Fractalkine, also termed neurotactin, is a membrane-bound CX3C chemokine. The mature protein is part of a 397-amino acid precursor consisting of a chemokine domain (76 amino acids), a mucin stalk of 241 residues, a putative transmembrane domain (18 amino acids), and an intracellular tail of 37 amino acids. Within the chemokine domain the first two cysteine residues are separated by 3 amino acids. Fractalkine message is found at high concentrations in the brain, and also in kidney, lung and heart. Fractalkine is chemotactic for monocytes and may play a role in brain inflammation.