Mycobacterium tuberculosis Exploits Human Interferon γ to Stimulate Macrophage Extracellular Trap Formation and Necrosis

Abstract

Human neutrophils form extracellular traps during M. tuberculosis infection, but a similar phenomenon has not been reported in human macrophages. Here we demonstrate that M. tuberculosis induces release of extracellular traps from human macrophages. This process is regulated by elastase activity, previously shown to regulate formation of extracellular traps by neutrophils. Interestingly, formation of extracellular traps by macrophages during M. tuberculosis infection is inducible by interferon γ (IFN-γ). These traps are mainly produced by heavily infected macrophages. Accordingly, IFN-γ is found to stimulate M. tuberculosis aggregation in macrophages. Both IFN-γ–inducible events, extracellular trap formation and mycobacterial aggregation, require the ESX-1 secretion system. In addition, IFN-γ is found to enhance ESX-1–mediated macrophage necrosis. In the absence of ESX-1, IFN-γ does not restore any extracellular trap formation, mycobacterial aggregation, or macrophage necrosis. Thus, initial characterization of macrophage extracellular trap formation due to M. tuberculosis infection led to the uncovering of a novel role for IFN-γ in amplifying multiple effects of the mycobacterial ESX-1.

NETosis: how vital is it?

“…42,44,[129][130][131][132][133] Although these events might occur, the evidence is less strong. In the case of eosinophils, the release of DNA covered with potent eosinophil-derived neurotoxin or major basic protein may be an important way of sequestering and directing dangerous molecules toward large parasites through a catapult-like mechanism.…”

“…The importance of DNA release from macrophages has only recently been reported, and this requires further exploration to understand the significance but could be an important mechanism in granuloma formation. [129][130][131] A debate once raged around the very existence of DNA. Yet today, this debate would seem irrational and preposterous.…”

Separable roles forMycobacterium tuberculosisESX-3 effectors in iron acquisition and virulence

“…Human macrophages were prepared as described (72) following the method of Vogt and Nathan (73) and differentiation with either 2 ng/mL recombinant human GM-CSF or 10 ng/mL recombinant human M-CSF (R&D Systems), as detailed in SI Materials and Methods. Following infection at a multiplicity of infection (MOI) of 0.02, mycobacterial growth was enumerated at 14 d postinfection by plating on 7H10 plates containing 200 ng/mL MbJ (Allied Monitor).…”

The innate immune response in human tuberculosis

“…In vitro , this mechanism has been observed in human but not in mouse macrophages infected by Mtb (Wong and Jacobs, 2013). The formation of extracellular traps by primary human macrophages during Mtb infection is inducible by IFN‐γ and requires the ESX‐1 secretion system (Wong and Jacobs, 2013). …”