Figure 1.

Conventional transmission electron microscopy (TEM) of resting and activated human eosinophils. (A) A representative eosinophil shows its typical cytoplasmic population of specific granules (Gr) with a unique morphology—an internal well-defined electron-dense crystalline core and an outer electron-lucent matrix [seen at higher magnification in (Ai)]. (B,C) In response to stimulation of eosinophils, their secretory granules undergo structural changes indicative of degranulation. CCL11 (B) induces granule content release in the absence of granule fusions while tumor necrosis factor alpha (TNF-α) (C) leads to fusions between secretory granules. Disarrangement of the crystalline cores is observed in stimulated (B,C) compared to unstimulated (A) cells. Note in (A,C), the typical bilobed nucleus (N). Eosinophils were isolated by negative selection from healthy donors, stimulated or not with CCL11 or TNF-α for 1 h, immediately fixed and prepared for TEM.