Figure 3.

Antimicrobial effectors inside the phagolysosome. The most distinctive characteristic of phagolysosomes is their low pH. The V-ATPase translocates protons (H⁺) into the lumen of the phagosome (17, 18). The NADPH oxidase is an enzymatic complex formed by two transmembrane proteins, such as CYBB and CYBA, and three cytosolic components: NCF-4, NCF-1, and NCF-2 (68, 69). Rac is also required for efficient activation of the enzyme complex (70, 71). Myeloperoxidase (MPO) can transform H₂O₂ into hypochlorous acid (65). Nitric oxide radicals (NO^⋅) are produced by the inducible nitric oxide synthase 2 (iNOS) (72), and NO^⋅ reacts with ${\text{O}}_2^{-}$ to form peroxynitrite (ONOO⁻) (73, 74). Lactoferrin captures Fe²⁺ that is essential for bacterial growth (75), and the transporter natural resistance-associated macrophage protein 1 (NRAMP-1) takes Fe²⁺ out of the phagosome (76). Defensins are antimicrobial peptides that form multimeric ion-permeable channels on bacteria (77, 78). Cathepsins are lysosomal proteases (79, 80). Lysozyme (81, 82) degrades peptidoglycan, a primary building block of the cell wall of bacteria, and the type IIA secreted phospholipase A2 (sPLA2-IIA) (83) degrades anionic phospholipids such as phosphatidylglycerol, the main phospholipid component of bacterial membranes.