Objective:To detect the expression of IDO, iNOS, gp91 NADPH ox releated with IFN-? function following Chlamydia trachomatis lung infection in mice and to investigate the immunological defense mechanism of IFN-?. Methods:A murine model of pneumonia induced by intranasal inoculation of Chlamydia trachomatis,mouse pneumonitis (MoPn) biovar,was used for this study. Chlamydial growth in the lung was assessed by inoculating HeLa 229 cell monolayer with lung homogenates followed by HRP conjugate anti-Chlamydial LPS mAb.The mRNA expressions of IDO, iNOS, gp91 NADPH ox and IFN-? in the lung were determined by RT-PCR on day 7 and 14 postinfection.Results:Chlamydial growth in the lung was observed on day 2 postinfection, peaking at day 7 with subsequent decline in quantity. At day 21 following inoculation, the IFU declined to the baseline. Contrast with the uninfected group, Th1-like cytokine IFN-? underwent a significant increase at day 7 and a decrease on day 14 postinfection. mRNA expression for IDO, iNOS, gp91 NADPH ox was significantly increased in the lungs on day 7 and 14 postinfection, IDO and gp91 mRNA expression was significantly highler at day 7(P