IFNG and infection: Furthermore, C57BL/6 mice deficient in the production of IFN-γ (IFN-γ−/− mice) failed to control a low-dose infection of Δrop5, Δrop17, or Δrop18 tachyzoites (Fig. 6B), suggesting that IFN-γ-stimulated mechanisms were necessary to control infection by these mutants.