The role of thymic epithelium in the acquisition of tolerance.

There are two separate mechanisms of induction of T-cell tolerance in the thymus. First, MHC molecules expressed on bone-marrow-derived cells can cause clonal deletion of autoreactive cells. Second, as discussed here by Elisabeth Houssaint and Martin Flajnik, thymic epithelial cells can generate a form of tolerance that does not eliminate self-reactive clones. This nondeletional mechanism, which is also a feature of the other MHC class-II-bearing epithelia, may contribute to the establishment of tolerance-maintaining regulatory networks.