Complements Flashcards
What are complements?
- group of serum proteins in inactive form
Once a complement is activated what are its main roles?
- lysis
- opsonization
- inflammation
List the 6 categories of complements.
- Initiators
- Enzymatic mediators
- Opsonins
- Inflammatory mediators (anaphylatoxins)
- Membrane attack proteins
- Complement receptors (macrophages)
What are the 3 major pathways of complement activation?
- Classical
- Lectin
- Alternative
All three complement pathways converge in the generation of:
A. C3b
B. C5 convertase
C. C3 convertase
D. C4
C. C3 convertase
C3 convertase cleaves which enzyme?
C3
- cleaves into C3a and C3b
C4b2a makes up….
A. C3 convertase
B. C5 convertase
C. Factor B
D. MASPs
A. C3 convertase
When C3b is added to C3 convertase to make C4b2a3b, what is the result?
C5 convertase
- cleaves C5 to C5a and C5b
How does C3b protect the host?
- Opsonization
- C3b binds to microbial surfaces to “tag” for recognition - Antigen-antibody complexes
- C3b attaches to Fc portion of antibodies for phagocytosis - C5 convertase
- C3b bind to complement proteins to form C5 convertase
The classical pathway activated by:
Antigen-antibody complexes
- only IgM and IgG
What is activated by binding to an antibody in the classical pathway, initiating the classical cascade?
A. C4
B. C1
C. C2
B. C1
C1 activation is followed by…..
cleavage of C4 and C2 into (C4a/C4b) (C2a/C2b)
C4b2a bound to the cell surface forms (____) and then cleaves C3 into (_____).
C3 convertase; C3a and C3b
C3b combines with (_____) to form (___) convertase.
C3 convertase (C4bC2a); C5 convertase (C4bC2aC3b)
C5 convertase cleaves which protein?
C5 protein
The lectin pathway is activated by:
mannose-binding lectins (MBLs)
What do lectins recognize?
- carbohydrate components on microbes
Lectins serve as docking sites for:
A. C1
B. C3b
C. MASPs
D. DAMPs
C. MASPs
MASPs initiate the lectin pathway and cleave (___) and (____) to form C3 convertase.
C2 and C4
How are MASPs activated?
- MLB binding to microbial surfaces
T/F. After C3 convertase is formed the lectin pathway uses the same downstream components as the classical pathway
True
The alternative pathway is activated by?
C3b
In the alternative pathway, what is C3 convertase and C5 convertase composed of?
C3 convertase = C3bBb
C5 convertase = C3bBbC3b
In the alternative tickover pathway, small amounts of C3 are spontaneously cleaved to yield:
fluid C3
Fluid C3 initiates or activates the alternative pathway?
initiates
Factor B binds to C3b on the microbial surface and is cleaved by
A. Ba
B. Factor D
C. C3Bb
B. Factor D
Cleaving of Factor B causes which protein to be released and bound to fluid C3?
Bb
Fluid-phase C3 convertase is:
Fluid C3Bb
C5 initiates the generation of the (____) complex.
MAC
The MAC complex is a result of which proteins on target cell membranes?
C5b, C6, C7, C8 , C9
What are the 3 complement receptors?
- CR1
- CR2
- C3aR/C5aR
CR1 receptor binds to (___) on leukocytes and erythrocytes.
C3b
CR2 receptor binds to (____) on B-cells.
C3d
C3aR/C5aR receptor binds to (____) and (____) on granulocytes.
C3a; C5a
Which complements act as anaphylatoxins or inducers of inflammation?
C3a and C5a
What bridges complements to effectors?
- CR1
- C3aR
How do complements enhance host defense against infections?
- MAC-induced cell death
- C3b mediated phagocytosis
- Inflammation via C3a+C5a
Identify this pathway.
Classical
Identify this pathway.
Lectin
Identify this pathway.
Alternative
