CX3CR1 is a G-protein-coupled seven-transmembrane chemokine receptor, also known as GPR13 or V28. It is expressed on NK cells, T cell subset, monocytes/macrophages, dendritic cells, and some malignant epithelial cells. CX3CL1 (known as fractalkine, neurotactin) is the ligand of CX3CR1. CX3CL1 is a unique transmembrane molecule with a CX3C-motif chemokine domain and a mucin-like stalk. CX3CL1 is expressed by activated-endothelial cells, neurons, and astrocytes. The interaction of CX3CR1 and its ligand mediates cell firm adhesion and migration.