Increased Galectin-9 Concentration and Number of CD4+Foxp3high+Cells in Bronchoalveolar Lavage Fluid of Patients with Cryptogenic Organizing Pneumonia

Purpose Galectin-9 (Gal-9) is a β-galactoside-binding protein that exhibits various biological reactions, such as chemoattraction, cell aggregation, and apoptosis. Recent studies demonstrated that Gal-9 has a role as an immunomodulator in excessive immunological reactions by expanded regulatory T cells (Tregs). We examined the role of Gal-9 in the pathogenesis of one of the major idiopathic interstitial pneumonias, cryptogenic organizing pneumonia (COP) as compared with idiopathic pulmonary fibrosis (IPF). Methods Gal-9, transforming growth factor-β1, and interleukin (IL)-10 levels in the bronchoalveolar lavage fluid (BALF) of patients with COP and IPF were estimated by enzyme-linked immunosorbent assay. Forkhead box protein 3 (Foxp3) expressing Tregs were evaluated by flow cytometry. The effect of Gal-9 on interactions between human lung fibroblast cells and hyarulonan was assessed in vitro. Results Gal-9 and IL-10 levels in the BALF were significantly higher in patients with COP than in patients with IPF. The number of CD4+Foxp3high+cells was significantly higher in the BALF of patients with COP than in those with IPF. Gal-9 levels significantly correlated with the absolute number of CD4+CD25+Foxp3+cells or CD4+Foxp3high+cells, but not with the absolute number of CD4+CD25+Foxp3-cells, in the BALF of patients with COP. Gal-9 suppressed the CD44-dependent interaction of human lung fibroblast cells with hyarulonan in a dose-dependent manner. Conclusions Our findings suggest that increased Gal-9 levels in the lung have a protective role against lung inflammation and fibrosis in patients with COP through the induction of Tregs in the lung and CD44-dependent inhibitory effects on lung fibroblast cells.