CX3CL1 (chemokine (C-X3-C motif) ligand 1) or fractalkine is a membrane protein, which is the only member of CXC3 family. Its chemokine domain (CKD) anchors it to the cell membrane through its mucin-like stalk. It acts as a ligand for the G-protein coupled receptor CX3CR1, which is found on smooth muscle cells, T-cells, natural killer (NK) cells and monocytes. Fractalkine is expressed on epithelial, endothelial and smooth muscle cells and neurons.

CX3CL1 (chemokine (C-X3-C motif) ligand 1) or fractalkine, along with CX3CR1, is involved in various disorders such as atherosclerosis, multiple sclerosis, neuropathic pain and rheumatic disorders. It facilitates the proliferation and survival of primary human vascular smooth muscle cells in an epidermal growth factor receptor (EGR)-dependent manner. It plays an essential role in cell survival and promotes the survival of cells such as monocytes, T-cells and microglia. In humans, it is thought be involved in atherogenesis, and thus, might have potential as a target in treatment of cardiovascular disease. In patients with sickle cell disease (SCD), the serum levels of this chemokine is increased, thus implicating it in the pathogenesis of inflammation associated with SCD.

Leukocyte chemoattractant protein and member of the chemokine superfamily possessing a CX₃C motif. The soluble chemokine domain of human fractalkine is reported to chemoattract T cells and monocytes.

Lyophilized from a 0.2 μm filtered solution in 30% acetonitrile and 0.1% trifluoroacetic acid containing 1.25 mg bovine serum albumin.

The biological activity is measured by its ability to flux calcium or chemoattract mouse BaF/3 cells transfected with hCX3CR1 cells with the ec50 range of 0.3-1.5 ng/ml. Fractalkine can also chemoattract freshly isolated peripheral blood lymphocytes.