FIG. 1.

Diagram of the method used for identification of neutralizing epitopes. Antibodies and VLPs were incubated together overnight as described in Materials and Methods. In the presence of wild-type HPV16 VLPs or hybrid VLPs that retained neutralizing epitopes, the effective concentrations of neutralizing antibodies are reduced. Pseudovirus was then added, the cells were infected, and secreted alkaline phosphatase activity was measured 3 days postinfection. If pretreatment of sera failed to adsorb neutralizing activity, low alkaline phosphatase activity was detected. Conversely, high alkaline phosphatase activity indicated a low concentration of neutralizing antibodies and that the VLPs used for pretreatment retained neutralizing epitopes.