The B-cell response to foot-and-mouth-disease virus in cattle following vaccination and live-virus challenge

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.

B cell memory responses induced by foot-and-mouth disease virus-like particles in BALB/c mice

A challenging but critical question is that new foot-and-mouth disease (FMD) vaccines should be to induce B cell memory to provide antibodies for long-term protection. The maintenance of B cell memory is dependent on long-lived plasma cells (LLPCs) and memory B cells. We developed a chimeric FMDV virus-like particles (FMDV-VLPs), fusing VP1-VP4 into HBcAg. In our study, we investigated if or how long B cell memory was induced by FMDV-VLPs in mice. The data showed that FMDV-VLPs can induce memory humoral responses with a high level of total IgG1, IgG2a, IgA, and FMDV-specific IgG antibodies in serum. The persistence of antibody levels in serum could depend on LLPCs. The proportion of LLPCs in CD19+ cells in bone marrow exhibited a dynamic trend with two peaks at 28 days post-immunization (dpi) and 72 dpi, respectively. Additionally, the proportion of memory B cells in CD19+ cells in the spleen increased significantly both at 7 days post primary immunization and at 7 days post -boost immunization. Of note, LLPCs together with memory B cells contribute to the production of FMDV-specific IgG and IgG1. The changes of LLPCs and memory B cells may be related to TNF-α, IL-6 and, CXCL12. Taken together, FMDV-VLPs could induce B cells memory responses. A further understanding of the mechanisms that FMDV-VLPs how we can manipulate the induction and maintenance of memory B cells and LLPCs will promote vaccine design and likely address several challenges to develop FMDV new vaccines in the future.

Foot-and-mouth disease virus localisation on follicular dendritic cells and sustained induction of neutralising antibodies is dependent on binding to complement receptors (CR2/CR1)

Previous studies have shown after the resolution of acute infection and viraemia, foot-and-mouth disease virus (FMDV) capsid proteins and/or genome are localised in the light zone of germinal centres of lymphoid tissue in cattle and African buffalo. The pattern of staining for FMDV proteins was consistent with the virus binding to follicular dendritic cells (FDCs). We have now demonstrated a similar pattern of FMDV protein staining in mouse spleens after acute infection and showed FMDV proteins are colocalised with FDCs. Blocking antigen binding to complement receptor type 2 and 1 (CR2/CR1) prior to infection with FMDV significantly reduced the detection of viral proteins on FDCs and FMDV genomic RNA in spleen samples. Blocking the receptors prior to infection also significantly reduced neutralising antibody titres, through significant reduction in their avidity to the FMDV capsid. Therefore, the binding of FMDV to FDCs and sustained induction of neutralising antibody responses are dependent on FMDV binding to CR2/CR1 in mice.

Universal detection of foot and mouth disease virus based on the conserved VP0 protein

Background: Foot and mouth disease virus (FMDV), a member of the picornaviridae that causes vesicular disease in ungulates, has seven serotypes and a large number of strains, making universal detection challenging. The mature virion is made up of 4 structural proteins, virus protein (VP) 1 – VP4, VP1-VP3 of which form the outer surface of the particle and VP4 largely contained within. Prior to mature virion formation VP2 and VP4 occur together as VP0, a structural component of the pre-capsid which, as a result of containing the internal VP4 sequence, is relatively conserved among all strains and serotypes. Detection of VP0 might therefore represent a universal virus marker. Methods: FMDV virus protein 0 (VP0) was expressed in bacteria as a SUMO fusion protein and the SUMO carrier removed by site specific proteolysis. Rabbit polyvalent sera were generated to the isolated VP0 protein and their reactivity characterised by a number of immunoassays and by epitope mapping on peptide arrays. Results: The specific VP0 serum recognised a variety of FMDV serotypes, as virus and as virus-like-particles, by a variety of assay formats. Epitope mapping showed the predominant epitopes to occur within the unstructured but highly conserved region of the sequence shared among many serotypes. When immunogold stained VLPs were assessed by TEM analysis they revealed exposure of epitopes on the surface of some particles, consistent with particle breathing hitherto reported for some other picornaviruses but not for FMDV. Conclusion: A polyvalent serum based on the VP0 protein of FMDV represents a broadly reactive reagent capable of detection of many if not all FMDV isolates. The suggestion of particle breathing obtained with this serum suggests a reconsideration of the FMDV entry mechanism.

Clearance of a persistent picornavirus infection is associated with enhanced pro-apoptotic and cellular immune responses

Long-term persistent viral infections cause substantial morbidity and associated economic losses in human and veterinary contexts. Yet, the mechanisms associated with establishment of persistent infections are poorly elucidated. We investigated immunomodulatory mechanisms associated with clearance versus persistence of foot-and-mouth disease virus (FMDV) in micro-dissected compartments of the bovine nasopharynx by microarray. The use of laser-capture microdissection allowed elucidation of differential gene regulation within distinct anatomic compartments critical to FMDV infection. Analysis of samples from transitional and persistent phases of infection demonstrated significant differences in transcriptome profiles of animals that cleared infection versus those that became persistently infected carriers. Specifically, it was demonstrated that clearance of FMDV from the nasopharyngeal mucosa was associated with upregulation of targets associated with activation of T cell-mediated immunity. Contrastingly, gene regulation in FMDV carriers suggested inhibition of T cell activation and promotion of Th2 polarization. These findings were corroborated by immunofluorescence microscopy which demonstrated relative abundance of CD8⁺ T cells in the nasopharyngeal mucosa in association with clearance of FMDV. The findings presented herein emphasize that a critical balance between Th1 and Th2 -mediated immunity is essential for successful clearance of FMDV infection and should be considered for development of next-generation vaccines and antiviral products.

The B Cell Response to Foot-and-Mouth Disease Virus in Cattle following Sequential Vaccination with Multiple Serotypes

Foot-and-mouth disease virus (FMDV) is a highly contagious viral disease. Antibodies are pivotal in providing protection against FMDV infection. Serological protection against one FMDV serotype does not confer interserotype protection. However, some historical data have shown that interserotype protection can be induced following sequential FMDV challenge with multiple FMDV serotypes. In this study, we have investigated the kinetics of the FMDV-specific antibody-secreting cell (ASC) response following homologous and heterologous inactivated FMDV vaccination regimes. We have demonstrated that the kinetics of the B cell response are similar for all four FMDV serotypes tested following a homologous FMDV vaccination regime. When a heterologous vaccination regime was used with the sequential inoculation of three different inactivated FMDV serotypes (O, A, and Asia1 serotypes) a B cell response to FMDV SAT1 and serotype C was induced. The studies also revealed that the local lymphoid tissue had detectable FMDV-specific ASCs in the absence of circulating FMDV-specific ASCs, indicating the presence of short-lived ASCs, a hallmark of a T-independent 2 (TI-2) antigenic response to inactivated FMDV capsid.IMPORTANCE We have demonstrated the development of intraserotype response following a sequential vaccination regime of four different FMDV serotypes. We have found indication of short-lived ASCs in the local lymphoid tissue, further evidence of a TI-2 response to FMDV.