Histological characteristics and stereological volume assessment of the ovine tonsils

Tonsils form a first line of defence against foreign antigens and therefore play a key role in immunity. Since documented information about ovine tonsils is limited, a study was performed in which the morphological characteristics and the volume of lymphoid tissue present in each ovine tonsil were determined. The tonsils of five adult healthy sheep were examined histologically and the volumes were estimated using the Cavalieri method. The pharyngeal tonsil had a mean volume of 1296.1 ± 205.9 mm³ and was by far the largest ovine tonsil, followed by the paired palatine tonsil with a mean volume of 715.0 ± 110.5 mm³. The tonsil of the soft palate, the paired tubal and paraepiglottic tonsils and the lingual tonsil were much smaller with a mean volume of, respectively, 90.3 ± 24.9 mm³, 80.1 ± 24.3 mm³, 29.7 ± 11.8 mm³ and 10.1 ± 2.8 mm³. The folds and crypts of the pharyngeal and palatine tonsils were covered by a reticular and a non-reticular epithelium. Both tonsils were mainly composed of primary and secondary lymph follicles. The palatine tonsils contained 1–3 crypts with a few secondary infoldings. Lymphoid tissue in the tonsil of the soft palate was located at the nasopharyngeal (dorsal) side of the soft palate. The tubal tonsil was lined with a pseudostratified columnar ciliated epithelium and consisted of scattered lymphoid cells and lymph follicles. The paraepiglottic tonsil consisted of lymph follicles and aggregated lymphoid cells. Its overlying keratinized stratified squamous epithelium was folded and often heavily infiltrated by lymphocytes. The ovine lingual tonsil was not macroscopically visible and did not contain clearly distinguishable lymph follicles. It consisted of aggregations of lymphoid cells that were mainly located within the vallate lingual papillae.     

Histological studies on the ontogeny of bovine palatine and pharyngeal tonsil: germinal center formation, IgG, and IgA mRNA expression

The development and distribution of lymphocyte subsets in calf palatine and pharyngeal tonsil were examined. During prenatal development, B cells were distributed in the subepithelial area, and T cells and MHC class II⁺ cells were found in the deep layer of B-cell area, respectively, in both tonsils. At neonatal stage, lymphoid follicle containing a few CD4⁺ cells have been formed in both tonsils. IgG⁺ and IgA⁺ cells were found in the parafollicular and epithelial area. At 3 months old, many germinal centers were recognized in both tonsils. CD4⁺ cells and IgG mRNA expression were detected in light zone of germinal centers. Many IgG, and IgA mRNA expressions also could be detected in the parafollicular and subepithelial area of both tonsils. The data suggest that both tonsils have an important role of local immune defense against invading antigen after birth. The comparison of the histological characteristics of tonsil and Peyer's patch during ontogeny is also discussed.     

Differences between the ovine tonsils based on an immunohistochemical quantification of the lymphocyte subpopulations

In sheep, the pharyngeal first defence line against oral and inhaled antigens is organized in six tonsils. Since tonsils are regarded as secondary lymphoid tissue and part of the acquired immune system which is subjected to induction through contact with antigens, an evaluation of the different lymphocyte populations in tonsils is useful to determine a tendency of the specific tonsils to more inductive or more effective immunity. By means of immunohistochemistry, different lymphocyte populations were quantified and localized using a panel of eight antibodies, i.e. anti-CD45, anti-CD21, anti-CD2, anti-CD3, anti-CD4, anti-CD8, anti-WC1 and anti-Ki67. The CD21+ B lymphocytes were localized within the tonsillar lymphoid follicles. The CD2+/CD3+ T lymphocytes were numerous in the interfollicular regions and were aligned underneath and within the epithelium but were also observed at the CD21+ pole of the lymphoid follicles. Near the lingual and tubal tonsils, and the tonsil of the soft palate, the CD45+ cells around the seromucous glands and in the lamina propria were mainly CD3+ T cells. In all tonsils, the WC1+ gamma delta T cells formed a small lymphocyte population which harboured the lamina propria and the interfollicular region. The relative percentages of the different lymphocyte populations of the large palatine and pharyngeal tonsils, which are macroscopically the most developed, were comparable. In contrast, the lingual tonsil was significantly different from the other tonsils not only by its small size and lack of lymphoid follicles, but also by the lymphocyte populations. Based on the lymphocyte populations, the ovine tonsils can be divided in three groups with the tonsil of the soft palate, the tubal and paraepiglottic tonsil forming an intermediate between the palatine and pharyngeal tonsils as true tonsils on the one side, and the lingual tonsil as a scattered lymphocyte aggregation on the other side.     

Anatomical localisation and histology of the ovine tonsils

The topography and histologic structure of the various tonsils were studied anatomically and microscopically in 15 sheep aged between 9 and 15 months. The palatine, pharyngeal and paraepiglottic tonsils were readily visible macroscopically. They consisted mainly of secondary lymph nodules and were encapsulated in dense connective tissues. The epithelium covering the tonsils and their crypts was frequently infiltrated heavily by lymphocytes. The tubal tonsil and the tonsil of the soft palate were macroscopically visible after fixation in 2% acetic acid. These tonsils consisted of scattered lymph nodules, aggregations of lymphocytes and diffuse lymphoid tissue. They were not encapsulated, and therefore the borders of these tonsils could not be clearly delineated. The lingual tonsil was not macroscopically visible in sheep and consisted of scattered small aggregations of lymphocytes.     

Histology, immunohistochemistry and ultrastructure of the equine palatine tonsil

The palatine tonsils of five young horses formed 10-12 cm elongated follicular structures extending from the root of the tongue on either side to the base of the epiglottis and lateral to the glossoepiglottic fold. The stratified squamous non-keratinized epithelium of the outer surface was modified into crypts as reticular epithelium by heavy infiltration of lymphoid cells from underlying lymphoid follicles. In places, lymphoid tissue reaching almost to the surface and with only one to two cell layers intact was identified as the lymphoepithelium. Langerhans cells with Birbeck granules were interspersed between epithelial cells. Lymphoid tissue organized in lymphoid follicles constituted the parenchyma of the palatine tonsil. CD4-positive cells were more numerous and CD8-positive lymphocytes less numerous compared with their distribution in the lingual tonsil. B cells and macrophages were also more numerous than in the lingual tonsil and lectins showed a different pattern of attachment. M cells were not observed. High endothelial venules with well-developed vesiculo-vacuolar organelle had structural evidence of transendothelial and interendothelial migration of lymphocytes. Striated muscles as seen in the deeper lamina propria mucosae of the lingual tonsil were absent. The immunohistological and ultrastructural characteristics of the equine palatine tonsil are similar to those of humans but differ from those of the lingual tonsil and are consistent with a role as an effector and inductor immunological organ.     

Tonsillar lesions in cattle naturally infected with Mycobacterium bovis

The upper respiratory tract surfaces, the palatine and pharyngeal tonsils and associated lymph nodes of 32 tuberculin reactor cattle were examined pathologically and bacteriologically. Tuberculous lesions were observed histologically in the palatine tonsils of five animals and in both the palatine and pharyngeal tonsils of a sixth. Mycobacterium bovis was cultured from the tonsils of four of these animals and from the palatine or pharyngeal tonsils of a further eight cattle in which no lesions were observed. The upper respiratory tract surfaces of 10 animals were M bovis-positive.     

山羊咽扁桃体和咽鼓管扁桃体的组织结构观察

选取健康10月龄奶山羊10头,断头宰杀后取咽扁桃体和咽鼓管扁桃体,应用组织学光镜和电镜制片技术研究咽扁桃体和咽鼓管扁桃体的显微和亚显微组织结构.结果表明:山羊咽扁桃体和咽鼓管扁桃体的黏膜上皮主要由2～3层多边形上皮细胞组成,部分区域只有单层扁平细胞,相邻上皮细胞间空隙很大,上皮细胞表面有丰富的微绒毛.上皮细胞之间和黏膜上皮下方固有层内有大量淋巴细胞浸润.扁桃体的实质部分由数个次级淋巴小结和弥散淋巴组织构成,弥散淋巴组织中有大量分布的淋巴管和毛细血管后微静脉.此外,在紧贴黏膜上皮细胞下方的固有层和淋巴滤泡中可观察到少量的树突状细胞.结果提示山羊的咽扁桃体和咽鼓管扁桃体可作为鼻腔免疫的主要诱导位点和效应部位.     

Histology, immunohistochemistry and ultrastructure of the tonsil of the soft palate of the horse

The tonsil of the soft palate was an oval, flat structure located centro-rostrally on the oral surface of the soft palate. Its stratified squamous non-keratinized epithelium was perforated by holes or small crypts the deeper parts of which were loosely spongiform inter-digitated with lymphoid tissue. These unusual features have not previously been reported in tonsils of any species. Crypts and reticulated epithelium as found in the lingual and palatine tonsils were not observed. Lectins showed varying affinities for specific layers of the epithelium. M cells were not observed. A few Langerhans cells were distributed among surface epithelial cells. Lymphoid tissue was arranged loosely and in isolated lymphoid follicles in the subepithelial lamina propria mucosae. Although IgA+ cells and macrophages were proportionately more numerous the amount of lymphoid tissue was much less than in the lingual and palatine tonsils. Most of the follicular germinal centres lacked a darkly stained corona. CD4 positive were more numerous than CD8+ lymphocytes and were distributed in the parafollicular and inter-follicular areas. Large clusters of mucus acini positive for glycogen, acidic and neutral mucopolysaccharides separated lymphoid tissue from deeply placed striated muscle. Only a few high endothelial venules were observed in the parafollicular and inter-follicular areas. These had relatively few vesiculo vacuolar or other organelles in their high endothelial cells and few lymphocytes attaching to their walls.     

Differential expression of homing receptors and vascular addressins in tonsils and draining lymph nodes: Effect of Brucella infection in sheep

The differential expression of homing receptors (HR) and complementary vascular addressins was studied in T and B lymphocytes from ovine tonsils and draining lymph nodes (LN) in uninfected and Brucella melitensis-infected sheep. In uninfected sheep, CD4+CD25+ T cells expressed proportionally more L-selectin and beta1 integrin than beta7 integrin in pharyngeal and palatine tonsils and in parotid LN (PLN), retropharyngeal LN (RLN) and the peripheral prescapular LN (PSLN). In contrast, memory CD4+CD45RA- T cells expressed an equivalent proportion of the three HR in PLN and PSLN, whereas beta1 and beta7 integrins were proportionally more expressed than L-selectin in pharyngeal tonsil. beta7 integrin was proportionally more expressed than beta1 integrin or L-selectin in palatine tonsils, RLN and the mucosal mesenteric LN (MLN). beta1 integrin was proportionally more expressed in IgG+ and IgA+ cells than beta7 integrin and L-selectin in tonsils, PLN and RLN. The main endothelial addressin expressed on venules in both pharyngeal and palatine tonsils, the PLN and RLN, as well as in the PSLN, was the peripheral PNAd, while in the MLN it was MAdCAM-1. Conjunctival infection by Brucella resulted in an increase of CD4+CD25+ and CD4+CD45RA- T cell subsets, which was associated to modifications of HR expression. CD4+CD45RA- T cells expressed proportionally more beta1 and beta7 integrins than L-selectin in regional PLN and RLN, but also in PSLN. The infection induced an increase of IgG+ and IgA+ cell percentages expressing beta1 integrin in all LN, and also beta7 integrin in the RLN. PNAd continued to be expressed on venules of tonsils and draining LN after Brucella infection, and MAdCAM-1 was also weakly expressed on RLN venules. These results suggest that lymphocyte trafficking through tonsils and draining LN could involve L-selectin/PNAd interactions, as well as beta1 or beta7 integrin, possibly in interaction with VCAM-1 or MAdCAM-1. The homing of antigen-specific lymphocytes in these tissues could be modulated after conjunctival infection with Brucella, which induces the recruitment of lymphocytes that express both beta1 and/or beta7 integrin in regional and more distant LN.     

The microanatomy of the palatine tonsils of the buffalo (Bos bubalus)

The palatine tonsils play a key role in initiating immune responses against antigens entering the body through the mouth. They are also replication sites of some pathogens. There is no data available about the structure of the palatine tonsils of the Egyptian water buffalo. Therefore, palatine tonsils of 14 clinically healthy buffalo bulls (2–3 years old) were examined macroscopically and microscopically using light, and transmission electron microscopes. The tonsils had an elongated kidney shape with a central invagination (tonsillar fossa) containing a single macroscopic opening leading to a small central cavity (tonsillar sinus). A number of macroscopic crypts originated from this sinus (internal crypts). Besides the tonsillar fossa, also small macroscopic crypts (external crypts) were present. The tonsils were enclosed by a thin connective tissue capsule and septa divided the tonsils into incomplete lobes. Within these encapsulated organs mucous glands were very obvious. Each crypt was highly branched and lined with stratified squamous non-keratinized epithelium. Several lymphoid cells infiltrated between the epithelial cells forming patches of lymphoepithelium. The crypt lumen contained lymphocytes, neutrophils and erythrocytes. Lymph nodules with clear germinal centers extended under the epithelial surface. Diffusely distributed lymphocytes were found in the narrow interfollicular region. High endothelial venules, interdigitating dendritic cells, macrophages and plasma cells were observed among the diffuse lymphocytes. Lymphatics filled with lymphocytes drained the tonsils.     

Distribution of the lingual tonsils of cattle designated as specified risk materials

The tonsils of cattle, including palatine tonsils, pharyngeal tonsils, tubal tonsils and lingual tonsils, are designated as specified risk materials (SRM). However, the detailed distribution of lingual tonsils in cattle is unknown. We therefore histologically examined their distribution in 198 tongue specimens from cattle. The examinations confirmed that the presence of lingual tonsils was limited to the tissue of the lamina propria on the dorsal and lateral aspects of the tongue, not reaching the muscular layer below. More than 90% of the lingual tonsils were located between the distribution center of the vallate papillae and the radix linguae (root of the tongue). However, they were also found in the area extending from the lingual torus to the rostral-most vallate papilla in an individual, suggesting that the complete removal of the lingual tonsils requires elimination of the lamina propria extending from the lingual torus to the radix linguae.     

Lymphocyte populations and adhesion molecule expression in bovine tonsils

Bovine tonsils are mucosal-associated lymphoid tissue (MALT) located at the entry of the pharynx where both inhaled and ingested antigens can induce an immune response. This study was conducted to determine the lymphocyte populations and adhesion molecule expression in the palatine tonsil (PT) and pharyngeal tonsil (PhT) of adult cattle and compare them with typical MALT (discrete Peyer's patches, PP) and a peripheral lymph node (parotid lymph node, PLN). The distribution of various lymphocyte subsets was determined in situ by immunofluorescence, and their proportions were determined by multicolor flow cytometry. The tonsils were similar to PP in the proportions of B- and T-cells (25-32% T-cells, 39-45% B-cells), and T cell subpopulations (CD4, CD8, and gammadelta). The PP contained the highest proportion of memory T-helper cells with beta7 integrin (30.3%+/-5.4), the tonsils intermediate (PT: 19.8%+/-4.4 and PhT: 19.7%+/-4.9), and the PLN had the lowest proportion (15.4%+/-3.1). The opposite relationship was observed with CD62L on na?ve T- helper cells as PP had the lowest proportion (14.2%+/-6.4), the tonsils intermediate (PT: 17.4%+/-2.5 and PhT: 24.3%+/-7.3), and the PLN the highest proportion (45.3%+/-6.5). MAdCAM-1 was highly expressed in the high endothelial venules (HEV) of PP, with variable and weak expression in the tonsils and PLN. PNAd, on the other hand, was highly expressed in HEV of tonsils and PLN, and weakly expressed in the PP. These results indicate that the bovine tonsils share characteristics with both PP and PLN. The alpha4beta7/MadCAM-land CD62L/PNAd interaction may be involved in lymphocyte migration to the tonsils, but it is likely that other adhesion molecules participate as well. Similarities between the human and bovine tonsils suggest that cattle may provide a good model to study the role of the tonsil in the respiratory immune response.     

Changes in the leucocyte subpopulations of the palatine tonsillar crypt epithelium of pigs in response to Streptococcus suis type 2 infection

The tonsils are portal of entry and a site of multiplication and persistence for a variety of pathogens, including Streptococcus suis (S. suis), which is a common cause of meningitis, septicemia and arthritis in pigs. Understanding the early changes that occur in the first barrier of the tonsil, i.e. the crypt epithelium, in response to S. suis infection is critical in clarifying the pathogenesis of this disease and for the future development of efficient methods of mucosal vaccination. In this study, we investigated the early changes, from 18 to 72 h, that occur in leucocyte subpopulations of the crypt epithelium of the palatine tonsils of 3-week-old pigs in response to S. suis type 2 infection. Monoclonal antibodies against leucocyte markers CD3, CD4, CD8, gammadelta T cell receptor, lambda-immunoglobulin light-chain, myeloid cells, and major histocompatibility complex class II molecule (MHC-II) were used in an avidin-biotin immunoperoxidase technique. An increase in the number of lambda-immunoglobulin light-chain positive cells (B cell subset) was noticed in crypts of S. suis-infected animals from 18 h after infection onwards. This increase was significant at 18 and 48 h after infection. The number of CD4 and CD8 cells was greater from 18 h onwards, with a significant increase at 24 and 72 h post-infection. No significant difference in numbers of CD3, gammadelta T cell receptor and MHC-II positive cells was detected in the crypts of infected animals compared to controls. Macrophages, neutrophils and crypt epithelial cells stained positively with the myeloid marker, and the area of crypt epithelium positive for this marker was increased in the crypts of infected animals, with a significant difference detected at 24 and 72 h after infection. These results suggest that there is participation of the innate immunity in the early phase of S. suis infection, represented by neutrophils, macrophages and likely epithelial cells, and that there is a potential for the initiation of both humoral and cellular responses against S. suis within the crypt epithelium of the palatine tonsil.     

Preliminary age-related histological studies of the lymphoid tissues of the respiratory tract and associated structures of the brushtail possum

Extract

Lymphoepithelium was observed in palatine and pharyngeal tonsils in possums from 2 months of age, but was not seen in the lung. Morphological maturity of lymphoid tissue occurred at about 4 months of age, coinciding with first emergence of young from the pouch. Peribronchiolar and/or perivascular lymphoid aggregations were first observed in the lung of a 3.5-month-old possum, and subpleural lymphoid aggregations were first seen at 7 months of age.     

Preliminary age-related histological studies of the lymphoid tissues of the respiratory tract and associated structures of the brushtail possum

Abstract Extract Lymphoepithelium was observed in palatine and pharyngeal tonsils in possums from 2 months of age, but was not seen in the lung. Morphological maturity of lymphoid tissue occurred at about 4 months of age, coinciding with first emergence of young from the pouch. Peribronchiolar and/or perivascular lymphoid aggregations were first observed in the lung of a 3.5-month-old possum, and subpleural lymphoid aggregations were first seen at 7 months of age.     

Histology, immunohistochemistry and ultrastructure of the equine tubal tonsil

The tubal tonsil of the horse surrounds the pharyngeal opening of the eustachian tube and is lined by pseudostratified columnar ciliated epithelium interspersed with areas of follicle-associated epithelium (FAE) heavily infiltrated by lymphocytes but devoid of goblet and ciliated cells. Scanning and transmission electron microscopy revealed microvillous cells and cells with features characteristic of M cells such as reduced microvilli or depressed bare surface, more numerous mitochondria, small vesicles and lysosomes, as well as vimentin filaments and epitopes specific for GS 1-B4 as previously seen in the nasopharyngeal tonsil. M cells were also identified in areas of respiratory epithelium not associated with lymphoid follicles and appeared to be the nasal mucosal counterparts of recently described intestinal villous M cells in the mouse. The underlying lymphoid tissue of the FAE was generally organized as solitary lymphoid follicles without germinal centres in contrast to the diffuse and large amount of organized lymphoid follicles with germinal centres that characterize the nasopharyngeal tonsil. CD8+ T and B-lymphocytes were much fewer than in the nasopharyngeal tonsil. High endothelial venules were mainly oriented towards the parafollicular area and contained much fewer endothelial pores and vesiculo-vacuolar organelles. Finally, scattered small clusters of mucus acini and striated muscles were other features that differentiated the tubal and nasopharyngeal tonsils.     

Interactions between Streptococcus suis serotype 2 and cells of the myeloid lineage in the palatine tonsil of the pig

Streptococcus suis is a major pathogen in pigs and causes significant morbidity and mortality in herds world-wide. A major problem with S. suis is the presence of asymptomatic carrier animals which can spread the organism within and between herds. The palatine tonsil is one of the main sites where the organism can be recovered, both in infected and carrier animals. The use of multiple-colour immunohistology allowed identification of the cell types associated with bacteria in the tonsils of infected gnotobiotic piglets. Bacteria were never associated with T-cells or B-cells but were always associated with cells of the myeloid lineage. Expression of CD16 and CD163 on these leukocytes suggested an association with mature macrophages in tonsil, which may lead to clearance or control of the micro-organism.     

Histochemical and immunohistochemical study of the mucosal lymphoid system in swine.

Enzyme histochemical and immunohistochemical techniques were used to examine palatine tonsils and aggregated lymphoid follicles (Peyer's patches) of the ileum in 6- to 9-day-old and in 6-month-old pigs. Histochemical techniques were used to detect alpha-naphthyl-acetate esterase (ANAE), alpha-naphthyl-butyrate esterase (ANBE), beta-glucuronidase, adenosine triphosphatase (ATPase), and acid phosphatase (AcP). Nonspecific esterases (ANAE, ANBE) were detected in macrophages, T-cell area lymphocytes, eosinophils, fibroblastic reticular cells (FRC), follicular dendritic cells (FDC), and interdigitating cells (IDC). beta-Glucuronidase reactivity was strong in macrophages, eosinophils, FDC, and IDC, and weaker in FRC. Adenosine triphosphatase reactivity was detected in B-cell area lymphocytes, FDC, FRC, and IDC. Cell types with acid phosphatase reactivity were macrophages, FDC, FRC, and IDC. Nonepithelial cells of tonsils and aggregated lymphoid follicles of the ileum had similar enzymatic reactions. In Peyer's patches, however, epithelial cells were positive for all enzymes studied; in tonsils, only nonspecific esterases were detected. Immunoperoxidase techniques were used to detect S-100 protein and cytoplasmic immunoglobulins (IgG, IgM, and IgA). The S-100 protein was detected in lymphocytes, FDC, and FRC of tonsils and Peyer's patches; in tonsillar epithelial and endothelial cells; and in IDC of Peyer's patches.(ABSTRACT TRUNCATED AT 250 WORDS)     

Bacterial colonization and invasion in pigs experimentally exposed to Streptococcus suis serotype 2 in aerosol

A recently developed porcine model for aerogenous infection with Streptococcus suis serotype 2 was applied in a study of the phases of bacterial colonization and initial invasion. Eighteen pigs were exposed to aerosolized S. suis serotype 2 after pre-exposure to mild acetic acid in aerosol. The animals were killed consecutively within the first six days after challenge. After death, all animals were necropsied and examined by bacteriology, histopathology, and immunohistochemistry. Systemic infection was established in four out of 18 animals exposed to S. suis serotype 2. All systemically infected animals developed clinical signs and lesions typical of the infection. In four additional animals, subclinical infection was demonstrated by re-isolation of S. suis from the palatine tonsil. However, in all 18 challenged animals, immunohistochemistry demonstrated S. suis serotype 2 antigen in the palatine and/or nasopharyngeal tonsils. In all four systemically infected animals, S. suis serotype 2 antigen was also found in the mandibular lymph node. These observations point towards the tonsils as possible portals of entry for S. suis serotype 2 with subsequent lymphogenous spread. Thus, the present findings parallel the proposed pathogenesis for S. suis serotype 1 infection in pigs.