CD4 and infection: To investigate whether dissimilar infectious dosages of MCMV differentially affect the immune system in lifelong infection, we inoculated C57BL/6 mice at 7 weeks of age with different dosages of MCMV-Smith (0, 103, 104, and 105 PFU) and monitored the CD4+ and CD8+ T cell frequencies over 300 days post-infection (dpi).