Complement system

Question 1

What is the complement system?

Answer 1

Cascade of proteins that act to enhance phagocytosis (by opsonisation) and generate a macro molecular complex

Question 2

Many of the proteins in the complement system are proteinases enzymes. Where are these produced?

Answer 2

Liver

Question 3

Where are complement porters found?

Answer 3

Most bodily fluids - systemic protection

Question 4

The complement system is one of the main pathways in what bodily response?

Answer 4

Inflammation

Question 5

What are the 3 main consequences of complement activation? (COC)

Answer 5

Cytolysis (cell death to kill pathogen)
Cell activation (inflammatory cels)
Opsonisation of pathogens (increasing uptake by phagocytes)

Question 6

What are complement components numbered from?

Answer 6

C1-C9

Many have sub-components a (diffuse through tissues easily) or b (don’t easily diffuse)

Question 7

What features of the complement system make it a cascade?

Answer 7

Triggering

Amplification - substrates themselves become enzymes after binding to a proteinase

Question 8

Is the triggering of the complement system fast or slow?

Answer 8

Fast - within microseconds

Question 9

What are the 3 pathways of complement cascades?

Answer 9

Classical pathway
Lectin pathway
Alternative pathway

Question 10

All 3 complement cascade routes (classical, lectin, alternative) lead to the cleavage of which complement component?

Answer 10

C3 cleavage

Key event in complement activation

Question 11

What activates the classical pathway?

Answer 11

Antibody component of immune complexes

IgG or IgM

Question 12

What activates the lectin pathway?

Answer 12

Lectin binding to pathogen surface via soluble protein

Question 13

What activates the alternative pathway?

Answer 13

C3 directly binding to pathogen surface

Question 14

What type of cells do all 3 pathways target in the complement system?

Answer 14

Bacteria
Viruses
Parasites
Fungi

Question 15

Which complement pathway takes longer? Why?

Answer 15

Classical

Due to need for antibodies

Question 16

What cells make C3? Where?

Answer 16

Macrophages

Liver

Question 17

What does C3 naturally break down into? What do these act as/do?

Answer 17

C3a - chemoattract or an anaphylotoxin

C3b - bind to microbe surfaces or host cells

Question 18

C3a, C4a and C5a are anaphylotoxins. What changes do they cause?

Answer 18

Smooth muscle contraction
Vasodilation - increases fluid in tissue and causes oedema
Activate neutrophils or mast cells

Question 19

The complement system is part of which immune response?

Answer 19

Innate

Non-specific

Question 20

What is the membrane attack complex (MAC)?

Answer 20

C5b,C6,C7, C8 and multiple C9

Endpoint of all complement activation pathways

Question 21

What does the MAC do?

Answer 21

Opens bacterial cell cytosol

Question 22

What happens to the bacterial cell when MAC opens the cytosol?

Answer 22

Loss of cellular components
Loss of homeostasis
Disrupts proton gradient
Allows penetration of host lysozyme

Question 23

What is canine C3 deficiency? What does it cause?

Answer 23

Inherited deficiency
Lack of C3 = increased susceptibility
Trouble making antibodies against pathogens, causes increased infections e..g pyometra, pneumonia

Question 24

What is porcine factor H deficiency? What does it cause?

Answer 24

Inherited recessive disease

Death from anaemia and renal failure

Question 25

What is factor H? What happens if there is a factor H deficiency?

Answer 25

Stops C3b activation

Deficiency = C3 accumulation on kidneys - no serum C3