Fractalkine is a membrane-associated chemokine expressed on endothelial cells, but not on leukocytes, suggesting, it is of particular importance for leukocyte recruitment from blood. Expression is also induced during inflammation. Fractalkine is membrane bound, thus blurring the traditional distinction between adhesion molecules and chemokines. It can directly mediate leukocyte adhesion to activated endothelium via its receptor CX3CR1. Booth T cells and macrophages express CX3CR1.