Virus-cell interactions (Oncogenes)

Question 1

The virus’ survival against the cell is hindered by which factors?

Answer 1

• Resistance
• Interferon production
• Latency
• Persistent infection
• Oncogenicity
• Cytopathic effects

Question 2

Abortive infection

Answer 2

No virus release

Question 3

Productive infection

Answer 3

Virus release and shedding

Question 4

Resistance

Answer 4

No surface receptor for vital attachment

• Not susceptible - host spectrum

Question 5

Interferon (IFN) production

Answer 5

• IFN: Cell-coded mediator protein - Cell defence mechanism
• Interferon inducer: dsRNA, RI forms → cascade - IFN release
• IFN effects on neighbouring cells:
  
  • Structural changes on the cytoplasmic membrane
    
    • Penetration
  • L-RNase: mRNA degradation
  • Proteinkinase: protein production inhibited

Question 6

Give the types of IFN

Answer 6

• • IFN-α (epithelial, leucocytes)
• IFN-β (fibroblast)
• IFN-γ (lymphocyte)

Question 7

IFN efficacy is at what dose?

Answer 7

10^-9 mg

Question 8

IFN production time

Answer 8

• 2-4 hours after infection
• Maximum after 12 hours
• Clearance after 24 hours

Question 9

Describe the specificity of IFNs

Answer 9

• Not virus specific
• Host specific

Question 10

Problems with IFN therapy

Answer 10

• Expensive
• Parenteral use, short-term efficiency
• The inducers are toxic
• Toxic side effects

Question 11

Latency

Answer 11

• After infection of the virus, no more multiplication
• Only NA + proteins are present
  
  • Episome
  • Integration
• No virus shedding/clinical signs
• Carrier
• Reactivation
  
  • Immunosuppression

Question 12

Persistent infection

Answer 12

• Virus production, but not severe cell damage
  
  • Continuous shedding
• In vitro cell cultures: diagnostic problems

Question 13

Viral oncogenicity effect

Answer 13

• Cell proliferation
• Less differentiated cell forms
• Less effective cell forms
• Usually not able to function effectively
  
  • Tumours

Question 14

Cellular oncogenesis

Answer 14

• Oncogenes: Genes necessary for cell division + maturation
• Active cell: Supressed proto-oncogenes (c-onc)
• Activation - oncogenesis

Question 15

Oncogenic virus examples

Answer 15

• DNA viruses: Papilloma-, Polyoma-
• RNA viruses: Retroviridae

Question 16

Types of tumours

Answer 16

• Benignant: Limited/less destructive
• Malignant: Invasive/ destructive

Question 17

Mechanism of viral oncogenesis: Activation of cellular oncogenes

Answer 17

1. DNA integration into cellular genome
2. Retroviral LTR regions → Intensive promoter → translation
3. c-onc activated
4. Oncoprotein expression → Cell proliferation
5. Development of lymphatic tumours

Question 18

Mechanism of viral oncogenesis: Expression of viral oncogenes

Answer 18

1. Recombination between and proviral genome
2. c-onc gene transposed into virus genome → v-__onc
3. Oncogene carried by the virion
4. Oncoprotein production
5. Development of malignant tumours
6. Replacing essential genes

The v-**onc gene isn’t essential for the virus

Question 19

Mechanism of viral oncogenesis: Viral proteins with consequent oncogenic effect

Answer 19

1. Oncogenic DNA viruses
2. Viral modulator proteins control cell machinery
3. Inactivation of cellular anti-oncogenic proteins
4. Inhibition of apoptosis

Usually benignant tumours

Question 20

In vitro cell cultures lead to

Answer 20

Malignant transformation