Human papillomavirus types 6 and 11 have antigenically distinct strongly immunogenic conformationally dependent neutralizing epitopes

Antibodies reactive to HPV types 6 and 11 were tested in ELISA and HPV-11 neutralization assays to determine whether these closely related types shared cross-reactive neutralizing epitopes. A series of HPV-11 neutralizing monoclonal antibodies (N-MAbs) that targeted conformational epitopes on infectious HPV-11 and HPV-11 L1 virus-like particles (VLPs) were tested for type-specificity of reactivity using intact HPV-6 L1 VLPs. Polyclonal antisera generated against intact HPV-6 Li VLPs were also tested for HPV-11 neutralizing capacity using the athymic mouse xenograft system. The results demonstrated that conformationally dependent neutralizing epitopes on HPV-11 were very type-specific. Three of the four HPV-11 N-MAbs were negative for binding to HPV-6 L1 VLP, and the fourth demonstrated binding to HPV-6 L1 VLPs that was several orders of magnitude weaker than its binding to HPV-11 L1 VLP. The polyclonal anti-HPV-8 L1 VLP antiserum was only partially protective against HPV-11 infectivity even at a low dilution of 1:100. In contrast, polyclonal anti-HPV-11 L1 VLP antiserum was completely protective at dilutions greater than 1:10,000.