CD4 and infection: By day 10 post-infection (p. i), a timepoint just before the CD4-depleted mice began to succumb to infection, plasmablast differentiation was 80% lower in CD4-depleted mice compared to infected controls (Fig 1D), and GC B-cell formation (Fig 1E) was almost abrogated (95% reduction compared to controls), with a similar, substantial impairment in Ig-class switching (Fig 1F).