Figure 1

Diagram of neutralization assay steps. A virus is incubated for an hour with neutralizing antibodies, then TZM-bl cells are added and the mixture is incubated for an additional two days. The TZM-bl cells have been genetically modified with Tat-inducible luciferease, so they will luminesce when infected. The extent of infection is measured by observing the luminescence of these cells. High levels of luminescence indicate high levels of infection, so antibodies have not had success in neutralizing the virus, leaving it free to infect cells.