Esophageal tonsil: a novel gut-associated lymphoid organ

Distribution and spatiotemporal development of organised lymphoid tissues in the chicken intestinal tract

Chickens exhibit a distinct immune architecture characterised by the absence of draining lymph nodes and the presence of a well-developed mucosa-associated lymphoid tissue. The structure and spatiotemporal development of chicken lymphoid tissues in the intestine are poorly documented. The macroscopically indistinct structure of chicken Peyer's patches has impeded studies into their development. The generation of CSF1R-eGFP reporter transgenic chickens enables visualisation of the development, organisation and extent of chicken lymphoid tissues by unique macroscopic views. CSF1R-eGFP reporter transgenic chickens were used to investigate the distribution and spatiotemporal development of PP and caecal tonsils in embryonic day 18 to 8-week-old chickens. Peyer's patch anlagen are present at ED18 with a similar frequency and distribution pattern observed in 2- and 8-week-old chickens. These findings can support in ovo and post-hatch mucosal vaccination strategies and the development of vaccine delivery systems targeted to the specialized epithelium overlying the Peyer's patches.

Age-dependent changes of gut-associated lymphoid tissue in one to four-month-old turkeys: A histological study

Gut-associated lymphoid tissue (GALT) has a pivotal role in the health of birds as the first line of defense against foodborne pathogens. On the other hand, this part of immune system is important for successful development of vaccines. Due to scarcity of knowledge on GALT of turkey as a major industrial species, this study aimed to evaluate histological features of GALT in this species. A total of 40 clinically healthy BUT6 turkeys from both sexes at the age of 1, 2, 3, and 4 months were included in the study. Samples were immediately removed after slaughter from different parts of the gut, including pharyngeal tonsil, cervical oesophagus, oesophageal tonsil, proventriculus, pyloric tonsil, ileum, Meckel’s diverticulum, caecal tonsil, the middle and apex of caecum, rectum, and cloaca. After fixation and routine procedures followed by hematoxylin-eosin staining, samples were studied histologically under light microscope. In addition, photomicrographs were taken from sections and were analysed for histomorphometric parameters using Zeiss Axio vision rel.4.8 software. According to the results, in one-month-old turkeys, lymphatic tissues in pharyngeal tonsil, pyloric tonsil, proventriculus, caecal tonsil, middle, and apex of caecum, Meckel’s diverticulum, and cloaca were completely developed, while in some other parts such as the cervical oesophagus and the rectum lymphatic structures were absent. In the ileum, the Peyer’s patch was observed as an aggregated structure, although the diffuse lymphatic tissue has properly evolved. In two months old turkeys, the dense lymphatic tissue including primary and secondary lymphatic follicles, was present in cervical oesophagus, Peyer’s patch, rectum, and cloaca. Many histomorphometric parameters of lymphoid tissue also developed age-dependently. In four months old birds the dense lymphatic tissue was obvious in all examined specimens. Moreover, no signs of tissue atrophy were seen at the age of four months (prepuberty) in the GALT specimens. In conclusion, the GALT of turkeys was histologically quite similar to those of other birds and these structures showed an age-dependent development from 1 to 4 months of age.

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.

Species-specific differences of the avian oesophagus: Histological and Ultrastructural study

The oesophagus is a muscular tube comprised of cervical and thoracic regions. Several studies have clarified the histological structure of the oesophagus. However, its histoarchitecture in relation to variable dietary habits of each species is still unclear. In the current study, 21 pigeons, cattle egrets and ducks, n = 7, each was used. Macroscopically, the oesophagus of cattle egrets either the cervical or thoracic parts was the longest among the pigeons and ducks. Histologically, the oesophagus comprised of four distinct tunicae: mucosa, propria submucosa, musculosa and adventitia or serosa. A great structural variation in these layers among the three investigated species was recorded. In the cervical oesophagus of pigeons, the superficial squamous cells showed perinuclear halo zone, the propria submucosa was characteristically lacked any gland. Moreover, its musculosa was very thick. On the other hand, the intraepithelial glands were characteristically distributed along the whole length of the cattle egret's oesophagus. Interestingly, the cervical esophagus of the ducks showed submucosal associated lymphatic tissue; diffuse and nodular Ultrastructurally, the oesophageal glands showed secretory granules of variable electron densities, electron-lucent in the pigeons and ducks and electron-dense in the cattle egrets.

Immunogenicity of Newcastle disease virus strain ZG1999HDS applied oculonasally or by means of nebulization to day-old chicks

Newcastle disease (ND) is one of the classic viral infections of poultry which resists all the efforts of eradication. Newcastle disease virus (NDV) strain ZG1999HDS was isolated during the outbreak in 1,999 at a broiler farm in Croatia. Previous trials in chickens confirmed it to be a lentogenic pathotype and immunogenic by stimulating humoral and cell mediated immunity. Further characterization by deduced amino acid sequence at the cleavage site of fusion protein confirmed its lentogenic nature, and in vitro tests its oncolytic capacity. Owing to its immunogenicity, strain ZG1999HDS is considered for vaccine development. In this study, 1-day-old chicks were vaccinated using strain ZG1999HDS oculonasally or by nebulization. Strain ZG1999HDS induced humoral immune response in both immunized groups The cell-mediated immune response occurred earlier in the group immunized by nebulization, as shown by a higher frequency rate of T and B lymphocytes, and significantly higher expression of IFN-α in respiratory organs and IFN-γ expression in the spleen. Viral genomic RNA was not detected in investigated organs. Thus, NDV strain ZG1999HDS is immunogenic when administered by means of nebulization or oculonasally without any adverse effects and is therefore suitable for further research and vaccine development. Further research is needed regarding its tropism.

Identification, tissue characterization, and innate immune role of Angiogenin-4 expression in young broiler chickens

Intestinal epithelial cells are major producers of antimicrobial proteins, which play an important role in innate immunity. In addition to defensins, the Ribonuclease A superfamily includes important antimicrobial proteins involved in host-defense mechanisms in vertebrates. Angiogenin-4 (Ang4), a member of this RNase superfamily, has been demonstrated to be secreted by Paneth cells in mice. We have successfully cloned and characterized a new chicken gene (chAng4), found for the first time in a nonmammalian species, from intestinal epithelial and lymphoid cells. Characterization of chAng4 revealed 99% nucleotide and 97% amino acid sequence homology to mouse Ang4. Similar functional regions were identified, suggesting a role in innate immunity and regulation of gut microbiota. Furthermore, the mRNA expression pattern of chAng4 was studied in broilers in the presence or absence of beneficial bacteria (probiotics) and organic acids. The results showed that one-day-old chickens expressed low levels of Ang4 in almost all the evaluated tissues (crop, proventriculus, duodenum, jejunum, ileum, and cecal tonsils), except in the bursa of Fabricius that presented the highest expression level. The addition of probiotics and organic acids for either 7 or 14 consecutive days demonstrated a direct effect of probiotics and organic acids on chAng4 expression; moreover, broilers receiving probiotics and organic acids for only 7 D showed higher levels of chAng4 expression compared with those treated for 14 D. Broilers without treatment had a constant high level of expression in cecal tonsils and bursa. In conclusion, we were able to identify and characterize a new antimicrobial gene in chickens (chAng4) throughout the gastrointestinal tract. chAng4 mRNA gene expression was associated with the presence of naturally occurring and supplemented (probiotic) bacteria. The encoded protein might have a potential bactericidal effect against intestinal nonpathogenic and pathogenic microbes, modulating the intestinal microbiota and the innate immunity, and thereby may help minimize the use of antibiotics in poultry feed.

Terminology of the tonsils

Many terms used for referring to tonsillar structures are applied in immunological research. However, in many cases, the use of these terms is not in compliance with official veterinary anatomical nomenclature. This is partly attributable to ambiguous descriptions present in conventional anatomical textbooks. This study gives an overview of pertaining controversial terms and promotes the official anatomical terminology applicable to the tonsils, to enhance the unequivocal transfer of knowledge generated during immunological research.

Cellular assessment of crop lymphoid tissue from specific-pathogen-free white leghorn chickens after Salmonella enteritidis challenge

The crop may be an important site along the upper alimentary tract in which a humoral immune response against Salmonella Enteritidis (SE) is elicited locally. The mucosal immune response within the crop (ingluvies) of specific-pathogen-free (SPF) white leghorn (WL) chickens against SE was investigated. Three trials were conducted using SPF WL pullets at age 5-6 wk. Trial 1 consisted of 77 birds evaluated for 10 wk post-SE infection (pi), trial 2 was composed of 72 birds monitored through 8 wk pi, and trial 3 was made up of 30 birds assessed for 5 wk pi. Birds were challenged per os with 10(8) colony-forming units/ml SE phage type 13. Crop lavage samples, crop tissues, ceca, and/or liver-spleen were collected preinfection and then at weekly intervals post-SE infection. Bacteriologic examination of cecal contents and/or liver-spleen occurred weekly to monitor progression of SE infection. Crop lavages were analyzed for SE-lipopolysaccharide (LPS)-specific immunoglobulin A (IgA) by enzyme-linked immunosorbent assay to assess humoral immune response. General histologic staining (hematoxylin and eosin [H&E] and methyl green-pyronin [MGP]) and immunohistochemical (IHC) staining (monoclonal antibodies CD45 and Bu-1) were applied to serial sections of crop to evaluate lymphoid tissue via light microscopy, to grade isolated lymphoid follicles (ILFs) by using score 0 (minimal, < 50 microm in diameter) to score 5 (sizable, > 200 microm in diameter) scale, and to characterize the cellular population of ILFs. Results revealed that cecum samples and liver-spleen samples were 100% SE culture positive at 1 wk pi, and then the percentage of SE positives progressively declined over time. Markedly increased crop SE-LPS-specific IgA antibodies were detected in crop samples by 2-3 wk pi, and the humoral response remained elevated above week 0 baseline for the duration of each trial. Crop ILFs of score 3 to 5 were observed in H&E-stained tissues, with an increased proportion of ILFs in post-SE-infected crops vs. uninfected. MGP staining showed plasma cells scattered within and at the periphery of ILFs. IHC staining revealed CD45 (pan-leukocyte) and Bu-1 (B-lymphocyte)-positive cells within crop ILFs. The chicken crop seems to be an organ in which lymphoid tissue may arise in response to enteric SE infection, and a site in which a humoral response may be generated against the SE pathogen.

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.

CMAP27, a novel chicken cathelicidin-like antimicrobial protein

Cathelicidins, antimicrobial peptides with broad spectrum activity, have been almost exclusively found in mammals. Here, we report the cloning of a novel avian cathelicidin, chicken myeloid antimicrobial peptide 27 (CMAP27) from chicken bone marrow cells. A combined expressed sequence tag (EST) and genomic based search revealed a cathelicidin-like gene located at the terminus of chromosome 2. Reverse transcriptase-polymerase chain reaction (RT-PCR) and 5'RACE techniques resulted in a 154 amino acid prepropeptide, homologous to chicken cathelicidin 1 (51%) and most similar to alpha-helical myeloid antibacterial peptides (MAPs; 29-33%). A putative elastase cleavage site (LVQRG/RF) suggests the production of a 27 amino acid antimicrobial peptide, predicted to adopt an alpha-helical configuration followed by a hydrophobic tail. Comparative analyses between antimicrobial peptide domains showed marked similarity between CMAP27 and MAP members of the bovidae family, but not with the alpha-helical chicken cathelicidin 1. Strongest expression of CMAP27 mRNA was found in myeloid/lymphoid tissues, testis and uropygial gland. In accordance with the phylogenetic tree analysis, these findings support the theory of a common ancestral cathelicidin gene and suggest an important role for cathelicidins in chicken innate host defense.

Impaired immune responses in broiler hatchling hindgut following delayed access to feed

One of the key stimulators of intestinal development in the chick is physical exposure to feed, while feed withholding delays the onset of gut development. A delay of 24-72 h in onset of feeding is quite common in the poultry industry due to variation in hatching time and hatchery treatments. As intestinal development occurs in concert with the development of the gut associated lymphoid tissue (GALT), we investigated the effects of short term feed withholding on development of GALT in broiler hatchlings. GALT activity was determined by antibody production (systemic and locally in the gut), distribution of B and T lymphocytes in the gut, expression of lymphocyte specific genes, and distribution of B and T lymphocytes in the cloacal bursa. Our findings show that while development of GALT in the foregut (duodenum, jejunum, ileum) was only slightly and temporarily impeded by feed withholding, GALT activity in the hindgut and the gut-related cloacal bursa was significantly delayed during the first 2 weeks of life: Systemic and intestinal antibody responses following rectal immunization to antigen were lower, colonization of the hindgut (cecum and colon) by T and B lymphocytes was delayed, as well as the expression of chIL-2 mRNA in hindgut T lymphocytes. We also found that the increase of B and T population size in the cloacal bursa was delayed with time. Full recovery occurred from 2 weeks of age. The 2-week vulnerable period should be seriously considered in circumstances where hatchlings are in transit for extended periods from hatcheries to farms.

Oesophageal tonsil of the chicken

The oesophageal tonsil of the chicken is a novel member of the mucosal-associated lymphoid tissue (MALT), which is located around the entrance of the proventriculus. It consists of 6 to 8 single units, which are surrounded by a thin fibrous capsule. Each one is organised around the bottom of the longitudinal folds of the oesophagus, and serves as a 'tonsillar crypt'. Stratified squamous epithelium is infiltrated by lymphoid cells, i.e. T cells, plasma cells, macrophages, and dendritic cells, but not B cells, to form lymphoepithelium (LE). In the LE vimentin-, MHC II- and ATPase-positive cells possibly represent Langerhans' cells, but the appearance of 74.3 positive cells in the LE is unusual, because the 74.3 monoclonal antibody (mAb) recognises chicken follicular dendritic cells in the germinal centre and medulla of the bursal follicles. The subepithelial lymphoid tissue is organised into T- and B-dependent regions, which are the interfollicular areas and the germinal centres, respectively. Existence of high-endothelial venules in the interfollicular region suggests an extensive cellular connection between the oesophageal tonsil and the other lymphoid organs. In the resting oesophagus the lumen is closed, but during swallowing a bolus the crypt opens and the lymphoepithelium can be exposed to undigested food, antigens, infectious agents and vaccines. The location of the oesophageal tonsil, cranial to the stomach, may provide this organ with a unique role as compared to the other parts of the MALT; namely, it may contribute to the replication of infectious bursal disease virus (IBDV) and/or the pathogenesis of infectious bursal disease.

Quail as the chimeric counterpart of the chicken: Morphology and ontogeny of the bursa of Fabricius

The quail is the chimeric and parabiotic counterpart of the chicken, thus increasing the value of quail in the field of developmental biology. Quail bursa of Fabricius was studied by light microscopy, electron microscopy, and immunocytochemical methods. The basic cellular composition and structural framework are comparable with those of the chicken bursa. One of the major structural differences is the absence of the continuous cortico-medullary arch. In addition to the epithelial reticular cell the bursal secretory dendritic cell is the other medullary-specific bursal cell. The bursal secretory dendritic cell is a highly elongated cell which expresses vimentin intermediate filaments and produces secretory granules. The substance of the granules can be visualized by NIC2 monoclonal antibody, which was produced against guinea fowl bursal secretory dendritic cell. The released granular content appears on the lateral surface of the bursal secretory dendritic cell and is gradually solubilized. Thus, the NIC2-positive substance may occur in membrane-bound and solubilized forms in the isolated environment of the medulla. The bursal secretory dendritic cell establishes membrane contact areas with the B cells; therefore, they may influence B-cell maturation by cell contact and chemical (humoral) product. During embryogenesis bursal secretory dendritic cell precursors enter the epithelium and 1) induce epithelial bud formation, and 2) produce an NIC2-positive substance. Senescent bursal secretory dendritic cells can be phagocytic and migrate into the follicle-associated epithelium. This physiological turnover of the bursal secretory dendritic cell represents a novel pathway of macrophage formation from dendritic cells.