Pathogen-associated molecular pattern

Source: Wikipedia, the free encyclopedia.

Pathogen-associated molecular patterns (PAMPs) are small molecular motifs conserved within a class of microbes, but not present in the host.[1] They are recognized by toll-like receptors (TLRs) and other pattern recognition receptors (PRRs) in both plants and animals.[2] This allows the innate immune system to recognize pathogens and thus, protect the host from infection.[3]: 494 

Although the term "PAMP" is relatively new, the concept that molecules derived from microbes must be detected by receptors from multicellular organisms has been held for many decades, and references to an "endotoxin receptor" are found in much of the older literature. The recognition of PAMPs by the PRRs triggers activation of several signaling cascades in the host immune cells like the stimulation of interferons (IFNs)[4] or other cytokines.[5]

Common PAMPs

A vast array of different types of molecules can serve as PAMPs, including

TLR9.[9] The CpG motifs must be internalized in order to be recognized by TLR9.[8] Viral glycoproteins, as seen in the viral-envelope, as well as fungal PAMPS on the cell surface or fungi are recognized by TLR2 and TLR4.[8]

Gram-negative bacteria

Bacterial

endotoxins, are found on the cell membranes of gram-negative bacteria,[10] are considered to be the prototypical class of PAMPs. The lipid portion of LPS, lipid A, contains a diglycolamine backbone with multiple acyl chains. This is the conserved structural motif that is recognized by TLR4, particularly the TLR4-MD2 complex.[11][12] Microbes have two main strategies in which they try to avoid the immune system, either by masking lipid A or directing their LPS towards an immunomodulatory receptor.[11]

Peptidoglycan (PG) is also found within the membrane walls of gram-negative bacteria[13] and is recognized by TLR2, which is usually in a heterodimer of with TLR1 or TLR6.[14][8]

Gram-positive bacteria

bacterial lipoproteins (sBLP), a phenol soluble factor from Staphylococcus epidermidis, and a component of yeast walls called zymosan, are all recognized by a heterodimer of TLR2[14] and TLR1 or TLR6.[8] However, LTAs result in a weaker pro-inflammatory response compared to lipopeptides, as they are only recognized by TLR2 instead of the heterodimer.[11]

History

First introduced by Charles Janeway in 1989, PAMP was used to describe microbial components that would be considered foreign in a multicellular host.[11] The term "PAMP" has been criticized on the grounds that most microbes, not only pathogens, express the molecules detected; the term microbe-associated molecular pattern (MAMP),[15][16][17] has therefore been proposed. A virulence signal capable of binding to a pathogen receptor, in combination with a MAMP, has been proposed as one way to constitute a (pathogen-specific) PAMP.[18] Plant immunology frequently treats the terms "PAMP" and "MAMP" interchangeably, considering their recognition to be the first step in plant immunity, PTI (PAMP-triggered immunity), a relatively weak immune response that occurs when the host plant does not also recognize pathogenic effectors that damage it or modulate its immune response.[19]

In mycobacteria

TLR1 can recognize cell wall lipoprotein antigens from Mycobacterium tuberculosis, which also induce production of cytokines by macrophages.[21]
TLR9 can be activated by mycobacterial DNA.

See also

References

  1. PMID 22889221
    .
  2. S2CID 26861625
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  3. OCLC 951918628.{{cite book}}: CS1 maint: location missing publisher (link
    )
  4. PMID 17892846
    .
  5. PMID 16497588
    .
  6. PMID 25578468
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  7. S2CID 14357403
    .
  8. ^
    S2CID 39036433
    .
  9. PMID 24032031
    .
  10. PMID 20452953
    .
  11. ^
    ISBN 978-3-0348-0620-6
    , retrieved 2023-03-10
  12. S2CID 31631310
    .
  13. PMID 20452953
    .
  14. ^
    PMID 23954282
    .
  15. S2CID 41603462
    .
  16. S2CID 7451505
    .
  17. PMID 15971103
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  18. S2CID 14300007
    . (Free full text available)
  19. PMID 17108957
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  20. PMID 15310472
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  21. PMID 11222859
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Further reading

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