Thymic nurse cells: Their functional ultrastructure

Abstract

Thymic nurse cells are defined in vitro as multicellular complexes of epithelial cells and thymocytes. Although these structures have been implicated in the intrathymic differentiation of thymocytes, little is known about the biology of this cell complex and about the occurrence of the cells in the thymus in situ. Therefore, to clarify the matter, in this review we have presented characteristics of epithelial cells capable of forming complexes with thymocytes, in light of the literature data and the experience of the authors. The structure of cells within the complexes allowed us to distinguish three types of thymic nurse cells. Three‐dimensional reconstruction of the thymus and observations employing TEM and SEM demonstrated the presence of distinct types of complexes in various topographic regions of the thymus. Where possible, the functional relevance of the morphological data was analyzed. Microsc. Res. Tech. 38:250–266, 1997. © 1997 Wiley‐Liss, Inc.

Thymic nurse cells exhibit epithelial progenitor phenotype and create unique extra-cytoplasmic membrane space for thymocyte selection

“…We believe that all of these structures are external to the cytoplasm of the TNC. Collectively, we propose these data to show that most thymocytes, as seen in classical micrographs (Figures 1 and 8, and [32]) of TNCs complexes, are external to cytoplasmic spaces. That is, the majority of trapped thymocytes dwell within the fenestrated cage-like structure where they are free to move (as seen in the video, Figure 9C).…”

Subtypes of thymic epithelial cells defined by neuroendocrine markers

“…outer and inner cortex differ from each other not only in the cellular composition. Such complexes have also been observed in situ, at various depths of the cortex (Brelińska and Warchol 1997;Hiramine et al 1996). At this stage of the studies participation of PGP 9.5-positive cells in the processes cannot be defined.…”

“…At this stage of the studies participation of PGP 9.5-positive cells in the processes cannot be defined. While the role of PGP 9.5 remains to be clarified, manifestation of the protein in TNC may suggest that its expression is linked to the biological activity of nurse cells, which are responsible for secretion of several humoral factors (Brelińska and Warchol 1997). Such cell clumps may correspond to the lymphoepithelial complexes of thymic nurse cells (TNC), described in vitro by Wekerle et al (1980).…”

Normal Structure, Function and Histology of the Thymus

“…All epithelial cells express MHC class I products, but MHC class II antigens are differentially expressed in the cortical and medullary epithelium. In the subcapsular region, specialized epithelial PEARSE TOXICOLOGIC PATHOLOGY cells known as thymic nurse cells engulf and form strong cell-cell membrane interactions with large numbers of developing lymphocytes (Brelinska and Warchol, 1997). These nurse cells are important in early T cell differentiation.…”