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* Department of Microbiology and Immunology and
Christchurch School of Medicine, University of Otago, Dunedin, New Zealand; and
Division of Immunobiology, Institute for Genetics, University of Bonn, Bonn, Germany
Exosomes are lipid-bound nanovesicles formed by inward budding of the endosomal membrane and released following fusion of the endosomal limiting membrane with the plasma membrane. We show here that primary leukocytes do not release exosomes unless subjected to potent activation signals, such as cytokine or mitogen stimulation. In particular, high levels of exosomes were released when murine splenic B cells were stimulated via CD40 and the IL-4 receptor. This property was shared by B cells from different anatomic locations, as newly formed, marginal zone and follicular B cells were capable of secreting exosomes upon CD40/IL-4 triggering. B cell exosomes expressed high levels of MHC class I, MHC class II, and CD45RA (B220), as well as components of the BCR complex, namely, surface Ig, CD19, and the tetraspanins CD9 and CD81. Ig on the plasma membrane of primary B cells was targeted to the exosome pathway, demonstrating a link between the BCR and this exocytic pathway. IgD and IgM were the predominant Ig isotypes associated with CD40/IL-4 elicited exosomes, though other isotypes (IgA, IgG1, IgG2a/2b, and IgG3) were also detected. Together, these results suggest that exosome release is not R constitutive activity of B cells, but may be induced following cell: cell signaling.
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
1 This work was supported by the Marsden Research Fund (Fast Start to A.D.M.), the Otago Research Committee, Lotteries Health, the Bendigo Trust, the H.S. & J.C. Anderson Trust, and a Senior Smeaton Scholarship for Experimental Science (to P.A.M.).
2 Current address: School of Chemistry, University of Sydney, Sydney, New South Wales, Australia.
3 Address correspondence and reprint requests to Dr. Alexander D. McLellan, Department of Microbiology and Immunology, University of Otago, Dunedin, 9001, New Zealand. E-mail address: alex.mclellan{at}stonebow.otago.ac.nz
4 Abbreviations used in this paper: DC, dendritic cell; MHC-I/II, MHC class I/II; sMHC, soluble MHC; DOC, deoxycholate; FPLC, fast protein liquid chromatography; CD40L, CD40 ligand; BMDC, bone marrow-derived DC.
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  Y. Qu, L. Ramachandra, S. Mohr, L. Franchi, C. V. Harding, G. Nunez, and G. R. Dubyak P2X7 Receptor-Stimulated Secretion of MHC Class II-Containing Exosomes Requires the ASC/NLRP3 Inflammasome but Is Independent of Caspase-1 J. Immunol., April 15, 2009; 182(8): 5052 - 5062. [Abstract] [Full Text] [PDF]
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