Cell proliferation is an essential function and highly structured event that when unregulated, can cause disease. We can measure proliferation through absolute cell counts or with a dye, such as CFSE. When cells labeled with CFSE divide, the dye is partitioned equally between daughter cells and we can measure the loss of CFSE fluorescence over time as the dye is continuously diluted. The mean fluorescence intensity (MFI) of the dye was also plotted with cell concentration over time to show the inverse relationship between the two. This type of assay is often used to look at changes in T lymphocyte activation.