CX3CR1 and Alzheimer disease: Expression of Cx3cr1, as well as cathepsin S (Ctss), the enzyme required for CX3CL1 cleavage (84), was also almost completely ablated, to the same extent as Csf1r. Microglia-associated transcripts are of particular interest given the emerging consensus that these cells are central players in the pathologic condition of Alzheimer disease.