CX3C motif chemokine receptor 1 (CX3CR1) is a G protein-coupled receptor found on microglia. Its ligand, fractalkine (also known as CX3CL1), is produced by neurons. CX3CR1 is often referred to as a marker of homeostatic microglia, as its expression is downregulated in various transgenic mouse models of neurodegenerative diseases, including Alzheimer’s disease (Keren-Shaul et al., 2017; Krasemann et al., 2017; Zhou et al., 2020). However, contrary to the observations in mice, expression of CX3CR1 was found to be upregulated in the brains of human Alzheimer’s subjects, compared with controls (Zhou et al., 2020).