A subpopulation of neutrophils that does not polymerize F-actin in response to fMLP stimulation is present in some MDS patients.

Human neutrophils were stimulated with 1 μM fMLP for the indicated time. Cells were fixed and permeabilized, and F-actin was stained with 2.5 U/mL Oregon Green 514–phalloidin. Fluorescence histograms are shown for a representative healthy control (A) and one of the MDS patients with a nonresponsive neutrophil subpopulation (B).