Neutralization of CRPV infectivity by monoclonal antibodies that identify conformational epitopes on intact virions

Monoclonal antibodies were generated against cottontail rabbit papillomavirus (CRPV) and tested for neutralization of CRPV-induced papillomas on domestic NZW rabbits. Intact CRPV was semi-purified on CsCl gradients and used to immunize BALB/c mice. Hybridomas were prepared from a fusion with lymph node cells, and supernatants from growing hybridomas were analyzed by enzyme-linked immunosorbent assay (ELISA) for reactivity to both intact and disrupted CRPV virion antigen. Supernatants from 22 cultures were initially selected that were responsive to CRPV. Ten were reactive to intact CRPV alone, 4 were reactive only to disrupted CRPV, and 8 were reactive to both intact and disrupted CRPV virion antigen. None of these supernatants contained antibodies which recognized epitopes on CRPV capsid proteins (L1 and L2) that were separated on Western blots. Five hybridomas which produced antibodies that bound to intact CRPV, and did not react to intact HPV-11 or BPV-1 were selected and tested for antibody-mediated neutralization of CRPV infectivity. All five monoclonal antibodies were neutralizing, and identified epitopes on intact CRPV virions which were non-linear and conformational in nature. The five neutralizing monoclonal antibodies appeared to recognize a similar epitope or epitope cluster on the intact CRPV virion as determined by competition ELISA.