Augmented Anti-Bactericidal Permeability-Increasing Protein Antibody Levels in Rheumatoid Arthritis Patients...

Objective: Chronic lung diseases (CLDs), for example, interstitial lung disease, manifest as an extra-articular complication of rheumatoid arthritis (RA). The contribution of anti-bactericidal permeability-increasing protein antibodies (BPI Abs) in lung involvement in RA or primary Sjögren's syndrome has been reported. Studies related to anti-BPI Abs in RA with CLD are infrequent. Here, the involvement of anti-BPI Abs with RA and CLD complications was evaluated. Methods: Enzyme-linked immunosorbent assays were used to measure anti-BPI Abs in RA sera. Results: Higher anti-BPI Ab amounts were present in the RA with usual interstitial pneumonia (UIP) than without CLD (mean ± standard deviation, 10.4 ± 23.5 [ng/mL] vs. 1.3 ± 3.8, p = 0.0020). Area under the curve values of receiver operating characteristic curves for anti-BPI Ab and Krebs von den lungen-6 were alike between RA with UIP and without CLD (0.8616, 95% CI 0.8184-0.9048; 0.8716, 95% CI 0.8151-0.9282, p = 0.5933, respectively). A relationship between anti-BPI Ab and anti-carbamylated protein Ab levels was observed in RA patients (rho 0.3508, p = 1.47 × 10^-14). Conclusions: Anti-BPI Abs were related to UIP in RA patients and might be biomarkers for UIP. These findings predict anti-BPI Abs involvement in UIP pathogenesis in RA.