pattern-recognition receptors
Pattern recognition receptors (PRR) are a class of innate immune response-expressed proteins that respond to pathogen-associated molecular patterns (PAMP) and endogenous stress signals termed danger-associated molecular patterns (DAMP).
▼ adaptive : adaptor proteins : alarmins : CARD domain : CATERPILLER : collectin : complement receptors : damage-associated molecular patterns : DAMP : helicases : innate : LGP2 : lipid transferases : Mal : Mda5 : multicellular animals : MyD88 : NALP : NLR : NOD : PAMP : pathogen-associated molecular patterns : pattern recognition receptors : pentraxin : PGR : plant R : PRR : RIG-I : RNA helicases : SARM : SARM action : TIR : TLR : TLR-1 : TLR-3 : Toll-like receptors : TRAM : TRIF ▼
Adaptive immunity employs clonally distributed B and T lymphocytes that are coated by millions of lymphoid cell-surface receptors, which are generated by complex VDJ recombination rearrangements so as to specifically recognize an enormous variety of antigens (specificity and memory). Evolutionarily more ancient, the innate immune system relies on a much smaller number of receptors, called pattern recognition receptors (PRRs).
Multicellular animals employ pattern recognition receptors to recognize pathogen-associated molecular patterns (PAMPs) in order to detect pathogens. However, cellular stressors are another causative agent of cell and tissue damage. Cells recognize both stressors and their associated tissue damage via receptor-mediated detection of intracellular proteins ("alarmins") released by the lysed cells.
Pattern recognition receptors (PRR) are a class of innate immune response-expressed proteins that respond to pathogen-associated molecular patterns (PAMP) and endogenous stress signals termed danger-associated molecular patterns (DAMP). The evolutionarily more recent adaptive immune response employs diverse surface receptors that display decremental binding affinities for epitope stimuli.
Pattern recognition receptors (PRRs) include:
● Membrane-associated PRR
_____ ● Toll-like receptors (TLR) sense pathogen-associated or danger-associated molecular patterns extracellularly or in endosomes and receptors may link innate and adaptive immune responses (Drosophila signaling Fig).
● Cytoplasmic PRR of the CATERPILLER family (also known as NACHT–leucine-rich repeat (NLR) proteins):
_____ ● Nucleotide-binding oligomerization domain proteins (NODs) recognize intracellular MDP (muramyl dipeptide) and transduce signals via NF-κB and MAP kinase pathways through the serine/threonine kinase RIP2. The nucleotide-binding oligomerization domain binds nucleotide triphosphate. NODs signal via N-terminal caspase recruitment (CARD) domains to activate downstream gene induction events.
_____ ● Pyrin domain–containing proteins (NALPs) contain contain a nucleotide binding site (NBS) for nucleotide triphosphates plus C-terminal leucine-rich repeats (LRRs), which appear to act as a regulatory domain and may be involved in the recognition of microbial pathogens. NALPs appear to recognize endogenous or microbial molecules or stress responses and to form oligomers with caspase-1, which cleave IL-1 into its active form.
_____ ● RNA helicases – LGP2 acts as a dominant-negative inhibitor, and RIG-I and Mda5 activate antiviral signaling. These RNA Helicases recruit factors via twin N-terminal CARD domains, activate antiviral gene programs.
_____ ● plant R proteins that share structural and functional similarity with PRRs found in higher animals.
● Secreted PRR
_____ ● Complement receptors
_____ ● Collectins
_____ ● Pentraxin proteins, such as serum amyloid P component (SAP), acute-phase C-reactive protein (CRP), cytokine-modulated PTX3 . Pentraxins utilize calcium dependant ligand binding and display a distinctive flattened β-jellyroll structure comprising five monomers with radial symmetry that form a ring approximately 95Å across and 35Å deep.
_____ ● Lipid transferases
_____ ● Peptidoglycan recognition proteins (PGRs) are most critical for insect immunity, and are less well characterized in mammals.
PAMPs are small molecular sequences consistently found on pathogens that are recognized by Toll-like receptors (TLRs) and other pattern recognition receptors (PRRs). PAMPs include bacterial lipopolysaccharide "endotoxin" (LPS→TLR4), bacterial flagellin, lipoteichoic acid, lipoproteins and peptidoglycan (→TLR1,-2,-6), mannose residues, N-formylmethionine, fungal glucans, endogenous heat shock proteins, extracellular matrix molecules, and nucleic acid variants associated with viruses (vRNA→TLR3, unmethylated cytosin-guanosin dinucleotide (CpG islands)→TLR9, dsRNA) and bacteria (bacterial DNA, unmethylated cytosin-guanosin dinucleotide (CpG)→TLR9).
DAMPs – Effector cells of innate and adaptive immunity employ nonclassical pathways to secrete alarmins when they are activated by PAMPs or other alarmins. Endogenous alarmins and exogenous PAMPs therefore elicit similar responses, and can be considered subgroups of a larger set, the damage-associated molecular patterns (DAMPs).
Toll-like receptors (TLRs) appear to be one of the most ancient, conserved components of the immune system, and are the basic signaling receptors of the innate immune system. TLRs (TLR1-TLR11) show homology with the Drosophila Toll protein and the human interleukin-1 receptor family, and are transmembrane proteins that recognize extracellular or endosomal pathogen-associated molecular patterns. The TLR family is characterized by the presence of leucine-rich repeats, which mediate ligand binding, and the Toll/interleukin-1 receptor-like domain (TIR), which mediate interaction with intracellular signaling proteins. TLRs function as homo- and heterodimers with different ligand-binding specificity, and rely upon TIR co-receptors for effective ligand sensitivity. Thus, the specificity of Toll-like receptor signaling is due to adaptor proteins containing Toll–interleukin 1 receptor (TIR) domains. Five TIR adaptors display activating functions: MyD88, Mal, TRIF, TRAM, and SARM. The adaptor proteins activate intracellular molecules, including protein kinases (IRAK1, IRAK4, TBK1, and IKKi) that amplify the signal, ultimately inducting or suppressing genes that orchestrate the inflammatory response. Thousands of genes are thus activated by TLR signaling, making TLRs one of the most important gateways for gene modulation.
TLRs are activated by molecules associated with pathogens (PAMPs) or with injured host cells/tissue (DAMPs). Most identified TLR ligands are either conserved microbial products that signal the presence of an infection, or endogenous ligands resulting from other danger conditions. TLRs trigger signals evoking synthesis and secretion of cytokines and activation of host defenses through NF-κB, MAP kinases, and costimulatory molecules.
To avoid excessive inflammatory responses, TLR signalling must be tightly regulated. MAPK phosphatase 1 (MKP1) is a key negative regulator of Toll-like receptor (TLR)-induced inflammation in vivo. Phosphorylation of MAPK p38 — which is associated with the modulation of cytokine production — is considerably increased and prolonged in the absence of MKP1. [MKP1]
Table Toll-like Receptors
Toll-like receptor-1 (TLR-1) displays homology to the receptor for interleukin-1 (IL-1) by virtue of similar cytoplasmic portions.
Toll-like receptor–3 (TLR-3) responds to double-stranded (ds) RNA, which is a viral replication intermediary for many viruses. TLR-3 activation transduces its signal into an intracellular transduction pathway, leading to activation of JNK, p38 MAPK, and NF-κB.
NF-κBs, Nuclear Factor kappa Bs, are ubiquitous transcription factors involved in responses to cellular stressors such as cytokines, bacterial antigens, and viral antigens. Free NF-κB translocates to the nucleus where it binds to specific κB sequences in DNA, initiating transcription of related genes, including those for immunoreceptors, cytokines, and its own inhibitor, IκB. Inhibitor of kappa B (IκB, IkappaBalpha) inactivates NF-κB by sequestering NF-κB dimers within the cytoplasm. Physiological activities mediated by NF-κB include cellular proliferation, and inflammatory, immune, and cellular survival responses.
[] signaling pathways []
The specificity of Toll-like receptor signaling is due to adaptor proteins containing Toll–interleukin 1 receptor (TIR) domains. Five TIR adaptors display activating functions: MyD88, Mal, TRIF, TRAM, and SARM.
SARM is a negative regulator of TRIF-dependent Toll-like receptor signaling, which blocks gene induction 'downstream' of TRIF but not of MyD88. The association fo SARM with TRIF, and the 'knockdown' of endogenous SARM expression by interfering RNA leads to enhanced TRIF-dependent cytokine and chemokine induction.[r]
▲ adaptive ф adaptive : adaptor proteins § adaptor protein : alarmins : allograft rejection : CARD domain § CARD domains : CATERPILLER ~ cellular stress response ~ chemokine : collectin : complement receptors ф complement system ф costimulatory molecules ~ cytokines : damage-associated molecular patterns : DAMP : graft rejection ~ heat shock proteins : helicases ~ helicases : innate ф innate ф immune response ф inflammatory response : LGP2 : lipid transferases : Mal ♦ MAPKs ♦ MAP kinases : Mda5 : multicellular animals : MyD88 : NALP : § NF-κB : NLR : NOD : PAMP ф pathogens : pathogen-associated molecular patterns : pattern recognition receptors : pentraxin : PGR : plant R : PRR : RIG-I : RNA helicases : SARM : SARM action ♦ serine/threonine kinases ф signaling ф surface receptors : TIR : TLR : TLR-1 : TLR-3 : Toll-like receptors : TRAM : TRIF ф VDJ recombination ▲ф
Tables Complement Receptors Cytokines Fc receptors Immune Cytokines Immunoglobulins Interferons Scavenger Receptors Toll-like Receptors
▲ Top ▲
[pdf review]
See TOLLing away in Brazil. Mitchell JA, Fitzgerald KA, Coyle A, Silverman N, Cartwright N. [Free Full Text] Nat Immunol. 2006 Jul;7(7):675-9.
Toll, A New Piece in the Puzzle of Innate Immunity. Wright SD. [Free Full Text Article] J Exp Med. 1999 Feb 15;189(4):605-9.
tags [Immunology] [pattern recognition] [cytokine] [Toll-like receptor] [receptor] [PAMP] [DAMP]
▼ adaptive : adaptor proteins : alarmins : CARD domain : CATERPILLER : collectin : complement receptors : damage-associated molecular patterns : DAMP : helicases : innate : LGP2 : lipid transferases : Mal : Mda5 : multicellular animals : MyD88 : NALP : NLR : NOD : PAMP : pathogen-associated molecular patterns : pattern recognition receptors : pentraxin : PGR : plant R : PRR : RIG-I : RNA helicases : SARM : SARM action : TIR : TLR : TLR-1 : TLR-3 : Toll-like receptors : TRAM : TRIF ▼
Adaptive immunity employs clonally distributed B and T lymphocytes that are coated by millions of lymphoid cell-surface receptors, which are generated by complex VDJ recombination rearrangements so as to specifically recognize an enormous variety of antigens (specificity and memory). Evolutionarily more ancient, the innate immune system relies on a much smaller number of receptors, called pattern recognition receptors (PRRs).
Multicellular animals employ pattern recognition receptors to recognize pathogen-associated molecular patterns (PAMPs) in order to detect pathogens. However, cellular stressors are another causative agent of cell and tissue damage. Cells recognize both stressors and their associated tissue damage via receptor-mediated detection of intracellular proteins ("alarmins") released by the lysed cells.
Pattern recognition receptors (PRR) are a class of innate immune response-expressed proteins that respond to pathogen-associated molecular patterns (PAMP) and endogenous stress signals termed danger-associated molecular patterns (DAMP). The evolutionarily more recent adaptive immune response employs diverse surface receptors that display decremental binding affinities for epitope stimuli.
Pattern recognition receptors (PRRs) include:
● Membrane-associated PRR
_____ ● Toll-like receptors (TLR) sense pathogen-associated or danger-associated molecular patterns extracellularly or in endosomes and receptors may link innate and adaptive immune responses (Drosophila signaling Fig).
● Cytoplasmic PRR of the CATERPILLER family (also known as NACHT–leucine-rich repeat (NLR) proteins):
_____ ● Nucleotide-binding oligomerization domain proteins (NODs) recognize intracellular MDP (muramyl dipeptide) and transduce signals via NF-κB and MAP kinase pathways through the serine/threonine kinase RIP2. The nucleotide-binding oligomerization domain binds nucleotide triphosphate. NODs signal via N-terminal caspase recruitment (CARD) domains to activate downstream gene induction events.
_____ ● Pyrin domain–containing proteins (NALPs) contain contain a nucleotide binding site (NBS) for nucleotide triphosphates plus C-terminal leucine-rich repeats (LRRs), which appear to act as a regulatory domain and may be involved in the recognition of microbial pathogens. NALPs appear to recognize endogenous or microbial molecules or stress responses and to form oligomers with caspase-1, which cleave IL-1 into its active form.
_____ ● RNA helicases – LGP2 acts as a dominant-negative inhibitor, and RIG-I and Mda5 activate antiviral signaling. These RNA Helicases recruit factors via twin N-terminal CARD domains, activate antiviral gene programs.
_____ ● plant R proteins that share structural and functional similarity with PRRs found in higher animals.
● Secreted PRR
_____ ● Complement receptors
_____ ● Collectins
_____ ● Pentraxin proteins, such as serum amyloid P component (SAP), acute-phase C-reactive protein (CRP), cytokine-modulated PTX3 . Pentraxins utilize calcium dependant ligand binding and display a distinctive flattened β-jellyroll structure comprising five monomers with radial symmetry that form a ring approximately 95Å across and 35Å deep.
_____ ● Lipid transferases
_____ ● Peptidoglycan recognition proteins (PGRs) are most critical for insect immunity, and are less well characterized in mammals.
PAMPs are small molecular sequences consistently found on pathogens that are recognized by Toll-like receptors (TLRs) and other pattern recognition receptors (PRRs). PAMPs include bacterial lipopolysaccharide "endotoxin" (LPS→TLR4), bacterial flagellin, lipoteichoic acid, lipoproteins and peptidoglycan (→TLR1,-2,-6), mannose residues, N-formylmethionine, fungal glucans, endogenous heat shock proteins, extracellular matrix molecules, and nucleic acid variants associated with viruses (vRNA→TLR3, unmethylated cytosin-guanosin dinucleotide (CpG islands)→TLR9, dsRNA) and bacteria (bacterial DNA, unmethylated cytosin-guanosin dinucleotide (CpG)→TLR9).
DAMPs – Effector cells of innate and adaptive immunity employ nonclassical pathways to secrete alarmins when they are activated by PAMPs or other alarmins. Endogenous alarmins and exogenous PAMPs therefore elicit similar responses, and can be considered subgroups of a larger set, the damage-associated molecular patterns (DAMPs).
Toll-like receptors (TLRs) appear to be one of the most ancient, conserved components of the immune system, and are the basic signaling receptors of the innate immune system. TLRs (TLR1-TLR11) show homology with the Drosophila Toll protein and the human interleukin-1 receptor family, and are transmembrane proteins that recognize extracellular or endosomal pathogen-associated molecular patterns. The TLR family is characterized by the presence of leucine-rich repeats, which mediate ligand binding, and the Toll/interleukin-1 receptor-like domain (TIR), which mediate interaction with intracellular signaling proteins. TLRs function as homo- and heterodimers with different ligand-binding specificity, and rely upon TIR co-receptors for effective ligand sensitivity. Thus, the specificity of Toll-like receptor signaling is due to adaptor proteins containing Toll–interleukin 1 receptor (TIR) domains. Five TIR adaptors display activating functions: MyD88, Mal, TRIF, TRAM, and SARM. The adaptor proteins activate intracellular molecules, including protein kinases (IRAK1, IRAK4, TBK1, and IKKi) that amplify the signal, ultimately inducting or suppressing genes that orchestrate the inflammatory response. Thousands of genes are thus activated by TLR signaling, making TLRs one of the most important gateways for gene modulation.
TLRs are activated by molecules associated with pathogens (PAMPs) or with injured host cells/tissue (DAMPs). Most identified TLR ligands are either conserved microbial products that signal the presence of an infection, or endogenous ligands resulting from other danger conditions. TLRs trigger signals evoking synthesis and secretion of cytokines and activation of host defenses through NF-κB, MAP kinases, and costimulatory molecules.
To avoid excessive inflammatory responses, TLR signalling must be tightly regulated. MAPK phosphatase 1 (MKP1) is a key negative regulator of Toll-like receptor (TLR)-induced inflammation in vivo. Phosphorylation of MAPK p38 — which is associated with the modulation of cytokine production — is considerably increased and prolonged in the absence of MKP1. [MKP1]
Table Toll-like Receptors
Toll-like receptor-1 (TLR-1) displays homology to the receptor for interleukin-1 (IL-1) by virtue of similar cytoplasmic portions.
Toll-like receptor–3 (TLR-3) responds to double-stranded (ds) RNA, which is a viral replication intermediary for many viruses. TLR-3 activation transduces its signal into an intracellular transduction pathway, leading to activation of JNK, p38 MAPK, and NF-κB.
NF-κBs, Nuclear Factor kappa Bs, are ubiquitous transcription factors involved in responses to cellular stressors such as cytokines, bacterial antigens, and viral antigens. Free NF-κB translocates to the nucleus where it binds to specific κB sequences in DNA, initiating transcription of related genes, including those for immunoreceptors, cytokines, and its own inhibitor, IκB. Inhibitor of kappa B (IκB, IkappaBalpha) inactivates NF-κB by sequestering NF-κB dimers within the cytoplasm. Physiological activities mediated by NF-κB include cellular proliferation, and inflammatory, immune, and cellular survival responses.
[] signaling pathways []
The specificity of Toll-like receptor signaling is due to adaptor proteins containing Toll–interleukin 1 receptor (TIR) domains. Five TIR adaptors display activating functions: MyD88, Mal, TRIF, TRAM, and SARM.
SARM is a negative regulator of TRIF-dependent Toll-like receptor signaling, which blocks gene induction 'downstream' of TRIF but not of MyD88. The association fo SARM with TRIF, and the 'knockdown' of endogenous SARM expression by interfering RNA leads to enhanced TRIF-dependent cytokine and chemokine induction.[r]
▲ adaptive ф adaptive : adaptor proteins § adaptor protein : alarmins : allograft rejection : CARD domain § CARD domains : CATERPILLER ~ cellular stress response ~ chemokine : collectin : complement receptors ф complement system ф costimulatory molecules ~ cytokines : damage-associated molecular patterns : DAMP : graft rejection ~ heat shock proteins : helicases ~ helicases : innate ф innate ф immune response ф inflammatory response : LGP2 : lipid transferases : Mal ♦ MAPKs ♦ MAP kinases : Mda5 : multicellular animals : MyD88 : NALP : § NF-κB : NLR : NOD : PAMP ф pathogens : pathogen-associated molecular patterns : pattern recognition receptors : pentraxin : PGR : plant R : PRR : RIG-I : RNA helicases : SARM : SARM action ♦ serine/threonine kinases ф signaling ф surface receptors : TIR : TLR : TLR-1 : TLR-3 : Toll-like receptors : TRAM : TRIF ф VDJ recombination ▲ф
Tables Complement Receptors Cytokines Fc receptors Immune Cytokines Immunoglobulins Interferons Scavenger Receptors Toll-like Receptors
▲ Top ▲
[pdf review]
See TOLLing away in Brazil. Mitchell JA, Fitzgerald KA, Coyle A, Silverman N, Cartwright N. [Free Full Text] Nat Immunol. 2006 Jul;7(7):675-9.
Toll, A New Piece in the Puzzle of Innate Immunity. Wright SD. [Free Full Text Article] J Exp Med. 1999 Feb 15;189(4):605-9.
tags [Immunology] [pattern recognition] [cytokine] [Toll-like receptor] [receptor] [PAMP] [DAMP]
Labels: DAMP, danger-associated molecular patterns, innate, PAMP, pathogen-associated molecular patterns, pattern recognition receptors, PRR, Toll-like receptors