Complement system

Question 1

Where are the proteins of the complement pathway produced?

Answer 1

complement proteins are synthesised in the liver

Question 2

What are the names of the different complement pathways?

Answer 2

1) classical 2) alternative 3) lectin

Question 3

Describe in simple terms what happens in the classical pathway

Answer 3

IgG or IgM antibodies bind to antigen at the variable region, then bind to C1 protein at the constant region (Fc), this leads to a series of events that produces C3 convertase which cleaves C3 to C3a and Cb

Question 4

Describe in simple terms what happens in the alternative pathway

Answer 4

Presence of a pathogenic antigen i.e. a bacterial endotoxin or lipopolysaccharide, sets off a chain reaction which forms C3 convertase which then cleaves C3 to C3 and C3b

Question 5

Describe in simple terms what happens in the lectin pathway

Answer 5

Pathogens like salmonella, Neisseria menigitidis and candida, cause the liver to produce mannose associated binding lectin. When lectin binds to these pathogens it triggers a chain reaction that results in the formation of C3 converstase that converts C3 to C3a and C3b

Question 6

Which complement pathway is antibody mediated?

Answer 6

Classical

Question 7

Which complement pathway responds to bacterial endotoxins?

Answer 7

Alternative

Question 8

Which steps of the complement pathway are significant and common in all three pathways?

Answer 8

C3 convertase is formed which converts C3a and C3b. C3b is involved in the formation of C5 convertase which converts C5a and C5b. C5b goes on to form the membrane attack complex

Question 9

What is the membrane attack complex?

Answer 9

A product of the complement system formed from c5b-c9b which is responsible for cell lysis

Question 10

What is the significance of C5b?

Answer 10

Involved in the formation of the membrane attack complex

Question 11

What is the significance of C5a?

Answer 11

Involved in chemotaxis and Mast cell degranulation

Question 12

What is the significant of C3b?

Answer 12

Involved in opsonisation and formation of C5 convertase

Question 13

What is the significance of C3a?

Answer 13

Joins C4 and 5 a to cause mast cell degranulation and histamine release

Question 14

What are the major outcomes of the complement cascade?

Answer 14

Membrane attack complex - cell lysis (c5b-9b)
Opsonisation - phagocytosis (c3b)
Chemotaxis (c5a)
Histamine release (c3-5a)

Question 15

Which complement protein induces opsonisation?

Answer 15

C3a

Question 16

Which complement protein induces chemotaxis?

Answer 16

C5a

Question 17

Which complement proteins form the membrane attack complex?

Answer 17

C5-9b

Question 18

Which complement proteins induce release of histamine?

Answer 18

C3-5a

Question 19

Where are complement proteins synthesised?

Answer 19

In the liver