FOXP3 and infection: When we analyzed expression of CD25 in FoxP3- CD4+ T cells from GITRL tg and WT mice, we found that GITRL tg mice had significantly higher levels of CD25+ FoxP3- effector CD4+ T cells early after infection (day 8 p.i.), which then declined, while in WT mice the abundance of these cells peaked a week later (day 15 p.i., Fig. 3A).