Figure 2
From: Vesicle-mediated secretion of human eosinophil granule-derived major basic protein
Major basic protein (MBP) is localized to specific granules and cytoplasmic vesicles in human eotaxin-stimulated eosinophils. Immunonanogold electron microscopy revealed MBP-positive vesicles surrounding (a and b) and arising (c) from granules undergoing depletion of their contents. (aii) is the boxed area of (ai) and shows a tubular vesicle (arrowheads) at the surface of a specific granule. Note that MBP is present in the granule and in the attached vesicle. In (b), a pool of vesicles around a secretory granule is labeled for MBP. Observe that (aii) and (b) show specific granules in progressive stages of content emptying, characterized by reduced electron density. In (c), a linear array of small, MBP-positive vesicles bud from a granule surface into the cell surface. The inset shows a vesicle fused with the plasma membrane at higher magnification. In (d), a granule, which demonstrates its disarranged core and matrix, is densely labeled for MBP. A similar image is seen at low magnification in ai (arrows). Bar, 800 nm (ai); 300 nm (aii and c); 500 nm (b and d). Gr, specific granules.
