Effect of human bone marrow CD34⁺ cells on cytokine synthesis by human osteoblasts. Bone marrow CD34⁺ cells (1.0 × 10⁴) were seeded directly onto confluent human osteoblast monolayers (HOB) as described in the Materials and Methods in 24-well tissue culture plates with 10% FBS. At 96 hours, conditioned medium was collected and assayed for G-CSF, GM-CSF, IL-6, LIF, or TGF-β₁ by ELISA. Individual data from three independent experiments are presented as the mean ± standard deviation for triplicate determinations. ^*Significant difference from no CD34⁺ (HOB) control to a statistical significance of P < .05.