The lyssavirus glycoprotein: how significant are the currently characterised antigenic sites in the induction of neutralising antibodies?

Rabies, the archetypal lyssavirus, is one of the most feared viruses known to man and causes >50,000 deaths per year. Other members of the lyssavirus genus cause clinical disease consistent with rabies. The lyssavirus glycoprotein is the sole target for virus neutralising antibodies and several amino acid epitopes have been linked to virus neutralisation. Lyssaviruses are segregated into phylogroups that indicate the level of protection afforded by current vaccines. It is generally accepted that an antibody response to rabies vaccines affords protection against all viruses that are categorised into phylogroup I. However, this antibody response does not protect against lyssavirus species within phylogroups II and III. Indeed, experimental data has shown that the antibody repertoire induced by rabies virus vaccines is completely unable to neutralise viruses in these phylogroups. In this study we have generated lentivirus pseudotypes containing chimeric lyssavirus glycoproteins that have had their antigenic sites swapped between phylogroup I and II viruses. With these we have assessed neutralisation of both wildtype and chimeric pseudotype particles with both phylogroup I and phylogroup II specific hyperimmune sera. We have used chimeric pseudotype viruses to analyse the role of defined antigenic domains in development of phylogroup specific immune responses