Localization of BPI in eosinophilic myelocytes. Cryosections of bone marrow cells incubated with anti-BPI and visualized by secondary gold-conjugated antibody. An area of an eosinophilic myelocyte is shown. Most of the granules do not possess a crystalloid, but two crystalloid-containing mature specific granules are present (c). BPI (arrows) is present in almost all granules and in the endoplasmic reticulum (er). Bars = 400 nm.