Chapter 11 - Animal Cell Culture Products: Viruses

Question 1

How are large quantites of viruses produced?

Answer 1

1. Embryonated hen eggs - embryonic membranes lining the various regions of the egg can be used for growing viruses

Amniotic cavity

Yolk sac

Allantoic sac

Chlorioallantoic membrane

2. Intact animals: harvest the antigen for the vaccine from humans; must circulate large amounts of surface antigen of the virus in the blood
3. Animal cell cultures: good because economy, simplicity, can use human cells and ethical considerations

Question 2

What are the 4 phases of the lytic cycle?

Answer 2

1. Absorption - viral proteins in capsid bind to host cell membrane
2. Penetration - viral particle enters or injects nucleic acids into the host cell
3. Replication - synthesis of viral components & assembly of viral particles
4. Release - lysis of viral particles to the extracellular fluid

Question 3

What is a plaque forming unit?

Answer 3

The ability of a single viral particle fo create a plaque on a cell monolayer

Question 4

What factors are conisdered when producing viruses in human cell cultures?

Answer 4

• Cells were derived from normal foetal tissue
• Little deviation in karyotype
• Normal morphology
• Absence of extraneous orgnaisms
• Lack in vivo tumourigenicity
• Give high yields of virus
• Sufficient supply of cells (cryopreseve in early stages)

Question 5

What types of cell cultures can be used to produce viruses?

Answer 5

Cell lines from tumours - cheaper to grow and do not need as much serum

Continuous cell lines

Question 6

How are viral pesticides different from chemical pesticides?

Answer 6

Viral pesticides are often specific to a few target insects and are relatively safe to use as compared with chemical pesticides

Question 7

What are advantages of Baculovirus insecticides?

Answer 7

• limited host range (targets specific insects and have few closely related insect species)
• minimal potential damage to the environment

Question 8

Describe the biphasic nature of the baculovirus replication cycle

Answer 8

Phase I - viral particles enter the cell via receptor mediated endocytosis and takes over the host cell in order to replicate viral proteins. The mature viral particles bud through the cell membrane and begin the secondary infection.

Phase II - The viral particles produced in phase I re-infect other cells and produce more particles placed in occlusion bodies. Eventually the cells will lyse and release the occlusion bodies.

Question 9

What cell lines are used to grow strains of baculovirus in vitro?

Answer 9

Spodoptera fungiperda (SF9 cells)