It has been well-established that CD4+ Th1 response, particularly IFN-γ production, is essential for protective recall immunity to chlamydial infection in animal models (Igietseme et al., 1993; Peterson et al., 1999; Farris and Morrison, 2011; Stary et al., 2015). Here, IFNG is linked to chlamydia trachomatis infectious disease.