pattern recognition receptors Flashcards
what are PRRs?
innate immune cells that detect pathogens via pathogen associated molecular patterns (PAMPs)
diverse range of molecules - lipids, polysaccharides, nucleic acids
not species specific
damage associates molecular patterns (DAMPs)
host cell molecules or structures not normally visible to the immune system but can be released from damaged or dying cells
micro-organism associated molecular patterns (MAMPs)
molecules or structures that are specific for microbes and viruses not normally visible on host cells
overlaps with PAMPs but include structures on commensal microbes
how are commensal micro-organisms in the gut and lung tolerated by the immune system
a complex relationship exists but they are required for normal immune function
changes in the micro biome can have adverse effects on the immune system
what are PAMPs recognised by and where are the expressed
recognised by PRRs
expressed on all innate immune cells and in some cases T, B and endothelial cells
classes of PRRs
membrane receptors = toll like, c type lectin
cytoplasmic receptors = nod like, DNA and RNA
Lipopolysaccharide (LPS)
a component of gram -ve bacterial cell calls, structure vaires between bacterial strain species, very potent PAMP
what does loss of toll like receptor 4 protect mice from
endotoxic shock
how does sepsis occur
from systemic, bacterial or fungal infection
excessive production of pro-inflammatory cytokines
massive inflammation leads to organ failure and death
mortality driven by over activation of the immune system rather than invading the pathogen
injection of bacterial endotoxin can give rise to a similar condition where cytokine driven inflammation results in endotoxic shock and death
toll like receptor function
pathogen killing = phagocytosis, production of reactive O2 species
recruitment of immune cells to site of infection and activation of other immune cells = production of chemokines and proinflam cytokines
TLRs in infection
play important roles in activation host response to pathogens
IRAK4/Myd88 muts = increased susceptibility to bacterial infection
in childhood there is a 30-40% mortality rate even when treated with antibiotics
TLRs in cancer
TLR activation occurs during the killing of cancer cells by the immune cells, this process is subverted by cancer cells during tumour development
what does aberrant activation of TLRs contribute to
development of auto immune disorder - see notes to learn specific cases
Toll like receptors
part of the IL-1 receptor family, no of TLR genes is species dependent, diff TLRs in diff locations, diff TLRs recognise diff PAMPs
why is the correct localisation important for TLRs
must be in the position to bind to see the pathogen, must be in a location that minimises exposure to endogenous host ligands
what is the leucine rich repeat for in TLRs
for ligand binding
what does the activation of TIR domain allow
signalling
what is the toll/ interleukin 1 receptor homology domain for and where is it found
it mediates the interaction between TLRs and adaptor proteins - this is crucial to initiate down stream signalling
found in TLRs and IL-1 receptors present in TLR/IL-1 adaptor proteins
how do TLRs activate signalling
via Myd88 of Trif dependent signalling
all TLRs except TLR3 couple via
what is the name of the 2nd adaptor promotes TLR2 TLR4 and Myd88 recruitment
what do TLR3 and 4 couple via
Myd88
Mal
Tram
why is IRAK4 essential for myd88 dependent signalling
irak4 is essential - KO of irak4 in mice blocks responses to LPS and increases infection
- inactivating muts in humans results in invasive bacterial infection
how is IRAK recruited to myd88 for myd88 dependent signalling
via interactions between the death domain of myd88 and IRAK4
what does IRAK4 recruit and phosphorylate for myd88 dependent signalling and what does it activate
IRAK1 and 2 which activates the kinase of IRAK1
in myd88 dependent signalling what does IRAK2 lack
lacks catalytic residues in the kinase active site and is therefore inactive
what can kinase dead mutants of IRAK1 do in myd88 dependent signalling and what does this suggest
they can mediate signalling suggesting that a major role of IRAK 1 and 2 is as scaffolding proteins
what do IRAK1 and 2 promote and how
IRAK 1 and 2 promote formation of a ubiquitin signalling complex
IRAK1 interacts with traf6 which adds a lys63 polyubiquitin chain to traf6 and IRAK1
traf6 has e3 ligase activity, physiological e3 ligase in TLR in signalling is not clear
lys63 chains are added to UBc13/UVE1A
linear polyubiquitin is then added by the lubac complex
what is Tak1
it plays a key role in TLR signalling
in MAPK kinase kinase family
Tak1 complex = Tak1 + subunits Tab1,2 and 3
Tab1 is a pseudophosphatase and is involved in regulating Tak1 activity in the cell
Tab2 and 3 have cterminal NFZ domains that bind specifically to lys63 polyubiquitin
NFkB activation (what is the pathway made of)
the pathway is made up of NFkB transcription factor IkB inhibitory proteins and IkB kinases
activated downstream of multiple stimuli
multiple activation mechanisms including canonical activation pathways in TLR signalling
before activation NFkB dimers are bound to IkB which localises them to the cytoplasm
on activation the IKK complex phosphorylates IkB which promotes IkB degradation via the proteasome then released NFkB dimer can translocate to the nucleus
Trif dependent signalling
both myd88 and trif can activate the same signalling pathways
for tlr4 deletion both myd88 and trif are required to block tlr4 mediated MAPK and NFkB activation
trif can activate TbK1 via Traf3
TbK1 activates transcription factor IRF3
IR£ stimulates production of INFbeta
once secreted INFbeta can restimulate cells to induce transcription of interferon genes which induces antiviral state in cells
how are cells responses to pathogens context dependent
moth pathogens dont express one single PAMP - several PRRs are likely to be activate upon immune cells encountering pathogens - this allows the response to be tailored to the pathogen
the correct response ti PRR activation is determined by the stage of inflamm reaction
the effects of stimulating PRRs can be modified by other signals that the cell recieves
how does dectin 1 modify the TLR response during infection by fungal pathogens
co-stimulation of TLR2 and dectin1 modifies the cytokine profile produced relative to the TLR stimulation
dectin 1 modifies the output of the TLR stimulation
what are the 3 types of cytoplasmic PRRs
nod like, RNA and DNA
nod like receptors
have a central nod domain and leucine rich repeats at c terminal
the n terminal varies
NOD1 recognises gamma-d-glutamyl-meso-diaminopinelic acid present on gram -ve bacteria and some gram +ve
nod2 recognises cystolic muramyl dipeptide which is found in bacterial peptidoglycan
ligands bind to LKR, nod multimers and recruit RIP2 via CARD-CARD domain interactions
polyubiquitination recruits TAK! and IRK complexes which activates signalling and cytokine production
IL-1 production of inflammosomes
activates gene expression
stimulates endothelial ells to express adhesion molecules and chemokines such as MCP1
stimulates cytokine production
promotes Th17 cell polarisation
with TNF and IL-6 it activates acute phase response
what are the 3 components of NLRP3 containing inflammosome
NLRP3 - sensor for activation
muts result in auto-inflammatory condition
ASC (apoptosis-associated spec-like protein containing CARD1) - adaptor allows recruitment of caspase 1 to NLRP3
Caspase 1 - made as an inactive proenzyme, contains a cysteine protease domain and a CARD domain
RNA receptor RIG-1 and Mda 5
RIG like helicase family
in the cytoplasm of most cells
MDA5 recognises long double stranded DNA
RIG-1 recognises single stranded RNA with 5’ triphosphate group and short dsRNA regions
