Oesophageal tonsil of the chicken

Chicken Secondary Lymphoid Tissues-Structure and Relevance in Immunological Research

Recent discoveries have indicated the importance of developing modern strategies for vaccinations, more ethical research models, and effective alternatives to antibiotic treatment in farm animals. Chickens (Gallus gallus) play a crucial role in this context given the commercial and economic relevance of poultry production worldwide and the search for analogies between the immune systems of humans and birds. Specifically, chicken secondary lymphoid tissues share similar features to their human counterparts. Chickens have several secondary or peripheral lymphoid tissues that are the sites where the adaptive immune response is initiated. The more general classification of these organs divides them into the spleen and skin-, pineal-, or mucosa-associated lymphoid tissues. Each of these tissues is further subdivided into separate lymphoid structures that perform specific and different functions along the animal's body. A review summarizing the state of the art of research on chicken secondary lymphoid organs is of great relevance for the design of future studies.

Morphohistology and Biometric Characteristics of Cecal Tonsils of Sonali Chicken at Post-Hatching Ages

Knowledge of basic structures is prerequisite for acquiring an in-depth idea about the physiology and immunology of the lymphoid system. The study evaluates the age related histomorphometry of cecal tonsil of Sonali chicken at different postnatal stages in Bangladesh as literatures regarding this are very scarce. The investigation was carried out on 25 healthy Sonali chickens representing different stage of postnatal life: days 1, 14, 28, 42, and 56 (n=5). After ethically sacrifice (cervical subluxation method), cecal tonsil was collected and subjected for both gross and histological studies. Haematoxylin and Eosin stain was done for microscopic study. Morphologically, cecal tonsils were located bilaterally at the junction of small and large intestine. It had tubular structure and yellowish white in color. All gross parameters (weight, length, and width) found to be increased significantly (P<0.05) throughout the whole study period. Weight was measured 0.022±0.001 g at day 1 and noticed 0.181±0.016 g at the end of study tenure. The microscopic observations revealed that at day 28 encapsulated lymphatic nodules was present along with the diffuse lymphocytes at the lamina propria and submucosa layer, which was absent at the previous study groups. At day 1, only small infiltration of lymphocytes was identified and at day 14, lymphocytes were aggregating to form lymphatic nodules. After that, age related development was noticed in histological features. The findings would be a milestone to give an idea about the gut health and immune status of Sonali chicken and provide a basis for further immunization research.

Content and location of lymphocyte subpopulations with markers CD4+, CD8+ and CD20+ in the esophageal tonsil of chickens and the Meckel diverticulum of ducks

Immune formations of birds' digestive organs, including the esophageal tonsil and Meckel’s diverticulum, protect the body from foreign antigens that enter the body with food and water and play an important role in maintaining the genetic constancy of its internal environment. This unique property of the immune system is formed during ontogenesis and is associated with maintaining the selection of lymphocyte clones that are able to respond to foreign antigens and carry out a specific immune response of two types: humoral and cellular. This article presents the results of a study of T- and B-lymphocyte subpopulations of the esophageal tonsil of Shever 579 cross chickens at the age of 25, 180 and 300 days, the Meckel diverticulum of the Blagovarsky cross ducks at the age of 30, 150 and 180 days. Immunohistochemical and statistical research methods were used to determine the localization and quantitative parameters of cell populations of lymphocytes (CD4+, CD8+, CD20+) using monoclonal antibodies and the DAKO EnVision FLEX+ imaging system (Dako Cytomation, Denmark). Separate subpopulations of T-lymphocytes (CD4+ - helpers, CD8+ -cytotoxic / T-suppressors) and mature B-lymphocytes (CD20+) were found in the esophageal tonsil and Meckel diverticulum of birds. Their presence confirms that antigen-independent proliferation and differentiation of lymphocytes into effector cells occur in the immune formations of the digestive system. The lymphoid tissue of these formations is represented mainly by a well-defined diffuse form and nodules with light centers (secondary). In the esophageal tonsil of chickens, these structures are located in the tunica mucosa and tela submucosa, and in the Meckel diverticulum of ducks – also in the tunica muscularis. The content of lymphocytes with these markers predominates in diffuse lymphoid tissue compared to that in secondary lymphoid nodules. In the diffuse lymphoid tissue of the esophageal tonsil, lymphocytes are located mainly near the adenomeres and excretory ducts of the esophageal glands, blood vessels, and under the surface epithelium, and in Meckel’s diverticulum – around the crypts, in their epithelium and in the epithelium of the villi. They are also found in the light centers of lymphoid nodules and on their periphery. The indices of the content of lymphocytes with the indicated markers in the esophageal tonsil and Meckel diverticulum which we determined were associated with age characteristics of the poultry in the postnatal period of ontogenesis. According to our observations, the content of CD20+ lymphocytes was the highest, while the populations of CD4+ and CD8+ lymphocytes were much smaller. This indicates an increase in the activity and predominance of the humoral immunity over the cellular one. The content of CD20+ lymphocytes was highest in birds at the age of 180 days, that is, during their sexual maturity. The data presented in the work can be used by morphologists researching the organs of the immune system, immunologists, poultry specialists involved in breeding, using and raising poultry and in educational work.

Histological and histomorphometric study of the cranial digestive tract of ostriches (Struthio camelus) with advancing age

The present study was conducted to determine the histological and histomorphometric variations in the tongue, oesophagus, proventriculus, and gizzard of ostriches (Struthio camelus) with regards to the sex and advancing age. A total of 40 healthy ostriches of both sexes and five age groups; young (up to 1 year, 1 to 2 years and 2 to 3 years) and adult (3 to 4 years and above 4 years) in equal numbers (n = 8) were used in this study. The organs under study were collected immediately after slaughtering the birds. Overall, the colour, shape, weight and various dimensions (length, width, and diameter) of the collected organs were recorded. The mean values of the gross anatomical variables of the studied organs increased (P < 0.05) among all the young groups (i.e., from 1 to 2 years, 2 to 3 years). Similarly, the organs under study in the adult groups (birds aged 3 to 4 years and above 4 years) grew (P < 0.05) as well. However, the differences between the adults were not significant. The histological analysis and histometric measurements were conducted on paraffin embedded tissue sections with Image J® analysis software. The statistical analysis revealed a significant increase in the thickness of the different tunics of the digestive organs in all the groups except those the adult groups. These findings may be of importance for the strategic manipulation of feed and nutrition to enhance the growth rate and also to diagnose pathological processes.

Immunomodulation of Avian Dendritic Cells under the Induction of Prebiotics

Simple Summary

Dendritic cells recognize pathogen-associated molecular patterns in chicken intestines and are part of the initial immune response. The immunoregulatory properties of prebiotics acting in several ways in poultry have been known for many years. According to their function, dendritic cells should play an indispensable role in the proven effects of prebiotics on the intestinal immune system, such as through activation of T and B cells and cytokine production. Currently, there are no studies concerning direct interactions in poultry between non-digestible feed components and dendritic cells. Whereas most in vitro experiments with chicken dendritic cells have studied their interactions with pathogens, in vitro studies are now needed to determine the impacts of prebiotics on the gastrointestinal dendritic cells themselves. The present lack of information in this area limits the development of effective feed additives for poultry production. The main purpose of this review is to explore ideas regarding potential mechanisms by which dendritic cells might harmonize the immune response after prebiotic supplementation and thereby provide a basis for future studies.

Abstract

Although the immunomodulatory properties of prebiotics were demonstrated many years ago in poultry, not all mechanisms of action are yet clear. Dendritic cells (DCs) are the main antigen-presenting cells orchestrating the immune response in the chicken gastrointestinal tract, and they are the first line of defense in the immune response. Despite the crucial role of DCs in prebiotic immunomodulatory properties, information is lacking about interaction between prebiotics and DCs in an avian model. Mannan-oligosaccharides, β-glucans, fructooligosaccharides, and chitosan-oligosaccharides are the main groups of prebiotics having immunomodulatory properties. Because pathogen-associated molecular patterns on these prebiotics are recognized by many receptors of DCs, prebiotics can mimic activation of DCs by pathogens. Short-chain fatty acids are products of prebiotic fermentation by microbiota, and their anti-inflammatory properties have also been demonstrated in DCs. This review summarizes current knowledge about avian DCs in the gastrointestinal tract, and for the first-time, their role in the immunomodulatory properties of prebiotics within an avian model.

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.

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.

Pyloric tonsil as a novel gut-associated lymphoepithelial organ of the chicken

The pyloric tonsil is a novel peripheral lymphoepithelial organ of the gastrointestinal tract in the chicken. It forms a complete lymphoid ring at the beginning of the duodenum, where crypts of Lieberkühn are transformed to tonsillar crypts with lymphoepithelial lining. The oesophageal (described previously) and pyloric tonsils are characteristic of the chicken, while they are absent in mammals. The lymphoid system develops from the middle germ layer, the mesoderm, and forms connections with the ecto- and endoderm, namely the skin and gut, respectively. These connections are based on the lymphoepithelial lining of the crypts, and provide gates for environmental antigens. Recent findings, taken together with the literature, suggest that in birds the lymphoid system forms connections with the endoderm-derived organs that are anatomically and histologically more extensive than the ectoderm-derived ones, which may be explained by the absence of regional lymph nodes, and the less developed lymphoid circulation of the skin.

Characterization of chicken epidermal dendritic cells

It has been known for 15 years that the chicken epidermis contains ATPase+ and major histocompatibility complex class II-positive (MHCII+) dendritic cells. These cells were designated as Langerhans cells but neither their detailed phenotype nor their function was further investigated. In the present paper we demonstrate a complete overlapping of ATPase, CD45 and vimentin staining in all dendritic cells of the chicken epidermis. The CD45+ ATPase+ vimentin+ dendritic cells could be divided into three subpopulations: an MHCII+ CD3- KUL01+ and 68.1+ (monocyte-macrophage subpopulation markers) subpopulation, an MHCII- CD3- KUL01- and 68.1- subpopulation and an MHCII- CD3+ KUL01- and 68.1- subpopulation. The first population could be designated as chicken Langerhans cells. The last population represents CD4- CD8- T-cell receptor-alphabeta- and -gammadelta- natural killer cells with cytoplasmic CD3 positivity. The epidermal dendritic cells have a low proliferation rate as assessed by bromodeoxyuridine incorporation. Both in vivo and in vitro experiments showed that dendritic cells could be mobilized from the epidermis. Hapten treatment of epidermis resulted in the decrease of the frequency of epidermal dendritic cells and hapten-loaded dendritic cells appeared in the dermis or in in vitro culture of isolated epidermis. Hapten-positive cells were also found in the so-called dermal lymphoid nodules. We suggest that these dermal nodules are responsible for some regional immunological functions similar to the mammalian lymph nodes.