6: Complement Flashcards
Two other systems that the complement works in cooperation with
- Blood coagulation pathways
2. Kinin-kallikrein system
Alternative C3 and C5 convertases
C3 convertase: C3bBb
C5 convertase: C3bBbC3b
Three extra proteins in alternative pathway
Properdin, factor B, factor D
Factor B (Bb)
Active enzyme of C3 and C5 convertases
Factor D
Cleaves factor B when bound to C3b
Properdin
Stabilizes alternative C3 convertase on microbe surfaces
What protein in alternative pathway is most abundant in serum
C3
Classical and lectin C3 and C5 convertases
C3 convertase: C4bC2a
C5 convertase: C4bC2aC3b
Four proteins involved in classical pathway
C1, C2a, C4a, C4b
C1: describe structure
C1q + tetramer of C1r (2) + C1s (2)
C1 function
Initiates classical pathway by binding IgM or IgG on Ag
C1q function
Binds Fc portion of Ab with 6 identical subunit arms
C1r function
Cleaves C1s to activate it
C1s function
Cleaves C4 and C2
Most abundant classical pathway protein in serum
C4