complement cascade (unit 1) Flashcards
why is it referred to as cascade
one protein will activate the other, so on and so forth
zymogens
inactive enzymes until cleaved/activated
effects of complement activation
killing of bacteria (membrane attack complex)
complement fixation: C3b works as opsonin to be engulfed
regulation of inflammation and immune response
clears immune complexes
enhances antibody response
split producs
a –> smaller and is an attractant (INFLAMMATION)
b –> larger (biologically active
exception split product
C2 –> a and b are switched
peptide fragment for vasodilation
C2b, C3a, and C5a
peptide fragment for chemotaxis
C5a
peptide fragment for anaphylaxis
C3a, C4a, and C5a
peptide fragment that works as opsonin
C3b
pathways similarities
all pathways lead to activation of C3
classical pathway (last pathway activated)
binding of antigen (REQUIRES ANTIBODIES) to FC region trigger C1q
REQUIRES 2 IgG or 1IgM
C1 cleaves C2 and C4
Forms C4b2a (C3 convertase)
cleaves C3 and forms C4b2a3b (C5 convertase)
cleaves C5 to form C5b6789
MEMBRANE ATTACK COMPLEX
alternative pathway
ALWAYS ON
activated by contact with foreign surface
factor b (zymogen) cleaved by factor d to form C3bB
C3bBb (C3 convertase) cleaves C3
Properdin binds C3 convertase on surface
forms C3bBb3b (C5 convertase)
then same MAC
lectin pathway
REQUIRES MANNOSE BINDING LECTIN
when lectin binds to mannose on surface of cell acts as C1 and cleaves C4 C2
then same as Classical pathway
alternative pathway amplification
Factor D on C3bBb (C3 convertase)
classical pathway amplification
C3 convertase
