CD4 and infection: Prior to YFV-17D infection and 5 days post infection, NFA2-HIS/Flt3LG mice were treated with anti-CD4 (α-CD4) or anti-CD8 (α-CD8) antibodies (n = 4 per group), which have previously been used to deplete CD4+ and CD8+ T cells, respectively, in humanized mice7,9 (Supplementary Figure 9a).