Phagocytosis

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Phagocytosis is an endocytosis process where the extracellular particle is ingested by phagocytes. The specialized cells actively involve in phagocytosis are monocyte, macrophage, neutrophil and dendritic cell.

Phagocytosis process

  1. Phagocyte surrounds the pathogen using pseudopodia.
  2. Bacteria is ingested into phagocyte and forming internal phagosome.
  3. Lysosome fuse with phagosome through the membrane. It forms phagolysosome.
  4. Lysosomal enzyme breakdown the cell wall of bacteria and digest it.
  5. The digested materials are released out from phagocyte via exocytosis.


 

Opsonization

Phagocytosis is enhanced by the attachment of opsonins such as antibodies and C3b on the membrane surface of the pathogens.

Digestion of pathogen

Digestion or degradation of pathogen can be performed by oxygen-dependent or oxygen-independent ways.

Oxygen-dependent degradation

Oxygen-dependent degradation depends on the availability of oxygen. Granule oxidase with the NADPH and NADPH oxidase reduce oxygen to reactive oxygen species, superoxide. Other reactive species are also produced such as hydrogen peroxide. These reactive oxygen species causes the formation of hypochlorus acid. Hypochlorus acid acts as oxidizing agent and kill the pathogen.

Oxygen-independent degradation

Granules containing several antimicrobial agents such as

  • Lysozyme – splits peptidoglycan
  • Proteolytic enzymes – degrade dead microbes
  • Lactoferrin – deprive pathogens
  • Defensins – damage microbial membrane

 

Related articles

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