Phagocytosis

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  • 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)

Video of phagocytosis of Candida albicans: [1]