Lecture 15

Question 1

What are the 5 signs of inflammation?

Answer 1

Heat (due to increased blood flow)
Redness (due to increased blood flow)
Swelling (due to an accumulation of fluid)
Pain (release of molecules that stimulate nerve endings)
Loss of function (multiple causes)

Question 2

What is the general process of inflammation?

Answer 2

Inflammation is a reaction of the circulation where serum proteins and leukocytes mover from the blood to extravascular tissues
It is regulated by vasoactive and chemotactic mediators
Vasodilation increases blood flow to the inflamed region
Increased microvasculature permeability leads to a loss of plasma proteins into the tissue
Increased expression of adhesion molecules on endothelial cells and release of chemotactic factors from the inflamed region lead facilitate the binding of leukocytes to vessel walls, extravasation and migration to the inflamed region
There is eventually a resolution to the inflammation

Question 3

What is the difference in cause of acute vs chronic inflammation?

Answer 3

Acute causes are often pathogens and injured tissues while chronic causes are more numerous including persistent inflammation due to non-degradable pathogens, viral infection, persistent foreign bodies or autoimmune reactions

Question 4

What is the difference in the cells involved in acute vs chronic inflammation

Answer 4

The cells involve in acute inflammation are typically neutrophils, basophils, eosinophils and mononuclear cells while those involved in chronic inflammation are mononuclear cells, lymphocytes and plasma cells and fibroblasts

Question 5

What is the difference in the primary mediators involved in acute vs chronic inflammation

Answer 5

In acute inflammation the mediators are vasoactive amines and eicosanoids while in chronic inflammation the mediators are inflammatory cytokines, growth factors, reactive oxygen species and hydrolytic enzymes

Question 6

What is the difference in onset of acute vs chronic inflammation

Answer 6

The onset of acute inflammation occurs within minutes or hours while the onset of chronic inflammation is delayed

Question 7

What is the difference in duration of acute vs chronic inflammation

Answer 7

The duration of acute inflammation is a few days while that of chronic inflammation can be many months or years

Question 8

What is the difference in outcomes of acute vs chronic inflammation

Answer 8

Acute inflammation typically results in either resolution, abscess or the formation of chronic inflammation while chronic inflammation itself with often result in tissue destruction, fibrosis or necrosis

Question 9

How are neutrophils involved in inflammation?

Answer 9

These are the first responders to inflamed tissues and contain secretory granules with pro-inflammatory proteins such as MPO, defensisn, lactoferrin, lysozyme and MMP9
These can eliminate microbes through both intracellular and extracellular mechanisms
These cells also require their numbers to be tightly regulated

Question 10

How are monocytes/macrophages involved in inflammation?

Answer 10

Monocytes are macrophage precursors which are released into the circulation
They often play an important homeostatic role
Monocytes mature into tissue macrophages where they will begin to perform immune surveillance activites such as phagocytosis, antigen presentation and immune suppression
They exhibit functional heterogeneity

Question 11

What is the temporal profile of white blood cells at a site of inflammation?

Answer 11

The neutrophils arrive first, they then undergo apoptosis with the macrophages arriving after the midpoint of this apoptotic phase

Question 12

What are the two phases of acute inflammation?

Answer 12

The inflammatory phase and the resolution phase

Question 13

What is the role of Hydrogen peroxide in white blood cell recruitment?

Answer 13

This is released by damaged cells and a gradient is established through the actions of Duox
This hydrogen peroxide is sensed by neutrophils through oxidation of cysteine residue causing phosphorylation of the tyrosine kinase Lyn causing them to migrate to the inflammatory site this leads to monoperoxidase activity from the neutrophil which consumes the wound derived hydrogen peroxide to produce the bactericidal hypocholorus acid

Question 14

How is neutrophil apoptosis as a driver of inflammation resolution?

Answer 14

Neutrophils have a short lifespan to limit their negative effect on host tissues
After contributing to pathogen clearance they undergo programmed cell death-apoptosis
This co-incides with arrival monocytes/macrophages of which phagocytosis neutrophil debris causes a phenotype switch in macrophages

Question 15

How is neutrophil life span controlled?

Answer 15

Life span depends on a balance between both pro and anti apoptotic stimuli
TNF, GM-CSF and hypoxia act to extend life-span while reactive oxygen species, annexin A1 and lactoferrin act to induce apoptosis
These signalling factors can have opposite effects on neutrophil life-span depending on their concentration

Question 16

How does macrophage clearance of apoptotic neutrophils occur?

Answer 16

Following the neutrophil apoptosis find me signals are released by the neutrophils including nucleotides, sphingosine 1-phosphate, lysophosphatidyl-choline
Macrophages detect gradients of these through receptors with purinergic G and protein coupled receptor, they then recognise the apoptotic neutrophils through ‘eat me’ signals like phosphatidylserine leading to phagocytosis and a phenotypic switch

Question 17

What occurs to macrophages after phagocytozing an apoptotic neutrophil?

Answer 17

This causes neutrophils to switch from a proinflammatory M1 macrophage to pro-resolving M2 macrophage which expresses molecules for antigen presentation and helps attract T and B lymphocytes, this switch is critical for the restoration of tissue homeostasis

Question 18

What are the mechanisms of internalization?

Answer 18

Reaching phagocytosis, sinking phagocytosis and triggered phagocytosis

Question 19

What is endocytosis?

Answer 19

This is an actin independent process of internalisation with multiple mechanisms including internalization via clatherin coated pits
This leads to the formation of endosomes which contain the internalised molecules and will fuse with lysosomes to facilitate digestion

Question 20

What is phagocytosis?

Answer 20

This is and actin dependent mechanism of internalising molecules used for larger targets (greater than .75 micrometers) than endocytosis and has many different mehcanisms like micropinocytosis

Question 21

What intracellular signalling occurs through phagocytosis?

Answer 21

Leukocytes acquire information about the target at various stages of phagocytosis with the initial detection occurring by cell-surface receptors to asses if it is a PAMP or DAMP
Degradation of the target exposes new ligands that are detected by intracellular receptors
The information collected by all of these signals is integrated to control the immune cell response through influencing target gene expression

Question 22

What is autophagy?

Answer 22

Engulfment of cytosolic content, where autophagosomes fuse with lysosomes for degradation of contents leading o recycling of organelles to amino acids, fatty acids etc to fuel catabolic and anabolic process ensuring cellular survival during starvation

Question 23

What is the inflammasome?

Answer 23

A intracellular multiprotein complex that mediates activation of caspase 1 (catalyzes processing of IL-1beta and IL-18)
It is found in macrophages, dendritic cells and epithelial cells and activated in response to intracellular DAMPs and PAMPs
Molecular composition of this is stimulation specific
It has been linked to IBD, gout, type 1 and 2 diabetes
Induces maturation and secretion of pro-inflammatory cytokines IL-1beta and IL-18 which have independent functions which include inducing pyroptotic death, inhibition of bacterial replication and activation of lipid metabolism

Question 24

What is the structure of inflammasome?

Answer 24

This is a multiprotein oligomer consisting of caspase 1, PYCARD, NALP and occasionally caspase 5 showing how this structure of composition is stimulus specific

Question 25

How does the inflammasome induce pyroptosis?

Answer 25

Pyroptosis is a form of poorly understood programmed cell death that requires caspase 1 activity it serves to eliminate infected immune cells allows the removal of intracellular replication niches
This apoptosis is immunologically silent as cytoplasmic contents packaged in apoptotic bodies