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Phagosome Definition
In cell biology, the phagosome is defined as a structure formed by pinching off from the cell membrane of a cell and contain the ingested particulate. The process of ingestion or engulfment of particles by the cell or phagocyte is known as phagocytosis. In mammals, the immune cells are the specialized cells that engulf and destroy foreign particles and also helps in the removal of waste particles and cell debris.
Macrophages, neutrophils, and dendritic cells are some examples of phagocytes. The waste particles that need to be degraded are engulfed by forming phagosomes. The phagosome results in the formation of the phagolysosome by fusing with the lysosome.
What is Phagosome?
The vesicle formed within a phagocyte is called a phagosome. The process of capturing foreign particles by phagosomes is known as phagocytosis. When the phagocyte engulfs a particulate, it forms the phagosome that covers the particulate with a cell membrane and then pinches off as a vesicle.
The vesicle is termed a phagosome. Another cytoplasmic structure named the lysosome contains various digestive enzymes and reactive oxygen species get fused with the phagosome. The enzymes and ROS present in the lysosome helps in degrading the particles and antigens such as viruses and bacteria.
Phagosome vs Endosome
There are several differences between a phagosome and an endosome. Endosome is also a type of vesicle which also can fuse with the lysosome for degradation. The Golgi apparatus originates the endosome from the trans-Golgi network. Despite that, the late endosome is also produced from the phagosomes of the phagocytic pathway whereas the maturing early endosome arises from the endocytic pathway. The phagosomes are relatively larger than endosomes and can ingest a whole bacterium or a senescent cell by forming a phagocyte.
Phagosome Function
The pathogens and particulates reside in a vesicle named a phagosome. It restricts all the contents inside it and moves along the microtubule. Later, for the disposal of its contents, the phagosome fuse with the endosome or with the lysosome.
Thus the phagosome has the major function of protection against pathogens and also helps in the removal of apoptotic and senescent cells and cellular debris. Several protists such as Amoeba use a phagosome as a food vacuole. In these organisms, the formation of phagosome occurs to ingest food material.
Importance of Phagosome
The process of removing cellular debris and other foreign bodies from the cell is defined as phagocytosis. It is an important mechanism that follows the phagocytic pathway. In the first step, the phagocyte recognizes and identifies the foreign body and then engulfs the targeted particulate by surrounding it with the cell membrane.
Then the vesicle pinches off from the cell membrane and undergoes maturation to become a late phagosome. The mature phagosome contains protein markers and hydrolytic enzymes. The engulfed material digests in a phagolysosome that is formed by the fusion of phagosome and lysosome.
After digestion, it releases extracellularly or intracellularly to undergo further processing. Oxidative burst is another mechanism for destroying pathogens in which the neutrophil’s granules and phagosome fuses and results in the production of toxic oxygen and chlorine derivatives.
The phagosomes formed by dendritic cells are slightly acidic and less hydrolytic thus cannot degrade the pathogens completely. The major histocompatibility complex receives the partially degraded and uses them for antigen presentation on the cell surface of the dendritic cell. The lymphocytes that are another group of immune cells identify them from the cell surface.
Phagosome Citations
- Listeriolysin O: A phagosome-specific cytolysin revisited. Cell Microbiol . 2019 Mar;21(3):e12988.
- Calcium Signaling Commands Phagosome Maturation Process. Int Rev Immunol . 2019;38(2):57-69.
- The NADPH Oxidase and the Phagosome. Adv Exp Med Biol . 2020;1246:153-177.
- Figures are created with BioRender.com
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