Although CD14+ cells can be infected, the lack of selection for Cal-1-marked cells in this subset is consistent with the limited proportions that express sufficient levels of CD4 and CCR5/CXCR4 to permit virus entry.48,49 The selective upregulation of mC46 in infection-susceptible cells highlights a potential use of Cal-1 to better understand viral pathogenesis in our SHIV-infection model. Here, CD4 is linked to infection.