A recent study investigating vaccine-induced protection to C. trachomatis in an experimental rodent model [72] showed that CD4+ T-cell IL-17A was partially protective in mice deficient in IFN-γ, while other animal models for chlamydial disease suggest a role for IL-17 in host defense against intracellular bacterial infection [73,74]. This evidence concerns the gene IL17A and chlamydia trachomatis infectious disease.