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Introduction: The thymus is located in the superior mediastinum and anterior part of the inferior mediastinum. It plays a crucial role in the development, differentiation, and clonal expansion of T lymphocytes. In forensic cases involving foetal death, accurate estimation of foetal age is essential. When the foetus is extensively damaged, other organs can be used to estimate age. The thymus, being retrosternal and well-protected, is easily accessible during dissection. Therefore, studying the gross features and histogenesis of the thymus can be helpful in estimating gestational age in cases of severely mutilated foetal specimens. Aim: To examine the morphological features and histogenesis of the thymus in aborted and stillborn foetuses from normal pregnancies. Materials and Methods: A pilot study was conducted using a cross-sectional design at the Department of Anatomy, BLDEDU’s Shri BM Patil Medical College, Vijayapura, Karnataka, India, from May 2016 to April 2018. The dimensions and histogenesis of the thymus were studied in a total of 50 human foetal thymus specimens, collected from normal pregnancies across different gestational age groups ranging from 12 to 40 weeks. The specimens were obtained from the Department of Pathology and the Department of Obstetrics and Gynaecology. The dimensions and weight of the thymus were recorded during autopsy. Slides were prepared, stained with Haematoxylin and Eosin (H&E), and examined under a compound microscope. The histogenesis of the thymus was studied to observe its maturation. Results: Foetal weight increased from 134.6±58.3 g at 12 weeks to 1942±598 g at 40 weeks. The weight of the thymus ranged from 0.2 g at 12 weeks to 5.9 g at 40 weeks. Crown rump length varied from 10.7 cm to 29.9 cm. The length of the thymus measured between 0.5 cm and 3.3 cm, breadth between 0.4 cm and 2.3 cm, and height between 0.2 cm and 0.9 cm from 12 to 40 weeks of gestation. Microscopic features observed in the present study at different gestational ages included a well-formed thick capsule at 17 weeks, lobulation starting at 19 weeks, cortico-medullary differentiation beginning at 17 weeks, appearance of epithelial cells around 19 weeks, and initial appearance of Hassal’s corpuscles at 17 weeks, with more numbers observed later on. Conclusion: The thymus can be used in forensic investigations to estimate the gestational age of mutilated foetuses. It exhibits varying features at different gestational ages, which can aid in thymectomy procedures. Additionally, these findings can be considered during prenatal imaging studies.

Introduction: The thymus is located in the superior mediastinum and anterior part of the inferior mediastinum. It plays a crucial role in the development, differentiation, and clonal expansion of T lymphocytes. In forensic cases involving foetal death, accurate estimation of foetal age is essential. When the foetus is extensively damaged, other organs can be used to estimate age. The thymus, being retrosternal and well-protected, is easily accessible during dissection. Therefore, studying the gross features and histogenesis of the thymus can be helpful in estimating gestational age in cases of severely mutilated foetal specimens. Aim: To examine the morphological features and histogenesis of the thymus in aborted and stillborn foetuses from normal pregnancies. Materials and Methods: A pilot study was conducted using a cross-sectional design at the Department of Anatomy, BLDEDU's Shri BM Patil Medical College, Vijayapura, Karnataka, India, from May 2016 to April 2018. The dimensions and histogenesis of the thymus were studied in a total of 50 human foetal thymus specimens, collected from normal pregnancies across different gestational age groups ranging from 12 to 40 weeks. The specimens were obtained from the Department of Pathology and the Department of Obstetrics and Gynaecology. The dimensions and weight of the thymus were recorded during autopsy. Slides were prepared, stained with Haematoxylin and Eosin (H&E), and examined under a compound microscope. The histogenesis of the thymus was studied to observe its maturation. Results: Foetal weight increased from 134.6±58.3 g at 12 weeks to 1942±598 g at 40 weeks. The weight of the thymus ranged from 0.2 g at 12 weeks to 5.9 g at 40 weeks. Crown rump length varied from 10.7 cm to 29.9 cm. The length of the thymus measured between 0.5 cm and 3.3 cm, breadth between 0.4 cm and 2.3 cm, and height between 0.2 cm and 0.9 cm from 12 to 40 weeks of gestation. Microscopic features observed in the present study at different gestational ages included a well-formed thick capsule at 17 weeks, lobulation starting at 19 weeks, cortico-medullary differentiation beginning at 17 weeks, appearance of epithelial cells around 19 weeks, and initial appearance of Hassal's corpuscles at 17 weeks, with more numbers observed later on. Conclusion: The thymus can be used in forensic investigations to estimate the gestational age of mutilated foetuses. It exhibits varying features at different gestational ages, which can aid in thymectomy procedures. Additionally, these findings can be considered during prenatal imaging studies. [ABSTRACT FROM AUTHOR]

Recently, the effects of exposure to clothianidin (CLO) on the thymus and gut microbiota have become clear, but no report has examined its next-generation impacts. Pregnant C57BL/6N mice were administered a no-observed-adverse-effect-level dose of CLO until weaning. We examined CLO's effects on the gut microbiota and immune organs of dams and their 3- and 10-week-old male offspring. CLO administration led to several alterations of the top 30 bacterial genera in the gut microbiota in dams and 3-week-old mice. Compared to controls, 10-week-old mice had more thymic Hassall's corpuscles, and both dams and 10-week-old mice had fewer macrophages. These results suggest that fetal and lactational CLO exposure may affect the immune system and gut microbiota of the next generation. [ABSTRACT FROM AUTHOR]

In this study, we describe the immunohistochemical characterisation of the thymus, the main lymphoid organ, in sturgeon. The wide range cytokeratin, vimentin, S-100 protein, LCA (CD45) and CD3 were selected as the immunohistochemical markers to map the thymus in juvenile sterlet (Acipenser ruthenus). The epithelial cells and Hassall's corpuscles were labelled with a wide range cytokeratin. The fibroblasts and connective tissue within the thin fibrous capsule on the thymic surface expressed vimentin positivity. The stromal reticular cells were S-100 protein positive. The Leukocyte Common Antigen LCA (CD45) was negative on the thymic lymphocytes. The CD3 was negative on the thymic lymphocytes with cross-reactivity on the non-targeted structures. In conclusion, the commercially available antibodies against the wide range cytokeratin, vimentin and S-100 protein can be used to differentiate components of the sturgeon thymus, while the LCA (CD45) and CD3 application failed. We suggest that further studies are needed to generate fish specific antibodies.

While there is convincing evidence on the role of Aire-positive medullary thymic epithelial cells (mTEC) in the induction of central tolerance, the nature and function of post-Aire mTECs and Hassall’s corpuscles have remained enigmatic. Here we summarize the existing data on these late stages of mTEC differentiation with special focus on their potential to contribute to central tolerance induction by triggering the unique pro-inflammatory microenvironment in the thymus. In order to complement the existing evidence that has been obtained from mouse models, we performed proteomic analysis on microdissected samples from human thymic medullary areas at different differentiation stages. The analysis confirms that at the post-Aire stages, the mTECs lose their nuclei but maintain machinery required for translation and exocytosis and also upregulate proteins specific to keratinocyte differentiation and cornification. In addition, at the late stages of differentiation, the human mTECs display a distinct pro-inflammatory signature, including upregulation of the potent endogenous TLR4 agonist S100A8/S100A9. Collectively, the study suggests a novel mechanism by which the post-Aire mTECs and Hassall’s corpuscles contribute to the thymic microenvironment with potential cues on the induction of central tolerance.

While there is convincing evidence on the role of Aire-positive medullary thymic epithelial cells (mTEC) in the induction of central tolerance, the nature and function of post-Aire mTECs and Hassall's corpuscles have remained enigmatic. Here we summarize the existing data on these late stages of mTEC differentiation with special focus on their potential to contribute to central tolerance induction by triggering the unique pro-inflammatory microenvironment in the thymus. In order to complement the existing evidence that has been obtained from mouse models, we performed proteomic analysis on microdissected samples from human thymic medullary areas at different differentiation stages. The analysis confirms that at the post-Aire stages, the mTECs lose their nuclei but maintain machinery required for translation and exocytosis and also upregulate proteins specific to keratinocyte differentiation and cornification. In addition, at the late stages of differentiation, the human mTECs display a distinct pro-inflammatory signature, including upregulation of the potent endogenous TLR4 agonist S100A8/S100A9. Collectively, the study suggests a novel mechanism by which the post-Aire mTECs and Hassall's corpuscles contribute to the thymic microenvironment with potential cues on the induction of central tolerance. [ABSTRACT FROM AUTHOR]

Cervical thymic cyst is a rare clinical entity, with approximately one hundred cases reported in the literature so far. The purpose of this case report is to highlight some certain features, along with an extensive research of the relevant literature. A 6-year-old boy was admitted to the Otorhinolaryngology Department due to the presence of a left-sided, painless, latero-cervical swelling, first observed by his parents 2 weeks ago. Physical examination revealed a painless, well-delineated mass, with no signs of inflammation. No enlarged cervical nodes were present. The mass extended from the mandibular angle, under the sternocleidomastoid muscle, in proximity with the ipsilateral neurovascular bundle. Ultrasound transverse gray-scale panoramic view detected a wellcircumscribed lesion, with fine echogenic foci, appearing in close proximity with the upper pole of the left thyroid lobe and the ipsilateral common carotid artery. Elective surgical intervention with complete mass excision was performed. Histopathological examination confirmed the diagnosis of a cervical thymic cyst. Cervical thymic remnants represent a group of neck masses that pediatricians and pediatric surgeons should consider in differential diagnosis of both cystic and solid neck masses. Most cystic cervical thymic masses are found in the lower third of the anterior neck, extending deep to the sternocleidomastoid muscle, featuring close anatomic relationship with the composites of the ipsilateral carotid sheath. Elective surgery is kept as the treatment of choice, after ruling out the possibility of subject immunologic disturbance.

In this study, we describe the immunohistochemical characterisation of the thymus, the main lymphoid organ, in sturgeon. The wide range cytokeratin, vimentin, S-100 protein, LCA (CD45) and CD3 were selected as the immunohistochemical markers to map the thymus in juvenile sterlet (Acipenser ruthenus). The epithelial cells and Hassall's corpuscles were labelled with a wide range cytokeratin. The fibroblasts and connective tissue within the thin fibrous capsule on the thymic surface expressed vimentin positivity. The stromal reticular cells were S-100 protein positive. The Leukocyte Common Antigen LCA (CD45) was negative on the thymic lymphocytes. The CD3 was negative on the thymic lymphocytes with cross-reactivity on the non-targeted structures. In conclusion, the commercially available antibodies against the wide range cytokeratin, vimentin and S-100 protein can be used to differentiate components of the sturgeon thymus, while the LCA (CD45) and CD3 application failed. We suggest that further studies are needed to generate fish specific antibodies. [ABSTRACT FROM AUTHOR]

Abstract Background Cervical thymic cysts are uncommon lesions, rarely considered in the differential diagnosis of neck cysts in children. Case presentation We report a rare case of multiloculated thymic cyst in an 8-year-old boy on the right side of the neck. Perioperative diagnosis was a cystic hygroma. Macroscopic examination showed a cystic mass measuring 6.5 cm in total length. Histopathology of the excised specimen revealed thymic tissue with prominent Hassall’s corpuscles associated with multiloculated cyst. The cyst wall is bordered by a flattened or multilayered epithelium, often abraded. Conclusion This case is presented here for its rarity and should be included in the differential diagnosis of neck masses in children. So, it’s a lesion to be well aware of, particularly by pathologists.

Objective: To study morphological features of Hassall's corpuscles (HC) and their microenvironment in newborns with increased thymus mass., Material and Methods: The study was carried out on autopsy material of children of the first month of life. Based on the thymic index (TI), 2 groups were identified: with normal (conditional norm) and increased TI value (increased thymus weight). The standard method of histological staining and immunohistochemical methods with antibodies to Pan-CK, CK19, CD68, CD3 and p53 were used in the study. The classification proposed by A.G. Beloveshkin (2013) was used to determine the degree of maturity of HC. Nonparametric Mann-Whitney test was used to determine statistically significant differences in the groups., Results: In the group of children with increased thymus weight, the number of HC decreased by 20%. It was found that the proportion of progressive and mature corpuscles in this group was reduced by 2.3 and 1.6 times, respectively, compared to the group of children with normal thymus weight, while the proportion of regressive corpuscles increased almost 2-fold. In the HC microenvironment, there is an increase in the total number of thymocytes, combined with a decrease in the expression of CD68, CD3 and p53 in them. A sharp decrease in CK19-expressing cells in this group is accompanied by a disruption in the formation of reticular structures characteristic of the comparison group., Conclusion: In the thymus with increased mass, the structural and functional organization changes: along with an increase in the total number of thymocytes in the cortical layer and a decrease in the number of macrophages, epithelial cells and HC (with a predominance of regressive corpuscles), disturbances in the processes of maturation, apoptosis and negative selection of lymphocytes occur, which can lead to development of immunogenesis disorders.

The features of the thymic morphology in hens and ducks were studied. Samples were obtained from 3 adult birds of each species. They were studied by light microscopy using classical methods of morphological research. The tissue samples were fixed in 10% neutral buffered formalin and embedded in paraffin block and finally the sections were cut at 5-10 μm thickness using sliding microtome and stained with hematoxylin and eosin, according to Van Gizon and Weigert and impregnated with silver nitrate according to Kelemen. It was established that the thymus of birds was represented by isolated cervical parts, which, in the form of strands, were located under the skin on the lateral surfaces of the neck, along the trachea, along the course of the neurovascular bundle, and consisted of individual lobes. In hens 5 to 8 lobes were included in each thymus and extended from the 3-cervical vertebra to the start of the thoraco-abdominal cavity. Thymus of ducks consisted of 3-4 lobes and was located in the posterior third of the neck. Its cranial end was at the level of 10-11 cervical vertebrae, and caudal end reached 12 cervical vertebra. Individual lobes of duck's thymus had a greater absolute mass than the lobes of hen's thymus. They were also more separated from each other. Lobes of hen's and duck's thymus had a variety of shapes. Among them, there were mainly oval, convex-oval, beanshaped, rounded, flat and, sometimes, sickle-shaped. Morphofunctional units of the thymus were lobules, which consisted of a cortex and a medulla. In birds the medulla occupied a larger area than the cortex. In the medulla, there were Hassall's corpuscles, that were better developed in ducks. [ABSTRACT FROM AUTHOR]

Hassall's corpuscles (HCs) are characteristic components of the medulla of the mammalian thymus and thymoma with an abundance of HCs is even more rare, with only five cases having been reported in the literature, to the best of our knowledge. Furthermore, their morphology usually resembles World Health Organization (WHO) type B2 or B3 thymoma. The biological behavior appears indolent and is rarely associated with myasthenia gravis. However, whether it is a separate entity or a variant of organotypical thymoma WHO B2 or B3 remains to be elucidated. The present case report reports a type B2 thymoma with a large presence of HCs from a 58‑year‑old Chinese woman, and investigates its histopathological characteristics, immunological features and biological behavior. Notably, the present case appeared biologically more aggressive compared with the cases reported previously. The aim of describing this rare case of thymoma with an abundance of HCs is so that it can be recognized and classified by pathologists. [ABSTRACT FROM AUTHOR]

Background: Cervical thymic cysts are uncommon lesions, rarely considered in the differential diagnosis of neck cysts in children. Case presentation: We report a rare case of multiloculated thymic cyst in an 8-year-old boy on the right side of the neck. Perioperative diagnosis was a cystic hygroma. Macroscopic examination showed a cystic mass measuring 6.5 cm in total length. Histopathology of the excised specimen revealed thymic tissue with prominent Hassall's corpuscles associated with multiloculated cyst. The cyst wall is bordered by a flattened or multilayered epithelium, often abraded. Conclusion: This case is presented here for its rarity and should be included in the differential diagnosis of neck masses in children. So, it's a lesion to be well aware of, particularly by pathologists. [ABSTRACT FROM AUTHOR]

Background & Aim: The present study is aimed to document the histological changes of thymus gland during different weeks of gestation in human fetuses. Materials & methods: Fifty-three human fetuses (30 males and 23 females) of different age groups ranging from 9th to 40th gestational week were procured from the Department of Obstetrics and Gynaecology, Sree Balaji Medical College and Hospital, Chennai and from Mahathma Gandhi Medical College, Puducherry. The fetuses were dissected. The thymic tissues thus obtained were immersed in 10% formalin for one week. After proper fixation, the tissue was subjected to routine processing and then the sections were stained with Haematoxylin and Eosin for microscopic examination. Results : Formation of lobules had started at 9th week and distinct formation of lobules was observed during the 12th week. The differentiation of the cortex and the medulla became well distinguished from the 14th week onwards. Presence of Hassall’s Corpuscles was observed from 14th week and was found in all sections from 15th week onwards. Hassall’s Corpuscles increased in number, size and maturity with the increase in the gestational age. Conclusion: Familiarity with the embryology, anatomy, and dynamic physiology of the thymus is essential for clinicians to avoid unnecessary imaging or invasive procedures.

Hassall’s corpuscles are the most prominent structures in the human thymus. However, relatively few analyses have been performed to determine their function and cellular origins during development. In this study, we evaluated the cellular microenvironment of human thymic Hassall’s corpuscles using histochemistry, immunohistochemistry, and transmission electron microscopy. We examined 95 human thymic tissue samples, which were perioperatively obtained from children undergoing cardiac surgery. To characterize the complex cellular microenvironment of human thymic corpuscles, we used a panel of 14 different antibodies to identify discrete cell types. We also utilized various histochemical methods (PAS reaction, alcian blue staining, alkaline phosphatase and acid phosphatase activity staining, von Kossa staining of calcified particles) and transmission electron microscopy to visualize these structures. Considerable variation in the sizes, shapes, and numbers of Hassall’s corpuscles was observed, even amongst children of the same age. Inside the largest Hassall’s corpuscles, cystic dilatation with an accumulation of cellular debris was found. These morphological observations might be associated with disruptions in the formation, migration, or differentiation of cardiac neural crest cells, which are essential for heart and thymus development. Immunohistochemical staining and electron microscopy revealed that Hassall’s corpuscles resemble other types of stratified squamous epithelia. Most Hassall’s corpuscles are heterocellular, consisting of thymic epithelial cells, macrophages, interdigitating dendritic cells, myoid cells, and, occasionally, mast cells and lymphocytes. To explore the potential functions of Hassall’s corpuscles, we found that the concentrations of B-lymphocytes and BCL2-positive lymphocytes suggested a role in regulation of lymphopoiesis. We also found that these structures do not originate from the perivascular epithelium as previously proposed, nor could we identify blood or lymph endothelial cells in close proximity. This leaves the origins of Hassall’s corpuscles an open question. [ABSTRACT FROM AUTHOR]

A comparative morphological study on Hassall's corpuscles of different maturity in vertebrate animals and humans with consideration of the age was carried out by light microscopy. It was found that the number and size of Hassall's corpuscles of different maturity depend on age, as well as the environmental conditions. Conclusions on the functional role of Hassall's corpuscles were drawn based on the present study. [ABSTRACT FROM AUTHOR]

Recently, the effects of exposure to clothianidin (CLO) on the thymus and gut microbiota have become clear, but no report has examined its next-generation impacts. Pregnant C57BL/6N mice were administered a no-observed-adverse-effect-level dose of CLO until weaning. We examined CLO's effects on the gut microbiota and immune organs of dams and their 3- and 10-week-old male offspring. CLO administration led to several alterations of the top 30 bacterial genera in the gut microbiota in dams and 3-week-old mice. Compared to controls, 10-week-old mice had more thymic Hassall's corpuscles, and both dams and 10-week-old mice had fewer macrophages. These results suggest that fetal and lactational CLO exposure may affect the immune system and gut microbiota of the next generation.

Sodium valproate (VPA) was shown to inhibit cell growth mechanisms such as cell cycle arrest, proliferation suppression, increase of apoptosis. Many aspects of the contribution of the VPA pharmacological mechanisms and their significance in gender-related processes have not been investigated. In our study, we have tested hypothesis that the influence of VPA on thymus weight and structure might be gender-related. The thymus of Wistar rats of both genders aged 8 weeks was investigated in the following groups ( n = 6 each): controls, treated with VPA, castrated male and female treated with VPA, and the castrated control of both genders. The thymus weight, structural changes and area of cortical and medullar parts of the gland in slides stained with hematoxylin and eosin and immunohistochemically were assessed. A comparison of thymus weight of castrated male and of castrated VPA-treated male rats showed a significant thymus weight loss after VPA treatment (0.66 ± 0.04 g vs. 0.43 ± 0.03 g, p < 0.05). The treatment with VPA caused an about 6-fold (0.39 ± 0.12 vs. 0.07 ± 0.03) increase of Hassall‘s corpuscles (HCs) numbers per 1 mm 2 in male and more than 4-fold increase (0.46 ± 0.07 vs. 0.10 ± 0.04) in female rats. In castrated males and females, the HCs number was also increased, but this increase was statistically significant only in male animals vs. controls (0.46 ± 0.10 vs. 0.07 ± 0.03, p < 0.001 in males; 0.29 ± 0.13 vs. 0.10 ± 0.04, p > 0.05 in females). When castrated male and female rats were treated with VPA, further increase of HC numbers was found. In our study, VPA has inhibited the proliferative capacity of thymocytes by diminishing the thymus weight and inducing a differentiation of thymic medullar epithelial cells into HCs. The diminishing of the gl. thymus weight under the influence of VPA was significant in castrated male rats. The number of HCs increased in animals of both genders under the influence of VPA. Gender differences in HCs development were noted in castrated animals. [ABSTRACT FROM AUTHOR]

Background: Hassall's corpuscles (HC) are commonly used as diagnostic features for identifying human thymus and are still present in thymuses undergoing fatty degeneration in young adults. However, few studies have been performed on human fetuses. Aim: A cross-sectional study was done, to study the morphology of HC in human fetuses. Materials and Methods: Twenty-eight thymuses were collected from fetuses of gestational age ranging from 11 to 40 weeks. Thymuses were processed by paraffin embedding methods and hematoxylin and eosin staining. Results: The size of HC varied from very small (100 microns) to very large corpuscles (> 900 microns). A high level of polymorphism was also observed, from round to unusual or odd shapes corpuscles. The degenerated reticulo-epithelial cells represented the starting point in HC formation. The growth of HC was rapid, especially near 28 weeks, and the level of HC polymorphism was significantly greater after 28 weeks of gestation. In advanced stages of gestation, the increase in size of some corpuscles reduced the spaces between them, and some patterns strongly supported the hypothesis that some HC had fused in a single and larger corpuscle. Conclusion: The rapid rise in number and size of HC around 28 weeks of gestation would fit with their role in the negative selection process of thymocytes. [ABSTRACT FROM AUTHOR]

The anatomy, histology and ultrastructure of the thymus of a dipnoan, the Australian lungfish, Neoceratodus forsteri, was studied by light and transmission electron microscopy. The thymic tissue showed clear demarcation into a cortex and medulla with ample vascularization. Large cells including foamy and giant multinucleated cells with periodic acid Schiff/Alcian blue positive staining properties were localized mainly in the medulla. The major cellular components were epithelial cells and lymphoid cells. The epithelial cells were classified by location and ultrastructure into six sub-populations: capsular cells, cortical and medullary reticular cells, perivascular endothelial cells, intermediate cells, nurse-like cells and Hassall-like corpuscles. Myoid cells were found mainly in the cortico-medullary boundary and medulla. Macrophages and secretory-like cells were also present. These findings will provide a base of knowledge about the cellular immune system of lungfish. [ABSTRACT FROM AUTHOR]

Abstract: Hassall''s corpuscles are regular structures in the medulla of the normal thymus and in non-neoplastic thymic conditions, e.g. in multilocular thymic cysts. In thymomas, however, they are inconsistently found, and are believed to indicate medullary differentiation of WHO type B1-3 thymomas. We present five organotypical thymomas resembling WHO type B2 and B3 thymomas, but with an abundance of Hassall''s corpuscles. We wonder whether this exceedingly rare observation might herald a distinct entity. Four tumors were asymptomatic, incidental findings and of low Masaoka stage (I or II) . One patient suffered from myasthenia gravis which disappeared upon surgical removal of the thymus, while all other patients had no concomitant autoimmune disease. Two patients had a relapse-free follow-up of 12 and 2 years, respectively, upon curative surgery, and another tumor was an autopsy finding; follow-up data of two more recent cases was not yet available. The neoplastic epithelium other than Hassall''s corpuscles was arranged either in a cortical type B2 pattern or in type B3 solid cords. In all examples, there was cyst formation, inflammatory reaction and repair, indicative of a long-standing condition. Immature T cells were present in all instances. “Corpuscular thymomas” morphologically resemble WHO type B2 and B3 thymomas, but appear biologically indolent and are rarely associated with myasthenia gravis. Whether they qualify for a separate entity has to be proven by larger series, including genetic studies. [Copyright &y& Elsevier]

We characterized herein the microarchitecture of the equine thymus along with post-natal development (6 months→18 years). Thymuses showed an involutional process, beginning before the puberty and defined by five histological grades, which consider the progressive cortical thymocyte depletion, shrinkage and rearrangement of the epithelial network and increase in extracellular matrix (ECM).A second feature of the equine thymus was the presence of eosinopoiesis, erythropoiesis, mastocytopoiesis and plasmacytogenesis. Additionally, lymphatic vessels, full of lymphocytes, were particularly prominent.Distribution of ECM proteins was heterogeneous, being denser in the medulla, as well as basement membranes of capsule, septa and perivascular spaces, thus similar to the patterns seen in other mammals. In vitro, horse thymic nurse cells produce ECM proteins, which are relevant in thymocyte/epithelial cell interactions.In conclusion, the equine thymus presents morphological and involutional characteristics similar to other mammals, exhibiting particular features, as prominent non-lymphoid hematopoiesis and lymphatic vessels. [Copyright &y& Elsevier]

Summary: Tight junctions (TJs), hallmark structures of one-layered epithelia and of endothelia, are of central biological importance as intramembranous “fences” and as hydrophobic “barriers” between lumina represented by liquid- or gas-filled spaces on the one hand and the mesenchymal space on the other. They have long been thought to be absent from stratified epithelia. Recently, however, constitutive TJ proteins and TJ-related structures have also been identified in squamous stratified epithelia, including the epidermis, where they occur in special positions, most prominently in the uppermost living epidermal cell layer, the stratum granulosum. Much to our surprise, however, we have now also discovered several major TJ proteins (claudins 1 and 4, occludin, cingulin, symplekin, protein ZO-1) and TJ-related structures in specific positions of formations of epithelium-derived tissues that lack any lumen and do not border on luminal or body surfaces. Using immunohistochemistry and electron microscopy we have localized TJ proteins and structures in peripheral cells of the Hassall''s corpuscles of human and bovine thymi as well as in specific central formations of tumor nests in squamous cell carcinomas, including the so-called “horn pearls”. Such structures have even been found in carcinoma metastases. In carcinomas, they often seem to separate certain tumor regions from others or from stroma. The structural significance and the possible functional relevance of the locally restricted synthesis of TJ proteins and of the formations of TJ-related structures are discussed. It is proposed to include the determination of the presence or absence of such proteins and structures in the diagnostic program of tumor pathology. [Copyright &y& Elsevier]

Calcineurin, a Ca2+/calmodulin-dependent protein phosphatase, plays an important role in various physiological functions including T cell activation. This enzyme is a target molecule for the immunosuppressants, cyclosporin A and FK506. In the present study, we investigated immunohistochemical localization of calcineurin and FKBP12, an FK506-binding protein, in human thymus and epidermis. The catalytic subunit (calcineurin A) of calcineurin was abundantly expressed in Hassall's corpuscles which were localized in the thymic medulla and represented the terminal stages of thymic medullary epithelium. The regulatory subunit (calcineurin B) of calcineurin was also expressed in high amounts in Hassall's corpuscles. In the epidermis, which shows similarities to Hassall's corpuscles, both subunits were also abundantly expressed, and their expression increased with the differentiation of keratinocytes. FKBP12 was observed to be expressed abundantly, both in Hassall's corpuscles and the entire epidermis. These findings suggest that the differentiated forms of the two cell types, which are the thymic medullary epithelial cell and the keratinocyte, are the target for pharmacological actions of FK506. [ABSTRACT FROM AUTHOR]

The janus kinases (JAK) and signal transducers and activators of transcription (STAT) pathway has been shown to play a key role in cytokine-mediated signal transduction, and to regulate growth, differentiation, and death of both normal and transformed cells. In the present study, we investigated immunohistochemically the distribution of the JAK-STAT pathway in the human thymus. Various elements of the pathway were abundantly expressed in Hassall's corpuscles, located in the thymus medulla and representing terminal stages of the thymic medullary epithelium. Furthermore, the elements of the pathway showed distinct localization in Hassall's corpuscles. JAK1, JAK2, and TYK2 were expressed in high amounts in the entirety of Hassall's corpuscles, whereas JAK3 was in the outer layer. STAT1, STAT2, and STAT6 were abundantly expressed in the entire Hassall's corpuscles, whereas STAT5 was in the outer layer. These findings strongly suggest that the JAK-STAT pathway may play a role in thymic medullary epithelial maturation. [ABSTRACT FROM AUTHOR]

The dissolution of Hassall's corpuscles by macrophages has been demonstrated in the sheep thymus. The findings indicate that enlarged Hassall's corpuscles are rapidly broken down by macrophages at the end of gestation or immediately after birth and replaced by newly formed corpuscles, and that these cyclic changes in Hassall's corpuscles persist, under normal physiological conditions, throughout life. [ABSTRACT FROM AUTHOR]

Substrate-histochemical, enzyme-hystochemical and ultrastructural investigations were performed on thymic tissue from children, obtained in heart operations. β-Amylaseresistant, PAS-positive and Hale-positive substrates presumably neutral and acid mucosubstances, can be demonstrated in the central concentric lamellae of Hassall's corpuscles (HC). These lamellae also give positive reactions for sulphydryl groups and disulphide groups. Some flattened cell elements gave strong reactions for phospholipids, and small sudanophilic droplets, presumably neutral fats, are scattered throughout the HC. All investigated hydrolases and dehydrogenases either give no or only very weak reactions in the central part of progressive HC, but react strongly positive in their peripheral hypertrophic epithelial cells. In the central part of regressive HC, positive reactions for acid phosphatase and β-D-glucuronidase were recognized. These lysosomal enzymes may indicate degenerative processes. By electron microscopy progressive HC show central concentric lamellae with an amorphous matrix tightly filled with tonofilaments. They are surrounded by a thickened plasma membrane (200 Å), and do not contain nuclei. These central lamellae resemble the horny cells of the epidermis. The peripheral hypertrophic epithelial cells have pale nuclei with one or two nucleoli. Their cytoplasm contains numerous tonofibrils. These cells resemble stratum spinosum cells of the epidermis. In regressive HC the central concentric lamellae loose their intercellular contacts. The widened intercellular spaces are filled with cellular debris, and are invaded by macrophages. Similarities between the ultrastructure and the patterns of the histochemically investigated substrates and enzymes in human HC and epidermis are discussed. [ABSTRACT FROM AUTHOR]

The article discusses a study which investigated the histogenesis and degeneration of Hassall's corpuscles in thymus of buffalo. The results show the histogenesis of Hassall's corpuscles began at seventy days in buffalo and the presence of three corpuscle types in the thymus of the buffalo namely unicellular, multicellular and giant type can be noted. Degeneration began at six months postnatal and disappeared completely by two years of age. The methods used in preparation, testing, and data analysis are also discussed.