CX3CR1 is one of the chemokine receptors that are required as co-receptors for HIV infection. The genes encoding human, mouse, and rat CX3CR1were cloned and designated V28 and CMKBRL1, CX3CR1, and RBS11, respectively, (1-4). The encoded seven transmembrane protein was recently identified as the receptor for a novel transmembrane molecule, fractalkine, and renamed CX3CR1 (5). Recently, CX3CR1 was found to serve as a co-receptor for HIV-1 and HIV-2 envelope fusion and virus infection, which can be inhibited by fractokine (6). CX3CR1 mediates leukocyte migration and adhesion (5). CX3CR1 is expressed in a variety of human tissues and cell lines (2).