Phagocytosis of isolated DVs by PMNs. (A) Electron microscopic appearance of DVs naturally liberated from late-stage parasitized RBCs showing ∼ 1- to 2-μM vesicles with varying content of hemozoin (arrow) bound by a limiting membrane. Scale bars indicate 1 μm. (B) DVs were incubated with PMNs prelabeled with PE-conjugated anti-CD16 IgG in 10% inactive serum. Microscopic Giemsa smears were prepared at the depicted times and flow cytometric analyses of phagocytosis were performed by gating PMNs and assessing the number of red fluorescent cells. Histograms of the corresponding dot plots are shown in the bottom panel (red: 0 minutes; green: 2 minutes; blue: 3 minutes; and black: 5 minutes). M1 is the region set for nonfluorescent cells and M2 for fluorescent cells. The numbers counted in the M2 region are shown in the dot plots. (C) Same experiment performed in active serum. The results of flow cytometric analyses are shown at 2 and 3 minutes to illustrate the abrupt onset of phagocytosis occurring in active serum. The findings in inactive serum remained stationary over the period of observation of 30 minutes. One representative experiment of 3 independent experiments is shown. Scale bars indicate 20 μm.