Characterisation and epitope mapping of neutralising monoclonal antibodies to A(24) Cruzeiro strain of FMDV

Characterisation of seven neutralising monoclonal antibodies (mAbs) produced against foot-and-mouth disease virus A(24) Cruzeiro revealed three reactivity groups. Gr-I recognised linear epitopes where as Gr-II was conformation-dependent and trypsin-insensitive. The Gr-III was also conformation-dependent, but trypsin-sensitive. Mar (mAb neutralisation resistant)-mutants could only be produced against Gr-I and Gr-III mAbs. Capsid sequence comparison of Gr-I mar-mutants with parent virus revealed changes in the G-H loop of VP1 at positions 141,143 and 147. Similarly, a Gr-III mar-mutant showed a change from a highly conserved glycine to a tryptophan at position 148 of VP1 along with three additional changes at the N-terminus of VP1, VP2 and VP4. This residue at 148 of VP1 is located at +2 position after "RGD" and is equivalent to the position identified by the mAb recognising site 5 in serotype O viruses. This site is probably formed because of the interaction of the G-H loop with other residues in different structural proteins.