ESCAPE MUTANTS OF FOOT-AND-MOUTH-DISEASE VIRUS SELECTED BY MONOCLONAL-ANTIBODIES DIRECTED TO A TRYPSIN-SENSITIVE NEUTRALIZATION EPITOPE

Five monoclonal antibodies (MoAbs) against Indian reference/vaccine st rain of foot-and-mouth disease (FMD) virus subtype A22 (IND17/77) and a guinea pig antibody against a synthetic peptide representing amino a cids (aa) 136-151 of VP1 polypeptide of A22 virus were used in the stu dy. All the antibodies either failed to react or showed a reduced reac tivity with trypsin-treated (TT)-146 S virus particles in enzyme-linke d immunosorbent assay (ELISA), and could neutralize the infectivity of the reference virus. The antibodies were hence identified as specific to a trypsin-sensitive neutralizable antigenic site of the virus. Usi ng the antibodies we isolated mutants which showed either no or reduce d reactivity with the homologous as well as heterologous antibodies in ELISA. The mutants could not be neutralized with the respective antib odies but were efficiently neutralized with the serum from vaccinated cattle (BVS). These results indicated that the antibodies elicited in cattle following vaccination protected them adequately against the mut ants selected and that the trypsin-sensitive neutralizable antigenic s ite of FMD A22 virus as identified by the MoAbs may not be dominant in eliciting a neutralizing antibody response in vaccinated cattle.