Interferon-Independent Protection by Interferon Regulatory Factor 3

Abstract

Abstract BACKGROUND Independent type I/III IFN regulation, interferon-regulatory factor 3 (IRF3) can mediate cell death and suppress proliferation during stress. Novel ‘suicide necrosis’ centers around IRF3 and is one protective mechanism against intracellular pathogens. Uterine epithelial cells infected with obligate intracellular Chlamydia trachomatis are typically shed 3–5 days post-infection (dpi) by unknown mechanism(s) and exhibit new growth. We have previously shown IRF3-deficient mice exhibit decreased epithelial shedding and 10-fold greater bacterial burdens during early infection. We hypothesize that IRF3-mediated cell death restricts chlamydial infection in the genital mucosa, providing a potentially novel mechanism to reduce pathogen load. METHODS Progesterone-treated C57BL/6J and IRF3 KO mice were infected vaginally with 3e5 IFUs of C. muridarum strain “Nigg” and histologically assessed 3 and 4 dpi for chlamydia inclusions, cell death and proliferation using proliferation marker PCNA. Cell death was assessed in vivo with PI delivery by NSET device 10 minutes before sacrifice 4 dpi. RESULTS/CONCL 3 dpi, uterine epithelia in WT and IRF3 KO mice remain intact with no epithelial shedding. WT show a single layer of infected epithelial cells, while IRF3 KO have several layers of infected cells, suggesting the next layer(s) of epithelial cells are generated before the first is shed. 4 dpi we see dramatic increases in epithelial shedding in WT mice when stained in vivo with PI. In contrast, IRF3 KO epithelia show relatively few PI-stained cells. We conclude that IRF3 is playing a significant and protective role during C. muridarum infection by facilitating cell death and limiting cellular proliferation of epithelial cells.