Unique features and distribution of the chicken CD83+ cell

Differential gene expression reveals host factors for viral shedding variation in mallards (Anas platyrhynchos) infected with low-pathogenic avian influenza virus

Intraspecific variation in pathogen shedding impacts disease transmission dynamics; therefore, understanding the host factors associated with individual variation in pathogen shedding is key to controlling and preventing outbreaks. In this study, ileum and bursa of Fabricius tissues of wild-bred mallards (Anas platyrhynchos) infected with low-pathogenic avian influenza (LPAIV) were evaluated at various post-infection time points to determine genetic host factors associated with intraspecific variation in viral shedding. By analysing transcriptome sequencing data (RNA-seq), we found that LPAIV-infected wild-bred mallards do not exhibit differential gene expression compared to uninfected birds, but that gene expression was associated with cloacal viral shedding quantity early in the infection. In both tissues, immune gene expression was higher in high/moderate shedding birds compared to low shedding birds, and significant positive relationships with viral shedding were observed. In the ileum, expression for host genes involved in viral cell entry was lower in low shedders compared to moderate shedders at 1 day post-infection (DPI), and expression for host genes promoting viral replication was higher in high shedders compared to low shedders at 2 DPI. Our findings indicate that viral shedding is a key factor for gene expression differences in LPAIV-infected wild-bred mallards, and the genes identified in this study could be important for understanding the molecular mechanisms driving intraspecific variation in pathogen shedding.

TLR2 and TLR4 molecules and antigen-presenting cell compositions in cecal tonsils of broiler chicks (Gallus gallus domesticus) in the first two weeks of the post-hatch period

Chickens do not have lymph nodes. Gut-associated lymphoid tissue is the major immunological organization for the digestive system. Cecal tonsils are an important part of this organization. This study is a descriptive and experimental study that was conducted to determine the histological development of the cecal tonsils and the distribution of Toll-like receptor (TLR) 2, TLR4 and antigen-presenting cells during the first 2 weeks of the chick's life. The tissue sections were stained using Crossmon's triple technique, Gordon and Sweet's silver impregnation, and streptavidin-biotin-peroxidase complex methods. The classical tonsil framework with fossa and tonsillar units were observed in 4 days cecal tissue. The web of reticular fibres forming the stroma of the tissue had the impression that the lymphoid cells filling in time. The development of cecal tonsil was completed histologically on the day 10 and following day 14 samples. Regardless of the antigenic stimulation, TLR2, TLR4 and CD83, major histocompatibility complex (MHC) class II molecules are present in proximal cecal tissue. However, CD83-positive dendritic cells in the germinal centre were first distinguished on day 7. Furthermore, the high antigen presentation capacity of the cecum with an intense MHC class II molecule expression was determined. Histological and immunohistochemical findings in this study revealed that both innate and adaptive cecal defence mechanisms were in the learning period during the first 2 weeks. The learning period of innate immunity may require more detailed research. However, the results obtained in this study will be taken into consideration in the vaccination programmes in chicks.

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.

Selectively targeting haemagglutinin antigen to chicken CD83 receptor induces faster and stronger immunity against avian influenza

The immunogenicity and protective efficacy of vaccines can be enhanced by the selective delivery of antigens to the antigen-presenting cells (APCs). In this study, H9N2 avian influenza virus haemagglutinin (HA) antigen, was targeted by fusing it to single-chain fragment variable (scFv) antibodies specific to CD83 receptor expressed on chicken APCs. We observed an increased level of IFNγ, IL6, IL1β, IL4, and CxCLi2 mRNA upon stimulation of chicken splenocytes ex vivo by CD83 scFv targeted H9HA. In addition, CD83 scFv targeted H9HA induced higher serum haemagglutinin inhibition activity and virus neutralising antibodies compared to untargeted H9HA, with induction of antibodies as early as day 6 post primary vaccination. Furthermore, chickens vaccinated with CD83 scFv targeted H9HA showed reduced H9N2 challenge virus shedding compared to untargeted H9HA. These results suggest that targeting antigens to CD83 receptors could improve the efficacy of poultry vaccines.

Porcine soluble CD83 alleviates LPS-induced abortion in mice by promoting Th2 cytokine production, Treg cell generation and trophoblast invasion

CD83, either in its membrance-bound form (mCD83) or soluble form (sCD83), is an important immunomodulatory molecule in humans and mice. While mCD83 is immunostimulatory, sCD83 exhibits striking immunosuppressive activities, suggesting that sCD83 may be used to combat inflammatory diseases, such as rheumatoid arthritis, graft-versus-host disease and habitual abortion. Although many studies had shed lights on the role of CD83 in humans and mice, little is known about CD83 in other animals. Recently, we showed that porcine CD83 had similar biochemical characteristics and immunoregulatory functions as its human counterpart. However, whether porcine sCD83 (psCD83) is involved in maintaining the immunological tolerance at the maternal-fetal interface and thereby prevents embryo loss and abortion during pregnancy is unclear. In this study, we used LPS-induced animal model to analyze the effect of porcine sCD83 on the mouse abortion. Results showed that psCD83 could significantly alleviate LPS-induced abortion in mice, indicating that the psCD83 had the function of fetal protection. Mechanically, psCD83-mediated fetal protection was related to the promotion on Th2 cytokine production, Treg cell differentiation and trophoblast invasion. This study provides a molecular basis for the fetal protection of psCD83, as well as a potential target for the regulation of maternal-fetal interfacial immune tolerance.

The CD83 Molecule - An Important Immune Checkpoint

The CD83 molecule has been identified to be expressed on numerous activated immune cells, including B and T lymphocytes, monocytes, dendritic cells, microglia, and neutrophils. Both isoforms of CD83, the membrane-bound as well as its soluble form are topic of intensive research investigations. Several studies revealed that CD83 is not a typical co-stimulatory molecule, but rather plays a critical role in controlling and resolving immune responses. Moreover, CD83 is an essential factor during the differentiation of T and B lymphocytes, and the development and maintenance of tolerance. The identification of its interaction partners as well as signaling pathways have been an enigma for the last decades. Here, we report the latest data on the expression, structure, and the signaling partners of CD83. In addition, we review the regulatory functions of CD83, including its striking modulatory potential to maintain the balance between tolerance versus inflammation during homeostasis or pathologies. These immunomodulatory properties of CD83 emphasize its exceptional therapeutic potential, which has been documented in specific preclinical disease models.

Comprehensive analysis of miRNAs, lncRNAs, and mRNAs reveals potential players of sexually dimorphic and left-right asymmetry in chicken gonad during gonadal differentiation

Despite thousands of sex-biased genes being found in chickens, the genetic control of sexually dimorphic and left-right asymmetry during gonadal differentiation is not yet completely understood. This study aimed to identify microRNAs (miRNAs), long noncoding RNAs (lncRNAs), messenger RNAs (mRNAs), and signaling pathways during gonadal differentiation in chick embryos (day 6/stage 29). The left and right gonads were collected for RNA sequencing. Sex-biased, side-biased miRNAs, lncRNAs, mRNAs, and shared differentially expressed miRNAs (DEmiRNA)–differentially expressed mRNAs (DEmRNA)–differentially expressed lncRNAs (DElncRNA) interaction networks were performed. A total of 8 DEmiRNAs, 183 DElncRNAs, and 123 DEmRNAs were identified for the sex-biased genes, and 7 DEmiRNAs, 189 DElncRNAs, and 183 DEmRNAs for the side-biased genes. The results of quantitative real-time PCR were generally consistent with the RNA-sequencing results. The study suggested that miRNAs and lncRNAs regulation were novel gene-specific dosage compensation mechanism and they could contribute to left-right asymmetry of chicken, but sex-biased and side-biased miRNAs, lncRNAs, and mRNAs were independent of each other. The competing endogenous RNA (ceRNA) networks showed that 17 target pairs including miR-7b (CYP19A1, FSHR, GREB1, STK31, CORIN, and TDRD9), miR-211 (FSHR, GREB1, STK31, CORIN, and TDRD9), miR-204 (FSHR, GREB1, CORIN, and TDRD9), and miR-302b-5p (CYP19A1 and TDRD9) may play crucial roles in ovarian development. These analyses provide new clues to uncover molecular mechanisms and signaling networks of ovarian development.

Development of innate immunity in chicken embryos and newly hatched chicks: a disease control perspective

Newly hatched chickens are confronted by a wide array of pathogenic microbes because their adaptive immune defences have limited capabilities to control these pathogens. In such circumstances, and within this age group, innate responses provide a degree of protection. Moreover, as the adaptive immune system is relatively naïve to foreign antigens, synergy with innate defences is critical. This review presents knowledge on the ontogeny of innate immunity in chickens pre-hatch and early post-hatch and provides insights into possible interventions to modulate innate responses early in the life of the bird. As in other vertebrate species, the chicken innate immune system which include cellular mediators, cytokine and chemokine repertoires and molecules involved in antigen detection, develop early in life. Comparison of innate immune systems in newly hatched chickens and mature birds has revealed differences in magnitude and quality, but responses in younger chickens can be boosted using innate immune system modulators. Functional expression of pattern recognition receptors and several defence molecules by innate immune system cells of embryos and newly hatched chicks suggests that innate responses can be modulated at this stage of development to combat pathogens. Improved understanding of innate immune system ontogeny and functionality in chickens is critical for the implementation of sound and safe interventions to provide long-term protection against pathogens. Next-generation tools for studying genetic and epigenetic regulation of genes, functional metagenomics and gene knockouts can be used in the future to explore and dissect the contributions of signalling pathways of innate immunity and to devise more efficacious disease control strategies.

Membrane-bound and soluble porcine CD83 functions antithetically in T cell activation and dendritic cell differentiation in vitro

Emerging evidence suggests that CD83, a dendritic cells (DCs) maturation marker in humans and mice, may prossess immunomodulatory capacities. Although porcine CD83 shares ∼75% sequence homology with its human counterpart, whether it functions as an immunoregulatory molecule remains unknown. To investigate porcine CD83 function, we deleted it in porcine DCs by RNA intereference. Results show that membrane-bound CD83 (mCD83) promotes DC-mediated T cell proliferation and cytokine production, thus confirming its immunoregulatory capacity. Intriguingly, porcine soluble CD83 (sCD83) treatment instead led to inhibition of DC-mediated T cell activation. Moreover, porcine sCD83 also inhibited differentiation of prepheral blood mononuclear cells (PBMCs) into DCs. These results collectively indicate that in addition to being a DC maturation maker, both membrane bound and souble porcine CD83 serve as immunoregulatory molecules with opposite effects on DC-mediated T cell activation and DC differentiation.

Histological and immunohistochemical studies of the proximal caecum and caecal tonsils of quail (Coturnix coturnix japonica)

The proximal caecum in quails consists of lymphoid and non-lymphoid structures. The caecal tonsils in the proximal part of the caecum are units of gut-associated lymphoid tissue in poultry. This study aimed to examine the histological characteristics of the proximal caecum, as well as compositions of dendritic cells (DCs) and antigen-presenting cells (APCs) in the caecal tonsil of quails. Tissue sections were stained with Crossman's triple, periodic acid-Schiff, Gordon and Sweet's silver, Congo red and methyl green-pyronin dyes, as well as immunohistochemically by the streptavidin-biotin-peroxidase complex method. Caecal lymphoid tissue was located in the lamina propria and submucosa. Germinative centres were observed within the lymphoid tissue. Reticular fibres were mainly distributed in the border area of the germinal centre with only a few fibres scattered in the centre. Plasma cells were observed in the subepithelial region and germinal centres. Eosinophil granulocytes were prevalent in the lymphoid tissue. Additionally, CD83-immunoreactive DCs and MHC class II immunoreactive APCs were present in the subepithelial area and diffuse lymphoid tissue. While DCs were seen in the germinal centres of tonsillar units, APCs were rarely present in the germinal centres, but they were noticed around the germinal centres. In conclusion, the histological structure of the proximal caecum in quails and the distributions of some immunological cells in the caecal tonsils were revealed. Therefore, the defensive role of the caecal tonsils in the digestive system may be better understood, and comparative studies may be carried out.

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.

Porcine CD83 is a glycosylated dimeric protein existing naturally in membrane-bound and soluble forms

Human and mouse CD83 have been well characteized, however, the other mammalian CD83 genes have not been cloned and characterized. In this study, the porcine CD83 (pCD83) was cloned, expressed and characterized, and showed that the pCD83 gene has 81% and 74% homologies with humans and mice, respectively, which was identified to be glycosylated when expressed in eukaryotic cells, existing naturally in two forms: membrance-bound CD83 (mCD83) and soluble CD83 (sCD83), the latter was identified to be generated mainly from mCD83 by proteolytic shedding. The pCD83 was a dimmer mediated by intermolecular disulfide bond formed by the fifth cysteine in the exrtracellular domain. Functionally, the recombinant porcine sCD83 was preliminarily tested to have the ability to inhibit DC-mediated T cell activition. This study provided necessary fundation for further investigation on pCD83 functions.

Characterization of Chicken Splenic-Derived Dendritic Cells Following Vaccine and Very Virulent Strains of Infectious Bursal Disease Virus Infection

Studies have shown that infectious bursal disease virus (IBDV) infects lymphoid cells, mainly B cells and macrophages. This study was aimed to examine the involvement of chicken splenic-derived dendritic cells (ch-sDCs) in specific-pathogen-free chickens following inoculation with IBDV vaccine strain (D78) and a very virulent (vv) strain (UPM0081). Following IBDV infection, enriched activated ch-sDCs were collected by using the negative selection method and were examined based on morphology and immunophenotyping to confirm the isolation method for dendritic cells (DCs). The presence of IBDV on enriched activated ch-sDCs was analyzed based on the immunofluorescence antibody test (IFAT), flow cytometry, and quantitative real-time PCR (RT-qPCR) while the mRNAs of several cytokines were detected using RT-qPCR. The isolated ch-sDCs resembled typical DC morphologies found in mammals by having a veiled shape and they grew in clusters. Meanwhile, the expression of DC maturation markers, namely CD86 and MHCII, were increased at day 2 and day 3 following vvIBDV and vaccine strain inoculation, respectively, ranging from 10% to 40% compared to the control at 2.55% (P < 0.05). At day 3 postinfection, IBDV VP3 proteins colocalized with CD86 were readily detected via IFAT and flow cytometry in both vaccine and vvIBDV strains. In addition, enriched activated ch-sDCs were also detected as positive based on the VP4 gene by RT-qPCR; however, a higher viral load was detected on vvIBDV compared to the vaccine group. Infection with vaccine and vvIBDV strains induced the enriched activated ch-sDCs to produce proinflammatory cytokines and Th1-like cytokines from day 3 onward; however, the expressions were higher in the vvIBDV group (P < 0.05). These data collectively suggest that enriched activated ch-sDCs were permissive to IBDV infection and produced a strong inflammatory and Th1-like cytokine response following vvIBDV infection as compared to the vaccine strain.

Avian dendritic cells: Phenotype and ontogeny in lymphoid organs

Dendritic cells (DC) are critically important accessory cells in the innate and adaptive immune systems. Avian DCs were originally identified in primary and secondary lymphoid organs by their typical morphology, displaying long cell processes with cytoplasmic granules. Several subtypes are known. Bursal secretory dendritic cells (BSDC) are elongated cells which express vimentin intermediate filaments, MHC II molecules, macrophage colony-stimulating factor 1 receptor (CSF1R), and produce 74.3+ secretory granules. Avian follicular dendritic cells (FDC) highly resemble BSDC, express the CD83, 74.3 and CSF1R molecules, and present antigen in germinal centers. Thymic dendritic cells (TDC), which express 74.3 and CD83, are concentrated in thymic medulla while interdigitating DC are found in T cell-rich areas of secondary lymphoid organs. Avian Langerhans cells are a specialized 74.3-/MHC II+ cell population found in stratified squamous epithelium and are capable of differentiating into 74.3+ migratory DCs. During organogenesis hematopoietic precursors of DC colonize the developing lymphoid organ primordia prior to immigration of lymphoid precursor cells. This review summarizes our current understanding of the ontogeny, cytoarchitecture, and immunophenotype of avian DC, and offers an antibody panel for the in vitro and in vivo identification of these heterogeneous cell types.

The several elements of intestinal innate immune system at the beginning of the life of broiler chicks

Functional capacity of digestive system and intestinal adaptive immunity are immature at hatching of broiler chicks. Therefore, intestinal innate immunity after hatching is vital to young chicks. The purpose of this study was to investigate expression and tissue distributions of several elements of the innate immune system (i.e., TLR2, TLR4, CD83, and MHC class II expressing cells) in the intestine of one-day-old chicks. For this purpose, ileum and cecum were examined the under different conditions, which included the control and 1, 3, 6, 12, or 24 h after injection of lipopolysaccharide (LPS) and phosphate buffered saline. The findings indicated that regardless of the antigenic stimulation, Toll-like receptor (TLR) 2 and TLR4 expressing cells were present in the intestinal tissues of one-day-old chicks. We noticed that the intestinal segments have different TLR expression levels after LPS stimulation. Dendritic cells were identified, and they left the intestinal tissue after LPS treatment. MHC class II molecules were diffusely present in both the ileum and cecum. This study demonstrates that the intestinal tissue of one-day-old chicks has remarkable defensive material, including histological properties and several elements of the innate immune system. Microsc. Res. Tech. 79:604-614, 2016. © 2016 Wiley Periodicals, Inc.

Immunoreactivity and morphological changes of bursal follicles in chickens infected with vaccine or wild-type strains of the infectious bursal disease virus

Infectious bursal disease (IBD) is characterized by immunosuppression due to the depletion of lymphocytes in the atrophied bursa of Fabricius (BF). We have sometimes encountered contradictory findings: chickens infected with the vaccine IBD virus (IBDV) strain have sometimes exhibited a highly atrophied BF, but not immunosuppression. In this study, chickens administered vaccine or wild-type strains of IBDV were later vaccinated with the B1 strain of the Newcastle disease virus (NDV). Bursal changes were examined histologically with a focus on the bursal follicle. The immunoreactivity to NDV was also evaluated with the hemagglutination inhibition test. In gross examination, we observed a few chickens with a severely atrophied BF in vaccine strain-administered groups (vaccine groups), and the level of severity was the same as that in the wild-type strain-administered group (wild-type group). However, these chickens retained humoral antibody responses to NDV and were revealed to possess a higher number of bursal follicles than those of the wild-type group. These results indicated that macroscopic evaluation dose not accurately reflect the immunoreactivity and degree of bursal damage in IBDV-administered chickens. We also found non-immunosuppressed chickens in the wild-type group. These non-immunosuppressed chickens retained a significantly higher number of normal follicles and total follicles according to our statistical analysis. Furthermore, a high correlation coefficient between the NDV-HI titer and the number of normal follicles was found in the wild-type group. These results implied that the retained number of normal follicles is important for the immunoreactivity of chickens infected with IBDV.

Existence of conventional dendritic cells in Gallus gallus revealed by comparative gene expression profiling

The existence of conventional dendritic cells (cDCs) has not yet been demonstrated outside mammals. In this article, we identified bona fide cDCs in chicken spleen. Comparative profiling of global and of immune response gene expression, morphology, and T cell activation properties show that cDCs and macrophages (MPs) exist as distinct mononuclear phagocytes in the chicken, resembling their human and mouse cell counterparts. With computational analysis, core gene expression signatures for cDCs, MPs, and T and B cells across the chicken, human, and mouse were established, which will facilitate the identification of these subsets in other vertebrates. Overall, this study, by extending the newly uncovered cDC and MP paradigm to the chicken, suggests that these two phagocyte lineages were already in place in the common ancestor of reptiles (including birds) and mammals in evolution. It opens avenues for the design of new vaccines and nutraceuticals that are mandatory for the sustained supply of poultry products in the expanding human population.

Retrospection to discovery of bursal function and recognition of avian dendritic cells; past and present

In 1954 the discovery of bursal function was one of the major contributions to the formation of the T and B cell concept of immunology. In 1978 the avian dendritic cells; bursal secretory dendritic cell (BSDC) and follicular dendritic cell (FDC) in the cecal tonsil were recognized. In 1982 the interdigitating dendritic cell was described in the periarteriolar lymphatic sheath (PALS) of the spleen. This paper is a retrospection of the stories of the discovery of bursal function and recognition of avian dendritic cells and includes the markers which can be used for monitoring and characterizing avian dendritic cells.

Potential directions for chicken immunology research

The importance of poultry, particularly chicken, as a food source continues to increase globally. Moreover, zoonotic infectious diseases such as avian influenza virus not only continue to impact poultry production, but also pose an increasing threat to public health. This review discusses the importance of poultry in both agricultural and public health arenas. Recent developments in avian immunology are described, with an emphasis on host-pathogen interactions and noting differences from mammalian systems. Next generation technologies including functional genomics and targeted gene disruption (e.g. zinc finger nucleases and meganucleases) are discussed as new approaches for not only understanding immune responses in poultry, but also as novel disease intervention strategies.

Expression of chicken DEC205 reflects the unique structure and function of the avian immune system

The generation of appropriate adaptive immune responses relies critically on dendritic cells, about which relatively little is known in chickens, a vital livestock species, in comparison with man and mouse. We cloned and sequenced chicken DEC205 cDNA and used this knowledge to produce quantitative PCR assays and monoclonal antibodies to study expression of DEC205 as well as CD83. The gene structure of DEC205 was identical to those of other species. Transcripts of both genes were found at higher levels in lymphoid tissues and the expression of DEC205 in normal birds had a characteristic distribution in the primary lymphoid organs. In spleen, DEC205 was seen on cells ideally located to trap antigen. In thymus it was found on cells thought to participate in the education of T cells, and in the bursa on cells that may be involved in presentation of antigen to B cells and regulation of B cell migration. The expression of DEC205 on cells other than antigen presenting cells (APC) is also described. Isolated splenocytes strongly expressing DEC205 but not the KUL01 antigen have morphology similar to mammalian dendritic cells and the distinct expression of DEC205 within the avian-specific Bursa of Fabricius alludes to a unique function in this organ of B cell diversification.

A toll-like receptor 3 ligand enhances protective effects of vaccination against Marek's disease virus and hinders tumor development in chickens

Marek's disease (MD) is caused by Marek's disease virus (MDV). Various vaccines including herpesvirus of turkeys (HVT) have been used to control this disease. However, HVT is not able to completely protect against very virulent strains of MDV. The objective of this study was to determine whether a vaccination protocol consisting of HVT and a Toll-like receptor (TLR) ligand could enhance protective efficacy of vaccination against MD. Hence, chickens were immunized with HVT and subsequently treated with synthetic double-stranded RNA polyriboinosinic polyribocytidylic [poly(I:C)], a TLR3 ligand, before or after being infected with a very virulent strain of MDV. Among the groups that were HVT-vaccinated and challenged with MDV, the lowest incidence of tumors was observed in the group that received poly(I:C) before and after MDV infection. Moreover, the groups that received a single poly(I:C) treatment either before or after MDV infection were better protected against MD tumors compared to the group that only received HVT. No association was observed between viral load, as determined by MDV genome copy number, and the reduction in tumor formation. Overall, the results presented here indicate that poly(I:C) treatment, especially when it is administered prior to and after HVT vaccination, enhances the efficacy of HVT vaccine and improves protection against MDV.

Development and characterization of mouse monoclonal antibodies reactive with chicken CD83

This study was carried out to develop and characterize mouse monoclonal antibodies (mAbs) against chicken CD83 (chCD83), a membrane-bound glycoprotein belonging to the immunoglobulin superfamily that is primarily expressed on mature dendritic cells (DCs). A recombinant chCD83/IgG4 fusion protein containing the extracellular region of chCD83 was expressed in Chinese Hamster Ovary (CHO) cells and isolated from the spent cell culture medium by protein G affinity chromatography. The extracellular region of the chCD83 protein was purified and used to immunize mice. A cell fusion was performed, from which 342 hybridomas were screened for mAbs to chCD83. Two mAbs, chCD83-159 and chCD83-227, stained the greatest percentage of chCD83-transfected CHO cells and were selected for further characterization. By flow cytometry, both mAbs reacted with a chicken macrophage cell line, HD11. Both mAbs also recognized a single 53 kDa protein on Western blots of lysates from lipopolysaccharide-stimulated spleen mononuclear cells or unstimulated HD11 cells. Immunostaining of chicken secondary lymphoid organs identified chCD83(+) cells with morphologic and subtissue localization properties comparable to mammalian DCs. In vitro stimulation of spleen mononuclear cells with concanavalin A (Con A) decreased the percentage of chCD83(+) cells compared with cells treated with medium alone. Interestingly, spleen cells treated with Con A in the presence of chCD83-227 mAb exhibited decreased percentage of MHCII(+) cells compared with cells treated with an isotype-matched negative control mAb. These chCD83 mAbs may be useful for future investigations of chicken immune cell maturation and mechanisms of action.

Antigen presenting cells in a non-mammalian model system, the chicken

The chicken has a different repertoire of tissues, cells and genes of the immune response compared to mammals, yet generally survives infection with viral, bacterial, protozoal and fungal pathogens, and also worms and ectoparasites, just like mammals. Poultry are also probably the most heavily vaccinated group of farmed animals. Antigen presentation to the adaptive immune response therefore obviously normally occurs efficiently in birds. Although comparatively much is known about macrophages and B cells in the chicken, there is as yet little work on the other, professional, antigen-presenting cells, the dendritic cells (DC). Birds also have at least two other sets of phagocytic cells, heterophils and thrombocytes, which may also have the ability to present antigen. Here we review the current state of knowledge about antigen presenting cells in the chicken, concentrating mainly on recent advances in our knowledge of DC.

Advances in avian immunology--prospects for disease control: a review

In order to develop novel solutions to avian disease problems, including novel vaccines and/or vaccine adjuvants, and the identification of disease resistance genes which can feed into conventional breeding programmes, it is necessary to gain a more thorough understanding of the avian immune response and how pathogens can subvert that response. Birds occupy the same habitats as mammals, have similar ranges of longevity and body mass, and face similar pathogen challenges, yet birds have a different repertoire of organs, cells, molecules and genes of the immune system compared to mammals. This review summarises the current state of knowledge of the chicken's immune response, highlighting differences in the bird compared to mammals, and discusses how the availability of the chicken genome sequence and the associated postgenomics technologies are contributing to theses studies and also to the development of novel intervention strategies againts avian and zoonotic disease.

Prospects for understanding immune-endocrine interactions in the chicken

Despite occupying the same habitats as mammals, having similar ranges of body mass and longevity, and facing similar pathogen challenges, birds have a different repertoire of organs, cells, molecules and genes of the immune system when compared to mammals. In other words, birds are not "mice with feathers", at least not in terms of their immune systems. Here we discuss differences between immune gene repertoires of birds and mammals, particularly those known to play a role in immune-endocrine interactions in mammals. If we are to begin to understand immune-endocrine interactions in the chicken, we need to understand these repertoires and also the biological function of the proteins encoded by these genes. We also discuss developments in our ability to understand the function of dendritic cells in the chicken; the function of these professional antigen-presenting cells is affected by stress in mammals. With regard to the endocrine system, we describe relevant chicken pituitary-adrenal hormones, and review recent findings on the expression of their receptors, as these receptors play a crucial role in modulating immune-endocrine interactions. Finally, we review the (albeit limited) work that has been carried out to understand immune-endocrine interactions in the chicken in the post-genome era.

Generation and characterization of chicken bone marrow-derived dendritic cells

Dendritic cells (DCs) are bone marrow-derived professional antigen-presenting cells. The in vitro generation of DCs from either bone marrow or blood is routine in mammals. Their distinct morphology and phenotype and their unique ability to stimulate naïve T cells are used to define DCs. In this study, chicken bone marrow cells were cultured in the presence of recombinant chicken granulocyte-macrophage colony-stimulating factor (GM-CSF) and recombinant chicken interleukin-4 (IL-4) for 7 days. The cultured population showed the typical morphology of DCs, with the surface phenotype of major histocompatibility complex (MHC) class II(+) (high), CD11c(+) (high), CD40(+) (moderate), CD1.1(+) (moderate), CD86(+) (low), CD83(-) and DEC-205(-). Upon maturation with lipopolysaccharide (LPS) or CD40L, surface expression of CD40, CD1.1, CD86, CD83 and DEC-205 was greatly increased. Endocytosis and phagocytosis were assessed by fluorescein isothiocyanate (FITC)-dextran uptake and fluorescent bead uptake, respectively, and both decreased after stimulation. Non-stimulated chicken bone marrow-derived DCs (chBM-DCs) stimulated both allogeneic and syngeneic peripheral blood lymphocytes (PBLs) to proliferate in a mixed lymphocyte reaction (MLR). LPS- or CD40L-stimulated chBM-DCs were more effective T-cell stimulators in MLR than non-stimulated chBM-DCs. Cultured chBM-DCs could be matured to a T helper type 1 (Th1)-promoting phenotype by LPS or CD40L stimulation, as determined by mRNA expression levels of Th1 and Th2 cytokines. We have therefore cultured functional chBM-DCs in a non-mammalian species for the first time.

Induction of mucosal immunity in the avian Harderian gland with a replication-deficient Ad5 vector expressing avian influenza H5 hemagglutinin

The chicken Harderian gland (HG) plays an important role in adaptive immune responses upon ocular exposure to avian pathogens such as avian influenza (AI). To determine the role of HGs in generating immunity, chickens were immunized ocularly with an adenovirus (Ad5) vector expressing the AI hemagglutinin H5 gene. The Ad5-H5 vector induced H5 transgene expression and induced H5- and Ad5-specific IgA and IgG spot-forming cells (SFCs) in the HGs. The IgA and IgG SFC peaked on day 9 forAd5 and day 11 for the H5 protein. In addition, Ad5- and H5-specific antibodies were induced in serum. IgA in chicken tears was predominantly dimeric, while in serum monomeric IgA was most abundant. Analysis of HG mRNA confirmed expression of the polymeric immunoglobulin receptor (plgR). These data demonstrated the importance of HGs to generate mucosal and systemic immunity to AI following ocular Ad5-H5 administration to chickens.

Interactions between commensal bacteria and the gut-associated immune system of the chicken

The chicken gut-associated lymphoid tissue is made up of a number of tissues and cells that are responsible for generating mucosal immune responses and maintaining intestinal homeostasis. The normal chicken microbiota also contributes to this via the ability to activate both innate defense mechanisms and adaptive immune responses. If left uncontrolled, immune activation in response to the normal microbiota would pose a risk of excessive inflammation and intestinal damage. Therefore, it is important that immune responses to the normal microbiota be under strict regulatory control. Through studies of mammals, it has been established that the mucosal immune system has specialized regulatory and anti-inflammatory mechanisms for eliminating or tolerating the normal microbiota. The mechanisms that exist in the chicken to control host responses to the normal microbiota, although assumed to be similar to that of mammals, have not yet been fully described. This review summarizes what is currently known about the host response to the intestinal microbiota, particularly in the chicken.

CD83 regulates lymphocyte maturation, activation and homeostasis

The transmembrane CD83 molecule, a conserved member of the immunoglobulin superfamily, is known as one of the most characteristic cell surface markers for fully matured dendritic cells (DCs) in the peripheral circulation. An essential role for CD83 on murine DCs has not been found; however, evidence shows that its function primarily lies in the regulation of T- and B-lymphocyte maturation and in the regulation of their peripheral responses. Here, we review evidence for a role of CD83 in central lymphocyte maturation and novel, sometimes contradictory findings, regarding the function of CD83 in peripheral immune responses.