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