Multinucleate cells in thymus of C3H mice

Morphometric Analysis of the Thymic Epithelial Cell (TEC) Network Using Integrated and Orthogonal Digital Pathology Approaches

The thymus, a central primary lymphoid organ of the immune system, plays a key role in T cell development. Surprisingly, the thymus is quite neglected with regards to standardized pathology approaches and practices for assessing structure and function. Most studies use multispectral flow cytometry to define the dynamic composition of the thymus at the cell population level, but they are limited by lack of contextual insight. This knowledge gap hinders our understanding of various thymic conditions and pathologies, particularly how they affect thymic architecture, and subsequently, immune competence. Here, we introduce a digital pathology pipeline to address these challenges. Our approach can be coupled to analytical algorithms and utilizes rationalized morphometric assessments of thymic tissue, ranging from tissue-wide down to microanatomical and ultrastructural levels. This pipeline enables the quantitative assessment of putative changes and adaptations of thymic structure to stimuli, offering valuable insights into the pathophysiology of thymic disorders. This versatile pipeline can be applied to a wide range of conditions that may directly or indirectly affect thymic structure, ranging from various cytotoxic stimuli inducing acute thymic involution to autoimmune diseases, such as myasthenia gravis. Here, we demonstrate applicability of the method in a mouse model of age-dependent thymic involution, both by confirming established knowledge, and by providing novel insights on intrathymic remodeling in the aged thymus. Our orthogonal pipeline, with its high versatility and depth of analysis, promises to be a valuable and practical toolset for both basic and translational immunology laboratories investigating thymic function and disease.

Are human placental bed giant cells merely aggregates of small mononuclear trophoblast cells? An ultrastructural and immunocytochemical study

The ultrastructure of placental bed giant cells in early human pregnancies of 7-12 weeks gestational age is described. Their nature and function was further characterized by confocal immunofluorescence microscopy of paraffin sections labelled for cytokeratin, gap junction connexins (CX) 32 or 43, and placental hormones, alpha-human chorionic gonadotrophin (alpha-HCG) and human placental lactogen (HPL). Placental bed giant cells were observed with two phenotypes; as single large trophoblast cells containing one or more nuclear profiles in a voluminous cytoplasm, and as cell aggregates comprising mononuclear trophoblast cells in close apposition separated by narrow intercellular spaces. Cells within the aggregates are attached to one another by desmosomes, and also possess gap junctions as shown by immunolabelling for CX32 and CX43. By contrast, gap junctions were absent in the true multinucleated giant cells. Organelles present within the cytoplasm of the giant cells and their immunoreactivity for HPL and alpha-HCG suggest protein synthesis.

Thymic nurse cells in culture: morphological and antigenic characterization

Epithelial monolayers were derived from thymic nurse cells (TNC), and were seeded onto collagen-coated dishes immediately after their isolation from young adult C3H-murine thymuses. Different media and supplements were tested in order to obtain cultures that were as pure as possible. Primary cultures were enriched in epithelial cells but always contained non-epithelial components among which fibroblasts predominated. Immunodetection of keratins, and repeated light- and electron-microscopic observations established the epithelial nature of the elongated cells derived from TNC; these elongated cells were cortical reticular cells, and were different from medullary globular cells that immediately adopted a mosaic pattern in vitro. At the beginning of the culture, the necrosis of cortical lymphocytes appeared to be toxic for epithelial cells; when epithelial cells survived, they showed a temporary lipid accumulation. After a 5-day culture, they still synthesized DNA but lost this capacity thereafter and dedifferentiated. The lympho-epithelial symbiosis appeared to be necessary to maintain some epithelial characteristics of the cultured cells, such as the clear vesicles and the expression of Ia antigens. In sub-cultures, the monolayers were almost purely epithelial in nature but growth was no longer observed. The cells remained reticular in shape, as they were in vivo, but their cytoplasm and their nucleus became larger and numerous cells were multinucleated. Confluence was not obtained with classical media even after mitogenic stimulation. The frequent observation of strongly keratinized areas suggested a process of terminal differentiation; this could not be avoided by using low serum concentration.

Epithelial cell heterogeneity in mammalian thymus: monoclonal antibody to high molecular weight keratins exclusively binds to Hassall's corpuscles

Hassall's corpuscles represent a subset of medullary thymic epithelial cells whose origin and function within the thymus still remain largely unknown. The present study shows that Hassall's corpuscles can be defined by their intracellular content in specific keratin subunits. Two monoclonal anti-keratin antibodies were used: KL1, directed to high molecular weight keratins, and KL4, specific for high and medium molecular weight polypeptides. In vivo, KL1 exclusively binds to Hassall's corpuscles of five mammalian species including mouse, rat, guinea-pig, rabbit and pig. Thus KL1 appears as an exclusive marker of Hassall's corpuscles in a large number of mammals. In vitro, thymic epithelial cells gave rise in certain species to Hassall's corpuscles. In contrast to its in vivo reactivity, KL1 never labelled Hassall's corpuscles developed in vitro. These data strongly support the following conclusions: (1) Hassall's corpuscles derive from medullary epithelial cells; (2) they represent advanced stages of thymic epithelial maturation; (3) thymic epithelial cell differentiation is impaired in vitro. Furthermore, this study provides additional evidence that thymic epithelium heterogeneity reflects different stages in epithelial maturation.

Multinucleate giant cells in the regressed corpus luteum of the bitch

The pigmented cell clusters which make up the residual luteal tissue in the canine ovary were found to be mostly syncytial in nature and to resemble the foreign-body and Langhan's-type giant cells of chronic inflammation.

Primary cultures of human myasthenia gravis thymus and normal thymus. Studies of cell morphology, cell proliferative pattern and localization of alpha-bungarotoxin binding sites on cultured thymic cells

We have established primary cultures of human myasthenia gravis (MG) thymuses and normal thymuses. In cultures of 19 thymuses with hyperplasia among 23 MG thymuses and 12 thymuses among 13 normal thymuses, epithelial cells migrated in a mosaic-like arrangement and were maintained for more than 5-10 weeks. There were, among mononuclear epithelial cells, some multinucleated cells, some of which were considered to be derived from epithelial cells because they had a desmosome-like structure and contained tonofilaments in their cytoplasm. There was no significant difference in the morphology of epithelial cells between MG thymuses and normal thymuses. The growth rate of thymic epithelial cells was identified by [3H]thymidine autoradiography(ARG), labeling indices rising to a peak around a week and falling to low levels gradually. There was no significant difference in the growth rate of epithelial cells between MG thymuses and normal thymuses. An autoradiographic method with 125I-labeled alpha-bungarotoxin was used to detect the presence of acetylcholine receptor (AChR) on the cultured cells. ARG of human MG thymuses and normal thymuses, which were cultured for 4 weeks, revealed diffusely distributed silver grains on the epithelial cells. Toxin binding sites (AChRs) were considered to be present on the epithelial cells. There was no significant difference in the distribution of AChR on the epithelial cells between MG thymuses and normal thymuses.

The thymus of Nu/+ mice

At one month, the thymus weight of NMRI mice heterozygous for the Nu gene was lower than that of the wild type. However, the thymic structure was normal and no significant anomalies at the ultrastructurallevel could be found either in epithelial cells or in thymocytes. Stereologic data showed that the loss of weight was only due to a decrease of the lymphoid population, whereas the absolute number of epithelial cells was unmodified. Several hypotheses that could explain the reduced number of thymocytes were discussed.