Mallegol Julia, Van Niel Guillaume, Lebreton Corinne, Lepelletier Yves, Candalh Céline, Dugave Christophe, Heath Joan K, Raposo Graça, Cerf-Bensussan Nadine, Heyman Martine
INSERM U793, Paris, France.
Gastroenterology. 2007 May;132(5):1866-76. doi: 10.1053/j.gastro.2007.02.043. Epub 2007 Feb 22.
BACKGROUND & AIMS: Intestinal epithelial cells release antigen-presenting vesicles (exosomes) bearing major histocompatibility complex class II/peptide complexes stimulating specific immune responses in vivo. To characterize further the role of human epithelial exosomes in antigen presentation, their capacity to load antigenic peptides, bind immune target cells, and induce T-cell activation was analyzed in vitro.
The capacity of exosomes derived from the HLA-DR4-expressing, intestinal epithelial cell line T84 to load the HLA-DR4-specific peptide (3)H-HSA 64-76 and to activate a HLA-DR4-restricted T-cell hybridoma was tested in the presence or absence of human monocyte-derived dendritic cells (DCs). Interaction of fluorescein isothiocyanate-labeled exosomes with T cells and DCs was analyzed by flow cytometry and confocal microscopy.
T84-derived exosomes, enriched in CD9, CD81, CD82, and A33 antigen, were capable of binding specifically human serum albumin (HSA) 64-76 peptide on HLA-DR4 molecules and of interacting preferentially with DCs. HSA-loaded exosomes were unable to activate the T-cell hybridoma directly but induced a productive T-cell activation through DCs. When HSA peptide was bound to exosomal HLA-DR4 molecules instead of in a soluble form, the threshold of peptide presentation by DCs was markedly decreased (x10(-3)).
Exosomes released by intestinal epithelial cells bear exogenous peptides complexed to major histocompatibility complex class II molecules and interact preferentially with DCs, strongly potentiating peptide presentation to T cells. Epithelial exosomes constitute a powerful link between luminal antigens and local immune cells by mediating the transfer of tiny amounts of luminal antigenic information and facilitating immune surveillance at mucosal surfaces.
肠上皮细胞释放携带主要组织相容性复合体II类/肽复合物的抗原呈递囊泡（外泌体），在体内刺激特异性免疫反应。为了进一步阐明人上皮外泌体在抗原呈递中的作用，我们在体外分析了它们加载抗原肽、结合免疫靶细胞以及诱导T细胞活化的能力。
在存在或不存在人单核细胞衍生的树突状细胞（DCs）的情况下，测试了源自表达HLA-DR4的肠上皮细胞系T84的外泌体加载HLA-DR4特异性肽（³H-HSA 64-76）并激活HLA-DR4限制性T细胞杂交瘤的能力。通过流式细胞术和共聚焦显微镜分析异硫氰酸荧光素标记的外泌体与T细胞和DCs的相互作用。
富含CD9、CD81、CD82和A33抗原的T84衍生外泌体能够在HLA-DR4分子上特异性结合人血清白蛋白（HSA）64-76肽，并优先与DCs相互作用。加载HSA的外泌体不能直接激活T细胞杂交瘤，但通过DCs诱导有效的T细胞活化。当HSA肽结合到外泌体HLA-DR4分子上而不是以可溶性形式存在时，DCs呈递肽的阈值显著降低（x10⁻³）。
肠上皮细胞释放的外泌体携带与主要组织相容性复合体II类分子复合的外源性肽，并优先与DCs相互作用，强烈增强肽向T细胞的呈递。上皮外泌体通过介导微量腔内抗原信息的传递并促进粘膜表面的免疫监视，构成了腔内抗原与局部免疫细胞之间的有力联系。
