Ly49Q defines 2 pDC subsets in mice

Plasmacytoid dendritic cells (pDCs) play an important primary role for antiviral innate immunity by rapidly producing large amounts of type 1 interferon (IFN) upon viral infection. To study pDC biology, we generated a monoclonal antibody, termed 2E6, that recognizes pDCs. Molecular cloning of a cDNA encoding the 2E6 antigen revealed that it is a type II C-type lectin, Ly49Q, that consists of 247 amino acids with high homology to the natural killer (NK) receptor family Ly49, with an immunoreceptor tyrosine-based inhibitory motif in the cytoplasmic domain. Ly49Q is expressed on pDCs but not on NK cells or myeloid dendritic cells. B220+, CD11c+, CD11b– pDCs in bone marrow were divided into Ly49Q+ and Ly49Q– subsets. While both subsets produced IFN-α upon cytosine-phosphate-guanosine (CpG) and herpes simplex virus stimulation, Ly49Q– pDCs responded poorly to influenza virus. In addition, Ly49Q– pDCs produced inflammatory cytokines such as interleukin 6 (IL-6), IL-12, and tumor necrosis factor α (TNF-α) upon stimulation at lower levels than those produced by Ly49Q+ pDCs. In contrast to bone marrow, Ly49Q+ pDCs were only found in peripheral blood, lymph nodes, and spleen. These results indicate that Ly49Q is a specific marker for peripheral pDCs and that expression of Ly49Q defines 2 subsets of pDCs in bone marrow.