Evolution of an expanded mannose receptor gene family

Delineation of chicken immune markers in the era of omics and multicolor flow cytometry

Multiparameter flow cytometry is a routine method in immunological studies incorporated in biomedical, veterinary, agricultural, and wildlife research and routinely used in veterinary clinical laboratories. Its use in the diagnostics of poultry diseases is still limited, but due to the continuous expansion of reagents and cost reductions, this may change in the near future. Although the structure and function of the avian immune system show commonalities with mammals, at the molecular level, there is often low homology across species. The cross-reactivity of mammalian immunological reagents is therefore low, but nevertheless, the list of reagents to study chicken immune cells is increasing. Recent improvement in multicolor antibody panels for chicken cells has resulted in more detailed analysis by flow cytometry and has allowed the discovery of novel leukocyte cell subpopulations. In this article, we present an overview of the reagents and guidance needed to perform multicolor flow cytometry using chicken samples and common pitfalls to avoid.

Enzyme-responsive mannose-grafted magnetic nanoparticles for breast and liver cancer therapy and tumor-associated macrophage immunomodulation

BACKGROUND

Chemo-immunotherapy modifies the tumor microenvironment to enhance the immune response and improve chemotherapy. This study introduces a dual-armed chemo-immunotherapy strategy combating breast tumor progression while re-polarizing Tumor-Associated Macrophage (TAM) using prodigiosin-loaded mannan-coated magnetic nanoparticles (PG@M-MNPs).

METHODS

The physicochemical properties of one-step synthetized M-MNPs were analyzed, including X-ray diffraction, FTIR, DLS, VSM, TEM, zeta potential analysis, and drug loading content were carried out. Biocompatibility, cancer specificity, cellular uptake, and distribution of PG@M-MNPs were investigated using fluorescence and confocal laser scanning microscopy, and flow cytometry. Furthermore, the expression levels of IL-6 and ARG-1 after treatment with PG and PG@M-MNPs on M1 and M2 macrophage subsets were studied.

RESULTS

The M-MNPs were successfully synthesized and characterized, demonstrating a size below 100 nm. The release kinetics of PG from M-MNPs showed sustained and controlled patterns, with enzyme-triggered release. Cytotoxicity assessments revealed an enhanced selectivity of PG@M-MNPs against cancer cells and minimal effects on normal cells. Additionally, immuno-modulatory activity demonstrates the potential of PG@M-MNPs to change the polarization dynamics of macrophages.

CONCLUSION

These findings highlight the potential of a targeted approach to breast cancer treatment, offering new avenues for improved therapeutic outcomes and patient survival.

Single-cell RNA-seq mapping of chicken peripheral blood leukocytes

BACKGROUND

Single-cell transcriptomics provides means to study cell populations at the level of individual cells. In leukocyte biology this approach could potentially aid the identification of subpopulations and functions without the need to develop species-specific reagents. The present study aimed to evaluate single-cell RNA-seq as a tool for identification of chicken peripheral blood leukocytes. For this purpose, purified and thrombocyte depleted leukocytes from 4 clinically healthy hens were subjected to single-cell 3' RNA-seq. Bioinformatic analysis of data comprised unsupervised clustering of the cells, and annotation of clusters based on expression profiles. Immunofluorescence phenotyping of the cell preparations used was also performed.

RESULTS

Computational analysis identified 31 initial cell clusters and based on expression of defined marker genes 28 cluster were identified as comprising mainly B-cells, T-cells, monocytes, thrombocytes and red blood cells. Of the remaining clusters, two were putatively identified as basophils and eosinophils, and one as proliferating cells of mixed origin. In depth analysis on gene expression profiles within and between the initial cell clusters allowed further identification of cell identity and possible functions for some of them. For example, analysis of the group of monocyte clusters revealed subclusters comprising heterophils, as well as putative monocyte subtypes. Also, novel aspects of TCRγ/δ + T-cell subpopulations could be inferred such as evidence of at least two subtypes based on e.g., different expression of transcription factors MAF, SOX13 and GATA3. Moreover, a novel subpopulation of chicken peripheral B-cells with high SOX5 expression was identified. An overall good correlation between mRNA and cell surface phenotypic cell identification was shown.

CONCLUSIONS

Taken together, we were able to identify and infer functional aspects of both previously well known as well as novel chicken leukocyte populations although some cell types. e.g., T-cell subtypes, proved more challenging to decipher. Although this methodology to some extent is limited by incomplete annotation of the chicken genome, it definitively has benefits in chicken immunology by expanding the options to distinguish identity and functions of immune cells also without access to species specific reagents.

Development and function of chicken XCR1+ conventional dendritic cells

Conventional dendritic cells (cDCs) are antigen-presenting cells (APCs) that play a central role in linking innate and adaptive immunity. cDCs have been well described in a number of different mammalian species, but remain poorly characterised in the chicken. In this study, we use previously described chicken cDC specific reagents, a novel gene-edited chicken line and single-cell RNA sequencing (scRNAseq) to characterise chicken splenic cDCs. In contrast to mammals, scRNAseq analysis indicates that the chicken spleen contains a single, chemokine receptor XCR1 expressing, cDC subset. By sexual maturity the XCR1+ cDC population is the most abundant mononuclear phagocyte cell subset in the chicken spleen. scRNAseq analysis revealed substantial heterogeneity within the chicken splenic XCR1+ cDC population. Immature MHC class II (MHCII)LOW XCR1+ cDCs expressed a range of viral resistance genes. Maturation to MHCIIHIGH XCR1+ cDCs was associated with reduced expression of anti-viral gene expression and increased expression of genes related to antigen presentation via the MHCII and cross-presentation pathways. To visualise and transiently ablate chicken XCR1+ cDCs in situ, we generated XCR1-iCaspase9-RFP chickens using a CRISPR-Cas9 knockin transgenesis approach to precisely edit the XCR1 locus, replacing the XCR1 coding region with genes for a fluorescent protein (TagRFP), and inducible Caspase 9. After inducible ablation, the chicken spleen is initially repopulated by immature CD1.1+ XCR1+ cDCs. XCR1+ cDCs are abundant in the splenic red pulp, in close association with CD8+ T-cells. Knockout of XCR1 prevented this clustering of cDCs with CD8+ T-cells. Taken together these data indicate a conserved role for chicken and mammalian XCR1+ cDCs in driving CD8+ T-cells responses.

Transcriptomic analysis reveals novel age-independent immunomodulatory proteins as a mode of cerebroprotection in P2X4R KO mice after ischemic stroke

Identification of new potential drug target proteins and their plausible mechanisms for stroke treatment is critically needed. We previously showed that genetic deletion and short-term pharmacological inhibition of P2X4R, a purinergic receptor for adenosine triphosphate ATP, provides acute cerebroprotection. However, potential mechanisms remain unknown. Therefore, we employed RNA-seq technology to identify the gene expression profiles, pathway analysis, and qPCR validation of differentially expressed genes (DEGs). This analysis identified roles of DEGs in certain biological processes responsible for P2X4R-dependent cerebroprotection after stroke. We subjected both young and aged male and female global P2X4 KO and littermate WT mice to ischemic stroke. After 3 days, mice were sacrificed, total RNA was isolated using Trizol, and subjected to RNA-seq and Nanostring-mediated qPCR. DESeq2, Gene Ontology (GO), and Ingenuity Pathway Analysis (IPA) were used to identify mRNA transcript expression profiles and biological pathways. We found 2246 DEGs in P2X4R KO vs WT tissue after stroke. Out of these DEGs, 1920 gene were downregulated, and 325 genes were upregulated in KO. GO/IPA analysis of the top 300 DEGs suggests an enrichment of inflammation and extracellular matrix component genes. qPCR validation of the top 30 DEGs revealed downregulation of two common age-independent genes in P2X4R KO mice: Interleukin-6 ( IL-6) , an inflammatory cytokine, and Cytotoxic T Lymphocyte-Associated Protein 2 alpha ( Ctla2a ), an immunosuppressive factor. These data suggest that P2X4R-mediated cerebroprotection after stroke is initiated by attenuation of immune modulatory pathways in both young and aged mice of both sexes.

Characterization of vaccine-induced immune responses against coccidiosis in broiler chickens

Coccidiosis, caused by Eimeria protozoan species, is an economically important enteric disease of poultry. Although commercial live vaccines are widely used for disease control, the vaccine-induced protective immune mechanisms are poorly characterized. The present study used a commercial broiler vaccine containing a mixture of E. acervulina, E. maxima, and E. tenella. One-day-old chicks were vaccinated by spray followed by a challenge at 21 days of age with a mixture of wild type Eimeria species via oral gavage. Oocyst shedding, immune gene expression and cellular responses in the spleen and cecal tonsils were measured at pre- (days 14 and 21) and post-challenge (days 24, 28 and 35) time points. Results showed that the oocyst counts were significantly reduced in the vaccinated chickens at post-challenge compared to unvaccinated control group. While the vaccinated birds had a significantly increased toll-like receptor (TLR) 21 gene expression at pre-challenge, the transcription of interferon (IFN)γ, Interleukin (IL)-12 and CD40 genes in spleen and cecal tonsils of these birds was significantly higher at post-challenge compared to unvaccinated chickens. Cellular immunophenotyping analysis found that vaccination led to increased frequency of macrophages and activated T cells (CD8⁺CD44⁺ and CD4⁺CD44⁺) in the spleen and cecal tonsils at post-challenge. Furthermore, in vitro stimulation of chicken macrophages (MQ-NCSU cells) with purified individual species of E. acervulina, E. maxima, and E. tenella showed a significantly increased expression of TLR21, TLR2 and IFNγ genes as well as nitric oxide production. Collectively, these findings suggest that TLR21 and TLR2 may be involved in the immune cell recognition of Eimeria parasites and that the vaccine can induce a robust macrophage activation leading to a T helper-1 dominated protective response at both local and systemic lymphoid tissues.

Erysipelothrix rhusiopathiae-specific T-cell responses after experimental infection of chickens selectively bred for high and low serum levels of mannose-binding lectin

Erysipelas, caused by infection with Erysipelothrix rhusiopathiae (ER) is an important emerging disease in laying hens. We have earlier observed prominent mannose-binding lectin (MBL) acute phase responses in experimentally ER infected chickens. The present study aimed to further examine immune responses to ER by using chickens selectively bred for high (L10H) and low (L10L) serum MBL levels. Chickens were infected with ER at 3 weeks of age and immune parameters and bacterial load were monitored in blood until day 18 after infection. Blood and spleen leukocytes collected on day 18 were stimulated in vitro with ER antigens and blast transformation of different T-cell populations was assessed. The ER infection gave a very varied outcome and no clear differences were observed between L10H and L10L chickens with respect to leukocyte counts, bacterial load or clinical outcome. Nonetheless, rapid innate responses, e.g., heterophilia and increased serum MBL levels were noted in bacteraemic chickens. All ER infected chickens also showed transient increased expression of mannose receptor MRC1L-B and decreased expression of major histocompatibility complex II on monocytes day 1 after infection indicating monocyte activation or relocation. In vitro ER stimulation showed antigen specific blast transformation of CD4+, TCRγ/δ-CD8αβ+ and TCRγ/δ+CD8αβ+ spleen cells from all infected chickens. For CD4+ and TCRγ/δ-CD8αβ+ cells the proportions of blast transformed cells were significantly higher for samples from L10L chickens than those for samples from L10H chickens. This is the first observation of ER-specific T-cells in chickens and interestingly a Th1-type response comprising cytotoxic T-cells was indicated.

Assessing the infiltration of immune cells in the upper trachea mucosa after infectious laryngotracheitis virus (ILTV) vaccination and challenge

The types of immune cells that populate the trachea after ILTV vaccination and infection have not been assessed. The objective of this study was to quantify CD4⁺, CD8α⁺, CD8β⁺, TCRγδ⁺, and MRC1LB⁺ cells that infiltrate the trachea after vaccination with chicken embryo origin (CEO), tissue culture origin (TCO), and recombinant herpesvirus of turkey-laryngotracheitis (rHVT-LT) vaccines, and after challenge of vaccinated and non-vaccinated chickens with a virulent ILTV strain. Eye-drop vaccination with CEO, or TCO, or in ovo vaccination with rHVT-LT did not alter the number of CD4⁺, CD8α⁺, CD8β⁺, TCRγδ⁺, and MRC1LB⁺ cells in the trachea. After challenge, the CEO vaccinated group of chickens showed swift clearance of the challenge virus, the mucosa epithelium of the trachea remained intact, and a limited number of CD4⁺, CD8α⁺, and CD8β⁺ cells were detected in the upper trachea mucosa. The TCO and rHVT-LT vaccinated groups of chickens showed narrow viral clearance with moderate disruption of the trachea epithelial integrity, and a significant increase in CD4⁺, CD8α⁺, CD8β⁺, and TCRγδ⁺ cells infiltrated the upper trachea mucosa. Non-vaccinated challenged chickens showed high levels of viral replication, the epithelial organization of the upper trachea mucosa was heavily disrupted, and the predominant infiltrates were CD4⁺, TCRγδ⁺, and MRC1LB⁺ cells. Hence, the very robust protection provided by CEO vaccination was characterized by minimal immune cell infiltration to the trachea mucosa. In contrast, partial protection induced by the TCO and rHVT-LT vaccines requires a prolonged period of T cell expansion to overcome the established infection in the trachea mucosa.

A detailed analysis of innate and adaptive immune responsiveness upon infection with Salmonella enterica serotype Enteritidis in young broiler chickens

Salmonella enterica serotype Enteritidis (SE) is a zoonotic pathogen which causes foodborne diseases in humans as well as severe disease symptoms in young chickens. More insight in innate and adaptive immune responses of chickens to SE infection is needed to understand elimination of SE. Seven-day-old broiler chickens were experimentally challenged with SE and numbers and responsiveness of innate and adaptive immune cells as well as antibody titers were assessed. SE was observed in the ileum and spleen of SE-infected chickens at 7 days post-infection (dpi). At 1 dpi numbers of intraepithelial cytotoxic CD8⁺ T cells were significantly increased alongside numerically increased intraepithelial IL-2Rα⁺ and 20E5⁺ natural killer (NK) cells at 1 and 3 dpi. At both time points, activation of intraepithelial and splenic NK cells was significantly enhanced. At 7 dpi in the spleen, presence of macrophages and expression of activation markers on dendritic cells were significantly increased. At 21 dpi, SE-induced proliferation of splenic CD4⁺ and CD8⁺ T cells was observed and SE-specific antibodies were detected in sera of all SE-infected chickens. In conclusion, SE results in enhanced numbers and activation of innate cells and we hypothesized that in concert with subsequent specific T cell and antibody responses, reduction of SE is achieved. A better understanding of innate and adaptive immune responses important in the elimination of SE will aid in developing immune-modulation strategies, which may increase resistance to SE in young broiler chickens.

Review of Dendritic Cells, Their Role in Clinical Immunology, and Distribution in Various Animal Species

Dendritic cells (DCs) are cells derived from the hematopoietic stem cells (HSCs) of the bone marrow and form a widely distributed cellular system throughout the body. They are the most efficient, potent, and professional antigen-presenting cells (APCs) of the immune system, inducing and dispersing a primary immune response by the activation of naïve T-cells, and playing an important role in the induction and maintenance of immune tolerance under homeostatic conditions. Thus, this review has elucidated the general aspects of DCs as well as the current dynamic perspectives and distribution of DCs in humans and in various species of animals that includes mouse, rat, birds, dog, cat, horse, cattle, sheep, pig, and non-human primates. Besides the role that DCs play in immune response, they also play a pathogenic role in many diseases, thus becoming a target in disease prevention and treatment. In addition, its roles in clinical immunology have also been addressed, which include its involvement in transplantation, autoimmune disease, viral infections, cancer, and as a vaccine target. Therefore, based on the current knowledge and understanding of the important roles they play, DCs can be used in the future as a powerful tool for manipulating the immune system.

The contribution of the immune response to enhanced colibacillosis upon preceding viral respiratory infection in broiler chicken in a dual infection model

Colibacillosis in chickens caused by avian pathogenic Escherichia coli (APEC) is known to be aggravated by preceding infections with infectious bronchitis virus (IBV), Newcastle disease virus (NDV) and avian metapneumovirus (aMPV). The mechanism behind these virus-induced predispositions for secondary bacterial infections is poorly understood. Here we set out to investigate the immunopathogenesis of enhanced respiratory colibacillosis after preceding infections with these three viruses. Broilers were inoculated intratracheally with APEC six days after oculonasal and intratracheal inoculation with IBV, NDV, aMPV or buffered saline. After euthanasia at 1 and 8 days post infection (dpi) with APEC, birds were macroscopically examined and tissue samples were taken from the trachea, lungs and air sacs. In none of the groups differences in body weight were observed during the course of infection. Macroscopic lesion scoring revealed most severe tissue changes after NDV-APEC and IBV-APEC infection. Histologically, persistent tracheitis was detected in all virus-APEC groups, but not after APEC-only infection. In the lungs, mostly APEC-associated transient pneumonia was observed. Severe and persistent airsacculitis was present after NDV-APEC and IBV-APEC infection. Bacterial antigen was detected by immunohistochemistry only at 1 dpi APEC, predominantly in NDV-APEC- and IBV-APEC-infected lungs. Higher numbers of CD4+ and CD8+ lymphocytes persisted over time in NDV-APEC- and IBV-APEC-infected tracheas, as did CD4+ lymphocytes in NBV-APEC- and IBV-APEC-infected air sacs. KUL01+ cells, which include monocytes and macrophages, and TCRγδ+ lymphocytes were observed mostly in lung tissue in all infected groups with transient higher numbers of KUL01+ cells over time and higher numbers of TCRγδ+ lymphocytes mainly at 8 dpi. qPCR analysis revealed mostly trends of transient higher levels of IL-6 and IFNγ mRNA in lung tissue after IBV-APEC and also NDV-APEC infection and persistent higher levels of IL-6 mRNA after aMPV-APEC infection. In spleens, transient higher levels of IL-17 mRNA and more persistent higher levels of IL-6 mRNA were observed after all co-infections. No changes in IL-10 mRNA expression were seen. These results demonstrate a major impact of dual infections with respiratory viruses and APEC, compared to a single infection with APEC, on the chicken respiratory tract and suggest that immunopathogenesis contributes to lesion persistence.

Kinetics of the Cellular and Transcriptomic Response to Eimeria maxima in Relatively Resistant and Susceptible Chicken Lines

Eimeria maxima is a common cause of coccidiosis in chickens, a disease that has a huge economic impact on poultry production. Knowledge of immunity to E. maxima and the specific mechanisms that contribute to differing levels of resistance observed between chicken breeds and between congenic lines derived from a single breed of chickens is required. This study aimed to define differences in the kinetics of the immune response of two inbred lines of White Leghorn chickens that exhibit differential resistance (line C.B12) or susceptibility (line 15I) to infection by E. maxima. Line C.B12 and 15I chickens were infected with E. maxima and transcriptome analysis of jejunal tissue was performed at 2, 4, 6 and 8 days post-infection (dpi). RNA-Seq analysis revealed differences in the rapidity and magnitude of cytokine transcription responses post-infection between the two lines. In particular, IFN-γ and IL-10 transcript expression increased in the jejunum earlier in line C.B12 (at 4 dpi) compared to line 15I (at 6 dpi). Line C.B12 chickens exhibited increases of IFNG and IL10 mRNA in the jejunum at 4 dpi, whereas in line 15I transcription was delayed but increased to a greater extent. RT-qPCR and ELISAs confirmed the results of the transcriptomic study. Higher serum IL-10 correlated strongly with higher E. maxima replication in line 15I compared to line C.B12 chickens. Overall, the findings suggest early induction of the IFN-γ and IL-10 responses, as well as immune-related genes including IL21 at 4 dpi identified by RNA-Seq, may be key to resistance to E. maxima.

Characterization of Conventional Dendritic Cells and Macrophages in the Spleen Using the CSF1R-Reporter Transgenic Chickens

The spleen is a major site for the immunological responses to blood-borne antigens that is coordinated by cells of the mononuclear phagocyte system (MPS). The chicken spleen is populated with a number of different macrophages while the presence of conventional dendritic cells (cDC) has been described. However, a detailed characterization of the phenotype and function of different macrophage subsets and cDC in the chicken spleen is limited. Using the CSF1R-reporter transgenic chickens (CSF1R-tg), in which cells of the MPS express a transgene under the control elements of the chicken CSF1R, we carried out an in-depth characterization of these cells in the spleen. Immunohistological analysis demonstrated differential expression of MRC1L-B by periarteriolar lymphoid sheaths (PALS)-associated CSF1R-tg+ cells. In the chicken's equivalent of the mammalian marginal zone, the peri-ellipsoid white-pulp (PWP), we identified high expression of putative CD11c by ellipsoid-associated cells compared to ellipsoid-associated macrophages. In addition, we identified a novel ellipsoid macrophage subset that expressed MHCII, CD11c, MRC1L-B, and CSF1R but not the CSF1R-tg. In flow cytometric analysis, diverse expression of the CSF1R-tg and MHCII was observed leading to the categorization of CSF1R-tg cells into CSF1R-tgdim MHCIIinter−hi, CSF1R-tghi MHCIIhi, and CSF1R-tghi MHCIIinter subpopulations. Low levels of CD80, CD40, MHCI, CD44, and Ch74.2 were expressed by the CSF1R-tghi MHCIIinter cells. Functionally, in vivo fluorescent bead uptake was significantly higher in the CSF1R-tghi MHCIIhi MRC1L-B+ cells compared to the CSF1R-tgdim and CSF1R-tghi MHCIIinter MRC1L-B+ subpopulations while LPS enhanced phagocytosis by the CSF1R-tghi MHCIIinter subpopulation. The analysis of bead localization in the spleen suggests the presence of ellipsoid-associated macrophage subsets. In addition, we demonstrated the functionality of ex vivo derived CSF1R-tg+ MRC1L-Bneg cDC. Finally, RNA-seq analysis of the CSF1R-tg subpopulations demonstrated that separating the CSF1R-tghi subpopulation into CD11chi and CD11cdim cells enriched for cDC and macrophage lineages, respectively, while the CSF1R-tghi MHCIIinter subpopulation was enriched for red pulp macrophages. However, our analysis could not define the cell lineage of the heterogeneous CSF1R-tgdim subpopulation. This detailed overview of the MPS in the chicken spleen will contribute to future research on their role in antigen uptake and presentation.

Clinical and Biological Implications of Cancer Stem Cells in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a malignant tumor with poor prognosis, and is one of the leading causes of cancer-related deaths worldwide. Recently, the development of therapeutic drugs via novel mechanisms of action, involving molecular-targeted drugs and immune checkpoint inhibitors, has progressed in the field of HCC. However, the recurrence rate remains high, and further improvement of the prognosis of patients with HCC is urgently needed. Cancer stem cells (CSCs) are a promising target for further development of novel anti-cancer drugs because they are reportedly involved in tumor initiation, maintenance, recurrence, and resistance to conventional therapies. Although several studies have already been conducted, the functions and roles of CSCs in the development and progression of tumors remain to be elucidated. In this review article, we will clarify the fundamental knowledge of CSCs necessary for the understanding of CSCs and will outline so-far identified markers specific to liver CSCs and the pathological and therapeutic implications of CSCs in HCC.

Immune responses upon experimental Erysipelothrix rhusiopathiae infection of naïve and vaccinated chickens

Erysipelas, a disease caused by Erysipelothrix rhusiopathiae (ER), is an increasing problem in laying hens housed in cage-free systems. This study aimed to monitor immune responses during ER infection of naïve chickens and chickens vaccinated intra muscularly with a commercial inactivated ER vaccine. Chickens were infected intra muscularly with ER at 30 days of age and blood leukocyte counts, serum levels of mannose binding lectin (MBL) and ER-specific IgY were monitored until the experiment was terminated at day 15 after infection. ER was detected in blood from more chickens and at higher bacterial counts in the naïve group (day 1: 1 of 7 chickens; day 3: 6 of 6 chickens) than in the vaccinated group (day 1: 0 of 7 chickens; day 3: 1 of 6 chickens). During the acute phase of infection transient increases in circulating heterophil numbers and serum MBL levels were detected in all ER infected chickens but these responses were prolonged in chickens from the naïve group compared to vaccinated chickens. Before infection IgY titers to ER in vaccinated chickens did not differ significantly from those of naïve chickens but vaccinated chickens showed significantly increased IgY titers to ER earlier after infection compared to chickens in the naïve group. In conclusion, the ER infection elicited prompt acute innate responses in all chickens. Vaccinated chickens did not have high IgY titers to ER prior to infection but did however show lower levels of bacteraemia and their acute immune responses were of shorter duration.

A method to differentiate chicken monocytes into macrophages with proinflammatory properties

Macrophages are part of the first line of defense against invading pathogens. In mammals, the in vitro culture of macrophages from blood monocytes or bone marrow cells is well established, including culturing conditions to differentiate them towards M1 or M2-like macrophages. In chicken, monocyte-derived macrophages have been used in several studies, but there is no uniform protocol or actual characterization of these cells. Therefore, to generate proinflammatory M1-like macrophages, in this study blood monocytes were differentiated using GM-CSF for 4 days and characterized based on cell morphology, surface marker expression and cytokine expression response to TLRs stimulation at each (daily) time point. Cell morphology showed that one-day-cultured cells contained a mixture of cell populations, while the homogenous population of cells on day 3 and day 4 were flat and had a 'fried-egg' like shape, similar to human M1 macrophages. In addition, cell surface marker staining showed that 3 and 4- days-cultured cells expressed a high level of MRC1L-B (KUL01) and MHC-II. Furthermore, LPS stimulation of the cultured cells induced gene expression of the proinflammatory cytokines IL-1β, IL-6 and IL-8 after 3 days of culture. Finally, it was shown that day 3 macrophages were able to phagocytose avian pathogenic E. coli (APEC) and respond by nitric oxide production. Overall, our systematic characterization of the monocyte derived cells from blood showed that a 3-days culture was optimal to obtain pro-inflammatory M1 like macrophages, increasing our knowledge about chicken macrophage polarization and providing useful information for studies on chicken macrophage phenotypes.

Characterization of splenic MRC1hiMHCIIlo and MRC1loMHCIIhi cells from the monocyte/macrophage lineage of White Leghorn chickens

Monocytes/macrophages, which are found in a variety of organs, maintain tissue homeostasis at a steady state and act as the first line of defence during pathogen-induced inflammation in the host. Most monocyte/macrophage lineage studies in chickens have been largely performed using cell lines, while few studies using primary cells have been conducted. In the present study, the phenotypic and functional characteristics of splenic monocyte/macrophage lineage cells during steady state and inflammatory conditions were examined. Splenic monocyte/macrophage lineage cells could be identified as MRC1^loMHCII^hi and MRC1^hiMHCII^lo cells based on their surface expression of MRC1 and MHCII. In the steady state, MRC1^loMHCII^hi cells were more frequently found among MRC1⁺ cells. MRC1^loMHCII^hi cells expressed a higher number of antigen-presenting molecules (MHCII, MHCI, and CD80) than MRC1^hiMHCII^lo cells. In contrast, MRC1^hiMHCII^lo cells showed better phagocytic and CCR5-dependent migratory properties than MRC1^loMHCII^hi cells. Furthermore, MRC1^hiMHCII^lo cells infiltrated the spleen in vivo and then became MRC1^loMHCII^hi cells. During lipopolysaccharide (LPS)-induced inflammatory conditions that were produced via intraperitoneal (i.p.) injection, the proportion and absolute number of MRC1^hiMHCII^lo cells were increased in the spleen. Uniquely, inflammation induced the downregulation of MHCII expression in MRC1^hiMHCII^lo cells. The major source of inflammatory cytokines (IL-1β, IL-6, and IL-12) was MRC1^loMHCII^hi cells. Furthermore, MRC1^hiMHCII^lo cells showed greater bactericidal activity than MRC1^loMHCII^hi cells during LPS-induced inflammation. Collectively, these results suggest that two subsets of monocyte/macrophage lineage cells exist in the chicken spleen that have functional differences.

Differential Effects of Drinking Water Quality on Phagocyte Responses of Broiler Chickens Against Fungal and Bacterial Challenges

Combinatorial effects of xenobiotics in water on health may occur even at levels within current acceptable guidelines for individual chemicals. Herein, we took advantage of the sensitivity of the immune system and an avian animal model to examine the impact of xenobiotic mixtures on animal health. Water was derived from an underground well in Alberta, Canada and met guidelines for consumption, but contained a number of contaminants. Changes to chicken immunity were evaluated following acute (7d) exposure to contaminated water under basal and immune challenged conditions. An increase in resident macrophages and a decrease in CD8+ lymphocytes were identified in the abdominal cavity, which served as a relevant site where immune leukocytes could be examined. Subsequent intra-abdominal immune stimulation detected differential in vivo acute inflammatory responses to fungal and bacterial challenges. Leukocyte recruitment into the challenge site and activation of phagocyte antimicrobial responses were affected. These functional responses paralleled molecular changes in the expression for pro-inflammatory and regulatory genes. In all, this study primarily highlights dysregulation of phagocyte responses following acute (7d) exposure of poultry to contaminated water. Given that production food animals hold a unique position at the interface of animal, environmental and human health, this emphasizes the need to consider the impact of xenobiotic mixtures in our assessments of water quality.

Analysis of the Progeny of Sibling Matings Reveals Regulatory Variation Impacting the Transcriptome of Immune Cells in Commercial Chickens

There is increasing recognition that the underlying genetic variation contributing to complex traits influences transcriptional regulation and can be detected at a population level as expression quantitative trait loci. At the level of an individual, allelic variation in transcriptional regulation of individual genes can be detected by measuring allele-specific expression in RNAseq data. We reasoned that extreme variants in gene expression could be identified by analysis of inbred progeny with shared grandparents. Commercial chickens have been intensively selected for production traits. Selection is associated with large blocks of linkage disequilibrium with considerable potential for co-selection of closely linked "hitch-hiker alleles" affecting traits unrelated to the feature being selected, such as immune function, with potential impact on the productivity and welfare of the animals. To test this hypothesis that there is extreme allelic variation in immune-associated genes we sequenced a founder population of commercial broiler and layer birds. These birds clearly segregated genetically based upon breed type. Each genome contained numerous candidate null mutations, protein-coding variants predicted to be deleterious and extensive non-coding polymorphism. We mated selected broiler-layer pairs then generated cohorts of F2 birds by sibling mating of the F1 generation. Despite the predicted prevalence of deleterious coding variation in the genomic sequence of the founders, clear detrimental impacts of inbreeding on survival and post-hatch development were detected in only one F2 sibship of 15. There was no effect on circulating leukocyte populations in hatchlings. In selected F2 sibships we performed RNAseq analysis of the spleen and isolated bone marrow-derived macrophages (with and without lipopolysaccharide stimulation). The results confirm the predicted emergence of very large differences in expression of individual genes and sets of genes. Network analysis of the results identified clusters of co-expressed genes that vary between individuals and suggested the existence of trans-acting variation in the expression in macrophages of the interferon response factor family that distinguishes the parental broiler and layer birds and influences the global response to lipopolysaccharide. This study shows that the impact of inbreeding on immune cell gene expression can be substantial at the transcriptional level, and potentially opens a route to accelerate selection using specific alleles known to be associated with desirable expression levels.

Identification and tissue-expression profiling of novel chicken c-type lectin-like domain containing proteins as potential targets for carbohydrate-based vaccine strategies

C-type lectin-like domain containing proteins (CTLDcps) mainly bind carbohydrate-based ligands, but also other ligands. CTLDcps are involved in several biological processes including cell adhesion, cell-cell interactions, and pathogen recognition. Pathogen recognition by myeloid cells, e.g. dendritic cells (DCs), can be facilitated through cell surface expressed CTLDcps. Cell surface expressed CTLDcps have been exploited in vaccine designs for specific targeting of human and mouse DCs using antibodies. In recent years, however, DC targeting using carbohydrate-based vaccines has gained interest due to low production cost, limited immunogenicity, and possibility of multivalent adjustment. In chicken, however, only a few CTLDcps have been identified. Identifying and annotating additional chicken CTLDcps (chCTLDcps) is needed to exploit carbohydrate-mediated DC targeting in chicken. Therefore, we searched the chicken GRCg6a assembly for novel chCTLDcps. We identified 28 chCTLDcps of which 10 had previously been described and also experimentally validated. RNA-seq and RT-qPCR confirmed mRNA expression of the remaining 18 identified chCTLDcps. A group of highly related chCTLDcps, moreover, was shown to be avian-specific and comprise novel members mapped to the proposed chicken natural killer gene complex. Two chCTLDcps, chCLEC17AL-A and chCLEC17AL-B, were found to share a recent common ancestor with CLEC17A. Putative mannose or fucose-binding sequence motifs, EPN and WND, were found in the CTLD of chCLEC17AL-A. Both contained intracellular internalisation and signalling sequence motifs. In conclusion, several chCTLDcps were identified and their expression confirmed. Both chCLEC17AL-A and -B showed promise as potential targets in carbohydrate-based chicken vaccine strategies. Determination of DC-specific expression of chCLEC17AL-A and -B, thus, might prove useful in chicken vaccinology.

Identification of CD206 as a potential biomarker of cancer stem-like cells and therapeutic agent in liver cancer

The mannose receptor (CD206) functions in endocytosis and phagocytosis, and plays an important role in immune homeostasis. Tumor-associated macrophages express high level of CD206 and are thought to contribute to cancer progression through tumor immunosuppression, metastasis and angiogenesis. However, the significance of CD206 in the pathology of liver cancer has not been investigated. The present study evaluated the clinical significance of CD206 in the progression and prognosis of liver cancer in pathological tissues from 327 patients. Increased CD206 expression was observed in liver cancer samples compared with healthy adjacent liver tissue (42.8 vs. 62.4%; P<0.05). CD206 expression was significantly associated with tumor size (P=0.009) and metastasis (P=0.041). The recurrence free survival rate of patients with CD206-positive liver cancer was significantly decreased compared with patients with CD206-negative liver cancer (P=0.003). A Cox regression model revealed that liver cancer survival was independently associated with tumor size, metastasis and α-fetoprotein value. The results further revealed that CD206 expression in cancer stem cell (CSC)-like cells was comparable to other internationally recognized biomarkers. Additionally, when CD206 expression was silenced in the liver cancer cell lines HepG2 and PLC/PRF/5 using a short hairpin RNA approach, migration and invasion of the cells significantly decreased compared with controls (P<0.01). CD206 expression in liver cancer significantly influences distant metastasis and spread, resulting in poor patient prognosis. Furthermore, CD206 may be a potential biomarker in CSC-like cells to predict the occurrence of liver cancer.

Avian coronavirus infection induces mannose-binding lectin production in dendritic cell precursors of chicken lymphoid organs

The aim of this immunocytochemical study was to compare mannose-binding lectin (MBL) production induced by avian coronavirus in the spleen and caecal tonsil (CT). One-day-old specific-pathogen-free (SPF) chickens were experimentally infected with six QX field isolates and the H120 vaccine strain. In the negative control birds, the spleen was MBL negative, while the CT showed scattered MBL-positive cells in close proximity and within the surface epithelium and germinal centre (GC)-like cell clusters. MBL was detectable in the ellipsoid-associated cells (EACs) and cell clusters in the periarterial lymphoid sheath (PALS) by 7 days post infection (dpi). In both organs, the MBL-positive cells occupy antigen-exposed areas, indicating that GC formation depends on resident precursors of dendritic cells. The majority of MBL-positive EACs express the CD83 antigen, providing evidence that coronavirus infection facilitated the maturation of dendritic cell precursors. Surprisingly, co-localisation of MBL and CD83 was not detectable in the CT. In the spleen (associated with circulation), the EACs producing MBL and expressing CD83 are a common precursor of both follicular (FDC) and interdigitating dendritic cells (IDC). In the CT (gut-associated lymphoid tissue, GALT) the precursors of FDC and IDC are MBL-producing cells and CD83-positive cells, respectively. In the CT the two separate precursors of lymphoid dendritic cells provide some 'autonomy' for the GALT.

Current insights into functions of phospholipase A2 receptor in normal and cancer cells: More questions than answers

Lipid signaling network was proposed as a potential target for cancer prevention and treatment. Several recent studies revealed that phospholipid metabolising enzyme, phospholipase A2 (PLA₂), is a critical regulator of cancer accelerating pathologies and apoptosis in several types of cancers. In addition to functioning as an enzyme, PLA₂ can activate a phospholipase A2 receptor (PLA2R1) in plasma membrane. While the list of PLA₂ targets extends to glucose homeostasis, intracellular energy balance, adipocyte development, and hepatic lipogenesis, the PLA2R1 downstream effectors are few and scarcely investigated. Among the most addressed PLA2R1 effects are regulation of pro-inflammatory signaling, autoimmunity, apoptosis, and senescence. Localized in glomeruli podocytes, the receptor can be identified by circulating anti-PLA2R1 autoantibodies leading to development of membranous nephropathy, a strong autoimmune inflammatory cascade. PLA2R1 was shown to induce activation of Janus-kinase 2 (JAK2) and estrogen-related receptor α (ERRα)-controlled mitochondrial proteins, as well as increasing the accumulation of reactive oxygen species, thus leading to apoptosis and senescence. These findings indicate the potential role of PLA2R1 as tumor suppressor. Epigenetic investigations addressed the role of DNA methylation, histone modifications, and specific microRNAs in the regulation of PLA2R1 expression. However, involvement of PLA2R1 in suppression of malignant growth and metastasis remains controversial. In this review, we summarize the recent findings that highlight the role of PLA2R1 in the regulation of carcinogenesis-related intracellular signaling.

CD205-positive, Sepharose-induced peritoneal exudate cells: a new resource for DC research in the chicken

Dendritic cells (DC) are important antigen-presenting cells and are among the least characterized immune cells in the chicken. In order to obtain chicken DC, current protocols require isolation of bone marrow myeloid progenitor cells and induction of DC differentiation with supplemental cytokines or negative selection of splenic cell preparations. Chicken peritoneal exudate cells (PEC) have traditionally been a source of various immune cells for ex vivo studies, primarily to investigate heterophils and macrophages. In this study, we observe the presence of CD205⁺ PEC populations, a marker of DC, as an additional resource to isolate and study chicken primary DCs. A panel of monoclonal antibodies was developed against the chicken CD205 DC marker and used to isolate CD205⁺ DC from the PEC population using magnetic bead cell sorting. This study reports the development of new anti-CD205 monoclonal antibodies as a reagent for chicken DC research, as well as PEC as a potential source of CD205⁺ DC for ex vivo studies in the chicken.

Macrophages from Susceptible and Resistant Chicken Lines have Different Transcriptomes following Marek's Disease Virus Infection

Despite successful control by vaccination, Marek’s disease (MD) has continued evolving to greater virulence over recent years. To control MD, selection and breeding of MD-resistant chickens might be a suitable option. MHC-congenic inbred chicken lines, 6₁ and 7₂, are highly resistant and susceptible to MD, respectively, but the cellular and genetic basis for these phenotypes is unknown. Marek’s disease virus (MDV) infects macrophages, B-cells, and activated T-cells in vivo. This study investigates the cellular basis of resistance to MD in vitro with the hypothesis that resistance is determined by cells active during the innate immune response. Chicken bone marrow-derived macrophages from lines 6₁ and 7₂ were infected with MDV in vitro. Flow cytometry showed that a higher percentage of macrophages were infected in line 7₂ than in line 6₁. A transcriptomic study followed by in silico functional analysis of differentially expressed genes was then carried out between the two lines pre- and post-infection. Analysis supports the hypothesis that macrophages from susceptible and resistant chicken lines display a marked difference in their transcriptome following MDV infection. Resistance to infection, differential activation of biological pathways, and suppression of oncogenic potential are among host defense strategies identified in macrophages from resistant chickens.

Characterization of Subpopulations of Chicken Mononuclear Phagocytes That Express TIM4 and CSF1R

The phosphatidylserine receptor TIM4, encoded by TIMD4, mediates the phagocytic uptake of apoptotic cells. We applied anti-chicken TIM4 mAbs in combination with CSF1R reporter transgenes to dissect the function of TIM4 in the chick (Gallus gallus). During development in ovo, TIM4 was present on the large majority of macrophages, but expression became more heterogeneous posthatch. Blood monocytes expressed KUL01, class II MHC, and CSF1R-mApple uniformly. Around 50% of monocytes were positive for surface TIM4. They also expressed many other monocyte-specific transcripts at a higher level than TIM4^- monocytes. In liver, highly phagocytic TIM4^hi cells shared many transcripts with mammalian Kupffer cells and were associated with uptake of apoptotic cells. Although they expressed CSF1R mRNA, Kupffer cells did not express the CSF1R-mApple transgene, suggesting that additional CSF1R transcriptional regulatory elements are required by these cells. By contrast, CSF1R-mApple was detected in liver TIM4^lo and TIM4^- cells, which were not phagocytic and were more abundant than Kupffer cells. These cells expressed CSF1R alongside high levels of FLT3, MHCII, XCR1, and other markers associated with conventional dendritic cells in mice. In bursa, TIM4 was present on the cell surface of two populations. Like Kupffer cells, bursal TIM4^hi phagocytes coexpressed many receptors involved in apoptotic cell recognition. TIM4^lo cells appear to be a subpopulation of bursal B cells. In overview, TIM4 is associated with phagocytes that eliminate apoptotic cells in the chick. In the liver, TIM4 and CSF1R reporters distinguished Kupffer cells from an abundant population of dendritic cell-like cells.

CATH-2 and LL-37 increase mannose receptor expression, antigen presentation and the endocytic capacity of chicken mononuclear phagocytes

Cathelicidins display in vitro and in vivo immunomodulatory activities and are part of the innate immune system. Previously, we found that in ovo treatment with chicken cathelicidin CATH-2 partially protects young broilers against respiratory E. coli infection. To determine the cellular aspects of this protection, we investigated immunomodulatory effects of CATH-2 and the human cathelicidin LL-37 on primary chicken peripheral blood mononuclear cells (PBMCs). Treatment of chicken PBMCs with L-CATH-2, D-CATH-2 or LL-37 increased the percentage of mononuclear phagocytes, but decreased that of B cells. L-CATH-2, D-CATH-2 and LL-37 treatment of chicken PBMCs also enhanced the expression levels of mannose receptor MRC1 and antigen presentation markers MHCII, CD40 and CD86 on mononuclear phagocytes, indicating increased antigen presentation capacity. Concomitantly, L-CATH-2, D-CATH-2 and LL-37 neutralized LPS-induced cytokine production, while increasing the endocytic capacity. We conclude that L-CATH-2, D-CATH-2 and LL-37 can modulate the immune response of primary chicken immune cells by increasing mannose receptor expression, antigen presentation, endocytosis and neutralizing LPS-induced cytokine production and as a result augment activation of the adaptive immune system.

Differential protein expression in chicken macrophages and heterophils in vivo following infection with Salmonella Enteritidis

In this study we compared the proteomes of macrophages and heterophils isolated from the spleen 4 days after intravenous infection of chickens with Salmonella Enteritidis. Heterophils were characterized by expression of MMP9, MRP126, LECT2, CATHL1, CATHL2, CATHL3, LYG2, LYZ and RSFR. Macrophages specifically expressed receptor proteins, e.g. MRC1L, LRP1, LGALS1, LRPAP1 and a DMBT1L. Following infection, heterophils decreased ALB and FN1, and released MMP9 to enable their translocation to the site of infection. In addition, the endoplasmic reticulum proteins increased in heterophils which resulted in the release of granular proteins. Since transcription of genes encoding granular proteins did not decrease, these genes remained continuously transcribed and translated even after initial degranulation. Macrophages increased amounts of fatty acid elongation pathway proteins, lysosomal and phagosomal proteins. Macrophages were less responsive to acute infection than heterophils and an increase in proteins like CATHL1, CATHL2, RSFR, LECT2 and GAL1 in the absence of any change in their expression at RNA level could even be explained by capturing these proteins from the external environment into which these could have been released by heterophils.

Different breeds, different blood: Cytometric analysis of whole blood cellular composition in chicken breeds

While haematological variation is well known in birds, variation in avian breeds (distinct morphotypes of the same species) remains unexplored. Poultry breeds, in particular, may show interesting evolutionary patterns and economically-relevant physiological differences. We performed a comparative examination of blood cellular composition in five chicken (Gallus gallus domesticus) breeds: Araucana, Booted bantam, Czech, Minorca and Rosecomb bantam. In standard-environment-reared hens whole-blood flow cytometry revealed remarkable differences in most erythrocyte- and leukocyte-related parameters. We identified two extremes: Czech, a European breed, with a low heterophil/lymphocyte (H/L) ratio and high CD4⁺ levels, and Araucana, a South-American breed, with a high H/L ratio and high relative monocyte count. Such variation may reflect a combination of artificial and natural selection acting on health- and stress-related traits in domestic populations. Different breeds have evolved different immunological adaptations reflecting their original need to fight pathogens and physiological constraint resulting from dissimilar physiological trade-offs.

Marek's disease virus infection of phagocytes: a de novo in vitro infection model

Marek's disease virus (MDV) is an alphaherpesvirus that induces T-cell lymphomas in chickens. Natural infections in vivo are caused by the inhalation of infected poultry house dust and it is presumed that MDV infection is initiated in the macrophages from where the infection is passed to B cells and activated T cells. Virus can be detected in B and T cells and macrophages in vivo, and both B and T cells can be infected in vitro. However, attempts to infect macrophages in vitro have not been successful. The aim of this study was to develop a model for infecting phagocytes [macrophages and dendritic cells (DCs)] with MDV in vitro and to characterize the infected cells. Chicken bone marrow cells were cultured with chicken CSF-1 or chicken IL-4 and chicken CSF-2 for 4 days to produce macrophages and DCs, respectively, and then co-cultured with FACS-sorted chicken embryo fibroblasts (CEFs) infected with recombinant MDV expressing EGFP. Infected phagocytes were identified and sorted by FACS using EGFP expression and phagocyte-specific mAbs. Detection of MDV-specific transcripts of ICP4 (immediate early), pp38 (early), gB (late) and Meq by RT-PCR provided evidence for MDV replication in the infected phagocytes. Time-lapse confocal microscopy was also used to demonstrate MDV spread in these cells. Subsequent co-culture of infected macrophages with CEFs suggests that productive virus infection may occur in these cell types. This is the first report of in vitro infection of phagocytic cells by MDV.