Resistance and susceptibility to Marek's disease: nitric oxide synthase/arginase activity balance

Metabolomic profiling of Marek's disease virus infection in host cell based on untargeted LC-MS

Marek's disease (MD) caused by Marek's disease virus (MDV), poses a serious threat to the poultry industry by inducing neurological disease and malignant lymphoma in infected chickens. However, the underlying mechanisms how MDV disrupts host cells and causes damage still remain elusive. Recently, the application of metabolomics has shown great potential for uncovering the complex mechanisms during virus-host interactions. In this study, chicken embryo fibroblasts (CEFs) infected with MDV were subjected to ultrahigh-performance liquid chromatography-quadrupole time-of-flight tandem mass spectrometry (UHPLC-QTOF-MS) and multivariate statistical analysis. The results showed that 261 metabolites were significantly altered upon MDV infection, with most changes occurring in amino acid metabolism, energy metabolism, nucleotide metabolism, and lipid metabolism. Notably, MDV infection induces an up-regulation of amino acids in host cells during the early stages of infection to provide the energy and intermediary metabolites necessary for efficient multiplication of its own replication. Taken together, these data not only hold promise in identifying the biochemical molecules utilized by MDV replication in host cells, but also provides a new insight into understanding MDV-host interactions.

Marek's Disease Virus Modulates T Cell Proliferation via Activation of Cyclooxygenase 2-Dependent Prostaglandin E2

Marek’s disease virus (MDV), an avian alphaherpesvirus, infects chickens, transforms CD4+ T cells, and induces immunosuppression early during infection. However, the exact mechanisms involved in MDV-induced immunosuppression are yet to be identified. Here, our results demonstrate that MDV infection in vitro and in vivo induces activation of cyclooxygenase-2 (COX-2) and production of prostaglandin E2 (PGE2). This exerts its inhibitory effects on T cell proliferation at day 21 post infection via PGE2 receptor 2 (EP2) and receptor 4 (EP4). Impairment of the MDV-induced T cell proliferation was associated with downregulation of IL-2 and transferrin uptake in a COX-2/PGE2 dependent manner in vitro. Interestingly, oral administration of a COX-2 inhibitor, meloxicam, during MDV infection inhibited COX-2 activation and rescued T cell proliferation at day 21 post infection. Taken together, our results reveal a novel mechanism that contributes to immunosuppression in the MDV-infected chickens.

The Interplay between Salmonella and Intestinal Innate Immune Cells in Chickens

Salmonellosis is a common infection in poultry, which results in huge economic losses in the poultry industry. At the same time, Salmonella infections are a threat to public health, since contaminated poultry products can lead to zoonotic infections. Antibiotics as feed additives have proven to be an effective prophylactic option to control Salmonella infections, but due to resistance issues in humans and animals, the use of antimicrobials in food animals has been banned in Europe. Hence, there is an urgent need to look for alternative strategies that can protect poultry against Salmonella infections. One such alternative could be to strengthen the innate immune system in young chickens in order to prevent early life infections. This can be achieved by administration of immune modulating molecules that target innate immune cells, for example via feed, or by in-ovo applications. We aimed to review the innate immune system in the chicken intestine; the main site of Salmonella entrance, and its responsiveness to Salmonella infection. Identifying the most important players in the innate immune response in the intestine is a first step in designing targeted approaches for immune modulation.

Secondary Functions of Arginine and Sulfur Amino Acids in Poultry Health: Review

Simple Summary

Historically, studies with amino acids have focused on protein synthesis and accretion, especially with eggs and meat, whereas less importance has been given to their secondary functions on the metabolism. However, certain amino acids, such as arginine, methionine, and cysteine are precursors for other essential molecules in the immune defense, antioxidant system, cell signaling, and gene expression, and can act as regulators in the growth and development of the animals. Because poultry are subjected to stressful conditions throughout their lives, the use of these amino acids and their secondary functions could beneficiate their general health. This review describes the metabolism of arginine, methionine, and cysteine and how they modulate different tissues, especially during challenging conditions. Arginine supplementation has been shown to modulate musculoskeletal health development, reduce fat accretion, and improve the antioxidant system. Moreover, methionine and cysteine could improve the bone development and have a potential in mitigating the negative effects caused by heat stress. Understanding how these amino acids can ameliorate stressful conditions may provide novel insights about their use as nutritional strategies to modulate the health status of chickens.

Abstract

Amino acids such as arginine, methionine, and cysteine are the precursors of essential molecules that regulate growth and health, being classified as functional amino acids. This review describes the metabolism of arginine and the sulfur amino acids and how they modulate, directly or indirectly, different tissues. Emphasis is placed on their effects in supporting health during challenging conditions, such as heat stress and Eimeria infection. The use of arginine has been shown to reduce abdominal fat pad in ducks and increase lean tissue and bone mineral density in broilers. Additionally, the sulfur amino acids have been shown to improve bone development and are beneficial during heat stress. The use of L-methionine increased the cortical and trabecular bone mineral densities, in laying hens. Moreover, the dietary inclusion of these amino acids could reduce the damage caused by Eimeria spp. infection by regulating the antioxidant system and cell repair. Understanding how these amino acids can mitigate stressful conditions may provide us novel insights of their use as nutritional strategies to modulate the health status of chickens.

Enhanced Replication of Virulent Newcastle Disease Virus in Chicken Macrophages Is due to Polarized Activation of Cells by Inhibition of TLR7

Newcastle disease (ND), caused by infections with virulent strains of Newcastle disease virus (NDV), is one of the most important infectious disease affecting wild, peridomestic, and domestic birds worldwide. Vaccines constructed from live, low-virulence (lentogenic) viruses are the most accepted prevention and control strategies for combating ND in poultry across the globe. Avian macrophages are one of the first cell lines of defense against microbial infection, responding to signals in the microenvironment. Although macrophages are considered to be one of the main target cells for NDV infection in vivo, very little is known about the ability of NDV to infect chicken macrophages, and virulence mechanisms of NDV as well as the polarized activation patterns of macrophages and correlation with viral infection and replication. In the present study, a cell culture model (chicken bone marrow macrophage cell line HD11) and three different virulence and genotypes of NDV (including class II virulent NA-1, class II lentogenic LaSota, and class I lentogenic F55) were used to solve the above underlying questions. Our data indicated that all three NDV strains had similar replication rates during the early stages of infection. Virulent NDV titers were shown to increase compared to the other lentogenic strains, and this growth was associated with a strong upregulation of both pro-inflammatory M1-like markers/cytokines and anti-inflammatory M2-like markers/cytokines in chicken macrophages. Virulent NDV was found to block toll-like receptor (TLR) 7 expression, inducing higher expression of type I interferons in chicken macrophages at the late stage of viral infection. Only virulent NDV replication can be inhibited by pretreatment with TLR7 ligand. Overall, this study demonstrated that virulent NDV activates a M1-/M2-like mixed polarized activation of chicken macrophages by inhibition of TLR7, resulting in enhanced replication compared to lentogenic viruses.

Interactive effects of dietary arginine and Eimeria acervulina infection on broiler growth performance and metabolism

The influence of dietary Arg concentration and Eimeria acervulina infection on broiler growth performance and plasma carotenoid, nitric oxide (NO), amino acid, and urea concentrations was evaluated. Male Ross × Ross 308 broilers (384 total) were fed a common diet for 10 d post-hatch and provided experimental diets formulated to contain 1.23 (HA) or 0.74% (LA) standardized ileal digestible Arg from 10 to 28 d. At 21 d, one-half of the broilers were switched to the opposite diet to create 4 dietary regimens where birds were fed the LA diet throughout, the LA diet replaced by the HA diet at 21 d, the HA diet throughout, or the HA diet replaced by the LA diet at 21 d. Broilers were orally inoculated 0 (uninfected) or 3.5 × 105 sporulated E. acervulina oocysts at 15 d, resulting in a factorial arrangement of 4 dietary regimens × 2 infection states (8 replicates/treatment). Overall (10 to 28 d) BW gain and G:F were greatest (P < 0.01) for birds fed the HA diet throughout, regardless of infection status. Eimeria acervulina infection decreased (P < 0.01) BW gain of birds from 15 to 21 d, and G:F was lowest (P < 0.05) for infected birds fed the LA diet during this period. There was no influence (P > 0.05) of E. acervulina on BW gain or G:F of broilers from 21 to 28 d. Plasma Arg, Lys, and Orn levels at 21 d indicated that the LA diet caused an imbalance in the Lys and Arg status of broilers, and E. acervulina infection increased (P < 0.01) the plasma concentration of these 3 amino acids. Diet × infection interactions (P < 0.05) were observed on 21 d for plasma carotenoids and NO, whereby infection decreased plasma carotenoids and increased plasma NO, but dietary Arg concentration only influenced these measures for uninfected birds. Thus, production of NO during E. acervulina infection was not impaired by dietary Arg limitation.

The role of myeloid cell activation and arginine metabolism in the pathogenesis of virus-induced diseases

When an antiviral immune response is generated, a balance must be reached between two opposing pathways: the production of proinflammatory and cytotoxic effectors that drive a robust antiviral immune response to control the infection and regulators that function to limit or blunt an excessive immune response to minimize immune-mediated pathology and repair tissue damage. Myeloid cells, including monocytes and macrophages, play an important role in this balance, particularly through the activities of the arginine-hydrolyzing enzymes nitric oxide synthase 2 (Nos2; iNOS) and arginase 1 (Arg1). Nitric oxide (NO) production by iNOS is an important proinflammatory mediator, whereas Arg1-expressing macrophages contribute to the resolution of inflammation and wound repair. In the context of viral infections, expression of these enzymes can result in a variety of outcomes for the host. NO has direct antiviral properties against some viruses, whereas during other virus infections NO can mediate immunopathology and/or inhibit the antiviral immune response to promote chronic infection. Arg1 activity not only has important wound healing functions but can also inhibit the antiviral immune response during some viral infections. Thus, depending on the specific virus and the tissue(s) involved, the activity of both of these arginine-hydrolyzing enzymes can either exacerbate or limit the severity of virus-induced disease. In this review, we will discuss a variety of viral infections, including HIV, SARS-CoV, LCMV, HCV, RSV, and others, where myeloid cells influence the control and clearance of the virus from the host, as well as the severity and resolution of tissue damage, via the activities of iNOS and/or Arg1. Clearly, monocyte/macrophage activation and arginine metabolism will continue to be important areas of investigation in the context of viral infections.

Modulation of chicken macrophage effector function by T(H)1/T(H)2 cytokines

Regulation of macrophage activity by T(H)1/2 cytokines is important to maintain the balance of immunity to provide adequate protective immunity while avoiding excessive inflammation. IFN-γ and IL-4 are the hallmark T(H)1 and T(H)2 cytokines, respectively. In avian species, information concerning regulation of macrophage activity by T(H)1/2 cytokines is limited. Here, we investigated the regulatory function of chicken T(H)1 cytokines IFN-γ, IL-18 and T(H)2 cytokines IL-4, IL-10 on the HD11 macrophage cell line. Chicken IFN-γ stimulated nitric oxide (NO) synthesis in HD11 cells and primed the cells to produce significantly greater amounts of NO when exposed to microbial agonists, lipopolysaccharide, lipoteichoic acid, peptidoglycan, CpG-ODN, and poly I:C. In contrast, chicken IL-4 exhibited bi-directional immune regulatory activity: it activated macrophage NO synthesis in the absence of inflammatory agonists, but inhibited NO production by macrophages in response to microbial agonists. Both IFN-γ and IL-4, however, enhanced oxidative burst activity of the HD11 cells when exposed to Salmonella enteritidis. IL-18 and IL-10 did not affect NO production nor oxidative burst in HD11 cells. Phagocytosis and bacterial killing by the HD11 cells were not affected by the treatments of these cytokines. Infection of HD11 cells with S.enteritidis was shown to completely abolish NO production regardless of IFN-γ treatment. This study has demonstrated that IFN-γ and IL-4 are important T(H)1 and T(H)2 cytokines that regulate macrophage function in chickens.

Proteomic analysis of host responses to Marek's disease virus infection in spleens of genetically resistant and susceptible chickens

Resistance to Marek's disease (MD) in chickens is genetically regulated and there are lines of chickens with differential susceptibility or resistance to this disease. The present study was designed to study comparative changes in the spleen proteomes of MD-susceptible B19 and MD-resistant B21 chickens in response to MDV infection. Spleen proteomes were examined at 4, 7, 14 and 21 days post-infection (d.p.i.) using two-dimensional gel electrophoresis and subsequently the protein spots were identified by one-dimensional liquid chromatography electrospray ionization tandem mass spectrometry (1D LC ESI MS/MS). On average, there were 520+/-27 distinct protein spots on each gel and 1.6+/-0.7% of the spots differed quantitatively in their expression (p< or =0.05 and fold change > or =2) between infected B19 and B21 chickens. There was one spot at 4d.p.i. and three spots each at the rest of the time points, which had a qualitative difference in expression. Most of the differentially expressed proteins at 4 and 7d.p.i. displayed increased expression in B21 chickens; conversely the differentially expressed proteins at 14 and 21d.p.i. showed an increase in expression in B19 chickens. The differentially expressed proteins identified in the present study included antioxidants, molecular chaperones, proteins involved in the formation of cytoskeleton, protein degradation and antigen presentation, signal transduction, protein translation and elongation, RNA processing and cell proliferation. These findings shed light on some of the underlying processes of genetic resistance or susceptibility to MD.

Differences in genetic background influence the induction of innate and acquired immune responses in chickens depending on the virulence of the infecting infectious bursal disease virus (IBDV) strain

Previous studies and field observations have suggested that genetic background influences infectious bursal disease virus (IBDV) pathogenesis. However, the influence of the virulence of the infecting IBDV strain and the mechanisms underlying the differences in susceptibility are not known. In the present study IBDV pathogenesis was compared between specific-pathogen-free layer-type (LT) chickens, which are the most susceptible chicken for IBDV and have been used as the model for pathogenesis studies, and broiler-type (BT) chickens, which are known to be less susceptible to clinical infectious bursal disease (IBD). The innate and acquired immune responses were investigated after inoculation of an intermediate (i), virulent (v) or very virulent (vv) strain of IBDV. IBDV pathogenesis was comparable among genetic backgrounds after infection with iIBDV. After infection with vIBDV and vvIBDV, LT birds showed severe clinical disease and mortality, higher bursal lesion scores and IBDV-antigen load relative to BT birds. Circulating cytokine induction varied significantly in both timing and quantity between LT and BT birds and among virus strains (P<0.05). Evaluation of different immune cell populations by flow-cytometric analysis in the bursa of Fabricius provided circumstantial evidence of a stronger local T cell response in BT birds vs. LT birds after infection with the virulent strain. On the other hand, LT birds showed a more significant increase in circulating macrophage-derived immune mediators such as total interferon (IFN) and serum nitrite than BT birds on days 2 and 3 post-vIBDV infection (P<0.05). Stronger stimulation of innate immune reactions especially after vIBDV infection in the early phase may lead to faster and more severe lesion development accompanied by clinical disease and death in LT chickens relative to BT chickens. Interestingly, no significant differences were seen between genetic backgrounds in induction of the IBDV-specific humoral response: timing of IBDV-antibody induction and antibody levels were comparable between BT and LT birds. This study clearly demonstrates a significant influence of chickens' genetic background on disease outcome. The difference between backgrounds in IBDV susceptibility is further influenced by the virulence of the infecting virus strain.