Identification of conformational epitopes of the BPV-1 capsid recognized by competitive inhibition of sera from infected or immunized animals

Conformational papillomavirus (PV) capsid epitopes are the major targets of neutralizing antibodies. BPV1 virion surface epitopes were analyzed for type-specificity, induction of neutralization, and topographical location with antibodies from selected humans, and BPV1 or -2 immunized or infected cattle, rabbits and mice. Rabbit sera produced against deer PV (DPV) or BPV2 and human sera reacted with intact BPV1 in ELISA, indicating the presence of cross-reactive conformational epitopes on the surface of BPV1 virions. However, competitive binding assays performed on intact BPV1 capsids using unlabeled and biotin-conjugated antibodies revealed that the conformational epitopes of BPV1 recognized by rabbit, bovine and human antibodies were topographically different. Only hyperimmune sera to intact BPV1, BPV2 or DPV neutralized BPV1-induced focus formation of C127 cells with the highest neutralizing titers observed for bovine and rabbit antibodies produced against intact BPV1. Our study showed the complexity of conformational capsid epitopes of BPV1 and their importance for inducing a protective humoral immune response in animals inoculated or immunized with BPV1.