The samples were considered positive if the OD values were ≥X2 above the day 0 sera. To assess the likely disruptive effect of the A− G-H loop deletion, the predicted amino

acid sequences of the VP1 polypeptides Vorinostat of either A+ or A− were substituted for that of O1/BFS 1860/UK/67 (accession 1FOD; [18]) using the structural prediction software ESyPred3D [19]. The subsequent structures were plotted using RasMol 2.7.3.1 [20]. Sequence comparison of the capsid coding regions of A+ and A− confirmed the absence of the VP1 G-H loop in A− (13 deletions located at residues 142–154) and only 2 other amino acid substitutions, both in VP1; residues 141 (A to V) and 155 (A to K). A comparison of the A+ and A− VP1 polypeptides Protein Tyrosine Kinase inhibitor using ESyPred3D, and based on the co-ordinates of O1/BFS 1860/UK/67 [18], demonstrated that the residual G-H loop amino acids of the A− virus were sufficient to form a smaller loop leaving the core tertiary structure of the protein unchanged (Fig. 1). To confirm the loss of

the antigenic site in the shortened VP1 G-H loop of A−, the characteristics of A+ and A− were examined by a panel of MAbs generated against A22/IRQ/24/64 (Fig. 2) whose epitopes are located on the VP1 G-H loop coding region and were similar to that of A+, differing at only six amino acid residues. These positions, namely 133, 136, 139, 140, 142 and 160, were not predicted as antigenically significant by Bolwell et al. [16]. All six of the anti VP1 G-H loop MAbs reacted well with A+ and homologous A22/IRQ/24/64 but did not react with A− or trypsin oxyclozanide treated A+ (Fig. 2). Sera collected on days 0, 7, 14 and 21 were tested by virus neutralisation test (VNT) to assess the virus neutralising antibody response to vaccination. Fig. 3 shows that vaccines prepared from A− or A+ produced a similar response and induced

detectable levels of anti-FMDV neutralising antibody as early as 7 days post vaccination with an identical response at day 21. In order to determine whether a vaccine prepared from A− is likely to protect cattle from challenge against the homologous and A+ viruses, serum antibody titres were used to calculate the degree of predicted protection by cross referencing serum neutralising titres obtained in this study against protection titres defined by Brehm et al. [21]. Brehm et al. [21] demonstrated that serum neutralising titres of 0.5, 1.0, 1.5, 2.0 and 2.5 can provide protection in 44%, 79%, 85%, 94% and 100%, respectively, of animals vaccinated with a high potency serotype A vaccine and then challenged with different serotype A viruses of variable antigenic relatedness to the vaccine strain [21]. Taking into account that this is a new approach for predicting protection which encompassed different sera and viruses and did not include control sera from the original Brehm study, relationship values (r1) were also determined from the serum neutralising antibody titres.