Natural Killer Cells Regulate Immunity Response Against Chlamydia Secondary Infection

Chlamydia is obligate intracellular bacterial pathogen, causing multiple human diseases. Chlamydia trachomatis (Ct) infection is the most common bacterial cause of salpingitis, infertility and the trachoma serovars of Ct is the leading cause of trachoma; Chlamydia pneumonia (Cpn) causes respiratory diseases such as pneumonia and bronchitis. Chlamydia infection is a long-term and reduplicative process. If the immune responses are not enough to eradicate the infected cells, it can be easy to convert to persistent infection and cause histopathological injury. Resistance to Ct infection is heavily dependent on CD4+ T cells. CD4+ T-helper type 1 response plays a dominant role in the resolution of Ct genital tract and pulmonary infection. IFN-y not only inhibits the duplication of Ct, but also regulates the adaptive immune cells. B cells and Ct specific antibody are also important. However CD8+ T cells play a feeble role in protecting against Ct infection.Natural killer (NK) cells are effector lymphocyte of innate immune system. NK cells are critical for combating pathegens infection. The activation of NK cells is modulated by activatory and inhibitory receptors. The function of NK cells is achieved by two main ways. Firstly, NK cells identify infected cells and play a cytotoxic role. The other way is implemented by producing cytokines. Traditionally, NK cells play a major effect in the initial infection stage. Recently, there were evidences supporting that NK cells also play an important role in defensing against pathogens secondary infection (such as::Mt, respiratory syncytial virus).Preliminary work in primary pulmonary chlamydia infection in mice have demonstrated that NK cells can regulate the response of Thl, Th17 and Treg cell subsets by secreting of cytokines or NK-DC crosstalk to defense against Chlamydia infection. This article further deplores the function of NK cells and its immune mechanism during secondary chlamydial infection.1. Objective:Compare the characteristics of CD4+T cell subsets between the primary and secondary chlamydia lung infection. Methods:C57BL/6 mice were infected intranasally with Chlamydia muridarum (Cm) 6-8 weeks after primary infection. The body weights of mice were monitored daily. The Cm burden of lung was assessed at day 3 and 6 after infection. The absolute number and proportion of CD4+T cells, IFN-y+CD4+T(Thl) cell subsets, Foxp3+CD25+CD4+T(Treg)cells were detected by flow cytometry and intracellular staining. Results:The secondary infected mice showed significantly reduced weight loss, significant reduction in lung IFUs, enhanced Thl response than primary infection mice. Conclusion:We successfully established Cm secondary infection. The mice during chlamydial secondary infection shown enhanced Thl type protective immune response, which is the main reason for rapidly recovery.2. Objective:Explore the effect and immune mechanism of NK cells in chlamydia secondary infection. Methods:We used anti-asialo GM1 antibody to deplete NK cells at-2,-1,1,3,5 days before and after secondary infection. Control mice received isotype antibody treatment at the same time point. Body weights of mice were monitored daily. The Cm burden of lung was assessed at day 3 and 6 after secondary infection. The expression of IFN-y in supernatant of single nuclear cells of spleen, mediastinal lymph nodes and lung were detected by ELISA. The proportion of CD4+T cell subsets (Thl, Treg) of spleen, mediastinal lymph nodes and lung were detected by flow cytometry and intracellular staining. Results:Anti-asialo GM1 antibody effectively depleted NK cells in the lung of secondary infected mice. During secondary infection, NK cells-depleted mice showed significantly increased lung IFUs, a significant reduction in the secretion of IFN-γ, reduced proportion of Thl cells and increased Treg cells. Conclusion:NK cells also have an important role in defensing against chlamydial secondary infection. The protective function is partly carried out by promoting Thl cells response and inhibiting Treg cells response.In conclusion, we found that mice during chlamydial secondary infection showed enhanced Thl cell response, which is the main reason for rapidly recovery. More importantly, we also demonstrated that NK cells depletion resulted in increase of lung IFUs during secondary infection. Compared with isotype control mice, NK cells-depleted mice showed significant reduction of IFN-y secretion, reduced proportion of Thl cells and increased Treg cells after secondary infection. Notably, Our results demonstrated that NK cells have protective effect on defensing against chlamydial secondary infection by regulating Thl and Treg cells response. Our finding expands our understanding on immunity against chlamydial secondary infection and provides immune basis for development of chlamydial vaccine.