Kinetics of foot-and-mouth disease vaccine-induced antibody responses in buffaloes (Bubalus bubalis): avidity ELISA as an alternative to the virus neutralization test.

The role of water buffaloes in foot-and-mouth disease (FMD) epidemiology as one of the major hosts of the virus that can develop persistent asymptomatic infection highlights the importance of sustaining surveillance on the antibody response elicited by vaccination in these animals. There is gap in the knowledge on how serological assays that measure antibodies against capsid proteins perform with buffalo samples and which would be the most reliable test to substitute the virus neutralization test (VNT) a cumbersome and low-throughput tool for field surveillance. Alternatively, the liquid-phase blocking sandwich ELISA (LPBE) is commonly used. Previous data from our laboratory demonstrated that the vaccine-induced antibodies assessed by the LPBE yielded low specificity with buffaloes' samples. In contrast, a single-dilution avidity ELISA (AE) aimed to detect high-avidity antibodies against exposed epitopes, combined with an indirect ELISA (IE) to assess IgG levels, produced more reliable results. Here we analyzed for the first time the kinetics of the antibodies induced by vaccination in two different buffalo herds (n = 91) over 120 days using AE, IE, LPBE, and the VNT. Kinetics were similar in the different assays, with an increase of antibodies between 0- and 14-days post-vaccination (dpv) which were maintained thereafter. VNT and AE results were concordant (Kappa value = 0.76), and both assays revealed a decay in the antibody response in calves with maternal antibodies at 90 and 120 dpv, which was not evidenced by the LPBE. These results show that kinetics of antibody responses to FMD vaccination are similar in buffalo and cattle, and support the use of indirect ELISA assays, in particular Avidity ELISA, as alternatives to the VNT for vaccine-immunity monitoring irrespectively of the animal's passive or active immune status.

Assessment on Different Vaccine Formulation Parameters in the Protection against Heterologous Challenge with FMDV in Cattle.

Foot-and-mouth disease (FMD) remains one of the major threats to animal health worldwide. Its causative agent, the FMD virus (FMDV), affects cloven-hoofed animals, including farm animals and wildlife species, inflicting severe damage to the international trade and livestock industry. FMDV antigenic variability remains one of the biggest challenges for vaccine-based control strategies. The current study analyzed the host's adaptive immune responses in cattle immunized with different vaccine protocols and investigated its associations with the clinical outcome after infection with a heterologous strain of FMDV. The results showed that antigenic payload, multivalency, and revaccination may impact on the clinical outcome after heterologous challenge with FMDV. Protection from the experimental infection was related to qualitative traits of the elicited antibodies, such as avidity, IgG isotype composition, and specificity diversity, modulating and reflecting the vaccine-induced maturation of the humoral response. The correlation analyses of the serum avidity obtained per vaccinated individual might suggest that conventional vaccination can induce high-affinity immunoglobulins against conserved epitopes even within different FMDV serotypes. Cross-reaction among strains by these high-affinity antibodies may support further protection against a heterologous infection with FMDV.

Avidity and subtyping of specific antibodies applied to the indirect assessment of heterologous protection against Foot-and-Mouth Disease Virus in cattle.

Serological assessment of the heterologous response among Foot-and-Mouth Disease Virus (FMDV) strains is mainly performed by virus neutralization test (VNT), liquid phase blocking ELISA and complement fixation assay. In this study two high-throughput ELISA techniques, avidity and IgG subtype ELISA, were developed and used to further characterize heterologous antibody responses in cattle during vaccination and challenge. Both assays were applied to a set of previously characterized sera from animals immunized with an inactivated A24 Cruzeiro/Brazil/55 (A24 Cruzeiro) strain monovalent FMDV vaccine and challenged with the heterologous A/Argentina/2001 (A/Arg/01) strain. Single dilution avidity ELISA assessment showed that animals that were protected against A/Arg/01 challenge had higher avidity antibodies to this heterologous strain than non-protected cattle. Animals with low or even undetectable anti-A/Arg/01 serum-neutralizing titers that passed the heterologous challenge presented higher IgG1/IgG2 ratio than non-protected animals. In this study, the three assessments (VNT and both ELISAs) discriminated between protected and not protected animals against a heterologous challenge. The combination of these techniques may be applied to complement current indirect serological vaccine-matching assessments. The measurement of these qualitative parameters may provide additional information to understand the mechanisms underlying FMD heterologous responses and the induction of cross-protection in cattle.

Multimerization of peptide antigens for production of stable immunogens in transgenic plants.

Previous literature addressing the production of recombinant proteins in heterologous systems has consistently shown that proteins capable of forming complex structures tend to accumulate within host cells at relatively higher levels than monomeric forms. In this report, we translationally fused a 21-aminoacids long highly immunogenic peptide (2L21), derived from canine parvovirus (CPV) VP2 protein to a 41-aminoacid long tetramerization domain (TD) from the transcriptional factor p53. The chimerical DNA construction 2L21-TD was cloned in a binary plant transformation vector and used to transform Arabidopsis thaliana plants. Fifteen of the 25 transgenic lines obtained in the experiment showed detectable 2L21-TD RNA accumulation and from these we chose 4 to study 2L21-TD protein accumulation. Non-denaturing immunoblotting assays revealed that 2L21-TD chimeras effectively formed tetrameric complexes with yields reaching up to 12mug/mg of soluble protein. Mice immunized by oral or intraperitoneal routes with crude protein extracts containing 2L21-TD protein were able to detect both 2L21-synthetic peptide and CPV VP2 proteins, with titers similar to those elicited by a previously reported fusion between 2L21 and the beta-glucuronidase protein. These results demonstrate that multimerization directed by the small TD domain contributed to the stabilization and consequently to the accumulation of the 2L21 peptide in transgenic plants, without altering its native antigenicity and immunogenicity.