Prion protein expression by mouse dendritic cells is restricted to the nonplasmacytoid subsets and correlates with the maturation state.

Expression of the physiological cellular prion protein (PrP(C)) is remarkably regulated during differentiation and activation of cells of the immune system. Among these, dendritic cells (DCs) display particularly high levels of membrane PrP(C), which increase upon maturation, in parallel with that of molecules involved in Ag presentation to T cells. Freshly isolated mouse Langerhans cells, dermal DCs, and DCs from thymus, spleen, and mesenteric lymph nodes expressed low to intermediate levels of PrP(C). Highest levels of both PrP(C) and MHC class II molecules were displayed by lymph node CD8alpha(int) DCs, which represent fully mature cells having migrated from peripheral tissues. Maturation induced by overnight culture resulted in increased levels of surface PrP(C), as did in vivo DC activation by bacterial LPS. Studies on Fms-like tyrosine kinase 3 ligand bone marrow-differentiated B220(-) DCs confirmed that PrP(C) expression followed that of MHC class II and costimulatory molecules, and correlated with IL-12 production in response to TLR-9 engagement by CpG. However, at variance with conventional DCs, B220(+) plasmacytoid DCs isolated from the spleen, or in vitro differentiated, did not significantly express PrP(C), both before and after activation by TLR-9 engagement. PrP knockout mice displayed higher numbers of spleen CD8alpha(+) DCs, but no significant differences in their maturation response to stimulation through TLR-4 and TLR-9 were noticed. Results are discussed in relation to the functional relevance of PrP(C) expression by DCs in the induction of T cell responses, and to the pathophysiology of prion diseases.

A gene signature of inhibitory MHC receptors identifies a BDCA3(+) subset of IL-10-induced dendritic cells with reduced allostimulatory capacity in vitro.

Dendritic cells (DC) are crucial gatekeepers in regulating immunity. Whereas mature immunostimulatory myeloid DC (DC(ims)) potently promote immune responses, IL-10-induced myeloid DC (DC-IL-10) counteract T cell activation. To elucidate the molecular repertoire by which DC-IL-10 secure reduced T cell activation, comparative gene expression profiling was done using Affymetrix U133A microarrays. Among the genes overexpressed in DC-IL-10, eight immunoreceptor tyrosine-based inhibitory motif (ITIM)-containing inhibitory molecules (ILT2, ILT3, ILT4, ILT5, DCIR, PILRA, FcgammaRIIB, SLAM) were found. Phenotypic analysis of DC-IL-10 defined an ILT(high) DC subset further characterized by expression of CD14, TLR2, DC-SIGN, and CD123 and the lack of lymphocyte, monocyte/macrophage, and plasmacytoid DC markers such as CD3, CD8, and CD68. A unique feature of the ILT(high) DC subset was expression of the novel DC marker BDCA3, which was not detected on monocytes, immature DC, DC(ims), or ILT(low) DC-IL-10. While the allogeneic T cell proliferation induced by the entire DC-IL-10 population was approximately 30% of that stimulated by DC(ims), allogeneic MLR responses driven by the ILT(high) DC subset were reduced to 8% of the allostimulatory capacity of DC(ims), although secretion of the inhibitory cytokine IL-10 and other Th1/Th2-associated cytokines was similar in these cells.