Morphological heterogeneity of myeloperoxidase-positive granules in normal circulating neutrophils: an ultrastructural study by cryosection.

Ultrastructural localization of myeloperoxidase (MPO) in the granules of human circulating neutrophils was examined by cryosection. On careful comparison with the morphological characteristics of the granules by conventional transmission electron microscopic study, large MPO-positive granules were divided into five types by immunocryoultramicrotomy using monoclonal antibody. Double staining of MPO and lactoferrin (or lysozyme) was also performed. Lactoferrin was generally detected in MPO-negative granules. Lysozyme immunostaining was present in MPO-positive and -negative granules. These data may suggest different functions among large MPO-positive granules of human circulating neutrophils.