Abstract
Mycobacterium tuberculosis is an intracellular pathogen of macrophages and escapes the macrophages' bactericidal effectors by interfering with phagosome-lysosome fusion. IFN-γ activation renders the macrophages capable of killing intracellular mycobacteria by overcoming the phagosome maturation block, nutrient deprivation and exposure to microbicidal effectors including nitric oxide (NO). While the importance about NO for the control of mycobacterial infection in murine macrophages is well documented, the underlying mechanism has not been revealed yet. In this study we show that IFN-γ induced apoptosis in mycobacteria-infected macrophages, which was strictly dependent on NO. Subsequently, NO-mediated apoptosis resulted in the killing of intracellular mycobacteria independent of autophagy. In fact, killing of mycobacteria was susceptible to the autophagy inhibitor 3-methyladenine (3-MA). However, 3-MA also suppressed NO production, which is an important off-target effect to be considered in autophagy studies using 3-MA. Inhibition of caspase 3/7 activation, as well as NO production, abolished apoptosis and elimination of mycobacteria by IFN-γ activated macrophages. In line with the finding that drug-induced apoptosis kills intracellular mycobacteria in the absence of NO, we identified NO-mediated apoptosis as a new defense mechanism of activated macrophages against M. tuberculosis.
Highlights
Macrophages are important effector cells in immunity to intracellular bacteria but at the same time are exploited as host cells by a number of microorganisms such as Mycobacterium tuberculosis (M. tuberculosis)
Mycobacteria are deprived of essential nutrients such as iron and exposed to microbicidal effectors generated by IFN-c activated macrophages such as anti-microbial peptides (AMP) and reactive oxygen or nitrogen intermediates, the products of NADPH oxidase and nitric oxide synthase (NOS2), respectively [4,5,6]
NO production and autophagy were proposed as key functions in IFN-c mediated killing of intracellular mycobacteria by murine macrophages
Summary
Macrophages are important effector cells in immunity to intracellular bacteria but at the same time are exploited as host cells by a number of microorganisms such as Mycobacterium tuberculosis (M. tuberculosis). Delivery of invading bacteria to phagolysosomes represents an important mechanism to eliminate intracellular pathogens by exposing them to cellular microbicides. Mycobacteria are deprived of essential nutrients such as iron and exposed to microbicidal effectors generated by IFN-c activated macrophages such as anti-microbial peptides (AMP) and reactive oxygen or nitrogen intermediates, the products of NADPH oxidase and nitric oxide synthase (NOS2), respectively [4,5,6]. Killing of intracellular mycobacteria by IFN-c activated macrophages has been linked to autophagy [5] whereas alternative activation by the Th2 cytokines IL-4 and IL-13 counter regulates autophagy and promotes mycobacterial growth probably by induction of arginase 1 and depletion of arginine, the substrate shared with NOS2 [7,8,9]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
