Increased levels of SCF in the BM of hpa-Tg mice stimulate adhesion of primitive cells to osteoblasts.(A) SCF mRNA levels in BM cells from WT or hpa-Tg mice, detected by real-time RT-PCR. Data are means plus or minus SE; n = 9 samples. (B) SCF levels in the BM of WT or hpa-Tg mice, detected by ELISA. Data are means plus or minus SE; n = 5 samples. (C) SCF staining (brown) of femoral bone from WT or hpa-Tg mice. Inset shows enlargement of sinusoidal endothelial region. Black arrows point at bone lining osteoblasts. Red arrowheads point at endothelial cells. Yellow arrowheads point at cells that highly express SCF and are in close proximity to sinusoids. Micrographs were acquired by staining with goat anti–mouse stem cell factor (R&D systems) and processed as in Figure 1C, except with a 40×/Plan-Apo objective. (D) mRNA levels of SCF in primary osteoblasts derived from WT or hpa-Tg mice. Data are means plus or minus SE; n = 4 experiments. (E) Percentage adhesion to primary osteoblasts of BM MNC Sca-1⁺/c-Kit⁺/Lin⁻ cells derived from hpa-Tg compared with control (WT) mice. In some experiments, leukocytes were pretreated with neutralizing anti-c-Kit antibodies before adhesion. Data are means plus or minus SE; n ≥ 4 experiments. (F) c-Kit receptor expression in the primitive c-Kit⁺/Lin⁻ cells following exogenous in vitro treatment with heparanase. Data are means plus or minus SE; n = 3 experiments (*P < .05).