APOE and infection: Consistent with macrophages representing a minority of acutely infected lung cells and the cell type-specific proviral role of ApoE we observed in vitro (Fig. 1A, B, and 5), there was no difference in MHV68 lung titers observed in BL6 and ApoE-/- mice at the peak (7 days, Fig. 6A) or clearance (10 days, Fig. 6B) phases of acute MHV68 infection in vivo.