Galectin-9 is a mammalian lectin with a molecular weight around 50 kD. It is a member of the beta-galactoside-binding family. With two conserved carbohydrate recognition domains (CRDs), galectin-9 binds small beta-galactosides as well as complex glycoconjugates. HAVCR2/TIM3 has been reported as one of its ligands. Galectin-9 may be retained intracellularly or transported to the cell surface where it can be cleaved to generate a soluble form. Galectin-9 is expressed by lymphocytes, dendritic cells, granulocytes, eosinophils, astrocytes, endothelial cells, fibroblasts, and thymus epithelial cells. It can be induced by cytokines in various cell types and is involved in cell aggregation, adhesion, chemotaxis, and apoptosis; galectin-9 induces regulatory T cells and suppresses Th1 and Th17 responses.