CX3CL1 and brain ischemia: Indeed, although it has been shown that CX3CL1 maintains microglia in a quiescent state (Lyons et al., 2009; Bachstetter et al., 2011), it has also been demonstrated that soluble CX3CL1 increases and is released in cerebral ischemia (Dénes et al., 2008), in response to apoptosis (Fuller and Van Eldik, 2008) and to glutamate excitotoxicity (Chapman et al., 2000) but its role as a neuroprotective or neurotoxic molecule remains unresolved (Lauro et al., 2015).