Complement System Flashcards
Complement system is defense against
mainly bacteria
proteins for CS are synthesized in
the liver
many CS proteins are present as
inactive form in blood and other fluids and require activation for effect
activation pathways
classical(CP), Alternative(AP) and Terminal(TP)
a deficiency in the terminal pathway components leads to
susceptibility to Neisseria Sp infections
Membrane attack complex (MAC)=
in terminal/common C5b, C6, C7, C8, C9
activation of classical pathway leads to
convergence with terminal pathway
Activation of classical pathway starts with
IgG(2 Fc’s needed) or IgM(only 1 needed) complex binds to C1
Pentameric IgM=
5Fc-mu’s available to bind
C1 cleaves
C4 to C4a and C4b and C2 to C2a and C2b
C1 Cleavage forms
C4b2a= C3 convertase(CP)
C3 convertase cleaves
C3 to C3a and C3b and forms C4b2a3b (C5 convertase)
C5 convertase cleaves
C5a and C5b
C5b binding to
the microbe surface initiations formation of MAC of the Terminal pathway
Alternative pathway is activated by
spontaneously generated C3b deposits on activating surface
Factor B binds to
C3b
Factor B is cleaved by
Factor D and forms teh C3bBb
C3bBbis also called
C3 convertase
Poperdin extends
the half life of C3bBb by 6-10 fold
C3bBb cleaves
C3 to C3a and C3b and forms C3bBb3b (C5 convertase)
C3bBb3b cleaves
C5 to C5a and C5b
classical proteins
C1,2,3,4,5
Terminal proteins
C5b, 6,7,8,9
Alternative proteins
C3b,3,5 Factor B, D Properdin
role of C3b
opsonin mediated phagocytosis and elimination of immune complexes
role of C3a, 4a, 5a
degranulation of mast cells and basophils
Role of C5a
chemotaxis of neutrophils
role of MAC
Osmotic lysis of bacteria
role of regulatory complement proteins
protect autologous cells from complement mediated damage
C1 INH, C1 esterase inhibitor binds
C1 to prevent spontaneous activation
C4bp(binding protein binds
the fluid phase of C4b preventing attachment to cells and formation of C3 convertase
Factor H binds
to C3b in fluid phase preventing the binding to the microbe
Factor H competitively binds
C3b which leads to dissociation of C3bBb if it has formed.
Decay accelerating Factor (DAF)
binds to membrane bound C3b or C4b blocking formation of C3 convertase or dissociating C3 convertases that formed.
Anaphylatoxin inhibitor binds
C3a, C4a and C5a and inhibits binding to Cr3a/4a. C45a
Factor I cleaves
C4b and C3b to inactive forms in presence of cofactors
S- protein, CD59, and Homolgous restriction factor (HRF
inihibit formation of MAC on autologous cells.
CR1
receptor on phagocytes and RBC that binds to C3b or C4b and is part of the opsonin/immune complex elimination
CR2
receptor on B cells that binds C3bi- is a mode of epstein barr virus infection
C3a/4a binds
C3a and C4a and is found on mast cells and basophils, it leads to degranulation and histamine release (CR5a binds C5a on mast cells and basophils for the same effect
CR5a on neutrophils binds
C5a which is used as a chemotaxis for neutrophils
Ch50 complement test
measures overall complement activity and whether or not it is low for c3 and c4
Tissue damage activates
the intrinsic coagulation system and activates factor XII
factor XII(a) activates
zymogen prekallikrein to kallikrein
role of kallikrein
- -cleave kininogen to kininogena and brady kinin
- -cleaves C5 to C5a and C5b because C5a is chemotactic for neutrophils
bradykinin increases
vascular permeability which is critical in inflammation
Killikrein is inactivated by
C1INH