M. tuberculosis-Induced Necrosis of Infected Neutrophils Promotes Bacterial Growth Following Phagocytosis by Macrophages

Abstract

Neutrophils represent the main infected cell population in the lungs of active tuberculosis patients. Efficient removal of infected and dying neutrophils is required to protect the surrounding tissue from bioactive neutrophil molecules and subsequent pathological sequelae. While the removal of apoptotic M. tuberculosis (Mtb)-infected cells, or efferocytosis, is considered beneficial for host defense, little is known about Mtb-infected necrotic neutrophils. We found that Mtb induces necrosis of human neutrophils in an ESX-1-dependent manner, and neutrophil-produced reactive oxygen species (ROS) drive this necrosis. Neutrophil necrosis was required for Mtb growth after uptake of infected neutrophils by human macrophages. Pharmacological inhibition of ROS production could prevent necrosis and restore the capability of macrophages to control Mtb growth, thereby identifying a potential host-directed therapy target. Taken together, necrosis represents the starting point for a vicious cycle including the uptake of infected necrotic cells by other phagocytes, Mtb growth therein, and sustained infection.

Keywords: ESAT-6; Mycobacterium tuberculosis; cell death; efferocytosis; host-directed therapy; macrophages; necrosis; neutrophils; respiratory burst; tuberculosis.