Exosomes from human macrophages and dendritic cells contain enzymes for leukotriene biosynthesis and promote granulocyte migration.
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.
Esser
Julia
J
Division of Physiological Chemistry II, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, Stockholm, Sweden.
Gehrmann
Ulf
U
D'Alexandri
Fabio Luiz
FL
Hidalgo-Estévez
Alicia M
AM
Wheelock
Craig E
CE
Scheynius
Annika
A
Gabrielsson
Susanne
S
Rådmark
Olof
O
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
D015289:Leukotrienes