The lysosomal membrane glycoproteins Lamp-1 and Lamp-2 are present in mobilizable organelles, but are absent from the azurophil granules of human neutrophils

Abstract

The subcellular localization of two members of a highly glycosylated protein group present in lysosomal membranes in most cells, the lysosome-associated membrane proteins 1 and 2 (Lamp-1 and Lamp-2), was examined in human neutrophil granulocytes. Antibodies that were raised against purified Lamp-1 adn Lamp-2 gave a distinct granular staining of the cytoplasm upon immunostaining of neutrophils. Subcellular fractionation was used to separate the azurophil and specific granules from a light-membrane fraction containing plasma membranes and secretory vesicles, and Western blotting was used to determine the presence of the Lamps in these fractions. The results show that Lamp-1 and Lamp-2 are present in the specific-granule-enriched fraction and in the light-membrane fraction, but not in the azurophil granules. Separation of secretory vesicles from plasma membranes disclosed that the light-membrane Lamps were present primarily in the secretory-vesicle-enriched fraction. During phagocytosis both Lamp-1 and Lamp-2 became markedly concentrated around the ingested particle and they both appear on the cell surface when the secretory organelles are mobilized.