The mRNA expression of PU.1 and C/EBPα, transcription factors regulating microglial proliferation, increases to similar levels in the HC of both WT and CCR2−/− mice with prion disease (ME7, 20wpi), although C/EBPα mRNA expression was found to be relatively less expressed in CCR2−/− ME7-animals, when compared with the WT ME7-animals (Fig. 2E) consistent with the smaller increase in Brdu labeled cells in the CCR2−/− ME7-animals. Here, CCR2 is linked to prion disease.