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]] | ||
| − | The innate immune system recognises components of pathogens which are intrinsically foreign (i.e. not present on normal mammalian cells), such as: | + | 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: |
| − | *Lipopolysaccharides of gram-negative bacteria | + | *Lipopolysaccharides of gram-negative [[bacteria]] |
*Peptidoglycans of gram-positive bacteria | *Peptidoglycans of gram-positive bacteria | ||
*Mannose sugars | *Mannose sugars | ||
| − | *D-isoform amino acids | + | *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. |
| − | |||
<br /> | <br /> | ||
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: | 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: | ||
*Recognition of pathogens via the cellular PRRs results in phagocytosis and inflammation | *Recognition of pathogens via the cellular PRRs results in phagocytosis and inflammation | ||
*Recognition of pathogens via the humoral PRRs results in various killing mechanisms | *Recognition of pathogens via the humoral PRRs results in various killing mechanisms | ||
| + | <br /> | ||
==Actions== | ==Actions== | ||
The engagement of PRRs by PAMPs triggers: | The engagement of PRRs by PAMPs triggers: | ||
* '''[[Phagocytosis|Phagocytosis]]''' | * '''[[Phagocytosis|Phagocytosis]]''' | ||
| − | * The expression of '''cytokines''', which brings about [[ | + | * The expression of '''[[Cytokines|cytokines]]''', which brings about [[Inflammation - Introduction|inflammation]] and other immune responses |
| + | <br /> | ||
==Pattern Recognition Receptors== | ==Pattern Recognition Receptors== | ||
| Line 29: | Line 30: | ||
|- | |- | ||
| TLR3 | | TLR3 | ||
| − | | Cell Membrane | + | | Cell Membrane (in Endosome) |
| dsRNA of RNA viruses (e.g. avian influenza) | | dsRNA of RNA viruses (e.g. avian influenza) | ||
|- | |- | ||
| Line 41: | Line 42: | ||
|- | |- | ||
| TLR9 | | TLR9 | ||
| − | | Cell Membrane | + | | Cell Membrane (in Endosome) |
| Bacterial DNA (CpG DNA) | | Bacterial DNA (CpG DNA) | ||
|- | |- | ||
| Line 64: | Line 65: | ||
| ds RNA of RNA viruses | | ds RNA of RNA viruses | ||
|} | |} | ||
| + | <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 | ||
| + | |jor = Nature Reviews Immunology|vol = 12|range = 168-179}}</ref></p> | ||
| + | <br><br> | ||
| + | |||
| + | ==References== | ||
| + | <references /> | ||
<br><br> | <br><br> | ||
| + | {{Robert J Francis | ||
| + | |date = May 10, 2012}} | ||
{{Jim Bee 2007}} | {{Jim Bee 2007}} | ||
| + | |||
[[Category:Innate Immune System]] | [[Category:Innate Immune System]] | ||
| + | [[Category:Robert J Francis reviewed]] | ||
Latest revision as of 11:06, 23 May 2012
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 (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.
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:
- Recognition of pathogens via the cellular PRRs results in phagocytosis and inflammation
- Recognition of pathogens via the humoral PRRs results in various killing mechanisms
Actions
The engagement of PRRs by PAMPs triggers:
- Phagocytosis
- The expression of cytokines, which brings about inflammation and other immune responses
Pattern Recognition Receptors
| Receptor | Location | Ligands |
|---|---|---|
| TLR2 (Toll-like receptor) | Cell Membrane | Peptidoglycan of gram +ve bacteria |
| TLR3 | Cell Membrane (in Endosome) | 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 (in Endosome) | Bacterial DNA (CpG DNA) |
| C-type lectins | Soluble | Carbohydrates, all bacteria, dead cells |
| fMLP | 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 |
For more information on Toll-like receptors see this review [1]
References
- ↑ Lee, C.C., Avalos, A.M. and Ploegh, H.L. (2012) Accessory molecules for Toll-like receptors and their function. Nature Reviews Immunology 12: pp.168-179.
 |
This article has been expert reviewed by Dr Robert J Francis BSc(Hons) PhD Date reviewed: May 10, 2012 |
|
Originally funded by the RVC Jim Bee Award 2007 |