title: Interleukin 1 beta is localized in the cytoplasmic ground substance but is largely absent from the Golgi apparatus and plasma membranes of stimulated human monocytes.
abstract: The subcellular location of IL-1 beta was determined using a postsectioning immunoelectron microscopic method on ultrathin frozen sections of human monocytes stimulated with LPS. This methodology permits access of antibody probes to all sectioned intracellular compartments, and their visualization at high resolution. Staining was performed with a rabbit antibody that specifically recognized amino acids 197-215 in the 33-kD IL-1 beta precursor molecule, followed by affinity-purified goat anti-rabbit IgG conjugated to 10 nm colloidal gold particles. Approximately 90% of the IL-1 beta antigens were localized in the ground substance of the cytoplasm at 4 or 20 h after activation, when both intracellular and extracellular accumulation of IL-1 beta was well underway. No significant IL-1 beta staining was observed on the outer cell membrane, nor within the lumens of the endoplasmic reticulum (ER), the Golgi apparatus, or secretory vesicles. In contrast, lysozyme was localized in the ER and dense secretory granules using these methods. Our results suggest that IL-1 beta is not anchored on the plasma membrane, and that its secretion occurs by a novel mechanism that does not use a secretory leader sequence, nor the classical secretory pathway involving the ER and Golgi apparatus.
authors.affiliation: Department of Biochemical and Molecular Pathology, Merck Institute for Therapeutic Research, Rahway, New Jersey 07065.
authors.forename: I I
authors.initials: II
authors.lastname: Singer
authors.forename: S
authors.initials: S
authors.lastname: Scott
authors.forename: G L
authors.initials: GL
authors.lastname: Hall
authors.forename: G
authors.initials: G
authors.lastname: Limjuco
authors.forename: J
authors.initials: J
authors.lastname: Chin
authors.forename: J A
authors.initials: JA
authors.lastname: Schmidt
mesh_terms: D000941:Antigens / Q000032:analysis; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D003593:Cytoplasm / Q000378:metabolism* / Q000648:ultrastructure; D003600:Cytosol / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D006056:Golgi Apparatus / Q000378:metabolism* / Q000648:ultrastructure; D006801:Humans; D007375:Interleukin-1 / Q000276:immunology / Q000378:metabolism*; D009000:Monocytes / Q000276:immunology* / Q000378:metabolism / Q000648:ultrastructure; D011498:Protein Precursors / Q000276:immunology / Q000378:metabolism
chemical_list: D000941:Antigens; D007375:Interleukin-1; D011498:Protein Precursors