Fractalkine is a type I membrane protein that signals through the CX3CR1 receptor. The extracellular domain of Fractalkine is released by protease cleavage – producing soluble Fractalkine. Fractalkine has been found in many tissues and shown to be up-regulated in endothelial cells and microglia in response to inflammatory signals. Fractalkine is also involved in leukocyte adhesion as well as attracting monocytes, microglia cells and NK cells.