phagolysosome
Summary
Intracellular vesicle formed by fusion of a phagosome with a lysosome, where ingested pathogens are degraded by reactive oxygen species and hydrolytic enzymes. Central to neutrophil and macrophage killing.
Detail
After phagocytosis, the phagosome fuses with lysosomes to form a phagolysosome where pathogen killing occurs via two main mechanisms: (1) oxygen-dependent killing — NADPH oxidase generates superoxide, myeloperoxidase converts H2O2 + Cl- to hypochlorous acid (bleach), and (2) oxygen-independent killing — lysozyme, lactoferrin, defensins, and acid hydrolases. Defects underlie classic immunodeficiencies: chronic granulomatous disease (NADPH oxidase deficiency, catalase-positive infections), MPO deficiency (Candida infections), and Chediak-Higashi syndrome (LYST mutation impairing phagosome-lysosome fusion, giant granules). Mycobacterium tuberculosis and Listeria evade killing by blocking fusion or escaping the phagosome. Boards: 'phagolysosome fusion failure' = Chediak-Higashi.
Sources
- First Aid for USMLE Step 1 2024
- Robbins Basic Pathology 10th ed
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