Lecture 29 - Inflammasomes

Question 1

Outline the clinical features of acute inflammation

What underlies these features?

Answer 1

IL-1 → vascular changes:

• Increased blood flow
  
  • ⇒ calor
  • ⇒ rubor
• Increased vascular permeability
  
  • Extravasation ​⇒ tumor
  • Recruitment of inflammatory leukocytes and release of inflammatory mediators ​⇒ dolor
• Dolor + tumor ​⇒ Function laesia

Question 2

What is the term for a protein produced by leukocytes?

Answer 2

Interleukin

Question 3

Which interleukin is most important in the induction of acute inflammation?

Outline some of its actions

Answer 3

IL-1

Actions:

• Hypothalamus ⇒ fever
• BM ⇒ neutrophilia
• Activation of neutrophils
• Stimulation of fibroblasts
• Liver ⇒ release of acute phase proteins (CRP)
• Activation of B and T cells

Question 4

Describe the effect of IL-1 on the hypothamaus

Answer 4

• Hypothalamus:
  
  • ​Gland in the brain, responsible for regulating bodily functions

1. ​IL-1 binds IL-1R in the hypothalamus
2. Hypothalamus responds by increasing body temperature
   
   • ​​Stimulation of the thyroid
   • Increases muscle tone
3. Fever

Question 5

What is a very useful clinical marker of acute inflammation?

Answer 5

C-reactive protein (CRP)

• Released by the liver during acute inflammation in response to IL-1

Question 6

What are the two types of IL-1?

Answer 6

IL-1α and IL-1β

Question 7

Describe the process of IL-1β activation

What could be a reason for this process?

Answer 7

Inactive form:

• 32 kDa

Activate form:

• Cleavage of N terminus by Caspase-1
• 18 kDa

This process endows a level of control of generation of IL-1β, as it does engender considerable physiological effects that could potentially be fatal (haemodynamic shock)

Question 8

Describe the disease familial cold urticaria

Answer 8

• Tendency to develop local and systemic acute inflammation in response to cold
• Rare inherited disease
  
  • Mutation in cryopyrin
    
    • Cryo: cold; pyro: inflammation
    • Associated with ICE:
      
      • ​Interleukin-1-converting enzyme
      • aka Caspase 1
  • Mutation renders cryopyrin overactive
  • Cleavage and activation of IL-1 occurs in response to low level stimuli (such as cold)

Question 9

What is cryopyrin?

What is ICE?

Answer 9

Cryopyrin:

• An enzyme that is associated with ICE
  
  • ​When bound to ICE, ICE becomes active
• Mutated and overactive in Familial cold urticaria
• It is a NLR

ICE: IL-1-converting enzyme / Caspase 1

• Responsible for enzymatically cleaving and activating IL-1
• Requires binding of cryopyrin to be active

Question 10

Describe the structure of inflammasomes

Describe the formation and function of inflammasomes

Answer 10

Structure:

• Very large protein aggregate comprising:
  
  • Caspase 1 (ICE)
  • NLRs (eg cryopyrin)

Activation:

1. NLR stimultes by PAMP or DAMP
2. NLR binds, cleaves and activates caspase 1
3. Large aggregate forms - inflammasome
4. Inflammasome enzymatically cleaves pro-IL1β ⇒ IL-1β
   
   • ​​Now evidence that the inflammasome can be secreted as well, and circulate around the body
5. IL-1β brings about inflammation

Question 11

What is Gout?

Answer 11

• Consumption of purine rich foods
  
  • ​Red meat, offal (liver, kidneys)
• **Monosodium urate **formation exceeds capacity for renal clearance
• Urate acid precipitates into crystals
• Crystals are deposited in joints, damaging the cartilage

Pathogenesis:

1. Urate crystals form in macrophages and are deposited in joints
2. Urate crystals stimulate NLRP3
3. ​​NLRP3 cleaves and activates caspase 1
4. Caspase 1 cleaves and activates IL-1B
5. IL-1B brings about acute inflammation in the joint

Question 12

How is gout treated nowadays?

Answer 12

Anakinra

• IL-1 receptor antagonist
• IL-1 has been shown to be the major causative agent of inflammation in the joints of individuals with gout

Question 13

Why is anakinra contraindicated by neutropaenia?

Answer 13

IL-1 is an important component of acute inflammation, which is important in controlling infection etc.

If this is removed (by anakinra) in indiviauls who are already suffering from decreased innate immunity, there could be significant ramifications

Question 14

How are inflammasomes named?

Answer 14

Inflammasomes are named based on the NLR

eg NLRP3 inflammasome

Question 15

List some things that can activate NLRPs

Answer 15

• Intracellular K⁺ concentration
  
  • When there is damage to the cell membrane, K⁺ is rapidly lost from the cytosol
  • This drop in K⁺ concentration is detected by NLRP3
• Viral RNA and DNA in cytosol
• Urate crystals

Question 16

Describe the two points at which IL-1β production is regulated

Answer 16

1. Pro-IL-1β production
   
   • ​​Triggered by TLR ligation by PAMP
   • ‘Priming signal’
2. Cleavage
   
   • ​​Triggered by inflammasome formation
   • Second signal

Question 17

Which molecules can be cleaved by the inflammasome?

How does regulation differ for these molecules?

Answer 17

• ​Pro-IL-1β
  
  • Large immunological and inflammatory consequences, thus the two points of regulation are important
  • Need both TLR and NLRP activation for production of IL-1β
• Pro-IL-18
  
  • NB pro-IL-18 is constitutively produced
  • IL-18 does not have as important inflammatory consequences, and thus it is less important to have the two points of regulation

Question 18

What pathology does Salmonella infection cause?

Answer 18

• Salmonella induced gastroenteritis
  
  • Bacteria infect and cause inflammation in the gastric epithelium
• Typhoid fever
  
  • Bacteria disseminate past the epithelial barrier
    
    • By infecting macrophages
  • Replication in liver, spleen, BM, gall bladder

Question 19

How does the immune system recognise and remove Salmonella?

Answer 19

1. Flagellin recognised by NLRC4
   
   • ​​Activation of caspase 1 in inflammasome
     
     • ​Production of IL-18
     • Pyroptosis
   • Macrophage dies, releasing bacteria into the extracellular space
   • Neutrophils, recruited by IL-18, can now access the bacteria for clearance
2. **IFN-γ **release
   
   • ​​IL-18 released in response to *Salmonella *recognition
   • IL-18 stimulates NK cells and CD8 T cells
   • These cells then release IFN-γ
   • Contributes to eliminating Salmonella from infected macrophages

Question 20

What are some of the features of metabolic syndrome?

Answer 20

• T2DM
• Fatty liver disease
• Central obesity
• Dyslipidaemia
• Hypertension
• CVD

Question 21

Describe the role of inflammasomes in Metabolic Syndrome

What does IL-1 do in MS?

Answer 21

Inflammasomes are involved in the pathogenesis of T2DM and atherosclerosis

• In adipose tissue:
  
  • Chronic inflammation in adipose tissue during MS
  • Production of Palmitate and Ceramides by adipose tissue
    
    • ​Metabolic products of fat
  • These form crystals, which are recognised by inflammasomes (NLRP3)
  • Triggers the generation of IL-1, and thus inflammation
  • Increased insulin resistance in adipose tissue and hepatocytes
• In pancreas
  
  • IAPP stimulates inflammasomes
  • IL-1 leads to death of beta islet cells
  • → T2DM
• In intima of arteries:
  
  • Fat taken up by macrophages in intima precipitate into crystals
  • Cholesterol crystals stimulate inflammasomes
  • Inflammation in the wall of the artery
  • Atherosclerosis
    
    • ​Occlusion of vessels
      
      • ​Turbulence
      • Endothelial damage
      • Thrombosis
    • Acute myocardial infarction

Role of IL-1:

• IL-1 increases insulin resistance
• Thus, inflammasomes contribute to the pathogenesis of T2DM in MS

Question 22

What are some current areas of research for therapeutics for metabolic syndrome?

Answer 22

Anakinra:

• IL-1 receptor antagonist
• Preliminary results indicate considerable effect on MS

Question 24

What is cryopryin?

Answer 24

Aka NLRP3