Galectin-9 is belonging to the lectin family, that containing total 15 mammalian lectin members. Similar to other galectins, There is a carbohydrate recognition binding domain that enables Galectin-9 binding to β-galactosides specifically. Most galectins are either bivalent or multivalent regarding their carbohydrate binding capacity, which enables the recognition of distinct signaling pathways. Galectin-9 may be retained intracellularly or transported to the cell surface where it can be cleaved to generate a soluble form. Galectin-9 functions in effector and regulatory phases of the immune response. During inflammation, the production of Galectin-9 in vivo generates a microenvironment that limits effector T cell responses. Galectin-9 can negatively regulate the Th1 immune response by engaging TIM-3 on T cells, which leads to induction of intracellular Ca2+ influx and activation of apoptosis pathways.