Essential roles in host defense for IFN-γ, and for CD4+ T cells that produce IFN-γ, were initially defined in the murine TB model using IFN-γ-deficient mice (23, 24), CD4+ T cell deficient mice, and adoptive transfer of CD4+ T cells in the murine TB model [reviewed in Ref. The gene discussed is IFNG; the disease is tuberculosis.