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* Unit of Immunotherapy of Human Tumours and
Unit of Immunohematology, Fondazione Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS), Istituto Nazionale dei Tumori, Milano, Italy;
Department of Immunology, University of Pittsburgh, PA 15203; and
Consorzio Microscopy and Image Analysis, Monza, Università Milano Bicocca, Italy
Glucose-regulated stress protein gp96 is known to be involved in the host response to pathogens and to cancer. Our study explored the relationships between gp96 and human blood plasmacytoid dendritic cells (pDC) and proved that gp96 directly targets pDC by a receptor-dependent interaction. Competition studies identified CD91 as a gp96 receptor on pDC, and laser confocal imaging indicated that CD91 triggering was followed by gp96 endocytosis and trafficking into early endosomes and later into the endoplasmic reticulum compartment. Using two alternative Abs, we showed that human blood pDC reproducibly expressed CD91, although different levels of expression were detectable among the analyzed donors. Moreover, CpG-matured pDC displayed CD91 receptor up-regulation that correlated with an increased gp96 binding. Functionally, gp96-pDC interaction activated the NF-
B pathway, leading to the nuclear translocation of the NF-B complex. gp96-treated pDC maintained an immature phenotype, while they down-modulated the release of IL-8, suggesting an anti-inflammatory role of this pathway, and they strongly up-regulated the cell surface expression of the gp96 receptor CD91. CpG-matured or gp96-treated pDC, expressing high levels of the gp96 receptor CD91, antagonized the gp96-induced activation of monocyte-derived dendritic cells in terms of cell surface phenotype and cytokine production. Altogether, these results suggest that gp96-pDC interaction might represent an active mechanism controlling the strength of the immune response to free, extracellular available gp96; this mechanism could be particularly relevant in wounds and chronic inflammation.
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 grants from Associazione Italiana per la Ricerca sul Cancro (AIRC, Milano) and European Community (Cancerimmunotherapy, contract 518234).
2 Current address: Unit of Immuno-Biotherapy of Solid Tumors, San Raffaele Scientific Institute, Milano, Italy.
3 Address correspondence and reprint requests to Dr. Chiara Castelli, Unit of Immunotherapy of Human Tumors, Fondazione Istituto Di Ricovero e Cura a Carattere Scientifico (IRCCS) Istituto Nazionale dei Tumori, Via G Venezian 1, 20133 Milano, Italy. E-mail address: chiara.castelli{at}istitutotumori.mi.it
4 Abbreviations used in this paper: HSP, heat shock protein; AF488, Alexa Fluor 488; BDCA-2, blood dendritic cell Ag 2; CBA, cytometric bead array; DC, dendritic cell; ER, endoplasmic reticulum; IKK2, IB kinase 2; LAMP-2, lysosome-associated membrane protein 2; MoDC, monocyte-derived DC; pDC, plasmacytoid DC; PFA, paraformaldehyde; RT, room temperature.
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