A Possible Role of Galectin-9 in the Pulmonary Fibrosis of Patients with Interstitial Pneumonia

Galectin-9 (Gal-9) is a beta-galactoside-binding protein that induces biological reactions, such as cell activation, chemoattraction, and apoptosis. We evaluated the role of Gal-9 in the pathogenesis of interstitial pneumonia (IP). Gal-9 levels in the bronchoalveolar lavage fluid (BALF) of patients with IP associated with collagen vascular disease (CVD-IP) and with idiopathic interstitial pneumonias (IIPs), including idiopathic pulmonary fibrosis (IPF) and idiopathic nonspecific interstitial pneumonia (idiopathic NSIP), were estimated by enzyme-linked immunosorbent assay. Gal-9 expression in the lungs of these patients was evaluated using immunohistochemistry. The effect of Gal-9 on the growth and apoptosis of human lung fibroblast cells was assessed in vitro. Gal-9 levels in the BALF were significantly higher in patients with CVD-IP than in patients with IIPs. Gal-9 levels significantly correlated with both the total cell count and the absolute number of lymphocytes in the BALF of patients with IIPs and CVD-IP. Strong reactivity with anti-Gal-9 antibody was observed in the cytoplasm of alveolar macrophages, lymphocytes, and type II pneumocytes in the lungs of patients with IP. Gal-9 expression in those cells was more remarkable in patients with CVD-IP than in patients with IPF and idiopathic NSIP. Gal-9 suppressed the growth of human lung fibroblast cells in a dose- dependent manner. Gal-9 induced apoptosis of human lung fibroblast cells in a dose-dependent manner. Our findings suggest that the expression level of Gal-9 in the lung is increased in patients with CVD-IP and that Gal-9 may have a protective role against pulmonary fibrosis of these patients.