Pathogen-associated molecular pattern
Encyclopedia
Pathogen-associated molecular patterns, or PAMPs, are molecules associated with groups of pathogens, that are recognized by cells of the innate immune system. These molecules can be referred to as small molecular motifs conserved within a class of microbes. They are recognized by Toll-like receptor
s (TLRs) and other pattern recognition receptor
s (PRRs) in both plants and animals.
They activate innate immune responses, protecting the host from infection, by identifying some conserved non-self molecules. Bacterial Lipopolysaccharide
(LPS), an endotoxin found on the bacterial cell membrane of a bacterium, is considered to be the prototypical PAMP. LPS is specifically recognised by TLR 4
, a recognition receptor of the innate immune system. Other PAMPs include bacterial flagellin
(recognized by TLR 5
), lipoteichoic acid
from Gram positive bacteria, peptidoglycan
, and nucleic acid variants normally associated with viruses, such as double-stranded RNA (dsRNA), recognized by TLR 3
or unmethylated CpG
motifs, recognized by TLR 9. 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 term "PAMP" has been criticized on the grounds that most microbes, not only pathogens, express the molecules detected; the term microbe-associated molecular pattern, or MAMP, 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. Plant immunology frequently treats the terms "PAMP" and "MAMP" interchangeably, considering them 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 which damage it or modulate its immune response.
Toll-like receptor
Toll-like receptors are a class of proteins that play a key role in the innate immune system. They are single, membrane-spanning, non-catalytic receptors that recognize structurally conserved molecules derived from microbes...
s (TLRs) and other pattern recognition receptor
Pattern recognition receptor
Pattern recognition receptors are a primitive part of the immune system. They are proteins expressed by cells of the innate immune system to identify pathogen-associated molecular patterns , which are associated with microbial pathogens or cellular stress, as well as damage-associated molecular...
s (PRRs) in both plants and animals.
They activate innate immune responses, protecting the host from infection, by identifying some conserved non-self molecules. Bacterial Lipopolysaccharide
Lipopolysaccharide
Lipopolysaccharides , also known as lipoglycans, are large molecules consisting of a lipid and a polysaccharide joined by a covalent bond; they are found in the outer membrane of Gram-negative bacteria, act as endotoxins and elicit strong immune responses in animals.-Functions:LPS is the major...
(LPS), an endotoxin found on the bacterial cell membrane of a bacterium, is considered to be the prototypical PAMP. LPS is specifically recognised by TLR 4
TLR 4
Toll-like receptor 4 is a protein that in humans is encoded by the TLR4 gene. TLR 4 is a toll-like receptor. It detects lipopolysaccharide from Gram-negative bacteria and is thus important in the activation of the innate immune system...
, a recognition receptor of the innate immune system. Other PAMPs include bacterial flagellin
Flagellin
Flagellin is a protein that arranges itself in a hollow cylinder to form the filament in bacterial flagellum. It has a mass of about 30,000 to 60,000 daltons...
(recognized by TLR 5
TLR 5
Toll-like receptor 5, also known as TLR5, is a protein which in humans is encoded by the TLR5 gene.- Function :The protein encoded by this gene is a member of the Toll-like receptor family which plays a fundamental role in pathogen recognition and activation of innate immunity...
), lipoteichoic acid
Lipoteichoic acid
Lipoteichoic acid is a major constituent of the cell wall of Gram-positive bacteria. These organisms have an inner membrane and, external to it, a thick peptidoglycan layer. It consists of teichoic acids, long chains of ribitol phosphate and is anchored to the lipid bilayer via a glyceride...
from Gram positive bacteria, peptidoglycan
Peptidoglycan
Peptidoglycan, also known as murein, is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of bacteria , forming the cell wall. The sugar component consists of alternating residues of β- linked N-acetylglucosamine and N-acetylmuramic acid...
, and nucleic acid variants normally associated with viruses, such as double-stranded RNA (dsRNA), recognized by TLR 3
TLR 3
Toll-like receptor 3 also known as CD283 is a protein that in humans is encoded by the TLR3 gene...
or unmethylated CpG
CpG
CpG can be:*CpG site - methylated sequences of DNA significant in gene regulation*CpG Oligodeoxynucleotide - unmethylated sequences of DNA that have immunostimulatory properties*CpG island - regions of DNA that contain several CpG sites...
motifs, recognized by TLR 9. 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 term "PAMP" has been criticized on the grounds that most microbes, not only pathogens, express the molecules detected; the term microbe-associated molecular pattern, or MAMP, 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. Plant immunology frequently treats the terms "PAMP" and "MAMP" interchangeably, considering them 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 which damage it or modulate its immune response.