CD4 and infection: Surviving mice were challenged with a second infectious dose 2 weeks after primary infection and similarly treated with Brefeldin A. When CD4+ T cells were isolated 48 h post-boost, % of IFN-γ+, TNF-α+, IL-2+, and IL-10+ CD4+ cells were similar, or only slightly higher, than those observed 96 h post-primary infection (see Supplementary Fig. S1).