Complement Pathway Flashcards
3 Complement Pathways
Classical
Lectin
Alternative
3 Actions of Complement Pathways
Recruits inflammatory cells
Opsonizes pathogens
Kills pathogens
Opsonization
Increasing phagocytotic ability
Classical Pathway Activation (2 long)
C1, first prot in complement pathway, has sub w/ heads that recognize Fc on IgG and M (NOT A&E)
Requires multiple Igs crosslinked and bound to Ag to bind heads on C1/crosslinking can activate protease subs leading to complement cascade
C3 Convertase (2)
Convergence point for all 3 pathways
Cleaves C3 into C3a and C3b
C3b
Binds surface of bacterium and is recognized by CR1 on macrophages to act as opsonin and encourage phagocytosis
C9 Complex
Binds surface of bacterium and creates a water pore, screwing up homeostasis of bacterium and killing it
C3-5a
Anaphylatoxins - potent inducers of inflammation by inducing permeability of endothelial cells & immune response
Lectin Binding Pathway Activation
Mannose-binding lectin and ficolins are almost identical to C1, with heads that bind to carbs on bacterial surface to activate protease subs
Alternative Complement Pathway (2)
Avoids needing Abs or correct surface carbs, instead C3 molecules just undergo spontaneous hydrolysis to form active C3 convertase
Self Protection from Alternative Complement Pathway
Own cells have things which degrade complement pathway products, like a lot have CR1 which degrades C3b when it binds - basically they have defenses against complements that bacteria don’t
CR2
Allows B cells to interact w/ C3d and augment its response
Complementary Phagocytosis Inducement (2)
CR1 on mac binds C3b coating on bacterium, but not phagocytosed until C5a also binds to mac
Removal of Immune Complexes (4)
IC in circulation
C3b binds to IC
CR1 on RBC binds to C3b
RBC reaches liver where macrophage better able to bind Fc on IC, so it takes IC and breaks it down
