T-cell tolerance.

Despite the acceptance of principles such as clonal deletion in the thymus and peripheral clonal anergy, several new issues have arisen in the study of T-cell tolerance. For example, in the case of thymic tolerance, it is now clear that several distinct components of the thymus, including various subsets of thymic epithelial cells, can all make contributions to the deletion of autoreactive T cells. In the case of peripheral T-cell tolerance, the induction of anergy now has been complicated by the possibility that bone marrow derived antigen presenting cells may, under certain conditions, be tolerogenic rather than stimulatory.