Flow cytometric measurements of phagocytosis. I. A methodical and comparative study

A flow cytometric technique is described for measurement of phagocytic activity in human leucocytes using FITC-labelled latex particles (0.77 micron). Cell suspensions separated from peripheral blood by dextran sedimentation were hemolyzed to avoid particle uptake by erythrocytes. The leucocytes were incubated for various time intervals with a standardized solution of 2 x 10(7) FITC-labelled latex particles per 2 x 10(5) leucocytes in 0.6 ml medium. Relative fluorescence per cell was measured on the basis of 10(5) cells, and a simple technique has been described to evaluate data characteristic for different steps of phagocytosis and to discriminate between phagocytizing and non-phagocytizing cells. In comparison, rice starch phagocytosis has been measured microscopically. A positive correlation between both methods has been found in 11 patients with different disease-related phagocytic capacity.