Activation of the host cell proinflammatory interleukin-8 response by Chlamydia trachomatis

Diseases associated with Chlamydia are caused by inflammation-associated tissue damage following repeated or chronic infection; however, the mechanism by which the inflammatory response is induced is unknown. The inflammatory cytokine interleukin-8 (IL-8) is produced by C. trachomatis-infected epithelial cells in a bacterial growth-dependent manner. We hypothesized that IL-8 is induced through activation of host signalling pathways within Chlamydia-infected cells. Bacterial protein synthesis occurring after 15 h post infection (hpi) was required for the induction of IL-8, thus, increases in IL-8 mRNA are due to chlamydial growth or a bacterial product produced at 15 hpi. The induction of IL-8 was not dependent on soluble factors in the supernatant of C. trachomatis-infected cells and therefore was associated with an internal cellular signal. The AP-1, NFIL6 (C/EBPbeta) and NFkappaB transcriptional regulatory sites of the IL-8 promoter and the host NFkappaB signalling pathway were necessary for IL-8 induction by C. trachomatis. We conclude that a C. trachomatis growth-dependent factor produced at mid-developmental stage induces IL-8 within the epithelial cell it infects through activation of host signalling pathways.