C-C motif chemokine 9(CCL9) is an 11 kDa, secreted, monomeric polypeptide that belongs to the beta (or CC) intercrine family of chemokines. It is expressed mainly in the liver, lung, and the thymus, although some expression has been detected in a wide variety of tissues except brain. Monokine has inflammatory, pyrogenic and chemokinetic properties. It circulates at high concentrations in the blood of healthy animals. Binding to a high-affinity receptor，it activates calcium release in neutrophils. It also inhibits colony formation of bone marrow myeloid immature progenitors. CCL9 can activate osteoclasts through its receptor CCR1 (the most abundant chemokine receptor found on osteoclasts) suggesting an important role for CCL9 in bone resorption.