Study On The Immunological Mechanism Of Susceptibility Differences Mediated By Regulatory T Cell In Chlamydial Lung Infection In The Mouse

Objective:To investigate the immunological mechanism of regulatory T cell(Treg) in susceptibility differences between genetically different inbred mouse strains during chlamydial lung infection.Methods:C3H/HeN and C57BL/6 mice aged 6-8 weeks were inoculated intranasally with 1×103 IFUs of Chlamydia muridarum (Cm) to build the murine model of pneumonia. The body weight changes, mortality, the growth of Cm and pathogenesis in the lung were monitored. Thl cytokine by speen in thses two stains of mice were assayed by ELISA.The proliferation of IFN-γ+CD8+T cell in the lung of these two mice were assayed by intracellular cytokine staining. To determine the Treg responses in the two strains of mice, intracellular cytokine staining was used to assay the proliferation of CD4+CD25+T cells and CD4+CD25+ Foxp3+ T cells in the spleen, mRNA expression of IL-10 and IL-2 in the lung was assayed by RT-PCR in the two strains of mice during the different infection period.Results:Intranasally infected with 1×103 IFUs of Cm in mice resulted in chlamydial mouse pneumonitis featured by body weight lost, chlamydia growth and severe pathological damage in the lung. C3H mice exhibited significantly body weight lost, higher mortality, greater organism growth and much more serious pathological changes than C57 mice. IFN-γproduction by speen in these two stains of mice appeared comparable during the process of infection. However,differences were seen in the proliferation of IFN-γ+CD8+T cell in the lung on day 7 post Cm infection.Compared with C57 mice, The mRNA expression of IL-2 in infected lung tissue and the proliferation of CD4+CD25 + T cells and CD4+CD25+Foxp3+T cells in the spleen were significantly higher in the C3H mice. The expression of IL-10mRNA in C3H mice was significantly increased than C57 mice on day 14 post Cm infection. Conclusion:Intranasally infected of Cm resulted in typical Chlamydia mouse pneumonitis. C3H strain was high susceptible phenotype to Cm infection compared to C57 strain. Increased expression of IL-2 in the lung of C3H mice induced massive infiltration of Treg.The increased Treg activity in C3H mice can have a stronger suppression on CD4 or CD8 immunity, which may be a reason that C3H mice existed high susceptibility to Cm infection.