Phagolysosom

A phagolysosome is an intracellular organelle formed when a phagosome fuses with a lysosome inside professional phagocytes such as macrophages, neutrophils, and dendritic cells. The phagolysosome is the site where engulfed microbes, dead cells, and other particles are degraded and neutralized.

Phagosome maturation involves sequential fusion with endosomes and lysosomes. Early phagosomes acquire Rab5 and EEA1, then mature to Rab7-positive late phagosomes that fuse with lysosomes to become phagolysosomes. The lumen is acidified by the vacuolar-type H+-ATPase, reaching a pH around 4.5–5.0, which activates acidic hydrolases.

Phagolysosomes contain a suite of hydrolases—including proteases such as cathepsins, nucleases, lipases, and glycosidases—as well as antimicrobial peptides. The digestive enzymes degrade proteins, lipids, nucleic acids, and complex carbohydrates, while reactive oxygen and nitrogen species produced at the phagosomal membrane contribute to microbial killing.

In addition to direct digestion, phagolysosomes participate in antigen processing for presentation on MHC class II molecules, linking innate and adaptive immunity. The efficiency of phagolysosome formation and function can influence susceptibility to infections and the outcome of inflammatory diseases.

Many pathogens have evolved strategies to avoid or subvert phagolysosome formation, enabling intracellular survival. For example, certain bacteria modify phagosome maturation to delay fusion with lysosomes.