Chemokine ligand 22 (CCL22), also known as macrophage-derived chemokine (MDC), is a member of the CC chemokine family.B-cells, microglia, dendritic cells, macrophages, monocytes, interferonγ-activated keratinocytes, colonic epithelial cells, CD4+ T-cells, thymic medullary epithelial cells (microsomes), and activated NK cells are all known to express CCL22. CCL22 is important for lymphocyte migration and it is a potent chemotactic agent for cell types such as dendritic cells, thymocytes and activated NK cells. CCL22 produced by antigen-presenting dendritic cells chemotaxis activated (or memory) T cells carrying CCR4, which enhances the immune response and increases effector function.CCL22 also has other functions, including activation of platelet function and inhibition of synaptic transmission between hippocampal neurons.