CCL15 was discovered by analyzing the upstream region of the CCL14 gene. CCL15 is arranged in tandem with CCL14 on human chromosome 17. CCL15, CCL6, CCL9, and CCL23 have an extended N-terminal domain upstream of the first two conserved chemokine cysteines. This domain is encoded by a different exon and includes 16 to 20 residues. CCL15 (1-92) is processed by cathepsin G to produce highly active forms of CCL15 [(24-92), (27-92) and (29-92)], and elastase processes CCL15 (1-92) predominantly to CCL15 (22-92). Also, CCL15 is cleaved by MT6-MMP/MMP25 to produce CCL15 with very high activity. MMP25 is localized primarily in neutrophil gelatinase granules, and it is released by neutrophil activation and degranulation in inflammatory reactions. High levels of CCL15 were detected in human renal cell carcinoma bone metastasis, and in vitro studies showed that CCL15 stimulates chemotaxis of osteoclast progenitors and enhances their differentiation in response to RANKL. CCL15 is abundant in bronchoalveolar lavage of patients with pulmonary sarcoidosis. Also, it is elevated in the serum of patients with severe asthma, and it is reduced by omalizumab, a humanized anti-IgE antibody that has been use in the treatment of asthma. It has been suggested that airway smooth muscle cells and basophils produce CCL15, and it might have an important role in asthma severity and persistence. In addition, high levels of CCL15 have been detected in the serum of patients with hepatocellular carcinoma, and human hepatic carcinoma cells express CCR1 and CCL15.