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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. [ABSTRACT FROM AUTHOR]

Background: Thymus is the primary lymphoid organ in avian. It is a site of differentiation and maturation of T lymphocytes. Quail thymus showed age related involution with decrease in its volume and cellular contents. It is a lymphoepithelial organ and thus plays a major role in the anti-infection defense mechanism. Methods: For the present study 48 Japanese quail birds reared and thymus was collected from 12 birds each at end of first week, second week, third week and fourth week. The tissue was processed for routine paraffin embedding and processed for different staining procedures for histomorphological studies. Result: In all age group of birds, each thymic lobe was enclosed by thin connective tissue capsule. Thymic lobule was found to be composed of outer cortex and inner medulla. Cortex was composed of lymphocytes, lymphoblasts, myoid cells, macrophages, plasma cells and epithelial reticular cells and that of medulla was composed of lymphocytes, lymphoblast, epithelial reticular cells, myoid cells, macrophages, plasma cells, cyst and Hassall's corpuscles. The cyst of various shapes and sizes were observed in cortex and medulla. In all age group of birds, unilamilar and multilamilar Hassall's corpuscles were observed. Number of Hassall's corpuscles and macrophages were increased with the advancement of age. [ABSTRACT FROM AUTHOR]

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]

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]

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]

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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]

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]

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]

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]