A novel approach for on line monitoring of apoptotic cell shrinkage in individual live lymphocytes

The apoptotic process occurs asynchronically in most cell populations and its duration is variable. Therefore, the ability to continuously monitor the death process occurring in individual blood cells before, during and following apoptosis induction is crucial in the evaluation of the efficiency of pro- or anti-apoptotic drugs. We applied a kinetic approach by performing real time measurements of individual living cells. This approach is based on an easy and unique method for monitoring intracellular staining reaction, which accompanied early apoptotic cell shrinkage. The intracellular enzymatic reaction rates were determined by taking repeated, sequential measurements of fluorescence intensity of the same individual cells. These rates were found to correlate with the respective radii of the cells under different conditions, and to decrease following apoptosis induction. The ability to remeasure the same cell before and after apoptosis induction enabled the detection of specific individual lymphocytes, which were more susceptible or resistant to pro-apoptotic stimulus.