Indeed, after a primary infection with the natural mouse parasite Heligmosomoides polygyrus, the early expansion (Grainger et al., 2010) and activation (Finney et al., 2007) of Foxp3-expressing T reg cells limits excessive T helper 2 cell (Th2 cell) responses and immunopathology, resulting in the establishment of chronic infections (Rausch et al., 2009). Here, FOXP3 is linked to infection.