Development of cytoplasmic CD3+/T cell receptor-negative cells in the peripheral lymphoid tissues of chickens

Inside-out chicken enteroids with leukocyte component as a model to study host-pathogen interactions

Mammalian three-dimensional (3D) enteroids mirror in vivo intestinal organisation and are powerful tools to investigate intestinal cell biology and host-pathogen interactions. We have developed complex multilobulated 3D chicken enteroids from intestinal embryonic villi and adult crypts. These avian enteroids develop optimally in suspension without the structural support required to produce mammalian enteroids, resulting in an inside-out enteroid conformation with media-facing apical brush borders. Histological and transcriptional analyses show these enteroids comprise of differentiated intestinal epithelial cells bound by cell-cell junctions, and notably, include intraepithelial leukocytes and an inner core of lamina propria leukocytes. The advantageous polarisation of these enteroids has enabled infection of the epithelial apical surface with Salmonella Typhimurium, influenza A virus and Eimeria tenella without the need for micro-injection. We have created a comprehensive model of the chicken intestine which has the potential to explore epithelial and leukocyte interactions and responses in host-pathogen, food science and pharmaceutical research.

The Postembryonic Development of the Immunological Barrier in the Chicken Spleens

The avian immune system improves with the development of the lymphoid organs. The chickens' spleen serves as the largest peripheral lymphoid organ, but little immunological research has been conducted on that spleen during postembryonic development. We investigated the blood-spleen barrier (BSB) by developing morphological architecture, resistance to the corpuscular antigen, immunocyte distribution, gene expression levels of TLR2/4 and cytokines in the spleens of hatched chickens of differing ages. Results demonstrated that the resistance of exogenous carbon particles of the BSB improved with the morphological and structural development of the chicken spleens. The cuboidal endothelial cells which lined the sheathed capillaries were gradually visible, and the discontinuous basement membrane was thickened during postembryonic development. There was an increased number of T and B cells and antigen-presenting cells in the chicken spleen between hatching and adulthood. The mRNA expression levels of TLR2/4, IL-2, IFN-γ, and TNF-α were higher two weeks after hatching, but these decreased and remain stable between 21 and 60 days. As the age increased, the BSB developed structurally and functionally. Our findings provide a better understanding of splenic immune function and the pathogenesis of avian immunology in infectious diseases.

MHC class I target recognition, immunophenotypes and proteomic profiles of natural killer cells within the spleens of day-14 chick embryos

Chicken natural killer (NK) cells are not well defined, so little is known about the molecular interactions controlling their activity. At day 14 of embryonic development, chick spleens are a rich source of T-cell-free CD8αα(+), CD3(-) cells with natural killing activity. Cell-mediated cytotoxicity assays revealed complex NK cell discrimination of MHC class I, suggesting the presence of multiple NK cell receptors. Immunophenotyping of freshly isolated and recombinant chicken interleukin-2-stimulated d14E CD8αα(+) CD3(-) splenocytes provided further evidence for population heterogeneity. Complex patterns of expression were found for CD8α, chB6 (Bu-1), CD1-1, CD56 (NCAM), KUL01, CD5, and CD44. Mass spectrometry-based proteomics revealed an array of NK cell proteins, including the NKR2B4 receptor. DAVID and KEGG analyses and additional immunophenotyping revealed NK cell activation pathways and evidence for monocytes within the splenocyte cultures. This study provides an underpinning for further investigation into the specificity and function of NK cells in birds.

Avian NK activities, cells and receptors

Natural killer (NK) activity has been examined in birds for over 30 years, but evidence that avian NK activity plays crucial roles in disease is only suggestive. In chickens, NK activity is mediated by TCR0 cells in the intestinal epithelium, but elsewhere subsets of alphabeta and gammadelta T cells (NKT cells) may be more important. There are few lectin-like NK receptor genes, located in the genomic region syntenic with the natural killer complex (NKC) as well as the major histocompatibility complex (MHC). In contrast, a huge number of Ig-like receptor genes are located in a region syntenic with the leukocyte receptor complex (LRC).

Study of host-pathogen interactions to identify sustainable vaccine strategies to Marek's disease

Marek's disease virus is a highly cell-associated, lymphotropic alpha-herpesvirus that causes paralysis and neoplastic disease in chickens. The disease has been contained by vaccination with attenuated viruses and provides the first evidence for a malignant cancer being controlled by an antiviral vaccine. Marek's disease pathogenesis is complex, involving cytolytic and latent infection of lymphoid cells and oncogenic transformation of CD4+ T cells in susceptible chickens. Innate and adaptive immune responses develop in response to infection, but infection of lymphocytes results in immunosuppressive effects. The remarkable ability of MDV to escape immune responses by interacting with, and down-regulating, some key aspects of the immune system will be discussed in the context of genetic resistance. Resistance conferred by vaccination and the implications of targeting replicative stages of the virus will also be examined.

Establishment of immune competence in the avian GALT during the immediate post-hatch period

Population dynamics of intestinal lymphocytes and the temporal development of lymphocyte functions were studied in broiler chicks during the first 2 weeks post-hatch. This period is of major immunological importance as the chick is immediately exposed to environmental antigens and pathogens. We show that the gut-associated lymphoid tissue contains functionally immature T and B lymphocytes at hatch, and that function is attained during the first 2 weeks of life as demonstrated by mRNA expression of both ChIL-2 and ChIFNgamma. Functional maturation occurred in two stages: the first-during the first week post-hatch, and the second during the second week, which was also accompanied by an increase in lymphocyte population, as determined by expression of antigen receptor genes. Evidence is presented to show that in the intestinal milieu cellular immune responses mature earlier, and are a prerequisite for humoral responses. Hence, the lack of antibody response in young chicks is primarily due to immaturity of T lymphocytes.

The enhancement of avian NK cell cytotoxicity by thymulin is not mediated by the regulation of IFN-gamma production

Preincubation with either thymulin or IFN-gamma can enhance NK activity. In addition, overnight in vitro pre-treatment with thymulin and IFN-gamma increases NK activity further than either treatment alone. It has been hypothesized that thymulin increases the responsiveness of immune cells to IFN-gamma by either increasing the expression of IFN-gammaR or by increasing the production and/or secretion of IFN-gamma. The effects of thymulin on IFN-gamma production and secretion were examined in this study. While an overnight incubation with the polyclonal activator Con A increased the number of cells positive for intracellular IFN-gamma, a similar incubation with thymulin produced no change in the percentages of cells labeling positive for intracellular IFN-gamma when compared to the media control cells. In addition, IFN-gamma was not secreted by splenocytes following an overnight incubation with thymulin, but increased secretion was induced by Con A stimulation. Taken together, these results suggest that thymulin does not increase IFN-gamma production or induce IFN-gamma secretion by avian splenocytes.

Evidence for the direct action of thymulin on avian NK cells

The ability of thymulin to directly enhance NK cell-mediated cytotoxicity was examined. Specific cell population depletions were done in K and SLD chicken splenocyte preparations using anti-CD3, CD4, and CD8 monoclonal antibodies and secondary complement-fixing polyclonal antibodies. The remaining cells were incubated overnight with in vitro treatments of thymulin and IFN-gamma, either separately or together, followed by an assay for cytotoxicity. Although the control K-strain had higher overall NK cell-mediated cytotoxicity than the thymulin-deficient SLD-strain, the following trends were seen in both strains. Thymulin continued to enhance NK activity following CD4 or CD3 cell depletion, but not after CD8 or CD8 and CD4 cell depletion. Since avian NK cells express CD8 alpha, but not CD3 or CD4 on their surface, these results suggest that the ability of in vitro thymulin treatments to enhance NK activity is not mediated by T-cells but may be due to direct effects on NK cells.

Lymphocytic infiltration in the chicken trachea in response to Mycoplasma gallisepticum infection

A prominent feature of disease induced by Mycoplasma gallisepticum is a lymphoproliferative response in the respiratory tract. Although this is also seen in other mycoplasma infections, including Mycoplasma pneumoniae, the phenotype of the lymphocytes infiltrating the respiratory tract has not been determined. In this study, the numbers and distribution of lymphocytes in the tracheas of chickens infected with a virulent strain of M. gallisepticum were examined. Three groups of chickens were experimentally infected with M. gallisepticum and three unchallenged groups were used as controls. One infected and one control group were culled at 1, 2 and 3 weeks post infection. Tracheas were removed and examined for the presence and number of T cells carrying CD4, CD8, TCRgamma7, TCRalphabeta1 or TCRalphabeta2 markers. There was no significant difference in the number of CD8+ cells in the upper, middle and lower trachea. High numbers of both CD4+ and CD8+ cells were found with variable numbers of TCRalphabeta1+ and TCRalphabeta2+, but no TCRgammadelta+, cells throughout the time course. The distribution of CD4 cells was dispersed, while the CD8+ cells were clustered in follicular-like arrangements. No difference was detected in the distribution of TCRalphabeta1+ and TCRalphabeta2+ cells. The titre of mycoplasma genomes in the trachea decreased significantly from 1 to 2 weeks, while the mucosal thickness of the trachea increased significantly from 1 to 2 weeks then decreased from 2 to 3 weeks, indicating resolution of the lesions following control of infection. This study is the first to examine the phenotypes of T lymphocytes infiltrating the respiratory tract during mycoplasma infections. The findings suggest involvement of specific stimulation of CD8+ cells, particularly in the acute phase of disease.

Intestinal immune responses to coccidiosis

Intestinal parasitism is a major stress factor leading to malnutrition and lowered performance and production efficiency of livestock and poultry. Coccidiosis is an intestinal infection caused by intracellular protozoan parasites belonging to several different species of Eimeria. Infection with coccidia parasites seriously impairs the growth and feed utilization of chickens and costs the US poultry industry more than $1.5 billion in annual losses. Although acquired immunity to Eimeria develops following natural infection, due to the complex life cycle and intricate host immune response to Eimeria, vaccine development has been difficult and a better understanding of the basic immunobiology of pertinent host-parasite interactions is necessary for developing effective immunological control strategies against coccidiosis. Chickens infected with Eimeria produce parasite specific antibodies in both the circulation and mucosal secretions but humoral immunity plays only a minor role in protection against this disease. Rather, recent evidence implicates cell-mediated immunity as the major factor conferring resistance to coccidiosis. This review will summarize current understanding of the avian intestinal immune system and its response to Eimeria as well as provide a conceptual overview of the complex molecular and cellular events involved in intestinal immunity to coccidiosis. It is anticipated that increased knowledge of the interaction between parasites and host immunity will stimulate the birth of novel immunological and molecular biological concepts in the control of intestinal parasitism.

Avian gut-associated lymphoid tissues and intestinal immune responses to Eimeria parasites

Coccidiosis, an intestinal infection caused by intracellular protozoan parasites belonging to several different species of Eimeria, seriously impairs the growth and feed utilization of livestock and poultry. Host immune responses to coccidial infection are complex. Animals infected with Eimeria spp. produce parasite-specific antibodies in both the circulation and mucosal secretions. However, it appears that antibody-mediated responses play a minor role in protection against coccidiosis. Furthermore, there is increasing evidence that cell-mediated immunity plays a major role in resistance to infection. T lymphocytes appear to respond to coccidial infection through both cytokine production and a direct cytotoxic attack on infected cells. The exact mechanisms by which T cells eliminate the parasites, however, remain unclear. Although limited information is available on the intestinal immune system of chickens, gut lymphoid tissues have evolved specialized features that reflect their role as the first line of defense at mucosal surfaces, including both immunoregulatory cells and effector cells. This review summarizes our current understanding of the avian intestinal immune system and mucosal immune responses to Eimeria spp., providing an overview of the complex cellular and molecular events involved in intestinal immune responses to enteric pathogens.

An anti-CD3 epsilon serum detects T lymphocytes in paraffin-embedded pathological tissues in many animal species

The in situ identification of T cells has been difficult and restricted to frozen tissue samples of a limited range of species. In this study, we demonstrate that an antiserum recognizing a phylogenetically conserved part of the CD3 epsilon cytoplasmic tail detects T cells of many avian and mammalian species in formalin-fixed paraffin-embedded tissue sections. This antiserum enables the morphological characterization of normal and pathological lymphoid tissues and lymphoid infiltrations in experimental work and in animal disease.

Preferential TCR V beta 1 gene usage by autoreactive T cells in spontaneous autoimmune thyroiditis of the obese strain of chickens

We studied T cell receptor variable beta (TCR V beta) gene usage by autoreactive T cells in spontaneous autoimmune thyroiditis (SAT) of obese strain (OS) chickens. Chicken alpha beta T cells may express either V beta 1 or V beta 2 genes, the products of which can be recognized by TCR2 and TCR3 monoclonal antibodies, respectively. Selective depletion of V beta 1+ or V beta 2+ T cells in OS chickens was accomplished by repeated injections of TCR2 or TCR3 antibodies into embryonic and 1-3-week-old chickens. The birds were killed at 20 days of age and their spleens and thyroid glands evaluated by immunohistochemistry. We found that V beta 1+ T cells preferentially infiltrated OS chicken thyroid glands. Antibody treatments resulted in a 41% reduction in frequency of V beta 1+, and a 87% reduction of the frequency of V beta 2+ cells in the circulation, and in a profound decrease of the respective T cells in spleens and thyroid glands. Selective suppression of V beta 1+ T cells partially inhibited SAT development in that thyroid-infiltrating cells and destruction of thyroid follicles were reduced by more than 50%. Thyroglobulin autoantibody serum levels were also reduced in V beta 1+ T cell-depleted OS chickens, whereas selective depletion of V beta 2+ T cells did not inhibit SAT development. These findings indicate preferential TCR V beta 1 gene usage by autoreactive T cells in SAT of OS chickens.

Characterization of avian natural killer cells and their intracellular CD3 protein complex

Natural killer (NK) cell activity appears to be conserved throughout vertebrate development but NK cells have only been well characterized in mammals. Candidate NK cells have been identified in the chicken as cytoplasmic CD3+ and surface T cell receptor (TCR)/CD3- (TCRO) lymphocytes that often express CD8. The fact that the TCRO cells are abundant in the embryonic spleen before T cells enter this organ allowed us to cultivate the embryonic TCRO cells using growth factors derived from activated adult lymphocytes. These TCRO cells were cytotoxic for an NK target cell line. They expressed cell surface CD8, a putative interleukin-2 receptor, CD45 and a receptor for IgG, but did not express CD4, major histocompatibility complex class II or immunoglobulin. Biochemical analysis of the cytoplasmic CD3 antigen revealed two of the three CD3 gamma, delta and epsilon homologues, and RNA transcripts for the third. The CD3 monoclonal antibody also precipitated a 32-kDa dimer that may represent a heterodimer of different CD3 constituents. TCR alpha and beta gene transcripts were not detected in the TCRO cells. These results indicate that the avian TCRO cell is the mammalian NK cell homologue. The shared evolutionary features of T cells and NK cells in birds and mammals support the idea that they derive from a common progenitor.

Postnatal development of intra-epithelial leukocytes in the chicken digestive tract: phenotypical characterization in situ

In the present study, we characterized intra-epithelial leukocytes in the digestive tract of chickens during postnatal development. Their phenotype was characterized by monoclonal antibodies in cryostat sections and the numbers of the different cell-types were counted in the epithelium of the esophagus, proventriculus, duodenum, jejunum, cecum, and colon. All intra-epithelial leukocytes bore the leukocyte-common antigen CD45; 35% were T lymphocytes, and 50% bore a B-cell marker. However, no immunoglobulin-bearing cells were detected in the epithelium. Monocytes and macrophages were found only in the epithelium of the esophagus. A remaining population of non-B, non-T, non-monocyte cells (15%) was present in all parts of the digestive tract. The number of intra-epithelial leukocytes was greatest in the duodenum and jejunum, and decreased in the proximal part of the cecum and in the colon. Intra-epithelial leukocytes were only sporadically detected in the proventriculus. The total number of intra-epithelial leukocytes increased until 8 weeks after hatching and then decreased at 18 months. In the esophagus, the total number of intra-epithelial leukocytes changed little during aging. We found that the intra-epithelial leukocytes of chickens and rodents are distinct in that chicken intra-epithelial leukocytes comprise a cell population that bears a B-cell antigen but that lacks surface immunoglobulins.

Retroviral transformation in vitro of chicken T cells expressing either alpha/beta or gamma/delta T cell receptors by reticuloendotheliosis virus strain T

Exposure of normal juvenile chicken bone marrow cells to the replication defective avian reticuloendotheliosis virus strain T (REV-T) (chicken syncytial virus [CSV]) in vitro resulted in the generation of transformed cell lines containing T cells. The transformed T cells derived from bone marrow included cells expressing either alpha/beta or gamma/delta T cell receptors (TCRs) in proportions roughly equivalent to the proportions of TCR-alpha/beta and TCR-gamma/delta T cells found in the normal bone marrow in vivo. Essentially all TCR-alpha/beta-expressing transformed bone marrow-derived T cells expressed CD8, whereas few, if any, expressed CD4. In contrast, among TCR-gamma/delta T cells, both CD8+ and CD8- cells were derived, all of which were CD4-. Exposure of ex vivo spleen cells to REV-T(CSV) yielded transformed polyclonal cell lines containing > 99% B cells. However, REV-T(CSV) infection of mitogen-activated spleen cells in vitro resulted in transformed populations containing predominantly T cells. This may be explained at least in part by in vitro activation resulting in dramatically increased levels of T cell REV-T(CSV) receptor expression. In contrast to REV-T(CSV)-transformed lines derived from normal bone marrow, transformed lines derived from activated spleen cells contained substantial numbers of CD4+ cells, all of which expressed TCR-alpha/beta. While transformed T cells derived from bone marrow were stable for extended periods of in vitro culture and were cloned from single cells, transformed T cells from activated spleen were not stable and could not be cloned. We have therefore dissociated the initial transformation of T cells with REV-T(CSV) from the requirements for long-term growth. These results provide the first demonstration of efficient in vitro transformation of chicken T lineage cells by REV-T(CSV). Since productive infection with REV-T(CSV) is not sufficient to promote long-term growth of transformed cells, these results further suggest that immortalization depends not only upon expression of the v-rel oncogene but also on intracellular factor(s) whose expression varies according to the state of T cell physiology and/or activation.

Intestinal T lymphocytes in the chicken express an integrin-like antigen

We report the characterization of a molecule recognized on chicken T cells by the murine A19 monoclonal antibody that was generated by immunization with intestinal intraepithelial lymphocytes. Immunofluorescence analysis indicated that both alpha beta and gamma delta T cell subpopulations in the intestine express the A19 antigen, but natural killer cells and B cells do not. The A19-marked T cells were preferentially localized in the intestinal epithelium and less frequently in the underlying lamina propria. T cells appearing in the intestine during embryonic life were A19 negative but acquired the antigen within the first few days after hatching. Although rarely found on cells in non-intestinal tissues at any age, very late expression of the A19 antigen could be induced by concanavalin A stimulation of splenic and circulating T cells. Transforming growth factor beta 1 enhanced this induction of A19 expression. The A19 molecules expressed by intestinal T cells and activated splenic T cells were biochemically identical, consisting of a multi-molecular complex of proteins with approximate M(r) of 205, 145 and 75 kDa under nonreducing conditions and 120, 90 and 28 kDa under reducing conditions. The characteristics of this multimolecular complex and its differential expression suggest that the A19 antigen is a member of the integrin family which may function in the retention of intestinal lymphocytes.

Thymic origin of embryonic intestinal gamma/delta T cells

Current evidence suggests both thymic and extrathymic origins for T cells. Studies in mice favor an in situ origin for a prominent population of intestinal intraepithelial lymphocytes that express gamma/delta T cell receptor (TCR). This developmental issue is explored in an avian model in which the gamma/delta lymphocytes constitute a major T cell subpopulation that is accessible for study during the earliest stages of lymphocyte development. In the chick embryo, cells bearing the gamma/delta TCR appear first in the thymus where they reach peak levels on days 14-15 of embryogenesis, just 2 d before gamma/delta T cells appear in the intestine. Using two congenic chick strains, one of which expresses the ov antigen, we studied the origin and kinetics of intestinal colonization by gamma/delta T cells. The embryonic gamma/delta+ thymocytes homed to the intestine where they survived for months, whereas an embryonic gamma/delta- thymocyte population enriched in thymocyte precursors failed to give rise to intestinal gamma/delta+ T cells. Embryonic hemopoietic tissues, bone marrow, and spleen, were also ineffective sources for intestinal gamma/delta+ T cells. Intestinal colonization by gamma/delta+ thymocytes occurred in two discrete waves in embryos and newly hatched birds. The data indicate that intestinal gamma/delta T cells in the chicken are primarily thymic migrants that are relatively long-lived.

Follicle-associated epithelium and medullary epithelial tissue of the bursa of fabricius are two different compartments

The bursae of Fabricius from the chicken and turkey were studied by light and electron microscopy and immunohistochemical methods. The study focused on the relationship of follicle-associated epithelium to the medulla. The follicle-associated epithelium was supported by 3 to 5 layers of stratified epithelial cells which were a continuation of the corticomedullary epithelial cells. The follicle-associated epithelium consisted of M cells and scattered secretory dendritic cells. The network of the reticular epithelial cells of the medulla was filled with secretory dendritic cells, B cells, and a few T cells and macrophages. The cellular content of the follicle-associated epithelium and the medulla suggested that they were different cellular compartments. Communication between the follicle associated epithelium and medullary epithelial compartment occurred through the supporting cells of the follicle-associated epithelium. When the supporting layers of the follicle-associated epithelium infolded into the medulla, they formed lamellated epithelial bodies similar to the thymic Hassall bodies. The lamellated bodies enclosed secretory dendritic cells but not lymphocytes. The infolding of supporting cells varied from follicle to follicle. The asynchronization of infolding contributed to heterogeneity of follicle composition. Follicle heterogeneity was demonstrated by differences in reactivity with a battery of monoclonal antibodies.

Peptidergic innervation of the Bursa Fabricii: interrelation with T-lymphocyte subsets

In birds, B-lymphocytes mature in a special immune organ, the Bursa Fabricii. This organ thus offers unique possibilities for the study of the microenvironment of B-lymphocyte differentiation. We previously reported tachykinin-, vasoactive intestinal peptide-, calcitonin gene-related peptide- and galanin-immunoreactive (ir) fibres in the chicken bursa. As judged from light microscopic studies, each of the peptides was found in fibres contacting B-lymphocytes. Vasoactive intestinal peptide-ir fibres contacted macrophages. Now, we demonstrate neuropeptide Y, indicating the sympathetic nervous system, in fibres associated with arteries, not entering the follicles. CD4- and CD8-positive T-lymphocytes were dispersed in bursal follicles and the connective tissue, most densely in subepithelial regions. We could not find close apposition of fibres with either T-cell subset. We conclude that the potential neuro-immune axis in the Bursa Fabricii may represent a neuro-B-cell-link with only indirect participation of T-lymphocytes. The sympathetic input may influence the bursal microenvironment primarily by regulating the blood supply.