Lecture 29 - Innate Immunity 2 Flashcards
What is the Danger-Stranger model?
It is not just foreign antigen that is recognised by PRRs, but also Danger signals:
DAMPs: Danger associated molecular patterns
+ DAMP receptors
DAMPs in their normal location (e.g. DNA) will not trigger the pathways, but when it is found in the cytosol. This indicates that severe damage has occurred and that the best things now for the cell is death.
What are PAMPs?
Give examples
Pathogen associated molecular patterns
Highly conserved molecules or molecular patterns in microbes
Enable discrimination between self and foreign
Examples: • viral DNA • viral RNA • Peptidoglycan • Flagellin • LPS • Mannan • Protozoan DNA
What are the various cellular sites of pathogen encounter?
Which types of pathogens can be encountered in each?
Cell membrane • Bacteria • Viruses • Parasites • Worms
Phagosomes / endosomes
• Bacteria
• Viruses
• Parasites
Cytosol
• Bacteria
• Viruses
What are Toll-like receptors?
What encodes them?
Where are they located?
Pattern recognition receptors; specifically recognise PAMPs
Germline encoded receptors (i.e. there is no rearrangement and education, as with BCRs and TCRs)
Location:
• Always associated with membranes
Which TLRs are found in the following locations:
• Cell membrane
• Phago-/endosome?
Cell membrane: • TLR 4 • TLR 2 • TLR 5 • TLR 11
Phago-/endosomes:
• TLR 3
• TLR 7
• TLR 9
Which interleukin is produced due to TLR 4 engagement?
IL-6
What leads to the release of IL-6?
What does it bring about?
Release: • Engagment of TLR or RLR • Transduction pathway • Activation of NFκB • Transcription of IL-6
Function:
• Induction of acute phase, CRP production in liver
• Th17 differentiation
• B cell differentiation
• Increased co-stimulatory molecule expression
• Systemic inflammatory responses (fever, fatigue)
Which cytokine is produced with TLR 3 stimulation?
IFN-α / IFN-β
i.e. type I IFN
What leads to the release of IFN-α / IFN-β?
- Engagement of TLR3 or RLRs
- Transduction pathways
- Activation of NFκB (TLR3) or other stuff (RLRs)
- Gene transcription of IFN-α / IFN-β
Which pathogens can be encountered in the cytosol?
Viruses Some bacteria (Listeria)
What are RLRs?
What do they recognise?
Describe signalling through RLRs
RIG-I-like receptors
Recognise viral RNA present in cytosol
Function:
- Viral RNA in cytosol binds to RIG-1
- RIG-1 associates with MAVS on mitochondrion
- MAVS dimerise
- MAVS activate transduction pathway
- Activation of NFκB and TRAF
- NFκB turns on gene transcription of type I interferon and IL-6
What are NLRs?
Where are they often found?
What is their structure?
NOD-like receptors
aka Inflammasomes
Structure:
• NLRs associate with additional molecules to form large protein complexes in the cytosol
• Including pro-caspase-1
What are inflammasomes?
Where are they found?
A multi protein oligomer
Containing:
• Caspases
• ASC
• NLRs
Responsible for activation of inflammatory processes and pyroptosis
Found in the cytosol
What are the ligands for the following receptors: • TLR 3 • TLR 4 • TLR 5 • TLR 9 • TLR 11 • RIG-I • MDA5 • NLRC4?
TLR 3: dsRNA
TLR 4: LPS
TLR 5: Flagellin
TLR 9: CpG-DNA
TLR 11: Flagellin
RIG-I: dsRNA
MDA5: dsRNA
NLRC4: Flagellin
What are the sources of the ligands of the following PRRs: • TLR 3 • TLR 4 • TLR 5 • TLR 9 • TLR 11 • RIG-I • MDA5 • NLRC4?
TLR 3: Viruses, Bacteria (dsRNA)
TLR 4: Bacteria (LPS)
TLR 5: Bacteria (Flagellin)
TLR 9: Virus, bacteria (CpG-DNA)
TLR 11: Bacteria (Flagellin)
RIG-I: Virus, Bacteria (dsRNA)
MDA5: Virus, Bacteria (dsRNA)
NLRC4: Bacteria (Flagellin)
Which sorts of PRR are membrane bound, and which are cytosolic?
TLRs: membrane bound
RLRs & NLRs: cytosolic
What are the effects of engagement of the following receptors: • TLR 3 • TLR 4 • TLR 5 • TLR 9 • TLR 11 • RIG-I • MDA5 • NLRC4?
TLR 3: IFN-α / IFN-β
TLR 4: IL-6
TLR 5: IL-6
TLR 9: IL-12, IFN-α / IFN-β
TLR 11: IL-6
RIG-I: IL-6, IFN-α / IFN-β
MDA5: IL-6, IFN-α / IFN-β
NLRC4: IL-1β, IL-18, IL-33
Which TLRs detect flagellin?
TLR 5
TLR 11
NLRC4
PRR engagement leading to IFN-α / IFN-β release indicates…
Viral infection
IL-6 generally upregulated in response to bacteria
Which sorts of pathogen do NLRs generally recognise?
Bacteria that have escaped the endosome
For example: Salmonella, Listeria
Why are the receptors called Toll-‘like’ receptors?
Because the ones found in humans are ‘like’ the ones found in Drosophila, which is the animal in which they were initially studied.
What is MyD88?
Molecule required for the transduction of TLR activation
All TLR signals with it, apart from TLR3
Which receptor activates both MyD88 and TRIF?
TLR 4
Which cytokine is good at stimulating the acute phase response?
IL-6
What is CRP?
Discuss its importance
C-reactive protein
Useful marker for the acute phase response
Only bacterial infectious elicit the acute phase response and thus CRP
In a clinical setting, CRP levels in serum can be used to determine whether a common cold is due to a viral or bacterial infection, and thus inform prudent use of antibiotics.
Which are the Type 1 IFNs, and which are type 2?
Type 1: IFN-α / IFN-β
Type 2: IFN-gamma
What do IFN-α and IFN-β bring about?
Induction of ‘antiviral state’:
Transcription of around 2000 genes
- Inhibition of viral protein synthesis
- Degradation of viral RNA
- Inhibition of virus assembly
- Increased co-stimulatory molecule expression
What is observed in mice that lack the IFN-α/IFN-β system?
Unable to control viruses
Herpes becomes lethal
Which organelle are RLRs always associated with?
Mitochondria
Describe what happens when there is damage to mitochondria
- Damage to mitochondria
- Mitochondrial DNA leaks into cytosol
- Activation of cytosolic receptors
- Induction of apoptosis
Describe inflammasome signalling
- Binding of complex with danger signals / Flagellin:NLRC interaction
- Activation of caspase 1
- Caspase 1 cleavage of pro-cytokines:
• Pro-IL-1β → bioactive IL-1β
• Pro-IL-18 → IL-18
Which receptors are very good are recognising DAMPs?
Inflammasomes
Ways in which they do this:
• Monitoring of the membrane
• Crystal recognition (e.g. Gout)
Which TLR brings about a response w/o the use of MyD88?
TLR3
What are the two different outcomes of TLR signalling?
- IL-6 transcription
• Acute phase response in liver → CRP → Fever, Fatigue
• Th17 induction
• B cell differentiation
• Increased co-stimulatory molecule expression
2. Type I IFN transcription • Induction of Anti-viral state • Upregulation of proteasome subunits • Degradation of viral RNA • Inhibition of viral protein synthesis • Inhibition of viral assembly • Increased co-stimulatory molecule expression
Compare the signal transduction in TLRs resulting in the following:
• IL-6
• IFNα/β
IL-6: • Engagement of TLR at surface • Association of MyD88 • MyD88 activates a phosphorylation cascade • Activation of NFκB • Transcription of IL-6
IFNα/β • Engagement of TLR (3) • Association of adaptor molecules • Signalling cascade • Activation of NFκB • Transcription of IFNα/β
