The effect of neutralizing monoclonal antibodies on early events in Rift Valley fever virus infectivity.

Monoclonal antibodies (mAb) were used to examine possible stages at which antibody-mediated neutralization of Rift Valley fever virus occurs, and to assess whether binding of antibody is dependent on viral protein structure in order that antibody recognition take place. Analysis of the structural properties of the antigenic determinants revealed that the neutralizing sites are highly conformation-dependent. None of the mAb prevented virus binding, suggesting that the epitopes they define are spatially separate from the site(s) responsible for virus attachment to the cellular receptor. The finding that many of the mAb also did not inhibit virus entry into the cell demonstrated that neutralization of RVFV infectivity by immune antibodies is not dependent on blocking at the early stages in the viral life cycle.