Receptor for the C-X3-C chemokine fractalkine (CX3CL1) present on many early leukocyte cells; CX3CR1-CX3CL1 signaling exerts distinct functions in different tissue compartments, such as immune response, inflammation, cell adhesion and chemotaxis (PubMed:9918795, PubMed:10187784). CX3CR1-CX3CL1 signaling mediates cell migratory functions (PubMed:11544273, PubMed:12871640, PubMed:16675847, PubMed:18322241). Responsible for the recruitment of natural killer (NK) cells to inflamed tissues (PubMed:11544273, PubMed:16675847). Acts as a regulator of inflammation process leading to atherogenesis by mediating macrophage and monocyte recruitment to inflamed atherosclerotic plaques, promoting cell survival (PubMed:12569158, PubMed:18971423). Involved in airway inflammation by promoting interleukin 2-producing T helper (Th2) cell survival in inflamed lung (PubMed:21037587). Involved in the migration of circulating monocytes to non-inflamed tissues, where they differentiate into macrophages and dendritic cells (PubMed:12871640). Acts as a negative regulator of angiogenesis, probably by promoting macrophage chemotaxis (PubMed:18322241). Plays a key role in brain microglia by regulating inflammatory response in the central nervous system (CNS) and regulating synapse maturation (PubMed:16732273, PubMed:21778362, PubMed:24487234). Required to restrain the microglial inflammatory response in the CNS and the resulting parenchymal damage in response to pathological stimuli (PubMed:16732273). Involved in brain development by participating in synaptic pruning, a natural process during which brain microglia eliminates extra synapses during postnatal development (PubMed:21778362). Synaptic pruning by microglia is required to promote the maturation of circuit connectivity during brain development (PubMed:24487234). Acts as an important regulator of the gut microbiota by controlling immunity to intestinal bacteria and fungi (PubMed:15653504, PubMed:29326275). Expressed in lamina propria dendritic cells in the small intestine, which form transepithelial dendrites capable of taking up bacteria in order to provide defense against pathogenic bacteria (PubMed:15653504). Required to initiate innate and adaptive immune responses against dissemination of commensal fungi (mycobiota) component of the gut: expressed in mononuclear phagocytes (MNPs) and acts by promoting induction of antifungal IgG antibodies response to confer protection against disseminated C.albicans or C.auris infection (PubMed:29326275, PubMed:33548172). Also acts as a receptor for C-C motif chemokine CCL26, inducing cell chemotaxis (By similarity). Found in a ternary complex with CX3CL1 and ITGAV:ITGB3 or ITGA4:ITGB1. Specifically expressed in subsets of leukocytes: expressed in monocytes, subsets of T-cells and natural killer (NK) cells in the circulation, dendritic cells, as well as in microglia in the central nervous system (CNS) (PubMed:10805752, PubMed:12871640, PubMed:16732273). Expression level subdivides blood monocytes into two major functional subsets; CD14(+)CD16(-)-CX3CR1(low) inflammatory monocytes and CD14(low)CD16(+)CX3CR1(high) homeostatic monocytes (PubMed:12871640). Expressed in myeloid-derived mucosal dendritic cells, which populate the entire lamina propria of the small intestine (PubMed:15653504). This protein is not N-glycosylated which is unusual for G-protein-coupled receptors. No visible phenotype in normal conditions; mice develop normally and are fertile (PubMed:10805752). Mice lacking both Cx3cr1 and Apoe show decreased atherogenesis (PubMed:12569158). In experimental autoimmune encephalomyelitis (EAE) model mice, recruitment of natural killer (NK) cells in the inflamed central nervous system (CNS) is impaired, leading to increased EAE-related mortality, nonremitting spastic paraplegia and hemorrhagic inflammatory lesions (PubMed:16675847). Mice show an increased microglial inflammatory response and neuronal death in several models of CNS insult (PubMed:16732273). Mice display reduced airway inflammation in lung after allergen sensitization (PubMed:21037587). Mice display a transient decrease in microglia density, leading to synaptic deficits characterized by an excess of weak excitatory synapses: defects are caused by a failure to eliminate immature synaptic connections during the second and third postnatal weeks (PubMed:21778362). Deficient synaptic pruning is associated with weak synaptic transmission, decreased functional brain connectivity, deficits in social interaction and increased repetitive-behavior phenotypes (PubMed:24487234). Defects of lamina propria dendritic cells are observed, leading to impair the sampling of bacteria from the intestinal lumen and affect their ability to take up invasive pathogens (PubMed:15653504). Mice are more susceptible to severe colitis that is rescued by antifungal treatment and display changes in gut fungal communities (PubMed:29326275). Belongs to the G-protein coupled receptor 1 family.