In contrast to the egg phase of infection, when Foxp3+ Treg cells actively control pathology (14, –, 17), there was no significant increase in the mean fluorescence intensity (MFI) of CD25 expression on Foxp3+ Treg cells in the lungs or at any other site measured during early-stage S. mansoni infection (Fig. 2B). This evidence concerns the gene FOXP3 and infection.