4.7 Viral Immune Evasion

Question 1

What is the ultimate goal of the immune response to a viral infection?

Answer 1

Eliminate both the virus and the host cells harbouring or replicating the virus

Question 2

What are the five functions of antibody in the anti-viral response? BRONK

Answer 2

Block viremic spread to target tissue
Resolve lytic viral infections
Opsonise virus for phagocytosis
Neutralise virus
Kill virus via complement cascade and antibody-mediated cytotoxicity

Question 3

Describe how antibody neutralises extracellular virus?

Answer 3

Blocks viral attachment proteins (glycoproteins, capsid proteins)

Destabilises viral structure

Question 4

Which Ig class is an indicator of recent infection?

Answer 4

IgM

Question 5

Which Ig class is a more effective anti-viral than IgM?

Answer 5

IgG

Question 6

Which Ig class is important for pretecting mucosal surfaces?

Answer 6

IgA

Question 7

What does HIV exist as?

Answer 7

Quasi-species/multiple clades

Question 8

How does HIV escape antibody recognition?

Answer 8

Exists as multiple quasi-species

Question 9

How does HBV and Ebola virus evade antibody recognition?

Answer 9

Encode secreted surface antigens that mop up antibody, stopping it from reaching virus particles or infected cells

Question 10

How many serotypes does Dengue Virus exist as?

Answer 10

4

Question 11

What triggers Dengue Haemorrhagic fever?

Answer 11

Previous infection with 1 dengue virus serotype followed by infection with another serotype

This causes the virus to enter immune cells via antibodies or Fc receptors, causing antibody-dependent enhancement of disease

Question 12

Which virus shows antigenic drift?

Answer 12

Influenza virus

Question 13

What is antigenic drift?

Answer 13

When viruses mutate and evolve each year

Question 14

Describe how influenza undergoes antigenic shift?

Answer 14

Influenza viruses can also acquire completely new antigens by reassortment with animal viruses

Question 15

Why is finding a cold vaccine difficult?

Answer 15

Rhinovirus is the most common cold causing pathogen and has too many serotypes

Question 16

What is the name of the small proteins released by virally infected cells that play a role in immune protection against viruses?

Answer 16

Interferons

Question 17

How is interferon production induced?

Answer 17

The presence of molecules made by viruses that are sensed by the cell as foreign or in the wrong cellular location

Question 18

What might trigger the production of interferon from a virally infected cell?

Answer 18

Double-stranded RNA
RNA that lacks a 5’ cap
DNA in the cytoplasm

Question 19

What does interferon do once secreted from the cell?

Answer 19

Binds to interferon recptors and activates the anti-viral state of the cell and surrounding cells

Question 20

What does the antiviral state involve?

Answer 20

Gene transcription to block viral replication

Question 21

What is synthesized in the anti-viral state through the transcription of anti-viral genes?

Answer 21

2’5’ oligoadenylate synthetase and protein kinase R

Question 22

What are the two type 1 IFNs?

Answer 22

IFN-α and IFN-β

Question 23

Which cells secrete IFN-β?

Answer 23

All cells

Question 24

Which cells secrete IFN-α?

Answer 24

Plasmacytoid dendritic cells (PDCs)

Question 25

Where is the IFN-α receptor found?

Answer 25

On all tissues

Question 26

How many genes are there for IFN-β and IFN-α?

Answer 26

There is one gene for IFN-β, but 13/14 isotypes of IFN-α

Question 27

What is type 2 IFN?

Answer 27

IFN-γ

Question 28

Which cells produce IFN-γ?

Answer 28

Activated T Cells and NK Cells

Question 29

Which receptor does IFN-γ signal through?

Answer 29

IFN-γR

Question 30

What is type 3 IFN?

Answer 30

IFN-λ

Question 31

What are the main IFN-λ receptors?

Answer 31

IL28R and IL10-β

Question 32

Where are IL28R and IL10-β found?

Answer 32

On epithelial surfaces

Question 33

How does hepatitis B block the production of Interferon?

Answer 33

Through the inhibition of IFN transcription

Question 34

How does influenza block the production of interferon?

Answer 34

Produces a protein (NS1) that **counters RNA sensing** and **prevents polyA processing**

Question 35

What 2 cytokines are NK Cells activated by?

Answer 35

IFN-α and interleukin-12

Question 36

What do activated NK cells release and what does this do?

Answer 36

IFN-γ which activates macrophages

Question 37

What do NK cells do?

Answer 37

NK cells target and kill virus-infected cells (especially enveloped viruses)

Question 38

Which types of viruses do NK cells specifically target?

Answer 38

Enveloped viruses

Question 39

When does an NK cell release toxic substances?

Answer 39

When the NK cell finds a cell displaying fewer than normal MHC molecules

Question 40

Which viruses might infect a cell and trigger NK cells to release toxic substances?

Answer 40

Cytomegalovirus or Herpes Simplex Virus infected cells with **fewer MHC molecules**

Question 41

What do macrophages do in the viral response?

Answer 41

Filter viral particles from the blood and inactivate opsonised virus particles

Question 42

What is a function which macrophages and DCs share?

Answer 42

Present antigen to CD4 T cells

Question 43

What is the viral peptide that cytotoxic CD8 T cells respond to?

Answer 43

Class I MHC protein complexes on the infected cell surface carrying viral proteins

Question 44

How do viruses like HSV and cytomegalovirus counter the T cell response?

Answer 44

Encode proteins that interfere with the MHC antigen processing pathway

Question 45

How does HIV evade the immune response?

Answer 45

Kills CD4 T cells and alters macrophage function

Question 46

How does HSV evade the immune response?

Answer 46

Prevents CD8 T cell killing by encoding proteins which interfere with the MHC antigen processing pathway