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.
where does positive selection of t cells occur
the thymus the thymus