Response of foot-and-mouth disease virus C3 Resende to immunological pressure exerted in vitro by antiviral polyclonal sera

Identification of novel epitopes in serotype O foot-and-mouth disease virus by in vitro immune selection

Foot-and-mouth disease virus (FMDV) displays various epitopes on the capsid outer surface. In addition to the five neutralizing antigenic sites, there is evidence of the existence of other, yet unidentified, epitopes that are believed to play a role in antibody-mediated protection. Previous attempts to identify these epitopes revealed two additional substitutions at positions VP2-74 and -191 (5M2/5 virus) to be of antigenic significance. However, complete resistance to neutralization was not obtained in the neutralization assay, indicating the existence of other, undisclosed epitopes. Results from this study provides evidence of at least two new neutralizing epitopes involving residues VP3-116 and -195 around the threefold axis that have significant impact on the antigenic nature of the virus. These findings extend our knowledge of the surface features of the FMDV capsid known to elicit neutralizing antibodies, and should help with rational vaccine design.

Prediction and characterization of novel epitopes of serotype A foot-and-mouth disease viruses circulating in East Africa using site-directed mutagenesis

Epitopes on the surface of the foot-and-mouth disease virus (FMDV) capsid have been identified by monoclonal antibody (mAb) escape mutant studies leading to the designation of four antigenic sites in serotype A FMDV. Previous work focused on viruses isolated mainly from Asia, Europe and Latin America. In this study we report on the prediction of epitopes in African serotype A FMDVs and testing of selected epitopes using reverse genetics. Twenty-four capsid amino acid residues were predicted to be of antigenic significance by analysing the capsid sequences (n = 56) using in silico methods, and six residues by correlating capsid sequence with serum-virus neutralization data. The predicted residues were distributed on the surface-exposed capsid regions, VP1-VP3. The significance of residue changes at eight of the predicted epitopes was tested by site-directed mutagenesis using a cDNA clone resulting in the generation of 12 mutant viruses involving seven sites. The effect of the amino acid substitutions on the antigenic nature of the virus was assessed by virus neutralization (VN) test. Mutations at four different positions, namely VP1-43, VP1-45, VP2-191 and VP3-132, led to significant reduction in VN titre (P value = 0.05, 0.05, 0.001 and 0.05, respectively). This is the first time, to our knowledge, that the antigenic regions encompassing amino acids VP1-43 to -45 (equivalent to antigenic site 3 in serotype O), VP2-191 and VP3-132 have been predicted as epitopes and evaluated serologically for serotype A FMDVs. This identifies novel capsid epitopes of recently circulating serotype A FMDVs in East Africa.

Selection and characterization of human respiratory syncytial virus escape mutants resistant to a polyclonal antiserum raised against the F protein

A human respiratory syncytial virus (HRSV) neutralization escape mutant was obtained after 56 serial passages in the presence of a polyclonal antiserum raised against the F protein. Nucleotide sequence analysis of this escape mutant virus revealed two amino acid substitutions: Asn268Ile and Val533Met. When this virus was allowed to grow in the absence of the anti-F polyclonal serum, only the mutation Asn268Ile was stably maintained. Both the double and single escape mutant viruses lost reactivity with mAbs belonging to antigenic site II of the fusion protein of RSV. Mutation Asn268Ile has already been reported in RS viruses that are resistant to mAbs 47F and 11 and palivizumab (PZ). We have thus identified a novel mutation (Val533Met) in the transmembrane domain of the F protein that was selected under immune pressure.

B cell epitopes within VP1 of type O foot-and-mouth disease virus for detection of viral antibodies

In this study, the coding region of type O FMDV capsid protein VP1 and a series of codon optimized DNA sequences coding for VP1 amino acid residues 141-160 (epitope1), tandem repeat 200-213 (epitope2 (+2)) and the combination of two epitopes (epitope1-2) was genetically cloned into the prokaryotic expression vector pP(RO)ExHTb and pGEX4T-1, respectively. VP1 and the fused epitopes GST-E1, GST-E2 (+2) and GST-E1-2 were successfully solubly expressed in the cytoplasm of Escherichia coli and Western blot analysis demonstrated they retained antigenicity. Indirect VP1-ELISA and epitope ELISAs were subsequently developed to screen a panel of 80 field pig sera using LPB-ELISA as a standard test. For VP1-ELISA and all the epitope ELISAs, there were clear distinctions between the FMDV-positive and the FMDV-negative samples. Cross-reactions with pig sera positive to the viruses of swine vesicular disease virus that produce clinically indistinguishable syndromes in pigs or guinea pig antisera to FMDV strains of type A, C and Asia1 did not occur. The relative sensitivity and specificity for the GST-E1 ELISA, GST-E2 (+2), GST-E1-2 ELISA and VP1-ELISA in comparison with LPB-ELISA were 93.3% and 85.0%, 95.0% and 90%, 100% and 81.8%, 96.6% and 80.9% respectively. This study shows the potential use of the aforementioned epitopes as alternatives to the complex antigens used in current detection for antibody to FMDV structural proteins.

A Novel Mucosal Vaccine Against Foot-and-Mouth Disease Virus Induces Protection in Mice and Swine

Epitopes of a foot-and-mouth disease virus (FMDV) capsid protein VP1 complex and a chimera of 6xHis-tagged cholera toxin B subunit (hCTB) were expressed in Hansenula polymorpha and used together as a mucosal vaccine. Antibody and cytokine responses to VP1-hCTB vaccine and protection against FMDV were evaluated by ELISA and a virus challenge test in mice, respectively. VP1-hCTB directly enhanced the expression of interleukin-5 (IL-5) both in serum and supernatants of cultured spleen cells. After challenging suckling mice with 10(5) FMDV (=50% lethal dosage per mouse) a greater protection was seen after intraperitoneal and intranasal vaccinations than after oral vaccination. In swine immunized with VP1-hCTB, immune responses were achieved after three administrations, and the vaccine protected swine (80%) when challenged with 10(6.5) FMDV (=50% infectious dosage per swine). These results demonstrated the possibility of using CTB as a mucosal adjuvant to elicit protective immune responses against FMDV.

Identification of a neutralizing epitope in the βE–βF loop of VP1 of equine rhinitis A virus, defined by a neutralization-resistant variant

Equine rhinitis A virus strain 393/76 (ERAV.393/76) was passaged in the presence of post-infection ERAV.393/76 equine polyclonal antiserum (EPA). Viruses with increased resistance to neutralization by EPA were obtained after 15 passages. Compared with the parent virus, five plaque-purified, neutralization-resistant mutant viruses, in addition to the non-plaque-purified viruses that were examined, had a Glu→Lys change at position 658, which is located in the predicted βE–βF (EF) loop of VP1. Rabbit antiserum was prepared against the isolated EF loop of ERAV.393/76 VP1 expressed as a fusion protein with glutathione S-transferase. This antiserum bound to purified ERAV.393/76 in Western blots, but not to the neutralization-resistant mutant virus or to ERAV.PERV/62, a naturally occurring ERAV strain that has a Lys residue at position 658. These results suggest that the EF loop of VP1 is involved in a neutralization epitope of ERAV.

Isolation of foot-and-mouth disease virus specific bovine antibody fragments from phage display libraries

Foot-and-mouth disease virus (FMDV) is an important veterinary pathogen which can cause widespread epidemics. Due to the high antigenic variability of FMDV, it is important to undertake mutation analysis under immunological pressure. To study the bovine antibody response at a molecular level, phage display technology was used to produce bovine anti-FMDV Fabs. CH1-VH chains with FMDV specific binding could be isolated after selection from a library made from vaccinated cattle. Though their involvement in the bovine immune response remains to be ascertained, it is planned to express the five different selected VH domains in bacterial or insect systems as sequence homologies with integrin beta6 chain could shed light on the basis of FMDV type receptor specificities.

High-level expression of codon optimized foot-and-mouth disease virus complex epitopes and cholera toxin B subunit chimera in Hansenula polymorpha

A codon optimized DNA sequence coding for foot-and-mouth disease virus (FMDV) capsid protein complex epitopes of VP1 amino acid residues 21-40, 135-160, and 200-213 was genetically fused to the N-terminal end of a 6x His-tagged cholera toxin B subunit (CTB) gene with the similar synonymous codons preferred by the methylotropic yeast Hansenula polymorpha. The fusion gene was synthesized based on a polymerase chain reaction (PCR) and subsequently overexpressed in H. polymorpha. The chimeric protein was successfully secreted into the culture medium (up to 100mg/L) and retained the antigenicity associated with CTB and FMDV antibodies by Western blot analysis. The chimera after purification through Co(2+)-charged resin column bound specifically to GM1 ganglioside receptor and thus retained the biological activity of CTB. This study has important implications in the construction of CTB chimera for mucosal vaccines against FMDV.

Characteristic in vitro evolution pattern of foot and mouth disease virus A81/Castellanos/Arg/87

The in vitro evolution of Foot and mouth disease virus (FMDV) A/81/Castellanos/Arg/87 (A/Castellanos/87) was studied by partial biological and biochemical characterization of viral populations selected after 25 passages on secondary fetal bovine kidney cell monolayers. These passages were performed in the presence or absence of immune pressure exerted in the form of antiviral polyclonal serum. While the viral populations passaged in the absence of immune pressure acquired characteristics such as antigenic heterogeneity, VP1 amino acid modification and plaque size reduction, the populations selected after immune pressure also presented both neutralizing resistance and attenuation for suckling mice. The comparison with other previously studied FMDV strains suggests that FMDV A/Castellanos/87 adopts a differential response to immunological pressure and other selective forces. In addition, the sequencing analysis of viral selected populations shows a restriction in the number and type of amino acid replacements tolerated by FMDV capsid proteins.