Prevalence, sensitivity and specificity of antibodies against carbamylated proteins in a monocentric cohort of patients with rheumatoid arthritis and other autoimmune rheumatic diseases

Abstract

BackgroundAntibodies against carbamylated proteins (anti-CarP) have been recently identified in the sera of patients with rheumatoid arthritis (RA). The objective of the study was to evaluate the prevalence, sensitivity and specificity of anti-CarP compared to anti-citrullinated peptide antibodies (ACPA) and rheumatoid factor (RF), replicating the existing data in a large cohort of Italian patients with RA and extending the evaluation to other autoimmune rheumatic diseases (AIRDs).MethodsSerum samples (n = 607) from 309 patients with RA, 200 disease controls and 98 normal healthy subjects (NHS) were evaluated. Anti-CarP were detected using carbamylated fetal calf serum as the antigen. ACPAs were detected using second-generation ELISA and IgM RF was assessed as part of routine analysis.ResultsAnti-CarP antibodies were detected in 117 patients with RA (34.4%), ACPA in 190 patients (61.4%) and RF in 202 patients (65.3%). Two (2.04%) of the NHS were positive for anti-CarP, one NHS (1.02%) was positive for ACPA and three NHS were positive for RF (3.06%). Among disease controls, anti-CarP antibodies were detected in 33 patients (16.5%), ACPA in 29 patients (14.5%) and RF in 64 patients (32%). In particular, 16.8% of patients with systemic lupus erythematosus and 31.1% of patients with Sjögren syndrome were positive for anti-CarP. The sensitivity of anti-CarP, ACPA and RF was 46.8%, 61.8% and 64.4%, respectively and specificity was 91.95%, 89.93% and 76.51%, respectively.ConclusionsThe present study extends the knowledge of anti-CarP antibodies, confirming previous data on the diagnostic accuracy of anti-CarP in RA in a large cohort of Italian patients. Anti-CarP antibodies demonstrated relatively low sensitivity and slightly higher specificity compared to ACPA and RF. Even if predominantly present in RA, anti-CarP was detected in a variable percentage of patients with other autoimmune rheumatic diseases and their generation could be attributed to the inflammatory status; the clinical relevance of anti-CarP antibodies in these latter patients should be further determined.

Autophagy induces protein carbamylation in fibroblast-like synoviocytes from patients with rheumatoid arthritis

“…Our results demonstrated a significant correlation between autophagy and carbamylation levels in mononuclear cells of naïve RA patients, although, at present, analysis of the relationship between clinical and laboratory parameters, and monocyte levels of autophagy and/or carbamylation, did not reveal any statistically significant correlation. It could be considered an early trigger for the appearance of anti-CarP Ab [39,40], which in turn precede the onset of RA [34]. Indeed, in this study we observed the presence of anti-CarP antibodies only in 23.3% of early-active RA patients, supporting the view that carbamylation represents an early trigger, which precedes the appearance of the antibodies.…”

Combination of ultrasound power Doppler‐verified synovitis and seropositivity accurately identifies patients with early‐stage rheumatoid arthritis

“…We observed that a combination such as (1) the presence of PD grade ≥2 articular synovitis or (2) the presence of PD grade ≥ 1 articular synovitis and RF and/or ACPA positivity, or the combination of (1) the presence of cPD grade 3 or (2) cPD grade ≥2 and RF and/or ACPA positivity had the best‐balanced diagnostic performance (Table ). The performance of ACPA for diagnosing RA is more specific than that of RF, but our present findings suggest the utility of the use of RF and/or ACPA for the early diagnosis of RA, probably due to the combinational use of the PD signal provided by US.…”

Association between antibodies to carbamylated proteins and subclinical atherosclerosis in rheumatoid arthritis patients

“…In brief, as we described previously [22], Nunc Maxisorp plates (Thermo Scientific) were coated overnight at + 4 °C with non-modified FCS and Ca-FCS (10 μg/ml in carbonate bicarbonate buffer). After washing plates were blocked with phosphate buffered saline (PBS) 1% bovine serum albumin (BSA) (Sigma) for 6 h at + 4 °C.…”