Complements

Question 1

What are complements?

Answer 1

• group of serum proteins in inactive form

Question 2

Once a complement is activated what are its main roles?

Answer 2

• lysis
• opsonization
• inflammation

Question 3

List the 6 categories of complements.

Answer 3

1. Initiators
2. Enzymatic mediators
3. Opsonins
4. Inflammatory mediators (anaphylatoxins)
5. Membrane attack proteins
6. Complement receptors (macrophages)

Question 4

What are the 3 major pathways of complement activation?

Answer 4

• Classical
• Lectin
• Alternative

Question 5

All three complement pathways converge in the generation of:
A. C3b
B. C5 convertase
C. C3 convertase
D. C4

Answer 5

C. C3 convertase

Question 6

C3 convertase cleaves which enzyme?

Answer 6

C3
- cleaves into C3a and C3b

Question 7

C4b2a makes up….
A. C3 convertase
B. C5 convertase
C. Factor B
D. MASPs

Answer 7

A. C3 convertase

Question 8

When C3b is added to C3 convertase to make C4b2a3b, what is the result?

Answer 8

C5 convertase
- cleaves C5 to C5a and C5b

Question 9

How does C3b protect the host?

Answer 9

1. Opsonization
   - C3b binds to microbial surfaces to “tag” for recognition
2. Antigen-antibody complexes
   - C3b attaches to Fc portion of antibodies for phagocytosis
3. C5 convertase
   - C3b bind to complement proteins to form C5 convertase

Question 10

The classical pathway activated by:

Answer 10

Antigen-antibody complexes
- only IgM and IgG

Question 11

What is activated by binding to an antibody in the classical pathway, initiating the classical cascade?
A. C4
B. C1
C. C2

Answer 11

B. C1

Question 12

C1 activation is followed by…..

Answer 12

cleavage of C4 and C2 into (C4a/C4b) (C2a/C2b)

Question 13

C4b2a bound to the cell surface forms (____) and then cleaves C3 into (_____).

Answer 13

C3 convertase; C3a and C3b

Question 14

C3b combines with (_____) to form (___) convertase.

Answer 14

C3 convertase (C4bC2a); C5 convertase (C4bC2aC3b)

Question 15

C5 convertase cleaves which protein?

Answer 15

C5 protein

Question 16

The lectin pathway is activated by:

Answer 16

mannose-binding lectins (MBLs)

Question 17

What do lectins recognize?

Answer 17

• carbohydrate components on microbes

Question 18

Lectins serve as docking sites for:
A. C1
B. C3b
C. MASPs
D. DAMPs

Answer 18

C. MASPs

Question 19

MASPs initiate the lectin pathway and cleave (___) and (____) to form C3 convertase.

Answer 19

C2 and C4

Question 20

How are MASPs activated?

Answer 20

• MLB binding to microbial surfaces

Question 21

T/F. After C3 convertase is formed the lectin pathway uses the same downstream components as the classical pathway

Answer 21

True

Question 22

The alternative pathway is activated by?

Answer 22

C3b

Question 23

In the alternative pathway, what is C3 convertase and C5 convertase composed of?

Answer 23

C3 convertase = C3bBb
C5 convertase = C3bBbC3b

Question 24

In the alternative tickover pathway, small amounts of C3 are spontaneously cleaved to yield:

Answer 24

fluid C3

Question 25

Fluid C3 initiates or activates the alternative pathway?

Answer 25

initiates

Question 26

Factor B binds to C3b on the microbial surface and is cleaved by A. Ba B. Factor D C. C3Bb

Answer 26

B. Factor D

Question 27

Cleaving of Factor B causes which protein to be released and bound to fluid C3?

Answer 27

Bb

Question 28

Fluid-phase C3 convertase is:

Answer 28

Fluid C3Bb

Question 29

C5 initiates the generation of the (____) complex.

Answer 29

MAC

Question 30

The MAC complex is a result of which proteins on target cell membranes?

Answer 30

C5b, C6, C7, C8 , C9

Question 31

What are the 3 complement receptors?

Answer 31

- CR1 - CR2 - C3aR/C5aR

Question 32

CR1 receptor binds to (___) on leukocytes and erythrocytes.

Answer 32

C3b

Question 33

CR2 receptor binds to (____) on B-cells.

Answer 33

C3d

Question 34

C3aR/C5aR receptor binds to (____) and (____) on granulocytes.

Answer 34

C3a; C5a

Question 35

Which complements act as anaphylatoxins or inducers of inflammation?

Answer 35

C3a and C5a

Question 36

What bridges complements to effectors?

Answer 36

- CR1 - C3aR

Question 37

How do complements enhance host defense against infections?

Answer 37

1. MAC-induced cell death 2. C3b mediated phagocytosis 3. Inflammation via C3a+C5a

Question 38

Identify this pathway.

Answer 38

Classical

Question 39

Identify this pathway.

Answer 39

Lectin

Question 40

Identify this pathway.

Answer 40

Alternative