Effect of CD34⁺ bone marrow cell number on IL-6 synthesis in coculture with osteoblasts. Bone marrow CD34⁺ cells (0 to 1.0 × 10⁴) were seeded directly onto confluent human osteoblast monolayers (HOB) in 96-well tissue culture plates containing 1% FBS. At 96 hours, conditioned medium was collected and assayed for IL-6 by ELISA. Data from a representative of three experiments are presented as the mean ± standard deviation for triplicate determinations. ^*Significant difference from no CD34⁺ cell control (HOB) to a statistical significance of P < .05.