Identification of epitopes on respiratory syncytial virus proteins by competitive binding immunoassay

To characterize the interrelationship of monoclonal antibodies (MAbs) against respiratory syncytial virus (RSV) and their respective epitopes, we developed a competitive binding assay based on the biotin-avidin system and a tissue culture enzyme-linked immunosorbent assay. The competitive binding assay clearly distinguished between competing and noncompeting MAbs. Eight MAbs against the fusion protein (F protein) demonstrated two blocking patterns consistent with two antigenic sites. MAbs reacting at one site neutralized the virus, while those reacting at the other site did not. Eight MAbs against the large glycoprotein (G protein) demonstrated five blocking patterns consistent with three antigenic sites, one with three epitopes and the other two with one each. None of the MAbs against G protein neutralized the virus. The reaction pattern of the MAbs against three strains of RSV identified three additional epitopes on the F protein and no additional epitopes on the G protein. The epitopes on G protein showed the greatest antigenic diversity among the three strains. These results help us better understand the functional and antigenic structure of the two surface glycoproteins of RSV.