Difference between revisions of "Phagocytosis"

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[[File:Neutrophil Phagocytosis.png|thumb|right|300px|Phagocytosis by a neutrophil - R.J.Francis, RVC 2012]]
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* Phagocytosis is a very primitive system of defence against infection
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Phagocytosis is a very primitive system of defence against infection, having even been shown to exist in invertebrates and single cell organisms. The discovery was made in starfish larvae by Elle Metchnikoff who subsequently won the Nobel Prize for Medicine or Physiology in 1908. The process of phagocytosis itself is a form of '''endocytosis''' (cell eating), with vesicular internalisation being the method of removal of pathogens and dead cells (those that have undergone '''apoptosis''', or '''Programmed Cell Death'''). This internalised vesicle is referred to as the "'''phagosome'''".
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** Even exists in invertebrates  
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* Phagocytosis is a form of endocytosis (cell eating), it is the method of removal of bacteria and dead cells by vesicular internalisation
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** The internalised vesicle is referred to as the "phagosome"
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To then either kill the pathogens or digest the dead cells, '''lysosomes''', which contain a large range of enzymes, fuse with the phagosome to form the '''phagolysosome'''. One example of a process that occurs in these vesicles is oxygen-dependent degradation which utilizes oxygen (O<sub>2</sub><sup>-</sup>) and chlorine (Cl*) free-radicals, hydrogen peroxide (OH), and nitric oxide (NO) to degrade the contents within the phagolysosome (OH + Cl* = HOCl (otherwise known as bleach!)). The essential enzyme within this process is NADPH oxidase. In humans, the lethal genetic disease chronic granulomatous disease (CGD) is caused by the lack of NADPH oxidase in the phagocytes, with sufferers rarely living past their mid-twenties (with the help of antibiotics) usually succumbing to lung infection.
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** '''Lysosomes''', which contain a large range of enzymes, fuse with the phagosome, killing the microbes in an energy-dependent way
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*** Oxygen-dependant degradation utilizes Oxygen and chlorine free-radicals, Hydrogen peroxide, and Nitric oxide
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*** Oxygen-independant degradation depends on granules containing proteolytic enzymes such as Defensins, Lysozyme, and cationic proteins
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Along with the direct degradation of some elements within the phagolysosome, the process also causes acidification of the phagolysosome vesicles. The lowering of the pH then activates other enzymes within the phagosome. These include:   
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**** In addition, these granules contain antimicrobial elements such as lactoferrin
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* Oxygen-independent proteolytic enzymes such as defensins, [[lysozyme]], and cationic proteins
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** Microbes are then digested by a number of different catabolic enzymes
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* Antimicrobial elements such as lactoferrin
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*** Glycosidases: Digest carbohydrates
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*** Lipases: Digest lipids
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*** Proteases: Digest protein
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To then complete the phagocytic process, microbes are then digested by a number of different catabolic enzymes:
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** Waste products of phagocytosis are either exocytosed or further degraded by the phagocyte
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* Glycosidases: digest carbohydrates
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* '''Neutrophils''' and '''macrophages''' are phagocytic
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* Lipases: digest lipids
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* '''Opsonins''' promote and accelerate phagocytosis
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* Proteases: digest protein (an important example is cathepsin)
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* 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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Video of phagocytosis [http://www.cellsalive.com/qtmovs/mac_mov.htm] of [[Candida spp.|''Candida albicans'']]
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The waste products of phagocytosis are then either exocytosed or further degraded by the phagocyte.
 
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The main effector cells of this process are the [[neutrophils|neutrophils]] ([[Heterophils|heterophils]] in birds and some reptile and mammalian species) and [[Macrophages|macrophages]] which recognise the pathogens, or with the case of macrophages, cells that have undergone apoptosis too. Phagocytic cells target pathogens by using cell membrane receptors ("Pathogen Recognition Receptors") that recognise intrinsically foreign components of microorganisms (pathogen-associated molecular patterns; PAMPs); or those that have been opsonised with either [[Complement|complement component C3bi]] or [[Immunoglobulins|antibodies]]; or with the case of cells that have undergone apoptosis, externalised phosphatidylserine (a phospholipid in the cell membrane).
 
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==Links==
 
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*[http://www.youtube.com/watch?v=fpOxgAU5fFQ Video of chemotaxis and phagocytosis]
 
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*[http://www.youtube.com/watch?v=U8QoO71lt-M&context=C4a8ea38ADvjVQa1PpcFO3vYijexJH_LpjoWjuUy831e6skih3JQA= Phagocytosis in 4D (3D + Time)]
 
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<br><br>
 
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{{Robert J Francis
 
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|date = May 17, 2012}}
 
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{{Jim Bee 2007}}
 
 
[[Category:Innate Immune System]]
 
[[Category:Innate Immune System]]
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[[Category:Robert J Francis reviewed]]
 

Revision as of 13:55, 23 September 2010

  • 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 [1] of Candida albicans

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