Biomarker for nontuberculous mycobacterial pulmonary disease in patients with rheumatoid arthritis: Anti-glycopeptidolipid core antigen immunoglobulin A antibodies

<p><b>Objective:</b> Nontuberculous mycobacterial (NTM) pulmonary disease is occasionally associated with rheumatoid arthritis (RA), influencing the therapeutic strategy of RA. Since chronic lung diseases are frequently associated with RA, the diagnosis of NTM pulmonary disease is quite difficult in RA patients. Recently, a serological diagnostic test detecting serum immunoglobulin A against the glycopeptidolipid (GPL) core antigen was developed. We investigated the serum levels of anti-GPL antibodies in RA patients to determine the usefulness for detecting NTM pulmonary disease.</p> <p><b>Methods:</b> Anti-GPL antibodies were detected in the sera from RA patients with or without NTM pulmonary disease.</p> <p><b>Results:</b> The positivity of anti-GPL antibodies in RA patients with NTM pulmonary disease was higher than in RA without (<i>p</i> = 1.76 × 10<sup>−14</sup>, odds ratio 70.29, 95% confidence interval [CI] 22.28–221.83). Anti-GPL Ab titers were increased in RA with NTM pulmonary disease (mean titer ± standard deviation [U/ml], RA with NTM pulmonary disease: 4.1 ± 7.0, RA without NTM pulmonary disease: 0.4 ± 1.6, <i>p</i> = 1.51 × 10<sup>−10</sup>). The area under the curve (AUC) value of the receiver operating characteristic (ROC) curve for anti-GPL antibodies was 0.917 (95%CI 0.860–0.974, <i>p</i> = 3.32 × 10<sup>−47</sup>).</p> <p><b>Conclusions:</b> Serum anti-GPL antibodies are useful for detecting NTM pulmonary disease in RA patients.</p>