pHi in phagocytosing neutrophils is determined by bacterial load.
Isolated human peripheral blood neutrophils were exposed to increasing densities of heat-killed opsonized E coli while intracellular pH (pHi) was monitored by flow cytometry using cytosolic pH-sensitive dyes and, in separate experiments, phagocytosis of fluorescently labeled bacteria was measured by flow cytometry. (A) The correlation between increasing pathogen-to-phagocyte ratio and mean number of bacteria ingested (mean channel fluorescence) by neutrophils (4 replicates each from 5 healthy donors, coefficient of determination r2 = 0.96). (B) The effect of increasing pathogen-to-phagocyte ratios and thus mean number of bacteria ingested (0:1-50:1) on pHi over time in normal neutrophils (4 replicates each from 10 healthy donors). pHiresponses at each pathogen-to-phagocyte ratio differed significantly from the others (by MANOVA, P < .01). (C,D) The correlation between bacterial load and the change in pHi after 5 minutes and the lowest pH recorded. All data mean ± SEM.
