Pathogenic Role of Circulating Citrullinated Antigens and Anti-Cyclic Monoclonal Citrullinated Peptide Antibodies in Rheumatoid Arthritis.

Pureun Won,Hyerin Jung,Youngkyun Kim,Dong Hyun Sohn,Ji Hyeon Ju,William H Robinson,Yeri Alice Rim,Su-Jin Moon

doi:10.3389/fimmu.2021.692242

Abstract

We examined whether it is possible to directly detect citrullinated antigens in the serum of rheumatoid arthritis (RA) patients using a monoclonal antibody (mAb) designed to be specific for citrullinated peptides. In order to confirm the potential of the mAb as a direct arthritis-inducing substance through experimental model of RA, a monoclonal antibody (mAb) 12G1 was generated using by immunization of mice with a challenging cyclic citrullinated peptide. Immunohistochemical analysis of RA-affected synovial tissue showed that our mAb 12G1 could indeed detect citrullinated proteins in target tissues. Subsequently, serum levels of citrullinated type II collagen and filaggrin were measured in healthy volunteers, patients with RA, ankylosing spondylitis (AS), and systemic lupus erythematosus (SLE) using a 12G1-based sandwich ELISA. This showed that citrullinated filaggrin showed 78.9% sensitivity and 85.9% specificity for RA diagnosis with a cutoff optical density (OD) value of 1.013, comparable with the results from a second-generation anti-citrullinated protein antibody (ACPA) test. Circulating citrullinated collagen and filaggrin were detected even in sera of RA patients who were negative for both rheumatoid factor (RF) and ACPA. ELISA results also showed that RF and ACPA titers showed significantly positive correlation with both citrullinated collagen and filaggrin OD values in sera of RA patients. 12G1 challenging aggravated the severity of murine arthritis. In summary, mAb 12G1 can directly detect citrullinated proteins in RA target tissue and in sera of RA patients and 12G1 showed direct arthritogenic potential in vivo. This, 12G1 might be useful for diagnosis of RA including seronegative RA and may help to elucidate the pathophysiological role of citrullination in RA.

Highlights

Rheumatoid arthritis (RA) is a chronic, systemic inflammatory disease characterized by inflammation of the synovial membrane lining the joints and progressive joint damage
To identify the presence of circulating autoantigens that could induce the production of anti-citrullinated protein antibody (ACPA), we generated a monoclonal antibody (mAb) specific for citrullinated antigens
Four mice were immunized with the circular citrullinated peptides (CCPs), and we examined the reactivity of their serum antibodies to the CCP and noncitrullinated peptide (NCP) (Figure 1C)

Summary

Introduction

Rheumatoid arthritis (RA) is a chronic, systemic inflammatory disease characterized by inflammation of the synovial membrane lining the joints and progressive joint damage. Autoantibodies, including rheumatoid factor (RF), can be detected in serum and synovial fluid (SF) samples from RA patients. Citrullination is a post-translational modification performed by the enzyme peptidyl-arginine deiminase (PAD), which converts the amino acid arginine into the noncoded amino acid citrulline. This modification can be detected in the inflamed joints of mice and in RA-affected synovial tissue in humans [2,3,4,5,6]. Proteins harboring citrullinated epitopes are the dominant antigens recognized by autoantibodies in serum from RA patients [7, 8]. Filaggrin contains many arginine residues, and citrullinated anti-filaggrin antibodies purified from RA sera can recognize (pro)filaggrins only when the filaggrins are citrullinated

Objectives

Methods

Results

Conclusion