2a: Complement System

Question 1

Alternative pathway is activated by and starts with what factor?

Answer 1

Activated by microbe surface molecules and starts with C3 (specifically C3b)

Question 2

Mannose-Binding Lectin Pathway is activated by and starts with what factor?

Answer 2

Activated by mannose residues on microbes and starts with C4

Usually fungal/bacteria

Question 3

Classical Pathway (ADAPTIVE IMMUNITY SYSTEM) is activated by and starts with what factor?

Answer 3

Activated by antibody binding to antigen and starts with C1

Question 4

Which complement is an opsonin?

Answer 4

C3b

Question 5

If there’s a C4 deficiency, what pathways are inhibited/unaffected?

Answer 5

Inhibited: Classical and MBL

Unaffected: Alternative

Question 6

If there’s a C2 deficiency, what pathways are inhibited/unaffected?

Answer 6

Inhibited: Classical and MBL

Unaffected: Alternative

Question 7

If there’s a C3 deficiency, what pathways are inhibited/unaffected?

Answer 7

Inhibited (all 3): Alternative, MBL, and Classical

Question 8

How are our cells protected from complement lysis? (4 enzymes)

Answer 8

MCP - inactivates C3b
DAF/CD55 - speeds up destruction of C3bBb
CD 59 - topple MAC before MAC punches holes in our cells
C1 INH: Inhibits C1

Question 9

Hereditary Angioedema is a deficiency of?

Answer 9

C1 INH (C1 inhibitor)

Question 10

Paroxysmal Nocturnal Hemoglobinuria is a deficiency of?

Answer 10

CD59, CD55/DAF

Question 11

Neisseria infections are a deficiency of?

Answer 11

MAC Proteins

Question 12

Biological functions of the Complement System (4)

Answer 12

1. Lysis - C5-C9
2. Opsonization - C3b
3. Activation of inflammatory response/extravasation: C5a, C3a, C4a (chemotactic agents)
4. Clearance of Immune Complexes: C3b
   Ag-Ab complex