ACPA-positive versus ACPA-negative rheumatoid arthritis: two distinct erosive disease entities on radiography and ultrasonography

A responsive nanoplatform with molecular and structural imaging capacity for assisting accurate diagnosis of early rheumatoid arthritis

Accurate early diagnosis of rheumatoid arthritis (RA) and prompt implementation of appropriate treatment approaches are crucial. In the clinic, magnetic resonance imaging (MRI) has been recommended for implementation to aid in the precise and early diagnosis of RA. However, they are still limited by issues regarding specificity and their ability to capture comprehensive information about the pathological features. Herein, a responsive multifunctional nanoplatform with targeting capabilities (hMnO2-IR@BSA-PEG-FA) is constructed through integrating a RA microenvironment-responsive MRI contrast agent with activatable near-infrared (NIR) fluorescence imaging, aiming to simultaneously acquire comprehensive pathological features of RA from both structural and molecular imaging perspectives. Moreover, taking advantage of its targeting function to synovial microphages, hMnO2-IR@BSA-PEG-FA demonstrated a remarkable capability to accumulate effectively at the synovial tissue. Additionally, hMnO2 responded to the mild acidity and reactive oxygen species (ROS) in the RA microenvironment, leading to the controlled release of Mn2+ ions and IR780, which separately caused special MRI contrast enhancement of synovial tissues and sensitively demonstrated the presence of ROS and weakly acid microenvironment by NIR imaging. Consequently, hMnO2-IR@BSA-PEG-FA is expected to serve as a promising nanoplatform, offering valuable assistance in the precise diagnosis of early-stage RA by specially providing comprehensive information about the pathological features.

Iguratimod inhibits protein citrullination and inflammation by downregulating NBCe2 in patients with rheumatoid arthritis

BACKGROUND

Bicarbonate has recently been identified as a crucial factor affecting peptidylarginine deiminase (PAD) activity; however, the mechanism underlying its role in rheumatoid arthritis (RA) remains unclear. Iguratimod (IGU), a small-molecule disease-modifying anti-rheumatic drug, requires further investigation. This study aimed to explore the mechanism by which bicarbonate affects citrullination and inflammation in RA and identify new targets for IGU.

METHODS

We enrolled 20 patients with RA in the study. Sodium bicarbonate cotransporter 2 (NBCe2) was detected in the peripheral blood neutrophils and peripheral blood mononuclear cells (PBMCs) of these patients. The effects of varying concentrations of IGU, methotrexate (MTX), dexamethasone (DXM), and S0859 (an NBCe2 inhibitor) on NBCe2, PAD2, PAD4, and citrullinated histone H3 (cit-H3) levels in, migration ability of, and cytokine production from neutrophils and PBMCs were examined.

RESULTS

Our findings showed that in patients with RA, citrullinated protein production by peripheral blood neutrophils instead of PBMCs, which showed higher NBCe2 expression levels, increased with an increase in the bicarbonate concentration. In addition, tumor necrosis factor-alpha (TNF-α) promoted NBCe2 expression in neutrophils from patients with RA. Furthermore, we revealed that the inhibitory effects of IGU on neutrophil NBCe2 and cit-H3 levels, degrees of inhibition of neutrophil and PBMC migration, and suppression of interleukin 6, TNF-α, and metalloproteinase-9 secretion from neutrophil-like differentiated HL-60 cells did not substantially differ from those of MTX, DXM, and S0859 at specific doses.

CONCLUSIONS

Bicarbonate promotes protein citrullination and inflammation in RA via NBCe2, and IGU can downregulate NBCe2.

Should ACR/EULAR criteria be revised changing the RF and ACPA scores?

Current classification criteria for rheumatoid arthritis (RA) encompass clinical and immunological items and are capable of correctly identifying the majority of symptomatic RA patients. The presence of positive rheumatoid factor (RF) and/or and anti-cyclic citrullinated protein/peptide antibodies (ACPA) gaining increasing importance according to their serological titer eases the recognition of RA, yet the debate is open on whether this scoring system ought to be optimized by hierarchizing ACPA or the combination of ACPA and RF over single positivity, prioritizing specificity over sensitivity. The risk of misdiagnosis and misclassification are often entangled, yet they are not the same. In fact, while ideal diagnosis requires 100% sensitivity and specificity, classification criteria are conceived to gather a homogeneous patient population, favoring specificity over sensitivity. Nevertheless, as they are frequently summoned to support the diagnostic process in clinical practice, issues arise on how comprehensive those should be and on how frequently they should be updated in light of novel acquisitions regarding measurable RA-related abnormalities. In this viewpoint two different views on the topic are confronted, discussing the performance of available criteria and the potentiality and pitfalls of their refinement according to novel data on ACPA and RF contribution and emergence of newly discovered specificities.

Porphyromonas gingivalis with collagen immunization induces ACPA-positive rheumatoid arthritis in C3H mice

The pathogenic anti-citrullinated protein antibodies (ACPA) are thought to play a vital role in the initiation and immune maintenance of rheumatoid arthritis (RA). However, it is noteworthy that ACPA is not a salient characteristic of any conventional RA animal model. Porphyromonas gingivalis (Pg) is the first microorganism identified to induce citrullination and a target of autoantibodies in early rheumatoid arthritis (RA). Thus, we employed C3H mice with specific MHC types and combined Pg infection with collagen immunity to develop an animal model of ACPA-positive RA. The resulting model exhibited citrullination characteristics, as well as pathological and immune cell changes. 1) Mice showed a significant increase in ACPA levels, and various organs and tissues exhibited elevated levels of citrullinated protein. 2) The mice experienced heightened pain, inflammation, and bone destruction. 3) The spleen and lymph nodes of the mice showed a significant increase in the proportion of Tfh-GCB cell subpopulations responsible for regulating autoantibody production. In conclusion, the C3H mouse model of Pg infection with collagen immunity demonstrated significant alterations in ACPA levels, citrullinated protein expression, and immune cell subpopulations, which could be a crucial factor leading to increased pain, inflammation, and bone destruction.

Anti-citrullinated protein antibodies as biomarkers in rheumatoid arthritis

INTRODUCTION

The serological biomarker anti-citrullinated protein antibodies (ACPAs) may have several functions but is especially important for the diagnosis of rheumatoid arthritis (RA) along with clinical symptoms.

AREAS COVERED

This review provides an overview of ACPAs, which are useful in RA diagnostics and may improve our understanding of disease etiology. PubMed was searched with combinations of words related to antibodies recognizing epitopes containing the post-translationally modified amino acid citrulline in combination with rheumatoid arthritis; cyclic citrullinated peptide, CCP, anti-CCP, anti-citrullinated protein antibodies, ACPA, citrullination, peptide/protein arginine deiminase, PAD, filaggrin, vimentin, keratin, collagen, perinuclear factor, EBNA1, EBNA2, and others. From this search, we made a qualitative extract of publications relevant to the discovery, characterization, and clinical use of these antibodies in relation to RA. We highlight significant findings and identify areas for improvement.

EXPERT OPINION

ACPAs have high diagnostic sensitivity and specificity for RA and recognize citrullinated epitopes from several proteins. The best-performing single epitope originates from Epstein-Barr Virus nuclear antigen 2 and contains a central Cit-Gly motif, which is recognized by ACPAS when located in a flexible peptide structure. In addition, ACPAs may also have prognostic value, especially in relation to early treatment, although ACPAs' main function is to aid in the diagnosis of RA.

Patients with ACPA-positive and ACPA-negative rheumatoid arthritis show different serological autoantibody repertoires and autoantibody associations with disease activity

Patients with rheumatoid arthritis (RA) can test either positive or negative for circulating anti-citrullinated protein antibodies (ACPA) and are thereby categorized as ACPA-positive (ACPA+) or ACPA-negative (ACPA-), respectively. In this study, we aimed to elucidate a broader range of serological autoantibodies that could further explain immunological differences between patients with ACPA+ RA and ACPA- RA. On serum collected from adult patients with ACPA+ RA (n = 32), ACPA- RA (n = 30), and matched healthy controls (n = 30), we used a highly multiplex autoantibody profiling assay to screen for over 1600 IgG autoantibodies that target full-length, correctly folded, native human proteins. We identified differences in serum autoantibodies between patients with ACPA+ RA and ACPA- RA compared with healthy controls. Specifically, we found 22 and 19 autoantibodies with significantly higher abundances in ACPA+ RA patients and ACPA- RA patients, respectively. Among these two sets of autoantibodies, only one autoantibody (anti-GTF2A2) was common in both comparisons; this provides further evidence of immunological differences between these two RA subgroups despite sharing similar symptoms. On the other hand, we identified 30 and 25 autoantibodies with lower abundances in ACPA+ RA and ACPA- RA, respectively, of which 8 autoantibodies were common in both comparisons; we report for the first time that the depletion of certain autoantibodies may be linked to this autoimmune disease. Functional enrichment analysis of the protein antigens targeted by these autoantibodies showed an over-representation of a range of essential biological processes, including programmed cell death, metabolism, and signal transduction. Lastly, we found that autoantibodies correlate with Clinical Disease Activity Index, but associate differently depending on patients' ACPA status. In all, we present candidate autoantibody biomarker signatures associated with ACPA status and disease activity in RA, providing a promising avenue for patient stratification and diagnostics.

Genetic variant in SPAG16 is associated with the susceptibility of ACPA-positive rheumatoid arthritis possibly via regulation of MMP-3

OBJECTIVES

In two previously published genome-wide association studies, a cluster of variants of sperm-associated antigen16 (SPAG16) were reported to be associated with the radiological progression rate of ACPA-positive rheumatoid arthritis (RA) patients from North American and Southern European ancestry. In this study, we aimed to investigate whether the reported RA-risk loci in SPAG16 are associated with the disease in the Chinese population and to further validate the functional role of the susceptible locus in RA tissues.

METHODS

A total of 500 ACPA-positive RA patients and 1000 age-matched healthy subjects were recruited. Two SNPs of SPAG16, including rs7607479 (C/T) and rs6435818 (A/C), were genotyped, and the genotyping data were compared with chi-square test. Gene expression analysis was performed in synovial tissues obtained from 40 RA patients and 30 non-RA controls surgically treated for bone fracture. The tissue expression of SPAG16 and matrix metalloproteinase 3 (MMP-3) was compared between the two groups by the Student's t test. The relationship between serum indexes and mRNA expression of SPAG16 and MMP-3 were evaluated by Spearman's correlation analysis.

RESULT

For rs7607479, the frequency of genotype TT was significantly higher in RA patients than in the controls (49.0% vs. 40.4%, p = 0.002). The RA patients were found to have significantly lower frequency of allele C than the controls (30.9% vs. 36.8%, p = 0.001). As for rs6435818, there was no significant difference of genotype or allele frequency between the two groups. The mRNA expression of MMP-3 was 1.63-fold higher in the RA patients than in the controls (p < 0.001). The expression of SPAG16 was comparable between the two groups (p = 0.43). The mRNA expression of MMP-3 was 1.39-fold higher in patients with genotype TT than in the patients with genotype CC (p = 0.006). The mRNA expression level of MMP-3 was significantly correlated with serum rheumatoid factor (r = 0.498, p < 0.001) and C-reactive protein (r = 0.272, p = 0.01), weakly correlated with erythrocyte sedimentation rate (r = 0.236, p = 0.09).

CONCLUSIONS

We validated a common genetic risk factor in ACPA-positive patients with RA, which is associated with the tissue production of MMP-3 and disease progression. Further functional analysis into the role of rs7607479 in MMP-3 expression can shed new light on the genetic architecture of ACPA-positive RA.

Bone resorption during therapy with denosumab in patients with rheumatoid arthritis, positive for the main immunological markers

Objective. Inflammation in rheumatoid arthritis (RA) leads to the development of local and generalized bone loss. Rheumatoid factor (RF) and anti-cyclic citrullinated peptide antibodies (ACCP) are believed to play a negative role in the radiological progression of RA. The use of such antiresorptive therapy as denosumab – monoclonal antibodies to RANKL (receptor activator of nuclear factor kappa-B ligand), reduces the activity of osteoclasts, increases bone mineral density (BMD), and also potentially affects the erosive process at RA. The aim of the study is to evaluate the effect of denosumab therapy on BMD and erosion count in patients with RA and osteoporosis (OP) in consideration of the positivity in the RF and ACCP in serum and the baseline RA activity. Materials and methods. The 12-month prospective study of the efficacy of denosumab therapy (60 mg subcutaneously every 6 months) in patients with RA and OP included 66 postmenopausal women; age – 59.4±7.5 years, duration of RA – 17.8±10.6 years, RF-positive – 47 (72%) patients, ACCP-positive – 48 (74%) patients. At baseline and after 12 months, dual-energy X-ray absorptiometry was performed with an assessment of BMD in the lumbar spine (L1– L4), proximal femur (hip neck and total hip), distal forearm; X-ray of the hands and distal parts of the feet in direct projection, followed by assessment of erosive-destructive changes according to the Sharp/van der Heijde method. Results. A significant increase in BMD was established in all studied sites of the skeleton despite the positivity of the RF and ACCP (for the hip neck p=0.05), while a significant increase in BMD in the RF- and ACCP-negative group was detected only in L1–L4 site. The progression of the increase in erosion count was noted in the RF- and ACCP-positive group while in the RF- and ACCP-negative group this indicator did not change. Regardless of the baseline activity of RA (by DAS28 (Disease Activity Score 28)) the BMD of most parts of the skeleton were stabilized. In patients with moderate RA activity, BMD increased significantly in L1–L4 in both groups: RF- and ACCP-positive and -negative , as well as in the total hip – in RF- and ACCP-positive group. The dynamics of the erosion count in RA patients did not depend on the baseline degree of DAS28 activity, no significant changes were detected in the analyzed groups. Conclusions. RF and ACCP positivity in serum in patients with RA and OP treated with denosumab did not have a negative effect on the dynamics of BMD, while the number of erosions increased. The baseline RA activity level did not affect the dynamics of the erosion count and the dynamics of BMD in most subgroups – BMD levels have been increased or stabilized.

Patients with seronegative rheumatoid arthritis have a different phenotype than seropositive patients: A clinical and ultrasound study

Introduction

Rheumatoid arthritis (RA) is an inflammatory disease whose clinical phenotype largely depends on the presence of rheumatoid factor (RF) and anti-citrullinated protein antibodies (ACPA). Seronegative RA appears to be a less severe disease, but this remains controversial. This study aimed to assess whether seronegative patients show a less severe disease than seropositive patients.

Methods

A cross-sectional study was conducted on RA outpatients from a single center. Clinical activity scales, laboratory evaluations, and cardiovascular risk scores were assessed. Musculoskeletal ultrasound (US) examinations were performed.

Results

One hundred and fourteen patients were enrolled. Eighty-five were seropositive (76% women) and 29 seronegative (93% women). Seropositive patients had a younger age at disease onset (43 ± 14 vs. 54 ± 11; p = 0.001) and used sulfasalazine (47 vs. 17%; p = 0.004) and glucocorticoids (36 vs. 10%; p = 0.007) more frequently. No differences in clinical activity scales and in 10-year cardiovascular risk were observed. Pathological US data were found more frequently in seropositive patients in the 2^nd metacarpophalangeal (MCP) joint, both in grayscale (71 vs. 38%; p = 0.008) and in power Doppler (PD; 53 vs. 9%; p < 0.001); erosions (36 vs. 9%; p = 0.020) were also more frequent. We found greater severity of PD signals in the 2nd MCP and 3rd MCP joints of the seropositive patients, while synovitis severity was higher only in the 2nd MCP joints. The percentage of total joints with erosions (9 vs. 1%; p < 0.001) and 2nd MCP joints with erosions (25 vs. 7%; p < 0.001) was higher in seropositive patients.

Conclusion

RA patients show a differentiated phenotype according to their ACPA and RF status. In seronegative patients, RA begins later in life and has a lower requirement for antirheumatic therapies. On US evaluation, seropositive patients show more joint damage, especially in MCP joints. Despite this, long-term cardiovascular risk is similar among RA patients, regardless of their RF and ACPA status.

Association Study of Anticitrullinated Peptide Antibody Status with Clinical Manifestations and SNPs in Patients Affected with Rheumatoid Arthritis: A Pilot Study

Introduction. Rheumatoid arthritis (RA) is an autoimmune disease of unknown etiology that leads to disability due to articular and extra-articular damage. RA prevalence is variable. The disease is most common among females with a 3 : 1 ratio. The interaction of environmental and host factors contributes to RA development. Currently, the genome-wide association studies (GWAS) give the opportunity to uncover the RA genetic background. Anticitrullinated peptide antibody (ACPA) is a highly specific RA antibody, associated with poor prognosis and severe course of RA, and regulated by numerous genes. Our study is aimed at investigating whether there are any clinical and genetic aspects correlate with ACPA presence in Kazakhstani patients with RA. Indeed, the available studies on this subject are focused on Caucasian and East Asian populations (mainly Japanese and Chinese), and there are scarce data from Central Asia. Methods. Our study included 70 RA patients. Patients’ blood samples were collected and genotyped for 14 SNPs by real-time polymerase chain reaction (RT-PCR). General examination, anamnestic, and clinical and laboratory data collection were carried out. Statistical analysis was performed using R statistics. Results and Conclusion. Our study revealed a significant association of ACPA positivity with Fc receptor-like 3 (FCRL3) and ACPA negativity with signal transducer and activator of transcription 4 (STAT4) genes, but not with T cell activation Rho GTPase activating protein (TAGAP). In addition, ACPA positivity was associated with radiographic progression, rheumatoid factor (RF), erythrocyte sedimentation rate (ESR), age of RA onset, the patient global assessment, body mass index (BMI), and Gamma globulin. Conclusion. Remained 11 earlier identified significantly associated in Caucasian and Asian population SNPs were not replicated in our cohort. Further studies on larger cohorts are needed to confirm our findings with higher confidence levels and stronger statistical power.

Comparison of Clinical Manifestations in Rheumatoid Arthritis vs. Spondyloarthritis: A Systematic Literature Review

INTRODUCTION

Misclassification of spondyloarthritis (SpA) as rheumatoid arthritis (RA) may lead to delayed SpA diagnosis and suboptimal therapeutic outcomes. Here, we evaluate the literature on clinical manifestations in patients with SpA and RA, particularly seronegative RA, to understand the potential overlap, distinctions, and most reliable approaches to accurate diagnosis.

METHODS

In this systematic literature review, conducted according to PRISMA guidelines, we searched key biomedical databases for English-language publications of original research articles (up to July 23, 2020) and rheumatology conference abstracts (January 1, 2018-July 31, 2020) reporting key SpA clinical presentations in patients with SpA or RA. Publications were assessed for eligibility by two independent reviewers; discrepancies were resolved by a third. Studies were evaluated for publication quality using the Downs and Black checklist.

RESULTS

Of 4712 records retrieved, 79 met the inclusion criteria and were included in the analysis. Of these, 54 included study populations with SpA and RA, and 25 with seropositive and/or seronegative RA. Entheseal abnormalities were more frequently reported among patients with SpA than RA and with seronegative vs. seropositive RA. Psoriasis, nail psoriasis, and dactylitis were exclusively seen in SpA vs. RA. In most publications (70 of 79), advanced imaging techniques allowed for more accurate distinction between SpA and RA. Overlapping clinical characteristics occur in SpA and RA, including inflammation and destruction of joints, pain, diminished functional ability, and increased risk for comorbidities. However, of 54 studies comparing SpA and RA populations, only seven concluded that no distinction can be made based on the SpA manifestations and outcomes examined.

CONCLUSIONS

Typical SpA-related clinical symptoms and signs were observed in patients with RA, suggesting that misclassification could occur. Availability of advanced imaging modalities may allow for more prompt and comprehensive evaluation of peripheral manifestations in SpA and RA, reducing misclassification and delayed diagnosis.

The EFSUMB Guidelines and Recommendations for Musculoskeletal Ultrasound - Part I: Extraarticular Pathologies

The first part of the guidelines and recommendations for musculoskeletal ultrasound, produced under the auspices of the European Federation of Societies for Ultrasound in Medicine and Biology (EFSUMB), provides information about the use of musculoskeletal ultrasound for assessing extraarticular structures (muscles, tendons, entheses, ligaments, bones, bursae, fasciae, nerves, skin, subcutaneous tissues, and nails) and their pathologies. Clinical applications, practical points, limitations, and artifacts are described and discussed for every structure. After an extensive literature review, the recommendations have been developed according to the Oxford Centre for Evidence-based Medicine and GRADE criteria and the consensus level was established through a Delphi process. The document is intended to guide clinical users in their daily practice.

Anti-citrullinated Protein Antibody Generation, Pathogenesis, Clinical Application, and Prospects

Anti-citrullinated protein antibodies (ACPAs) are autoantibodies commonly observed in patients with rheumatoid arthritis (RA). Currently, most of the mechanisms of ACPA formation and bone destruction are well-understood, however, some unknown mechanisms still exist. There have been many new advances in ACPA-related clinical applications and targeted therapies. However, the existence of different ACPA subtypes is a limitation of targeted therapy. Herein, we present an overview of the process of ACPA generation, the underlying pathogenesis, and relevant clinical application and prospects.

Citrullinated Antigens with Multiple Citrulline Similar Motif in the Diagnosis of Rheumatoid Arthritis: A Preliminary Single-Center Study

The presence of anti-citrullinated protein antibodies (ACPAs) in the serum is one of the immunological features of rheumatoid arthritis (RA). Anti-cyclic citrullinated peptide (CCP) assay has been widely used in clinic for the diagnosis of RA. However, up to 40% of RA patients are anti-CCP negative and the diagnostic sensitivity in this population needs to be improved for better clinical management. In this study, peptides with Multiple Citrulline Similar Motif (MCSM) were synthesized and a new ELISA system, which we called RA_CP, was developed to detect citrullinated antigens with MCSM present in the serum. 106 RA,48 other arthritis patients and 41 sex- and age-matched healthy controls (HCs) were included in this study. Patients with RA have a significantly higher amount of citrullinated antigens with MCSM than other arthritis patients and HCs. RA patients with positive anti-CCP are also MCSM positive, whereas 75% anti-CCP negative patients are positive for MCSM. The diagnostic sensitivity for anti-CCP and MCSM was 81.1% and 95.3%, while the specificity was 100% and 94.4%, respectively. ROC curve analyses showed that the area under the curve (AUC) values were 0.906 (95% CI: 0.860-0.951) for anti-CCP and 0.948 (95% CI: 0.912-0.985) for MCSM while the combination of MCSM and anti-CCP test has the highest AUC (0.971, 95% CI: 0.946-0.996). Our results suggest that detection of citrullinated antigens with MCSM has improved sensitivity compared with anti-CCP assay and could serve as a biomarker in diagnosis of RA patients.

Structural damage in rheumatoid arthritis assessed by musculoskeletal ultrasound: A systematic literature review by the Structural Joint Damage Task Force of the OMERACT Ultrasound Working Group

OBJECTIVES

To identify and synthesize the evidence for the use and measurement properties of musculoskeletal ultrasound in assessing structural joint damage in patients with rheumatoid arthritis (RA).

METHODS

A systematic literature search (SLR) of the PubMed, Embase and Cochrane Library was performed. Original articles were included published in English reporting on ultrasound of bone erosion, cartilage damage and the measurement properties of ultrasound according to the OMERACT filter 2.1.

RESULTS

Of the 1.495 identified articles 149 were included in the final review, most of which reported on cross-sectional studies and used the OMERACT definitions for ultrasonographic pathology. Among these, bone erosions were assessed in 139 (93.3%), cartilage damage in 24 (16.1%), enthesophytes in 8 (5.4%), osteophytes in 15 (10.1%) and malalignment and ankylosis in a single (0.9%) study, respectively. Most studies (126/149, 84.6%) assessed the joints of the hands. The overwhelming majority of studies (127/149, 85.2%) assessed structural joint damage bilaterally. Validity, reliability and responsiveness were assessed in 21 (14.1%), 34 (22.8%) and 17 (11.4%) studies, respectively.

CONCLUSION

While the results of this SLR suggest that ultrasound is a sensitive, reliable and feasible tool to detect damage in RA, they also highlight the need for further research and validation. Findings of this SLR will inform the next steps of the OMERACT Ultrasound Working Group in developing an ultrasound score for assessing structural joint damage in patients with RA.

ACPA Status Correlates with Differential Immune Profile in Patients with Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a progressive erosive autoimmune disease that affects 1% of the world population. Anti-citrullinated protein autoantibodies (ACPA) are routinely used for the diagnosis of RA, however 20–30% of patients are ACPA negative. ACPA status is a delineator of RA disease endotypes with similar clinical manifestation but potentially different pathophysiology. Profiling of key peripheral blood and synovial tissue immune populations including B cells, T follicular helper (Tfh) cells and CD4 T cell proinflammatory cytokine responses could elucidate the underlying immunological mechanisms involved and inform a treat to target approach for both ACPA-positive and ACPA-negative RA. Detailed high dimensionality flow cytometric analysis with supervised and unsupervised algorithm analysis revealed unique RA patient peripheral blood B cell and Tfh cell profiles. Synovial tissue single cell analysis of B cell subpopulation distribution was similar between ACPA− and ACPA+ RA patients, highlighting a key role for specific B cell subsets in both disease endotypes. Interestingly, synovial tissue single cell analysis of CD4 T cell proinflammatory cytokine production was markedly different between ACPA− and APCA+ RA patients. RNAseq analysis of RA patient synovial tissue highlighted disease endotype specific gene signatures. ACPA status associates with unique immune profile signatures that reinforce the need for a treat to target approach for both endotypes of RA.

Diagnostic value of anti-citrullinated α-enolase peptide 1 antibody in patients with rheumatoid arthritis: A systematic review and meta-analysis

Aim

To evaluate the diagnostic value of anti‐citrullinated α‐enolase peptide 1 (anti‐CEP 1) antibody in patients with rheumatoid arthritis (RA) by conducting a systematic review and meta‐analysis.

Methods

The PubMed, Web of Science, Embase, Scopus, and Cochrane Library databases were searched for relevant studies published until September 23, 2020. A bivariate mixed‐effects model was used to calculate the diagnostic indices from primary data of eligible studies. We performed meta‐regression and subgroup analysis to explore the sources of heterogeneity.

Results

Twenty‐four articles, with a total of 17 380 patients with RA and 7505 control participants, met the criteria for inclusion in the meta‐analysis. The pooled sensitivity, specificity, and positive and negative likelihood ratios for the anti‐CEP 1 antibody were 44% (95% CI: 38%‐51%), 97% (95% CI: 96%‐98%), and 14.81 (95% CI: 10.66‐20.57) and 0.57 (95% CI: 0.52‐0.64), respectively. The pooled positive and negative predictive values were 0.96 (95% CI: 0.95‐0.97) and 0.53 (95% CI: 0.43‐0.63), respectively. The area under the summary receiver operating characteristic curve was 0.86. Meta‐regression indicated that the anti‐CEP 1 antibody detection method may be a source of heterogeneity. The subgroup analysis of the group in which the anti‐CEP 1 antibody was detected by using a commercial enzyme‐linked immunosorbent assay (ELISA) kit had a sensitivity of 59% (95% CI: 50%‐68%) and a specificity of 93% (95% CI: 85%‐97%).

Conclusions

The anti‐CEP 1 antibody had moderate RA diagnostic value with relatively low sensitivity and high specificity. An ELISA may increase the RA diagnostic sensitivity.

Ameliorated Autoimmune Arthritis and Impaired B Cell Receptor-Mediated Ca2+ Influx in Nkx2-3 Knock-out Mice

B cells play a crucial role in the pathogenesis of rheumatoid arthritis. In Nkx2-3-deficient mice (Nkx2-3^−/−) the spleen’s histological structure is fundamentally changed; therefore, B cell homeostasis is seriously disturbed. Based on this, we were curious, whether autoimmune arthritis could be induced in Nkx2-3^−/− mice and how B cell activation and function were affected. We induced arthritis with immunization of recombinant human proteoglycan aggrecan G1 domain in Nkx2-3^−/− and control BALB/c mice. We followed the clinical picture, characterized the radiological changes, the immune response, and intracellular Ca²⁺ signaling of B cells. Incidence of the autoimmune arthritis was lower, and the disease severity was milder in Nkx2-3^−/− mice than in control BALB/c mice. The radiological changes were in line with the clinical picture. In Nkx2-3^−/− mice, we measured decreased antigen-induced proliferation and cytokine production in spleen cell cultures; in the sera, we found less anti-CCP-IgG2a, IL-17 and IFNγ, but more IL-1β, IL-4 and IL-6. B cells isolated from the lymph nodes of Nkx2-3^−/− mice showed decreased intracellular Ca²⁺ signaling compared to those isolated from BALB/c mice. Our findings show that the transcription factor Nkx2-3 might regulate the development of autoimmune arthritis most likely through modifying B cell activation.