Complement

Question 1

what is the complement system

Answer 1

first line system of plasma proteins that mark pathogens

Question 2

what are the complement proteins produced by

Answer 2

liver

Question 3

where are they

Answer 3

circulatory system

Question 4

what are the functions of complement

Answer 4

-perforation of pathogen membranes
- recruits phagocytes
- coats surface of bacteria and viruses to enhance phagocytosis

Question 5

what are the 3 complement activation pathways

Answer 5

• alternate
• lectin
• classical

Question 6

which complement protein is most key

Answer 6

C3

Question 7

C3 deficiency leads to

Answer 7

regular severe infections

Question 8

complement proteins are activated by

Answer 8

cleavage

Question 9

What are the steps of the alternative pathway

Answer 9

1. cleavage of C3 to C3a and C3b
2. cleavage of C3 exposes thioester bond
3. nucleophillic attack on the thioester bond

Question 10

formation of C3b convertase

Answer 10

1. factor B attaches to C3 then factor D attaches onto factor B they factor d leaves and splits factor B allowing another C3 to come and cleave the C3 to form C3b
2. factor b attaches onto C3b and factor d then attaches and splits factor b allowing a new C3 to attach and both are cleaved to C3a, C3b or goes back and attached to another C3

Question 11

What are the 5 proteins that regulate C3b deposition

Answer 11

-properdin
- Factors H and I
- Decay- accelerating factor
- Membrane co-factor protein

Question 12

what is the function of properdin

Answer 12

stabalizes C3b convertase which increases the rate of C3b formation

Question 13

what is the function of Factor H and I

Answer 13

H facilitates Factor I cleavage of C3b to iC3b ( inactive) which decreases the amount of C3b

Question 14

What is the function of DAF

Answer 14

binds C3b and dissociates Bb ,inactivates C3b convertase

Question 15

MCP function is

Answer 15

binds C3b and dissociates Bb but also makes C3b subject to cleavage by factor I

Question 16

classic is mediated by

Answer 16

IgG or IgM

Question 17

alternative is on

Answer 17

microbe surface molecules

Question 18

what do each cause!!!! high-yield
C3b
C3a,C4a, C5a
C5a
C5b-9

Answer 18

opsonization
anaphylaxis
neutrophil chemotaxis
pathogen cell lysis

Question 19

Lectin binds

Answer 19

bacterial mannose

Question 20

classical binds

Answer 20

host C-reactive protein

Question 21

what are the steps in lectin pathway

Answer 21

1- MBL binds to mannose from C1 complex

2- c1-like complex spilts c4 and c2 into c4a, c4b, c2a, c2b

3- C4b2b forms C3 convertase

4- C4b2a3b forms c5 convertase

Question 22

what are the steps in classical

Answer 22

• C1 complex spilts C4 and c2
• C4b2b forms C3 convertase
• C4b2b3b forms c5 convertase

Question 23

what two things do complement cause

Answer 23

membrane attack (pathogen lysis)
Opsonization ( phagocytosis)

Question 24

explain the picture of the membrane attack complex

Answer 24

C5b, C6, C7, C8 form a complex and they recruit C9 which forms a big ring structure on the lipid bilayer causing pathogen lysis

Question 25

explain the opsonization picture

Answer 25

C3b is on the bacterial cell surface and that it binds on the CR1 surface receptor of the macrophage which then gets engulfed , the macrophage membrase fuse creating a vesicle trapping the bacteria , and the lysosomes fuse with phagosomes forming phagolysomes

Question 26

Deficiences in : C1,C2,C4 C3 C5-C9 factors D and P Factor 9 DAF,CD59

Answer 26

- no IgG-Ab complex removal - no complement cascade - no membrane attack complex ( MAC) - Reduced formation of MAC - all C3 converted to C3b - alternative pathway uncontrolled