Figure 2.

The IL2 biological dose-response relationship is determined at the single cell level by a marked heterogeneity of responsiveness. Asynchronously proliferating IL2R+ cells were exposed to varying concentrations of IL2 for 18 hours. Subsequently, cell aliquots were either pulsed for 4 hours with ³H-TdR, or stained with propidium iodide prior to single cell analysis by flow cytometry. The cell population incorporates ³H-TdR in an IL2 concentration dependent manner, and the amount of ³H-TdR incorporation at each IL2 concentration is determined by the absolute number of cells that have entered S-phase, as indicated by the single cell analysis by propidium iodide staining. From reference 26.