CD63-depleted HL-60 cells show a lack of morphologically normal granules and contain MPO-positive cytoplasmic vacuoles lacking NE—immunoelectron microscopy. Wild-type (wt), CD63 siRNA mock, CD63 siRNA, and CD63 dom neg HL-60 cells were examined. Ultrathin cryosections were labeled (A) with rabbit anti-MPO (10-nm gold) or (B) with rabbit anti-NE (10-nm gold). The CD63-depleted cells lacked normal granules and contained more vacuoles. MPO labeling was localized both to the granules of the wild-type and mock cells and to the vacuoles of CD63 siRNA and CD63 dom neg cells. NE labeling was seen in granules of wild-type and mock cells. Table 1 shows the NE-positive fraction of MPO-positive vacuoles/granules, obtained by counting gold particles in cell sections from 100 different cells of a CD63 siRNA clone and a CD63 dom neg clone. A lack of NE labeling was observed in 70% to 80% of the cytoplasmic vacuoles/granules of CD63 siRNA and CD63 dom neg cells. Labeling was sometimes observed on the Golgi (G) and trans-Golgi network (TGN) of CD63-depleted cells. Scrambled siRNA controls are shown in Figure S2F.