Phagocytosis

Phagocytosis by a neutrophil

Phagocytosis is a very primitive system of defence against infection
- Even exists in invertebrates
Phagocytosis is a form of endocytosis (cell eating), it is the method of removal of bacteria and dead cells by vesicular internalisation
- The internalised vesicle is referred to as the "phagosome"
- Lysosomes, which contain a large range of enzymes, fuse with the phagosome, killing the microbes in an energy-dependent way
  - Oxygen-dependant degradation utilizes Oxygen and chlorine free-radicals, Hydrogen peroxide, and Nitric oxide
  - Oxygen-independant degradation depends on granules containing proteolytic enzymes such as Defensins, Lysozyme, and cationic proteins
    - In addition, these granules contain antimicrobial elements such as lactoferrin
- Microbes are then digested by a number of different catabolic enzymes
  - Glycosidases: Digest carbohydrates
  - Lipases: Digest lipids
  - Proteases: Digest protein
- Waste products of phagocytosis are either exocytosed or further degraded by the phagocyte
Neutrophils and macrophages are phagocytic
Opsonins promote and accelerate phagocytosis
Phagocytic cells target pathogens by using cell membrane receptors (PRRs) that recognise intrinsically foreign components of microorganisms (pathogen-associated molecular patterns; PAMPs)

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Originally funded by the RVC Jim Bee Award 2007