FOXP3 and infection: To determine whether the increased frequencies of ST2+ Tregs in IL-33-treated animals accounted for the severe course of disease in CR-infected mice, we performed infection experiments with and without IL-33 treatment of ST2flox/flox x FIC-Cre mice (ST2fl/fl/FIC), in which ST2 is ablated specifically in Foxp3+ Tregs (Fig. 5b).