CCL22 is a protein that in humans is encoded by the CCL22 gene, which locates on the Chr. 16. The protein is highly expressed in macrophage, monocyte-derived dendritic cell and thymus, additionally, also detected in the tissues of thymus, lymph node and appendix. CCL22 can bind to CCR4, and is a chemoattractant for monocytes, monocyte-derived dendritic cells, and natural killer cells, but not for neutrophils, eosinophils, and resting T-lymphocytes. After secreted from monocyte-derived dendritic cells, the protein can be proteolytic cleaved into three forms: MDC (3-69), MDC (5-69), MDC (7-69).