Antigenic analysis of the F protein of the bovine respiratory syncytial virus: identification of two distinct antigenic sites involved in fusion inhibition. 
From two independent fusions, fifteen MAbs directed to the F protein of the bovine respiratory syncytial virus (BRSV) were characterized by radio-immunoprecipitation assays.  Competition binding assays among these MAbs identified two distinct antigenic sites (A and B) and one overlapping site (AB).  All of the MAbs specific to epitopes belonging to site A neutralized the infectivity of the virus in vitro and recognized human and bovine RSV strains.  Only two out of the five MAbs directed to epitopes of site B were neutralizing and three reacted with all of the RSV strains tested, suggesting that the epitopes constituting this domain present heterogeneous characteristics.  In each of sites A and B, one of the neutralizing MAbs also inhibited cell fusion.  The biological relevance of these domains was established by competing representative MAbs and sera from BRSV-infected calves.