SG deficiency in GPS neutrophils. (A-B) IEM identification of MPO-positive AGs (A) and lactoferrin-positive SGs (B) in GPS neutrophils. The arrow indicates an example of positive granule labeling. (C) The numbers of lactoferrin- and MPO-positive granules per cell were determined by counting the number of positive granules in control and GPS neutrophils. (D-E) Neutrophils from controls and patients with GPS were stimulated with cytochalasin B (5 μg/mL)/fMLF (1 μM) or PAF (1 μM)/fMLF (1 μM), and plasma membrane expression of CD63 (azurophilic; D, left graph) and CD66b (specific; E, left graph) was measured by flow cytometry. The extracellular concentrations of elastase (azurophilic; D, right graph) and lactoferrin (specific; E, right graph) were measured by enzyme-linked immunosorbent assay. Results are means ± SEM, n = 3-5. An unpaired, 2-tailed t test was used. **P < .01, ****P < .0001. MFI, mean fluorescence intensity.