APP and Alzheimer disease: We did however observe an impact of CCR2 deficiency on the expansion of the perivascular macrophage population driven by prion disease (Galea et al., 2005), which is somewhat different compared to the results reported for the APP/PS1 model of AD (Mildner et al., 2011), even though the innate immune response in APP transgenics and experimental models of prion disease share many similarities.