Complement system

Question 1

Give a brief summary of the classical pathway of activation of the complement system.

Answer 1

C1q binds to a pathogen or antibody-antigen complex.
Cleavage of subsequent complement proteins occurs.
C3 convertase released

Question 2

Give a brief summary of the mannose-binding lectin pathway of activation of the complement system.

Answer 2

Mannose-binding lectin (protein produced in liver) binds to mannose (carbohydrate) on surface of pathogens.
MASP activated (protease).
MASP cleaves downstream complement proteins, C3 convertase produced.

Question 3

Give a brief summary of the alternative pathway of activation of the complement system.

Answer 3

Activated by a lipopolysaccharide on the surface of gram negative bacteria.
Results in hydrolysis of C3 to form C3b.
C3b combines with other factors to make C3 convertase.