RasGRP1 is dispensable for thymocyte clonal deletion but is required for positive selection and regulates the expression of molecules induced by high-affinity TCR stimulation. HY^cd4 mice were crossed onto the RasGRP1 KO background, and thymi from male and female HY^cd4 animals were examined. (A) CD4 and CD8 profiles of T3.70⁺ thymocytes from the indicated mice. (B) Percentages of active caspase 3⁺ T3.70⁺ DP^bright and DP^dull cells. Error bars indicate SEM. (C) PD-1 and Helios profiles of T3.70⁺ DP^bright and DP^dull cells from the indicated mice. (D) CD4^−/dullCD8^−/dull cells from the indicated mice were examined for expression of CD5 and T3.70 (top). T3.70^hiCD5^hi thymocytes were analyzed for expression of CD5 and CD122 (bottom). Data in A–C are representative of four individual experiments; n = 4. D is representative of three individual experiments; n = 3.