CX3CL1 is a member of the delta chemokine subfamily that contains a unique CX3C cysteine motif near the N-terminal. Unlike other known chemokines, it is a type 1 membrane protein containing a chemokine domain tethered on a long mucin-like stalk. CX3CL1, a leukocyte chemoattractant, is expressed in various tissues including the brain, heart, lung, kidney, skeletal muscle, and testis. The expression is reported to be up-regulated in endothelial cells and microglia by inflammatory signals. CX3CR1, a specific receptor for fractalkine, mediates both leukocyte migration and adhesion.