Peptidylarginine deiminase from Porphyromonas gingivalis citrullinates human fibrinogen and α-enolase: implications for autoimmunity in rheumatoid arthritis

Salivary ammonia levels and Tannerella forsythia are associated with rheumatoid arthritis: A cross sectional study

The aim of this paper is to evaluate the relationship of salivary ammonium levels and the presence of bacteria with rheumatoid arthritis (RA) clinical disease activity in a cross-sectional study of Mexican patients. From a periodontal and disease activity standpoint, 132 consecutive RA patients fulfilling clinical criteria were evaluated. Ammonia levels (including peptidyl arginine deiminase activity) were evaluated by colorimetric assay and the presence of Porphyromonas gingivalis, Tannerella forsythia, and Prevotella intermedia was evaluated by polymerase chain reaction (PCR) technique. After a multivariate analysis, adjusting for clinical and serological parameters, a significant association was only observed between severe periodontitis and probing depth with high RA disease activity. Additionally, in contrast to P. gingivalis, the presence of T. forsythia was significantly associated with high disease RA activity even after multivariable adjustment analysis. There was also a significant increase in ammonium levels in the high RA activity group and a significant correlation between salivary ammonia and RA disease activity but not with autoantibody titers. Similarly, we observed a significant increase in the ammonium levels derived from the cultures of P. gingivalis and T. forsythia, with respect to P. intermedia and S. gordonii cultures, or even healthy donors. These results suggest that RA activity is associated with severe periodontitis, high salivary ammonium levels and the presence of T. forsythia.

The Type IX Secretion System (T9SS): Highlights and Recent Insights into Its Structure and Function

Protein secretion systems are vital for prokaryotic life, as they enable bacteria to acquire nutrients, communicate with other species, defend against biological and chemical agents, and facilitate disease through the delivery of virulence factors. In this review, we will focus on the recently discovered type IX secretion system (T9SS), a complex translocon found only in some species of the Bacteroidetes phylum. T9SS plays two roles, depending on the lifestyle of the bacteria. It provides either a means of movement (called gliding motility) for peace-loving environmental bacteria or a weapon for pathogens. The best-studied members of these two groups are Flavobacterium johnsoniae, a commensal microorganism often found in water and soil, and Porphyromonas gingivalis, a human oral pathogen that is a major causative agent of periodontitis. In P. gingivalis and some other periodontopathogens, T9SS translocates proteins, especially virulence factors, across the outer membrane (OM). Proteins destined for secretion bear a conserved C-terminal domain (CTD) that directs the cargo to the OM translocon. At least 18 proteins are involved in this still enigmatic process, with some engaged in the post-translational modification of T9SS cargo proteins. Upon translocation across the OM, the CTD is removed by a protease with sortase-like activity and an anionic LPS is attached to the newly formed C-terminus. As a result, a cargo protein could be secreted into the extracellular milieu or covalently attached to the bacterial surface. T9SS is regulated by a two-component system; however, the precise environmental signal that triggers it has not been identified. Exploring unknown systems contributing to bacterial virulence is exciting, as it may eventually lead to new therapeutic strategies. During the past decade, the major components of T9SS were identified, as well as hints suggesting the possible mechanism of action. In addition, the list of characterized cargo proteins is constantly growing. The actual structure of the translocon, situated in the OM of bacteria, remains the least explored area; however, new technical approaches and increasing scientific attention have resulted in a growing body of data. Therefore, we present a compact up-to-date review of this topic.

Theoretical insights into the protonation states of active site cysteine and citrullination mechanism of Porphyromonas gingivalis peptidylarginine deiminase

Porphyromonas gingivalis peptidylarginine deiminase (PPAD) catalyzes the citrullination of peptidylarginine, which plays a critical role in the rheumatoid arthritis (RA) and gene regulation. For a better understanding of citrullination mechanism of PPAD, it is required to establish the protonation states of active site cysteine, which is still a controversial issue for the members of guanidino-group-modifying enzyme superfamily. In this work, we first explored the transformation between the two states: State N (both C351 and H236 are neutral) and State I (both residues exist as a thiolate-imidazolium ion pair), and then investigated the citrullination reaction of peptidylarginine, using a combined QM/MM approach. State N is calculated to be more stable than State I by 8.46 kcal/mol, and State N can transform to State I via two steps of substrate-assisted proton transfer. Citrullination of the peptidylarginine contains deamination and hydrolysis. Starting from State N, the deamination reaction corresponds to an energy barrier of 18.82 kcal/mol. The deprotonated C351 initiates the nucleophilic attack to the substrate, which is the key step for deamination reaction. The hydrolysis reaction contains two chemical steps. Both the deprotonated D238 and H236 can act as the bases to activate the hydrolytic water, which correspond to similar energy barriers (∼17 kcal/mol). On the basis of our calculations, C351, D238, and H236 constitute a catalytic triad, and their protonation states are critical for both the deamination and hydrolysis processes. In view of the sequence similarity, these findings may be shared with human PAD1-PAD4 and other guanidino-group-modifying enzymes. Proteins 2017; 85:1518-1528. © 2017 Wiley Periodicals, Inc.

Cellular and molecular perspectives in rheumatoid arthritis

Synovial immunopathology in rheumatoid arthritis is complex involving both resident and infiltrating cells. The synovial tissue undergoes significant neovascularization, facilitating an influx of lymphocytes and monocytes that transform a typically acellular loose areolar membrane into an invasive tumour-like pannus. The microvasculature proliferates to form straight regularly-branching vessels; however, they are highly dysfunctional resulting in reduced oxygen supply and a hypoxic microenvironment. Autoantibodies such as rheumatoid factor and anti-citrullinated protein antibodies are found at an early stage, often before arthritis has developed, and they have been implicated in the pathogenesis of RA. Abnormal cellular metabolism and mitochondrial dysfunction thus ensue and, in turn, through the increased production of reactive oxygen species actively induce inflammation. Key pro-inflammatory cytokines, chemokines and growth factors and their signalling pathways, including nuclear factor κB, Janus kinase-signal transducer, are highly activated when immune cells are exposed to hypoxia in the inflamed rheumatoid joint show adaptive survival reactions by activating. This review attempts to highlight those aberrations in the innate and adaptive immune systems including the role of genetic and environmental factors, autoantibodies, cellular alterations, signalling pathways and metabolism that are implicated in the pathogenesis of RA and may therefore provide an opportunity for therapeutic intervention.

Pre-symptomatic autoimmunity in rheumatoid arthritis: when does the disease start?

It is well recognised that a state of autoimmunity, in which immunological tolerance is broken, precedes the development of symptoms in the majority of patients with rheumatoid arthritis (RA). For individuals who will later develop seropositive disease, this manifests as autoantibodies directed against proteins that have undergone specific post-translational modifications. There is evidence that the induction of this autoantibody response occurs at peripheral extra-articular mucosal sites, such as the periodontium and lung. In addition to their utility as diagnostic markers, these autoantibodies may have a pathogenic role that helps localise disease to the synovium. Alongside the development of autoantibodies, other factors contributing to pre-symptomatic autoimmunity may include dysbiosis of the gastrointestinal tract, abnormal development of lymphoid tissue, and dysregulated autonomic and lipid-mediated anti-inflammatory signalling. These factors combine to skew the balance between pro-inflammatory and anti-inflammatory signalling in a manner that is permissive for the development of clinical arthritis. We present data to support the concept that the transitions from at-risk states to systemic autoimmunity and then to classifiable RA depend on multiple “switches”. However, further prospective studies are necessary to define the molecular basis of these switches and the specific features of pre-symptomatic autoimmunity, so that preventative treatments can be targeted to individuals at high risk for RA. In this review, we analyse mechanisms that may contribute to the development of autoimmunity in at-risk individuals and discuss the relationship between this pre-symptomatic state and subsequent development of RA.

Microbiota, Immune Subversion, and Chronic Inflammation

Several host-adapted pathogens and commensals have evolved mechanisms to evade the host innate immune system inducing a state of low-grade inflammation. Epidemiological studies have also documented the association of a subset of these microorganisms with chronic inflammatory disorders. In this review, we summarize recent studies demonstrating the role of the microbiota in chronic inflammatory diseases and discuss how specific microorganisms subvert or inhibit protective signaling normally induced by toll-like receptors (TLRs). We highlight our work on the oral pathogen Porphyromonas gingivalis and discuss the role of microbial modulation of lipid A structures in evasion of TLR4 signaling and resulting systemic immunopathology associated with atherosclerosis. P. gingivalis intrinsically expresses underacylated lipid A moieties and can modify the phosphorylation of lipid A, leading to altered TLR4 signaling. Using P. gingivalis mutant strains expressing distinct lipid A moieties, we demonstrated that expression of antagonist lipid A was associated with P. gingivalis-mediated systemic inflammation and immunopathology, whereas strains expressing agonist lipid A exhibited modest systemic inflammation. Likewise, mice deficient in TLR4 were more susceptible to vascular inflammation after oral infection with P. gingivalis wild-type strain compared to mice possessing functional TLR4. Collectively, our studies support a role for P. gingivalis-mediated dysregulation of innate and adaptive responses resulting in immunopathology and systemic inflammation. We propose that anti-TLR4 interventions must be designed with caution, given the balance between the protective and destructive roles of TLR signaling in response to microbiota and associated immunopathologies.

Quantitative proteomic analysis of extracellular matrix extracted from mono- and dual-species biofilms of Fusobacterium nucleatum and Porphyromonas gingivalis

The Gram-negative bacteria Fusobacterium nucleatum and Porphyromonas gingivalis are members of a complex dental biofilm associated with periodontal disease. In this study, we cultured F. nucleatum and P. gingivalis as mono- and dual-species biofilms, and analyzed the protein composition of the biofilms extracellular polymeric matrix (EPM) by high-resolution liquid chromatography-tandem mass spectrometry. Label-free quantitative proteomic analysis was used for identification of proteins and sequence-based functional characterization for their classification and prediction of possible roles in EPM. We identified 542, 93 and 280 proteins in the matrix of F. nucleatum, P. gingivalis, and the dual-species biofilm, respectively. Nearly 70% of all EPM proteins in the dual-species biofilm originated from F. nucleatum, and a majority of these were cytoplasmic proteins, suggesting an enhanced lysis of F. nucleatum cells. The proteomic analysis also indicated an interaction between the two species: 22 F. nucleatum proteins showed differential levels between the mono and dual-species EPMs, and 11 proteins (8 and 3 from F. nucleatum and P. gingivalis, respectively) were exclusively detected in the dual-species EPM. Oxidoreductases and chaperones were among the most abundant proteins identified in all three EPMs. The biofilm matrices in addition contained several known and hypothetical virulence proteins, which can mediate adhesion to the host cells and disintegration of the periodontal tissues. This study demonstrated that the biofilm matrix of two important periodontal pathogens consists of a multitude of proteins whose amounts and functionalities vary largely. Relatively high levels of several of the detected proteins might facilitate their potential use as targets for the inhibition of biofilm development.

The role and therapeutic targeting of IL-6 in rheumatoid arthritis

INTRODUCTION

Rheumatoid arthritis (RA) is an autoimmune chronic disease with joint and systemic inflammation and it has been found that interleukin-6 (IL-6) plays a key role in RA. Indeed, various clinical studies have proved that the first-in-class IL-6 inhibitor, tocilizumab, a humanized anti-IL-6 receptor monoclonal antibody, showed outstanding efficacy in RA. Areas covered: We review here the role of IL-6 in the inflammatory conditions and how IL-6 contributes to pathogenesis of RA, what induces IL-6 and how IL-6 expression is regulated. Furthermore, clinical studies of tocilizumab for RA are summarized, Expert commentary: We review and discuss the prospects for future applications of IL-6 targeting therapy and new therapeutic strategies targeting IL-6. Finally, we discuss relevant issues with regard to the clinical management of IL-6 blockade in RA.

Genetic and environmental risk factors for rheumatoid arthritis

Multiple genetic and environmental factors have been associated with an increased risk for rheumatoid arthritis (RA). Of these, the strongest associations have been seen with female sex, a family history of RA, the genetic factor the "shared epitope," and exposure to tobacco smoke. There is also renewed interest in mucosal inflammation and microbial factors as contributors to the development of RA. However, the identification of a "preclinical" period of RA that can be defined as local or systemic autoimmunity as measured by autoantibodies and other biomarkers prior to the development of clinically apparent synovitis suggests that the risk factors for RA are acting long prior to first clinical evidence of IA. As such, a major challenge to the field will be to investigate the full spectrum of the development of RA, from initiation and propagation of autoimmunity during preclinical RA and transition to clinically apparent synovitis and classifiable RA, to determine which genetic and environmental factors are important at each stage of disease development. Understanding the exact role and timing of action of risk factors for RA is especially important given the advent of prevention trials in RA, and the hope that a full understanding of genetic and environmental factors in RA could lead to effective preventive interventions.

Causes and consequences of endoplasmic reticulum stress in rheumatic disease

Rheumatic diseases represent a heterogeneous group of inflammatory conditions, many of which involve chronic activation of both innate and adaptive immune responses by multiple genetic and environmental factors. These immune responses involve the secretion of excessive amounts of cytokines and other signalling mediators by activated immune cells. The endoplasmic reticulum (ER) is the cellular organelle that directs the folding, processing and trafficking of membrane-bound and secreted proteins, including many key components of the immune response. Maintaining homeostasis in the ER is critical to cell function and survival. Consequently, elaborate mechanisms have evolved to sense and respond to ER stress through three main signalling pathways that together comprise the unfolded protein response (UPR). Activation of the UPR can rapidly resolve the accumulation of misfolded proteins, direct permanent changes in the size and function of cells during differentiation, and critically influence the immune response and inflammation. Recognition of the importance of ER stress and UPR signalling pathways in normal and dysregulated immune responses has greatly increased in the past few years. This Review discusses several settings in which ER stress contributes to the pathogenesis of rheumatic diseases and considers some of the therapeutic opportunities that these discoveries provide.

The autoimmunity-oral microbiome connection

To date, there is a major effort in deciphering the role of complex microbial communities, especially the oral and gut microbiomes, in the pathogenesis of various diseases. Increasing evidence indicates a key role for the oral microbiome in autoimmune diseases. In this review article, we discuss links of the oral microbiota to a group of autoimmune diseases, that is, Sjögren's syndrome (SS), systemic lupus erythematosus (SLE), Crohn's disease (CD), and rheumatoid arthritis (RA). We particularly focus on factors that affect the balance between the immune system and the composition of microbiota leading to dysbiosis, loss of tolerance and subsequent autoimmune disease progression and maintenance.

Cross-Sectional Evaluation of Periodontal Status and Microbiologic and Rheumatoid Parameters in a Large Cohort of Patients With Rheumatoid Arthritis

BACKGROUND

This study evaluates periodontal conditions and microbiologic findings and their influence on rheumatologic disease parameters in patients with rheumatoid arthritis (RA).

METHODS

One hundred and sixty-eight patients with RA were included. A healthy control group (HC, n = 168) was composed according to age, sex, and smoking habits. Rheumatologic data (duration of illness, Disease Activity Score 28, rheumatic factor [RF], anti-cyclic citrullinated peptide [aCCP], medications) were extracted from patients' records. Dental examination included: 1) dental findings (decayed, missing, and/or filled adult teeth [DMF-T] index); 2) gingival inflammation (papillary bleeding index [PBI]); and 3) periodontal status (probing depth [PD], attachment loss [AL]). Periodontal condition was classified as healthy/mild, moderate, or severe periodontitis. Subgingival biofilm was analyzed regarding 11 periodontopathogenic bacteria. Statistical analyses included: 1) Kolmogorov-Smirnov test; 2) Mann-Whitney U test; 3) Pearson χ² test; 4) Kruskal-Wallis test; and 5) regression analysis; level of significance α = 5%.

RESULTS

Mean DMF-T was significantly higher in patients with RA (19.3 ± 4.8) than in HC group (16.9 ± 5.8), especially owing to number of missing teeth (RA = 6.0 ± 5.4, HC = 3.1 ± 3.3; P <0.01). Patients with RA had a significantly higher proportion of increased PD (P <0.01) and AL compared with HC group (P <0.01). Moderate to severe periodontitis was noted in 98% of patients with RA and 82% of the HC group (P <0.01). RF-positive patients with RA suffered from worse periodontal conditions than RF-negative patients (P = 0.01). Age, PBI, and presence of Treponema denticola (P <0.03) are related to periodontal condition in patients with RA. Although not statistically significant, Porphyromonas gingivalis and Fusobacterium nucleatum occur in higher concentrations more often in aCCP-positive patients with RA (P = 0.06).

CONCLUSIONS

Patients with RA had worse periodontal conditions than HC participants. Although a trend for higher F. nucleatum and P. gingivalis concentrations in aCCP-positive patients with RA was found, importance of periodontal pathogenic bacteria and rheumatoid parameters in the interrelationship between periodontitis and RA remains unclear.

NETosis as Source of Autoantigens in Rheumatoid Arthritis

In neutrophils (but also in eosinophils and in mast cells), different inflammatory stimuli induce histone deimination, chromatin decondensation, and NET formation. These web-like structures that trap and kill microbes contain DNA, cationic granule proteins, and antimicrobial peptides, but the most abundant proteins are core histones. Histones contained in NETs have been deiminated, and arginines are converted in citrullines. While deimination is a physiological process amplified in inflammatory conditions, only individuals carrying genetic predisposition to develop rheumatoid arthritis (RA) make antibodies to deiminated proteins. These antibodies, collectively identified as anti-citrullinated proteins/peptides antibodies (ACPA), react with different deiminated proteins and display partially overlapping specificities. In this paper, we will summarize current evidence supporting the role of NETosis as critical mechanism in the breach of tolerance to self-antigens and in supporting expansion and differentiation of autoreactive cells. In fact, several lines of evidence connect NETosis with RA: RA unstimulated synovial fluid neutrophils display enhanced NETosis; sera from RA patients with Felty's syndrome bind deiminated H3 and NETs; a high number of RA sera bind deiminated H4 contained in NETs; human monoclonal antibodies generated from RA synovial B cells decorate NETs and bind deiminated histones. In RA, NETs represent on one side an important source of autoantigens bearing posttranslational modifications and fueling the production of ACPA. On the other side, NETs deliver signals that maintain an inflammatory milieu and contribute to the expansion and differentiation of ACPA-producing B cells.

Correlation of Periodontal Disease With Inflammatory Arthritis in the Time Before Modern Medical Intervention

BACKGROUND

Controversy exists regarding possible correlation of periodontal disease with rheumatoid arthritis (RA) and ankylosing spondylitis (AS). Confounding factors may relate to stringency of inflammatory disease diagnosis and the effect of therapeutic intervention for RA on periodontal disease. These factors are investigated in this study.

METHODS

Forty-five individuals with documented RA (n = 15), spondyloarthropathy (n = 15), and calcium pyrophosphate deposition disease (CPPD) (n = 15), from the Hamann-Todd collection of human skeletons compiled from 1912 to 1938, and 15 individuals contemporarily incorporated in the collection were examined for tooth loss, cavity occurrence, average and maximum lingual and buccal depth of space between tooth and bone, periosteal reaction, serpentine bone resorption, abscess formation, and root penetration of the bone surface and analyzed by analysis of variance.

RESULTS

Tooth loss was common, but actual number of teeth lost, cavity occurrence, average and maximum lingual and buccal depth of space between tooth and bone, periosteal reaction, serpentine grooving surrounding teeth (considered a sign of inflammation), abscess formation, and root exposure (penetration of bone surface) were indistinguishable among controls and individuals with RA, spondyloarthropathy, and CPPD.

CONCLUSIONS

Although many factors can affect periodontal disease, presence of inflammatory arthritis does not appear to be one of them. The implication is that dental disease was common in the general population and not necessarily associated with arthritis, at least before the advent of modern rheumatologic medications. As specific diagnosis did not affect prevalence, perhaps current prevalence controversy may relate to current intervention, a subject for further study.

The role of the gastrointestinal tract in the pathogenesis of rheumatic diseases

Dysregulation of the intestinal epithelial barrier in genetically susceptible individuals may lead to both intestinal and extraintestinal autoimmune disorders. There is emerging literature on the role of microbiota changes in the pathogenesis of systemic rheumatic diseases such as rheumatoid arthritis, spondyloarthropathies, and connective tissue diseases. Although the role of the gastrointestinal tract in the pathogenesis of spondyloartropathies is well defined and many studies underline the importance of gastrointestinal inflammation in modulating local and systemic inflammation, the data are inconclusive regarding the effect of dysbiosis on rheumatoid arthritis and connective tissue diseases. This review aims to summarize current data on the role of the gastrointestinal involvement and intestinal microbiota in the pathogenesis of systemic rheumatic disease.

Effects by periodontitis on pristane-induced arthritis in rats

Background

An infection-immune association of periodontal disease with rheumatoid arthritis has been suggested. This study aimed to investigate the effect of pre-existing periodontitis on the development and the immune/inflammatory response of pristane-induced arthritis.

Methods

We investigated the effect of periodontitis induced by ligature placement and Porphyromonas gingivalis (P. gingivalis) infection, in combination with Fusobacterium nucleatum to promote its colonization, on the development of pristane-induced arthritis (PIA) in rats (Dark Agouti). Disease progression and severity of periodontitis and arthritis was monitored using clinical assessment, micro-computed tomography (micro-CT)/intraoral radiographs, antibody response, the inflammatory markers such as α-1-acid glycoprotein (α-1-AGP) and c-reactive protein (CRP) as well as cytokine multiplex profiling at different time intervals after induction.

Results

Experimentally induced periodontitis manifested clinically (P < 0.05) prior to pristane injection and progressed steadily until the end of experiments (15 weeks), as compared to the non-ligated arthritis group. Injection of pristane 8 weeks after periodontitis-induction led to severe arthritis in all rats demonstrating that the severity of arthritis was not affected by the pre-existence of periodontitis. Endpoint analysis showed that 89% of the periodontitis-affected animals were positive for antibodies against arginine gingipain B and furthermore, the plasma antibody levels to a citrullinated P. gingivalis peptidylarginine deiminase (PPAD) peptide (denoted CPP3) were significantly (P < 0.05) higher in periodontitis rats with PIA. Additionally, there was a trend towards increased pro-inflammatory and anti-inflammatory cytokine levels, and increased α-1-AGP levels in plasma from periodontitis-challenged PIA rats.

Conclusions

Pre-existence of periodontitis induced antibodies against citrullinated peptide derived from PPAD in rats with PIA. However, there were no differences in the development or severity of PIA between periodontitis challenged and periodontitis free rats.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-1067-6) contains supplementary material, which is available to authorized users.

Decision Making in the Treatment of Patients With Rheumatoid Arthritis and Periodontitis: Scientific Evidence and Clinical Experience

Focused Clinical Question: What are the key considerations for coordination of care for a patient with rheumatoid arthritis (RA) and chronic periodontitis (CP), and what are the clinical implications of RA on periodontal health? Summary: Both RA and CP involve hyper-immune response and osseous destruction. However, despite emerging evidence that RA and CP may have common etiologies and patients with RA have increased risk of CP, periodontal evaluation and treatment remain largely similar for patients with and without RA. More fully assessing inflammatory burden in patients with RA and CP may allow practitioners to more accurately assess the risk profile of a patient for RA and periodontal disease progression and to better evaluate adequate end points to periodontal therapy. Furthermore, coordination of care for patients with RA and CP with their rheumatologist or treating physician could allow for advanced screening and prophylactic care that may prevent disease development or progression. Conclusion: For patients with RA and CP, evaluation of their rheumatoid disease activity score and periodontal inflamed surface area score, rather than traditional periodontal clinical measurements, along with additional biologic sampling methods may be appropriate measures to more accurately assess inflammatory burden in these susceptible patients.

Rheumatoid arthritis

Rheumatoid arthritis is a chronic inflammatory joint disease, which can cause cartilage and bone damage as well as disability. Early diagnosis is key to optimal therapeutic success, particularly in patients with well-characterised risk factors for poor outcomes such as high disease activity, presence of autoantibodies, and early joint damage. Treatment algorithms involve measuring disease activity with composite indices, applying a treatment-to-target strategy, and use of conventional, biological, and newz non-biological disease-modifying antirheumatic drugs. After the treatment target of stringent remission (or at least low disease activity) is maintained, dose reduction should be attempted. Although the prospects for most patients are now favourable, many still do not respond to current therapies. Accordingly, new therapies are urgently required. In this Seminar, we describe current insights into genetics and aetiology, pathophysiology, epidemiology, assessment, therapeutic agents, and treatment strategies together with unmet needs of patients with rheumatoid arthritis.

Elevated IgA Plasmablast Levels in Subjects at Risk of Developing Rheumatoid Arthritis

OBJECTIVE

The disease process in rheumatoid arthritis (RA) starts years before the clinical diagnosis is made, and elevated levels of disease-specific autoantibodies can be detected during this period. Early responses to known or novel autoantigens likely drive the eventual production of pathogenic autoimmunity. Importantly, the presence of disease-specific autoantibodies can identify individuals who are at high risk of developing RA but who do not currently have arthritis. The goal of the current study was to characterize plasmablasts from individuals at risk of developing RA.

METHODS

We investigated antibody-secreting plasmablasts derived from a well-characterized cohort of individuals who were at risk of developing RA, based on RA-related serum autoantibody positivity, as compared to patients with early (<1 year) seropositive RA as well as healthy control subjects. The plasmablast antibody repertoires of at-risk subjects were analyzed using DNA barcode-based methods with paired heavy- and light-chain gene sequencing. Cells were single-cell sorted, the cell- and plate-specific DNA barcodes were sequentially added, and next-generation sequencing was performed.

RESULTS

Total plasmablast levels were similar in the antibody-positive (1%) and control (0.4-1.6%) groups. However, increased frequencies of IgA+ versus IgG+ plasmablasts were observed in the antibody-positive group (39% IgA+ and 37% IgG+) as compared to other groups (1-9% IgA+ and 71-87% IgG+). Paired antibody sequences from antibody-positive subjects revealed cross-isotype clonal families and similar sequence characteristics in the IgA and IgG plasmablast repertoires. Antibody-positive individuals also demonstrated elevated serum levels of IgA isotype anti-cyclic citrullinated peptide 3 antibodies.

CONCLUSION

The IgA plasmablast dominance in these antibody-positive individuals suggests that a subset of RA-related autoantibodies may arise from mucosal immune responses and may be involved in early disease pathogenesis in individuals who are at risk of developing RA.

The human microbiome and juvenile idiopathic arthritis

Juvenile idiopathic arthritis (JIA) is the most common rheumatic disease in childhood. The pathogenesis of JIA is thought to be the result of a combination of host genetic and environmental triggers. However, the precise factors that determine one's susceptibility to JIA remain to be unravelled. The microbiome has received increasing attention as a potential contributing factor to the development of a wide array of immune-mediated diseases, including inflammatory bowel disease, type 1 diabetes and rheumatoid arthritis. Also in JIA, there is accumulating evidence that the composition of the microbiome is different from healthy individuals. A growing body of evidence indeed suggests that, among others, the microbiome may influence the development of the immune system, the integrity of the intestinal mucosal barrier, and the differentiation of T cell subsets. In turn, this might lead to dysregulation of the immune system, thereby possibly playing a role in the development of JIA. The potential to manipulate the microbiome, for example by faecal microbial transplantation, might then offer perspectives for future therapeutic interventions. Before we can think of such interventions, we need to first obtain a deeper understanding of the cause and effect relationship between JIA and the microbiome. In this review, we discuss the existing evidence for the involvement of the microbiome in JIA pathogenesis and explore the potential mechanisms through which the microbiome may influence the development of autoimmunity in general and JIA specifically.

Concentration of antibodies against Porphyromonas gingivalis is increased before the onset of symptoms of rheumatoid arthritis

Background

The periodontal pathogen Porphyromonas gingivalis is hypothesized to be important in rheumatoid arthritis (RA) aetiology by inducing production of anti-citrullinated protein antibodies (ACPA). We have shown that ACPA precede RA onset by years, and that anti-P. gingivalis antibody levels are elevated in RA patients. The aim of this study was to investigate whether anti-P. gingivalis antibodies pre-date symptom onset and ACPA production.

Methods

A case–control study (251 cases, 198 controls) was performed within the Biobank of Northern Sweden. Cases had donated blood samples (n = 422) before the onset of RA symptoms by 5.2 (6.2) years (median (interquartile range)). Blood was also collected from 192 RA patients following diagnosis. Antibodies against P. gingivalis virulence factor arginine gingipainB (RgpB), and a citrullinated peptide (CPP3) derived from the P. gingivalis peptidylarginine deiminase enzyme, were analysed by ELISA.

Results

Anti-RgpB IgG levels were significantly increased in pre-symptomatic individuals (mean ± SEM; 152.7 ± 14.8 AU/ml) and in RA patients (114.4 ± 16.9 AU/ml), compared with controls (p < 0.001). Anti-CPP3 antibodies were detected in 5 % of pre-symptomatic individuals and in 8 % of RA patients, with elevated levels in both subsets (4.33 ± 0.59 and 9.29 ± 1.81 AU/ml, respectively) compared with controls (p < 0.001). Anti-CPP3 antibodies followed the ACPA response, with increasing concentrations over time, whilst anti-RgpB antibodies were elevated and stable in the pre-symptomatic individuals with a trend towards lower levels after RA diagnosis.

Conclusions

Anti-P. gingivalis antibody concentrations were significantly increased in RA patients compared with controls, and were detectable years before onset of symptoms of RA, supporting an aetiological role for P. gingivalis in the development of RA.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-016-1100-4) contains supplementary material, which is available to authorized users.

Periodontitis is associated with rheumatoid arthritis: a study with longstanding rheumatoid arthritis patients in Korea

BACKGROUND/AIMS

A cross-sectional study was undertaken to investigate the association between severity of periodontitis and clinical manifestation of rheumatoid arthritis (RA).

METHODS

Two hundred sixty-four RA patients and 88 age- and sex-matched controls underwent dental exam. Additionally, clinical manifestations including disease activity and anti-citrullinated protein antibodies were evaluated in RA patients.

RESULTS

The prevalence of moderate or severe periodontitis was higher in RA patients compared to controls (63.6% vs 34.1%, p < 0.001). In markers of periodontal inflammation, bleeding on probing was correlated with disease activity score 28 (r = 0.128, p = 0.041), RA disease duration (r = 0.211, p = 0.001), erythrocyte sedimentation rate (ESR; r = 0.141, p = 0.023), anti-cyclic citrullinated peptide antibody (r = 0.183, p = 0.009), and anti-citrullinated α-enolase peptide-1 antibody (r = 0.143, p = 0.025). Gingival index was correlated with RA duration (r = 0.262, p < 0.001), ESR (r = 0.162, p = 0.009), anti-cyclic citrullinated peptide antibody (r = 0.203, p = 0.004) and anti-citrullinated α-enolase peptide-1 antibody (r = 0.225, p < 0.001). Periodontal structural damage represented by probing pocket depth and clinical attachment level were less in RA patients with human leukocyte antigen (HLA)-DRB1 shared epitope compared than those without shared epitope (p = 0.005 and p =0.006, respectively).

CONCLUSIONS

The prevalence of moderate or severe periodontitis was increased in RA patients compared to controls. Periodontal inflammation was correlated with RA disease duration, ESR, and anti-citrullinated protein antibodies. Periodontal structural damage was less in RA patients with HLA-DRB1 shared epitope.

Porphyromonas gingivalis infection exacerbates the onset of rheumatoid arthritis in SKG mice

Epidemiological studies have linked periodontitis to rheumatoid arthritis (RA). Porphyromonas gingivalis (Pg) was reported recently to produce citrullinated protein (CP) and increase anti-cyclic CP antibody (ACPA), both of which have been identified as causative factors of RA. In the present study, we determined the effects of Pg infection on the exacerbation of RA in a mouse model. RA model mice (SKG mice) were established by an intraperitoneal (i.p.) injection of laminarin (LA). Mice were divided into six groups, Ctrl (PBS injection), LA (LA injection), Pg/LA (Pg + LA injection), Pg (Pg injection), Ec/LA (Escherichia coli and LA injection) and Ec (E. coli injection). In order to evaluate RA, joint swelling by the arthritis score, bone morphology by microcomputed tomography (microCT), haematoxylin and eosin staining, ACPA, matrix metalloproteinase-3 (MMP-3) and cytokine level in serum by enzyme-linked immunosorbent assay were determined. Osteoclast differentiation from bone marrow mononuclear cells (BMCs) was examined to clarify the underlying mechanisms of RA. The presence of Pg and CP in joint tissue was also investigated. The arthritis score was threefold higher in the Pg/LA group than in the LA group. Severe bone destruction was observed in joint tissue of the Pg/LA group. A microCT analysis of the Pg/LA group revealed a decrease in bone density. ACPA, MMP-3, interleukin (IL)-2, IL-6, CXCL1 and macrophage inflammatory protein (MIP)-1α levels from the Pg/LA group were the highest. The osteoclastogenesis of BMCs was enhanced in the Pg/LA group. Furthermore, large amounts of Pg components and CP were detected in the Pg/LA group. In conclusion, Pg infection has the potential to exacerbate RA.

Serum antibody levels against Porphyromonas gingivalis in patients with and without rheumatoid arthritis - a systematic review and meta-analysis

OBJECTIVES

Since the peptidyl arginine deiminase of Porphyromonas gingivalis is able to citrullinate peptides and proteins, various studies have suggested the species as a possible link between periodontal disease (PD) and rheumatoid arthritis (RA). This systematic review including meta-analysis was aimed to evaluate whether differences in terms of antibody titers against P. gingivalis exist between RA patients and systemically healthy individuals with and without PD.

MATERIALS AND METHODS

The following focused question was addressed: Are the antibody titers against P. gingivalis of RA patients different from systemically healthy individuals with and without PD? A systematic data search was conducted in MEDLINE and EMBASE. The collected data underwent a meta-analysis to detect statistically significant differences in terms of antibody levels between the groups.

RESULTS

From 114 articles found by the search 13 articles met the inclusion criteria and provided data suitable for meta-analysis. After analyzing various levels of confinement the meta-analysis revealed a statistically significant higher antibody titer against P. gingivalis in patients suffering from RA in comparison with systemically and periodontally healthy controls (p < 0.01) and systemically healthy patients with PD (p < 0.01).

CONCLUSION

The present findings indicate that RA is often accompanied by the presence of an immune response against P. gingivalis.

CLINICAL RELEVANCE

The significantly higher antibody response to P. gingivalis in comparison to systemically healthy individuals supports the link between PD and RA by P. gingivalis. Screening of the regularly taken blood samples of RA patients for P. gingivalis antibodies may help to sensitize rheumatologists and RA patients for improving periodontal health.

Impaired Porphyromonas gingivalis-Induced Tumor Necrosis Factor Production by Dendritic Cells Typifies Patients With Rheumatoid Arthritis

OBJECTIVE

The prevalence of periodontitis is increased in patients with rheumatoid arthritis (RA), and the severity of periodontitis can affect the level of arthritis. Porphyromonas gingivalis is one of the main bacteria involved in periodontitis. Our aim was to determine if there are differences in the innate immune response against P gingivalis between healthy controls and RA patients.

METHODS

Monocyte-derived dendritic cells (DCs) from healthy controls, RA patients, and patients with psoriatic arthritis (PsA) were stimulated with P gingivalis, a range of other bacteria, and Toll-like receptor agonists. Cytokine production was determined, and blocking studies were performed to determine which receptors were involved in differential recognition of P gingivalis. Effects on T cell cytokines were also determined in cultures of peripheral blood mononuclear cells (PBMCs).

RESULTS

Upon stimulation with P gingivalis, RA patient DCs produced less tumor necrosis factor as compared to healthy control DCs, which was not observed in PsA patients or upon stimulation with other bacteria. In addition, P gingivalis-mediated activation of RA patient PBMCs showed a clear reduction of interferon-γ production. Among the various possible underlying mechanisms investigated, only blockade of CR3 abolished the difference between RA patients and healthy controls, suggesting the involvement of CR3 in this process.

CONCLUSION

Immune cells from RA patients display a reduced response to P gingivalis, which has functional consequences for the immune response. This may result in prolonged survival of P gingivalis, possibly driving autoantibody formation and a self-perpetuating loop of chronic inflammation. The possible role of CR3 in this process warrants further investigation.

Citrullinated Autoantigens: From Diagnostic Markers to Pathogenetic Mechanisms

The conversion of an arginine residue in a protein to a citrulline residue, a reaction carried out by enzymes called peptidylarginine deiminases (PADs), is rather subtle. One of the terminal imide groups in arginine is replaced by oxygen in citrulline, thus resulting in the loss of positive charge and the gain of 1 dalton. This post-translational modification by PAD enzymes is conserved in vertebrates and affects specific substrates during development and in various mature cell lineages. Citrullination offers a unique perspective on autoimmunity because PAD activity is stringently regulated, yet autoantibodies to citrullinated proteins predictably arise. Autoantigens recognized by anti-citrullinated protein antibodies (ACPA) include extracellular proteins such as filaggrin, collagen II, fibrinogen, and calreticulin; membrane-associated proteins such as myelin basic protein; cytoplasmic proteins such as vimentin and enolase; and even nuclear proteins such as histones. Some ACPA are remarkably effective as diagnostics in autoimmune disorders, most notably rheumatoid arthritis (RA). Several ACPA can be observed before other clinical RA manifestations are apparent. In patients with RA, ACPA may attain a sensitivity that exceeds 70 % and specificity that approaches 96-98 %. The biological context that may account for the induction of ACPA emerges from studies of the cellular response of the innate immune system to acute or chronic stimuli. In response to infections or inflammation, neutrophil granulocytes activate PAD, citrullinate multiple autoantigens, and expel chromatin from the cell. The externalized chromatin is called a neutrophil extracellular "trap" (NET). Citrullination of core and linker histones occurs prior to the release of chromatin from neutrophils, thus implicating the regulation of citrullinated chromatin release in the development of autoreactivity. The citrullination of extracellular autoantigens likely follows the release of NETs and associated PADs. Autoantibodies to citrullinated histones arise in RA, systemic lupus erythematosus, and Felty's syndrome patients. The citrullination of linker histone H1 may play a key role in NET release because the H1 histone regulates the entry and exit of DNA from the nucleosome. Juxtaposition of citrullinated histones with infectious pathogens and complement and immune complexes may compromise tolerance of nuclear autoantigens and promote autoimmunity.

Microbiota and chronic inflammatory arthritis: an interwoven link

BACKGROUND

Only recently, the scientific community gained insights on the importance of the intestinal resident flora for the host's health and disease. Gut microbiota in fact plays a crucial role in modulating innate and acquired immune responses and thus interferes with the fragile balance inflammation versus tolerance.

MAIN BODY

Correlations between gut bacteria composition and the severity of inflammation have been studied in inflammatory bowel diseases. More recently similar alterations in the gut microbiota have been reported in patients with spondyloarthritis, whereas in rheumatoid arthritis an accumulating body of evidence evokes a pathogenic role for the altered oral microbiota in disease development and course. In the context of dysbiosis it is also important to remember that different environmental factors like stress, smoke and dietary components can induce strong bacterial changes and consequent exposure of the intestinal epithelium to a variety of different metabolites, many of which have an unknown function. In this perspective, and in complex disorders like autoimmune diseases, not only the genetic makeup, sex and immunologic context of the individual but also the structure of his microbial community should be taken into account.

CONCLUSIONS

Here we provide a review of the role of the microbiota in the onset, severity and progression of chronic inflammatory arthritis as well as its impact on the therapeutic management of these patients. Furthermore we point-out the complex interwoven link between gut-joint-brain and immune system by reviewing the most recent data on the literature on the importance of environmental factors such as diet, smoke and stress.

Autoantibodies From Single Circulating Plasmablasts React With Citrullinated Antigens and Porphyromonas gingivalis in Rheumatoid Arthritis

OBJECTIVE

Anti-citrullinated protein antibodies (ACPAs) are highly specific for rheumatoid arthritis (RA). However, the molecular basis for ACPA production is still unclear. The purpose of this study was to determine if circulating plasmablasts from RA patients produce ACPAs and whether Porphyromonas gingivalis facilitates the generation of ACPAs.

METHODS

Using a single-cell antibody cloning approach, we generated 217 and 110 monoclonal recombinant antibodies from circulating plasmablasts from 7 RA patients and 4 healthy controls, respectively. Antibody reactivity with citrullinated antigens was tested by a second-generation anti-cyclic citrullinated peptide (anti-CCP) kit and by enzyme-linked immunosorbent assays (ELISAs) against citrullinated human antigens. Antibody reactivity with P gingivalis was tested by ELISAs against outer membrane antigens (OMAs) and citrullinated enolase from P gingivalis.

RESULTS

Approximately 19.5% of plasmablast-derived antibodies from anti-CCP-positive RA patients, but none from 1 anti-CCP-negative RA patient or the healthy controls, specifically recognized citrullinated antigens. The immunoglobulin genes encoding these ACPAs were highly mutated, with increased ratios of replacement mutations to silent mutations, suggesting the involvement of active antigen selection in ACPA generation. Interestingly, 63% of the ACPAs cross-reacted with OMAs and/or citrullinated enolase from P gingivalis. The reactivity of ACPAs against citrullinated proteins from P gingivalis was confirmed by immunoblotting and mass spectrometry. Furthermore, some germline-reverted ACPAs retained their reactivity with P gingivalis antigens but completely lost their reactivity with citrullinated human antigens.

CONCLUSION

These results suggest that circulating plasmablasts in RA patients produce ACPAs and that this process may be facilitated by anti-P gingivalis immune responses.

Microbiota at the crossroads of autoimmunity

Autoimmune diseases have a multifactorial etiology including genetic and environmental factors. Recently, there has been increased appreciation of the critical involvement of the microbiota in the pathogenesis of autoimmunity, although in many cases, the cause and the consequence are not easy to distinguish. Here, we suggest that many of the known cues affecting the function of the immune system, such as genetics, gender, pregnancy and diet, which are consequently involved in autoimmunity, exert their effects by influencing, at least in part, the microbiota composition and activity. This, in turn, modulates the immune response in a way that increases the risk for autoimmunity in predisposed individuals. We further discuss current microbiota-based therapies.

How the microbiota shapes rheumatic diseases

The human gut harbours a tremendously diverse and abundant microbial community that correlates with, and even modulates, many health-related processes. The mucosal interfaces are particularly active sites of microorganism-host interplay. Growing insight into the characteristic composition and functionality of the mucosal microbiota has revealed that the microbiota is involved in mucosal barrier integrity and immune function. This involvement affects proinflammatory and anti-inflammatory processes not only at the epithelial level, but also at remote sites such as the joints. Here, we review the role of the gut microbiota in shaping local and systemic immune responses and how disturbances in the host-microorganism interplay can potentially affect the development and progression of rheumatic diseases. Increasing our understanding of how to promote host-microorganism homeostasis could therefore reveal novel strategies for the prevention or alleviation of rheumatic disease.

Anti-citrullinated peptide antibodies and their value for predicting responses to biologic agents: a review

Anti-citrullinated peptide antibodies (ACPAs) play an important pathogenic role both at the onset and during the disease course. These antibodies precede the clinical appearance of rheumatoid arthritis (RA) and are associated with a less favorable prognosis, both clinically and radiologically. The objective of this work was to conduct a comprehensive review of studies published through September 2015 of ACPAs' role as a predictor of the therapeutic response to the biological agents in RA patients. The review also includes summary of the biology and detection of ACPAs as well as ACPAs in relation to joint disease and CV disease and the possible role of seroconversion. The reviews of studies examining TNF inhibitors and tocilizumab yielded negative results. In the case of rituximab, the data indicated a greater probability of clinical benefit in ACPA(+) patients versus ACPA(-) patients, as has been previously described for rheumatoid factor. Nonetheless, the effect is discreet and heterogeneous. Another drug that may have greater effectiveness in ACPA(+) patients is abatacept. Some studies have suggested that the drug is more efficient in ACPA(+) patients and that those patients show greater drug retention. In a subanalysis of the AMPLE trial, patients with very high ACPA titers who were treated with abatacept had a statistically significant response compared to patients with lower titers. In summary, the available studies suggest that the presence of or high titers of ACPA may predict a better response to rituximab and/or abatacept. Evidence regarding TNFi and tocilizumab is lacking. However, there is a lack of studies with appropriate designs to demonstrate that some drugs are superior to others for ACPA(+) patients.

Autoimmunity of the lung and oral mucosa in a multisystem inflammatory disease: The spark that lights the fire in rheumatoid arthritis?

There is a growing body of evidence to suggest that autoimmunity in patients with rheumatoid arthritis (RA) is initiated outside the joint. This is supported by the observation that circulating autoantibodies, including both rheumatoid factor and anti-citrullinated protein antibody, can be detected in many subjects years before the development of initial joint symptoms leading to an RA diagnosis. Of the potential extra-articular sites implicated in disease initiation, mucosal tissues have garnered increasing attention. Several lines of investigation have separately implicated mucosal tissues from varying anatomic locations as possible initiating sites for RA, including those from the lung and oral cavity. In this review we summarize recent reports incriminating these mucosal tissues as the initial site of autoantibody generation and inflammation in patients with RA.

Prevalence of Periodontitis in Patients with Established Rheumatoid Arthritis: A Swedish Population Based Case-Control Study

INTRODUCTION

The possible hypothesis of a link between periodontitis and rheumatoid arthritis (RA), specifically anti-citrullinated protein antibody (ACPA) positive RA, prompted us to investigate the prevalence of periodontitis in the Swedish Epidemiological Investigation of RA (EIRA), a well-characterised population-based RA case-control cohort.

METHODS

Periodontal status of 2,740 RA cases and 3,942 matched controls was retrieved through linking EIRA with the National Dental Health Registry (DHR), where dental diagnostic- and treatment codes on the adult Swedish population have been registered. Dental records from 100 cases and controls were reviewed to validate the periodontal diagnostic codes in DHR.

RESULTS

The reviewed dental records confirmed 90% of the periodontitis diagnoses in DHR among RA cases, and 88% among controls. We found the positive predictive value of periodontitis diagnoses in the DHR to be 89% (95% CI 78 to 95%) with a sensitivity of 77% (95% CI: 65 to 86%). In total, 86% of EIRA participants were identified in DHR. The risk for periodontitis increased by age and current smoking status in both cases as well as controls. No significant differences in prevalence of periodontal disease in terms of gingivitis, periodontitis, peri-implantitis or increased risk for periodontitis or peri-implantitis were observed between RA cases and controls. In addition, there was no difference on the basis of seropositivity, ACPA or rheumatoid factor (RF), among patients with RA.

CONCLUSIONS

Our data verify that smoking and ageing are risk factors for periodontitis, both in RA and controls. We found no evidence of an increased prevalence of periodontitis in patients with established RA compared to healthy controls, and no differences based on ACPA or RF status among RA subjects.

Toll-like receptors and chronic inflammation in rheumatic diseases: new developments

In the past few years, new developments have been reported on the role of Toll-like receptors (TLRs) in chronic inflammation in rheumatic diseases. The inhibitory function of TLR10 has been demonstrated. Receptors that enhance the function of TLRs, and several TLR inhibitors, have been identified. In addition, the role of the microbiome and TLRs in the onset of rheumatic diseases has been reported. We review novel insights on the role of TLRs in several inflammatory joint diseases, including rheumatoid arthritis, systemic lupus erythematosus, gout and Lyme arthritis, with a focus on the signalling mechanisms mediated by the Toll-IL-1 receptor (TIR) domain, the exogenous and endogenous ligands of TLRs, and the current and future therapeutic strategies to target TLR signalling in rheumatic diseases.

Myelin Basic Protein Citrullination in Multiple Sclerosis: A Potential Therapeutic Target for the Pathology

Multiple sclerosis (MS) is a multifactorial demyelinating disease characterized by neurodegenerative events and autoimmune response against myelin component. Citrullination or deimination, a post-translational modification of protein-bound arginine into citrulline, catalyzed by Ca(2+) dependent peptidylarginine deiminase enzyme (PAD), plays an essential role in physiological processes include gene expression regulation, apoptosis and the plasticity of the central nervous system, while aberrant citrullination can generate new epitopes, thus involving in the initiation and/or progression of autoimmune disorder like MS. Myelin basic protein (MBP) is the major myelin protein and is generally considered to maintain the stability of the myelin sheath. This review describes the MBP citrullination and its consequence, as well as offering further support for the "inside-out" hypothesis that MS is primarily a neurodegenerative disease with secondary inflammatory demyelination. In addition, it discusses the role of MBP citrullination in the immune inflammation and explores the potential of inhibition of PAD enzymes as a therapeutic strategy for the disease.

B cell depletion with rituximab in patients with rheumatoid arthritis: Multiplex bead array reveals the kinetics of IgG and IgA antibodies to citrullinated antigens

The serology of patients with Rheumatoid arthritis (RA) is characterized by persistently raised levels of autoantibodies: Rheumatoid Factors (RhF) against Fc of IgG, and to citrullinated (Cit) protein/peptide sequences: ACPA, recognizing multiple Cit-sequences. B cell depletion therapy based on rituximab delivers good clinical responses in RA patients, particularly in the seropositive group, with responses sometimes lasting beyond the phase of B cell reconstitution. In general, ACPA levels fall following rituximab, but fluctuations with respect to predicting relapse have proved disappointing. In order to identify possible immunodominant specificities within either IgG- or IgA-ACPA we used a Multiplex bead-based array consisting of 30 Cit-peptides/proteins and 22 corresponding native sequences. The kinetics of the serum ACPA response to individual specificities was measured at key points (Baseline, B cell depletion phase, Relapse) within an initial cycle of rituximab therapy in 16 consecutive patients with severe, active RA. All had achieved significant decreases in Disease Activity Scores-28 and maintained B cell depletion in the peripheral blood (<5 CD19+cells/μl) for at least 3 months. At Baseline, mean fluorescence intensity shown by individual IgG- and IgA-ACPA were strongly correlated (R(2) = 0.75; p < 0.0001) but IgA-ACPA were approximately 10-fold lower. Data were Z-normalised in order to compare serial results and antibody classes. At Baseline, a total of 68 IgG- and 51 IgA-ACPA had Z-scores ≥ 1 (above population mean) were identified, with at least one Cit-antigen identified in each serum. ACPA to individual specificities subsequently fluctuated with 3 different patterns. Most 51/68 (75%) IgG- and 48/51 IgA-ACPA (94%) fell between Baseline and Depletion, of which 57% IgG- and 65% IgA-ACPA rebounded pre-Relapse. Interestingly, 17/68 IgG-ACPA (25%) and some IgA-ACPA (3/51; 6%) transiently increased from Baseline, subsequently falling pre-Relapse. Individual responses to particular Cit-epitopes were not linked to particular patterns of fluctuation, but IgG- and IgA-ACPA to individual Cit-antigens often followed similar courses. Some new IgG- and IgA-ACPA, generally to different Cit-antigens however, arose at Relapse in 4 patients. The complexities of the ACPA response after rituximab may therefore reflect its ability to deplete or modify the function of parent B cell clones, which varies between patients. Although relapse following rituximab invariably follows naïve B cell exit from the bone marrow, these studies show that interactions between both 'new' and residual autoreactive memory B cells may be key to resumption of symptoms. The lack of identification of any immunodominant specificity suggests that the process of citrullination, rather than any particular Cit-antigen drives the autoimmune response in RA patients.

Bronchiectasis: Current Concepts in Pathogenesis, Immunology, and Microbiology

Bronchiectasis is a disorder of persistent lung inflammation and recurrent infection, defined by a common pathological end point: irreversible bronchial dilatation arrived at through diverse etiologies. This suggests an interplay between immunogenetic susceptibility, immune dysregulation, bacterial infection, and lung damage. The damaged epithelium impairs mucus removal and facilitates bacterial infection with increased cough, sputum production, and airflow obstruction. Lung infection is caused by respiratory bacterial and fungal pathogens, including Pseudomonas aeruginosa, Haemophilus, Aspergillus fumigatus, and nontuberculous mycobacteria. Recent studies have highlighted the relationship between the lung microbiota and microbial-pathogen niches. Disease may result from environments favoring interleukin-17-driven neutrophilia. Bronchiectasis may present in autoimmune disease, as well as conditions of immune dysregulation, such as combined variable immune deficiency, transporter associated with antigen processing-deficiency syndrome, and hyperimmunoglobulin E syndrome. Differences in prevalence across geography and ethnicity implicate an etiological mix of genetics and environment underpinning susceptibility.

The Roles of Cigarette Smoking and the Lung in the Transitions Between Phases of Preclinical Rheumatoid Arthritis

While the etiology of rheumatoid arthritis (RA) remains to be fully elucidated, recent research has advanced the understanding of RA pathogenesis to the point where clinical trials for RA prevention are underway. The current paradigm for RA pathogenesis is that individuals progress through distinct preclinical phases prior to the onset of clinically apparent RA. These preclinical RA phases consist of genetic risk, local inflammation, presence of RA-related autoantibodies, asymptomatic systemic inflammation, and early non-specific symptoms prior to clinical seropositive RA. Epidemiologic studies have been important in forming hypotheses related to the biology occurring in preclinical RA. Specifically, studies associating cigarette smoking with overall RA risk as well as transitions between phases of preclinical RA were vital in helping to establish the lung as a potential important initiating site in the pathogenesis of seropositive RA. Herein, we review the epidemiology associating smoking with transitions in preclinical phases of RA as well as the recent literature supporting the lung as a critical site in RA pathogenesis.

Antibodies to Porphyromonas gingivalis Indicate Interaction Between Oral Infection, Smoking, and Risk Genes in Rheumatoid Arthritis Etiology

OBJECTIVE

To investigate the role of the periodontal pathogen Porphyromonas gingivalis in the etiology of rheumatoid arthritis (RA) by analyzing the antibody response to the P gingivalis virulence factor arginine gingipain type B (RgpB) in relation to anti-citrullinated protein antibodies (ACPAs), smoking, and HLA-DRB1 shared epitope (SE) alleles in patients with periodontitis, patients with RA, and controls.

METHODS

Anti-RgpB IgG was measured by enzyme-linked immunosorbent assay in 65 periodontitis patients and 59 controls without periodontitis, and in 1,974 RA patients and 377 controls without RA from the Swedish population-based case-control Epidemiological Investigation of Rheumatoid Arthritis (EIRA) study. Autoantibody status, smoking habits, and genetic data were retrieved from the EIRA database. Differences in antibody levels were examined using the Mann-Whitney U test. Unconditional logistic regression was used to calculate odds ratios (ORs) with 95% confidence intervals (95% CIs) for the association of anti-RgpB IgG with different subsets of RA patients.

RESULTS

Anti-RgpB antibody levels were significantly elevated in periodontitis patients compared to controls without periodontitis, in RA patients compared to controls without RA, and in ACPA-positive RA patients compared to ACPA-negative RA patients. There was a significant association between anti-RgpB IgG and RA (OR 2.96 [95% CI 2.00, 4.37]), which was even stronger than the association between smoking and RA (OR 1.37 [95% CI 1.07, 1.74]), and in ACPA-positive RA there were interactions between anti-RgpB antibodies and both smoking and the HLA-DRB1 SE.

CONCLUSION

Our study suggests that the previously reported link between periodontitis and RA could be accounted for by P gingivalis infection, and we conclude that P gingivalis is a credible candidate for triggering and/or driving autoimmunity and autoimmune disease in a subset of RA patients.

Dysbiosis May Trigger Autoimmune Diseases via Inappropriate Post-Translational Modification of Host Proteins

The gut ecosystem with myriads of microorganisms and the high concentration of immune system cells can be considered as a separate organ on its own. The balanced interaction between the host and microbial cells has been shaped during the long co-evolutionary process. In dysbiotic conditions, however, this balance is compromised and results in abnormal interaction between the host and microbiota. It is hypothesize here that the changed spectrum of microbial enzymes involved in post-translational modification of proteins (PTMP) may contribute to the aberrant modification of host proteins thus generating autoimmune responses by the host, resulting in autoimmune diseases.

Application of synthetic peptides for detection of anti-citrullinated peptide antibodies

Anti-citrullinated protein antibodies (ACPAs) are a hallmark of rheumatoid arthritis (RA) and represent an important tool for the serological diagnosis of RA. In this study, we describe ACPA reactivity to overlapping citrullinated Epstein-Barr virus nuclear antigen-1 (EBNA-1)-derived peptides and analyze their potential as substrates for ACPA detection by streptavidin capture enzyme-linked immunosorbent assay. Using systematically overlapping peptides, containing a 10 amino acid overlap, labelled with biotin C-terminally or N-terminally, sera from 160 individuals (RA sera (n=60), healthy controls (n=40), systemic lupus erythematosus (n=20), Sjögren's syndrome (n=40)) were screened for antibody reactivity. Antibodies to a panel of five citrullinated EBNA-1 peptides were found in 67% of RA sera, exclusively of the IgG isotype, while 53% of the patient sera reacted with a single peptide, ARGGSRERARGRGRG-Cit-GEKR, accounting for more than half of the ACPA reactivity alone. Moreover, these antibodies were detected in 10% of CCP2-negative RA sera. In addition, 47% of the RA sera reacted with two or three citrullinated EBNA-1 peptides from the selected peptide panel. Furthermore, a negative correlation between the biotin attachment site and the location of citrulline in the peptides was found, i.e. the closer the citrulline was located to biotin, the lower the antibody reactivity. Our data suggest that citrullinated EBNA-1 peptides may be considered a substrate for the detection of ACPAs and that the presence of Epstein-Barr virus may play a role in the induction of these autoantibodies.

Potential protein targets of the peptidylarginine deiminase 2 and peptidylarginine deiminase 4 enzymes in rheumatoid synovial tissue and its possible meaning

OBJECTIVE

The molecular mechanism of citrullination involves the calcium-dependent peptidylarginine deiminase (PAD) family of enzymes. These enzymes induce a stereochemical modification of normal proteins and transform them into autoantigens, which in rheumatoid arthritis trigger a complex cascade of joint inflammatory events followed by chronic synovitis, pannus formation, and finally, cartilage destruction. By hypothesizing that PAD2 and PAD4 enzymes produce autoantigens, we investigated five possible synovial protein targets of PAD enzymes.

MATERIAL AND METHODS

We measured PAD2, PAD4, and citrullinated proteins in 10 rheumatoid and 10 osteoarthritis synovial biopsies and then assessed the post-translational modifications of fibrinogen, cytokeratin, tubulin, IgG, and vimentin proteins using a double-fluorescence assay with specific antibodies and an affinity-purified anti-citrullinated peptide (CCP) antibody. The degree of co-localization was analyzed, and statistical significance was determined by ANOVA, Fisher's exact test, and regression analysis.

RESULTS

The principal results of this study demonstrated that citrullinated proteins, such as fibrinogen, IgG, and other probed proteins, were targets of PAD2 and PAD4 activity in rheumatoid synovial biopsies, whereas osteoarthritis biopsies were negative for this enzyme (p<0.0001). An analysis of citrullination sites using the UniProtKB/Swiss-Prot data bank predicts that the secondary structure of the analyzed proteins displays most of the sites for citrullination; a discussion regarding its possible meaning in terms of pathogenesis is made.

CONCLUSION

Our results support the conclusion that the synovial citrullination of proteins is PAD2 and PAD4 dependent. Furthermore, there is a collection of candidate proteins that can be citrullinated.