Vet Viral Immune Evasion

Question 1

What is immune evasion?

Answer 1

Deliberate modulation of a host immune system to benefit the infectious agent
- all viruses employ this
- prevent detection, fake signals, stop effector mechanisms

Question 2

Impact of viral immune evasion is dependent on:

Answer 2

• target of immune evasion
• relative success of immune evasion
• mechanism of immune evasion

Question 3

What are the two main targets against viruses?

Answer 3

• extra cellular phase (target the viruses between host cells)
• intracellular viruses (target infected host cells)

Question 4

What do NK cells do?

Answer 4

distinguish infected from uninfected host cells by MH class 1 interaction

Question 5

Why are inferons important in the viral immune response?

Answer 5

• early anti-viral response
• inferon releases IFNB
• produced by virally infected cells within hours
• lead to the production of anti-viral components

Question 6

What does MHC class 1 do?

Answer 6

• presents intracellular antigens
• helps detect and kill infected cells

Question 7

What does MHC class 2 do?

Answer 7

• presents mostly extracellular antigens
• helps respond to extracellular and intracellular infections

Question 8

What do Th1 cells do during a viral infection?

Answer 8

• enhances macrophage activity, antigen processing, more nutralising antibody production
• Produce IFN-y (DIFFERENTATION OF tH CELLS)- target of vet viruses

Question 9

How does Pox-virus impact IFN-y?

Answer 9

• produces soluble IFN-y receptors
• leads to blocking of the signal before its received
• Other chemokine and cytokine decoy receptors used

Question 10

What do neutralising antibodies do?

Answer 10

-can block viruses and bacteria from binding to receptor by which they enter the host cell
- making them a target

Question 11

How are neutralising antibodies evaded?

Answer 11

changes in the ammino acid sequence of the epitope causes no immunity/limited cross-reactivity

Question 12

mechanisms of neutralising antibody evasion:

Answer 12

Antigenic drift: single nucleotide / small scale changes that impact recognition of surface antigens

Antigenic Shift: major changes of genes are swapped between viruses

Question 13

How does pestivirus (bvdb) evade the immune system?

Answer 13

• immune tolerance
• cytopathic and non cytopathic
• causes inter-uterine infection (infecting primary lymphoid tissues)
• Removes any T and B cells responding to self

Question 14

What does cytopathic mean?

Answer 14

causing death/changes to cells in culture

Question 15

How do herpesvirus cause viral evasion?

Answer 15

• latency

Question 16

What is latency?

Answer 16

• virus enters a dormant stage of development
• not detectable (extracellular virus present)
• can be reactivated (recrudesence)

Question 17

How does latency cause evasion?

Answer 17

• viral genome present in host cells
• very little protien synthisis
• no release of new viruses until reactivated
• trends towards latency in specific cell types

Question 18

How do retroviruses evade the immune system?

Answer 18

transformation and immunosuppression

Question 19

how does transformation cause evasion?

Answer 19

• genome is inserted into the host cells genome
• hidden as self
• persistent infection
  -can impact expression of host genes
• some retoviruses also contain oncongenes in genome
• no control on proliferation

Question 20

How does immunosupression cause immune evasion?

Answer 20

• leads to lyphmomas
• FIV FeLV targets CD4 T lympocytes
• increases chance of persistant infection
• increases chance of secondary infections
  -0 increases chance if neoplasia (reduced immunosurvalence)