iMacs isolated from the spleen of tumor-bearing mice are CD11b⁺/ Gr-1⁺/CD31⁺.

(A) Splenocytes from mice bearing a subcutaneous TS/A tumor were stained with FITC–anti-Gr-1, PE–anti-CD11b, and biotin–anti-CD31 antibodies, followed by Tricolor-streptavidin. After gating CD11b⁺/Gr-1⁺ cells (left panel), the cytometric profile for CD31 marker was plotted (histograms to the right of the arrow). Isotype-matched mAbs were used as controls for background staining (shaded areas). (B) Gr-1⁺ splenocytes from the same mice were depleted by panning with the specific mAbs. The resulting population was stained with the same mAbs used in panel A, and expression of CD31 (right panel) was evaluated among the CD11b⁺ cells (left panel). Staining with a secondary antirat Ab revealed a number of positive cells <1% confirming that negativity for Gr-1 was not due to Ab competition.