title: What do we know about the structure of human thymic Hassall's corpuscles? A histochemical, immunohistochemical, and electron microscopic study.
abstract: 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.
authors.affiliation: Institute of Histology and Embryology, Faculty of Medicine, Comenius University in Bratislava, Sasinkova 4, 811 08 Bratislava, Slovak Republic.
authors.forename: Renáta
authors.initials: R
authors.lastname: Mikušová
authors.affiliation: Institute of Histology and Embryology, Jessenius Faculty of Medicine in Martin, Comenius University in Bratislava, Mala Hora 4, 036 01 Martin, Slovak Republic.
authors.forename: Veronika
authors.initials: V
authors.lastname: Mešťanová
authors.affiliation: Institute of Histology and Embryology, Faculty of Medicine, Comenius University in Bratislava, Sasinkova 4, 811 08 Bratislava, Slovak Republic.
authors.forename: Štefan
authors.initials: Š
authors.lastname: Polák
authors.affiliation: Institute of Histology and Embryology, Faculty of Medicine, Comenius University in Bratislava, Sasinkova 4, 811 08 Bratislava, Slovak Republic. Electronic address: ivan.varga@fmed.uniba.sk.
authors.forename: Ivan
authors.initials: I
authors.lastname: Varga
mesh_terms: D060833:Cellular Microenvironment; D002648:Child; D002675:Child, Preschool; D004847:Epithelial Cells / Q000737:chemistry / Q000648:ultrastructure*; D005260:Female; D006801:Humans; D008214:Lymphocytes / Q000737:chemistry / Q000648:ultrastructure*; D008297:Male; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013950:Thymus Gland / Q000737:chemistry / Q000648:ultrastructure*
keywords: Dendritic cells; Endothelial cells; Epithelial cells; Hassall’s corpuscles; Human thymus; Lymphocytes; Macrophages