Antigenicity of bovine papillomavirus type 1 (BPV-1) L1 virus-like particles compared with that of intact BPV-1 virions

Virus-like-particles (VLPs) of various papillomavirus (PV) types have been produced by expressing recombinant L1 proteins in eukaryotic cells. Although VLPs have the same ultrastructural appearance as native virions and their immunogenicity appears to be similar, their antigenicity has not been carefully evaluated. For this reason, the antigenicity of intact bovine PV type 1 (BPV-I) virions was compared with that of BPV-1 recombinant L1 VLPs by ELISA using a well-characterized panel of polyclonal and monoclonal antibodies generated against intact and denatured BPV-1 particles. The structural integrity of the authentic virions and recombinant VLPs was verified by electron microscopy. The specificity of antibodies raised against intact BPV-I virions and their reactivity with VLPs revealed that the immunodominant, type-specific, conformational epitopes of intact virions were reproduced on VLPs. However, many monoclonal antibodies that define cross-reactive, non-conformational (linear) epitopes cryptic to the authentic BPV-1 virion tested positively when reacted with intact VLPs. One monoclonal antibody, which recognizes a BPV-1 and deer PV surface conformational epitope, did not react with VLPs. Therefore, although VLPs can be used to immunize animals against infection, the external exposure of broadly cross-reactive epitopes of intact L1 VLPs suggests that the use of L1 VLPs in antigenicity studies such as serological screening should be done with caution.