Macrophage Inflammatory Protein 3 β (MIP-3 β), also known as CCL19, is a chemokine that is expressed in the thymus, lymph nodes, and activated bone marrow stromal cells. MIP-3 β signals through the G protein-coupled receptor CCR7 to regulate normal lymphocyte recirculation. MIP-3 β also functions during T cell trafficking to the thymus, and in T cell and B cell homing to the lymph nodes and secondary lymphoid organs. Human MIP-β ? shows activity on mouse cells.