Expression of citrulline and homocitrulline residues in the lungs of non-smokers and smokers: implications for autoimmunity in rheumatoid arthritis

A citrullinated antigenic vaccine in treatment of autoimmune arthritis

Rheumatoid arthritis (RA) is an inflammatory autoimmune disease triggered by antigenic peptides with environmental and genetic risk factors. It has been shown that antigen-specific targeting could be a promising therapeutical strategy for RA by restoring immune tolerance to self-antigens without compromising normal immunity. Citrullination of antigens enhances antigenic properties and induces autoimmune responses. Here, we showed that citrullinated antigenic (citAg) vaccine ameliorated collagen-induced arthritis (CIA) with decreased T-helper 1 (Th1) and Th17 cells, downregulated proinflammatory cytokines including interlukin-6 and tumor necrosis factor-α, and inhibited antigen recall responses. B cell receptor (BCR) sequencing further revealed that citAg vaccine could dampen the dysregulated V(D)J recombination, restoring the immune repertoire. Taken together, the results demonstrated that citAg vaccine might have a therapeutic effect on RA.

Helicobacter pylori upregulates PAD4 expression via stabilising HIF-1α to exacerbate rheumatoid arthritis

OBJECTIVE

Helicobacter pylori infection has been reported to aggravate rheumatoid arthritis (RA), but the relevant mechanism remains unclear. This study aimed to investigate the underlying pathogenic mechanism of H. pylori infection in the progression of RA.

METHODS

The Disease Activity Score (DAS-28) and serum anticitrullinated protein antibody (ACPA) levels were compared between H. pylori-negative and H. pylori-positive patients with RA. MH7A cells were stimulated with polyclonal ACPA purified from the peripheral blood of patients with RA. The citrullination levels were assessed by western blot in GES-1 cells and sera. ChIP, luciferase reporter assays, mass spectrometry and ELISA were applied to explore the molecular mechanism of H. pylori infection in RA progression.

RESULTS

The DAS-28 and ACPA levels of patients with RA in the H. pylori-positive group were significantly higher than those in the H. pylori-negative group. Polyclonal ACPA derived from H. pylori-positive patients promoted cell proliferation and induced secretion of IL-6 and IL-8. For the first time, we found that H. pylori infection induces cellular protein citrullination by upregulating protein arginine deiminase type 4 (PAD4). Furthermore, we confirmed a direct functional binding of hypoxia-inducible factor 1α on the PADI4 gene promoter. We demonstrated that PAD4 interacts with and citrullinates keratin 1 (K1), and serum and synovial fluid levels of anti-Cit-K1 antibody were markedly increased in H. pylori-infected patients with RA.

CONCLUSION

Our findings reveal a novel mechanism by which H. pylori infection contributes to RA progression. Therapeutic interventions targeting H. pylori may be a viable strategy for the management of RA.

Rheumatoid arthritis extra-articular lung disease: new insights on pathogenesis and experimental drugs

INTRODUCTION

Pulmonary involvement is one of the most common extra-articular manifestations of rheumatoid arthritis (RA), a systemic inflammatory disease characterized by joint swelling and tenderness. All lung compartments can be interested in the course of RA, including parenchyma, airways, and, more rarely, pleura and vasculature.

AREAS COVERED

The aim of this paper is to review the main RA lung manifestations, focusing on pathogenesis, clinical and therapeutic issues of RA-related interstitial lung disease (ILD). Despite an increasing number of studies in the last years, pathogenesis of RA-ILD remains largely debated and the treatment of RA patients with lung involvement is still challenging in these patients.

EXPERT OPINION

Management of RA-ILD is largely based on expert-opinion. Due to the broad clinical manifestations, including both joints and pulmonary involvement, multidisciplinary discussion, including rheumatologist and pulmonologist, is essential, not only for diagnosis, but also to evaluate the best therapeutic approach and follow-up. In fact, the coexistence of different lung manifestations may influence the treatment response and safety. The identification of biomarkers and risk-factors for an early identification of RA patients at risk of developing ILD remains a need that still needs to be fulfilled, and that will require further investigation in the next years.

Neutrophil-Derived Peptidyl Arginine Deiminase Activity Contributes to Pulmonary Emphysema by Enhancing Elastin Degradation

In chronic obstructive pulmonary disease (COPD), inflammation gives rise to protease-mediated degradation of the key extracellular matrix protein, elastin, which causes irreversible loss of pulmonary function. Intervention against proteolysis has met with limited success in COPD, due in part to our incomplete understanding of the mechanisms that underlie disease pathogenesis. Peptidyl arginine deiminase (PAD) enzymes are a known modifier of proteolytic susceptibility, but their involvement in COPD in the lungs of affected individuals is underexplored. In this study, we showed that enzyme isotypes PAD2 and PAD4 are present in primary granules of neutrophils and that cells from people with COPD release increased levels of PADs when compared with neutrophils of healthy control subjects. By examining bronchoalveolar lavage and lung tissue samples of patients with COPD or matched smoking and nonsmoking counterparts with normal lung function, we reveal that COPD presents with markedly increased airway concentrations of PADs. Ex vivo, we established citrullinated elastin in the peripheral airways of people with COPD, and in vitro, elastin citrullination significantly enhanced its proteolytic degradation by serine and matrix metalloproteinases, including neutrophil elastase and matrix metalloprotease-12, respectively. These results provide a mechanism by which neutrophil-released PADs affect lung function decline, indicating promise for the future development of PAD-based therapeutics for preserving lung function in patients with COPD.

The peculiar features, diversity and impact of citrulline-reactive autoantibodies

Since entering the stage 25 years ago as a highly specific serological biomarker for rheumatoid arthritis, anti-citrullinated protein antibodies (ACPAs) have been a topic of extensive research. This hallmark B cell response arises years before disease onset, displays interpatient autoantigen variability, and is associated with poor clinical outcomes. Technological and scientific advances have revealed broad clonal diversity and intriguing features including high levels of somatic hypermutation, variable-domain N-linked glycosylation, hapten-like peptide interactions, and clone-specific multireactivity to citrullinated, carbamylated and acetylated epitopes. ACPAs have been found in different isotypes and subclasses, in both circulation and tissue, and are secreted by both plasmablasts and long-lived plasma cells. Notably, although some disease-promoting features have been reported, results now demonstrate that certain monoclonal ACPAs therapeutically block arthritis and inflammation in mouse models. A wealth of functional studies using patient-derived polyclonal and monoclonal antibodies have provided evidence for pathogenic and protective effects of ACPAs in the context of arthritis. To understand the roles of ACPAs, one needs to consider their immunological properties by incorporating different facets such as rheumatoid arthritis B cell biology, environmental triggers and chronic antigen exposure. The emerging picture points to a complex role of citrulline-reactive autoantibodies, in which the diversity and dynamics of antibody clones could determine clinical progression and manifestations.

Does Rheumatoid Arthritis Increase the Risk of COPD?: A Nationwide Retrospective Cohort Study

BACKGROUND

Most reports of pulmonary manifestations in rheumatoid arthritis (RA) have been related to interstitial lung diseases. RA and COPD are both chronic inflammatory systemic diseases.

RESEARCH QUESTION

Does RA increase the risk of developing COPD? Is there a difference between seropositive and seronegative RA in the risk of COPD?

STUDY DESIGN AND METHODS

Using the Korean National Health Insurance Database, we screened individuals diagnosed with RA between 2010 and 2017. We identified 46,030 patients with RA (32,608 with seropositive RA and 13,422 with seronegative RA) and 230,150 matched control individuals; we monitored them until December 2019. We used multivariate Cox proportional hazard models to estimate the adjusted hazard ratio (aHR) of risk factors for the development of COPD.

RESULTS

The incidence of COPD among patients with RA was 5.04 per 1,000 person-years; it was 2.23 per 1,000 person-years in the control group. Patients with RA showed a higher risk of developing COPD (aHR, 2.11; 95% CI, 1.96-2.28) compared with the control group. Although both seropositive RA and seronegative RA were associated with an increased risk of COPD, patients with seropositive RA had a higher risk for the development of COPD (aHR, 1.26; 95% CI, 1.09-1.46) than patients with seronegative RA. In the subgroup analyses, smoking history did not demonstrate significant interactions between RA and COPD development.

INTERPRETATION

RA was shown to be associated with an increased risk of COPD development, augmented by seropositivity. Physicians should monitor respiratory symptoms and pulmonary function carefully in patients with RA.

Citrullinated and MMP-degraded vimentin is associated with chronic pulmonary diseases and genetic variants in PADI3/PADI4 and CFH in postmenopausal women

Citrullinated vimentin has been linked to several chronic and autoimmune diseases, but how citrullinated vimentin is associated with disease prevalence and genetic variants in a clinical setting remains unknown. The aim of this study was to obtain a better understanding of the genetic variants and pathologies associated with citrullinated and MMP-degraded vimentin. Patient Registry data, serum samples and genotypes were collected for a total of 4369 Danish post-menopausal women enrolled in the Prospective Epidemiologic and Risk Factor study (PERF). Circulating citrullinated and MMP-degraded vimentin (VICM) was measured. Genome-wide association studies (GWAS) and phenome wide association studies (PheWAS) with levels of VICM were performed. High levels of VICM were significantly associated with the prevalence of chronic pulmonary diseases and death from respiratory and cardiovascular diseases (CVD). GWAS identified 33 single nucleotide polymorphisms (SNPs) with a significant association with VICM. These variants were in the peptidylarginine deiminase 3/4 (PADI3/PADI4) and Complement Factor H (CFH)/KCNT2 gene loci on chromosome 1. Serum levels of VICM, a marker of citrullinated and MMP-degraded vimentin, were associated with chronic pulmonary diseases and genetic variance in PADI3/PADI4 and CFH/ KCNT2. This points to the potential for VICM to be used as an activity marker of both citrullination and inflammation, identifying responders to targeted treatment and patients likely to experience disease progression.

Peptidyl Arginine Deiminases in Chronic Diseases: A Focus on Rheumatoid Arthritis and Interstitial Lung Disease

Protein citrullination is accomplished by a broad enzyme family named Peptidyl Arginine Deiminases (PADs), which makes this post-translational modification in many proteins that perform physiological and pathologic mechanisms in the body. Due to these modifications, citrullination has become a significant topic in the study of pathological processes. It has been related to some chronic and autoimmune diseases, including rheumatoid arthritis (RA), interstitial lung diseases (ILD), multiple sclerosis (MS), and certain types of cancer, among others. Antibody production against different targets, including filaggrin, vimentin, and collagen, results in an immune response if they are citrullinated, which triggers a continuous inflammatory process characteristic of autoimmune and certain chronic diseases. PAD coding genes (PADI1 to PADI4 and PADI6) harbor variations that can be important in these enzymes' folding, activity, function, and half-life. However, few studies have considered these genetic factors in the context of chronic diseases. Exploring PAD pathways and their role in autoimmune and chronic diseases is a major topic in developing new pharmacological targets and valuable biomarkers to improve diagnosis and prevention. The present review addresses and highlights genetic, molecular, biochemical, and physiopathological factors where PAD enzymes perform a major role in autoimmune and chronic diseases.

A review on the potential risks and mechanisms of heavy metal exposure to Chronic Obstructive Pulmonary Disease

Chronic Obstructive Pulmonary Disease (COPD) is a chronic disease that affects patients as well as the health and economic stability of society as a whole. At the same time, heavy metal pollution is widely recognized as having a possible impact on the environment and human health. Therefore, these diseases have become important global public health issues. In recent years, researchers have shown great interest in the potential association between heavy metal exposure and the development of COPD, and there has been a substantial increase in the number of related studies. However, we still face the challenge of developing a comprehensive and integrated understanding of this complex association. Therefore, this review aimed to evaluate the existing epidemiological studies to clarify the association between heavy metal exposure and COPD. In addition, we will discuss the biological mechanisms between the two to better understand the multiple molecular pathways and possible mechanisms of action involved, and provide additional insights for the subsequent identification of potential strategies to prevent and control the effects of heavy metal exposure on the development of COPD in individuals and populations.

Citrullination of matrisomal proteins in health and diseases

Proteins once translated are subjected to post-translational modifications (PTMs) that can critically modify their characteristics. Citrullination is a unique type of PTM that is catalysed by peptidylarginine deiminase (PAD) enzymes, which regulate a multitude of physiological functions such as apoptosis, gene expression and immune response by altering the structure and function of cellular proteins. However, emerging data have unravelled compelling evidence to support that PAD-mediated citrullination is not exclusive to cellular proteins; rather citrullination of extracellular matrix (ECM) proteins also plays a major contributing role in various physiological/pathological conditions. Here, we discuss putative mechanisms for citrullination-induced alterations in the function of ECM proteins. Further, we put emphasis on influential roles of ECM citrullination in various pathological scenarios to underscore the clinical potential of its manipulation in human diseases. This article is part of the Theo Murphy meeting issue 'The virtues and vices of protein citrullination'.

Modifiable risk factors linked to the development of rheumatoid arthritis: evidence, immunological mechanisms and prevention

Rheumatoid Arthritis (RA) is a common autoimmune disease that targets the synovial joints leading to arthritis. Although the etiology of RA remains largely unknown, it is clear that numerous modifiable risk factors confer increased risk to developing RA. Of these risk factors, cigarette smoking, nutrition, obesity, occupational exposures and periodontal disease all incrementally increase RA risk. However, the precise immunological mechanisms by which these risk factors lead to RA are not well understood. Basic and translational studies have provided key insights into the relationship between inflammation, antibody production and the influence in other key cellular events such as T cell polarization in RA risk. Improving our general understanding of the mechanisms which lead to RA will help identify targets for prevention trials, which are underway in at-risk populations. Herein, we review the modifiable risk factors that are linked to RA development and describe immune mechanisms that may be involved. We highlight the few studies that have sought to understand if modification of these risk factors reduces RA risk. Finally, we speculate that modification of risk factors may be an appealing avenue for prevention for some at-risk individuals, specifically those who prefer lifestyle interventions due to safety and economic reasons.

Molecular Factors in PAD2 (PADI2) and PAD4 (PADI4) Are Associated with Interstitial Lung Disease Susceptibility in Rheumatoid Arthritis Patients

Around 50% of rheumatoid arthritis (RA) patients show some extra-articular manifestation, with the lung a usually affected organ; in addition, the presence of anti-citrullinated protein antibodies (ACPA) is a common feature, which is caused by protein citrullination modifications, catalyzed by the peptidyl arginine deiminases (PAD) enzymes. We aimed to identify single nucleotide variants (SNV) in PADI2 and PADI4 genes (PAD2 and PAD4 proteins, respectively) associated with susceptibility to interstitial lung disease (ILD) in RA patients and the PAD2 and PAD4 levels. Material and methods: 867 subjects were included: 118 RA-ILD patients, 133 RA patients, and 616 clinically healthy subjects (CHS). Allelic discrimination was performed in eight SNVs using qPCR, four in PADI2 and four in PADI4. The ELISA technique determined PAD2 and PAD4 levels in serum and bronchoalveolar lavage (BAL) samples, and the population structure was evaluated using 14 informative ancestry markers. Results: The rs1005753-GG (OR = 4.9) in PADI2 and rs11203366-AA (OR = 3.08), rs11203367-GG (OR = 2.4) in PADI4 are associated with genetic susceptibility to RA-ILD as well as the ACTC haplotype (OR = 2.64). In addition, the PAD4 protein is increased in RA-ILD individuals harboring the minor allele homozygous genotype in PADI4 SNVs. Moreover, rs1748033 in PADI4, rs2057094, and rs2076615 in PADI2 are associated with RA susceptibility. In conclusion, in RA patients, single nucleotide variants in PADI4 and PADI2 are associated with ILD susceptibility. The rs1748033 in PADI4 and two different SNVs in PADI2 are associated with RA development but not ILD. PAD4 serum levels are increased in RA-ILD patients.

Citrullinated fibrinogen-SAAs complex causes vascular metastagenesis

Primary tumor cells metastasize to a distant preferred organ. However, the most decisive host factors that determine the precise locations of metastases in cancer patients remain unknown. We have demonstrated that post-translational citrullination of fibrinogen creates a metastatic niche in the vulnerable spots. Pulmonary endothelial cells mediate the citrullination of fibrinogen, changing its conformation, surface charge, and binding properties with serum amyloid A proteins (SAAs), to make it a host tissue-derived metastatic pathogen. The human-specific SAAs-citrullinated fibrinogen (CitFbg) complex recruits cancer cells to form a protein-metastatic cell aggregation in humanized SAA cluster mice. Furthermore, a CitFbg peptide works as a competitive inhibitor to block the homing of metastatic cells into the SAAs-CitFbg sites. The potential metastatic sites in the lungs of patients are clearly visualized by our specific antibody for CitFbg. Thus, CitFbg deposition displays metastatic risks for cancer patients, and the citrullinated peptide is a new type of metastasis inhibitor.

Association of rheumatoid arthritis with bronchial asthma and asthma-related comorbidities: A population-based national surveillance study

Background

The aim of this study was to investigate the impact of rheumatoid arthritis (RA) on the prevalence of bronchial asthma and asthma-related comorbidities. We also aimed to identify the influence of RA on interrelationship between asthma and asthma-related comorbidities.

Methods

From the Korean National Health and Nutrition Examination Survey, participants >40 years of age who completed questionnaires and spirometry tests were enrolled. Patient data on RA, asthma, allergic rhinitis, atopic dermatitis, chronic obstructive pulmonary disease (COPD), sinusitis, otitis media, and body mass index (BMI) were collected. Logistic regression and network analyses were performed.

Results

A total of 14,272 subjects were enrolled, among which, 334 (2.4%) had RA. RA was significantly associated with asthma (OR 2.32; 95% CI 1.51–3.57), allergic rhinitis (OR 1.51; 95% CI 1.08–2.10), and sinusitis (OR 1.64; 95% CI 1.08–2.50). The network analysis of total patients revealed a positive interrelationship between asthma and allergic rhinitis, sinusitis, otitis media, atopic dermatitis, BMI, and RA. The interrelationship between asthma and sinusitis was stronger in the RA group. Of note, the relationship between asthma and BMI was distinctively found only in the RA group (r = 0.214, P < 0.05). In patients with asthma, the prevalence of obesity was 64% in the presence of RA, and 40% in the absence of RA (P = 0.034).

Conclusion

This study supports the positive association of RA with asthma, allergic rhinitis, and sinusitis. Our analysis suggests a notable interrelationship between the presence of asthma and higher BMI values in patients with RA, indicating that asthma is more obesity-related in patients with RA.

Impact of cigarette smoking on rheumatoid arthritis-associated lung diseases: a retrospective case control study on clinical and radiological features and prognosis

Our study aimed to investigate the clinical and radiological features and prognosis of male smoker patients with rheumatoid arthritis (RA). We consecutively enrolled male inpatients with RA who received chest HRCT during hospitalization in Peking University Third Hospital from Jan 1st, 2012 to August 1st, 2021. 154 male patients with RA were eligible for analysis, of whom 76.6% (n = 118) were current smokers or had a history of cigarette smoking. Compared to never-smokers, smoker patients had more respiratory symptoms, including cough (31.4% vs 5.6%, p = 0.002) and sputum production (26.3% vs 2.8%, p = 0.002), and a higher positive rate of rheumatoid factor (RF) (77.6% vs 58.8%, p = 0.030). A higher percentage of smoker patients showed emphysema (45.8% vs 16.7%, p = 0.002) and signs of lung fibrosis (51/54, 94.4% vs 7/13, 53.8%, p < 0.001) in those with interstitial lung disease (ILD, n = 67) on chest HRCT. The overall survival rate was different between smoker and never-smoker patients (p = 0.031), but instead of cigarette smoking, lung fibrosis on HRCT was the risk factor for survival of our patients. In conclusion, male patients with RA who were current smokers or had a history of cigarette smoking presented more respiratory symptoms and a higher positive rate of RF. They also showed more emphysema and signs of lung fibrosis on chest HRCT. Cigarette smoking impacted on the overall survival as a confounding factor in this cohort of male patients with RA.

Mechanistic study of salidroside on ovalbumin-induced asthmatic model mice based on untargeted metabolomics analysis

Salidroside (SAL) is a natural component derived from Rhodiola rosea and is well known for its wide range of biological activities such as its anti-inflammatory and anti-oxidative properties. However, its effects and mechanisms of action related to asthma have not been well explored yet. Recent studies have found that changes in host metabolism are closely related to the progression of asthma. Many natural components can ameliorate asthma by affecting host metabolism. The use of untargeted metabolomics can allow for a better understanding of the metabolic regulatory mechanisms of herbs on asthma. This study aimed to demonstrate the anti-asthmatic effects and metabolic regulatory mechanisms of SAL. In this study, the therapeutic effects of SAL on asthmatic mice were tested at first. Secondly, the effects of SAL on the airway inflammatory reaction, oxidative stress, and airway remodeling were investigated. Finally, untargeted metabolomics analysis was used to explore the influence of SAL on lung metabolites. The results showed that SAL had a significant therapeutic effect on asthmatic model mice. Moreover, SAL treatment lowered interleukin (IL)-4, IL-5, and IL-13 levels but elevated interferon gamma (IFN-γ) and IL-10 levels in bronchoalveolar lavage fluid (BALF). Additionally, it also increased superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities and decreased methane dicarboxylic aldehyde (MDA) levels in the lungs. Besides, SAL-treated mice showed decreased expression of smooth muscle actin (α-SMA), matrix metallopeptidase 2 (MMP2), matrix metallopeptidase 9 (MMP9), and transforming growth factor-beta 1 (TGF-β1) in the lung. Untargeted metabolomics analysis showed 31 metabolites in the lungs that were influenced by SAL. These metabolites were related to pyrimidine metabolism, steroid hormone biosynthesis, and tricarboxylic acid (TCA) cycle. In conclusion, SAL treatment can reduce the inflammatory response, oxidative stress, and airway remodeling in asthmatic model mice. The mechanism of SAL in the treatment of asthma may be related to the regulation of pyrimidine metabolism, steroid hormone biosynthesis, and the TCA cycle. Further studies can be carried out using targeted metabolomics and in vitro models to deeply elucidate the anti-inflammatory and anti-oxidative mechanisms of SAL on asthma based on regulating metabolism.

Mining the pathogenesis of rheumatoid arthritis, the leading role of the environment

The environment plays a crucial role in the pathogenesis of various diseases, including rheumatic musculoskeletal diseases (RMDs). Chronic exposure to air pollution has been associated with a number of detrimental effects on the immune system, including direct activation of autoimmunity and autoantibodies production. Rheumatoid arthritis (RA) is a paradigmatic example of the link between environmental stimuli and development of autoimmunity. Recent evidence has confirmed such association and provided further indication of the strict relationship between the lungs and the synovial tissue. Hard rock mining and chronic exposure to airborne fine particulate matter have been associated with higher risk of developing RA. In addition, new evidence showed a peculiar association between acute exposure to toxic inhalants and risk of RA flare. In conclusion, the environment is the straw that breaks the camel's back, unfortunately the "straws" are rapidly accumulating, and their burden is projected to increase accordingly.

Host and bacterial factors linking periodontitis and rheumatoid arthritis

Observations from numerous clinical, epidemiological and serological studies link periodontitis with severity and progression of rheumatoid arthritis. The strong association is observed despite totally different aetiology of these two diseases, periodontitis being driven by dysbiotic microbial flora on the tooth surface below the gum line, while rheumatoid arthritis being the autoimmune disease powered by anti-citrullinated protein antibodies (ACPAs). Here we discuss genetic and environmental risk factors underlying development of both diseases with special emphasis on bacteria implicated in pathogenicity of periodontitis. Individual periodontal pathogens and their virulence factors are argued as potentially contributing to putative causative link between periodontal infection and initiation of a chain of events leading to breakdown of immunotolerance and development of ACPAs. In this respect peptidylarginine deiminase, an enzyme unique among prokaryotes for Porphyromonas gingivalis, is elaborated as a potential mechanistic link between this major periodontal pathogen and initiation of rheumatoid arthritis development.

Disease mechanisms in preclinical rheumatoid arthritis: A narrative review

In the last decades, the concept of preclinical rheumatoid arthritis (RA) has become established. In fact, the discovery that disease mechanisms start years before the onset of clinical RA has been one of the major recent insights in the understanding of RA pathogenesis. In accordance with the complex nature of the disease, preclinical events extend over several sequential phases. In a genetically predisposed host, environmental factors will further increase susceptibility for incident RA. In the initial steps of preclinical disease, immune disturbance mechanisms take place outside the joint compartment, namely in mucosal surfaces, such as the lung, gums or gut. Herein, the persistent immunologic response to altered antigens will lead to breach of tolerance and trigger autoimmunity. In a second phase, the immune response matures and is amplified at a systemic level, with epitope spreading and widening of the autoantibody repertoire. Finally, the synovial and bone compartment are targeted by specific autoantibodies against modified antigens, initiating a local inflammatory response that will eventually culminate in clinically evident synovitis. In this review, we discuss the elaborate disease mechanisms in place during preclinical RA, providing a broad perspective in the light of current evidence.

Role of Cellular Metabolism in the Formation of Neutrophil Extracellular Traps in Airway Diseases

Neutrophil extracellular traps (NETs) are a recently described mechanism of neutrophils that play an important role in health and disease. NETs are an innate defense mechanism that participate in clearance of pathogens, but they may also cause collateral damage in unrelated host tissues. Neutrophil dysregulation and NETosis occur in multiple lung diseases, such as pathogen-induced acute lung injury, pneumonia, chronic obstructive pulmonary disease (COPD), severe asthma, cystic fibrosis, and recently, the novel coronavirus SARS-CoV-2. More recently, research into immunometabolism has surged due to the possibility of reprogramming metabolism in order to modulate immune functions. The present review analyzes the different metabolic pathways associated with NETs formation, and how these impact on pathologies of the airways.

Pathophysiological Role of Vimentin Intermediate Filaments in Lung Diseases

Vimentin intermediate filaments, a type III intermediate filament, are among the most widely studied IFs and are found abundantly in mesenchymal cells. Vimentin intermediate filaments localize primarily in the cytoplasm but can also be found on the cell surface and extracellular space. The cytoplasmic vimentin is well-recognized for its role in providing mechanical strength and regulating cell migration, adhesion, and division. The post-translationally modified forms of Vimentin intermediate filaments have several implications in host-pathogen interactions, cancers, and non-malignant lung diseases. This review will analyze the role of vimentin beyond just the epithelial to mesenchymal transition (EMT) marker highlighting its role as a regulator of host-pathogen interactions and signaling pathways for the pathophysiology of various lung diseases. In addition, we will also examine the clinically relevant anti-vimentin compounds and antibodies that could potentially interfere with the pathogenic role of Vimentin intermediate filaments in lung disease.

Fibrinogen mediates cadmium-induced macrophage activation and serves as a predictor of cadmium exposure in chronic obstructive pulmonary disease

The etiologies of chronic obstructive pulmonary disease (COPD) remain unclear. Cadmium (Cd) causes both pulmonary fibrosis and emphysema; however, the predictors for Cd exposure and the mechanisms by which Cd causes COPD remain unknown. We demonstrated that Cd burden was increased in lung tissue from subjects with COPD and this was associated with cigarette smoking. Fibrinogen levels increased markedly in lung tissue of patients with smoked COPD compared with never-smokers and control subjects. Fibrinogen concentration also correlated positively with lung Cd load, but inversely with the predicted % of FEV1 and FEV1/FVC. Cd enhanced the secretion of fibrinogen in a cdc2-dependent manner, whereas fibrinogen further mediated Cd-induced peptidylarginine deiminase 2 (PAD2)-dependent macrophage activation. Using lung fibroblasts from CdCl2-treated Toll-like receptor 4 (TLR4) wild-type and mutant mice, we demonstrated that fibrinogen enhanced Cd-induced TLR4-dependent collagen synthesis and cytokine/chemokine production. We further showed that fibrinogen complexed with connective tissue growth factor (CTGF), which in turn promoted the synthesis of plasminogen activator inhibitor-2 (PAI-2) and fibrinogen and inhibited fibrinolysis in Cd-treated mice. The amounts of fibrinogen were increased in the bronchoalveolar lavage fluid (BALF) of Cd-exposed mice. Positive correlations were observed between fibrinogen with hydroxyproline. Our data suggest that fibrinogen is involved in Cd-induced macrophage activation and increases in fibrinogen in patients with COPD may be used as a marker of Cd exposure and predict disease progression.

Association between social deprivation and disease activity in rheumatoid arthritis: a systematic literature review

Physical and mental illnesses are driven by ethnicity, social, environmental and economic determinants. Novel theoretical frameworks in rheumatoid arthritis (RA) focus on links and adverse interactions between and within biological and social factors. This review aimed to summarise associations between socioeconomic status (SES) and RA disease activity, and implications for future research. Articles studying the association between SES and RA disease activity were identified, from 1946 until March 2021. The research question was: Is there an association between social deprivation and disease activity in people with RA? Articles meeting inclusion criteria were examined by one author, with 10% screened at abstract and full paper stage by a second author. Disagreements were resolved with input from a third reviewer. Information was extracted on definition/measure of SES, ethnicity, education, employment, comorbidities, disease activity and presence/absence of association between SES and disease activity. Initially, 1750 articles were identified, with 30 articles ultimately included. SES definition varied markedly-10 articles used a formal scale and most used educational attainment as a proxy. Most studies controlled for lifestyle factors including smoking and body mass index, and comorbidities. Twenty-five articles concluded an association between SES and RA disease activity; two were unclear; three found no association. We have demonstrated the association between low SES and worse RA outcomes. There is a need for further research into the mechanisms underpinning this, including application of mixed-methods methodology and consideration of syndemic frameworks to understand bio-bio and bio-social interactions, to examine disease drivers and outcomes holistically.

Serum rheumatoid factor IgA, anti-citrullinated peptide antibodies with secretory components, and anti-carbamylated protein antibodies associate with interstitial lung disease in rheumatoid arthritis

Objective

Rheumatoid arthritis (RA) is often complicated with chronic lung diseases (CLD), including interstitial lung disease (ILD) and airway disease, which occur as extra-articular manifestations. CLD in RA have been associated with the production of rheumatoid factor (RF), anti-citrullinated peptide antibody (ACPA), or anti-carbamylated protein (CarP) antibody. However, few validation studies have been performed thus far. In the present study, we investigated the association of RF, ACPA, and anti-CarP antibodies with RA complicated with CLD.

Methods

Sera from RA patients with or without CLD were collected. The levels of serum RF, RF immunoglobulin A (IgA), ACPA IgG, ACPA IgA, and ACPA secretory component (SC) were measured using enzyme-linked immunosorbent assay.

Results

The comparison of RA patients with and without CLD showed that RF IgA was associated with ILD (mean ± standard deviation: 206.6 ± 400.5 vs. 95.0 ± 523.1 U/ml, respectively, P = 1.13 × 10^− 8), particularly usual interstitial pneumonia (UIP) (263.5 ± 502.0 U/ml, P = 1.00 × 10^− 7). ACPA SC was associated with RA complicated with ILD (mean ± standard deviation: 8.6 ± 25.1 vs. 2.3 ± 3.4 U/ml, respectively, P = 0.0003), particularly nonspecific interstitial pneumonia (NSIP) (10.7 ± 31.5 U/ml, P = 0.0017). Anti-CarP antibodies were associated with RA complicated with ILD (0.042 ± 0.285 vs. 0.003 ± 0.011 U/ml, respectively, P = 1.04X10^− 11).

Conclusion

RF IgA and ACPA SC in RA were associated with UIP and NSIP, respectively, suggesting different specificities in patients with RA. Anti-CarP antibodies were associated with ILD in RA. These results may help elucidate the different pathogeneses of UIP and NSIP in RA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-04985-0.

Screening for preclinical parenchymal lung disease in rheumatoid arthritis

OBJECTIVES

Pulmonary disease is a common extraarticular manifestation of RA associated with increased morbidity and mortality. No current strategies exist for screening this at-risk population for parenchymal lung disease, including emphysema and interstitial lung disease (ILD).

METHODS

RA patients without a diagnosis of ILD or chronic obstructive pulmonary disease underwent prospective and comprehensive clinical, laboratory, functional and radiological evaluations. High resolution CT (HRCT) scans were scored for preclinical emphysema and preclinical ILD and evaluated for other abnormalities.

RESULTS

Pulmonary imaging and/or functional abnormalities were identified in 78 (74%) of 106 subjects; 45% had preclinical parenchymal lung disease. These individuals were older with lower diffusion capacity but had similar smoking histories compared with no disease. Preclinical emphysema (36%), the most commonly detected abnormality, was associated with older age, higher anti-cyclic citrullinated peptide antibody titres and diffusion abnormalities. A significant proportion of preclinical emphysema occurred among never smokers (47%) with a predominantly panlobular pattern. Preclinical ILD (15%) was not associated with clinical, laboratory or functional measures.

CONCLUSION

We identified a high prevalence of undiagnosed preclinical parenchymal lung disease in RA driven primarily by isolated emphysema, suggesting that it may be a prevalent and previously unrecognized pulmonary manifestation of RA, even among never smokers. As clinical, laboratory and functional evaluations did not adequately identify preclinical parenchymal abnormalities, HRCT may be the most effective screening modality currently available for patients with RA.

Immunomodulation by heavy metals as a contributing factor to inflammatory diseases and autoimmune reactions: Cadmium as an example

Cadmium (Cd) represents a unique hazard because of the long biological half-life in humans (20-30 years). This metal accumulates in organs causing a continuum of responses, with organ disease/failure as extreme outcome. Some of the cellular and molecular alterations in target tissues can be related to immune-modulating potential of Cd. This metal may cause adverse responses in which components of the immune system function as both mediators and effectors of Cd tissue toxicity, which, in combination with Cd-induced alterations in homeostatic reparative activities may contribute to tissue dysfunction. In this work, current knowledge concerning inflammatory/autoimmune disease manifestations found to be related with cadmium exposure are summarized. Along with epidemiological evidence, animal and in vitro data are presented, with focus on cellular and molecular immune mechanisms potentially relevant for the disease susceptibility, disease promotion, or facilitating development of pre-existing pathologies.

Association of sinusitis and upper respiratory tract diseases with incident rheumatoid arthritis: A case-control study

OBJECTIVE

We aimed to determine whether specific respiratory tract diseases are associated with increased rheumatoid arthritis (RA) risk.

METHODS

This case-control study within the Mass General Brigham Biobank matched newly diagnosed RA cases to three controls on age, sex, and electronic health record history. We identified RA using a validated algorithm and confirmed by medical record review. Respiratory tract disease exposure required one inpatient or two outpatient codes at least two years before index date of RA clinical diagnosis or matched date. Logistic regression models calculated odds ratios (OR) for RA with 95% confidence intervals (CI), adjusting for confounders. We then stratified by serostatus ("seropositive" was positive rheumatoid factor and/or anti-citrullinated protein antibodies) and smoking.

RESULTS

We identified 741 RA cases and 2,223 controls (both median age 55, 76% female). Acute sinusitis (OR 1.61, 95% CI:1.05,2.45), chronic sinusitis (OR 2.16, 95% CI:1.39,3.35), and asthma (OR 1.39, 95% CI:1.03,1.87) were associated with increased risk of RA. Acute respiratory tract disease burden during the pre-index exposure period was also associated with increased RA risk (OR 1.30 per 10 codes, 95% CI:1.08,1.55). Acute pharyngitis was associated with seronegative (OR 1.68, 95% CI:1.02,2.74) but not seropositive RA; chronic rhinitis/pharyngitis was associated with seropositive (OR 2.46, 95% CI:1.01,5.99) but not seronegative RA. Respiratory tract diseases tended towards higher associations in smokers, especially >10 packyears (OR 1.52, 95% CI:1.02,2.27; p=0.10 for interaction).

CONCLUSION

Acute/chronic sinusitis and pharyngitis and acute respiratory burden increased RA risk. The mucosal paradigm of RA pathogenesis may involve the upper respiratory tract.

Crosstalk between B cells and neutrophils in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic, systemic autoimmune disease without known cure that primarily affects synovial joints. RA has a prevalence of approximately 1% of the population worldwide. A vicious circle between two critical immune cell types, B cells and neutrophils, develops and promotes disease. Pathogenic anti‐citrullinated protein antibodies (ACPA) directed against a range of citrullinated epitopes are abundant in both plasma and synovial fluid of RA patients. In addition to stimulating numerous cell types, ACPA and other autoantibodies, notably rheumatoid factor, form immune complexes (ICs) that potently activate neutrophils. Attracted to the synovium by abundant chemokines, neutrophils are locally stimulated by ICs. They generate cytokines and release cytotoxic compounds including neutrophil extracellular traps (NETs), strands of decondensed chromatin decorated with citrullinated histones and granule‐derived neutrophil proteins, which are particularly abundant in the synovial fluid. In this way, neutrophils generate citrullinated epitopes and release peptidylarginine deiminase (PAD) enzymes capable of citrullinating extracellular proteins in the rheumatic joint, contributing to renewed ACPA generation. This review article focusses on the central function of citrullination, a post‐translational modification of arginine residues in RA. The discussion includes ACPA and related autoantibodies, somatic hypermutation‐mediated escape from negative selection by autoreactive B cells, promotion of the dominance of citrullinated antigens by genetic and lifestyle susceptibility factors and the vicious circle between ACPA‐producing pathogenic B cells and NET‐producing neutrophils in RA.

Citrullinated vimentin mediates development and progression of lung fibrosis

The mechanisms by which environmental exposures contribute to the pathogenesis of lung fibrosis are unclear. Here, we demonstrate an increase in cadmium (Cd) and carbon black (CB), common components of cigarette smoke (CS) and environmental particulate matter (PM), in lung tissue from subjects with idiopathic pulmonary fibrosis (IPF). Cd concentrations were directly proportional to citrullinated vimentin (Cit-Vim) amounts in lung tissue of subjects with IPF. Cit-Vim amounts were higher in subjects with IPF, especially smokers, which correlated with lung function and were associated with disease manifestations. Cd/CB induced the secretion of Cit-Vim in an Akt1- and peptidylarginine deiminase 2 (PAD2)-dependent manner. Cit-Vim mediated fibroblast invasion in a 3D ex vivo model of human pulmospheres that resulted in higher expression of CD26, collagen, and α-SMA. Cit-Vim activated NF-κB in a TLR4-dependent fashion and induced the production of active TGF-β1, CTGF, and IL-8 along with higher surface expression of TLR4 in lung fibroblasts. To corroborate ex vivo findings, mice treated with Cit-Vim, but not Vim, independently developed a similar pattern of fibrotic tissue remodeling, which was TLR4 dependent. Moreover, wild-type mice, but not PAD2^-/- and TLR4 mutant (MUT) mice, exposed to Cd/CB generated high amounts of Cit-Vim, in both plasma and bronchoalveolar lavage fluid, and developed lung fibrosis in a stereotypic manner. Together, these studies support a role for Cit-Vim as a damage-associated molecular pattern molecule (DAMP) that is generated by lung macrophages in response to environmental Cd/CB exposure. Furthermore, PAD2 might represent a promising target to attenuate Cd/CB-induced fibrosis.

To Trap a Pathogen: Neutrophil Extracellular Traps and Their Role in Mucosal Epithelial and Skin Diseases

Neutrophils are the most abundant circulating innate immune cells and comprise the first immune defense line, as they are the most rapidly recruited cells at sites of infection or inflammation. Their main microbicidal mechanisms are degranulation, phagocytosis, cytokine secretion and the formation of extracellular traps. Neutrophil extracellular traps (NETs) are a microbicidal mechanism that involves neutrophil death. Since their discovery, in vitro and in vivo neutrophils have been challenged with a range of stimuli capable of inducing or inhibiting NET formation, with the objective to understand its function and regulation in health and disease. These networks composed of DNA and granular components are capable of immobilizing and killing pathogens. They comprise enzymes such as myeloperoxidase, elastase, cathepsin G, acid hydrolases and cationic peptides, all with antimicrobial and antifungal activity. Therefore, the excessive formation of NETs can also lead to tissue damage and promote local and systemic inflammation. Based on this concept, in this review, we focus on the role of NETs in different infectious and inflammatory diseases of the mucosal epithelia and skin.

Antigen-driven autoantibody production in lungs of interstitial lung disease with autoimmune disease

Interstitial lung disease (ILD) sometimes becomes a life-threatening complication of systemic autoimmune diseases; however, little is known about the immune response in lung lesions. We aimed to investigate humoural immunity in ILD associated with rheumatoid arthritis (RA), sjögren's syndrome (SjS), and mixed connective tissue disease (MCTD), using bronchoalveolar fluid (BALF) and serum samples from 15 patients with autoimmune disease associated-ILD. We first showed that BALF contained higher titers of disease-related autoantibodies than serum, suggesting the possibility of autoantibody production in lungs. Next, we produced 326 monoclonal antibodies from antibody-secreting cells in BALF, and the reactivity and their revertants, in which somatic hypermutations were reverted to germline, were analyzed. Among 123 antibodies from RA-ILD, 16 disease-related antibodies (anti-modified protein antibodies and rheumatoid factors) were identified, of which one antibody had both properties. The revertant antibodies changed their target modification in a complicated manner, suggesting that the antibodies were selected against various modifications in lungs. Among 146 antibodies from SjS-ILD and/or MCTD-ILD, seven anti-SSA/Ro60 antibodies and 15 anti-RNP antibodies were identified. Some of the anti-RNP antibodies recognized multiple RNP constituent proteins simultaneously, indicating that epitope spreading may progress in lungs. Our results revealed the existence of an active autoimmunity in the lungs of autoimmune disease associated-ILD.

Protein expression profiling suggests relevance of noncanonical pathways in isolated pulmonary embolism

Patients with isolated pulmonary embolism (PE) have a distinct clinical profile from those with deep vein thrombosis (DVT)-associated PE, with more pulmonary conditions and atherosclerosis. These findings suggest a distinct molecular pathophysiology and the potential involvement of alternative pathways in isolated PE. To test this hypothesis, data from 532 individuals from the Genotyping and Molecular Phenotyping of Venous ThromboEmbolism Project, a multicenter prospective cohort study with extensive biobanking, were analyzed. Targeted, high-throughput proteomics, machine learning, and bioinformatic methods were applied to contrast the acute-phase plasma proteomes of isolated PE patients (n = 96) against those of patients with DVT-associated PE (n = 276) or isolated DVT (n = 160). This resulted in the identification of shared molecular processes between PE phenotypes, as well as an isolated PE-specific protein signature. Shared processes included upregulation of inflammation, response to oxidative stress, and the loss of pulmonary surfactant. The isolated PE-specific signature consisted of 5 proteins: interferon-γ, glial cell line-derived neurotrophic growth factor, polypeptide N-acetylgalactosaminyltransferase 3, peptidyl arginine deiminase type-2, and interleukin-15 receptor subunit α. These proteins were orthogonally validated using cis protein quantitative trait loci. External replication in an independent population-based cohort (n = 5778) further validated the proteomic results and showed that they were prognostic for incident primary isolated PE in individuals without history of VTE (median time to event: 2.9 years; interquartile range: 1.6-4.2 years), supporting their possible involvement in the early pathogenesis. This study has identified molecular overlaps and differences between VTE phenotypes. In particular, the results implicate noncanonical pathways more commonly associated with respiratory and atherosclerotic disease in the acute pathophysiology of isolated PE.

Neutrophils Modulate Fibrogenesis in Chronic Pulmonary Diseases

Chronic inflammatory pulmonary diseases are characterized by recurrent and persistent inflammation of the airways, commonly associated with poor clinical outcomes. Although their etiologies vary tremendously, airway neutrophilia is a common feature of these diseases. Neutrophils, as vital regulators linking innate and adaptive immune systems, are a double-edged sword in the immune response of the lung involving mechanisms such as phagocytosis, degranulation, neutrophil extracellular trap formation, exosome secretion, release of cytokines and chemokines, and autophagy. Although neutrophils serve as strong defenders against extracellular pathogens, neutrophils and their components can trigger various cascades leading to inflammation and fibrogenesis. Here, we review current studies to elucidate the versatile roles of neutrophils in chronic pulmonary inflammatory diseases and describe the common pathogenesis of these diseases. This may provide new insights into therapeutic strategies for chronic lung diseases.

Elevated Anti-Citrullinated Protein Antibodies Prior to Rheumatoid Arthritis Diagnosis and Risks for Chronic Obstructive Pulmonary Disease or Asthma

OBJECTIVE

To investigate elevation of anti-citrullinated protein antibodies (ACPAs) before diagnosis of rheumatoid arthritis (RA) and risks for chronic obstructive pulmonary disease (COPD) or asthma.

METHODS

We performed a matched cohort study nested within the Nurses' Health Studies among women who donated blood. Women with incident RA after blood draw (self-reported, then confirmed by medical records) were each matched to 3 controls by age, cohort, year, and menopausal factors. Pre-RA ACPA positivity was defined as >99th percentile of control distribution by a research assay or by cyclic citrullinated peptide in a subset. Incident COPD and asthma after index date (date of blood draw) were identified by questionnaires. Cox regression estimated hazard ratios (HRs) for incident COPD or asthma (in separate analyses) associated with pre-RA, pre-RA ACPA+, or pre-RA ACPA- phenotypes each compared to their matched non-RA controls.

RESULTS

We analyzed 283 women who were pre-RA and 842 controls; blood was donated a mean ± SD of 9.7 ± 5.8 years before RA diagnosis. Fifty-nine women (20.8%) were pre-RA ACPA+. There were 107 cases of incident COPD and 105 incident asthma cases during 21,489 person-years of follow-up. Pre-RA ACPA+ was associated with increased COPD risk (HR 3.04 [95% confidence interval (95% CI) 1.33-7.00]) after adjusting for covariates including smoking pack-years. Pre-RA ACPA+ had an HR for asthma of 1.74 (multivariable 95% CI 0.72-4.24), similar to the risk of asthma for pre-RA ACPA- (HR 1.65 [95% CI 1.11-2.46]).

CONCLUSION

Women with elevated ACPA before RA diagnosis had increased risk for developing COPD compared to controls. Women who later developed RA were more likely to develop asthma than controls, regardless of pre-RA ACPA status.

Citrullinated and homocitrullinated low- density lipoprotein in rheumatoid arthritis

Objective: Antibodies to citrullinated and homocitrullinated (also known as carbamylated) proteins, specific for rheumatoid arthritis (RA), are associated with cardiovascular disease (CVD). Immune complexes containing these proteins have been identified in the atherosclerotic plaque of CVD patients. In mice, homocitrullinated low-density lipoprotein (HomoCitLDL) promotes foam cell formation, which is critical in the pathogenesis of atherosclerosis. We aimed to investigate the atherogenic potential of HomoCitLDL and citrullinated low-density lipoprotein (CitLDL) in RA.Method: Human LDL was homocitrullinated in potassium cyanate and citrullinated by rabbit skeletal muscle peptidyl arginine deiminase-2. The modifications were confirmed by mass spectrometry. Primary human monoctyes from healthy subjects (N = 8) were differentiated to macrophages using macrophage colony-stimulating factor and incubated with modified LDL. Foam cells were visualized using Oil Red O staining. Serum from RA patients (N = 101) and controls (N = 32) was tested for immunoglobulin G antibodies to modified LDL using enzyme-linked immunosorbent assay.Results: HomoCitLDL and CitLDL strongly induced foam cell production (> 90%) versus unmodified LDL (11%) (p < 0.0001). The characteristics of the RA subjects were: 73% females, median age 60 [interquartile range (IQR) 17] years and disease duration 7.5 (IQR 13) years; 11% had a prior major cardiovascular event, 66% were ever smokers, 32% had hypertension, 33% dyslipidaemia, and 14% diabetes. Antibodies to HomoCitLDL were detected in 18% of RA patients; they were significantly associated with dyslipidaemia [odds ratio (OR) 3.86; 95% confidence interval (CI) 1.22, 12.17] and antibodies to other homocitrullinated antigens (OR 10.61; 95% CI 1.31, 86.11).Conclusions: HomoCitLDL and CitLDL have atherogenic properties in vitro. Antibody responses to HomoCitLDL, but not CitLDL, were detected in RA patients.

Association of Agricultural, Occupational, and Military Inhalants With Autoantibodies and Disease Features in US Veterans With Rheumatoid Arthritis

OBJECTIVE

To determine the association of inhalant exposures with rheumatoid arthritis (RA)-related autoantibodies and severity in US veterans.

METHODS

Participants in the Veterans Affairs Rheumatoid Arthritis (VARA) registry were mailed surveys assessing occupational, agricultural, and military inhalant exposures. Demographic characteristics, disease activity, functional status, and extraarticular features were obtained from the VARA registry, while HLA-DRB1 shared epitope (SE) status, anti-cyclic citrullinated peptide (anti-CCP) antibodies, and rheumatoid factor (RF) were measured using banked DNA/serum from enrollment. Associations between inhalant exposures and RA-related factors (autoantibodies, severity, and extraarticular features) were assessed using multivariable linear and logistic regression models adjusted for age, sex, race, and tobacco use and stratified by SE status. Adjusted odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated.

RESULTS

Questionnaires were returned by 797 of 1,566 participants (50.9%). Survey respondents were older, more often White or male, and less frequently smokers, and had lower disease activity compared to nonrespondents. Anti-CCP positivity was more common among veterans exposed to burn pits (OR 1.66 [95% CI 1.02, 2.69]) and military waste disposal (OR 1.74 [95% CI 1.04, 2.93]) independent of other factors. Among participants who were positive for SE alleles, burn pit exposure (OR 5.69 [95% CI 2.73, 11.87]) and military waste disposal exposure (OR 5.05 [95% CI 2.42, 10.54]) were numerically more strongly associated with anti-CCP positivity. Several inhalant exposures were associated with the presence of chronic lung disease, but not with the presence of RF or the level of disease activity.

CONCLUSION

Military burn pit exposure and military waste disposal exposure were independently associated with the presence of anti-CCP antibodies in RA patients. These findings are consistent with emerging evidence that various inhalant exposures influence autoantibody expression and RA risk.

Orchestration of Neutrophil Extracellular Traps (Nets), a Unique Innate Immune Function during Chronic Obstructive Pulmonary Disease (COPD) Development

Morbidity, mortality and economic burden caused by chronic obstructive pulmonary disease (COPD) is a significant global concern. Surprisingly, COPD is already the third leading cause of death worldwide, something that WHO had not predicted to occur until 2030. It is characterized by persistent respiratory symptoms and airway limitation due to airway and/or alveolar abnormalities usually caused by significant exposure to noxious particles of gases. Neutrophil is one of the key infiltrated innate immune cells in the lung during the pathogenesis of COPD. Neutrophils during pathogenic attack or injury decide to undergo for a suicidal death by releasing decondensed chromatin entangled with antimicrobial peptides to trap and ensnare pathogens. Casting neutrophil extracellular traps (NETs) has been widely demonstrated to be an effective mechanism against invading microorganisms thus controlling overwhelming infections. However, aberrant and massive NETs formation has been reported in several pulmonary diseases, including chronic obstructive pulmonary disease. Moreover, NETs can directly induce epithelial and endothelial cell death resulting in impairing pulmonary function and accelerating the progression of the disease. Therefore, understanding the regulatory mechanism of NET formation is the need of the hour in order to use NETs for beneficial purpose and controlling their involvement in disease exacerbation. For example, DNA neutralization of NET proteins using protease inhibitors and disintegration with recombinant human DNase would be helpful in controlling excess NETs. Targeting CXC chemokine receptor 2 (CXCR2) would also reduce neutrophilic inflammation, mucus production and neutrophil-proteinase mediated tissue destruction in lung. In this review, we discuss the interplay of NETs in the development and pathophysiology of COPD and how these NETs associated therapies could be leveraged to disrupt NETopathic inflammation as observed in COPD, for better management of the disease.

Respiratory Diseases as Risk Factors for Seropositive and Seronegative Rheumatoid Arthritis and in Relation to Smoking

OBJECTIVE

The link and interplay between different airway exposures and rheumatoid arthritis (RA) risk are unclear. This study was undertaken to determine whether respiratory disease is associated with development of RA, and specifically to examine this relationship by RA serostatus and smoking exposure.

METHODS

Using data from the Epidemiological Investigation of Rheumatoid Arthritis study, this analysis included 1,631 incident RA cases and 3,283 matched controls recruited from 2006 to 2016. Linking these individuals to the National Patient Register provided information on past acute or chronic, upper or lower respiratory disease diagnoses. For each disease group, we estimated adjusted odds ratios (OR_adj ) with 95% confidence intervals (95% CI) for RA, using logistic regression models adjusted for age, sex, residential area, body mass index, and education both overall and stratified by anti-citrullinated protein antibody (ACPA)/rheumatoid factor (RF) status and by smoking status.

RESULTS

Respiratory disease diagnoses were associated with risk of RA, with an OR_adj of 1.2 for acute upper respiratory disease (95% CI 0.8-1.7), 1.4 for chronic upper respiratory disease (95% CI 1.1-1.9), 2.4 for acute lower respiratory disease (95% CI 1.5-3.6), and 1.6 for chronic lower respiratory disease (95% CI 1.5-3.6). These associations were present irrespective of RF or ACPA status, though the association was somewhat stronger for ACPA/RF-positive than ACPA/RF-negative RA. The association between any respiratory disease and RA was stronger for nonsmokers (OR_adj 2.1 [95% CI 1.5-2.9]) than for smokers (OR_adj 1.2 [95% CI 0.9-1.5]).

CONCLUSION

Respiratory diseases increase the risk for both seropositive and seronegative RA, but only among nonsmokers. These findings raise the hypothesis that smoking and airway disease are associated with RA development through partly different mechanisms.

HLA-DRB1 Alleles are Associated With COPD in a Latin American Admixed Population

INTRODUCTION

While the molecular mechanisms of COPD pathogenesis remain obscure, there is mounting evidence supporting a key role for autoimmunity. Although human leukocyte antigens (HLA) alleles have been repeatedly associated with autoimmune processes, the relation between HLA and COPD remains largely unexplored, especially in Latin American (LA) populations. Consequently, this study aimed to investigate the presence of HLA class I and II alleles in COPD patients and healthy controls in a LA population with admixed ancestry.

METHODS

COPD patients (n=214) and age-matched controls (n=193) were genotyped using the Illumina Infinium Global Screening Array. The classic HLA alleles were imputed using HLA Genotype Imputation with Attribute Bagging (HIBAG) and the Hispanic reference panel. Finally, the distribution of HLA-DRB1 alleles was reexamined in 510 randomly recruited unrelated volunteers.

RESULTS

CODP patients showed a higher HLA-DRB1*01:02 allele frequency (6.54%) than healthy controls (3.27%, p=0.04, OR=2.07). HLA-DRB1*01:02 was also significantly associated with FEV₁ (p=0.04) and oxygen saturation (p=0.02), and the FEV₁/FVC ratio was higher in HLA-DRB1*15:01-positive patients (p=9×10^-3).

CONCLUSION

We report an association among HLA-DRB1 alleles, COPD risk and pulmonary function parameters for the first time in Latin Americans. Since HLA-DRB1 genetic variability relates to the individual autoimmune response, these results support a role of autoimmunity in the pathogenesis of COPD.

Bacterial citrullinated epitopes generated by Porphyromonas gingivalis infection-a missing link for ACPA production

OBJECTIVES

Porphyromonas gingivalis (P.g.) is discussed to be involved in triggering self-reactive immune responses. The aim of this study was to investigate the autocitrullinated prokaryotic peptidylarginine deiminase (PPAD) from P.g. CH2007 (RACH2007-PPAD) from a rheumatoid arthritis (RA) patient and a synthetic citrullinated PPAD peptide (CPP) containing the main autocitrullination site as potential targets for antibody reactivity in RA and to analyse the possibility of citrullinating native human proteins by PPAD in the context of RA.

METHODS

Recombinant RACH2007-PPAD was cloned and expressed in Escherichia coli. Purified RACH2007-PPAD and its enzymatic activity was analysed using two-dimensional electrophoresis, mass spectrometry, immunoblot and ELISA. Autoantibody response to different modified proteins and peptides was recorded and bioinformatically evaluated.

RESULTS

RACH2007-PPAD was capable to citrullinate major RA autoantigens, such as fibrinogen, vimentin, hnRNP-A2/B1, histone H1 and multiple peptides, which identify a common RG/RGG consensus motif. 33% of RA patients (n=30) revealed increased reactivity for α-cit-RACH2007-PPAD before RA onset. 77% of RA patients (n=99) presented α-cit-specific signals to CPP amino acids 57-71 which were positively correlated to α-CCP2 antibody levels. Interestingly, 48% of the α-CPP-positives were rheumatoidfactor IgM/anti-citrullinated peptide/protein antibodies (ACPA)-negative. Anti-CPP and α-RACH2007-PPAD antibody levels increase with age. Protein macroarrays that were citrullinated by RACH2007-PPAD and screened with RA patient sera (n=6) and controls (n=4) uncovered 16 RACH2007-PPAD citrullinated RA autoantigens and 9 autoantigens associated with lung diseases. We showed that the α-CPP response could be an important determinant in parenchymal changes in the lung at the time of RA diagnosis (n=106; p=0.018).

CONCLUSIONS

RACH2007-PPAD induced internal citrullination of major RA autoantigens. Anti-RACH2007-PPAD correlates with ACPA levels and interstitial lung disease autoantigen reactivity, supporting an infection-based concept for induction of ACPAs via enzymatic mimicry.

Secretory anti-citrullinated protein antibodies in serum associate with lung involvement in early rheumatoid arthritis

Objective

A ‘mucosal connection’ in RA presently attracts increasing attention. We recently described the occurrence of secretory antibodies to citrullinated protein (SC-ACPA) in sera from patients with recent-onset RA. The current study was performed to evaluate possible associations between serum levels of secretory ACPA and signs of lung involvement in patients with early, untreated RA.

Methods

One hundred and forty-two RA patients were included as part of the ‘LUng Investigation in newly diagnosed RA’ study. One hundred and six patients were examined with high-resolution CT (HRCT) and 20 patients underwent bronchoscopy, where bronchial biopsies and bronchoalveolar lavage fluid (BALF) samples were obtained. SC-ACPA in serum and BALF were detected by an enzyme-linked immunoassay. Antibody levels were related to smoking history, pulmonary function, HRCT, BALF cell counts and findings in bronchial biopsies.

Results

SC-ACPA occurred in 16% of the serum samples and in 35% of the BALF samples. SC-ACPA levels in serum correlated with SC-ACPA levels in BALF (σ = 0.50, P = 0.027) and were higher among patients with HRCT parenchymal lung abnormalities (P = 0.022) or bronchiectasis (P = 0.042). Also, ever smoking was more frequent among serum SC-ACPA-positive patients (91% vs 67%, P = 0.023), and the SC-ACPA levels correlated with the number of pack-years (σ=0.20, P = 0.020).

Conclusion

In early, untreated RA, serum levels of SC-ACPA reflect lung involvement in terms of local ACPA levels, smoking and lung abnormalities on HRCT. These findings strengthen the link between mucosal ACPA responses and the lungs in RA.

Reinterpreting Evidence of Rheumatoid Arthritis-Associated Interstitial Lung Disease to Understand Etiology

Interstitial Lung Disease (ILD) is a well-known complication of rheumatoid arthritis (RA) which often results in significant morbidity and mortality. It is often diagnosed late in the disease process via descriptive criteria. Multiple subtypes of RA-ILD exist as defined by chest CT and histopathology. In the absence of formal natural history studies and definitive diagnostics, a conventional dogma has emerged that there are two major subtypes of RA-ILD (nonspecific interstitial pneumonia (NSIP) and Usual Interstitial Pneumonia (UIP)). These subtypes are based on clinical experience and correlation studies. However, recent animal model data are incongruous with established paradigms of RA-ILD and beg reassessment of the clinical evidence in order to better understand etiology, pathogenesis, prognosis, and response to therapy. To this end, here we: 1) review the literature on epidemiology, radiology, histopathology and clinical outcomes of the various RAILD subtypes, existing animal models, and current theories on RA-ILD pathogenesis; 2) highlight the major gaps in our knowledge; and 3) propose future research to test an emerging theory of RAILD that posits initial rheumatic lung inflammation in the form of NSIP-like pathology transforms mesenchymal cells to derive chimeric disease, and subsequently develops into frank UIP-like fibrosis in some RA patients. Elucidation of the pathogenesis of RA-ILD is critical for the development of effective interventions for RA-ILD.

Expansion of Rare and Harmful Lineages is Associated with Established Rheumatoid Arthritis

Objectives: To characterize the gut microbiota profile in rheumatoid arthritis (RA) patients and investigate its association with certain characteristics of RA. Patients and methods: A nested case–control cohort of 40 patients with RA and 40 sex-age matched controls was studied. Subjects with diabetes, with any other inflammatory disease, practicing extreme diets, taking antibiotics, probiotics or under any new treatment for at least three months prior to sampling were excluded. The microbiota composition was determined by 16S rRNA pyrosequencing and bioinformatics analysis by Quantitative Insights Into Microbial Ecology (QIIME). Other variables included clinical-laboratory variables and average Disease Activity Score 28 points during the follow-up period. Multiple linear regression models were constructed to investigate the possible risk factors for the microbiota. Results: β-diversity data showed that patients tend to differ from healthy subjects according to their microbiota (p = 0.07). The analysis showed an increase in Collinsella aerofaciens, Sedimentibacter and Enterococcus genera in patients compared to controls, as well as a decrease in Dorea formicigenerans. Likewise, an increase in the activity of arginine deiminase was observed, which was found in approximately 90% of the RA genes of the genus Collinsela. The sequence number of Collinsella aerofaciens was independently associated with age (B (95%CI), −0.347 (−21.6, −2.1)), high ACPA (0.323 (27.4–390.0)) and smoking (0.300 (8.8–256.4)) in RA patients. In addition, we observed decreases in Sarcina, 02d06 and Porphyromonas bacterial lineages. Conclusion: Patients with RA present dysbiosis, resulting from an abundance of certain bacterial lineages and a decrease in others. These alterations could influence the maintenance of autoimmunity to this disease.

Anti-carbamylated proteins antibody repertoire in rheumatoid arthritis: evidence of a new autoantibody linked to interstitial lung disease

OBJECTIVE

To analyse the association between anti-carbamylated protein antibodies (Anti-CarP) and interstitial lung disease (ILD) in rheumatoid arthritis (RA) patients.

METHODS

Cross-sectional study including RA patients fulfilling the 2010 ACR/EULAR criteria. The main population comprised two groups: (1) RA patients diagnosed with RA-ILD (RA-ILD group); (2) RA patients without ILD (non-ILD RA group). Non-ILD RA patients in whom ILD was suspected underwent a diagnostic work-up and, if ILD was diagnosed, were switched to the RA-ILD group. ILD was diagnosed by high-resolution computed tomography and confirmed by a multidisciplinary committee. An independent replication sample was also obtained. Three Anti-CarP IgG autoantibodies against fetal calf serum (Anti-FCS), fibrinogen (Anti-Fib) and chimeric fibrine/filagrine homocitrullinated peptide (Anti-CFFHP) and one Anti-CarP IgA against FCS (Anti-FCS-IgA) were determined by home-made ELISA. Associations between Anti-CarP and ILD were analysed using multivariable logistic regression adjusted by smoking, sex, age, RA disease duration, rheumatoid factor and anticitrullinated protein antibodies.

RESULTS

We enrolled 179 patients: 37 (21%) were finally diagnosed with RA-ILD. Anti-CarP specificities were more frequent in RA-ILD patients (Anti-FCS 70% vs 43%; Anti-Fib 73% vs 51%; Anti-CFFHP 38% vs 19%; Anti-CarP-IgA 51% vs 20%, p<0.05 for all comparisons). Serum titers of Anti-CarP were significantly higher in RA-ILD patients. Anti-CarP specificities showed a robust effect towards increasing the odds of ILD in the multivariate analysis (Anti-FCS (OR: 3.42; 95% CI: 1.13 to 10.40), Anti-Fib (OR: 2.85; 95% CI: 0.83 to 9.70), Anti-CFFHP (OR: 3.11; 95% CI: 1.06 to 9.14) and Anti-FCS-IgA (OR: 4.30; 95% CI: 1.41 to 13.04)). Similar findings were observed in the replication sample.

CONCLUSIONS

Anti-CarP were strongly associated with ILD. The role of homocitrullination in RA-ILD merits further investigation.

A predominant involvement of the triple seropositive patients and others with rheumatoid factor in the association of smoking with rheumatoid arthritis

The major environmental risk factor for rheumatoid arthritis (RA) is smoking, which according to a widely accepted model induces protein citrullination in the lungs, triggering the production of anti-citrullinated protein antibodies (ACPA) and RA development. Nevertheless, some research findings do not fit this model. Therefore, we obtained six independent cohorts with 2253 RA patients for a detailed analysis of the association between smoking and RA autoantibodies. Our results showed a predominant association of smoking with the concurrent presence of the three antibodies: rheumatoid factor (RF), ACPA and anti-carbamylated protein antibodies (ACarPA) (3 Ab vs. 0 Ab: OR = 1.99, p = 2.5 × 10^–8). Meta-analysis with previous data (4491 patients) confirmed the predominant association with the concurrent presence of the three antibodies (3 Ab vs. 0 Ab: OR = 2.00, p = 4.4 ×10^–16) and revealed that smoking was exclusively associated with the presence of RF in patients with one or two antibodies (RF⁺₁₊₂vs. RF⁻₀₊₁₊₂: OR = 1.32, p = 0.0002). In contrast, no specific association with ACPA or ACarPA was found. Therefore, these results showed the need to understand how smoking favors the concordance of RA specific antibodies and RF triggering, perhaps involving smoking-induced epitope spreading and other hypothesized mechanisms.

Citrullination Alters the Antiviral and Immunomodulatory Activities of the Human Cathelicidin LL-37 During Rhinovirus Infection

Human rhinoviruses (HRV) are the most common cause of viral respiratory tract infections. While normally mild and self-limiting in healthy adults, HRV infections are associated with bronchiolitis in infants, pneumonia in immunocompromised patients, and exacerbations of asthma and COPD. The human cathelicidin LL-37 is a host defense peptide (HDP) with broad immunomodulatory and antimicrobial activities that has direct antiviral effects against HRV. However, LL-37 is known to be susceptible to the enzymatic activity of peptidyl arginine deiminases (PAD), and exposure of the peptide to these enzymes results in the conversion of positively charged arginines to neutral citrullines (citrullination). Here, we demonstrate that citrullination of LL-37 reduced its direct antiviral activity against HRV. Furthermore, while the anti-rhinovirus activity of LL-37 results in dampened epithelial cell inflammatory responses, citrullination of the peptide, and a loss in antiviral activity, ameliorates this effect. This study also demonstrates that HRV infection upregulates PAD2 protein expression, and increases levels of protein citrullination, including histone H3, in human bronchial epithelial cells. Increased PADI gene expression and HDP citrullination during infection may represent a novel viral evasion mechanism, likely applicable to a wide range of pathogens, and should therefore be considered in the design of therapeutic peptide derivatives.

Established rheumatoid arthritis - Redefining the concept

During the last few years, there has been a shift of focus in rheumatoid arthritis (RA) research towards earlier disease states. The terms early and established RA are inseparable, and having a clear definition of these two terms is crucial in conducting research and trying to understand the immunopathological mechanisms behind these different disease states. Established RA has been connected to chronic inflammation and a high burden of long-standing disease, with joint damage and comorbidities as a consequence of chronic inflammation. A chronological definition does not ensure us clear differentiation between early and established disease, because diagnosis can be delayed significantly. Similarly, a radiological definition does not ensure a clear differentiation either, as there is significant heterogeneity in the RA patient population, with some patients never developing structural damage, even after many years of disease. As the focus is now more on the early stages of disease, we propose to use the term established RA from the time of a definite clinical diagnosis of RA, irrespective of the symptoms' duration or the presence of irreversible damage, to distinguish established disease to a stage of undifferentiated arthritis (UA) or risk for developing RA, which might never progress to RA.

Obstructive lung diseases and risk of rheumatoid arthritis

Introduction: Smoking is an established risk factor for both lung diseases and rheumatoid arthritis (RA). Chronic mucosal airway inflammation may result in immune tolerance loss, neoantigen formation, and production of RA-related autoantibodies that increase the subsequent risk of RA. In this review, we aimed to summarize the current evidence supporting the role of obstructive lung diseases and subsequent risk of RA.Areas covered: We identified scientific articles discussing the biologic mechanisms linking mucosal airway inflammation and RA risk. We also identified studies investigating asthma, chronic obstructive pulmonary disease, bronchiectasis, cystic fibrosis, chronic tuberculous and nontuberculous mycobacterial infections, and interstitial lung disease with subsequent risk for RA.Expert opinion: The current evidence supports the hypothesis that mucosal airway inflammation may increase the risk of developing RA. However, most studies investigating this relationship have been retrospective and may not have adequately addressed the role of smoking. Larger prospective studies may provide stronger evidence for obstructive lung disease and RA risk. Determining the role of obstructive lung disease in RA pathogenesis may provide opportunity for RA prevention and screening strategies, while identifying novel biologic mechanisms that could offer targets to improve treatment and outcomes.