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

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

Author information

1
Department of Rheumatology and Clinical Immunology.
2
Department of the Control for Rheumatic Diseases.
3
Medical Research Support Center.
4
Department of Orthopaedic Surgery, Graduate School of Medicine, Kyoto University, Kyoto.
5
Department of Clinical Immunology and Rheumatology, Wakayama Medical University, Wakayama.
6
Tokyo Metropolitan Institute of Gerontology, Molecular Regulation of Aging, Tokyo.
7
Department of Biomedical Statistics and Bioinformatics, Graduate School of Medicine, Kyoto University, Kyoto, Japan.

Abstract

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

PMID:
28398552
PMCID:
PMC5850724
DOI:
10.1093/rheumatology/kex088
[Indexed for MEDLINE]
Free PMC Article

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