Ultrastructure of human mast cells cultured in the presence or absence of IL-4. HCMCs grown in the presence of SCF (100 ng/mL) and IL-6 (80 ng/mL) for 10 weeks were further cultured with (d, e, and f) or without IL-4 (a, b, and c; 10 ng/mL) in the presence of SCF and IL-6 for 28 days. HCMCs cultured without IL-4 has few cytoplasmic projections and has an immature nucleus with a large, bright nucleolus (a). Discrete scrolls and lamellar structures with a few rough particles (P in c) are found in the same granules (a and c), and some granules have irregular lamellar structure (b). HCMCs cultured with IL-4 has abundant cytoplasmic projections, well-developed Golgi apparatus (G in d) and numerous granules, which contain dense, crystal materials (d and e), as well as compact electron-dense nondiscrete scrolls (f). Representative results are shown. (Original magnifications: a, ×9,000; b, ×20,000; c, ×20,000; d, ×6,000; e, ×16,000; f, ×22,000.)