ACR Meeting Abstracts

ACR Meeting Abstracts

Abstract Number: 1739

Mass Spectrometry Identified Rheumatoid Arthritis-Specific Modified Proteins and the Discovery of Antigen-Specific Hidden Autoantibodies

Khetam Ghannam1, Marieluise Kirchner2, Holger Bang3, Thomas Häupl4, Sarah Ohrndorf1, Jan Zernicke1, Ulrike Kuckelkorn5, Philipp Mertins6, Eugen Feist7 and Gerd Burmester8, 1Department of Rheumatology and Clinical Immunology, Charité - Universitätsmedizin Berlin, Berlin, Germany, 2Proteomics Platform at Max Delbrück Center for Molecular Medicine and Berlin Institute of Health (BIH), Berlin, Germany, 3Orgentec Diagnostika GmbH, Mainz, Germany, 4Helios Department of Rheumatology, Vogelsang-Gommern, Germany, 5Institute of Biochemistry, Berlin, Germany, 6Proteomics Platform at Max Delbrück Center for Molecular Medicine and Berlin Institute of Health (BIH), Berlin, Germany, 7Helios Department of Rheumatology and Clinical Immunology, Vogelsang-Gommern, Germany, 8Charité – Universitätsmedizin Berlin, Department of Rheumatology and Clinical Immunology, Berlin, Germany

Meeting: ACR Convergence 2023

Keywords: ,

Session Information

Date: Tuesday, November 14, 2023

Title: (1734–1775) RA – Etiology and Pathogenesis Poster

Session Type: Poster Session C

Session Time: 9:00AM-11:00AM

Background/Purpose: Rheumatoid arthritis (RA) is a chronic and systemic autoimmune disease characterized by synovial inflammation and progressive joint destruction. Given the presumed pathophysiologic role of anti-modified protein autoantibodies (AMPAs) in RA, it is important to obtain a comprehensive overview of the post-translational modified (PTM) proteins present in SF and serum of RA in order to reveal those autoantigens that might promote the expansion of autoreactive B cells. Therefore, mass spectrometry was used to identify citrullinated, carbamylated and acetylated proteins present within monomeric and IC (immune complexes) of synovial fluid (SF) and serum of RA, and serum of healthy donors (HD), which served as a control.

Methods: This study included 42 RA patients fulfilling the 2010 ACR/EULAR classification criteria, 44 patients with other arthritic diseases who served as the control group, and 47 HD. Proteins isolated from SF and serum were fractionated by sucrose gradient centrifugation and monomeric and IC IgG were isolated from the respective fractions according to protein markers. Mass spectrometry was used to identify PTMs within monomeric and IC IgG fractions. Rheumatoid factor (RF), anti-citrullinated, anti-carbamylated, and anti-acetylated antigen antibodies were analyzed by ELISA.

Results: In SF and serum of RA, positivity to anti-acetylated and anti-carbamylated IgG was restricted to samples positive for anti-cyclic citrullinated peptide (CCP) IgG. Anti- citrullinated IgG antibodies differentiated between RA and CG in serum and SF, while anti-acetylated IgG reactivities were significantly increased in RA-SF compared with CG. Monomeric and IC IgG isolated from formally seronegative RA patients showed very strong reactivity mainly against citrullinated peptides, indicating a “hidden” antibody response. Although mass spectrometry analysis identified citrullinated, carbamylated and acetylated proteins in all samples tested – SF from RA and serum from RA and HD – quality analysis revealed modified autoantigens unique to RA, and many were found in double or even triple modified isoforms. The frequency of modified carbamylated and acetylated proteins was significantly higher in RA than in HD.

Conclusion: Many RA-related autoantigens underwent single as well as multifold-modifications were identified within monomeric and IC of RA patients. Carbamylated and acetylated proteins distinguish between RA and HD. Monomers and IC isolated from formally seronegative patients showed hidden anti-citrullinated reactivities undetectable by conventional assays.

Disclosures: K. Ghannam: None; M. Kirchner: None; H. Bang: Orgentec Diagnostika GmbH, 3; T. Häupl: None; S. Ohrndorf: None; J. Zernicke: None; U. Kuckelkorn: None; P. Mertins: None; E. Feist: AbbVie, 12, has received honoraria and research grants, BMS, 12, has received honoraria and research grants, Galapagos, 12, has received honoraria and research grants, Lilly, 12, has received honoraria and research grants, MSD, 12, has received honoraria and research grants, Novartis, 12, has received honoraria and research grants, Pfizer, 12, has received honoraria and research grants, Roche, 12, has received honoraria and research grants, Sobi, 12, has received honoraria and research grants; G. Burmester: AbbVie, 2, 6, Boehringer Ingelheim, 2, 6, Bristol-Myers Squibb, 2, 6, Chugai, 6, Galapagos, 2, 6, Lilly, 2, 6, Pfizer, 2, 6, Sanofi, 2, 6.

To cite this abstract in AMA style:

Ghannam K, Kirchner M, Bang H, Häupl T, Ohrndorf S, Zernicke J, Kuckelkorn U, Mertins P, Feist E, Burmester G. Mass Spectrometry Identified Rheumatoid Arthritis-Specific Modified Proteins and the Discovery of Antigen-Specific Hidden Autoantibodies [abstract]. Arthritis Rheumatol. 2023; 75 (suppl 9). https://acrabstracts.org/abstract/mass-spectrometry-identified-rheumatoid-arthritis-specific-modified-proteins-and-the-discovery-of-antigen-specific-hidden-autoantibodies/. Accessed .

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