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 L1 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 L1 proteins in order to determine the forms of conformational epitopes expressed by recombinant L1 proteins. Using both immunofluorescence and immunoprecipitation techniques, polyclonal and monoclonal antibodies (MAbs) generated against native HPV-11 virions reacted with expressed L1 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 L1 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 L1 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 L1 protein of both HPV-6 and HPV-11. These results demonstrate that expressed HPV L1 proteins retain type-specific, neutralizing, and nonneutralizing conformational epitopes and that cos cells may be utilized to evaluate host immune responses to such epitopes.