The Complement System Flashcards
System of plasma proteins which completes the process initiated by the interaction of antigen and antibody combination-lysis
complement system
Series of more than ________ that interact to enhance host defense reactions
more than 25 serum proteins
Most are _________ that are converted to active enzymes in a precise order
inactive enzyme precursors
It constitutes ________, heat labile that are present in normal human serum and all tissue fluids except urine and CSF
5% of normal serum protein
The key mediator in all pathways
C3
Sequential activation of complement components occurs via one of the three pathways
Classical Pathway
Alternative Pathway
Lectin Pathway
Initiated by formation of antigen-antibody complex
Classical pathway
Initiated by foreign cell surface; antibody independent ; part of innate immunity
Alternative pathway
Initiated by host proteins binding microbial surface
Lectin pathway
CASCADE ACTIVATION
Complement proteins are often designated by an
uppercase letter C and are inactive until they are split into products
C1
CASCADE ACTIVATION
When the products are split they become active. The
active products are usually designated with a lower
case a or b
C1a and C1b
All classes of immunoglobulin do not fix complement
only ______, ______, ______, and ______ fix in the respective order
IgM, IgG3, IgG1 and IgG2
These Ig do not fix complement
IgG4, IgA, IgD and IgE
Complement does not bind to ______ and ______
antigen and antibody
Activated by antibodies bound to antigen
classical pathway
Activated on microbial cell surfaces in the absence of antibody
alternative pathway
Activated by plasma lectin that binds to mannose residues on microbes
lectin pathway
4 important functions of complement system
lysis
opsonization
activation of inflammatory response
clearance of immune complexes
Overview of the complement pathways indicating
components required for _______, _______, _______. ______, and _______
recognition, enzymatically active components and complexes, major opsonic, inflammatory, and membranolytic products
4 components of alternative pathway
C3, factor B, factor D, properdin
Triggering substances may be pathogens or nonpathogens:
○ Bacterial cell wall components
○ Fungi
○ Viruses
○ Parasites
○ Immune complexes
○ RBCs
○ Polymers
alternative pathway
activation of alternative pathway
proteolysis of C3
Binding site for factor B covalently tethered to surface of microbial or host cell
C3b
Bound factor B cleaved by ________
factor D (serine protease)
C3 convertase
C3bBb
Properdin bind to and stabilize _________
C3bBb complex
C5 convertase
C3bBb3b
A protein that binds to CHO
lectin
It binds to mannose on many bacterial cells
mannose-binding lectin pathway (MBL)
It produced by liver in acute phase inflammatory reactions
MBL
Once MBL binds to target cell, 2 serine proteases _______ and _______ bind
MASP-1, MASP-2
acts like C1
MBL pathway
an acute phase protein, binds to mannose residues
MBL
When MBL complex binds to a pathogen surface, MASP-2 is activated to cleave _____ and _____
C4 and C2
Importance in innate host defense mechanism in early childhood
MBL pathway
activation of MBL pathway
D-mannose, GIcNAc (microbial polysaccharides)
Binding to circulating lectins, [e.g., Mannose-binding
lectin (MBL), or to _________ recognizing lectins (ficolins) collectin family and structurally resemble C1q
N-acetylglucosamine
MASP-1 cleaves to _____
C3
MASP-2 cleaves to _____ and _____
C4 and C2
C3 convertase
MASP-1
C5 convertase
C4b2b3b
regulation of the complement cascade
short half life of:
C3b, C3bBb, C5b
It inhibits the C1s activity
C1 inhibitor
Glycophosphatidylinositol-linked membrane protein
DAF