Lecture 3.2 - Innate Immunity

Question 1

When does an infectious disease occur?

Answer 1

When a pathogen succeeds in either evading or overwhelming the immune defences

Question 2

What are the 3 major roles of the immune system?

Answer 2

• Recognise pathogen and remembering it for the future
• Containing and eliminating the infection
• Regulate itself ensuring minimal damage to host

Question 3

What is the aim of the first lines of immune defence?

Answer 3

Preventing entry of the pathogens

Question 4

What are the 4 major first lines of defence?

Answer 4

• Physical barriers
• Chemical barriers
• Physiological barriers
• Biological barrier

Question 5

Give an example of a physical barrier

Answer 5

Skin

Question 6

Give an example of a physiological immune barrier?

Answer 6

Vomiting

Question 7

What sort of barrier is formed by the low pH of the skin, stomach and vagina?

Answer 7

Chemical barrier

Question 8

What forms the body’s biological barrier?

Answer 8

The normal flora

Question 9

In which 3 ways might normal flora allow an infection to take hold?

Answer 9

• Migrating to another site where it is pathogenic
• Overgrowing and becoming pathogenic
• Becoming depleted by antibiotics, allowing pathogens to establish

Question 10

What are the roles of the normal flora?

Answer 10

Out competing pathogens
Producing antimicrobial chemicals
Synthesising vitamins

Question 11

What is the aim of the second lines of defence?

Answer 11

Contain and eliminate the infection once the pathogens have breached the first lines of defence

Question 12

What are the 2 major second lines of defence?

Answer 12

Cells

Chemicals

Question 13

What is the role of phagocytes?

Answer 13

Recognise and kill microbes

Question 14

What are the 3 major phagocytes?

Answer 14

Monocytes
Macrophages
Neutrophils

Question 15

Where are monocytes found?

Answer 15

In the blood - they are recruited to infected tissue where they differentiate to become macrophages

Question 16

What do macrophages do?

Answer 16

Phagocytosis
Antigen presentation
Production of cytokines and chemokines

Question 17

Where are neutrophils present?

Answer 17

In the blood - then recruited to site of infection by chemokines

Question 18

Briefly outline the process of pathogen recognition by phagocytes

Answer 18

Phagocytes all have pathogen-recognition receptors (PRRs), specifically toll-like receptors, which recognise PAMPs on the pathogen. These PAMPs may be carbohydrate, lipid, protein or nucleic acid.

Question 19

What is opsonisation?

Answer 19

The process whereby proteins called opsonins bind to the surface of a microbe, enhancing attachment of phagocytes.

Question 20

For which sort of bacteria is opsonisation particularly key?

Answer 20

Bacteria with a thick capsid, e.g. Neisseria meningitidis

Question 21

Briefly outline the stages of phagocytosis

Answer 21

1) Binding of microbe to phagocyte via PAMP-TLR complex
2) Ingestion of microbe by phagocyte
3) Phagosome, then phagolysosome
4) Microbe digested by enzymes
5) Formation of residual body and waste materials released from cell

Question 22

By which 2 mechanisms may intracellular killing occur?

Answer 22

Oxygen dependent - respiratory burst

Oxygen independent - lysozyme etc…

Question 23

Give an example of why phagocytosis might be hindered

Answer 23

Decreased neutrophil number due to chemotherapy

Question 24

What is the complement system, and how is it activated?

Answer 24

A system of around 20 serum proteins, which is activated either by the MBL pathway or the alternative pathway

Question 25

What is the role of complement proteins C3a + C5a?

Answer 25

Recruit phagocytes

Question 26

Which complement proteins are involved in opsonisation?

Answer 26

C3b - C4b

Question 27

Which complement proteins kill pathogens?

Answer 27

C5 - C9

Question 28

Give 3 major roles of cytokines/chemokines

Answer 28

• Chemoattraction
• Phagocyte activation
• Inflammation

Question 29

What is the immune system?

Answer 29

Cells and organs which contribute to the immune defences against infectious and non-infectious conditions