Citrullinated proteins: sparks that may ignite the fire in rheumatoid arthritis

Anti-cyclic citrullinated peptide antibodies in ulcerative colitis, and its relation with disease activity

BACKGROUND

Ulcerative colitis an inflammatory bowel disease (IBD) and chronically idiopathic immune related that associates with extraintestinal manifestations such as arthritis. Despite of the highly specificity of anticyclic citrullinated peptide (CCP) antibodies for rheumatoid arthritis, their role in IBD remains unclear. There are only a few studies on the prevalence of anti-CCP antibodies in patients with IBD. This study aimed to assess the prevalence of anti- CCP antibodies in ulcerative colitis and to investigate possible associations with their clinical and laboratory characteristics Methods: In this cross-sectional study, 93 consecutive patients with ulcerative colitis referred to gastroenterology clinics in Razi referral hospital of Rasht, Iran, from September 2010 to September 2011. Rheumatologic examination, demographic data and clinical presentation of patients were recorded on specially prepared data sheets. Blood sample was collected for assessment of anti-CCP and other laboratory tests. Data were analyzed by the Chi square test, Fisher Exact test and student t test, using the SPSS 20 software for Windows, and P value less than 0.05 was considered significant.

RESULTS

Of 93 patients, anti-CCP antibodies detected in 10.8% of cases (CI 95%: 4.5-17.1%). There were a significant relation between the prevalence of anti CCP positivity and aphthous ulcers and ocular manifestations whereas other parameters were not significantly related.

CONCLUSION

Anti CCP may have a possible role in some ulcerative colitis manifestations but there was no association between the presence of these antibodies and activity or extension of inflammatory colitis. We suggest other studies especially molecular studies to investigate other aspects of these antibodies in IBD patients.

Serum biomarkers reflecting specific tumor tissue remodeling processes are valuable diagnostic tools for lung cancer

Extracellular matrix (ECM) proteins, such as collagen type I and elastin, and intermediate filament (IMF) proteins, such as vimentin are modified and dysregulated as part of the malignant changes leading to disruption of tissue homeostasis. Noninvasive biomarkers that reflect such changes may have a great potential for cancer. Levels of matrix metalloproteinase (MMP) generated fragments of type I collagen (C1M), of elastin (ELM), and of citrullinated vimentin (VICM) were measured in serum from patients with lung cancer (n = 40), gastrointestinal cancer (n = 25), prostate cancer (n = 14), malignant melanoma (n = 7), chronic obstructive pulmonary disease (COPD) (n = 13), and idiopathic pulmonary fibrosis (IPF) (n = 10), as well as in age-matched controls (n = 33). The area under the receiver operating characteristics (AUROC) was calculated and a diagnostic decision tree generated from specific cutoff values. C1M and VICM were significantly elevated in lung cancer patients as compared with healthy controls (AUROC = 0.98, P < 0.0001) and other cancers (AUROC = 0.83 P < 0.0001). A trend was detected when comparing lung cancer with COPD+IPF. No difference could be seen for ELM. Interestingly, C1M and VICM were able to identify patients with lung cancer with a positive predictive value of 0.9 and an odds ratio of 40 (95% CI = 8.7–186, P < 0.0001). Biomarkers specifically reflecting degradation of collagen type I and citrullinated vimentin are applicable for lung cancer patients. Our data indicate that biomarkers reflecting ECM and IMF protein dysregulation are highly applicable in the lung cancer setting. We speculate that these markers may aid in diagnosing and characterizing patients with lung cancer.

The Frequency of anti-CCP antibodies in patients with rheumatoid arthritis and psoriatic arthritis and their relationship with clinical features and parameters of angiogenesis: A comparative study

OBJECTIVE

Macrophage migration inhibitory factor (MIF) and vascular endothelial growth factor (VEGF), as crucial parameters of angiogenesis and inflammation, were evaluated to identify the role of cyclic citrullinated peptide antibodies (anti-CCP) during angiogenesis in rheumatoid arthritis (RA) and psoriatic arthritis (PsA).

MATERIAL AND METHODS

A total of 145 patients with RA, 44 patients with PsA, and 73 healthy subjects were included in this study. The clinical features, total blood counts, and acute phase parameters of RA and PsA patients were recorded. Anti-CCP antibody, VEGF, and MIF levels were determined with enzyme-linked immunosorbent assay (ELISA).

RESULTS

Anti-CCP positivity was significantly higher in the RA group (69%) than in both PsA (20.6%) and controls (8.2%) (p values<0.001). There was no difference between anti-CCP-positive and -negative RA patients regarding the extra-articular manifestations (p>0.05). VEGF and MIF levels were similar in anti-CCP-positive and -negative RA patients (all p values>0.05). The specificity of anti-CCP antibodies for RA was found to be 87.2%. No relationship was found between anti-CCP antibody positivity and clinical features, disease activity, functional disability as assessed by health assessment questionnaire scores, and extra-articular manifestations. There was no relationship between parameters of angiogenesis and anti-CCP antibody positivity. Both RF and anti-CCP antibodies were observed to be positive in most patients with RA.

CONCLUSION

Either RF or anti-CCP antibody was positive in a considerable proportion of our RA patients. Therefore, anti-CCP antibodies are important in the diagnosis of RF-negative patients who present with clinical findings of RA.

Gene-environmental interaction between smoking and shared epitope on the development of anti-cyclic citrullinated peptide antibodies in rheumatoid arthritis: a meta-analysis

OBJECTIVE

The aim of this study was to determine the gene-environment interactions of smoking and shared epitope (SE) both separately and combined on anti-cyclic citrullinated peptide (CCP) antibodies in patients with rheumatoid arthritis (RA).

METHODS

The literature was searched using the MEDLINE, EMBASE and Cochrane databases. A meta-analysis on the associations between tobacco exposure (TE) and/or SE and the development of anti-CCP antibodies in patients with RA was performed.

RESULTS

Eight comparison studies with 5317 RA patients were considered in this meta-analysis. The odds ratio (OR) for positive anti-CCP antibodies in TE+/SE- patients with RA was increased compared with TE-/SE- patients (OR = 1.373, 95% CI = 1.111-1.698, P = 0.003). The ORs for positive anti-CCP antibodies in TE-/SE+ patients and TE+/SE+ patients with RA were also increased compared with TE-/SE- patients (OR = 2.678, 95% CI = 2.031-3.532, P < 1.0 × 1(0-9) in TE-/SE+; OR = 4.233, 95% CI = 2.458-7.291, P = 1.9 × 10(-8) in TE+/SE+). Stratification by ethnicity indicated the same pattern as that shown in the overall group. The OR for positive anti-CCP antibodies in TE+/SE+ patients with RA was much higher than in TE-/SE- patients in Europeans and Asians (OR = 3.879, 95% CI = 2.203-6.830, P = 2.6 × 10(-7); OR = 10.504, 95% CI = 3.182-34.67, P = 1.1 × 10(-4)).

CONCLUSIONS

This meta-analysis suggests a gene-environmental interaction between smoking and SE for the development of anti-CCP antibodies.

A molecular basis for the association of the HLA-DRB1 locus, citrullination, and rheumatoid arthritis

Rheumatoid arthritis (RA) is strongly associated with the human leukocyte antigen (HLA)-DRB1 locus that possesses the shared susceptibility epitope (SE) and the citrullination of self-antigens. We show how citrullinated aggrecan and vimentin epitopes bind to HLA-DRB1*04:01/04. Citrulline was accommodated within the electropositive P4 pocket of HLA-DRB1*04:01/04, whereas the electronegative P4 pocket of the RA-resistant HLA-DRB1*04:02 allomorph interacted with arginine or citrulline-containing epitopes. Peptide elution studies revealed P4 arginine-containing peptides from HLA-DRB1*04:02, but not from HLA-DRB1*04:01/04. Citrullination altered protease susceptibility of vimentin, thereby generating self-epitopes that are presented to T cells in HLA-DRB1*04:01(+) individuals. Using HLA-II tetramers, we observed citrullinated vimentin- and aggrecan-specific CD4(+) T cells in the peripheral blood of HLA-DRB1*04:01(+) RA-affected and healthy individuals. In RA patients, autoreactive T cell numbers correlated with disease activity and were deficient in regulatory T cells relative to healthy individuals. These findings reshape our understanding of the association between citrullination, the HLA-DRB1 locus, and T cell autoreactivity in RA.

Anti-citrullinated protein antibodies and their clinical utility in rheumatoid arthritis

One of the most important serological discoveries in rheumatology in recent years has been the characterization of autoantigens in rheumatoid arthritis (RA) containing the amino acid citrulline. There are many citrullinated proteins in the inflamed RA synovium. Rheumatoid factor (RF), which is the immunologic hallmark of RA, is not specific for RA, as it is found in 5% of healthy individuals and in 10-20% of those over the age of 65 years. RFs are of low titer in early disease stages when a clear diagnosis is often not yet possible; But anti-citrullinated protein antibodies (ACPAs) can be found early in the disease course of RA, even years before the onset of clinical symptoms. The identification of citrullinated epitopes led to the development of the first and later second generation anti-cyclic citrullinated peptide (anti-CCP) antibody assays. Anti-CCP2 antibody has shown a specificity of 98% in sera from patients with established RA and 96% in sera from subjects with early RA. Anti-CCP can predict erosive disease, therefore could be a good serological marker for RA diagnosis.

The role of the microbiome in rheumatic diseases

There is a growing understanding of the mechanisms by which the influence of the microbiota projects beyond sites of primary mucosal occupation to other human body systems. Bacteria present in the intestinal tract exert a profound effect on the host immune system, both locally and at distant sites. The oral cavity has its own characteristic microbiota, which concentrates in periodontal tissues and is in close association with a permeable epithelium. In this review we examine evidence which supports a role for the microbiome in the aetiology of rheumatic disease. We also discuss how changes in the composition of the microbiota, particularly within the gastrointestinal tract, may be affected by genetics, diet, and use of antimicrobial agents. Evidence is presented to support the theory that an altered microbiota is a factor in the initiation and perpetuation of inflammatory diseases, including rheumatoid arthritis (RA), spondyloarthritis (SpA), and inflammatory bowel disease (IBD). Mechanisms through which the microbiota may be involved in the pathogenesis of these diseases include altered epithelial and mucosal permeability, loss of immune tolerance to components of the indigenous microbiota, and trafficking of both activated immune cells and antigenic material to the joints. The potential to manipulate the microbiome, by application of probiotics and faecal microbial transplant (FMT), is now being investigated. Both approaches are in their infancy with regard to management of rheumatic disease but their potential is worthy of consideration, given the need for novel therapeutic approaches, and the emerging recognition of the importance of microbial interactions with human hosts.

Identification of novel autoantigen in the synovial fluid of rheumatoid arthritis patients using an immunoproteomics approach

Rheumatoid arthritis (RA) is a chronic, autoimmune and inflammatory joint disease with a poorly understood etiology. Despite widespread diagnostic use of anti-citrullinated protein antibodies and rheumatoid factor proteins there is a strong demand for novel serological biomarkers to improve the diagnosis this disease. The present study was aimed to identify novel autoantigens involved in rheumatoid arthritis (RA) pathogenesis through immune-proteomic strategy. Synovial fluid samples from clinically diagnosed RA patients were separated on two-dimensional gel electrophoresis (2-DE). Samples from patients with non-RA rheumatisms (osteoarthritis and trauma) were used as controls. Immunoreactive proteins were spotted by Western blotting followed by identification through Q-TOF mass spectrometer analysis. Forty Western blots were generated using plasma from ten individual RA patients and 33 reactive spots were identified, 20 from the high molecular weight (HMW) gel and 13 from the low molecular weight (LMW) gel. Among the 33 common immunogenic spots, 18 distinct autoantigens were identified, out of which 14 are novel proteins in this context. Expression analysis of five important proteins, vimentin, gelsolin, alpha 2 HS glycoprotein (AHSG), glial fibrillary acidic protein (GFAP), and α1B-glycoprotein (A1BG) by Western blot analysis using their specific antibodies revealed their higher expression in RA synovial fluid as compared to non-RA samples. Recombinantly expressed GFAP and A1BG protein were used to develop an in-house ELISA to quantify the amount of autoantibodies in the RA patients. RA patients revealed an increase in the expression of GFAP and A1BG in the plasma as compared to osteoarthritis patients. Therefore, GFAP and A1BG can be proposed as potential new autoantigens of diagnostic importance for RA subjects. Further characterization of these proteins in rheumatoid arthritis will be helpful in understanding the role of these proteins in the disease pathogenesis providing new diagnostic tool with better specificity and accurate detection of the disease.

Dendritic cells and the promise of antigen-specific therapy in rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic inflammatory disease resulting from an autoimmune response to self-antigens, leading to inflammation of synovial tissue of joints and subsequent cartilage and bone erosion. Current disease-modifying anti-rheumatic drugs and biologic inhibitors of TNF, IL-6, T cells and B cells block inflammation nonspecifically, which may lead to adverse effects, including infection. They do not generally induce long-term drug-free remission or restoration of immune tolerance to self-antigens, and lifelong treatment is usual. The development of antigen-specific strategies in RA has so far been limited by insufficient knowledge of autoantigens, of the autoimmune pathogenesis of RA and of the mechanisms of immune tolerance in man. Effective tolerance-inducing antigen-specific immunotherapeutic strategies hold promise of greater specificity, of lower toxicity and of a longer-term solution for controlling or even preventing RA. This paper reviews current understanding of autoantigens and their relationship to immunopathogenesis of RA, and emerging therapeutics that aim to leverage normal tolerance mechanisms for implementation of antigen-specific therapy in RA.

Citrullinated fibronectin inhibits apoptosis and promotes the secretion of pro-inflammatory cytokines in fibroblast-like synoviocytes in rheumatoid arthritis

Introduction

Rheumatoid arthritis (RA) is characterized by synovial lining hyperplasia, in which there may be an imbalance between the growth and death of fibroblast-like synoviocytes (FLSs). Antibodies against citrullinated proteins are proposed to induce RA. This study aimed to investigate the pathogenic role of citrullinated fibronectin (cFn) in RA.

Methods

The distribution of fibronectin (Fn) and cFn in synovial tissues from RA and osteoarthritis (OA) patients was examined by immunohistochemical and double immunofluorescence analysis. FLSs were isolated from RA and OA patients and treated with Fn or cFn. Apoptosis was detected by flow cytometry and TUNEL assay. The expression of survivin, caspase-3, cyclin-B1, Bcl-2 and Bax was detected by real-time PCR. The secretion of proinflammatory cytokines was measured by ELISA.

Results

Fn formed extracellular aggregates that were specifically citrullinated in synovial tissues of RA patients, but no Fn deposits were observed in those of OA patients. Fn induced the apoptosis of RA and OA FLSs while cFn inhibited the apoptosis of RA and OA FLSs. Fn significantly increased the expression of caspase-3 and decreased the expression of survivin and cyclin-B1 in FLSs from RA and OA patients. cFn significantly increased the expression of survivin in RA FLSs. Furthermore, cFn increased the secretion of TNF-α and IL-1 by FLSs.

Conclusions

cFn plays a potential pathophysiologic role in RA by inhibiting apoptosis and increasing proinflammatory cytokine secretion of FLSs.

T-cell autoreactivity to citrullinated autoantigenic peptides in rheumatoid arthritis patients carrying HLA-DRB1 shared epitope alleles

Introduction

Anti-citrullinated peptide antibodies are found in rheumatoid arthritis (RA) patients with HLA-DRβ chains encoding the shared epitope (SE) sequence. Citrullination increases self-antigen immunogenicity, through increased binding affinity to SE-containing HLA-DR molecules. To characterise T-cell autoreactivity towards citrullinated self-epitopes, we profiled responses of SE⁺ healthy controls and RA patients to citrullinated and unmodified epitopes of four autoantigens.

Methods

We compared T-cell proliferative and cytokine responses to citrullinated and native type II collagen 1,237 to 1,249, vimentin 66 to 78, aggrecan 84 to 103 and fibrinogen 79 to 91 in six SE⁺ healthy controls and in 21 RA patients with varying disease duration. Cytokine-producing cells were stained after incubation with peptide in the presence of Brefeldin-A.

Results

Although proliferative responses were low, IL-6, IL-17 and TNF were secreted by CD4⁺ T cells of SE⁺ RA patients and healthy controls, as well as IFNγ and IL-10 secreted by RA patients, in response to citrullinated peptides. Of the epitopes tested, citrullinated aggrecan was most immunogenic. Patients with early RA were more likely to produce IL-6 in response to no epitope or to citrullinated aggrecan, while patients with longstanding RA were more likely to produce IL-6 to more than one epitope. Cytokine-producing CD4⁺ T cells included the CD45RO⁺ and CD45RO^- and the CD28⁺ and CD28^- subsets in RA patients.

Conclusion

Proinflammatory cytokines were produced by CD4⁺ T cells in SE⁺ individuals in response to citrullinated self-epitopes, of which citrullinated aggrecan was most immunogenic. Our data suggest that the T-cell response to citrullinated self-epitopes matures and diversifies with development of RA.

Inhibiting citrullination in rheumatoid arthritis: taking fuel from the fire

Citrullination is a post-translational modification catalysed by peptidylarginine deiminase and is a common feature of inflammation. The presence of anti-citrullinated protein/peptide antibodies (ACPA), however, is unique to rheumatoid arthritis. Several lines of evidence suggest that ACPA are important in the pathogenesis of rheumatoid arthritis. A popular hypothesis for this pathogenesis is a two-hit model. The first hit gives rise to ACPA, and the second hit, an unrelated episode of synovial inflammation accompanied by citrullination, is perpetuated by the pre-existing antibodies. This model suggests that reducing citrullination might ameliorate disease. Recent findings indicate that citrullination closely correlates with inflammation, and that glucocorticoids decrease peptidylarginine deiminase expression independent of their other anti-inflammatory effects.

Oxidative stress-induced modifications of histidyl-tRNA synthetase affect its tRNA aminoacylation activity but not its immunoreactivity

The aminoacyl-tRNA synthetases are ubiquitously expressed enzymes that catalyze the esterification of amino acids to their cognate tRNAs. Autoantibodies against several aminoacyl-tRNA synthetases are found in autoimmune polymyositis and dermatomyositis patients. Because necrosis is often found in skeletal muscle biopsies of these patients, we hypothesized that cell-death-induced protein modifications may help in breaking immunological tolerance. Since cell death is associated with oxidative stress, the effect of oxidative stress on the main myositis-specific autoantibody target Jo-1 (histidyl-tRNA synthetase; HisRS) was studied in detail. The exposure of Jurkat cells to hydrogen peroxide resulted in the detection of several oxidized methionines and one oxidized tryptophan residue in the HisRS protein, as demonstrated by mass spectrometry. Unexpectedly, the tRNA aminoacylation activity of HisRS appeared to be increased upon oxidative modification. The analysis of myositis patient sera did not lead to the detection of autoantibodies that are specifically reactive with the modified HisRS protein. The results of this study demonstrate that the Jo-1/HisRS autoantigen is modified under oxidative stress conditions. The consequences of these modifications for the function of HisRS and its autoantigenicity are discussed.

Mutated citrullinated vimentin antibodies in rheumatoid arthritis

Rheumatoid arthritis (RA) is the most common inflammatory systemic autoimmune disease, primarily affecting the peripheral joints. The past decade has been marked with revolutionary changes both in the therapeutic and diagnostic perspectives of RA. The discovery of an RA-specific citrullination-driven immune reaction gave a substantial contribution in the diagnostic approach to RA. Efforts directed towards the identification of the antigenic target specifically recognized by these autoantibodies resulted in the identification of vimentin in citrullinated form as the potential native antigen, among other proteins. Furthermore, it was found that the mutation of vimentin represents an independent trigger of antigenic properties, in addition to citrullination. As a result of this discovery, a commercial ELISA using mutated citrullinated vimentin (MCV) was developed. Increasingly, data now support the use of anti-MCV in RA diagnosis and prognosis for errosion. This review summarizes the research to date on the use of anti-MCV in RA diagnosis and prognosis and its potential use as a therapeutic marker. The pathologic role of these antibodies in RA disease is also discussed.

A systematic review of serum biomarkers anti-cyclic citrullinated Peptide and rheumatoid factor as tests for rheumatoid arthritis

This systematic review assesses the current status of anti-cyclic citrullinated peptide (anti-CCP) and rheumatoid factor (RF) tests in the diagnosis and prognosis of rheumatoid arthritis (RA). We reviewed publications on tests and biomarkers for early diagnosis of RA from English-language MEDLINE-indexed journals and non-MEDLINE-indexed sources. 85 publications were identified and reviewed, including 68 studies from MEDLINE and 17 non-MEDLINE sources. Anti-CCP2 assays provide improved sensitivity over anti-CCP assays and RF, but anti-CCP2 and RF assays in combination demonstrate a positive predictive value (PPV) nearing 100%, greater than the PPV of either of the tests alone. The combination also appears to be able to distinguish between patients whose disease course is expected to be more severe and both tests are incorporated in the 2010 ACR Rheumatoid Arthritis Classification Criteria. While the clinical value of anti-CCP tests has been established, differences in cut-off values, sensitivities and specificities exist between first-, second- and third-generation tests and harmonization efforts are under way. Anti-CCP and RF are clinically valuable biomarkers for the diagnosis and prognosis of RA patients. The combination of the two biomarkers in conjunction with other clinical measures is an important tool for the diagnosis and management of RA patients.

Citrullination of CNS proteins in the pathogenesis of multiple sclerosis

Multiple sclerosis is a chronic immune-mediated disease of the CNS. Although it is a predominantly T-cell mediated condition, B cells and autoreactive antibodies play an important role in its pathogenesis, with the presence of oligoclonal immunoglobulins in the cerebrospinal fluid being an important diagnostic indicator. The target of these immunoglobulins has not yet been fully characterized. However, post-translational modifications of CNS-specific proteins are thought to contribute to their production through the generation of novel epitopes. One post-translational modification in particular, the conversion of the amino acid arginine to the nonstandard amino acid, citrulline, has been increasingly described in the literature as a factor in the pathogenesis of this condition. In this article, we summarize and discuss the current knowledge on citrullination in multiple sclerosis, the importance of this in relation to its pathogenesis and, potentially, its diagnosis.

Citrullination of autoantigens: upstream of TNFα in the pathogenesis of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterised by synovial inflammation and destruction of joints. Over 20 years ago, tumour necrosis factor alpha (TNFα) was identified as a key player in a cytokine network, whose multifunctional effects could account for both the inflammation and destruction in RA. The remarkable efficacy of TNF inhibitors in the treatment of RA has resulted in extensive research addressing the regulation of TNFα production responsible for this excessive production. The discovery of autoimmunity to citrullinated protein/peptide antigens (ACPA) has led the concept that ACPA may be the essential link between disease susceptibility factors and the production of TNFα, which ultimately accounts for the disease phenotype. In this review we will consider (1) the mechanisms of citrullination, both physiological and pathological, (2) how known genetic and environmental factors could drive this peculiar form of autoimmunity and (3) how the immune response could lead to excessive production of TNFα by the synovial cells and ultimately to the disease phenotype (Fig. 1).

Anti-CCP antibodies: the past, the present and the future

Rheumatoid arthritis (RA) is an autoimmune disease characterized by autoantibodies against citrullinated antigens. The importance of citrulline for the epitopes bound by these autoantibodies, referred to as ACPA (anti-citrullinated peptide/protein antibodies), was first described in 1998. In addition to citrullinated proteins, cyclic citrullinated peptides (CCP) can also be used as test substrates for detecting ACPA. The standard test for these antibodies is the second-generation CCP (CCP2) test, which is one of the best in terms of sensitivity and specificity. The generation of ACPA is an early event in the disease course, and is dependent on the presence of certain MHC class II alleles. ACPA in the inflamed synovium have been shown to associate with citrullinated antigens to form immune complexes, resulting in progression of the inflammatory process. The involvement of ACPA in the chronicity of RA is probably the reason why ACPA-positive patients have a more erosive disease course than ACPA-negative patients. The presence of ACPA has been included in the 2010 RA classification criteria. Thus, it is important to further standardize ACPA testing, for example by including an internal serum standard, which may lead to a better distinction between low and high ACPA levels.

Environmental pathways to autoimmune diseases: the cases of primary biliary cirrhosis and multiple sclerosis

The pathways leading to autoimmunity remain enigmatic despite numerous lines of experimental inquiry and epidemiological evidence. The mechanisms leading to the initiation and perpetuation of specific diseases such as primary biliary cirrhosis (PBC) or multiple sclerosis (MS) remain largely enigmatic, although it is established that a combination of genetic predisposition and environmental stimulation is required. The growing number of genome-wide association studies and the largely incomplete concordance for autoimmune diseases in monozygotic twins concur to support the role of the environment (including infectious agents and chemicals) in the breakdown of tolerance leading to autoimmunity through different mechanisms. In the present article we illustrate the current hypotheses related to an environmental impact on the onset of PBC and MS as two representative conditions investigated with complementary approaches. Indeed, while a role of post-translational antigen modifications has been proposed for MS, this field remain unexplored in PBC where, conversely, most evidence is gathered from geoepidemiology and experimental data on xenobiotics or infectious agents.

Development and use of clickable activity based protein profiling agents for protein arginine deiminase 4

The protein arginine deiminases (PADs), which catalyze the hydrolysis of peptidyl-arginine to form peptidyl-citrulline, are potential targets for the development of a rheumatoid arthritis (RA) therapeutic, as well as other human diseases including colitis and cancer. Additionally, these enzymes, and in particular PAD4, appear to play important roles in a variety of cell signaling pathways including apoptosis, differentiation, and transcriptional regulation. To better understand the factors that regulate in vivo PAD4 activity, we set out to design and synthesize a series of activity-based protein profiling (ABPP) reagents that target this enzyme. Herein we describe the design, synthesis, and evaluation of six ABPPs including (i) FITC-conjugated F-amidine (FFA1 and 2) and Cl-amidine (FCA1 and 2), and (ii) biotin-conjugated F-amidine (BFA) and Cl-amidine (BCA). We further demonstrate the utility of these probes for labeling PAD4 in cells, as well as for isolating PAD4 and PAD4 binding proteins. These probes will undoubtedly prove to be powerful tools that can be used to dissect the factors controlling the dynamics of PAD4 expression, activity, and function.

Autoantibody testing for autoimmune disease

The proper use and interpretation of serologic testing for diagnosing autoimmune diseases presents a challenge to clinicians for several reasons. Most laboratory tests for autoimmune disease are significantly less than 100% sensitive or specific. In addition, different techniques for the same antibody test may give different results, such as indirect immunofluorescence and multiplex bead assay for antinuclear antibody. Autoantibody testing should only be performed in the context of the clinical workup of patients who have a reasonable likelihood of having the disease for which the testing is relevant. Otherwise, the predictive value of a positive test is too low. Particularly with antinuclear antibody and antineutrophil cytoplasmic antibody testing, clinicians must know the methodology through which the tests are being performed, and should develop a relationship with the laboratory pathologist so that inconsistent or surprising results can be investigated.

Rheumatoid arthritis and periodontitis; a possible link via citrullination

Rheumatoid Arthritis (RA) and chronic and aggressive periodontitis are chronic inflammatory disorders characterized by deregulation of the host inflammatory response. Increased secretion of pro-inflammatory mediators results in soft and hard tissue destruction of the synovium and periodontium respectively. Both diseases share risk factors and have pathological pathways in common, resulting in loss of function and disability as a final clinical outcome. This article discusses possible interactions, particularly related to the periodontal pathogen Porphyromonas gingivalis, which could explain the observed association between these two prevalent diseases.

Immune complexes containing citrullinated fibrinogen costimulate macrophages via Toll-like receptor 4 and Fcγ receptor

OBJECTIVE

Rheumatoid arthritis (RA) is associated with the presence of anti-citrullinated protein antibodies (ACPAs). Nearly two-thirds of patients with ACPA-positive RA have immune complexes that contain citrullinated fibrinogen, and these citrullinated fibrinogen-containing immune complexes (cFb-IC) can exacerbate disease in murine models of RA; however, the exact role of such ACPA ICs in RA pathogenesis has remained elusive. We undertook the present study to investigate a novel mechanism by which ACPAs specifically targeting citrullinated fibrinogen may directly stimulate macrophage tumor necrosis factor (TNF) production.

METHODS

Murine or human macrophages were stimulated with native fibrinogen (nFb), cFb, or in vitro-generated nFb-IC or cFb-IC, and TNF production was measured by enzyme-linked immunosorbent assay. ICs were generated with either polyclonal anti-Fb antibodies or pooled IgG from patients with ACPA-positive RA. To evaluate the role of the Toll-like receptor 4 (TLR-4)/myeloid differentiation protein (MyD88) pathway and the Fcγ receptor (FcγR) pathway in the induction of TNF by Fb and Fb-IC, parallel experiments were performed using 1) TLR-4-deficient or MyD88-deficient macrophages, and 2) inhibitors of TLR-4 or FcγR.

RESULTS

Citrullinated Fb stimulated macrophage TNF production more potently than did native Fb. Incorporation of cFb into ICs augmented its ability to stimulate TNF production by macrophages. Stimulation of TNF by cFb was dependent on TLR-4 and MyD88, while stimulation by cFb-IC was dependent on both TLR-4/MyD88 and FcγR.

CONCLUSION

We demonstrated that cFb-IC can costimulate macrophages via dual engagement of TLR-4 and FcγR, resulting in the synergistic induction of TNF production. Our findings suggest a potential role of citrullination in increasing the potency of an endogenous innate immune ligand and provide insight into the mechanism by which anticitrulline autoimmunity may contribute to the onset and propagation of inflammation in RA.

The relevance of citrullinated vimentin in the production of antibodies against citrullinated proteins and the pathogenesis of rheumatoid arthritis

Antibodies against citrullinated proteins (ACPAs) are highly specific for RA. Since the discovery of these antibodies, several of studies that focused on the presence and identity of citrullinated proteins in the joints of RA patients have been carried out. The best-known antigens that bind ACPAs are citrullinated filaggrin, Type II collagen (CII), α-enolase, fibrinogen and vimentin. This review compares citrullinated filaggrin, CII, α-enolase and fibrinogen with vimentin in their contribution to ACPA triggering, and gives an overview of the literature in which the role of citrullinated and non-citrullinated vimentin in the onset of ACPA production and the pathogenesis of RA is discussed.

Citrullinated collagens in the pathogenesis of rheumatoid arthritis

Citrulline formation through the deimination of arginine residues has recently been identified as an enzymatic post-translational modification of proteins that could be related to breaking the tolerance to self-antigens in the development of rheumatoid arthritis. Autoantibodies recognizing citrullinated peptides are highly specific indicators of early rheumatoid arthritis. However, current knowledge of the natural proteins that are citrullinated does not explain the main manifestations of the disease, that is, progressive damage to cartilage and bone - tissues rich in extracellular matrix. Several collagen types are present in the joint, where they provide the structural scaffold of the tissues. Recent findings indicate that both the ubiquitous Type I collagen and the cartilage-specific Type II collagen can be enzymatically citrullinated in vitro. Synthetic citrullinated peptides related to collagen sequences can be used as antigens. Autoantibodies to these citrullinated forms are found in patients with early rheumatoid arthritis. This review summarizes what is known regarding the occurrence of citrulline in a major class of extracellular matrix proteins, the fibrillar collagens and the significance of autoantibodies to citrulline in these proteins.

Peptidyl arginine deiminase type IV (PADI4) haplotypes interact with shared epitope regardless of anti-cyclic citrullinated peptide antibody or erosive joint status in rheumatoid arthritis: a case control study

INTRODUCTION

Anti-cyclic citrullinated peptide autoantibodies (anti-CCP) are the most specific serologic marker for rheumatoid arthritis (RA). Genetic polymorphisms in a citrullinating (or deiminating) enzyme, peptidyl arginine deiminase type IV (PADI4) have been reproducibly associated with RA susceptibility in several populations. We investigated whether PADI4 polymorphisms contribute to anti-CCP-negative as well as -positive RA, whether they influence disease severity (erosive joint status), and whether they interact with two major risk factors for RA, Human Leukocyte Antigen-DRB1 (HLA-DRB1) shared epitope (SE) alleles and smoking, depending on anti-CCP and erosive joint status.

METHODS

All 2,317 unrelated Korean subjects including 1,313 patients with RA and 1,004 unaffected controls were genotyped for three nonsynonymous (padi4_89, padi4_90, and padi4_92) and one synonymous (padi4_104) single-nucleotide polymorphisms (SNPs) in PADI4 and for HLA-DRB1 by direct DNA sequence analysis. Odds ratios (OR) were calculated by multivariate logistic regression. Interaction was evaluated by attributable proportions (AP), with 95% confidence intervals (CI).

RESULTS

A functional haplotype of the three fully correlated nonsynonymous SNPs in PADI4 was significantly associated with susceptibility to not only anti-CCP-positive (adjusted OR 1.73, 95% CI 1.34 to 2.23) but also -negative RA (adjusted OR 1.75, 95% CI 1.15 to 2.68). A strong association with both non-erosive (adjusted OR 1.62, 95% CI 1.29 to 2.05) and erosive RA (adjusted OR 1.62, 95% CI 1.14 to 2.31) was observed for PADI4 haplotype. Gene-gene interactions between the homozygous RA-risk PADI4 haplotype and SE alleles were significant in both anti-CCP-positive (AP 0.45, 95% CI 0.20 to 0.71) and -negative RA (AP 0.61, 95% CI 0.29 to 0.92). Theses interactions were also observed for both non-erosive (AP 0.48, 95% CI 0.25 to 0.72) and erosive RA (AP 0.46, 95% CI 0.14 to 0.78). In contrast, no interaction was observed between smoking and PADI4 polymorphisms.

CONCLUSIONS

A haplotype of nonsynonymous SNPs in PADI4 contributes to development of RA regardless of anti-CCP or erosive joint status. The homozygous PADI4 haplotype contribution is affected by gene-gene interactions with HLA-DRB1 SE alleles.

Pathogenic role of antibodies to citrullinated proteins in rheumatoid arthritis

In the last 10 years, the discovery that antibodies to citrullinated proteins are highly specific for rheumatoid arthritis has led to a model of pathogenesis that ties together the genetic and environmental risk factors for susceptibility and severity of disease. The authors propose that the chronic inflammation is driven by two phases of an immune response. The first phase is the priming of autoimmunity, which may occur many years before the onset of disease and is caused by environmental factors, such as smoking and infectious agents, in the context of disease susceptibility alleles. This may occur in sites outside the joint, such as the respiratory tract. The second phase is the induction of arthritis, which is associated with the generation of citrullinated proteins within the joint, which is then perpetuated as the erosive disease by a local chronic immune response. The identity of candidate synovial citrullinated antigen(s), whether fibrin, vimentin, alpha-enolase, collagen type II or others yet to be described, may be the key to the pathogenesis of the destructive disease characteristic of rheumatoid arthritis. There is emerging evidence that citrullination may already be modified by established therapy in rheumatoid arthritis, but more specific inhibitors of deimination may provide new agents for future treatments.

Low prevalence of antibodies to cyclic citrullinated peptide in patients with inflammatory bowel disease regardless of the presence of arthritis

OBJECTIVES

Crohn's disease (CD) and ulcerative colitis are chronic idiopathic inflammatory bowel diseases (IBD) often associated with axial and/or peripheral arthritis. Antibodies against cyclic citrullinated peptide (anti-CCP) are highly specific for rheumatoid arthritis, whereas their role in IBD remains unclear. Antitumour necrosis factor-alpha agents such as infliximab (IFX) may achieve and maintain remission of both IBD and rheumatoid arthritis; however, they may also trigger the development of various autoantibodies and autoimmune manifestations. This study aims at assessing the prevalence and clinical associations of anti-CCP antibodies in IBD patients with and without arthritis under either conventional treatment or IFX.

METHODS

Eighty four consecutive patients with CD [36 (42.8%) patients on IFX scheduled maintenance therapy (5 mg/kg intravenously every 8 weeks) and 48 (57.2%) on nonbiological treatment] and 50 patients with ulcerative colitis [20 (40%) patients on IFX (as described earlier) and 30 (60%) on nonbiological treatment] were evaluated. Among these 134 patients, 48 (35.8%) patients presented with concurrent arthritis. Ninety healthy individuals matched for sex and age with the IBD patients served as controls. Anti-CCP antibodies were detected using a commercially available enzyme-linked immunosorbent assay.

RESULTS

Anti-CCP antibodies were detected in one CD patient on IFX maintenance therapy without evidence of arthritis. Neither the presence of arthritis nor treatment with IFX was associated with the presence of anti-CCP antibodies in IBD patients.

CONCLUSION

Our data suggest that the prevalence of anti-CCP antibodies is very low in IBD patients regardless of the presence of arthritis and/or of IFX treatment.

Haloacetamidine-based inactivators of protein arginine deiminase 4 (PAD4): evidence that general acid catalysis promotes efficient inactivation

Dysregulated protein arginine deiminase (PAD) activity, particularly PAD4, has been suggested to play a role in the onset and progression of numerous human diseases, including rheumatoid arthritis (RA). Given the potential role of PAD4 in RA, we set out to develop inhibitors/inactivators that could be used to modulate PAD activity and disease progression. This effort led to the discovery of two mechanism-based inactivators, denoted F- and Cl-amidine, that inactivate PAD4 by the covalent modification of an active-site cysteine that is critical for catalysis. To gain further insights into the mechanism of inactivation by these compounds, the effect of pH on the rates of inactivation was determined. These results, combined with the results of solvent isotope effect and proton inventory studies, strongly suggest that the inactivation of PAD4 by F- and Cl-amidine proceeds by a multistep mechanism that involves the protonation and stabilization of the tetrahedral intermediate formed upon nucleophilic attack by the active-site cysteine, that is, Cys645. Stabilization of this intermediate would help to drive the halide-displacement reaction, which results in the formation of a three-membered sulfonium ring that ultimately collapses to form the inactivated enzyme. This finding-that protonation of the tetrahedral intermediate is important for enzyme inactivation-also suggests that, during catalysis, protonation of the analogous intermediate is required for efficient substrate turnover.

Characterization and inactivation of an agmatine deiminase from Helicobacter pylori

Helicobacter pylori encodes a potential virulence factor, agmatine deiminase (HpAgD), which catalyzes the conversion of agmatine to N-carbamoyl putrescine (NCP) and ammonia - agmatine is decarboxylated arginine. Agmatine is an endogenous human cell signaling molecule that triggers the innate immune response in humans. Unlike H. pylori, humans do not encode an AgD; it is hypothesized that inhibition of this enzyme would increase the levels of agmatine, and thereby enhance the innate immune response. Taken together, these facts suggest that HpAgD is a potential drug target. Herein we describe the optimized expression, isolation, and purification of HpAgD (10-30 mg/L media). The initial kinetic characterization of this enzyme has also been performed. Additionally, the crystal structure of wild-type HpAgD has been determined at 2.1A resolution. This structure provides a molecular basis for the preferential deimination of agmatine, and identifies Asp198 as a key residue responsible for agmatine recognition, which has been confirmed experimentally. Information gathered from these studies led to the development and characterization of a novel class of haloacetamidine-based HpAgD inactivators. These compounds are the most potent AgD inhibitors ever described.

Effect of the human leukocyte antigen HLA-DRB1 and anti-cyclic citrullinated peptide on the outcome of rheumatoid arthritis patients

Our objective was to determine whether the presence of the human leukocyte antigen HLA-DRB1 locus is associated with production of anti-cyclic citrullinated peptide antibodies (anti-CCP Abs) and to what extent they are associated with increased susceptibility to and severity of rheumatoid arthritis (RA) in Egyptian patients. Twenty-nine RA patients gave informed consent to participate in a case-control study that was approved by the Ain Shams University Medical Ethics Committee. RA disease activity and severity were determined using the simplified disease activity index and Larsen scores, respectively. We used a wide scale national study on the pattern of HLA typing in normal Egyptians as a control study. Anti-CCP Abs and HLA-DRB1 typing were determined for all subjects. The alleles most strongly associated with RA were HLA-DRB1 [*01 , *04 and *06] (41.4%). RA patients with serum anti-CCP Ab titers above 60 U/mL had a significantly higher frequency of HLA-DRB1*01 (58.3%) and HLA-DRB1*04 alleles (83.3%). Significant positive correlations were found between serum and synovial anti-CCP Ab titer, RA disease activity, and severity (r = 0.87, 0.66 and 0.63, respectively; P < 0.05). HLA-DRB1 SE+ alleles [*01 and *04] were highly expressed among Egyptian RA patients. The presence of these alleles was associated with higher anti-CCP Ab titer, active and severe RA disease. Early determination of HLA-DRB1 SE+ alleles and serum anti-CCP Ab could facilitate the prediction of the clinical course and prognosis of RA when first evaluated leading to better disease control.

Born-Oppenheimer ab initio QM/MM molecular dynamics simulations of the hydrolysis reaction catalyzed by protein arginine deiminase 4

Protein arginine deiminase 4 (PAD4) catalyzes the citrullination of the peptidylarginine via two successive stages: deimination and hydrolysis. Herein, by employing state-of-the-art Born-Oppenheimer ab initio QM/MM molecular dynamics simulations with the umbrella sampling method, we characterized the catalytic mechanism of the hydrolysis reaction: first, the nucleophilic attack of a water molecule to the C(zeta) of the thiouronium intermediate yields a stable tetrahedral intermediate, and then the S-C(zeta) bond breaks to generate the final product, citrulline. Throughout the hydrolysis reaction, His471 and Asp473 play pivotal catalytic roles by first enhancing the nucleophilic ability of the active water through forming shorter and low-barrier hydrogen bonds and then by serving as proton-accepting groups to deprotonate the water molecule, which is consistent with experimental findings. At the transition state, the spontaneous proton transfer among the reactive water, His471 and Asp473 have been observed. The determined overall free energy barrier for this hydrolysis stage is 16.5 kcal x mol(-1), which is lower than the barrier of 20.9 kcal x mol(-1) for the deimination stage determined previously with the same computational approach [J. Phys. Chem. B 2009, 113, 12750-12758]. Thus, the rate-determining step of the PAD4-catalyzed citrullination is the first step of the deimination. Our current work further demonstrates the strength and applicability of the ab initio QM/MM MD approach in simulating enzyme reactions.

Active site cysteine is protonated in the PAD4 Michaelis complex: evidence from Born-Oppenheimer ab initio QM/MM molecular dynamics simulations

The protein arginine deiminase 4 (PAD4) catalyzes the citrullination of the peptidylarginine and plays a critical role in rheumatoid arthritis (RA) and gene regulation. Understanding its catalytic mechanism is not only of fundamental importance but also of significant medical interest for the rational design of new inhibitors. By employing on-the-fly Born-Oppenheimer ab initio QM/MM molecular dynamics simulations, we have demonstrated that it is unlikely for the active site cysteine and histidine to exist as a thiolate-imidazolium ion pair in the PAD4 Michaelis reactant complex. Instead, a substrate-assisted proton transfer mechanism for the deimination reaction step has been characterized: both Cys645 and His471 in the PAD4 active site are neutral prior to the reaction; the deprotonation of Cys645 by the substrate arginine occurs in concert with the nucleophilic addition of the Cys thiolate to Czeta of the substrate, and leads to a covalent tetrahedral intermediate; then, the Czeta-Neta1 bond cleaves and the resulted ammonia is displaced by a solvent water molecule. The initial deprotonation and nucleophilic attack step is found to be rate-determining. The computed free energy barrier with B3LYP(6-31G*) QM/MM MD simulations and umbrella sampling is 20.9 kcal.mol(-1), consistent with the experimental kinetic data. During the deimination, His471 plays an important role in stabilizing the transition state through the formation of the hydrogen bond with the guanidinium group. Our current studies further demonstrated the viability and strength of the ab initio QM/MM molecular dynamics approach in simulating enzyme reactions.

Anti-citrullinated peptide antibody assays and their role in the diagnosis of rheumatoid arthritis

Increasingly, assays for the detection of anti-citrullinated peptide antibodies (ACPA) are used in RA diagnosis. This review summarizes the biologic basis and development of ACPA assays, available ACPA assays and their performance characteristics, and diagnostic properties of ACPA alone and compared to rheumatoid factor (RF) in early RA. We also review correlations, precision, costs and cost-effectiveness, availability, stability and reproducibility of the available assays. Taken together, data indicate that ACPA has a higher specificity than RF for early RA, good predictive validity, high sensitivity, apparent cost-effectiveness and good stability and reproducibility. Given its superior performance characteristics and increasing availability, ACPA is emerging as the most useful single assay for the diagnosis of RA.

Anti-cyclic citrullinated peptide antibodies as a discriminating marker between rheumatoid arthritis and chronic hepatitis C-related polyarthropathy

Articular involvement is a frequent extrahepatic manifestation of hepatitis C virus (HCV) infection. The distinction between HCV-related polyarthropathy and true RA may be very difficult, especially with recent onset RA before articular damage and erosions develop. The objective of the study is to assess the diagnostic utility of anti-CCP antibodies and compare it with that of rheumatoid factor (RF) in distinguishing between rheumatoid arthritis (RA) and HCV-related polyarthropathy. Anti-cyclic citrullinated peptide (CCP) antibodies and RF were determined in the sera of 30 patients with RA and 22 patients with HCV-related polyarthropathy. Anti-CCP antibodies were positive in 83.3% of patients with RA and in 4.5% in patients with HCV and polyarthropathy. RF was positive in 90% of RA patients and in 81.1% of HCV patients with polyarthropathy. The anti-CCP antibodies showed higher specificity for RA compared with RF (95.4 vs. 18.2%). However, the sensitivity of anti-CCP was comparable to that of RF (83.3 vs. 90%). In conclusions, anti-CCP antibodies are reliable laboratory markers to differentiate between RA and HCV-related polyarthropathy.

The role of anti-cyclic cytrullinate antibodies testing in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic, progressive inflammatory disease, which leads to joint destruction and deformity and is often accompanied by systemic complications. It is generally considered an autoimmune disease characterized by several autoantibodies. The impressive advances made in understanding the biological mechanisms of RA have led to more focused, directed therapies that have joined, and in many cases overcome, more traditional treatments. Along the last decade, the so-called biological anti-TNF-alpha agents have been shown to reduce disease activity, to slow disease progression and to improve patients' quality of life. The clear evidence that an early therapeutic intervention improves the overall outcome of the disease supports the importance of an early diagnosis. In the last years, several studies showed that anti-cyclic citrullinated peptide antibodies (anti-CCP) represent a sensitive and specific serologic marker for RA. Moreover, a large body of evidence has shown that anti-CCP may also serve as an early diagnostic and prognostic marker in RA. The aim of this article is to provide an overview of the current state of knowledge regarding anti-CCP focusing in particular on their clinical specificity and prognostic value in RA.

Increased expression of activation-induced cytidine deaminase is associated with anti-CCP and rheumatoid factor in rheumatoid arthritis

Rheumatoid arthritis (RA) is associated with higher levels of autoantibodies and IL-17. Here, we investigated if ectopic lymphoid follicles and peripheral blood mononuclear cells (PBMCs) from RA patients exhibit increased activation-induced cytidine deaminase (AID), and if increased AID is correlated with serum levels of autoantibodies and IL-17. The results of immunohistochemical staining showed that organized AID(+) germinal centres were observed in six of the 12 RA synovial samples, and AID(+) cells were found almost exclusively in the B-cell areas of these follicles. Aggregated but not organized lymphoid follicles were found in only one OA synovial sample without AID(+) cells. Significantly higher levels of AID mRNA (Aicda) detected by RT-PCR were found in the PBMCs from RA patients than PBMCs from normal controls (P < 0.01). In the PBMCs from RA patients, AID was expressed predominately by the CD10(+)IgM(+)CD20(+) B-cell population and the percentage of these cells that expressed AID was significantly higher than in normal controls (P < 0.01). AID expression in the PBMCs correlated significantly and positively with the serum levels of rheumatoid factor (RF) (P </= 0.0001) and anti-cyclic citrullinated peptide (CCP) (P = 0.0005). Serum levels of IFN-gamma (P = 0.0005) and IL-17 (P = 0.007), but not IL-4, also exhibited positive correlation with the expression of AID. These results suggest that the higher levels of AID expression in B cells of RA patients correlate with, and may be associated with the higher levels of T helper cell cytokines IFN-gamma and IL-17, leading to the development of anti-CCP and RF.

Targeted Synovial Fluid Proteomics for Biomarker Discovery in Rheumatoid Arthritis

Objective

Rheumatoid arthritis (RA) is an autoimmune disease that targets the synovium. The autoantigens involved in the autoantibody responses in RA are unknown. A targeted proteomics approach was used to identify proteins in RA synovial fluid (SF) that are recognized by autoantibodies in RA sera.

Methods

RA SF, depleted of abundant proteins, was fractionated by two-dimensional liquid chromatography (chromatofocusing followed by reverse phase HPLC). Protein arrays constructed from these fractions were probed with RA and normal control sera, and proteins within reactive fractions were identified by mass spectrometry. The reactivity of RA sera to an identified peptide was confirmed by ELISA.

Results

RA sera specifically reacted to a SF fraction containing fibrin. Mass spectrometry analyses established the presence of a citrullinated arginine at position 271 of the fibrin fragment present in RA SF. A synthetic peptide corresponding to fibrin residues 259–287, containing the citrulline substitution at Arg 271, was recognized by 10 of 12 RA sera, but by two of 18 normal control sera and one of 10 systemic lupus erythematosus sera.

Conclusion

Proteomics methodology can be used to directly characterize post-translational modifications in candidate autoantigens isolated from sites of disease activity. The finding that RA sera contain antibodies to the citrullinated fibrin 259–287 peptide may ultimately lead to improved diagnostic tests for RA and/or biomarkers for disease activity.

Deficiency of the DNA repair enzyme ATM in rheumatoid arthritis

In rheumatoid arthritis (RA), dysfunctional T cells sustain chronic inflammatory immune responses in the synovium. Even unprimed T cells are under excessive replication pressure, suggesting an intrinsic defect in T cell regeneration. In naive CD4 CD45RA⁺ T cells from RA patients, DNA damage load and apoptosis rates were markedly higher than in controls; repair of radiation-induced DNA breaks was blunted and delayed. DNA damage was highest in newly diagnosed untreated patients. RA T cells failed to produce sufficient transcripts and protein of the DNA repair kinase ataxia telangiectasia (AT) mutated (ATM). NBS1, RAD50, MRE11, and p53 were also repressed. ATM knockdown mimicked the biological effects characteristic for RA T cells. Conversely, ATM overexpression reconstituted DNA repair capabilities, response patterns to genotoxic stress, and production of MRE11 complex components and rescued RA T cells from apoptotic death. In conclusion, ATM deficiency in RA disrupts DNA repair and renders T cells sensitive to apoptosis. Apoptotic attrition of naive T cells imposes lymphopenia-induced proliferation, leading to premature immunosenescence and an autoimmune-biased T cell repertoire. Restoration of DNA repair mechanisms emerges as an important therapeutic target in RA.

Inflammatory Disease Processes and Interactions with Nutrition

Inflammation is a stereotypical physiological response to infections and tissue injury; it initiates pathogen killing as well as tissue repair processes and helps to restore homeostasis at infected or damaged sites. Acute inflammatory reactions are usually self-limiting and resolve rapidly, due to the involvement of negative feedback mechanisms. Thus, regulated inflammatory responses are essential to remain healthy and maintain homeostasis. However, inflammatory responses that fail to regulate themselves can become chronic and contribute to the perpetuation and progression of disease. Characteristics typical of chronic inflammatory responses underlying the pathophysiology of several disorders include loss of barrier function, responsiveness to a normally benign stimulus, infiltration of inflammatory cells into compartments where they are not normally found in such high numbers, and overproduction of oxidants, cytokines, chemokines, eicosanoids and matrix metalloproteinases. The levels of these mediators amplify the inflammatory response, are destructive and contribute to the clinical symptoms. Various dietary components including long chain ω-3 fatty acids, antioxidant vitamins, plant flavonoids, prebiotics and probiotics have the potential to modulate predisposition to chronic inflammatory conditions and may have a role in their therapy. These components act through a variety of mechanisms including decreasing inflammatory mediator production through effects on cell signaling and gene expression (ω-3 fatty acids, vitamin E, plant flavonoids), reducing the production of damaging oxidants (vitamin E and other antioxidants), and promoting gut barrier function and anti-inflammatory responses (prebiotics and probiotics). However, in general really strong evidence of benefit to human health through anti-inflammatory actions is lacking for most of these dietary components. Thus, further studies addressing efficacy in humans linked to studies providing greater understanding of the mechanisms of action involved are required.

Comparative performance analysis of 4 different anti-citrullinated protein assays in the diagnosis of rheumatoid arthritis

OBJECTIVE

To evaluate the diagnostic performances of 2 recently developed assays, third-generation anti-cyclic citrullinated peptide (anti-CCP3) and anti-mutated citrullinated vimentin (anti-MCV), in comparison to conventional second-generation anti-cyclic citrullinated peptide (anti-CCP2) assay; and to assess a novel fully automated, random-access AxSYM anti-CCP assay for early diagnosis of rheumatoid arthritis (RA).

METHODS

A cohort of 176 patients was enrolled in our study; 93 were diagnosed as having RA. The non-RA group consisted of 83 patients including 38 with systemic lupus erythematosus, 17 with primary Sjögren's syndrome, 11 with osteoarthritis, and 17 healthy controls. All were tested for presence of anti-CCP2, anti-CCP3, AxSYM anti-CCP, anti-MCV, and rheumatoid factor (RF)-IgM according to the manufacturers' instructions.

RESULTS

Diagnostic performance of the assays revealed the highest area under the curve for the novel AxSYM anti-CCP [89.1; 95% confidence interval (CI) 84.3-93.8], followed by anti-CCP3 (86.7; 95% CI 81.6-91.9), anti-CCP2 (82; 95% CI 75.8-88.3), and anti-MCV (71.9; 95% CI 64.4-79.5). The sensitivities and specificities were 60.2% and 98.8% for anti-CCP2, 61.3% and 97.6% for anti-CCP3, 80.6% and 84.3% for AxSYM anti-CCP, 49.8% and 91.6% for anti-MCV, and 67.8% and 91.6% for RF-IgM, respectively.

CONCLUSION

At cutoff of 5 U/ml, AxSYM anti-CCP emerged as a highly sensitive first-line early diagnostic tool for RA, with the greatest discrimination power, above 16 U/ml, in case of positive result. Using a single easily performed automated assay at 2 determined decision limits we were able to diagnose 81% of cases of RA and missing only 1.2%.