Antibodies against carbamylated proteins: prevalence and associated disease characteristics in Belgian patients with rheumatoid arthritis or other rheumatic diseases

Abstract

Objectives: Anti-carbamylated protein antibodies (anti-CarP) are reported to be associated with increased disease activity and with more severe joint damage in rheumatoid arthritis (RA) patients. The present study investigated the presence of anti-CarP in various rheumatic diseases, and their specific clinical significance in RA, in Belgian rheumatology patients.

Method: We tested sera from 254 RA patients, 56 healthy controls, and 153 patients with different rheumatic conditions: juvenile idiopathic arthritis (JIA), axial spondyloarthritis, systemic sclerosis, and Sjögren’s syndrome (SS). An in-house enzyme-linked immunosorbent assay was used to detect immunoglobulin G antibodies against carbamylated foetal calf serum.

Results: Anti-CarP were detected in 88 RA patients (34.6%), of whom 82% were also positive for anti-citrullinated protein antibodies (ACPAs) and 81% were also rheumatoid factor (RF) positive. Of note, 11 anti-CarP single-positive patients were detected (4.3%). The previously reported association with joint erosions was not detected. However, in ACPA- and RF-negative RA patients, the presence of anti-CarP was associated with higher disease activity and disability. Fifteen per cent of JIA patients and 30% of SS patients also tested positive for anti-CarP and their antibody levels did not differ significantly from those of anti-CarP-positive RA patients. Anti-CarP levels were, however, significantly higher in ACPA- or RF-positive patients.

Conclusion: Anti-CarP antibodies were detected in the sera of a cohort of Belgian RA patients. Moreover, they were also detected in primary SS patients and in JIA patients. In the seronegative subset of RA patients, anti-CarP antibodies showed prognostic value.

Acknowledgements

We would like to thank LA Trouw and MK Verheul (LUMC) for their help and guidance in setting up the in-house ELISA technique for anti-CarP detection.

This study was supported by the Erasme Fund for Medical Research (Fonds Erasme pour la Recherche Médicale), Belgium (PS). DC is a Senior Research Associate from the FRS-FNRS. This project is supported by the charity fund CAP48 from RTBF Project ‘Polyarthritis in children and young adults CAP48’ (Polyarthrite de l’enfant et du jeune adulte CAP48) [B403201317717].

Disclosure statement

No potential conflict of interest was reported by the authors.

Supporting Information

Additional Supporting Information may be found in the online version of this article.

Supplementary index. CAP48 RA inclusion criteria, Disease controls inclusion criteria, Clinical assessment, ELISAs for antibody detection, RF, and ACPA assays.

Supplementary table S1. Baseline characteristics of the RA study population.

Supplementary table S2. Anti-CarP in Sjögren’s syndrome patients.

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