Distinct granule populations in human neutrophils and lysosomal organellesidentified by immuno-electron microscopy

In this paper, we illustrate the fine structural localization of distinct m arker proteins in the organelles of human neutrophils and outline our prefe rred methods for processing ultrathin cryosections for use with immunoelect ron microscopy. Previous work has determined the subcellular localization o f certain marker proteins within intact polymorphonuclear neutrophilic leuk ocytes (PMN) and PMN fractions. These are as follows: :myeloperoxidase (MPO ) for azurophilic granules, lactoferrin for specific/secondary granules, ge latinase for gelatinase/tertiary granules, albumin for the secretory vesicl es, and HLA class I and L-selectin for the plasma membrane. In addition to analyzing the heterogeneity of the PMN granule populations, new information on the lysosomal system of this cell is reviewed and extended by the local ization of the lysosome-associated membrane proteins (LAMPs) and the cation -independent mannose 6-phosphate receptor (CI-M6PR). LAMPs were absent in a ll identified granule populations, but were found in the membranes of vesic les, multivesicular bodies (MVB), and multilaminar compartments (MLC). We s how here that MVB contain CI-M6PR whereas MLC do not. Furthermore, since ML C contain LAMPs but not the receptor, they probably correspond to the late endosome. By current criteria, the true lysosomes of the resting PMN are MV B and MLC, Finally, although azurophil granules contain acid hydrolases the ir membranes do not contain LAMPs and they cannot be classified as lysosome s, but rather are more similar to regulated secretory granules. (C) 1999 El sevier Science B.V. All rights reserved.