Complement System

Question 1

Complement system overview:

Answer 1

Involves complement proteins labeled C1-9

Involves a series of reactions that happen along the membrane of a pathogenic cell — ultimately resulting in the cells death

Complement system can work on its own to generate inflammation and destroy pathogens (via the lectin and alternative pathways)

Also forms a key way in which antibodies can generate inflammation and lead to pathogen destruction (via the classical pathway)

Question 2

3 Complement pathway triggers:

Answer 2

Classical

Lectin

Alternative

Question 3

Classical pathway

Answer 3

activated by antibody-antigen complexes binding to C1 (called complement fixation)

Question 4

Lectin Pathway

Answer 4

Activated when mannose-binding protein binds to monnose on pathogens

Which then binds to MBL-associated serum protease (MASP)

MASP activates the pathway

Question 5

Alternative pathway:

Answer 5

C3 is spontaneously activated along cell membranes

In membranes of normal cells there are proteins that deactivate the pathway

In pathogens without the regulatory process the pathway remains activated

Question 6

Outcomes of the Complement Pathway:

Answer 6

1) C3b is created – which acts as an opsonin for phagocytosis of the attached cell
2) C5a is created – which attracts cells to the site of inflammation (neutrophils, monocytes and eosinophils)
3) C3a, C4a, C5a – activate mast cell degranulation
4) C3a and C5a – activate eosinophil degranulation

5) Membrane Attack Complex (C5b678) – is a large molecule that can enter cell membranes and creates a hole that leads to cell lysis
- -> C9 molecule can be added to this complex to make the hole in the cell membrane larger