Phagolysosome

A phagolysosome -or endolysosome is a cytoplasmic body formed by the fusion of a phagosome with a lysosome in a process that occurs during phagocytosis.

The lysosome, containing hydrolytic enzymes digests the ingested particles in the phagosome when the phagosome migrates to the cytoplasm during phagocytosis. Membrane fusion of the phagosome and lysosome is regulated by Rab 5 protein. This G Protein allows the exchange of material between these two organelles but prevents complete fusion of their membranes. Formation of phagolysosomes are essential for the intracellular destruction of microorganisms and pathogens and requires an increase in intracellular calcium ion concentration. Reactive oxygen species and reactive nitrogen species are produced in the nutrient-limiting environment of phagolysosomes. Research studies show that phagolysosomes may contain more carbon sources and nutrients than other organelles in the endo-lysosomal pathway.

When the membranes of the phagosome and lysosome 'collide',the lysosomal contents are discharged in an explosive manner and toxic molecules are released into the phagosome. Products of the digestion are either moved into the cytoplasm (useful materials) or exported by exocytosis.

Phagolysosomes function by reducing the pH of their internal environment thus making them acidic.This serves as a defense mechanism against microbes and other harmful parasites and also provides a suitable medium for degradative enzyme activity.

The Q fever causative agent,Coxiella burnetii thrives and replicates in the acidic phagolysosomes of its host cell. The acidity of the phagolysosome is essential for C.burnetii to transport glucose,glutamate,proline and also for the synthesis of nucleic acids and proteins.

Phagolysosome formation is important for the destruction of microbes and parasites.Microbes are destroyed by a combination of oxidative and non-oxidative processes in phagolysosomes.The oxidative process also known as respiratory burst includes the "non-mitochondrial" production of reactive oxygen species.

Phagolysomes inhibit fungal growth due to high cation concentration and low carbon and nitrogen sources .A typical example is the inhbition of Candida albicans filamentation.

Leishmania amastigotes obtain all their purine sources,various vitamins and a number of essential amino acids from the phagolysosome of its host.Uptake of these substances is facilitated by proton symporters.Leishmania also obtain amino acids and heme from the proteolysis of proteins in the host phagolysosome and exogenous proteins are transported to the phagolysosome by autophagy and endocytosis.

...
Wikipedia