Sensing pathogens and tuning immune responses

Helicobacter pylori antigens as immunomodulators of immune system

Helicobacter pylori (H. pylori) is one of the most prevalent human pathogens and the leading cause of chronic infection in almost half of the population in the world (~59%). The bacterium is a major leading cause of chronic gastritis, gastric and duodenal ulcers, and two type of malignancies, gastric adenocarcinoma and mucosa-associated lymphoid tissue (MALT) lymphoma. Despite the immune responses mounted by the host, the bacteria are not cleared from the body resulting in a chronic infection accompanied by a chronic inflammation. Herein, a review of the literature discussing H. pylori antigens modulating the immune responses is presented. The mechanisms that are involved in the modulation of innate immune response, include modulation of recognition by pattern recognition receptors (PRRs) such as modulation of recognition by toll like receptors (TLR)4 and TLR5, modulation of phagocytic function, and modulation of phagocytic killing mediated by reactive oxygen species (ROS) and nitric oxide (NO). On the other hands, H. pylori modulates acquired immune response by the induction of tolerogenic dendritic cells (DCs), modulation of apoptosis, induction of regulatory T cells, modulation of T helper (Th)1 response, and modulation of Th17 response.

Balancing act: the complex role of NK cells in immune regulation

Natural killer (NK) cells, as fundamental components of innate immunity, can quickly react to abnormalities within the body. In-depth research has revealed that NK cells possess regulatory functions not only in innate immunity but also in adaptive immunity under various conditions. Multiple aspects of the adaptive immune process are regulated through NK cells. In our review, we have integrated multiple studies to illuminate the regulatory function of NK cells in regulating B cell and T cell responses during adaptive immune processes, focusing on aspects including viral infections and the tumor microenvironment (TME). These insights provide us with many new understandings on how NK cells regulate different phases of the adaptive immune response.

Human β-defensins are correlated with the immune infiltration and regulated by vitamin D3 in periodontitis

OBJECTIVE

Exploring the correlation between human β-defensins (HBDs) and immune infiltration in periodontitis, and whether it is regulated by vitamin D3 .

BACKGROUND

The human body produces essential antimicrobial peptides called HBDs, which are associated with periodontitis. There is a strong link between periodontal tissue destruction and the immune cell infiltration. Moreover, vitamin D3 has been reported to regulate the expression of immune cell chemokines. However, the relationship between vitamin D3 , HBDs, and immune infiltration in periodontitis remains to be investigated.

METHODS

The Gene Expression Omnibus database was accessed to obtain transcriptomic information of gingival samples taken from periodontitis patients. The expression value of HBD-2 and HBD-3 was calculated. Additionally, using the online program ImmuCellAl, 10 immune cells were scored for immune infiltration in the high-HBDs-expression group and the low-HBDs-expression group, separately. After that, transcriptome sequencing was done based on human gingival fibroblasts that had received vitamin D3 treatment. Furthermore, hGFs were treated by vitamin D3 , tumor necrosis factor-α (TNF-α), and Porphyromonas gingivalis lipopolysaccharide (Pg-LPS). The expressions of HBD-2, HBD-3, interleukin-8 (IL-8), and monocyte chemoattractant protein-1 (MCP-1) were detected. To seek the potential mechanism, CYP27A1 siRNA was employed to reduce the expression of CYP27A1, and nuclear factor-gene binding protein 65 (NF-κB p65) was examined.

RESULTS

In GSE10334, the expressions of HBD-2 and HBD-3 were down-regulated in periodontitis group. Meanwhile, monocyte, macrophage, and CD4_T cell were less infiltrated in low-HBD-2-expression group, while less Gamma-delta T-cell infiltration was found in low-HBD-3-expression group. Transcriptome sequencing found that 21 genes were significantly expressed, of which the function was enriched in response to bacterial origin and TNF signal pathway. Vitamin D3 could significantly up-regulate the expression of HBD-2 and HBD-3, which could be controlled by knocking down CYP27A1 mRNA expression. With prolonged vitamin D3 stimulation, the expression of HBD-2 and HBD-3 increased. TNF-α/Pg-LPS could significantly increase the expression of HBD-2, HBD-3, IL-8, MCP-1, and p65, all of which were reduced by vitamin D3 .

CONCLUSION

HBDs are correlated with immune infiltration in periodontitis. Vitamin D3 inhibits the expression of HBDs and chemokines induced by TNF-α/Pg-LPS, possibly through NF-κB pathway, in human gingival fibroblasts.

Transcriptional profiling of macrophages in situ in metastatic melanoma reveals localization-dependent phenotypes and function

Modulation of immune function at the tumor site could improve patient outcomes. Here, we analyze patient samples of metastatic melanoma, a tumor responsive to T cell-based therapies, and find that tumor-infiltrating T cells are primarily juxtaposed to CD14+ monocytes/macrophages rather than melanoma cells. Using immunofluorescence-guided laser capture microdissection, we analyze transcriptomes of CD3+ T cells, CD14 + monocytes/macrophages, and melanoma cells in non-dissociated tissue. Stromal CD14+ cells display a specific transcriptional signature distinct from CD14+ cells within tumor nests. This signature contains LY75, a gene linked with antigen capture and regulation of tolerance and immunity in dendritic cells (DCs). When applied to TCGA cohorts, this gene set can distinguish patients with significantly prolonged survival in metastatic cutaneous melanoma and other cancers. Thus, the stromal CD14+ cell signature represents a candidate biomarker and suggests that reprogramming of stromal macrophages to acquire DC function may offer a therapeutic opportunity for metastatic cancers.

Synthesis of bodipy-labeled bacterial polysaccharides and their interaction with human dendritic cells

In this report, we describe the fluorescent labeling of bacterial polysaccharides (Escherichia coli O86:B7, Escherichia coli O19ab, Pseudomonas aeruginosa O10a10b, and Shigella flexneri 2b) at the "natural" amino group of their phosphoethanolamine moiety. Two protocols for labeling are compared: 1) on a scale of a few mg of the polysaccharide, with a dialysis procedure for purification from excessive reagents; and 2) on a scale of 0.1 mg of the polysaccharide, with a simple precipitation procedure instead of dialysis. The microscale version is sufficient for comfortable cytofluorometric analysis. The resulting probes were found to specifically bind to human dendritic cells in a dose-dependent manner. The used limited set of polysaccharides did not allow us even to get close to understanding which dendritic cell-associated lectins and which cognate polysaccharide epitopes are involved in recognition, but the proposed microscale protocol allows to generate a library of fluorescent probes for further mapping of the polysaccharide specificity of the dendritic cells.

SND1 promotes Th1/17 immunity against chlamydial lung infection through enhancing dendritic cell function

To date, no reports have linked the multifunctional protein, staphylococcal nuclease domain-containing protein 1 (SND1), to host defense against intracellular infections. In this study, we investigated the role and mechanisms of SND1, by using SND1 knockout (SND1-/-) mice, in host defense against the lung infection of Chlamydia muridarum, an obligate intracellular bacterium. Our data showed that SND1-/- mice exhibited significantly greater body weight loss, higher organism growth, and more severe pathological changes compared with wild-type mice following the infection. Further analysis showed significantly reduced Chlamydia-specific Th1/17 immune responses in SND1-/- mice after infection. Interestingly, the dendritic cells (DCs) isolated from SND1-/- mice showed lower costimulatory molecules expression and IL-12 production, but higher IL-10 production compared with those from wild-type control mice. In the DC-T cell co-culture system, DCs isolated from SND1-/- infected mice showed significantly reduced ability to promote Chlamydia-specific IFN-γ producing Th1 cells but enhanced capacity to induce CD4+T cells into Foxp3+ Treg cells. Adoptive transfer of DCs isolated from SND1-/- mice, unlike those from wild-type control mice, failed to protect the recipients against challenge infection. These findings provide in vivo evidence that SND1 plays an important role in host defense against intracellular bacterial infection, and suggest that SND1 can promote Th1/17 immunity and inhibit the expansion of Treg cells through modulation of the function of DCs.

Differential TLR7-mediated cytokine expression by R848 in M-CSF- versus GM-CSF-derived macrophages after LCMV infection

Granulocyte-macrophage colony-stimulating factor (GM-CSF) and macrophage colony-stimulating factor (M-CSF) play an important role in macrophage (MФ) development by influencing their differentiation and polarization. Our goal was to explore the difference between M-CSF- and GM-CSF-derived bone marrow MФ responsiveness to TLR7-mediated signalling pathways that influence cytokine production early after infection in a model of acute virus infection. To do so, we examined cytokine production and TLR7-mediated signalling at 1 h post-lymphocytic choriomeningitis virus (LCMV) Armstrong (ARM) infection. We found that R848-induced cytokine expression was enhanced in these cells, with GM-CSF cells exhibiting higher proinflammatory cytokine expression and M-CSF cells exhibiting higher anti-inflammatory cytokine expression. However, R848-mediated signalling molecule activation was diminished in LCMV-infected M-CSF and GM-CSF macrophages. Interestingly, we observed that TLR7 expression was maintained during LCMV infection of M-CSF and GM-CSF cells. Moreover, TLR7 expression was significantly higher in M-CSF cells compared to GM-CSF cells. Taken together, our data demonstrate that although LCMV restrains early TLR7-mediated signalling, it primes differentiated MФ to enhance expression of their respective cytokine profiles and maintains levels of TLR7 expression early after infection.

Hepatitis B virus exploits C-type lectin receptors to hijack cDC1s, cDC2s and pDCs

Objectives

C‐type lectin receptors (CLRs) are key receptors used by DCs to orchestrate responses to pathogens. During infections, the glycan–lectin interactions shape the virus–host interplay and viruses can subvert the function of CLRs to escape antiviral immunity. Recognition of virus/viral components and uptake by CLRs together with subsequent signalling cascades are crucial in initiating and shaping antiviral immunity, and decisive in the outcome of infection. Yet, the interaction of hepatitis B virus (HBV) with CLRs remains largely unknown. As HBV hijacks DC subsets and viral antigens harbour glycan motifs, we hypothesised that HBV may subvert DCs through CLR binding.

Methods

We investigated here the pattern of CLR expression on BDCA1⁺ cDC2s, BDCA2⁺ pDCs and BDCA3⁺ cDC1s from both blood and liver of HBV‐infected patients and explored the ability of HBsAg to bind DC subsets through specific CLRs.

Results

We highlighted for the first time that the CLR repertoire of circulating and intrahepatic cDC2s, cDC1s and pDCs was perturbed in patients with chronic HBV infection and that some CLR expression levels correlated with plasma HBsAg and HBV DNA levels. We also identified candidate CLR responsible for HBsAg binding to cDCs (CD367/DCIR/CLEC4A, CD32/FcɣRIIA) and pDCs (CD369/DECTIN1/CLEC7A, CD336/NKp44) and demonstrated that HBsAg inhibited DC functions in a CLR‐ and glycosylation‐dependent manner.

Conclusion

HBV may exploit CLR pathways to hijack DC subsets and escape from immune control. Such advances bring insights into the mechanisms by which HBV subverts immunity and pave the way for developing innovative therapeutic strategies to restore an efficient immune control of the infection by manipulating the viral glycan–lectin axis.

Bladder urothelium converts bacterial lipopolysaccharide information into neural signaling via an ATP-mediated pathway to enhance the micturition reflex for rapid defense

When bacteria enter the bladder lumen, a first-stage active defensive mechanism flushes them out. Although urinary frequency induced by bacterial cystitis is a well-known defensive response against bacteria, the underlying mechanism remains unclear. In this study, using a mouse model of acute bacterial cystitis, we demonstrate that the bladder urothelium senses luminal extracellular bacterial lipopolysaccharide (LPS) through Toll-like receptor 4 and releases the transmitter ATP. Moreover, analysis of purinergic P2X₂ and P2X₃ receptor-deficient mice indicated that ATP signaling plays a pivotal role in the LPS-induced activation of L6–S1 spinal neurons through the bladder afferent pathway, resulting in rapid onset of the enhanced micturition reflex. Thus, we revealed a novel defensive mechanism against bacterial infection via an epithelial-neural interaction that induces urinary frequency prior to bacterial clearance by neutrophils of the innate immune system. Our results indicate an important defense role for the bladder urothelium as a chemical-neural transducer, converting bacterial LPS information into neural signaling via an ATP-mediated pathway, with bladder urothelial cells acting as sensory receptor cells.

Innate immune responses in RNA viral infection

RNA viruses cause a multitude of human diseases, including several pandemic events in the past century. Upon viral invasion, the innate immune system responds rapidly and plays a key role in activating the adaptive immune system. In the innate immune system, the interactions between pathogen-associated molecular patterns and host pattern recognition receptors activate multiple signaling pathways in immune cells and induce the production of pro-inflammatory cytokines and interferons to elicit antiviral responses. Macrophages, dendritic cells, and natural killer cells are the principal innate immune components that exert antiviral activities. In this review, the current understanding of innate immunity contributing to the restriction of RNA viral infections was briefly summarized. Besides the main role of immune cells in combating viral infection, the intercellular transfer of pathogen and host-derived materials and their epigenetic and metabolic interactions associated with innate immunity was discussed. This knowledge provides an enhanced understanding of the innate immune response to RNA viral infections in general and aids in the preparation for the existing and next emerging viral infections.

IL-18 Responsiveness Defines Limitations in Immune Help for Specialized FcRγ- NK Cells

Despite being prolific innate killers, NK cells are also key helper cells in antiviral defense, influencing adaptive immune responses via interactions with dendritic cells (DCs). In addition to causing NK cell dysfunction, HIV-1 infection contributes to the expansion of a rare population of NK cells deficient in FcRγ (FcRγ^-), an intracellular adaptor protein that associates with CD16. The implications of this inflated NK cell subset in treated HIV-1 infection remain unclear. In this study, we explored the helper function of human NK cells in chronic HIV-1 infection, with a particular focus on characterizing FcRγ^- NK cells. Exposure of NK cells to innate DC-derived costimulatory factors triggered their helper activity, defined by their ability to produce IFN-γ and to drive the maturation of high IL-12-producing DCs. In this setting, however, FcRγ^- NK cells were defective at producing the dominant DC-polarizing agent IFN-γ. The reduced responsiveness of FcRγ^- NK cells to IL-18 in particular, which was attributable to impaired inducible expression of IL-18Rα, extended beyond an inability to produce IFN-γ, as FcRγ^- NK cells showed limited potential to differentiate into CD16^-/CD25⁺/CD83⁺ helper cells. Notwithstanding their deficiencies in responsiveness to innate environmental cues, FcRγ^- NK cells responded robustly to adaptive Ab-mediated signaling through CD16. The presence of an expanded population of FcRγ^- NK cells with a diminished capacity to respond to IL-18 and to effectively modulate DC function may contribute to disturbances in proper immune homeostasis associated with HIV-1 infection and to defects in the initiation of optimal adaptive antiviral responses.

Dendritic cells and Brucella spp. interaction: the sentinel host and the stealthy pathogen

As dendritic cells (DCs) are among the first cells to encounter antigens, these cells trigger both innate and T cell responses, and are the most potent antigen-presenting cells. Brucella spp., which is an intracellular facultative and stealthy pathogen, is able to evade the bactericidal activities of professional phagocytes. Several studies have demonstrated that Brucella can survive and replicate intracellularly, thereby provoking impaired maturation of DCs. Therefore, the interaction between DCs and Brucella becomes an interesting model to study the immune response. In this review, we first will describe the most common techniques for DCs differentiation in vitro as well as general features of brucellosis. Then, the interaction of DCs and Brucella, including pathogen recognition, molecular mechanisms of bacterial pathogenesis, and intracellular trafficking of Brucella to subvert innate response, will be reviewed. Finally, we will debate diversity in immunological DC response and the controversial role of DC activation against Brucella infection.

HTLV-1 infection of myeloid cells: from transmission to immune alterations

Human T cell leukemia virus type 1 (HTLV-1), the etiological agent of adult T-cell leukemia/lymphoma (ATLL) and the demyelinating neuroinflammatory disease known as HTLV-1-Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP), was the first human retrovirus to be discovered. T-cells, which represent the main reservoir for HTLV-1, have been the main focus of studies aimed at understanding viral transmission and disease progression. However, other cell types such as myeloid cells are also target of HTLV-1 infection and display functional alterations as a consequence. In this work, we review the current investigations that shed light on infection, transmission and functional alterations subsequent to HTLV-1 infection of the different myeloid cells types, and we highlight the lack of knowledge in this regard.

Radiation therapy and anti-tumor immunity: exposing immunogenic mutations to the immune system

The expression of antigens that are recognized by self-reactive T cells is essential for immune-mediated tumor rejection by immune checkpoint blockade (ICB) therapy. Growing evidence suggests that mutation-associated neoantigens drive ICB responses in tumors with high mutational burden. In most patients, only a few of the mutations in the cancer exome that are predicted to be immunogenic are recognized by T cells. One factor that limits this recognition is the level of expression of the mutated gene product in cancer cells. Substantial preclinical data show that radiation can convert the irradiated tumor into a site for priming of tumor-specific T cells, that is, an in situ vaccine, and can induce responses in otherwise ICB-resistant tumors. Critical for radiation-elicited T-cell activation is the induction of viral mimicry, which is mediated by the accumulation of cytosolic DNA in the irradiated cells, with consequent activation of the cyclic GMP-AMP synthase (cGAS)/stimulator of interferon (IFN) genes (STING) pathway and downstream production of type I IFN and other pro-inflammatory cytokines. Recent data suggest that radiation can also enhance cancer cell antigenicity by upregulating the expression of a large number of genes that are involved in the response to DNA damage and cellular stress, thus potentially exposing immunogenic mutations to the immune system. Here, we discuss how the principles of antigen presentation favor the presentation of peptides that are derived from newly synthesized proteins in irradiated cells. These concepts support a model that incorporates the presence of immunogenic mutations in genes that are upregulated by radiation to predict which patients might benefit from treatment with combinations of radiotherapy and ICB.

TLR9-Activating CpG-B ODN but Not TLR7 Agonists Triggers Antibody Formation to Factor IX in Muscle Gene Transfer

Innate immune signals that promote B cell responses in gene transfer are generally ill-defined. In this study, we evaluate the effect of activating endosomal Toll-like receptors 7, 8, and 9 (TLR7, TLR7/8, and TLR9) on antibody formation during muscle-directed gene therapy with adeno-associated virus (AAV) vectors. We examined whether activation of endosomal TLRs, by adenine analog CL264 (TLR7 agonist), imidazolquinolone compound R848 (TLR7/8 agonist), or class B CpG oligodeoxynucleotides ODN1826 (TLR9 agonist), could augment antibody formation upon intramuscular administration of AAV1 expressing human clotting factor IX (AAV1-hFIX) in mice. The TLR9 agonist robustly enhanced antibody formation by the 1st week, thus initially eliminating systemic hFIX expression. By contrast, the TLR7 and TLR7/8 agonists did not markedly promote antibody formation, or significantly reduce circulating hFIX. We concurrently investigated the effects of these TLR agonists during muscle gene transfer on mature B cells and dendritic cells (DCs) in the draining lymph nodes including conventional DCs (CD11b+ or CD8α+ cDCs), monocyte-derived dendritic cells (moDCs), and plasmacytoid dendritic cells (pDCs). Only TLR9 stimulation caused a striking increase in the frequency of moDCs within 24 h. The TLR7/8 and TLR9 agonists activated pDCs, both subsets of cDCs, and mature B cells, whereas the TLR7 agonist had only mild effects on these cells. Thus, these TLR ligands have distinct effects on DCs and mature B cells, yet only the TLR9 agonist enhanced the humoral immune response against AAV-expressed hFIX. These new findings indicate a unique ability of certain TLR9 agonists to stimulate B cell responses in muscle gene transfer through enrichment of moDCs.

Macrophages: Their Untold Story in T Cell Activation and Function

The complexity of T cell activation to maintain homeostasis and provide host defense is highlighted by the intricate step-wise process which is coordinated by multiple cell types. Crucial to T cell activation is the requirement of antigen-presenting cells (APCs) such as macrophages at each step of the activation and effector stages. Macrophages are central regulators in T cell activation and are involved in each step including initiating the series of events leading to T cell activation. Macrophages identify and present foreign antigens in classes I and II major histocompatibility complexes (MHC) to T cells, which recognize the MHC-antigen complex through their T cell receptor. This initial step is all in vain if additional costimulatory and cytokine signaling does not occur concurrently. Macrophages can mediate and provide the required costimulatory signaling and cytokine secretion required for effective T cell activation. While other cell types, especially other APCs, may be capable of playing a role during different stages of T cell activation, this review will focus on how macrophages can modulate T cell activation and effector function. This is in no way an attempt to minimize the role of other APCs but instead to bring to light to the role macrophages can play during this process. Here, the role macrophages play in cancer to either activate or inhibit T cells based on macrophage phenotype, costimulatory molecules, and cytokine secretion is highlighted as an example of how macrophages can significantly alter T cell activation and effector function in human disease.

The Regulation of Inflammation by Innate and Adaptive Lymphocytes

Inflammation plays an essential role in the control of pathogens and in shaping the ensuing adaptive immune responses. Traditionally, innate immunity has been described as a rapid response triggered through generic and nonspecific means that by definition lacks the ability to remember. Recently, it has become clear that some innate immune cells are epigenetically reprogrammed or “imprinted” by past experiences. These “trained” innate immune cells display altered inflammatory responses upon subsequent pathogen encounter. Remembrance of past pathogen encounters has classically been attributed to cohorts of antigen-specific memory T and B cells following the resolution of infection. During recall responses, memory T and B cells quickly respond by proliferating, producing effector cytokines, and performing various effector functions. An often-overlooked effector function of memory CD4 and CD8 T cells is the promotion of an inflammatory milieu at the initial site of infection that mirrors the primary encounter. This memory-conditioned inflammatory response, in conjunction with other secondary effector T cell functions, results in better control and more rapid resolution of both infection and the associated tissue pathology. Recent advancements in our understanding of inflammatory triggers, imprinting of the innate immune responses, and the role of T cell memory in regulating inflammation are discussed.

Microbial biomarkers for immune checkpoint blockade therapy against cancer

Three major standard treatments, i.e., surgery, chemotherapy, and radiotherapy, were traditionally applied to the treatment of cancer and saved many patients. Meanwhile, clinical studies as well as basic research of immunotherapy are being actively conducted for intractable or advanced malignancies that cannot be cured by the conventional standard treatments. Remarkable therapeutic efficacies have been recently reported in clinical trials on some cancer types, and immunotherapy is now being recognized as the "fourth" standard therapy against cancer. In particular, immune checkpoint inhibitor therapy (ICI) has demonstrated the effectiveness of immunotherapy through large-scale randomized clinical trials, leading to the paradigm-shift in cancer treatment. Immune checkpoint molecules transduce co-inhibitory signals to immunocompetent cells including T cells, and crucially contribute to the formation of an immunosuppressive microenvironment in tumor tissues, which intrinsically confers the treatment resistance. Programmed death-1 (PD-1, CD279) is one of the typical immune checkpoint molecules. Anti-tumor therapies targeting PD-1 and its ligands had been developed and approved in many countries, and various studies utilizing clinical specimens are currently progressing. In this review, we provide an overview of the biomarkers based on the analysis of enteric microbiota that correlate with the clinical efficacy/inefficacy of PD-1-based therapy.

Environmental influence on Pristionchus pacificus mouth form through different culture methods

Environmental cues can impact development to elicit distinct phenotypes in the adult. The consequences of phenotypic plasticity can have profound effects on morphology, life cycle, and behavior to increase the fitness of the organism. The molecular mechanisms governing these interactions are beginning to be elucidated in a few cases, such as social insects. Nevertheless, there is a paucity of systems that are amenable to rigorous experimentation, preventing both detailed mechanistic insight and the establishment of a generalizable conceptual framework. The mouth dimorphism of the model nematode Pristionchus pacificus offers the rare opportunity to examine the genetics, genomics, and epigenetics of environmental influence on developmental plasticity. Yet there are currently no easily tunable environmental factors that affect mouth-form ratios and are scalable to large cultures required for molecular biology. Here we present a suite of culture conditions to toggle the mouth-form phenotype of P. pacificus. The effects are reversible, do not require the costly or labor-intensive synthesis of chemicals, and proceed through the same pathways previously examined from forward genetic screens. Different species of Pristionchus exhibit different responses to culture conditions, demonstrating unique gene-environment interactions, and providing an opportunity to study environmental influence on a macroevolutionary scale.

Dendritic Cell Sensing of Hydrophobic Di- and Triacylated Lipopeptides Self-Assembled within Synthetic Virus-like Particles

Dendritic cells (DCs) play critical roles in developing immune defenses. One important aspect is interaction with pathogen-associated molecular patterns (PAMPs)/danger-associated molecular patterns, including di- and triacylated lipopeptides. Isolated or synthetic lipopeptides are potent vaccine adjuvants, interacting with cell surface TLR2 heterodimers. In contrast, deep embedment within bacteria cell walls would impair lipopeptide interaction with cell surface TLR2, requiring degradation for PAMP recognition. Accordingly, DC processing in the absence of surface TLR2 ligation was defined using synthetic virus-like particles (SVLPs) carrying hydrophobic TLR2 PAMPs within di- and triacylated lipopeptide cores (P2Cys-SVLPs and P3Cys-SVLPs) compared with SVLPs lacking immunomodulatory lipopeptides. DCs rapidly and efficiently internalized SVLPs, which was dominated by slow endocytic processing via macropinocytosis, although some caveolar endocytosis was implicated. This delivered SVLPs primarily into macropinosomes often interacting with EEA-1⁺ early endosomes. Although endoplasmic reticulum association was occasionally noted, association with recycling/sorting structures was not observed. Involvement of LysoTracker⁺ structures slowly increased with time, with SVLPs present in such structures ultimately dominating. Only SVLPs carrying di- and triacylated lipopeptide cores induced DC activation and maturation independently of surface TLR2 ligation. Intracellular recognition of SVLP TLR2 ligands was confirmed by observing SVLPs' association with internal TLR2, which had similar kinetics to SVLP association with LysoTracker. This related to inflammatory cytokine induction by SVLP⁺ DCs, with adaptive immune response activation ex vivo/in vivo. Importantly, particular DCs, not monocytes, recognized intracellular exposure of the TLR2 PAMPs carried by di- and triacylated SVLP cores, which indicates subset-distinct recognition of functional internal TLR2 ligands. Thus, vaccines carrying hydrophobic TLR2 ligands would interact with particular DCs for efficient induction of specific immunity in the absence of additional adjuvant.

Increased expression of negative regulators of cytokine signaling during chronic HIV disease cause functionally exhausted state of dendritic cells

Mechanisms of functional impairment of dendritic cells (DCs) during chronic HIV-1 infection are not well understood. In order to understand this phenomenon, we aimed to study the expression of negative regulators of cytokine signaling and correlate with DC exhaustion during chronic HIV-1 disease. Monocyte-derived DCs (mo-DCs) from 27 HIV-1 infected patients (CD4+ T-cell counts: 429±44 cells/μL, plasma viral load: Log₁₀3.9±1.0copies/ml) and 19 healthy controls (HCs) were stimulated ex vivo with TLR4 agonist, lipopolysaccharide (LPS) for 2days to evaluate their functional fitness. The expression of a set of genes associated with cytokine signaling was evaluated in a custom designed PCR array by Real-Time PCR. The mo-DCs from HIV-1 infected patients depicted functional exhaustion as evident by decreased allo-stimulation index (mean±SD: 10±6 vs. 24±16) (p<0.05), decreased cytokine production (pg/ml) (IL-12: 4.6±16 vs. 25±85; TNF-α: 128±279 vs. 286±544; IL-10: 6±12 vs. 13±20; IL-8: 10,688±11,748 vs. 17,470±125,049) and retained endocytosis (1.1±0.3 vs. 1.0±0.29) (p<0.05) even after LPS-stimulation, as compared to HCs. Significantly upregulated expression of SOCS-1 (mean±SD fold change: 2.2±2vs.0.8±0.6), SOCS-3 (6.3±7.4vs.1.4±0.4), PIAS-1 (1.6±0.1vs.1.0±0.3) and SHP-1 (0.8±0.4vs.0.4±0.2) correlated positively with PD-L1 expression in these DCs (Spearman's coefficient, SOCS-1: 0.63, SOCS-3: 1.0 and PIAS-1: 0.7) (p<0.05). The expression of these molecules trended positively with plasma viral load and negatively with CD4+ T-cell counts. These findings suggest that the upregulation of negative regulatory factors during chronic HIV disease have profound down-modulatory effects on DC functions and establishment of an overall exhausted state. Understanding mechanisms causing upregulation of these factors may lead to the design of new generation therapeutics based on silencing of their gene expression.

NK-DC Crosstalk in Immunity to Microbial Infection

The interaction between natural killer (NK) cell and dendritic cell (DC), two important cellular components of innate immunity, started to be elucidated in the last years. The crosstalk between NK cells and DC, which leads to NK cell activation, DC maturation, or apoptosis, involves cell-cell contacts and soluble factors. This interaction either in the periphery or in the secondary lymphoid organs acts as a key player linking innate and adaptive immune responses to microbial stimuli. This review focuses on the mechanisms of NK-DC interaction and their relevance in antimicrobial responses. We specifically aim to emphasize the ability of various microbial infections to differently influence NK-DC crosstalk thereby contributing to distinct adaptive immune response.

Cross-Linking Cell Surface Chemokine Receptors Leads to Isolation, Activation, and Differentiation of Monocytes into Potent Dendritic Cells

Monocytes express on the cell surface several kinds of chemokine receptors that facilitate chemotaxis followed by differentiation in target tissues. In the present study, we found that a large number of monocytes from peripheral blood mononuclear cells (PBMCs) tightly adhered to plastic cell culture plates precoated with a monoclonal antibody (mAb, clone T312) specific for human CCR5 but not an isotype control after overnight incubation. Soluble T312 did not induce such adhesion, indicating that cross-linking of CCR5 is required for the enhanced adhesion of monocytes. The adhesion was blocked by a PI3-K inhibitor and an anti-CD18 blocking mAb. Following the cross-linking of CCR5, monocytes synthesized high levels of M-CSF, RANTES, MIP-1α, and MIP-1β associated with a readily detectable downmodulation of CD14, CD4, CCR5, and CXCR4 expression. The T312-enriched monocytes differentiated into dendritic cells (DCs) in the presence of interleukin-4 alone. After maturation with β-interferon, the T312-induced DCs stimulated proliferation of allogeneic naïve CD4+ T cells accompanied by the synthesis of high levels of γ-interferon in vitro. Furthermore, the T312-induced DCs were capable of stimulating antigen-specific human T- and B-cell immune responses in our hu-PBL-SCID mouse system. Finally, screening of other anti-chemokine receptor mAbs showed that select clones of mAbs against CXCR4 and CCR3 were also capable of facilitating enrichment of monocytes similar to T312. These results show that cross-linking of chemokine receptors on monocytes by appropriate mAbs leads to activation and differentiation of monocytes and that the method described herein provides an alternate simple strategy for adherence-based isolation of monocytes and generation of functional DCs.

Recombinant Sj16 from Schistosoma japonicum contains a functional N-terminal nuclear localization signal necessary for nuclear translocation in dendritic cells and interleukin-10 production

Sj16 is a Schistosoma japonicum-derived protein (16 kDa in molecular weight) that has been identified as an immune modulation molecule, but the mechanisms of modulation of immune responses are not known. In this report, we aimed to investigate the host immune regulation mechanism by recombinant Sj16 (rSj16) and thus illuminate the molecular mechanism of immune evasion by S. japonicum. The effect of rSj16 and rSj16 mutants on the biology of dendritic cells (DCs) was assessed by examining DC maturation, cytokine production, and expression of surface markers by flow cytometry and enzyme-linked immunosorbent assay. We found that rSj16 significantly stimulated interleukin (IL)-10 production and inhibited LPS-induced bone marrow-derived dendrite cell (BMDC) maturation in a dose-dependent manner. By using antibody neutralization experiments and IL-10-deficient (knockout) mice, we confirmed that the inhibitory effect of rSj16 on LPS-induced BMDCs is due to its induction of IL-10 production. To understand how rSj16 induces the production of IL-10, we analyzed the protein sequence and revealed two potential nuclear localization signals (NLS) in Sj16. The N-terminal NLS (NLS1) is both necessary and sufficient for translocation of rSj16 to the nucleus of BMDCs and is important for subsequent induction of IL-10 production and the inhibition of BMDC maturation by rSj16. The results of our study concluded that the ability of rSj16 to inhibit DC functions is IL-10 dependent which is operated by IL-10R signal pathway. This study also confirmed that NLS is an important domain associated with increased production of IL-10. Our findings will extend the current understanding on host-schistosome relationship and provide insight about bottleneck of parasitic control.

An efficient method for gene silencing in human primary plasmacytoid dendritic cells: silencing of the TLR7/IRF-7 pathway as a proof of concept

Plasmacytoid dendritic cells (pDC) are specialized immune cells that produce massive levels of type I interferon in response to pathogens. Unfortunately, pDC are fragile and extremely rare, rendering their functional study a tough challenge. However, because of their central role in numerous pathologies, there is a considerable need for an efficient and reproducible protocol for gene silencing in these cells. In this report, we tested six different methods for siRNA delivery into primary human pDC including viral-based, lipid-based, electroporation, and poly-ethylenimine (PEI) technologies. We show that lipid-based reagent DOTAP was extremely efficient for siRNA delivery into pDC, and did not induce cell death or pDC activation. We successfully silenced Toll-Like Receptor 7 (TLR7), CXCR4 and IFN regulatory factor 7 (IRF-7) gene expression in pDC as assessed by RT-qPCR or cytometry. Finally, we showed that TLR7 or IRF-7 silencing in pDC specifically suppressed IFN-α production upon stimulation, providing a functional validation of our transfection protocol.

RNA-sequencing study of peripheral blood monocytes in chronic periodontitis

BACKGROUND

Monocytes are an important cell type in chronic periodontitis (CP) by interacting with oral bacteria and mediating host immune response. The aim of this study was to reveal new functional genes and pathways for CP at monocyte transcriptomic level.

METHODS

We performed an RNA-sequencing (RNA-seq) study of peripheral blood monocytes (PBMs) in 5 non-smoking moderate to severe CP (case) individuals vs. 5 controls. We took advantage of a microarray study of periodontitis to support our findings. We also performed pathway-based analysis on the identified differentially expressed (DEx) transcripts/isoforms using DAVID (Database for Annotation, Visualization and Integrated Discovery).

RESULTS

Through differential expression analyses at both whole gene (or whole non-coding RNA) and isoform levels, we identified 380 DEx transcripts and 5955 DEx isoforms with a PPEE (posterior probability of equal expression) of <0.05. Pervasive up-regulation of transcripts at isoform level in CP vs. control individuals was observed, suggesting a more functionally active monocyte transcriptome for CP. By comparing with the microarray dataset, we identified several CP-associated novel genes (e.g., FACR and CUX1) that have functions to interact with invading microorganisms or enhance TNF production on lipopolysaccharide stimulation. DAVID analysis of both the RNA-seq and the microarray datasets leads to converging evidence supporting "endocytosis", "cytokine production" and "apoptosis" as significant biological processes in CP.

CONCLUSIONS

As the first RNA-seq study of PBMs for CP, this study provided novel findings at both gene (e.g., FCAR and CUX1) and biological process level. The findings will contribute to better understanding of CP disease mechanisms.

MGL Receptor and Immunity: When the Ligand Can Make the Difference

C-type lectin receptors (CLRs) on antigen-presenting cells (APCs) facilitate uptake of carbohydrate antigens for antigen presentation, modulating the immune response in infection, homeostasis, autoimmunity, allergy, and cancer. In this review, we focus on the role of the macrophage galactose type C-type lectin (MGL) in the immune response against self-antigens, pathogens, and tumor associated antigens (TAA). MGL is a CLR exclusively expressed by dendritic cells (DCs) and activated macrophages (MØs), able to recognize terminal GalNAc residues, including the sialylated and nonsialylated Tn antigens. We discuss the effects on DC function induced throughout the engagement of MGL, highlighting the importance of the antigen structure in the modulation of immune response. Indeed modifying Tn-density, the length, and steric structure of the Tn-antigens can result in generating immunogens that can efficiently bind to MGL, strongly activate DCs, mimic the effects of a danger signal, and achieve an efficient presentation in HLA classes I and II compartments.

Eosinophils from Murine Lamina Propria Induce Differentiation of Naïve T Cells into Regulatory T Cells via TGF-β1 and Retinoic Acid

Treg cells play a crucial role in immune tolerance, but mechanisms that induce Treg cells are poorly understood. We here have described eosinophils in lamina propria (LP) that displayed high aldehyde dehydrogenase (ALDH) activity, a rate-limiting step during all-trans retinoic acid (ATRA) synthesis, and expressed TGF-β1 mRNA and high levels of ATRA. Co-incubation assay confirmed that LP eosinophils induced the differentiation of naïve T cells into Treg cells. Differentiation promoted by LP eosinophils were inhibited by blocked either TGF-β1 or ATRA. Peripheral blood (PB) eosinophils did not produce ATRA and could not induce Treg differentiation. These data identifies LP eosinophils as effective inducers of Treg cell differentiation through a mechanism dependent on TGF-β1 and ATRA.

The Role of Invariant Natural Killer T Cells in Dendritic Cell Licensing, Cross-Priming, and Memory CD8(+) T Cell Generation

New vaccination strategies focus on achieving CD8⁺ T cell (CTL) immunity rather than on induction of protective antibody responses. While the requirement of CD4⁺ T (Th) cell help in dendritic cell (DC) activation and licensing, and in CTL memory induction has been described in several disease models, CTL responses may occur in a Th cell help-independent manner. Invariant natural killer T cells (iNKT cells) can substitute for Th cell help and license DC as well. iNKT cells produce a broad spectrum of Th1 and Th2 cytokines, thereby inducing a similar set of costimulatory molecules and cytokines in DC. This form of licensing differs from Th cell help by inducing other chemokines, while Th cell-licensed DCs produce CCR5 ligands, iNKT cell-licensed DCs produce CCL17, which attracts CCR4⁺ CD8⁺ T cells for subsequent activation. It has recently been shown that iNKT cells do not only enhance immune responses against bacterial pathogens or parasites but also play a role in viral infections. The inclusion of iNKT cell ligands in influenza virus vaccines enhanced memory CTL generation and protective immunity in a mouse model. This review will focus on the role of iNKT cells in the cross-talk with cross-priming DC and memory CD8⁺ T cell formation.

Mitochondrial antiviral-signalling protein plays an essential role in host immunity against human metapneumovirus

Human metapneumovirus (hMPV) is a common cause of respiratory tract infection in the paediatrics population. Recently, we and others have shown that retinoic acid-inducible gene 1 (RIG-I)-like receptors (RLRs) are essential for hMPV-induced cellular antiviral signalling. However, the contribution of those receptors to host immunity against pulmonary hMPV infection is largely unexplored. In this study, mice deficient in mitochondrial antiviral-signalling protein (MAVS), an adaptor of RLRs, were used to investigate the role(s) of these receptors in pulmonary immune responses to hMPV infection. MAVS deletion significantly impaired the induction of antiviral and pro-inflammatory cytokines and the recruitment of immune cells to the bronchoalveolar lavage fluid by hMPV. Compared with WT mice, mice lacking MAVS demonstrated decreased abilities to activate pulmonary dendritic cells (DCs) and abnormal primary T-cell responses to hMPV infection. In addition, mice deficient in MAVS had a higher peak of viral load at day 5 post-infection (p.i.) than WT mice, but were able to clear hMPV by day 7 p.i. similarly to WT mice. Taken together, our data indicate a role of MAVS-mediated pathways in the pulmonary immune responses to hMPV infection and the early control of hMPV replication.

Dendritic cell interactions with Histoplasma and Paracoccidioides

Fungi are among the most common microbes encountered by humans. More than 100, 000 fungal species have been described in the environment to date, however only a few species cause disease in humans. Fungal infections are of particular importance to immunocompromised hosts in whom disease is often more severe, especially in those with impaired cell-mediated immunity such as individuals with HIV infection, hematologic malignancies, or those receiving TNF-α inhibitors. Nevertheless, environmental disturbances through natural processes or as a consequence of deforestation or construction can expose immunologically competent people to a large number of fungal spores resulting in asymptomatic acquisition to life-threatening disease. In recent decades, the significance of the innate immune system and more importantly the role of dendritic cells (DC) have been found to play a fundamental role in the resolution of fungal infections, such as in dimorphic fungi like Histoplasma and Paracoccidioides. In this review article the general role of DCs will be illustrated as the bridge between the innate and adaptive immune systems, as well as their specific interactions with these 2 dimorphic fungi.

The varieties of immunological experience: of pathogens, stress, and dendritic cells

In the 40 years since their discovery, dendritic cells (DCs) have been recognized as central players in immune regulation. DCs sense microbial stimuli through pathogen-recognition receptors (PRRs) and decode, integrate, and present information derived from such stimuli to T cells, thus stimulating immune responses. DCs can also regulate the quality of immune responses. Several functionally specialized subsets of DCs exist, but DCs also display functional plasticity in response to diverse stimuli. In addition to sensing pathogens via PRRs, emerging evidence suggests that DCs can also sense stress signals, such as amino acid starvation, through ancient stress and nutrient sensing pathways, to stimulate adaptive immunity. Here, I discuss these exciting advances in the context of a historic perspective on the discovery of DCs and their role in immune regulation. I conclude with a discussion of emerging areas in DC biology in the systems immunology era and suggest that the impact of DCs on immunity can be usefully contextualized in a hierarchy-of-organization model in which DCs, their receptors and signaling networks, cell-cell interactions, tissue microenvironment, and the host macroenvironment represent different levels of the hierarchy. Immunity or tolerance can then be represented as a complex function of each of these hierarchies.

Trial watch: Dendritic cell-based anticancer therapy

The use of patient-derived dendritic cells (DCs) as a means to elicit therapeutically relevant immune responses in cancer patients has been extensively investigated throughout the past decade. In this context, DCs are generally expanded, exposed to autologous tumor cell lysates or loaded with specific tumor-associated antigens (TAAs), and then reintroduced into patients, often in combination with one or more immunostimulatory agents. As an alternative, TAAs are targeted to DCs in vivo by means of monoclonal antibodies, carbohydrate moieties or viral vectors specific for DC receptors. All these approaches have been shown to (re)activate tumor-specific immune responses in mice, often mediating robust therapeutic effects. In 2010, the first DC-based preparation (sipuleucel-T, also known as Provenge®) has been approved by the US Food and Drug Administration (FDA) for use in humans. Reflecting the central position occupied by DCs in the regulation of immunological tolerance and adaptive immunity, the interest in harnessing them for the development of novel immunotherapeutic anticancer regimens remains high. Here, we summarize recent advances in the preclinical and clinical development of DC-based anticancer therapeutics.

Differential expression of the fractalkine chemokine receptor (CX3CR1) in human monocytes during differentiation

Circulating monocytes (Mos) may continuously repopulate macrophage (MAC) or dendritic cell (DC) populations to maintain homeostasis. MACs and DCs are specialized cells that play different and complementary immunological functions. Accordingly, they present distinct migratory properties. Specifically, whereas MACs largely remain in tissues, DCs are capable of migrating from peripheral tissues to lymphoid organs. The aim of this work was to analyze the expression of the fractalkine receptor (CX3CR1) during the monocytic differentiation process. Freshly isolated Mos express high levels of both CX3CR1 mRNA and protein. During the Mo differentiation process, CX3CR1 is downregulated in both DCs and MACs. However, MACs showed significantly higher CX3CR1 expression levels than did DC. We also observed an antagonistic CX3CR1 regulation by interferon (IFN)-γ and interleukin (IL)-4 during MAC activation through the classical and alternative MAC pathways, respectively. IFN-γ inhibited the loss of CX3CR1, but IL-4 induced it. Additionally, we demonstrated an association between CX3CR1 expression and apoptosis prevention by soluble fractalkine (sCX3CL1) in Mos, DCs and MACs. This is the first report demonstrating sequential and differential CX3CR1 modulation during Mo differentiation. Most importantly, we demonstrated a functional link between CX3CR1 expression and cell survival in the presence of sCX3CL1.

Trial watch: Dendritic cell-based interventions for cancer therapy

Dendritic cells (DCs) occupy a central position in the immune system, orchestrating a wide repertoire of responses that span from the development of self-tolerance to the elicitation of potent cellular and humoral immunity. Accordingly, DCs are involved in the etiology of conditions as diverse as infectious diseases, allergic and autoimmune disorders, graft rejection and cancer. During the last decade, several methods have been developed to load DCs with tumor-associated antigens, ex vivo or in vivo, in the attempt to use them as therapeutic anticancer vaccines that would elicit clinically relevant immune responses. While this has not always been the case, several clinical studies have demonstrated that DC-based anticancer vaccines are capable of activating tumor-specific immune responses that increase overall survival, at least in a subset of patients. In 2010, this branch of clinical research has culminated with the approval by FDA of a DC-based therapeutic vaccine (sipuleucel-T, Provenge^®) for use in patients with asymptomatic or minimally symptomatic metastatic hormone-refractory prostate cancer. Intense research efforts are currently dedicated to the identification of the immunological features of patients that best respond to DC-based anticancer vaccines. This knowledge may indeed lead to personalized combination strategies that would extend the benefit of DC-based immunotherapy to a larger patient population. In addition, widespread enthusiasm has been generated by the results of the first clinical trials based on in vivo DC targeting, an approach that holds great promises for the future of DC-based immunotherapy. In this Trial Watch, we will summarize the results of recently completed clinical trials and discuss the progress of ongoing studies that have evaluated/are evaluating DC-based interventions for cancer therapy.

Soluble toll like receptor 2 (TLR-2) is increased in saliva of children with dental caries

Background

Dental caries is the most common microbial disease affecting mankind. Caries risk assessment methods, identification of biomarkers and vaccine development strategies are being emphasized to control the incidence of the largely preventable disease. Pattern recognition receptors such as the toll like receptors (TLR) have been implicated as modulators of host-microbial interactions. Soluble TLR-2 and its co-receptor, CD14 identified in saliva can bind the cell wall components of cariogenic bacteria and modulate the disease process. The objective of this study is to determine the potential of salivary sTLR-2 and sCD14 as biomarkers of caries activity and indirect measures of the cariogenic bacterial burden.

Methods

Unstimulated whole saliva was collected from twenty caries free and twenty caries active children between the ages of 5 and 13 years. The concentration of sCD14 and sTLR-2 together with that of the cytokine IL-8 reported to be increased in dental caries was assessed by the enzyme linked immunosorbent assay.

Results

While the level of sCD14 and that of IL-8 was equivocal between the two groups, the sTLR-2 concentration in caries active saliva was significantly higher than that in caries free saliva.

Conclusions

The sTLR-2 in saliva could serve as a potential biomarker for caries activity.

Differential infection outcome of Chlamydia trachomatis in human blood monocytes and monocyte-derived dendritic cells

Background

Chlamydia trachomatis is an intracellular bacteria which consist of three biovariants; trachoma (serovars A-C), urogenital (serovars D-K) and lymphogranuloma venereum (L1-L3), causing a wide spectrum of disease in humans. Monocytes are considered to disseminate this pathogen throughout the body while dendritic cells (DCs) play an important role in mediating immune response against bacterial infection. To determine the fate of C. trachomatis within human peripheral blood monocytes and monocyte-derived DCs, these two sets of immune cells were infected with serovars Ba, D and L2, representative of the three biovariants of C. trachomatis.

Results

Our study revealed that the different serovars primarily infect monocytes and DCs in a comparable fashion, however undergo differential infection outcome, serovar L2 being the only candidate to inflict active infection. Moreover, the C. trachomatis serovars Ba and D become persistent in monocytes while the serovars predominantly suffer degradation within DCs. Effects of persistence gene Indoleamine 2, 3-dioxygenase (IDO) was not clearly evident in the differential infection outcome. The heightened levels of inflammatory cytokines secreted by the chlamydial infection in DCs compared to monocytes seemed to be instrumental for this consequence. The immune genes induced in monocytes and DCs against chlamydial infection involves a different set of Toll-like receptors, indicating that distinct intracellular signalling pathways are adopted for immune response.

Conclusion

Our results demonstrate that the host pathogen interaction in chlamydia infection is not only serovar specific but manifests cell specific features, inducing separate immune response cascade in monocytes and DCs.

HIV-1 gp120 activates the STAT3/interleukin-6 axis in primary human monocyte-derived dendritic cells

Dendritic cells (DCs) are fundamental for the initiation of immune responses and are important players in AIDS immunopathogenesis. The modulation of DC functional activities represents a strategic mechanism for HIV-1 to evade immune surveillance. Impairment of DC function may result from bystander effects of HIV-1 envelope proteins independently of direct HIV-1 infection. In this study, we report that exposure of immature monocyte-derived DCs (MDDCs) to HIV-1 R5 gp120 resulted in the CCR5-dependent production of interleukin-6 (IL-6) via mitogen-activated protein kinase (MAPK)/NF-κB pathways. IL-6 in turn activated STAT3 by an autocrine loop. Concomitantly, gp120 promoted an early activation of STAT3 that further contributed to IL-6 induction. This activation paralleled a concomitant upregulation of the STAT3 inhibitor PIAS3. Notably, STAT3/IL-6 pathway activation was not affected by the CCR5-specific ligand CCL4. These results identify STAT3 as a key signaling intermediate activated by gp120 in MDDCs and highlight the existence of a virus-induced dysregulation of the IL-6/STAT3 axis. HIV-1 gp120 signaling through STAT3 may provide an explanation for the impairment of DC function observed upon HIV exposure.

IMPORTANCE

This study provides new evidence for the molecular mechanisms and signaling pathways triggered by HIV-1 gp120 in human DCs in the absence of productive infection, emphasizing a role of aberrant signaling in early virus-host interaction, contributing to viral pathogenesis. We identified STAT3 as a key component in the gp120-mediated signaling cascade involving MAPK and NF-κB components and ultimately leading to IL-6 secretion. STAT3 now is recognized as a key regulator of DC functions. Thus, the identification of this transcription factor as a signaling molecule mediating some of gp120's biological effects unveils a new mechanism by which HIV-1 may deregulate DC functions and contribute to AIDS pathogenesis.

Chemical Composition and Anti-inflammatory Activity of Chamaecyparis obtusa f. formosana Wood Essential Oil from Taiwan

Chamaecyparis obtusa Siebold & Zucc. f. formosana Hayata (Cupressaceae) is one of the treasured conifers in Taiwan. In this study, the wood essential oil of the species was extracted and its anti-inflammatory bioactivities analyzed. The composition analysis of the essential oil yielded a total of 57 compounds with α-terpineol (19.4%), τ-muurolol (16.9%), borneol (16%), and α-cadinol (10.9%) predominating. The anti-inflammatory assays of the essential oil suggest that C. obtusa f. formosana wood oil has no cytotoxicity, and was capable of inhibiting the expressions of tumor necrosis factor (TNF-α), IL-6, IL-1, pro IL-1β, NO, iNOS, and NLRP3 in murine macrophage cells. It was unable, however, to inhibit the expression of COX-2. Further investigation of the effect of the essential oil on the cellular signal transduction indicated that it was capable of inhibiting ERK1/2, JNK1/2 and p38; it also showed excellent inhibition against ROS. Thus, the overall results indicated that C. obtusa f. formosana wood oil had very good anti-inflammatory efficacies.

Dendritic cell-associated miRNAs are modulated via chromatin remodeling in response to different environments

INTRODUCTION

Epigenetic modification plays a critical role in regulating gene expression. To understand how epigenetic modification alters miRNA expression in monocyte-derived dendritic cells (moDCs) in different environments, we analyzed the connections between H3K4me3 and H3K27me3 modification and the expression of miRNAs in LPS- and TGF-β-conditioned moDCs.

RESULTS

In moDCs, H3K4me3 modification was strongly associated with the expression of activating miRNAs, whereas H3K27me3 was related to repressive miRNAs. The regulation of miRNA expression by H3K4me3 and H3K27me3 was further confirmed by silencing or inhibiting methyltransferases or methylation-associated factors in LPS- and TGF-β-conditioned moDCs. siRNAs targeting H3K4me3-associated mixed lineage leukemia (MLL) and retinoblastoma binding protein 5 (RBBP5) reduced H3K4me3 enrichment and downregulated miRNA expression; conversely, silencing H3K27me3-associated enhancer of zeste homolog 2 (EZH2) and embryonic ectoderm development (EED) genes upregulated the DC-associated miRNAs. However, LPS-mediated miRNAs were often associated with H3K4me3 redistribution from the transcription start site (TSS) to the miRNA-coding region. Silencing LPS-associated NF-κB p65 and CBP/p300 not only inhibited H3K4m3 redistribution but also reduced miRNA expression. LPS-upregulated RBBP4 and RBBP7, which are involved in chromatin remodeling, also affected the redistribution of H3K4me3 and reduced the expression of miRNAs.

CONCLUSION

In LPS- and TGF-β-conditioned moDCs, miRNAs may be modulated not only by H3K4m3 and H3K27me3 modification but also by redistribution of H3K4me3 around the transcriptional start site of miRNAs. Thus, H3K4me3 and H3K27me3 epigenetic modification may play an important role in regulating DC differentiation and function in the presence of tumor or inflammatory environments.

Human metapneumovirus M2-2 protein inhibits innate immune response in monocyte-derived dendritic cells

Human metapneumovirus (hMPV) is a leading cause of lower respiratory infection in young children, the elderly and immunocompromised patients. Repeated hMPV infections occur throughout life. However, immune evasion mechanisms of hMPV infection are largely unknown. Recently, our group has demonstrated that hMPV M2-2 protein, an important virulence factor, contributes to immune evasion in airway epithelial cells by targeting the mitochondrial antiviral-signaling protein (MAVS). Whether M2-2 regulates the innate immunity in human dendritic cells (DC), an important family of immune cells controlling antigen presenting, is currently unknown. We found that human DC infected with a virus lacking M2-2 protein expression (rhMPV-ΔM2-2) produced higher levels of cytokines, chemokines and IFNs, compared to cells infected with wild-type virus (rhMPV-WT), suggesting that M2-2 protein inhibits innate immunity in human DC. In parallel, we found that myeloid differentiation primary response gene 88 (MyD88), an essential adaptor for Toll-like receptors (TLRs), plays a critical role in inducing immune response of human DC, as downregulation of MyD88 by siRNA blocked the induction of immune regulatory molecules by hMPV. Since M2-2 is a cytoplasmic protein, we investigated whether M2-2 interferes with MyD88-mediated antiviral signaling. We found that indeed M2-2 protein associated with MyD88 and inhibited MyD88-dependent gene transcription. In this study, we also identified the domains of M2-2 responsible for its immune inhibitory function in human DC. In summary, our results demonstrate that M2-2 contributes to hMPV immune evasion by inhibiting MyD88-dependent cellular responses in human DC.

Dendritic-cell-based therapeutic cancer vaccines

The past decade has seen tremendous developments in novel cancer therapies through the targeting of tumor-cell-intrinsic pathways whose activity is linked to genetic alterations and the targeting of tumor-cell-extrinsic factors, such as growth factors. Furthermore, immunotherapies are entering the clinic at an unprecedented speed after the demonstration that T cells can efficiently reject tumors and that their antitumor activity can be enhanced with antibodies against immune-regulatory molecules (checkpoint blockade). Current immunotherapy strategies include monoclonal antibodies against tumor cells or immune-regulatory molecules, cell-based therapies such as adoptive transfer of ex-vivo-activated T cells and natural killer cells, and cancer vaccines. Herein, we discuss the immunological basis for therapeutic cancer vaccines and how the current understanding of dendritic cell and T cell biology might enable the development of next-generation curative therapies for individuals with cancer.