Protective epitopes on the fusion protein of respiratory syncytial virus recognized by murine and bovine monoclonal antibodies

AFRC Institute for Animal Health, Compton Laboratory, Compton, Nr Newbury, Berkshire RG16 0NN, U.K. The regions of the fusion protein of respiratory syncytial virus (RSV) that react with neutralizing, fusion-inhibiting and highly protective bovine and murine monoclonal antibodies (MAbs) were mapped by two methods: (i) competitive binding assays and (ii) production and analysis of antibody-escape mutants. Competitive binding assays with 16 murine and 10 bovine MAbs identified 11 antigenic sites on the fusion (F) protein, many of which overlapped extensively, and indicated that cattle, a natural host for RSV, and mice recognize similar epitopes. Neutralizing MAbs identified four sites, two of which were also fusion-inhibiting and highly protective in mice. The pattern of reactivity of antibody-escape mutants with the MAbs confirmed the mapping of the protective epitopes deduced from competitive binding assays. A comparison of the biological properties of MAbs to the F protein indicated that protection against RSV infection correlated with fusion inhibition rather than neutralization titre or complement-dependent lysis of virus-infected cells. Received 20 March 1992; accepted 11 May 1992.