Association of Antibodies to Prevotella copri in Anti-Cyclic Citrullinated Peptide-Positive Individuals At Risk of Developing Rheumatoid Arthritis and in Patients With Early or Established Rheumatoid Arthritis.

OBJECTIVE: Prevotella copri (P copri), a gut commensal, has been reported to be an immune-relevant organism in individuals with rheumatoid arthritis (RA). This study sought to evaluate anti-P copri (anti-Pc) antibody responses in our participant cohorts and to determine when in the natural history of RA such responses develop. METHODS: We analyzed serum levels of immunoglobulin A (IgA) and IgG antibodies from a 27-kd protein of P copri (anti-Pc-p27), an immunogenic P copri protein, in study participants at risk of developing RA, participants who transitioned to RA, participants with early RA (<1 year of disease), and participants with established RA, with comparisons made to their matched controls. We also evaluated anti-Pc-p27 antibody levels in individuals stratified by RA-related autoantibody status. RESULTS: Overall, participants with RA had significantly higher IgA anti-Pc-p27 antibody levels and trended toward higher IgG anti-Pc-p27 antibody levels compared with matched controls. When stratified by early versus established RA, participants with early RA had median IgG anti-Pc-p27 antibody levels that were overall higher, whereas median IgA anti-Pc-p27 antibody levels were statistically significantly higher in participants with established RA compared with their matched controls. In the autoantibody-specific analyses, the at-risk population with anti-cyclic citrullinated peptide (anti-CCP) antibodies, but not rheumatoid factor (RF), trended toward increased levels of IgG anti-Pc-p27. Additionally, RA participants who were seropositive for both CCP and RF had significantly increased levels of IgA anti-Pc-p27 antibodies and trended toward higher levels of IgG anti-Pc-p27 antibodies compared with matched controls. CONCLUSION: Our findings support a potential etiologic role for P copri in both RA preclinical evolution and the subsequent pathogenesis of synovitis.

Identification of Novel, Immunogenic HLA-DR-Presented Prevotella copri Peptides in Patients With Rheumatoid Arthritis.

OBJECTIVE: We previously identified HLA-DR-presented epitopes from a 27-kd protein of Prevotella copri (Pc) obtained from peripheral blood mononuclear cells (PBMCs) from 1 rheumatoid arthritis (RA) patient. Herein, we sought to identify other HLA-DR-presented Pc peptides and source proteins in PBMCs from additional patients to better understand Pc immune responses and RA disease pathogenesis. METHODS: Using tandem mass spectrometry, we searched for HLA-DR-presented Pc peptides in PBMCs from RA and Lyme arthritis (LA) patients. The identified peptides and source proteins were tested for reactivity in RA patients, those with other arthritides, and the general population. These results were assessed for correlation with clinical findings. RESULTS: Including Pc-p27, we identified 5 HLA-DR-presented Pc peptides, each derived from a different Pc protein, in 3 of 4 RA patients, but none in 2 LA patients. When tested in our RA cohort, 14 of 19 patients (74%) had T cell responses, and 47 of 89 patients (53%) had IgG or IgA responses to ≥1 of the 5 Pc peptides or proteins, most commonly IgA reactivity with Pc-p27. Additionally, 74% of RA patients with IgA antibodies to ≥1 Pc protein had anti-citrullinated protein antibodies (ACPAs) compared with 49% of patients who lacked IgA Pc antibody responses (P = 0.05), and IgA Pc antibody levels correlated with ACPA values. CONCLUSION: The majority of the RA patients had Pc immune responses. The correlation of IgA Pc antibody responses, particularly to Pc-p27, with ACPA supports the hypothesis that specific microbial antigens in the mucosa have a role in shaping or amplifying immune responses in RA joints.