The lung airway epithelial surface is heavily covered with sialic acids as the terminal carbohydrate on most cell surface glycoconjugates and can be removed by microbial neuraminidases or endogenous sialidases. By desialylating the lung epithelial surface, neuraminidase acts as an important virulence factor in many mucosal pathogens, such as influenza and S. pneumoniae. Desialylation exposes the subterminal galactosyl moieties - the binding glycotopes for galectins, a family of carbohydrate-recognition proteins playing important roles in various aspects of immune responses. Galectin-1 and galectin-3 have been extensively studied in their roles related to host immune responses, but some questions about their role(s) in leukocyte recruitment during lung bacterial infection remain unanswered. In this study, we found that both galectin-1 and galectin-3 bind to polymorphonuclear leukocytes (PMNs) and enhance the interaction of endothelial intercellular adhesion molecule-1 (ICAM-1) with PMNs, which is further increased by PMN desialylation. In addition, we observed that in vitro galectin-1 mediates the binding of PMNs, particularly desialylated PMNs, onto the endothelial cells. Finally, in a murine model for LPS-mediated acute lung injury, we observed that galectin-1 modulates PMN infiltration to the lung without altering the expression of chemoattractant cytokines. We conclude that galectins, particularly galectin-1, may function as adhesion molecules that mediate PMN-endothelial cell interactions, and modulate PMN infiltration during acute lung injury.
