Bacterial and viral induction of chicken thrombocyte inflammatory responses

The Immunological Capacity of Thrombocytes

Thrombocytes are numerous in the blood of aves (birds) and ichthyoids (fish). The origin of this cell type is a common hematopoietic stem cell giving rise to a cell that is active in blood coagulation, inflammatory functions, and the immune response in general. It has been well documented that thrombocytes can phagocytize small particles and bacteria. While phagocytosis with an associated oxidative burst has been reported for chicken thrombocytes, some questions remain as to the degradation capacity of phagosomes in ichthyoids. As innate cells, thrombocytes can be stimulated by bacterial, viral, and fungal pathogens to express altered gene expression. Furthermore, there have been observations that led researchers to state that platelets/thrombocytes are capable of serving as "professional antigen presenting cells" expressing CD40, CD80/86, MHC I, and MHC II. This indeed may be the case or, more likely at this time, provide supporting evidence that these cells aid and assist in the role of professional antigen-presenting cells to initiate adaptive immune responses.

Plant-Derived Quorum Sensing Inhibitors (Quercetin, Vanillin and Umbelliferon) Modulate Cecal Microbiome, Reduces Inflammation and Affect Production Efficiency in Broiler Chickens

Quorum sensing inhibitors (QSIs) are an attractive alternative to antibiotic growth promoters in farmed animal nutrition. The goal of the study was the diet supplementation of Arbor Acres chickens with quercetin (QC), vanillin (VN), and umbelliferon (UF), which are plant-derived QSIs preliminarily showing cumulative bioactivity. Chick cecal microbiomes were analyzed by 16s rRNA sequencing, inflammation status was assessed by blood sample analyses, and zootechnical data were summarized in the European Production Efficiency Factor (EPEF). When compared to the basal diet control group, a significant increase in the Bacillota:Bacteroidota ratio in the cecal microbiome was found in all experimental subgroups, with the highest expression > 10 at VN + UV supplementation. Bacterial community structure in all experimental subgroups was enriched with Lactobacillaceae genera and also changed in the abundance of some clostridial genera. Indices of richness, alpha diversity, and evenness of the chick microbiomes tended to increase after dietary supplementation. The peripheral blood leukocyte content decreased by 27.9-45.1% in all experimental subgroups, likely due to inflammatory response reduction following beneficial changes in the cecal microbiome. The EPEF calculation showed increased values in VN, QC + UF, and, especially, VN + UF subgroups because of effective feed conversion, low mortality, and broiler weight daily gain.

Chicken Immune Cell Assay to Model Adaptive Immune Responses In Vitro

Simple Summary

Knowledge about the modes of action of immunomodulating compounds such as pathogens, drugs, or feed additives, e.g., probiotics, will allow the development of targeted nutrition strategies, prevent infectious diseases and the usage of antimicrobials, and promote the health of animals. To investigate the mechanisms of action of immunomodulating compounds, controlled in vitro systems using freshly isolated immune cells from blood represent a promising alternative to animal experiments. Immune cell isolation from the blood of chickens is a complex and difficult process since the immune cell fractions are significantly contaminated with red blood cells and platelets. To our knowledge, a robust protocol for immune cell isolation from chicken blood and the subsequent cultivation of immune cells is not available. Here, we established a protocol for blood sampling and immune cell isolation and cultivation from chicken blood, which could be applied for the investigation of direct effects of immunomodulating compounds. This protocol, combining different techniques of immune cell isolation, cultivation, and differentiation of distinct immune cell populations, will serve as a potential alternative to animal testing in vivo. By gaining knowledge about the mechanisms of action of immunomodulating compounds, this in vitro model will contribute to promote health and welfare in chicken farming.

Abstract

Knowledge about the modes of action of immunomodulating compounds such as pathogens, drugs, or feed additives, e.g., probiotics, gained through controlled but animal-related in vitro systems using primary cultured peripheral blood mononuclear cells (PBMCs) will allow the development of targeted nutrition strategies. Moreover, it could contribute to the prevention of infectious diseases and the usage of antimicrobials, and further promote the health of the animals. However, to our knowledge, a protocol for the isolation of PBMCs with reduced thrombocyte count from chicken blood and subsequent cell culture over several days to assess the effects of immunomodulating compounds is not available. Therefore, we established an optimized protocol for blood sampling and immune cell isolation, culture, and phenotyping for chicken PBMCs. For blood sampling commercial Na–citrate tubes revealed the highest count of vital cells compared to commercial Li–heparin (p < 0.01) and K3EDTA (p < 0.05) tubes. Using combined dextran and ficoll density gradient separation, the thrombocyte count was significantly reduced (p < 0.01) compared to slow-speed centrifugation with subsequent ficoll. For cell culture, the supplementation of RPMI-1640 medium with 10% chicken serum resulted in the lowest relative cell count of thrombocytes compared to fetal calf serum (FCS) (p < 0.05). To validate the ability of the cell culture system to respond to stimuli, concanavalin A (conA) was used as a positive control. The optimized protocol allows the isolation and cultivation of vital PBMCs with reduced thrombocyte count from chicken blood for subsequent investigation of the modes of action of immunomodulating compounds.

The Chicken Embryo Model: A Novel and Relevant Model for Immune-Based Studies

Dysregulation of the immune system is associated with many pathologies, including cardiovascular diseases, diabetes, and cancer. To date, the most commonly used models in biomedical research are rodents, and despite the various advantages they offer, their use also raises numerous drawbacks. Recently, another in vivo model, the chicken embryo and its chorioallantoic membrane, has re-emerged for various applications. This model has many benefits compared to other classical models, as it is cost-effective, time-efficient, and easier to use. In this review, we explain how the chicken embryo can be used as a model for immune-based studies, as it gradually develops an embryonic immune system, yet which is functionally similar to humans'. We mainly aim to describe the avian immune system, highlighting the differences and similarities with the human immune system, including the repertoire of lymphoid tissues, immune cells, and other key features. We also describe the general in ovo immune ontogeny. In conclusion, we expect that this review will help future studies better tailor their use of the chicken embryo model for testing specific experimental hypotheses or performing preclinical testing.

Interaction of Salmonella Gallinarum and Salmonella Enteritidis with peripheral leucocytes of hens with different laying performance

Salmonella enterica ssp. enterica serovars Enteritidis (SE) and Gallinarum (SG) cause different diseases in chickens. However, both are able to reach the blood stream where heterophils and monocytes are potentially able to phagocytose and kill the pathogens. Using an ex vivo chicken whole blood infection model, we compared the complex interactions of the differentially host-adapted SE and SG with immune cells in blood samples of two White Leghorn chicken lines showing different laying performance (WLA: high producer; R11: low producer). In order to examine the dynamic interaction between peripheral blood leucocytes and the Salmonella serovars, we performed flow cytometric analyses and survival assays measuring (i) leucocyte numbers, (ii) pathogen association with immune cells, (iii) Salmonella viability and (iv) immune gene transcription in infected whole blood over a four-hour co-culture period. Inoculation of blood from the two chicken lines with Salmonella led primarily to an interaction of the bacteria with monocytes, followed by heterophils and thrombocytes. We found higher proportions of monocytes associated with SE than with SG. In blood samples of high producing chickens, a decrease in the numbers of both heterophils and Salmonella was observed. The Salmonella challenge induced transcription of interleukin-8 (IL-8) which was more pronounced in SG- than SE-inoculated blood of R11. In conclusion, the stronger interaction of monocytes with SE than SG and the better survivability of Salmonella in blood of low-producer chickens shows that the host-pathogen interaction and the strength of the immune defence depend on both the Salmonella serovar and the chicken line.

Local and systemic inflammatory responses to lipopolysaccharide in broilers: new insights using a two-window approach

The inflammatory response involves a complex interplay of local tissue activities designed to recruit leukocytes and proteins from the blood to the infected tissue. For egg-type chickens, we established the growing feather (GF) as an accessible tissue test site to monitor tissue responses to injected test-material. For commercial broilers, whose health depends to a large extent on innate immune system functions, the GF test system offers an important novel window to directly assess their natural defenses. This study was conducted to adapt the GF test system for use in broilers, and use it to simultaneously examine local (GF) and systemic (blood) inflammatory responses initiated by GF pulp injection of lipopolysaccharide (LPS). Specifically, GF of 12 male and 12 female, 5-week-old broilers were injected with LPS (16 GF/chicken; 1 μg LPS/GF). Blood and GF were collected at 0 (before), 6, and 24 h after GF injection. GF pulp was used to determine leukocyte-infiltration and gene-expression profiles, reactive-oxygen-species generation, and superoxide dismutase (SOD) activity. Blood was used to determine blood cell profiles and SOD activity. A time effect (P ≤ 0.05) was observed for most aspects examined. In GF, LPS injection resulted in heterophil and monocyte infiltration reaching maximal levels at 6 and 24 h, respectively. Reactive-oxygen-species generation, SOD activity, and mRNA levels of IL-1β, IL-8, IL-6, IL-10, and cathelicidin B1 were elevated, whereas those of TNF-α, LITAF, SOD1, and SOD2 decreased after LPS injection. In blood, levels of heterophils and monocytes were elevated at 6 h, lymphocytes and RBC decreased at 6 h, and thrombocytes and SOD activity increased at 24 h. Assessment of LPS-induced activities at the site of inflammation (GF) provided novel and more relevant insights into temporal, qualitative, and quantitative aspects of inflammatory responses than blood. Knowledge generated from this dual-window approach may find direct application in identification of individuals with robust, balanced innate defenses and provide a platform for studying the effects of exogenous treatments (e.g., nutrients, probiotics, immunomodulators, etc.) on inflammatory responses taking place in a complex tissue.

Toll-like receptor ligand-dependent inflammatory responses in chick skeletal muscle myoblasts

Toll-like receptors (TLRs) are a group of sensory receptors which are capable of recognizing a microbial invasion and activating innate immune system responses, including inflammatory responses, in both immune and non-immune cells. However, TLR functions in chick myoblasts, which are myogenic precursor cells contributing to skeletal muscle development and growth, have not been studied. Here, we report the expression patterns of TLR genes as well as TLR ligand-dependent transcriptions of interleukin (IL) genes in primary-cultured chick myoblasts. Almost TLR genes were expressed both in layer and broiler myoblasts but TLR1A was detected only in embryonic layer chick myoblasts. Chick TLR1/2 ligands, Pam₃CSK₄ and FSL-1, induced inflammatory ILs in both layer and broiler myoblasts but a TLR4 ligand, lipopolysaccharide, scarcely promoted. This is the first report on TLR ligand-dependent inflammatory responses in chick myoblasts, which may provide useful information to chicken breeding and meat production industries.

Quantification and phenotypic characterisation of peripheral IFN-γ producing leucocytes in chickens vaccinated against Newcastle disease

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An avian ICS assay for detection of chIFN-γ was established.

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Commercially available chIFN-γ antibodies were evaluated using tranfected CHO cells.

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Functional T cell responses were addressed in NDV vaccination study.

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Circulating T cells producing IFN-γ were quantified and phenotyped by flow cytometry.

The aim of this study was to optimise and evaluate an intracellular cytokine staining (ICS) assay for assessment of T cell IFN-γ responses in chickens vaccinated against Newcastle disease (ND). We aimed to validate currently available antibodies to chicken IFN-γ using transfected CHO cells. Moreover, this ICS assay was evaluated for use to detect mitogen and antigen induced IFN-γ production in chicken peripheral blood leucocytes.

Chickens from an inbred white leghorn line containing two MHC haplotypes, B19 and B21, were divided into three experimental groups; one group was kept as naive controls, one group was vaccinated intramuscularly twice with a commercial inactivated ND virus (NDV) vaccine, and the last group was vaccinated orally twice with a commercial live attenuated NDV vaccine. PBMC were ex vivo stimulated with ConA or with NDV antigen. The ICS assay was used to determine the phenotype and frequency of IFN-γ positive cells. ConA stimulation induced extensive IFN-γ production in both CD3⁺TCRγδ⁺ (γδ T cells) cells and CD3⁺TCRγδ⁻ cells (αβ T cells), but no significant differences were observed between the experimental groups. Furthermore, a large proportion of the IFN-γ producing cells were CD3⁻ indicating that other cells than classic T cells, secreted this cytokine. NDV antigen stimulation induced IFN-γ production but to a lower extent than ConA and with a large variation between individuals. The CD3⁺TCR1γδ⁻CD8α⁺ (CTL) population produced the highest NDV specific IFN-γ responses, with significantly elevated levels of IFN-γ producing cells in the B19 chickens vaccinated orally with live attenuated NDV vaccine. This was not the case in the B21 animals, indicating a haplotype restricted variation. In contrast, the CD3⁺TCR1γδ⁻CD4⁺ (Th) population did not show a significant increase in IFN-γ production in NDV stimulated samples which was in part due to a high number of IFN-γ producing cells after incubation with medium alone. In conclusion, an ICS assay for phenotyping of IFN-γ producing chicken leukocytes was set up that proved useful in identifying cytokine producing cells upon either mitogen or antigen-specific stimulation.

Lipopolysaccharide induced Interleukin-6 production is mediated through activation of ERK 1/2, p38 MAPK, MEK, and NFκB in chicken thrombocytes

Thrombocytes express Toll-like receptor 4 and apparently use both mitogen-activated protein kinase (MAPK) and nuclear factor kappa-light-chain-enhancer of activated B cells (NFKB) pathways for nuclear signaling. However, it is not well known if the same enzyme systems found in mammalian cells are fully functional in chickens. Therefore, kinase inhibitors were used with thrombocytes to block kinases in lipopolysaccharide (LPS) stimulated cells to determine if interleukin (IL)-6 expression and production would be diminished. Results demonstrated that extracellular-signal-regulated kinase (ERK)1/2 and p38 MAPK pathways influence gene expression of IL-6 through treatment with either ERK or p38 MAPK inhibitor. In addition, thrombocyte lysates from cells treated with ERK, p38, mitogen-activated protein kinase kinase (MEK)1/2 and inhibitor of nuclear factor kappa-B kinase (IKK) inhibitor showed different levels of the phosphorylated form of ERK1/2, p38 and NFκB. Furthermore, IL-6 gene expression and production were significantly upregulated in LPS stimulated thrombocytes relative to all inhibitor-treated cells.

Bacterial and Viral Products Affect Differential Pattern Recognition Receptor Activation of Chicken Thrombocytes Evidenced through RNA Sequencing

It is now well understood that thrombocytes (nucleated platelets) express TLRs and respond to both bacterial and viral products. Release of proinflammatory molecules can be expected following relatively short exposure times to LPS, lipoteichoic acid (LTA), thymidine homopolymer phosphorothioate oligonucleotide [Poly(dT)], and polyinosinic-polycytidylic acid [Poly(I:C)]. This study reports the varied expressions of genes encoded for components of the TLR, nucleotide binding oligomerization domain-like receptor, and retinoic acid-inducible gene RIG-like receptor signaling pathways in response to the TLR ligands listed above. Highly sensitive RNA-sequencing technologies were used to analyze the complete transcriptome of thrombocytes treated with all four microbial products for a period of 1 h. A total of 14,326 gene transcripts were found in chicken thrombocytes across all ligand exposures. After 1 h of stimulation with ligands, 87, 138, 1013, and 22 genes were upregulated for LTA, LPS, Poly(dT), and Poly(I:C), and 12, 142, 249, and 16 genes were downregulated for LTA, LPS, Poly(dT), and Poly(I:C), respectively, with at least a 1-fold change relative to unexposed thrombocytes. Summarizations of biological processes, protein classes, and biochemical pathways reveal the role of chicken thrombocytes in proinflammatory responses linked to key signaling pathways. TLR, nucleotide binding oligomerization domain-like receptor, and retinoic acid-inducible gene RIG-like receptor pathways were mapped based on the transcriptome results with gene expression for common signal and proinflammatory mediators highlighted. The information reported in this study is useful for defining a limited set of proinflammatory molecules to evaluate in cases of either bacterial or viral disease monitoring.

Transcriptome Profile of the Chicken Thrombocyte: New Implications as an Advanced Immune Effector Cell

Thrombocytes are nucleated platelets involved in immune functions such as pathogen recognition and release of pro-inflammatory bioactive compounds when exposed to bacterial and viral molecules. However, the complete role of these cells in innate and adaptive immune responses is not understood, and little is known about their biology at the molecular-genetic level. Highly sensitive RNA-sequencing technologies were used to analyze the complete transcriptome of thrombocytes for the first time with analytical resolution focused on cell-based components of the immune system/response. Amongst all the genes listed in the current chicken genome assembly, 10,041 gene transcripts were found in the chicken thrombocyte. After 1-hour in vitro stimulation with lipopolysaccharide (LPS, Salmonella minnesota), 490 genes were upregulated and 359 genes were downregulated, respectively, with at least a 1-fold change relative to unexposed thrombocytes. Additionally, by constructing a de novo assembly, we were able to identify a total of 3,030 novel genes in the thrombocyte transcriptome. The information generated here is useful in development of novel solutions to lower the economic burden and zoonotic threat that accompanies infectious diseases for birds and fish. In addition, the resources created here have translational utility as a model system to find orthologous genes and genes related to its enucleated counterpart, the platelet.

Replication of Toxoplasma gondii in chicken erythrocytes and thrombocytes compared to macrophages

Toxoplasma (T.) gondii is able to infect various cell types in different hosts. The replication of this parasite within different peripheral mononuclear blood cell populations in chicken has not yet been fully understood. Aim of the present study was to investigate the impact of chicken erythrocytes and thrombocytes as potential host cells for T. gondii. Cultures of primary avian erythrocytes and thrombocytes were inoculated with tachyzoites of T. gondii type II strain ME49. Parasite replication was detected by a quantitative real-time PCR at different times postinoculation until 24 or 48 h, respectively, displaying long-term investigations for the chosen cultures. The parasite replication curve showed a continuous decrease of parasite stages in erythrocytes and thrombocytes. Observations by light microscopy showed massive destruction for both cell populations. Few macrophages in between the infected thrombocytes were viable during the investigation period and showed internalised tachyzoites by confocal laser scanning microscopy. These findings show that T. gondii is not capable of replication in chicken erythrocytes and thrombocytes; therefore, both cannot be considered as potential host cells. In further consequence, monocyte-derived macrophages seem to be the key to the dissemination mechanisms for T. gondii in chicken.

Immune-relevant thrombocytes of common carp undergo parasite-induced nitric oxide-mediated apoptosis

Common carp thrombocytes account for 30-40% of peripheral blood leukocytes and are abundant in the healthy animals' spleen, the thrombopoietic organ. We show that, ex vivo, thrombocytes from healthy carp express a large number of immune-relevant genes, among which several cytokines and Toll-like receptors, clearly pointing at immune functions of carp thrombocytes. Few studies have described the role of fish thrombocytes during infection. Carp are natural host to two different but related protozoan parasites, Trypanoplasma borreli and Trypanosoma carassii, which reside in the blood and tissue fluids. We used the two parasites to undertake controlled studies on the role of fish thrombocytes during these infections. In vivo, but only during infection with T. borreli, thrombocytes were massively depleted from the blood and spleen leading to severe thrombocytopenia. Ex vivo, addition of nitric oxide induced a clear and rapid apoptosis of thrombocytes from healthy carp, supporting a role for nitric oxide-mediated control of immune-relevant thrombocytes during infection with T. borreli. The potential advantage for parasites to selectively deplete the host of thrombocytes via nitric oxide-induced apoptosis is discussed.