Single-cell measurement of superoxide anion and hydrogen peroxide production by human neutrophils with digital imaging fluorescence microscopy

Abstract

Besides flow cytometry, fluorescence microscopy combined with computerized image analysis offers an alternative tool for assessing phagocyte oxidant generation at the single-cell level. This technique provides an opportunity for the direct visualization of cells and simultaneous measurement of cellular fluorescence intensity. Thus, we developed a simple method for the quantitative evaluation of intracellular superoxide anion and hydrogen peroxide production with image cytometry by using hydroethidine and dihydrorhodamine 123 dyes, respectively. Human neutrophils stimulated with phorbol dibutyrate and labeled by these fluorogenic substrates showed intense, well recognizable red or green fluorescence. The intensity of signals from individual granulocytes of cytospin preparations were quantitatively measured in digitized images. There was a great heterogeneity in response to the stimulus within the granulocyte population as shown by the integrated fluorescence intensity values. In agreement with the results of parallel flow cytometric experiments, this simple image analysis performed on cells of cytospin preparations was able to detect the defects in the oxidative metabolism of neutrophils from patients with cervix carcinoma. We demonstrated that even minor alterations in superoxide anion/hydrogen peroxide generation can be detected by image cytometry as efficiently as by flow cytometry. This result validates imaging microscopy as an alternative to flow cytometry in such experiments. In addition, the image cytometric technique allows the observation of the kinetics of free radical production in individual cell under adherent conditions. Therefore, we carried out image analysis of the oxidative burst of neutrophils adherent to uncoated glass and fibronectin- and type IV collagen-coated surfaces in response to stimulation with phorbol dibutyrate or N-formyl-methionyl-leucyl-phenylalanine. We elaborated a calibration technique for the quantitative measurement of the ethidium bromide generation mediated by superoxide anion within individual adherent granulocytes. The ethidium bromide production varied between 0.48 and 1.17 amol/cell/min.