Description: CCL19, also known as MIP-3 beta （Macrophage Inflammatory Protein 3 beta）, is a member of the CC- subfamily of chemokines. It is most closely related to CCL21, with which it shares 32% amino acid sequence homology. CCL19 and CCL21 are expressed mainly by stromal cells in the T cell-rich zones of lymph nodes. They are critical mediators of the homeostatic trafficking of naïve T cells and activated dendritic cells into the secondary lymphoid organs. CCL19 and CCL21 also play a role in T cell priming and activation, as well as the recruitment of lymphocytes to inflamed tissue. Both proteins signal via the G protein-coupled receptor, CCR7, which is expressed on T cells and mature dendritic cells. Although CCL19 and CCL21 both exhibit the same affinity for CCR7, only the binding of CCL19 results in the desensitization and internalization of the receptor.