During an infection, C. trachomatis can encounter Trp starvation as a result of interferon-γ (IFNγ) binding to its receptor on the host cell, which activates the production of indoleamine 2,3-dioxygenase (IDO) that catabolizes Trp into N′-formylkynurenine (26, 27). The gene discussed is IFNG; the disease is infection.