Plaque reduction neutralization test

The Plaque reduction neutralization test is used to quantify the titer of neutralising antibody for a virus.

The serum sample or solution of antibody to be tested is diluted and mixed with a viral suspension. This is incubated to allow the antibody to react with the virus. This is poured over a confluent monolayer of host cells. The surface of the cell layer is covered in a layer of agar or carboxymethyl cellulose to prevent the virus from spreading indiscriminately. The concentration of plaque forming units can be estimated by the number of plaques (regions of infected cells) formed after a few days. Depending on the virus, the plaque forming units are measured by microscopic observation, fluorescent antibodies or specific dyes that react with infected cells.