Viral-Host Cell Interaction, Host Early Defenses

Question 1

Transformation

Answer 1

induces unregulated cellular growth; cells form tumors in susceptible hosts

Question 2

Permissive Cell

Answer 2

permits production of progeny virus particles and/or viral transformation

Question 3

Non-permissive Cell

Answer 3

virus cannot replicate, but it may be able to transform the cell

Question 4

Abortive Infection

Answer 4

no progeny virus particles are produced; however, the cell may die because early viral functions

Question 5

Interference

Answer 5

Infection by virus A will inhibit second infection with virus B

Question 6

Persistent Infection

Answer 6

small number of or no virus particles are produced; little or no (cytopatic effects) CPE

Question 7

Latency

Answer 7

viral genetic material remains in host cell without production of virus; may be activated at a later time to produce virus and/or transform the host cell

Question 8

Cytopathic Effects (CPE)

Answer 8

• Nucleus: inclusion bodies, thickening of the nucleus, swelling, nucleolar changes
• Cytoplasm: inclusion bodies, vacuoles

Question 9

One Step Growth Curve

Answer 9

Cells are infected at high multiplicity of infection (MOI) to ensure that every cell is infected. The number of infectious virions inside and outside the cells is measured at various times.

Question 10

Latent Phase

Answer 10

no virions outside the cells, still inside cell, incubation

Question 11

Eclipse Phase

Answer 11

no virions outside or inside the cells, the period of time between infection by a virus and the appearance of the mature virus within the cell.

Question 12

Early Phase

Answer 12

synthetic phase, viral gene expression for genome replication

Question 13

Late Phase

Answer 13

begins with synthesis of proteins necessary for construction of the new particles

Question 14

Burst Size

Answer 14

number of infectious virions released per average cell. Range less than 10 to millions. For the figure burst size is 1000.

Question 15

Interferon

Answer 15

Small proteins produced by cells in response to virus infection, mitogens or immune stimulus.

Question 16

Three major types of interferon:

Answer 16

• INF-α (Leukocyte) virus induced
• INF-β (Fibroblasts) virus induced
• INF-γ (T-cells) antigen or mitogen induced

Question 17

How is interferon activated?

Answer 17

• Interferon is activated by double stranded RNA upon viral infection through TLRs.
• Both RNA and DNA viruses induce interferon production.

Question 18

Interferon activates 2 enzymes:

Answer 18

• Production of an oligoadenylate synthetase which in turn, activates production of ribonuclease that degrades mRNA.
• Production of a protein kinase that phosphorylates and inactivates one of the subunits of initiation factor eIF-2) necessary for protein synthesis.

*The action of both enzymes requires the presence of double stranded RNA

Question 19

Wait…how is there ds RNA in a DNA virus?

Answer 19

•mRNA folds for stability - this happens in humans as well, but viruses have an increased G + C content –> better interactions –> bigger stems –> induces interferon