MyD88-dependent SHIP1 regulates proinflammatory signaling pathways in dendritic cells after monophosphoryl lipid A stimulation of TLR4

Monosaccharide-Based Synthetic TLR4 Agonist Enhances Vaccine Efficacy against Pseudomonas aeruginosa Challenge

Vaccine adjuvants are critical to improve the immunogenicity, efficacy, and durability of vaccines; however, their development has lagged behind that of vaccine antigens. Monophosphoryl lipid A (MPLA), a clinically approved adjuvant that stimulates Toll-like receptor 4 (TLR4), faces manufacturing challenges due to its complex and long synthesis. With the aim of simplifying the structure of MPLA while retaining its biological activity, we developed monosaccharide-based molecules FP18 and FP20Rha that activate TLR4 signaling. Both TLR4 agonists induced robust antibody activity against the model antigen, ovalbumin. Here, we report the potential of these TLR4 agonists to enhance the protective efficacy of the well-characterized OprF antigen against P. aeruginosa infection. OprF adjuvanted with FP18 showed reduced bacterial loads in lungs and spleens, relative to antigen alone in an acute P. aeruginosa pneumonia model. FP18-adjuvanted OprF also enhanced the production of anti-OprF antibodies and stimulated IFNγ and TNF in CD4+ T cells, suggesting a Th1-skewed cellular immune response. These adjuvants have promise for accelerating the development of effective vaccines against P. aeruginosa and other infectious diseases.

SHIP-1 Differentially Regulates IgE-Induced IL-10 and Antiviral Responses in Human Monocytes

IgE-mediated stimulation of monocytes regulates multiple cellular functions including cellular maturation, cytokine release, antiviral responses, and T-cell differentiation. Expression of the high-affinity IgE receptor, FcεRI, is closely linked to serum IgE levels and atopic disease. The signaling molecules regulating FcεRI effector functions have been well studied in mast cells and basophils; however, less is known about the signaling and regulatory mechanisms in monocytes. This study sought to identify regulators of IgE-mediated cytokine release in human monocytes. SHIP-1 was identified as a negative regulator of IgE-induced IL-10 production. It was also determined that IgE-mediated stimulation and SHIP-1 inhibition decreased antiviral IP-10 production after liposomal poly(I:C) stimulation, indicating differential regulation by SHIP-1 in IgE-driven and antiviral response pathways. SHIP-1 and NF-κB were activated following IgE-mediated stimulation of monocytes, and NF-κB activation was related to both SHIP-1 and FcεRIα cellular expression levels. To our knowledge, this is the first study to identify a role for SHIP-1 in regulating IgE-mediated and antiviral responses in human monocytes. Given the importance of monocytes in inflammation and immune responses, a better understanding of the signaling and regulatory mechanisms downstream of the FcεRI receptor could lead to new therapeutic targets in allergic disease.

Microglial lipid phosphatase SHIP1 limits complement-mediated synaptic pruning in the healthy developing hippocampus

The gene inositol polyphosphate-5-phosphatase D (INPP5D), which encodes the lipid phosphatase SH2-containing inositol polyphosphate 5-phosphatase 1 (SHIP1), is associated with the risk of Alzheimer's disease (AD). How it influences microglial function and brain physiology is unclear. Here, we showed that SHIP1 was enriched in early stages of healthy brain development. By combining in vivo loss-of-function approaches and proteomics, we discovered that mice conditionally lacking microglial SHIP1 displayed increased complement and synapse loss in the early postnatal brain. SHIP1-deficient microglia showed altered transcriptional signatures and abnormal synaptic pruning that was dependent on the complement system. Mice exhibited cognitive defects in adulthood only when microglial SHIP1 was depleted early postnatally but not at later stages. Induced pluripotent stem cell (iPSC)-derived microglia lacking SHIP1 also showed increased engulfment of synaptic structures. These findings suggest that SHIP1 is essential for proper microglia-mediated synapse remodeling in the healthy developing brain. Disrupting this process has lasting behavioral effects and may be linked to vulnerability to neurodegeneration.

SHIP1 and its role for innate immune regulation-Novel targets for immunotherapy

Phosphoinositide-3-kinase/AKT (PI3K/AKT) signaling plays key roles in the regulation of cellular activity in both health and disease. In immune cells, this PI3K/AKT pathway is critically regulated by the phosphoinositide phosphatase SHIP1, which has been reported to modulate the function of most immune subsets. In this review, we summarize our current knowledge of SHIP1 with a focus on innate immune cells, where we reflect on the most pertinent aspects described in the current literature. We also present several small-molecule agonists and antagonists of SHIP1 developed over the last two decades, which have led to improved outcomes in several preclinical models of disease. We outline these promising findings and put them in relation to human diseases with unmet medical needs, where we discuss the most attractive targets for immune therapies based on SHIP1 modulation.

Astragalus Saponins, Astragaloside VII and Newly Synthesized Derivatives, Induce Dendritic Cell Maturation and T Cell Activation

Astragaloside VII (AST VII), a triterpenic saponin isolated from Astragalus species, shows promise as a vaccine adjuvant, as it supported a balanced Th1/Th2 immune response in previous in vivo studies. However, the underlying mechanisms of its adjuvant activity have not been defined. Here, we investigated the impact of AST VII and its newly synthesized semi-synthetic analogs on human whole blood cells, as well as on mouse bone marrow-derived dendritic cells (BMDCs). Cells were stimulated with AST VII and its derivatives in the presence or absence of LPS or PMA/ionomycin and the secretion of cytokines and the expression of activation markers were analyzed using ELISA and flow cytometry, respectively. AST VII and its analogs increased the production of IL-1β in PMA/ionomycin-stimulated human whole blood cells. In LPS-treated mouse BMDCs, AST VII increased the production of IL-1β and IL-12, and the expression of MHC II, CD86, and CD80. In mixed leukocyte reaction, AST VII and derivatives increased the expression of the activation marker CD44 on mouse CD4+ and CD8+ T cells. In conclusion, AST VII and its derivatives strengthen pro-inflammatory responses and support dendritic cell maturation and T cell activation in vitro. Our results provide insights into the mechanisms of the adjuvant activities of AST VII and its analogs, which will be instrumental to improve their utility as a vaccine adjuvant.

Toll-like receptors change morphine-induced antinociception, tolerance and dependence: Studies using male and female TLR and signalling gene KO mice

Toll-like receptors (TLR) have been proposed as a site of action that alters opioid pharmacodynamics. However, a comprehensive assessment of acute opioid antinociception, tolerance and withdrawal behaviours in genetic null mutant strains with altered innate immune signalling has not been performed. Nor has the impact of genetic deletion of TLR2/4 on high-affinity opioid receptor binding. Here we show that diminished TLR signalling potentiates acute morphine antinociception equally in male and female mice. However, only male TIR8 null mutant mice showed reduced morphine analgesia. Analgesic tolerance was prevented in TLR2 and TLR4 null mutants, but not MyD88 animals. Withdrawal behaviours were only protected in TLR2^-/- mice. In silico docking simulations revealed opioid ligands bound preferentially to the LPS binding pocket of MD-2 rather than TLR4. There was no binding of [³H](-)-naloxone or [³H]diprenorphine to TLR4 in the concentrations explored. These data confirm that opioids have high efficacy activity at innate immune pattern recognition binding sites but do not bind to TLR4 and identify critical pathway and sex-specific effects of the complex innate immune signalling contributions to opioid pharmacodynamics. These data further support the behavioural importance of the TLR-opioid interaction but fail to demonstrate direct evidence for high-affinity binding of the TLR4 signalling complex to ligands.

Mechanisms of TLR4-Mediated Autophagy and Nitroxidative Stress

Pathogenic infections have badly affected public health and the development of the breeding industry. Billions of dollars are spent every year fighting against these pathogens. The immune cells of a host produce reactive oxygen species and reactive nitrogen species which promote the clearance of these microbes. In addition, autophagy, which is considered an effective method to promote the destruction of pathogens, is involved in pathological processes. As research continues, the interplay between autophagy and nitroxidative stress has become apparent. Autophagy is always intertwined with nitroxidative stress. Autophagy regulates nitroxidative stress to maintain homeostasis within an appropriate range. Intracellular oxidation, in turn, is a strong inducer of autophagy. Toll-like receptor 4 (TLR4) is a pattern recognition receptor mainly involved in the regulation of inflammation during infectious diseases. Several studies have suggested that TLR4 is also a key regulator of autophagy and nitroxidative stress. In this review, we describe the role of TLR4 in autophagy and oxidation, and focus on its function in influencing autophagy-nitroxidative stress interactions.

Cell-intrinsic and -extrinsic roles of miRNAs in regulating T cell immunity

T cells are crucial to generate an effective response against numerous invading microbial pathogens and play a pivotal role in tumor surveillance and elimination. However, unwanted T cell activation can also lead to deleterious immune-mediated inflammation and tissue damage. To ensure that an optimal T cell response can be established, each step, beginning from T cell development in the thymus to their activation and function in the periphery, is tightly regulated by many transcription factors and epigenetic regulators including microRNAs (miRNAs). Here, we first summarize recent progress in identifying major immune regulatory miRNAs in controlling the differentiation and function of distinct T cell subsets. Moreover, as emerging evidence has demonstrated that miRNAs can impact T cell immunity through targeting both immune- and non-immune cell populations that T cells closely interact with, the T cell-extrinsic role of miRNAs in regulating different aspects of T cell biology is also addressed. Finally, we discuss the complex nature of miRNA-mediated control of T cell immunity and highlight important questions that remain to be further investigated.

MicroRNA-155: Regulation of Immune Cells in Sepsis

MicroRNAs are small noncoding RNAs which regulate gene expression at the posttranscriptional level. miR-155 is encoded by the miR-155 host gene (miR155HG), also known as the noncoding B cell integration cluster (BIC). MicroRNAs are widely expressed in various hematopoietic cells and are involved in regulating the immune system. In this review, we summarized how miR-155 modulates specific immune cells and the regulatory role of miR-155 in sepsis. miR-155 is expressed by different populations of innate and adaptive immune cells and is involved in the regulation of development, proliferation, and function in these cells. Sepsis is associated with uncontrollable inflammatory responses, accompanied by unacceptably high mortality. Due to the inadequacy of diagnostic markers as well as treatment strategies, treating sepsis can be a huge challenge. So far, a large number of experiments have shown that the expression of miR-155 is increased at an early stage of sepsis and that this increase is positively correlated with disease progression and severity. In addition, by blocking the proinflammatory effects of miR-155, it can effectively improve sepsis-related organ injury, providing novel insights to identify potential biomarkers and therapeutic targets for sepsis. However, since most of the current research is limited to animal experiments, further clinical research is required to determine the function of miR-155 and its mechanism related to sepsis.

Adenosine Receptor Signaling Targets Both PKA and Epac Pathways to Polarize Dendritic Cells to a Suppressive Phenotype

Extracellular adenosine accumulates in tumors and causes suppression of immune cells. Suppressive adenosine signaling is achieved through adenosine A2A and A2B receptors, which are Gs coupled, and their activation elevates cAMP levels. Gs-coupled GPCR signaling causes cAMP accumulation, which plays an anti-inflammatory role in immune cells. Protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac) are two intracellular receptors of cAMP. In this study we showed that adenosine receptor signaling polarizes activated murine dendritic cells (DCs) into a tumor-promoting suppressive phenotype. Adenosine receptor signaling activates cAMP pathway and upregulates the negative regulators of NF-κB but does not influence phosphorylation of immediate inflammatory signaling molecules downstream of TLR signaling. Pharmacologic activation of both PKA and Epac pathways by specific cAMP analogues phenocopied the effects of adenosine signaling on murine DCs, such as suppression of proinflammatory cytokines, elevation of anti-inflammatory IL-10, increased expression of regulators of NF-κB pathway, and finally suppression of T cell activation. Inhibition of effector cytokine, IL-12p40 production, and increased immunosuppressive IL-10 production by adenosine signaling is significantly reversed only when both PKA and Epac pathways were inhibited together. Adenosine signaling increased IL-10 secretion while decreasing IL-12p40 secretion in human monocyte-derived DCs. Stimulation of both PKA and Epac pathways also caused combinatorial effects in regulation of IL-12p40 secretion in human monocyte-derived DCs. Interestingly, PKA signaling alone caused similar increase in IL-10 secretion to that of adenosine signaling in human monocyte-derived DCs. Our data suggest adenosine/cAMP signaling targets both PKA/Epac pathways to fully differentiate DCs into a suppressive phenotype.

Stroma: the forgotten cells of innate immune memory

All organisms are exposed constantly to a variety of infectious and injurious stimuli. These induce inflammatory responses tailored to the threat posed. While the innate immune system is the front line of response to each stimulant, it has been considered traditionally to lack memory, acting in a generic fashion until the adaptive immune arm can take over. This outmoded simplification of the roles of innate and acquired arms of the immune system has been challenged by evidence of myeloid cells altering their response to subsequent encounters based on earlier exposure. This concept of 'innate immune memory' has been known for nearly a century, and is accepted among myeloid biologists. In recent years other innate immune cells, such as natural killer cells, have been shown to display memory, suggesting that innate immune memory is a trait common to several cell types. During the last 30 years, evidence has slowly accumulated in favour of not only haematopoietic cells, but also stromal cells, being imbued with memory following inflammatory episodes. A recent publication showing this also to be true in epithelial cells suggests innate immune memory to be widespread, if under-appreciated, in non-haematopoietic cells. In this review, we will examine the evidence supporting the existence of innate immune memory in stromal cells. We will also discuss the ramifications of memory in long-lived tissue-resident cells. Finally, we will pose questions we feel to be important in the understanding of these forgotten cells in the field of innate memory.

Specific features of human monocytes activation by monophosphoryl lipid A

We deciphered the mechanisms of production of pro- and anti-inflammatory cytokines by adherent human blood mononuclear cells (PBMC) activated by lipopolysaccharide (LPS) or monophosphoryl lipid A (MPLA). Both LPS and MPLA induced tumor necrosis factor (TNF) production proved to be dependent on the production of interleukin-1β (IL-1β). Of note, MPLA induced IL-1β release in human adherent PBMCs whereas MPLA was previously reported to not induce this cytokine in murine cells. Both LPS and MPLA stimulatory effects were inhibited by Toll-like receptor-4 (TLR4) antagonists. Only monocytes activation by LPS was dependent on CD14. Other differences were noticed between LPS and MPLA. Among the different donors, a strong correlation existed in terms of the levels of TNF induced by different LPSs. In contrast, there was no correlation between the TNF productions induced by LPS and those induced by MPLA. However, there was a strong correlation when IL-6 production was analyzed. Blocking actin polymerization and internalization of the agonists inhibited MPLA induced TNF production while the effect on LPS induced TNF production depended on the donors (i.e. high TNF producers versus low TNF producers). Finally, conventional LPS, tolerized adherent PBMCs to TLR2 agonists, while MPLA primed cells to further challenge with TLR2 agonists.

An NF-κB-microRNA regulatory network tunes macrophage inflammatory responses

The innate inflammatory response must be tightly regulated to ensure effective immune protection. NF-κB is a key mediator of the inflammatory response, and its dysregulation has been associated with immune-related malignancies. Here, we describe a miRNA-based regulatory network that enables precise NF-κB activity in mouse macrophages. Elevated miR-155 expression potentiates NF-κB activity in miR-146a-deficient mice, leading to both an overactive acute inflammatory response and chronic inflammation. Enforced miR-155 expression overrides miR-146a-mediated repression of NF-κB activation, thus emphasizing the dominant function of miR-155 in promoting inflammation. Moreover, miR-155-deficient macrophages exhibit a suboptimal inflammatory response when exposed to low levels of inflammatory stimuli. Importantly, we demonstrate a temporal asymmetry between miR-155 and miR-146a expression during macrophage activation, which creates a combined positive and negative feedback network controlling NF-κB activity. This miRNA-based regulatory network enables a robust yet time-limited inflammatory response essential for functional immunity.

MicroRNAs (miR) are important regulators of gene transcription, with miR-155 and miR-146a both implicated in macrophage activation. Here the authors show that NF-κB signalling, miR-155 and miR-146a form a complex network of cross-regulations to control gene transcription in macrophages for modulating inflammatory responses.

MicroRNA-155 Mediates Augmented CD40 Expression in Bone Marrow Derived Plasmacytoid Dendritic Cells in Symptomatic Lupus-Prone NZB/W F1 Mice

Systemic lupus erythematosus (SLE) is a chronic multi-organ autoimmune disease characterized by hyperactivated immune responses to self-antigens and persistent systemic inflammation. Previously, we reported abnormalities in circulating and bone marrow (BM)-derived plasmacytoid dendritic cells (pDCs) from SLE patients. Here, we aim to seek for potential regulators that mediate functional aberrations of pDCs in SLE. BM-derived pDCs from NZB/W F1 mice before and after the disease onset were compared for toll-like receptor (TLR) induced responses and microRNA profile changes. While pDCs derived from symptomatic mice were phenotypically comparable to pre-symptomatic ones, functionally they exhibited hypersensitivity to TLR7 but not TLR9 stimulation, as represented by the elevated upregulation of CD40, CD86 and MHC class II molecules upon R837 stimulation. Upregulated induction of miR-155 in symptomatic pDCs following TLR7 stimulation was observed. Transfection of miR-155 mimics in pre-symptomatic pDCs induced an augmented expression of Cd40, which is consistent with the increased CD40 expression in symptomatic pDCs. Overall, our results provide evidence for miR-155-mediated regulation in pDC functional abnormalities in SLE. Findings from this study contribute to a better understanding of SLE pathogenesis and ignite future interests in evaluating the molecular regulation in autoimmunity.

The cholesterol transporter ABCG1 links cholesterol homeostasis and tumour immunity

ATP-binding Cassette Transporter G1 (ABCG1) promotes cholesterol efflux from cells and regulates intracellular cholesterol homeostasis. Here, we demonstrate a role of ABCG1 as a mediator of tumor immunity. Abcg1^−/− mice have dramatically suppressed subcutaneous MB49-bladder carcinoma and B16-melanoma growth and prolonged survival. We show that reduced tumor growth in Abcg1^−/− mice is myeloid cell-intrinsic and is associated with a phenotypic shift of the macrophages from a tumor-promoting M2 to a tumor-fighting M1 within the tumor. Abcg1^−/− macrophages exhibit an intrinsic bias toward M1 polarization with increased NF-κB activation and direct cytotoxicity for tumor cells in vitro. Overall, our study demonstrates that absence of ABCG1 inhibits tumor growth through modulation of macrophage function within the tumor and illustrates a link between cholesterol homeostasis and cancer.

Genome-wide immunity studies in the rabbit: transcriptome variations in peripheral blood mononuclear cells after in vitro stimulation by LPS or PMA-Ionomycin

Background

Our purpose was to obtain genome-wide expression data for the rabbit species on the responses of peripheral blood mononuclear cells (PBMCs) after in vitro stimulation by lipopolysaccharide (LPS) or phorbol myristate acetate (PMA) and ionomycin. This transcriptome profiling was carried out using microarrays enriched with immunity-related genes, and annotated with the most recent data available for the rabbit genome.

Results

The LPS affected 15 to 20 times fewer genes than PMA-Ionomycin after both 4 hours (T4) and 24 hours (T24), of in vitro stimulation, in comparison with mock-stimulated PBMCs. LPS induced an inflammatory response as shown by a significant up-regulation of IL12A and CXCL11 at T4, followed by an increased transcription of IL6, IL1B, IL1A, IL36, IL37, TNF, and CCL4 at T24. Surprisingly, we could not find an up-regulation of IL8 either at T4 or at T24, and detected a down-regulation of DEFB1 and BPI at T24. A concerted up-regulation of SAA1, S100A12 and F3 was found upon stimulation by LPS.

PMA-Ionomycin induced a very early expression of Th1, Th2, Treg, and Th17 responses by PBMCs at T4. The Th1 response increased at T24 as shown by the increase of the transcription of IFNG and by contrast to other cytokines which significantly decreased from T4 to T24 (IL2, IL4, IL10, IL13, IL17A, CD69) by comparison to mock-stimulation. The granulocyte-macrophage colony-stimulating factor (CSF2) was by far the most over-expressed gene at both T4 and T24 by comparison to mock-stimulated cells, confirming a major impact of PMA-Ionomycin on cell growth and proliferation. A significant down-regulation of IL16 was observed at T4 and T24, in agreement with a role of IL16 in PBMC apoptosis.

Conclusions

We report new data on the responses of PBMCs to LPS and PMA-Ionomycin in the rabbit species, thus enlarging the set of mammalian species for which such reports exist. The availability of the rabbit genome assembly together with high throughput genomic tools should pave the way for more intense genomic studies for this species, which is known to be a very relevant biomedical model in immunology and physiology.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1218-9) contains supplementary material, which is available to authorized users.

Monophosphoryl lipid A inhibits the cytokine response of endothelial cells challenged with LPS

Monophosphoryl lipid A (MPLA) is a TLR4 agonist that is used as an immunomodulator in human vaccines; additionally, it has been shown to be protective in models of sepsis. As endothelial cells regulate inflammation, we hypothesized that MPLA would decrease activation of human umbilical vein endothelial cells (HUVECs) to LPS. We studied HUVECs challenged with LPS (100 ng/ml), MPLA (0.001-100 µg/ml) or a combination. Secretion of IL-6, RANTES (CCL5) and IP-10 (CXCL10) were assessed by ELISA. Activation of MAPK phosphorylation and cytokine transcription were assessed by Western blot analysis and PCR, respectively. MPLA alone was a weak stimulator of myeloid differentiation primary response protein 88-dependent IL-6 and did not induce TIR-domain-containing adapter-inducing IFN-β (TRIF)-dependent chemokine responses. MPLA significantly reduced LPS-mediated IL-6 production. This inhibitory effect was also conferred for the TRIF-dependent chemokines RANTES and IP-10. Inhibition of LPS-mediated activation by MPLA was associated with reduced p38 phosphorylation and mRNAs encoding inflammatory cytokines. MPLA inhibition of LPS signaling appeared to be at the level of the TLR4 receptor, acting as a receptor antagonist with weak agonistic properties. This study provides evidence of a novel mechanism for the inhibitory effect of MPLA on LPS-induced endothelial activation.

Myeloid expression of adenosine A2A receptor suppresses T and NK cell responses in the solid tumor microenvironment

High concentrations of adenosine in tumor microenvironments inhibit antitumor cytotoxic lymphocyte responses. Although T cells express inhibitory adenosine A2A receptors (A2AR) that suppress their activation and inhibit immune killing of tumors, a role for myeloid cell A2ARs in suppressing the immune response to tumors has yet to be investigated. In this study, we show that the growth of transplanted syngeneic B16F10 melanoma or Lewis lung carcinoma cells is slowed in Adora2a(f/f)-LysMCre(+/-) mice, which selectively lack myeloid A2ARs. Reduced melanoma growth is associated with significant increases in MHCII and IL12 expression in tumor-associated macrophages and with >90% reductions in IL10 expression in tumor-associated macrophages, dendritic cells (DC), and Ly6C(+) or Ly6G(+) myeloid-derived suppressor cells (MDSC). Myeloid deletion of A2ARs significantly increases CD44 expression on tumor-associated T cells and natural killer (NK) cells. Depletion of CD8(+) T cells or NK cells in tumor-bearing mice indicates that both cell types initially contribute to slowing melanoma growth in mice lacking myeloid A2A receptors, but tumor suppression mediated by CD8(+) T cells is more persistent. Myeloid-selective A2AR deletion significantly reduces lung metastasis of melanomas that express luciferase (for in vivo tracking) and ovalbumin (as a model antigen). Reduced metastasis is associated with increased numbers and activation of NK cells and antigen-specific CD8(+) T cells in lung infiltrates. Overall, the findings indicate that myeloid cell A2ARs have direct myelosuppressive effects that indirectly contribute to the suppression of T cells and NK cells in primary and metastatic tumor microenvironments. The results indicate that tumor-associated myeloid cells, including macrophages, DCs, and MDSCs all express immunosuppressive A2ARs that are potential targets of adenosine receptor blockers to enhance immune killing of tumors.

TLR4-mediated expression of Mac-1 in monocytes plays a pivotal role in monocyte adhesion to vascular endothelium

Toll-like receptor 4 (TLR4) is known to mediate monocyte adhesion to endothelial cells, however, its role on the expression of monocyte adhesion molecules is unclear. In the present study, we investigated the role of TLR4 on the expression of monocyte adhesion molecules, and determined the functional role of TLR4-induced adhesion molecules on monocyte adhesion to endothelial cells. When THP-1 monocytes were stimulated with Kdo2-Lipid A (KLA), a specific TLR4 agonist, Mac-1 expression was markedly increased in association with an increased adhesion of monocytes to endothelial cells. These were attenuated by anti-Mac-1 antibody, suggesting a functional role of TLR4-induced Mac-1 on monocyte adhesion to endothelial cells. In monocytes treated with MK886, a 5-lipoxygenase (LO) inhibitor, both Mac-1 expression and monocyte adhesion to endothelial cells induced by KLA were markedly attenuated. Moreover, KLA increased the expression of mRNA and protein of 5-LO, suggesting a pivotal role of 5-LO on these processes. In in vivo studies, KLA increased monocyte adhesion to aortic endothelium of wild-type (WT) mice, which was attenuated in WT mice treated with anti-Mac-1 antibody as well as in TLR4-deficient mice. Taken together, TLR4-mediated expression of Mac-1 in monocytes plays a pivotal role on monocyte adhesion to vascular endothelium, leading to increased foam cell formation in the development of atherosclerosis.

Adjuvants containing natural and synthetic Toll-like receptor 4 ligands

The last decade has seen an increased focus on the development of adjuvants for vaccines, and several novel adjuvants are now in licensed products or in late-stage clinical development. These advancements have been aided by the discovery of receptors and signaling pathways of the innate immune system and an increased understanding of how these innate responses influence the adaptive immune response. Successful vaccine development relies on knowledge of which adjuvants to use and the proper formulation of adjuvants and antigens to achieve safe, stable and immunogenic vaccines. In this review, the authors focus on the current use of natural and synthetic lipopolysaccharide analogues that retain their adjuvant properties with reduced toxicity compared with the parent compound for use in emerging vaccines. The authors review how these compounds initiate signal transduction through Toll-like receptor 4, insights from structure-function studies and how formulation parameters can influence their effectiveness as vaccine adjuvants.

In vivo and in vitro characterization of the immune stimulating activity of the Neisserial porin PorB

Vaccines play a vital role in modern medicine. The development of novel vaccines for emerging and resistant pathogens has been aided in recent years by the use of novel adjuvants in subunit vaccines. A deeper understanding of the molecular pathways behind adjuvanticity is required to better select immunostimulatory molecules for use in individual vaccines. To this end, we have undertaken a study of the essential signaling pathways involved in the innate and adaptive immune responses to the Neisseria meningitidis outer membrane protein Porin B (PorB). We have previously demonstrated that PorB is an agonist of Toll-Like Receptor 2 (TLR2) and acts as an adjuvant in vaccines for protein, carbohydrate and lipopolysaccharide antigens using murine models. Here we demonstrate NFκB translocation following stimulation with PorB only occurs in the presence of TLR2. IL-6 and TNF-α secretion was shown to be MAPK dependent. Surface expression of activation markers on macrophages, including CD40, CD69, and CD86, was increased following PorB stimulation in vitro. Interestingly, some upregulation of CD54 and CD69 was still observed in macrophages obtained from TLR2 KO mice, indicating a possible non-TLR2 mediated activation pathway induced by PorB. In a murine vaccination model, using ovalbumin as the antigen and PorB as the adjuvant, a decreased antigen-specific IgG production was observed in TLR2 KO mice; adjuvant-dependent increased IgG production was entirely ablated in MyD88 KO mice. These observations demonstrate the importance of the above pathways to the adjuvant activity of PorB. The potential TLR2 independent effect is currently being explored.

Extracellular adenosine regulates naive T cell development and peripheral maintenance

Adenosine receptor signaling inhibits TCR-induced activation of PI3K–Akt to reduce IL-7Rα expression on T cells, thereby regulating development and maintenance of naive T cells in the periphery.

Adenosine produced as a byproduct of metabolic activity is present in all tissues and produces dose-dependent suppression of TCR signaling. Naive T cell maintenance depends on inhibition of TCR signals by environmental sensors, which are yet to be fully defined. We produced mice with a floxed adenosine A_2A receptor (A_2AR) gene, Adora2a, and show that either global A_2AR deletion or cre-mediated T cell deletion elicits a decline in the number of naive but not memory T cells. A_2AR signaling maintains naive T cells in a quiescent state by inhibiting TCR-induced activation of the phosphatidylinositide 3-kinase (PI3K)–AKT pathway, thereby reducing IL-7Rα down-regulation and naive T cell apoptosis. Patterns of IL-7Rα expression on T cells in chimeric mice reconstituted with Adora2a^+/+ and Adora2a^−/− bone marrow cells suggest that decreased IL-7Rα in naive T cells is a cell-intrinsic consequence of Adora2a deletion. In addition, A_2AR expression increases in early thymic T cell development and contributes to progression of double-negative thymic precursors to single-positive thymocytes with increased IL-7Rα expression. Therefore, A_2AR signaling regulates T cell development and maintenance to sustain normal numbers of naive T cells in the periphery.

Characterization of AQX-1125, a small-molecule SHIP1 activator: Part 2. Efficacy studies in allergic and pulmonary inflammation models in vivo

BACKGROUND

The efficacy of AQX-1125, a small-molecule SH2-containing inositol-5'-phosphatase 1 (SHIP1) activator and clinical development candidate, is investigated in rodent models of inflammation.

EXPERIMENTAL APPROACH

AQX-1125 was administered orally in a mouse model of passive cutaneous anaphylaxis (PCA) and a number of rodent models of respiratory inflammation including: cigarette smoke, LPS and ovalbumin (OVA)-mediated airway inflammation. SHIP1 dependency of the AQX-1125 mechanism of action was investigated by comparing the efficacy in wild-type and SHIP1-deficient mice subjected to an intrapulmonary LPS challenge.

RESULTS

AQX-1125 exerted anti-inflammatory effects in all of the models studied. AQX-1125 decreased the PCA response at all doses tested. Using bronchoalveolar lavage (BAL) cell counts as an end point, oral or aerosolized AQX-1125 dose dependently decreased the LPS-mediated pulmonary neutrophilic infiltration at 3-30 mg kg⁻¹ and 0.15-15 μg kg⁻¹ respectively. AQX-1125 suppressed the OVA-mediated airway inflammation at 0.1-10 mg kg⁻¹. In the smoke-induced airway inflammation model, AQX-1125 was tested at 30 mg kg⁻¹ and significantly reduced the neutrophil infiltration of the BAL fluid. AQX-1125 (10 mg kg⁻¹) decreased LPS-induced pulmonary neutrophilia in wild-type mice but not in SHIP1-deficient mice.

CONCLUSIONS

The SHIP1 activator, AQX-1125, suppresses leukocyte accumulation and inflammatory mediator release in rodent models of pulmonary inflammation and allergy. As shown in the mouse model of LPS-induced lung inflammation, the efficacy of the compound is dependent on the presence of SHIP1. Pharmacological SHIP1 activation may have clinical potential for the treatment of pulmonary inflammatory diseases.

Inefficient TLR4/MD-2 heterotetramerization by monophosphoryl lipid A

Synthetic forms of E. coli monophosphoryl lipid A (sMLA) weakly activate the MyD88 (myeloid differentiation primary response protein) branch of the bifurcated TLR4 (Toll-like receptor 4) signaling pathway, in contrast to diphosphoryl lipid A (sDLA), which is a strong activator of both branches of TLR4. sMLA's weak MyD88 signaling activity is apparent downstream of TLR4/MyD88 signaling as we show that sMLA, unlike sDLA, is unable to efficiently recruit the TNF receptor-associated factor 6 (TRAF6) to the Interleukin-1 receptor-associated kinase 1 (IRAK1). This reduced recruitment of TRAF6 explains MLA's lower MAPK (Mitogen Activated Protein Kinase) and NF-κB activity. As further tests of sMLA's ability to activate TLR4/Myeloid differentiation factor 2 (MD-2), we used the antibody MTS510 as an indicator for TLR4/MD-2 heterotetramer formation. Staining patterns with this antibody indicated that sMLA does not effectively drive heterotetramerization of TLR4/MD-2 when compared to sDLA. However, a F126A mutant of MD-2, which allows lipid A binding but interferes with TLR4/MD-2 heterotetramerization, revealed that while sMLA is unable to efficiently form TLR4/MD-2 heterotetramers, it still needs heterotetramer formation for the full extent of signaling it is able to achieve. Monophosphoryl lipid A's weak ability to form TLR4/MD-2 heterotetramers was not restricted to synthetic E. coli type because cells exposed to a biological preparation of S. minnesota monophosphoryl lipid A (MPLA) also showed reduced TLR4/MD-2 heterotetramer formation. The low potency with which sMLA and MPLA drive heterotetramerization of TLR4/MD-2 contributes to their weak MyD88 signaling activities.

Inositol polyphosphate phosphatases in human disease

Phosphoinositide signalling molecules interact with a plethora of effector proteins to regulate cell proliferation and survival, vesicular trafficking, metabolism, actin dynamics and many other cellular functions. The generation of specific phosphoinositide species is achieved by the activity of phosphoinositide kinases and phosphatases, which phosphorylate and dephosphorylate, respectively, the inositol headgroup of phosphoinositide molecules. The phosphoinositide phosphatases can be classified as 3-, 4- and 5-phosphatases based on their specificity for dephosphorylating phosphates from specific positions on the inositol head group. The SAC phosphatases show less specificity for the position of the phosphate on the inositol ring. The phosphoinositide phosphatases regulate PI3K/Akt signalling, insulin signalling, endocytosis, vesicle trafficking, cell migration, proliferation and apoptosis. Mouse knockout models of several of the phosphoinositide phosphatases have revealed significant physiological roles for these enzymes, including the regulation of embryonic development, fertility, neurological function, the immune system and insulin sensitivity. Importantly, several phosphoinositide phosphatases have been directly associated with a range of human diseases. Genetic mutations in the 5-phosphatase INPP5E are causative of the ciliopathy syndromes Joubert and MORM, and mutations in the 5-phosphatase OCRL result in Lowe's syndrome and Dent 2 disease. Additionally, polymorphisms in the 5-phosphatase SHIP2 confer diabetes susceptibility in specific populations, whereas reduced protein expression of SHIP1 is reported in several human leukaemias. The 4-phosphatase, INPP4B, has recently been identified as a tumour suppressor in human breast and prostate cancer. Mutations in one SAC phosphatase, SAC3/FIG4, results in the degenerative neuropathy, Charcot-Marie-Tooth disease. Indeed, an understanding of the precise functions of phosphoinositide phosphatases is not only important in the context of normal human physiology, but to reveal the mechanisms by which these enzyme families are implicated in an increasing repertoire of human diseases.

Effects of Differences in Lipid A Structure on TLR4 Pro-Inflammatory Signaling and Inflammasome Activation

The vertebrate immune system exists in equilibrium with the microbial world. The innate immune system recognizes pathogen-associated molecular patterns via a family of Toll-like receptors (TLR) that activate cells upon detection of potential pathogens. Because some microbes benefit their hosts, mobilizing the appropriate response, and then controlling that response is critical in the maintenance of health. TLR4 recognizes the various forms of lipid A produced by Gram-negative bacteria. Depending on the structural form of the eliciting lipid A molecule, TLR4 responses range from a highly inflammatory endotoxic response involving inflammasome and other pro-inflammatory mediators, to an inhibitory, protective response. Mounting the correct response against an offending microbe is key to maintaining health when exposed to various bacterial species. Further study of lipid A variants may pave the way to understanding how TLR4 responses are generally able to avoid chronic inflammatory damage.

microRNAs in the regulation of dendritic cell functions in inflammation and atherosclerosis

Atherosclerosis has been established as a chronic inflammatory disease of the vessel wall. Among the mononuclear cell types recruited to the lesions, specialized dendritic cells (DCs) have gained increasing attention, and their secretory products and interactions shape the progression of atherosclerotic plaques. The regulation of DC functions by microRNAs (miRNAs) may thus be of primary importance in disease. We here systematically summarize the biogenesis and functions of miRNAs and provide an overview of miRNAs in DCs, their targets, and potential implications for atherosclerosis, with a particular focus on the best characterized miRNAs in DCs, namely, miR-155 and miR-146. MiRNA functions in DCs range from regulation of lipid uptake to cytokine production and T cell responses with a complex picture emerging, in which miRNAs cooperate or antagonize DC behavior, thereby promoting or counterbalancing inflammatory responses. As miRNAs regulate key functions of DCs known to control atherosclerotic vascular disease, their potential as a therapeutic target holds promise and should be attended to in future research.