Functional analysis of a novel inhibitory receptor expressed on plasmacytoid dendritic cells

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Inhibitory receptors play crucial roles for fine regulation and termination of immune responses by negatively regulating cellular functions. A number of inhibitory receptors have been identified on various types of cells. In particular, inhibitory receptors on natural killer cells have been well characterized. It has been postulated that recognition of MHC class I, or related molecules, on target cells by inhibitory NK receptors allows NK cells to prevent self killing but destroy inappropriate cells possessing decreased levels of MHC class I.Ly49Q is an ITIM-bearing inhibitory receptor belonging to Ly49 family that is known as one of subfamilies of NK receptors. Even though Ly49Q is classified into Ly49 family because of highly structural similarities and of its chromosomal location, Ly49Q has unique features different from other Ly49 family members. Ly49Q is not expressed on NK and NKT cells, but predominantly expressed on macrophages and plasmacytodi dendritic cells. Ly49Q has an abi … More lity to associate with both SHP-1 and SHP-2 in a tyrosine phosphorylation-dependent manner.We here demonstrate that different expression levels of Ly49Q defined sequential maturational stages of PDCs in bone marrow. Moreover, we identified functionally different subsets of PDCs according to the expression of Ly49Q. Most CD11c^+B220^+PDCs in spleen and lymph node expressed high levels of Ly49Q. However, a significant portion of PDCs in BM, blood, liver and lung lacked Ly49Q expression. Ly49Q^- PDCs possessed lower abilities to produced IFN-αβ/, IL-6 and IL-12 p70 than Ly49Q^+ PDCs in response to TLR ligands. Interestingly, however, Ly49Q^- PDCs bore an ability to produce equivalent levels of TNF-α to Ly49Q^+ PDCs when exposed to CpG and HVJ. Thus, Ly49Q is a useful marker to reveal maturation process of PDCs and to distinguish functionally different subsets of PDCs. Our results suggest that cytokine profiles of PDCs alter during their maturational processes and that PDCs play different immunological functions depending on their maturational stages. To understand functional relevance of Ly49Q as well as MHC class I recognition by macrophages and dendritic cells, we started to establish transgenic mice expressing Ly49Q. Less