CD4 and infection: (C–F) RhIV viremia (log10 RNA copies/ml of plasma, upper rows) and blood CD4+ T-cell proportion (% of CD3+ cells, lower rows) in A1Ifnar-/- mice (C), A1Ifnar-/-, C18Ifnar-/-, and B4Ifnar-/- mice (D, F) or A1Ifnar+/+ mice (E) at the indicated times following infection with the indicated RhIV strains.