CCR9 (previously called orphan receptor GPR 9-6) is highly expressed in the thymus on both mature and immature T-cells. It is also abundant in T-cells of the intestine but is lowly expressed in lymph nodes and the spleen. Alternative splicing produces two receptors, called CCR9A and CCR9B, CCR9A containing 12 additional amino acids at its N terminus as compared with CCR9B (Yu CR et al, 2000). The A and B forms of the receptor were expressed at a ratio of approximately 10:1. CCR9 has a specific ligand in CCL25 (Thymus-expressed chemokine, TECK) (Zaballos A et al, 1999) and transduces the signal by intracellular calcium mobilization.