Use of a FACS III for fluorescence depolarization with DPH

We have previously demonstrated age-related differences in human lymphocyte membrane fluidity, by use of steady-state polarization measurements on bulk cell suspensions with the fluorescence probe DPH. However, for exact analysis of the possible functional importance of these changes, single-cell measurements were deemed of interest. We have now used an analog division device to measure fluorescence depolarization "p" of DPH in real time with a FACS III flow cytometer. The measurements are reliable, as we have been able to confirm the differences in DPH "p" between monocytes and lymphocytes previously shown in bulk suspension and to demonstrate the expected differences in fluidity of lipid-modulated cells. We also found significant differences in DPH "p" between lymphocytes of young and elderly blood donors. Lymphocyte subsets did not differ in polarization values but did differ in fluorescence intensity with Th less than Ts less than B = NK cells.