Dendritic cells (DCs) are professional antigen presenting cells involved not only in provoking innate immune responses but also in establishing adaptive immune responses. In order to clarify the critical in vivo roles of DCs, generation of gene-manipulated mice for DC ablation is very useful. DCs are heterogeneous and consist of various subsets, including plasmacytoid DCs (pDCs) or conventional DCs (cDCs). These DC subsets show the subset-specific functions. We have recently generated the mutant mice in which CD103⁺CD11b^- cDCs can be selectively ablated. The system is based on the selective expression of a chemokine receptor, XCR1, in the DC subset. CD103⁺CD11b^- cDCs are known for their high ability to incorporate dying cells and crosspresent the antigens to generate cytotoxic T cells. These functions are critical for protective responses against viral infection or tumors, but additional roles of the DC subset are largely unknown. By using our mutant mice, critical in vivo roles of the DC subset have been clarified. Our mutant mice are superior to the mutant mice generated so far in terms of the selectivity of the cell ablation and marking. Therefore, the mice should contribute to the clarification of additional roles of the DC subset. The DC subset is present also in the human. So the knowledge based on the mutant mice can be applicable to the human system.

Human dendritic cell (DC) subsets are composed of CD141⁺ myeloid DCs (mDCs), CD1c⁺ mDCs, and plasmacytoid DCs (pDCs). These DC subsets have different functions, and reagents that differentially regulate functions of the subsets may represent novel therapies for immune disorders. A proteasome inhibitor for multiple myeloma, bortezomib, suppresses the survival and immunostimulatory function of pDCs by targeting two critical points, intracellular trafficking of nucleic acid-sensing Toll-like receptors and endoplasmic reticulum homeostasis. A tyrosine kinase inhibitor for chronic myeloid leukemia with multiple targets, dasatinib, suppresses IFN-α production by pDCs stimulated with CpG DNA without reducing viability. This suppression is likely due to the abrogation of endosomal retention of CpG DNA, which is critical for the large amount of IFN-α production by pDCs. It has been reported that pDCs cause inflammatory disorders such as lupus and psoriasis. Thus, these studies illustrate that vesicular trafficking characteristic of pDCs may constitute a target to develop novel therapies for inflammatory disorders. 1α, 25-dihydroxyvitamin D₃ (VD₃) is an important immunomodulatory vitamin. VD₃ induces CD1c⁺ mDCs to produce a vitamin A derivative, retinoic acid (RA). Furthermore, the CD1c⁺ mDCs induce naïve CD4⁺ T cells to differentiate into guthoming Th2 cells in an RA-dependent manner. The “vitamin D – CD1c⁺ mDC – RA” axis may constitute an important immune component for maintaining tissue homeostasis in humans. Long-lasting efforts to clarify the mechanisms by which DCs perform immunoregulatory functions and to apply the accumulating knowledge to developing novel therapies will continue to be an exciting field in immunology.

Th2-type immune response is critical for development of allergic inflammation. We have recently identified periostin as one of the inducible genes upon stimulation with IL-13, a representative Th2 cytokine. Periostin is a matricellular protein that binds to both matrix proteins and cells to modulate cellular activation. The expression/production of periostin is indeed augmented in multiple allergic diseases such as atopic dermatitis, allergic rhinitis, and bronchial asthma. Particularly, serum periostin measurement has been proven useful to predict the effectiveness of the molecularlytargeted drugs against IgE as well as IL-13 in the treatment of patients with bronchial asthma. Mechanistically, periostin is produced mainly by fibroblasts, and acts on multiple cell types including epithelial cells, fibroblasts themselves, and eosinophils via integrins. Periostin contributes to the production of thymic stromal lymphopoietin by keratinocytes and interleukin-6 by fibroblasts either directly or indirectly, and chemotaxis of activated eosinophils, thus amplifying the Th2-type immune response. Periostin is a promising novel target of molecular medicine in allergic diseases for both diagnosis and treatment.

Dendritic cells (DCs) are the master cells in activating immune responses through enhancing innate immunity by cytokine production and initiating acquired immunity by priming naïve CD4+ T cells. However, DCs play not only a central role in antimicrobial immune response in host defense but also a pathogenic role in the development of the several inflammatory disorders such as allergy and autoimmune diseases. In allergy, epithelial cell-derived thymic stromal lymphopoietin stimulates myeloid DC subset to express OX40L and CCL17 that induce and maintain Th2 cell responses. In systemic lupus erythematosus (SLE), aberrant continuous type I IFN production by plasmacytoid DCs causes vicious spiral of pathogenic autoimmune responses. Thus, myeloid DC and plasmacytoid DC subsets represent key cellular pathogenic cells in allergy and SLE, respectively. Accordingly, control of the dysregulated myeloid DC functions and pDC-derived type I IFNs provides an alternative treatment strategy for allergy and SLE. We focus on specific roles of statins in controlling the myeloid DCs-dependent Th2 pathway and plasmacytoid DC-dependent IFN pathway and state their therapeutic potentials for allergy and SLE.

The combination anti-retroviral therapy (cART) was introduced into the treatment of AIDS, the mortality due to the AIDS markedly decreased, and the convalescence of the patient was improved drastically. Although, the membrane fusion of host's T cells and HIV-1 is an essential step of early infection of HIV-1, there is low number of drugs targeting this step and it will be hope to develop new HIV-1 entry inhibitors. Moreover, it was reported that decreasing of cell membrane fluidity suppresses HIV-1 entry and cell-cell fusion. Here, we focused on the viral entry as initial step of HIV-1 infection and evaluated to establish the novel screening analysis using flow cytometry. Firstly, we screened the reagents modified cell membrane fluidity using fluorescent depolarization methods. Next, we performed cell-cell fusion inhibition assay. In this model, Tetinducible HIV-1 envelope protein (Env) expressing T cell and Target T cell were labeled with green and red fluorescent dyes, respectively and cells were co-cultured. Then, fused cells are taken on yellow color due to merge green and red color with fluorescent microscopy and can detect as double positive cells by flow cytometric analysis. We identified Cepharanthine and GUT-70 as novel viral entry/fusion inhibitors targeting host cell membrane and the availability of our screening analysis was confirmed. Our study suggests the possibility of rapidly screening for viral entry inhibitors using flow cytometry. The rapidly screening of anti-viral reagents is possible to reduce the time to apply for clinical use.