A novel flow cytometric method for measuring protein digestion within the phagocytic vacuole of polymorphonuclear neutrophils

The use of flow cytometry to measure neutrophil function

Neutrophils are important professional phagocytic cells that provide the host with a first line of defense against acute bacterial and fungal diseases and recurrent, severe or unusual infections are associated with inherited defects of neutrophil function. Furthermore, abundant evidence links inappropriate neutrophil-mediated tissue damage to the pathogenesis of conditions such as acute respiratory distress syndrome, septicemia with multiorgan failure, ischemia-reperfusion injury and rheumatoid arthritis. Flow cytometry has been increasingly used to evaluate the functional capabilities of neutrophils. In this review, we discuss the use of flow cytometry to assess neutrophil functional responses including calcium mobilization, F-actin assembly, adhesion, aggregation, degranulation, phagocytosis and reactive oxygen species (ROS) production. The use of flow cytometry to identify neutrophil priming is also discussed. The advantage of flow cytometry is that the majority of neutrophil functions can be measured using a small volume of whole blood that reduces artifactual changes in function caused by purification procedures. The advent of numerous new fluorochromes and multiparametric analysis allows the simultaneous measurement of several neutrophil functions in the same population of cells. Flow cytometric analysis provides a rapid screen for abnormalities of neutrophil function and reflects more accurately their behavior in vivo.

Flow cytometric assay for quantifying opsonophagocytosis and killing of Staphylococcus aureus by peripheral blood leukocytes

We describe a novel flow cytometric method for quantifying opsonophagocytosis and killing of Staphylococcus aureus in cell-rich plasma obtained after dextran sedimentation of erythrocytes. To analyze opsonophagocytosis, phagocytes were labeled with a phycoerythrin-conjugated monoclonal antibody and were incubated with viable staphylococci containing carboxyfluorescein as a vital fluorescent dye. Phagocytosing cells assumed a dual, orange-green fluorescence. The relative numbers of bacteria associating with phagocytes could be determined by quantifying the decrease of free green fluorescent particles. A parallel incubation of fluorescent bacteria with unlabeled cell-rich plasma was performed to assess phagocytic killing. Blood cells were lysed with 3-[(3-cholamidopropyl)-dimethyl-ammonio]-1-propanesulfonate. This detergent spared viable bacteria, and residual green fluorescent particles were counted. The decrease in the number of these particles relative to the controls yielded the degree of killing. At bacteria-to-phagocyte ratios of 1:1 and 10:1, approximately 36 and 75% of the phagocytes participated in opsonophagocytosis, respectively. Over 90% of the staphylococci were phagocyte associated after 30 to 60 min. Killing rates were on the order of 66% +/- 12% and 80% +/- 7% after 1 and 2 h of incubation, respectively. These numbers, which were confirmed by colony countings, were significantly lower than those reported in the majority of past reports.

Quantitative analysis of opsonophagocytosis and of killing of Candida albicans by human peripheral blood leukocytes by using flow cytometry

We describe a simple, rapid, automated procedure for measuring opsonophagocytosis and killing of Candida albicans by human peripheral blood leukocytes. Yeast cells are labelled by allowing uptake and cleavage of membrane-permeable bis-carboxyethyl-carboxyfluorescein pentaacetoxymethylester to its membrane-impermeable fluorescent derivative bis-carboxyethyl-carboxyfluorescein. The yeast cells are added to cell-rich plasma obtained after dextran sedimentation of erythrocytes. Opsonophagocytosis and killing are quantified by using automated fluorescent cell analysis, and the following parameters can be obtained: (i) relative percentage of phagocytes that participate in opsonophagocytosis, (ii) relative percentage of yeast cells that become associated with phagocytes, and (iii) percentage of killing of C. albicans. The first two parameters are obtained through the additional use of a phycoerythrin-conjugated monoclonal antibody that selectively labels monocytes and polymorphonuclear granulocytes in peripheral blood. Killing is assessed by solubilizing blood cells with deoxycholate to liberate yeast cells from the phagocytes. Viable yeast cells retain carboxyfluorescein, but nonviable cells lose the fluorescent marker; thus, the reduction in number of fluorescent particles directly reflects phagocytic killing. Results obtained by the present method correlated excellently with parallel enumerations by colony counting. Test results with seven healthy individuals revealed a marked dissociation between the process of opsonophagocytosis, which was essentially complete after 20 min at 37 degrees C, and killing rates, which were 48% +/- 11% and 63% +/- 9% (standard deviation) after 1 and 2 h, respectively, when yeast cell-to-phagocyte ratios were in the range of 0.5:1 to 2:1. The described assay is unrivaled in simplicity, rapidity, and reproducibility and generates results for a large number of samples within hours.