Thymus-expressed chemokine (TECK), or CCL25, is a member of the CC family of chemokines that regulates the movement of lymphocytes in the thymus and in the small intestine. TECK induces chemoattraction by binding the chemokine receptor CCR9, which is expressed on immature pre-T cells and thymocytes (Youn et al.; Uehara et al.). In the thymus, TECK is produced by stromal cells, whereas in the small intestine TECK is primarily produced by epithelial cells (Vicari et al.; Bowman et al.; Kunkel et al.). CCR9 is a G protein-coupled receptor and is expressed on most thymocytes, but not on natural killer cells, monocytes, eosinophils, basophils, and neutrophils (Wu et al). In Jurkat cells, binding of TECK to CCL9 has been shown to increase levels of intracellular calcium (Cheng-Rong et al). TECK/CCR9 signaling has also been linked to many cancers, as these molecules have been shown to mediate anti-apoptotic processes by activating the PI3K/AKT signaling pathway, weakening the effect of cytotoxic T cells by regulating STAT signaling. Additionally, TECK induces metastasis by increasing the expression of MMP2 and MMP9 (Tu et al.).