Exoenzyme T Plays a Pivotal Role in the IFN-γ Production after Pseudomonas Challenge in IL-12 Primed Natural Killer Cells.

Mickael Vourc’H,Philippe Hulin,Alexis Broquet,Antoine Roquilly,Karim Asehnoune,Christelle Retiere,Jocelyne Caillon,Cedric Jacqueline,Gaelle David

doi:10.3389/fimmu.2017.01283

Abstract

Pseudomonas aeruginosa (PA) expresses the type III secretion system (T3SS) and effector exoenzymes that interfere with intracellular pathways. Natural killer (NK) cells play a key role in antibacterial immunity and their activation is highly dependent on IL-12 produced by myeloid cells. We studied PA and NK cell interactions and the role of IL-12 using human peripheral blood mononuclear cells, sorted human NK cells, and a human NK cell line (NK92). We used a wild-type (WT) strain of PA (PAO1) or isogenic PA-deleted strains to delineate the role of T3SS and exoenzymes. Our hypotheses were tested in vivo in a PA-pneumonia mouse model. Human NK cells or NK92 cell line produced low levels of IFN-γ in response to PA without IL-12 stimulation, whereas PA significantly increased IFN-γ after IL-12 priming. The modulation of IFN-γ production by PA required bacteria-to-cell contact. Among T3SS effectors, exoenzyme T (ExoT) upregulates IFN-γ production and control ERK activation. In vivo, ExoT also increases IFN-γ levels and the percentage of IFN-γ+ NK cells in lungs during PA pneumonia, confirming in vitro data. In conclusion, our results suggest that T3SS could modulate the production of IFN-γ by NK cells after PA infection through ERK activation.

Highlights

Pseudomonas aeruginosa (PA) is an opportunistic pathogen that causes lung infections in cystic fibrosis (CF) [1] as well as in intensive care unit (ICU) patients [2]
While the treatment of natural killer (NK) cells by myeloid-derived cytokines is required for the production of IFN-γ, our results demonstrate that PA can directly alter IFN-γ production via the modulation of ERK through exoenzyme injection in NK cells
IFN-γ was already documented to enhance the synthesis of virulence factor of PA

Summary

Introduction

Pseudomonas aeruginosa (PA) is an opportunistic pathogen that causes lung infections in cystic fibrosis (CF) [1] as well as in intensive care unit (ICU) patients [2]. In ICU patients, PA-related ventilator-associated pneumonia reduces survival and worsens outcome. The high level of PA recurrence is related to its high virulence and hypermutable genome [3], while the ability to subvert immunity may explain chronic infection. Pseudomonas aeruginosa alters innate lymphoid cells, including natural killer (NK) cells, which play a key role in immunity against PA [4]. NK cells are a major source of IFN-γ, which participates in antimicrobial immunity and stimulates monocyte differentiation [6]. PA can divert cytokine response and use IFN-γ to enhance its virulence factors [7]

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