Complement System

Question 1

What are the 2 main functions of the complement system and which pathways are involved?

Answer 1

1. Generate inflammation + destroy pathogens on own
   - lectin + alternative pathways
2. Generates inflammation associated with antibodies
   - classical pathway

Question 2

What are the 3 pathways and what activates these pathways?

What complement protein do the pathways converge on?

Answer 2

Classical pathway
-antibody-antigen complexes bind to C1

Lectin pathway

• mannose binding proteins binds mannose on pathogens
• this then binds to MASP to activate pathway

Alternative pathway

• C3 spontaneously activated
• normal cells have proteins which can deactivate the pathway but pathogens don’t have the same regulatory process

C3

Question 3

What are the functions of the different components of the complement system?

Answer 3

C3b= acts as opsonin
C5b= attracts cells to site of inflammation
C3a/4a/5a= activate mast cell degranulation
C3a/C5a= activate eosinophil degranulation
Membrane Attack Complex= C5b/6/7/8 come together to come large MAC molecule which is able to punch hole in cell membrane an induce cell lysis