Question

A very prominent virologist, you decided to play in your laboratory growing different viruses. You have obtained one enveloped, icohahedral positive strand RNA virus. The replication of this virus is insensitive to any nucleic acid synthesis inhibitor you can think of. Your only problem is that the susceptible cells are human lung epithelial cells, which you do not have.

During a recent meeting of the American Society of the Frustrated Virologists, you heard a paper describing how monkey kidney cells (Vero) could be successfully infected with the virus you have. The trick is to co-infect or pre-infect Vero cells with a virus that would cause fusion from without between normal and infected cells.

Back in your Fort, you decide to try this experiment. You have two viruses that can help you, RSV and Sendai virus, both are paramyxoviruses, Which virus will you use?

Be specific when answering the following:

a. Discuss the mechanism that would allow your virus to establish a productive infection, in otherwise non-susceptible cells

b. Will the progeny virions be able to continue infecting Vero cells?

Hint: Fusii\on from without between two cells can occur within 30 minutes following infection with an m.o.i of 5. Such cell fusion is also achieved even if the fusing virus has been inactivated by ultra violet radiation prior to infect

You infected 3,000,000 cells with 9,000,000 pfu of the fusing virus (titer determined before the start of the experiment)

Answer 1

1. Sendai viruses or murine parainfluenza type I viruses are negative sense RNA viruses. Co-infection using this virus helps in expressing many exogenous genes that helps in assembling and replication of the infective virus. In other word, Sendai virus acts as helper virus.

2. Co-infecting your virus along with the Sendai virus would help in causing infection in non-succeptible cells. The procedure is:

• Cultue non-succeptible cells in a culture plate
• Infect the cultured cells with the virus that you have (positive strand RNA virus)
• Co-infect the virally infected cells with Sendai viruses that acts as a helper virus to aid in replication and packaging of the viral cells.
• This was the viral particles will kill the non-succeptible cells and form plaques.

3. The progeny virions will continue to infect Vero cells because during the packaging procedure, the infectious part or protein of the Sendai virus was involved with your viral particles and hence that will help in infecting the next cells that are infected with the virions.