Prevalence and clinical significance of antibodies to citrullinated fibrinogen (ACF) in Chinese patients with rheumatoid arthritis

Impacts of Porphyromonas gingivalis periodontitis on rheumatoid arthritis autoimmunity

In RA patients' synovial sites, citrullinated RA-related antigens such as type II collagens, fibrin (ogen), vimentin, and α-enolase could be targeted by ACCPAs. Since ACCPA production can be initiated a long time before RA sign appearance, primary auto-immunization against these citrullinated proteins can be originated from extra-articular sites. It has been shown that there is a significant association between P. gingivalis periodontitis, anti- P. gingivalis antibodies, and RA. P. gingivalis gingipains (Rgp, Kgp) can degrade proteins such as fibrin and α-enolase into some peptides in the form of Arg in the C-terminal which is converted to citrulline by PPAD. Also, PPAD can citrullinate type II collagen and vimentins (SA antigen). P. gingivalis induces inflammation and chemoattraction of immune cells such as neutrophils and macrophages through the increase of C5a (gingipain C5 convertase-like activity) and SCFA secretion. Besides, this microorganism stimulates anoikis, a special type of apoptosis, and NETosis, an antimicrobial form of neutrophil death, leading to the release of PAD1-4, α-enolase, and vimentin from apoptotic cells into the periodontal site. In addition, gingipains can degrade macrophages CD14 and decrease their ability in apoptotic cell removal. Gingipains also can cleave IgGs in the Fc region and transform them into rheumatoid factor (RF) antigens. In the present study, the effects of P. gingivalis on rheumatoid arthritis autoimmune response have been reviewed, which could attract practical insight both in bench and clinic.

Autoantibodies as Diagnostic Markers and Mediator of Joint Inflammation in Arthritis

Rheumatoid arthritis is a systemic, polygenic, and multifactorial syndrome characterized by erosive polyarthritis, damage to joint architecture, and presence of autoantibodies against several self-structures in the serum and synovial fluid. These autoantibodies (anticitrullinated protein/peptide antibodies (ACPAs), rheumatoid factors (RF), anticollagen type II antibodies, antiglucose-6 phosphate isomerase antibodies, anticarbamylated protein antibodies, and antiacetylated protein antibodies) have different characteristics, diagnostic/prognostic value, and pathological significance in RA patients. Some of these antibodies are present in the patients' serum several years before the onset of clinical disease. Various genetic and environmental factors are associated with autoantibody production against different autoantigenic targets. Both the activating and inhibitory FcγRs and the activation of different complement cascades contribute to the downstream effector functions in the antibody-mediated disease pathology. Interplay between several molecules (cytokines, chemokines, proteases, and inflammatory mediators) culminates in causing damage to the articular cartilage and bones. In addition, autoantibodies are proven to be useful disease markers for RA, and different diagnostic tools are being developed for early diagnosis of the clinical disease. Recently, a direct link was proposed between the presence of autoantibodies and bone erosion as well as in the induction of pain. In this review, the diagnostic value of autoantibodies, their synthesis and function as a mediator of joint inflammation, and the significance of IgG-Fc glycosylation are discussed.

Diagnostic value of anti-citrullinated fibrinogen antibody in rheumatoid arthritis: A meta-analysis

AIM

To evaluate the overall diagnostic value of anti-citrullinated fibrinogen (ACF) antibody in patients with rheumatoid arthritis (RA).

METHODS

Published studies were systematically retrieved from PubMed, Web of Science, China National Knowledge Infrastructure (CNKI), Wan Fang, China Biology Medicine (CBM) disc, and Chinese VIP databases. QUADAS-2 tool was applied to evaluate the quality of eligible studies. Subgroup analysis and meta-regression were used to explore the sources of heterogeneity. Egger's test was used to evaluate for the presence of publication bias.

RESULTS

Seven studies were included in this meta-analysis. The pooled sensitivity, specificity, pooled positive likelihood ratio, negative likelihood ratio and diagnostic odds ratio of ACF were 0.61 (95% CI: 0.57-0.64), 0.93 (95% CI: 0.92-0.94), 9.33 (95% CI: 5.15-16.92), 0.39 (95% CI: 0.30-0.53) and 24.58 (95% CI: 11.47-52.64), respectively. The area under the curve was 0.8018. The results of subgroup analysis and meta-regression indicated that the factors we analyzed might not be the leading causes of heterogeneity. No significant publication bias was found.

CONCLUSION

The ACF antibody had a moderate diagnostic accuracy on RA.

A new look at rheumatology in China--opportunities and challenges

In the past two decades, Chinese rheumatology has developed rapidly in terms of both clinical practice and basic research. Many rheumatology departments and divisions have been established, creating positions for more residents to join rheumatology practices. Numerous studies of rheumatic diseases have been published in recent years by Chinese rheumatologists and immunologists, supported by government funding that has dramatically increased over the past few years. These studies are focused mainly on epidemiology, mechanisms, early diagnosis and interventions of rheumatic diseases. Increasing numbers of national and international scientific activities in China, including research collaborations, education programmes and conferences have greatly helped the development of rheumatology. In this APLAR series article, the major, high-impact studies and latest developments in Chinese rheumatology are reviewed.

A citrullinated fibrinogen-specific T cell line enhances autoimmune arthritis in a mouse model of rheumatoid arthritis

Citrullinated proteins, derived from the conversion of peptidyl-arginine to peptidyl-citrulline, are present in the joints of patients with rheumatoid arthritis (RA), who also uniquely produce high levels of anti-citrullinated protein Abs. Citrullinated fibrinogen (CF) is abundant in rheumatoid synovial tissue, and anti-citrullinated protein Ab-positive RA patients exhibit circulating immune complexes containing CF. Thus, CF is a potential major target of pathogenic autoimmunity in RA. T cells are believed to be involved in this process by initiating, controlling, and driving Ag-specific immune responses in RA. In this study, we isolated a CD4 T cell line specific for CF that produces inflammatory cytokines. When transferred into mice with collagen-induced arthritis (CIA), this T cell line specifically enhanced the severity of autoimmune arthritis. Additionally, pathogenic IgG2a autoantibody levels to mouse type II collagen were increased in mice that received the T cells in CIA, and levels of these T cells were increased in the synovium, suggesting the T cells may have had systemic effects on the B cell response as well as local effects on the inflammatory environment. This work demonstrates that CD4 T cells specific for CF can amplify disease severity after onset of CIA.

Discovering new clinical markers in the field of glycomics

Glycosylation modifications have been reported in a number of disease states and, as a result, there is significant focus on the discovery and development of glycan-based biomarkers. Glyco-biomarkers have the potential to enhance the efficacy and efficiency of the diagnostic procedures for these diseases.

Diagnostic and prognostic value of antibodies against chimeric fibrin/filaggrin citrullinated synthetic peptides in rheumatoid arthritis

INTRODUCTION

Evidence suggests that citrullinated fibrin(ogen) may be a potential in vivo target of anticitrullinated protein/peptide antibodies (ACPA) in rheumatoid arthritis (RA). We compared the diagnostic yield of three enzyme-linked immunosorbent assay (ELISA) tests by using chimeric fibrin/filaggrin citrullinated synthetic peptides (CFFCP1, CFFCP2, CFFCP3) with a commercial CCP2-based test in RA and analyzed their prognostic values in early RA.

METHODS

Samples from 307 blood donors and patients with RA (322), psoriatic arthritis (133), systemic lupus erythematosus (119), and hepatitis C infection (84) were assayed by using CFFCP- and CCP2-based tests. Autoantibodies also were analyzed at baseline and during a 2-year follow-up in 98 early RA patients to determine their prognostic value.

RESULTS

With cutoffs giving 98% specificity for RA versus blood donors, the sensitivity was 72.1% for CFFCP1, 78.0% for CFFCP2, 71.4% for CFFCP3, and 73.9% for CCP2, with positive predictive values greater than 97% in all cases. CFFCP sensitivity in RA increased to 80.4% without losing specificity when positivity was considered as any positive anti-CFFCP status. Specificity of the three CFFCP tests versus other rheumatic populations was high (> 90%) and similar to those for the CCP2. In early RA, CFFCP1 best identified patients with a poor radiographic outcome. Radiographic progression was faster in the small subgroup of CCP2-negative and CFFCP1-positive patients than in those negative for both autoantibodies. CFFCP antibodies decreased after 1 year, but without any correlation with changes in disease activity.

CONCLUSIONS

CFFCP-based assays are highly sensitive and specific for RA. Early RA patients with anti-CFFCP1 antibodies, including CCP2-negative patients, show greater radiographic progression.

Citrullinated fibrinogen shows defects in FPA and FPB release and fibrin polymerization catalyzed by thrombin

BACKGROUND

Antibody-antigen complexes formed by IgG autoantibodies against citrullinated proteins and citrullinated forms of the alpha- and beta-chains of fibrin in rheumatoid synovial tissue play a key role in the pathophysiology of rheumatoid arthritis.

METHODS

Recombinant fibrinogen was citrullinated by rabbit skeletal muscle peptidylarginine deiminase so that we could analyze the function of citrullinated fibrinogen. Namely, thrombin-catalyzed fibrin polymerization and fibrinopeptide release, protection against plasmin digestion, and factor XIIIa-catalyzed cross-linking of fibrin or fibrinogen were performed.

RESULTS

Strong citrullination of the Aalpha- and Bbeta-chains and weak citrullination of the gamma-chain were detected by an anti-modified citrulline detection kit. Citrullinated fibrinogen did not release FPA or FPB by thrombin catalyzation and no thrombin-stimulated conversion of fibrinogen into fibrin occurred. The citrullination of fibrinogen did not affect the 3 functions of the C-terminal gamma-chain, "a-hole," low affinity Ca binding, and gamma-gamma cross-linking.

CONCLUSION

Our functional analyses demonstrated that no thrombin-stimulated conversion of fibrinogen into fibrin occurred, because citrullinated fibrinogen did not release FPA or FPB after thrombin catalyzation. Our results and those of other reports suggest that citrullinated fibrin and fibrinogen are present in the synovium and might both be associated with the pathophysiology of RA.