Analysis of the relationship between bronchoalveolar lavage lymphocyte fraction and detailed autoimmune features in patients with idiopathic interstitial pneumonia.

Bronchoalveolar lavage (BAL) is crucial for the diagnosis of interstitial lung disease (ILD). Although BAL lymphocytosis is found in patients with connective tissue disease (CTD)-related ILD, the effects of CTD-associated features on BAL lymphocytosis have not been elucidated. To identify CTD-associated features that affect BAL lymphocyte fraction in patients with idiopathic interstitial pneumonia (IIP). This post hoc analysis of a prospective, multicentre cohort study was conducted between 2015 and 2020. Overall, 222 patients newly diagnosed with IIP were consecutively enrolled, and 74 autoimmune features were comprehensively analysed during IIP diagnosis. The median age was 71 years, and the median observation period was 36 months. The clinical characteristics related to a significant increase in BAL lymphocyte fraction were consolidation opacity on high-resolution computed tomography (HRCT), morphologic domain of interstitial pneumonia with autoimmune features (IPAF), serum CXCL10 concentration, and acute/subacute onset (all p < 0.05). In contrast, presence of joint lesion/mucocutaneous lesion/dry symptoms, autoantibodies, or other CTD-like features on HRCT and surgical lung biopsy did not affect the BAL lymphocyte fraction (all p ≥ 0.05). Furthermore, a high BAL lymphocyte fraction (≥ 8.5%) was related to a low proportion of progressive pulmonary fibrosis (p < 0.001) and favourable survival (log-rank, p = 0.020) in patients with non-idiopathic pulmonary fibrosis (IPF). IPAF morphologic domain especially with consolidation opacity on HRCT and high CXCL10 concentration, but not CTD-like symptoms, autoantibodies, or CTD-like features on lung biopsy, were related to a high BAL lymphocyte fraction with favourable survival in patients with non-IPF.