Surface membrane alterations in guinea pig basophils undergoing anaphylactic degranulation. A scanning electron microscopic study.

Purified guinea pig blood basophils in short-term tissue culture were studied by scanning and transmission electron microscopy and by 1-micrometer. light microscopic Epon sections after exposure to specific antigen (sheep serum), to guinea pig serum, or to serum-free medium at intervals from 1 minute to 48 hours. Basophils fixed before culture, or after culture in serum-free medium, were spherical cells with uniformly distributed microvilli, ridges, and folds. In cultures with guinea pig serum, basophils frequently assumed a hand mirror configuration, characteristic of motile cells, with a single posterior, microvilli-bearing uropod and anterior ruffles. Specific antigen induced basophils to become rounded, regardless of the culture medium, and resulted in basophil degranulation and histamine release within 5 to 20 minutes. Exposure of cytoplasmic granules to the external medium was initiated by the development, early in degranulation, of a single, 1 to 2 micrometer. in diameter, opening (degranulation pore) in the plasma membrane. The degranulation pore enlarged progressively over 24 to 36 hours, ultimately permitting the egress of membrane-free cytoplasmic granules. The cell pole opposite the degranulation orifice bore numerous prominent folds and ruffles, changes that persisted for at least 24 hours. By 48 hours after exposure to specific antigen (sheep serum), the surface features of basophils had reverted to those exhibited by unstimulated control cells.