Expression of Runx1 in peripheral lymphocytes. (A) Spleen cells were isolated from either wild-type or Runx1-IRES-GFP^k/k mice and stained for B220, surface IgM, and surface IgD. The dot plot depicts the expression of IgM and IgD in B220⁺ B lymphocytes and shows the gating strategy used. GFP expression in IgM⁺IgD^-, IgM⁺IgD⁺, and IgM^dimIgD⁺ cells is depicted in panels i, ii, and iii, respectively. The filled and open curves indicate GFP expression in wild-type and Runx1-IRES-GFP^k/k cells, respectively. The MFI of GFP expression of Runx1-IRES-GFP^k/k cells in each subset is indicated in the figure. (B) Peripheral T-cell lymph node subsets were stained for CD3, CD4, and CD8. GFP expression in CD3⁺CD4⁺ and CD3⁺CD8⁺ subsets was determined by flow cytometry using the gating strategy shown. The MFI of GFP expression of Runx1-IRES-GFP^k/k CD4⁺ and CD8⁺ cells is 16.68 and 7.39, respectively. (C) Determination of the relative level of Runx1 mRNA expression by real-time RT-PCR in sorted CD4⁺ and CD8⁺ lymph node cells from Runx1-IRES-GFP^k/k mice. The Runx1 values were normalized relative to that of the corresponding GAPDH level, to account for differences in the amount of RNA analyzed.