The Contribution of Interleukin-12/Interferon-γ Axis in Protection Against Neonatal Pulmonary Chlamydia muridarum Challenge

Neonatal Chlamydia trachomatis pneumonia has been associated with respiratory sequelae in later life. We recently established a mouse model of neonatal pulmonary Chlamydia muridaum infection and found an important contribution of IFN-gamma to protective immunity. In this study, we further characterized the role of Th1-type cytokines; IL-12, IFN-gamma, and IFN-gamma signaling using mice genetically deficient in IL-12, IFN-gamma, or IFN-gamma receptor 1. All 3 knockout (KO) mice challenged intranasally with C. muridarum 1 day after birth exhibited 100% mortality by day 17 post-challenge whereas wild-type (WT) animals survived the monitoring period of 1 month. The KO mice exhibited greater lung bacterial burdens and enhanced dissemination to the liver, compared to WT animals. The inflammatory cellular infiltration in C. muridarum-challenged KO animals was significantly reduced in the lungs, but markedly enhanced in the livers of the KO mice compared to similarly challenged WT mice. It was also found that a deficiency in IL-12 or IFN-gamma resulted in correspondingly reduced IFN-gamma or IL-12 production, respectively, suggesting an intricate interdependence in the induction of these cytokines. Collectively, these results suggest that the IL-12/ IFN-gamma axis induces pulmonary cellular infiltration, induces bacterial clearance from the lung, reduces dissemination to other organs, and promotes the survival of the host during neonatal pulmonary chlamydial infection.