Characterization of fractalkine in rat brain cells: Migratory and activation signals for CX3CR-1-expressing microglia

Molecular analyses of the chemokine fractalkine and its receptor CX3C-R1 in the rat brain have revealed a striking polarization: fractalkine is expres sed constitutively in neurons and is up-regulated by TNF-alpha and IL-1 bet a in astrocytes. Expression of its specific receptor, CX3C-R1, is restricte d to astrocytes and microglia, We have analyzed the functional correlates o f this expression and demonstrate that fractalkine induces microglial cell migration and activation. However, the activity of this chemokine on astroc ytes may also be highly relevant in inducing astrocyte-microglia cell inter actions through cytokine/mediator release leading to microglial activation.