MULTI-HIT MODEL FOR NEUTRALIZATION OF ANIMAL VIRUSES

Neutralization of animal viruses by antibodies has been studied in many virus-antiserum-cell systems, and the relevant literature has been extensively reviewed on several occasions (Burnet, Keogh & Lush, 1937; Fazekas de St Groth, 1962; Svehag, 1968; Osterrieth, 1972). There is at present no consensus of opinion on whether a general mechanism of neutralization exists by attachment of a single antibody molecule, or of several antibody molecules, to the surface of a virus particle; both a single-hit mechanism (Dulbecco, Vogt & Strickland, 1956; Fazekas de St Groth, 1962; Mandel, 1960, 1976) and a multi-hit mechanism (Gard, 1957; Westaway, 1965b, 1968a; Hierholzer & Dowdle, 1970; Wallis, 1971) have been proposed. The discussion to follow deals only with animal viruses; plant and bacterial viruses are excluded because their modes of entry into host cells differ from those of animal viruses and because antibody is not a defence mechanism of their hosts against infection. It should be noted that the data reviewed relates to conditions of antibody excess (rather than to antigen excess). Such experiments are the most useful in the context of neutralization because the percentage law applies, i.e. in the presence of excess antibody, the percentage or fraction measured as surviving virus remains constant with increasing or decreasing virus concentration.