3-4: Acute Inflammation

Question 1

State the “Big Picture” steps of inflammation

Answer 1

Recognise -> Recruit -> Vascular Changes -> Inf. Cells enter tissues -> Repair

Question 2

What is the general timeframe and extent of an acute inflammation response (and what are the common causes)?

Answer 2

• Minutes to hours after injury/infection
• Often self-limiting
• Pathogens
• Tissue necrosis
• Physical (e.g. splinters)
• Chemicals
• Hypersensitivity (e.g. cold air)

Question 3

Describe three macroscopic features of an inflamed area?

Answer 3

Purulent (pus containing dead/dying neutrophils)

Fibrinous (exudate contains fibriongen, which leads to fibrin -> polymerisation -> scarring if not broken down)

Pseudomembranous (appearance of a false membrane)

Question 4

Name the characteristic vascular and systemic effects of acute inflammation

Answer 4

Vascular:
- Red, Wheal (permeability), Flare (axon reflex)
- Loss of function

Systemic:
- Fever
- Loss of appetite
- Lethary
- Leukocytosis and APPs

Question 5

What recognise offending agents and what are the two groups that they recognise?

Answer 5

PRRs (pattern recognition receptors) recongise PAMPs (Pathogen Associated Molecular Patterns)

and DAMPs (Damage associated molecular patterns)

Question 6

Give some examples of PAMPs and DAMPs

Answer 6

PAMPs
- highly conserved structures in viruses and bacteria, e.g., LPS

DAMPs
- intracellular or ECM proteins
- uric acid
- K+
- ROS
- HSP70/90

Question 7

Name 7 families of PRRs

Answer 7

Pentraxin
Toll-Like Receptors (TLRs)
NOD-Like Receptors (NLRs)
Mannose-binding Lectin
C-type lectin receptors (CLRs)
RIG-I-like receptors
AIM-2 like receptors

Question 8

Where are pentraxins found and what do they recognise? (and give 1 example)

Answer 8

Pentraxins (e.g. C-Reactive Protein) are Extracellular, and recognise Phosphocholines in microbial membranes

Question 9

Where are TLRs found and what do they recongise?

Answer 9

Plasma membrane (recognise LPS, flagellin, HSPs, ECM components, oxLDL)

Endosome membrane (recognise Microbial RNA/DNA)

Location is tailored to best respond to ligand

Question 10

How many TLRs are there?

Answer 10

13 (1-10 are found in humans), 3/7/8/9 are found in the endosome, rest in PM

Question 11

Describe the general structure and function of a TLR

Answer 11

Leucine-rich repeats (LRRs) form the extracellular domain - a horseshoe shaped ligand binding domain (often requiring an accessory molecule, e.g. MD2 links LPS to LRR)

Toll/IL-1 intracellular domain which initiates downstream signalling

TLRs dimerise upon ligand binding

Question 12

Summarise the TLR signalling pathway(s)

Answer 12

1. Upon dimerisation, MYD88 or TRIF is recruited (depending on TLR)
2. -» activate MAPKs/JNK/p38
3. -» activate NFkB or IRFs
4. -» activated TFs translocate to nucleus and activate transcription (NFkB -> Pro-Inf Cytokines; IRFs -> INFa and INFß)

Question 13

Describe the NLR group

Answer 13

A major family of CYTOSOLIC PRRs consisting of 4 families - NLR A/B/C/P

B, C and P function in the innate immune system, with P including NLRP3 (-> Inflammasome -> Casp1)

Question 14

Describe the general structure of NLRs

Answer 14

• A C-terminal Leu-rich domain
• A central Nucleotide-binding Oligomerisation Domain (NOD)
• An N-terminal effector domain (depends on family, nlrP = Pyrin)

Question 15

Describe the first part of the processthat leads to NLRP3 activation

Answer 15

Signal 1 = Priming

-> NFkB activated by TLRs
-> NF-kB activates transcription of NLRP3, pro-IL-1ß and pro-IL-8

Question 16

Describe the second part of the response to NLRP3 activation

Answer 16

Signal 2 = Activation!

NLRP3 oligomerises -> INFLAMMOSOME -> recruits and oligomerises ASC -> Casp1 activation

Casp1 then cleaves (pro-)IL-1ß, IL-8 and Gasdermin-D, activating them all

Active Gasdermin-D forms pores in cell membrane, allowing others to leave and sometimes induce pyroptosis

Question 17

Name some common signals that can act as Activators for NLRP3 (and comment on the diversity thereof)

Answer 17

Fatty Acids, Ceramides, Uric Acid, ß-amyloids, Cholesterol

It is unclear exactly how NLRP3 can respond to so many - possibly an integration signal?

Also, unclear why evolution selected NLRP3 (read more for essay)

Question 18

What diseases are associated with NLRP3?

Answer 18

Mutations in NLRP3 -> recurrent inflammation (due to excessive Casp1 activation), leading to Cryopyrin-associated periodic syndromes/CAPS

This contributes to Alzheimer’s, Parkinsons, Atherosclerosis, Type II, Multiple Sclerosis

Potentially a drug target?

Question 19

What are the main vascular changes seen in Acute Inflammation?

Answer 19

1. Vasodilation + increase in blood flow
2. Increase in endothelium permeability to allow leukocytes + plasma proteins to enter tissues

Question 20

What are the main two vasodilators of VSM in acute inflammation?

Answer 20

Nitric Oxide (NO) and Histamine

Question 21

Describe the pressure changes that cause extravasation of leukocytes into tissues during acute inflammation

Answer 21

• Endothelial cells contract, allowing exudate to leak through (containing Edema, then neutrophils (6-24h), then monocytes (24-48h)
• Vasodilation -> Increased flow -> Increased HYDROSTATIC PRESSURE
• Osmotic pressure decreases due to proteins leaking out into tissues
• Overall, MORE PRESSURE OUT, forcing leukocytes into tissues (extravasation)

Question 22

Define the difference between Exudate and Transudate (which is Edema, and which is pus?)

Answer 22

Exudate = high [protein] and cellular debris, associated with inflammation

Transudate = low [protein] and no cell debris

Edema can be either, PUS is an inflammatory exudate

Question 23

State the order of steps in leukocyte vasation + migration

Answer 23

Capture, Rolling, Arrest, ADHESION (Cascade), Crawling, Migration

Question 24

Name all the components that might be found in Exudate during inflammation

Answer 24

• Edema
• Leukocytes (Neutrophils 6-24h and Monocytes 24-48h)
• Erythrocytes
• Proteins, 50g/L [CRP, Complement, Immunoglobulins and Fibrinogen]

Question 25

Name the 5 (mentioned) Endothelial molecules involved in Leukocyte adhesion, and the Leukocyte molecule they bind to

Answer 25

1. P-selectin (P-s glycoprotein ligand-1, PSGL1) 2. E-selectin (E-s ligand-1, ESL1) 3. GlyCam1/CD34 (L-selectin) 4. ICAM1/2 (Integrins, LFA1) 5. VCAM1 (Integrins, VLA4)

Question 26

Describe the steps of the Adhesion cascade

Answer 26

1. Macrophages that have detected pathogens secrete cytokines (e.g. TNF, IL1) to upregulate P/E/L-selectins and their ligands 2. Loose attachment between selectins and their ligands (capture + rolling) 3. Chemokines switch on leukocyte integrins, TNF/IL1 induce expression of integrin LIGANDS on endothelium 4. Adhesion between leukocyte integrins + adhesion molecules (ICAM1/2 and VCAM1) Note: ICAM1/2 also play roles in arrest and transmigration

Question 27

[If time, make FCs from Supplementary Info on Inflammatory Cells)

Answer 27

Okay (thumbs up emoji)

Question 28

Name the drug that prevents pain crises in sickle-cell disease, and how it functions

Answer 28

Crizanlizumab It is a monoclonal antibody that binds to P-selectin and prevents binding to its ligand PSGL1, thus reducing vaso-occlusion and sickle-cell crisis

Question 29

Which types of cells carry out phagocytosis?

Answer 29

Neutrophils and Macrophages

Question 30

Name and describe the three groups of local hormones (autacoids) that are VASOACTIVE in acute inflammation

Answer 30

1. Histamine and Serotonin (preformed + stored for FAST release, both induce vasodilation and endothelial gaps) 2. Kinins e.g. Bradykinin (increases prostaglandin and NO production -> indirect vasodilation and PAIN) 3. Eicosanoids e.g. PGs, TXs, Lipoxins, LTs (NOT preformed, on demand, various functions)

Question 31

Describe the pathway(s) that activates the Eicosanoids

Answer 31

Cell Damage -> Phosphorylation of Phospholipase A (PLA) -> Activation of Arachidonate: -> Cyclooxygenase -> Prostaglandins -> Lipoxygenase -> Leukotrienes -> Lipoxins

Question 32

Describe what Platelet Activating Factor does and how it is activated

Answer 32

It is a more potent vasodilator than histamine (also a bronchoconstrictor and chemotaxin) Prodced by platelets, basophils, masts, neutrophils, macrophages AND endothelial cells; Like eicosanoids, it is activated downstream of Phospholipase A, but it is activated by Lyso-glyceryl-phosphorylcholine instead of Arachidonate

Question 33

Name some key groups of cytokines (plus examples) and what cells are the main manufacturers of them?

Answer 33

Interleukins (IL1, IL10) Chemokines (IL8, MCP1) Interferons (INFa/ß,y) Plus TNFa Many cell types manufacture these, but especially Macrophages

Question 34

What are the effects of IL-1ß and TNFa?

Answer 34

Upregulation of endothelial adhesion molecules, Secretion of other cytokines, Systemic effects (due to upregulating APPs) IL1ß also causes Fever

Question 35

What are the effects of IL6, IL8 and CXCL8?

Answer 35

IL6 = Systemic Effects (Fever, Leukocytosis, upregulates APPs) IL8 and CXCL8 (plus other chemokines) = Recruits Leukocytes

Question 36

Describe two specific local effects of IL-1ß and TNFa (besides Adhesion and Leukocyte Activation)

Answer 36

Increased Procoagulent activity; Increased Proliferation of Fibroblasts and Collagen Synthesis (REPAIR)

Question 37

What causes the upregulation of Acute Phase Proteins?

Answer 37

Interleukins, e.g. IL1, Il6, TNFa

Question 38

Name 5 Acute Phase Proteins that are upregulated by pro-inflammatory interleukins, and state their effects

Answer 38

1. Fibrinogen (Coagulation) 2. Mannose-binding lectin (a PRR for Mannose) 3. Complement (Complement Cascade) 4. Serum amyloid (Leukocyte recruitment) 5. C-Reactive Protein (a pentraxin PRR that acts as an opsonin to enhance phagocytosis)