Fractalkine or Chemokine (C-X3-C motif) ligand 1 (CX3CL1) is a member of the CX3C chemokine family. Fractalkine / CX3CL1 is a unique chemokine that functions not only as a chemoattractant but also as an adhesion molecule and is expressed on endothelial cells activated by proinflammatory cytokines, such as interferon-gamma and tumor necrosis factor-alpha. Fractalkine/CX3CL1 is expressed in a membrane-bound form on activated endothelial cells and mediates attachment and firm adhesion of T cells, monocytes and NK cells. Fractalkine / CX3CL1 is associated with dendritic cells (DC) in epidermis and lymphoid organs. The fractalkine receptor, CX3CR1, is expressed on cytotoxic effector lymphocytes, including natural killer (NK) cells and cytotoxic T lymphocytes, which contain high levels of intracellular perforin and granzyme B, and on macrophages. Soluble fractalkine causes migration of NK cells, cytotoxic T lymphocytes, and macrophages, whereas the membrane-bound form captures and enhances the subsequent migration of these cells in response to secondary stimulation with other chemokines.