🌞 Complement System

Question 1

What are the three major complement activation pathways?

Answer 1

1. Classical
2. Lectin
3. Alternative

Question 2

What triggers the classical complement pathway?

Answer 2

Ab binding

Question 3

What triggers the lectin pathway?

Answer 3

Mannose binding

Question 4

What triggers the alternative pathway?

Answer 4

Microbial surfaces

Question 5

What is the role of C3 convertase?

Answer 5

Cleaves C3 → C3a + C3b

Question 6

What is the function of C3a vs C3b?

Answer 6

C3a: inflamm mediator
- ↑ Vascular permeability
- Protein leakage
- Phagocyte recruitment

C3b: opsonin
- Binds microbial surfaces
- Opsonisation → recognised by CRs

Question 7

What is the membrane attack complex (MAC) and what does it do?

Answer 7

• Triggered by c5 activ
• Components: C5–C9
• Forms pore in bacterial membrane → disrupts PM integrity and proton gradient

Question 8

How does complement contribute to opsonisation?

Answer 8

Activation → C3b coats pathogen → bind CRs → enhances phag

Question 9

How does complement promote inflammation?

Answer 9

C3a = inflamm mediator → inc vasc perm + P leakage → recruit phags

Question 10

How does the complement system bridge innate and adaptive immunity?

Answer 10

Enhances phag → Ag processing → Ag pres on MHC on APCs → T cell activ

Inflamm mediator → inc vasc perm → enhance IC recruitment