The CCR9 receptor is a GPCR expressed selectively in the thymus, lymph node, spleen, and the small bowel (SB). CCR9 binds to Thymus-expressed chemokine ligand (TECK / CCL25) (Zaballos et al. 1999, Yu et al., 2000, Carramolino et al., 2001), and is involved in directing the movement of mature T cells in the thymus. CCR9 also plays an important role in the pathogenesis of SB Crohn's disease (Papadakis et al, 2001). The CCR9 selective expression in the small bowel but not the colon indicates the the role of CCR9 in the specialized immune response in the SB. It was also shown that CCR9-mediated antiapoptosis could help in the study of cell survival mechanism and T cell malfunctioning. The cloned human CCR9-expressing cell line is made in the Chem-1 host, which supports high levels of recombinant CCR9 expression on the cell surface and contains high levels of the promiscuous Gα15 protein to couple the receptor to the calcium signaling pathway. Thus, the cell line is an ideal tool for screening for antagonists of interactions between CCR9 and its ligands.