FLOW CYTOMETRIC ASSAY OF PHAGOCYTIC-ACTIVITY OF HUMAN NEUTROPHILS ANDMONOCYTES IN WHOLE-BLOOD BY NEUTRAL RED UPTAKE

In a new, simple, and fast flow-cytometric method for the simultaneous measurement of phagocytic activity of human neutrophils and monocytes in whole blood, the fluorescence capability of the well-known vital s tain, neutral red was used. The incubation of 0.5 ml heparinized human blood with the phagocytic stimulus of zymosan dose- and time-dependen tly increased the percentage and the red fluorescence intensity of bot h neutrophils (4.3 +/- 1.2 times) and monocytes (2.7 +/- 0.7 times) me asured cytofluorimetrically. De creased uptake of neutral red was obse rved in a patient with phagocytic disorder, based upon impaired engulf ment of particles and production of reactive oxygen species. In a pati ent with chronic granulomatosis, how ever, no decrease of neutral red uptake was measured. Platelet activating factor and phorbol myristate acetate were also able to increase the uptake of neutral red by both m onocytes and neutrophils, but to a lesser extent than zymosan. The adv antage of this method is the possibility for the simultaneous measurem ent of phagocytic activities of monocytes and neutrophils stimulated b y either particles or soluble activators. This method is suitable for the selective measurement of activation processes not related to the p roduction of free radicals in the phagocytes.