Abstract:
Recombinant single-chain variable fragments (scFvs) of antibodies make it possible to localize antigenic
and immunogenic determinants, identify protective epitopes and can be exploited for the design of
improved diagnostic tests and vaccines. A neutralizing epitope, as well as other potential antigenic sites of
a SAT2 foot-and-mouth disease virus (FMDV) were identified using phage-displayed scFvs. Three unique
ZIM/7/83-specific scFvs, designated scFv1, scFv2 and scFv3, were isolated. Further characterization of
these scFvs revealed that only scFv2 was capable of neutralizing the ZIM/7/83 virus and was used to
generate neutralization-resistant virus variants. Sequence analysis of the P1 region of virus escaping
neutralization revealed a residue change from His to Arg at position 159 of the VP1 protein. Residue
159 is not only surface exposed but is also located at the C-terminal base of the G–H loop, a known
immunogenic region of FMDV. A synthetic peptide, of which the sequence corresponded to the predicted
antigenic site of the VP1 G–H loop of ZIM/7/83, inhibited binding of scFv2 to ZIM/7/83 in a concentrationdependent
manner. This region can therefore be considered in the design of SAT2 vaccine seed viruses
for the regional control of FMD in Africa.
