CCR9 is a G protein-coupled receptor member of the CC chemokine subfamily of receptors. Human CCR9 is 369 amino acids (aa) in length with a predicted molecular weight of 42 kDa. Mouse and rat CCR9 share 86% aa sequence identity with the human protein. Most chemokine receptors exhibit promiscuous binding properties whereby several different chemokines signal through the same receptor. Chemokine ligand receptor binding results in G protein activation as well as the activation of downstream signaling cascades, including the Akt and NFkB pathways. Chemokine receptors mediate the chemotactic actions of chemokine ligands and activation of these receptors leads to cytoskeleton rearrangement and chemotactic cell migration.