The fluorescence properties of fluorescein bound to protein are used to quantitate by flow cytofluorometry the degradation of fluorescein-labeled alpha-glucosylated serum albumin (fluorescein-labeled neoglycoprotein) after endocytosis by the membrane lectin of Lewis lung carcinoma cells (3LL cells). The quantum yield of fluorescein bound to a protein decreases when the number of fluorescein residues per protein molecule increases; however, after proteolytic digestion the mean fluorescence intensity of a fluorescein molecule is constant and equal to that of free fluorescein. The extent of the degradation of the endocytosed neoglycoprotein was determined with a flow cytofluorometer by using two neoglycoproteins containing either a small or a large number of fluorescein residues per neoglycoprotein molecule. At 4 degrees C, 3LL cells bind 750,000 molecules of fluorescein-labeled alpha-glucosylated serum albumin with an apparent binding constant of 2 X 10(6) 1 X mole-1. At 37 degrees C, after 4 hr incubation 2.2 X 10(6) molecules of fluorescent alpha-glucosylated serum albumin were cell-associated, and of these at least one third were degraded.

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Two populations of phagocytic cells from trehalose dimycolate-elicited mouse peritoneal cells are demonstrated by flow cytofluorometry, using two fluorescent probes excited at the same wavelength (488 nm). Liposomes containing diethylenetriaminepentaacetate daunorubicin conjugate (maximum emission wavelength: 590 nm) allow the discrimination of phagocytes and non-phagocytic cells. Among the phagocytes, an activated population is revealed by a cell-associated fluorescence of the oxidation product of dichlorofluorescein diacetate (maximum emission wavelength: 520 nm).