EBV Conference 2008 Guangzhou - Baylor College of Medicine

154 (RegID: 1245)
Michiel Pegtel
Institution: Free University Amsterdam
e-mail: d.pegtel@vumc.nl
LMP1 TRAFFICKING TO EXOSOMES THROUGH THE ENDOCYTIC PATHWAY
Pegtel DM, Eijndhoven ME, Hopmans E, Neefjes JJ, Middeldorp JM
Posterabstract:
Exosomes are nano-sized vesicles and function as intercellular signaling devices that originate from
intraluminal vesicles (ILV’s) of multi-vesicular multivesicular-bodies (MVBs). In MVBs of antigen
presenting cells (APCs), ILV’s facilitate class II peptide loading. APC derived exosomes also harbor
co-stimulatory molecules and perhaps not surprisingly, these vesicles are potent inducers of T cell
activation. Several pathogens have evolved to hijack the highly specialized MVB antigen processing
pathway and negatively influence immune recognition.
In EBV-infected lymphoblastoid B cell-lines, only a small fraction of the endogenous latent membrane
protein 1 (LMP1) is present on the plasmamembrane, while the bulk of LMP1 resides in poorly defined
intercellular compartments. We show that endogenous LMP1 is co-expressed with the tetraspannin CD63
a marker for early and late endosomes. Furthermore, when cells are treated pharmacologically with
wortmannin and/or chloroquine, we detect intracellular LMP1 and HLA-DR in distinct microdomains of
presumably MVBs. A recent study proposes that exosomes may originate from (lipid) micro-domains in
the limiting membrane of MVBs1. Interestingly, both HLA-DR and LMP1 proteins are known to
aggregate in “lipid raft like” domains of the plasmamembrane. We confirmed by electron microscopic
immunogold labeling that LMP1 protein is present in HLA-DR positive exosomes. In addition, lysates of
exosomes captured by anti-HLA-DR coupled dynal-beads contain significant amounts of LMP1 protein.
These results show for the first time that endogenous LMP1 is secreted via exosomes by trafficking to
intercellular compartments, specialized in antigen loading. Due to the known immunosuppressive
properties of LMP1, we propose that LMP1 may have co-opted the endosomal sorting pathway to
manipulate antigen presentation and/or exosome function.
EBV Conference 2008 Guangzhou
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