CX3CR1 is a G-protein-coupled seven-transmembrane chemokine receptor, also known as GPR13 or V28. It is expressed on microglia, astrocytes, NK cells, monocytes/macrophages, and a subpopulation of T cells. CX3CR1 is the receptor for fractalkine (CX3CL1) and mediates both its adhesive and migratory functions. It also acts as coreceptor with CD4 for HIV-1 virus envelope protein (in vitro), and some variations in the gene of CX3CR1 lead to increased susceptibility to HIV-1 infection and rapid progression to AIDS. Defects in CX3CR1 are a cause of susceptibility to age-related macular degeneration type 12 (ARMD12).