Chemokine (C-X3-C motif) ligand 1(CX3CL1), also known as fractalkine, is a large cytokine protein of 373 amino acids, and is the only known member of the CX3C chemokine family. Soluble CX3CL1 has been identified in serum, urine, cerebrospinal, amniotic and synovial fluids. CX3CL1 is predominantly expressed by vascular endothelium and smooth muscle, neurons and dendritic cells. Most CX3CL1 expression is induced by inflammatory cytokines such as TNF-α and IFN-γ. CX3CL1 elicits its adhesive and migratory functions by interacting with the chemokine receptor CX3CR1. Soluble CX3CL1 potently chemoattracts T cells and monocytes, while the cell-bound chemokine promotes strong adhesion of leukocytes to activated endothelial cells. CX3CL1 may be associated with antitumor activity and is important in resolving normal inflammatory processes such as wound healing. It may also contribute to the pathogenesis of some conditions.