Inflammation

Question 1

Outline cytokines

Answer 1

Soluble messengers between cells:
• Examples: Interleukins (ILs),Interferons (INFs), Tumour necrosis factors (TNFs), Growth factors (GFs), Colony-stimulating factors, chemokines (chemotactic cytokines)
• Work together- pleiotropism (diff effects on diff cells), redundancy (more than one has same effect), synergism, antagonism
• Peoduced by activated immune cells, epithelium, stromal cells
• Involved in inflammation:

• Induction Phase
- Pro-inflammatory cytokines (TNF-α, IL-6, IL-1β)- local effects and long range- liver, fever
- Interferons (INFα, INFβ)- induces by viral infection and prevent viral replication, activate DC, macrophages, NK, induce chemokines
• Resolution Phase
- Anti-inflammatory cytokines (TGFβ (repair), IL-10)- inhibit synthesis of pro inflammatory cytokines

Question 2

Outline chemokines

Answer 2

• Large family of small polypeptides (9-15kDa)
• Naming- cysteine-cysteine ligand CCL/CXCL1,2,3etc. Can have more than one name (CCL2=MCP-1). Chemokine receptors identified by numbers but don’t correlate CCR1,2,3
• Redundancies- eg neutrophils attracted by CXCR8, CXCL12
• Produced mainly by activated macrophages and DCs, only during inflammatory episodes
• Cellular distribution of receptors dictates type of leukocyte recruited into tissues- influences selective recruitment together with cellular adhesion molecules

Question 3

What is Complement?

Answer 3

Set of 30 or more different proteins which act in an enzymic amplification cascade system to generate a number of active Complement components involved in several aspects of the immune response

Question 4

Outline the Complement activation pathways

Answer 4

Classical:
C1 complex recognises antigen and antibody

Lectin:
Mannose-binding lectin MBL binds bacterial cell walls

Alternative:
Direct recognition of microbial cell surfaces

Key event: cleaving of C3-> C3a+C3b by C3 convertase (C4b2a/C3bBb)
C3b helps form C5 convertases

• Importance of C3&5 cleavage:

• mast cell degranulation (activation- Increases vascular permeability)- C3a, C4a, C5a
• neutrophil chemotaxis- C5a
• microbe opsonization- C3b, C4b
• cell lysis- C5b-C9 (MAC)
• RBC clearance of immune complexes- C3b (to liver and spleen)

Question 5

Outline the formation of MAC

Answer 5

1. C5b binds C6 and C7
2. C5b67 complexes bind to membrane via C7
3. C8 binds to complex and inserts into membrane
4. C9 molecules (10-16) bind to complex and polymerise to form a pore

Question 6

What’s involved in acute inflammation? Outline it

Answer 6

Complement
Adhesion molecules
Chemoattractants
Mast cells
Neutrophils

• Vascular phase- blood flow, vascular permeability, adhesive endothelium
• Cellular phase- leukocytes accumulate in local vasculature and migrate into infected tissue
• Removal of infectious agent

Question 7

Outline tissue mast cells

Answer 7

• Release mediators
• Respond to C3a, C5a, PAMPs, DAMPs
• Contain granules with preformed histamine
• Degranulation- release of these vasoactive amines, cytokines, chemotactic factors-> vasodilation
• Formation of lipid mediators- use phospholipase A2 to break down arachidonic acid into either leukotrienes (lipoxygenase pathway) or prostaglandins (cyclo-oxygenase pathway)
—> attract neutrophils and increase inflammation

Question 8

Outline tissue macrophages

Answer 8

• Role in acute inflammation
• Release:
- cytokines- initiate cytokine cascade (TNF-α, IL-6, IL-1β)
- chemokines- recruit more cells
- inflammatory mediators (lipid derived)- leukotrienes and prostaglandins
• Antigen presentation to T cells

Question 9

What do proinflammatory cytokines do?

Answer 9

Act on the liver to increase secretion of acute phase proteins (APPs)
-C3
-C-reactive protein (activates Complement
-fibrinogen (coagulation)
—> affect site of inflammation but also brain- no appetite during fever

Question 10

Outline extravasation

Answer 10

Neutrophils entering tissue from blood:
• P-selection is first receptor to be expressed on endothelium during inflammation
• Neutrophils with P-selection ligand (PSGL-1) will slow and interact
• Integrins then expressed on endothelium (ICAM-1, VCAM-1) induced by TNFα, IL-1, LPSs
• Neutrophils have core receptors (LFA-1 for ICAM and VLA for VCAM)- bind and stop neutrophils
• Diapedesis- neutrophil releases enzymes to dissolve junction between cells
• Neutrophils then enter tissue and follow chemokine/complement gradient

Question 11

Outline resolution phase

Answer 11

End point of acute inflammation
• Neutrophils enter tissue and begin phagocytosis and remove extra mediators
• Monocytes enter some hours later and differentiate into macrophages
• Chemokines promote further recruitment and clearance of infection
• Neutrophils undergo apoptosis and signal to be ingested by macrophages (efferocytosis). They also release phosphatidylserine-> triggers Mφ release of anti-inflammatory cytokines (IL-10, TGFβ)-> macrophages switch from pro-inflammatory to proresolving

Question 12

Which cellular infiltrates are in acute and chronic inflammation?

Answer 12

Mainly neutrophils in acute

Monocytes, macrophages and lymphocytes in chronic

Question 13

What causes chronic inflammation?

Answer 13

• Persistent injury/infection- TB, ulcer, viruses
• Prolonged exposure to toxic agent- pulmonary silicosis (silica in lung)
• Autoimmune disease- RA, MS