Infection of A1Ifnar-/- mice with reduced doses of RhIVBG505, RhIVDu156, RhIVSF162, or RhIVCH505 revealed that 103 PFU established robust infection with profound CD4+ T-cell depletion, albeit with reduced peak plasma viremia (105–107 RNA copies/ml, Figure 4—figure supplement 1A). Here, CD4 is linked to infection.