Although the Th1 cytokine IFN-γ and the Th2 cytokines IL-4 and IL-5 have been shown to be elevated in Giardia-infection models [31,73,74], both IFN-γ-deficient and IL-4-deficient mice can still eliminate Giardia [75], suggesting that the Th1 and Th2 responses are not essential for clearance. This evidence concerns the gene IFNG and giardiasis.