IL-17A Synergizes with IFN-γ to Upregulate iNOS and NO Production and Inhibit Chlamydial Growth

Yongci Zhang,Xi Yang,Hong Bai,Guosheng Zhao,Jianyun Ren,Haiping Wang,Ye Jing,Donghong Xing,Xiaofei Tang,Zhi Yao,Charaf Benarafa

doi:10.1371/journal.pone.0039214

Abstract

IFN-γ-mediated inducible nitric oxide synthase (iNOS) expression is critical for controlling chlamydial infection through microbicidal nitric oxide (NO) production. Interleukin-17A (IL-17A), as a new proinflammatory cytokine, has been shown to play a protective role in host defense against Chlamydia muridarum (Cm) infection. To define the related mechanism, we investigated, in the present study, the effect of IL-17A on IFN-γ induced iNOS expression and NO production during Cm infection in vitro and in vivo. Our data showed that IL-17A significantly enhanced IFN-γ-induced iNOS expression and NO production and inhibited Cm growth in Cm-infected murine lung epithelial (TC-1) cells. The synergistic effect of IL-17A and IFN-γ on Chlamydia clearance from TC-1 cells correlated with iNOS induction. Since one of the main antimicrobial mechanisms of activated macrophages is the release of NO, we also examined the inhibitory effect of IL-17A and IFN-γ on Cm growth in peritoneal macrophages. IL-17A (10 ng/ml) synergizes with IFN-γ (200 U/ml) in macrophages to inhibit Cm growth. This effect was largely reversed by aminoguanidine (AG), an iNOS inhibitor. Finally, neutralization of IL-17A in Cm infected mice resulted in reduced iNOS expression in the lung and higher Cm growth. Taken together, the results indicate that IL-17A and IFN-γ play a synergistic role in inhibiting chlamydial lung infection, at least partially through enhancing iNOS expression and NO production in epithelial cells and macrophages.

Highlights

Chlamydia trachomatis, as an obligate intracellular bacterium, causes a wide variety of human and animal diseases including ocular, pulmonary, and genital infections
We found that IL-17A (10 ng/ml or 100 ng/ml) could synergize with high (200 ng/ml), but not low concentration (10 ng/ml), of IFN-c for inhibiting intracellular Chlamydia muridarum (Cm) growth in macrophages (Fig. 5–A), In the low IFN-c (10 ng/ml) concentration, the inhibition rates by both concentrations of IL-17A (10 ng/ml or 100 ng/ml) with IFN-c were not significantly higher than IFN-c alone (Fig. 5A)
The present study has demonstrated a significant synergistic effect of IL-17A on IFNc-mediated enhancement of inducible nitric oxide synthase (iNOS) expression and nitric oxide (NO) production, and inhibition of chlamydial growth in mouse lung epithelial and macrophage cells

Summary

Introduction

As an obligate intracellular bacterium, causes a wide variety of human and animal diseases including ocular, pulmonary, and genital infections. Strong Th1 responses marked by IFN-c production are crucial for controlling chlamydial infection [1]. IFN-c mediates antimicrobial action by activation of phagocytes for rapid uptake and degradation of pathogenic particles, and by inducing cellular enzymes, such as indoleamine 2, 3-dioxygenase (IDO), which cause tryptophan deprivation [2,3] and inducible nitric oxide synthase (iNOS) which promote microbicidal nitric oxide (NO) production [1,4]. It has been reported that iNOS rather than IDO is important for chlamydial control in mice [1,5]. Proper modulation of iNOS-mediated NO release is important for therapeutic optimization of protective immunity and prevention of detrimental effects of inflammation during chlamydial infection [8,9]

Methods

Results

Conclusion