VNT (Virus Neutralisation Tests)
All Biobest virus neutralisation tests follow a similar format. Serial dilutions of heat inactivated test serum are prepared in a 96 well plate and are incubated with a set amount (usually 100 TCID50) of infectious virus. Following this incubation, virus susceptible cells are added to the virus-serum mixture, and the final virus/serum/cell combination is incubated for a period of 2-3 days.
After this incubation period the test is read by examining each well of the plate for the presence of viral infection. Depending on the virus, this may be by direct microscopic examination of the plate for evidence of viral Cytopathic effect (CPE) or, if the virus causes little or no CPE, by immunofluorescent staining of the test wells for the presence of viral antigen in the cell monolayer. Sera which contain antibodies to the virus in question are able to neutralise the aliquot of virus used in the test, thus preventing infection of the cells when they are added to the plate. Where high concentrations of antibody to the virus in question are present in the serum sample, virus neutralisation will occur even at high serum dilutions.
Conversely, where little or no antibody to the virus is present in the test sample, it will be unable to neutralise the aliquot of infectious virus at the first dilution used in the test. The result of the test is the point at which the serum sample has been diluted such that it is no longer able to neutralise all the virus in the test. This dilution, or its log equivalent, is reported as the titre of the serum tested.