CX3CL1 and Alzheimer disease: Interestingly, CX3CR1 has been associated with neurotoxic and neuroprotective functions in the AD model, and its diverse role in AD has been attributed in part to the competitive interaction of CX3CR1 with its endogenous ligand CX3CL1 or its pathological ligand tau, which can differentially affect microglial phagocytosis or activation response [18,245].