Thymic progenitors of TCRαβ CD8αα intestinal intraepithelial lymphocytes require RasGRP1 for development.

Strong T cell receptor (TCR) signaling largely induces cell death during thymocyte development, whereas weak TCR signals induce positive selection. However, some T cell lineages require strong TCR signals for differentiation through a process termed agonist selection. The signaling relationships that underlie these three fates are unknown.