Host Responses to Viral Infections

Question 1

What are the 4 effects of Viruses on cells?

Answer 1

1. CPE (Cytopathic Effects)- detectable morphological changes or inclusion bodies in host cell.
2. Syncytia- Cell Fusion
3. Growth-
4. Apoptosis

Question 2

What are the two types of damage in CPE?

Answer 2

Direct Damage: Results from diversion of cell’s energy, shutdown of macromolecular synthesis, competition between viral and host promoters.

Indirect Damage: Integration of viral genome, induction of mutations in host genome, inflammation, and host immune response.

Question 3

What are the two types of growth caused by viruses?

Answer 3

Permissive: Where host cells provide machinery for viral replication

Non-permissive: Results in latent or transforming infections

Question 4

How does the interferon response work?

Answer 4

When a cell is infected with a virus, it releases IFN, which induces an anti-viral state in neighboring cells.

The anti-viral state is facilitated by dsRNA which activates IFN responsive genes. dsRNA comes from the replication cycle of some viruses.

Question 5

What is the result of the anti-viral state?

Answer 5

Blockade of cell division
Reduction of cell metabolism
Increase in NK activity including IFN production
Expression of APC
Apoptosis

Question 6

What are some of the characteristics of the Innate immune response to viruses?

Answer 6

• Includes NATURAL BARRIERS
• Includes INTRACELLULAR RESTRICTION FACTORS to block post-entry steps of virus
• Depends on TLRs and Helicases
• Produces IFNs

Question 7

Why are INTRACELLULAR RESTRICTION FACTORS not effective in blocking post-entry steps of viruses?

Answer 7

Viruses have evolved faster than hosts.

Question 8

What are the two genes that are key in establishing an Anti-Viral State?

Answer 8

PKR and OAS

These are activated by viral dsRNA

Question 9

Which type of IFN is produced by most infected cells within HOURS of infection?

Answer 9

Type 1 (IFNa and IFNb)

Question 10

What produces Type II IFNs? What is the main IFN in this type?

Answer 10

T Cells and NK cells

IFNg

Question 11

What is the fxn of IgA in adaptive responses to viruses?

Answer 11

Inhibit viral attachment, neutralize toxins

Question 12

What is the fxn of IgG in adaptive responses to viruses?

Answer 12

• Prevents enveloped viruses from fusing
• Opsinization
• Compliment lysis of virus

Question 13

What is the fxn of IgM in adaptive responses to viruses?

Answer 13

• Opsinization
• Compliment lysis of virus
• Coat and agglutinate viruses (think of the size of IgM)

Question 14

Which is involved more in humoral response? TH1 or Th2?

Answer 14

Th2

Question 15

Which type of T-cell eliminates infected host cells?

Answer 15

CD8 T cell

Question 16

Where do neutralizing antibodies bind?

Answer 16

Viral envelope proteins on a free virus or the same proteins on an infected cell.

Question 17

Where do non-neutralizing antibodies bind?

Answer 17

To viral proteins expressed primarily on infected cells but not on free virus.

Question 18

Compare antibodies produced in primary and secondary anti-viral response.

Answer 18

Secondary has higher affinity and quicker response due to memory cells.

Question 19

Which cell is involved in containing a viral infection? NK or CTL?

Answer 19

NK cells.

CTLs are responsible for clearing the infection.

Question 20

How do viruses evade/manipulate host defenses?

Answer 20

1. Interfering with IFN pathway (signaling, transcription, translation, production, etc)
2. Antigenic Mutation
3. Inhibit apoptosis and cell cycle control
4. Infect immune system
5. Release “decoy proteins” for antibodies to bind to.