Antibodies to a Citrullinated Porphyromonas gingivalis Epitope Are Increased in Early Rheumatoid Arthritis, and Can Be Produced by Gingival Tissue B Cells: Implications for a Bacterial Origin in RA Etiology

Abstract

Based on the epidemiological link between periodontitis and rheumatoid arthritis (RA), and the unique feature of the periodontal bacterium Porphyromonas gingivalis to citrullinate proteins, it has been suggested that production of anti-citrullinated protein antibodies (ACPA), which are present in a majority of RA patients, may be triggered in the gum mucosa. To address this hypothesis, we investigated the antibody response to a citrullinated P. gingivalis peptide in relation to the autoimmune ACPA response in early RA, and examined citrulline-reactivity in monoclonal antibodies derived from human gingival B cells. Antibodies to a citrullinated peptide derived from P. gingivalis (denoted CPP3) and human citrullinated peptides were analyzed by multiplex array in 2,807 RA patients and 372 controls; associations with RA risk factors and clinical features were examined. B cells from inflamed gingival tissue were single-cell sorted, and immunoglobulin (Ig) genes were amplified, sequenced, cloned and expressed (n=63) as recombinant monoclonal antibodies, and assayed for citrulline-reactivities by enzyme-linked immunosorbent assay. Additionally, affinity-purified polyclonal anti-cyclic-citrullinated peptide (CCP2) IgG, and monoclonal antibodies derived from RA blood and synovial fluid B cells (n=175), were screened for CPP3-reactivity. Elevated anti-CPP3 antibody levels were detected in RA (11%), mainly CCP2+ RA, compared to controls (2%), p<0.0001, with a significant association to HLA-DRB1 shared epitope alleles, smoking and baseline pain, but with low correlation to autoimmune ACPA fine-specificities. Monoclonal antibodies derived from gingival B cells showed cross-reactivity between P. gingivalis CPP3 and human citrullinated peptides, and a CPP3+/CCP2+ clone, derived from an RA blood memory B cell, was identified. Our data support the possibility that immunity to P. gingivalis derived citrullinated antigens, triggered in the inflamed gum mucosa, may contribute to the presence of ACPA in RA patients, through mechanisms of molecular mimicry.

Molecular Mimicry of the Rheumatoid Arthritis-Related Immunodominant T-Cell Epitope within Type II Collagen (CII260-270) by the Bacterial L-Asparaginase

“…Usually, the contribution of microorganisms to the pathogenesis of RA is explained either by the local inflammation of mucosal surfaces or citrullination of bacterial and human proteins [ 9 , 10 ]. In the present study, we focused our investigations on molecular mimicry.…”

“…In search of homology between bacterial proteins and RA-related T-cell epitopes using an immunoinformatics analysis, Repac et al were able to retrieve the major RA-triggering candidates among which are Proteus mirabilis , Escherichia coli , Mycobacterium tuberculosis , Klebsiella pneumoniae , Streptococcus pyogenes, and Prevotella species [ 6 ]. A possible role of some oral and gut microbial species ( Porphyromonas gingivalis and Prevotella copri ) in RA pathogenicity has also been discussed [ 9 , 10 ]. During dysbiosis, these species can mediate the process of the citrullination of bacterial or human proteins triggering an immune response and production of anti-citrullinated antibodies that cross-react with human citrullinated peptides through molecular mimicry [ 9 , 10 ].…”

“…A possible role of some oral and gut microbial species ( Porphyromonas gingivalis and Prevotella copri ) in RA pathogenicity has also been discussed [ 9 , 10 ]. During dysbiosis, these species can mediate the process of the citrullination of bacterial or human proteins triggering an immune response and production of anti-citrullinated antibodies that cross-react with human citrullinated peptides through molecular mimicry [ 9 , 10 ].…”

“…HLA-DR alleles that have a particular sequence in the beta chain (HLA-DRB1) at positions 70–74 are known as “shared epitope alleles” (SE alleles) [ 11 , 14 ]. The presence of HLA-SE alleles increases the risk of developing RA and in most cases, this is associated with the production of anti-citrullinated protein antibodies (ACPA) in those RA patients (ACPA-positive RA patients) [ 9 , 10 , 11 , 15 ].…”

The bacterial link with rheumatoid arthritis

“…The periodontitis‐causing bacterium, Porphyromonas gingivalis has been considered as a candidate causing RA because it expresses peptidyl arginine deiminase that converts arginine into citrulline in a protein. Indeed, antibodies to a citrullinated P. gingivalis are increased in ACPA‐positive RA patients, suggesting P. gingivalis as an etiology in these patients 8 . Furthermore, experimentally chronic oral infection of P. gingivalis in Lewis rats results in severe periodontitis and arthritis with bone erosion and ACPA production 9 .…”