IL13 and infection: CD4+ T cells do not commit to the Tfh lineage until days 6–10 of infection 39, and at day 7 of H. polygyrus infection, on the cusp of Tfh-cell commitment, the numbers of IL-4 and IL-13 producing CD4+ T cells in the MLNs were equivalent in WT and ICOS−/− mice (Fig. 4A and B).