Why does plaque reduction confirm antiviral efficacy in this assay?

A decrease in plaque-forming units indicates that the antiviral drug inhibits viral replication, spread, or both, providing direct evidence of efficacy. This metric allows quantification of drug potency through dose-response analysis.

How does serial dilution improve accuracy in virus titer measurement?

Serial dilution ensures that individual virions infect single cells, preventing overlap and enabling discrete plaque formation for accurate counting. It allows extrapolation of titer from countable dilutions to the original sample.

What quantitative output enables antiviral potency ranking?

Plaque count per well, converted to plaque-forming units per milliliter (PFU/mL), provides a quantitative measure of infectious virus titer. Comparing PFU/mL between treated and untreated samples reveals drug-induced reduction in viral load.

Why are replication requirements important for assay validity?

Running experiments in triplicate ensures statistical reliability and accounts for biological variability in tissue samples and viral stocks. Consistent plaque reduction across replicates strengthens confidence in antiviral efficacy.

What statistical analysis is needed before interpreting plaque assay results?

Results require calculation of mean and standard deviation from triplicate plaque counts to assess variability. Significant reduction in PFU/mL relative to control, typically assessed via t-test or ANOVA, confirms antiviral effect.

Determining Antiviral Efficacy of Experimental Drugs Through a Plaque Assay

JoVE Encyclopedia of Experiments

Immunology

0 views • 2:48 min • July 8th, 2025

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Begin with a virus-containing sample obtained from an infected porcine cornea treated with an antiviral drug.

Perform a serial dilution of the sample to create a sequence of decreasing virus concentrations.

Optimum dilution prevents single-cell infection by multiple viruses.

Introduce the diluted samples to a host-cell monolayer and incubate.

The virus attaches to the host-cell receptor, enters the cell, and initiates its replication. The infected cell lyses, releasing virions.

Add methylcellulose, a viscous substance that confines the viruses to the nearby cells.

Subsequently, the viruses cause cell death and plaque formation in the infected region.

Add methanol to fix the cells.

Use crystal violet to stain the live cells.

Observe plaques as clear zones indicating infected cells and cell death, surrounded by crystal violet-stained uninfected cells.

Finally, count the number of plaques at the highest dilution to quantify the virus titer in the starting solution to determine the efficacy of the antiviral drug.

To quantify the amount of virus collected from each cornea, prepare a log₁₀one-fold dilution of the virus in serum-free medium in microcentrifuge tubes until a dilution of 1 x 10^-8 is reached.

After aspirating the growth medium from each well of cells, transfer 1 milliliter of each virus dilution, starting at 1 x 10^-3 to the plated cell monolayers, and place the infected cells in the cell culture incubator for two hours. At the end of the incubation, gently wash each well 2 times with PBS before adding 2 milliliters of methylcellulose-laden medium to each well for a 72-hour incubation, or until the formation of plaques can be observed.

Upon plaque observation, slowly add 1 milliliter of methanol to the corner of each well for a 15-minute incubation at room temperature. At the end of the incubation, slowly aspirate the contents from each well without disturbing the cell monolayer.

Next, label each well with 1 milliliter of crystal violet working solution, taking care that all of the cells are covered for a 30-minute incubation protected from light. At the end of the incubation, discard the solution and dry the wells on a sheet of absorbent paper. Then, count the number of plaques at the highest dilution well to quantify the total virus content in the starting solution 3 times.