Gr-1⁺CD11b⁺F4/80⁺ cells from RMA-S tumor-bearing mice express RAE-1 and suppress T cell proliferation. (A) Peripheral blood leukocytes (PBLs) of naive and tumor-bearing mice isolated on day 21 after tumor cell inoculation were stained with mAbs specific for Gr-1 and CD11b in combination with mAbs directed against F4/80 and CD124 (IL-4Rα). Plots are gated on Gr-1⁺CD11b⁺ cells. Histograms were further gated on Gr-1⁺CD11b⁺F4/80⁻ (R1) or Gr-1⁺CD11b⁺F4/80⁺ (R2) cells to analyze the expression of CD124 (solid lines) compared with the respective isotype-matched control Ig (gray filled histograms). Flow cytometric analysis of PBLs of one representative of 5 animals per group is shown. (B) PBLs from tumor-bearing mice were gated on Gr-1⁺CD11b⁺F4/80⁻ (R1) or Gr-1⁺CD11b⁺F4/80⁺ (R2) as described above and analyzed for the expression of Ly6G. Gated cells are also depicted in a forward and side scatter plot. (C) PBLs from naive and tumor-bearing mice (day 21) were stained with mAbs specific for Gr-1 and F4/80 in combination with a mAb directed against panRAE-1 (solid lines) or the respective isotype-matched Ig controls (gray filled histograms). Histograms are gated on Gr-1⁺F4/80⁻ (R1) or Gr-1⁺F4/80⁺ (R2). For R1 and R2, percentages among all PBLs are indicated in the plots. (A-C) One representative experiment of at least 3 independent experiments is shown.