CD27 expression and kinetics of peripheral blood B cells in healthy young subjects. Fraction of cells labeled (F) at time points after 24-hour infusion of 6,6-²H₂-glucose in B cells separated into CD27⁺ (⬡, solid line) and CD27^- (○, dashed line) subsets. Error bars indicate SD of GCMS measurement of enrichment. Lines show the best fit to the model, assuming peak labeling at 24 hours. All graphs are on the same scale.