Foot-and-mouth disease virus: biology and prospects for disease control

Ferritin Vaccine Platform for Animal and Zoonotic Viruses

Viral infections in animals continue to pose a significant challenge, affecting livestock health, welfare, and food safety, and, in the case of zoonotic viruses, threatening global public health. The control of viral diseases currently relies on conventional approaches such as inactivated or attenuated vaccines produced via platforms with inherent limitations. Self-assembling ferritin nanocages represent a novel vaccine platform that has been utilized for several viruses, some of which are currently undergoing human clinical trials. Experimental evidence also supports the potential of this platform for developing commercial vaccines for veterinary viruses. In addition to improved stability and immunogenicity, ferritin-based vaccines are safe and DIVA-compatible, and can be rapidly deployed in response to emerging epidemics or pandemics. This review discusses the structural and functional properties of ferritin proteins, followed by an overview of the design and production of ferritin-based vaccines, the mechanisms of immune responses, and their applications in developing vaccines against animal and zoonotic viruses.

Enhanced Effects of ISA 207 Adjuvant via Intradermal Route in Foot-and-Mouth Disease Vaccine for Pigs

In South Korea, a mandatory nation-wide foot-and-mouth disease (FMD) vaccination policy is in place. However, a major side effect of the current method of intramuscular (IM) administration of oil-adjuvanted FMD vaccines is the formation of granulomas in the muscles of pigs. To address this issue, we assessed the possible application of intradermal (ID) vaccination. Initially, we compared the serological immune response in specific pathogen-free pigs inoculated with FMD vaccines formulated with eight different adjuvants, administered twice at the neck site using a syringe with a needle via the ID route. Among the formulations (water-in-oil-in-water (W/O/W), oil-in-water (O/W), and polymer nanomaterials), ISA 207 of W/O/W was the most effective in inducing immunogenicity followed by ISA 201 of W/O/W. ISA 207 was further tested in formulations of different antigen doses (12 or 1.2 μg) delivered via both IM and ID routes. All four treatments successfully protected the pigs against FMD virus challenges. To assess the feasibility of the field application of the vaccines with ISA 207, we conducted ID vaccination of conventional pigs using a needle-free device, resulting in the detection of significant levels of neutralizing antibodies. ISA 207 was shown to be superior to ISA 201 in inducing immunogenicity via the ID route. In conclusion, ISA 207 could be a suitable adjuvant for ID vaccination in terms of vaccine efficacy for FMD, allowing for alternate use of ID vaccination and subsequent reduction in the incidences of granuloma formation in the field.

The antiviral response triggered by the cGAS/STING pathway is subverted by the foot-and-mouth disease virus proteases

Propagation of viruses requires interaction with host factors in infected cells and repression of innate immune responses triggered by the host viral sensors. Cytosolic DNA sensing pathway of cyclic GMP-AMP synthase (cGAS) and stimulator of interferon genes (STING) is a major component of the antiviral response to DNA viruses, also known to play a relevant role in response to infection by RNA viruses, including foot-and-mouth disease virus (FMDV). Here, we provide supporting evidence of cGAS degradation in swine cells during FMDV infection and show that the two virally encoded proteases, Leader (Lpro) and 3Cpro, target cGAS for cleavage to dampen the cGAS/STING-dependent antiviral response. The specific target sequence sites on swine cGAS were identified as Q140/T141 for the FMDV 3Cpro and the KVKNNLKRQ motif at residues 322-330 for Lpro. Treatment of swine cells with inhibitors of the cGAS/STING pathway or depletion of cGAS promoted viral infection, while overexpression of a mutant cGAS defective for cGAMP synthesis, unlike wild type cGAS, failed to reduce FMDV replication. Our findings reveal a new mechanism of RNA viral antagonism of the cGAS-STING innate immune sensing pathway, based on the redundant degradation of cGAS through the concomitant proteolytic activities of two proteases encoded by an RNA virus, further proving the key role of cGAS in restricting FMDV infection.

The role of zinc sulfate in enhancing cellular and humoral immune responses to foot-and-mouth disease vaccine

Foot-and-mouth disease (FMD) is a rapidly propagating infectious disease of cloven-hoofed animals, especially cattle and pigs, affecting the productivity and profitability of the livestock industry. Presently, FMD is controlled and prevented using vaccines; however, conventional FMD vaccines have several disadvantages, including short vaccine efficacy, low antibody titers, and safety issues in pigs, indicating the need for further studies. Here, we evaluated the efficacy of a novel bivalent vaccine containing zinc sulfate as an immunostimulant and FMD type O and A antigens (O PA2 and A YC, respectively) against FMD virus in mice and pigs. Zinc sulfate induced cellular immunity in murine peritoneal exudate cells (PECs) and porcine peripheral blood mononuclear cells (PBMCs) by increasing IFNγ secretion. Additionally, FMD vaccine containing O PA2 and A YC antigens and zinc sulfate induced early, mid-, and long-term immune responses in mice and pigs, and enhanced cellular and humoral immunity by regulating the expression of pathogen recognition receptors (PRRs), transcription factors, co-stimulatory molecules, and cytokines in porcine PBMCs from vaccinated pigs. Overall, these results indicated that the novel immunostimulant zinc sulfate induced potent cellular and humoral immune responses by stimulating antigen-presenting cells (APCs) and T and B cells, and enhanced long-term immunity by promoting the expression of co-stimulatory molecules. These outcomes suggest that zinc sulfate could be used as a novel vaccine immunostimulant for difficult-to-control viral diseases, such as African swine fever (ASF) or COVID-19.

Knowledge, attitude and practice (KAP) of smallholder farmers on foot-and-mouth disease in Cattle in West Kazakhstan

BACKGROUND

This study was performed to assess the knowledge, attitudes and practices (KAPs) of farmers and veterinary professionals towards foot-and-mouth disease (FMD) in the area studied.

METHODS

The study was based on a comprehensive questionnaire administered through face-to-face interviews. Between January and May 2022, 543 households and 27 animal health practitioners (AHP) were visited in 4 provinces of the West Kazakhstan region to assess their KAPs towards FMD.

RESULTS

A large proportion of herd owners (84%) had known the name of the disease, and nearly a half (48) of respondents had heard of FMD cases on farms in the neighbourhood. Oral mucosa lesions were the most consistent with clinical sign characteristic of FMD among farmers (31.4%), followed by hoof blisters (27.6%) and excessive salivation (18.6%). Farmers reported that new animal introduction was potentially the main factor associated with FMD occurrence in their herds. Over half of farmers (54%) interviewed prefer not to purchase livestock from unknown or potentially epidemiologically disadvantaged areas.

CONCLUSION

All AHPs (27) reported that in their zone of veterinary responsibilities, vaccination against FMD is not practised because the area investigated possesses FMD-free status. However, in the past few years, numerous FMD outbreaks have been detected throughout the region. For this reason, immediate actions need to be taken to prevent further FMD occurrences by giving the region a status of an FMD-free zone with vaccination. The current study demonstrated that inadequate quarantine controls of imported animals, absence of regular vaccination and unrestricted animal movement within the country were the primary obstacles in controlling and preventing FMD in the investigated area.

Use of Foot-and-Mouth Disease Virus Non-coding Synthetic RNAs as Vaccine Adjuvants

The ncRNAs are short RNA transcripts with sequence and structure resembling that of specific domains in the non-coding regions of the foot-and-mouth disease (FMD) virus (FMDV ) genome. These synthetic molecules induce a robust antiviral response and have been shown to enhance the immune response and protection induced by an FMD inactivated vaccine in pigs. Here, we describe the method for ncRNAs synthesis, formulation, and delivery into mice and pigs for studies focused on testing the adjuvant effect of RNA-based strategies in combination with veterinarian vaccines.

RNA Helicase A Regulates the Replication of RNA Viruses

The RNA helicase A (RHA) is a member of DExH-box helicases and characterized by two double-stranded RNA binding domains at the N-terminus. RHA unwinds double-stranded RNA in vitro and is involved in RNA metabolisms in the cell. RHA is also hijacked by a variety of RNA viruses to facilitate virus replication. Herein, this review will provide an overview of the role of RHA in the replication of RNA viruses.

A Review on the Use of Antimicrobial Peptides to Combat Porcine Viruses

Viral infectious diseases pose a serious threat to animal husbandry, especially in the pig industry. With the rapid, continuous variation of viruses, a series of therapeutic measures, including vaccines, have quickly lost their efficacy, leading to great losses for animal husbandry. Therefore, it is urgent to find new drugs with more stable and effective antiviral activity. Recently, it has been reported that antimicrobial peptides (AMPs) have great potential for development and application in animal husbandry because of their significant antibacterial and antiviral activity, and the antiviral ability of AMPs has become a research hotspot. This article aims to review the research situation of AMPs used to combat viruses in swine production of animal husbandry, clarify the mechanism of action of AMPs on viruses and raise some questions, and explore the future potential of AMPs in animal husbandry.

Advances in Foot-and-Mouth Disease Virus Proteins Regulating Host Innate Immunity

Foot-and-mouth disease (FMD) is a highly contagious disease that affects cloven-hoofed animals such as pigs, cattle, and sheep. The disease is caused by the foot-and-mouth disease virus (FMDV) which has a non-enveloped virion with icosahedral symmetry that encapsulates a positive-sense, single-stranded RNA genome of ∼8.4 kb. FMDV infection causes obvious immunosuppressive effects on the host. In recent years, studies on the immunosuppressive mechanism of FMDV have become a popular topic. In addition, studies have shown that many FMDV proteins are involved in the regulation of host innate immunity and have revealed mechanisms by which FMDV proteins mediate host innate immunity. In this review, advances in studies on the mechanisms of interaction between FMDV proteins and host innate immunity are summarized to provide a comprehensive understanding of FMDV pathogenesis and the theoretical basis for FMD prevention and control.

MDA5 cleavage by the Leader protease of foot-and-mouth disease virus reveals its pleiotropic effect against the host antiviral response

The RIG-I-like receptor (RLR) melanoma differentiation-associated gene 5 (MDA5) plays a key role in triggering innate antiviral response during infection by RNA viruses. MDA5 activation leads to transcription induction of type-I interferon (IFN) and proinflammatory cytokines. MDA5 has also been associated with autoimmune and autoinflammatory diseases by dysfunctional activation of innate immune response in the absence of infection. Here, we show how foot-and-mouth disease virus (FMDV) counteracts the specific antiviral effect exerted by MDA5 targeting the protein for cleavage by the viral Leader protease (Lpro). MDA5 overexpression had an inhibitory effect on FMDV infection in IFN-competent cells. Remarkably, immunostimulatory viral RNA co-immunoprecipitated with MDA5 in infected cells. Moreover, specific cleavage of MDA5 by Lpro was detected in co-transfected cells, as well as during the course of FMDV infection. A significant reduction in IFN induction associated with MDA5 cleavage was detected by comparison with a non-cleavable MDA5 mutant protein with preserved antiviral activity. The Lpro cleavage site in MDA5 was identified as the RGRAR sequence in the conserved helicase motif VI, coinciding with that recently reported for Lpro in LGP2, another member of the RLRs family involved in antiviral defenses. Interestingly, specific mutations within the MDA5 Lpro target sequence have been associated with immune disease in mice and humans. Our results reveal a pleiotropic strategy for immune evasion based on a viral protease targeting phylogenetically conserved domains of immune sensors. Identification of viral strategies aimed to disrupt MDA5 functionality may also contribute to develop new treatment tools for MDA5-related disorders.

hnRNP K Is a Novel Internal Ribosomal Entry Site-Transacting Factor That Negatively Regulates Foot-and-Mouth Disease Virus Translation and Replication and Is Antagonized by Viral 3C Protease

Cap-independent translation initiation on picornavirus mRNAs is mediated by an internal ribosomal entry site (IRES) in the 5' untranslated region. The regulation of internal initiation requires the interaction of IRES-transacting factors (ITAFs) with the IRES. In this study, we identified a novel ITAF, heterogeneous nuclear ribonucleoprotein K (hnRNP K), which negatively regulates foot-and-mouth disease virus (FMDV) translation and viral replication. Further investigation revealed that the KH2 and KH3 domains of hnRNP K directly bind to domains II, III, and IV of the FMDV IRES, resulting in the inhibition of IRES-mediated translation by interfering with the recognition of another positive ITAF, polypyrimidine tract-binding protein (PTB). Conversely, hnRNP K-mediated inhibition was antagonized by the viral 3C protease through the cleavage of hnRNP K at the Glu-364 residue during FMDV infection. Interestingly, the N-terminal cleavage product, hnRNP K1-364, retained partial inhibitory effects on IRES activity, whereas the C-terminal cleavage product, hnRNP K364-465, became a positive regulator of FMDV replication. Our findings expand the current understanding of virus-host interactions concerning viral recruitment and the modulation of ITAFs, providing new insights into translational control during viral infection.IMPORTANCE The translation of picornaviral genome RNA mediated by the internal ribosomal entry site (IRES) is a crucial step for virus infections. Virus-host interactions play a critical role in the regulation of IRES-dependent translation, but the regulatory mechanism remains largely unknown. In this study, we identified an ITAF, hnRNP K, that negatively regulates FMDV replication by inhibiting viral IRES-mediated translation. In addition, we describe a novel translational regulation mechanism involving the proteolytic cleavage of hnRNP K by FMDV protease 3C. The cleavage of hnRNP K yields two cleavage products with opposite functions: the cleavage product hnRNP K1-364 retains a partial inhibitory effect on IRES activity, and the cleavage product hnRNP K364-465 becomes a positive regulator of FMDV replication. Our findings shed light on the effect of a novel ITAF on the translational regulation of picornavirus and provide new insights into translational control during viral infection.

Capsid proteins of foot-and-mouth disease virus interact with TLR2 and CD14 to induce cytokine production

The mechanism of recognition of the foot-and-mouth disease virus (FMDV) by host innate immune cells is not well-understood. In this study, we first found that binary ethylenimine inactivated-FMDV (BEI-FMDV) with structurally intact capsid activated TLR2, but not other TLRs, and this specific activation was blocked by anti-TLR2 Abs or knockout of TLR2. BEI-FMDV activated NF-κB to induce cytokines, notably interferon-β and IL-6, in a TLR2 and MyD88-dependent manner. Coexpression of TLR6 and CD14 showed additive effects on BEI-FMDV/TLR2-mediated activation of NF-κB. Further studies demonstrated that recombinant capsid proteins rVP1 and rVP3 of FMDV but not rVP0 bound directly with CD14 and TLR2. The rVP1- and rVP3-mediated activation of TLR2 and NF-κB were enhanced by the coexpression of TLR1 or TLR6. Immunoprecipitation of either rVP1 or rVP3 with mouse macrophage cell extracts revealed that rVP1 or rVP3 associated with TLR2, CD14 and TLR6 suggesting that rVP1 and rVP3 interact with CD14, TLR2/TLR1, and TLR2/TLR6 heterodimer. Additional study confirmed that rVP1 and rVP3 interacted with the swine TLR2 signaling pathway to induce IL-6 in swine macrophages. Our results identify VP1 and VP3 of FMDV as novel TLR agonists whose recognition by CD14, TLR2/TLR1, and TLR2/TLR6 of host innate immune cells is critical for the induction of cytokine production.

A Single Dose of Dendrimer B2T Peptide Vaccine Partially Protects Pigs against Foot-and-Mouth Disease Virus Infection

Foot-and-mouth disease virus (FMDV) causes a highly contagious disease of cloven-hoofed animals whose control relies on efficient vaccination. We have reported that dendrimer peptide B₂T, with two copies of FMDV B-cell epitope VP1 (136–154) linked through maleimide units to T-cell epitope 3A (21–35)], elicits potent B- and T-cell specific responses and confers solid protection in pigs to type-O FMDV challenge after two doses of peptide. Herein we now show that B₂T evokes specific protective immune responses after administration of a single dose of either 2 or 0.5 mg of peptide. High titers of ELISA and neutralizing antibodies against FMDV were detectable at day 15 post-immunization. Likewise, activated T cells and induced IFN-γ response to in vitro recall with FMDV peptides were also detected by the same day. Further, in 70% of B₂T-vaccinated pigs, full protection—no clinical signs of disease—was observed upon virus challenge at day 25 post-immunization. These results strengthen the potential of B₂T as a safe, cost-effective candidate vaccine conferring adequate protection against FMDV with a single dose. The finding is particularly relevant to emergency scenarios permitting only a single shot immunization.

Caracterización de la proteína no capsidal 3D, del virus de la fiebre aftosa y producción de anticuerpos policlonales

Las proteínas no capsidales del virus de la fiebre aftosa se utilizan como marcadoras en la evaluación de animales que han estado en contacto con el virus, a diferencia de los inmunizados, ya que la vacuna no debe tener estas proteínas, por lo tanto los animales no deben presentar anticuerpos contra ellas. El objetivo de esta investigación fue la caracterización de la proteína no capsidal 3D y la producción de anticuerpos policlonales in vivo. La proteína se purificó del cultivo de virus inactivo, por cromatografía de intercambio iónico. La elución de los picos fue sometida a electroforesis uni-bidimensional; demostrándose un alto grado de pureza (>90%) en el pico tres, donde se identifico la proteína 3D, por la técnica de MALDI-TOF y electroespray de trampa iónica. La proteína purificada, se inoculó en cabras y el suero hiperinmune fue precipitado y sometido a cromatografía de afinidad para la obtención de inmunoglobulinas; la reacción inmunitaria se con­firmó por medio de inmunodifusión y Western blot. El proceso de purificación demostró ser eficiente y útil para la obtención de anticuerpos específicos, los cuales tendrán utilidad en la elaboración de un ensayo inmunoenzimático que mida la pureza de la vacuna frente al contenido de estas proteínas. 

Development of a recombinant vaccine against foot and mouth disease utilizing mutant attenuated Listeria ivanovii strain as a live vector

The drawbacks of conventional inactivated Foot and Mouth Disease (FMD) vaccine, such as escaping of the virus during manufacture processes prompted researchers to explore novel types of vaccine to overcome these disadvantages. Listeria ivanovii (LI) is an intracellular microorganism that possesses immune-stimulatory properties, making it appropriate for use as a live bacterial vaccine vector. The Foot and mouth disease virus (FMDV) VP1 protein is the most immunogenic part of FMDV capsid, it has most of the antigenic sites for viral neutralization. The expression of antigen gene cassette in vitro was confirmed by Western blot analysis. Mice were able to eliminate LI△actAplcB-vp1 from the liver and spleen within few days revealed a safety of the candidate vaccine. Two doses of LI△actAplcB-vp1 with 14 days of interval were injected into mice. High levels of specific IgG antibodies and CD8⁺ and CD4⁺ T cells secreted cytokines including IFN-γ, TNF-α and IL-2 against FMDV-VP1 were achieved. Based on the obtained results, LI△actAplcB-vp1 candidate vaccine utilizing Listeria ivanovii as a live vector-based vaccine could enhance a specific cellular and humoral immune responses against the inserted FMDV-vp1 heterologous genes. LI△actAplcB-vp1 candidate vaccine could be a modern tool to overcome the disadvantages of the traditional inactivated FMD vaccine.

Antiviral effect of amiloride on replication of foot and mouth disease virus in cell culture

Recently, amiloride was shown to potently suppress Coxsackievirus B3 (CVB3) replication. In the current study, we investigated whether amiloride could also exhibit antiviral activity against foot-and-mouth disease virus (FMDV), which belongs to the same family (Picornaviridae) as CVB3. We found that amiloride exerted antiviral activity in a dose-dependent manner against two strains of FMDV in IBRS-2 cells, with slight cytotoxicity at 1000 μM. Besides, amiloride did not inhibit the attachment and entry of FMDV in IBRS-2 cells, but prevented early viral replication. These data implied that amiloride could be a promising candidate for further research as a potential antiviral drug against FMDV infection.

Effect of IL-2 co-expressed or co-inoculated with immuno-dominant epitopes from VP1 protein of FMD virus on immune responses in BALB/c mice

Objective(s):

The results of studies on vaccine development for foot-and-mouth disease (FMD) virus show that the use of inactivated vaccines for FMD virus is not completely effective. Novel vaccinations based on immuno-dominant epitopes have been shown to induce immune responses. Furthermore, for safety of immunization, access to efficient adjuvants against FMD virus seems to be critical.

Materials and Methods:

In this study, we produced epitope recombinant vaccines from the VP1 protein of the FMD virus for serotype O of Iran. Constructs were included polytope (tandem-repeat multiple-epitope), polytope coupled with interleukin-2 (polytope-IL 2) as a molecular adjuvant and IL-2. Three expression vectors were constructed and expressed in Escherichia coli BL21 (DE3). To evaluate whether these recombinant vaccines induce immune responses, BALB/c mice were injected with the recombinant vaccines and their immune responses were compared with a negative control group. The humoral and cellular immune responses were measured by ELISA.

Results:

The results showed that IL-2 co-expressed or co-inoculated with Polytope protein enhances the immune effect of multiple epitope recombinant vaccine against FMD virus. The results of total immunoglobulin G (IgG), IgG1, and IgG2a levels and secretion of interferon gamma (IFN-γ), IL-4 and IL-10 revealed that there were significant differences between negative control group and other injected mice with the recombinant vaccines (P<0.05).

Conclusion:

Observations indicated that the epitope recombinant plasmid of the VP1 protein co-expressed or co-inoculated with IL-2 was effective in inducing an enhanced immune response. Therefore, IL-2 can be recommended as a potential adjuvant for epitope recombinant vaccine of the VP1 protein from FMD virus.

Immunogenic evaluation of FMD virus immuno-dominant epitopes coupled with IL-2/FcIgG in BALB/c mice

Previous studies on vaccine development against foot-and-mouth disease (FMD) virus reported that application of the inactivated vaccines for FMD virus is not completely effective. Novel vaccinations based on immune-dominant epitopes showed they induced immune responses. In addition, for better and safer immunization, access to of efficient adjuvants against FMD virus seems to be critical. In this study, we produced epitope recombinant vaccines from the VP1 protein of the FMD virus for serotype O of Iran that conjugated with Fc Immunoglobulin (FcIgG) and Interleukin-2 (IL-2). Multiple-epitope constructs included Polytope, Polytope-IL2-FcIgG, Polytope-IL2, Polytope-FcIgG that cloned and expressed in E. coli BL21 (DE3). To evaluate whether these epitope recombinant vaccines induce immune responses, BALB/c mice were injected with the epitope recombinant vaccines and their immune responses were compared with a negative control group. The humoral and cellular immune responses were measured by ELISA. The results showed there were significant differences between the negative control group and other immunized mice with recombinant epitope proteins (p < 0.05). The results of total IgG, IgG1, IgG2a levels and secretion of IFN-γ, IL-4 and IL-10 revealed that immune responses were enhanced when the epitope recombinant vaccine of FMD virus coupled with IL-2 and FcIgG. Observations indicated that the epitope recombinant plasmid of the VP1 protein co-expressed with IL-2 and FcIgG was effective in inducing an enhanced immune response. Therefore, IL-2 and FcIgG could be recommended as a potential adjuvant for epitope recombinant vaccine of the VP1 protein from FMD virus.

Virus-like particles of recombinant PCV2b carrying FMDV-VP1 epitopes induce both anti-PCV and anti-FMDV antibody responses

Mixed infection of porcine circovirus type 2 (PCV2) and foot-and-mouth disease virus (FMDV) is devastating to swine populations. To develop an effective vaccine that can protect the pigs from the infection of PCV2 and FMDV, we used the neutralizing B cell epitope region (aa 135-160) of FMDV to replace the regions aa 123-151 and aa 169-194 of the PCV2b Cap protein to generate a recombinant protein designated as Capfb. The Capfb protein was expressed in Escherichia coli system and the purified Capfb protein assembled into virus-like particles (VLPs) through dialysis. The ability of the Capfb protein to induce effective immune response against FMDV and PCV2b was tested in mice and guinea pigs. The results showed that the Capfb-VLPs could elicit anti-PCV2b and anti-FMDV antibody response in mice and guinea pigs without inducing antibodies against decoy epitope. Moreover, the Capfb-VLPs could enhance the percentage and activation of B cells in lymph nodes when the mice were stimulated with inactivated FMDV or PCV2b. These data suggested that the Capfb-VLPs could be an efficacious candidate antigen for developing a novel PCV2b-FMDV bivalent vaccine.

Innate immune sensor LGP2 is cleaved by the Leader protease of foot-and-mouth disease virus

The RNA helicase LGP2 (Laboratory of Genetics and Physiology 2) is a non-signaling member of the retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs), whose pivotal role on innate immune responses against RNA viruses is being increasingly uncovered. LGP2 is known to work in synergy with melanoma differentiation-associated gene 5 (MDA5) to promote the antiviral response induced by picornavirus infection. Here, we describe the activity of the foot-and-mouth disease virus (FMDV) Leader protease (Lpro) targeting LGP2 for cleavage. When LGP2 and Lpro were co-expressed, cleavage products were observed in an Lpro dose-dependent manner while co-expression with a catalytically inactive Lpro mutant had no effect on LGP2 levels or pattern. We further show that Lpro localizes and immunoprecipitates with LGP2 in transfected cells supporting their interaction within the cytoplasm. Evidence of LGP2 proteolysis was also detected during FMDV infection. Moreover, the inhibitory effect of LGP2 overexpression on FMDV growth observed was reverted when Lpro was co-expressed, concomitant with lower levels of IFN-β mRNA and antiviral activity in those cells. The Lpro target site in LGP2 was identified as an RGRAR sequence in a conserved helicase motif whose replacement to EGEAE abrogated LGP2 cleavage by Lpro. Taken together, these data suggest that LGP2 cleavage by the Leader protease of aphthoviruses may represent a novel antagonistic mechanism for immune evasion.

Transcriptomic analysis of porcine PBMCs in response to FMDV infection

Foot-and-mouth disease (FMD) is a significant zoonotic infectious disease. It has an important economic impact throughout the world. As well, it is a considerable threat to food security. At present, the molecular mechanism of FMDV infection is not clear to a large extent. Innate immune response is the first line of defense against infectious diseases. The systematic analysis of the host immune response to infection has an important role in understanding the pathogenesis of infection. However, there are few reports about effect of immune regulation on virus replication in the interaction of virus and host cellular. High-throughput RNA-seq technology as a powerful and efficient means for transcript analysis provides a new insight into FMDV study. In this study, RNA extracted from pig PBMCs infected with O subtype FMDV at 4 dpi. A total of 29942658 and 31452917 Illumina read pairs were obtained from the non-infected (NI) group and infected (I) group, respectively. The clean bases for all samples are 3.61G (NI group) and 3.79G (I group), respectively. The clean reads of the NI and I group that mapped to pig genome data were 47195073 (81.82%) and 46556714 (76.85%), respectively. Most of the clean reads were distributed in the exon region, followed by intron region and intergenic region. Differently expressed (DE) genes were analyzed using edgeR software. 451 genes were differentially expressed between the infected and the non-infected groups. According to the comparison analysis, more genes were down-regulated in the non-infected samples than in those infected with FMDV.66 out of 451 genes were down-regulated, 385 out of 451 genes were up-regulated following FMDV infection. For function classification and pathway analysis, among 17741 assembled unigenes, there are 349 genes which are different genes of GO notes. Moreover, 49 genes were down-regulated, 300 genes were up-regulated associate with GO term. 1621 were successfully annotated by GO assignments, belonging to one or more of the three categories: biological process, cellular component, and molecular function. According to KEGG analysis,the main pathway was represented including protein processing in endoplasmic reticulum, phagosome, cell cycle and cytokine-cytokine receptor interaction. Some key DE genes related to immune process and signaling pathways were analyzed and quantified by RT-PCR. This is the first systematical transcriptome analysis of pig PBMCs infected by FMDV. These findings will help us better understand the host Cell-FMDV interaction and its relationship to pathogenesis, as well as contribute to the prevention and control of FMDV.

Molecular Mechanisms of Foot-and-Mouth Disease Virus Targeting the Host Antiviral Response

Foot-and-mouth disease virus (FMDV) is the causative agent of an acute vesicular disease affecting pigs, cattle and other domestic, and wild animals worldwide. The aim of the host interferon (IFN) response is to limit viral replication and spread. Detection of the viral genome and products by specialized cellular sensors initiates a signaling cascade that leads to a rapid antiviral response involving the secretion of type I- and type III-IFNs and other antiviral cytokines with antiproliferative and immunomodulatory functions. During co-evolution with their hosts, viruses have acquired strategies to actively counteract host antiviral responses and the balance between innate response and viral antagonism may determine the outcome of disease and pathogenesis. FMDV proteases Lpro and 3C have been found to antagonize the host IFN response by a repertoire of mechanisms. Moreover, the putative role of other viral proteins in IFN antagonism is being recently unveiled, uncovering sophisticated immune evasion strategies different to those reported to date for other members of the Picornaviridae family. Here, we review the interplay between antiviral responses induced by FMDV infection and viral countermeasures to block them. Research on strategies used by viruses to modulate immunity will provide insights into the function of host pathways involved in defense against pathogens and will also lead to development of new therapeutic strategies to fight virus infections.

Combined administration of synthetic RNA and a conventional vaccine improves immune responses and protection against foot-and-mouth disease virus in swine

Foot-and-mouth disease virus (FMDV) is the causative agent of a highly contagious disease and a major concern in animal health worldwide. We have previously reported the use of RNA transcripts mimicking structural domains in the non-coding regions of the FMDV RNA as potent type-I interferon (IFN) inducers showing antiviral effect in vivo, as well as their immunomodulatory properties in combination with an FMD vaccine in mice. Here, we describe the enhancing effect of RNA delivery on the immunogenicity and protection induced by a suboptimal dose of a conventional FMD vaccine in pigs. Animals receiving the RNA developed earlier and higher levels of neutralizing antibodies against homologous and heterologous isolates, compared to those immunized with the vaccine alone, and had higher anti-FMDV titers at late times post-vaccination. RNA delivery also induced higher specific T-cell response and protection levels against FMDV challenge. Peripheral blood mononuclear cells from pigs inoculated with RNA and the vaccine had a higher IFN-γ specific response than those from pigs receiving the vaccine alone. When challenged with FMDV, all three animals immunized with the conventional vaccine developed antibodies to the non-structural viral proteins 3ABC and two of them developed severe signs of disease. In the group receiving the vaccine together with the RNA, two pigs were fully protected while one showed delayed and mild signs of disease. Our results support the immunomodulatory effect of these RNA molecules in natural hosts and suggest their potential use for improvement of FMD vaccines strategies.

Immunogenicity of adenovirus-derived porcine parvovirus-like particles displaying B and T cell epitopes of foot-and-mouth disease

Virus-like particles (VLPs) vaccines combine many of the advantages of whole-virus vaccines and recombinant subunit vaccines, integrating key features that underlay their immunogenicity, safety and protective potential. We have hypothesized here the effective insertion of the VP1 epitopes (three amino acid residues 21-40, 141-160 and 200-213 in VP1, designated VPe) of foot-and-mouth disease (FMDV) within the external loops of PPV VP2 could be carried out without altering assembly based on structural and antigenic data. To investigate the possibility, development of two recombinant adenovirus rAd-PPV:VP2-FMDV:VPe a or rAd-PPV:VP2-FMDV:VPe b were expressed in HEK-293 cells. Out of the two insertion strategies tested, one of them tolerated an insert of 57 amino acids in one of the four external loops without disrupting the VLPs assembly. Mice were inoculated with the two recombinant adenoviruses, and an immunogenicity study showed that the highest levels of FMDV-specific humoral responses and T cell proliferation could be induced by rAd-PPV:VP2-FMDV:VPe b expressing hybrid PPV:VLPs (FMDV) in the absence of an adjuvant. Then, the protective efficacy of inoculating swine with rAd-PPV:VP2-FMDV:VPe b was tested. All pigs inoculated with rAd-PPV:VP2-FMDV:VPe b were protected from viral challenge, meanwhile the neutralizing antibody titers were significantly higher than those in the group inoculated with swine FMD type O synthetic peptide vaccine. Our results clearly demonstrate the potential usefulness of adenovirus-derived PPV VLPs as a vaccine strategy in prevention of FMDV.

A recombinant porcine circovirus type 2 expressing the VP1 epitope of the type O foot-and-mouth disease virus is infectious and induce both PCV2 and VP1 epitope antibodies

Porcine circovirus type 2 (PCV2) is the etiological agent of postweaning multisystemic wasting syndrome, a disease that causes huge economic damage in swine industry. A recombinant PCV2 expressing the neutralizing VP1 epitope (aa 141-160) of the foot-and-mouth disease virus (FMDV) was rescued using an infectious cloning technique. The PCV2 antigen and FMDV-VP1 antigenic epitope of the cloned strain recPCV2-CL-VP1 were confirmed by an immunoperoxidase monolayer assay (IPMA) and a capture enzyme-linked immunosorbent assay (ELISA). The morphological features of the recPCV2-CL-VP1 were not discernibly different from those of its parental strain (PCV2-CL). However, the recombinant virus could be differentiated from its parental virus by PCR and capture ELISA. The recPCV2-CL-VP1 was demonstrated to replicate stably in PK-15 cells through ten passages. An infection experiment using BALB/c mice showed that both recPCV2-CL-VP1 and PCV2-CL could replicate in the mice, cause various pathological changes, and induce a high level of anti-Cap antibodies. The recombinant virus emulsified with Freund's adjuvant was used to immunize BALB/c mice and induced antibodies against the FMDV-VP1 epitope. Hence, the recombinant PCV2 strain, which expressed the neutralizing FMDV-VP1 epitope, provides a valuable platform to develop novel genetic vaccines.

An overview of live attenuated recombinant pseudorabies viruses for use as novel vaccines

Pseudorabies virus (PRV) is a double-stranded, DNA-based swine virus with a genome approximating 150 kb in size. PRV has many nonessential genes which can be replaced with genes encoding heterologous antigens but without deleterious effects on virus propagation. Recombinant PRVs expressing both native and foreign antigens are able to stimulate immune responses. In this paper, we review the current status of live attenuated recombinant PRVs and live PRV-based vector vaccines with potential for controlling viral infections in animals.

Foot-and-mouth disease: technical and political challenges to eradication

Foot-and-mouth disease (FMD) is a highly-contagious livestock disease with global socioeconomic ramifications. The disease negatively impacts both individual farmers through reduced herd viability and nations through trade restrictions of animals and animal derivatives. Vaccines for FMD prevention have existed for over 70 years, yet the disease remains enzootic in a large percentage of the globe. FMD persistence is due in part to technical limitations of historic and current vaccine technologies. There also exist many socioeconomic and political barriers to global FMD eradication. Here we highlight the barriers to eradication and discuss potential avenues toward FMD eradication.

Prediction of province-level outbreaks of foot-and-mouth disease in Iran using a zero-inflated negative binomial model

To identify events that could predict province-level frequency of foot-and-mouth disease (FMD) outbreaks in Iran, 5707 outbreaks reported from April 1995 to March 2002 were studied. A zero-inflated negative binomial model was used to estimate the probability of a 'no-outbreak' status and the number of outbreaks in a province, using the number of previous occurrences of FMD for the same or adjacent provinces and season as covariates. For each province, the probability of observing no outbreak was negatively associated with the number of outbreaks in the same province in the previous month (odds ratio [OR]=0.06, 95% confidence interval [CI]: 0.01, 0.30) and in 'the second previous month' (OR=0.10, 95% CI: 0.02, 0.51), the total number of outbreaks in the second previous month in adjacent provinces (OR=0.57, 95% CI: 0.36, 0.91) and the season (winter [OR=0.18, 95% CI: 0.06, 0.55] and spring [OR=0.27, 95% CI: 0.09, 0.81], compared with summer). The expected number of outbreaks in a province was positively associated with number of outbreaks in the same province in previous month (coefficient [coef]=0.74, 95% CI: 0.66, 0.82) and in the second previous month (coef=0.23, 95% CI: 0.16, 0.31), total number of outbreaks in adjacent provinces in the previous month (coef=0.32, 95% CI: 0.22, 0.41) and season (fall [coef=0.20, 95% CI: 0.07, 0.33] and spring [coef=0.18, 95% CI: 0.05, 0.31], compared to summer); however, number of outbreaks was negatively associated with the total number of outbreaks in adjacent provinces in the second previous month (coef=-0.19, 95% CI: -0.28, -0.09). The findings indicate that the probability of an outbreak (and the expected number of outbreaks if any) may be predicted based on previous province information, which could help decision-makers allocate resources more efficiently for province-level disease control measures. Further, the study illustrates use of zero inflated negative binomial model to study diseases occurrence where disease is infrequently observed.

Development of porcine respiratory and reproductive syndrome virus replicon vector for foot-and-mouth disease vaccine

PURPOSE

Foot-and-mouth disease (FMD) is an economically important global animal disease. To control FMD virus (FMDV) outbreaks, a lot of different novel approaches have been attempted. In this study, we proposed a novel porcine reproductive and respiratory syndrome virus (PRRSV) as a replicon vector to express FMDV structural protein.

MATERIALS AND METHODS

PRRSV infectious clone (PRRSVK418DM) was used to develop an expression vector through the reverse genetic manipulation of PRRSV; FMDVP12A3C gene of serotype O was synthesized and used for an antigen. MARC-145 cells (African green monkey kidney epithelial cell line) were used for electroporation mediated transfection. The transfection or the expression of P12A3C and N protein of PRRSV was analyzed by either replicon containing PRRSV alone or by co-infection of helper PRRSV.

RESULTS

We constructed PRRSVK418DM replicon vector containing FMDVP12A3C, and genome sequences were confirmed by subsequent sequence analysis. In vitro expression of P12A3C and PRRSV N protein was confirmed by immunofluorescence antibody assay using antibodies specific for PRRSV N protein (anti-PRRSV N MAb), FMDV-VP1 (anti-VP1 MAb).

CONCLUSION

The results indicate that PRRSV replicon vector can be a promising novel vector system to control FMDV and useful for vaccine development in the future.

Characterization of a nuclear localization signal in the foot-and-mouth disease virus polymerase

We have experimentally tested whether the MRKTKLAPT sequence in FMDV 3D protein (residues 16 to 24) can act as a nuclear localization signal (NLS). Mutants with substitutions in two basic residues within this sequence, K18E and K20E, were generated. A decreased nuclear localization was observed in transiently expressed 3D and its precursor 3CD, suggesting a role of K18 and K20 in nuclear targeting. Fusion of MRKTKLAPT to the green fluorescence protein (GFP) increased the nuclear localization of GFP, which was not observed when GFP was fused to the 3D mutated sequences. These results indicate that the sequence MRKTKLAPT can be functionally considered as a NLS. When introduced in a FMDV full length RNA replacements K18E and K20E led to production of revertant viruses that replaced the acidic residues introduced (E) by K, suggesting that the presence of lysins at positions 18 and 20 of 3D is essential for virus multiplication.

Delivery of synthetic RNA can enhance the immunogenicity of vaccines against foot-and-mouth disease virus (FMDV) in mice

We have recently described the antiviral effect in mice of in vitro-transcribed RNAs mimicking structural domains in the non-coding regions of the foot-and-mouth disease virus (FMDV) genome RNA. These small, synthetic and non-infectious RNA molecules (ncRNAs) are potent type-I interferon (IFN) inducers in vivo. In this work, the immunomodulatory effect of the ncRNA corresponding to the internal ribosome entry site (IRES) on immunization with two different FMD vaccine formulations, both based on inactivated virus, including or not a commercial adjuvant, was analyzed in the mice model. The effect of the time interval between RNA inoculation and immunization was also studied. RNA delivery consistently increased the titers of specific anti-FMDV antibodies, including neutralizing antibodies, elicited after vaccination. Moreover, at day 2 after immunization, significant differences in mean antibody titers could be detected between the groups of mice receiving either vaccine co-administered with the RNA and the control group, unlike those immunized with the vaccine alone. When vaccinated mice were challenged with FMDV, the mean values of viral load were lower in the groups receiving the RNA together with the vaccine. Our results show the enhancing effect of the IRES RNA on the immune response elicited after vaccination and suggest the potential of this molecule as an adjuvant for new FMD vaccine design.

Engagement of soluble resistance-related calcium binding protein (sorcin) with foot-and-mouth disease virus (FMDV) VP1 inhibits type I interferon response in cells

Foot-and-mouth disease (FMD) is an acute, highly contagious animal disease caused by FMD virus (FMDV). Although FMDV-induced immunosuppression in host has been well established, the exact molecular mechanism for such induction is not very clear. We report here the identification of FMDV VP1 as an interferon-suppressor by interacting with soluble resistance-related calcium binding protein (sorcin). We found that VP1 suppressed tumor necrosis factor (TNF)-α or Sendai virus (SeV)-induced type I interferon response in HEK293T cells, and that this suppression could be completely abolished by knockdown of sorcin by shRNA. Furthermore, overexpression of sorcin inhibited type I interferon response. Conversely, TNF- or SeV-induced type I interferon response increased when sorcin knocked down, leading to inhibition of vesicular stomatitis virus (VSV) replication. Thus, VP1-induced suppression of type I interferon is mediated by interacting with sorcin, a protein that appears to regulate cell response to viral infections.

Requirements for improved vaccines against foot-and-mouth disease epidemics

Inactivated foot-and-mouth disease (FMD) vaccines are currently used worldwide. With the emergence of various FMD virus serotypes and subtypes, vaccines must become more suitable for field-based uses under the current circumstances in terms of the fast and proper selection of vaccine strains, an extended vaccine development period for new viruses, protecting against the risk of virus leakage during vaccine manufacture, counteracting the delayed onset of immune response, counteracting shorter durations of immunity, and the accurate serological differentiation of infected and vaccinated animals and multiple vaccination. The quality of vaccines should then be improved to effectively control FMD outbreaks and minimize the problems that can arise among livestock after vaccinations. Vaccine improvement should be based on using attenuated virus strains with high levels of safety. Moreover, when vaccines are urgently required for newly spread field strains, the seed viruses for new vaccines should be developed for only a short period. Improved vaccines should offer superior immunization to all susceptible animals including cattle and swine. In addition, they should have highly protective effects without persistent infection. In this way, if vaccines are developed using new methods such as reverse genetics or vector vaccine technology, in which live viruses can be easily made by replacing specific protective antigens, even a single vaccination is likely to generate highly protective effects with an extended duration of immunity, and the safety and stability of the vaccines will be assured. We therefore reviewed the current FMD vaccines and their adjuvants, and evaluated if they provide superior immunization to all susceptible animals including cattle and swine.

Examination of soluble integrin resistant mutants of foot-and-mouth disease virus

Background

Foot-and-mouth disease virus (FMDV) initiates infection via recognition of one of at least four cell-surface integrin molecules α_vβ₁, α_vβ₃, α_vβ₆, or α_vβ₈ by a highly conserved Arg-Gly-Asp (RGD) amino acid sequence motif located in the G-H loop of VP1. Within the animal host, the α_vβ₆ interaction is believed to be the most relevant. Sub-neutralizing levels of soluble secreted α_vβ₆ (ssα_vβ₆) was used as a selective pressure during passages in vitro to explore the plasticity of that interaction.

Results

Genetically stable soluble integrin resistant (SIR) FMDV mutants derived from A24 Cruzeiro were selected after just 3 passages in cell culture in the presence of sub-neutralizing levels of ssα_vβ₆. SIR mutants were characterized by: replication on selective cell lines, plaque morphology, relative sensitivity to ssα_vβ₆ neutralization, relative ability to utilize α_vβ₆ for infection, as well as sequence and structural changes. All SIR mutants maintained an affinity for α_vβ₆. Some developed the ability to attach to cells expressing heparan sulfate (HS) proteoglycan, while others appear to have developed affinity for a still unknown third receptor. Two classes of SIR mutants were selected that were highly or moderately resistant to neutralization by ssα_vβ₆. Highly resistant mutants displayed a G145D substitution (RGD to RDD), while moderately resistant viruses exhibited a L150P/R substitution at the conserved RGD + 4 position. VP1 G-H loop homology models for the A-type SIR mutants illustrated potential structural changes within the integrin-binding motif by these 2 groups of mutations. Treatment of O1 Campos with ssα_vβ₆ resulted in 3 SIR mutants with a positively charged VP3 mutation allowing for HS binding.

Conclusions

These findings illustrate how FMDV particles rapidly gain resistance to soluble receptor prophylactic measures in vitro. Two different serotypes developed distinct capsid mutations to circumvent the presence of sub-neutralizing levels of the soluble cognate receptor, all of which resulted in a modified receptor tropism that expanded the cell types susceptible to FMDV. The identification of some of these adaptive mutations in known FMDV isolates suggests these findings have implications beyond the cell culture system explored in these studies.

Modulation of foot-and-mouth disease virus pH threshold for uncoating correlates with differential sensitivity to inhibition of cellular Rab GTPases and decreases infectivity in vivo

The role of cellular Rab GTPases that govern traffic between different endosome populations was analysed on foot-and-mouth disease virus (FMDV) infection. Changes of viral receptor specificity did not alter Rab5 requirement for infection. However, a correlation between uncoating pH and requirement of Rab5 for infection was observed. A mutant FMDV with less acidic uncoating pH threshold was less sensitive to inhibition of Rab5, whereas another mutant with more acidic requirements was more sensitive to inhibition of Rab5. On the contrary, opposed correlations between uncoating pH and dependence of Rab function were observed upon expression of dominant-negative forms of Rab7 or 11. Modulation of uncoating pH also reduced FMDV virulence in suckling mice. These results are consistent with FMDV uncoating inside early endosomes and indicate that displacements from optimum pH for uncoating reduce viral fitness in vivo.

Host predilection and transmissibility of vesicular stomatitis New Jersey virus strains in domestic cattle (Bos taurus) and swine (Sus scrofa)

BACKGROUND

Epidemiologic data collected during epidemics in the western United States combined with limited experimental studies involving swine and cattle suggest that host predilection of epidemic vesicular stomatitis New Jersey virus (VSNJV) strains results in variations in clinical response, extent and duration of virus shedding and transmissibility following infection in different hosts. Laboratory challenge of livestock with heterologous VSNJV strains to investigate potential viral predilections for these hosts has not been thoroughly investigated. In separate trials, homologous VSNJV strains (NJ82COB and NJ82AZB), and heterologous strains (NJ06WYE and NJOSF [Ossabaw Island, sand fly]) were inoculated into cattle via infected black fly bite. NJ82AZB and NJ06WYE were similarly inoculated into swine.

RESULTS

Clinical scores among viruses infecting cattle were significantly different and indicated that infection with a homologous virus resulted in more severe clinical presentation and greater extent and duration of viral shedding. No differences in clinical severity or extent and duration of viral shedding were detected in swine.

CONCLUSIONS

Differences in clinical presentation and extent and duration of viral shedding may have direct impacts on viral spread during epidemics. Viral transmission via animal-to-animal contact and insect vectored transmission are likely to occur at higher rates when affected animals are presenting severe clinical signs and shedding high concentrations of virus. More virulent viral strains resulting in more severe disease in livestock hosts are expected to spread more rapidly and greater distances during epidemics than those causing mild or inapparent signs.

A critical role of N-myc and STAT interactor (Nmi) in foot-and-mouth disease virus (FMDV) 2C-induced apoptosis

Foot-and-mouth disease virus (FMDV) 2C, is one of the most highly-conserved viral proteins among the serotypes of FMDV. However, its effect on host cells is not very clear. Using yeast two-hybrid system and immunoprecipitation approaches, we found that FMDV 2C interacted with the N-myc and STAT interactor (Nmi) protein. When expressed in cells, FMDV 2C is mainly associated with endoplasmic reticulum in the forms of speckles. In the absence of FMDV 2C, Nmi was distributed diffusely in the cytoplasm. However, upon FMDV 2C overexpression Nmi was recruited into FMDV 2C containing speckles where both proteins are co-localized. In addition, FMDV 2C induced apoptosis in BHK-21 cells, which was markedly inhibited by Nmi knockdown, suggesting that Nmi may play a critical role in FMDV 2C-induced apoptosis. These findings may help to further understand the molecular mechanism of pathogenesis of FMDV infection.

The nuclear protein Sam68 is cleaved by the FMDV 3C protease redistributing Sam68 to the cytoplasm during FMDV infection of host cells

Picornavirus infection can lead to disruption of nuclear pore traffic, shut-off of cell translation machinery, and cleavage of proteins involved in cellular signal transduction and the innate response to infection. Here, we demonstrated that the FMDV 3C(pro) induced the cleavage of nuclear RNA-binding protein Sam68 C-terminus containing the nuclear localization sequence (NLS). Consequently, it stimulated the redistribution of Sam68 to the cytoplasm. The siRNA knockdown of Sam68 resulted in a 1000-fold reduction in viral titers, which prompted us to study the effect of Sam68 on FMDV post-entry events. Interestingly, Sam68 interacts with the internal ribosomal entry site within the 5' non-translated region of the FMDV genome, and Sam68 knockdown decreased FMDV IRES-driven activity in vitro suggesting that it could modulate translation of the viral genome. The results uncover a novel role for Sam68 in the context of picornaviruses and the proteolysis of a new cellular target of the FMDV 3C(pro).

Foot-and-mouth disease virus particles inactivated with binary ethylenimine are efficiently internalized into cultured cells

Conventional foot-and-mouth disease (FMD) vaccines are produced from virus grown in cell culture that is chemically inactivated by using binary ethylenimide (BEI). Here, we show that BEI treatment preserves both the architecture of FMDV particles, as inactivated viral particles showed by electron microscopy characteristics similar to those of infectious virions, as well as the general features of infectious virus internalization. Binding of inactivated particles to BHK-21 cells was blocked by preincubation with either a FMDV-specific monoclonal antibody or a synthetic peptide spanning the integrin-binding viral motif Arg-Gly-Asp (RGD). In addition, these particles were internalized into cultured cells through endocytosis, being directed to early endosomes, as indicated by their colocalization with the marker protein Rab5. When purified BEI-inactivated virions were labelled and their interaction with live cultured cells analyzed by time-lapse fluorescence microscopy, a major subpopulation of virus particles, about 80%, was shown to undergo internalization into a static endosome population, insensitive to the microtubule depolymerization exerted by nocodazole, while the remaining subpopulation (about 20%) was dynamic and sensitive to this drug. Thus, BEI-inactivated particles provide an interesting tool to study early steps in FMDV-cell interactions enabling a distinction between FMDV internalization and productive infection. Possible implications for FMDV immune response elicited following vaccine administration are discussed.

Inoculation of newborn mice with non-coding regions of foot-and-mouth disease virus RNA can induce a rapid, solid and wide-range protection against viral infection

We have recently described the ability of in vitro-transcribed RNAs, mimicking structural domains in the 5' and 3' non-coding regions (NCRs) of the foot-and-mouth disease virus (FMDV) genome, to trigger the innate immune response in porcine cultured cells and mice. In this work, the antiviral effect exerted in vivo by these small synthetic non-infectious RNA molecules was analyzed extensively. The susceptibility of transfected newborn Swiss mice to FMDV challenge was tested using a wide range of viral doses. The level of protection depended on the specific RNA inoculated and was dose-dependent. The RNA giving the best protection was the internal ribosome entry site (IRES), followed by the transcripts corresponding to the S fragment. The time course of resistance to FMDV of the RNA-transfected mice was studied. Our results show the efficacy of these RNAs to prevent viral infection as well as to contain ongoing FMDV infection in certain time intervals. Protection proved to be independent of the serotype of FMDV used for challenge. These results support the potential use of the FMDV NCR transcripts as both prophylactic and therapeutic molecules for new FMDV control strategies.

RNA structural domains in noncoding regions of the foot-and-mouth disease virus genome trigger innate immunity in porcine cells and mice

The induction of type I interferons (alpha/beta interferon [IFN-α/β]) in response to viral infection is a crucial step leading to the antiviral state in the host. Viruses produce double-stranded RNA (dsDNA) during their replication cycle that is sensed as nonself by host cells through different receptors. A signaling cascade then is activated to block viral replication and spread. Foot-and-mouth disease virus (FMDV) is a picornavirus that is highly sensitive to IFN, and it causes one of the world's most important animal diseases. In this study, we showed the ability of structural domains predicted to enclose stable dsRNA regions in the 5'- and 3'-noncoding regions (NCRs) of the FMDV genome to trigger an IFN-α/β response in porcine kidney cultured cells and newborn mice. These RNAs, generated by in vitro transcription, were able to stimulate IFN-β transcription and induce an antiviral state in SK-6 cells. The induction levels elicited by the different NCR RNAs were compared. Among them, the 3'NCR was identified as a potent IFN activator, and the features in this region involved in signaling have been analyzed. To address whether the FMDV NCR transcripts were able to trigger the innate immune response in vivo, Swiss suckling mice were inoculated intraperitoneally with the RNAs. All transcripts induced the innate response in transfected animals, measured as IFN-α/β protein levels, antiviral activity in sera, and reduced susceptibility to FMDV infection. Our work provides new insight into innate responses against FMDV and identifies these small noninfectious RNA molecules as potential adjuvants for vaccine improvement and antiviral strategies against picornaviruses.

Modelling foot-and-mouth disease virus dynamics in oral epithelium to help identify the determinants of lysis

Foot-and-mouth disease virus (FMDV) causes an economically important disease of cloven-hoofed livestock; of interest here is the difference in lytic behaviour that is observed in bovine epithelium. On the skin around the feet and tongue, the virus rapidly replicates, killing cells, and resulting in growing lesions, before eventually being cleared by the immune response. In contrast, there is usually minimal lysis in the soft palate, but virus may persist in tissue long after the animal has recovered from the disease. Persistence of virus has important implications for disease control, while identifying the determinant of lysis in epithelium is potentially important for the development of prophylactics. To help identify which of the differences between oral and pharyngeal epithelium are responsible for such dramatically divergent FMDV dynamics, a simple model has been developed, in which virus concentration is made explicit to allow the lytic behaviour of cells to be fully considered. Results suggest that localised structuring of what are fundamentally similar cells can induce a bifurcation in the behaviour of the system, explicitly whether infection can be sustained or results in mutual extinction, although parameter estimates indicate that more complex factors may be involved in maintaining viral persistence, or that there are as yet unquantified differences between the intrinsic properties of cells in these regions.

Hsp70 enhances presentation of FMDV antigen to bovine CD4+ T cells in vitro

Foot-and-mouth disease virus (FMDV) is the causative agent of a highly contagious acute vesicular disease affecting cloven-hoofed animals, including cattle, sheep and pigs. The current vaccine induces a rapid humoral response, but the duration of the protective antibody response is variable, possibly associated with a variable specific CD4⁺ T cell response. We investigated the use of heat shock protein 70 (Hsp70) as a molecular chaperone to target viral antigen to the Major Histocompatibility Complex (MHC) class II pathway of antigen presenting cells and generate enhanced MHC II-restricted CD4⁺ T cell responses in cattle. Monocytes and CD4⁺ T cells from FMDV vaccinated cattle were stimulated in vitro with complexes of Hsp70 and FMDV peptide, or peptide alone. Hsp70 was found to consistently improve the presentation of a 25-mer FMDV peptide to CD4⁺ T cells, as measured by T cell proliferation. Complex formation was required for the enhanced effects and Hsp70 alone did not stimulate proliferation. This study provides further evidence that Hsp70:peptide complexes can enhance antigen-specific CD4⁺ T cell responses in vitro for an important pathogen of livestock.