Pivotal role of plasmacytoid dendritic cells in inflammation and NK-cell responses after TLR9 triggering in mice.

The physiologic role played by plasmacytoid dendritic cells (pDCs) in the induction of innate responses and inflammation in response to pathogen signaling is not well understood. Here, we describe a new mouse model lacking pDCs and establish that pDCs are essential for the in vivo induction of NK-cell activity in response to Toll-like receptor 9 (TLR9) triggering. Furthermore, we provide the first evidence that pDCs are critical for the systemic production of a wide variety of chemokines in response to TLR9 activation. Consequently, we observed a profound alteration in monocyte, macrophage, neutrophil, and NK-cell recruitment at the site of inflammation in the absence of pDCs in response to CpG-Dotap and stimulation by microbial pathogens, such as Leishmania major, Escherichia coli, and Mycobacterium bovis. This study, which is based on the development of a constitutively pDC-deficient mouse model, highlights the pivotal role played by pDCs in the induction of innate immune responses and inflammation after TLR9 triggering.