Deletion of Rac1 or Rac1/Rac2 in HSCs results in decreased T-lymphocyte cellularity in spleen that is associated with increased apoptosis. (A) Number of T cells in splenocytes was determined by staining the splenocytes with anti-CD4, -CD8, and -TCRβ antibodies followed by flow cytometry. (B) The apoptotic T-cell subpopulations in splenocytes were measured by the antibody and annexin V costaining followed by flow cytometry. The results are representative of 2 experiments. n = 5 for each genotype. **P < .01. Error bars represent SD.