Anti-carbamylated protein antibody isotype pattern differs between palindromic rheumatism and rheumatoid arthritis

[Background]: A restricted response against citrullinated peptides/proteins, with less isotype usage, has been found in palindromic rheumatism (PR) in comparison with rheumatoid arthritis (RA). We hypothesized that this different antibody response may be observed for other post-translational modified proteins. We compared the prevalence and isotype usage of two specificities of anti-carbamylated peptide/protein antibodies (Anti-CarP) in patients with PR and RA.
[Methods]: Cross-sectional study including 54 patients with pure PR and 53 patients with RA, matched by sex, age, disease duration and ACPA. Anti-CarP specificities were determined by home-made enzyme-linked immunosorbent assay tests using a synthetic chimeric fibrin/filaggrin homocitrullinated peptide (CFFHP) and fetal calf serum (FCS) homocitrullinated protein as antigens. IgG, IgA and IgM isotypes were measured.
[Results]: Anti-CarP were positive (CFFHP or FCS) in 24% and 64% of patients with PR and RA, respectively (p
[Conclusion]: Anti-CarP are found in patients with PR but in a lower proportion and with a different isotype usage from in RA, suggesting a distinct B cell response to homocitrullinated antigens in PR.
The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study was supported by the Hospital Clinic of Barcelona, Research, Innovation and Education Department (Grant # 37933 to RC) and the Spanish Ministry of Economy, Industry and Competitiveness and the European Regional Development Fund (Grant # RTI2018-094120-B-I00 to IH).