Exosomal-like vesicles with immune-modulatory features are present in human plasma and can induce CD4+ T-cell apoptosis in vitro.
BACKGROUND
Exosomes are small membrane vesicles that are secreted from many cell types into various body fluids. These vesicles are thought to play a role in cell-cell interactions.


METHODS
Vesicles were isolated from human plasma of healthy donors by differential ultracentrifugation and ultrafiltration. The vesicles were identified by transmission electron microscopy, and their biochemical characteristics were analyzed by Western blot and flow cytometry. The immune-modulatory ability of exosomal-like vesicles was examined by incubating them with CD4+ T cells for CD4+ T-cell proliferation and apoptosis assays in vitro.


RESULTS
Vesicles purified from human plasma displayed shapes and sizes similar to those of previously described exosomes and contained exosomes marker proteins CD63 and CD81. They also expressed molecules such as MHC Class II molecules, CD80, CD86, and the cell signal transduction molecules Wnt3a, Wnt5a, and FasL. Furthermore, functional analysis showed that allogeneic plasma exosomes restrained the survival of CD4+ T cells. Plasma exosomes can induce dose-dependent suppression of proliferation of activated CD4+ T cells, with the strongest responses induced by 500 µg/mL exosomes in vitro. Antibodies against exosomes FasL can block the activity of exosomes on CD4+ T-cell apoptosis. Moreover, three different concentrations of CD4+ T cells were inhibited by plasma exosomes and the suppressive function was not dependent on interleukin-2.


CONCLUSIONS
Exosomes present in human plasma contain immunity-associated molecules and can induce CD4+ T-cell apoptosis in vitro. Plasma exosomes have the capacity to influence immune responses.
Blood Engineering Laboratory, Shanghai Blood Center, Shanghai, China.
Yana
Y
Ren
Jie
J
Yang
Rufeng
R
Xie
Li
L
Gao
Yiming
Y
Yang
Huahua
H
Fan
Kaicheng
K
Qian
D057134:Antibodies, Neutralizing / Q000097:blood / Q000276:immunology; D017209:Apoptosis / Q000276:immunology*; D001782:Blood Donors; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D055354:Exosomes / Q000276:immunology* / Q000648:ultrastructure; D053222:Fas Ligand Protein / Q000276:immunology; D006801:Humans; D007108:Immune Tolerance / Q000276:immunology; D056747:Immunomodulation / Q000276:immunology*; D016130:Immunophenotyping; D066298:In Vitro Techniques; D007376:Interleukin-2 / Q000276:immunology; D046529:Microscopy, Electron, Transmission; D010949:Plasma / Q000276:immunology*; D014461:Ultracentrifugation
D057134:Antibodies, Neutralizing; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D007376:Interleukin-2