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Toll-like receptors expression and interferon-γ production by NK cells in human sepsis

Fernando Souza-Fonseca-Guimaraes1, Marianna Parlato1, François Philippart2, Benoît Misset2, Jean-Marc Cavaillon1, Minou Adib-Conquy1* and the Captain study group

Author Affiliations

1 Unité Cytokines & Inflammation, Département Infection et Epidemiology, Institut Pasteur, 28 rue Dr. Roux, 75015 Paris, France

2 Groupe hospitalier Paris Saint Joseph, Medical and surgical Intensive care unit, Paris Descartes University, Paris, France

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Critical Care 2012, 16:R206  doi:10.1186/cc11838

Published: 25 October 2012

Abstract

Introduction

During the course of infection, natural killer (NK) cells contribute to innate immunity by producing cytokines, particularly interferon-gamma (IFN-γ). In addition to their beneficial effects against infection, NK cells may play a detrimental role during systemic inflammation, causing lethality during sepsis. Little is known on the immune status of NK cells in patients with systemic inflammatory response syndrome (SIRS) or sepsis in terms of cell surface markers expression and IFN-γ production.

Methods

We investigated 27 sepsis patients and 11 patients with non-infectious SIRS. CD56bright and CD56dim NK cell subsets were identified by flow cytometry and Toll-like receptor (TLR)2, TLR4, TLR9, CX3CR1, CD16 and CD69 expression were analyzed, as well as ex vivo IFN-γ production by NK cells in whole blood samples.

Results

We first showed that in NK cells from healthy controls, TLR2 and TLR4 expression is mainly intracellular, similarly to TLR9. Intracellular levels of TLR2 and TLR4, in both CD56bright and CD56dim NK cell subsets from sepsis patients, were increased compared to healthy subjects. In addition, the percentage of CD69+ cells was higher among NK cells of sepsis patients. No difference was observed for TLR9, CX3CR1, and CD16 expression. The ex vivo stimulation by TLR4 or TLR9 agonists, or whole bacteria in synergy with accessory cytokines (IL-15+IL-18), resulted in significant production of IFN-γ by NK cells of healthy controls. In contrast, for SIRS and sepsis patients this response was dramatically reduced.

Conclusions

This study reports for the first time an intracellular expression of TLR2 and TLR4 in human NK cells. Surface TLR4 expression allows discriminating sepsis and SIRS. Furthermore, during these pathologies, NK cells undergo an alteration of their immune status characterized by a profound reduction of their capacity to release IFN-γ.