Prior studies have demonstrated an increased frequency of antibodies to Porphyromonas gingivalis (Pg), a leading agent of periodontal disease, in rheumatoid arthritis (RA) patients. However, these patients generally had long-standing disease, and clinical associations with these antibodies were inconsistent. Our goal was to examine Pg antibody responses and their clinical associations in patients with early RA prior to and after disease-modifying antirheumatic drug (DMARD) therapy.

Serum samples from 50 DMARD-naïve RA patients were tested using an enzyme-linked immunosorbent assay with whole-Pg sonicate. For comparison, serum samples were tested from patients with late RA, patients with other connective tissue diseases (CTDs), age-similar healthy hospital personnel and blood bank donors. Pg antibody responses in early RA patients were correlated with standard RA biomarkers, measures of disease activity and function.

At the time of enrollment, 17 (34%) of the 50 patients with early RA had positive immunoglobulin G (IgG) antibody responses to Pg, as did 13 (30%) of the 43 patients with late RA. RA patients had significantly higher Pg antibody responses than healthy hospital personnel and blood bank donors (P < 0.0001). Additionally, RA patients tended to have higher Pg antibody reactivity than patients with other CTDs (P = 0.1), and CTD patients tended to have higher Pg responses than healthy participants (P = 0.07). Compared with Pg antibody-negative patients, early RA patients with positive Pg responses more often had anti-cyclic citrullinated peptide (anti-CCP) antibody reactivity, their anti-CCP levels were significantly higher (P = 0.03) and the levels of anti-Pg antibodies correlated directly with anti-CCP levels (P < 0.01). Furthermore, at the time of study entry, the Pg-positive antibody group had greater rheumatoid factor values (P = 0.04) and higher inflammatory markers (erythrocyte sedimentation rate, or ESR) (P = 0.05), and they tended to have higher disease activity scores (Disease Activity Score based on 28-joint count (DAS28)-ESR and Clinical Disease Activity Index) and more functional impairment (Health Assessment Questionnaire). In Pg-positive patients, greater disease activity was still apparent after 12 months of DMARD therapy.

A subset of early RA patients had positive Pg antibody responses. The responses correlated with anti-CCP antibody reactivity and to a lesser degree with ESR values. There was a trend toward greater disease activity in Pg-positive patients, and this trend remained after 12 months of DMARD therapy. These findings are consistent with a role for Pg in disease pathogenesis in a subset of RA patients.