Intracellular immunity

Question 1

MHC1 is restricted to presenting antigen to which type of cells?

Answer 1

CD8 T-cells

Question 2

What is the role of interferons in preventing a viral infection?

Answer 2

• Secreted within hours of infection

- Antiviral = protects neighbouring cells from infection by binding and blocking viral receptors

Question 3

What is the role of type 1 interferons and where are they secreted from?

Answer 3

• Induce resistance to viral replication in all cells
• Increase MHC1 expression and antigen presentation
• Stimulate NK activity against viral cells and secretion of INFg
  They are released from tissues e.g. fibroblasts

Question 4

Where are type II interferons released from?

Answer 4

Activated T and NK cells

Question 5

What is the role of type II interferons in preventing viral infection?

Answer 5

They come a couple of days after type I and prevent viral growth in cells by induction of nitric oxide secretion
They activate macrophages
Induces more intracellular INF production

Question 6

Explain why Th1 responses are key to removing intracellular infections

Answer 6

• Virus or bacteria in a cell can be targeted for killing by CD8
• They cause loss of membrane integrity but are non-specific so don’t just attack infected cells

Question 7

How are macrophages involved in removing intracellular infections?

Answer 7

They receive activating signals from Th1 cells and express nitric oxide and oxygen radicals which cause host cell death

Question 8

How do NK cells know when to attack cells?

When do their levels increase?

Answer 8

They recognise MHC1 on a healthy cell so do not kill it.
A healthy cell that does not present MHC1 is killed.
It is common in viral infections for MHC levels on the surface to increase, which triggers NK cell killing.

Question 9

What is antigenic drift?

Answer 9

• Viruses evolving (due to their short half life)
• Changing the antigenic shape
• Reassortment of the major structures of the virus
• Makes the pre-existing antibody response ineffective

Question 10

What is a lytic infection?

Answer 10

Result in the destruction of the host cell, caused by virulent factors

Question 11

Describe a persistent infection

Answer 11

Does not lead to cell lysis and release viral particles slowly over long periods

Question 12

What is a latent infection?

Answer 12

Delay between the infection by the virus and the appearance of symptoms

Question 13

What are the possible adverse consequences of viral immunity?

Answer 13

• Inappropriate or excessive immune responses

- Leads to damage of infected/neighbouring cells

Question 14

Give 2 conditions caused by an adverse consequences of viral immunity

Answer 14

• Distemper

- Canine adenovirus

Question 15

What are the 2 main endotoxins attached to bacteria?

Answer 15

LPS and Lipid A

Question 16

How does LPS work as an endotoxin?

Answer 16

Found in the outer leaf of gram -ve bacteria

- activates macrophages to release inflammatory cytokines which lead to tissue degranulation

Question 17

How does lipid A work as an endotoxin?

Answer 17

• Toxic if present in the bloodstream

- Activated coagulation

Question 18

How does endotoxic shock occur?

Answer 18

• Excessive release of cytokines, often triggered by LPS
• Leads to intravascular coagulation leading to defective clotting, increased vascular permeability, loss of fluid in tissues, fall in blood pressure and circulatory collapse

Question 19

What is a superantigen?

Answer 19

A polyclonal T-cell activator produced by bacteria to induce ineffective host immunity

Question 20

How do superantigens work?

Answer 20

• Hyperstimulate the immune system
• Leads to shock
• Causes toxic shock syndrome