IMI2

Question 1

5 stages of lectin complement pathway

Answer 1

1. Mannose binding lectins and ficolins bind to bacterial surface
2. MBLs opsonised by MASPs
3. MASPs cleave C4 into C4a and C4b
4. Promotion of C2 cleavage into C2a and C2b
5. C3 convertase formed by C2a and C4b

Question 2

3 stages of classical complement pathway

Answer 2

1. Antibody-antigen complexes bound to by C1 to activate it
2. C1 triggers cleavage of C2 into C2a & C2b and C4 into C4a & C4b
3. C2a and C4b form C3 convertase

Question 3

2 stages of alternative complement pathway

Answer 3

1. C3 spontaneously cleaves into C3a and C3b

2. C3b reacts with factor B, factor D and properdin to form C3 convertase