Differentiation of Langerhans Cells from Monocytes and Their Specific Function in Inducing IL-22-Specific Th Cells.

Human mucosal tissues and skin contain two distinct types of dendritic cell (DC) subsets, epidermal Langerhans cells (LCs) and dermal DCs, which can be distinguished by the expression of C-type lectin receptors, Langerin and DC-SIGN, respectively. Although peripheral blood monocytes differentiate into these distinct subsets, monocyte-derived LCs (moLCs) induced by coculture with GM-CSF, IL-4, and TGF-ß1 coexpress both Langerin and DC-SIGN, suggesting that the environmental cues remain unclear. In this study, we show that LC differentiation is TGF-ß1 dependent and that cofactors such as IL-4 and TNF-α promote TGF-ß1-dependent LC differentiation into Langerin+DC-SIGN- moLCs but continuous exposure to IL-4 blocks differentiation. Steroids such as dexamethasone greatly enhanced TNF-α-induced moLC differentiation and blocked DC-SIGN expression. Consistent with primary LCs, dexamethasone-treated moLCs express CD1a, whereas monocyte-derived DCs (moDCs) express CD1b, CD1c, and CD1d. moDCs but not moLCs produced inflammatory cytokines after stimulation with CD1b and CD1d ligands mycolic acid and α-galactosylceramide, respectively. Strikingly, CD1a triggering with squalene on moLCs but not moDCs induced strong IL-22-producing CD4+ helper T cell responses. As IL-22 is an important cytokine in the maintenance of skin homeostasis, these data suggest that CD1a on LCs is involved in maintaining the immune barrier in the skin.

HMGB1 released from intestinal epithelia damaged by cholera toxin adjuvant contributes to activation of mucosal dendritic cells and induction of intestinal cytotoxic T lymphocytes and IgA.

Cholera toxin (CT) is a potent mucosal adjuvant and oral administration of ovalbumin (OVA) antigens plus CT induces OVA-specific CD8+ cytotoxic T lymphocytes (CTLs) and IgA production in intestinal mucosa. However, the mechanisms of induction of these immune responses remain unknown. Intestinal OVA-specific CD8+ CTLs were not induced by oral administration of the CT active (CTA) or CT binding (CTB) subunit as an adjuvant and CD11c+ DCs were involved in cross-priming of intestinal CTLs. CD8+CD103+CD11c+CD11b-DCs and DCIR2+CD103+CD11c+CD11b+ DCs were distributed in the intestinal lamina propria and mesenteric lymph nodes, both DC subsets expressed DEC-205, and the expression of co-stimulatory molecules such as CD80 and CD86 was enhanced in both DC subsets after oral administration of intact CT but not the CTA or CTB subunit. Intestinal DCs activated by the oral administration of OVA plus CT cross-presented OVA antigens and DCs that captured OVA antigen through DEC-205, but not DCIR2, could cross-present antigen. We found that oral administration of intact CT, but not the CTA or CTB subunit, enhanced cell death, cytoplasmic expression of high-mobility group box 1 protein (HMGB1) in epithelial cell adhesion molecule (EpCAM)+CD45- intestinal epithelial cells (IECs), and HMGB1 levels in fecal extracts. HMGB1 dose-dependently enhanced the expression of CD80 and CD86 on DCs in vitro, and intravenous or oral administration of glycyrrhizin, an HMGB1 inhibitor, significantly suppressed activation of mucosal DCs and induction of intestinal OVA-specific CTLs and IgA by oral CT administration. These results showed that oral administration of intact CT triggers epithelial cell death in the gut and the release of HMGB1 from damaged IECs, and that the released HMGB1 may mediate activation of mucosal DCs and induction of CTLs and IgA in the intestine.

Detection Method for Aquatic Bacteria of the Fingers, as a Potential Origin of the Aqueous Solution Contamination.

　Aquatic bacteria were isolated from the hands of working staffs by an adapted culture protocol. When the sample solution obtained by the" glove juice method" was incubated for 3 days at room temperature, viable cell counts increased up to 105-fold, and the majority of the isolated colonies were shown to be Gram-negative aquatic bacteria, which carry the risk of contaminating water. Using R2A medium, coagulase-negative staphylococci were the dominant microbes immediately after recovery from the hands. Here it was revealed that bacteria of the phylum Proteobacteria isolated from the hand can be the causative bacteria of aqueous contamination. This modification in the GJ method may be useful as an effective training protocol to demonstrate the importance of hand hygiene and clean operation for aseptic manufacturing.

Induction of langerin+ Langerhans cell-like cells expressing reduced TLR3 from CD34+ cord blood cells stimulated with GM-CSF, TGF-ß1, and TNF-α.

Langerhans cells (LCs), a subset of dendritic cells (DCs), reside in body surface presenting antigens from various pathogens and activate immune system after migrating to vicinal lymph nodes. We recently demonstrated that the E-cadherin interaction allowed peripheral blood (PB) CD14+ cells to differentiate into LC-like cells that closely resemble primary LCs. Here, with a combination of GM-CSF, TGF-ß, and TNF-α, we induced LC-like cells from umbilical cord blood (UCB)derived CD34+ cells and compared them with those induced from PB CD14+ cells. In contrast to PB CD14+ cell-derived LC-like cells with an undetectable surface level of toll-like receptor (TLR)4 and an unresponsiveness feature to bacterial lipopolysaccharide (LPS), CB CD34+ cellsderived LC like cells expressed a low, but apparent, surface level of TLR4 and a reduced level of intracellular TLR3. Consistent with this result, they responded to bacterial LPS, but poorly to poly(I:C) reflecting viral RNA. These findings suggest that LC-precursors from circulating PB CD14+ cells seem to be arranged in the outer barrier of skin, while LC-precursors from local undifferentiated UCB-derived CD34+ cells may be arranged in the inner barrier of mucosal tissues and work together to combat against external pathogens as well as internal malignancies throughout body surface.

Hemopoietic cell kinase (Hck) and p21-activated kinase 2 (PAK2) are involved in the down-regulation of CD1a lipid antigen presentation by HIV-1 Nef in dendritic cells.

Dendritic cells (DCs) play a major role in in vivo pathogenesis of HIV-1 infection. Therefore, DCs may provide a promising strategy to control and eventually overcome the fatal infection. Especially, immature DCs express all CD1s, the non-MHC lipid antigen -presenting molecules, and HIV-1 Nef down-regulates CD1 expression besides MHC. Moreover, CD1d-restricted CD4(+) NKT cells are infected by HIV-1, reducing the number of these cells in HIV-1-infected individuals. To understand the exact role of DCs and CD1-mediated immune response during HIV-1 infection, Nef down-regulation of CD1a-restricted lipid/glycolipid Ag presentation in iDCs was analyzed. We demonstrated the involvement of the association of Nef with hemopoietic cell kinase (Hck) and p21-activated kinase 2 (PAK2), and that Hck, which is expressed strongly in iDCs, augmented this mutual interaction. Hck might be another therapeutic target to preserve the function of HIV-1 infected DCs, which are potential reservoirs of HIV-1 even after antiretroviral therapy.

A possible origin of emerged HIV-1 after interrupting anti-retroviral therapy.

Although HIV-1 can be successfully eradicated from the circulating blood of HIV-1-infected individuals using anti-retroviral therapy (ART), HIV-1 virions emerge immediately after the interruption of ART. This study was aimed to investigate the origin of the emerged HIV-1. After obtaining informed consent, blood samples from nine HIV-1-infected individuals and endoscopic ileum samples from five of the individuals were obtained. Purified peripheral mononuclear cells (PBMCs)and ileum cells were analyzed by flow-cytometry, and the V3 loop sequences of the HIV-1 envelope protein were determined. By comparing the V3 loop sequences of the samples, we confirmed that the provirus hidden in the CD4(+) PBMCs was not the source of the HIV-1 that emerged after the interruption of ART. Although free virus and HIV-1-p24 antigen (p24)-positive cells were not seen in the blood of patients receiving ART, proviral DNA and p24 could be detected in the ileum from the same patient. Among the HIV-1-infected CD4(+) cells in the ileum samples, Vα24(+) natural killer T (NKT) cells were the major p24-positive cells. These results suggest that the innate NKTcells in the mucosal compartment are the most likely candidates for the origin of the HIV-1 that emerged after ART was interrupted.

Inhibition of R5-tropic HIV type-1 replication in CD4⁺ natural killer T cells by γδ T lymphocytes.

After the development of highly active anti-retroviral therapy, it became clear that the majority of emergent HIV-1 is macrophage-tropic and infects CD4⁺, CCR5-expressing cells (R5-tropic). There are three distinct cell populations, R5-tropic, HIV-1-susceptible CD4⁺ cells: (i) natural killer T (NKT) cells, (ii) dendritic cells and macrophages, and (iii) tissue-associated T cells residing primarily at mucosal surfaces. We have confirmed that CD4⁺ NKT cells derived from peripheral blood mononuclear cells (PBMCs) predominantly express CCR5 rather than CXCR4, whereas the reverse is true for CD4⁺ T cells derived from circulating PBMCs, and that R5-tropic HIV-1 expands efficiently in the CD4⁺ NKT cells. Moreover, when PBMCs depleted of CD8α⁺ cells were stimulated in the presence of α-galactosylceramide (α-GalCer) and R5-tropic HIV-1 [NL(AD8)], the production of HIV-1 virions was not suppressed, whereas, similar to the untreated PBMCs, depletion of CD8ß⁺ cells from PBMCs significantly inhibited virion production. These findings suggest that CD8αα⁺ but not CD8αß⁺ cells may have the ability to inhibit R5-tropic HIV-1 replication in CD4⁺ NKT cells. Here, we show that co-culturing R5-tropic HIV-1-infected CD4⁺ NKT cells with CD8αα⁺ γδ T cells, in particular Vγ1Vδ1 cells, but not with CD8αα⁺ NKT cells or CD8αα⁺ dendritic cells, inhibits HIV-1 replication mainly by secreting chemokines, such as macrophage inflammatory proteins 1α and 1ß and RANTES. Collectively, these results indicate the importance of CD8αα⁺ γδ T cells in the control of R5-tropic HIV-1 replication and persistence in CD4⁺ NKT cells.

Ribavirin modulates the conversion of human CD4(+) CD25(-) T cell to CD4(+) CD25(+) FOXP3(+) T cell via suppressing interleukin-10-producing regulatory T cell.

Because regulatory T (Treg) cells play an important role in modulating the immune system response against both endogenous and exogenous antigens, their control is critical to establish immunotherapy against autoimmune disorders, chronic viral infections and tumours. Ribavirin (RBV), an antiviral reagent used with interferon, is known to polarize the T helper (Th) 1/2 cell balance toward Th1 cells. Although the immunoregulatory mechanisms of RBV are not fully understood, it has been expected that RBV would affect T reg cells to modulate the Th1/2 cell balance. To confirm this hypothesis, we investigated whether RBV modulates the inhibitory activity of human peripheral CD4(+)  CD25(+)  CD127(-) T cells in vitro. CD4(+)  CD25(+)  CD127(-) T cells pre-incubated with RBV lose their ability to inhibit the proliferation of CD4(+)  CD25(-) T cells. Expression of Forkhead box P3 (FOXP3) in CD4(+)  CD25(-) T cells was down-modulated when they were incubated with CD4(+)  CD25(+)  CD127(-) T cells pre-incubated with RBV without down-modulating CD45RO on their surface. In addition, transwell assays and cytokine-neutralizing assays revealed that this effect depended mainly on the inhibition of interleukin-10 (IL-10) produced from CD4(+)  CD25(+)  CD127(-) T cells. These results indicated that RBV might inhibit the conversion of CD4(+)  CD25(-)  FOXP3(-) naive T cells into CD4(+)  CD25(+)  FOXP3(+) adaptive Treg cells by down-modulating the IL-10-producing Treg 1 cells to prevent these effector T cells from entering anergy and to maintain Th1 cell activity. Taken together, our findings suggest that RBV would be useful for both elimination of long-term viral infections such as hepatitis C virus infection and for up-regulation of tumour-specific cellular immune responses to prevent carcinogenesis, especially hepatocellular carcinoma.

Interferon-gamma and tumor necrosis factor-alpha induce an immunoinhibitory molecule, B7-H1, via nuclear factor-kappaB activation in blasts in myelodysplastic syndromes.

During disease progression in myelodysplastic syndromes (MDS), clonal blasts gain a more aggressive nature, whereas nonclonal immune cells become less efficient via an unknown mechanism. Using MDS cell lines and patient samples, we showed that the expression of an immunoinhibitory molecule, B7-H1 (CD274), was induced by interferon-gamma (IFNgamma) and tumor necrosis factor-alpha (TNFalpha) on MDS blasts. This induction was associated with the activation of nuclear factor-kappaB (NF-kappaB) and nearly completely blocked by an NF-kappaB inhibitor, pyrrolidine dithiocarbamate (PDTC). B7-H1(+) MDS blasts had greater intrinsic proliferative capacity than B7-H1(-) MDS blasts when examined in various assays. Furthermore, B7-H1(+) blasts suppressed T-cell proliferation and induced T-cell apoptosis in allogeneic cocultures. When fresh bone marrow samples from patients were examined, blasts from high-risk MDS patients expressed B7-H1 molecules more often compared with those from low-risk MDS patients. Moreover, MDS T cells often overexpressed programmed cell death 1 (PD-1) molecules that transmit an inhibitory signal from B7-H1 molecules. Taken together, these findings provide new insight into MDS pathophysiology. IFNgamma and TNFalpha activate NF-kappaB that in turn induces B7-H1 expression on MDS blasts. B7-H1(+) MDS blasts have an intrinsic proliferative advantage and induce T-cell suppression, which may be associated with disease progression in MDS.

Inhibition of DC-SIGN-mediated transmission of human immunodeficiency virus type 1 by Toll-like receptor 3 signalling in breast milk macrophages.

The majority of cells in early/colostrum milk are breast milk macrophages (BrMMø) expressing dendritic cell (DC)-specific intercellular adhesion molecule 3 (ICAM3) grabbing nonintegrin (DC-SIGN), and the expression level of DC-SIGN on BrMMø will determine cell-to-cell human immunodeficiency virus type 1 (HIV-1) transmissibility. Thus, one of the strategies to prevent vertical transmission of HIV-1 through breast-feeding is to find a way to suppress DC-SIGN expression on BrMMø. As for the expression of Toll-like receptors (TLRs) in BrMMø, TLR3 was always seen in BrMMø but not in peripheral blood monocytes (PBMo). Also, the expression of TLR3 was slightly enhanced in BrMMø when the cells were treated with interleukin (IL)-4. Moreover, when TLR3 was stimulated with its specific ligand, the double-stranded RNA (dsRNA) poly(I:C), DC-SIGN expression on BrMMø was reduced even in the IL-4-mediated enhanced state. Some reduction may be caused by type I interferons (IFNs), such as IFN-alpha/beta, secreted from BrMMø. Indeed, both IFNs, particularly IFN-beta, showed a strong capacity to suppress the enhancement of DC-SIGN expression on IL-4-treated BrMMø and such TLR3-mediated DC-SIGN suppression was partially abrogated by the addition of anti-IFN-alpha/beta-receptor-specific antibodies. As expected, DC-SIGN-mediated HIV-1 transmission to CD4-positive cells by BrMMø was inhibited by either poly(I:C) stimulation or by treatment with type I IFNs. These findings suggest a possible strategy for preventing mother-to-child transmission (MTCT) of HIV-1 via breast-feeding through TLR3 signalling.

A pathological study of bamboo nodule of the vocal fold.

We examined pathologically a bamboo nodule of the vocal fold by means of immunohistochemical studies and scanning electron microscopic examination. A 38-year-old female showed a high index of antinuclear antibodies without any systemic symptoms but had complained of progressive voice disorder for 9 months. She had used her voice excessively in her occupation and for singing. Hematoxylin and eosin staining showed submucosal edema with lymphocyte and neutrocyte infiltrations and hyaline degeneration. Periodic acid methenamine silver staining showed hypertrophy of the basal lamina of the blood vessels. Immunohistochemical study showed IgG-positive cells in the blood vessel walls. Scanning electron microscopic study demonstrated immune complexes deposited as fine granules of high electrodense materials in the hypertrophic walls of the micro-blood vessels. After surgical resection of the bamboo nodules and advising her to avoid using her voice excessively, her voice improved gradually and the levels of IgG, immune complexes, and antinuclear antibody decreased for 1 year. These findings suggest that the bamboo nodules were not induced by an organ-specific reaction to an autoimmune disease, but mechanical damage to the micro-blood vessels induced by phonation injury of the vocal fold might have caused the deposit of high-molecular weight immune complexes in the damaged micro-blood vessels at the midportion of the vocal folds, which induced secondary inflammatory change at the midportion of the vocal fold.

Quick method of multimeric protein production for biologically active substances such as human GM-CSF (hGM-CSF).

The C-terminal fragment of C4b-binding protein (C4BP)-based multimerizing system was applied to hGM-CSF to induce dendritic cells (DCs) from peripheral blood monocytes (PBMCs), to see whether the C4BP could stimulate immature DCs, since DCs, equipped with pattern recognition receptors such as toll-like receptors (TLRs), are hypersensitive to various immunologically active molecules like LPS. hGM-CSF gene was merged to the 3'-terminal region of the C4BPalpha-chain gene, and the transfected human 293FT cells produced sufficient amount of octameric hGM-CSF, which resulted in iDCs with the same phenotype and the same response to a TRL4 ligand, LPS and a TLR3 ligand, poly I:C, as those induced with authentic monomeric hGM-CSF. These results suggest that the C4BP-based multimerizing system could facilitate the design of self-associating multimeric recombinant proteins without stimulating iDCs, which might be seen with the other multimerizing systems such as that using Fc fragment of IgM.

Functional B7.2 and B7-H2 molecules on myeloma cells are associated with a growth advantage.

PURPOSE: B7 family molecules expressed on antigen-presenting cells stimulate or inhibit normal immune responses. The aim of this study was to investigate whether functional B7.2 and B7-H2 molecules are expressed on myeloma cells and, if so, whether they are associated with pathophysiology in myeloma. EXPERIMENTAL DESIGN: The expression of B7.2 and B7-H2 molecules on normal plasma and neoplastic (myeloma) plasma cells was analyzed. The cell proliferation and immunomodulatory function of myeloma cells related to B7.2 and B7-H2 expression were examined. RESULTS: Human myeloma cell lines commonly expressed B7.2 and B7-H2 molecules. B7.2 expression on plasma cells was more common in myeloma patients (n = 35) compared with that in patients with monoclonal gammopathy of unknown significance (n = 12) or hematologically normal individuals (n = 10). Plasma cells expressing B7-H2 were observed in myeloma patients alone, although rarely. Patients whose myeloma cells showed high B7.2 expression were more anemic and thrombocytopenic than other myeloma patients. The expression of these molecules was induced or augmented by cultivating myeloma cells with autologous stroma cells or tumor necrosis factor-alpha, a key cytokine in myeloma biology. Cell proliferation was more rapid in the B7.2+ and B7-H2+ populations compared with the B7.2(-) and B7-H2(-) populations, respectively, in the human myeloma cell lines examined. B7.2 and B7-H2 molecules on myeloma cells induced normal CD4+ T cells to proliferate and produce soluble factors, including interleukin-10 that stimulate myeloma cell proliferation. CONCLUSIONS: Functional B7.2 and B7-H2 molecules detected on myeloma cells may be involved in the pathophysiology of myeloma.

A possible mechanism of intravesical BCG therapy for human bladder carcinoma: involvement of innate effector cells for the inhibition of tumor growth.

Intravesical bacillus Calmette-Guerin (BCG) therapy is considered the most successful immunotherapy against solid tumors of human bladder carcinoma. To determine the actual effector cells activated by intravesical BCG therapy to inhibit the growth of bladder carcinoma, T24 human bladder tumor cells, expressing very low levels of class I MHC, were co-cultured with allogeneic peripheral blood mononuclear cells (PBMCs) with live BCG. The proliferation of T24 cells was markedly inhibited when BCG-infected dendritic cells (DCs) were added to the culture although the addition of either BCG or uninfected DCs alone did not result in any inhibition. The inhibitory effect was much stronger when the DCs were infected with live BCG rather than with heat-inactivated BCG. The live BCG-infected DCs secreted TNF-alpha and IL-12 within a day and this secretion continued for at least a week, while the heat-inactivated BCG-infected DCs secreted no IL-12 and little TNF-alpha. Such secretion of cytokines may activate innate alert cells, and indeed NKT cells expressing IL-12 receptors apparently proliferated and were activated to produce cytocidal perforin among the PBMCs when live BCG-infected DCs were externally added. Moreover, depletion of gammadelta T-cells from PBMCs significantly reduced the cytotoxic effect on T24 cells, while depletion of CD8beta cells did not affect T24 cell growth. Furthermore, the innate effectors seem to recognize MICA/MICB molecules on T24 via NKG2D receptors. These findings suggest the involvement of innate alert cells activated by the live BCG-infected DCs to inhibit the growth of bladder carcinoma and provide a possible mechanism of intravesical BCG therapy.

Suppression of virus replication via down-modulation of mitochondrial short chain enoyl-CoA hydratase in human glioblastoma cells.

Several viruses have been demonstrated to be the etiologic agent in chronic progressive diseases, associated with persistence; however, major questions concerning the pathogenic mechanisms of viral persistence are still unanswered. With the aim of identifying host cellular proteins that may play a role in viral replication, we established long-term persistently infected human glioblastoma cell lines with mutant measles virus (MV) and analyzed the host proteins by two-dimensional gel electrophoresis (2-DE) with mass spectrometry. We observed significant down-modulation in the expression of mitochondrial short chain enoyl-CoA hydratase (ECHS), which catalyzes the beta-oxidation pathway of fatty acid. Knockdown of this gene by a short interference RNA (siRNA) apparently impaired wild-type MV replication and the cytopathic effects (CPEs) of MV were significantly reduced in siRNA-transfected cells. These findings will shed light upon a new important notion for the interaction between virus replication and lipid metabolism in host cells and might provide a new strategy for virus control.

Transmission of macrophage-tropic HIV-1 by breast-milk macrophages via DC-SIGN.

Recent findings suggest that macrophage-tropic human immunodeficiency virus type 1 (HIV-1) produced in colostrum/early breast milk may hold a clue to determine the mechanisms of transmission of HIV-1 via breast-feeding. Here, we show that the majority of CD4(+) cells in the colostrum are CD14(+) macrophages expressing both chemokine receptors and DC-SIGN, a dendritic cell-specific receptor for HIV-1. The R5-type macrophage-tropic HIV-1 isolate NL(AD8) infected such breast-milk macrophages and caused them to secrete virus particles efficiently; however, the secreted virions showed only a weak transmissibility to their susceptible target, MAGIC-5 cells. When stimulated with interleukin-4, the breast-milk macrophages demonstrated a striking enhancement of expression of DC-SIGN and showed a strong capacity to transmit NL(AD8) virions to MAGIC-5 cells, which was specifically blocked by anti-DC-SIGN-specific antibody. These results suggest that HIV-1 virions captured by DC-SIGN, but not secreted cell-free virions, may be more efficiently transmitted to other compartments, such as the gastrointestinal tract, through acidic gastric juice.

Endogenously expressed HIV-1 nef down-regulates antigen-presenting molecules, not only class I MHC but also CD1a, in immature dendritic cells.

The effects of Nef molecules on immature dendritic cells (iDCs) were analyzed using recombinant human immunodeficiency virus type 1 (HIV-1) with intact nef gene, pseudotyped with vesicular stomatitis virus glycoprotein, HIV/VSV-G/+Nef. When iDCs were infected with HIV/VSV-G/+Nef, the surface expression of CD1a, a molecule for presenting glycolipid/lipid antigens, was selectively down-regulated among CD1 molecules (CD1a, -b, -c, and -d) as well as class I MHC. Moreover, the CD1a molecules were also down-modulated and co-localized with DsRed2-tagged-Nef in CD1a-transfected cells. Their co-localization was dependent upon CD1a cytoplasmic tail and the CD1a was redistributed from cell surface to LAMP-1+ late endosomal/lysosomal compartment. These findings reveal that the HIV-1-Nef interferes with the intracellular trafficking of CD1a, and suggest the involvement of CD1a-restricted immune effectors in the protective immunity against HIV-1 infection, which implicates the feasibility of virus-derived glycolipid/lipid antigens together with epitope peptides for the vaccine development.

Down-regulation of Toll-like receptor expression in monocyte-derived Langerhans cell-like cells: implications of low-responsiveness to bacterial components in the epidermal Langerhans cells.

In the skin, there are unique dendritic cells called Langerhans cells, however, it remains unclear why this particular type of dendritic cell resides in the epidermis. Langerhans cell-like dendritic cells (LCs) can be generated from CD14(+) monocytes in the presence of GM-CSF, IL-4, and TGF-beta1. We compared LCs with monocyte-derived dendritic cells (DCs) generated from CD14(+) monocytes in the presence of GM-CSF and IL-4 and examined the effect of exposure to two distinct bacterial stimuli via Toll-like receptors (TLRs), such as peptidoglycan (PGN) and lipopolysaccharide (LPS) on LCs and DCs. Although stimulation with both ligands induced a marked up-regulation of CD83 expression on DCs, PGN but not LPS elicited up-regulation of expression CD83 on LCs. Consistent with these results, TLR2 and TLR4 were expressed on DCs, whereas only TLR2 was weakly detected on LCs. These findings suggest the actual feature of epidermal Langerhans cells with low-responsiveness to skin commensals.