Extracellular ATP Activates the NLRP3 Inflammasome and Is an Early Danger Signal of Skin Allograft Rejection

Emerging role of immunogenic cell death in cancer immunotherapy: Advancing next-generation CAR-T cell immunotherapy by combination

Immunogenic cell death (ICD) is a stress-driven form of regulated cell death (RCD) in which dying tumor cells' specific signaling pathways are activated to release damage-associated molecular patterns (DAMPs), leading to the robust anti-tumor immune response as well as a reversal of the tumor immune microenvironment from "cold" to "hot". Chimeric antigen receptor (CAR)-T cell therapy, as a landmark in anti-tumor immunotherapy, plays a formidable role in hematologic malignancies but falls short in solid tumors. The Gordian knot of CAR-T cells for solid tumors includes but is not limited to, tumor antigen heterogeneity or absence, physical and immune barriers of tumors. The combination of ICD induction therapy and CAR-T cell immunotherapy is expected to promote the intensive use of CAR-T cell in solid tumors. In this review, we summarize the characteristics of ICD, stress-responsive mechanism, and the synergistic effect of various ICD-based therapies with CAR-T cells to effectively improve anti-tumor capacity.

Alloreactive memory CD4 T cells promote transplant rejection by engaging DCs to induce innate inflammation and CD8 T cell priming

Alloreactive memory T cells have been implicated as central drivers of transplant rejection. Perplexingly, innate cytokines, such as IL-6, IL-1β, and IL-12, are also associated with rejection of organ transplants. However, the pathways of innate immune activation in allogeneic transplantation are unclear. While the role of microbial and cell death products has been previously described, we identified alloreactive memory CD4 T cells as the primary triggers of innate inflammation. Memory CD4 T cells engaged MHC II-mismatched dendritic cells (DCs), leading to the production of innate inflammatory cytokines. This innate inflammation was independent of several pattern recognition receptors and was primarily driven by TNF superfamily ligands expressed by alloreactive memory CD4 T cells. Blocking of CD40L and TNFα resulted in dampened inflammation, and mice genetically deficient in these molecules exhibited prolonged survival of cardiac allografts. Furthermore, myeloid cell and CD8 T cell infiltration into cardiac transplants was compromised in both CD40L- and TNFα-deficient recipients. Strikingly, we found that priming of naive alloreactive CD8 T cells was dependent on licensing of DCs by memory CD4 T cells. This study unravels the key mechanisms by which alloreactive memory CD4 T cells contribute to destructive pathology and transplant rejection.

Bacillus Calmette-Guérin immunotherapy induces an efficient antitumor response to control murine melanoma depending on MyD88 signaling

Bacillus Calmette-Guérin (BCG) is the first line treatment for bladder cancer and it is also proposed for melanoma immunotherapy. BCG modulates the tumor microenvironment (TME) inducing an antitumor effective response, but the immune mechanisms involved still poorly understood. The immune profile of B16-F10 murine melanoma cells was assessed by infecting these cells with BCG or stimulating them with agonists for different innate immune pathways such as TLRs, inflammasome, cGAS-STING and type I IFN. B16-F10 did not respond to any of those stimuli, except for type I IFN agonists, contrasting with bone marrow-derived macrophages (BMDMs) that showed high production of proinflammatory cytokines. Additionally, we confirmed that BCG is able to infect B16-F10, which in turn can activate macrophages and spleen cells from mice in co-culture experiments. Furthermore, we established a subcutaneous B16-F10 melanoma model for intratumoral BCG treatment and compared wild type mice to TLR2-/-, TLR3-/-, TLR4-/-, TLR7-/-, TLR3/7/9-/-, caspase 1-/-, caspase 11-/-, IL-1R-/-, cGAS-/-, STING-/-, IFNAR-/-, MyD88-/-deficient animals. These results in vivo demonstrate that MyD88 signaling is important for BCG immunotherapy to control melanoma in mice. Also, BCG fails to induce cytokine production in the co-culture experiments using B16-F10 and BMDMs or spleen cells derived from MyD88-/- compared to wild-type (WT) animals. Immunotherapy with BCG was not able to induce the recruitment of inflammatory cells in the TME from MyD88-/- mice, impairing tumor control and IFN-γ production by T cells. In conclusion, MyD88 impacts on both innate and adaptive responses to BCG leading to an efficient antitumor response against melanoma.

The purinergic receptor P2X7 as a modulator of viral vector-mediated antigen cross-presentation

Introduction

Modified Vaccinia Virus Ankara (MVA) is a safe vaccine vector inducing long- lasting and potent immune responses. MVA-mediated CD8+T cell responses are optimally induced, if both, direct- and cross-presentation of viral or recombinant antigens by dendritic cells are contributing.

Methods

To improve the adaptive immune responses, we investigated the role of the purinergic receptor P2X7 (P2RX7) in MVA-infected feeder cells as a modulator of cross-presentation by non-infected dendritic cells. The infected feeder cells serve as source of antigen and provide signals that help to attract dendritic cells for antigen take up and to license these cells for cross-presentation.

Results

We demonstrate that presence of an active P2RX7 in major histocompatibility complex (MHC) class I (MHCI) mismatched feeder cells significantly enhanced MVA-mediated antigen cross-presentation. This was partly regulated by P2RX7-specific processes, such as the increased availability of extracellular particles as well as the altered cellular energy metabolism by mitochondria in the feeder cells. Furthermore, functional P2RX7 in feeder cells resulted in a delayed but also prolonged antigen expression after infection.

Discussion

We conclude that a combination of the above mentioned P2RX7-depending processes leads to significantly increased T cell activation via cross- presentation of MVA-derived antigens. To this day, P2RX7 has been mostly investigated in regards to neuroinflammatory diseases and cancer progression. However, we report for the first time the crucial role of P2RX7 for antigen- specific T cell immunity in a viral infection model.

NLRP3 Inflammasome in Acute and Chronic Liver Diseases

NLRP3 (NOD-, LRR-, and pyrin domain-containing protein 3) is an intracellular complex that upon external stimuli or contact with specific ligands, recruits other components, forming the NLRP3 inflammasome. The NLRP3 inflammasome mainly mediates pyroptosis, a highly inflammatory mode of regulated cell death, as well as IL-18 and IL-1β production. Acute and chronic liver diseases are characterized by a massive influx of pro-inflammatory stimuli enriched in reactive oxygen species (ROS) and damage-associated molecular patterns (DAMPs) that promote the assemblage and activation of the NLRP3 inflammasome. As the major cause of inflammatory cytokine storm, the NLRP3 inflammasome exacerbates liver diseases, even though it might exert protective effects in regards to hepatitis C and B virus infection (HCV and HBV). Here, we summarize the current knowledge concerning NLRP3 inflammasome function in both acute and chronic liver disease and in the post liver transplant setting, focusing on the molecular mechanisms involved in NLRP3 activity.

DAMPs and DAMP-sensing receptors in inflammation and diseases

Damage-associated molecular patterns (DAMPs) are endogenous danger molecules produced in cellular damage or stress, and they can activate the innate immune system. DAMPs contain multiple types of molecules, including nucleic acids, proteins, ions, glycans, and metabolites. Although these endogenous molecules do not trigger immune response under steady-state condition, they may undergo changes in distribution, physical or chemical property, or concentration upon cellular damage or stress, and then they become DAMPs that can be sensed by innate immune receptors to induce inflammatory response. Thus, DAMPs play an important role in inflammation and inflammatory diseases. In this review, we summarize the conversion of homeostatic molecules into DAMPs; the diverse nature and classification, cellular origin, and sensing of DAMPs; and their role in inflammation and related diseases. Furthermore, we discuss the clinical strategies to treat DAMP-associated diseases via targeting DAMP-sensing receptors.

VCP Inhibition Augments NLRP3 Inflammasome Activation

Lysosomal membrane permeabilization caused either via phagocytosis of particulates or the uptake of protein aggregates can trigger the activation of NLRP3 inflammasome- an intense inflammatory response that drives the release of the pro-inflammatory cytokine IL-1β by regulating the activity of CASPASE 1. The maintenance of lysosomal homeostasis and lysosomal membrane integrity is facilitated by the AAA+ ATPase, VCP/p97 (VCP). However, the relationship between VCP and NLRP3 inflammasome activity remains unexplored. Here, we demonstrate that the VCP inhibitors, DBeQ and ML240 elicit the activation of NLRP3 inflammasome in bone marrow-derived macrophages (BMDMs) when used as activation stimuli. Moreover, genetic inhibition of VCP or VCP chemical inhibition enhances lysosomal membrane damage and augments LLoME-associated NLRP3 inflammasome activation in BMDMs. Similarly, VCP inactivation also augments NLRP3 inflammasome activation mediated by aggregated alpha-synuclein fibrils and lysosomal damage. These data suggest that VCP is a participant in the complex regulation of NLRP3 inflammasome activation.

Purinergic signaling influences the neuroinflammatory outcomes of a testosterone-derived synthetic in female rats: Resistance training protective effects on brain health

Physical exercise is recognized as a non-pharmacological approach to treat and protect against several neuroinflammatory conditions and thus to prevent brain disorders. However, the interest in ergogenic resources by athletes and bodybuilding practitioners is widespread and on the rise. These substances shorten the process of performance gain and improve aesthetics, having led to the prominent use and abuse of hormones in the past years. Recent evidence has shown that the purinergic system, composed of adenine nucleotides, nucleosides, enzymes, and receptors, participates in a wide range of processes within the brain, such as neuroinflammation, neuromodulation, and cellular communication. Here, we investigated the effects of the anabolic androgenic steroid (AAS) testosterone (TES) at a dose of 70 mg/kg/week in female rats and the neuroprotective effect of resistance exercise related to the purinergic system and oxidative stress parameters. Our findings showed a decrease in ATP and ADO hydrolysis in treated and trained animals. Furthermore, there was an increase in the density of purinoceptors (P2X7 and A2A) and inflammatory markers (IBA-1, NRLP3, CASP-1, IL-1β, and IL-6) in the cerebral cortex of animals that received AAS. On the other hand, exercise reversed neuroinflammatory parameters such as IBA-1, NLRP3, CASP-1, and IL-1β and improved antioxidant response and anti-inflammatory IL-10 cytokine levels. Overall, this study shows that the use of TES without indication or prescription disrupts brain homeostasis, as demonstrated by the increase in neuroinflammation, and that the practice of exercise can protect brain health.

Immunometabolic Regulation of Bacterial Infection, Biofilms, and Antibiotic Susceptibility

BACKGROUND

Upon infection, mucosal tissues activate a brisk inflammatory response to clear the pathogen, i.e., resistance to disease. Resistance to disease is orchestrated by tissue-resident macrophages, which undergo profound metabolic reprogramming after sensing the pathogen. These metabolically activated macrophages release many inflammatory factors, which promote their bactericidal function. However, in immunocompetent individuals, pathogens like Pseudomonas aeruginosa, Staphylococcus aureus, and Salmonella evade this type of immunity, generating communities that thrive for the long term.

SUMMARY

These organisms develop features that render them less susceptible to eradication, such as biofilms and increased tolerance to antibiotics. Furthermore, after antibiotic therapy withdrawal, "persister" cells rapidly upsurge, triggering inflammatory relapses that worsen host health. How these pathogens persisted in inflamed tissues replete with activated macrophages remains poorly understood.

KEY MESSAGES

In this review, we discuss recent findings indicating that the ability of P. aeruginosa, S. aureus, and Salmonella to evolve biofilms and antibiotic tolerance is promoted by the similar metabolic routes that regulate macrophage metabolic reprogramming.

"Other Than NLRP3" Inflammasomes: Multiple Roles in Brain Disease

Human neuroinflammatory and neurodegenerative diseases, whose prevalence keeps rising, are still unsolved pathobiological/therapeutical problems. Among others, recent etiology hypotheses stressed as their main driver a chronic neuroinflammation, which is mediated by innate immunity-related protein oligomers: the inflammasomes. A panoply of exogenous and/or endogenous harmful agents activates inflammasomes' assembly, signaling, and IL-1β/IL-18 production and neural cells' pyroptotic death. The underlying concept is that inflammasomes' chronic activation advances neurodegeneration while their short-lasting operation restores tissue homeostasis. Hence, from a therapeutic standpoint, it is crucial to understand inflammasomes' regulatory mechanisms. About this, a deluge of recent studies focused on the NLRP3 inflammasome with suggestions that its pharmacologic block would hinder neurodegeneration. Yet hitherto no evidence proves this view. Moreover, known inflammasomes are numerous, and the mechanisms regulating their expression and function may vary with the involved animal species and strains, as well as organs and cells, and the harmful factors triggered as a result. Therefore, while presently leaving out some little-studied inflammasomes, this review focuses on the "other than NLRP3" inflammasomes that participate in neuroinflammation's complex mechanisms: NLRP1, NLRP2, NLRC4, and AIM2. Although human-specific data about them are relatively scant, we stress that only a holistic view including several human brain inflammasomes and other potential pathogenetic drivers will lead to successful therapies for neuroinflammatory and neurodegenerative diseases.

Post-Transplant Cyclophosphamide Combined with Brilliant Blue G Reduces Graft-versus-Host Disease without Compromising Graft-versus-Leukaemia Immunity in Humanised Mice

Allogeneic haematopoietic stem cell transplantation (HSCT) leads to the establishment of graft-versus-leukaemia (GVL) immunity, but in many cases also results in the development of graft-versus-host disease (GVHD). This study aimed to determine if P2X7 antagonism using Brilliant Blue G (BBG) could improve the beneficial effects of post-transplant cyclophosphamide (PTCy) in a humanised mouse model of GVHD, without comprising GVL immunity. NOD.Cg-Prkdcscid Il2rgtm1Wjl (NSG) mice were injected with human peripheral blood mononuclear cells (PBMCs) (Day 0), then with cyclophosphamide (33 mg/kg) on Days 3 and 4, and with BBG (50 mg/kg) (or saline) on Days 0-10. PTCy with BBG reduced clinical GVHD development like that of PTCy alone. However, histological analysis revealed that the combined treatment reduced liver GVHD to a greater extent than PTCy alone. Flow cytometric analyses revealed that this reduction in liver GVHD by PTCy with BBG corresponded to an increase in human splenic CD39+ Tregs and a decrease in human serum interferon-γ concentrations. In additional experiments, humanised NSG mice, following combined treatment, were injected with human THP-1 acute myeloid leukaemia cells on Day 14. Flow cytometric analyses of liver CD33+ THP-1 cells showed that PTCy with BBG did not mitigate GVL immunity. In summary, PTCy combined with BBG can reduce GVHD without compromising GVL immunity. Future studies investigating P2X7 antagonism in combination with PTCy may lead to the development of novel treatments that more effectively reduce GVHD in allogeneic HSCT patients without promoting leukaemia relapse.

NLRP3 Contributes to Sarcopenia Associated to Dependency Recapitulating Inflammatory-Associated Muscle Degeneration

Sarcopenia, a complex and debilitating condition characterized by progressive deterioration of skeletal muscle, is the primary cause of age-associated disability and significantly impacts healthspan in elderly patients. Despite its prevalence among the aging population, the underlying molecular mechanisms are still under investigation. The NLRP3 inflammasome is crucial in the innate immune response and has a significant impact on diseases related to inflammation and aging. Here, we investigated the expression of the NLRP3 inflammasome pathway and pro-inflammatory cytokines in skeletal muscle and peripheral blood of dependent and independent patients who underwent hip surgery. Patients were categorized into independent and dependent individuals based on their Barthel Index. The expression of NLRP3 inflammasome components was significantly upregulated in sarcopenic muscle from dependent patients, accompanied by higher levels of Caspase-1, IL-1β and IL-6. Among older dependent individuals with sarcopenia, there was a significant increase in the MYH3/MYH2 ratio, indicating a transcriptional shift in expression from mature to developmental myosin isoforms. Creatine kinase levels and senescence markers were also higher in dependent patients, altogether resembling dystrophic diseases and indicating muscle degeneration. In summary, we present evidence for the involvement of the NLRP3/ASC/NEK7/Caspase-1 inflammasome pathway with activation of pro-inflammatory SASP in the outcome of sarcopenia in the elderly.

P2X4 signalling contributes to hyperactivity but not pain sensitization comorbidity in a mouse model of attention deficit/hyperactivity disorder

Introduction: Attention deficit/hyperactivity disorder (ADHD) is a common neurodevelopmental disorder characterized by hyperactivity, inattention, and impulsivity that often persist until adulthood. Frequent comorbid disorders accompany ADHD and two thirds of children diagnosed with ADHD also suffer from behavioural disorders and from alteration of sensory processing. We recently characterized the comorbidity between ADHD-like symptoms and pain sensitisation in a pharmacological mouse model of ADHD, and we demonstrated the implication of the anterior cingulate cortex and posterior insula. However, few studies have explored the causal mechanisms underlying the interactions between ADHD and pain. The implication of inflammatory mechanisms has been suggested but the signalling pathways involved have not been explored. Methods: We investigated the roles of purinergic signalling, at the crossroad of pain and neuroinflammatory pathways, by using a transgenic mouse line that carries a total deletion of the P2X4 receptor. Results: We demonstrated that P2X4 deletion prevents hyperactivity in the mouse model of ADHD. In contrast, the absence of P2X4 lowered thermal pain thresholds in sham conditions and did not affect pain sensitization in ADHD-like conditions. We further analysed microglia reactivity and the expression of inflammatory markers in wild type and P2X4KO mice. Our results revealed that P2X4 deletion limits microglia reactivity but at the same time exerts proinflammatory effects in the anterior cingulate cortex and posterior insula. Conclusion: This dual role of P2X4 could be responsible for the differential effects noted on ADHD-like symptoms and pain sensitization and calls for further studies to investigate the therapeutic benefit of targeting the P2X4 receptor in ADHD patients.

The regulatory role of eosinophils in adipose tissue depends on autophagy

Introduction

Obesity is a metabolic condition that elevates the risk of all-cause mortality. Brown and beige adipose tissues, known for their thermogenic properties, offer potential therapeutic targets for combating obesity. Recent reports highlight the role of immune cells, including eosinophils, in adipose tissue homeostasis, while the underlying mechanisms are poorly understood.

Methods

To study the role of autophagy in eosinophils in this process, we used a genetic mouse model lacking autophagy-associated protein 5 (Atg5), specifically within the eosinophil lineage (Atg5 eoΔ).

Results

The absence of Atg5 in eosinophils led to increased body weight, impaired glucose metabolism, and alterations in the cellular architecture of adipose tissue. Our findings indicate that Atg5 modulates the functional activity of eosinophils within adipose tissue rather than their abundance. Moreover, RNA-seq analysis revealed upregulation of arginase 2 (Arg2) in Atg5-knockout eosinophils. Increased Arg2 activity was shown to suppress adipocyte beiging. Furthermore, we observed enrichment of the purine pathway in the absence of Atg5 in eosinophils, leading to a pro-inflammatory shift in macrophages and a further reduction in beiging.

Discussion

The data shed light on the importance of autophagy in eosinophils and its impact on adipose tissue homeostasis by suppressing Arg2 expression and limiting inflammation in adipose tissue.

Modulatory immune responses in fungal infection associated with organ transplant - advancements, management, and challenges

Organ transplantation stands as a pivotal achievement in modern medicine, offering hope to individuals with end-stage organ diseases. Advancements in immunology led to improved organ transplant survival through the development of immunosuppressants, but this heightened susceptibility to fungal infections with nonspecific symptoms in recipients. This review aims to establish an intricate balance between immune responses and fungal infections in organ transplant recipients. It explores the fundamental immune mechanisms, recent advances in immune response dynamics, and strategies for immune modulation, encompassing responses to fungal infections, immunomodulatory approaches, diagnostics, treatment challenges, and management. Early diagnosis of fungal infections in transplant patients is emphasized with the understanding that innate immune responses could potentially reduce immunosuppression and promise efficient and safe immuno-modulating treatments. Advances in fungal research and genetic influences on immune-fungal interactions are underscored, as well as the potential of single-cell technologies integrated with machine learning for biomarker discovery. This review provides a snapshot of the complex interplay between immune responses and fungal infections in organ transplantation and underscores key research directions.

Regulated cell death and inflammasome activation in gut injury following traumatic surgery in vitro and in vivo: implication for postoperative death due to multiorgan dysfunction

Postoperative multi-organ dysfunction (MOD) is associated with significant mortality and morbidity. Necroptosis has been implicated in different types of solid organ injury; however, the mechanisms linking necroptosis to inflammation require further elucidation. The present study examines the involvement of necroptosis and NLR family pyrin domain containing 3 (NLRP3) inflammasome in small intestine injury following traumatic surgery. Kidney transplantation in rats and renal ischaemia-reperfusion (I/R) in mice were used as traumatic and laparotomic surgery models to study necroptosis and inflammasome activation in the small intestinal post-surgery; additional groups also received receptor-interacting protein kinase 1 (RIPK1) inhibitor necrostatin-1s (Nec-1s). To investigate whether necroptosis regulates inflammasome activity in vitro, necroptosis was induced in human colonic epithelial cancer cells (Caco-2) by a combination of tumour necrosis factor-alpha (TNFα), SMAC mimetic LCL-161 and pan-caspase inhibitor Q-VD-Oph (together, TLQ), and necroptosis was blocked by Nec-1s or mixed lineage kinase-domain like (MLKL) inhibitor necrosulfonamide (NSA). Renal transplantation and renal ischaemia-reperfusion (I/R) upregulated the expression of necroptosis mediators (RIPK1; RIPK3; phosphorylated-MLKL) and inflammasome components (P2X purinoceptor subfamily 7, P2X7R; NLRP3; caspase-1) in the small intestines at 24 h, and Nec-1s suppressed the expression of inflammasome components. TLQ treatment induced NLRP3 inflammasome, promoted cleavage of caspase-1 and interleukin-1 beta (IL-1β), and stimulated extracellular ATP release from Caco-2 cells, and MLKL inhibitor NSA prevented TLQ-induced inflammasome activity and ATP release from Caco-2 cells. Our work suggested that necroptosis and inflammasome interactively promote remote postoperative small intestinal injury, at least in part, through ATP purinergic signalling. Necroptosis-inflammasome axis may be considered as novel therapeutic target for tackling postoperative MOD in the critical care settings.

P2X7 receptor blockade reduces pyroptotic inflammation and promotes phagocytosis in Vibrio vulnificus infection

Vibrio vulnificus, a gram-negative bacterium, causes serious wound infections and septicemia. Once it develops into early phase sepsis, hyperinflammatory immune responses result in poor prognosis in patients. The present study aimed to examine the possible underlying pathogenic mechanism and explore potential agents that could protect against V. vulnificus cytotoxicity. Here, we report that infection of mouse macrophages with V. vulnificus triggers antiphagocytic effects and pyroptotic inflammation via ATP-mediated purinergic P2X7 receptor (P2X7R) signaling. V. vulnificus promoted P2X7-dependent nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) p65 translocation, modulating the expression of the inflammasome sensor NLR family pyrin domain containing 3 (NLRP3), adaptor apoptosis-associated speck-like protein containing a card (ASC), and pyroptotic protein gasdermin D (GSDMD) in mouse macrophages. V. vulnificus induced the NLRP3/caspase-1 inflammasome signaling complex expression that drives GSDMD transmembrane pore formation and secretion of interleukin (IL)-1β, IL-18, and macrophage inflammatory protein-2 (MIP-2). This effect was blocked by P2X7R antagonists, indicating that the P2X7R mediates GSDMD-related pyroptotic inflammation in macrophages through the NF-κB/NLRP3/caspase-1 signaling pathway. Furthermore, blockade of P2X7R reduced V. vulnificus-colony-forming units in the spleen, immune cell infiltration into the skin and lung tissues, and serum concentrations of IL-1β, IL-18, and MIP-2 in mice. These results indicate that P2X7R plays a vital role in mediating phagocytosis by macrophages and pyroptotic inflammation during V. vulnificus infection and provides new opportunities for therapeutic intervention in bacterial infections.

Exosomes derived from LPS-preconditioned bone marrow-derived MSC modulate macrophage plasticity to promote allograft survival via the NF-κB/NLRP3 signaling pathway

OBJECTIVES

This study investigated whether exosomes from LPS pretreated bone marrow mesenchymal stem cells (LPS pre-MSCs) could prolong skin graft survival.

METHODS

The exosomes were isolated from the supernatant of MSCs pretreated with LPS. LPS pre-Exo and rapamycin were injected via the tail vein into C57BL/6 mice allografted with BALB/c skin; graft survival was observed and evaluated. The accumulation and polarization of macrophages were examined by immunohistochemistry. The differentiation of macrophages in the spleen was analyzed by flow cytometry. For in vitro, an inflammatory model was established. Specifically, bone marrow-derived macrophages (BMDMs) were isolated and cultured with LPS (100 ng/ml) for 3 h, and were further treated with LPS pre-Exo for 24 h or 48 h. The molecular signaling pathway responsible for modulating inflammation was examined by Western blotting. The expressions of downstream inflammatory cytokines were determined by Elisa, and the polarization of macrophages was analyzed by flow cytometry.

RESULTS

LPS pre-Exo could better ablate inflammation compared to untreated MSC-derived exosomes (BM-Exo). These loaded factors inhibited the expressions of inflammatory factors via a negative feedback mechanism. In vivo, LPS pre-Exo significantly attenuated inflammatory infiltration, thus improving the survival of allogeneic skin graft. Flow cytometric analysis of BMDMs showed that LPS pre-Exo were involved in the regulation of macrophage polarization and immune homeostasis during inflammation. Further investigation revealed that the NF-κB/NLRP3/procaspase-1/IL-1β signaling pathway played a key role in LPS pre-Exo-mediated regulation of macrophage polarization. Inhibiting NF-κB in BMDMs could abolish the LPS-induced activation of inflammatory pathways and the polarization of M1 macrophages while increasing the proportion of M2 cells.

CONCLUSION

LPS pre-Exo are able to switch the polarization of macrophages and enhance the resolution of inflammation. This type of exosomes provides an improved immunotherapeutic potential in prolonging graft survival.

Single-cell analysis of graft-infiltrating host cells identifies caspase-1 as a potential therapeutic target for heart transplant rejection

Aims

Understanding the cellular mechanisms underlying early allograft rejection is crucial for the development of effective immunosuppressant strategies. This study aims to investigate the cellular composition of graft-infiltrating cells during the early rejection stage at a single-cell level and identify potential therapeutic targets.

Methods

A heterotopic heart transplant model was established using enhanced green fluorescent protein (eGFP)-expressing mice as recipients of allogeneic or syngeneic grafts. At 3 days post-transplant, eGFP-positive cells infiltrating the grafts were sorted and subjected to single-cell RNA-seq analysis. Potential molecular targets were evaluated by assessing graft survival and functions following administration of various pharmacological inhibitors.

Results

A total of 27,053 cells recovered from syngrafts and allografts were classified into 20 clusters based on expression profiles and annotated with a reference dataset. Innate immune cells, including monocytes, macrophages, neutrophils, and dendritic cells, constituted the major infiltrating cell types (>90%) in the grafts. Lymphocytes, fibroblasts, and endothelial cells represented a smaller population. Allografts exhibited significantly increased proportions of monocyte-derived cells involved in antigen processing and presentation, as well as activated lymphocytes, as compared to syngrafts. Differential expression analysis revealed upregulation of interferon activation-related genes in the innate immune cells infiltrating allografts. Pro-inflammatory polarization gene signatures were also enriched in these infiltrating cells of allografts. Gene profiling and intercellular communication analysis identified natural killer cells as the primary source of interferon-γ signaling, activating inflammatory monocytes that displayed strong signals of major histocompatibility complexes and co-stimulatory molecules. The inflammatory response was also associated with promoted T cell proliferation and activation in allografts during the early transplant stages. Notably, caspase-1 exhibited specific upregulation in inflammatory monocytes in response to interferon signaling. The regulon analysis also revealed a significant enrichment of interferon-related motifs within the transcriptional regulatory network of downstream inflammatory genes including caspase-1. Remarkably, pharmacological inhibition of caspase-1 was shown to reduce immune infiltration, prevent acute graft rejection, and improve cardiac contractile function.

Conclusion

The single-cell transcriptional profile highlighted the crucial role of caspase-1 in interferon-mediated inflammatory monocytes infiltrating heart transplants, suggesting its potential as a therapeutic target for attenuating rejection.

Baricitinib with cyclosporine eliminates acute graft rejection in fully mismatched skin and heart transplant models

Solid organ transplant represents a potentially lifesaving procedure for patients suffering from end-stage heart, lung, liver, and kidney failure. However, rejection remains a significant source of morbidity and immunosuppressive medications have significant toxicities. Janus kinase (JAK) inhibitors are effective immunosuppressants in autoimmune diseases and graft versus host disease after allogeneic hematopoietic cell transplantation. Here we examine the role of JAK inhibition in preclinical fully major histocompatibility mismatched skin and heart allograft models. Baricitinib combined with cyclosporine A (CsA) preserved fully major histocompatibility mismatched skin grafts for the entirety of a 111-day experimental period. In baricitinib plus CsA treated mice, circulating CD4+T-bet+ T cells, CD8+T-bet+ T cells, and CD4+FOXP3+ regulatory T cells were reduced. Single cell RNA sequencing revealed a unique expression profile in immune cells in the skin of baricitinib plus CsA treated mice, including decreased inflammatory neutrophils and increased CCR2- macrophages. In a fully major histocompatibility mismatched mismatched heart allograft model, baricitinib plus CsA prevented graft rejection for the entire 28-day treatment period compared with 9 days in controls. Our findings establish that the combination of baricitinib and CsA prevents rejection in allogeneic skin and heart graft models and supports the study of JAK inhibitors in human solid organ transplantation.

Sterile inflammation in liver transplantation

Sterile inflammation is the immune response to damage-associated molecular patterns (DAMPs) released during cell death in the absence of foreign pathogens. In the setting of solid organ transplantation, ischemia-reperfusion injury results in mitochondria-mediated production of reactive oxygen and nitrogen species that are a major cause of uncontrolled cell death and release of various DAMPs from the graft tissue. When properly regulated, the immune response initiated by DAMP-sensing serves as means of damage control and is necessary for initiation of recovery pathways and re-establishment of homeostasis. In contrast, a dysregulated or overt sterile inflammatory response can inadvertently lead to further injury through recruitment of immune cells, innate immune cell activation, and sensitization of the adaptive immune system. In liver transplantation, sterile inflammation may manifest as early graft dysfunction, acute graft failure, or increased risk of immunosuppression-resistant rejection. Understanding the mechanisms of the development of sterile inflammation in the setting of liver transplantation is crucial for finding reliable biomarkers that predict graft function, and for development of therapeutic approaches to improve long-term transplant outcomes. Here, we discuss the recent advances that have been made to elucidate the early signs of sterile inflammation and extent of damage from it. We also discuss new therapeutics that may be effective in quelling the detrimental effects of sterile inflammation.

Variation in CD8 T cell IFNγ differentiation to strains of Toxoplasma gondii is characterized by small effect QTLs with contribution from ROP16

Introduction

Toxoplasma gondii induces a strong CD8 T cell response characterized by the secretion of IFNγ that promotes host survival during infection. The initiation of CD8 T cell IFNγ responses in vitro differs widely between clonal lineage strains of T. gondii, in which type I strains are low inducers, while types II and III strains are high inducers. We hypothesized this phenotype is due to a polymorphic "Regulator Of CD8 T cell Response" (ROCTR).

Methods

Therefore, we screened F1 progeny from genetic crosses between the clonal lineage strains to identify ROCTR. Naïve antigen-specific CD8 T cells (T57) isolated from transnuclear mice, which are specific for the endogenous and vacuolar TGD057 antigen, were measured for their ability to become activated, transcribe Ifng and produce IFNγ in response to T. gondii infected macrophages.

Results

Genetic mapping returned four non-interacting quantitative trait loci (QTL) with small effect on T. gondii chromosomes (chr) VIIb-VIII, X and XII. These loci encompass multiple gene candidates highlighted by ROP16 (chrVIIb-VIII), GRA35 (chrX), TgNSM (chrX), and a pair of uncharacterized NTPases (chrXII), whose locus we report to be significantly truncated in the type I RH background. Although none of the chromosome X and XII candidates bore evidence for regulating CD8 T cell IFNγ responses, type I variants of ROP16 lowered Ifng transcription early after T cell activation. During our search for ROCTR, we also noted the parasitophorous vacuole membrane (PVM) targeting factor for dense granules (GRAs), GRA43, repressed the response suggesting PVM-associated GRAs are important for CD8 T cell activation. Furthermore, RIPK3 expression in macrophages was an absolute requirement for CD8 T cell IFNγ differentiation implicating the necroptosis pathway in T cell immunity to T. gondii.

Discussion

Collectively, our data suggest that while CD8 T cell IFNγ production to T. gondii strains vary dramatically, it is not controlled by a single polymorphism with strong effect. However, early in the differentiation process, polymorphisms in ROP16 can regulate commitment of responding CD8 T cells to IFNγ production which may have bearing on immunity to T. gondii.

Immunogenic cell death in cancer immunotherapy

Cancer immunotherapy has been acknowledged as a new paradigm for cancer treatment, with notable therapeutic effects on certain cancer types. Despite their significant potential, clinical studies over the past decade have revealed that cancer immunotherapy has low response rates in the majority of solid tumors. One of the key causes for poor responses is known to be the relatively low immunogenicity of solid tumors. Because most solid tumors are immune desert 'cold tumors' with antitumor immunity blocked from the onset of innate immunity, combination therapies that combine validated T-based therapies with approaches that can increase tumor-immunogenicity are being considered as relevant therapeutic options. This review paper focuses on immunogenic cell death (ICD) as a way of enhancing immunogenicity in tumor tissues. We will thoroughly review how ICDs such as necroptosis, pyroptosis, and ferroptosis can improve anti-tumor immunity and outline clinical trials targeting ICD. Finally, we will discuss the potential of ICD inducers. as an adjuvant for cancer immunotherapy.[BMB Reports 2023; 56(5): 275-286].

Immunogenic cell death in cancer immunotherapy

Cancer immunotherapy has been acknowledged as a new paradigm for cancer treatment, with notable therapeutic effects on certain cancer types. Despite their significant potential, clinical studies over the past decade have revealed that cancer immunotherapy has low response rates in the majority of solid tumors. One of the key causes for poor responses is known to be the relatively low immunogenicity of solid tumors. Because most solid tumors are immune desert 'cold tumors' with antitumor immunity blocked from the onset of innate immunity, combination therapies that combine validated T-based therapies with approaches that can increase tumor-immunogenicity are being considered as relevant therapeutic options. This review paper focuses on immunogenic cell death (ICD) as a way of enhancing immunogenicity in tumor tissues. We will thoroughly review how ICDs such as necroptosis, pyroptosis, and ferroptosis can improve anti-tumor immunity and outline clinical trials targeting ICD. Finally, we will discuss the potential of ICD inducers. as an adjuvant for cancer immunotherapy.[BMB Reports 2023; 56(5): 275-286].

Activation of immune signals during organ transplantation

The activation of host's innate and adaptive immune systems can lead to acute and chronic graft rejection, which seriously impacts graft survival. Thus, it is particularly significant to clarify the immune signals, which are critical to the initiation and maintenance of rejection generated after transplantation. The initiation of response to graft is dependent on sensing of danger and stranger molecules. The ischemia and reperfusion of grafts lead to cell stress or death, followed by releasing a variety of damage-associated molecular patterns (DAMPs), which are recognized by pattern recognition receptors (PRRs) of host immune cells to activate intracellular immune signals and induce sterile inflammation. In addition to DAMPs, the graft exposed to 'non-self' antigens (stranger molecules) are recognized by the host immune system, stimulating a more intense immune response and further aggravating the graft damage. The polymorphism of MHC genes between different individuals is the key for host or donor immune cells to identify heterologous 'non-self' components in allogeneic and xenogeneic organ transplantation. The recognition of 'non-self' antigen by immune cells mediates the activation of immune signals between donor and host, resulting in adaptive memory immunity and innate trained immunity to the graft, which poses a challenge to the long-term survival of the graft. This review focuses on innate and adaptive immune cells receptor recognition of damage-associated molecular patterns, alloantigens and xenoantigens, which is described as danger model and stranger model. In this review, we also discuss the innate trained immunity in organ transplantation.

ATP and its metabolite adenosine cooperatively upregulate the antigen-presenting molecules on dendritic cells leading to IFN-γ production by T cells

Dendritic cells (DCs) present foreign antigens to T cells via the major histocompatibility complex (MHC), thereby inducing acquired immune responses. ATP accumulates at sites of inflammation or in tumor tissues, which triggers local inflammatory responses. However, it remains to be clarified how ATP modulates the functions of DCs. In this study, we investigated the effects of extracellular ATP on mouse bone marrow-derived dendritic cells (BMDCs), as well as the potential for subsequent T cell activation. We found that high concentrations of ATP (1 mM) upregulated the cell surface expression levels of MHC-I, MHC-II, and co-stimulatory molecules CD80 and CD86, but not those of co-inhibitory molecules PD-L1 and PD-L2 in BMDCs. Increased surface expression of MHC-I, MHC-II, CD80, and CD86 was inhibited by a pan-P2 receptor antagonist. In addition, the upregulation of MHC-I and MHC-II expression was inhibited by an adenosine P1 receptor antagonist and by inhibitors of CD39 and CD73, which metabolize ATP to adenosine. These results suggest that adenosine is required for the ATP-induced upregulation of MHC-I and MHC-II. In the mixed leukocyte reaction assay, ATP-stimulated BMDCs activated CD4 and CD8 T cells and induced interferon-gamma (IFN-γ) production by these T cells. Collectively, these results suggest that high concentrations of extracellular ATP upregulate the expression of antigen-presenting and co-stimulatory molecules but not that of co-inhibitory molecules in BMDCs. Cooperative stimulation of ATP and its metabolite adenosine was required for the upregulation of MHC-I and MHC-II. These ATP-stimulated BMDCs induced the activation of IFN-γ-producing T cells upon antigen presentation.

Topical Application of Adenosine A2-Type Receptor Agonists Prevents Contact Hypersensitivity Reactions in Mice by Affecting Skin Dendritic Cells

Adenosine (Ado) produced by skin and skin migratory CD73⁺ dendritic cells is critically involved in tolerance to haptens. We therefore investigated the use of Ado receptor agonists for the treatment of contact hypersensitivity reactions. A_2A- 4-[2-[[6-Amino-9-(N-ethyl-β-D-ribofuranuronamidosyl)-9H-purin-2-yl]amino] ethyl]benzenepropanoic acid hydrochloride (CGS) and A_2B- 2-[[6-Amino-3,5-dicyano-4-[4-[cyclopropylmethoxy]phenyl]-2-pyridinyl]thio]-acetamide (BAY) specific Ado receptor agonists were epicutaneously applied to the skin before sensitization and challenge with DNFB. Both agonists reduced ear swelling compared with solvent controls. This was accompanied by fewer activated T cells in the skin after the challenge and by higher numbers of T cells expressing anergic markers such as LAG-3, CD137, PD-1, CD272, and TIM-3 in the lymph nodes of CGS-treated groups. In ear tissue, Ado receptor agonist treatment reduced the production of proinflammatory cytokines and chemokines as well as the infiltration by neutrophils after sensitization. Moreover, reduced numbers of skin migratory dendritic cells producing less IL-12 and exhibiting lower expression of CD86 were recorded in lymph nodes after sensitization. In cocultures of skin migratory dendritic cells from CGS-treated mice with T cells, reduced proliferation of T cells and decreased secretion of proinflammatory cytokines compared with that of solvent controls were apparent. In conclusion, topical application of Ado receptor agonists to the skin prevents sensitization of T cells against haptens by reducing the migration and activation of skin migratory dendritic cells.

Role of Damage-Associated Molecular Patterns (DAMPS) in the Postoperative Period after Colorectal Surgery

Anastomotic leakage (AL) is a defect of the intestinal wall at the anastomotic site and is one of the most severe complications in colorectal surgery. Previous studies have shown that the immune system response plays a significant role in the development of AL. In recent years, DAMPs (damage-associated molecular patterns) have been identified as cellular compounds with the ability to activate the immune system. The NLRP3 inflammasome plays an important role in the inflammatory responses which are mediated by DAMPs such as ATP, HSP proteins or uric acid crystals, when found in extracellular environments. Recent publications suggest that systemic concentration of DAMPs in patients with colorectal surgery may determine the inflammatory process and have a role in the occurrence of AL and other post-surgery complications. This review provides valuable knowledge about the current evidence supporting this hypothesis and highlights the possible role of these compounds in postoperative processes, which could open a new path to explore new strategies to prevent possible post-surgical complications.

Pharmacological suppression of NLRP3 inflammasome attenuated the development of autoimmune thyroiditis

Autoimmune thyroiditis (AIT), characterized by an endless inflammatory process of self-destruction, ultimately leads to chronic swelling of the thyroid gland and its dysfunction. Here, we investigated the involvement of the NLR pyrin domain-containing 3 (NLRP3) inflammasome in AIT development. We found that NLRP3 is significantly upregulated in the thyroid of AIT patients and mice with experimental autoimmune thyroiditis (EAT). Pharmacological suppression of NLRP3 using its inhibitor MCC950 suppressed the progression of EAT in vivo. Furthermore, MCC950 treatment significantly reduced the numbers of infiltrating CD4⁺ and CD8⁺ T cells in the thyroid. Moreover, MCC950 significantly lowered the amounts of T helper 1 cells, T helper 17 cells, interferon gamma, and interleukin-17A; however, it significantly increased regulatory-T-cell numbers and interleukin-10 levels. These results suggest that suppression of NLRP3 inflammasome activation reverses AIT by inhibiting Th1- and Th17-cell responses and promoting Treg cell responses. Hence, the NLRP3 inflammasome is a promising therapeutic and theragnostic target in AIT. inhibits Th1- and Th17-cell responses and promotes Treg cell responses.

NLRP3 inflammasome in neurodegenerative disease

Neurodegenerative diseases are characterized by a dysregulated neuro-glial microenvironment, culminating in functional deficits resulting from neuronal cell death. Inflammation is a hallmark of the neurodegenerative microenvironment and despite a critical role in tissue homeostasis, increasing evidence suggests that chronic inflammatory insult can contribute to progressive neuronal loss. Inflammation has been studied in the context of neurodegenerative disorders for decades but few anti-inflammatory treatments have advanced to clinical use. This is likely due to the related challenges of predicting and mitigating off-target effects impacting the normal immune response while detecting inflammatory signatures that are specific to the progression of neurological disorders. Inflammasomes are pro-inflammatory cytosolic pattern recognition receptors functioning in the innate immune system. Compelling pre-clinical data has prompted an intense interest in the role of the NLR family pyrin domain containing 3 (NLRP3) inflammasome in neurodegenerative disease. NLRP3 is typically inactive but can respond to sterile triggers commonly associated with neurodegenerative disorders including protein misfolding and aggregation, mitochondrial and oxidative stress, and exposure to disease-associated environmental toxicants. Clear evidence of enhanced NLRP3 inflammasome activity in common neurodegenerative diseases has coincided with rapid advancement of novel small molecule therapeutics making the NLRP3 inflammasome an attractive target for near-term interventional studies. In this review, we highlight evidence from model systems and patients indicating inflammasome activity in neurodegenerative disease associated with the NLRP3 inflammasome's ability to recognize pathologic forms of amyloid-β, tau, and α-synuclein. We discuss inflammasome-driven pyroptotic processes highlighting the potential utility of evaluating extracellular inflammasome-related proteins in the context of biomarker discovery. We complete the report by pointing out gaps in our understanding of intracellular modifiers of inflammasome activity and mechanisms regulating the resolution of inflammasome activation. The literature review and perspectives provide a conceptual platform for continued analysis of inflammation in neurodegenerative diseases through the study of inflammasomes and pyroptosis, mechanisms of inflammation and cell death now recognized to function in multiple highly prevalent neurological disorders.

Inflammasomes as biomarkers and therapeutic targets in traumatic brain injury and related-neurodegenerative diseases: A comprehensive overview

Given the ambiguity surrounding traumatic brain injury (TBI) pathophysiology and the lack of any Food and Drug Administration (FDA)-approved neurotherapeutic drugs, there is an increasing need to better understand the mechanisms of TBI. Recently, the roles of inflammasomes have been highlighted as both potential therapeutic targets and diagnostic markers in different neurodegenerative disorders. Indeed, inflammasome activation plays a pivotal function in the central nervous system (CNS) response to many neurological conditions, as well as to several neurodegenerative disorders, specifically, TBI. This comprehensive review summarizes and critically discusses the mechanisms that govern the activation and assembly of inflammasome complexes and the major methods used to study inflammasome activation in TBI and its implication for other neurodegenerative disorders. Also, we will review how inflammasome activation is critical in CNS homeostasis and pathogenesis, and how it can impact chronic TBI sequalae and increase the risk of developing neurodegenerative diseases. Additionally, we discuss the recent updates on inflammasome-related biomarkers and the potential to utilize inflammasomes as putative therapeutic targets that hold the potential to better diagnose and treat subjects with TBI.

Trained immunity - basic concepts and contributions to immunopathology

Trained immunity is a functional state of the innate immune response and is characterized by long-term epigenetic reprogramming of innate immune cells. This concept originated in the field of infectious diseases - training of innate immune cells, such as monocytes, macrophages and/or natural killer cells, by infection or vaccination enhances immune responses against microbial pathogens after restimulation. Although initially reported in circulating monocytes and tissue macrophages (termed peripheral trained immunity), subsequent findings indicate that immune progenitor cells in the bone marrow can also be trained (that is, central trained immunity), which explains the long-term innate immunity-mediated protective effects of vaccination against heterologous infections. Although trained immunity is beneficial against infections, its inappropriate induction by endogenous stimuli can also lead to aberrant inflammation. For example, in systemic lupus erythematosus and systemic sclerosis, trained immunity might contribute to inflammatory activity, which promotes disease progression. In organ transplantation, trained immunity has been associated with acute rejection and suppression of trained immunity prolonged allograft survival. This novel concept provides a better understanding of the involvement of the innate immune response in different pathological conditions, and provides a new framework for the development of therapies and treatment strategies that target epigenetic and metabolic pathways of the innate immune system.

P2X7 receptor activation impairs antitumour activity of natural killer cells

BACKGROUND AND PURPOSE

A high number of intratumoural infiltrating natural killer (NK) cells is associated with better survival in several types of cancer, constituting an important first line of defence against tumours. Hypoxia in the core of solid tumours induces cellular stress and ATP release into the extracellular space where it triggers purinergic receptor activation on tumour-associated immune cells. The aim of this study was to assess whether activation of the purinergic receptor P2X7 by extracellular ATP plays a role in the NK cells antitumour activity.

EXPERIMENTAL APPROACH

We carried out in vitro experiments using purified human NK cells triggered through P2X7 by extracellular ATP. NK cell killing activity against the tumour target cells K562 was studied by means of NK cytotoxicity assays. Likewise, we designed a subcutaneous solid tumour in vivo mouse model.

KEY RESULTS

In this study we found that human NK cells, expressing a functional plasma membrane P2X7, acquired an anergic state after ATP treatment, which impaired their antitumour activity and decreased IFN-γ secretion. This effect was reversed by specific P2X7 antagonists and pretreatment with either IL-2 or IL-15. Furthermore, genetic P2rx7 knockdown resulted in improved control of tumour size by NK cells. In addition, IL-2 therapy restored the ability of NK cells to diminish the size of tumours.

CONCLUSIONS AND IMPLICATIONS

Our results show that P2X7 activation represents a new mechanism whereby NK cells may lose antitumour effectiveness, opening the possibility of generating modified NK cells lacking P2X7 but with improved antitumour capacity.

Danger signals released during cold ischemia storage activate NLRP3 inflammasome in myeloid cells and influence early allograft function in liver transplantation

BACKGROUND

Innate immunity plays a fundamental role in solid organ transplantation. Myeloid cells can sense danger signals or DAMPs released after tissue or cell damage, such as during ischemia processes. This study aimed to identify DAMPs released during cold ischemia storage of human liver and analyze their ability to activate the inflammasome in myeloid cells and the possible implications in terms of short-term outcomes of liver transplantation.

METHODS

79 samples of organ preservation solution (OPS) from 79 deceased donors were collected after cold static storage. We used different analytical methods to measure DAMPs in these end-ischemic OPS (eiOPS) samples. We also used eiOPS in the human macrophage THP-1 cell line and primary monocyte cultures to study inflammasome activation.

FINDINGS

Different DAMPs were identified in eiOPS, several of which induced both priming and activation of the NLRP3 inflammasome in human myeloid cells. Cold ischemia time and donation after circulatory death negatively influenced the DAMP signature. Moreover, the presence of oligomeric inflammasomes and interleukin-18 in eiOPS correlated with early allograft dysfunction in liver transplant patients.

INTERPRETATION

DAMPs released during cold ischemia storage prime and activate the NLRP3 inflammasome in liver macrophages after transplantation, inducing a pro-inflammatory environment that will complicate the outcome of the graft. The use of pharmacological blockers targeting DAMPs or the NLRP3 inflammasome in liver ischemia during static cold storage or through extracorporeal organ support could be a suitable strategy to increase the success of liver transplantation.

FUNDING

Fundación Mutua Madrileña and Instituto de Salud Carlos III, Madrid, Spain.

Emerging Role of NLRP3 Inflammasome and Pyroptosis in Liver Transplantation

The nucleotide-binding domain leucine-rich repeat-receptor, pyrin domain-containing-3 (NLRP3) inflammasome contributes to the inflammatory response by activating caspase-1, which in turn participates in the maturation of interleukin (IL)-1β and IL-18, which are mainly secreted via pyroptosis. Pyroptosis is a lytic type of cell death that is controlled by caspase-1 processing gasdermin D. The amino-terminal fragment of gasdermin D inserts into the plasma membrane, creating stable pores and enabling the release of several proinflammatory factors. The activation of NLRP3 inflammasome and pyroptosis has been involved in the progression of liver fibrosis and its end-stage cirrhosis, which is among the main etiologies for liver transplantation (LT). Moreover, the NLRP3 inflammasome is involved in ischemia-reperfusion injury and early inflammation and rejection after LT. In this review, we summarize the recent literature addressing the role of the NLRP3 inflammasome and pyroptosis in all stages involved in LT and argue the potential targeting of this pathway as a future therapeutic strategy to improve LT outcomes. Likewise, we also discuss the impact of graft quality influenced by donation after circulatory death and the expected role of machine perfusion technology to modify the injury response related to inflammasome activation.

P2X7 receptor as the regulator of T-cell function in intestinal barrier disruption

The intestinal mucosa is a highly compartmentalized structure that forms a direct barrier between the host intestine and the environment, and its dysfunction could result in a serious disease. As T cells, which are important components of the mucosal immune system, interact with gut microbiota and maintain intestinal homeostasis, they may be involved in the process of intestinal barrier dysfunction. P2X7 receptor (P2X7R), a member of the P2X receptors family, mediates the effects of extracellular adenosine triphosphate and is expressed by most innate or adaptive immune cells, including T cells. Current evidence has demonstrated that P2X7R is involved in inflammation and mediates the survival and differentiation of T lymphocytes, indicating its potential role in the regulation of T cell function. In this review, we summarize the available research about the regulatory role and mechanism of P2X7R on the intestinal mucosa-derived T cells in the setting of intestinal barrier dysfunction.

An Overview on Immunogenic Cell Death in Cancer Biology and Therapy

Immunogenic cell death (ICD) is a modality of regulated cell death that is sufficient to promote an adaptive immune response against antigens of the dying cell in an immunocompetent host. An important characteristic of ICD is the release and exposure of damage-associated molecular patterns, which are potent endogenous immune adjuvants. As the induction of ICD can be achieved with conventional cytotoxic agents, it represents a potential approach for the immunotherapy of cancer. Here, different aspects of ICD in cancer biology and treatment are reviewed.

Biology of macrophage fate decision: Implication in inflammatory disorders

The activation of immune cells in response to stimuli present in their microenvironment is regulated by their metabolic profile. Unlike the signal transduction events, which overlap to a huge degree in diverse cellular processes, the metabolome of a cell reflects a more precise picture of cell physiology and function. Different factors governing the cellular metabolome include receptor signaling, macro and micronutrients, normoxic and hypoxic conditions, energy needs, and biomass demand. Macrophages have enormous plasticity and can perform diverse functions depending upon their phenotypic state. This review presents recent updates on the cellular metabolome and molecular patterns associated with M1 and M2 macrophages, also termed "classically activated macrophages" and "alternatively activated macrophages," respectively. M1 macrophages are proinflammatory in nature and predominantly Th1-specific immune responses induce their polarization. On the contrary, M2 macrophages are anti-inflammatory in nature and primarily participate in Th2-specific responses. Interestingly, the same macrophage cell can adapt to the M1 or M2 phenotype depending upon the clues from its microenvironment. We elaborate on the various tissue niche-specific factors, which govern macrophage metabolism and heterogeneity. Furthermore, the current review provides an in-depth account of deregulated macrophage metabolism associated with pathological disorders such as cancer, obesity, and atherosclerosis. We further highlight significant differences in various metabolic pathways governing the cellular bioenergetics and their impact on macrophage effector functions and associated disorders.

Blocking P2X purinoceptor 4 signalling alleviates cigarette smoke induced pulmonary inflammation

Background

Chronic obstructive pulmonary disease (COPD) is associated with elevated ATP levels in the extracellular space. Once released, ATP serves as danger signal modulating immune responses by activating purinergic receptors. Accordingly, purinergic signalling has been implicated in respiratory inflammation associated with cigarette smoke exposure. However, the role of P2X4-signalling has not been fully elucidated yet.

Methods

Here, we analysed the P2X4 mRNA expression in COPD patients as well as cigarette smoke-exposed mice. Furthermore, P2X4-signalling was blocked by either using a specific antagonist or genetic depletion of P2rx4 in mice applied to an acute and prolonged model of cigarette smoke exposure. Finally, we inhibited P2X4-signalling in macrophages derived from THP-1 before stimulation with cigarette smoke extract.

Results

COPD patients exhibited an increased P2X4 mRNA expression in cells isolated from the bronchoalveolar lavage fluid and peripheral mononuclear cells. Similarly, P2rx4 expression was elevated in lung tissue of mice exposed to cigarette smoke. Blocking P2X4-signalling in mice alleviated cigarette smoke induced airway inflammation as well as lung parenchyma destruction. Additionally, human macrophages derived from THP-1 cells released reduced concentrations of proinflammatory cytokines in response to cigarette smoke extract stimulation when P2X4 was inhibited.

Conclusion

Taken together, we provide evidence that P2X4-signalling promotes innate immunity in the immunopathologic responses induced by cigarette smoke exposure.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-022-02072-z.

Homogeneous Polyporus Polysaccharide Inhibit Bladder Cancer by Resetting Tumor-Associated Macrophages Toward M1 Through NF-κB/NLRP3 Signaling

Bladder cancer(BC)is one of the most common urinary system tumors, which characterized by a high incidence. Polyporus polysaccharide is the main active component of polyporus, which is clinically used in the treatment of bladder cancer, but the mechanism is not clear. In previous study, we isolated homogeneous polyporus polysaccharide(HPP) with high purity from polyporus. The goal of this study was to assess the polarization of macrophages induced by HPP in the bladder tumor microenvironment and explored its anti-bladder cancer mechanism through BBN bladder cancer rat model and Tumor associated macrophages(TAM). The results suggested that HPP regulates TAM polarization to improve the tumor inflammatory microenvironment, possibly through the NF-κB/NLRP3 signaling pathway. Our results suggested that HPP may be a potential therapeutic agent for bladder tumors.

Enhanced autophagy alleviated corneal allograft rejection via inhibiting NLRP3 inflammasome activity

Autophagy has been reported to be involved in many aspects of innate and adaptive immunity. Manipulating autophagy is recognized as a promising therapeutic approach for treating immunological diseases, including allograft rejection, and graft-versus-host disease. However, whether autophagy was closely associated with the pathogenesis of corneal allograft rejection remains largely unknown. Here, we showed that rapamycin (RAPA)-induced autophagy alleviated corneal allograft rejection. By contrast, blocking autophagic activity using 3-methyladeine (3-MA) aggravated corneal transplantation rejection. Mechanistically, we revealed that the enhanced autophagic turnover by RAPA inhibited NLRP3 inflammasome activity through NLRP3 degradation. While blocking the fusion of autophagosomes with lysosomes by bafilomycin A1(BafA1), the reduced NLRP3 inflammasome activity induced by RAPA was significantly restored, with increased protein levels of NLRP3 and cleaved Casp-1(p10), as well as IL-1β secretion. Moreover, we further revealed that pharmacologically blocking NLRP3 inflammasome signaling prolonged the survival of corneal allografts. Taken together, these findings underscored the critical roles of enhanced autophagy in treating corneal allograft rejection, which provided an alternative intervention strategy to control corneal transplantation rejection.

The long β2,3-sheets encoded by redundant sequences play an integral role in the channel function of P2X7 receptors

P2X receptors are a class of nonselective cation channels widely distributed in the immune and nervous systems, and their dysfunction is a significant cause of tumors, inflammation, leukemia, and immune diseases. P2X7 is a unique member of the P2X receptor family with many properties that differ from other subtypes in terms of primary sequence, the architecture of N- and C-terminals, and channel function. Here, we suggest that the observed lengthened β2- and β3-sheets and their linker (loop β2,3), encoded by redundant sequences, play an indispensable role in the activation of the P2X7 receptor. We show that deletion of this longer structural element leads to the loss of P2X7 function. Furthermore, by combining mutagenesis, chimera construction, surface expression, and protein stability analysis, we found that the deletion of the longer β2,3-loop affects P2X7 surface expression but, more importantly, that this loop affects channel gating of P2X7. We propose that the longer β2,3-sheets may have a negative regulatory effect on a loop on the head domain and on the structural element formed by E171 and its surrounding regions. Understanding the role of the unique structure of the P2X7 receptor in the gating process will aid in the development of selective drugs targeting this subtype.

PM2.5 exposure inducing ATP alteration links with NLRP3 inflammasome activation

Fine particulate matter (PM_2.5) has been the primary air pollutant and the fourth leading risk factor for disease and death in the world. Exposure to PM_2.5 is related to activation of the NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome, but the mechanism of PM_2.5 affecting the NLRP3 inflammasome is still unclear. Previous studies have shown that PM_2.5 can cause alterations in adenosine triphosphate (ATP), and an increase in extracellular ATP and a decrease in intracellular ATP can trigger the activation process of the NLRP3 inflammasome. Therefore, we emphasize that ATP changes may be the central link and key mechanism of PM_2.5 exposure that activates the NLRP3 inflammasome. This review briefly elucidates and summarizes how PM_2.5 acts on ATP and subsequently further impacts the NLRP3 inflammasome. Investigation of ATP changes due to exposure to PM_2.5 may be essential to regulate NLRP3 inflammasome activation and treat inflammation-related diseases such as coronavirus disease 2019 (COVID-19).

Galvanic current activates the NLRP3 inflammasome to promote type I collagen production in tendon

The NLRP3 inflammasome coordinates inflammation in response to different pathogen- and damage-associated molecular patterns, being implicated in different infectious, chronic inflammatory, metabolic and degenerative diseases. In chronic tendinopathic lesions, different non-resolving mechanisms produce a degenerative condition that impairs tissue healing and which therefore complicates their clinical management. Percutaneous needle electrolysis consists of the application of a galvanic current and is an emerging treatment for tendinopathies. In the present study, we found that galvanic current activates the NLRP3 inflammasome and induces an inflammatory response that promotes a collagen-mediated regeneration of the tendon in mice. This study establishes the molecular mechanism of percutaneous electrolysis that can be used to treat chronic lesions and describes the beneficial effects of an induced inflammasome-related response.

The Role of NLRP3 Inflammasome in Alzheimer’s Disease and Potential Therapeutic Targets

Alzheimer’s disease (AD) is a common age-related neurodegenerative disease characterized by progressive cognitive dysfunction and behavioral impairment. The typical pathological characteristics of AD are extracellular senile plaques composed of amyloid ß (Aβ) protein, intracellular neurofibrillary tangles formed by the hyperphosphorylation of the microtubule-associated protein tau, and neuron loss. In the past hundred years, although human beings have invested a lot of manpower, material and financial resources, there is no widely recognized drug for the effective prevention and clinical cure of AD in the world so far. Therefore, evaluating and exploring new drug targets for AD treatment is an important topic. At present, researchers have not stopped exploring the pathogenesis of AD, and the views on the pathogenic factors of AD are constantly changing. Multiple evidence have confirmed that chronic neuroinflammation plays a crucial role in the pathogenesis of AD. In the field of neuroinflammation, the nucleotide-binding oligomerization domain-like receptor pyrin domain-containing 3 (NLRP3) inflammasome is a key molecular link in the AD neuroinflammatory pathway. Under the stimulation of Aβ oligomers and tau aggregates, it can lead to the assembly and activation of NLRP3 inflammasome in microglia and astrocytes in the brain, thereby causing caspase-1 activation and the secretion of IL-1β and IL-18, which ultimately triggers the pathophysiological changes and cognitive decline of AD. In this review, we summarize current literatures on the activation of NLRP3 inflammasome and activation-related regulation mechanisms, and discuss its possible roles in the pathogenesis of AD. Moreover, focusing on the NLRP3 inflammasome and combining with the upstream and downstream signaling pathway-related molecules of NLRP3 inflammasome as targets, we review the pharmacologically related targets and various methods to alleviate neuroinflammation by regulating the activation of NLRP3 inflammasome, which provides new ideas for the treatment of AD.

Implication of mitochondrial ROS-NLRP3 inflammasome axis during two-hit mediated acute lung injury in mice

Acute lung injury (ALI) caused by acid aspiration often accompanies bacterial components leading to exaggerated inflammation and can result in acute respiratory distress syndrome (ARDS), but the underlying mechanisms behind such an exacerbation remain unclear. NLRP3 inflammasome and mitochondrial ROS (mtROS) have been implicated in ALI but its role in injury caused through two hit i.e. Hydrochloric acid (HCl) + Lipopolysaccharide (LPS) is not known. Therefore, the present study is designed to elucidate the role of mtROS-NLPR3 inflammasome upon "two-hit" mediated ALI. Our data showed that "two-hit" induced ALI results in aggravated lung inflammation as compared to either of single hit(s) as reflected by a steep increase in inflammatory cells particularly neutrophils in bronchoalveolar lavage fluid (BALF). Further, enhanced inflammation was associated with increased mtROS as depicted by data on mean fluorescence intensity (MFI) of MitoSOX⁺ neutrophils and macrophages in BALF of two-hit simulated mice. Importantly, ALI results in activation of NLRP3 inflammasome as reflected by active caspase-1 protein expression and IL-1β levels. Interestingly, NLRP3 inflammasome inhibitor, MCC950 suppressed the lung inflammation remarkably. Further, Mito-tempo, a mitochondrial-targeted antioxidant, halted "two-hit" mediated NLRP3 inflammasome activation and IL-1β release followed by amelioration of lung inflammation. Suppression in MFI of MitoSOX⁺ stained neutrophils and macrophages by Mito-tempo was associated with down-regulation of phospho-p65-NF-κB and its dependent genes (IL-1β/TNF-α/IL-6). Overall, our data suggest that NLRP3 inflammasome activation by mtROS plays a critical role in pathogenesis of exaggerated inflammation and therefore targeting mtROS-NLRP3 inflammasome axis may be an attractive option for combating ALI/ARDS.

Agonists, Antagonists, and Modulators of P2X7 Receptors

The P2X7 receptor has been proposed as a novel drug target for different types of diseases associated with inflammation, including brain diseases, peripheral inflammation, and cancers. Structurally diverse P2X7 receptor antagonists, mainly negative allosteric modulators (NAMs), have been developed in recent years, and several P2X7 receptor antagonists are currently evaluated in clinical trials. The P2X7 receptor requires high micro- to even millimolar ATP concentrations to be activated. Selective agonists for the P2X7 receptor are not available. Positive allosteric modulators (PAMs) have been described, but PAMs with high potency and selectivity are still lacking. This chapter discusses medicinal chemistry approaches toward the development of P2X7 receptor modulators and presents a selection of recommended tool compounds for studying P2X7 receptors in humans and rodents.

Characterization of P2X7 Receptors in Human Blood Cells

P2X7 receptors are expressed in different circulating immune cells. Depending on the cell in which they are expressed, their function could vary from activation of the leucine-rich repeat receptor pyrin domain containing 3 (NLRP3) inflammasome or the shedding of different surface receptors. The P2X7 receptor has been involved in the evolution of several inflammatory diseases, and thus its characterization in blood samples is important to investigate its role in human diseases. In this chapter, we present different methods to detect the presence and the activation of P2X7 receptors in whole blood samples. These methods could be used to evaluate the degree of P2X7 receptor activation in blood samples from patients suffering different chronic inflammatory diseases.

P2X7 receptor: the regulator of glioma tumor development and survival

P2X7 is an ionotropic nucleotide receptor, forming the cation channel upon ATP stimulation. It can also function as a large membrane pore as well as transmit ATP-dependent signal without forming a channel at all. P2X7 activity in somatic cells is well-known, but remains poorly studied in glioma tumors. The current paper presents the comprehensive study of P2X7 activity in C6 and glioma cell line showing the wide range of effects the receptor has on glioma biology. We observed that P2X7 stimulation boosts glioma cell proliferation and increases cell viability. P2X7 activation promoted cell adhesion, mitochondria depolarization, and reactive oxygen species overproduction in C6 cells. P2X7 receptor also influenced glioma tumor growth in vivo via activation of pro-survival signaling pathways and ATP release. Treatment with Brilliant Blue G, a selective P2X7 antagonist, effectively inhibited glioma tumor development; decreased the expression of negative prognostic cancer markers pro-survival and epithelial-mesenchymal transition (EMT)-related proteins; and modulated the immune response toward glioma tumor in vivo. Finally, pathway-specific enrichment analysis of the microarray data from human patients also showed an upregulation of P2X7 receptor in gliomas from grades I to III. The presented results shed more light on the role of P2X7 receptor in the biology of this disease.