Gasdermin D promotes hyperinflammation and immunopathology during severe influenza A virus infection.

Excessive inflammation and tissue damage during severe influenza A virus (IAV) infection can lead to the development of fatal pulmonary disease. Pyroptosis is a lytic and pro-inflammatory form of cell death executed by the pore-forming protein gasdermin D (GSDMD). In this study, we investigated a potential role for GSDMD in promoting the development of severe IAV disease. IAV infection resulted in cleavage of GSDMD in vivo and in vitro in lung epithelial cells. Mice genetically deficient in GSDMD (Gsdmd-/-) developed less severe IAV disease than wildtype mice and displayed improved survival outcomes. GSDMD deficiency significantly reduced neutrophil infiltration into the airways as well as the levels of pro-inflammatory cytokines TNF, IL-6, MCP-1, and IL-1α and neutrophil-attracting chemokines CXCL1 and CXCL2. In contrast, IL-1ß and IL-18 responses were not largely impacted by GSDMD deficiency. In addition, Gsdmd-/- mice displayed significantly improved influenza disease resistance with reduced viral burden and less severe pulmonary pathology, including decreased epithelial damage and cell death. These findings indicate a major role for GSDMD in promoting damaging inflammation and the development of severe IAV disease.

The histone deacetylase Hdac7 supports LPS-inducible glycolysis and Il-1ß production in murine macrophages via distinct mechanisms.

TLRs reprogram macrophage metabolism, enhancing glycolysis and promoting flux through the tricarboxylic acid cycle to enable histone acetylation and inflammatory gene expression. The histone deacetylase (HDAC) family of lysine deacetylases regulates both TLR-inducible glycolysis and inflammatory responses. Here, we show that the TLR4 agonist LPS, as well as agonists of other TLRs, rapidly increase enzymatic activity of the class IIa HDAC family (HDAC4, 5, 7, 9) in both primary human and murine macrophages. This response was abrogated in murine macrophages deficient in histone deacetylase 7 (Hdac7), highlighting a selective role for this specific lysine deacetylase during immediate macrophage activation. With the exception of the TLR3 agonist polyI:C, TLR-inducible activation of Hdac7 enzymatic activity required the MyD88 adaptor protein. The rapid glycolysis response, as assessed by extracellular acidification rate, was attenuated in Hdac7-deficient mouse macrophages responding to submaximal LPS concentrations. Surprisingly however, reconstitution of these cells with either wild-type or an enzyme-dead mutant of Hdac7 enhanced LPS-inducible glycolysis, whereas only the former promoted production of the inflammatory mediators Il-1ß and Ccl2. Thus, Hdac7 enzymatic activity is required for TLR-inducible production of specific inflammatory mediators, whereas it acts in an enzyme-independent fashion to reprogram metabolism in macrophages responding to submaximal LPS concentrations. Hdac7 is thus a bifurcation point for regulated metabolism and inflammatory responses in macrophages. Taken together with existing literature, our findings support a model in which submaximal and maximal activation of macrophages via TLR4 instruct glycolysis through distinct mechanisms, leading to divergent biological responses.

IL-18 (Interleukin-18) Produced by Renal Tubular Epithelial Cells Promotes Renal Inflammation and Injury During Deoxycorticosterone/Salt-Induced Hypertension in Mice.

IL-18 (interleukin-18) is elevated in hypertensive patients, but its contribution to high blood pressure and end-organ damage is unknown. We examined the role of IL-18 in the development of renal inflammation and injury in a mouse model of low-renin hypertension. Hypertension was induced in male C57BL6/J (WT) and IL-18−/− mice by uninephrectomy, deoxycorticosterone acetate (2.4 mg/d, s.c.) and 0.9% drinking saline (1K/DOCA/salt). Normotensive controls received uninephrectomy and placebo (1K/placebo). Blood pressure was measured via tail cuff or radiotelemetry. After 21 days, kidneys were harvested for (immuno)histochemical, quantitative-PCR and flow cytometric analyses of fibrosis, inflammation, and immune cell infiltration. 1K/DOCA/salt-treated WT mice developed hypertension, renal fibrosis, upregulation of proinflammatory genes, and accumulation of CD3+ T cells in the kidneys. They also displayed increased expression of IL-18 on tubular epithelial cells. IL-18−/− mice were profoundly protected from hypertension, renal fibrosis, and inflammation. Bone marrow transplantation between WT and IL-18−/− mice revealed that IL-18-deficiency in non-bone marrow-derived cells alone afforded equivalent protection against hypertension and renal injury as global IL-18 deficiency. IL-18 receptor subunits­interleukin-18 receptor 1 and IL-18R accessory protein­were upregulated in kidneys of 1K/DOCA/salt-treated WT mice and localized to T cells and tubular epithelial cells. T cells from kidneys of 1K/DOCA/salt-treated mice produced interferon-γ upon ex vivo stimulation with IL-18, whereas those from 1K/placebo mice did not. In conclusion, IL-18 production by tubular epithelial cells contributes to elevated blood pressure, renal inflammation, and fibrosis in 1K/DOCA/salt-treated mice, highlighting it as a promising therapeutic target for hypertension and kidney disease.

Circulating BiP/Grp78 is a novel prognostic marker for sepsis-mediated immune cell death.

Sepsis remains to be a major contributor to mortality in ICUs, and immune suppression caused by immune cell apoptosis determines the overall patient survival. However, diagnosis of sepsis-induced lymphopenia remains problematic with no accurate prognostic techniques or biomarkers for cell death available. Developing reliable prognostic tools for sepsis-mediated cell death is not only important for identifying patients at increased risk of immune suppression but also to monitor treatment progress of currently trialed immunotherapy strategies. We have previously shown an important role for endoplasmic reticulum stress (ER stress) in inducing sepsis-mediated cell death and here report on the identification of a secreted form of the ER chaperone BiP (immunoglobulin binding protein) as a novel circulating prognostic biomarker for immune cell death and ER stress during sepsis. Using biochemical purification and mass spectrometry coupled with an established in vitro sepsis cell death assay, we identified BiP/Grp78 as a factor secreted by lipopolysaccharide-activated macrophages that is capable of inducing cell death in target cells. Quantitative ELISA analysis showed significantly elevated levels of circulating BiP in mice undergoing polymicrobial sepsis, which was absent in Bim-/- mice that are protected from sepsis-induced lymphopenia. Using blood serum from human sepsis patients, we could detect a significant difference in levels of secreted BiP in sepsis patients compared to nonseptic controls, suggesting that secreted circulating BiP could indeed be used as a prognostic marker that is directly correlative to immune cell death during sepsis.

STAT3 serine phosphorylation is required for TLR4 metabolic reprogramming and IL-1ß expression.

Detection of microbial components such as lipopolysaccharide (LPS) by Toll-like receptor 4 (TLR4) on macrophages induces a robust pro-inflammatory response that is dependent on metabolic reprogramming. These innate metabolic changes have been compared to aerobic glycolysis in tumour cells. However, the mechanisms by which TLR4 activation leads to mitochondrial and glycolytic reprogramming are unknown. Here we show that TLR4 activation induces a signalling cascade recruiting TRAF6 and TBK-1, while TBK-1 phosphorylates STAT3 on S727. Using a genetically engineered mouse model incapable of undergoing STAT3 Ser727 phosphorylation, we show ex vivo and in vivo that STAT3 Ser727 phosphorylation is critical for LPS-induced glycolytic reprogramming, production of the central immune response metabolite succinate and inflammatory cytokine production in a model of LPS-induced inflammation. Our study identifies non-canonical STAT3 activation as the crucial signalling intermediary for TLR4-induced glycolysis, macrophage metabolic reprogramming and inflammation.

Novel mineralocorticoid receptor mechanisms regulate cardiac tissue inflammation in male mice.

MR activation in macrophages is critical for the development of cardiac inflammation and fibrosis. We previously showed that MR activation modifies macrophage pro-inflammatory signalling, changing the cardiac tissue response to injury via both direct gene transcription and JNK/AP-1 second messenger pathways. In contrast, MR-mediated renal electrolyte homeostasis is critically determined by DNA-binding-dependent processes. Hence, ascertaining the relative contribution of MR actions via DNA binding or alternative pathways on macrophage behaviour and cardiac inflammation may provide therapeutic opportunities which separate the cardioprotective effects of MR antagonists from their undesirable renal potassium-conserving effects. We developed new macrophage cell lines either lacking MR or harbouring a mutant MR incapable of DNA binding. Western blot analysis demonstrated that MR DNA binding is required for lipopolysaccharide (LPS), but not phorbol 12-myristate-13-acetate (PMA), induction of the MAPK/pJNK pathway in macrophages. Quantitative RTPCR for pro-inflammatory and pro-fibrotic targets revealed subsets of LPS- and PMA-induced genes that were either enhanced or repressed by the MR via actions that do not always require direct MR-DNA binding. Analysis of the MR target gene and profibrotic factor MMP12 identified promoter elements that are regulated by combined MR/MAPK/JNK signalling. Evaluation of cardiac tissue responses to an 8-day DOC/salt challenge in mice selectively lacking MR DNA-binding in macrophages demonstrated levels of inflammatory markers equivalent to WT, indicating non-DNA binding-dependent MR signalling in macrophages is sufficient for DOC/salt-induced tissue inflammation. Our data demonstrate that the MR regulates a macrophage pro-inflammatory phenotype and cardiac tissue inflammation, partially via pathways that do not require DNA binding.

The Single Nucleotide Polymorphism Mal-D96N Mice Provide New Insights into Functionality of Mal in TLR Immune Responses.

MyD88 adaptor-like (Mal) protein is the most polymorphic of the four key adaptor proteins involved in TLR signaling. TLRs play a critical role in the recognition and immune response to pathogens through activation of the prototypic inflammatory transcription factor NF-κB. The study of single nucleotide polymorphisms in TLRs, adaptors, and signaling mediators has provided key insights into the function of the corresponding genes but also into the susceptibility to infectious diseases in humans. In this study, we have analyzed the immune response of mice carrying the human Mal-D96N genetic variation that has previously been proposed to confer protection against septic shock. We have found that Mal-D96N macrophages display reduced cytokine expression in response to TLR4 and TLR2 ligand challenge. Mal-D96N macrophages also display reduced MAPK activation, NF-κB transactivation, and delayed NF-κB nuclear translocation, presumably via delayed kinetics of Mal interaction with MyD88 following LPS stimulation. Importantly, Mal-D96N genetic variation confers a physiological protective phenotype to in vivo models of LPS-, Escherichia coli-, and influenza A virus-induced hyperinflammatory disease in a gene dosage-dependent manner. Together, these results highlight the critical role Mal plays in regulating optimal TLR-induced inflammatory signaling pathways and suggest the potential therapeutic advantages of targeting the Mal D96 signaling nexus.

Pharmacological inhibition of the NLRP3 inflammasome reduces blood pressure, renal damage, and dysfunction in salt-sensitive hypertension.

AIMS: Renal inflammation, leading to fibrosis and impaired function is a major contributor to the development of hypertension. The NLRP3 inflammasome mediates inflammation in several chronic diseases by processing the cytokines pro-interleukin (IL)-1ß and pro-IL-18. In this study, we investigated whether MCC950, a recently-identified inhibitor of NLRP3 activity, reduces blood pressure (BP), renal inflammation, fibrosis and dysfunction in mice with established hypertension. METHODS AND RESULTS: C57BL6/J mice were made hypertensive by uninephrectomy and treatment with deoxycorticosterone acetate (2.4 mg/day, s.c.) and 0.9% NaCl in the drinking water (1K/DOCA/salt). Normotensive controls were uninephrectomized and received normal drinking water. Ten days later, mice were treated with MCC950 (10 mg/kg/day, s.c.) or vehicle (saline, s.c.) for up to 25 days. BP was monitored by tail-cuff or radiotelemetry; renal function by biochemical analysis of 24-h urine collections; and kidney inflammation/pathology was assessed by real-time PCR for inflammatory gene expression, flow cytometry for leucocyte influx, and Picrosirius red histology for collagen. Over the 10 days post-surgery, 1K/DOCA/salt-treated mice became hypertensive, developed impaired renal function, and displayed elevated renal levels of inflammatory markers, collagen and immune cells. MCC950 treatment from day 10 attenuated 1K/DOCA/salt-induced increases in renal expression of inflammasome subunits (NLRP3, ASC, pro-caspase-1) and inflammatory/injury markers (pro-IL-18, pro-IL-1ß, IL-17A, TNF-α, osteopontin, ICAM-1, VCAM-1, CCL2, vimentin), each by 25-40%. MCC950 reduced interstitial collagen and accumulation of certain leucocyte subsets in kidneys of 1K/DOCA/salt-treated mice, including CD206+ (M2-like) macrophages and interferon-gamma-producing T cells. Finally, MCC950 partially reversed 1K/DOCA/salt-induced elevations in BP, urine output, osmolality, [Na+], and albuminuria (each by 20-25%). None of the above parameters were altered by MCC950 in normotensive mice. CONCLUSION: MCC950 was effective at reducing BP and limiting renal inflammation, fibrosis and dysfunction in mice with established hypertension. This study provides proof-of-concept that pharmacological inhibition of the NLRP3 inflammasome is a viable anti-hypertensive strategy.

Membrane vesicles from Pseudomonas aeruginosa activate the noncanonical inflammasome through caspase-5 in human monocytes.

Outer membrane vesicles (OMVs) are constitutively produced by Gram-negative bacteria both in vivo and in vitro. These lipid-bound structures carry a range of immunogenic components derived from the parent cell, which are transported into host target cells and activate the innate immune system. Recent advances in the field have shed light on some of the multifaceted roles of OMVs in host-pathogen interactions. In this study, we investigated the ability of OMVs from two clinically important pathogens, Pseudomonas aeruginosa and Helicobacter pylori, to activate canonical and noncanonical inflammasomes. P. aeruginosa OMVs induced inflammasome activation in mouse macrophages, as evidenced by "speck" formation, as well as the cleavage and secretion of interleukin-1ß and caspase-1. These responses were independent of AIM2 and NLRC4 canonical inflammasomes, but dependent on the noncanonical caspase-11 pathway. Moreover, P. aeruginosa OMVs alone were able to activate the inflammasome in a TLR-dependent manner, without requiring an exogenous priming signal. In contrast, H. pylori OMVs were not able to induce inflammasome activation in macrophages. Using CRISPR/Cas9 knockout THP-1 cells lacking the human caspase-11 homologs, caspase-4 and -5,we demonstrated that caspase-5 but not caspase-4 is required for inflammasome activation by P. aeruginosa OMVs in human monocytes. In contrast, free P. aeruginosa lipopolysaccharide (LPS) transfected into cells induced inflammasome responses via caspase-4. This suggests that caspase-4 and caspase-5 differentially recognize LPS depending on its physical form or route of delivery into the cell. These findings have relevance to Gram-negative infections in humans and the use of OMVs as novel vaccines.

Macrophage migration inhibitory factor is required for NLRP3 inflammasome activation.

Macrophage migration inhibitory factor (MIF) exerts multiple effects on immune cells, as well as having functions outside the immune system. MIF can promote inflammation through the induction of other cytokines, including TNF, IL-6, and IL-1 family cytokines. Here, we show that inhibition of MIF regulates the release of IL-1α, IL-1ß, and IL-18, not by affecting transcription or translation of these cytokines, but via activation of the NLRP3 inflammasome. MIF is required for the interaction between NLRP3 and the intermediate filament protein vimentin, which is critical for NLRP3 activation. Further, we demonstrate that MIF interacts with NLRP3, indicating a role for MIF in inflammasome activation independent of its role as a cytokine. These data advance our understanding of how MIF regulates inflammation and identify it as a factor critical for NLRP3 inflammasome activation.

Solution structure of the TLR adaptor MAL/TIRAP reveals an intact BB loop and supports MAL Cys91 glutathionylation for signaling.

MyD88 adaptor-like (MAL) is a critical protein in innate immunity, involved in signaling by several Toll-like receptors (TLRs), key pattern recognition receptors (PRRs). Crystal structures of MAL revealed a nontypical Toll/interleukin-1 receptor (TIR)-domain fold stabilized by two disulfide bridges. We therefore undertook a structural and functional analysis of the role of reactive cysteine residues in the protein. Under reducing conditions, the cysteines do not form disulfides, but under oxidizing conditions they are highly amenable to modification. The solution structure of the reduced form of the MAL TIR domain, determined by NMR spectroscopy, reveals a remarkable structural rearrangement compared with the disulfide-bonded structure, which includes the relocation of a ß-strand and repositioning of the functionally important "BB-loop" region to a location more typical for TIR domains. Redox measurements by NMR further reveal that C91 has the highest redox potential of all cysteines in MAL. Indeed, mass spectrometry revealed that C91 undergoes glutathionylation in macrophages activated with the TLR4 ligand lipopolysaccharide (LPS). The C91A mutation limits MAL glutathionylation and acts as a dominant negative, blocking the interaction of MAL with its downstream target MyD88. The H92P mutation mimics the dominant-negative effects of the C91A mutation, presumably by preventing C91 glutathionylation. The MAL C91A and H92P mutants also display diminished degradation and interaction with interleukin-1 receptor-associated kinase 4 (IRAK4). We conclude that in the cell, MAL is not disulfide-bonded and requires glutathionylation of C91 for signaling.

Porphyromonas gulae Activates Unprimed and Gamma Interferon-Primed Macrophages via the Pattern Recognition Receptors Toll-Like Receptor 2 (TLR2), TLR4, and NOD2.

Porphyromonas gulae is an anaerobic, Gram-negative coccobacillus that has been associated with periodontal disease in companion animals. The aims of this study were to analyze the ligation of pattern recognition receptors by P. gulae and the subsequent activation of macrophages. Exposure of HEK cells transfected with Toll-like receptors (TLRs) or NOD-like receptors to P. gulae resulted in the ligation of TLR2, TLR4, and NOD2. The effects of this engagement of receptors were investigated by measuring the synthesis of nitric oxide (NO), CD86 expression, and inflammatory cytokine production by wild-type, TLR2-/-, and TLR4-/- macrophages. The addition of P. gulae to unprimed and gamma interferon (IFN-γ)-primed (M1 phenotype) macrophages significantly increased the surface expression of CD86, but only M1 macrophages produced nitric oxide. P. gulae-induced expression of CD86 on unprimed macrophages was dependent on both TLR2 and TLR4, but CD86 expression and NO production in M1 macrophages were only TLR2 dependent. P. gulae induced an increase in secretion of interleukin-1α (IL-1α), IL-1ß, IL-6, IL-12p70, IL-13, tumor necrosis factor alpha (TNF-α), granulocyte colony-stimulating factor (G-CSF), monocyte chemoattractant protein 1 (MCP-1), and macrophage inflammatory protein 1α (MIP-1α) by M1 macrophages compared to that by unprimed controls. Among these cytokines, secretion of IL-6 and TNF-α by M1 macrophages was dependent on either TLR2 or TLR4. Our data indicate that TLR2 and TLR4 are important for P. gulae activation of unprimed macrophages and that activation and effector functions induced in M1 macrophages by P. gulae are mainly dependent on TLR2. In conclusion, P. gulae induces a strong TLR2-dependent inflammatory M1 macrophage response which may be important in establishing the chronic inflammation associated with periodontal disease in companion animals.

Anakinra reduces blood pressure and renal fibrosis in one kidney/DOCA/salt-induced hypertension.

OBJECTIVE: To determine whether a clinically-utilised IL-1 receptor antagonist, anakinra, reduces renal inflammation, structural damage and blood pressure (BP) in mice with established hypertension. METHODS: Hypertension was induced in male mice by uninephrectomy, deoxycorticosterone acetate (2.4mg/d,s.c.) and replacement of drinking water with saline (1K/DOCA/salt). Control mice received uninephrectomy, a placebo pellet and normal drinking water. 10days post-surgery, mice commenced treatment with anakinra (75mg/kg/d, i.p.) or vehicle (0.9% saline, i.p.) for 11days. Systolic BP was measured by tail cuff while qPCR, immunohistochemistry and flow cytometry were used to measure inflammatory markers, collagen and immune cell infiltration in the kidneys. RESULTS: By 10days post-surgery, 1K/DOCA/salt-treated mice displayed elevated systolic BP (148.3±2.4mmHg) compared to control mice (121.7±2.7mmHg; n=18, P<0.0001). The intervention with anakinra reduced BP in 1K/DOCA/salt-treated mice by ∼20mmHg (n=16, P<0.05), but had no effect in controls. In 1K/DOCA/salt-treated mice, anakinra modestly reduced (∼30%) renal expression of some (CCL5, CCL2; n=7-8; P<0.05) but not all (ICAM-1, IL-6) inflammatory markers, and had no effect on immune cell infiltration (n=7-8, P>0.05). Anakinra reduced renal collagen content (n=6, P<0.01) but paradoxically appeared to exacerbate the renal and glomerular hypertrophy (n=8-9, P<0.001) that accompanied 1K/DOCA/salt-induced hypertension. CONCLUSION: Despite its anti-hypertensive and renal anti-fibrotic actions, anakinra had minimal effects on inflammation and leukocyte infiltration in mice with 1K/DOCA/salt-induced hypertension. Future studies will assess whether the anti-hypertensive actions of anakinra are mediated by protective actions in other BP-regulating or salt-handling organs such as the arteries, skin and brain.

Disruption of Serinc1, which facilitates serine-derived lipid synthesis, fails to alter macrophage function, lymphocyte proliferation or autoimmune disease susceptibility.

During immune cell activation, serine-derived lipids such as phosphatidylserine and sphingolipids contribute to the formation of protein signaling complexes within the plasma membrane. Altering lipid composition in the cell membrane can subsequently affect immune cell function and the development of autoimmune disease. Serine incorporator 1 (SERINC1) is a putative carrier protein that facilitates synthesis of serine-derived lipids. To determine if SERINC1 has a role in immune cell function and the development of autoimmunity, we characterized a mouse strain in which a retroviral insertion abolishes expression of the Serinc1 transcript. Expression analyses indicated that the Serinc1 transcript is readily detectable and expressed at relatively high levels in wildtype macrophages and lymphocytes. The ablation of Serinc1 expression in these immune cells, however, did not significantly alter serine-derived lipid composition or affect macrophage function and lymphocyte proliferation. Analyses of Serinc1-deficient mice also indicated that systemic ablation of Serinc1 expression did not affect viability, fertility or autoimmune disease susceptibility. These results suggest that Serinc1 is dispensable for certain immune cell functions and does not contribute to previously reported links between lipid composition in immune cells and autoimmunity.

PB1-F2 Peptide Derived from Avian Influenza A Virus H7N9 Induces Inflammation via Activation of the NLRP3 Inflammasome.

The emergence of avian H7N9 influenza A virus in humans with associated high mortality has highlighted the threat of a potential pandemic. Fatal H7N9 infections are characterized by hyperinflammation and increased cellular infiltrates in the lung. Currently there are limited therapies to address the pathologies associated with H7N9 infection and the virulence factors that contribute to these pathologies. We have found that PB1-F2 derived from H7N9 activates the NLRP3 inflammasome and induces lung inflammation and cellular recruitment that is NLRP3-dependent. We have also shown that H7N9 and A/Puerto Rico/H1N1 (PR8)PB1-F2 peptide treatment induces significant mitochondrial reactive oxygen production, which contributes to NLRP3 activation. Importantly, treatment of cells or mice with the specific NLRP3 inhibitor MCC950 significantly reduces IL-1ß maturation, lung cellular recruitment, and cytokine production. Together, these results suggest that PB1-F2 from H7N9 avian influenza A virus may be a major contributory factor to disease pathophysiology and excessive inflammation characteristic of clinical infections and that targeting the NLRP3 inflammasome may be an effective means to reduce the inflammatory burden associated with H7N9 infections.

The immune modulatory peptide FhHDM-1 secreted by the helminth Fasciola hepatica prevents NLRP3 inflammasome activation by inhibiting endolysosomal acidification in macrophages.

The NLRP3 inflammasome is a multimeric protein complex that controls the production of IL-1ß, a cytokine that influences the development of both innate and adaptive immune responses. Helminth parasites secrete molecules that interact with innate immune cells, modulating their activity to ultimately determine the phenotype of differentiated T cells, thus creating an immune environment that is conducive to sustaining chronic infection. We show that one of these molecules, FhHDM-1, a cathelicidin-like peptide secreted by the helminth parasite, Fasciola hepatica, inhibits the activation of the NLRP3 inflammasome resulting in reduced secretion of IL-1ß by macrophages. FhHDM-1 had no effect on the synthesis of pro-IL-1ß. Rather, the inhibitory effect was associated with the capacity of the peptide to prevent acidification of the endolysosome. The activation of cathepsin B protease by lysosomal destabilization was prevented in FhHDM-1-treated macrophages. By contrast, peptide derivatives of FhHDM-1 that did not alter the lysosomal pH did not inhibit secretion of IL-1ß. We propose a novel immune modulatory strategy used by F. hepatica, whereby secretion of the FhHDM-1 peptide impairs the activation of NLRP3 by lysosomal cathepsin B protease, which prevents the downstream production of IL-1ß and the development of protective T helper 1 type immune responses that are detrimental to parasite survival.-Alvarado, R., To, J., Lund, M. E., Pinar, A., Mansell, A., Robinson, M. W., O'Brien, B. A., Dalton, J. P., Donnelly, S. The immune modulatory peptide FhHDM-1 secreted by the helminth Fasciola hepatica prevents NLRP3 inflammasome activation by inhibiting endolysosomal acidification in macrophages.

Reassessing the role of the NLRP3 inflammasome during pathogenic influenza A virus infection via temporal inhibition.

The inflammasome NLRP3 is activated by pathogen associated molecular patterns (PAMPs) during infection, including RNA and proteins from influenza A virus (IAV). However, chronic activation by danger associated molecular patterns (DAMPs) can be deleterious to the host. We show that blocking NLRP3 activation can be either protective or detrimental at different stages of lethal influenza A virus (IAV). Administration of the specific NLRP3 inhibitor MCC950 to mice from one day following IAV challenge resulted in hypersusceptibility to lethality. In contrast, delaying treatment with MCC950 until the height of disease (a more likely clinical scenario) significantly protected mice from severe and highly virulent IAV-induced disease. These findings identify for the first time that NLRP3 plays a detrimental role later in infection, contributing to IAV pathogenesis through increased cytokine production and lung cellular infiltrates. These studies also provide the first evidence identifying NLRP3 inhibition as a novel therapeutic target to reduce IAV disease severity.

Toll-like receptors: the swiss army knife of immunity and vaccine development.

Innate immune cells have a critical role in defense against infection and disease. Central to this is the broad specificity with which they can detect pathogen-associated patterns and danger-associated patterns via the pattern recognition receptors (PRRs) they express. Several families of PRRs have been identified including: Toll-like receptors (TLRs), C-type lectin-like receptors, retinoic acid-inducible gene-like receptors and nucleotide-binding oligomerization domain-like receptors. TLRs are one of the most largely studied families of PRRs. The binding of ligands to TLRs on antigen presenting cells (APCs), mainly dendritic cells, leads to APC maturation, induction of inflammatory cytokines and the priming of naive T cells to drive acquired immunity. Therefore, activation of TLRs promotes both innate inflammatory responses and the induction of adaptive immunity. Consequently, in the last two decades mounting evidence has inextricably linked TLR activation with the pathogenesis of immune diseases and cancer. It has become advantageous to harness these aspects of TLR signaling therapeutically to accelerate and enhance the induction of vaccine-specific responses and also target TLRs with the use of biologics and small molecule inhibitors for the treatment of disease. In these respects, TLRs may be considered a 'Swiss Army' knife of the immune system, ready to respond in a multitude of infectious and disease states. Here we describe the latest advances in TLR-targeted therapeutics and the use of TLR ligands as vaccine adjuvants.

HIV Blocks Interferon Induction in Human Dendritic Cells and Macrophages by Dysregulation of TBK1.

UNLABELLED: Dendritic cells (DCs) and macrophages are present in the tissues of the anogenital tract, where HIV-1 transmission occurs in almost all cases. These cells are both target cells for HIV-1 and represent the first opportunity for the virus to interfere with innate recognition. Previously we have shown that both cell types fail to produce type I interferons (IFNs) in response to HIV-1 but that, unlike T cells, the virus does not block IFN induction by targeting IFN regulatory factor 3 (IRF3) for cellular degradation. Thus, either HIV-1 inhibits IFN induction by an alternate mechanism or, less likely, these cells fail to sense HIV-1. Here we show that HIV-1 (but not herpes simplex virus 2 [HSV-2] or Sendai virus)-exposed DCs and macrophages fail to induce the expression of all known type I and III IFN genes. These cells do sense the virus, and pattern recognition receptor (PRR)-induced signaling pathways are triggered. The precise stage in the IFN-inducing signaling pathway that HIV-1 targets to block IFN induction was identified; phosphorylation but not K63 polyubiquitination of TANK-binding kinase 1 (TBK1) was completely inhibited. Two HIV-1 accessory proteins, Vpr and Vif, were shown to bind to TBK1, and their individual deletion partly restored IFN-ß expression. Thus, the inhibition of TBK1 autophosphorylation by binding of these proteins appears to be the principal mechanism by which HIV-1 blocks type I and III IFN induction in myeloid cells. IMPORTANCE: Dendritic cells (DCs) and macrophages are key HIV target cells. Therefore, definition of how HIV impairs innate immune responses to initially establish infection is essential to design preventative interventions, especially by restoring initial interferon production. Here we demonstrate how HIV-1 blocks interferon induction by inhibiting the function of a key kinase in the interferon signaling pathway, TBK1, via two different viral accessory proteins. Other viral proteins have been shown to target the general effects of TBK1, but this precise targeting between ubiquitination and phosphorylation of TBK1 is novel.

The acetyltransferase HAT1 moderates the NF-κB response by regulating the transcription factor PLZF.

To date, the activities of protein kinases have formed the core of our understanding of cell signal transduction. Comprehension of the extent of protein acetylation has raised expectations that this alternate post-transcriptional modification will be shown to rival phosphorylation in its importance in mediating cellular responses. However, limited instances have been identified. Here we show that signalling from Toll-like or TNF-α receptors triggers the calcium/calmodulin-dependent protein kinase (CaMK2) to activate histone acetyltransferase-1 (HAT1), which then acetylates the transcriptional regulator PLZF. Acetylation of PLZF promotes the assembly of a repressor complex incorporating HDAC3 and the NF-κB p50 subunit that limits the NF-κB response. Accordingly, diminishing the activity of CaMK2, the expression levels of PLZF or HAT1, or mutating key residues that are covalently modified in PLZF and HAT1, curtails control of the production of inflammatory cytokines. These results identify a central role for acetylation in controlling the inflammatory NF-κB transcriptional programme.