Question

The following are the results of an experiment where interferon was added to plates of virally infected cells two hours after initial inoculation with high titers of a virus. The control represents a plate of virally infected cells before and two hours after addition of culture medium. Which of the following patterns of growth would be expected in the control group, assuming the virus is cytolytic?

Short answer

The control group would show a decrease in cell viability due to cytolytic viral activity.

Step-by-step solution

Understand the Definition of Cytolytic Virus

A cytolytic virus is one that causes the destruction of infected cells, leading to cell death. Viruses propagate by breaking open (lysing) the host cell.

Identify Experimental Setup

Recall that interferon was added to the experimental plates two hours after virus inoculation. The control group did not receive interferon but was also observed before and after two hours of culture medium addition.

Determine Growth Pattern in Control Group

Since the virus is cytolytic and no interferon was added to the control group, it is expected that the virus would continue to infect and lyse cells over time. This means the control group should show a decrease in cell viability and an increase in cytopathic effects due to ongoing viral lysis.

Key concepts

cytolytic virus

A cytolytic virus is a type of virus that causes the infected cells to burst open, a process known as cell lysis. This mechanism of action is how the virus spreads within the host. When a cytolytic virus infects a cell, it hijacks the cell's machinery to replicate itself.
As the viral particles multiply, they accumulate inside the cell until eventually, the cell membrane can't hold them all. The cell bursts open, releasing the new viral particles into the surrounding environment. This newly released virus can then infect neighboring cells, continuing the cycle.
Cytolytic viruses are known for causing significant tissue damage. Common examples include certain types of herpes viruses and the common cold virus. Understanding the behavior of cytolytic viruses is crucial in experimental virology and the development of antiviral therapies.

interferon

Interferons are proteins produced by the cells in your body as a defense mechanism against viruses. When a virus infects a cell, the cell releases interferons to alert neighboring cells of the viral threat. This process helps to establish an antiviral state in nearby cells, decreasing their susceptibility to viral infection.
Interferons work by binding to specific receptors on the surface of cells. This binding initiates a signaling cascade that activates the expression of various antiviral genes within the cell. These genes produce proteins that interfere with viral replication and enhance the immune system's ability to combat the virus.
In the experiment mentioned, interferon was added to the plates of virally infected cells. The goal was to see if the interferon could decrease the cytopathic effects caused by the cytolytic virus. By delaying the addition of interferon until two hours after viral inoculation, the experimental design aimed to mimic a typical antiviral response in the body.

control group

In scientific experiments, the control group is a critical component for drawing valid conclusions. It is a standard or baseline group that does not receive the experimental treatment. This allows researchers to compare the effects of the treatment against a known standard.
In this particular experiment, the control group consisted of virally infected cells that did not receive interferon. Instead, they were observed before and after the addition of culture medium two hours post-infection.
The purpose of the control group was to monitor the natural progression of the viral infection and to serve as a benchmark for evaluating the effectiveness of interferon. By comparing the control group with the treated group, researchers can assess the impact of interferon on cell viability and the extent of cell lysis caused by the cytolytic virus.

cell lysis

Cell lysis is the process where a cell breaks down or bursts open, releasing its contents. In the context of a cytolytic virus, cell lysis is a crucial mechanism for viral propagation.
When the virus infects a cell, it takes over the cell's machinery to replicate its genetic material and produce new viral particles. This leads to an accumulation of viral particles within the cell. Eventually, the cell cannot contain the growing number of viral particles, resulting in its rupture, or lysis.
The release of newly formed viruses upon cell lysis leads to the infection of neighboring cells, perpetuating the cycle of infection. This not only facilitates the spread of the virus but also leads to tissue damage and the symptoms associated with viral infections.
In the experiment, the control group of cells continued to undergo cell lysis in the absence of interferon, showing a decrease in cell viability as the infection progressed. Understanding cell lysis's role in viral life cycles is essential for developing strategies to interrupt viral propagation and mitigate disease impact.