Analysis of the antigenic sites of O₁Kaufbeuren foot-and-mouth disease virus
Sequence analysis of monoclonal antibody (MAb) neutralisation resistant mutants of the O₁Kaufbeuren (O₁K) strain of foot-and-mouth disease virus (FMDV) confirmed the existence of four antigenic sites previously defined by cross-neutralisation experiments. All three surface exposed capsid proteins were found to contribute to the antigenicity of the virus. Antigenic site 1 involved residues 144, 148, 154 and 208 of VP1. Antigenic site 2 was located on VP2, and involved residues 70, 71, 72, 73, 75, 77 and 131. Antigenic site 3 involved rsidues 43, 44 and 45 of VP1. Antigenic site 4 involved residues 56 and 58 of VP3. The amino acid residues idenitifed as contributing to the antigenic sites formed discreet clusters located on the surface of the three-dimensional structure of the virus. The antigenic sites identified are analogous to the antigenic sites identified in other picornaviruses. Five poliovirus/FMDV antigen chimaeras were constructed in collaboration with Karen Burke at Reading University. Viable virus was recovered from four of these constructs in which antigenic site 1 of poliovirus type 1 Sabin was replaced with sequences corresponding to O1K FMDV VP1 residues 40-49 (chimaera 5/6), 141-154 (chimaera 1/2), 147-156 (chimaera 3/4) 140-160 (chimaera ABCD). Only chimaera ABCD reacted with FMDV specific MAbs and polyclonal sera in immune diffusion and neutralisation assays. Chimaera ABCD was neutralised by polyclonal anti-FMDV sera, and by three of five MAbs directed against FMDV antigenic site 1. Two neutralisation resistant variants of this chimaera were selected using polyclonal anti-FMDV sera or a FMDV site 1 specific MAb. A single amino acid substitution was identified in both variants at a position equivalent to FMDV residue 148. Chimaeras 5/6 and ABCD induced significant levels of FMDV neutralising antibody in guinea pigs. Reduced neutralisation titres were observed with these sera against MAb neutralisation resistant variants of FMDV, demonstrating the specificity of the antibodies for the FMDV sequence in the chimaera. In preliminary experiments, immunisation of guinea pigs with chimaera ABCD could protect against FMDV challenge.