Macrophage-Derived Chemokine (MDC; CCL22) is expressed highly in macrophages and in monocyte-derived dendritic cells. High expression is detected in normal thymus and lower expression in lung and spleen. MDC is expressed by a subset of macrophages within regions of advanced atherosclerotic plaques that contain plaque micro-vessels. MDC is a potent chemoattractant for neutrophilic granulocytes, enhancing their bactericidal activity and stimulating the release of lysozyme.

The protein encoded by this gene is secreted by dendritic cells and macrophages, and elicits its effects on its target cells by interacting with cell surface chemokine receptors such as CCR4.[4] The gene for CCL22 is located in human chromosome 16 in a cluster with other chemokines called CX3CL1 and CCL17.