Vaccination of cattle with bovine papillomavirus type 4 L2 elicits the production of virus-neutralizing antibodies

1 Department of Veterinary Pathology and 2 the Beatson Institute for Cancer Research, Garscube Estate, Glasgow G61 1BD, UK Prophylactic vaccination of cattle with the N terminus (L2a, aa 11–200) of the minor capsid protein L2 completely prevented bovine papillomavirus type 4 (BPV-4) infection of the alimentary canal. To investigate the mechanisms underlying protection from viral infection, sera from vaccinated animals were analysed in neutralization assays both in the nude mouse xenograft system and in cattle. BPV-4 retained its infectivity when incubated with pre-immune cattle sera, whereas, when incubated with immune sera from animals vaccinated with either whole L2 or its N terminus L2a, its infectivity was greatly reduced, indicating that the immune sera had neutralizing activity against the virus. This activity could be abrogated by absorbing the immune sera with L2 or L2a, thus indicating that virus neutralization was due to the presence in the immune sera of anti-L2 antibodies. Received 25 January 1996; accepted 1 March 1996.