title: Exosomes from human macrophages and dendritic cells contain enzymes for leukotriene biosynthesis and promote granulocyte migration.
abstract: BACKGROUND
  Leukotrienes (LTs) are potent proinflammatory lipid mediators with key roles in the pathogenesis of asthma and inflammation. Recently, nanovesicles (exosomes), released from macrophages and dendritic cells (DCs), have become increasingly appreciated as messengers in immunity.
  
  
  OBJECTIVE
  We investigated whether exosomes from human macrophages, DCs, and plasma contain enzymes for LT biosynthesis and studied potential roles for exosomes in transcellular LT metabolism and granulocyte chemotaxis.
  
  
  METHODS
  The presence of LT pathway enzymes and LT biosynthesis in exosomes and cells was analyzed by Western blot, immunoelectron microscopy, and enzyme activity assays. Surface marker expression was evaluated by flow cytometry, and granulocyte migration was assessed in a multiwell chemotaxis system.
  
  
  RESULTS
  Exosomes from macrophages and DCs contain functional enzymes for LT biosynthesis. After incubation of intact cells with the LT biosynthesis intermediate LTA(4), LTB(4) was the major product of macrophages, whereas DCs primarily formed LTC(4). However, in exosomes from both cell types, LTC(4) was the predominant LTA(4) metabolite. Exosomal LTC(4) formation (per milligram protein) exceeded that of cells. In macrophages and DCs, TGF-β1 upregulated LTA(4) hydrolase along with increased LTB(4) formation also in the exosomes. Moreover, TGF-β1 modified the expression of surface marker proteins on cells and exosomes and reduced the exosome yield from macrophages. On Ca(2+)-ionophore and arachidonic acid stimulation, exosomes produced chemotactic eicosanoids and induced granulocyte migration. Interestingly, active LTA(4) hydrolase and LTC(4) synthase were present also in exosomes from human plasma.
  
  
  CONCLUSIONS
  Our findings indicate that exosomes can contribute to inflammation by participation in LT biosynthesis and granulocyte recruitment.
authors: Division of Physiological Chemistry II, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, Stockholm, Sweden.
authors: Julia
authors: J
authors: Esser
authors: Ulf
authors: U
authors: Gehrmann
authors: Fabio Luiz
authors: FL
authors: D'Alexandri
authors: Alicia M
authors: AM
authors: Hidalgo-Estévez
authors: Craig E
authors: CE
authors: Wheelock
authors: Annika
authors: A
authors: Scheynius
authors: Susanne
authors: S
authors: Gabrielsson
authors: Olof
authors: O
authors: Rådmark
mesh_terms: D015153:Blotting, Western; D002469:Cell Separation; D002634:Chemotaxis, Leukocyte / Q000276:immunology*; D003713:Dendritic Cells / Q000201:enzymology* / Q000276:immunology; D055354:Exosomes / Q000201:enzymology* / Q000276:immunology; D005434:Flow Cytometry; D006098:Granulocytes / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D015289:Leukotrienes / Q000096:biosynthesis* / Q000276:immunology; D008264:Macrophages / Q000201:enzymology* / Q000276:immunology; D016253:Microscopy, Immunoelectron
chemical_list: D015289:Leukotrienes