Objective To analyse the association between anti-carbamylated protein antibodies (Anti-CarP) and interstitial lung disease (ILD) in rheumatoid arthritis (RA) patients.
Methods Cross-sectional study including RA patients fulfilling the 2010 ACR/EULAR criteria. The main population comprised two groups: (1) RA patients diagnosed with RA-ILD (RA-ILD group); (2) RA patients without ILD (non-ILD RA group). Non-ILD RA patients in whom ILD was suspected underwent a diagnostic work-up and, if ILD was diagnosed, were switched to the RA-ILD group. ILD was diagnosed by high-resolution computed tomography and confirmed by a multidisciplinary committee. An independent replication sample was also obtained. Three Anti-CarP IgG autoantibodies against fetal calf serum (Anti-FCS), fibrinogen (Anti-Fib) and chimeric fibrine/filagrine homocitrullinated peptide (Anti-CFFHP) and one Anti-CarP IgA against FCS (Anti-FCS-IgA) were determined by home-made ELISA. Associations between Anti-CarP and ILD were analysed using multivariable logistic regression adjusted by smoking, sex, age, RA disease duration, rheumatoid factor and anticitrullinated protein antibodies.
Results We enrolled 179 patients: 37 (21%) were finally diagnosed with RA-ILD. Anti-CarP specificities were more frequent in RA-ILD patients (Anti-FCS 70% vs 43%; Anti-Fib 73% vs 51%; Anti-CFFHP 38% vs 19%; Anti-CarP-IgA 51% vs 20%, p<0.05 for all comparisons). Serum titers of Anti-CarP were significantly higher in RA-ILD patients. Anti-CarP specificities showed a robust effect towards increasing the odds of ILD in the multivariate analysis (Anti-FCS (OR: 3.42; 95% CI: 1.13 to 10.40), Anti-Fib (OR: 2.85; 95% CI: 0.83 to 9.70), Anti-CFFHP (OR: 3.11; 95% CI: 1.06 to 9.14) and Anti-FCS-IgA (OR: 4.30; 95% CI: 1.41 to 13.04)). Similar findings were observed in the replication sample.
Conclusions Anti-CarP were strongly associated with ILD. The role of homocitrullination in RA-ILD merits further investigation.
- rheumatoid arthritis
- pulmonary fibrosis
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RC-M and SCR-G contributed equally.
Contributors RC-M, SCR-G, IH and RS contributed to the conception and study design. RC-M, JR, JG-P, VR-E, IC-S, SH and JDC contributed to data collection. RC-M, SCR-G and MJG analysed the data. RC-M, SCR-G, VR-E and IH contributed to interpretation of the data. RC-M, SCR-G and RS wrote the first version of the manuscript and AC, JR, JG-P, JDC, VR-E, IC-S, SH and IH revised it critically. All authors read and approved the final manuscript.
Funding Financial support from the Hospital Clinic of Barcelona, Research, Innovation and Education Department (Grant # 37 933 to RC-M and the Spanish Ministry of Economy, Industry and Competitiveness and the European Regional Development Fund (Grant # RTI2018-094120-B-I00 to IH).
Competing interests None declared.
Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.
Patient consent for publication Not required.
Ethics approval The study was conducted in accordance with the Declaration of Helsinki and was approved by the Hospital Clinic of Barcelona Ethics Committee (approval number 2017/0679).
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data are available upon reasonable request. Data is available upon reasonable request, all data relevant to the study are included in the article.
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