IFN-I exacerbates the inflammatory response of epithelial cells to Chlamydia trachomatis infection by enhancing TLR3 expression

Abstract

The inflammation induced by Chlamydia trachomatis infection in the female genital tract (FGT) can have severe consequences. Recent observations in women and mice infected with Chlamydia suggest that type I interferon (IFN-I) may have deleterious effects. This study aimed at elucidating the consequences of IFN-I production on C. trachomatis-induced inflammation in epithelial cells and the molecular pathway(s) involved. We showed that combination of IFN-I and Chlamydia resulted in a stronger induction of inflammation than Chlamydia alone, while IFN-I alone had no effect. Inhibiting AKT and mTOR, but not silencing STAT1, significantly attenuated the synergetic effect between IFN-I and bacteria on inflammation. Inhibition of ERK also blocked this synergistic effect, although ERK were not activated by IFN-I. We hypothesized that IFN-I enhanced the expression of a pathogen recognition receptor of the host, thereby potentiating detection of the bacteria and the subsequent inflammatory response. IFN-I, but not C. trachomatis infection, increased the expression of Toll-like receptor 3 (TLR3), and silencing or knocking-out TLR3 prevented the synergetic effect between infection and IFN-I. Furthermore, our data support the presence of dsRNA in infected cells and the activation of the MAPK/ERK and AP-1/ATF2 signaling cascades downstream of TLR3. Taken together, our data demonstrate that IFN-I exacerbates the host inflammatory response triggered by Chlamydia by increasing TLR3 expression and activation, leading to hyperinflammation. The identified signaling cascades represent potential targets for therapeutical intervention to limit tissue damage upon Chlamydia infection.