Blockade of OSMRß signaling ameliorates skin lesions in a mouse model of human atopic dermatitis.

Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by severe pruritus and eczematous skin lesions. Although IL-31, a type 2 helper T (Th2)-derived cytokine, is important to the development of pruritus and skin lesions in AD, the blockade of IL-31 signaling does not improve the skin lesions in AD. Oncostatin M (OSM), a member of IL-6 family of cytokines, plays important roles in the regulation of various inflammatory responses through OSM receptor ß subunit (OSMRß), a common receptor subunit for OSM and IL-31. However, the effects of OSM on the pathogenesis of AD remain to be elucidated. When AD model mice were treated with OSM, skin lesions were exacerbated and IL-4 production was increased in the lymph nodes. Next, we investigated the effects of the monoclonal antibody (mAb) against OSMRß on the pathogenesis of AD. Treatment with the anti-OSMRß mAb (7D2) reduced skin severity score in AD model mice. In addition to skin lesions, scratching behavior was decreased by 7D2 mAb with the reduction in the number of OSMRß-positive neurons in the dorsal root ganglia of AD model mice. 7D2 mAb also reduced the serum concentration of IL-4, IL-13, and IgE as well as the gene expressions of IL-4 and IL-13 in the lymph nodes of AD model mice. Blockade of both IL-31 and OSM signaling is suggested to suppress both pruritus and Th2 responses, resulting in the improvement of skin lesions in AD. The anti-OSMRß mAb may be a new therapeutic candidate for the treatment of AD.

PACSIN1 regulates the TLR7/9-mediated type I interferon response in plasmacytoid dendritic cells.

Plasmacytoid dendritic cells (pDCs) are the professional interferon (IFN)-producing cells of the immune system. pDCs specifically express Toll-like receptor (TLR)7 and TLR9 molecules and produce massive amounts of type I IFN by sensing microbial nucleic acids via TLR7 and TLR9. Here we report that protein kinase C and casein kinase substrate in neurons (PACSIN) 1, is specifically expressed in human and mouse pDCs. Knockdown of PACSIN1 by short hairpin RNA (shRNA) in a human pDC cell line significantly inhibited the type I IFN response of the pDCs to TLR9 ligand. PACSIN1-deficient mice exhibited normal levels of conventional DCs and pDCs, demonstrating that development of pDCs was intact although PACSIN1-deficient pDCs showed reduced levels of IFN-α production in response to both cytosine guanine dinucleotide (CpG)-oligonucleotide (ODN) and virus. In contrast, the production of proinflammatory cytokines in response to those ligands was not affected in PACSIN1-deficient pDCs, suggesting that PACSIN1 represents a pDC-specific adaptor molecule that plays a specific role in the type I IFN signaling cascade.

Cell-intrinsic role for IFN-α-STAT1 signals in regulating murine Peyer patch plasmacytoid dendritic cells and conditioning an inflammatory response.

Plasmacytoid dendritic cells (pDCs) reside in bone marrrow and lymphoid organs in homeostatic conditions and typically secrete abundant quantities of type I interferons (IFNs) on Toll-like receptor triggering. Recently, a pDC population was identified within Peyer patches (PPs) of the gut that is distinguished by its lack of IFN production; however, the relationship of PP pDCs to pDCs in other organs has been unclear. We report that PP pDCs are derived from common DC progenitors and accumulate in response to Fms-like tyrosine kinase 3 ligand, yet appear divergent in transcription factor profile and surface marker phenotype, including reduced E2-2 and CCR9 expression. Type I IFN signaling via STAT1 has a cell-autonomous role in accrual of PP pDCs in vivo. Moreover, IFN-α enhances pDC generation from DC progenitors by a STAT1-dependent mechanism. pDCs that have been developed in the presence of IFN-α resemble PP pDCs, produce inflammatory cytokines, stimulate Th17 cell generation, and fail to secrete IFN-α on Toll-like receptor engagement. These results indicate that IFN-α influences the development and function of pDCs by inducing emergence of an inflammatory (Th17-inducing) antigen-presenting subset, and simultaneously regulating accumulation of pDCs in the intestinal microenvironment.

Oncostatin M deficiency leads to thymic hypoplasia, accumulation of apoptotic thymocytes and glomerulonephritis.

Oncostatin M (OSM) has been implicated in immune regulation, though its precise role remains elusive. Here we show that OSM plays a crucial role in the prevention of autoimmune diseases. OSM-deficient mice showed normal development of T cells, B cells and DC; however, their thymus showed hypoplasia and altered medullary structure. Autoantibodies against dsDNA accumulated and glomerulonephritis developed in aged OSM-deficient mice. Apoptotic cells accumulated in the thymus of OSM-deficient mice, and the administration of dexamethasone in young OSM-deficient mice resulted in the massive accumulation of apoptotic thymocytes and production of autoantibodies. These results suggest that OSM plays a key role in the prevention of autoimmune disease by regulating the clearance of apoptotic thymocytes.

E-box protein E2-2 is a crucial regulator of plasmacytoid DC development.

DC play central roles in priming both innate and adaptive immune responses. Multiple DC subsets have been identified on the basis of their phenotype and function. Plasmacytoid DC (pDC) are professional IFN-producing cells that play an essential role in anti-viral immunity. A series of recent studies demonstrates that the regulation of pDC development is different from other types of DC. In this issue of the European Journal of Immunology, new insight is provided into how human pDC development is regulated by various transcription factors, in particular by the Ets family protein Spi-B and E-box protein E2-2.

The signal transducer STAT5 inhibits plasmacytoid dendritic cell development by suppressing transcription factor IRF8.

The development of distinct dendritic cell (DC) subsets is regulated by cytokines. The ligand for the FMS-like tyrosine kinase 3 receptor (Flt3L) is necessary for plasmacytoid DC (pDC) and conventional DC (cDC) maturation. The cytokine GM-CSF inhibits Flt3L-driven pDC production while promoting cDC growth. We show that GM-CSF selectively utilized its signal transducer STAT5 to block Flt3L-dependent pDC development from the lineage-negative, Flt3+ (lin- Flt3+) bone-marrow subset. The signaling molecule STAT3, by contrast, was necessary for expansion of DC progenitors but not pDC maturation. In vivo, STAT5 suppressed pDC formation during repopulation of the DC compartment after bone-marrow ablation. GM-CSF-dependent STAT5 signaling rapidly extinguished pDC-related gene expression in lin- Flt3+ progenitors. Inspection of the Irf8 promoter revealed that STAT5 was recruited during GM-CSF-mediated suppression, indicating that STAT5 directly inhibited transcription of this critical pDC gene. Our results therefore show that GM-CSF controls the production of pDCs by employing STAT5 to suppress IRF8 and the pDC transcriptional network in lin- Flt3+ progenitors.

A critical role of costimulation during intrathymic development of invariant NK T cells.

CD1d-restricted Valpha14(+) invariant NK T (iNKT) cells are a specialized alphabeta T cell subset that regulates both innate and adaptive immunity. Although costimulatory molecules are required for the activation of conventional T cells and for the development of Foxp3(+) T cells, their role in iNKT cell regulation is unclear. Here we report that mice deficient in CD80/CD86 and/or B7h exhibit severe defects in thymic iNKT cell maturation, associated with largely reduced iNKT cell number in the thymus and the periphery. We show that costimulation is necessary for the optimal expansion of postselected NK1.1(-) immature iNKT cells in the thymus and for the proper expression of the maturation markers T-bet and CD122. Surprisingly, costimulatory molecules on both hemopoietic and nonhematopoietic cells are required for iNKT cell development. Our results thus demonstrate a previously unknown function of costimulation in the intrathymic development of iNKT cells, distinct from that of conventional T cells and regulatory T cells.

IL-18 produced by thymic epithelial cells induces development of dendritic cells with CD11b in the fetal thymus.

Thymic dendritic cells (DCs) are suggested to be involved in T cell selection; however, their exact origin and function remain to be established. Although DCs in the adult thymus are mostly CD8alpha(+)CD11b(-), we found that CD8alpha(-)CD11b(+) DCs were abundantly present in the fetal thymus and they possessed antigen-presenting activity. Interestingly, these CD11b(+) DCs were significantly decreased in mice deficient for TNFR-associated factor 6 (TRAF6), a key signaling molecule downstream of IL-1 and tumor necrosis factor-alpha that have been known to induce DCs from intra-thymic precursor cells. CD11b(+) DCs were induced from CD4(-)CD8(-) thymocytes by fetal thymic epithelial cells (TECs). Analysis of cytokine expression in TECs revealed that none of the cytokines previously shown to induce DCs were expressed. Instead, we found strong expression of IL-18 that transmits signals through TRAF6. IL-18 induced CD11b(+) DCs from CD4(-)CD8(-) thymocytes in vitro, which exhibited strong antigen-presenting activity and formed conjugates with CD4(+)CD8(+) T cells efficiently. Taken together, these results strongly suggest that CD11b(+) DCs are differentiated from CD4(-)CD8(-) thymocytes by IL-18 produced from TECs and that they are involved in T cell selection in the fetal thymus.

Development of CD4+ macrophages from intrathymic T cell progenitors is induced by thymic epithelial cells.

It was recently demonstrated that there are CD4(+) macrophages, which exhibit strong phagocytic activity, in the thymus. They are suggested to play an important role for the elimination of apoptotic thymocytes. However, the origin and nature of CD4(+) macrophages in the thymus remain unexplored. In this study, we describe that the most immature intrathymic progenitors (CD25(-)/CD44(+)/FcR(+)) give rise to CD4(+) macrophages by oncostatin M-responsive thymic epithelial cells (ORTEC) in an IL-7-dependent manner. Neither conditioned medium of ORTEC nor a mixture of cytokines induced CD4(+) macrophages, and oncostatin M receptor was not expressed in thymocytes, suggesting that the development of CD4(+) macrophages from the immature thymocytes requires a direct interaction with ORTEC. These results collectively suggest that the development of CD4(+) macrophages from the intrathymic T cell progenitors is induced by thymic epithelial cells.

Cutting Edge: A possible role for CD4+ thymic macrophages as professional scavengers of apoptotic thymocytes.

A vast majority of thymocytes are eliminated during T cell development by apoptosis. However, apoptotic thymocytes are not usually found in the thymus, indicating that apoptotic thymocytes must be eliminated rapidly by scavengers. Although macrophages and dendritic cells are believed to play such role, little is known about scavengers in the thymus. We found that CD4(+)/CD11b(+)/CD11c(-) cells were present in the thymus and that they expressed costimulatory molecules for T cell selection and possessed Ag-presenting activity. Moreover, these CD4(+)/CD11b(+) cells phagocytosed apoptotic thymocytes much more efficiently than thymic CD4(-)/CD11b(+) cells as well as activated peritoneal macrophages. CD4(+)/CD11b(+) cells became larger along with thymus development, while no such change was observed in CD4(-)/CD11b(+) cells. Finally, engulfed nuclei were frequently found in CD4(+)/CD11b(+) cells. These results strongly suggest that thymic CD4(+)/CD11b(+) cells are major scavengers of apoptotic thymocytes.