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Depending on whether the T cell binds MHC I or II, it will become a CD8+ or CD4+ T cell, respectively. Positive selection occurs in the thymic cortex with the help of thymic epithelial cells that contain surface MHC I and MHC II molecules. During negative selection, T cells are tested for their affinity to self. If they bind a self peptide ...
Major function of cTECs is to positively select those T cells that are capable to recognize and interact with MHC molecules on their surface [3]. Once T cell precursors enter the thymic cortex, they start their transformation from double negative stages (T cell without surface expression of CD4 and CD8 co-receptors) to a double positive stage (T cell with surface expression of both co ...
However the repertoire of peptides in the cortex is limited to those expressed by epithelial cells, and double positive cells are poor at undergoing negative selection. Therefore, the most important site for negative selection is the medulla, once cells are at the single positive stage.
A figure depicting the process of T cell / thymocyte positive and negative selection in the thymus. mTEC shown in orange. Medullary thymic epithelial cells (mTECs) represent a unique stromal cell population of the thymus which plays an essential role in the establishment of central tolerance.
By layer, epithelium is classed as either simple epithelium, only one cell thick (unilayered), or stratified epithelium having two or more cells in thickness, or multi-layered – as stratified squamous epithelium, stratified cuboidal epithelium, and stratified columnar epithelium, [8]: 94, 97 and both types of layering can be made up of any of ...
The thymus is made up of immature T cells called thymocytes, as well as lining cells called epithelial cells which help the thymocytes develop. T cells that successfully develop react appropriately with MHC immune receptors of the body (called positive selection) and not against proteins of the body (called negative selection). The thymus is ...
BerEp4 has a high sensitivity and specificity in being positive only in BCC cells. [1] BerEp4 is normally negative in squamous epithelium and mesothelium, but otherwise normally positive most epithelial cells of the body. [3] It can also help in distinguishing pulmonary adenocarcinoma (positive BerEp4) from mesothelioma (generally negative BerEp4).
TECs originate from non-hematopoietic cells that are characterized by negative expression of CD45 and positive expression of EpCAM. Then TECs are divided into two phenotypically and functionally different groups that have distinct location, cytokeratin expression, surface markers, maturation factors, proteases and function in a T cell selection.