IL4 and giardiasis: In contrast, Singer et al l [39] reported that in Giardia-infected mice deficient in production of IFN-γ, IL-4 and IL-13 did not require Th1 or the Th2 lymphocytes required for protection against Giardia. Singer et al [39] concluded that a T-cell dependent mechanism plays an important role in protection against Giardia-infection but is not dependent on antibody and B cells.