title: Carbamylated albumin is one of the target antigens of anti-carbamylated protein antibodies.
abstract: 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.
  
  
  
  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.
  
  
  
  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.
  
  
  
  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.
authors.affiliation: Department of Rheumatology and Clinical Immunology.
authors.forename: Shuichiro
authors.initials: S
authors.lastname: Nakabo
authors.affiliation: Department of the Control for Rheumatic Diseases.
authors.forename: Motomu
authors.initials: M
authors.lastname: Hashimoto
authors.affiliation: Medical Research Support Center.
authors.forename: Shinji
authors.initials: S
authors.lastname: Ito
authors.affiliation: Department of the Control for Rheumatic Diseases.|Department of Orthopaedic Surgery, Graduate School of Medicine, Kyoto University, Kyoto.
authors.forename: Moritoshi
authors.initials: M
authors.lastname: Furu
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Kyoto University, Kyoto.
authors.forename: Hiromu
authors.initials: H
authors.lastname: Ito
authors.affiliation: Department of Rheumatology and Clinical Immunology.|Department of Clinical Immunology and Rheumatology, Wakayama Medical University, Wakayama.
authors.forename: Takao
authors.initials: T
authors.lastname: Fujii
authors.affiliation: Department of Rheumatology and Clinical Immunology.
authors.forename: Hajime
authors.initials: H
authors.lastname: Yoshifuji
authors.affiliation: Department of Rheumatology and Clinical Immunology.
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Imura
authors.affiliation: Department of Rheumatology and Clinical Immunology.
authors.forename: Ran
authors.initials: R
authors.lastname: Nakashima
authors.affiliation: Department of Rheumatology and Clinical Immunology.
authors.forename: Kosaku
authors.initials: K
authors.lastname: Murakami
authors.affiliation: Department of Rheumatology and Clinical Immunology.
authors.forename: Nobuo
authors.initials: N
authors.lastname: Kuramoto
authors.affiliation: Department of the Control for Rheumatic Diseases.
authors.forename: Masao
authors.initials: M
authors.lastname: Tanaka
authors.affiliation: Medical Research Support Center.
authors.forename: Junko
authors.initials: J
authors.lastname: Satoh
authors.affiliation: Tokyo Metropolitan Institute of Gerontology, Molecular Regulation of Aging, Tokyo.
authors.forename: Akihito
authors.initials: A
authors.lastname: Ishigami
authors.affiliation: Department of Biomedical Statistics and Bioinformatics, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Morita
authors.affiliation: Department of Rheumatology and Clinical Immunology.
authors.forename: Tsuneyo
authors.initials: T
authors.lastname: Mimori
authors.affiliation: Department of Rheumatology and Clinical Immunology.
authors.forename: Koichiro
authors.initials: K
authors.lastname: Ohmura
mesh_terms: D000328:Adult; D000418:Albumins / Q000276:immunology / Q000378:metabolism; D001172:Arthritis, Rheumatoid / Q000276:immunology* / Q000503:physiopathology; D001323:Autoantibodies / Q000097:blood*; D001324:Autoantigens / Q000097:blood*; D015415:Biomarkers / Q000097:blood; D015153:Blotting, Western; D002219:Carbamates / Q000276:immunology*; D002853:Chromatography, Liquid; D016208:Databases, Factual; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D007564:Japan; D008297:Male; D008875:Middle Aged; D010456:Peptides, Cyclic / Q000097:blood* / Q000276:immunology; D012189:Retrospective Studies; D012217:Rheumatoid Factor / Q000097:blood; D018709:Statistics, Nonparametric; D053719:Tandem Mass Spectrometry
chemical_list: D000418:Albumins; D001323:Autoantibodies; D001324:Autoantigens; D015415:Biomarkers; D002219:Carbamates; D010456:Peptides, Cyclic; D012217:Rheumatoid Factor
keywords: autoantibodies; autoantigens; laboratory diagnosis; neutrophils; rheumatoid arthritis