Flow cytometric assay of phagocytic activity of human neutrophils and monocytes in whole blood by neutral red uptake

In a new, simple, and fast flow-cytometricmethod for the simultaneous measurement of phagocyticactivity of human neutrophils and monocytes inwhole blood, the fluorescence capability of the wellknownvital stain, neutral red was used. The incubationof 0.5 ml heparinized human blood with the phagocyticstimulus of zymosan dose- and time-dependently increasedthe percentage and the red fluorescence intensityof both neutrophils (4.3 _ 1.2 times) and monocytes(2.7_+0.7 times) measured cytofluorimetrically. Decreaseduptake of neutral red was observed in a patientwith phagocytic disorder, based upon impaired engulfmentof particles and production of reactive oxygenspecies. In a patient with chronic granulomatosis, however,no decrease of neutral red uptake was measured.Platelet activating factor and phorbol myristate acetatewere also able to increase the uptake of neutral red byboth monocytes and neutrophils, but to a lesser extentthan zymosan. The advantage of this method is the possibilityfor the simultaneous measurement of phagocyticactivities of monocytes and neutrophils stimulated byeither particles or soluble activators. This method issuitable for the selective measurement of activationprocesses not related to the production of free radicalsin the phagocytes