Lipopolysaccharide can block the potential of monocytes to differentiate into dendritic cells

We examined whether priming monocytes (MO) with lipopolysaccharide (LPS) influenced their further differentiation into either macrophages (Mphi) or dendritic cells (DC). LPS-primed MO differentiated into Mphi when cultured further with Mphi colony-stimulating factor (M-CSF) but, if cultured then with granulocyte/Mphi (GM)-CSF and IL-4 (interleukin-4), only about 30% of the cells differentiated into CD1a+ CD14- DC and half became CD1a- CD14+ Mphi. Cytokines present during LPS priming could affect subsequent MO differentiation. Relative to priming with LPS alone, adding M-CSF to LPS did not modify differentiation of MO to Mphi in further culture with M-CSF, nor did it change the way of differentiation of MO into DC was altered if culture was later switched to GM-CSF/IL-4. Using GM-CSF/IL-4 plus LPS upon priming did not modify differentiation of MO to Mphi in further culture with M-CSF, as compared to priming with GM-CSF/IL-4 alone, but it counteracted the effect of LPS on the differentiation of MO to DC in further culture with GM-CSF/IL-4: about 75% of cells then became DC. Alternatively, despite activation by LPS, mature M-CSF-induced Mphi preserved the potential to differentiate into DC on subsequent culture with GM-CSF/IL-4. Thus, LPS, a bacterial product known to sustain maturation of MO/Mphi as well as of DC, may block the differentiation of MO into DC, except if signal triggering DC differentiation is delivered concomitantly, and modulate in this manner the induction of adaptive immune responses to infection.     

Echinococcus granulosus antigen B impairs human dendritic cell differentiation and polarizes immature dendritic cell maturation towards a Th2 cell response

Despite inducing a strong host cellular and humoral immune response, the helminth Echinococcus granulosus is a highly successful parasite that develops, progresses, and ultimately causes chronic disease. Although surgery remains the preferred therapeutic option, pharmacological research now envisages antihelminthic strategies. To understand the mechanisms that E. granulosus uses to escape host immunosurveillance and promote chronic infection, we investigated how two hydatid cyst components, purified antigen B (AgB) and sheep hydatid fluid (SHF), act on host dendritic cell (DC) differentiation from monocyte precursors and how they influence maturation of DC that have already differentiated. We evaluated the immunomodulatory potential of these antigens by performing immunochemical and cytofluorimetric analyses of monocyte-derived DCs from healthy human donors. During monocyte differentiation, AgB and SHF downmodulated CD1a expression and upregulated CD86 expression. Compared with immature DCs differentiated in medium alone (iDCs), AgB- and SHF-differentiated cells stimulated with lipopolysaccharide included a significantly lower percentage of CD83(+) cells (P < 10(-4)) and had weaker costimulatory molecule expression. When stimulated with AgB and SHF, iDCs matured and primed lymphocytes towards the Th2 response typical of E. granulosus infection. SHF and particularly AgB reduced the production of interleukin-12p70 (IL-12p70) and tumor necrosis factor alpha in lipopolysaccharide-stimulated iDCs. Anti-IL-10 antibodies increased the levels of IL-12p70 secretion in AgB- and SHF-matured DCs. AgB and SHF induced interleukin-1 receptor-associated kinase phosphorylation and activated nuclear factor-kappaB, suggesting that Toll-like receptors could participate in E. granulosus-stimulated DC maturation. These results suggest that E. granulosus escapes host immunosurveillance in two ways: by interfering with monocyte differentiation and by modulating DC maturation.     

Inhibition of murine dendritic cell activation by synthetic phosphorothioate oligodeoxynucleotides

Depending on sequence and backbone structure, DNA can inhibit as well as stimulate immune responses. As previously shown, single-base phosphorothioate (Ps) oligodeoxynucleotides (ODN) can inhibit murine macrophage activation. To determine whether these compounds can also affect dendritic cells (DC), the effects of 30-mer Ps ODN (SdA, SdT, SdG, and SdC) on DC activation were assessed in an in vitro system. With DC preparations obtained from murine bone marrow cultured in granulocyte macrophage-colony stimulating factor, the Ps ODN blocked the production of interleukin-12 and nitric oxide induced by bacterial DNA, an immunostimulatory cytosine phosphate guanosine dinucleotide (CpG) ODN and lipopolysaccharide (LPS). Furthermore, these compounds inhibited up-regulation of costimulatory molecules CD40 and CD86 as well as major histocompatibility complex-II molecules, indicating an effect on DC maturation. Although the Ps ODN limited uptake of CpG ODN as assessed by flow cytometry, the Ps ODN did not affect LPS uptake, suggesting that these compounds inhibit DC responses by effects on downstream signaling pathways. Together, these observations extend the range of action of inhibitory ODN to DC and suggest a role of these compounds as immunomodulatory agents.     

CCK-8对LPS诱导树突状细胞成熟的影响

目的: 观察八肽胆囊收缩素(CCK-8)对脂多糖(LPS)诱导树突状细胞(DCs)成熟的影响。方法: 采用粒-巨噬细胞集落刺激因子(GM-CSF)诱导法培养小鼠骨髓来源DCs,在LPS诱导其成熟过程中用不同浓度的CCK-8进行干预,采用流式细胞分析技术检测DCs表面主要组织相容性复合物II(MHC II)、分化群80(CD80)和分化群86(CD86)的表达;ELISA法检测DCs培养上清中白细胞介素1β(IL-1β)、白细胞介素6(IL-6)和肿瘤坏死因子α(TNF-α)的含量;MTT法检测CCK-8处理DCs对同种异体T细胞增殖反应的影响。结果: CCK-8剂量依赖性地抑制LPS诱导DCs表面CD80、CD86和MHC II表达(P<0.01, P<0.05 );CCK-8抑制LPS诱导DCs分泌IL-1β、IL-6和TNF-α(P<0.01);并且,CCK-8降低LPS诱导DCs刺激同种异体T淋巴细胞增殖的活性(P<0.05,P<0.01)。结论: CCK-8对LPS诱导DCs成熟过程中的细胞表型、细胞因子分泌和抗原提呈功能有抑制作用,提示CCK-8有可能在抗感染和抵抗自身免疫性疾病过程中发挥重要调节作用。     

Interferon γ Stimulates Cellular Maturation of Dendritic Cell Line DC2.4 Leading to Induction of Efficient Cytotoxic T Cell Responses and Antitumor Immunity

Dendritic cells （DCs） are the most potent antigen-presenting cells （APCs） for the initiation of antigen （Ag）-specific immune responses. In most studies, mature DCs are generated from bone marrow cells or peripheral monocytes; in either case, the harvested cells are then cultured in medium containing recombinant GM-CSF, IL-4 and TNF-α for 7-10 days and stimulated with lipopolysaccharide （LPS）. However, this approach is time-consuming and expensive. There is another less cost approach of using immobilized DC cell lines, which can easily grow in the medium. A disadvantage with the immobilized DC cell lines, however, is that they are immature DCs and lack expression of MHC class Ⅱ and costimulatory CD40 and CD80 molecules. This, therefore, limits their capacity for inducing efficient antitumor immunity. In the current study, we investigated the possible efficacy of various stimuli （IL-1β, IFN-γ, TNF-α CpG and LPS） in converting the immature dendritic cell line DC2.4 to mature DCs. Our findings were quite interesting since we demonstrated for the first time that IFN-γ was able to stimulate the maturation of DC2.4 cells. The IFN-γ-activated ovalbumin （OVA）-pulsed DC2.4 cells have capacity to upregulate MHC class Ⅱ, CD40, CD80 and CCR7, and to more efficiently stimulate in vitro and in vivo OVA-specific CD8^＋ T cell responses and antitumor immunity. Therefore, IFN-γ-activated immortal DC2.4 ceils may prove to be useful in the study of DC biology and antitumor immunity.     

Human monocyte isolation methods influence cytokine production from in vitro generated dendritic cells

There is growing interest in the in vitro generation of dendritic cells (DC) from peripheral blood monocytes, but the effect of the method chosen to isolate CD14+ monocytes for subsequent DC generation is poorly documented. The method used to isolate monocytes may have an impact on the subsequent function of DC by affecting their ability to express costimulatory molecules (CD80/86), maturation marker (CD83) and/or to produce important immunomodulatory cytokines. In this study, we show that the positive selection of monocytes by anti-CD14-coated microbeads inhibits the lipopolysaccharide (LPS)-induced production of interleukin (IL)-12, IL-10 and tumour necrosis factor-alpha (TNF-alpha) from human DC. However, when DC were grown from monocytes isolated by plastic adherence, LPS induced the production of much higher levels of these cytokines. DC derived from adherence-isolated monocytes induced the development of potent cytotoxic T lymphocytes of the Tc1 subset specific for influenza matrix protein, as confirmed by interferon-gamma (IFN-gamma) enzyme-linked immunosorbent spot-forming cell assay (ELISPOT), cytotoxicity assay, major histocompatibility complex (MHC)-peptide tetrameric complexes and T helper 1/T helper 2 (Th1/Th2) cytokine production assays.     

Human lung dendritic cells have an immature phenotype with efficient mannose receptors.

Dendritic cells (DC) can be present at distinct stages of differentiation within the immune system. Sallusto and colleagues have recently described an in vitro culture system suitable for analyzing the maturation processes of DC (Sallusto and colleagues, J. Exp. Med. 1994;179:1109-1118). Monocytes cultured for 6 d in the presence of granulocyte macrophage colony-stimulating factor and interleukin-4 develop into immature DC with a high endocytic capacity but a low capacity to stimulate T cells. When challenged by lipopolysaccharide, these cells upregulate costimulatory molecules, express CD83, and become mature DC. CCR1 and CCR5 chemokine receptors are highly expressed on immature DC and downregulated on mature DC. This in vitro system was used to characterize human lung DC. Lung DC were shown to express some characteristics of in vitro immature DC. These are: (1) low expression of the costimulatory molecules CD40, CD80, and CD86; (2) poor expression of the differentiation marker CD83 and no CD1a; and (3) good capacity to incorporate dextran. Lung DC express moderate levels of CCR1 and CCR5. However, lung DC, like in vitro mature DC, express high levels of major histocompatibility complex Class II molecules, show low expression of CD14 and CD64, and are characterized by their high capacity to stimulate allogeneic T cells to proliferate during mixed leukocyte reactions (MLRs). Although lung DC express low levels of CD80 and CD86, the important role of these costimulatory molecules in inducing high MLR was demonstrated by using blocking antibodies. Therefore, while lung DC have overall a phenotype and an endocytic capacity close to in vitro immature DC, they share, like in vitro mature DC, a powerful capacity to stimulate T cells.     

Enhanced antigen-presenting activity and tumour necrosis factor-α-independent activation of dendritic cells following treatment with Mycobacterium bovis bacillus Calmette–Guérin

Dendritic cells (DCs) are most potent among the antigen-presenting cells and are believed to be crucial for the initiation of a primary T-cell response to foreign antigens. Mycobacterial infection within macrophages is controlled by cell-mediated immunity. To elucidate the stimulation of immune response by Mycobacterium bovis bacillus Calmette-Guérin (BCG), we purified DCs from precursor cells in human peripheral blood mononuclear cells (PBMC) by culturing them with granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4) and characterized their surface antigen expression. The interaction of cultured DCs with BCG resulted in increased surface expression of several DC-related marker antigens. BCG also induced reduction of endocytosis, enhancement of CD83 expression as well as B7 costimulatory molecules and IL-12 production, suggesting that BCG treatment directly induces DCs to mature. BCG-treated DCs were much more potent antigen-presenting cells in allogeneic immune response than untreated DCs. Moreover, while the neutralization of tumour necrosis factor-alpha (TNF-alpha) significantly blocked the DC maturation induced by lipopolysaccharide (LPS), it could not inhibit the induction of DC maturation by the BCG treatment, indicating that TNF-alpha production plays a minor role in the BCG-induced DC maturation. However, the neutralization of TNF-alpha resulted in decreased IL-12 production by activated DCs. These results suggest that infection with BCG might evoke direct activation and maturation of DC and the general immune stimulant effect of BCG might be related with the activation of DCs.     

Activation of human dendritic cells is modulated by components of the outer membranes of Neisseria meningitidis

Neisseria meningitidis serogroup B is a major cause of life-threatening meningitis and septicemia worldwide, and no effective vaccine is available. Initiation of innate and acquired immune responses to N. meningitidis is likely to be dependent on cellular responses of dendritic cells (DC) to antigens present in the outer membrane (OM) of the meningococcus. In this study, the responses of human monocyte-derived DC (mo-DC) to OM isolated from parent (lipopolysaccharide [LPS]-replete) meningococci and from a mutant deficient in LPS were investigated. Parent OM selectively up-regulated Toll-like receptor 4 (TLR4) mRNA expression and induced mo-DC maturation, as reflected by increased production of chemokines, proinflammatory cytokines, and CD83, CD80, CD86, CD40, and major histocompatibility complex (MHC) class II molecules. In contrast, LPS-deficient OM selectively up-regulated TLR2 mRNA expression and induced moderate increases in both cytokine production and expression of CD86 and MHC class II molecules. Preexposure to OM, with or without LPS, augmented the allostimulatory properties of mo-DC, which induced proliferation of naive CD4+ CD45RA+ T cells. In addition, LPS-replete OM induced a greater gamma interferon/interleukin-13 ratio in naive T cells, whereas LPS-deficient OM induced the reverse profile. These data demonstrate that components of the OM, other than LPS, are also likely to be involved in determining the levels of DC activation and the nature of the T-helper immune response.     

Impaired dendritic cell differentiation and maturation in the absence of C3

Human monocytes can be differentiated into immature dendritic cells (DCs) in the presence of serum and cytokines. One of the main functions of immature DCs is to capture and process antigens. Following maturation, they differentiate into antigen presenting cells. The role of complement in the differentiation process from monocytes towards immature DCs remains elusive. Here we demonstrate that complement 3 (C3) has a regulatory impact on the expression of specific DC surface molecules and DC-derived cytokine production during DC differentiation. We isolated human adherent peripheral blood mononuclear cells, which were cultured in the presence of GM-CSF plus IL-4 in medium supplemented with normal human serum or C3 deficient serum. The lack of C3 during DC differentiation negatively impacted the expression of C-type lectin receptor DC-SIGN, the antigen presenting molecules HLA-DR and CD1a, and the costimulatory molecules CD80 and CD86. Further, the spontaneous production of IL-6 and IL-12 was reduced in the absence of C3. Moreover, the maturation of immature DCs in response to LPS challenge was impaired in the absence of C3 as evidenced by reduced MHC-II, co-stimulatory molecule expression as well as modulated IL-12 and TNF-alpha production. Collectively, our results provide evidence for a novel role of C3 as a critical cofactor in human DC differentiation and maturation.     

Dendritic cell activation and cytokine production induced by group B Neisseria meningitidis: interleukin-12 production depends on lipopolysaccharide expression in intact bacteria

Interactions between dendritic cells (DCs) and microbial pathogens are fundamental to the generation of innate and adaptive immune responses. Upon stimulation with bacteria or bacterial components such as lipopolysaccharide (LPS), immature DCs undergo a maturation process that involves expression of costimulatory molecules, HLA molecules, and cytokines and chemokines, thus providing critical signals for lymphocyte development and differentiation. In this study, we investigated the response of in vitro-generated human DCs to a serogroup B strain of Neisseria meningitidis compared to an isogenic mutant lpxA strain totally deficient in LPS and purified LPS from the same strain. We show that the parent strain, lpxA mutant, and meningococcal LPS all induce DC maturation as measured by increased surface expression of costimulatory molecules and HLA class I and II molecules. Both the parent and lpxA strains induced production of tumor necrosis factor alpha (TNF-alpha), interleukin-1alpha (IL-1alpha), and IL-6 in DCs, although the parent was the more potent stimulus. In contrast, high-level IL-12 production was only seen with the parent strain. Compared to intact bacteria, purified LPS was a very poor inducer of IL-1alpha, IL-6, and TNF-alpha production and induced no detectable IL-12. Addition of exogenous LPS to the lpxA strain only partially restored cytokine production and did not restore IL-12 production. These data show that non-LPS components of N. meningitidis induce DC maturation, but that LPS in the context of the intact bacterium is required for high-level cytokine production, especially that of IL-12. These findings may be useful in assessing components of N. meningitidis as potential vaccine candidates.     

Cord blood mesenchymal stem cells propel human dendritic cells to an intermediate maturation state and boost interleukin‐12 production by mature dendritic cells

Pathogen‐derived entities force the tissue‐resident dendritic cells (DCs) towards a mature state, followed by migration to the draining lymph node to present antigens to T cells. Bone marrow mesenchymal stem cells (MSCs) modulate the differentiation, maturation and function of DCs. In umbilical cord blood an immature MSC population was identified. Remarkably, these immature stem cells modulated DCs in a different way. Marker expression was unchanged during the differentiation of monocytes towards immature DCs (iDCs) when cocultured with cord blood MSC [unrestricted somatic stem cells (USSCs)]. The maturation to mature DCs (mDCs) was enhanced when DCs were co‐cultured with USSC, as evidenced by the up‐regulation of costimulatory molecules. Endocytosis of dextran by iDCs was hampered in the presence of USSCs, which is indicative for the maturation of iDCs. Despite this maturation, the migration of iDCs cocultured with USSCs appeared to be identical to iDCs cultured alone. However, USSCs increased the migration of mDCs towards CCL21 and boosted interleukin‐12 production. So, USSCs mature iDCs, thereby redirecting the antigen‐uptake phenotype towards a mature phenotype. Furthermore, DC maturation by lipopolysaccharide (LPS) or USSCs reflects two distinct pathways because migration was unaffected when iDCs were matured by coculture with USSCs, while it was strongly enhanced in the presence of LPS. DCs are able to discriminate the different MSC subtypes, resulting in diverse differentiation programmes.     

Bruton's tyrosine kinase defect in dendritic cells from X-linked agammaglobulinaemia patients does not influence their differentiation,maturation and antigen-presenting cell function

X‐linked agammaglobulinaemia (XLA) is a primary immunodeficiency disease characterized by very low levels or even absence of circulating antibodies. The immunological defect is caused by deletions or mutations of Bruton's tyrosine kinase gene (Btk), whose product is critically involved in the maturation of pre‐B lymphocytes into mature B cells. Btk is expressed not only in B lymphocytes but also in cells of the myeloid lineage, including dendritic cells (DC). These cells are professional antigen presenting cells (APC) that play a fundamental role in the induction and regulation of T‐cell responses. In this study, we analysed differentiation, maturation, and antigen‐presenting function of DC derived from XLA patients (XLA‐DC) as compared to DC from age‐matched healthy subjects (healthy‐DC). We found that XLA‐DC normally differentiate from monocyte precursors and mature in response to lipopolysaccharide (LPS) as assessed by de novo expression of CD83, up‐regulation of MHC class II, B7·1 and B7·2 molecules as well as interleukin (IL)‐12 and IL‐10 production. In addition, we demonstrated that LPS stimulated XLA‐DC acquire the ability to prime naïve T cells and to polarize them toward a Th1 phenotype, as observed in DC from healthy donors stimulated in the same conditions. In conclusion, these data indicate that Btk defect is not involved in DC differentiation and maturation, and that XLA‐DC can act as fully competent antigen presenting cells in T cell‐mediated immune responses.     

IL-17A 协同GM-CSF 和LPS 促进骨髓细胞衍生树突状细胞的分化和成熟研究

目的:探讨IL鄄17A 对小鼠骨髓细胞衍生树突状细胞分化和成熟的影响。方法:分离小鼠骨髓细胞,加入含GM-CSF(20 ng/ ml)RPMI1640 完全培基培养8 d,诱导小鼠骨髓单个核细胞向DC 分化,加入LPS(1 滋g/ ml)继续培养36 h,进一步诱导DC 成熟,同时在骨髓细胞衍生诱导DC 分化及成熟的不同阶段加入不同浓度的rmIL-17A(10、100 ng/ ml),采用流式细胞术检测DC 表面共刺激分子的表达,ELISA 方法检测DC 培养上清中IL-12p40 和IL-10 水平。结果:rmIL-17A 可促进GM-CSF 诱导骨髓细胞衍生DC 表面共刺激分子CD40、CD80、CD86 和MHC域的表达,且具有剂量依赖性,其中以高浓度rmIL-17A刺激组的CD40 及MHC域表达增加最显著;在LPS 诱导DC 成熟阶段加入rmIL-17A,骨髓细胞衍生DC 共刺激分子CD40、CD80、CD86 和MHC域的表达均明显增加,并且随着rmIL-17A 浓度的增加,CD86 和MHC域的表达水平也随之增高;同时与未加rmIL鄄17A 的对照组相比,低浓度rmIL-17A 组LPS 刺激骨髓细胞衍生DC 分泌IL-12p40 和IL鄄10 水平均显著增加(P <0.001),高浓度rmIL-17A 组IL-12p40 水平显著增高(P<0.001),但IL-10 水平没有变化。结论:IL-17A 可促进GM-CSF 诱导的骨髓细胞衍生DC 前体细胞表型发展,并能协同LPS 诱导骨髓衍生DC 的分化和成熟。     

Fractalkine, a CX3C chemokine, is expressed by dendritic cells and is up-regulated upon dendritic cell maturation.

The lone CX3C chemokine, fractalkine (FK), is expressed in a membrane-bound form on activated endothelial cells and mediates attachment and firm adhesion of T cells, monocytes and NK cells. We now show that FK is associated with dendritic cells (DC) in epidermis and lymphoid organs. In normal human skin, dual-color fluorescence microscopy co-localized FK expression with Langerhans cells expressing CD1a. In tonsil, FK-positive DC expressed CD83, a marker for mature DC. Human and murine cultured DC up-regulated FK mRNA expression with maturation. Furthermore, CD40 ligation, but not TNF-alpha or lipopolysaccharide treatment, of activated, migratory DC that had migrated from skin explants resulted in a 2.5-fold increase of surface expression of FK without significant alterations of expression of CD80, CD86, CD54 or MHC class II. Since FK mediates adhesion of T cells to activated endothelial cells, the increased expression of FK during DC maturation (and particularly by CD40 ligation) may play a role in the ability of T cells and mature DC to form conjugates and engage in cell-cell communication.     

Dendritic cells derived from TBP-2-deficient mice are defective in inducing T cell responses

Thioredoxin-binding protein-2 (TBP-2), also known as vitamin D3-up-regulated protein 1 (VDUP1), was identified as an endogenous molecule interacting with thioredoxin (TRX). Here, we show that dendritic cells (DC) derived from TBP-2-deficient mice are defective in the function of T cell activation. To compare TBP-2(-/-) DC function with wild-type (WT) DC, we stimulated DC with lipopolysaccharide (LPS). Although TBP-2(-/-) DC and WT DC expressed comparable levels of MHC class II and costimulatory molecules such as CD40, CD80 and CD86, the IL-12p40, IL-12p70 and IL-6 productions of TBP-2(-/-) DC were attenuated. In a mixed leukocyte reaction (MLR), the concentrations of IL-2, IFN-gamma, IL-4 and IL-10 in the culture supernatant of MLR with TBP-2(-/-) DC were significantly lower than those in the cultures with WT DC. In MLR also, as with LPS stimulation, IL-12p40 and IL-12p70 production from TBP-2(-/-) DC was less than that from WT DC. Proliferation of T cells cultured with TBP-2(-/-) DC was poorer than that with WT DC. In vivo delayed-type hypersensitivity responses in TBP-2(-/-) mice immunized with ovalbumin were significantly reduced compared to WT mice. These results indicate that TBP-2 plays a crucial role in DC to induce T cell responses.     

Paradoxical effects of interleukin-10 on the maturation of murine myeloid dendritic cells

The immunoregulatory cytokine, interleukin-10 (IL-10), has been shown to inhibit the maturation of human myeloid dendritic cells (DC). In the present study, we demonstrate that IL-10 has paradoxical effects on the maturation of murine myeloid bone marrow-derived DC. On the one hand, IL-10 inhibits the maturation of murine myeloid DC. The addition of IL-10 to granulocyte-macrophage colony-stimulating factor (GM-CSF)-supported murine BM-derived DC cultures reduced the frequency of major histocompatibility complex (MHC) class IIbright cells. These IL-10-pretreated DC have a reduced capacity to stimulate T cells in an allogeneic mixed leucocyte reaction. On the other hand, however, and in contrast to the effects of IL-10 on human DC, we found that the addition of IL-10 from the initiation of the culture onwards induced an up-regulation of the expression of the costimulatory molecules CD40, CD80 and CD86 on murine myeloid DC, as compared to DC generated with GM-CSF only. Moreover, a subpopulation of IL-10-pretreated MHC class IIdim DC lacked the capacity to take up dextran-fluorescein isothiocyanate (FITC), a feature of DC maturation. Taken together, our data demonstrate that the generation of murine myeloid DC in the presence of IL-10 results in a population of incompletely matured MHC class IIdim CD80+ CD86+ DC. These DC lack T-cell stimulatory capacity, suggesting a role for IL-10 in conferring tolerogenic properties on murine myeloid DC.     

Lysophosphatidic acid modulates the activation of human monocyte-derived dendritic cells

Lysophosphatidic acid (LPA) is a biologically active lysophospholipid that can regulate immune activation. LPA can activate T cells and dendritic cells (DCs), but the effects of LPA on the ability of DCs to influence T cell polarization are not well understood. Human monocyte-derived DCs were differentiated in vitro in the presence of interleukin-4 (IL-4) and granulocyte-macrophage colonystimulating factor (GM-CSF), and matured with LPA and lipopolysaccharide (LPS) alone or in combination. DC activation was monitored by analyzing cell-surface expression of co-stimulatory receptors and cytokine production. The ability of DCs to influence T cell activation was determined using two models of DC:T cell co-culture. Maturation with LPS induced dose-dependent DC activation characterized by enhanced expression of co-stimulatory molecules (e.g., CD86) and production of cytokines including IL-6 and IL-10. Co-incubation with LPA attenuated the LPS-induced production of IL-6, without significantly affecting IL-10 secretion or the ability of DC to promote T cell proliferation. DCs matured in the presence of both LPA and LPS enhanced the production of interferon-gamma (IFN-gamma) when co-cultured with allogeneic T cells, compared with DC matured by LPS alone. Similar results were found using a model of allogeneic na?ve T cell differentiation, where LPA- plus LPS-matured DC enhanced IFN-gamma as well as IL-4 secretion after restimulation. Lysophosphatidic acid fine-tunes the effects of LPS on human myeloid DC maturation, but does not exert a dominant effect on the ability of DC to influence Th cell polarization.     

Serum concentration of the growth medium markedly affects monocyte-derived dendritic cells' phenotype, cytokine production profile and capacities to stimulate in MLR

We have investigated how the maturation of monocyte-derived dendritic cells (Mo-DC) is affected by the serum concentration of the culture medium. Day 6 DC cultured in 1% human serum were a heterogeneous population of CD1a(-) and CD1a(+) DC that were separated by flow sorting. In contrast, Mo-DC generated in 10% human serum formed a homogenous population of CD1a(-) cells. Other phenotypically immature characteristics also varied, and three subsets were still distinguishable upon maturation in LPS. Furthermore, CD1a(-) DC and CD1a(+) DC from 1% culture conditions were excellent stimulators in MLR, while DC cultured in 10% serum were poor stimulators. Similarly, different cytokine profiles of the three subsets were identified. DC cultured in 1% serum had low expression of interleukin-12 (IL-12) p40 and IL-10 mRNA at day 6. Upon maturation, expression of IL-12 p40 mRNA was upregulated in CD1a(+) DC, whereas the level remained relatively low in CD1a(-) DC. In contrast, DC cultured in 10% had high levels of IL-10 mRNA at day 6 that was downregulated upon maturation. We conclude that the differentiation of monocytes into DC is significantly influenced by the serum concentration of the growth medium with effects on phenotype, cytokine profile and stimulatory activity.     

Critical role of protein kinase C epsilon for lipopolysaccharide-induced IL-12 synthesis in monocyte-derived dendritic cells

In the present study we have investigated the potential involvement of protein kinase C (PKC) in the maturation of human dendritic cells (DC) by bacterial lipopolysaccharide (LPS). LPS stimulation of DC derived from human monocytes resulted in PKC phosphorylation. Inhibition of PKC activation using bisindolylmaleimide (Bis), a pan-PKC inhibitor, was associated with a dose-dependent decrease of LPS-induced IL-12 production. In contrast, up-regulation of MHC class II, CD80 and CD86 was not altered. Consistent with the diminished IL-12 synthesis, DC stimulated with LPS in presence of Bis were deficient in the induction of IFN-gamma production by allogeneic CD4+ T cells. Furthermore, we found that PKC inhibition impaired LPS-induced I kappa B-alpha degradation and subsequent nuclear factor (NF)-kappa B activation in DC. LPS resulted in the phosphorylation of conventional alpha/beta and novel epsilon PKC isoforms in DC. Inhibition of LPS-induced PKC activity using pseudosubstrate peptides specific for PKC isoforms established that PKC epsilon but not PKC alpha/beta was involved in the production of IL-12 and TNF-alpha. Overall, these data provide evidence that PKC inhibition impairs LPS signaling in DC and identify PKC epsilon as a potential target for the inhibition of Toll-like receptor-4-mediated, IL-12-dependent Th1 type responses.