Complement

Question 1

What does complement do

Answer 1

Enhances host defense mechanisms

Question 2

Where is complement mostly synthesized

Answer 2

Liver

Question 3

Classical pathway is triggered by what

Answer 3

Antigen-antibody combination

Question 4

Alternative pathway triggered by what

Answer 4

Antibody independent means

Question 5

Lectin pathway activated by what

Answer 5

Mannose found on cell walls or coating of bacteria, yeast, viruses, protozoa
- Mannose binding lectin MBL

Question 6

Four main functions of complement

Answer 6

• Lysis
• Opsonization
• Activation of inflammatory response
• Clearance of immune complexes

Question 7

When complement components split, how are the pieces classified?

List 3 ways and some examples

Answer 7

• Anaphylatoxins
• Chemotaxins
• Opsonins

C3a. C4a. C5a

Question 8

How does C5a help?

Answer 8

Chemotaxin that draws in immune cells to the antigen concentration source

Question 9

How do C4b and C3b help?

Answer 9

Facilitate phagocytosis

Question 10

Main goal of the complement pathways?

Answer 10

Activate C3 and C5

Question 11

What is the recognition unit

Answer 11

C1, classical pathway only

Question 12

What is the activation unit

Answer 12

C4, C2, C4

Question 13

What is the membrane attack unit

Answer 13

C5-C9

Question 14

Classical pathway overview before terminal pathway

the basic steps

Answer 14

1. Antibody binds
2. C1 cleaves C4 and C2 to reveal binding sites, C4 and C2 bind together
3. C4b2a or C3 convertase forms
4. C3 convertase can activate other C3 molecules or bind with C3 itself to form C4b2a3b or C5 convertase
5. C5 convertase cleaves C5 into C5b and C5a

Question 15

Alternative pathway special properties

Purpose, protein

Answer 15

Destroys pathogen in the absence of antibodies, more of an innate response
- Special protein: properdin, factor B, factor D
- Properdin stablizes C3 convertase

Question 16

Alternative pathway overview of steps

Answer 16

1. C3 binds to cell surface and causes factor B to bind
2. Exposes cleavage site on B, Factor D binds
3. Releases Ba and Bb, binds to C3B, forms C3bBb = alternative pathway C3 convertase which cleaves another C3
4. C5 convertase = C3bBbC3b which cleaves C5 and starts terminal pathway

Question 17

Lectin pathway steps overview

Answer 17

Mannose binding lectin finds mannose on extracellular pathogen, binds to it instead of using C1
- MBL associated serine protease, MASP
1. MASP-2 cleaves C4 and C2
2. Same as classical pathway from here

Question 18

Terminal pathway steps overview

Answer 18

1. C5 is cleaved by C5 convertases
2. C5b binds C6 > C5b678
3. Forms membrane attack complex

Question 19

Complement pathway inhibitor goals

Answer 19

Stop C3b from accumulating since its in all 3 pathways

Question 20

Decay accelerating factor

Answer 20

Increases rate of dissociation of C4b2a and C3bBb, classical and alternative C3 convertase