Acridine orange fluorescence cytochemistry for detecting lymphocyte immunoreactivity

Acridine orange staining reveals changes within 3 hours of in vitro stimulation of normal rat lymphocytes with mitogens, and of immune rat lymphocytes with the sensitizing antigen. An increased number of red fluorescent cytoplasmic organelles, presumably lysosomes are seen by fluorescence microscopy. Fluorimetry of the supernatants from stained cell suspension suggests an overall decreased cell uptake of the dye. The microscopy and fluorimetry detected early events in the reaction of lymphocytes from tumour-bearing rats with the target tumour cells. It would appear that the changes in intracellular behavior of the dye and ii overall cell uptake after immune stimulation are a reflection of dissociated variations in internal and external cell membrane permeability, and may provide simple general means for recognizing cellular immune reactions.