In natural infection settings, peripheral blood mononuclear cells (PBMCs) from koalas with active chlamydial disease have been found to have higher expression of IFN-γ and TNF-α than koalas with asymptomatic chlamydial infection or no chlamydial infection/disease [50,51,52]. The gene discussed is IFNG; the disease is chlamydia trachomatis infectious disease.