The Expressed L1 Proteins of HPV-1 HPV-6, and HPV-11 Display Type-Specific Epitopes with Native Conformation and Reactivity with Neutralizing and Nonneutralizing Antibodies
Previous studies demonstrated that the human papillomavirus (HPV) type 1 LI protein, expressed in cos cells by an SV40-based vector, displays conformational epitopes characteristic of native virions. In this study, we analyzed the expression of HPV-1, HPV-6, and HPV-11 LI proteins in order to determine the forms of conformational epitopes expressed by recombinant LI proteins. Using both immunofluorescence and immunoprecipitation techniques, polyclonal and monoclonal antibodies (MAbs) generated against native HPV-11 virions reacted with expressed LI proteins of HPV-6 and/or HPV-11, but not HPV-1. Similarly, polyclonal antibodies and MAbs generated against HPV-1 virions reacted with the expressed LI protein of HPV-1, but not HPV-6 or HPV-11. Of two MAbs that neutralized HPV-11 infection of murine fetal foreskin xenografts, one reacted with the expressed LI protein of both HPV-6 and HPV-11, and the other reacted with HPV-11 only. A nonneutralizing conformationally dependent MAb reacted with the expressed LI protein of both HPV-6 and HPV-11. These results demonstrate that expressed HPV LI proteins retain type-specific, neutralizing, and nonneutralizing conformational epitopes and that cos cells may be utilized to evaluate host immune responses to such epitopes.