Diagnostic values, association with disease activity and possible risk factors of anti-PAD4 in rheumatoid arthritis: a meta-analysis.

OBJECTIVE: Anti-peptidyl arginine deaminase 4 (anti-PAD4) antibody has been a subject of investigation in RA in the last two decades. This meta-analysis investigated the diagnostic values, association with disease activity and possible risk factors of anti-PAD4 antibody in rheumatoid arthritis. METHOD: We searched studies from five databases up to 1 December 2022. Bivariate mixed-effect models were used to pool the diagnostic accuracy indexes, and the summary receiver operating characteristics (SROC) curve was plotted. The quality of diagnostic studies was assessed using QUADAS-2. Non-diagnostic meta-analyses were conducted using the random-effects model. Sensitivity analysis, meta-regression, subgroup analyses and Deeks' funnel plot asymmetry test were used to address heterogeneity. RESULT: Finally, 24 journal articles and one letter were included. Anti-PAD4 antibody had a good diagnostic value between RA and healthy individuals, but it might be lower between RA and other rheumatic diseases. Moreover, anti-PAD4 could slightly enhance RA diagnostic sensitivity with a combination of ACPA or ACPA/RF. Anti-PAD4 antibody was positively correlated with HLA-SE and negatively correlated with ever or current smoking in patients with RA. RA patients with anti-PAD4 antibody had higher DAS28, ESR, swollen joint count (SJC) and the possibility of having interstitial lung disease (ILD) and pulmonary fibrosis compared with those without. CONCLUSION: Our study suggests that anti-PAD4 antibody is a potentially useful diagnostic biomarker and clinical indicator for RA. Further mechanistic studies are required to understand the impact of HLA-SE and smoking on the production of anti-PAD4 antibody.

Anti-peptidylarginine deiminase-4 antibodies at mucosal sites can activate peptidylarginine deiminase-4 enzyme activity in rheumatoid arthritis.

BACKGROUND: Mucosal sites are hypothesized to play a role in the development of rheumatoid arthritis (RA). Since serum anti-peptidylarginine deiminase (PAD)4 antibodies, including a subset that cross-react with PAD3 (PAD3/4), are specific for RA and associate with severe disease, we sought to examine whether anti-PAD4 and anti-PAD3/4 antibodies were present in the lung and oral mucosa of subjects with RA and "at-risk" for RA. METHODS: We included 37 RA, 25 healthy control, and 46 subjects "at-risk" for RA based on familial RA and/or serum anti-citrullinated protein antibody (ACPA) positivity. Paired serum, sputum, and saliva were evaluated for anti-PAD4 and anti-PAD3/4 using immunoprecipitation and ACPA using ELISA. Immunoglobulins (Ig) were purified from representative samples, and their effect on citrullination of histone H3 by recombinant human PAD4 was measured by anti-citH3 immunoblot. RESULTS: Anti-PAD4 antibodies were detected in the serum of 6/37 (16.2%), sputum of 3/37 (8.1%), and saliva of 3/33 (9.1%) RA subjects and in the serum and sputum of 1/46 (2.2%) at-risk subjects. None of the healthy controls had anti-PAD4 antibodies at any site. Serum, sputum, and salivary anti-PAD4 antibodies were more prevalent in RA subjects with RA duration >2 years. Purified antibodies from representative anti-PAD4-positive and anti-PAD3/4-positive sputum were primarily of the IgA isotype and able to increase PAD4 enzymatic activity. CONCLUSIONS: Anti-PAD4 antibodies are present in the sputum and saliva of a portion of RA patients and are infrequent in at-risk subjects. Importantly, the ability of anti-PAD4, and particularly anti-PAD3/4, antibodies in the sputum to enhance PAD4 enzymatic activity suggests that anti-PAD4 may play an active role in the RA lung.

The value of anti-CarP and anti-PAD4 as markers of rheumatoid arthritis in ACPA/RF negative rheumatoid arthritis patients.

BACKGROUND: Anti-citrullinated protein antibodies (ACPAs) and rheumatoid factor (RF) are key factors in the American College of Rheumatology/European League Against Rheumatism rheumatoid arthritis (RA) classification criteria markers. However, about 30% of patients diagnosed with RA are seronegative, rationalizing the need for new serologic markers for RA. Antibodies against carbamylated proteins (anti-CarP) and against peptidyl-arginine deiminase type 4 (anti-PAD4) have been postulated to be useful RA markers. The purpose of this study is to evaluate the value of anti-CarP and anti-PAD4 in a well-characterized population of RA patients and healthy controls (HCs). METHODS: A total of 122 RA patients and 30 HCs were enrolled in the study. Serum levels of ACPA, anti-PAD4, anti-CarP and RF were determined by enzyme-linked immunosorbent immunoassays (ELISAs). Synthetic carbamylated peptides were used in the ELISA assay to determine the protein targets of the anti-CarP antibodies. RESULTS: Rates of ACPA, RF, anti-PAD4 and anti-CarP positivity were 85.2%, 67.2%, 55.7% and 46.7% in RA, and 0%, 0%, 6.7% and 6.7% in HC respectively. In the RA population, 25.4% of patients had all four types of antibodies positive, while 6.6% had no antibodies. There was a significant correlation between anti-PAD4 and ACPAs (r s = 0.39), RF and ACPAs, (r s = 0.3) and RF and anti-CarP, (r s = 0.3). There was no correlation between ACPAs and anti-CarP. Anti-CarP positivity was noted in 49 (47.1%) and 45 (54.9%) of ACPAs and RF positive patients respectively. In addition, five anti-CarP+ patients did not have ACPA nor RF. CONCLUSION: Anti-CarP but not anti-PAD4 may be a useful biomarker in identifying ACPA/RF negative RA patients. This antibody may identify an additional RA population who may benefit from early implementation of aggressive therapy.

Autoantibodies to protein-arginine deiminase (PAD) 4 in rheumatoid arthritis: immunological and clinical significance, and potential for precision medicine.

Introduction: The protein-arginine deiminase (PAD) 4 enzyme plays an important role in the pathogenesis of rheumatoid arthritis (RA) and also represents an antigenic target. Anti-PAD4 antibodies can be present in RA and are associated with specific clinical features. Areas covered: This review aims to analyze the current knowledge and recent findings on anti-PAD4 antibodies in RA and their clinical and immunological significance. Expert opinion: Anti-PAD4 antibodies are not currently used in clinical practice for the management of RA. Nevertheless, there is growing evidence of their relevance in RA, and of their potential utility to improve diagnosis, patient stratification, and prognosis.

Clinical and immunological aspects of anti-peptidylarginine deiminase type 4 (anti-PAD4) autoantibodies in rheumatoid arthritis.

Rheumatoid arthritis (RA) is the most common rheumatic autoimmune disease worldwide, which causes progressive joint damage and can lead to functional disability. Despite prominent advances in RA diagnosis and treatment during the last 20years, there is still a need for novel biomarkers that aid in diagnosis and prognosis of this heterogeneous disease. Citrullination is a key post-translational modification implicated on anti-citrullinated protein/peptide antibodies (ACPA) production in RA, catalyzed by human peptidylarginine deiminases (PADs). Among these enzymes, PAD4 has been recognized as an important player in RA pathogenesis and the enzyme itself is a target of autoantibodies (anti-PAD4) in a subgroup of RA patients. Accumulating evidence suggests that anti-PAD4 autoantibodies may be useful as a severity biomarker in RA and recent studies have also shed light on the functional significance of these autoantibodies. This review summarizes the evidence on anti-PAD4 autoantibodies in RA, and addresses its usefulness for disease diagnosis and prognosis. Novel immunological aspects of anti-PAD4 antibodies and their relevance to RA pathogenesis are also discussed.

Lack of Association among Peptidyl Arginine Deiminase Type 4 Autoantibodies, PADI4 Polymorphisms, and Clinical Characteristics in Rheumatoid Arthritis.

OBJECTIVE: We aimed to jointly investigate the role of antipeptidyl arginine deiminase type 4 antibodies (anti-PAD4) and polymorphisms in the PADI4 gene together with clinical variables in rheumatoid arthritis (RA). METHODS: Serum IgG autoantibodies to human recombinant PAD4 were identified by DELFIA technique in 745 patients with RA (366 available from previous studies). Genotyping of PADI4 was performed using TaqMan assays in 945 patients and 1118 controls. Clinical data, anticitrullinated protein antibodies (ACPA) status, shared epitope status, and a combined genetic risk score were also available. RESULTS: Anti-PAD4 antibodies were detected in 193 (26%) of 745 patients with RA; 149 (77%) of these were also ACPA-positive. No association was observed between anti-PAD4 status and clinical characteristics, PADI4 polymorphisms, or genetic risk scores after stratification for ACPA status. CONCLUSION: Taken together, the results from these combined serological, genetic, and clinical analyses suggest that anti-PAD4 appears to be a bystander autoantibody with no current clinical utility in RA.

Meta-analysis: diagnostic accuracy of antibody against peptidylarginine deiminase 4 by ELISA for rheumatoid arthritis.

The antibody against peptidylarginine deiminase (PAD) 4 is a biomarker that might be helpful in the diagnosis of rheumatoid arthritis (RA). We aim to estimate the diagnostic value of anti-PAD4 antibody for RA by meta-analysis. We searched PubMed, Embase, the Cochrane Library, Web of Science, and Scopus for studies published in any languages in March 1, 2017 that evaluated the diagnostic accuracy of the anti-PAD4 antibody for the diagnosis of RA. The articles that detected the anti-PAD4 antibody by enzyme-linked immunosorbent assay (ELISA) and used healthy donors or patients without arthritis or arthralgia as controls were included for meta-analysis. The articles were assessed by Quality Assessment of Diagnostic Accuracy Studies tool. A bivariate mixed-effects model was used to summarize the diagnostic indexes from eight eligible studies. The pooled sensitivity, specificity, and positive and negative likelihood ratios for anti-PAD4 antibody were 38% (95% CI 30.0-46.0%), 96% (95% CI 93.0-98.0%), 8.96 (95% CI 5.00-16.05), and 0.65 (95% CI 0.57-0.74), respectively. The summary diagnostic odds ratios were 13.74 (95% CI 7.23-26.09), and the area under the summary receiver operator characteristic curve was 86% (95% CI 83-89%). Anti-PAD4 antibody detected by ELISA shows a high value in the diagnosis of RA with high specificity, but relatively low sensitivity.

Association of anti-peptidyl arginine deiminase antibodies with radiographic severity of rheumatoid arthritis in African Americans.

BACKGROUND: Evidence suggests that the presence of peptidyl arginine deiminase type 4 (PAD4) antibodies is associated with radiographic-severity rheumatoid arthritis (RA) among Caucasian patients. The presence of anti-PAD4 antibodies that were cross-reactivity against PAD3 was associated with more aggressive erosive disease (compared with the presence of anti-PAD4 antibodies without anti-PAD3 crossreactivity) in Caucasian RA patients. The objectives of this study were to determine the prevalence of serum anti-PAD4 and anti-PAD4/PAD3 cross-reactive autoantibodies in African Americans with RA and whether these antibodies associate with radiographic severity and radiographic progression. METHODS: Serum anti-PAD4 and anti-PAD4/PAD3 antibodies were measured by immunoprecipitation, and the temporal trends in titers were analyzed. We compared total radiographic scores among anti-PAD4-positive, anti-PAD4/PAD3-positive, and anti-PAD4-negative patients and used a zero-inflated negative binomial model to determine associations between radiographic severity and antibody status. Logistic regression was used to analyze radiographic progression. RESULTS: Of 192 African-American patients with RA, 73 % were anti-citrullinated peptide/protein antibody (ACPA)-positive, 46 out of 192 (24 %) of whom had serum anti-PAD4 antibodies. Median (interquartile range) total Sharp van der Heijde radiographic scores were 2 (1-97.5) in ACPA-positive patients and 0 (0-3) in ACPA-negative patients (P < 0.001). Of the 46 anti-PAD4-positive patients, 20 had anti-PAD4 antibodies that cross-reacted with PAD3. In patients with early RA, anti-PAD4 and anti-PAD4/PAD3 antibody titers increased over time (P = 0.006, P = 0.001, respectively). Median (interquartile range) total radiographic scores were higher for anti-PAD4-positive than for anti-PAD4-negative patients (3 (1-115) versus 2 (0-11), respectively; P = 0.005). Median (interquartile range) total radiographic score for anti-PAD4/PAD3-positive patients was 76 (3-117) (P < 0.001) versus anti-PAD4-negative patients. Only anti-PAD4/PAD3 antibodies associated with radiographic severity (incidence rate ratio = 2.81; 95 % confidence interval 1.23, 6.43). CONCLUSION: This analysis suggests that autoantibodies against PAD4 and PAD3 proteins may serve as biomarkers for identifying African-American patients with RA and higher radiographic severity.