To understand how thymic selection gives rise to T cells that are capable of major histocompatibility complex (MHC)-restricted recognition of antigen but are tolerant of self, we directly examined how peptide/MHC ligands expressed on thymic epithelial cells trigger the positive selection of immature thymocytes. We demonstrate that abundant self-peptides, purified from the H-2Db molecules of thymic epithelial cells, are specifically recognized during the positive selection of CD8+ T cells, implying that positive selection generates a repertoire of T cells that is weakly self- reactive. We also found that this recognition is somewhat cross-reactive, thereby providing an explanation for how the specific recognition of a limited repertoire of thymic self-peptides can select a diverse repertoire of T cells.
Hu, Q., Bazemore Walker, C. R., Girao, C., Opferman, J. T., Sun, J., Shabanowitz, J., … Ashton-Rickardt, P. G. (1997). Specific recognition of thymic self-peptides induces the positive selection of cytotoxic T lymphocytes. Immunity, 7(2), 221–231. https://doi.org/10.1016/S1074-7613(00)80525-7