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Role of plasmacytoid dendritic cells in the orchestration of in vivo immune responses

Final Report Summary - ORCHESTRATE (Role of plasmacytoid dendritic cells in the orchestration of in vivo immune responses)

Type I IFNs are critical effector molecules with unique antiviral properties. In addition to their in vivo function, interferons have been exploited as therapeutic agents for treating viral infections (e.g. hepatitis C virus). Plasmacytoid dendritic cells (pDCs) are considered professional type I IFN producing cells as they produce extraordinarily high amounts of IFNs. Initially, it was reported that recognition of viral nucleic acids (ssRNA engaging TLR7 or dsDNA stimulating TLR9) is responsible for the activation and migration of pDCs to the T cell area and lymphoid organs where they produce significant amounts of type I IFN. Subsequent data has demonstrated that self nucleic acid (e.g. mRNA or hypomethylated CpG islands) are capable of activating pDCs, extending the role of pDCs beyond viral immunity. Indeed, there is now clear evidence for their playing an important role in tumor immunity and autoimmune disorders.

The ability of pDCs to migrate from blood to draining lymph organs and to sites of inflammation suggests a central role in the induction of innate immunity as well as in the coordination of adaptive immune functions. It has been shown that pDC-derived IFNs modulate the phenotype and function of conventional DCs. Moreover, pDCs (and cDCs) contribute to the activation of NK cells through both IFN-dependent and independent mechanisms. In addition to type I IFNs, pDCs produce cytokines (TNF) and chemokines (CCL3, CCL4, CXCL10) that selectively attract NK cells and activated T cells. Thus pDC appear specialized for initiation of innate response and have certain capabilities of inducing and modulating adaptive immune responses. But still, there are critical unknowns partly due to not sophisticate enough tools available (e.g. depletion studies performed using mAbs which are not pDC specific).

The research project Role of plasmacytoid dendritic cells in the orchestration of in vivo immune responses was designed to get a better understanding of the fundamental cellular and molecular mechanisms by which pDCs facilitate the establishment of an inflammatory microenvironment, and assist in orchestration of NK cell activity and CD8+ T cell priming by conventional DC (cDC). In this project several new tools and innovative methodologies were used in order to offer new perspectives on pDC biology in vivo. New mouse mutant in which pDCs are the only cell type capable to produce type I IFN allowed us to perform careful analysis of the pDC mediated inflammatory network. The project also benefited from the xMAP luminex technology to characterize the array of cytokines and chemokines produced under various experimental conditions. Results obtained provide the first in vivo model for cell and tissue-restricted type I IFN production and demonstrate that pDC-derived IFNs are sufficient to achieve NK cell mediated control of MCMV infection in restricted organs.