Human CCL13 (MCP-4) was initially identified in a library constructed from human fetal mRNA. CCL13 shares a high similarity with CCL2 (MCP-1, 61%), CCL7 (MCP-3, 58%), and CCL8 (MCP-2, 55%). CCL13 is constitutively expressed at high levels in the small intestine, colon, and lung. Original data showed that CCL13 was less effective than MCP-1 and MCP-3 in monocyte and lymphocyte chemoattraction, but equivalent to eotaxin as a chemoattractant for eosinophils. Chemokines are very important in the inflammatory process, initially in the influx of PMN by CXC chemokines and subsequently chemoattracting monocytes where the MCPs participate, including CCL13. The bioactivity of pro-inflammatory chemokines is regulated by MMPs in order to regulate the influx of different cell subpopulations. In the case of CCL13, it is inactivated by MMP-12 by truncation at position 4-5 generating a CCR antagonist and decreasing the arrival of monocytes. CCL13 binds to CCR2, and this receptor also binds to CCL2, CCL8, CCL7, CCL11, CCL24, and CCL26. CCL13 is involved in inflammatory diseases such as rheumatoid arthritis (RA), atherosclerosis, and asthma. High levels of CCL13 have been detected in the synovial fluid of patients with RA, in serum of asthmatic patients, and in plasma of patients with symptomatic carotid atherosclerosis.