Ultrastructural localization of lysozyme in human neutrophils by immunogold

The subcellular localization of lysozyme (LZ) has been investigated by immunogold electron microscopic cytochemistry in human neutrophils from bone marrow and blood. Intact cells or subcellular granule fractions were fixed in glutaraldehyde and embedded in glycol methacrylate. Thin sections were incubated with monospecific antibodies followed by antiglobulins coupled to colloidal gold. LZ was detected within both elliptical and spherical primary granules in bone marrow neutrophil promyelocytes. In myelocytes and more mature neutrophils immunolabeling for LZ was observed within the primary granules, although fainter than in promyelocytes. However secondary granules from bone marrow and blood neutrophils were not consistently labeled by gold particles. Immunogold staining was then performed on sections of subcellular fractions of secondary granules: immunogold staining of lactoferrin demonstrated 95% of secondary granules in this fraction. Labeling for LZ of this granule fraction was intense, and except that the few primary granules were also labeled, looked similar to that of lactoferrin. In conclusion, this study is the first to utilize electron microscopic cytochemistry to show that LZ is present in both the primary and secondary granules of blood and bone marrow neutrophils. This technique has the advantage of allowing LZ distribution to be studied within a single organelle and/or in relation to the rest of the cell structure.