DN1 and DN2 thymocytes develop to functional macrophages. Sorted DN1 and DN2 thymocytes were plated at 20 cells/well of 96-well plates on ST-2 stromal cells in the presence of IL-7. (A) Light microscopy photograph of macrophage-like–looking cells derived from DN2 thymocytes after 3 weeks in culture. Image was obtained using Diavert (Leica Microsystems AG, Glattbrugg, Switzerland), inverted microscope 40 ×, 10/0.25, air, no stain, camera Nikon DXM 1200F, Japan. (B-C) Flow cytometric analysis of cultures shown in panel A with no antibody staining and stained with anti-CD11c together with anti-F4.80 fluorochrome-labeled mAb. (D) Fluorescence microscopy photograph of macrophage colonies derived from DN2 thymocytes that have ingested fluorescent latex beads. Image was obtained using Axioskop (Zeiss, Zurich, Switzerland) fluorescence microscope, 250 ×,25 × 12 × 0.63 water, no stain, camera Nikon DXM 1200F, Japan.