Mitogen-induced changes in the fluorescence polarization of fluorescein in normal human lymphocytes: a membrane event?

The fluorescence polarization of human lymphocytes undergoing fluorescein fluorochromasia was measured in a system in which antifluorescein IgG was used to quench the extracellular emission of fluorescein leaked from the cells. The polarization values obtained from control cells were similar to those obtained by other investigators, as was the decrease in polarization in response to exposure to phytohemagglutinin or concanavalin A. However, the changes in polarization resulting from mitogen stimulation depended on the amount of antibody used, which suggests an increased or altered permeability of the plasma membrane to fluorescein efflux rather than a cytoplasmic reorganization.