Inflammation Flashcards
How do many cells recognise the presence of danger
By expressing Pattern Recognition Receptors (PRRs) which recognise PAMPs and DAMPs
Give 5 facts about PAMPs
Shared by classes of organisms
Essential for survival of the pathogen
Highly conserved
Absent from the vertebrate host
Allow the innate system to distinguish between self and non-self
What are PAMPs usually apart of in the bacteria’s anatomy
Essential components of the bacterial cell wall or cell membrane (eg peptidoglycan)
Name a PAMP for gram positive and gram negative bacteria
Gram positive: lipoteichoic acid
Gram negative: LPS (lipopolysacchride)
Are PAMPs shared between gram positive and negative bacteria?
Some are (lipoproteins) but some are specific to gram positive (lipoteichoic acid) or gram negative (LPS)
What differentiates bacteria genome from the host DNA
Unmethylated CpG - mammals have a lower frequency of CpG dinucleotide which are misty methylated
Define PRR
Germline encoded molecules that monitor the internal and/or external environment of the cell for PAMPs and DAMPs
true or false
All pattern recognition receptors are found at the plasma membrane
False
They can be located at the plasma membrane, in endosomes, or in the cytosol
Name a soluble PRR
CRP
Give three functions of pattern recognition receptors
Stimulate ingestion of microbes by phagocytosis
Act as chemotactic receptors and guide cells to sites of infection
Produce effector molecules that assist both the innate and adaptive response
What was the first family of PRRs to be identified
Describe them
TLRs (Toll Like Receptors)
Transmembrane proteins that act as sensors of microbes in extracellular spaces
When are TLRs functional
As dimers (either homo- or heterodimers)
Each dimer pair is specific for a different set of pathogen products
How many functional TLR genes do humans have
10
What happens upon recognition of a TLR’s specific ligand
TLR induces signalling cascades that lead to activation of innate immune responses that combat infection
Which TLRs are located on the cell-service
TLRs 1,2,4,5,6,10
Which TLRs are located in endosomes?
What do these recognise
TLRs 3,7,8,9
Microbial Nucleic acid including dsRNA, ssRNA and DNA
What do TLRs do when activated
Recruit signalling adaptor molecules - importantly MyD88 and TRIF - and initiate downstream signalling events (activation of NF-κB, AP-1, and IRF 3 and 7) leading to release of products (eg inflammatory cytokines, Type 1 interferons, chemokines)
What are the most important signalling adaptor molecules recruited by TLRs
MyD88
TRIF
Give an example of a host DAMP recognised by TLRs
High Mobility Group Box-1 (HMGB-1)
In general what do the following stimulate in TLRs:
a) bacterial products
b) viral products
a) pro-inflammatory response (NF-κB and AP-1)
b) anti-viral interferon response (IRFs)
Name three other major families of PRR (not TLRs)
What are each important in
C-type lectin receptors (CLR) - fungal infections
RIG-I-like receptors (RLR) - detection of viral RNA in the cytoplasm
Cytosolic NOD-like receptors (NLR) - cytosolic receptors which recognise both PAMPs and DAMPs
What do NOD1 and 2 do generally?
What does NOD2 detect
Recognise fragments of peptidoglycan from bacteria
Muramyl dipeptide
What releases NOD2
Why does it do this
What happens if NOD2 is mutated
Gut microbiota
NOD2 helps gut homeostasis
Mutations are associated with Crohn’s disease and IBS
True or false
The NLR NLRP3 is specific to only one molecule
False
It has a wide specificity recognising pieces of peptideoglycan, bacterial DNA, ATP, toxins, ds-RNA
What is the large cytosolic structure formed by NLRP3
The inflammasome
Name three disease is associated with the inflammasome
Atherosclerosis, gout, Type II diabetes
How does the inflammasome induce inflammation
Activating casp-1 which stimulates IL-1β
Why is casp 1 different to other caspases
It is involved with inflammation rather than apoptosis
What are DAMPs usually
Intracellular molecules that appear in the wrong location, often after necrosis
DAMPs are associated with sterile inflammation
Give some examples of DAMPs
Proteins from chromatin (HMGB-1)
Molecules eg ATP, DNA, RNA
Heat shock proteins
ECM components uncovered by tissue damage
Which molecule involved in atherosclerosis is recognised by TLR4/TLR6
Oxidised LDL
What Is the purpose of the acute inflammatory response
To dilute blood vessels
Increase permeability
Recruit cells
Why does the acute inflammatory response increase permeability of the vessel wall
To allow a protein rich fluid into the tissues
A fibrin web forms and complement and CRP are recruited
What do the granules in mast cells contain
How long does it take to release these
Histamine
Can be released in seconds
What do you mast cells synthesise
How long does this take
Prostaglandins and leukotrienes
This takes some time (slow reacting substance of anaphylaxis (SRS-A))
Mast cells have PRRs but how else can they be activated
By neurogenic information, responding to substance P released from nerve fibres
What do you macrophages do at the site of infection?
Phagocytose microbes and produce a range of cytokines
Overall the response induces:
Vasodilation, vascular permeability and activation of endothelium leading to recruitment of the acute inflammatory exudate
What produces endogenous pyrogens?
What type of molecule are they
Macrophages
Cytokines
What do endogenous pyrogens from macrophages do (give a local and systemic effect)
They have local effects on the vascular endothelium and systemic effects such as acute phase protein response (IL-6)
What are the four steps of recruitment of leucocytes to the site of infection
Rolling (weak tethering)
Tight adhesion
Diapedesis (extravasation)
Migration
What is the rolling step of recruitment to the site of infection
Thrombin and histamine rapidly induce P-selectin on endothelial cells
E-selectin appears 1-2 hours later
The selectins bind to glycoprotein ligands (Sialyl Lewis X) present on the neutrophil
Describe the affinity between selectin and the glycoprotein ligands on the neutrophil
These are low affinity interactions that break easily by the force of blood flow resulting in the rolling of cells along with the endothelium
Where is P-selectin released from
Weibel- Palade bodies (intracellular stores in endothelial cells
Which cytokines induce E-selectin release
Where are these cytokines derived from
IL-1 and TNF-α
Tissue macrophages
What are the names of the glycoprotein ligands present on neutrophils
Sialyl Lewis X
What does tight binding of neutrophils result from
Interaction between integrin family adhesion molecules (LFA-1) bonding to Ig super family molecules (ICAMs) on the endothelium
What are ICAMs
Intercellular Adhesion Molecules
Why is CXCL8 important in the tight adhesion step of recruitment of leukocytes to sites of infection
Initially interactions are weak but signalling through chemokine receptors (like CXCL8) causes a conformational change in LFA-1, resulting in a high binding affinity state
What are the following associated with
a) ILC1
b) ILC2
c) ILC3
a) IFNγ
b) asthma
c) IBS
Describe the diapedesis stage of leukocyte recruitment
leukocytes squeeze through the gaps between endothelial cells (extravasation) into the tissues.
This involves interactions between LFA-1 and CD31 on the endothelial cell. The neutrophil secretes enzymes (e.g. elastase) that degrade the basement membrane.
Describe the migration stage of leukocyte recruitment
neutrophil then follows a gradient of CXCL8 to the site of infection
How is the CXLC8 gradient used in leukocyte recruitment created
CXCL8 secreted by activated macrophages sticks to extracellular matrix in the tissues
Give a disease related to leukocyte recruitment
Leukocyte adhesion deficiency (LAD); a rare immunodeficiency caused by a defect in the recruitment of neutrophils. LAD1 is caused by a defect in CD18, the b-chain subunit of LFA-1.
It results in recurrent life-threatening bacterial infection in infants. An identical condition is seen in cattle BLAD (Bovine Leukocyte Adhesion Deficiency).
When are monocytes recruited to the site of inflammation cf. neutrophils
Monocytes are recruited later because the interaction involving endothelial adhesion molecule (VCAM-1), which binds to monocyte integrins (VLA-4, very late antigen-4) is upregulated more slowly (24 hours).
What stops local infections entering the blood
why might infection be able to spread
Blood clotting and local expression of TNF-a
if infection is widespread, as in severe burns where there is loss of skin, infection can spread. Endotoxins such as LPS can provoke widespread TNF-a release.
When does sepsis occur
when pathogens enter the blood stream. Macrophages in the liver and spleen secrete TNF-a into the circulation.
What can be the consequences of sepsis
can be catastrophic as the vasodilation and movement of fluid into the tissues, triggered in part by TNF-a, contributes to loss of blood pressure,
a state that can progress to septic shock and heart failure.
released TNF-a also triggers blood clotting in the small vessels throughout the body (disseminated intravascular coagulation).
Failure of major
organs can occur due to loss of normal blood
perfusion.
Massive consumption of clotting proteins leads to lack of clotting capacity in the blood and bleeding.
How does acute inflammation usually stop (3)
Many inflammatory mediators have short half-lives (neutrophils apoptose after few hours)
lipid mediator class–switch:
Instead of macrophages producing pro-inflammatory leukotrienes from arachidonic acid, the lipoxygenase system switches to producing anti-inflammatory lipoxin
switch to anti-inflammatory cytokines such as IL-10 and TGF-b
What triggers the switch to turn off inflammation
triggered by engulfment of apoptotic neutrophils by macrophages.
What is granulation tissue
what does this involve
After cell damage an attempt will be made to replace the dead tissue with healthy cells
essentially involves the recruitment of endothelial cells to form new blood vessels and fibroblasts to lay down extracellular matrix (ECM). The ECM is then remodelled to form strengthened scar tissue
Which cells are pivotal to controlling repair after inflammation
macrophages
Give 5 roles of macrophages in healing after inflammation
They phagocytose debris including RBCs, apoptotic neutrophils, dead organisms etc.
They produce reactive oxygen intermediates and nitric oxide to kill
microbes.
They recruit fibroblasts (FGF, fibroblast growth factor) which lay down new ECM
They recruit endothelial cells (VEGF) to form new blood vessels
They secrete metalloproteinases to allow remodelling of ECM
How are fibroblasts involved in repair and healing - recruitment and role
recruited to the site of injury by cytokines (FGF) produced by
macrophages.
They are induced to increase collagen synthesis and produce other ECM proteins eventually leading to the formation of a collagen scar.
How do vessels recently created by angiogenesis acquire endothelium
Endothelial cells break off from the basement membrane of pre-existing vessels, migrate to the site of injury and repair, proliferate and then differentiate to form a lumen and acquire supporting pericytes and smooth muscle to form the mature vessel.
What can result in chronic inflammation (4)
Injurious agent may be endogenous: e.g. stomach acid (peptic ulcer)
Injurious agent may be non-degradable: e.g. silica, dust particles
Injurious agent may evade host defences: e.g. tuberculosis
Host may attack self components (autoimmunity): e.g. rheumatoid arthritis
Which cells are important for chronic inflammation
what do they do
macrophages
Chronically activated macrophages accumulate releasing cytokines that stimulate proliferation of fibroblasts and collagen production- fibrosis
Use an example to demonstrate granuloma formation
Mycobacteria can resist killing by macrophages.
They are not eliminated by the immune response but ‘walled off’ from surrounding tissue.
The central core of macrophages is surrounded by T cells.
Macrophages may fuse to become multinucleate giant cells or appear as large epithelioid cells. The central core is often necrotic.
