower compared to patients without SNHL.

Conclusion.

In MCTD, SNHL is a specific organ manifestation and appears frequently. We have found that pathogenic autoantibodies, decreased levels of regulatory T cells, and overexpression of proinflammatory cytokines may play a role in the pathogenesis of immune mediated inner ear disorders in MCTD.

Anti-ribonucleoprotein antibodies mediate enhanced lung injury following mesenteric ischemia/reperfusion inRag-1−/−mice

Natural Abs and autoantibodies bind antigens displayed by ischemia-conditioned tissues, followed by complement activation and enhanced tissue injury during reperfusion. Anti-ribonucleoprotein (RNP) Ab is associated with lung disease in patients with autoimmune disease but it is not known whether these abs contribute to lung injury. Mesenteric I/R in mice leads to local and remote lung injury. Accordingly, we used this model to investigate whether anti-RNP Abs would reconstitute I/R damage with prominent lung damage in injury-resistant Rag1(-/-) animals. Rag1(-/-) mice injected with anti-RNP Ab containing serum and subjected to mesenteric I/R suffered greater intestinal injury than control-treated and sham-operated animals. The magnitude of the reconstituted damage was anti-RNP Ab titer-dependent. Anti-RNP Ab-treated animals demonstrated a dose-dependent increase in lung histologic injury scores compared to control and sham animals. Anti-RNP mediated injury was shown to be complement dependent. These experiments reveal a novel mechanism whereby anti-RNP Abs contributes to the development of pulmonary pathology in patients with autoimmune diseases following exposure of remote organs to I/R injury.

Immune pathogenesis of Mixed Connective Tissue Disease: a short analytical review

Mixed Connective Tissue Disease (MCTD) was first described 35 years ago by Gordon C. Sharp and his colleagues. In the ensuing decades, a clearer understanding of the clinical and serologic features of MCTD has emerged. Classification criteria now exist to define MCTD for study purposes, the long-term outcome of the disease has been established, and novel genetic associations within the major histocompatibility complex on chromosome 6 and select regions on chromosome 3 have been identified. Studies on immune pathogenesis have made substantial progress in advancing our understanding of MCTD. In MCTD, there is a complex interaction of the innate and adaptive immune system that culminates in autoimmune disease. Antigenic structural modification occurring during apoptosis or other modifications of self antigens leads to an autoantigen driven immune process with innate immune activation, immunoglobulin G autoantibody production directed against select components of the spliceosome, B lymphocyte activation, and CD4 and CD8 T lymphocyte participation.

Anti-RNP immunity: Implications for tissue injury and the pathogenesis of connective tissue disease

Certain autoantibodies are characteristic of autoimmune disease manifestations and contribute to organ pathology. The presence of high-titer antibodies to U1-RNP are associated with mixed connective tissue disease, although these antibodies may also be present in systemic lupus erythematosus and systemic sclerosis. However, the role of antibodies to U1-RNP in the pathogenesis of connective tissue disease remains unclear. Data from recent experimental studies promote the hypothesis that U1-RNP antibodies participate in both innate and adaptive immune responses, implicating them in the pathogenesis of connective tissue disease.