Short communication Characterisation and epitope mapping of neutralising monoclonal antibodies to A 24 Cruzeiro strain of FMDV M. Mahapatra a, *, C. Seki b , S. Upadhyaya a , P.V. Barnett a , J. La Torre b , D.J. Paton a a Institute for Animal Health, Pirbright Laboratory, Ash Road, Woking, Surrey GU24 0NF, UK b RIIDFA (Red Institucional de Investigacio ´n y Desarrollo en Fiebre Aftosa), Centro de Virologı´a Animal Instituto de Ciencia y Tecnologı´a Dr. Cesar Milstein, CONICET, Saladillo 2468, C1440FFX Ciudad de Buenos Aires, Argentina Foot-and-mouth-disease (FMD) is an economically devastating disease of cloven hoofed animals with almost global distribution. The causative agent foot-and-mouth disease virus (FMDV), is a single stranded positive sense RNA virus belonging to the genus Aphthovirus in the family Picornaviridae. The virus has a high mutation rate and exists as seven serotypes (O, A, C, Asia 1, SAT1, SAT2 and SAT3) with numerous and constantly evolving subtypes showing a spectrum of antigenic diversity. Several studies have been carried out in the last three decades to identify the neutralising antigenic sites present on FMDV and monoclonal antibodies (mAbs) have been used as powerful tools for identifying the amino acid footprint of different antigenic sites by sequencing mAb neutralisation resistant (mar) mutants. This approach has been successful in delineating the neutralising antigenic sites of viruses representing serotype O (Kitson et al., 1990; Crowther et al., 1993; Barnett et al., 1989; Aktas and Samuel, 2000), A (Thomas et al., 1988; Baxt et al., 1989; Bolwell et al., 1989), C(Mateu et al., 1990), Asia I (Grazioli et al., 2004) and SAT (Grazioli et al., 2006). The results from these studies indicate that the critical amino acid residues for the different ‘‘neutralising’’ antigenic sites reside in the three capsid proteins VP1, VP2 and VP3. Out of the seven serotypes of FMDV, serotype O has been studied most extensively and to date five neutralising antigenic sites have been reported for O1 Kaufbeuren (O1K) virus. Out of these site 1 is linear and trypsin sensitive whereas the others have been reported to be conformation dependent. Crystallographic studies have identified the structure of the FMDV capsid (Lea et al., 1994, 1995; Curry et al., 1992) and immunological epitopes have mostly been found on surface oriented interconnecting loops between structural elements. The bG–bH loop and carboxy terminus of VP1 contribute to neutralising antigenic site 1, with critical residues at Veterinary Microbiology 149 (2011) 242–247 ARTICLE INFO Article history: Received 17 June 2010 Received in revised form 20 October 2010 Accepted 1 November 2010 Keywords: FMD virus Epitopes Monoclonal antibodies Neutralisation escape mutants ABSTRACT 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. ß 2010 Elsevier B.V. All rights reserved. * Corresponding author at: Institute for Animal Health, Pirbright Laboratory, Ash Road, Woking, Surrey GU24 0NF, UK. Tel.: +44 1483 232441; fax: +44 1483 232448. E-mail address: mana.mahapatra@bbsrc.ac.uk (M. Mahapatra). Contents lists available at ScienceDirect Veterinary Microbiology journal homepage: www.elsevier.com/locate/vetmic 0378-1135/$ – see front matter ß 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.vetmic.2010.11.003