Carbamylated albumin is one of the target antigens of anti-carbamylated protein antibodies

Rheumatology (Oxford). 2017 Jul 1;56(7):1217-1226. doi: 10.1093/rheumatology/kex088.


Objectives: Anti-carbamylated protein (anti-CarP) antibodies are detected in RA patients. Fetal calf serum is used as an antigen source in anti-CarP ELISA, and the precise target antigens have not been found. We aimed to identify the target antigens of anti-CarP antibodies.

Methods: Western blotting of anti-CarP antibodies was conducted. Anti-carbamylated human albumin (CarALB) antibody was detected by in-house ELISA for 493 RA patients and 144 healthy controls (HCs). An inhibition ELISA of anti-CarP antibodies by CarALB and citrullinated albumin (citALB) was performed using eight RA patients' sera. Serum CarALB was detected by liquid chromatography-tandem mass spectroscopy (LC/MS/MS), and the serum MPO concentration was measured by ELISA.

Results: We focused on carbamylated albumin because it corresponded to the size of the thickest band detected by western blotting of anti-CarP antibodies. Anti-CarALB antibody was detected in 31.4% of RA patients, and the correlation of the titres between anti-CarALB and anti-CarP was much closer than that between anti-citALB and anti-CCP antibodies (ρ = 0.59 and ρ = 0.16, respectively). The inhibition ELISA showed that anti-CarP antibodies were inhibited by CarALB, but not by citALB. CarALB was detected in sera from RA patients by LC/MS/MS. The serum MPO concentration was correlated with disease activity and was higher in RA patients with anti-CarALB antibody than in those without.

Conclusion: We found that carbamylated albumin is a novel target antigen of anti-CarP antibodies, and it is the first reported target antigen that has not been reported as the target of ACPA.

Keywords: autoantibodies; autoantigens; laboratory diagnosis; neutrophils; rheumatoid arthritis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Albumins / immunology
  • Albumins / metabolism
  • Arthritis, Rheumatoid / immunology*
  • Arthritis, Rheumatoid / physiopathology
  • Autoantibodies / blood*
  • Autoantigens / blood*
  • Biomarkers / blood
  • Blotting, Western
  • Carbamates / immunology*
  • Chromatography, Liquid
  • Databases, Factual
  • Enzyme-Linked Immunosorbent Assay
  • Female
  • Humans
  • Japan
  • Male
  • Middle Aged
  • Peptides, Cyclic / blood*
  • Peptides, Cyclic / immunology
  • Retrospective Studies
  • Rheumatoid Factor / blood
  • Statistics, Nonparametric
  • Tandem Mass Spectrometry


  • Albumins
  • Autoantibodies
  • Autoantigens
  • Biomarkers
  • Carbamates
  • Peptides, Cyclic
  • Rheumatoid Factor