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

Abstract

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.

Figure 1.

Unadjusted and adjusted comparisons of IgA and IgG anti-Pc-p27 levels among RA and at-risk participants compared to matched controls. The solid line on 1a-1d represents the positive cutoff. 1a, levels of IgA anti-Pc-p27 are significantly higher in RA cases compared to matched controls (median [IQR] Control= 0.06 [0.04–0.10], median [IQR] RA= 0.08 [0.05–0.17]). 1b, levels of IgA anti-Pc-p27 are not different in at-risk participants compared to matched controls (median [IQR] Control= 0.10 [0.05–0.17], median [IQR] At-Risk= 0.11 [0.07–0.18]). 1c, levels of IgG anti-Pc-p27 are not different in RA participants compared to matched controls (median [IQR] Control= 0.11 [0.07–0.21], median [IQR] RA= 0.17 [0.10–0.24]). 1d, levels of IgG anti-Pc-p27 are not different in at-risk participants compared to matched controls (median [IQR] Control= 0.16 [0.06–0.24], median [IQR] At-Risk= 0.18 [0.09–0.32]). 1e, association between IgA and IgG anti-Pc-p27 among RA and at-risk participants compared to matched controls. Results are shown as odds ratios with error bars showing the 95% confidence intervals. Estimates are conditioned on matched pair. RA participants are more likely to have higher levels of IgA anti-Pc-p27 compared to matched controls (OR: 1.44; 95% CI: 1.10–1.90; p=0.01).

Figure 2.

Unadjusted and adjusted comparisons of IgA and IgG anti-Pc-p27 levels among early RA and established RA participants compared to matched controls. The solid line on 2A-2D represents the positive cutoff. 2A, levels of IgA anti-Pc-p27 do not significantly differ between early RA participants and matched controls (median [IQR] Control= 0.06 [0.03–0.08], median [IQR] Early RA= 0.07 [0.04–0.13]). 2B, levels of IgA anti-Pc-p27 are significantly higher in established RA participants compared to matched controls (median [IQR] Control= 0.06 [0.04–0.10], median [IQR] Established RA= 0.09 [0.06–0.17]). 2C, levels of IgG anti-Pc-p27 are higher in early RA participants compared to matched controls (median [IQR] Control= 0.09 [0.05–0.14], median [IQR] Early RA= 0.18 [0.12–0.22]), however, non-significant after multiple comparison adjustment (p=0.01, p_adj=0.11). 2D, levels of IgG anti-Pc-p27 do not significantly differ between established RA participants compared to matched controls (median [IQR] Control= 0.12 [0.08–0.24], median [IQR] Established RA= 0.17 [0.08–0.25]). 2E, association between IgA and IgG anti-Pc-p27 levels among early RA and established RA compared to matched controls. Results shown as odds ratios with error bars showing 95% confidence intervals. Established RA participants are more likely to have higher levels of IgA anti-Pc-p27 compared to matched controls (OR: 1.42; 95% CI:1.03–1.95; p=0.03).

Figure 3.

Longitudinal analysis of IgA and IgG anti-Pc-p27 among participants who transitioned to IA during follow-up. The solid line on each plot represents the positive cutoff. 3A, levels of IgA anti-Pc-p27 did not significantly change from the first selected study visit to the study visit where IA was determined. 3B, levels of IgG anti-Pc-p27 did not significantly change from the first selected study visit to the study visit where IA was determined.

Figure 4.

Unadjusted and adjusted comparisons of IgA and IgG anti-Pc-p27 levels among RA and at-risk participants compared to matched controls by autoantibody status. The solid line on 4a-4d represents the positive cutoff. 4A, levels of IgA anti-Pc-p27 are significantly higher in RA participants who are anti-CCP+ and RF+ (IgA and/or IgM) compared to matched controls (p<0.01, p_adj=0.01). 4B, levels of IgA anti-Pc-p27 do not significantly differ between at-risk participants compared to matched controls. 4C, levels of IgG anti-Pc-p27 do not significantly differ between RA participants compared to matched controls. 4D, levels of IgG anti-Pc-p27 are overall higher in at-risk participants who are anti-CCP+/RF-compared to matched controls, however, non-significant after multiple comparison adjustment(p=0.05, p_adj=0.19).