Mobilization of dendritic cells into lymphatic vessels requires cytokine stimulation and induction of the chemokine receptor CCR7. The respective roles of the CCR7 ligands CCL19 and CCL21 in mediating migration are not fully defined, but chemotaxis to CCL19 mediates Langerhans cell exit from the epidermis. Optimal chemotaxis to CCL19 occurs when DCs are triggered with exogenous leukotriene C₄, an eicosanoid transported out of the cell via the ATP binding cassette (ABC) transporter multidrug resistance related protein 1 (MRP1, ABCC1). Indeed, MRP1 and the related multidrug resistance protein 1 (MDR1, p-glycoprotein, ABCB1) may control the intracellular and extracellular accumulation of key signaling lipids that regulate dendritic cell migration.