The lack of Foxp3+ Treg cell expansion during the larval stages of infection in C57BL/6 mice contrasts with the evident Foxp3+ Treg cell activity during the chronic phase of infection, following egg release (week 5 onwards) (14, –, 17), although it is not known whether Foxp3+ Treg cells are recruited to or activated in the lungs during pulmonary schistosomiasis. Here, FOXP3 is linked to infection.