where does positive selection of t cells occur
T cell About 98% of thymocytes die during the development processes in the thymus by failing either positive selection or negative selection, whereas the other 2% survive and leave the thymus to become mature immunocompetent T cells. Increasing evidence indicates microRNAs, which are small noncoding regulatory RNAs, could impact the clonal selection process during thymic development. For example, miR-181a was found to play a role in the positive selection of T lymphocytes.[31]