Immunosuppression during acute infection with foot-and-mouth disease virus in swine is mediated by IL-10

Analysis of Chromatin Accessibility Changes Induced by BMMC Recognition of Foot-and-Mouth Disease Virus-like Particles through ATAC-seq

Mast cells can recognize foot-and-mouth disease virus-like particles (FMDV-VLPs) via mannose receptors (MRs) to produce differentially expressed cytokines. The regulatory role of chromatin accessibility in this process is unclear. Bone marrow-derived mast cells (BMMCs) were cultured, and an assay of transposase-accessible chromatin sequencing (ATAC-seq) was applied to demonstrate the regulation of chromatin accessibility in response to the BMMCs' recognition of FMDV-VLPs. A pathway enrichment analysis showed that peaks associated with the nuclear factor-κB (NF-κB), mitogen-activated protein kinase (MAPK), phosphatidylinositol 3 kinase-protein kinase B (PI3K-Akt), and other signaling pathways, especially the NF-κB pathway, were involved in the BMMCs' recognition of VLPs. Moreover, transcription factors including SP1, NRF1, AP1, GATA3, microphthalmia-associated transcription factor (MITF), and NF-κB-p65 may bind to the motifs with altered chromatin accessibility to regulate gene transcription. Furthermore, the expression of NF-κB, interleukin (IL)-9, tumor necrosis factor (TNF)-α, and interferon (IFN)-γ in the BMMCs of the VLP group increased compared with that of the BMMCs in the control group, whereas the expression of IL-10 did not differ significantly between groups. After inhibiting the MRs, the expression of NF-κB, IL-9, TNF-α, and IFN-γ decreased significantly, whereas the expression of IL-10 increased. The expression of MAPK and IL-6 showed no significant change after MR inhibition. This study demonstrated that MRs expressed on BMMCs can affect the NF-κB pathway by changing chromatin accessibility to regulate the transcription of specific cytokines, ultimately leading to the differential expression of cytokines. These data provide a theoretical basis and new ideas for the development of a novel vaccine for FMD.

Histone acetylation regulates BMMCs recognition of foot-and-mouth disease virus-like particles

Foot-and-mouth disease (FMD) is one of the most economically and socially devastating diseases affecting animal agriculture worldwide. Foot-and-mouth disease virus (FMDV) virus-like particles (VLPs) have been widely studied as a candidate vaccine. Mast cells (MCs) are highly versatile innate immunity cells that perform various functions in regulating innate and adaptive immune responses. Recently, we found that MCs can recognize recombinant FMDV VP1-VP4 protein to produce various cytokines with differential expression, suggesting that this may be epigenetically regulated. In this study, we evaluated the effect of trichostatin A (TSA), a histone deacetylase inhibitor, on bone marrow-derived mast cells (BMMCs) recognition of FMDV-VLPs in vitro. BMMCs can recognize FMDV-VLPs via mannose receptors (MRs) and resulted in enhanced expression and secretion of tumour necrosis factor α (TNF-α) and interleukin (IL)-13. Nevertheless, BMMCs recognition of FMDV-VLPs to secrete IL-6 was irrelevant to MRs, and MRs may play a negative regulation for IL-10 secretion. Pre-treatment with TSA caused decreased expression of IL-6, TNF-α and IL-13, and increased expression of IL-10. Furthermore, the expression of nuclear factor-kappa B (NF-κB) was supressed in TSA treated BMMCs, suggesting histone acetylation may alter NF-κB expression to influence the TNF-α and IL-13 secretion. Pre-treatment with TSA had no influence on the expression of microphthalmia-associated transcription factor (MITF) and GATA-2. These data therefore suggest that altered histone acetylation regulates the immune responses induced by BMMCs recognition of FMDV-VLPs, providing an understanding and theory basis for the prevention and control of FMD based MCs.

Mutation of FMDV Lpro H138 residue drives viral attenuation in cell culture and in vivo in swine

The foot-and-mouth disease virus (FMDV) leader proteinase (L^pro) is a papain like protease that cleaves the viral polyprotein and several host factors affecting host cell translation and induction of innate immunity. Introduction of L^pro mutations ablating catalytic activity is not tolerated by the virus, however, complete coding sequence deletion or introduction of targeted amino acid substitutions can render viable progeny. In proof-of-concept studies, we have previously identified and characterized FMDV L^pro mutants that are attenuated in cell culture and in animals, while retaining their capacity for inducing a strong adaptive immunity. By using molecular modeling, we have now identified a His residue (H138), that resides outside the substrate binding and catalytic domain, and is highly conserved across serotypes. Mutation of H138 renders possible FMDV variants of reduced virulence in vitro and in vivo. Kinetics studies showed that FMDV A12-L_H138L mutant replicates similarly to FMDV A12-wild type (WT) virus in cells that do not offer immune selective pressure, but attenuation is observed upon infection of primary or low passage porcine epithelial cells. Western blot analysis on protein extracts from these cells, revealed that while processing of translation initiation factor eIF-4G was slightly delayed, no degradation of innate sensors or effector molecules such as NF-κB or G3BP2 was observed, and higher levels of interferon (IFN) and IFN-stimulated genes (ISGs) were induced after infection with A12-L_H138L as compared to WT FMDV. Consistent with the results in porcine cells, inoculation of swine with this mutant resulted in a mild, or in some cases, no clinical disease but induction of a strong serological adaptive immune response. These results further support previous evidence that L^pro is a reliable target to derive numerous viable FMDV strains that alone or in combination could be exploited for the development of novel FMD vaccine platforms.

A Morbillivirus Infection Shifts DC Maturation Toward a Tolerogenic Phenotype to Suppress T Cell Activation

Viruses have evolved numerous strategies to impair immunity so that they can replicate more efficiently. Among those, the immunosuppressive effects of morbillivirus infection can be particularly problematic, as they allow secondary infections to take hold in the host, worsening disease prognosis. In the present work, we hypothesized that the highly contagious morbillivirus peste des petits ruminants virus (PPRV) could target monocytes and dendritic cells (DC) to contribute to the immunosuppressive effects produced by the infection. Monocytes isolated from healthy sheep, a natural host of the disease, were able be infected by PPRV and this impaired the differentiation and phagocytic ability of immature monocyte-derived DC (MoDC). We also assessed PPRV capacity to infect differentiated MoDC. Ovine MoDC could be productively infected by PPRV, and this drastically reduced MoDC capacity to activate allogeneic T cell responses. Transcriptomic analysis of infected MoDC indicated that several tolerogenic DC signature genes were upregulated upon PPRV infection. Furthermore, PPRV-infected MoDC could impair the proliferative response of autologous CD4⁺ and CD8⁺ T cell to the mitogen concanavalin A (ConA), which indicated that DC targeting by the virus could promote immunosuppression. These results shed new light on the mechanisms employed by morbillivirus to suppress the host immune responses. IMPORTANCE Morbilliviruses pose a threat to global health given their high infectivity. The morbillivirus peste des petits ruminants virus (PPRV) severely affects small-ruminant-productivity and leads to important economic losses in communities that rely on these animals for subsistence. PPRV produces in the infected host a period of severe immunosuppression that opportunistic pathogens exploit, which worsens the course of the infection. The mechanisms of PPRV immunosuppression are not fully understood. In the present work, we demonstrate that PPRV can infect professional antigen-presenting cells called dendritic cells (DC) and disrupt their capacity to elicit an immune response. PPRV infection promoted a DC activation profile that favored the induction of tolerance instead of the activation of an antiviral immune response. These results shed new light on the mechanisms employed by morbilliviruses to suppress the immune responses.

Interleukin-10-Mediated Lymphopenia Caused by Acute Infection with Foot-and-Mouth Disease Virus in Mice

Foot-and-mouth disease (FMD) is characterized by a pronounced lymphopenia that is associated with immune suppression. However, the mechanisms leading to lymphopenia remain unclear. In this study, the number of total CD4⁺, CD8⁺ T cells, B cells, and NK cells in the peripheral blood were dramatically reduced in C57BL/6 mice infected with foot-and-mouth disease virus (FMDV) serotype O, and it was noted that mice with severe clinical symptoms had expressively lower lymphocyte counts than mice with mild or without clinical symptoms, indicating that lymphopenia was associated with disease severity. A further analysis revealed that lymphocyte apoptosis and trafficking occurred after FMDV infection. In addition, coinhibitory molecules were upregulated in the expression of CD4⁺ and CD8⁺ T cells from FMDV-infected mice, including CTLA-4, LAG-3, 2B4, and TIGIT. Interestingly, the elevated IL-10 in the serum was correlated with the appearance of lymphopenia during FMDV infection but not IL-6, IL-2, IL-17, IL-18, IL-1β, TNF-α, IFN-α/β, TGF-β, and CXCL1. Knocking out IL-10 (IL-10^-/-) mice or blocking IL-10/IL-10R signaling in vivo was able to prevent lymphopenia via downregulating apoptosis, trafficking, and the coinhibitory expression of lymphocytes in the peripheral blood, which contribute to enhance the survival of mice infected with FMDV. Our findings support that blocking IL-10/IL-10R signaling may represent a novel therapeutic approach for FMD.

Induction of antiviral and cell mediated immune responses significantly reduce viral load in an acute foot-and-mouth disease virus infection in cattle

Foot-and-mouth disease virus (FMDV) causes a severe infection in ruminant animals. Here we present an in-depth transcriptional analysis of soft-palate tissue from cattle experimentally infected with FMDV. The differentially expressed genes from two Indian cattle (Bos indicus) breeds (Malnad Gidda and Hallikar) and Holstein Friesian (HF) crossbred calves, highlighted the activation of metabolic processes, mitochondrial functions and significant enrichment of innate antiviral immune response pathways in the indigenous calves. The results of RT-qPCR based validation of 12 genes was in alignment with the transcriptome data. The indigenous calves showing lesser virus load, elicited early neutralizing antibodies and IFN-γ immune responses. This study revealed that induction of potent innate antiviral response and cell mediated immunity in indigenous cattle, especially Malnad Gidda, significantly restricted FMDV replication during acute infection. These data highlighting the molecular processes associated with host-pathogen interactions, could aid in the conception of novel strategies to prevent and control FMDV infection in cattle.

Prevalence of tick-borne haemoparasites and their perceived co-occurrences with viral outbreaks of FMD and LSD and their associated factors

Species of Theileria, Babesia, and Anaplasma are Tick-borne pathogens (TBPs) that are prevalent throughout the world, particularly in the tropical and subtropical regions. Associated diseases of Theileriosis, Babesiosis, and Anaplasmosis, respectively, represents a major threat to livestock production in many countries. TBPs have a high prevalence in different geographical locations in Egypt. Foot and mouth disease (FMD) and Lumpy skin disease (LSD) are considered endemic bovine viral diseases in Egypt. Our clinical observations during the epidemics of LSD and FMD viruses showed higher prevalence rates for the TBPs. To investigate this correlation, a total of 670 samples from cattle and buffalo were collected during the summers of 2017 and 2018 distributed throughout ranches and smallholders in two geographical locations in Egypt. Two farms with a recent clinical outbreak of LSD with a total of 270 animals, while the other location included three farms with a recent FMD outbreak with a combined 400 cattle. Examined animals were classified mainly according to age, gender, species, breed (native versus crossbred), and the presence of ticks. Whole blood samples were collected for TBPs and viral (LSD and FMD) examinations, while tissue specimens were collected for detection of FMD and LSD viruses by real-time PCR.

Our results confirmed significantly higher prevalence rates for the TBPs in LSD-positive than LSD-negative animals, while no significant difference could be detected for the prevalence rate of the TBPs in the FMD positive and negative groups. The prevalence of Babesia and Theileria was significantly (P < 0.05) higher in cross-breeds than native cattle. Infections with Anaplasma and co-infections with Babesia-Anaplasma and Theileria-Anaplasma were significantly higher in native than cross-breeds cattle. The intensity of parasitic infection (parasitemia) has a significant difference in the positive groups for the two viruses compared to the negative groups. These results collectively confirming the enhancing role of LSD on the prevalence rate of the haemoprotozoal infections leading to more serious outcomes to the livestock infections, and therefore the control of haemoprotozoal infections should be implemented as a part of viral epidemics control.

Virus-Host Interactions in Foot-and-Mouth Disease Virus Infection

Foot-and-mouth disease (FMD) is a highly contagious disease of cloven-hoofed animals, which has been regarded as a persistent challenge for the livestock industry in many countries. Foot-and-mouth disease virus (FMDV) is the etiological agent of FMD that can spread rapidly by direct and indirect transmission. FMDV is internalized into host cell by the interaction between FMDV capsid proteins and cellular receptors. When the virus invades into the cells, the host antiviral system is quickly activated to suppress the replication of the virus and remove the virus. To retain fitness and host adaptation, various viruses have evolved multiple elegant strategies to manipulate host machine and circumvent the host antiviral responses. Therefore, identification of virus-host interactions is critical for understanding the host defense against virus infections and the pathogenesis of the viral infectious diseases. This review elaborates on the virus-host interactions during FMDV infection to summarize the pathogenic mechanisms of FMD, and we hope it can provide insights for designing effective vaccines or drugs to prevent and control the spread of FMD and other diseases caused by picornaviruses.

Use of IFN-Based Biotherapeutics to Harness the Host Against Foot-And-Mouth Disease

Foot-and-mouth disease (FMD) is a highly contagious vesicular disease of cloven-hoofed animals that severely constrains international trade of livestock and animal products. Currently, disease control measures include broad surveillance, enforcement of sanitary policy, and use of an inactivated vaccine. While use of these measures has contributed to eliminating foot-and-mouth disease virus (FMDV) from a vast area of the world, the disease remains endemic in three continents, and outbreaks occasionally appear in previously declared FMD-free zones, causing economic and social devastation. Among others, a very fast rate of viral replication and the need for 7 days to achieve vaccine-induced protection are the main limitations in controlling the disease. New fast-acting antiviral strategies targeted to boost the innate immunity of the host to block viral replication are needed. Here we review the knowledge on the multiple strategies FMDV has evolved to block the host innate immunity, with particularly focus on the past and current research toward the development of interferon (IFN)-based biotherapeutics in relevant livestock species.

Foot and mouth disease virus undergoes non-progressive replication in mice peritoneal macrophages and induces M1 polarization

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Non-progressive replication of foot and mouth disease virus was observed in mice peritoneal macrophages.

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Macrophages turns to M1 type polarization in response to FMDV infection.

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Upregulation of pro-inflammatory cytokines was peak by 8 h FMDV infection.

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Type I IFN and viperin showed marked upregulation following FMDV infection in the macrophages.

Despite the fact that macrophages link the innate and adaptive arms of immunity, it’s role in the early infection of foot and mouth disease virus (FMDV) is largely unknown. Recently, depletion of macrophages in vivo after vaccination has shown to drastically diminish the protection against FMDV challenge in mouse model. Even the ability of macrophages to reduce or resist FMDV infection is not known hitherto. Therefore, we examined the replication ability of FMDV in mice peritoneal macrophages and the responsiveness in terms of macrophage polarization and cytokine production. Negative strand specific RT-PCR indicated replication of FMDV RNA in macrophages. Absolute quantitation of FMDV transcripts, immunofluorescence studies and titre of the infectious progeny virus revealed that replication peaked at 12 hpi and significantly declined by 18 hpi indicating non-progressive replication in the infected macrophages. Further, significant up regulation of inducible nitric oxide synthase by 8 –12 hpi and increase of M1 specific CD11c + cells by 42.6 % after infection showed that FMDV induce M1 polarization. A significant up regulation of TNFα and IL12 transcripts at 8 hpi supported that M1 macrophages were functional. Further, we studied the expression of Type I to III interferons (IFN) and other antiviral molecules. The results indicate a marked up regulation of Type I IFNα and β by 9.2 and 11.2 fold, respectively at 8 hpi. Of the four IFN stimulated genes (ISG), viperin showed a significant up regulation by 286-fold at 12 hpi in the mice macrophages. In conclusion, the results suggest that replication of FMDV in mice peritoneal macrophages is non-progressive with up regulation of Type I IFN and ISGs. Further, FMDV induces M1 polarization in murine peritoneal macrophages.

The first molecular detection of Clostridium perfringens from pneumonic cases associated with foot and mouth disease in cattle and buffalo in Egypt

Panting syndrome and respiratory infection have been recorded in complicated cases of foot and mouth disease (FMD) in cattle. However, investigations on the causative agents of respiratory disease in such cases are scarce. In this study, 30 animals (13 buffalo and 17 cattle) suffering from respiratory distress associated with signs of FMD were examined. Serum samples were collected and FMD infection was confirmed. Bacteriological examination of lungs from eight necropitized cases revealed the presence of C. perfringens. Multiplex polymerase chain reaction (mPCR) was performed on the positive samples followed by sequencing analysis. The alpha toxin gene (plc) of C. perfringens was identified in six cases. The present investigation highlights the role of clostridial infection as a complication of FMD in cattle and buffalo. This is the first report identifying the C. perfringens toxins from lung of animals with respiratory distress associated with FMD infection.

The Different Tactics of Foot-and-Mouth Disease Virus to Evade Innate Immunity

Like all pathogens, foot-and-mouth disease virus (FMDV) is recognized by the immune system inducing a heightened immune response mainly mediated by type I and type III IFNs. To overcome the strong antiviral response induced by these cytokines, FMDV has evolved many strategies exploiting each region of its small RNA genome. These include: (a) inhibition of IFN induction at the transcriptional and translational level, (b) inhibition of protein trafficking; (c) blockage of specific post-translational modifications in proteins that regulate innate immune signaling; (d) modulation of autophagy; (e) inhibition of stress granule formation; and (f) in vivo modulation of immune cell function. Here, we summarize and discuss FMDV virulence factors and the host immune footprint that characterize infection in cell culture and in the natural hosts.

Tumor Necrosis Factor Receptor-Associated Factor 5 Interacts with the NS3 Protein and Promotes Classical Swine Fever Virus Replication

Classical swine fever, caused by classical swine fever virus (CSFV), is a highly contagious and high-mortality viral disease, causing huge economic losses in the swine industry worldwide. CSFV non-structural protein 3 (NS3), a multifunctional protein, plays crucial roles in viral replication. However, how NS3 exactly exerts these functions is currently unknown. Here, we identified tumor necrosis factor receptor-associated factor 5 (TRAF5) as a novel binding partner of the NS3 protein via yeast two-hybrid, co-immunoprecipitation and glutathione S-transferase pull-down assays. Furthermore, we observed that TRAF5 promoted CSFV replication in porcine alveolar macrophages (PAMs). Additionally, CSFV infection or NS3 expression upregulated TRAF5 expression, implying that CSFV may exploit TRAF5 via NS3 for better growth. Moreover, CSFV infection and TRAF5 expression activated p38 mitogen activated protein kinase (MAPK) activity, and inhibition of p38 MAPK activation by the SB203580 inhibitor suppressed CSFV replication. Notably, TRAF5 overexpression did not promote CSFV replication following inhibition of p38 MAPK activation. Our findings reveal that TRAF5 promotes CSFV replication via p38 MAPK activation. This work provides a novel insight into the role of TRAF5 in CSFV replication capacity.

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.

Foot-and-mouth disease virus infection stimulates innate immune signaling in the mouse macrophage RAW 264.7 cells

The innate immune system acts as the first line of defense against invasion by bacterial and viral pathogens. The role of macrophages in innate immune responses to foot-and-mouth disease virus (FMDV) is poorly understood. To determine the mechanism underlying activation of innate immunity after FMDV infection in macrophages, we performed FMDV infection in mouse macrophage RAW 264.7 cells and found that FMDV serotype O infection induced a cytopathic effect. We then evaluated the gene expression profile in macrophage RAW 264.7 cells after FMDV infection using systematic microarray analysis. Gene ontology annotation and enrichment analysis revealed that FMDV promoted expression in a group of genes that are enriched in innate immune response and inflammatory response processes. Further research demonstrated that FMDV serotype O infection enhanced NF-κB, Toll-like, and RIG-I-like receptor signaling pathways and proteins expression and increased transcription and expression of a series of cytokines and interferons, as proved by qRT-PCR, Western blot, ELISA, and dual-luciferase reporter assay. Our study concluded that FMDV infection triggers the innate immune response in macrophages after activation of multiple innate immune pathway receptors and proteins by FMDV serotype O, resulting in activation and secretion of a series of cytokines and interferons.

IL-10: A Multifunctional Cytokine in Viral Infections

The anti-inflammatory master regulator IL-10 is critical to protect the host from tissue damage during acute phases of immune responses. This regulatory mechanism, central to T cell homeostasis, can be hijacked by viruses to evade immunity. IL-10 can be produced by virtually all immune cells, and it can also modulate the function of these cells. Understanding the effects of this multifunctional cytokine is therefore a complex task. In the present review we discuss the factors driving IL-10 production and the cellular sources of the cytokine during antiviral immune responses. We particularly focus on the IL-10 regulatory mechanisms that impact antiviral immune responses and how viruses can use this central regulatory pathway to evade immunity and establish chronic/latent infections.

Systemic immune response and virus persistence after foot-and-mouth disease virus infection of naïve cattle and cattle vaccinated with a homologous adenovirus-vectored vaccine

Background

In order to investigate host factors associated with the establishment of persistent foot-and-mouth disease virus (FMDV) infection, the systemic response to vaccination and challenge was studied in 47 steers. Eighteen steers that had received a recombinant FMDV A vaccine 2 weeks earlier and 29 non-vaccinated steers were challenged by intra-nasopharyngeal deposition of FMDV A24. For up to 35 days after challenge, host factors including complete blood counts with T lymphocyte subsets, type I/III interferon (IFN) activity, neutralizing and total FMDV-specific antibody titers in serum, as well as antibody-secreting cells (in 6 non-vaccinated animals) were characterized in the context of viral infection dynamics.

Results

Vaccination generally induced a strong antibody response. There was a transient peak of FMDV-specific serum IgM in non-vaccinated animals after challenge, while IgM levels in vaccinated animals did not increase further. Both groups had a lasting increase of specific IgG and neutralizing antibody after challenge.

Substantial systemic IFN activity in non-vaccinated animals coincided with viremia, and no IFN or viremia was detected in vaccinated animals. After challenge, circulating lymphocytes decreased in non-vaccinated animals, coincident with viremia, IFN activity, and clinical disease, whereas lymphocyte and monocyte counts in vaccinated animals were unaffected by vaccination but transiently increased after challenge. The CD4⁺/CD8⁺ T cell ratio in non-vaccinated animals increased during acute infection, driven by an absolute decrease of CD8⁺ cells.

Conclusions

The incidence of FMDV persistence was 61.5 % in non-vaccinated and 54.5 % in vaccinated animals. Overall, the systemic factors examined were not associated with the FMDV carrier/non-carrier divergence; however, significant differences were identified between responses of non-vaccinated and vaccinated cattle.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-016-0838-x) contains supplementary material, which is available to authorized users.

The Pathogenesis of Foot-and-Mouth Disease in Pigs

The greatest proportion of foot-and-mouth disease (FMD) clinical research has been dedicated to elucidating pathogenesis and enhancing vaccine protection in cattle with less efforts invested in studies specific to pigs. However, accumulated evidence from FMD outbreaks and experimental investigations suggest that critical components of FMD pathogenesis, immunology, and vaccinology cannot be extrapolated from investigations performed in cattle to explain or to predict outcomes of infection or vaccination in pigs. Furthermore, it has been shown that failure to account for these differences may have substantial consequences when FMD outbreaks occur in areas with dense pig populations. Recent experimental studies have confirmed some aspects of conventional wisdom by demonstrating that pigs are more susceptible to FMD virus (FMDV) infection via exposure of the upper gastrointestinal tract (oropharynx) than through inhalation of virus. The infection spreads rapidly within groups of pigs that are housed together, although efficiency of transmission may vary depending on virus strain and exposure intensity. Multiple investigations have demonstrated that physical separation of pigs is sufficient to prevent virus transmission under experimental conditions. Detailed pathogenesis studies have recently demonstrated that specialized epithelium within porcine oropharyngeal tonsils constitute the primary infection sites following simulated natural virus exposure. Furthermore, epithelium of the tonsil of the soft palate supports substantial virus replication during the clinical phase of infection, thus providing large amounts of virus that can be shed into the environment. Due to massive amplification and shedding of virus, acutely infected pigs constitute a considerable source of contagion. FMDV infection results in modulation of several components of the host immune response. The infection is ultimately cleared in association with a strong humoral response and, in contrast to ruminants, there is no subclinical persistence of FMDV in pigs. The aim of this review is to provide an overview of knowledge gained from experimental investigations of FMD pathogenesis, transmission, and host response in pigs. Details of the temporo-anatomic progression of infection are discussed in relation to specific pathogenesis events and the likelihood of transmission. Additionally, relevant aspects of the host immune response are discussed within contexts of conventional and novel intervention strategies of vaccination and immunomodulation.

Effect of Foot-and-Mouth Disease Virus Infection on the Frequency, Phenotype and Function of Circulating Dendritic Cells in Cattle

Foot-and-mouth disease virus (FMDV) is a highly contagious virus that causes one of the most devastating diseases in cloven-hoofed animals. Disease symptoms develop within 2 to 3 days of exposure and include fever and vesicular lesions on the tongue and hooves. Dendritic cells (DC) play an essential role in protective immune responses against pathogens. Therefore, investigating their role during FMDV infection would lead to a better understanding of host-pathogen interactions. In this study, following infection of cattle with FMDV, we investigated the frequency and function of conventional (cDC) and plasmacytoid DC (pDC) in blood by using multi-color flow cytometry. We show that the frequency of cDC and pDC increased following FMDV infection and peaked 3 to 4 days post-infection. During peak viremia, the cattle became lymphopenic, the expression of MHC class II molecules on cDC and pDC was dramatically down-regulated, the processing of exogenous antigen by cDC and pDC was impaired, and there was an increase in IL-10 production by DC and monocytes. Notably, after clearance of FMDV from the blood, MHC class II expression returned to pre-infection levels. Altogether, our study demonstrates that in cattle, FMDV inhibits the function of DC, thereby retarding the initiation of adaptive immune responses, potentially enhancing virus shedding during the acute phase of infection.

Evaluation of a Fiber-Modified Adenovirus Vector Vaccine against Foot-and-Mouth Disease in Cattle

Novel vaccination approaches against foot-and-mouth disease (FMD) include the use of replication-defective human adenovirus type 5 (Ad5) vectors that contain the capsid-encoding regions of FMD virus (FMDV). Ad5 containing serotype A24 capsid sequences (Ad5.A24) has proved to be effective as a vaccine against FMD in livestock species. However, Ad5-vectored FMDV serotype O1 Campos vaccine (Ad5.O1C.2B) provides only partial protection of cattle against homologous challenge. It has been reported that a fiber-modified Ad5 vector expressing Arg-Gly-Asp (RGD) enhances transduction of antigen-presenting cells (APC) in mice. In the current study, we assessed the efficacy of a fiber-modified Ad5 (Adt.O1C.2B.RGD) in cattle. Expression of FMDV capsid proteins was superior in cultured cells infected with the RGD-modified vector. Furthermore, transgene expression of Adt.O1C.2B.RGD was enhanced in cell lines that constitutively express integrin αvβ6, a known receptor for FMDV. In contrast, capsid expression in cattle-derived enriched APC populations was not enhanced by infection with this vector. Our data showed that vaccination with the two vectors yielded similar levels of protection against FMD in cattle. Although none of the vaccinated animals had detectable viremia, FMDV RNA was detected in serum samples from animals with clinical signs. Interestingly, CD4(+) and CD8(+) gamma interferon (IFN-γ)(+) cell responses were detected at significantly higher levels in animals vaccinated with Adt.O1C.2B.RGD than in animals vaccinated with Ad5.O1C.2B. Our results suggest that inclusion of an RGD motif in the fiber of Ad5-vectored FMD vaccine improves transgene delivery and cell-mediated immunity but does not significantly enhance vaccine performance in cattle.

Interleukin-10 production at the early stage of infection with foot-and-mouth disease virus related to the likelihood of persistent infection in cattle

The factors leading to persistent infection of foot-and-mouth disease (FMD) virus in ruminants are not well defined. This paper provides evidence of the presence of interleukin-10 (IL-10) early in the course of infection (1–4 days) as a factor in the development of persistence of FMD virus in cattle. Results showed that serum IL-10 in carrier cattle infected with FMD virus type O (n = 4) was detected and peaked at 1 or 2 days post infection and rapidly declined thereafter. In contract, serum IL-10 levels in non-carrier cattle (n = 21) were very low or undetectable during the same period.

Serotyping of foot and mouth disease virus and Pasteurella multocida from Indian gaurs (Bos gaurus), concurrently infected with foot and mouth disease and haemorrhagic septicaemia

We report the serotyping of foot-and-mouth disease virus (FMDV) and Pasteurella multocida from Indian gaurs which were concurrently infected with foot-and-mouth disease (FMD) and haemorrhagic septicaemia. Bannerghatta biological park (BBP), a national park located in the outskirts of Bengaluru city, Karnataka, India, is bordered by several villages. These villages witnessed massive outbreaks of FMD which spread rapidly to the herbivores at BBP. Post-mortem was conducted on carcasses of two Indian gaurs that died with symptoms of FMD. The salient gross findings included extensive vesicular lesions on the tongue, gums, cheeks, upper palate and hooves. Haemorrhagic tracheitis and ecchymotic haemorrhages on the heart were characteristic. The vesicular lesions of oral cavity were positive for 'O' type of FMD virus by sandwich enzyme-linked immuno sorbent assay (ELISA). The heart blood and spleen samples yielded growth of pure cultures of P. multocida. The isolates were typed as P. multocida type B using KTSP61 and KTT72 primers yielding specific amplicons of 620 bp. The phylogenetic analysis of the isolates was carried by sequencing of 1.4-Kbp nucleotides on the 16S ribosomal RNA (rRNA) gene of the isolates.

The N-N non-covalent domain of the nucleocapsid protein of type 2 porcine reproductive and respiratory syndrome virus enhances induction of IL-10 expression

Porcine reproductive and respiratory syndrome virus (PRRSV) usually establishes a prolonged infection and causes an immunosuppressive state. It has been proposed that IL-10 plays an important role in PRRSV-induced immunosuppression. However, this mechanism has not been completely elucidated. In this study, we found that transfection of 3D4/2 macrophages with the N protein gene of type 2 PRRSV significantly upregulated IL-10 expression at the transcriptional level. Moreover, alanine substitution mutation analysis revealed that the N protein residues 33-37, 65-68 and 112-123 were related to the upregulation of IL-10 promoter activity. Recombinant PRRSV with mutations at residues 33-37 in the N protein (rQ33-5A and rS36A) recovered from corresponding infectious cDNA clones and induced significantly lower levels of IL-10 production in infected monocyte-derived dendritic cells, as compared with their revertants rQ33-5A(R) and rS36A(R), and the wild-type recombinant PRRSV strain rNT/wt. These data indicate that the type 2 PRRSV N protein plays an important role in IL-10 induction and the N-N non-covalent domain is associated with this activity.

Laboratory animal models to study foot-and-mouth disease: a review with emphasis on natural and vaccine-induced immunity

Laboratory animal models have provided valuable insight into foot-and-mouth disease virus (FMDV) pathogenesis in epidemiologically important target species. While not perfect, these models have delivered an accelerated time frame to characterize the immune responses in natural hosts and a platform to evaluate therapeutics and vaccine candidates at a reduced cost. Further expansion of these models in mice has allowed access to genetic mutations not available for target species, providing a powerful and versatile experimental system to interrogate the immune response to FMDV and to target more expensive studies in natural hosts. The purpose of this review is to describe commonly used FMDV infection models in laboratory animals and to cite examples of when these models have failed or successfully provided insight relevant for target species, with an emphasis on natural and vaccine-induced immunity.

Out-of-sequence signal 3 as a mechanism for virus-induced immune suppression of CD8 T cell responses

Virus infections are known to induce a transient state of immune suppression often associated with an inhibition of T cell proliferation in response to mitogen or cognate-antigen stimulation. Recently, virus-induced immune suppression has been linked to responses to type 1 interferon (IFN), a signal 3 cytokine that normally can augment the proliferation and differentiation of T cells exposed to antigen (signal 1) and co-stimulation (signal 2). However, pre-exposure of CD8 T cells to IFN-inducers such as viruses or poly(I∶C) prior to antigen signaling is inhibitory, indicating that the timing of IFN exposure is of essence. We show here that CD8 T cells pretreated with poly(I∶C) down-regulated the IFN receptor, up-regulated suppressor of cytokine signaling 1 (SOCS1), and were refractory to IFNβ-induced signal transducers and activators of transcription (STAT) phosphorylation. When exposed to a viral infection, these CD8 T cells behaved more like 2-signal than 3-signal T cells, showing defects in short lived effector cell differentiation, reduced effector function, delayed cell division, and reduced levels of survival proteins. This suggests that IFN-pretreated CD8 T cells are unable to receive the positive effects that type 1 IFN provides as a signal 3 cytokine when delivered later in the signaling process. This desensitization mechanism may partially explain why vaccines function poorly in virus-infected individuals.

IL-10 encoded by viruses: a remarkable example of independent acquisition of a cellular gene by viruses and its subsequent evolution in the viral genome

Many viruses have evolved strategies to deregulate the host immune system. These strategies include mechanisms to subvert or recruit the host cytokine network. IL-10 is a pleiotropic cytokine that has both immunostimulatory and immunosuppressive properties. However, its key features relate mainly to its capacity to exert potent immunosuppressive effects. Several viruses have been shown to upregulate the expression of cellular IL-10 (cIL-10) with, in some cases, enhancement of infection by suppression of immune functions. Other viruses encode functional orthologues of cIL-10, called viral IL-10s (vIL-10s). The present review is devoted to these virokines. To date, vIL-10 orthologues have been reported for 12 members of the family Herpesviridae, two members of the family Alloherpesviridae and seven members of the family Poxviridae. Study of vIL-10s demonstrated several interesting aspects on the origin and the evolution of these viral genes, e.g. the existence of multiple (potentially up to nine) independent gene acquisition events at different times during evolution, viral gene acquisition resulting from recombination with cellular genomic DNA or cDNA derived from cellular mRNA and the evolution of cellular sequence in the viral genome to restrict the biological activities of the viral orthologues to those beneficial for the virus life cycle. Here, various aspects of the vIL-10s described to date are reviewed, including their genetic organization, protein structure, origin, evolution, biological properties and potential in applied research.

Porcine reproductive and respiratory syndrome virus infection activates IL-10 production through NF-κB and p38 MAPK pathways in porcine alveolar macrophages

Porcine reproductive and respiratory syndrome virus (PRRSV) is an emerging animal virus that has caused high economic losses for the swine industry worldwide. Previous in vitro and in vivo studies demonstrated that PRRSV infection induces significant production of interleukin 10 (IL-10), a pleiotropic cytokine with immuno-modulatory functions involved in host defense. However, the underlying regulatory mechanisms during PRRSV remain largely unknown. In the present study, we analyzed the expression kinetics of IL-10 in PRRSV-infected primary porcine alveolar macrophages (PAMs) and showed that PRRSV infection induced IL-10 mRNA and protein expression in a time- and dose-dependent manner. Inhibition of various molecules of the Toll-like receptor (TLR) or RIG-I-like receptor (RLR) signaling pathways demonstrated that the TLR adaptor myeloid differentiation primary response gene 88 (MyD88) has an important role in IL-10 induction during PRRSV infection. Furthermore, treatment with specific inhibitors or siRNA knockdown assays demonstrated that NF-κB and p38 MAPK (mitogen-activated protein kinase) are required for PRRSV-induced IL-10. Taken together, PRRSV infection significantly induced IL-10 expression and this induction depends on NF-κB activation and p38 MAPK in PAMs.

Interaction between innate immunity and porcine reproductive and respiratory syndrome virus

Innate immunity provides frontline antiviral protection and bridges adaptive immunity against virus infections. However, viruses can evade innate immune surveillance potentially causing chronic infections that may lead to pandemic diseases. Porcine reproductive and respiratory syndrome virus (PRRSV) is an example of an animal virus that has developed diverse mechanisms to evade porcine antiviral immune responses. Two decades after its discovery, PRRSV is still one of the most globally devastating viruses threatening the swine industry. In this review, we discuss the molecular and cellular composition of the mammalian innate antiviral immune system with emphasis on the porcine system. In particular, we focus on the interaction between PRRSV and porcine innate immunity at cellular and molecular levels. Strategies for targeting innate immune components and other host metabolic factors to induce ideal anti-PRRSV protection are also discussed.

Dendritic cells in the pathogenesis and treatment of human diseases: a Janus Bifrons?

Dendritic cells (DCs) represent the bridging cell compartment between a variety of nonself antigens (i.e., microbial, cancer and vaccine antigens) and adaptive immunity, orchestrating the quality and potency of downstream immune responses. Because of the central role of DCs in the generation and regulation of immunity, the modulation of DC function in order to shape immune responses is gaining momentum. In this respect, recent advances in understanding DC biology, as well as the required molecular signals for induction of T-cell immunity, have spurred many experimental strategies to use DCs for therapeutic immunological approaches for infections and cancer. However, when DCs lose control over such 'protective' responses - by alterations in their number, phenotype and/or function - undesired effects leading to allergy and autoimmune clinical manifestations may occur. Novel therapeutic approaches have been designed and currently evaluated in order to address DCs and silence these immunopathological processes. In this article we present recent concepts of DC biology and some medical implications in view of therapeutic opportunities.

Inoculation of swine with foot-and-mouth disease SAP-mutant virus induces early protection against disease

Foot-and-mouth disease virus (FMDV) leader proteinase (L(pro)) cleaves itself from the viral polyprotein and cleaves the translation initiation factor eIF4G. As a result, host cell translation is inhibited, affecting the host innate immune response. We have demonstrated that L(pro) is also associated with degradation of nuclear factor κB (NF-κB), a process that requires L(pro) nuclear localization. Additionally, we reported that disruption of a conserved protein domain within the L(pro) coding sequence, SAP mutation, prevented L(pro) nuclear retention and degradation of NF-κB, resulting in in vitro attenuation. Here we report that inoculation of swine with this SAP-mutant virus does not cause clinical signs of disease, viremia, or virus shedding even when inoculated at doses 100-fold higher than those required to cause disease with wild-type (WT) virus. Remarkably, SAP-mutant virus-inoculated animals developed a strong neutralizing antibody response and were completely protected against challenge with WT FMDV as early as 2 days postinoculation and for at least 21 days postinoculation. Early protection correlated with a distinct pattern in the serum levels of proinflammatory cytokines in comparison to the levels detected in animals inoculated with WT FMDV that developed disease. In addition, animals inoculated with the FMDV SAP mutant displayed a memory T cell response that resembled infection with WT virus. Our results suggest that L(pro) plays a pivotal role in modulating several pathways of the immune response. Furthermore, manipulation of the L(pro) coding region may serve as a viable strategy to derive live attenuated strains with potential for development as effective vaccines against foot-and-mouth disease.

Cattle remain immunocompetent during the acute phase of foot-and-mouth disease virus infection

Infection of cattle with foot-and-mouth disease virus (FMDV) results in the development of long-term protective antibody responses. In contrast, inactivated antigen vaccines fail to induce long-term protective immunity. Differences between susceptible species have also been observed during infection with FMDV, with cattle often developing persistent infections whilst pigs develop more severe symptoms and excrete higher levels of virus. This study examined the early immune response to FMDV in naïve cattle after in-contact challenge. Cattle exposed to FMDV were found to be viraemic and produced neutralising antibody, consistent with previous reports. In contrast to previous studies in pigs these cattle did not develop leucopenia, and the proliferative responses of peripheral blood mononuclear cells to either mitogen or third party antigen were not suppressed. Low levels of type 1 interferon and IL-10 were detected in the circulation. Taken together, these results suggest that there was no generalised immunosuppression during the acute phase of FMDV infection in cattle.

Role of macrophages in early protective immune responses induced by two vaccines against foot and mouth disease

Foot and Mouth Disease (FMD) is an acute disease of cloven-hoofed species. We studied the protection and early immune response induced in the murine model by vaccines formulated with inactivated virus and two different adjuvants. The presence of IMS12802PR or ISA206VG adjuvants yielded protection against viral challenge at early times post vaccination and induced FMDV-specific, but non neutralizing, antibody titers. In vivo macrophage depletion in vaccinated mice severely decreased the protection levels after virus challenge, indicating a central role of this cell population in the response elicited by the vaccines. Accordingly, opsonophagocytosis of FITC-labelled virus was augmented in 802-FMDVi and 206-FMDVi vaccinated mice. These results demonstrate the ability of the studied adjuvants to enhance the protective responses of these inactivated vaccines without the increase in seroneutralizing antibodies and the main role of opsonization and phagocytosis in the early protective immune responses against FMD infection in the murine model.

Evidence of activation and suppression during the early immune response to foot-and-mouth disease virus

Foot-and-mouth disease virus causes a serious disease of livestock species, threatening free global trade and food security. The disease spreads rapidly between animals, and to ensure a window of opportunity for such spread, the virus has evolved multiple mechanisms to subvert the early immune response. The cycle of infection in the individual animal is very short, infection is initiated, disseminated throughout the body and infectious virus produced in <7 days. Foot-and-mouth disease virus has been shown to disrupt the innate response in vitro and also interacts directly with antigen-presenting cells and their precursors. This interaction results in suboptimal immune function, favouring viral replication and the delayed onset of specific adaptive T-cell responses. Detailed understanding of this cycle is crucial to effectively control disease in livestock populations. Knowledge-based vaccine design would specifically target and induce the immunological mechanisms of early protection and of robust memory induction. Specifically, information on the contribution of cytokines and interferon, innate immune cells as well as humoral and cellular immunity can be employed to design vaccines promoting such responses. Furthermore, understanding of viral escape mechanisms of immunity can be used to create attenuated viruses that could be used to develop novel vaccines and to study viral pathogenesis.

Virus-induced transient immune suppression and the inhibition of T cell proliferation by type I interferon

Vaccine-induced memory is necessary for protective immunity to pathogens, but many viruses induce a state of transient immune suppression that might contribute to the inability of a vaccine to elicit immunity. We evaluated here the fate of bystander T cells activated by third party cognate antigens during acute viral infections in vivo, using distinct models to track and specifically activate HY and P14 transgenic bystander CD8 T cells in vivo during acute arenavirus infections of mice. Viral infections acted as stimulatory adjuvants when bystander T cells were exposed to an inflammatory milieu and cognate antigens at the beginning of infections, but bystander CD8 T cell proliferation in response to cognate antigen was inhibited 3 to 9 days after virus infection. Reduced proliferation was not dependent on Fas-FasL- or tumor necrosis factor (TNF)-induced activation-induced cell death or on deficiencies of antigen presentation. Instead, reduced proliferation was associated with a delayed onset of division that was an intrinsic defect of T cells. Inhibition of proliferation could be simulated by exposure of T cells to the Toll-like receptor agonist and type I interferon (IFN) inducer poly(I · C). T cells lacking IFN-α/β receptors resisted both the suppressive effects of preexposure to poly(I · C) and the stimulatory effects of type I IFN, indicating that the timing of exposure to IFN can have negative or positive effects on T cell proliferation. Inhibition of T cell receptor-stimulated bystander CD8 T cell proliferation during acute viral infections may reflect the reduced ability of vaccines to elicit protective immunity when administered during an acute illness.

DNA immunization of pigs with foot-and-mouth disease virus minigenes: from partial protection to disease exacerbation

Despite several attempts to design new vaccines, there are as of yet no available alternatives to the conventional FMDV vaccines. Here, we present the divergent results obtained in pigs after immunization with two experimental DNA vaccines encoding one B and two T cell FMDV epitopes, either expressed alone (pCMV-BTT) or fused to a strong signal peptide (pCMV-spBTT). While all pigs vaccinated with pCMV-spBTT showed both a delay in the disease onset and reduced severity of signs and lesions after FMDV challenge, pigs immunized with pCMV-BTT showed an exacerbation of the disease and most of the pigs remained viremic at 10 days post-infection, the end-point of the experiment, thus opening concerns about FMDV-suboptimal immunization. Interestingly, only one of the four pigs vaccinated with pCMV-spBTT showed neutralizing antibodies before challenge, demonstrating that partial protection against FMDV could be afforded in the absence of preexisting neutralizing antibodies.

A replication analysis of foot-and-mouth disease virus in swine lymphoid tissue might indicate a putative carrier stage in pigs

Foot-and-mouth disease virus (FMVD), one of the most contagious viruses of cloven-hoofed animals, may cause a prolonged, asymptomatic but persistent infection in ruminants, named the "carrier state". However, it remains an open question whether this carrier state occurs in pigs. Here we present quantitative analyses of the duration of FMDV RNA and infectivity in lymphoid and epithelial tissues in experimentally infected pigs with FMDV C-S8c1. The data indicated that although FMDV RNA remained in blood until day 14 post-infection (pi), viremia was cleared by day 7 pi. However, all tissues tested were positive for FMDV until day 14-17 pi. Interestingly, the specific infectivity of FMDV in these tissues was in some cases even higher than the FMDV C-S8c1. We therefore propose that a "pseudopersistent state" may occur in pigs in which virus replicates in lymphoid tissues for a prolonged period of time, thereby representing a potential source of virus.

Foot-and-mouth disease virus exhibits an altered tropism in the presence of specific immunoglobulins, enabling productive infection and killing of dendritic cells

Foot-and-mouth disease virus (FMDV) causes an acute vesicular disease of farm animals. The development of successful control strategies is limited by an incomplete understanding of the immune response to FMDV. Dendritic cells (DC) mediate the induction of immunity to pathogens, but their role in FMDV infection of cattle is uncharacterized. Bovine monocyte-derived DC (moDC) were exposed to integrin-binding and cell culture-adapted strains of FMDV in vitro. MoDC were not largely susceptible to infection by integrin-binding FMDV but were susceptible to culture-adapted virus. Binding specific antibodies to integrin-binding FMDV at neutralizing or subneutralizing IgG concentrations significantly enhanced infection via CD32 (FcγR). Monocytes also expressed CD32 but were nonsusceptible to FMDV immune complex (IC) infection, indicating a requirement for additional factors involved in cellular susceptibility. Infection of moDC by the FMDV IC was productive and associated with high levels of cell death. Infected moDC were unable to efficiently stimulate FMDV-specific CD4(+) memory T cells, but exposing moDC to IC containing inactivated FMDV resulted in significantly increased T cell stimulation. Thus, neutralized FMDV concurrently loses its ability to infect susceptible cells while gaining the capacity to infect immune cells. This represents a change in the tropism of FMDV that could occur after the onset of the antibody response. We propose that IC could dynamically influence the anti-FMDV immune response and that this may explain why the early immune response to FMDV has evolved toward T cell independence in vivo. Moreover, we propose that DC targeting could prove useful in the development of effective vaccines against FMDV.

Assessment of the efficacy of commercially available and candidate vaccines against a pandemic H1N1 2009 virus

Background. The emergence and global spread of the pandemic H1N1 2009 influenza virus have raised questions regarding the protective effect of available seasonal vaccines and the efficacy of a newly produced matched vaccine.

Methods. Ferrets were immunized with the 2008–2009 formulations of commercially available live attenuated (FluMist; MedImmune) or split-inactivated (Fluviral; GlaxoSmithKline) vaccines, a commercial swine vaccine (FluSure; Pfizer), or a laboratory-produced matched inactivated whole-virus vaccine (A/Mexico/InDRE4487/2009). Adaptive immune responses were monitored, and the animals were challenged with A/Mexico/InDRE4487/2009 after 5 weeks.

Results. Only animals that received the swine or matched vaccines developed detectable hemagglutination- inhibiting antibodies against the challenge virus, whereas a T cell response was exclusively detected in animals vaccinated with FluMist. After challenge, all animals had high levels of virus replication in the upper respiratory tract. However, preexisting anti—pandemic H1N1 2009 antibodies resulted in reduced clinical signs and improved survival. Surprisingly, FluMist was associated with a slight increase in mortality and greater lung damage, which correlated with early up-regulation of interleukin-10.

Conclusions. The present study demonstrates that a single dose of matched inactivated vaccine confers partial protection against a pandemic H1N1 2009 virus, and it suggests that a higher dose or prime-boost regimen may be required. The consequences of mismatched immunity to influenza merit further investigation.

Interferon-induced protection against foot-and-mouth disease virus infection correlates with enhanced tissue-specific innate immune cell infiltration and interferon-stimulated gene expression

Previously, we demonstrated that type I interferon (IFN-alpha/beta) or a combination of IFN-alpha/beta and type II IFN (IFN-gamma) delivered by a replication-defective human adenovirus 5 (Ad5) vector protected swine when challenged 1 day later with foot-and-mouth disease virus (FMDV). To gain a more comprehensive understanding of the mechanism of protection induced by IFNs, we inoculated groups of six swine with Ad5-vectors containing these genes, challenged 1 day later and euthanized 2 animals from each group prior to (1 day postinoculation [dpi]) and at 1 (2 dpi) and 6 days postchallenge (7 dpi). Blood, skin, and lymphoid tissues were examined for IFN-stimulated gene (ISG) induction and infiltration by innate immune cells. All IFN-inoculated animals had delayed and decreased clinical signs and viremia compared to the controls, and one animal in the IFN-alpha treated group did not develop disease. At 1 and 2 dpi the groups inoculated with the IFNs had increased numbers of dendritic cells and natural killer cells in the skin and lymph nodes, respectively, as well as increased levels of several ISGs compared to the controls. In particular, all tissues examined from IFN-treated groups had significant upregulation of the chemokine 10-kDa IFN-gamma-inducible protein 10, and preferential upregulation of 2',5'-oligoadenylate synthetase, Mx1, and indoleamine 2,3-dioxygenase. There was also upregulation of monocyte chemotactic protein 1 and macrophage inflammatory protein 3alpha in the skin. These data suggest that there is a complex interplay between IFN-induced immunomodulatory and antiviral activities in protection of swine against FMDV.

Immune response and viral persistence in Indian buffaloes (Bubalus bubalis) infected with foot-and-mouth disease virus serotype Asia 1

Despite their potential role in the spread of foot-and-mouth disease (FMD), the immune response and viral persistence in FMD virus (FMDV)-infected Indian buffaloes (Bubalus bubalis) have been unexplored. We found similar kinetics of neutralizing antibody responses in the sera and secretory fluids of buffaloes following experimental FMDV Asia 1 infection, but the lymphocyte-proliferative response in infected buffaloes was of low magnitude. Despite inducing a significant systemic and secretory immune response, viral persistence seems to be a common outcome in buffaloes following FMDV Asia 1 infection, which is associated with a weak cellular immune response.