IMMUNOCYTOCHEMICAL EVIDENCE FOR A MODULATION OF GALECTIN-3 (MAC-2), ACARBOHYDRATE-BINDING PROTEIN, IN PULMONARY FIBROSIS

Galectin 3 is an endogenous mammalian carbohydrate-binding protein wit h affinity for terminal beta-galactose residues, polylactosamine glyca ns, and ABH-blood group carbohydrate epitopes. To determine the distri bution and regulation of galectin 3 during pulmonary injury, which is known to be accompanied by profound changes in the carbohydrate moieti es of cell surface glycoproteins of alveolar cells, a rat model of irr adiation-induced lung inflammation and repair was used. Immunocytochem istry showed that in normal rat lungs, galectin 3 was localized to alv eolar macrophages, with weaker staining of bronchial epithelial cells. Shortly after irradiation-induced lung injury, when there is active p roliferation of type II alveolar epithelial cells and re-epithelializa tion of alveolar basement membranes by type I cells, the total galecti n concentration in the lung increased dramatically. This increase was due in part to an increased population of galectin 3-positive intersti tial and alveolar macrophages. In addition, galectin 3 was expressed p rominently at the surface of the newly formed type I alveolar epitheli um and to lesser extent at the apical surface of type Il cells. These findings suggest that the increased synthesis and secretion of galecti n 3 during irradiation-induced lung injury, together with ligation of secreted lectin at the surface of alveolar epithelial cells, may play roles in pulmonary alveolar epithelial expansion and differentiation d uring injury and repair.