In vivo imaging of inflammasome activation reveals a subcapsular macrophage burst response that mobilizes innate and adaptive immunity

Innate and adaptive immune responses that control lymph-borne viruses in the draining lymph node

The interstitial fluids in tissues are constantly drained into the lymph nodes (LNs) as lymph through afferent lymphatic vessels and from LNs into the blood through efferent lymphatics. LNs are strategically positioned and have the appropriate cellular composition to serve as sites of adaptive immune initiation against invading pathogens. However, for lymph-borne viruses, which disseminate from the entry site to other tissues through the lymphatic system, immune cells in the draining LN (dLN) also play critical roles in curbing systemic viral dissemination during primary and secondary infections. Lymph-borne viruses in tissues can be transported to dLNs as free virions in the lymph or within infected cells. Regardless of the entry mechanism, infected myeloid antigen-presenting cells, including various subtypes of dendritic cells, inflammatory monocytes, and macrophages, play a critical role in initiating the innate immune response within the dLN. This innate immune response involves cellular crosstalk between infected and bystander innate immune cells that ultimately produce type I interferons (IFN-Is) and other cytokines and recruit inflammatory monocytes and natural killer (NK) cells. IFN-I and NK cell cytotoxicity can restrict systemic viral spread during primary infections and prevent serious disease. Additionally, the memory CD8+ T-cells that reside or rapidly migrate to the dLN can contribute to disease prevention during secondary viral infections. This review explores the intricate innate immune responses orchestrated within dLNs that contain primary viral infections and the role of memory CD8+ T-cells following secondary infection or CD8+ T-cell vaccination.

A broadly applicable protein-polymer adjuvant system for antiviral vaccines

Although protein subunit vaccines generally have acceptable safety profiles with precise antigenic content, limited immunogenicity can lead to unsatisfactory humoral and cellular immunity and the need for vaccine adjuvants and delivery system. Herein, we assess a vaccine adjuvant system comprising Quillaja Saponaria-21(QS-21) and cobalt porphyrin polymeric micelles that enabling the display of His-tagged antigen on its surface. The nanoscale micelles promote antigen uptake and dendritic cell activation to induce robust cytotoxic T lymphocyte response and germinal center formation. Using the recombinant protein antigens from influenza A and rabies virus, the micelle adjuvant system elicited robust antiviral responses and protected mice from lethal challenge. In addition, this system could be combined with other antigens to induce high titers of neutralizing antibodies in models of three highly pathogenic viral pathogens: Ebola virus, Marburg virus, and Nipah virus. Collectively, our results demonstrate this polymeric micelle adjuvant system can be used as a potent nanoplatform for developing antiviral vaccine countermeasures that promote humoral and cellular immunity.

Anti-PD-1 therapy triggers Tfh cell-dependent IL-4 release to boost CD8 T cell responses in tumor-draining lymph nodes

Anti-PD-1 therapy targets intratumoral CD8+ T cells to promote clinical responses in cancer patients. Recent evidence suggests an additional activity in the periphery, but the underlying mechanism is unclear. Here, we show that anti-PD-1 mAb enhances CD8+ T cell responses in tumor-draining lymph nodes by stimulating cytokine production in follicular helper T cells (Tfh). In two different models, anti-PD-1 mAb increased the activation and proliferation of tumor-specific T cells in lymph nodes. Surprisingly, anti-PD-1 mAb did not primarily target CD8+ T cells but instead stimulated IL-4 production by Tfh cells, the major population bound by anti-PD-1 mAb. Blocking IL-4 or inhibiting the Tfh master transcription factor BCL6 abrogated anti-PD-1 mAb activity in lymph nodes while injection of IL-4 complexes was sufficient to recapitulate anti-PD-1 mAb activity. A similar mechanism was observed in a vaccine model. Finally, nivolumab also boosted human Tfh cells in humanized mice. We propose that Tfh cells and IL-4 play a key role in the peripheral activity of anti-PD-1 mAb.

Subcapsular sinus macrophages maximize germinal center development in non-draining lymph nodes during blood-borne viral infection

Lymph node (LN) germinal centers (GCs) are critical sites for B cell activation and differentiation. GCs develop after specialized CD169+ macrophages residing in LN sinuses filter antigens (Ags) from the lymph and relay these Ags into proximal B cell follicles. Many viruses, however, first reach LNs through the blood during viremia (virus in the blood), rather than through lymph drainage from infected tissue. How LNs capture viral Ag from the blood to allow GC development is not known. Here, we followed Zika virus (ZIKV) dissemination in mice and subsequent GC formation in both infected tissue-draining and non-draining LNs. From the footpad, ZIKV initially disseminated through two LN chains, infecting LN macrophages and leading to GC formation. Despite rapid ZIKV viremia, non-draining LNs were not infected for several days. Non-draining LN infection correlated with virus-induced vascular leakage and neutralization of permeability reduced LN macrophage attrition. Depletion of non-draining LN macrophages significantly decreased GC B cells in these nodes. Thus, although LNs inefficiently captured viral Ag directly from the blood, GC formation in non-draining LNs proceeded similarly to draining LNs through LN sinus CD169+ macrophages. Together, our findings reveal a conserved pathway allowing LN macrophages to activate antiviral B cells in LNs distal from infected tissue after blood-borne viral infection.

Dynamic Multiplex Tissue Imaging in Inflammation Research

Inflammation is a highly dynamic process with immune cells that continuously interact with each other and parenchymal components as they migrate through tissue. The dynamic cellular responses and interaction patterns are a function of the complex tissue environment that cannot be fully reconstructed ex vivo, making it necessary to assess cell dynamics and changing spatial patterning in vivo. These dynamics often play out deep within tissues, requiring the optical focus to be placed far below the surface of an opaque organ. With the emergence of commercially available two-photon excitation lasers that can be combined with existing imaging systems, new avenues for imaging deep tissues over long periods of time have become available. We discuss a selected subset of studies illustrating how two-photon microscopy (2PM) has helped to relate the dynamics of immune cells to their in situ function and to understand the molecular patterns that govern their behavior in vivo. We also review some key practical aspects of 2PM methods and point out issues that can confound the results, so that readers can better evaluate the reliability of conclusions drawn using this technology.

Modulating Antigen Availability in Lymphoid Organs to Shape the Humoral Immune Response to Vaccines

Primary immune responses following vaccination are initiated in draining lymph nodes, where naive T and B cells encounter Ag and undergo coordinated steps of activation. For humoral immunity, the amount of Ag present over time, its localization to follicles and follicular dendritic cells, and the Ag's structural state all play important roles in determining the subsequent immune response. Recent studies have shown that multiple elements of vaccine design can impact Ag availability in lymphoid tissues, including the choice of adjuvant, physical form of the immunogen, and dosing kinetics. These vaccine design elements affect the transport of Ag to lymph nodes, Ag's localization in the tissue, the duration of Ag availability, and the structural integrity of the Ag. In this review, we discuss these findings and their implications for engineering more effective vaccines, particularly for difficult to neutralize pathogens.

Nanoscale organization of the endogenous ASC speck

The NLRP3 inflammasome is a central component of the innate immune system. Its activation leads to formation of the ASC speck, a supramolecular assembly of the inflammasome adaptor protein ASC. Different models, based on ASC overexpression, have been proposed for the structure of the ASC speck. Using dual-color 3D super-resolution imaging (dSTORM and DNA-PAINT), we visualized the ASC speck structure following NLRP3 inflammasome activation using endogenous ASC expression. A complete structure was only obtainable by labeling with both anti-ASC antibodies and nanobodies. The complex varies in diameter between ∼800 and 1000 nm, and is composed of a dense core with emerging filaments. Dual-color confocal fluorescence microscopy indicated that the ASC speck does not colocalize with the microtubule-organizing center at late time points after Nigericin stimulation. From super-resolution images of whole cells, the ASC specks were sorted into a pseudo-time sequence indicating that they become denser but not larger during formation.

Quantitative proteomics defines mechanisms of antiviral defence and cell death during modified vaccinia Ankara infection

Modified vaccinia Ankara (MVA) virus does not replicate in human cells and is the vaccine deployed to curb the current outbreak of mpox. Here, we conduct a multiplexed proteomic analysis to quantify >9000 cellular and ~80% of viral proteins throughout MVA infection of human fibroblasts and macrophages. >690 human proteins are down-regulated >2-fold by MVA, revealing a substantial remodelling of the host proteome. >25% of these MVA targets are not shared with replication-competent vaccinia. Viral intermediate/late gene expression is necessary for MVA antagonism of innate immunity, and suppression of interferon effectors such as ISG20 potentiates virus gene expression. Proteomic changes specific to infection of macrophages indicate modulation of the inflammatory response, including inflammasome activation. Our approach thus provides a global view of the impact of MVA on the human proteome and identifies mechanisms that may underpin its abortive infection. These discoveries will prove vital to design future generations of vaccines.

Assembly mechanism of the inflammasome sensor AIM2 revealed by single molecule analysis

Pathogenic dsDNA prompts AIM2 assembly leading to the formation of the inflammasome, a multimeric complex that triggers the inflammatory response. The recognition of foreign dsDNA involves AIM2 self-assembly concomitant with dsDNA binding. However, we lack mechanistic and kinetic information on the formation and propagation of the assembly, which can shed light on innate immunity's time response and specificity. Combining optical traps and confocal fluorescence microscopy, we determine here the association and dissociation rates of the AIM2-DNA complex at the single molecule level. We identify distinct mechanisms for oligomer growth via the binding of incoming AIM2 molecules to adjacent dsDNA or direct interaction with bound AIM2 assemblies, resembling primary and secondary nucleation. Through these mechanisms, the size of AIM2 oligomers can increase fourfold in seconds. Finally, our data indicate that single AIM2 molecules do not diffuse/scan along the DNA, suggesting that oligomerization depends on stochastic encounters with DNA and/or DNA-bound AIM2.

Bridging the Gap: Investigating the Link between Inflammasomes and Postoperative Cognitive Dysfunction

Postoperative cognitive dysfunction (POCD) is a cluster of cognitive problems that may arise after surgery. POCD symptoms include memory loss, focus inattention, and communication difficulties. Inflammasomes, intracellular multiprotein complexes that control inflammation, may have a significant role in the development of POCD. It has been postulated that the NLRP3 inflammasome promotes cognitive impairment by triggering the inflammatory response in the brain. Nevertheless, there are many gaps in the current literature to understand the underlying pathophysiological mechanisms and develop future therapy. This review article underlines the limits of our current knowledge about the NLRP3 (NOD-, LRR- and pyrin domain-containing protein 3) inflammasome and POCD. We first discuss inflammasomes and their types, structures, and functions, then summarize recent evidence of the NLRP3 inflammasome's involvement in POCD. Next, we propose a hypothesis that suggests the involvement of inflammasomes in multiple organs, including local surgical sites, blood circulation, and other peripheral organs, leading to systemic inflammation and subsequent neuronal dysfunction in the brain, resulting in POCD. Research directions are then discussed, including analyses of inflammasomes in more clinical POCD animal models and clinical trials, studies of inflammasome types that are involved in POCD, and investigations into whether inflammasomes occur at the surgical site, in circulating blood, and in peripheral organs. Finally, we discuss the potential benefits of using new technologies and approaches to study inflammasomes in POCD. A thorough investigation of inflammasomes in POCD might substantially affect clinical practice.

Integrated NLRP3, AIM2, NLRC4, Pyrin inflammasome activation and assembly drive PANoptosis

Inflammasomes are important sentinels of innate immune defense; they sense pathogens and induce the cell death of infected cells, playing key roles in inflammation, development, and cancer. Several inflammasome sensors detect and respond to specific pathogen- and damage-associated molecular patterns (PAMPs and DAMPs, respectively) by forming a multiprotein complex with the adapters ASC and caspase-1. During disease, cells are exposed to several PAMPs and DAMPs, leading to the concerted activation of multiple inflammasomes. However, the molecular mechanisms that integrate multiple inflammasome sensors to facilitate optimal host defense remain unknown. Here, we discovered that simultaneous inflammasome activation by multiple ligands triggered multiple types of programmed inflammatory cell death, and these effects could not be mimicked by treatment with a pure ligand of any single inflammasome. Furthermore, NLRP3, AIM2, NLRC4, and Pyrin were determined to be members of a large multiprotein complex, along with ASC, caspase-1, caspase-8, and RIPK3, and this complex drove PANoptosis. Furthermore, this multiprotein complex was released into the extracellular space and retained as multiple inflammasomes. Multiple extracellular inflammasome particles could induce inflammation after their engulfment by neighboring macrophages. Collectively, our findings define a previously unknown regulatory connection and molecular interaction between inflammasome sensors, which drives the assembly of a multiprotein complex that includes multiple inflammasome sensors and cell death regulators. The discovery of critical interactions among NLRP3, AIM2, NLRC4, and Pyrin represents a new paradigm in understanding the functions of these molecules in innate immunity and inflammasome biology as well as identifying new therapeutic targets for NLRP3-, AIM2-, NLRC4- and Pyrin-mediated diseases.

Understanding How Cationic Polymers' Properties Inform Toxic or Immunogenic Responses via Parametric Analysis

Cationic polymers are widely used materials in diverse biotechnologies. Subtle variations in these polymers' properties can change them from exceptional delivery agents to toxic inflammatory hazards. Conventional screening strategies optimize for function in a specific application rather than observing how underlying polymer-cell interactions emerge from polymers' properties. An alternative approach is to map basic underlying responses, such as immunogenicity or toxicity, as a function of basic physicochemical parameters to inform the design of materials for a breadth of applications. To demonstrate the potential of this approach, we synthesized 107 polymers varied in charge, hydrophobicity, and molecular weight. We then screened this library for cytotoxic behavior and immunogenic responses to map how these physicochemical properties inform polymer-cell interactions. We identify three compositional regions of interest and use confocal microscopy to uncover the mechanisms behind the observed responses. Finally, immunogenic activity is confirmed in vivo. Highly cationic polymers disrupted the cellular plasma membrane to induce a toxic phenotype, while high molecular weight, hydrophobic polymers were uptaken by active transport to induce NLRP3 inflammasome activation, an immunogenic phenotype. Tertiary amine- and triethylene glycol-containing polymers did not invoke immunogenic or toxic responses. The framework described herein allows for the systematic characterization of new cationic materials with different physicochemical properties for applications ranging from drug and gene delivery to antimicrobial coatings and tissue scaffolds.

The Role of Cytokines in Neutrophil Development, Tissue Homing, Function and Plasticity in Health and Disease

Neutrophils are crucial innate immune cells and comprise 50-70% of the white blood cell population under homeostatic conditions. Upon infection and in cancer, blood neutrophil numbers significantly increase because of the secretion of various chemo- and cytokines by, e.g., leukocytes, pericytes, fibroblasts and endothelial cells present in the inflamed tissue or in the tumor microenvironment (TME). The function of neutrophils in cancer has recently gained considerable attention, as they can exert both pro- and anti-tumorigenic functions, dependent on the cytokine milieu present in the TME. Here, we review the effect of cytokines on neutrophil development, tissue homing, function and plasticity in cancer and autoimmune diseases as well as under physiological conditions in the bone marrow, bloodstream and various organs like the spleen, kidney, liver, lung and lymph nodes. In addition, we address several promising therapeutic options, such as cytokine therapy, immunocytokines and immunotherapy, which aim to exploit the anti-tumorigenic potential of neutrophils in cancer treatment or block excessive neutrophil-mediated inflammation in autoimmune diseases.

Suppression of NLRP3 inflammasome by ivermectin ameliorates bleomycin-induced pulmonary fibrosis

Ivermectin is a US Food and Drug Administration (FDA)-approved antiparasitic agent with antiviral and anti-inflammatory properties. Although recent studies reported the possible anti-inflammatory activity of ivermectin in respiratory injuries, its potential therapeutic effect on pulmonary fibrosis (PF) has not been investigated. This study aimed to explore the ability of ivermectin (0.6 mg/kg) to alleviate bleomycin-induced biochemical derangements and histological changes in an experimental PF rat model. This can provide the means to validate the clinical utility of ivermectin as a treatment option for idiopathic PF. The results showed that ivermectin mitigated the bleomycin-evoked pulmonary injury, as manifested by the reduced infiltration of inflammatory cells, as well as decreased the inflammation and fibrosis scores. Intriguingly, ivermectin decreased collagen fiber deposition and suppressed transforming growth factor-‍β1 (TGF-‍β1) and fibronectin protein expression, highlighting its anti-fibrotic activity. This study revealed for the first time that ivermectin can suppress the nucleotide-binding oligomerization domain (NOD)‍-like receptor family pyrin domain-containing protein 3 (NLRP3) inflammasome, as manifested by the reduced gene expression of NLRP3 and the apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), with a subsequent decline in the interleukin‍-‍1β (IL‍-‍1β) level. In addition, ivermectin inhibited the expression of intracellular nuclear factor-‍κB (NF‍-‍κB) and hypoxia‑inducible factor‑1α (HIF‍-‍1α) proteins along with lowering the oxidative stress and apoptotic markers. Altogether, this study revealed that ivermectin could ameliorate pulmonary inflammation and fibrosis induced by bleomycin. These beneficial effects were mediated, at least partly, via the downregulation of TGF-‍β1 and fibronectin, as well as the suppression of NLRP3 inflammasome through modulating the expression of HIF‑1α and NF-‍κB.

Complement-dependent mpox-virus-neutralizing antibodies in infected and vaccinated individuals

Mpox virus (MPXV) caused a multi-country outbreak in non-endemic areas in 2022. Following historic success of smallpox vaccination with vaccinia virus (VACV)-based vaccines, the third generation modified vaccinia Ankara (MVA)-based vaccine was used as prophylaxis for MPXV, but its effectiveness remains poorly characterized. Here, we applied two assays to quantify neutralizing antibodies (NAbs) in sera from control, MPXV-infected, or MVA-vaccinated individuals. Various levels of MVA NAbs were detected after infection, historic smallpox, or recent MVA vaccination. MPXV was minimally sensitive to neutralization. However, addition of complement enhanced detection of responsive individuals and NAb levels. Anti-MVA and -MPXV NAbs were observed in 94% and 82% of infected individuals, respectively, and 92% and 56% of MVA vaccinees, respectively. NAb titers were higher in individuals born before 1980, highlighting the impact of historic smallpox vaccination on humoral immunity. Altogether, our results indicate that MPXV neutralization is complement dependent and uncover mechanisms underlying vaccine effectiveness.

Apoptotic cell fragments locally activate tingible body macrophages in the germinal center

Germinal centers (GCs) that form within lymphoid follicles during antibody responses are sites of massive cell death. Tingible body macrophages (TBMs) are tasked with apoptotic cell clearance to prevent secondary necrosis and autoimmune activation by intracellular self antigens. We show by multiple redundant and complementary methods that TBMs derive from a lymph node-resident, CD169-lineage, CSF1R-blockade-resistant precursor that is prepositioned in the follicle. Non-migratory TBMs use cytoplasmic processes to chase and capture migrating dead cell fragments using a "lazy" search strategy. Follicular macrophages activated by the presence of nearby apoptotic cells can mature into TBMs in the absence of GCs. Single-cell transcriptomics identified a TBM cell cluster in immunized lymph nodes which upregulated genes involved in apoptotic cell clearance. Thus, apoptotic B cells in early GCs trigger activation and maturation of follicular macrophages into classical TBMs to clear apoptotic debris and prevent antibody-mediated autoimmune diseases.

Zika virus spreads through infection of lymph node-resident macrophages

To disseminate through the body, Zika virus (ZIKV) is thought to exploit the mobility of myeloid cells, in particular monocytes and dendritic cells. However, the timing and mechanisms underlying shuttling of the virus by immune cells remains unclear. To understand the early steps in ZIKV transit from the skin, at different time points, we spatially mapped ZIKV infection in lymph nodes (LNs), an intermediary site en route to the blood. Contrary to prevailing hypotheses, migratory immune cells are not required for the virus to reach the LNs or blood. Instead, ZIKV rapidly infects a subset of sessile CD169+ macrophages in the LNs, which release the virus to infect downstream LNs. Infection of CD169+ macrophages alone is sufficient to initiate viremia. Overall, our experiments indicate that macrophages that reside in the LNs contribute to initial ZIKV spread. These studies enhance our understanding of ZIKV dissemination and identify another anatomical site for potential antiviral intervention.

Ponatinib Drives Cardiotoxicity by S100A8/A9-NLRP3-IL-1β Mediated Inflammation

BACKGROUND

The tyrosine kinase inhibitor ponatinib is the only treatment option for chronic myelogenous leukemia patients with T315I (gatekeeper) mutation. Pharmacovigilance analysis of Food and Drug Administration and World Health Organization datasets has revealed that ponatinib is the most cardiotoxic agent among all Food and Drug Administration-approved tyrosine kinase inhibitors in a real-world scenario. However, the mechanism of ponatinib-induced cardiotoxicity is unknown.

METHODS

The lack of well-optimized mouse models has hampered the in vivo cardio-oncology studies. Here, we show that cardiovascular comorbidity mouse models evidence a robust cardiac pathological phenotype upon ponatinib treatment. A combination of multiple in vitro and in vivo models was employed to delineate the underlying molecular mechanisms.

RESULTS

An unbiased RNA sequencing analysis identified the enrichment of dysregulated inflammatory genes, including a multifold upregulation of alarmins S100A8/A9, as a top hit in ponatinib-treated hearts. Mechanistically, we demonstrate that ponatinib activates the S100A8/A9-TLR4 (Toll-like receptor 4)-NLRP3 (NLR family pyrin domain-containing 3)-IL (interleukin)-1β signaling pathway in cardiac and systemic myeloid cells, in vitro and in vivo, thereby leading to excessive myocardial and systemic inflammation. Excessive inflammation was central to the cardiac pathology because interventions with broad-spectrum immunosuppressive glucocorticoid dexamethasone or specific inhibitors of NLRP3 (CY-09) or S100A9 (paquinimod) nearly abolished the ponatinib-induced cardiac dysfunction.

CONCLUSIONS

Taken together, these findings uncover a novel mechanism of ponatinib-induced cardiac inflammation leading to cardiac dysfunction. From a translational perspective, our results provide critical preclinical data and rationale for a clinical investigation into immunosuppressive interventions for managing ponatinib-induced cardiotoxicity.

Nanoreporter for Real-Time Monitoring of Inflammasome Activity and Targeted Therapy

Inflammasome activation is associated with a myriad of inflammatory diseases. However, existing methods provides a limited understanding of spatiotemporal kinetics of inflammasome activation, with restricted scope for early detection of associated treatment efficacy. This limitation offers an opportunity for the development of biocompatible in-vivo inflammasome monitoring tools with translational prospects. To achieve this, they report developing a pair of lipid-based nanoparticle systems, a reporter nanoparticle consisting of a caspase-1 activatable probe alone, and a theranostic nanoparticle combining the probe with an inflammasome-inhibiting drug. This biocompatible platform enhances the probe's residence time in circulation by preventing its opsonization and allowing its sustained release over time. Their results demonstrate the specificity of reporter nanoparticles towards caspase-1 activity and provides early-on monitoring of inflammasome activation both in-vitro as well as in-vivo. Additionally, the delivery of disulfiram, an inflammasome-inhibiting drug, along with reporter probe using theranostic nanoparticles enables real-time tracking of treatment efficacy in the gouty-arthritis inflammatory model. In summary, they report an unparalleled pair of the inflammasome-associated reporter and theranostic platforms suited not only for diagnostic applications but can also detect inflammasome-targeted treatment efficiency in real-time. These findings establish two novel, sensitive nanotools for non-invasive evaluation of inflammasome-targeted immunotherapy.

Measuring NLR Oligomerization II: Detection of ASC Speck Formation by Confocal Microscopy and Immunofluorescence

Inflammasomes are crucial sentinels of the innate immune system that sense clues of infection, cellular stress, or metabolic imbalances. Upon activation, the inflammasome sensor (e.g., NLRP3) recruits the adaptor protein apoptosis-associated speck-like protein containing a CARD (ASC). ASC rapidly oligomerizes to form a micron-sized structure termed "ASC speck." These are crucial for the activation of caspase-1 and downstream inflammatory signals released following a specific form of lytic cell death called pyroptosis. Hence, due to their considerably large size, ASC specks can be easily visualized by microscopy as a simple upstream readout for inflammasome activation. Here, we provide three detailed protocols for imaging ASC specks: (1) live-cell imaging of macrophage cell lines expressing a fluorescent protein fusion form of ASC, (2) imaging of human primary cells using immunofluorescence staining of endogenous ASC, and (3) visualization and quantification of specks on a single-cell level using imaging flow cytometry.

Methods to Measure NLR Oligomerization I: Size Exclusion Chromatography, Co-immunoprecipitation, and Cross-Linking

Protein oligomerization is a common principle of regulating cellular responses. Oligomerization of NLRs is essential for the formation of NLR signaling platforms and can be detected by several biochemical techniques. Some of these biochemical methods can be combined with functional assays, such as caspase-1 activity assay. Size exclusion chromatography (SEC) allows separation of native protein lysates into different sized complexes by FPLC for follow-up analysis. Using co-immunoprecipitation (co-IP), combined with SEC or on its own, enables subsequent antibody-based purification of NLR complexes and associated proteins, which can then be analyzed by immunoblot and/or subjected to functional caspase-1 activity assay. Native gel electrophoresis also allows detection of the NLR oligomerization state by immunoblot. Chemical cross-linking covalently joins two or more molecules, thus capturing the oligomeric state with high sensitivity and stability. ASC oligomerization has been successfully used as readout for NLR/ALR inflammasome activation in response to various PAMPs and DAMPs in human and mouse macrophages and THP-1 cells. Here, we provide a detailed description of the methods used for NLRP7 oligomerization in response to infection with Staphylococcus aureus (S. aureus) in primary human macrophages, co-immunoprecipitation, and immunoblot analysis of NLRP7 and NLRP3 inflammasome complexes as well as caspase-1 activity assays. Also, ASC oligomerization is shown in response to dsDNA, LPS/ATP, and LPS/nigericin in mouse bone marrow-derived macrophages (BMDMs) and/or THP-1 cells or human primary macrophages.

Directly targeting ASC by lonidamine alleviates inflammasome-driven diseases

BACKGROUND

Dysregulated activation of the inflammasome is involved in various human diseases including acute cerebral ischemia, multiple sclerosis and sepsis. Though many inflammasome inhibitors targeting NOD-like receptor protein 3 (NLRP3) have been designed and developed, none of the inhibitors are clinically available. Growing evidence suggests that targeting apoptosis-associated speck-like protein containing a CARD (ASC), the oligomerization of which is the key event for the assembly of inflammasome, may be another promising therapeutic strategy. Lonidamine (LND), a small-molecule inhibitor of glycolysis used as an antineoplastic drug, has been evidenced to have anti-inflammation effects. However, its anti-inflammatory mechanism is still largely unknown.

METHODS

Middle cerebral artery occlusion (MCAO), experimental autoimmune encephalomyelitis (EAE) and LPS-induced sepsis mice models were constructed to investigate the therapeutic and anti-inflammasome effects of LND. The inhibition of inflammasome activation and ASC oligomerization by LND was evaluated using western blot (WB), immunofluorescence (IF), quantitative polymerase chain reaction (qPCR) and enzyme-linked immunosorbent assay (ELISA) in murine bone marrow-derived macrophages (BMDMs). Direct binding of LND with ASC was assessed using molecular mock docking, surface plasmon resonance (SPR), and drug affinity responsive target stability (DARTS).

RESULTS

Here, we find that LND strongly attenuates the inflammatory injury in experimental models of inflammasome-associated diseases including autoimmune disease-multiple sclerosis (MS), ischemic stroke and sepsis. Moreover, LND blocks diverse types of inflammasome activation independent of its known targets including hexokinase 2 (HK2). We further reveal that LND directly binds to the inflammasome ligand ASC and inhibits its oligomerization.

CONCLUSIONS

Taken together, our results identify LND as a broad-spectrum inflammasome inhibitor by directly targeting ASC, providing a novel candidate drug for the treatment of inflammasome-driven diseases in clinic.

Poxviruses and the immune system: Implications for monkeypox virus

Poxviruses (PXVs) are mostly known for the variola virus, being the cause of smallpox; however, re-emerging PXVs have also shown a great capacity to develop outbreaks of pox-like infections in humans. The situation is alarming; PXV outbreaks have been involving both endemic and non-endemic areas in recent decades. Stopped smallpox vaccination is a reason offered mainly for this changing epidemiology that implies the protective role of immunity in the pathology of PXV infections. The immune system recognizes PXVs and elicits responses, but PXVs can antagonize these responses. Here, we briefly review the immunology of PXV infections, with emphasis on the role of pattern-recognition receptors, macrophages, and natural killer cells in the early response to PXV infections and PXVs’ strategies influencing these responses, as well as taking a glance at other immune cells, which discussion over them mainly occurs in association with PXV immunization rather than PXV infection. Throughout the review, numerous evasion mechanisms are highlighted, which might have implications for designing specific immunotherapies for PXV in the future.

SPICE-Met: profiling and imaging energy metabolism at the single-cell level using a fluorescent reporter mouse

The regulation of cellular energy metabolism is central to most physiological and pathophysiological processes. However, most current methods have limited ability to functionally probe metabolic pathways in individual cells. Here, we describe SPICE-Met (Single-cell Profiling and Imaging of Cell Energy Metabolism), a method for profiling energy metabolism in single cells using flow cytometry or imaging. We generated a transgenic mouse expressing PercevalHR, a fluorescent reporter for cellular ATP:ADP ratio. Modulation of PercevalHR fluorescence with metabolic inhibitors was used to infer the dependence of energy metabolism on oxidative phosphorylation and glycolysis in defined cell populations identified by flow cytometry. We applied SPICE-Met to analyze T-cell memory development during vaccination. Finally, we used SPICE-Met in combination with real-time imaging to dissect the heterogeneity and plasticity of energy metabolism in single macrophages ex vivo and identify three distinct metabolic patterns. Functional probing of energy metabolism with single-cell resolution should greatly facilitate the study of immunometabolism at a steady state, during disease pathogenesis or in response to therapy.

Dynamic CD8+ T Cell Cooperation with Macrophages and Monocytes for Successful Cancer Immunotherapy

Simple Summary

Innate and adaptive immunity mutually regulate one another in a dynamic fashion during immune responses. In infectious contexts, positive interactions between macrophages, monocytes and T cells are well recognized, but this is not the case in the field of cancer, where the growth of tumors disturbs the immune response. However, recent advances revealed that successful immunotherapy profoundly remodels the tumor microenvironment, promoting the activation of both T cells and myeloid cells. This review highlights the studies that hint at positive CD8⁺ T cell cooperation with monocytes and macrophages in this context, and discusses the potential mechanisms behind this.

Abstract

The essential roles endorsed by macrophages and monocytes are well established in response to infections, where they contribute to launching the differentiation of specific T-lymphocytes for long-term protection. This knowledge is the result of dynamic studies that can inspire the cancer field, particularly now that cancer immunotherapies elicit some tumor regression. Indeed, immune responses to cancer have mainly been studied after tumors have escaped immune attacks. In particular, the suppressive functions of macrophages were revealed in this context, introducing an obvious bias across the literature. In this review, we will focus on the ways inwhich monocytes and macrophages cooperate with T-lymphocytes, leading to successful immune responses. We will bring together the preclinical studies that have revealed the existence of such positive cooperation in the cancer field, and we will place particular emphasis on proposing the underlying mechanisms. Finally, we will give some perspectives to decipher the functional roles of such T-cell and myeloid cell interactions in the frame of human cancer immunotherapy.

Spatiotemporal dynamics of calcium signals during neutrophil cluster formation

Neutrophils form cellular clusters or swarms in response to injury or pathogen intrusion. Yet, intracellular signaling events favoring this coordinated response remain to be fully characterized. Here, we show that calcium signals play a critical role during mouse neutrophil clustering around particles of zymosan, a structural fungal component. Pioneer neutrophils recognizing zymosan or live Candida albicans displayed elevated calcium levels. Subsequently, a transient wave of calcium signals in neighboring cells was observed followed by the attraction of neutrophils that exhibited more persistent calcium signals as they reached zymosan particles. Calcium signals promoted LTB4 production while the blocking of extracellular calcium entry or LTB4 signaling abrogated cluster formation. Finally, using optogenetics to manipulate calcium influx in primary neutrophils, we show that calcium signals could initiate recruitment of neighboring neutrophils in an LTB4-dependent manner. Thus, sustained calcium responses at the center of the cluster are necessary and sufficient for the generation of chemoattractive gradients that attract neutrophils in a self-reinforcing process.

The C5a-C5aR1 complement axis is essential for neutrophil recruitment to draining lymph nodes via high endothelial venules in cutaneous leishmaniasis

Neutrophils are specialized innate immune cells known for their ability to fight pathogens. However, the mechanisms of neutrophil trafficking to lymph nodes are not fully clear. Using a murine model of dermal infection with Leishmania parasites, we observe a transient neutrophil influx in draining lymph nodes despite sustained recruitment to the infection site. Cell-tracking experiments, together with intravital two-photon microscopy, indicate that neutrophil recruitment to draining lymph nodes occurs minimally through lymphatics from the infected dermis, but mostly through blood vessels via high endothelial venules. Mechanistically, neutrophils do not respond to IL-1β or macrophage-derived molecules. Instead, they are guided by the C5a-C5aR1 axis, using L-selectin and integrins, to extravasate into the draining lymph node parenchyma. We also report that C5, the C5a precursor, is locally produced in the draining lymph node by lymphatic endothelial cells. Our data establish and detail organ-specific mechanisms of neutrophil trafficking.

Nanobodies dismantle post-pyroptotic ASC specks and counteract inflammation in vivo

Inflammasomes sense intracellular clues of infection, damage, or metabolic imbalances. Activated inflammasome sensors polymerize the adaptor ASC into micron‐sized “specks” to maximize caspase‐1 activation and the maturation of IL‐1 cytokines. Caspase‐1 also drives pyroptosis, a lytic cell death characterized by leakage of intracellular content to the extracellular space. ASC specks are released among cytosolic content, and accumulate in tissues of patients with chronic inflammation. However, if extracellular ASC specks contribute to disease, or are merely inert remnants of cell death remains unknown. Here, we show that camelid‐derived nanobodies against ASC (VHH_ASC) target and disassemble post‐pyroptotic inflammasomes, neutralizing their prionoid, and inflammatory functions. Notably, pyroptosis‐driven membrane perforation and exposure of ASC specks to the extracellular environment allowed VHH_ASC to target inflammasomes while preserving pre‐pyroptotic IL‐1β release, essential to host defense. Systemically administrated mouse‐specific VHH_ASC attenuated inflammation and clinical gout, and antigen‐induced arthritis disease. Hence, VHH_ASC neutralized post‐pyroptotic inflammasomes revealing a previously unappreciated role for these complexes in disease. VHH_ASC are the first biologicals that disassemble pre‐formed inflammasomes while preserving their functions in host defense.

Imaging viral infection in vivo to gain unique perspectives on cellular antiviral immunity

The past decade has seen near continual global public health crises caused by emerging viral infections. Extraordinary increases in our knowledge of the mechanisms underlying successful antiviral immune responses in animal models and during human infection have accompanied these viral outbreaks. Keeping pace with the rapidly advancing field of viral immunology, innovations in microscopy have afforded a previously unseen view of viral infection occurring in real-time in living animals. Here, we review the contribution of intravital imaging to our understanding of cell-mediated immune responses to viral infections, with a particular focus on studies that visualize the antiviral effector cells responding to infection as well as virus-infected cells. We discuss methods to visualize viral infection in vivo using intravital microscopy (IVM) and significant findings arising through the application of IVM to viral infection. Collectively, these works underscore the importance of developing a comprehensive spatial understanding of the relationships between immune effectors and virus-infected cells and how this has enabled unique discoveries about virus/host interactions and antiviral effector cell biology.

Information flow in the spatiotemporal organization of immune responses

Immune responses must be rapid, tightly orchestrated, and tailored to the encountered stimulus. Lymphatic vessels facilitate this process by continuously collecting immunological information (ie, antigens, immune cells, and soluble mediators) about the current state of peripheral tissues, and transporting these via the lymph across the lymphatic system. Lymph nodes (LNs), which are critical meeting points for innate and adaptive immune cells, are strategically located along the lymphatic network to intercept this information. Within LNs, immune cells are spatially organized, allowing them to efficiently respond to information delivered by the lymph, and to either promote immune homeostasis or mount protective immune responses. These responses involve the activation and functional cooperation of multiple distinct cell types and are tailored to the specific inflammatory conditions. The natural patterns of lymph flow can also generate spatial gradients of antigens and agonists within draining LNs, which can in turn further regulate innate cell function and localization, as well as the downstream generation of adaptive immunity. In this review, we explore how information transmitted by the lymph shapes the spatiotemporal organization of innate and adaptive immune responses in LNs, with particular focus on steady state and Type-I vs. Type-II inflammation.

Inflammasome activation in neutrophils of patients with severe COVID-19

Infection by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) engages the inflammasome in monocytes and macrophages and leads to the cytokine storm in COVID-19. Neutrophils, the most abundant leukocytes, release neutrophil extracellular traps (NETs), which have been implicated in the pathogenesis of COVID-19. Our recent study shows that activation of the NLRP3 inflammasome is important for NET release in sterile inflammation. However, the role of neutrophil inflammasome formation in human disease is unknown. We hypothesized that SARS-COV-2 infection may induce inflammasome activation in neutrophils. We also aimed to assess the localization of inflammasome formation, (i.e. ASC speck assembly), and timing relative to NETosis in stimulated neutrophils by real time video microscopy. Neutrophils isolated from severe COVID-19 patients demonstrated that approximately 2% of neutrophils in both the peripheral blood and tracheal aspirates presented ASC speck. ASC speck was observed in neutrophils with an intact poly-lobulated nucleus, suggesting early formation during neutrophil activation. Additionally, 40% of nuclei were positive for citrullinated histone H3, and there was a significant correlation between speck formation and nuclear histone citrullination. Time-lapse microscopy in LPS-stimulated neutrophils from fluorescent ASC reporter mice showed that ASC speck formed transiently and at the microtubule organizing center, long before NET release. Our study shows that ASC speck is present in neutrophils from COVID-19 patients with respiratory failure and that it forms early in NETosis. Our findings suggest that inhibition of neutrophil inflammasomes may be beneficial in COVID-19.

Role of Damage-Associated Molecular Pattern/Cell Death Pathways in Vaccine-Induced Immunity

Immune responses induced by natural infection and vaccination are known to be initiated by the recognition of microbial patterns by cognate receptors, since microbes and most vaccine components contain pathogen-associated molecular patterns. Recent discoveries on the roles of damage-associated molecular patterns (DAMPs) and cell death in immunogenicity have improved our understanding of the mechanism underlying vaccine-induced immunity. DAMPs are usually immunologically inert, but can transform into alarming signals to activate the resting immune system in response to pathogenic infection, cellular stress and death, or tissue damage. The activation of DAMPs and cell death pathways can trigger local inflammation, occasionally mediating adaptive immunity, including antibody- and cell-mediated immune responses. Emerging evidence indicates that the components of vaccines and adjuvants induce immunogenicity via the stimulation of DAMP/cell death pathways. Furthermore, strategies for targeting this pathway to enhance immunogenicity are being investigated actively. In this review, we describe various DAMPs and focus on the roles of DAMP/cell death pathways in the context of vaccines for infectious diseases and cancer.

NLRP3 inflammasome activation triggers gasdermin D-independent inflammation

[Figure: see text].

Imaging Approaches to Monitor Inflammasome Activation

Inflammasomes are a critical component of innate immune response which plays an important role in the pathogenesis of various chronic and acute inflammatory disease conditions. An inflammasome complex consists of a multimeric protein assembly triggered by any form of pathogenic or sterile insult, resulting in caspase-1 activation. This active enzyme is further known to activate downstream pro-inflammatory cytokines along with a pore-forming protein, eventually leading to a lytic cell death called pyroptosis. Understanding the spatiotemporal kinetics of essential inflammasome components provides a better interpretation of the complex signaling underlying inflammation during several disease pathologies. This can be attained via in-vitro and in-vivo imaging platforms, which not only provide a basic understanding of molecular signaling but are also crucial to develop and screen targeted therapeutics. To date, numerous studies have reported platforms to image different signaling components participating in inflammasome activation. Here, we review several elements of inflammasome signaling, a common molecular mechanism combining these elements and their respective imaging tools. We anticipate that future needs will include developing new inflammasome imaging systems that can be utilized as clinical tools for diagnostics and monitoring treatment responses.

Arf6 exacerbates allergic asthma through cell-to-cell transmission of ASC inflammasomes

Asthma is a chronic inflammatory disease of the airways associated with excess production of Th2 cytokines and lung eosinophil accumulation. This inflammatory response persists in spite of steroid administration that blocks autocrine/paracrine loops of inflammatory cytokines, and the detailed mechanisms underlying asthma exacerbation remain unclear. Here, we show that asthma exacerbation is triggered by airway macrophages through a prion-like cell-to-cell transmission of extracellular particulates, including ASC protein, that assemble inflammasomes and mediate IL-1β production. OVA-induced allergic asthma and associated IL-1β production were alleviated in mice with small GTPase Arf6-deficient macrophages. The extracellular ASC specks were slightly engulfed by Arf6^–/– macrophages, and the IL-1β production was reduced in Arf6^–/– macrophages compared with that in WT macrophages. Furthermore, pharmacological inhibition of the Arf6 guanine nucleotide exchange factor suppressed asthma-like allergic inflammation in OVA-challenged WT mice. Collectively, the Arf6-dependent intercellular transmission of extracellular ASC specks contributes to the amplification of allergic inflammation and subsequent asthma exacerbation.

Neutrophils in secondary lymphoid organs

Neutrophils are traditionally considered short‐lived, circulating innate immune cells that are rapidly recruited to sites of inflammation in response to infectious and inflammatory stimuli. Neutrophils efficiently internalize, kill or entrap pathogens, but their effector molecules may cause collateral tissue damage. More recently, it has been appreciated that neutrophils can also influence adaptive immunity. Lymph nodes (LNs) are immune cell‐rich secondary lymphoid organs that provide an ideal platform for cellular interaction and the integration of immunological information collected from local tissues. A variety of peripheral stimuli promote neutrophil migration to draining LNs via blood or lymphatics, utilizing differing molecular cues depending on the site of entry. Within LNs, neutrophils interact with other innate and adaptive cells. Crosstalk with subcapsular sinus macrophages contributes to the control of pathogen spread beyond the LN. Neutrophils can influence antigen presentation indirectly by interacting with DCs or directly by expressing major histocompatibility complex (MHC) and costimulatory molecules for antigen presentation. Interactions between neutrophils and adaptive lymphocytes can alter B‐cell antibody responses. Studies have shown conflicting results on whether neutrophils exert stimulatory or inhibitory effects on other LN immune cells, with stimulus‐specific and temporal differences in the outcome of these interactions. Furthermore, neutrophils have also been shown to traffick to LNs in homeostasis, with a potential role in immune surveillance, antigen capture and in shaping early adaptive responses in LNs. Understanding the mechanisms underpinning the effects of neutrophils on LN immune cells and adaptive immunity could facilitate the development of neutrophil‐targeted therapies in inflammatory diseases.

Effect of Curcumol on NOD-Like Receptor Thermoprotein Domain 3 Inflammasomes in Liver Fibrosis of Mice

OBJECTIVE

To investigate the effect of curcumol on NOD-like receptor thermoprotein domain 3 (NLRP3) inflammasomes, and analyze the mechanism underlying curcumol against liver fibrosis.

METHODS

Thirty Kunming mice were divided into a control group, a model group and a curcumol group according to a random number table, 10 mice in each group. Mice were intraperitoneally injected with 40% carbon tetrachloride (CCl₄:peanut oil, 2:3 preparation) at 5 mL/kg for 6 weeks, twice a week, for developing a liver fibrosis model. The mice in the control group were given the same amount of peanut oil twice a week for 6 weeks. The mice in the curcumol group were given curcumol (30 mL/kg) intragastrically, and the mice in the model and control groups were given the same amount of normal saline once a day for 6 weeks. Changes in liver structure were observed by hematoxylin and eosin (HE) and Masson staining. Liver function, liver fiber indices, and the expression of interleukin (IL)-10 and tumor necrosis factor-α (TNF-α) levels were determined by automatic biochemical analyzer and enzyme linked immunosorbent assay kit. Immunoblotting and reverse transcription-quantitative PCR (RT-qPCR) were performed to detect the expression of NLRP3 inflammasome-related molecules, TGF-β and collagen.

RESULTS

HE and Masson staining results showed that the hepatocytes of the model group were arranged irregularly with pseudo-lobular structure and a large amount of collagen deposition. The mice in the curcumol group had a significant decrease in liver function and liver fibers indices compared with the model group (P<0.05); RT-qPCR and Western blotting results reveal that, in the curcumol group, the mRNA and protein expression levels of NLRP3, IL-1 β, Caspase 1 and gasdermin D decreased significantly compared with the model group (P<0.05); immunohistochemical results showed that in the curcumol group, the protein expression levels of NLRP3 and IL-1 β decreased significantly compared with the model group (P<0.05).

CONCLUSION

A potential anti-liver fibrosis mechanism of curcumol may be associated with the inhibition of NLRP3 inflammasomes and decreasing the downstream inflammatory response.

Topical Application of the Antimicrobial Agent Triclosan Induces NLRP3 Inflammasome Activation and Mitochondrial Dysfunction

5-Chloro-2-(2,4-dichlorophenoxy)phenol (triclosan) is an antimicrobial chemical widely used in consumer household and clinical healthcare products. Human and animal studies have associated triclosan exposure with allergic disease. Mechanistic studies have identified triclosan as a mitochondrial uncoupler; recent studies suggest that mitochondria play an important role in immune cell function and are involved in activation of the NLRP3 inflammasome. In this study, early immunological effects were evaluated via NLRP3 activation following dermal triclosan application in a BALB/c murine model. These investigations revealed rapid caspase-1 activation and mature IL-1β secretion in the skin and draining lymph nodes (dLNs) after 1.5% and 3% triclosan exposure. Correspondingly, pro-Il-1b and S100a8 gene expression increased along with extracellular ATP in the skin. Peak gene expression of chemokines associated with caspase-1 activation occurred after 2 days of exposure in both skin tissue and dLNs. Phenotypic analysis showed an increase in neutrophils and macrophages in the dLN and myeloid and inflammatory monocytes in the skin tissue. Triclosan also caused mitochondrial dysfunction shown through effects on mitochondrial reactive oxygen species, mass, mitochondrial membrane potential, and mitochondrial morphology. These results indicate that following triclosan exposure, activation of the NLRP3 inflammasome occurs in both the skin tissue and dLNs, providing a possible mechanism for triclosan's effects on allergic disease and further support a connection between mitochondrial involvements in immunological responses.

Lymph-Derived Neutrophils Primarily Locate to the Subcapsular and Medullary Sinuses in Resting and Inflamed Lymph Nodes

Neutrophils are the first immune cells to be recruited from the blood to the tissue site of an infection or inflammation. It has been suggested that neutrophils are capable of migrating from the infected tissue via lymphatic vessels to the draining lymph nodes. However, it remains elusive as to which areas within the lymph nodes can be reached by such reversely migrating cells. To address this question, we applied a model for adoptive neutrophil transfer into the afferent lymphatic vessel that drains towards the popliteal lymph node in mice. We showed that resting and in vitro-activated neutrophils did not enter the lymph node parenchyma but localized primarily in the subcapsular and medullary sinuses. Within the medulla, neutrophils show random migration and are able to sense laser-induced sterile tissue injury by massively swarming to the damaged tissue site. Co-injected dendritic cells supported the entry of resting neutrophils into the lymph node parenchyma via the subcapsular sinus. In contrast, in vivo-activated adoptively transferred neutrophils were capable of migrating into the interfollicular areas of the lymph node. Collectively, the data presented here give further insights into the functional behavior of neutrophils within the lymph nodes.

Vaccinia Virus Infection Inhibits Skin Dendritic Cell Migration to the Draining Lymph Node

There is a paucity of information on dendritic cell (DC) responses to vaccinia virus (VACV), including the traffic of DCs to the draining lymph node (dLN). In this study, using a mouse model of infection, we studied skin DC migration in response to VACV and compared it with the tuberculosis vaccine Mycobacterium bovis bacille Calmette-Guérin (BCG), another live attenuated vaccine administered via the skin. In stark contrast to BCG, skin DCs did not relocate to the dLN in response to VACV. Infection with UV-inactivated VACV or modified VACV Ankara promoted DC movement to the dLN, indicating that interference with skin DC migration requires replication-competent VACV. This suppressive effect of VACV was capable of mitigating responses to a secondary challenge with BCG in the skin, ablating DC migration, reducing BCG transport, and delaying CD4+ T cell priming in the dLN. Expression of inflammatory mediators associated with BCG-triggered DC migration were absent from virus-injected skin, suggesting that other pathways invoke DC movement in response to replication-deficient VACV. Despite adamant suppression of DC migration, VACV was still detected early in the dLN and primed Ag-specific CD4+ T cells. In summary, VACV blocks skin DC mobilization from the site of infection while retaining the ability to access the dLN to prime CD4+ T cells.

Glycogen synthase kinase-3β inhibition alleviates activation of the NLRP3 inflammasome in myocardial infarction

Inflammasome-promoted sterile inflammation following cardiac damage is critically implicated in heart dysfunction after myocardial infarction (MI). Glycogen synthase kinase-3 (GSK-3β) is a prominent mediator of the inflammatory response, and high GSK-3 activity is associated with various heart diseases. We investigated the regulatory mechanisms of GSK-3β in activation of the nod-like receptor family pyrin domain containing 3 (NLRP3) inflammasome in a rat model with successful induction of MI on days 2-28. An in vitro investigation was performed using newborn rat/human cardiomyocytes and fibroblast cultures under typical inflammasome stimulation and hypoxia treatment. GSK-3β inhibition markedly improved myocardial dysfunction and prevented remodeling, with parallel reduction in the parameters of NLRP3 inflammasome activation after MI. GSK-3β inhibition reduced NLRP3 inflammasome activation in cardiac fibroblasts, but not in cardiomyocytes. GSK-3β's interaction with activating signal cointegrator (ASC) as well as GSK-3β inhibition reduced ASC phosphorylation and oligomerization at the tissues and cellular levels. Taken together, these data show that GSK-3β directly mediates NLRP3 inflammasome activation, causing cardiac dysfunction in MI.

Squalene emulsion-based vaccine adjuvants stimulate CD8 T cell, but not antibody responses, through a RIPK3-dependent pathway

The squalene-based oil-in-water emulsion (SE) vaccine adjuvant MF59 has been administered to more than 100 million people in more than 30 countries, in both seasonal and pandemic influenza vaccines. Despite its wide use and efficacy, its mechanisms of action remain unclear. In this study we demonstrate that immunization of mice with MF59 or its mimetic AddaVax (AV) plus soluble antigen results in robust antigen-specific antibody and CD8 T cell responses in lymph nodes and non-lymphoid tissues. Immunization triggered rapid RIPK3-kinase dependent necroptosis in the lymph node which peaked at 6 hr, followed by a sequential wave of apoptosis. Immunization with alum plus antigen did not induce RIPK3-dependent signaling. RIPK3-dependent signaling induced by MF59 or AV was essential for cross-presentation of antigen to CD8 T cells by Batf3-dependent CD8⁺ DCs. Consistent with this, RIPK3 deficient or Batf3 deficient mice were impaired in their ability to mount adjuvant-enhanced CD8 T cell responses. However, CD8 T cell responses were unaffected in mice deficient in MLKL, a downstream mediator of necroptosis. Surprisingly, antibody responses were unaffected in RIPK3-kinase or Batf3 deficient mice. In contrast, antibody responses were impaired by in vivo administration of the pan-caspase inhibitor Z-VAD-FMK, but normal in caspase-1 deficient mice, suggesting a contribution from apoptotic caspases, in the induction of antibody responses. These results demonstrate that squalene emulsion-based vaccine adjuvants induce antigen-specific CD8 T cell and antibody responses, through RIPK3-dependent and-independent pathways, respectively.

NLRP12 collaborates with NLRP3 and NLRC4 to promote pyroptosis inducing ganglion cell death of acute glaucoma

BACKGROUND

Acute glaucoma, characterized by a sudden elevation in intraocular pressure (IOP) and retinal ganglion cells (RGCs) death, is a major cause of irreversible blindness worldwide that lacks approved effective therapies, validated treatment targets and clear molecular mechanisms. We sought to explore the potential molecular mechanisms underlying the causal link between high IOP and glaucomatous RGCs death.

METHODS

A murine retinal ischemia/ reperfusion (RIR) model and an in vitro oxygen and glucose deprivation/reoxygenation (OGDR) model were used to investigate the pathogenic mechanisms of acute glaucoma.

RESULTS

Our findings reveal a novel mechanism of microglia-induced pyroptosis-mediated RGCs death associated with glaucomatous vision loss. Genetic deletion of gasdermin D (GSDMD), the effector of pyroptosis, markedly ameliorated the RGCs death and retinal tissue damage in acute glaucoma. Moreover, GSDMD cleavage of microglial cells was dependent on caspase-8 (CASP8)-hypoxia-inducible factor-1α (HIF-1α) signaling. Mechanistically, the newly identified nucleotide-binding leucine-rich repeat-containing receptor (NLR) family pyrin domain-containing 12 (NLRP12) collaborated with NLR family pyrin domain-containing 3 (NLRP3) and NLR family CARD domain-containing protein 4 (NLRC4) downstream of the CASP8-HIF-1α axis, to elicit pyroptotic processes and interleukin-1β (IL-1β) maturation through caspase-1 activation, facilitating pyroptosis and neuroinflammation in acute glaucoma. Interestingly, processing of IL-1β in turn magnified the CASP8-HIF-1α-NLRP12/NLRP3/NLRC4-pyroptosis circuit to accelerate inflammatory cascades.

CONCLUSIONS

These data not only indicate that the collaborative effects of NLRP12, NLRP3 and NLRC4 on pyroptosis are responsible for RGCs death, but also shed novel mechanistic insights into microglial pyroptosis, paving novel therapeutic avenues for the treatment of glaucoma-induced irreversible vision loss through simultaneously targeting of pyroptosis.

Inflammasome Adaptor ASC Is Highly Elevated in Lung Over Plasma and Relates to Inflammation and Lung Diffusion in the Absence of Speck Formation

Rationale: Caspase-1 is a zymogen whose activation predominantly depends upon the assembly of ASC monomers into insoluble prion-like polymers (specks). ASC polymers support caspase-1 dimer formation inducing a proximity mediated auto-activation of caspase-1. Therefore, the amount and nature of ASC monomers and polymers in lung bronchoalveolar lavage fluid (BALF) might serve as a marker of lung inflammasome activity.

Objectives: To determine whether lung ASC concentrations or oligomerization status predicts lung function or activity of lung inflammation.

Methods: BALF ASC amount and oligomerization status was studied in three distinct cohorts: (1) young healthy non-smokers, vapers and smokers; (2) healthy HIV+ smokers who underwent detailed lung function studies; and (3) hospitalized patients with suspected pneumonia. We quantified cell free BALF ASC levels by ELISA and immunoblot. Oligomers (i.e., ASC specks) were identified by chemical crosslinking and ability to sediment with centrifugation.

Measurement and Main Results: ASC levels are significantly higher in lung lining fluid than in plasma as well as higher in smoker lungs compared to non-smoker lungs. In this context, ASC levels correlate with macrophage numbers, smoking intensity and loss of lung diffusion capacity in a well-characterized cohort of healthy HIV+ smokers. However, only monomeric ASC was found in our BALF samples from all subjects, including patients with lung infections.

Conclusions: Even though, most, if not all, extracellular ASC in BALF exists in the soluble, monomeric form, monomeric ASC concentrations still reflect the inflammatory status of the lung microenvironment and correlate with loss of lung function.

The lymph node at a glance - how spatial organization optimizes the immune response

A hallmark of the mammalian immune system is its ability to respond efficiently to foreign antigens without eliciting an inappropriate response to self-antigens. Furthermore, a robust immune response requires the coordination of a diverse range of cells present at low frequencies within the host. This problem is solved, in part, by concentrating antigens, antigen-presenting cells and antigen-responsive cells in lymph nodes (LNs). Beyond housing these cell types in one location, LNs are highly organized structures consisting of pre-positioned cells within well-defined microanatomical niches. In this Cell Science at a Glance article and accompanying poster, we outline the key cellular populations and components of the LN microenvironment that are present at steady state and chronicle the dynamic changes in these elements following an immune response. This review highlights the LN as a staging ground for both innate and adaptive immune responses, while providing an elegant example of how structure informs function.

MyD88-dependent influx of monocytes and neutrophils impairs lymph node B cell responses to chikungunya virus infection via Irf5, Nos2 and Nox2

Humoral immune responses initiate in the lymph node draining the site of viral infection (dLN). Some viruses subvert LN B cell activation; however, our knowledge of viral hindrance of B cell responses of important human pathogens is lacking. Here, we define mechanisms whereby chikungunya virus (CHIKV), a mosquito-transmitted RNA virus that causes outbreaks of acute and chronic arthritis in humans, hinders dLN antiviral B cell responses. Infection of WT mice with pathogenic, but not acutely cleared CHIKV, induced MyD88-dependent recruitment of monocytes and neutrophils to the dLN. Blocking this influx improved lymphocyte accumulation, dLN organization, and CHIKV-specific B cell responses. Both inducible nitric oxide synthase (iNOS) and the phagocyte NADPH oxidase (Nox2) contributed to impaired dLN organization and function. Infiltrating monocytes expressed iNOS through a local IRF5- and IFNAR1-dependent pathway that was partially TLR7-dependent. Together, our data suggest that pathogenic CHIKV triggers the influx and activation of monocytes and neutrophils in the dLN that impairs virus-specific B cell responses.

Elucidating mechanisms by which viruses subvert B cell immunity and establish persistent infection is essential for the development of new therapeutic strategies against chronic viral infections. The humoral immune response initiates in the lymph node draining the site of viral infection. However, how persistent viruses evade B cell responses is poorly understood. In this study, we find that infection with pathogenic, persistent chikungunya virus triggers rapid recruitment of neutrophils and monocytes to the draining lymph node, which impair structural organization, lymphocyte accumulation, and downstream virus-specific B cell responses that are important for control of infection. This work enhances our understanding of the pathogenesis of acute and chronic CHIKV disease and highlights how local innate immune responses in draining lymphoid tissue dictate the effectiveness of downstream adaptive immunity.

From the Cradle to the Grave of an Infection: Host-Pathogen Interaction Visualized by Intravital Microscopy

During infections, interactions between host immune cells and the pathogen occur in distinct anatomical locations and along defined time scales. This can best be assessed in the physiological context of an infection in the living tissue. Consequently, intravital imaging has enabled us to dissect the critical phases and events throughout an infection in real time in living tissues. Specifically, advances in visualizing specific cell types and individual pathogens permitted tracking the early events of tissue invasion of the pathogen, cellular interactions involved in the induction of the immune response as well the events implicated in clearance of the infection. In this respect, two vantage points have evolved since the initial employment of this technique in the field of infection biology. On the one hand, strategies acquired by the pathogen to establish within the host and circumvent or evade the immune defenses have been elucidated. On the other hand, analyzing infections from the immune system's perspective has led to insights into the dynamic cellular interactions that are involved in the initial recognition of the pathogen, immune induction as well as effector function delivery and immunopathology. Furthermore, an increasing interest in probing functional parameters in vivo has emerged, such as the analysis of pathogen reactivity to stress conditions imposed by the host organism in order to mediate clearance upon pathogen encounter. Here, we give an overview on recent intravital microscopy findings of host-pathogen interactions along the course of an infection, from both the immune system's and pathogen's perspectives. We also discuss recent developments and future perspectives in extracting intravital information beyond the localization of pathogens and their interaction with immune cells. Such reporter systems on the pathogen's physiological state and immune cell functions may prove useful in dissecting the functional dynamics of host-pathogen interactions. © 2019 The Authors. Cytometry Part A published by Wiley Periodicals, Inc. on behalf of International Society for Advancement of Cytometry.

From atoms to physiology: what it takes to really understand inflammasomes

Rapid inflammatory responses to cytosolic threats are mediated by inflammasomes - large macromolecular signalling complexes that control the activation of the pro-inflammatory cytokines interleukin (IL)-1β and IL-18, as well as cell death by pyroptosis. Different inflammasome sensors are activated by diverse direct and indirect signals, and subsequently nucleate the polymerization of the adaptor molecule ASC to form signalling platforms macroscopically observed as ASC specks. Caspase-1 is autocatalytically activated at these sites and subsequently matures pro-inflammatory cytokines and the pore-forming effector molecule gasdermin D. While most molecules and basic assembly principles have been deduced from reductionist experimental systems, we still lack fundamental information on the structure and regulation of these complexes in their physiological environment and in the interplay with other signalling pathways. In this review, novel experimental approaches are proposed, including some that rely on nanobodies and single domain antibodies, to understand inflammasome assembly and regulation in the context of the relevant tissues or cells.

The Remarkable Plasticity of Macrophages: A Chance to Fight Cancer

It is well established that tumor-associated macrophages (TAM) found in most advanced tumors have a pro-tumoral role. In this context, TAM limit the activity of tumor-infiltrating lymphocytes (TIL), and a number of mechanisms have been described including a trapping in the stroma, impeding TIL to reach malignant cells. Based on these results, a number of therapeutic approaches have been designed to deplete TAM. However, during tumor regression induced by immunotherapeutic treatments, recent studies revealed that TAM can switch from pro-tumoral to anti-tumoral and actively cooperate with TIL. Here, we will review the two faces of TAM in their interaction with TIL. We will summarize how they can inhibit T cell activities in growing tumors, and how they may also, together with T cells, successfully contribute to tumor eradication after an appropriate stimulation. Finally, we will discuss current promising therapies combining TAM reprogramming with T cell-based immunotherapy.