Microneutralization Assay for Swine Influenza Virus in Swine Serum

The microneutralization (MN) assay is a modification of the serum virus neutralization assay and is a serological test to detect the presence of functional systemic antibodies that prevent infectivity of virus. When infectious virus is mixed with serum antibody, the virus infectivity can be “neutralized” if the antibodies bind to blocking epitopes on the virus. The neutralization effect can be demonstrated by inoculation of susceptible cells or organisms with the antibody–virus mixture, such as cells in culture, embryonated eggs, or susceptible hosts. The results of the MN assay described here are measured based on cell culture in a microtiter plate format and a color change detected by an automated plate reader. The test is performed with a constant amount of virus and serial dilutions of serum samples to an end point where virus neutralization is no longer detected. The neutralizing antibody titer is thus the reciprocal number of the last dilution of serum with neutralizing activity. The MN assay can be used to detect antibody from pigs with natural exposure or vaccination and can potentially be used to predict cross-protection between strains of influenza A virus.