Infection with H. polygyrus did not change the percentage of MLN CD4+Foxp3+ Treg cells in either WT or ICOS−/− mice (Fig. 2E), indicating that ICOS deficiency impaired the expansion of CD4+Foxp3+ Treg cells and CD4+Foxp3− Teff cells to a similar extent. Here, ICOS is linked to infection.