CCL25 (thymus expressed chemokine) is a novel CC chemokine that is distantly related (approximately 20% amino acid sequence identity) to other CC chemokines. Mouse CCL25 cDNA has also been cloned and shown to encode a 144 aa protein that exhibits 49% aa sequence identity to human CCL25. The expresssion of human and mouse CCL25 was shown to be highly restricted to the thymus and small intestine. Although dendritic cells have been demonstrated to be the source of CCL25 production in the thymus, dendritic cells derived from bone marrow do not express CCL25. Recombinant human and mouse CCL25 have been shown to be chemotactic for activated macrophages, dendritic cells and thymocytes. CCL25 signals through the CCR9 receptor.