Large pre-BII, but not pro-B/pre-BI, cells are found in close contact with GAL1-expressing stromal cells. Large pre-B II cells (A-B) and pro-B/pre-BI cells (C) were purified from the BM of C57Bl/6 mice by flow cytometry and stained with PKH26. Labeled cells were then injected intravenously in stroma-GFP mice treated with HU. Mice were killed 15 hours after injection. BM sections were stained with anti-GAL1, anti-GFP antibodies, and Sytox Blue (nuclei) as indicated. The presence or the absence of contacts between PKH26-labeled B cells and GAL1⁺GFP⁺ stromal cells was determined by analyzing 10-μm-thick z sections by confocal microscopy (original magnification 63×/1.4 NA oil objectives). Bar represents 10 μm. Confocal images are representative of 3 (A-B) and 2 (C) independent experiments. Cell counts are presented in Table 1. Images acquired on Zeiss LSM310 Meta and analyzed with ImageJ 1.44.