Single-cell transcriptomic analysis of blood and bronchoalveolar lavage fluid in progressive fibrosing interstitial lung diseases.

This study investigates the pathophysiology of progressive fibrosing interstitial lung disease (PF-ILD) and identifies biomarkers that predict PF-ILD in patients with ILD by analyzing immune cells in both the blood and bronchoalveolar lavage fluid (BALF). This prospective cohort study involved 43 newly diagnosed ILD patients with various connective tissue diseases, from whom BALF and blood samples were collected for analysis. Using Seq-Well, a portable platform for single-cell RNA sequencing, we assessed gene expression in immune cells from both BALF and blood. Additionally, levels of cytokines, chemokines, and complements in the BALF supernatant and plasma were measured using an enzyme-linked immunosorbent assay. In total, 12 patients fulfilled the diagnostic criteria for PF-ILD and exhibited an increase in mononuclear myeloid cells expressing chemokines, such as CCL10 and CCL4, along with plasma cells in their BALF. Additionally, elevated levels of cytokines, including IL-6, CXCL10, and arginase, as well as increased complement activation, were observed in the BALF of patients with PF-ILD. Our findings suggest that active inflammation by macrophages and plasma cells along with complement activation in the lungs may be associated with the progression of pulmonary fibrosis. BALF analysis is beneficial for assessing immune responses and predicting progressive fibrosis in the lungs.