Figure 2.

Series of reactive oxygen species generated in response to intracellular mycobacteria infection. Macrophages and neutrophils produce reactive oxygen species to kill intracellular microbes in a series of reaction which can be initiated by the conversion of NADPH to NADP ⁺ via the NADPH oxidase (NOX) and the production of superoxide O₂⁻ in presence of O₂. O₂⁻ can enter in the phagosome and later in the mycobacteria through porins or crosses the outer membrane that is partially permeabilized by antimicrobial peptides. O₂⁻ is a substrate for superoxide dismutase (SodCI, SodA) to produce H₂O₂ which can freely diffuse across membranes. The hydroxyl radical (OH^•) is produced from H₂O₂ and superoxide via Fenton reaction. Mycobacteria produce the catalase KatG to detoxify H₂O₂. The production of NO from arginine metabolism via nitric oxide synthase (NOS2) can generate nitric oxide which in presence of O₂⁻ produce ONOO⁻ and NO₂⁻, which present some toxic proprieties against mycobacteria.