Analysis of foot-and-mouth disease virus type O1 Brugge neutralization epitopes using monoclonal antibodies.

Monoclonal antibodies (MAbs) were elicited with inactivated, purified foot-and-mouth disease virus (FMDV) type O1 strain Brugge (140S) and with 12S protein subunits. Each MAb was tested for its capacity to bind to FMDV O1 Brugge 140S virions, 12S subunits and purified VP1 by radioimmunoassay (RIA) and to neutralize viral infectivity in mouse protection assays. Those MAbs which reacted only with 12S subunits in RIA did not neutralize infectious virus. One MAb, 12FE9.2.1, reacted with 140S, 12S and purified VP1 of FMDV O1 Brugge and neutralized infectious virus. Reactions with different biosynthetic FMDV type O1 Campos VP1 polypeptides localized the binding site of 12FE9.2.1 between amino acid residues 135 and 172. Eight MAbs reacted with both 140S virions and 12S subunits and neutralized infectious virus. Monoclonal antibodies that reacted only with 12S protein subunits or with 140S, 12S and VP1 did not compete in RIA with 140S/12S-reactive neutralizing MAbs for 12S binding sites. The ability of 140S/12S-reactive MAbs to compete for the 12S binding site defined by MAb 10GA4.2.2 was directly related to their capacity to neutralize infectious virus, suggesting that these MAbs were all affecting a single neutralization site. In mouse protection and plaque reduction neutralization assays, 10GA4.2.2 and 12FE9.2.1 were equally effective in neutralizing the homologous FMDV type O1 Brugge, and in cross-neutralization assays both exhibited high titres against four additional strains of type O1 FMDV.