The Study On The Immunological Mechanism Of Susceptibility Differences Mediated By Polymorphonuclear Leucocyte In Chlamydia Trachomatis Lung Infection In The Mouse

Objective:To investigate the immunological mechanism of polymorphnuclear neutrophils(PMN) in susceptibility differences between genetically different inbred mouse strains during Chlamydial lung infection by detecting PMN activity, adhesion molecules and TLR expression in the lung.Methods:C57BL/6 and C3H/HeN mice were inoculated intranasally with 3×10~3 inclusion-forming units (IFUs) of mouse pneumonitis biovar of Chlamydia trachomatis (MoPn) to build the murine model of pneumonia. To determine the in vivo growth of the organism, the lung homogenates were used to infect Hep-2 cells for counting IFU. To determine the morbid state, mice were monitored for body weight changes, mortality and the lung histopathology at different day postinfection. The infiltration of PMN in the lung was detected by counting lung inflammatory cell and quantifing myeloperoxidase (MPO) in two different strains of mice. mRNA expression of ICAM-1,VCAM-1, P-selectin, L-selectin, E-selecein, TLR2, TLR4, MyD88 in the lung were assayed by RT-PCR in the two strains of mice during the different infection period. To determine the difference in the PMN activity between the two strains of mice, PMN was isolated from the peripheral blood and the lung during the MoPn infection and strained with the fluorescein-labeled anti-CD11b antibody.Results:Intranasally infected with 3×10~3IFU Ct MoPn in mice resulted in Chlamydial mouse pneumonitis featured by body weight lost, Chlamydia growth and massive infiltration of neutrophils in the lung. Using the murine pneumonia model, we observed the susceptibility difference between C3H and C57 mice to Ct MoPn infection. Our data showed that C3H mice exhibited significantly body weight lost, higher mortality, greater organism growth, much more serious pathological changes and more persistent neutrophil infiltration in the lung than C57 mice. Compared with the normal control group, mRNA expression of adhesion molecule (VCAM-1 and ICAM-1),selectin molecule(P-selectin and E-selectin),Toll like receptor(TLR2,TLR4) and MyD88 in infected lung tissue were significantly increased. The massive neutrophil infiltration in C3H mice was paralleled by higher expression of MPO, VCAM-1, P-selectin,E-selectin,TLR2 and MyD88 in the lung at day 7 and day 14 postinfection. Following infection with Ct MoPn,CD11b expression of PMN in peripheral blood and the lung was much higher than control mice.CD11b expression in the lung by C3H mice had more significant upregulation at day 7 postinfection than C57 mice but subsequently decrease at day 14 postinfection.Conclusion:Intranasally infected of Ct MoPn resulted in typical Chlamydia mouse pneumonitis. The susceptibility difference was seen between C3H and C57 mice following Ct MoPn lung infection. C3H strain was high susceptible phenotype to Ct MoPn infection compared to C57 strain. Increased expression of adhesion molecule and TLR in the lung of C3H mice induced massive infiltration of neutrophils. The decreased PMN activity in C3H mice during the late period of infection may be the major reason that C3H mice existed high susceptibility to Ct MoPn infection and pesistant disease process.