Role of fractalkine in leukocyte adhesion and migration and in vascular injury.

Leukocyte adhesion and trafficking at the endothelium requires both cellular adhesion molecules and chemotactic factors. Fractalkine, a recently identified chemokine, has a unique architecture, a Cys-X-X-X-Cys chemokine domain presented on top of an extended mucin-like stalk as a part of transmembrane protein, and is expressed in a membrane-bound form on tumor necrosis factor-alpha and interleukin-1-activated endothelial cells. Fractalkine receptor CX3CR1 is expressed on natural killer (NK) cells, monocytes and some portions of CD8(+) T cells. Interactions between fractalkine and CX3CR1 can mediate not only chemotaxis but also cell adhesion in the absence of substrates for other adhesion molecules. Furthermore, fractalkine activates NK cells, resulting in enhanced cytolysis of fractalkine expressing endothelial cells. Since endothelial cells are primary targets of immunologic attack, fractalkine seems to be involved in pathogenesis of vascular injury.