The Role And Mechanism Of Chlamydia Trachomatis Cryptic Plasmid In Respiratoty Tract Infection

PARTⅠ EFFECT OF CRYPTIC PLASMID ON CHLAMYDIA TRACHOMATIS INFECTION IN HUMAN BRONCHIAL EPITHELIAL CELLObjective: To study the virulence role of C. trachomatis plasmid using a human bronchial epithelial cell with C. trachomatis infection.Methods: Using different starins infected human bronchial epithelial cell as models, characterized 3 different C. trachomatis survival curve by titration, Morphological analysis 3 different C. trachomatis strains by immunofluorescence staining assay.Results: We find that these C. trachomatis strains display a similar growth trend in BEAS-2B cells, but the WT strain showed more release in BEAS-2B cell. The PF strains inclusions were smaller than WT strain observed in microscopy.Conclusion: Chlamydia trachomatis containing plasmid or not showed different phenotype in BEAS-2B cells. Plasmid of C. trachomatis is related to its inclusion enlargement and release.PARTⅡ EFFECT OF CRYPTIC PLASMID ON CHLAMYDIA TRACHOMATIS INFECTION IN THE NEONATAL MICE’S PNEUMONIA MODELObjective: To study the pathogenic role of C. trachomatis plasmid using a model of neonatal mice pneumonia induced by C. trachomatis.Methods: Forty-eight neonatal BALB/c mice were randomly divided into four group( each n=9) within 24 h after birth, Wild type(WT) group(infected with C. trachomatis serovar D wild type), plasmid free type(PF) group(infected with C. trachomatis serovar D plasmid free type), PBS group(phosphate buffer) and Normal group. Four mice in each group were sacrificed at 4, 7, 11 days. The lung tissue was collected for pathological analysis and counts of neutrophils infiltration. The expression of omp A gene, level of TNF-α and IFN-γ were determined by RT-PCR and ELISA assays respectively. Activation of TLR2 and NF-κB was tested by SEAP reporter assays.Results: C. trachomatis collected from homogenates was negative whereas omp A m RNA was detected in infection groups. The mice infected with PF strain had obvious pathological changes with neutrophils infiltration(1.10±0.19 and 21.06±10.92, respectively), both decreased significantly than those of WT-infected mice(1.44±0.17 and 43.90±17.17, respectively),(P= 0.048, 0.005). The WT-infected mice had obviously increased secretion of TNF-α and IFN-γ(623.35±37.23 and 2206.83±854.22, respectively) in lung, compared with non-infection mice(470.93±20.83 and 737.97±79.89, respectively),(P = 0.000, 0.038). Those cytokines in PF-infected mice(531.59±34.14 and 1099.86±427.39, respectively) had no statistic difference with those of non-infection mice(P >0.05). In addition, the PF strain showed increased TLR2 activation(F=483.199, P=0.000),which was poorer than WT strain in vitro(P=0.000). NF-κB activation was restricted in PF strain, which had no significance comparing with control group(F=229.884, P=1.000).Conclusion: Plasmid-deficient C. trachomatis exhibits attenuated pathology in lung infection of neonatal mice. This would be related to down- regulated activation of NF-κB and TLR2 mediated by an unknown factor encoded by Chlamydia plasmid.