The Evolutionary Significance of Neutralization Sites
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Neutralization sites are regions on the surface of a virus particle which on binding antibody result in the loss of infectivity. Neutralizability is a particular property since many viruses have other, different sites which are immunogenic and bind antibody but do not result in neutralization (see below). Nearly all viruses have neutralization sites and, to the knowledge of this reviewer, only African swine fever virus (HESS 1981 ; ViñUela 1985) and Marburg and Ebola viruses of the Filoviridae (Regnery et al. 1981) lack the ability to be neutralized. Non-neutralizing virus-specific antibodies are made during infection, or by immunization with these viruses, and it is assumed that infection is controlled by cellular immunity. Loss of neutralizability is known to occur in vivo: after neuroadaptation Sindbis virus retains the ability to bind antibody that neutralizes the original virulent strain but is itself no longer neutralized (Stanley et al. 1985); the same occurs with poliovirus after attenuation, and reversion is accompanied by a return to neutralizability (Crainic et al. 1983). The existence of epitopes which are neutralizing in one strain and non-neutralizing in another has already been mentioned (Sect. 17; Table 4), and may be a reflection of the same phenomenon.