Difference between revisions of "Recognition of Microorganisms"

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[[Image:PRRs.jpg|thumb|right|150px|Pattern Recognition Receptors - B. Catchpole, RVC 2008]]
 
[[Image:PRRs.jpg|thumb|right|150px|Pattern Recognition Receptors - B. Catchpole, RVC 2008]]
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The [[Innate Immune System - Introduction|innate immune system]] recognises components of pathogens which are intrinsically foreign (i.e. not present on normal mammalian cells), such as:
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* The innate immune system recognises components of pathogens which are intrinsically foreign (i.e. not present on normal mammalian cells), such as:
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*Lipopolysaccharides of gram-negative [[bacteria]]
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**Lipopolysaccharides of gram-negative bacteria
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*Peptidoglycans of gram-positive bacteria
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**Peptidoglycans of gram-positive bacteria
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*Mannose sugars
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**Mannose sugars
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*D-isoform amino acids (abundant in Peptidoglycans) - almost all (>99%) amino acids in multicellular organisms are the L-isoform of amino acids as it is only the L-isoform amino acids that are used for protein synthesis.
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**D-isoform amino acids
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<br />
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*These are given away as foreign by expressing '''pathogen-associated molecular patterns''' (PAMPs)
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These are known to the body as foreign as they are expressed as '''pathogen-associated molecular patterns''' (PAMPs) which are recognised by '''pattern recognition receptors''' (PRRs) expressed on mammalian cells. These receptors are expressed on many different cell types, not just on phagocytes, though not all are expressed by all cells: different cell types express a different range of PRRs. PRRs are either intracellular, membrane-associated or soluble:
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* PAMPs are recognised by '''pattern recognition receptors''' (PRRs) expressed on mammalian cells
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*Recognition of pathogens via the cellular PRRs results in phagocytosis and inflammation
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** Pattern recognition receptors are expressed on many different cell types, not just on phagocytes
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*Recognition of pathogens via the humoral PRRs results in various killing mechanisms
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** Not all are expressed by all cells: different cell types express a different range of PRRs
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<br />
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** PRRs are either intracellular, membrane-associated or soluble:
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==Actions==
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*** Recognition of pathogens via the cellular PRRs results in phagocytosis and inflammation
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The engagement of PRRs by PAMPs triggers:
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*** Recognition of pathogens via the humoral PRRs results in various killing mechanisms
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* '''[[Phagocytosis|Phagocytosis]]'''
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* Engagement of PRRs by PAMPs triggers:
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* The expression of '''[[Cytokines|cytokines]]''', which brings about [[Inflammation - Introduction|inflammation]] and other immune responses
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** '''Phagocytosis'''
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<br />
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** The expression of '''cytokines''', which brings about [[:Category:Inflammation|inflammation]] and other immune responses
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==Pattern Recognition Receptors==
 
 
<big><center>'''''Examples of Pattern Recognition Receptors'''''</center></big>
 
<big><center>'''''Examples of Pattern Recognition Receptors'''''</center></big>
  
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|-
 
|-
 
| TLR3
 
| TLR3
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| Cell Membrane (in Endosome)
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| Cell Membrane
 
| dsRNA of RNA viruses (e.g. avian influenza)
 
| dsRNA of RNA viruses (e.g. avian influenza)
 
|-
 
|-
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|-
 
|-
 
| TLR9
 
| TLR9
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| Cell Membrane (in Endosome)
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| Cell Membrane
 
| Bacterial DNA (CpG DNA)
 
| Bacterial DNA (CpG DNA)
 
|-
 
|-
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| Carbohydrates, all bacteria, dead cells
 
| Carbohydrates, all bacteria, dead cells
 
|-
 
|-
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| fMLP
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| fmlf
 
| Soluble
 
| Soluble
 
| Formyl peptides (i.e. all bacteria)
 
| Formyl peptides (i.e. all bacteria)
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| ds RNA of RNA viruses
 
| ds RNA of RNA viruses
 
|}
 
|}
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<p> For more information on Toll-like receptors see this review <ref>{{citation|initiallast = Lee|initialfirst = C.C|2last = Avalos|2first = A.M|finallast = Ploegh|finalfirst = H.L|year = 2012|jtitle = Accessory molecules for Toll-like receptors and their function
 
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|jor = Nature Reviews Immunology|vol = 12|range = 168-179}}</ref></p>
 
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<br><br>
 
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==References==
 
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<references />
 
 
<br><br>
 
<br><br>
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{{Robert J Francis
 
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|date = May 10, 2012}}
 
 
{{Jim Bee 2007}}
 
{{Jim Bee 2007}}
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[[Category:Innate Immune System]]
 
[[Category:Innate Immune System]]
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[[Category:Robert J Francis reviewed]]
 

Revision as of 16:22, 16 March 2012

Pattern Recognition Receptors - B. Catchpole, RVC 2008
  • The innate immune system recognises components of pathogens which are intrinsically foreign (i.e. not present on normal mammalian cells), such as:
    • Lipopolysaccharides of gram-negative bacteria
    • Peptidoglycans of gram-positive bacteria
    • Mannose sugars
    • D-isoform amino acids
  • These are given away as foreign by expressing pathogen-associated molecular patterns (PAMPs)
  • PAMPs are recognised by pattern recognition receptors (PRRs) expressed on mammalian cells
    • Pattern recognition receptors are expressed on many different cell types, not just on phagocytes
    • Not all are expressed by all cells: different cell types express a different range of PRRs
    • PRRs are either intracellular, membrane-associated or soluble:
      • Recognition of pathogens via the cellular PRRs results in phagocytosis and inflammation
      • Recognition of pathogens via the humoral PRRs results in various killing mechanisms
  • Engagement of PRRs by PAMPs triggers:
    • Phagocytosis
    • The expression of cytokines, which brings about inflammation and other immune responses


Examples of Pattern Recognition Receptors
Receptor Location Ligands
TLR2 (Toll-like receptor) Cell Membrane Peptidoglycan of gram +ve bacteria
TLR3 Cell Membrane dsRNA of RNA viruses (e.g. avian influenza)
TLR4 Cell Membrane Lipoplysaccharide from gram-negative bacteria (e.g. E. coli, Salmonella)
TLR5 Cell Membrane Bacterial flagellin
TLR9 Cell Membrane Bacterial DNA (CpG DNA)
C-type lectins Soluble Carbohydrates, all bacteria, dead cells
fmlf Soluble Formyl peptides (i.e. all bacteria)
Complement receptors Soluble Fixed complement components (e.g. iC3b)
NOD2 Cytoplasm Peptidoglycan of gram +ve bacteria
dsRNA-dependent Protein Kinase Receptor Cytoplasm ds RNA of RNA viruses



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