Bovine CD2-/NKp46+ cells are fully functional natural killer cells with a high activation status

Bovine NK subsets in the afferent lymph and lymph nodes have distinct expression of naïve and activation-associated cell surface expressed molecules, and are differentially stimulated by BCG vaccination

Bovine natural killer (bNK) cells are heterogeneous cell populations defined by constitutive expression of the natural cytotoxicity receptor, NKp46 (CD335). Two major subsets of bNK cells, classified by differential expression of CD2, display divergent functions in innate immunity, and are hypothesised to contribute to adaptive immunity following vaccination. Here we characterised phenotypic variation of bNK cells within afferent lymph and lymph node (LN) tissues and between CD2+ and CD2- bNK subsets, and report phenotypic changes induced by BCG vaccination. CD2- bNK cells, which dominate in the afferent lymph and LN, displayed lower expression of the activation marker CD25 within the LN, with CD25+ cells being less than half as frequent as in afferent lymph. Furthermore, we found bNK cells had a lower expression of CD45RB, associated in cattle with naïve cell status, within LN compared to afferent lymph. Following BCG vaccination, bNK cells in afferent lymph draining the vaccination site showed increased CD2-CD25+ frequencies and increased expression of CD25 on CD2+ bNK cells, although the frequency of these cells remained unchanged. In summary, we provide an overview of the phenotype of bNK cells within bovine lymphatic tissues, and provide an indication of how subsets may diverge following BCG vaccination.

Evaluation of Antigenic Comparisons Among BVDV Isolates as it Relates to Humoral and Cell Mediated Responses

Antigenic differences between bovine viral diarrhea virus (BVDV) vaccine strains and field isolates can lead to reduced vaccine efficacy. Historically, antigenic differences among BVDV strains were evaluated using techniques based on polyclonal and monoclonal antibody activity. The most common method for antigenic comparison among BVDV isolates is determination of virus neutralization titer (VNT). BVDV antigenic comparisons using VNT only account for the humoral component of the adaptive immune response, and not cell mediated immunity (CMI) giving an incomplete picture of protective responses. Currently, little data is available regarding potential antigenic differences between BVDV vaccine strains and field isolates as measured by CMI responses. The goal of the current paper is to evaluate two groups of cattle that differed in the frequency they were vaccinated, to determine if similar trends in CMI responses exist within each respective group when stimulated with antigenically different BVDV strains. Data from the current study demonstrated variability in the CMI response is associated with the viral strain used for stimulation. Variability in IFN-γ mRNA expression was most pronounced in the CD4⁺ population, this was observed between the viruses within each respective BVDV subgenotype in the Group 1 calves. The increase in frequency of CD25⁺ cells and IFN-γ mRNA expression in the CD8⁺ and CD335⁺ populations were not as variable between BVDV strains used for stimulation in the Group 1 calves. Additionally, an inverse relationship between VNT and IFN-γ mRNA expression was observed, as the lowest VNT and highest IFN-γ mRNA expression was observed and vice versa, the highest VNT and lowest IFN-γ mRNA expression was observed. A similar trend regardless of vaccination status was observed between the two groups of calves, as the BVDV-1b strain had lower IFN-γ mRNA expression. Collectively, data from the current study and previous data support, conferring protection against BVDV as a method for control of BVDV in cattle populations is still a complex issue and requires a multifactorial approach to understand factors associated with vaccine efficacy or conversely vaccine failure. Although, there does appear to be an antigenic component associated with CMI responses as well as with humoral responses as determined by VNT.

Methods of feeding colostrum and their effect on the passive immunity

Passive transport of colostral immunoglobulins is essential for calves to maintain optimal health. There are many factors that influence the absorption of immunoglobulins such as colostrum density, timing of ingestion, volume of colostrum but also the method of feeding. This study compares two manners of feeding calves – the esophageal tube feeder (n = 97) and the nipple bottle (n = 97), and their effect on the number of all absorbed immunoglobulins (IgG, IgM, IgA, IgD, and IgE). It was statistically proven that absorption of immunoglobulins is better with the nipple bottle (P < 0.0001). The feeding of calves through a nipple bottle is more beneficial because the content of total protein is the higher than by the feeding through an esophageal tube feeder.

Characterization of bovine interleukin-2 stably expressed in HEK-293 cells

Interleukin 2 (IL-2) is a pleotropic cytokine and well-known as a T cell growth factor in immunology. It is now known to exert both immunostimulatory and immunosuppressive effects, optimizing immunological microenvironments for effector and regulatory T cell responses. The immunomodulatory role of IL-2 is critical for deciding whether or not T cell responses against specific antigens result in protection. We have established a mammalian cell line (HEK-293) stably expressing bovine IL-2 (boIL-2) (designated as HEK-293/boIL-2), using the piggyBac transposon system. The concentration of recombinant bovine IL-2 (rboIL-2) in the culture supernatant of HEK-293/boIL-2 reached 100 ng/ml on day 7 and showed similar proliferative activity to recombinant human IL-2 (rhuIL-2) for bovine peripheral mononuclear blood cells. Although rhuIL-2 has been often used to activate bovine T cells, our results indicate that characteristics of the T cell activation through rboIL-2 and huIL-2 appear slightly but significantly different. Interestingly, the rboIL-2/anti-boIL-2 monoclonal antibody (C5) (rboIL-2/C5) complex strongly induced proliferation of bovine NKp46⁺cells, natural killer (NK) cells, in vitro. This indicates that the rboIL-2/C5 complex could function as an IL-2 agonist specifically to increase the NK cell population, which in turn could enhance the activity of NK cells leading to protective immunity.

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.

T cells in mesenteric and subcutaneous adipose tissue of Holstein-Friesian cows

The importance of immune cells present in the adipose tissue to metabolic homeostasis has been increasingly recognized. Nevertheless, in bovines few studies have so far addressed the immune cell populations resident in this tissue. Here we developed an eight-colour flow cytometry panel to address T cell populations present in bovine adipose tissue. Our results showed that γδ T cells, CD4⁺ and CD8⁺ CD3⁺ non-γδ T cells, as well as NK cells, are present in the mesenteric and subcutaneous adipose tissue of Holstein-Friesian cows. The frequency of both γδ T cells and CD8⁺ non-γδ T cells was found higher in mesenteric than in subcutaneous adipose tissue. The majority of T cells in adipose tissue presented a CD45RO⁺CD62L^- phenotype, characteristic of effector memory cells, and the frequency of these cellular populations was higher than in the blood. The ratio of CD4⁺ T cells over CD8⁺ T cells was similar between subcutaneous and mesenteric adipose tissue but different from the one found in blood. Overall, our results highlight particular phenotypic characteristics of bovine adipose tissue T cell populations.

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.

Bovine cryptosporidiosis: impact, host-parasite interaction and control strategies

Gastrointestinal disease caused by the apicomplexan parasite Cryptosporidium parvum is one of the most important diseases of young ruminant livestock, particularly neonatal calves. Infected animals may suffer from profuse watery diarrhoea, dehydration and in severe cases death can occur. At present, effective therapeutic and preventative measures are not available and a better understanding of the host-pathogen interactions is required. Cryptosporidium parvum is also an important zoonotic pathogen causing severe disease in people, with young children being particularly vulnerable. Our knowledge of the immune responses induced by Cryptosporidium parasites in clinically relevant hosts is very limited. This review discusses the impact of bovine cryptosporidiosis and describes how a thorough understanding of the host-pathogen interactions may help to identify novel prevention and control strategies.

PDI regulates seizure activity via NMDA receptor redox in rats

Redox modulation of cysteine residues is one of the post-translational modifications of N-methyl-D-aspartate receptor (NMDAR). Protein disulfide isomerases (PDI), an endoplasmic reticulum (ER) chaperone, plays a crucial role in catalyzing disulfide bond formation, reduction, and isomerization. In the present study, we found that PDI bound to NMDAR in the normal hippocampus, and that this binding was increased in chronic epileptic rats. In vitro thiol reductase assay revealed that PDI increased the amount of thiols on full-length recombinant NR1 protein. PDI siRNA, 5-5'-dithio-bis(2-nitrobenzoic acid) (DTNB), bacitracin and PDI antibody reduced seizure susceptibility in response to pilocarpine. In addition, PDI knockdown effectively ameliorated spontaneous seizure activity in chronic epileptic rats. Anticonvulsive effects of PDI siRNA were correlated to the reduction of the amount of free- and nitrosothiols on NMDAR, accompanied by the inhibition of PDI activity. However, PDI knockdown did not lead to alteration in basal neurotransmission or ER stress under physiological condition. These findings provide mechanistic insight into sulfhydration of disulfide bonds on NMDAR by PDI, and suggest that PDI may represent a target of potential therapeutics for epilepsy, which avoids a possible side effect on physiological receptor functionality.

Frequency and phenotype of natural killer cells and natural killer cell subsets in bovine lymphoid compartments and blood

Natural killer (NK) cells are widely distributed in lymphoid and non‐lymphoid tissues, but little is known about the recirculation of NK cells between blood and tissues. This is relevant to understanding recirculation in the steady‐state and also for determining the roles for NK cells in vaccine‐induced immunity and responses to infection. Therefore, the percentage of NK cells and their phenotype across peripheral blood, afferent lymph and lymph nodes in steady‐state conditions was investigated in cattle using the pseudo‐afferent lymphatic cannulation model. CD2⁺ CD25^lo NK cells were the predominant subset of NK cells within the blood. In contrast, CD2⁻ CD25^hi NK cells were the main subset present within the skin‐draining afferent lymphatic vessels and lymph nodes, indicating that CD2⁻ NK cells are the principal NK cell subset trafficking to lymph nodes via the afferent lymphatic vessel. Furthermore, a low percentage of NK cells were present in efferent lymph, which were predominantly of the CD2⁻ subset, indicating that NK cells can egress from lymph nodes and return to circulation in steady‐state conditions. These compartmentalization data indicate that NK cells represent a population of recirculating lymphocytes in steady‐state conditions and therefore may be important during immune responses to vaccination or infection.

Interactions between natural killer cells and dendritic cells favour T helper1-type responses to BCG in calves

Vaccination of neonatal calves with BCG induces a significant level of protection from infection with Mycobacterium bovis, the causative agent of bovine tuberculosis. Since neonatal vaccination of humans with BCG induces activation of NK cells, and young calves have high circulating numbers of these cells, we hypothesised that NK cells are important in the protective response to BCG. Furthermore, since NK cells play a role in shaping adaptive immune responses through interactions with DCs, we investigated the interactions between NK cells and DCs in the context of BCG. DCs infected with BCG expressed significantly higher levels of MHC class II and the co-stimulatory molecules CD40 and CD80, alongside augmented production of the Th1 polarising cytokine IL-12, when compared with uninfected DCs. Following in vitro co-culture with BCG-infected DCs, NK cells increased their expression of the activatory molecule CD25, with preferential activation of the CD2- NK cell subset. NK cell effector function, as measured by production of IFN-γ, was also significantly enhanced following co-culture with BCG-infected DCs. This study provides novel evidence to demonstrate that NK cells phenotypically and functionally mature after interactions with DCs in the context of BCG. Furthermore, through the production of IFN-γ and IL-12 by NK cells and DCs respectively, this interaction may drive protective Th1-type immune responses to Mycobacteria.

Expression of bovine non-classical major histocompatibility complex class I proteins in mouse P815 and human K562 cells

Major histocompatibility complex class I (MHC-I) proteins can be expressed as cell surface or secreted proteins. To investigate whether bovine non-classical MHC-I proteins are expressed as cell surface or secreted proteins, and to assess the reactivity pattern of monoclonal antibodies with non-classical MHC-I isoforms, we expressed the MHC proteins in murine P815 and human K562 (MHC-I deficient) cells. Following antibiotic selection, stably transfected cell lines were stained with H1A or W6/32 antibodies to detect expression of the MHC-I proteins by flow cytometry. Two non-classical proteins (BoLA-NC1*00501 and BoLA-NC3*00101) were expressed on the cell surface in both cell lines. Surprisingly, the BoLA-NC4*00201 protein was expressed on the cell membrane of human K562 but not mouse P815 cells. Two non-classical proteins (BoLA-NC1*00401, which lacks a transmembrane domain, and BoLA-NC2*00102) did not exhibit cell surface expression. Nevertheless, Western blot analyses demonstrated expression of the MHC-I heavy chain in all transfected cell lines. Ammonium-sulfate precipitation of proteins from culture supernatants showed that BoLA-NC1*00401 was secreted and that all surface expressed proteins where shed from the cell membrane by the transfected cells. Interestingly, the surface expressed MHC-I proteins were present in culture supernatants at a much higher concentration than BoLA-NC1*00401. This comprehensive study shows that bovine non-classical MHC-I proteins BoLA-NC1*00501, BoLA-NC3*00101, and BoLA-NC4*00201 are expressed as surface isoforms with the latter reaching the cell membrane only in K562 cells. Furthermore, it demonstrated that BoLA-NC1*00401 is a secreted isoform and that significant quantities of membrane associated MHC-I proteins can be shed from the cell membrane.

Immune response to bovine viral diarrhea virus--looking at newly defined targets

Bovine viral diarrhea virus (BVDV) has long been associated with a wide variety of clinical syndromes and immune dysregulation, many which result in secondary bacterial infections. Current understanding of immune cell interactions that result in activation and tolerance are explored in light of BVDV infection including: depletion of lymphocytes, effects on neutrophils, natural killer cells, and the role of receptors and cytokines. In addition, we review some new information on the effect of BVDV on immune development in the fetal liver, the role of resident macrophages, and greater implications for persistent infection.

Endoplasmic reticulum (ER) stress protein responses in relation to spatio-temporal dynamics of astroglial responses to status epilepticus in rats

In the present study, we investigated whether endoplasmic reticulum (ER) stress is associated with neuronal- and astroglial-death in the hippocampus using LiCl-pilocarpine-induced status epilepticus (SE) rat model. Glucose-related protein (GRP) 78 and protein disulfide isomerase (PDI) expressions were transiently increased in CA1 neurons and dentate granule cells, and subsequently decreased in these cells following SE. GRP94 and calnexin (CNX) expression was gradually reduced in CA1 neurons, not in dentate granule cells. Phospho-protein kinase RNA (PKR)-like ER kinase (pPERK), phospho-eukaryotic initiation factor 2α (peIF2A) and CCAAT/enhancer-binding protein homologous protein (CHOP) immunoreactivities were observed in 17%, 12% and 7% of degenerating CA1 neurons, respectively. GRP 78 and PDI expressions were also up-regulated in reactive astrocytes within the CA1-3 regions. In the molecular layer of the dentate gyrus, PDI-positive astrocytes showed TUNEL signal, nuclear apoptosis inducing factor translocation and pPERK/peIF2A/CHOP immunoreactivities. Four weeks after SE, clasmatodendritic astrocytes showed pPERK peIF2A and CNX immunoreactivities without CHOP expression. These findings indicate that SE-induced ER stress may be associated with astroglial apoptosis and autophagic astroglial death in the regional-specific pattern.

Cattle NK Cell Heterogeneity and the Influence of MHC Class I

Primate and rodent NK cells form highly heterogeneous lymphocyte populations owing to the differential expression of germline-encoded receptors. Many of these receptors are polymorphic and recognize equally polymorphic determinants of MHC class I. This diversity can lead to individuals carrying NK cells with different specificities. Cattle have an unusually diverse repertoire of NK cell receptor genes predicted to encode receptors that recognize MHC class I. To begin to examine whether this genetic diversity leads to a diverse NK cell population, we isolated peripheral NK cells from cattle with different MHC homozygous genotypes. Cytokine stimulation differentially influenced the transcription of five receptors at the cell population level. Using dilution cultures, we found that a further seven receptors were differentially transcribed, including five predicted to recognize MHC class I. Moreover, there was a statistically significant reduction in killer cell lectin-like receptor mRNA expression between cultures with different CD2 phenotypes and from animals with different MHC class I haplotypes. This finding confirms that cattle NK cells are a heterogeneous population and reveals that the receptors creating this diversity are influenced by the MHC. The importance of this heterogeneity will become clear as we learn more about the role of NK cells in cattle disease resistance and vaccination.

Endothelial NOS activation induces the blood-brain barrier disruption via ER stress following status epilepticus

The blood-brain barrier (BBB) maintains the unique brain microenvironment, which is separated from the systemic circulating system. Since the endoplasmic reticulum (ER) is an important cell organelle that is responsible for protein synthesis, the correct folding and sorting of proteins contributing to cell survivals, ER stress is a potential cause of cell damage in various diseases. Therefore, it would be worthy to explore the the relationship between the ER stress and BBB disruption during vasogenic edema formation induced by epileptogenic insults. In the present study, we investigated the roles of ER stress in vasogenic edema and its related events in rat epilepsy models provoked by pilocarpine-induced status epilepticus (SE). SE-induced eNOS activation induces BBB breakdown via up-regulation of GRP78 expression and dysfunction of SMI-71 (an endothelial BBB marker) in the piriform cortex (PC). In addition, caveolin-1 peptide (an eNOS inhibitor) effectively attenuated GRP78 expression and down-regulation of SMI-71. Taken together, our findings suggest that eNOS-mediated ER stress may participate in SE-induced vasogenic edema formation. Therefore, the modulation of ER stress may be a considerable strategy for therapy in impairments of endothelial cell function.

Infection with foot-and-mouth disease virus (FMDV) induces a natural killer (NK) cell response in cattle that is lacking following vaccination

Natural killer (NK) cells play a role in innate antiviral immunity by directly lysing virus-infected cells and producing antiviral cytokines such as interferon gamma (IFN-γ). We developed a system for characterizing the bovine NK response to foot-and-mouth disease virus (FMDV), which causes a disease of cloven-hoofed animals and remains a threat to livestock industries throughout the world. IL-2 stimulation of PBMC resulted in poor killing of human K562 cells, which are often used as NK target cells, while lysis of the bovine BL3.1 cell line was readily detected. Depletion of NKp46-expressing cells revealed that 80% of the killing induced by IL-2 could be attributed to NKp46(+) cells. In order to characterize the response of NK cells against FMDV in vivo, we infected groups of cattle with three different strains of the virus (A24 Cruzeiro, O1 Manisa, O Hong Kong) and evaluated the cytolytic ability of NK cells through the course of infection. We consistently observed a transient increase in cytolysis, although there was variation in magnitude and kinetics. This increase in cytolysis remained when CD3(+) cells were removed from the preparation of lymphocytes, indicating that cytolysis was independent of MHC-T cell receptor interaction or γδ T cell activation. In contrast, animals monitored following vaccination against FMDV did not exhibit any increase in NK killing. These data suggest that NK cells play a role in the host immune response of cattle against FMDV, and contrast with the suppression of NK activity previously observed in swine infected with FMDV.

Stimulation and analysis of the immune response in calves from vaccinated pregnant cows

The effect of vaccinating pregnant cows with an inactivated vaccine against Mannheimia haemolytica, BRSV and PI3V infections on selected immune responses in their offspring was examined. Blood samples were collected weekly for 12 weeks from six newborn calves from each of vaccinated (experimental) and unvaccinated (control) dams. Specific antibodies to M. haemolytica, BRSV and PI3V and mean values of IgA, IgG concentrations were significantly higher in the experimental calves compared with the controls. However, specific antibody titres to adenovirus type 3, BHV1 and BVDV in the experimental calves had constant levels while the control group levels changed. The IgM, Hp and SAA concentrations generally increased until week 8 in the experimental group, but the control group titres became higher after week 9. This study demonstrates that specific immunisation of cows pre-partum significantly stimulated parameters associated with immunity and it also controlled the acute phase response intensity in their offspring. Therefore the vaccination of dams may provide additional antibody protection against infection to their offspring.

Induction of interferon-gamma and downstream pathways during establishment of fetal persistent infection with bovine viral diarrhea virus

Development of transplacental infection depends on the ability of the virus to cross the placenta and replicate within the fetus while counteracting maternal and fetal immune responses. Unfortunately, little is known about this complex process. Non-cytopathic (ncp) strains of bovine viral diarrhea virus (BVDV), a pestivirus in the Flaviviridae family, cause persistent infection in early gestational fetuses (<150 days; persistently infected, PI), but are cleared by immunocompetent animals and late gestational fetuses (>150 days; transiently infected, TI). Evasion of innate immune response and development of immunotolerance to ncp BVDV have been suggested as possible mechanisms for the establishment of the persistent infection. Previously we have observed a robust temporal induction of interferon (IFN) type I (innate immune response) and upregulation of IFN stimulated genes (ISGs) in BVDV TI fetuses. Modest chronic upregulation of ISGs in PI fetuses and calves reflects a stimulated innate immune response during persistent BVDV infection. We hypothesized that establishing persistent fetal BVDV infection is also accompanied by the induction of IFN-gamma (IFN-γ). The aims of the present study were to determine IFN-γ concentration in blood and amniotic fluid from control, TI and PI fetuses during BVDV infection and analyze induction of the IFN-γ downstream pathways in fetal lymphoid tissues. Two experiments with in vivo BVDV infections were completed. In Experiment 1, pregnant heifers were infected with ncp BVDV type 2 on day 75 or 175 of gestation or kept naïve to generate PI, TI and control fetuses, respectively. Fetuses were collected by Cesarean section on day 190. In Experiment 2, fetuses were collected on days 82, 89, 97, 192 and 245 following infection of pregnant heifers on day 75 of gestation. The results were consistent with the hypothesis that ncp BVDV infection induces IFN-γ secretion during acute infection in both TI and PI fetuses and that lymphoid tissues such as spleen, liver and thymus, serve both as possible sources of IFN-γ and target organs for its effects. Notably, induction of IFN-γ coincides with a decrease in BVDV RNA concentrations in PI fetal blood and tissues. This is the first report indicating the possible presence of an adaptive immune response in persistent BVDV infections, which may be contributing to the observed reduction of viremia in PI fetuses.

Natural Killer Cells in Afferent Lymph Express an Activated Phenotype and Readily Produce IFN-γ

Natural killer (NK) cells are motile cells that migrate between peripheral blood (PB), lymph nodes (LNs), and various organs. Domestic animals have frequently been used to study cellular migration, and offer unique opportunities for such studies. The aim of this study was to characterize the phenotype and cytokine producing capacity of NK cells in bovine skin-draining lymph. NKp46/NCR1⁺ CD3⁻ cells constituted 2–11% of mononuclear cells in afferent lymph (AL), a majority of cells were CD16⁺, CD8α⁺, and CD2^−/low, and elevated CD25 and CD44 expression indicated an activated phenotype. Interestingly, significantly fewer AL NK cells expressed the early activation marker CD69 compared to PB NK cells. A large proportion of lymph and blood NK cells produced interferon (IFN)-γ following stimulation with IL-2 and IL-12. Notably, in AL, but not blood, a similar amount of IFN-γ⁺ NK cells was observed when cells were stimulated with IL-12 alone. Overall, AL NK cells were more similar to LN-residing NK cells than those circulating in PB. We conclude that AL appears to be an important migration route for tissue-activated NK cells, and may represent an alternative route for NK cell traffic to LNs. These findings may have important implications in the development of adjuvant strategies that aim to target NK cells in a vaccine response.

Cell mediated innate responses of cattle and swine are diverse during foot-and-mouth disease virus (FMDV) infection: a unique landscape of innate immunity

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Harnessing the innate immunity can protect domestic animals from viruses.

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Innate immune cells have potential capacity to afford protection against infection.

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Understanding the innate and adaptive immunity will aid rational vaccine design.

Pathogens in general and pathogenic viruses in particular have evolved a myriad of mechanisms to escape the immune response of mammalian species. Viruses that cause acute disease tend to bear characteristics that make them very contagious, as survival does not derive from chronicity of infection, but spread of disease throughout the herd. Foot-and-mouth disease virus (FMDV) is one of the most contagious viruses known. Upon infection of susceptible species, cloven-hoofed animals, the virus proliferates rapidly and causes a vesicular disease within 2–4 days. Disease symptoms resolve by 10 days to 2 weeks and in most cases, virus can no longer be detected. Periods of fever and viremia are usually brief, 1–3 days. In vivo control of virus infection and clearance of the virus during and following acute infection is of particular interest. The interaction of this virus with cells mediating the early, innate immune response has been analyzed in a number of recent studies. In most reports, the virus has a distinct inhibitory effect on the response of cells early in infection. Here we review these new data and discuss the dynamics of the interaction of virus with different cell types mediating the immune response to infection.

Differential recruitment and activation of natural killer cell sub-populations by Mycobacterium bovis-infected dendritic cells

Through complex interplay with APCs, subsets of NK cells play an important role in shaping adaptive immune responses. Bovine tuberculosis, caused by Mycobacterium bovis, is increasing in incidence and detailed knowledge of host-pathogen interactions in the natural host is essential to facilitate disease control. We investigated the interactions of NK-cell sub-populations and M. bovis-infected DCs to determine early innate mechanisms in the response to infection. A sub-population of NK cells (NKp46(+) CD2(-) ) selectively expressing lymphoid homing and inflammatory chemokine receptors were induced to migrate towards M. bovis-infected DCs. This migration was associated with increased expression of chemokines CCL3, 4, 5, 20 and CXCL8 by M. bovis-infected DCs. Activation of NKp46(+) CD2(-) NK cells and secretion of IFN-γ was observed, a response reliant on localised IL-12 release and direct cellular interaction. In a reciprocal manner, NKp46(+) CD2(-) cells induced an increase in the intensity of cell surface MHC class II expression on DCs. In contrast, NKp46(+) CD2(+) NK cells were unable to secrete IFN-γ and did not reciprocally affect DCs. This study provides novel evidence to demonstrate distinct effector responses between bovine NK-cell subsets during mycobacterial infection.

BCG vaccination of neonatal calves: potential roles for innate immune cells in the induction of protective immunity

Bovine tuberculosis is a disease of increasing incidence in the UK causing major economic losses and with significant impact on bovine and, potentially human health: the causative agent Mycobacterium bovis is a zoonotic pathogen. Neonatal vaccination with the attenuated M. bovis Bacille Calmette Guerin (BCG) vaccine confers a significant degree of protection in cattle, and is a widely used control strategy for human TB. The adaptive immune system is relatively immature in neonates and increased numbers of innate effector cells present in young animals and human infants may compensate for this, enabling effective immune responses to vaccination. Natural killer cells and subsets of γδ TCR+ T lymphocytes secrete high levels of interferon gamma and can interact with antigen presenting cells to promote both innate and adaptive immune responses. These cell populations may be pivotal in determining immune bias following neonatal vaccination with BCG.

Rapid and transient activation of γδ T cells to IFN-γ production, NK cell-like killing, and antigen processing during acute virus infection

γδ T cells are the majority peripheral blood T cells in young cattle. The role of γδ T cells in innate responses against infection with foot-and-mouth disease virus was analyzed on consecutive 5 d following infection. Before infection, bovine WC1(+) γδ T cells expressed a nonactivated phenotype relative to CD62L, CD45RO, and CD25 expression and did not produce IFN-γ ex vivo. Additionally, CD335 expression was lacking and no spontaneous target cell lysis could be detected in vitro, although perforin was detectable at a very low level. MHC class II and CD13 expression were also lacking. Following infection with foot-and-mouth disease virus, expression of CD62L and CD45RO was greatly reduced on WC1(+) γδ T cells, and unexpectedly, CD45RO expression did not recover. A transient increase in expression of CD25 correlated with production of IFN-γ. Expression of CD335 and production of perforin were detected on a subset of γδ T cells, and this correlated with an increased spontaneous killing of xenogeneic target cells. Furthermore, increased MHC class II expression was detected on WC1(+) γδ T cells, and these cells processed protein Ags. These activities are rapidly induced, within 3 d, and wane by 5 d following infection. All of these functions, NK-like killing, Ag processing, and IFN-γ production, have been demonstrated for these cells in various species. However, these results are unique in that all these functions are detected in the same samples of WC1(+) γδ T cells, suggesting a pivotal role of these cells in controlling virus infection.

NKp46 defines ovine cells that have characteristics corresponding to NK cells

Natural killer (NK) cells are well recognized as playing a key role in innate immune defence through cytokine production and cytotoxic activity; additionally recent studies have identified several novel NK cell functions. The ability to study NK cells in the sheep has been restricted due to a lack of specific reagents. We report the generation of a monoclonal antibody specific for ovine NKp46, a receptor which in a number of mammals is expressed exclusively in NK cells. Ovine NKp46⁺ cells represent a population that is distinct from CD4⁺ and γδ⁺ T-cells, B-cells and cells of the monocytic lineage. The NKp46⁺ cells are heterogenous with respect to expression of CD2 and CD8 and most, but not all, express CD16 - characteristics consistent with NK cell populations in other species. We demonstrate that in addition to populations in peripheral blood and secondary lymphoid organs, ovine NKp46⁺ populations are also situated at the mucosal surfaces of the lung, gastro-intestinal tract and non-gravid uterus. Furthermore, we show that purified ovine NKp46⁺ populations cultured in IL-2 and IL-15 have cytotoxic activity that could be enhanced by ligation of NKp46 in re-directed lysis assays. Therefore we conclude that ovine NKp46⁺ cells represent a population that by phenotype, tissue distribution and function correspond to NK cells and that NKp46 is an activating receptor in sheep as in other species.

Cloning, expression, and polymorphisms of natural killer cell receptor NCR1 in pigs

NCR1 (NKp46) is expressed on the surfaces of natural killer cells and recognizes hemagglutinin on the influenza virus. We cloned the NCR1 gene in pigs and found that porcine NCR1 was minimally expressed in the thymus, suggesting that NCR1 could be a useful marker of natural killer cells in pigs. We observed three nonsynonymous single nucleotide polymorphisms and one deletion of three nucleotides in the coding sequence of porcine NCR1; these may affect the function of NCR1. The polymorphisms detected here may be useful markers for breeding for influenza resistance in pigs.

Comparative analysis of NK-cell receptor expression and function across primate species: Perspective on antiviral defenses

Natural killer (NK) cells are lymphoid effectors that are involved in the innate immune surveillance against infected and/or tumor cells. Their function is under the fine-tuning control of cell surface receptors that display either inhibitory or activating function and in healthy condition, mediate self-tolerance. It is known that inhibitory receptors are characterized by clonal and stochastic distribution and are extremely sensible to any modification, downregulation or loss of MHC class I surface expression that are induced in autologous cells upon viral infection or cancer transformation. This alteration of the MHC class I expression weakens the strength of the inhibitory receptor-induced interaction, thus resulting in a prompt triggering of NK cell function, which ends up in the inhibition of tumor progression and proliferation of pathogen-infected cells. Thus, the inhibitory function of NK cells is only one face of the coin, since NK-cell activation is controlled by different arrays of activating receptors that finally are involved in the induction of cytolysis and/or cytokine release. Interestingly, the inhibitory NK-cell receptors that are involved in dampening NK cell-mediated responses evolved during speciation in different, often structurally unrelated surface-expressed molecules, all using a conserved signaling pathway. In detail, during evolution, the inhibitory receptors that assure the recognition of MHC class I molecules, originate in, at least, three different ways. This ended up in multigene families showing marked structural divergences that coevolved in a convergent way with the availability of appropriate MHC ligand molecules.

Ovine CD16+/CD14- blood lymphocytes present all the major characteristics of natural killer cells

Natural killer (NK) cells have a key role in the innate immune response against pathogens because of their cytotoxic properties and production of interferon-gamma (IFN-gamma). Some insight into ruminant NK cell biology has been gained through the characterization of bovine NK cells as NKp46(+)/CD3(-) cells. However, ovine NK cells have been little studied because of the lack of specific antibodies. Most NK cells in humans and cattle express CD16. We found that an antibody against human CD16 that cross-reacts with bovine NK cells also recognizes cell populations in ovine peripheral blood mononuclear cells. Using double labelling with CD14 revealed the same profile as described in other species, and we identified a putative NK cell population. We therefore sorted this ovine CD16(+)/CD14(-) cell population and tested it for NK cell characteristics. More than 80% of sorted CD16(+)/CD14(-) cells expressed perforin. After a week of culture in the presence of IL-2 and IL-15, ovine CD16(+)/CD14(-) cells had become large cells with intra-cytoplasmic granules containing perforin, and the vast majority displayed an activated CD2(-/low)/CD25(+)/CD8(+) phenotype, as observed for bovine NKp46(+)/CD3(-) cells. Moreover, these cells expressed transcripts for the NKp46 receptor, and were cytotoxic in a CD16-mediated redirected lysis assay against a murine cell line, P815, and in a direct lysis assay against the ovine cell line, IDO5. Finally, ovine CD16(+)/CD14(-) cells having expanded for 7 days in culture secreted IFN-gamma in response to IL-12 in a dosedependent manner. Taken together, these findings led us to conclude that the ovine CD16(+)/CD14(-) lymphocyte sub-population displays the phenotype and functional characteristics of NK cells.

Canine CD8 T cells showing NK cytotoxic activity express mRNAs for NK cell-associated surface molecules

Natural killer (NK) cells have been considered to be a group of lymphocytes lacking clonally distributed receptors for antigens typical of T cells and B cells. In some mammalian species, including humans, a subpopulation of CD8(+) peripheral blood lymphocytes (PBLs) exhibits NK activity. This NK subpopulation has not been well characterized in mammals and its characterization is particularly poor in the dog. In this study, we demonstrated that a subset of canine CD8(+) cells derived from PBLs and lymphokine (IL-2)-activated killers (LAKs) of PBLs that was CD3(+), CD4(-), CD21(-), CD5(lo), alpha/betaTCR(+), and gamma/deltaTCR(-) contained substantially higher levels of mRNAs for NK cell-related receptors (NKp30, NKp44, NKG2D, 2B4, and CD16 for PBL, and NKG2D and CD56 for LAK) than the corresponding CD8(-) cells. This subset of CD8(+) lymphocytes derived from LAKs also displayed significantly higher NK cytotoxic activity than the corresponding CD8(-) cells. In contrast, CD8(+) cells derived from nonstimulated PBLs showed very low levels of NK cytotoxic activity. Our results indicate that, in IL-2-stimulated PBLs, canine CD8(+) cells are an important subset associated with NK cytotoxic activity.

Bovine neonate natural killer cells are fully functional and highly responsive to interleukin-15 and to NKp46 receptor stimulation

Natural killer (NK) cells are key components of the innate immune system with their killing and cytokine producing abilities. Bovine NK cells have been characterized as NKp46⁺/CD3⁻ lymphocytes, but little is known about these cells in neonatal calves. As the newborn calf, with an insufficiently developed acquired immunity, has to employ the innate immune system, we wanted to investigate whether neonate NK cells had the same characteristics as cells from older calves. Freshly isolated neonate and calf NK cells presented the same resting CD2⁺/CD25^low/CD8^−/low phenotype. Neonates less than 8 days old had one third of the circulating NKp46⁺ cells of older calves, but the NK cells proliferated more actively in vitro in the presence of interleukin (IL)-2 or IL-15. Moreover, neonate NK cells were more cytotoxic both in an NKp46 mediated redirected lysis assay and in direct killing of a bovine cell line MDBK when cultured in the presence of IL-15. Neonate and calf NK cells cultured in the presence of IL-2 and then stimulated with IL-12 produced similar dose-dependent interferon (IFN)-γ amounts, while IL-15 cultured NK cells did not give such a response whatever the age. However, neonatal NK cells cultured in IL-15 and stimulated by IL-12 concomitantly with cross-linking of NKp46, produced 4 to 5 times more IFN-γ than calf NK cells. These data suggest that although present in lower number at birth, neonate NK cells are fully functional and are more responsive to IL-15 and activation through the NKp46 receptor than NK cells from older calves.

Natural killer cell number and phenotype in bovine peripheral blood is influenced by age

Natural killer (NK) cells are critical to the innate defence against intracellular infection. High NK cell frequencies have been detected in human neonates, which may compensate for the relative immaturity of the specific immune response. Additionally, phenotypic subsets of NK cells have been identified in humans with different functional properties. In this study, we examined the age distribution and phenotype of NK populations in bovine peripheral blood, including neonatal animals. We found that the NK cell populations defined by the phenotypes CD3(-)CD2(+) and NKp46(+) largely overlapped, so that the majority of NK cells in bovine peripheral blood were CD3(-)CD2(+)NKp46(+). The remainder of the NK-like cells comprised two minor populations, CD3(-)CD2(+)NKp46(-) and CD3(-)CD2(-)NKp46(+); the relative proportions of these varied with age. The lowest frequency of NK cells was recorded in 1-day-old calves, with the highest frequency in day 0 calves. The phenotypic characteristics of CD3(-)CD2(+) and NKp46(+) NK populations were similar; both populations expressed CD45RO, CD45RB, CD11b, CC84, CD8alphaalpha and CD8alphabeta and did not express CD21, WC1, CD14 or gammadelta TCR. Age-related phenotypic differences were apparent. The phenotypic characteristics of three NK subpopulations were described; a significantly greater proportion of the CD3(-)CD2(-)NKp46(+) population expressed CD8alpha compared to CD3(-)CD2(+)NKp46(+) cells. Furthermore, a significantly greater proportion of the CD3(-)CD2(+)NKp46(-) population expressed CD8 compared to total CD3(-)CD2(+) cells. Adult cattle had a significantly higher proportion of perforin(+) cells compared to calves aged </=6 weeks. In this age group, the majority of perforin(+) cells expressed NKp46, while in adults the majority of perforin(+) cells were NKp46(-). However, the proportion of NKp46(+) and CD3(-)CD2(+) cells that expressed perforin was not significantly different in any age group tested.

Bovine natural killer cells

Natural killer (NK) cells have received much attention due to their cytotoxic abilities, often with a focus on their implications for cancer and transplantation. But despite their name, NK cells are also potent producers of cytokines like interferon-gamma. Recent discoveries of their interplay with dendritic cells and T-cells have shown that NK cells participate significantly in the onset and shaping of adaptive cellular immune responses, and increasingly these cells have become associated with protection from viral, bacterial and parasitic infections. Furthermore, they are substantially present in the placenta, apparently participating in the establishment of normal pregnancy. Consequently, NK cells have entered arenas of particular relevance in veterinary immunology. Limited data still exist on these cells in domestic animal species, much due to the lack of specific markers. However, bovine NK cells can be identified as NKp46 (CD335) expressing, CD3(-) lymphocytes. Recent studies have indicated a role for NK cells in important infectious diseases of cattle, and identified important bovine NK receptor families, including multiple KIRs and a single Ly49. In this review we will briefly summarize the current understanding of general NK cell biology, and then present the knowledge obtained thus far in the bovine species.

Development of a bovine ileal cannulation model to study the immune response and mechanisms of pathogenesis of paratuberculosis

An ileal cannulation model was developed in conjunction with a flow cytometric assay to gain a better understanding of the mechanisms of immunopathogenesis of Johne's disease caused by Mycobacterium avium subsp. paratuberculosis. Initial studies with calves showed that M. avium subsp. paratuberculosis DNA is detectable by PCR in ileal biopsies during the first months following experimental infection. Inflammatory lesions were not detected on endoscopic evaluation up to 8 months postexperimental infection. M. avium subsp. paratuberculosis DNA was detected in multiple tissues at necropsy 8 months postinfection. Examination of the activation status of epithelial lymphocytes from the jejunum and ileum from infected and control animals at necropsy revealed that none of the major subsets of lymphocytes (NK, CD2(+), and CD2(-) gammadelta T lymphocytes, or CD4 and CD8 alphabeta T lymphocytes) expressed activation molecules CD25, CD26, CD71, ACT1, or ACT16. Subsets of CD4 and CD8 T lymphocytes from control and infected animals expressed CD26. The majority of CD4 and CD8 T lymphocytes expressed CD45R0, the memory T-lymphocyte marker. An immune response to M. avium subsp. paratuberculosis was detected by 3 months postinfection, dominated by a strong proliferative response of CD4 memory T lymphocytes. The findings indicate an immune response develops following initial exposure to M. avium subsp. paratuberculosis that controls but does not eliminate the pathogen. This persistence of M. avium subsp. paratuberculosis possibly leads to erosion and dysregulation of protective immunity at later time points postinfection. Continuous access to the ileum offers an opportunity to elucidate the cellular and molecular events leading to immune dysregulation and development of chronic inflammatory ileitis.

NKp44 expression, phylogenesis and function in non-human primate NK cells

Molecular and functional characterization of the natural cytotoxicity receptor (NCR) NKp44 in species other than Homo sapiens has been elusive, so far. Here, we provide complete phenotypic, molecular and functional characterization for NKp44 triggering receptor on Pan troglodytes NK cells, the closest human relative, and the analysis of NKp44-genomic locus and transcription in Macaca fascicularis. Similar to H. sapiens, NKp44 expression is detectable on chimpanzee NK cells only upon activation. However, basal NKp44 transcription is 5-fold higher in chimpanzees with lower differential increases upon cell activation compared with humans. Upon activation, an overall 12-fold lower NKp44 gene expression is observed in P. troglodytes compared with H. sapiens NK cells with only a slight reduction in NKp44 surface expression. Functional analysis of 'in vitro' activated purified NK cells confirms the NKp44 triggering potential compared with other major NCRs. These findings suggest the presence of a post-transcriptional regulation that evolved differently in H. sapiens. Analysis of cynomolgus NKp44-genomic sequence and transcription pattern showed very low levels of transcription with occurrence of out-of-frame transcripts and no surface expression. The present comparative analysis suggests that NKp44-genomic organization appears during macaque speciation, with considerable evolution of its transcriptional and post-transcriptional tuning. Thus, NKp44 may represent an NCR being only recently emerged during speciation, acquiring functional relevance only in non-human primates closest to H. sapiens.

NK cell receptors in rodents and cattle

Natural killer (NK) cells discriminate between normal syngeneic cells and infected, neoplastic or MHC-disparate allogeneic cells. The reactivity of NK cells appears to be regulated by a balance between activating receptors that recognize non-self or altered self, and inhibitory receptors recognizing normal, self-encoded MHC class I molecules. Subfamilies of NK receptors undergo rapid evolution, and appear to co-evolve with the MHC. We here review present views on the evolution and function of NK cell receptors, with an emphasis on knowledge gained in cattle and rodents.

Bovine WC1(-) gammadeltaT cells incubated with IL-15 express the natural cytotoxicity receptor CD335 (NKp46) and produce IFN-gamma in response to exogenous IL-12 and IL-18

The gammadeltaT cells of ruminants are believed to participate in innate immunity and have been described with regulatory, inflammatory and cytotoxic functions. Here we describe a subset of CD3(+) TcR1(+) WC1(-)gammadeltaT cells expressing CD335 (NKp46), classically associated with CD3(-) natural killer (NK) cells, as a consequence of incubation with IL-15. This population, undetectable at the time of collection, developed after 2 week of IL-15 culture from splenic leukocytes (SPL) reaching greater than 50% of the total gammadeltaT cells. However, they did not grow well from peripheral blood leukocytes (PBL). Splenic gammadeltaT cells positively selected by magnetic separation prior to incubation with IL-15 and analyzed by flow cytometry, consistently yielded CD3(+) cells expressing CD335. These cells arose from the CD335(-)gammadeltaT cell population suggesting that the new population represents up-regulation of CD335 by gammadeltaT cells. CD335 mRNA expression from sorted IL-15-incubated SPL CD335(+)gammadeltaT cells or NK cells exceeded that of CD335(-)gammadeltaT cells. Incubation with IL-12 and IL-18 increased the number of CD335(+)gammadeltaT cells in both the PBL and SPL fractions as compared to controls or IL-12 or IL-18 alone. In addition, CD335(+)gammadeltaT cells demonstrated a robust ability to produce IFN-gamma in response to exogenous IL-12 and IL-18. Taken as a whole, we describe a new phenotypically distinct bovine gammadeltaT cell sub-population capable of participating in type 1 immune responses.

Natural killer cells in lymph nodes of healthy calves express CD16 and show both cytotoxic and cytokine-producing properties

Natural killer (NK) cells were recently shown to play an important immunomodulatory role in lymph nodes. We here report the presence, phenotype and function of NK cells resident in lymph nodes of several anatomical sites of healthy calves. NKp46+/CD3-lymphocytes, recently demonstrated to precisely identify NK cells in all tested species, were present in the paracortex and the medulla of bovine lymph nodes. Most lymph node-derived NK cells expressed CD16 and perforin, and a lytic capacity was demonstrated, while a well-developed interferon-gamma response to interleukin-2 and interleukin-12 stimulation was also seen. Lymph node-derived NK cells differed from those in blood by a higher expression of the activation markers CD44 and CD25, as well as CD8. L-selectin (CD62L) was expressed by the majority of lymph node-derived NK cells, consistent with a dependency of this molecule for migration to lymph nodes. Unlike in blood, the majority of lymph node NK cells had little or no CD2 expression. Compared to available literature, calf lymph nodes contained NK cells in numbers equal to or higher than reported in humans, and clearly higher than in mice. These findings suggest a cytotoxic role of lymph node residing NK cells, beyond the predominantly cytokine-producing role previously inferred from studies on human NK cells.

Complexity in cattle KIR genes: transcription and genome analysis

Killer immunoglobulin (Ig)-like receptors (KIRs) are the major functional natural killer (NK) cell receptors in human. The presence of KIR genes has only recently been demonstrated in other (non-primate) species, and their expression, genomic arrangement, and function in these species have yet to be investigated. In this study, we describe the KIR gene family in cattle. KIR sequences were amplified from cDNA derived from four animals. Seventeen new sequences were identified in total. Some are alleles of two previously described genes, and the remainder are representative of at least four additional genes. These cDNA data, together with analysis of the cattle genome sequence, confirm that, as in humans, cattle have multiple inhibitory and activating KIR genes, with variable haplotype composition, and putative framework genes. In contrast to human, the majority of the cattle KIR genes encode three Ig-domain KIRs; most of the inhibitory genes encode only one immunoreceptor tyrosine-based inhibitory motif (ITIM), and the activating genes encode molecules with arginine rather than the more usual lysine in the transmembrane domain. A divergent gene, 2DL1, encodes a two Ig-domain KIR with an unusual D0-D2 structure, and a distinct signaling domain with two ITIMs. Similarity to pig and human two Ig-domain (D0-D2) KIRs suggest these may be more related to an ancestral gene than the other cattle KIR genes. Cattle have multiple NKG2A-related genes and at least one Ly49 gene; thus, the data presented here suggest that they have the potential to express more major histocompatibility complex-binding NK receptors than other species.

Effects of road transportation on lymphocyte subsets in calves

The effect of transportation on peripheral blood lymphocyte subsets in 24 calves was investigated by flow cytometry. Blood was collected before departure, on arrival, at 24h and 1 week after arrival. Highest leucocyte and neutrophil counts, associated with increased concentrations of cortisol and catecholamines, indicated that stress was maximal upon arrival. At this time, a decrease in the percentages of all T lymphocyte subsets was evident, while they did not decrease as absolute counts. The proportion of CD21(+) cells did not change, indicating that the relative reduction of T lymphocyte subsets was not related to an increase in B lymphocytes. These variations may be due to the increase of a natural killer (NK) cell subset. NK cell expansion, together with increasing lymphocyte count and increasing major histocompatibility complex class II expression, may indicate stress-induced stimulation of the immune system.