The data suggest that the systems of protective immunity involve interferon-gamma (IFN-γ)-dependent cell-mediated immunity (CMI). Studies conducted on animals with genital chlamydial infection indicate that the solution of infection is determined principally via type-1 CD4+ T helper 1 (Th1) lymphocyte response that is principally facilitated via IFN-γ. Here, IFNG is linked to infection.