Thymus epithelial cell

Thymus-epithelial cells (mTEC) are found in the thymus both in the medulla and in the cortex. In the medulla they form the Hassall corpuscles whose function has not yet been finally clarified. mTECs play an important role in "self-tolerance" (see below tolerance; see below immune tolerance). In mTECs, in contrast to all other known cells, proteins are formed which have no special function for the cell itself. They are produced to develop self-tolerance.

With the help of proteasomes, these proteins are broken down into short fragments. These peptides are then presented to the T-cells of the thymus in the peptide binding pockets of histocompatibility antigens(MHC). It is of fundamental importance that each T cell recognises only one specific antigen. This recognition mechanism takes place via T-cell receptors that are expressed on the surface of T-cells. In a thymus epithelial cell, about 5% of all human proteins are produced purely statistically. With about 100 mTECs, the peptides of all human endogenous proteins can be presented to maturing T-lymphocytes in the thymus. These T cell receptors are generated by randomly assembled gene segments. This infinitely varied "randomness" explains the different populations of T cells. So also randomly formed T-cells with receptors that are directed against the body's own proteins. These must be eliminated.

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