Viral Immune Evasion Flashcards

1
Q

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

A

eliminate both the virus and the host cells harbouring or replicating the virus.

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2
Q

Describe how antibody neutralises extracellular virus?

A
  1. It blocks viral attachment proteins (e.g., glycoproteins, capsid proteins)
  2. It destabilises viral structure
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3
Q

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

A
  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
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4
Q

Which Ig class is an indicator of recent infection?

A

IgM

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5
Q

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

A

IgG

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6
Q

Which Ig class is important for pretecting mucosal surfaces?

A

IgA

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7
Q

What does HIV exist as?

A

Quasi-species / multiple clades

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8
Q

How does HIV escape antibody recognition?

A

Exists as multiple quasi-species

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9
Q

How does HBV and Ebola virus evade antibody recognition?

A

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

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10
Q

How many serotypes does Dengue Virus exist as?

A

4 Serotypes

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11
Q

What triggers Dengue Haemorrhagic fever?

A

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.

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12
Q

Which virus shows antigenic drift?

A

Influenza virus

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13
Q

What is antigenic drift?

A

When viruses like flu mutate and evolve each year

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14
Q

Describe how influenza undergoes antigenic shift?

A

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

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15
Q

Why is finding a cold vaccine difficult?

A

Rhinovirus - the most common cold causing pathogen, has too many serotypes

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16
Q

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

A

Interferons (IFN)

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17
Q

How is interferon production induced?

A

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

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18
Q

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

A

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

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19
Q

What does interferon do once secreted from the cell?

A

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

20
Q

What does the antiviral state involve?

A

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

21
Q

what does IFN activate?

A

NK cells

22
Q

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

A

2’5’ oligoadenylate synthetase and protein kinase R.

23
Q

What are the two type 1 IFNs?

A

IFN-α and IFN-β

24
Q

Which cells secrete IFN-β?

A

All cells

25
Q

Which cells secrete IFN-α?

A

Plasmacytoid dendritic cells (PDCs)

26
Q

Where is the IFN-αR receptor found?

A

On all tissues

27
Q

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

A

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

28
Q

What is type 2 IFN?

A

Type II IFN is IFN-γ

29
Q

Which cells produce IFN-γ?

A

Activated T Cells and NK Cells

30
Q

Which receptor does IFN-γ signal through?

A

IFN-γR

31
Q

What is type 3 IFN?

A

Type III IFN is IFN-λ

32
Q

What are the main IFN-λ receptors?

A

IL28R and IL10-β

33
Q

Where are IL28R and IL10-β found?

A

On epithelial surfaces

34
Q

How does Hepatitis B block the production of Interferon?

A

Through the inhibition of IFN transcription

35
Q

How does influenza block the production of interferon?

A

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

36
Q

How are NK Cells activated?

A

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

37
Q

What do NK cells do?

A

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

38
Q

Which types of viruses do NK cells specifically target?

A

Enveloped viruses

39
Q

When does an NK cell release toxic substances?

A

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

40
Q

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

A

Cytomegalovirus or Herpes Simplex Virus infected cells

41
Q

What do macrophages do in the viral response?

A

filter viral particles from the blood and inactivate opsonised virus particles

42
Q

What is a function which macrophages and DCs share?

A

Present antigen to CD4 T cells

43
Q

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

A

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

44
Q

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

A

encode proteins that interfere with the MHC antigen processing pathway.

45
Q

How does HIV evade the immune response?

A

kills CD4 T cells and alters macrophage function.

46
Q

How does HSV evade the immune response?

A

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