The chemokine CCL2 is the main CCR2 ligand and is upregulated in brains of AD patients and mouse models of AD (Ishizuka et al., 1997; Grammas and Ovase, 2001; Simard et al., 2006; El Khoury et al., 2007; Naert and Rivest, 2011a), suggesting the preferential recruitment of CCR2+ monocytes. Here, CCR2 is linked to Alzheimer disease.