The Study On The Infiltration Mechanism Of Polymorphonuclear Neutrophils During Chlamydial Muridarum Lung Infection In The Mouse

Objective:Mice were inoculated intranasally with Cm to induce mrine Chlamydia pneumonitis. To investigate the infiltration mechanism of polymorphonuclear neutrophils (PMN) during Chlamydial muridarum (Cm) lung infection, we detected the level of PMN infiltration, adhesion molecules, Toll-like receptors, selectin molecules, pro-inflammatory cytokines and chemoattractants expression as well as the relevance between neutrophils aggregation and IL-17secretion in the lung at different day post infection.Methods:C57BL/6(C57) mice were inoculated intranasally with3×103inclusion-forming units (IFU) of Cm to build the murine model of Chlamydia pneumonitis. To confirm the infiltration of neutrophils in the lung during infection, lung histopathology was done and PMN cells were isolated from lung tissues to examine the number and detect the activity of myeloperoxidase (MPO) at different day post infection. At the same time, the isolated cells were assayed by flow Cytometry to determine the PMN activity. In order to investigate the impact of IL-17to neutrophils infiltration following Cm infection, The expression of IL-17in the lung was assayed by RT-PCR and ELISA. Using anti-mouse IL-17mAbs to neutralize endogenous IL-17following Cm lung infection, PMN numbers were determined by counting BAL cells and pathological staning of lung tissue, RT-PCR was used to detect the mRNA expression of adhesion molecules ICAM-1, selectin molecules (E-selectin, P-selectin, L-selectin), Toll like receptor (TLR2,TLR4, MyD88), proinflammatory cytokines (IL-1, IL-6, TNF-α) and chemoattractants (MIP-2, LIX, KC, MCP-1) mRNA expression.Results:Intranasally infected with3×103IFU of Cm, mice were featured by body weight lost, Chlamydia growth and severe infiltration of neutrophils in the lung. Compered with the normal control group (un-infection), the number and percentage of neutrophils along with the activity of MPO were significantly increased,especially at the day7post infection (P<0.05, P<0.01). It is the Cm infection that induced the expression and secretion of IL-17in lung tissue. The number of PMN in the lung and the bronchoalveolar lavage fluid of IL-17-neutralized mice were significantly lower than that of IgG2a treated mice, which demonstrated that the secretion level of IL-17 in lung tissue is positively corelated with the infiltration of PMN during Cm lung infection. While the expression of PMN infiltration related cytokines such as ICAM-1, E-selectin, P-selectin, L-selectin, TLR2, TLR4, MyD88, IL-1β, IL-6,TNF-α,MIP-2, LIX, KC and MCP-1mRNA were increased during the infection.Conclusions:An appropriate dose of Cm could induce mice chlamydia pneumonia via lung infection, while large number of active PMN infiltrated in the lung tissue. The aggregation of PMN was positively corelated with the amount of IL-17produced after infection. The high level of expression of pre-inflammatory cytokines, PMN related chemokines, adhesion molecules, selectins, TLRs and so forth played important roles in chemotexis and infiltrations of PMN.