The importance of IFN-γ in the host during chlamydial infection is evidenced by the elevated chlamydial load in IFN-γ -/-, IFN-γR -/- mice or mice treated with anti-IFN-γ antibody compared with that in the wild/control group (20–22). The gene discussed is IFNG; the disease is chlamydia trachomatis infectious disease.