Toll样受体与树突状细胞介导的天然免疫和获得性免疫

树突状细胞(dendritic cells,DCs)作为迄今所发现的抗原提呈功能最强的一类抗原提呈细胞,是联结天然免疫和获得性免疫的桥梁。Toll样受体(Toll-like receptors,TLRs)是一类进化保守的胚系编码的模式识别受体,在DCs的抗原识别、递呈及激活T细胞等方面具有重要作用,是机体受外来抗原入侵后作出适当免疫反应的调控点。现就TLRs在不同DCs亚群中的分布、与DCs介导的天然免疫和获得性免疫的关系及DCs功能可塑性的分子基础作一综述。     

Mononuclear phagocyte-derived IL-10 suppresses the innate IL-12/IFN-gamma axis in lung-challenged aged mice

Previously, we reported that IL-10-producing mononuclear phagocytes increase in lungs of aged mice, causing impaired innate cytokine expression. Since dendritic cells (DCs) contribute to innate NK cell and adaptive T cell immunity, we tested the hypothesis that age-related IL-10 might influence DC function with effects on NK and T cell activation. The results showed that DC recruitment to sites of lung inflammation was normal in aged mice (>20 mo). However, IFN-gamma-producing NK cells in LPS-challenged lungs were decreased in aged as compared with young mice, which was associated with increased IL-10(+)CD11b(+)Gr-1(low)CD11c(-) cells consistent with mononuclear phagocytes. In vivo or in vitro blockade of IL-10 signaling restored IFN-gamma-producing NK cells. This restoration was reversed by IL-12 neutralization, indicating that IL-10 suppressed sources of IL-12 in aged mice. To probe DC function in adaptive immunity, we transferred young naive OVA-specific TCR transgenic T cells to old mice. Following challenge with OVA plus LPS, Ag presentation in the context of MHC-I and MHC-II occurred with similar kinetics and intensity in draining lymph nodes of young and old recipients as measured by proliferation. Despite this, aged hosts displayed impaired induction of IFN-gamma(+)CD4(+), but not IFN-gamma(+)CD8(+), effector T cells. Blockade of IL-10 signaling reversed age-associated defects. These studies indicate that the innate IL-12/IFN-gamma axis is not intrinsically defective in lungs of aged mice, but is rather suppressed by enhanced production of mononuclear phagocyte-derived IL-10. Our data identify a novel mechanism of age-associated immune deficiency.     

Immature human dendritic cells infected with Leishmania infantum are resistant to NK-mediated cytolysis but are efficiently recognized by NKT cells

Dendritic cells (DC) play an important role in innate and adaptive immunity, interacting with T cells, NK, and NKT cells. A critical step in the interaction of the parasitic protozoa Leishmania with their host is the evasion of both innate and adaptive immunity, producing a long-lasting chronic infection. There is growing evidence that these parasites can modify the Ag-presenting and immunoregulatory functions of DCs. The cells and mechanisms involved in innate immune response against Leishmania are still poorly understood. In this study, we investigated how Leishmania infantum infection affects DC interactions with NK and invariant NKT (iNKTs) cells in humans. We found that infected immature DCs (iDCs) do not up-regulate HLA class I molecules. Despite this, iDCs become resistant to killing mediated by autologous NK cells due to the up-regulation of HLA-E expression, which protects target cells from NK-mediated lysis through interaction with the inhibitory receptor CD94/NKG2A. Furthermore, iDCs infected with L. infantum up-regulate CD1d cell surface expression and consequently can be efficiently recognized and killed by iNKT cells that produce IFN-gamma. These data suggest that L. infantum could be able to evade NK recognition; in contrast, iNKTs may play an important role in the immune response against Leishmania.     

Type I IFN stimulates lymph node stromal cells from adult and old mice during a West Nile virus infection

Advanced age is a significant risk factor during viral infection due to an age-associated decline in the immune response. Older individuals are especially susceptible to severe neuroinvasive disease after West Nile virus (WNV) infection. Previous studies have characterized age-associated defects in hematopoietic immune cells during WNV infection that culminate in diminished antiviral immunity. Situated amongst immune cells in the draining lymph node (DLN) are structural networks of nonhematopoietic lymph node stromal cells (LNSCs). LNSCs are comprised of numerous, diverse subsets, with critical roles in the coordination of robust immune responses. The contributions of LNSCs to WNV immunity and immune senescence are unclear. Here, we examine LNSC responses to WNV within adult and old DLNs. Acute WNV infection triggered cellular infiltration and LNSC expansion in adults. Comparatively, aged DLNs exhibited diminished leukocyte accumulation, delayed LNSC expansion, and altered fibroblast and endothelial cell subset composition, signified by fewer LECs. We established an ex vivo culture system to probe LNSC function. Adult and old LNSCs both recognized an ongoing viral infection primarily through type I IFN signaling. Gene expression signatures were similar between adult and old LNSCs. Aged LNSCs were found to constitutively upregulate immediate early response genes. Collectively, these data suggest LNSCs uniquely respond to WNV infection. We are the first to report age-associated differences in LNSCs on the population and gene expression level during WNV infection. These changes may compromise antiviral immunity, leading to increased WNV disease in older individuals.     

Isolation and characterization of dendritic cells and macrophages from the mouse intestine

Within the intestine reside unique populations of innate and adaptive immune cells that are involved in promoting tolerance towards commensal flora and food antigens while concomitantly remaining poised to mount inflammatory responses toward invasive pathogens. Antigen presenting cells, particularly DCs and macrophages, play critical roles in maintaining intestinal immune homeostasis via their ability to sense and appropriately respond to the microbiota. Efficient isolation of intestinal DCs and macrophages is a critical step in characterizing the phenotype and function of these cells. While many effective methods of isolating intestinal immune cells, including DCs and macrophages, have been described, many rely upon long digestions times that may negatively influence cell surface antigen expression, cell viability, and/or cell yield. Here, we detail a methodology for the rapid isolation of large numbers of viable, intestinal DCs and macrophages. Phenotypic characterization of intestinal DCs and macrophages is carried out by directly staining isolated intestinal cells with specific fluorescence-labeled monoclonal antibodies for multi-color flow cytometric analysis. Furthermore, highly pure DC and macrophage populations are isolated for functional studies utilizing CD11c and CD11b magnetic-activated cell sorting beads followed by cell sorting.     

Calcitonin Gene-Related Peptide Regulates Type IV Hypersensitivity through Dendritic Cell Functions

Dendritic cells (DCs) play essential roles in both innate and adaptive immune responses. In addition, mutual regulation of the nervous system and immune system is well studied. One of neuropeptides, calcitonin gene-related peptide (CGRP), is a potent regulator in immune responses; in particular, it has anti-inflammatory effects in innate immunity. For instance, a deficiency of the CGRP receptor component RAMP 1 (receptor activity-modifying protein 1) results in higher cytokine production in response to LPS (lipopolysaccharide). On the other hand, how CGRP affects DCs in adaptive immunity is largely unknown. In this study, we show that CGRP suppressed Th1 cell differentiation via inhibition of IL-12 production in DCs using an in vitro co-culture system and an in vivo ovalbumin-induced delayed-type hypersensitivity (DTH) model. CGRP also down-regulated the expressions of chemokine receptor CCR2 and its ligands CCL2 and CCL12 in DCs. Intriguingly, the frequency of migrating CCR2⁺ DCs in draining lymph nodes of RAMP1-deficient mice was higher after DTH immunization. Moreover, these CCR2⁺ DCs highly expressed IL-12 and CD80, resulting in more effective induction of Th1 differentiation compared with CCR2⁻ DCs. These results indicate that CGRP regulates Th1 type reactions by regulating expression of cytokines, chemokines, and chemokine receptors in DCs.     

Salmonella enterica Serovar Typhi Plasmid Impairs Dendritic Cell Responses to Infection

Salmonella enterica serovar Typhi (S. typhi) evades from innate immunity by expression of a variety of pathogenic factors. The "pR(ST98)" plasmid of S. typhi is involved in multidrug-resistant and virulence of S. typhi. However, its exact effect on host cell function remains elusive. Dendritic cells (DCs) play an important role in shaping immune response against Salmonella. For the purpose of investigation whether pR(ST98) might target DCs involved in adaptive immune response, murine DCs were infected with S. typhi wild type and mutant strains. S. typhi stimulation resulted in up-regulation of costimulatory molecules on DCs. S. typhi wild type resulted in decreased up-regulation of CD40, CD80, and CD86 expression. Experiments with S. typhi pR(ST98) mutant (S. typhi-Δ-pR(ST98)) and S. typhi-Δ-pR(ST98) with a complemented plasmid encoding pR(ST98) (S. typhi-c-pR(ST98)) revealed that pR(ST98) accounts for inhibition of surface molecule expression and functional maturity. S. typhi-Δ-pR(ST98) gave maximal levels of IL-12 and IFN-γ release compared with wild type S. typhi or the complemented strains. In contrast to IL-12 and IFN-γ, IL-10 secretion by S. typhi-Δ-pR(ST98)-infected DCs was significantly lower than induction by S. typhi wild type. This indicates that immunity in response to pR(ST98) is skewed away from a protective Th1 response. Moreover, infection with S. typhi-Δ-pR(ST98) induced autophagy in DCs. We herein demonstrate S. typhi pR(ST98) plays essential roles in modulating DCs maturation, activation, inflammatory responses, and autophagy. Together, these data prove that pR(ST98) targets functions of DCs that are required for T-cell activation. This might contribute to evasion of adaptive immune responses by S. typhi.     

Murine gammaherpesvirus-68 inhibits antigen presentation by dendritic cells

Dendritic cells (DCs) play a central role in initiating adaptive immunity. Murine gammaherpesvirus-68 (MHV-68), like many persistent viruses, infects DCs during normal host colonization. It therefore provides a means to understanding what host and viral genes contribute to this aspect of pathogenesis. The infected DC phenotype is likely to depend on whether viral gene expression is lytic or latent and whether antigen presentation is maintained. For MHV-68, neither parameter has been well defined. Here we show that MHV-68 infects immature but not mature bone marrow-derived DCs. Infection was predominantly latent and these DCs showed no obvious defect in antigen presentation. Lytically infected DCs were very different. These down-regulated CD86 and MHC class I expression and presented a viral epitope poorly to CD8(+) T cells. Antigen presentation improved markedly when the MHV-68 K3 gene was disrupted, indicating that K3 fulfils an important function in infected DCs. MHV-68 infects only a small fraction of the DCs present in lymphoid tissue, so K3 expression is unlikely to compromise significantly global CD8(+) T cell priming. Instead it probably helps to maintain lytic gene expression in DCs once CD8(+) T cell priming has occurred.     

Identification of Genes Responsive to Solar Simulated UV Radiation in Human Monocyte-Derived Dendritic Cells

Ultraviolet (UV) irradiation has profound effects on the skin and the systemic immune system. Several effects of UV radiation on Dendritic cells (DCs) functions have been described. However, gene expression changes induced by UV radiation in DCs have not been addressed before. In this report, we irradiated human monocyte-derived DCs with solar-simulated UVA/UVB and analyzed regulated genes on human whole genome arrays. Results were validated by RT-PCR and further analyzed by Gene Set Enrichment Analysis (GSEA). Solar-simulated UV radiation up-regulated expression of genes involved in cellular stress and inflammation, and down-regulated genes involved in chemotaxis, vesicular transport and RNA processing. Twenty four genes were selected for comparison by RT-PCR with similarly treated human primary keratinocytes and human melanocytes. Several genes involved in the regulation of the immune response were differentially regulated in UVA/UVB irradiated human monocyte-derived DCs, such as protein tyrosine phosphatase, receptor type E (PTPRE), thrombospondin-1 (THBS1), inducible costimulator ligand (ICOSL), galectins, Src-like adapter protein (SLA), IL-10 and CCR7. These results indicate that UV-exposure triggers the regulation of a complex gene repertoire involved in human-DC–mediated immune responses.     

Shaping immune responses through the activation of dendritic cells–P2 receptors

Dendritic cells (DCs) activate and shape the adaptive immune response by capturing antigens, migrating to peripheral lymphoid organs where naïve T cells reside, expressing high levels of MHC and costimulatory molecules and secreting cytokines and chemokines. DCs are endowed with a high degree of functional plasticity and their functions are tightly regulated. Besides initiating adaptive immune responses, DCs play a key role in maintaining peripheral tolerance toward self-antigens. On the basis of the information gathered from the tissue where they reside, DCs adjust their functional activity to ensure that protective immunity is favoured while unwanted or exaggerated immune responses are prevented. A wide variety of signals from neighbouring cells affecting DC functional activity have been described. Here we will discuss the complex role of extracellular nucleotides in the regulation of DC function and the role of P2 receptors as possible tools to manipulate immune responses.     

Regulation of dendritic cell function through Toll-like receptors

Higher animals establish host defense by orchestrating innate and adaptive immunity. This is mediated by professional antigen presenting cells, i.e. dendritic cells (DCs). DCs can incorporate pathogens, produce a variety of cytokines, maturate, and present pathogen-derived peptides to T cells, thereby inducing T cell activation and differentiation. These responses are triggered by microbial recognition through type I transmembrane proteins, Toll-like receptors (TLRs) on DCs. TLRs consist of ten members and each TLR is involved in recognizing a variety of microorganism-derived molecular structures. TLR ligands include cell wall components, proteins, nucleic acids, and synthetic chemical compounds, all of which can activate DCs as immune adjuvants. Each TLR can activate DCs in a similar, but distinct manner. For example, TLRs can be divided into subgroups according to their type I interferon (IFN) inducing ability. TLR2 cannot induce IFN-alpha or IFN-beta, but TLR4 can lead to IFN-beta production. Meanwhile, TLR3, TLR7, and TLR9 can induce both IFN-alpha and IFN-beta. Recent evidences suggest that cytoplamic adapters for TLRs are especially crucial for this functional heterogeneity. Clarifying how DC function is regulated by TLRs should provide us with critical information for manipulating the host defense against a variety of diseases.     

MicroRNA-148/152 impair innate response and antigen presentation of TLR-triggered dendritic cells by targeting CaMKIIα

MicroRNAs (miRNAs) are involved in the regulation of immunity, including the lymphocyte development and differentiation, and inflammatory cytokine production. Dendritic cells (DCs) play important roles in linking innate and adaptive immune responses. However, few miRNAs have been found to regulate the innate response and APC function of DCs to date. Calcium/calmodulin-dependent protein kinase II (CaMKII), a major downstream effector of calcium (Ca(2+)), has been shown to be an important regulator of the maturation and function of DCs. Our previous study showed that CaMKIIα could promote TLR-triggered production of proinflammatory cytokines and type I IFN. Inspired by the observations that dicer mutant Drosophila display defect in endogenous miRNA generation and higher CaMKII expression, we wondered whether miRNAs can regulate the innate response and APC function of DCs by targeting CaMKIIα. By predicting with software and confirming with functional experiments, we demonstrate that three members of the miRNA (miR)-148 family, miR-148a, miR-148b, and miR-152, are negative regulators of the innate response and Ag-presenting capacity of DCs. miR-148/152 expression was upregulated, whereas CaMKIIα expression was downregulated in DCs on maturation and activation induced by TLR3, TLR4, and TLR9 agonists. We showed that miR-148/152 in turn inhibited the production of cytokines including IL-12, IL-6, TNF-α, and IFN-β upregulation of MHC class II expression and DC-initiated Ag-specific T cell proliferation by targeting CaMKIIα. Therefore, miRNA-148/152 can act as fine-tuner in regulating the innate response and Ag-presenting capacity of DCs, which may contribute to the immune homeostasis and immune regulation.     

Oncostatin M induces dendritic cell maturation and Th1 polarization

Oncostatin M (OSM) is a pleiotropic cytokine and a member of the gp130/IL-6 cytokine family that has been found to be involved in both pro- and anti-inflammatory responses in cell-mediated immunity. Maturation of dendritic cells (DCs) is crucial for initiation of primary immune responses and is regulated by several stimuli. In this study, the role of OSM in the phenotypic and functional maturation of DCs was evaluated in vitro. Stimulation with OSM upregulated the expression of CD80, CD86, MHC class I and MHC class II and reduced the endocytic capacity of immature DCs. Moreover, OSM induced the allogeneic immunostimulatory capacity of DCs by stimulating the production of the Th1-promoting cytokine IL-12. OSM also increased the production of IFN-γ by T cells in mixed-lymphocyte reactions, which would be expected to contribute to the Th1 polarization of the immune response. The expression of surface markers and cytokine production in DCs was mediated by both the MAPK and NF-κB pathways. Taken together, these results indicate that OSM may play a role in innate immunity and in acquired immunity by enhancing DCs maturation and promoting Th1 immune responses.     

Regulation of dendritic cell function through toll-like receptors

Higher animals establish host defense by orchestrating innate and adaptive immunity. This is mediated by professional antigen presenting cells, i.e. dendritic cells (DCs). DCs can incorporate pathogens, produce a variety of cytokines, maturate, and present pathogen-derived peptides to T cells, thereby inducing T cell activation and differentiation. These responses are triggered by microbial recognition through type I transmembrane proteins, Toll-like receptors (TLRs) on DCs. TLRs consist of ten members and each TLR is involved in recognizing a variety of microorganism-derived molecular structures. TLR ligands include cell wall components, proteins, nucleic acids, and synthetic chemical compounds, all of which can activate DCs as immune adjuvants.     

CCR6 as a mediator of immunity in the lung and gut

Chemokines are key mediators of leukocyte recruitment during pathogenic insult and also play a prominent role in homeostasis. While most chemokine receptors bind to multiple chemokines, CCR6 is unique in that this receptor is one of only a few that can bind only a single chemokine ligand, CCL20. CCR6 is an important receptor that is involved in regulating several aspects of mucosal immunity, including the ability to mediate the recruitment of immature dendritic cells (DCs) and mature DCs, and professional antigen presenting cells (APCs) to the sites of epithelial inflammation. Further, CCR6 mediates the homing of both CD4⁺ T (T-helper; Th) cells and DCs to the gut mucosal lymphoid tissue. DCs, which are known to be essential immune cells in innate immunity and in the initiation of adaptive immunity, play a central role in initiating a primary immune response. Herein, we summarize the role of CCR6 in immune responses at epithelial and mucosal sites in both the lung and gut based on a review of the current literature.