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

Describe how antibody neutralises extracellular virus?

Answer 2

1. It blocks viral attachment proteins (e.g., glycoproteins, capsid proteins)
2. It destabilises viral structure

Question 3

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

Answer 3

1. neutralise extracellular virus
2. Opsonise virus for pathogocytosis
3. promotes killing of target cell by the complement cascade and antibody-dependent cellular cytotoxicity.
4. resolves lytic viral infections.
5. blocks viremic spread to target tissue

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 reaching virus particles or infected cells.

Question 10

How many serotypes does Dengue Virus exist as?

Answer 10

4 Serotypes

Question 11

What triggers Dengue Haemorrhagic fever?

Answer 11

Previous infection with one serotype followed by infection with a different serotype can lead to antibody dependent enhancement of disease as virus enters immune cells via antibody and the Fc-Receptor.

Question 12

Which virus shows antigenic drift?

Answer 12

Influenza virus

Question 13

What is antigenic drift?

Answer 13

When viruses like flu 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 - the most common cold causing pathogen, 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 (IFN)

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

The Antiviral state involves transcription of hundreds of genes that block viral replication

Question 21

what does IFN activate?

Answer 21

NK cells

Question 22

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

Answer 22

2’5’ oligoadenylate synthetase and protein kinase R.

Question 23

What are the two type 1 IFNs?

Answer 23

IFN-α and IFN-β

Question 24

Which cells secrete IFN-β?

Answer 24

All cells

Question 25

Which cells secrete IFN-α?

Answer 25

Plasmacytoid dendritic cells (PDCs)

Question 26

Where is the IFN-αR receptor found?

Answer 26

On all tissues

Question 27

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

Answer 27

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

Question 28

What is type 2 IFN?

Answer 28

Type II IFN is IFN-γ

Question 29

Which cells produce IFN-γ?

Answer 29

Activated T Cells and NK Cells

Question 30

Which receptor does IFN-γ signal through?

Answer 30

IFN-γR

Question 31

What is type 3 IFN?

Answer 31

Type III IFN is IFN-λ

Question 32

What are the main IFN-λ receptors?

Answer 32

IL28R and IL10-β

Question 33

Where are IL28R and IL10-β found?

Answer 33

On epithelial surfaces

Question 34

How does Hepatitis B block the production of Interferon?

Answer 34

Through the inhibition of IFN transcription

Question 35

How does influenza block the production of interferon?

Answer 35

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

Question 36

How are NK Cells activated?

Answer 36

IFN-α and interleukin-12, which activate macrophages with IFN-γ.

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

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