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 11 C-type lectin, Ly49Q, that consists of 247 amino acids with high homology to the natural killer (NK) receptor family Ly49, with an immunoreceptor tyrosinebased 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-alpha 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 alpha (TNF-alpha) 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.