FOXP3 and infection: In confirmation of this, by day 7 post-infection, IL-10+ CD4+ T cells were almost exclusively CD25− indicating that, since the majority of Foxp3+ cells maintain CD25 expression during P. yoelii infection (Figure 5B), CD25−Foxp3− CD4+ T cells are the primary source of IL-10 during both PyL and PyNL infection.