Fractalkine, also known as CX3CL1, is a cytokine protein containing a CX3C chemokine motif atop a mucin stalk. Fractalkine is produced by non-hemopoietic cells, including neurons and astrocytes. Soluble fractalkine functions as a chemoattractant for T cells and monocytes. Cell-membrane-bound fractalkine, which is induced on activated endothelial cells, promotes leukocyte adhesion. The transmembrane chemokine receptor CX3CR1 mediates the adhesive and chemoattractant functions of fractalkine.