Flow cytometric assessment of APF and HPF fluorescence intensity for calculating HOCl production in neutrophils. Granulocytes were gated according to their forward and side scatter (dot blots). The gated cells were then presented according to side scatter and APF/HPF fluorescence intensity (fluorescein isothiocyanate [FITC]). (A) APF stimulation with H₂O₂ plus inhibition of MPO using ABAH/AP. (B) HPF stimulation with H₂O₂ plus inhibition of MPO using ABAH/AP. (C) Histograms representing the findings in (A). (D) Histograms representing the findings in (B). (A-D) A representative example of age-related controls and MDS, respectively. (E) Upon stimulation with H₂O₂, ΔAPF-ΔHPF is a measure of HOCl production. The difference in HOCl production between age-adjusted controls (black columns) and MDS samples (gray columns) only reached statistical significance when MPO activity was diminished by inhibitors. *P = .01.