Intracellular interleukin-1α mediates interleukin-8 production induced by Chlamydia trachomatis infection via a mechanism independent of type I interleukin-1 receptor

Chlamydia trachomatis infection induces a wide array of inflammatory cytokines and chemokines, which may contribute to chlamydia-induced pathologies. However, the precise mechanisms by which Chlamydia induces cytokines remain unclear. Here we demonstrate that the proinflammatory cytokine interleukin-1 alpha (IL-1 alpha) plays an essential role in chlamydial induction of the chemokine IL-8. Cells deficient in IL-1 alpha expression or IL-1 alpha-competent cells treated with IL-1 alpha-specific small interfering RNA failed to produce IL-8 in response to chlamydial infection. However, neutralization of extracellular IL-1 alpha or blockade of or deficiency in type I IL-1 receptor (IL-1RI) signaling did not affect chlamydial induction of IL-8 in cells capable of producing IL-1 alpha. These results suggest that IL-1 alpha can mediate the chlamydial induction of IL-8 via an intracellular mechanism independent of IL-1RI, especially during the early stage of the infection cycle. This conclusion is further supported by the observations that expression of a transgene-encoded full-length IL-1 alpha fusion protein in the nuclei enhanced IL-8 production and that nuclear localization of chlamydia-induced precursor IL-1 alpha correlated with chlamydial induction of IL-8. Thus, we have identified a novel mechanism for chlamydial induction of the chemokine IL-8.