APOE and infection: Our scRNA-seq analysis highlighted intrinsic differences in expression of notable ligand genes in macrophage populations between C3HeB/FeJ and C57BL/6 mice prior to and during infection, including higher expression of Spp1 and Siglec1 (CD169) by C3HeB/FeJ mice and higher expression of Apoe by several populations, particularly MDMs, in C57BL/6 mice.