Lecture 9: Acute Inflammation: Cytokines And Cells Flashcards
What are cytokines produced by
Inflammatory cells and other cells during inflammation
What are cytokines?
Low-molecular weight proteins
List some examples of cytokines
TNF tumour necrosis factor
ILs the 35 different species of interleukins
IFNs interferons
What are chemokines
More than 50 species of chemoattractants
What do chemokines do?
Enable cells to locate to sites of injury and infection
What does TNF do?
Up regulates inflammation
When were the effects of TNF first inferred?
A century ago
Who were they inferred by
New York physician William Colely
What did Coley do?
Inoculated cancer patients with bacterial preparations
What happens to those cancer patients?
Tumour regression occurre
Which bacterial products were injected into mice?
Tuberculosis vaccine BCG and
Bacterial lipopolisaccharide LPS
What did these two bacterial products elicit in mice?
The production of a protein (TNF) which caused some tumours to become necrotic
What was this protein called?
Tumour necrosis factor
What is cachexia
The loss of stores of fat and muscle protein
To whom does cachexia occur?
To people with cancer and other chronic inflammatory conditions
How was cachexia in cancer / chronic inflammatory patients shown experimentally?
Mice infected with sleeping sickness parasite trypanosoma. It was found the mediator of cachexia is cachectin (same as TNF)
Why does TNF have limited use as an anti cancer agent?
Induces unpleasant flu like symptoms
Not effective against most common cancer types (from carcinogens)
What do cytokines like TNF and IL-1 induce at low concentrations?
Protein synthesis in target cells
What does protein synthesis in target cells lead to?
Vasodilation
Vasopermeability
Expression of endothelial cell adhesion molecules that recruit inflammatory cells
Name some endothelial cell adhesion molecules which are expressed when protein synthesis is induced in target cells, by cytokines
Selections, ICAM-1, VCAM-1
What do cytokines (such as TNF and IL-1) induce at high concentrations?
Fever
Coagulation cascade
Progressive development of scar tissue, fibrosis
Cachexia (over time)
Which leukocyte comprises the major cell population in acute inflammation?
Neutrophils
What is the role of the neutrophil?
To exist in an armed and dangerous state
What do neutrophils possess that contain molecules used in defence and signalling?
Granules
Name the three type of polymorphonuclear leukocytes
Neutrophil
Eosinophil
Mast cell / basophil
What are polymorphonuclear leukocytes also known as?
Granulocytes
Neutrophils comprise _% of leukocytes?
75%
What is the function of a neutrophil
Phagocytosis of tissue debris, micrboes
What harmful effects can neutrophils cause?
Tissue injury
What percentage of leukocytes do eosinophils make up?
1%
What are the function of eosinophils
Anti-parasitic (helminth)
What harmful effects can eosinophils cause?
Allergies
What percentage of leukocytes do mast cell/basophils make up?
<1%
What is the function of a basophil
Regulation of inflammation
What harmful effects can basophils produce on a cell?
Allergy
What does injury without infection generate?
Sterile inflammation
How are cellular responses initiated in sterile inflammation
They are initiated by molecules released from dead cells and damaged ECM
When there is also infection, what do microbes release?
PAMPs- pathogen associated molecular patterns
Name the 5 different types of damage associated molecular patterns which initiate cellular responses
ECM fragments
Intracellular proteins
DNA and RNA
ATP
Crystals
Give an example of an ECM fragment acts as a DAMP
Hyaluronan
Give an example of intracellular proteins that acts as a DAMP
HMGB1 from chromatin
Give an example of crystals which act as a DAMP
MSU (monosodium urate), Cholesterol
What receptor do ECM fragments like hyaluronan target?
Toll like receptors, TLRs
What sort of receptors do intracellular proteins like HMGB1 from chromatin target?
TLRs, RAGE (receptors of advanced glycation end products)
What kind of receptors do DNA and RNA target?
TLRs
What sort of receptors does ATP target?
P2X7Rs purinergic
What sort of receptors do crystals like MSU and cholesterol target?
Components of inflammasomes
What does signalling from TLRs and P2X7Rs activate?
Inflammasomes
What is activated that cleaves Pro-IL-1β into active IL-1β
Caspase -1
Which intracellular cytokine is released when cells lyse?
IL-1α
What do IL-1α induce endothelial cells to become?
Adhesive for leukocytes
Recruitment of circulating neutrophils requires what?
Adherence to the endothelium
What is marination?
Adherence to the endothelium
What does blood flow rate decrease with?
Loss of plasma and increased blood viscosity
Where do neutrophils in venules leave from?
The axial central stream
Where do neutrophils concentrate?
In the plasma tic zone
What is the plasmatic zone?
The boundary layer adjacent to the endothelium
How do neutrophils loosely contact the endothelium?
By rolling along the surface
What are neutrophil rolling mediated by?
P and E- selectins on stimulated endothelial cells
Glycoproteins with sugar residues (sialyl-Lewis-x) on neutrophils
How long does maximal mediation take to occur?
Within a few minutes
What is sialyl-Lewis-x?
A sugar residue (attached to glycoproteins on neutrophils, help mediate neutrophil rolling along endothelium
When does firm adhesion with flattening occur?
Inflammatory mediators up-regulate intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 on endothelial cells and the leukocyte function-associated antigen-1 on neutrophils
What is ICAM-1
Intercellular adhesion molecule-1
What is VCAM-1
Vascular cell adhesion molecule-1
What is LFA-1
Leukocyte function-associated antigen-1 which is an integrin
What happens in neutrophil transmigration
Adherent neutrophils extrude pseudopodia and push their way between or through endothelial cells
What protease do neutrophils release when transmigration?
Elastase
What is the purpose of elastase release when neutrophils are transmigration?
It digests the basement membrane so neutrophils can enter the extravasulcar tissue
Leukocytes move directionally in response to what?
Chemical signals
What kind of chemical signals elicit leukocyte directional response?
Chemotaxis (or necrotaxis if sterile inflammation)
What kind of chemo signals guide the cells in circulation?
Chemotactic signals
Give an example of chemotactic signals
Chemokine IL-8 on endothelial cells
What do chemotactic cells in the tissues include?
Proteins - released from broken cells
Chemokines, leukotriene and complement products C3a and C5a
Bacterial products
What kind of proteins are released from broken cells which act as a chemotactic signal
Mitochondrial proteins with an N-formulated methione (like N-formylated peptides, NFPs)
What are mT proteins like N-formylated peptides recognised by?
Formylated peptide receptor-1 (FPR-1)
What effects does the recognition of NFPs override?
The effects of Chemokines in the circulation
What is LTB4?
Leukotriene B4
What are the three coordinated processes which phagocytes undergo to remove damaged tissues and destroy microbes
Phagocytosis
Degranulation
Respiratory burst
What makes damaged cells or bacterial get phagocytosed more readily?
When cells or bacterial are coated with molecules called opsonins
Give some examples of opsonins
Immunoglobulins and C3b
How do phagocytes attach to opsonised micro-organisms
They use receptors for immunoglobulins and for C3b
What is the receptor for C3b?
The Mac-1 integrin
Which receptors bind bacteria directly? (Non opsonic phagocytosis)
Receptors for LPS (lipopolisaccharide)
What do pseudopodia extend around
Particles
Where are particles internalised during phagocytosis?
In membrane bound vesicles called phagosomes
What is the fluid in the phagosome
A sample of the extracellular medium, non toxic
What do phagosomes fuse with?
Lysosomes
What do lysosomes contain?
Hydrolytic enzymes
What do phagosomes and lysosomes form?
Phagocytic vacuoles or phagolysosomes
Why is this step termed degranulation
The lysosomal granules disappear from the cytoplasm
What is the pH of the fluid in phagocytic vacuoles?
Acidified. PH 4.5-5.0
What then, do phagocytes undergo?
A respiratory burst
How does this respiratory burst occur
Electron transport complex NADPH oxidase assembles on phagocytic vacuole membranes and reduces oxygen to superoxide
The superoxide may depolarise the value which induces a K+ influx that releases cationic proteases from anionic sulphated proteoglycans
The super oxide reduces to hydrogen peroxide by superoxide dismutase . Myeloperoxidase catalyses reaction of hydrogen peroxide with chloride to generate hypochlorous acid.
Reactive proteases and oxidants degrade cell debris and kill microorganisms
List the processes of leukocyte function in order
Opsonisation, adhesion, phagocytosis, degranulation, respiratory burst
What reduces oxygen to superoxide?
NADPH oxidase, from the electron transport complex (NOX2)
What are the two things the superoxide could do
- Depolarise the vacuole which induces a K+ influx
2. Be reduced to hydrogen peroxide by superoxide dismutase
What does K+ influx cause?
K+ releases cationic proteases like cathespin G, elastase from anionic sulphated proteoglycans
What does super oxide reduction to hydrogen peroxide affect?
Causes a reaction with chloride, catalysed by myeloperoxidase. This generates hypochlorous acid
List the outcomes acute inflammation can have on the body
Liquefactive necrosis
Systemic responses
Out of control inflammation
Processing of microbial molecules activating immunity
Repair with resolution
What is liquefactive necrosis also known as?
Suppuration
Infection with pus forming agents in solid tissues leads to what?
The accumulation of dead neutrophils and tissue cells
What is pyogenic
Pus forming
What is pus
Dead neutrophils and tissue cells
Give the two kinds of lesions that may form as a result
Localised (like an abscess such as a boil) Or spreading (like cellulitis)
What are three different kinds of systemic responses?
Fever, acute phase response and leucytosis
What is fever caused by?
Pyrogens like TNF, IL-1 and PGE2
What are pyrogens produced by?
Peripheral macrophages, and in the brain
What do pyrogens affect?
Hypothalamic thermoregulation
What is the acute phase response stimulated by?
IL-6 , when the liver produces many plasma proteins like coagulation factors and opsonins
What is leukocytosis
An increase in the number of leukocytes due to the release of leukocytes from the bone marrow
What are the two cases of out of control inflammation?
Systemic inflammatory response syndrome (SIRS, occurs with sterile injury) and sepsis (occurs with infection)
What are SIRS and sepsis induced by?
Release and circulation of DAMPs (NFPs and mT DNA), proinflammatory cytokines (TNF, IL-1)
Increase in pro-coagulants to anti-coagulant ratio
Activation if complement
Generation of reactive oxygen species
What results from induced SIRS or sepsis?
Widespread vascular dilation and permeability»_space; blood volume loss
Formation of thrombi in small blood vessels (disseminated intravascular coagulation DIC)
Depletion of clotting factors»_space; uncontrolled bleeding
Inadequate organ perfusion, ischaemia
Multi organ failure (of which morality is greater than 30%)
What is the inflammatory response turned off by?
Eliminating stimulators effects of dead cell and bacterial products
Negative feedback loops involving anti-inflammatory cytokines and lipid mediators and protease inhibitors
During inflammation the life time of neutrophils is extend by what?
Cytokines, growth factors and activated endothelium
During phagocytosis, the C3b receptor Mac-1 induces what?
Respiratory burst
What does respiratory burst generate?
Reactive oxidative species
What do ROS directly activate?
Caspases
What follows after caspase activation?
Neutrophil apoptosis
Failure to resolve acute inflammation leads to what?
Chronic inflammation
