Innate Immunity: Complement Proteins

Question 1

Where are complement proteins produced?

Answer 1

liver

Question 2

Where do complement proteins live?

Answer 2

the blood and lymph

Question 3

zymogens

Answer 3

complement proteins are not activated until cleaved

Question 4

activation pathway order

Answer 4

1. alternative
2. lectin
3. classical

Question 5

alternative pathway

Answer 5

• spontaneous hydrolysis of C3 into C3b
• C3b binds to pathogen surface with the help of Factor B & D and Properdin
• C4 or C2 not used

Question 6

lectin pathway

Answer 6

• lectins from host (such as Mannose-Binding Lectins (MBL)) recognize the pathogen and bind to carbs on the surface
• C4, C3, and C2 activated

Question 7

classical pathway

Answer 7

C1 complex binds to antibodies on pathogen surface and leads to C4, C3, and C2 activation

Question 8

All pathways lead to what?

Answer 8

C3 activation, C3b binding, and C3a release

Question 9

C1 complex binds to what?

Answer 9

aggregated antibodies on pathogen surface

Question 10

Classical pathway steps

Answer 10

1. C1 complex binds to aggregated antibodies
2. C1 cleaves C4
3. C4a anaphylatoxic
4. C4b binds to pathogen
5. C2 binds to C4b and is cleaved
6. C2b released, C2a bound
7. C4bC2a (C3 convertase) activates C3
8. C3 combine with C3 convertase to form C4bC2aC3b (C5 convertase)
9. C5 convertase activates C5
10. C5a released, C5b bound
11. C5b initiates Membrane Attack Complex formation

Question 11

Membrane Attack Complex (MAC)

Answer 11

• result of deposition of C5b, C6, C7, C8, and many C9
• disrupts osmotic integrity and causes death

Question 12

opsonization

Answer 12

a coat of opsonins (commonly C3b) that are more easily recognized by phagocytic receptors and increase phagocytosis rate by ~100x

Question 13

Which complement proteins are anaphylatoxic?

Answer 13

• C3a
• C4a
• C5a

Question 14

What do anaphylatoxins do?

Answer 14

increase vascular permeability