Rate of IL-6 synthesis in coculture of CD34⁺ bone marrow cells with osteoblasts. Bone marrow CD34⁺ cells (1.0 × 10⁴) were seeded directly onto confluent human osteoblast monolayers (HOB) in 96-well tissue culture plates containing 1% FBS. At 24, 48, and 96 hours, conditioned medium was collected and assayed for IL-6 by ELISA. Data from a representative of three independent experiments are presented as the mean ± standard deviation for triplicate determinations. ^*Significant difference from no CD34⁺ (HOB). ⁺Significant difference from previous time point to a statistical significance of P < .05.