Analysis of modulated gene expression in a model of Interferon-γ-induced persistence of Chlamydia trachomatis in HEp-2 cells

• Published in: Microbial pathogenesis Vol. 49; no. 5; pp. 217 - 225
• Main Authors: Kokab, Abas, Jennings, Roy, Eley, Adrian, Pacey, Allan A., Cross, Neil A.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier India Pvt Ltd 01.11.2010; Elsevier
• Subjects: Bacteriology; Biological and medical sciences; Cell Line; Chlamydia trachomatis; Chlamydia trachomatis - immunology; Chlamydia trachomatis - pathogenicity; Fundamental and applied biological sciences. Psychology; Gene Expression Profiling; Gene Expression Regulation, Bacterial; Heat-shock protein; Hepatocytes - immunology; Hepatocytes - microbiology; Host-Pathogen Interactions; Humans; Inclusion Bodies - microbiology; Interferon; Interferon-gamma - immunology; Microbiology; Microscopy, Fluorescence; Miscellaneous; Persistence; Reverse Transcriptase Polymerase Chain Reaction; Persistence; IFN; Interferon; Chlamydia trachomatis; HSP; Heat-shock protein; Chlamydiaceae; Cytokine; Heat shock protein; Chlamydiales; Bacteria; Models; Gene expression; Gamma interferon
• ISSN: 0882-4010; 1096-1208
• DOI: 10.1016/j.micpath.2010.06.002

Chlamydia trachomatis is an important pathogen, being the commonest sexually transmitted bacterial disease in the Western world and is also implicated in a number of acute and chronic diseases. Persistent infections of C. trachomatis are particularly associated with chronic infections, which although eliciting an immune response, result in tissue damage leading to complications such as pelvic inflammatory disease. Interferon (IFN)-γ is known to induce persistent infections of C. trachomatis both in vitro and in vivo. A model of IFN-γ-induced persistence containing aberrant inclusions of C. trachomatis was developed in the HEp-2 cell line. Morphological changes to inclusions were assessed by fluorescence immunocytochemistry and transcript levels determined by Real-Time RT-PCR. To assess infectivity of C. trachomatis in an IFN-γ-induced persistent state, cultures containing aberrant inclusions were inoculated onto fresh HEp-2 monolayers. IFN-γ induced aberrant inclusion formation at 0.01 ng/ml. Doses from 0.05 to 100 ng/ml did not significantly increase numbers of aberrant inclusions, and some normal inclusions were observed at the highest dose of IFN-γ. Transfer of IFN-γ-treated C. trachomatis onto fresh cultures confirmed the infectivity of these cultures. Real-Time RT-PCR identified apparent increased expression of the C. trachomatis heat-shock response genes ct604 and ct755 at 96-h post-infection. However comparisons with control cultures suggest that this more likely reflects a failure to down regulate gene expression as observed in untreated cultures. These data show that whereas IFN-γ induces aberrant inclusion formation, many normal inclusions are still observed at high doses of IFN-γ, and that the infectivity of such cultures is presumably from these. Transcriptional changes observed in response to IFN-γ suggest a failure of the C. trachomatis life cycle in response to IFN-γ, however IFN-γ-induced transcriptional changes may be masked by the presence of normal inclusions. The implications of these observations in relation to models of persistence of C. trachomatis are discussed.