Given the role of IL-4 and IL-13 in mediating helminth expulsion [20] and the contribution of innate lymphoid and adaptive T-cell populations to the production of these cytokines following helminth infection [21], we hypothesized that the late phase of worm expulsion would be determined by the balance of regulatory and effector (Treg:Teff) T-cell responses established in the initial priming phases of infection. This evidence concerns the gene IL4 and infection.