Effect of time between GM-CSF stimulation/fixation and evaluation by flow cytometry on the change in CD11bSurface. Fresh, heparinized blood was collected from healthy people, incubated with or without GM-CSF within 1 hour of phlebotomy, staining with antibodies to CD11bSurface, and fixed (closed symbols) or stored at room temperature for various times (open symbols) before stimulation, immunostaining and analysis by flow cytometry as described in the Methods. Symbols represent the mean ± SD for n = 3 per point. Comparisons to the corresponding value on day zero were made by ANOVA with Dunnett's test; * = P<0.05, *** = P<0.001.