An ultrastructural study of primary granule subtypes in human neutrophils

To investigate the heterogeneity of primary neutrophil granules, neutrophils in the bone marrow of 68 patients with hematologic and non-hematologic diseases were observed by electron microscopy. In addition to typical primary granules, 3 primary granule subtypes, i.e., parallel tubular granules (PTGs), fibrillar granules (FGs), and periodic lamellar granules (PLGs), were present in neutrophils. PTGs were found in only one case of chronic neutrophilic leukemia (CNL). On the other hand, FGs and PLGs were present in various cases at varying frequencies. Three subtype granules were seen preferentially in immature neutrophils. These subtypes were positive for myeloperoxidase, showing that they represent primary granules. In addition, hybrid PTG/FG granules, hybrid PTG/PLG granules, and hybrid FG/PLG granules were seen in the PTG-positive CNL case. This shows that a close association is present between PTGs, FGs, and PLGs.