Airway hypersensitive reaction (AHR) is an animal model for asthma, which is caused or

Type I interferons (IFNs) derived from plasmacytoid dendritic cells (PDCs) are critical for antiviral responses; however, the mechanisms underlying their production remain unclear. We have identified a receptor, PDC-TREM, which is associated with Plexin-A1 (PlxnA1) on the PDC cell surface and is preferentially expressed after TLR-stimulation. Limited TLR signals induced PDC-TREM expression but failed to induce IFN-α production. However, when coupled with Sema6D, a ligand for Plexin-A1, limited TLR-stimulation resulted in PDC-TREM-mediated DAP12-dependent phosphorylation of phosphoinositide 3-kinase (PI3K) and extracellular regulated kinase (Erk) 1/2 at 6–9 h, and IFN-α was produced. Inhibition of PDC-TREM expression by pdctrem -shRNA, blocking of PDC-TREM-binding with PlxnA1 by PDC-TREM mAb, and DAP12 deficiency all resulted in greatly reduced PDC-TREM-dependent activation of signaling molecules and IFN-α production. Thus, PDC-TREM is responsible for IFN-α production, whereas TLR signals are essential for PDC-TREM expression.

Establishment of a system with efficient generation of natural killer T (NKT) cells from embryonic stem (ES) cells would enable us to identify the cells with NKT- IntroductionNatural killer T (NKT) cells are characterized by their expression of an invariant receptor encoded by V␣14-J␣18 in mice 1 and by V␣24-J␣18 in humans. 2,3 Because the invariant receptor is used only by NKT cells and not by conventional T cells, NKT cells are a distinct lineage from conventional T cells. NKT cells produce both T helper 1 (Th1) and Th2 cytokines, mediating strong adjuvant activity through their Th1 cytokine production essential for protective responses against tumors 4-6 and pathogens 7-9 and also protecting autoimmune disease development through their Th2 cytokine production. 10,11 Despite the importance of this cell type in the immune system, the identity of NKT progenitor cells and their subsequent development remain poorly understood. In previous reports, cells with NKT-cell potential were detected in the CD4CD8 double-positive (DP) thymocyte population, 12,13 indicating that NKT cells are branched off from conventional ␣␤T-cell precursors at the DP stage in the thymus. [12][13][14] It has also been shown that the early immature CD4 NKT cells produce only interleukin-4 (IL-4), but their potential to produce interferon ␥ (IFN-␥) is acquired at a later developmental stage. 15,16 However, it is still possible that NKT cells might be derived from a precursor population distinct from that of conventional ␣␤T cells, because it has previously been shown that NKT precursor cells express on their cell surface granulocyte-macrophage colony-stimulating factor receptor (GM-CSFR), 17 which is known to be a unique marker for myeloid cell lineages but not for lymphoid cells. In addition, because the invariant V␣14 receptor is used only by NKT cells and not by conventional T cells, NKT cells may be a distinct lineage from conventional ␣␤T cells. 18 Embryonic stem (ES) cells are a powerful model system in which to study in vitro lymphocyte differentiation, addressing the questions on the cells with NKT precursor potential and the ability of NKT cells to produce both Th1 and Th2 cytokines during their development. For example, embryoid bodies generated from ES cells contain CD34 ϩ cells that develop into lymphocytes when cocultured with OP9 stromal cells plus appropriate cytokines. 19 However, in most cases, ES cells generate B and NK cells, but not T or NKT cells on OP9 coculture. 20,21 To overcome these problems, OP9 stromal cells transduced with Notch ligand delta-like1 (OP9/Dll-1) are used for the directed differentiation of ES cells to T-cell lineages. Induction of Notch signals directs stem cells to differentiate into immature DP T cells and inhibits B-cell development, indicating that Notch signaling is required as a proximal event in T-cell commitment from progenitors. 22,23 Another approach is to use cloned ES (NKT-ES) cells established by nuclear transfer of a cell with a rearranged T-cell receptor (TCR) gene. 24,25 Interestingly...