Abstract
BACKGROUND: Idiopathic pulmonary fibrosis (IPF) and rheumatoid arthritis-associated interstitial lung disease (RA-ILD) share several risk factors, genetic backgrounds, and morphological features, including the usual interstitial pneumonia pattern on computed tomography and histopathology. Anti-cyclic citrullinated peptide antibodies (ACPAs) are RA-related autoantibodies that are associated with RA-ILD. ACPA production can be induced in the lungs of patients with IPF. METHODS: Forty-four patients with IPF and 10 patients with RA-ILD underwent bronchoalveolar lavage fluid (BALF) collection. The concentrations of IgG ACPAs in the BALF were measured and corrected for total IgG levels. The relationships between corrected BALF ACPA levels and clinical features were investigated. RESULTS: The proportion of ACPAs (ACPA-IgG level adjusted by total IgG level) in the BALF was significantly lower in patients with IPF than in those with RA-ILD (1222 ± 1424 U/mg vs. 9058 ± 15159 U/mg, p < 0.01). Compared with the group with low ACPA proportions (n = 29), the IPF group with high ACPA proportions (n = 15) in the BALF was younger (65.2 ± 9.4 years vs. 70.9 ± 6.8 years, p = 0.03) and had more females (6 out of 15 (40%) vs. 2 out of 29 (7%), p = 0.01). Additionally, the IPF patients with a high ACPA proportion in the BALF had significantly better outcomes than those with a low ACPA proportion did (median overall survival time: 92.4 months vs. 41.1 months, p = 0.04). CONCLUSION: The corrected BALF ACPA level might be an important biomarker for identifying IPF phenotypes with favourable outcomes.