Time-dependent expression of MIP-1 receptors on LP CD34⁺ in short-term suspension culture. Cells were cultured at a concentration of 1 to 2 × 10⁵ cells in 1 mL of IMDM supplemented with 15% (vol/vol) FCS and incubated in 5% CO₂ and 5%O₂ in nitrogen for various time periods (4, 10, and 24 hours) in the absence or presence of TNF- (2 ng/mL). MIP-1 receptor expression was assessed by determining the mean fluorescence (A) and the percentage of CD34⁺ cells expressing MIP-1 receptors (B). (C) Shows a representative experiment. Overlay plots of the histograms (cell number against MFI) for the different cell populations at successive time-points are shown. T = 0 hours, empty area represents the untreated cell population stained for MIP-1 receptors (FITC). T = 10 hours and T = 24 hours, shaded and empty areas represent MIP-1 receptor expression in TNF-–treated and untreated cells, respectively. Data points in (A) and (B) are the mean ± SEM of four independent experiments. Nonspecific binding of avidin-FITC in TNF-–treated cultures was not increased over untreated cells at T = 0 hours. (*) Denotes significant differences between the TNF-–treated and untreated cells (P < .05). (**) Indicates significant differences in comparison to control values at 0 hours incubation (P < .05).