Critical role for mast cells in interleukin-1β-driven skin inflammation associated with an activating mutation in the nlrp3 protein

Lipid-orchestrated paracrine circuit coordinates mast cell maturation and anaphylaxis through functional interaction with fibroblasts

Interaction of mast cells (MCs) with fibroblasts is essential for MC maturation within tissue microenvironments, although the underlying mechanism is incompletely understood. Through a phenotypic screening of >30 mouse lines deficient in lipid-related genes, we found that deletion of the lysophosphatidic acid (LPA) receptor LPA1, like that of the phospholipase PLA2G3, the prostaglandin D2 (PGD2) synthase L-PGDS, or the PGD2 receptor DP1, impairs MC maturation and thereby anaphylaxis. Mechanistically, MC-secreted PLA2G3 acts on extracellular vesicles (EVs) to supply lysophospholipids, which are converted by fibroblast-derived autotaxin (ATX) to LPA. Fibroblast LPA1 then integrates multiple pathways required for MC maturation by facilitating integrin-mediated MC-fibroblast adhesion, IL-33-ST2 signaling, L-PGDS-driven PGD2 generation, and feedforward ATX-LPA1 amplification. Defective MC maturation resulting from PLA2G3 deficiency is restored by supplementation with LPA1 agonists or PLA2G3-modified EVs. Thus, the lipid-orchestrated paracrine circuit involving PLA2G3-driven lysophospholipid, eicosanoid, integrin, and cytokine signaling fine-tunes MC-fibroblast communication, ensuring MC maturation.

CANE, a Component of the NLRP3 Inflammasome, Promotes Inflammasome Activation

The nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3, also called cryopyrin) inflammasome is an intracellular innate immune complex, which consists of the pattern-recognition receptor NLRP3, the adaptor apoptosis-assciated speck-like protein containing a caspase recruitment domain, and procaspase-1. Aberrant activation of the NLRP3 inflammasome causes an autoinflammatory disease called cryopyrin-associated periodic syndrome (CAPS). CAPS is caused by gain-of-function mutations in the NLRP3-encoding gene CIAS1; however, the mechanism of CAPS pathogenesis has not been fully understood. Thus, unknown regulators of the NLRP3 inflammasome, which are associated with CAPS development, are being investigated. To identify novel components of the NLRP3 inflammasome, we performed a high-throughput screen using a human protein array, with NLRP3 as the bait. We identified a NLRP3-binding protein, which we called the cryopyrin-associated nano enhancer (CANE). We demonstrated that CANE increased IL-1β secretion after NLRP3 inflammasome reconstitution in human embryonic kidney 293T cells and formed a "speck" in the cytosol, a hallmark of NLRP3 inflammasome activity. Reduced expression of endogenous CANE decreased IL-1β secretion upon stimulation with the NLRP3 agonist nigericin. To investigate the role of CANE in vivo, we developed CANE-transgenic mice. The PBMCs and bone marrow-derived macrophages of CANE-transgenic mice exhibited increased IL-1β secretion. Moreover, increased autoinflammatory neutrophil infiltration was observed in the s.c. tissue of CANE-transgenic versus wild-type mice; these phenotypes were consistent with those of CAPS model mice. These findings suggest that CANE, a component of the NLRP3 inflammasome, is a potential modulator of the inflammasome and a contributor to CAPS pathogenesis.

Metabolism-inflammasome crosstalk shapes innate and adaptive immunity

Inflammasomes are a central component of innate immunity and play a vital role in regulating innate immune response. Activation of inflammasomes is also indispensable for adaptive immunity, modulating the development and response of adaptive immunity. Recently, increasing studies have shown that metabolic alterations and adaptations strongly influence and regulate the differentiation and function of the immune system. In this review, we will take a holistic view of how inflammasomes bridge innate and adaptive (especially T cell) immunity and how inflammasomes crosstalk with metabolic signals during the immune responses. And, special attention will be paid to the metabolic control of inflammasome-mediated interactions between innate and adaptive immunity in disease. Understanding the metabolic regulatory functions of inflammasomes would provide new insights into future research directions in this area and may help to identify potential targets for inflammasome-associated diseases and broaden therapeutic avenues.

The mast cell-T lymphocyte axis impacts cancer: Friend or foe?

Crosstalk between mast cells (MCs) and T lymphocytes (TLs) releases specific signals that create an environment conducive to tumor development. Conversely, they can protect against cancer by targeting tumor cells for destruction. Although their role in immunity and cancer is complex, their potential in anticancer strategies is often underestimated. When peripheral MCs are activated, they can affect cancer development. Tumor-infiltrating TLs may malfunction and contribute to aggressive cancer and poor prognoses. One promising approach for cancer patients is TL-based immunotherapies. Recent reports suggest that MCs modulate TL activity in solid tumors and may be a potential therapeutic layer in multitargeting anticancer strategies. Pharmacologically modulating MC activity can enhance the anticancer cytotoxic TL response in tumors. By identifying tumor-specific targets, it has been possible to genetically alter patients' cells into fully humanized anticancer cellular therapies for autologous transplantation, including the engineering of TLs and MCs to target and kill cancer cells. Hence, recent scientific evidence provides a broader understanding of MC-TL activity in cancer.

Anaphylactic degranulation by mast cells requires the mobilization of inflammasome components

The inflammasome components NLRP3 and ASC are cytosolic proteins, which upon sensing endotoxins or danger cues, form multimeric complexes to process interleukin (IL)-1β for secretion. Here we found that antigen (Ag)-triggered degranulation of IgE-sensitized mast cells (MCs) was mediated by NLRP3 and ASC. IgE-Ag stimulated NEK7 and Pyk2 kinases in MCs to induce the deposition of NLRP3 and ASC on granules and form a distinct protein complex (granulosome) that chaperoned the granules to the cell surface. MCs deficient in NLRP3 or ASC did not form granulosomes, degranulated poorly in vitro and did not evoke systemic anaphylaxis in mice. IgE-Ag-triggered anaphylaxis was prevented by an NLRP3 inhibitor. In endotoxin-primed MCs, pro-IL-1β was rapidly packaged into granules after IgE-Ag stimulation and processed within granule remnants by proteases after degranulation, causing lethal anaphylaxis in mice. During IgE-Ag-mediated degranulation of endotoxin-primed MCs, granulosomes promoted degranulation, combined with exteriorization and processing of IL-1β, resulting in severe inflammation.

The discovery of NLRP3 and its function in cryopyrin-associated periodic syndromes and innate immunity

From studies of individual families to global collaborative efforts, the NLRP3 inflammasome is now recognized to be a key regulator of innate immunity. Activated by a panoply of pathogen-associated and endogenous triggers, NLRP3 serves as an intracellular sensor that drives carefully coordinated assembly of the inflammasome, and downstream inflammation mediated by IL-1 and IL-18. Initially discovered as the cause of the autoinflammatory spectrum of cryopyrin-associated periodic syndrome (CAPS), NLRP3 is now also known to play a role in more common diseases including cardiovascular disease, gout, and liver disease. We have seen cohesion in results from clinical studies in CAPS patients, ex vivo studies of human cells and murine cells, and in vivo murine models leading to our understanding of the downstream pathways, cytokine secretion, and cell death pathways that has solidified the role of autoinflammation in the pathogenesis of human disease. Recent advances in our understanding of the structure of the inflammasome have provided ways for us to visualize normal and mutant protein function and pharmacologic inhibition. The subsequent development of targeted therapies successfully used in the treatment of patients with CAPS completes the bench to bedside translational loop which has defined the study of this unique protein.

Pathogenic NLRP3 mutants form constitutively active inflammasomes resulting in immune-metabolic limitation of IL-1β production

Cryopyrin-associated periodic syndrome (CAPS) is an autoinflammatory condition resulting from monoallelic NLRP3 variants that facilitate IL-1β production. Although these are gain-of-function variants characterized by hypersensitivity to cell priming, patients with CAPS and animal models of the disease may present inflammatory flares without identifiable external triggers. Here we find that CAPS-associated NLRP3 variants are forming constitutively active inflammasome, which induce increased basal cleavage of gasdermin D, IL-18 release and pyroptosis, with a concurrent basal pro-inflammatory gene expression signature, including the induction of nuclear receptors 4 A. The constitutively active NLRP3-inflammasome of CAPS is responsive to the selective NLRP3 inhibitor MCC950 and its activation is regulated by deubiquitination. Despite their preactivated state, the CAPS inflammasomes are responsive to activation of the NF-κB pathway. NLRP3-inflammasomes with CAPS-associated variants affect the immunometabolism of the myeloid compartment, leading to disruptions in lipids and amino acid pathways and impaired glycolysis, limiting IL-1β production. In summary, NLRP3 variants causing CAPS form a constitutively active inflammasome inducing pyroptosis and IL-18 release without cell priming, which enables the host's innate defence against pathogens while also limiting IL-1β-dependent inflammatory episodes through immunometabolism modulation.

KCNN4 links PIEZO-dependent mechanotransduction to NLRP3 inflammasome activation

Immune cells sense the microenvironment to fine-tune their inflammatory responses. Patients with cryopyrin-associated periodic syndrome (CAPS), caused by mutations in the NLRP3 gene, develop autoinflammation triggered by nonantigenic cues such as from the environment. However, the underlying mechanisms are poorly understood. Here, we uncover that KCNN4, a calcium-activated potassium channel, links PIEZO-mediated mechanotransduction to NLRP3 inflammasome activation. Yoda1, a PIEZO1 agonist, lowered the threshold for NLRP3 inflammasome activation. PIEZO-mediated sensing of stiffness and shear stress increased NLRP3-dependent inflammation. Myeloid-specific deletion of PIEZO1/2 protected mice from gouty arthritis. Mechanistically, activation of PIEZO1 triggers calcium influx, which activates KCNN4 to evoke potassium efflux and promotes NLRP3 inflammasome activation. Activation of PIEZO signaling was sufficient to activate the inflammasome in cells expressing CAPS-causing NLRP3 mutants via KCNN4. Last, pharmacological inhibition of KCNN4 alleviated autoinflammation in cells of patients with CAPS and in mice bearing a CAPS mutation. Thus, PIEZO-dependent mechanical inputs boost inflammation in NLRP3-dependent diseases, including CAPS.

Regulated cell death in neutrophils: From apoptosis to NETosis and pyroptosis

Neutrophils are among the most abundant immune cells, representing about 50%- 70% of all circulating leukocytes in humans. Neutrophils rapidly infiltrate inflamed tissues and play an essential role in host defense against infections. They exert microbicidal activity through a variety of specialized effector mechanisms, including phagocytosis, production of reactive oxygen species, degranulation and release of secretory vesicles containing broad-spectrum antimicrobial factors. In addition to their homeostatic turnover by apoptosis, recent studies have revealed the mechanisms by which neutrophils undergo various forms of regulated cell death. In this review, we will discuss the different modes of regulated cell death that have been described in neutrophils, with a particular emphasis on the current understanding of neutrophil pyroptosis and its role in infections and autoinflammation.

Functionalized nanomaterials targeting NLRP3 inflammasome driven immunomodulation: Friend or Foe

The advancement in drug delivery systems in recent times has significantly enhanced therapeutic effects by enabling site-specific targeting through nanocarriers. These nanocarriers serve as invaluable tools for pharmacotherapeutic advancements against various disorders that enhance the effectiveness of encapsulated drugs by reducing their toxicity and increasing the efficacy of less potent drugs, thereby improving the therapeutic index. Inflammasomes, protein complexes located in the activated immune cell cytoplasm, regulate the activation of caspases involved in inflammation. However, aberrant activation of inflammasomes can result in uncontrolled tissue responses, contributing to the development of various diseases. Therefore, achieving a precise balance between inflammasome inhibition and activation is crucial for effectively treating inflammatory disorders through targeted functionalized nanocarriers. Despite the wealth of available data on the relevance of functionalized nanocarriers in inflammatory disorders, the nanotechnological potential to modulate inflammasomes has not been adequately explored. In this comprehensive review, we highlight the latest research on the modulation of the inflammasome cascade, both upregulating and downregulating its function, using nanocarriers in the context of inflammatory disorders. The utilization of nanocarriers as a therapeutic strategy holds immense potential for researchers aiming to effectively target and modulate inflammasomes in the treatment of inflammatory disorders, thus improving disease severity outcomes.

Histamine elevation in familial Mediterranean fever: A study from the Juvenile Inflammatory Rheumatism cohort

BACKGROUND

Familial Mediterranean Fever (FMF) is the most frequent monogenic autoinflammatory disease (AID). Some patients have persistent symptoms despite colchicine intake. Mast cells (MC) are innate immune cells involved in inflammatory conditions including AID. Their activation is responsible for various symptoms such as abdominal pain, bloating and pruritus.

OBJECTIVE

Our objective was to evaluate features of a systemic MC activation in FMF adult patients.

METHODS

FMF adult patients prospectively filled a MC activation survey and usual MC mediators (tryptase and histamine in whole blood, plasma and urine) were measured. They were compared with a healthy control group (HC) and a systemic mastocytosis (SM) group. When digestive biopsies were realized during follow-up, MC infiltration in digestive mucosa was analyzed in FMF, in comparison with SM, Crohn disease (CD) and normal biopsies.

RESULTS

Forty-four FMF patients, 44 HC and 44 SM patients were included. Thirty-one (70%) FMF patients had symptoms of mast cell activation, versus 14 (32%) in the HC group (p = 0.0006). Thirty (68%) FMF patients had at least one elevated MC mediator: mainly whole blood histamine, in 19 (43%) and urinary histamine, in 14 (32%), which were significantly higher than in HC subjects. MC infiltration was comparable in FMF digestive biopsies, biopsies of CD and normal biopsies but was lower than in SM biopsies.

CONCLUSION

FMF patients show frequent symptoms of MC activation and an increase of blood or urinary histamine never described before in this disease. This suggests an implication of MC and possibly basophils in FMF pathophysiology.

Similarities and differences in autoinflammatory diseases with urticarial rash, cryopyrin-associated periodic syndrome and Schnitzler syndrome

Cryopyrin-associated periodic syndromes (CAPS) and Schnitzler syndrome (SchS) are autoinflammatory diseases that present with urticaria-like rashes. CAPS is characterized by periodic or persistent systemic inflammation caused by the dysfunction of the NLRP3 gene. With the advent of IL-1-targeted therapies, the prognosis of CAPS has improved remarkably. SchS is considered an acquired form of autoinflammatory syndrome. Patients with SchS are adults of relatively older age. The pathogenesis of SchS remains unknown and is not associated with the NLRP3 gene. Previously, the p.L265P mutation in the MYD88 gene, which is frequently detected in Waldenström macroglobulinemia (WM) with IgM gammopathy, was identified in several cases of SchS. However, because persistent fever and fatigue are symptoms of WM that require therapeutic intervention, it is a challenge to determine whether these patients truly had SchS or whether advanced WM was misidentified as SchS. There are no established treatments for SchS. The treatment algorithm proposed with the diagnostic criteria is to use colchicine as first-line treatment, and systemic administration of steroids is not recommended due to concerns about side effects. In difficult-to-treat cases, treatment targeting IL-1 is recommended. If targeted IL-1 treatment does not improve symptoms, the diagnosis should be reconsidered. We hope that the efficacy of IL-1 therapy in clinical practice will serve as a stepping stone to elucidate the pathogenesis of SchS, focusing on its similarities and differences from CAPS.

Pyroptosis in neutrophils: Multimodal integration of inflammasome and regulated cell death signaling pathways

Pyroptosis is a proinflammatory mode of lytic cell death mediated by accumulation of plasma membrane (PM) macropores composed of gasdermin-family (GSDM) proteins. It facilitates two major functions in innate immunity: (i) elimination of intracellular replicative niches for pathogenic bacteria; and (ii) non-classical secretion of IL-1 family cytokines that amplify host-beneficial inflammatory responses to microbial infection or tissue damage. Physiological roles for gasdermin D (GSDMD) in pyroptosis and IL-1β release during inflammasome signaling have been extensively characterized in macrophages. This involves cleavage of GSDMD by caspase-1 to generate GSDMD macropores that mediate IL-1β efflux and progression to pyroptotic lysis. Neutrophils, which rapidly accumulate in large numbers at sites of tissue infection or damage, become the predominant local source of IL-1β in coordination with their potent microbiocidal capacity. Similar to macrophages, neutrophils express GSDMD and utilize the same spectrum of diverse inflammasome platforms for caspase-1-mediated cleavage of GSDMD. Distinct from macrophages, neutrophils possess a remarkable capacity to resist progression to GSDMD-dependent pyroptotic lysis to preserve their viability for efficient microbial killing while maintaining GSDMD-dependent mechanisms for export of bioactive IL-1β. Rather, neutrophils employ cell-specific mechanisms to conditionally engage GSDMD-mediated pyroptosis in response to bacterial pathogens that use neutrophils as replicative niches. GSDMD and pyroptosis have also been mechanistically linked to induction of NETosis, a signature neutrophil pathway that expels decondensed nuclear DNA into extracellular compartments for immobilization and killing of microbial pathogens. This review summarizes a rapidly growing number of recent studies that have produced new insights, unexpected mechanistic nuances, and some controversies regarding the regulation of, and roles for, neutrophil inflammasomes, pyroptosis, and GSDMs in diverse innate immune responses.

Mast Cells and Interleukins

Mast cells play a critical role in inflammatory diseases and tumor growth. The versatility of mast cells is reflected in their ability to secrete a wide range of biologically active cytokines, including interleukins, chemokines, lipid mediators, proteases, and biogenic amines. The aim of this review article is to analyze the complex involvement of mast cells in the secretion of interleukins and the role of interleukins in the regulation of biological activities of mast cells.

Mast Cell Cytokines in Acute and Chronic Gingival Tissue Inflammation: Role of IL-33 and IL-37

Much evidence suggests autoimmunity in the etiopathogenesis of periodontal disease. In fact, in periodontitis, there is antibody production against collagen, DNA, and IgG, as well as increased IgA expression, T cell dysfunction, high expression of class II MHC molecules on the surface of gingival epithelial cells in inflamed tissues, activation of NK cells, and the generation of antibodies against the azurophil granules of polymorphonuclear leukocytes. In general, direct activation of autoreactive immune cells and production of TNF can activate neutrophils to release pro-inflammatory enzymes with tissue damage in the gingiva. Gingival inflammation and, in the most serious cases, periodontitis, are mainly due to the dysbiosis of the commensal oral microbiota that triggers the immune system. This inflammatory pathological state can affect the periodontal ligament, bone, and the entire gingival tissue. Oral tolerance can be abrogated by some cytokines produced by epithelial cells and activated immune cells, including mast cells (MCs). Periodontal cells and inflammatory-immune cells, including mast cells (MCs), produce cytokines and chemokines, mediating local inflammation of the gingival, along with destruction of the periodontal ligament and alveolar bone. Immune-cell activation and recruitment can be induced by inflammatory cytokines, such as IL-1, TNF, IL-33, and bacterial products, including lipopolysaccharide (LPS). IL-1 and IL-33 are pleiotropic cytokines from members of the IL-1 family, which mediate inflammation of MCs and contribute to many key features of periodontitis and other inflammatory disorders. IL-33 activates several immune cells, including lymphocytes, Th2 cells, and MCs in both innate and acquired immunological diseases. The classic therapies for periodontitis include non-surgical periodontal treatment, surgery, antibiotics, anti-inflammatory drugs, and surgery, which have been only partially effective. Recently, a natural cytokine, IL-37, a member of the IL-1 family and a suppressor of IL-1b, has received considerable attention for the treatment of inflammatory diseases. In this article, we report that IL-37 may be an important and effective therapeutic cytokine that may inhibit periodontal inflammation. The purpose of this paper is to study the relationship between MCs, IL-1, IL-33, and IL-37 inhibition in acute and chronic inflamed gingival tissue.

Antimicrobial peptides with cell-penetrating activity as prophylactic and treatment drugs

Health is fundamental for the development of individuals and evolution of species. In that sense, for human societies is relevant to understand how the human body has developed molecular strategies to maintain health. In the present review, we summarize diverse evidence that support the role of peptides in this endeavor. Of particular interest to the present review are antimicrobial peptides (AMP) and cell-penetrating peptides (CPP). Different experimental evidence indicates that AMP/CPP are able to regulate autophagy, which in turn regulates the immune system response. AMP also assists in the establishment of the microbiota, which in turn is critical for different behavioral and health aspects of humans. Thus, AMP and CPP are multifunctional peptides that regulate two aspects of our bodies that are fundamental to our health: autophagy and microbiota. While it is now clear the multifunctional nature of these peptides, we are still in the early stages of the development of computational strategies aimed to assist experimentalists in identifying selective multifunctional AMP/CPP to control nonhealthy conditions. For instance, both AMP and CPP are computationally characterized as amphipatic and cationic, yet none of these features are relevant to differentiate these peptides from non-AMP or non-CPP. The present review aims to highlight current knowledge that may facilitate the development of AMP’s design tools for preventing or treating illness.

Mast cell tissue heterogeneity and specificity of immune cell recruitment

Mast cells occupy a unique niche within tissues as long lived perpetrators of IgE mediated hypersensitivity and anaphylaxis, as well as other immune responses. However, mast cells are not identical in different tissues and the impact of this tissue heterogeneity on the interaction with other immune cells and on defined immune responses is still unclear. In this review, we synthesize the characteristics of mast cell heterogeneity in the gut and the skin. Furthermore, we attempt to connect mast cell heterogeneity with functional diversity by exploring differences in mast cell-induced immune cell recruitment in these two model organs. The differential expression of certain receptors on mast cells of different tissues, notably tissue-specific expression patterns of integrins, complement receptors and MRGPRX2, could indicate that tissue environment-dependent factors skew mast cell-immune cell interactions, for example by regulating the expression of these receptors.

Nlrp3 inflammasome activation in macrophages suffices for inducing autoinflammation in mice

Cryopyrin-associated periodic syndromes (CAPS) are a spectrum of autoinflammatory disorders caused by gain-of-function NLRP3 mutant proteins that form hyperactive inflammasomes leading to overproduction of the pro-inflammatory cytokines IL-1β and IL-18. Expressing the murine gain-of-function Nlrp3^A350V mutant selectively in neutrophils recapitulates several autoinflammatory features of human CAPS, but the potential contribution of macrophage inflammasome hyperactivation to CAPS development is poorly defined. Here, we show that expressing Nlrp3^A350V in macrophages is sufficient for driving severe multi-organ autoinflammation leading to perinatal lethality in mice. In addition, we show that macrophages contribute to autoinflammation also in adult mice, as depleting macrophages in mice ubiquitously expressing Nlrp3^A350V significantly diminishes splenic and hepatic IL-1β production. Interestingly, inflammation induced by macrophage-selective Nlrp3^A350V expression does not provoke an influx of mature neutrophils, while neutrophil influx is still occurring in macrophage-depleted mice with body-wide Nlrp3^A350V expression. These observations identify macrophages as important cellular drivers of CAPS in mice and support a cooperative cellular model of CAPS development in which macrophages and neutrophils act independently of each other in propagating severe autoinflammation.

Maternal Gut Microbiome Decelerates Fetal Endochondral Bone Formation by Inducing Inflammatory Reaction

To investigate the effect of the maternal gut microbiome on fetal endochondral bone formation, fetuses at embryonic day 18 were obtained from germ-free (GF) and specific-pathogen-free (SPF) pregnant mothers. Skeletal preparation of the fetuses’ whole bodies did not show significant morphological alterations; however, micro-CT analysis of the tibiae showed a lower bone volume fraction in the SPF tibia. Primary cultured chondrocytes from fetal SPF rib cages showed a lower cell proliferation and lower accumulation of the extracellular matrix. RNA-sequencing analysis showed the induction of inflammation-associated genes such as the interleukin (IL) 17 receptor, IL 6, and immune-response genes in SPF chondrocytes. These data indicate that the maternal gut microbiome in SPF mice affects fetal embryonic endochondral ossification, possibly by changing the expression of genes related to inflammation and the immune response in fetal cartilage. The gut microbiome may modify endochondral ossification in the fetal chondrocytes passing through the placenta.

The Interactions Between Autoinflammation and Type 2 Immunity: From Mechanistic Studies to Epidemiologic Associations

Autoinflammatory diseases are a group of clinical syndromes characterized by constitutive overactivation of innate immune pathways. This results in increased production of or responses to monocyte- and neutrophil-derived cytokines such as interleukin-1β (IL-1β), Tumor Necrosis Factor-α (TNF-α), and Type 1 interferon (IFN). By contrast, clinical allergy is caused by dysregulated type 2 immunity, which is characterized by expansion of T helper 2 (Th2) cells and eosinophils, as well as overproduction of the associated cytokines IL-4, IL-5, IL-9, and IL-13. Traditionally, type 2 immune cells and autoinflammatory effectors were thought to counter-regulate each other. However, an expanding body of evidence suggests that, in some contexts, autoinflammatory pathways and cytokines may potentiate type 2 immune responses. Conversely, type 2 immune cells and cytokines can regulate autoinflammatory responses in complex and context-dependent manners. Here, we introduce the concepts of autoinflammation and type 2 immunity. We proceed to review the mechanisms by which autoinflammatory and type 2 immune responses can modulate each other. Finally, we discuss the epidemiology of type 2 immunity and clinical allergy in several monogenic and complex autoinflammatory diseases. In the future, these interactions between type 2 immunity and autoinflammation may help to expand the spectrum of autoinflammation and to guide the management of patients with various autoinflammatory and allergic diseases.

Inflammatory Response to Regulated Cell Death in Gout and Its Functional Implications

Gout, a chronic inflammatory arthritis disease, is characterized by hyperuricemia and caused by interactions between genetic, epigenetic, and metabolic factors. Acute gout symptoms are triggered by the inflammatory response to monosodium urate crystals, which is mediated by the innate immune system and immune cells (e.g., macrophages and neutrophils), the NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) inflammasome activation, and pro-inflammatory cytokine (e.g., IL-1β) release. Recent studies have indicated that the multiple programmed cell death pathways involved in the inflammatory response include pyroptosis, NETosis, necroptosis, and apoptosis, which initiate inflammatory reactions. In this review, we explore the correlation and interactions among these factors and their roles in the pathogenesis of gout to provide future research directions and possibilities for identifying potential novel therapeutic targets and enhancing our understanding of gout pathogenesis.

The TLR-chaperone CNPY3 is a critical regulator of NLRP3-Inflammasome activation

Toll like receptors (TLRs) mediate the recognition of microbial and endogenous insults to orchestrate the inflammatory response. TLRs localize to the plasma membrane or endomembranes, depending on the member, and rely critically on endoplasmic reticulum-resident chaperones to mature and reach their subcellular destinations. The chaperone canopy FGF signaling regulator 3 (CNPY3) is necessary for the proper trafficking of multiple TLRs including TLR1/2/4/5/9 but not TLR3. However, the exact role of CNPY3 in inflammatory signalling downstream of TLRs has not been studied in detail. Consistent with the reported client specificity, we report here that functional loss of CNPY3 in engineered macrophages impairs downstream signalling by TLR2 but not TLR3. Unexpectedly, CNPY3-deficient macrophages show reduced interleukin-1β (IL-1ß) and IL-18 processing and production independent of the challenged upstream TLR species, demonstrating a separate, specific role for CNPY3 in inflammasome activation. Mechanistically, we document that CNPY3 regulates caspase-1 localization to the apoptosis speck and auto-activation of caspase-1. Importantly, we were able to recapitulate these findings in macrophages from an early infantile epileptic encephalopathy (EIEE) patient with a novel CNPY3 loss-of-function variant. Summarizing, our findings reveal a hitherto unknown, TLR-independent role of CNPY3 in inflammasome activation, highlighting a more complex and dedicated role of CNPY3 to the inflammatory response than anticipated. This article is protected by copyright. All rights reserved.

Interaction between the inflammasome and commensal microorganisms in gastrointestinal health and disease

The inflammasome is a cytosolic multiprotein complex that plays a crucial role in inflammation and cell death. The sensor proteins in the inflammasome complex detect various microbial and endogenous stimuli, leading to subsequent caspase activation. The activation of caspases results in the maturation of pro-inflammatory cytokines IL-1β and IL-18 or pyroptosis. Inflammasome dysfunction is associated with the pathogenesis of various diseases, including autoimmune disease and cancer. It appears that the interactions between the gut microbiota and the inflammasome play crucial roles in the gastrointestinal tract. The gut microbiota induces the expression and activation of inflammasome proteins, which contribute to both homeostasis and disease in the gut. Likewise, although controversial, mounting evidence suggests that inflammasome activation can modulate the composition of the gut microbiota, which, in turn, affects disease progression. In this review, we summarize the current concepts and recent insights linking the inflammasome and gut commensal microorganisms. We describe how the reciprocal interaction between the inflammasome and the commensal microbiota relates to physiological and pathophysiological consequences in the host.

Cytotoxin-associated gene A (CagA) promotes aortic endothelial inflammation and accelerates atherosclerosis through the NLRP3/caspase-1/IL-1β axis

Atherosclerosis is a chronic inflammatory disease. Pathophysiological similarities between chronic infections and atherosclerosis triggered interests between these conditions. The seroepidemiological study showed that Helicobacter pylori strains that express cytotoxin-associated gene A (CagA), an oncoprotein and a major virulence factor, was positively correlated with atherosclerosis and related clinical events. Nevertheless, the underlying mechanism is poorly understood. In this study, the seroprevalence of infection by H. pylori and by strains express CagA assessed by enzyme-linked immunosorbent assay (ELISA) showed that the prevalence of CagA strains rather than H. pylori in patients was positively correlated with atherogenesis. Correspondingly, we found that CagA augmented the growth of plaque of ApoE^-/- mice in the early stage of atherosclerosis and promoted the expression of adhesion molecules and inflammatory cytokines in mouse aortic endothelial cells (MAECs). Mechanistically, both si-NLRP3 and si-IL-1β mitigated the promoting effect of CagA on the inflammatory activation of HAECs. In vivo, the inhibition of NLRP3 by MCC950 significantly attenuated the promoting effect of CagA on plaque growth of ApoE^-/- mice. We also propose NLRP3 as a potential therapeutic target for CagA-positive H. pylori infection-related atherosclerosis and emphasize the importance of inflammation in atherosclerosis pathology.

Neutrophil-specific gain-of-function mutations in Nlrp3 promote development of cryopyrin-associated periodic syndrome

Gain-of-function mutations in NLRP3 are responsible for a spectrum of autoinflammatory diseases collectively referred to as “cryopyrin-associated periodic syndromes” (CAPS). Treatment of CAPS patients with IL-1–targeted therapies is effective, confirming a central pathogenic role for IL-1β. However, the specific myeloid cell population(s) exhibiting inflammasome activity and sustained IL-1β production in CAPS remains elusive. Previous reports suggested an important role for mast cells (MCs) in this process. Here, we report that, in mice, gain-of-function mutations in Nlrp3 restricted to neutrophils, and to a lesser extent macrophages/dendritic cells, but not MCs, are sufficient to trigger severe CAPS. Furthermore, in patients with clinically established CAPS, we show that skin-infiltrating neutrophils represent a substantial biological source of IL-1β. Together, our data indicate that neutrophils, rather than MCs, can represent the main cellular drivers of CAPS pathology.

NLRP3 Inflammasome Activation of Mast Cells by Estrogen via the Nuclear-Initiated Signaling Pathway Contributes to the Development of Endometriosis

Endometriosis is an estrogen-dependent gynecological disease. The pathogenesis of endometriosis remains controversial, although it is generally accepted that the inflammatory immune response plays a crucial role in this process. Mast cells (MCs) are multifunctional innate immune cells that accumulate in endometriotic lesions. However, the molecular mechanism by which estrogen modulates MCs in the development of endometriosis is not well understood. Here we report that estrogen can induce the expression of NOD-like receptor family pyrin domain containing 3 (NLRP3) through estrogen receptor (ER)-α via the estrogen responsive element (ERE) in MCs. Such transcriptional regulation is necessary for the activation of NLRP3 inflammasome and the production of mature interleukin (IL)-1β in MCs. Targeted inhibition of NLRP3 significantly restrained lesion progression and fibrogenesis in a mouse model of endometriosis. Collectively, these findings suggest that MCs contribute to the development of endometriosis through NLRP3 inflammasome activation mediated by nuclear-initiated estrogen signaling pathway.

The Pathogenesis of Chronic Spontaneous Urticaria: The Role of Infiltrating Cells

Chronic spontaneous urticaria is characterized by a perivascular non-necrotizing cellular infiltrate around small venules of the skin. It consists primarily of CD4(+) lymphocytes, a prominence of the T helper (Th)2 subtype but also Th1 cells, with Th17 cell-derived cytokines elevated in plasma. There are also neutrophils, eosinophils, basophils, and monocytes. Chemokines derived from mast cells and activated endothelial cells drive the process. Although the role of the cellular infiltrate has not previously been addressed, each constituent can contribute to the overall pathogenesis. It is of interest that CSU responds to corticosteroid, yet, short-term steroids do not affect autoimmunity or degranulation of mast cells, and act on margination of cells along the endothelium and chemotaxis to enter the surrounding dermis. In this review, we address each cell's contribution to the overall inflammatory response, as it is currently understood, with a view toward development of therapeutic options that impede the function of critical cells and/or their secretory products.

Mast Cells as a Double Edged Sword in Immunity: Disorders of Mast Cell Activation and Therapeutic Management. Second of Two Parts

Mast cells (MCs) bear many receptors that allow them to respond to a variety of exogenous and endogenous stimuli. However, MC function is dual since they can initiate pathological events or protect the host against infectious challenges. The role of MCs in disease will be analyzed in a broad sense, describing cellular and molecular mechanisms related to their involvement in auto-inflammatory diseases, asthma, autoimmune diseases and cancer. On the other hand, their protective role in the course of bacterial, fungal and parasitic infections will also be illustrated. As far as treatment of MC-derived diseases is concerned, allergen immunotherapy as well as other attempts to reduce MC-activation will be outlined according to the recent data. Finally, in agreement with current literature and our own data polyphenols have been demonstrated to attenuate type I allergic reactions and contact dermatitis in response to nickel. The use of polyphenols in these diseases will be discussed also in view of MC involvement.

Dysregulated skin barrier function in Tmem79 mutant mice promotes IL-17A-dependent spontaneous skin and lung inflammation

BACKGROUND

Atopic dermatitis (AD) is associated with a dysregulation of the skin barrier and may predispose to the development of secondary allergic conditions, such as asthma. Tmem79^ma/ma mice harbor a mutation in the gene encoding Transmembrane Protein 79 (or Mattrin), which has previously been associated with AD. As a result of the Tmem79 gene mutation, these mice have a defective skin barrier and develop spontaneous skin inflammation. In this study, Tmem79^ma/ma mice were assessed for the underlying immunological response in the development of spontaneous skin and lung inflammation.

METHODS

Development of spontaneous skin and lung inflammation in Tmem79^ma/ma mice was analyzed. We further investigated susceptibility to cutaneous Staphylococcus aureus infection. Tmem79^ma/ma were crossed to IL-17A-deficient mice to address the contribution of IL-17A to spontaneous skin and lung disease.

RESULTS

Tmem79^ma/ma mice developed IL-17A-dependent spontaneous AD-like inflammation and were refractory to S aureus infection. Mutant mice progressed to airway inflammation subsequent to the occurrence of dermatitis. The progression from skin to lung disease is dependent on adaptive immunity and is facilitated by cutaneous expansion of Th17 and TCRγδ T cells.

CONCLUSION

Mice lacking Tmem79/Mattrin expression have a defective skin barrier. In adulthood, these mice develop dermatitis with secondary progression to lung inflammation. The development of skin and lung inflammation is IL-17A-dependent and mediated by TCRγδ T cells.

The microbiome and cytosolic innate immune receptors

The discovery of innate immune sensors (pattern recognition receptors, PRRs) has profoundly transformed the notion of innate immunity, in providing a mechanistic basis for host immune interactions with a wealth of environmental signals, leading to a variety of immune-mediated outcomes including instruction and activation of the adaptive immune arm. As part of this growing understanding of host-environmental cross talk, an intimate connection has been unveiled between innate immune sensors and signals perceived from the commensal microbiota, which may be regarded as a hub integrating a variety of environmental cues. Among cytosolic PRRs impacting on host homeostasis by interacting with the commensal microbiota are nucleotide-binding domain, leucine-rich repeat-containing protein receptors (NLRs), together with a number of cytosolic DNA sensors and the family of absent in melanoma (AIM)-like receptors (ALRs). NLR sensors have been a particular focus of research, and some NLRs have emerged as key orchestrators of inflammatory responses and host homeostasis. Some NLRs achieve this through the formation of cytoplasmic multiprotein complexes termed inflammasomes. More recently discovered PRRs include retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs), cyclic GMP-AMP synthase (cGAS), and STING. In the present review, they summarize recent advancements in knowledge on structure and function of cytosolic PRRs and their roles in host-microbiota cross talk and immune surveillance. In addition, we discuss their relevance for human health and disease and future therapeutic applications involving modulation of their activation and signaling.

The Role of Microbiomes in Pregnant Women and Offspring: Research Progress of Recent Years

Pregnancy is a complicated and delicate process, the maternal body undergoes changes on hormones, immunity, and metabolism during pregnancy to support fetal development. Microbiomes in the human body mainly live in the intestine, and the human gut microbiomes are complex, which composed of more than 500 to 1500 different bacteria, archaea, fungi, and viruses. Studies have shown that these microbiomes are not only involved in the digestion and absorption of food but also indispensable in regulating host health. In recent years, there has been increasing evidence that microbiomes are important for pregnant women and fetuses. During pregnancy, there will be great changes in gut microbiomes. Regulating gut microbiomes is beneficial to the health of the mother and the fetus. In addition, many complications during pregnancy are related to gut microbiomes, such as gestational diabetes, obesity, preeclampsia, digestive disorders, and autoimmune diseases. Moreover, the microbiomes in mother's milk and vagina are closely related to the colonization of microbiomes in the early life of infants. In this review, we systematically review the role of maternal microbiomes in different gestational complications, and elucidate the function and mechanism of maternal microbiomes in the neural development and immune system of offspring. These will provide a clear knowledge framework or potential research direction for researchers in related fields.

The role of NLRP3 inflammasome in infection-related, immune-mediated and autoimmune skin diseases

Inflammasomes are large intracellular multi-protein signaling complexes which are responsible for the activation of inflammatory responses. Among multifarious subtypes of inflammasomes, NLRP3 has been associated with a variety of inflammatory and autoimmune skin conditions, including dermatophytosis, psoriasis, acne, urticaria and bullous pemphigoid and other different skin diseases which have been a subject of intensive investigation. NLRP3 is considered to be a sensor of microbial and other danger signals and plays a crucial role in immune responses, dysregulation of NLRP3 inflammasome activation is involved in skin diseases. With the in-depth research, targeting NLRP3 inflammasome and its downstream signaling will provide new insights into the development of future therapeutic strategies. In this review, we summarize the molecular mechanism of NLRP3 inflammasome activation as well as the current knowledge on the contribution of the NLRP3 inflammasome in infection-related, immune-mediated and autoimmune skin diseases.

The Theranostics Role of Mast Cells in the Pathophysiology of Rosacea

Rosacea is a chronic inflammatory cutaneous disorder that adversely affects patient's health and quality of life due to the complex course and the need for repeated treatment. The exact molecular mechanisms of rosacea are unclear. Mast cells are innate immune cells that can be found in virtually all tissues. Recently, increasing evidence has indicated that mast cells have important effects on the pathogenesis of rosacea. In this review article, we describe recent advances of skin mast cells in the development of rosacea. These studies suggested that mast cells can be an important immune cell that connected innate immunity, nerves, and blood vessels in the development of rosacea. Moreover, we review the inhibition of mast cells for the potential treatment of rosacea.

Mast Cells as a Double-Edged Sword in Immunity: Their Function in Health and Disease. First of Two Parts

Mast cells (MCs) have recently been re-interpreted in the context of the immune scenario in the sense that their pro-allergic role is no longer exclusive. In fact, MCs even in steady state conditions maintain homeostatic functions, producing mediators and intensively cross-talking with other immune cells. Here, emphasis will be placed on the array of receptors expressed by MCs and the variety of cytokines they produce. Then, the bulk of data discussed will provide readers with a wealth of information on the dual ability of MCs not only to defend but also to offend the host. This double attitude of MCs relies on many variables, such as their subsets, tissues of residency and type of stimuli ranging from microbes to allergens and food antigens. Finally, the relationship between MCs with basophils and eosinophils will be discussed.

Spontaneous atopic dermatitis in mice with a defective skin barrier is independent of ILC2 and mediated by IL-1β

BACKGROUND

Atopic dermatitis (AD) is one of the most common skin diseases with a multifactorial etiology. Mutations leading to loss of skin barrier function are associated with the development of AD with group 2 innate lymphoid cells (ILC2) promoting acute skin inflammation. Filaggrin-mutant (Flgft/ft ) mice develop spontaneous skin inflammation accompanied by an increase in skin ILC2 numbers, IL-1β production, and other cytokines recapitulating human AD. Here, we investigated the role of ILC2, effector cytokines, inflammasome activation, and mast cell function on the development of chronic AD-like inflammation in mice.

METHODS

Mice with a frameshift mutation in the filaggrin gene develop spontaneous dermatitis. Flgft/ft mice were crossed to cell- or cytokine-deficient mouse strains, or bred under germ-free conditions. Skin inflammation was scored, and microbiome composition was analyzed. Skin protein expression was measured by multiplex immunoassay. Infiltrating cells were analyzed by flow cytometry.

RESULTS

Wild-type and Flgft/ft mice significantly differ in their microbiome composition. Furthermore, mutant mice do not develop skin inflammation under germ-free conditions. ILC2 deficiency did not ameliorate chronic dermatitis in Flgft/ft mice, which was also independent of IL-4, IL-5, IL-9, IL-13, IL-17A, and IL-22. Inflammation was independent of NLRP3 inflammasome activation but required IL-1β and IL-1R1-signaling. Mechanistically, IL-1β promoted hyperactivation of IL-1R1-expressing mast cells. Treatment with anti-IL-1β-antibody alleviated dermatitis exacerbation, while antibiotic intervention ameliorated dermatitis in neonatal mice but not in adults with established inflammation.

CONCLUSIONS

In summary, we identified a critical role for the microbiome and IL-1β mediating chronic inflammation in mice with an impaired skin barrier.

Sonic Hedgehog signaling limits atopic dermatitis via Gli2-driven immune regulation

Hedgehog (Hh) proteins regulate development and tissue homeostasis, but their role in atopic dermatitis (AD) remains unknown. We found that on induction of mouse AD, Sonic Hedgehog (Shh) expression in skin and Hh pathway action in skin T cells were increased. Shh signaling reduced AD pathology and the levels of Shh expression determined disease severity. Hh-mediated transcription in skin T cells in AD-induced mice increased Treg populations and their suppressive function through increased active transforming growth factor–β (TGF-β) in Treg signaling to skin T effector populations to reduce disease progression and pathology. RNA sequencing of skin CD4⁺ T cells from AD-induced mice demonstrated that Hh signaling increased expression of immunoregulatory genes and reduced expression of inflammatory and chemokine genes. Addition of recombinant Shh to cultures of naive human CD4⁺ T cells in iTreg culture conditions increased FOXP3 expression. Our findings establish an important role for Shh upregulation in preventing AD, by increased Gli-driven, Treg cell–mediated immune suppression, paving the way for a potential new therapeutic strategy.

CAPS and NLRP3

Cryopyrin-associated periodic syndrome (CAPS) is a rare inherited autoinflammatory disorder characterized by systemic, cutaneous, musculoskeletal, and central nervous system inflammation. Gain-of-function mutations in NLRP3 in CAPS patients lead to activation of the cryopyrin inflammasome, resulting in the inappropriate release of inflammatory cytokines including IL-1β and CAPS-related inflammatory symptoms. Several mechanisms have been identified that are important for the normal regulation of the cryopyrin inflammasome in order to prevent uncontrolled inflammation. Investigators have taken advantage of some of these pathways to develop and apply novel targeted therapies, which have resulted in improved quality of life for patients with this orphan disease.

Mast Cell Neural Interactions in Health and Disease

Mast cells (MCs) are located in the periphery as well as the central nervous system (CNS). Known for sterile inflammation, MCs play a critical role in neuroinflammation, which is facilitated by their close proximity to nerve fibers in the periphery and meninges of the spinal cord and the brain. Multifaceted activation of MCs releasing neuropeptides, cytokines and other mediators has direct effects on the neural system as well as neurovascular interactions. Emerging studies have identified the release of extracellular traps, a phenomenon traditionally meant to ensnare invading pathogens, as a cause of MC-induced neural injury. In this review article, we will discuss mechanisms of MC interaction with the nervous system through degranulation, de novo synthesis, extracellular vesicles (EVs), tunneling nanotubes, and extracellular traps with implications across a variety of pathological conditions.

Perinatal Interactions between the Microbiome, Immunity, and Neurodevelopment

The microbiome modulates host immune function across the gastrointestinal tract, peripheral lymphoid organs, and central nervous system. In this review, we highlight emerging evidence that microbial effects on select immune phenotypes arise developmentally, where the maternal and neonatal microbiome influence immune cell ontogeny in the offspring during gestation and early postnatal life. We further discuss roles for the perinatal microbiome and early-life immunity in regulating normal neurodevelopmental processes. In addition, we examine evidence that abnormalities in microbiota-neuroimmune interactions during early life are associated with altered risk of neurological disorders in humans. Finally, we conclude by evaluating the potential implications of microbiota-immune interventions for neurological conditions. Continued progress toward dissecting mechanistic interactions between the perinatal microbiota, immune system, and nervous system might uncover fundamental insights into how developmental interactions across physiological systems inform later-life health and disease.

Mast cells as sources of cytokines, chemokines, and growth factors

Mast cells are hematopoietic cells that reside in virtually all vascularized tissues and that represent potential sources of a wide variety of biologically active secreted products, including diverse cytokines and growth factors. There is strong evidence for important non-redundant roles of mast cells in many types of innate or adaptive immune responses, including making important contributions to immediate and chronic IgE-associated allergic disorders and enhancing host resistance to certain venoms and parasites. However, mast cells have been proposed to influence many other biological processes, including responses to bacteria and virus, angiogenesis, wound healing, fibrosis, autoimmune and metabolic disorders, and cancer. The potential functions of mast cells in many of these settings is thought to reflect their ability to secrete, upon appropriate activation by a range of immune or non-immune stimuli, a broad spectrum of cytokines (including many chemokines) and growth factors, with potential autocrine, paracrine, local, and systemic effects. In this review, we summarize the evidence indicating which cytokines and growth factors can be produced by various populations of rodent and human mast cells in response to particular immune or non-immune stimuli, and comment on the proven or potential roles of such mast cell products in health and disease.

Association of CCL2 with systemic inflammation in Schnitzler syndrome

BACKGROUND

Schnitzler syndrome (SchS) is a rare autoinflammatory disease characterized by urticarial exanthema, bone and joint alterations, fever and monoclonal gammopathy, which manifest mostly in the second half of life. It involves overactivation of the interleukin (IL)-1 system, but the exact pathophysiological pathways remain largely unknown.

OBJECTIVES

To identify and characterize the pathogenetic players in SchS.

METHODS

Blood parameters were quantified in patients with SchS compared with healthy controls and patients with psoriasis and hidradenitis suppurativa using enzyme-linked immunosorbent assay (ELISA). CCL2 expression in cultured primary cells was analysed by quantitative reverse-transcriptase polymerase chain reaction and ELISA.

RESULTS

CCL2, a chemoattractant for monocytic and further mononuclear immune cells, was found to be significantly elevated in patients with SchS. CCL2 levels showed a positive association with global disease activity, especially with bone pain, but not disease duration, gammopathy, neutrophilia or skin disease. In vitro stimulation assays demonstrated a strong CCL2 production capacity of mononuclear immune cells and fibroblasts, but not epithelial or endothelial cells. Among a range of inflammatory mediators, only IL-1β (immune cells, fibroblasts) and tumour necrosis factor (TNF)-α (fibroblasts) were important CCL2 inducers. TNF-α, but not IL-17, strengthened the CCL2-inducing effect of IL-1β in fibroblasts. Accordingly, CCL2 levels positively correlated with both TNF-α and IL-1β serum levels in patients with SchS. Therapeutic IL-1β blockade decreased CCL2 blood levels in these patients as early as 1 week after the initiation of treatment.

CONCLUSIONS

CCL2 may be an important component of the pathogenetic cascade leading to bone alterations, and a suitable marker of disease activity in patients with SchS.

Visions of Eye Commensals: The Known and the Unknown About How the Microbiome Affects Eye Disease

Until recently, the ocular surface is thought by many to be sterile and devoid of living microbes. It is now becoming clear that this may not be the case. Recent and sophisticated PCR analyses have shown that microbial DNA-based "signatures" are present within various ethnic, geographic, and contact lens wearing communities. Furthermore, using a mouse model of ocular surface disease, we have shown that the microbe, Corynebacterium mastitidis (C. mast), can stably colonize the ocular mucosa and that a causal relationship exists between ocular C. mast colonization and beneficial local immunity. While this constitutes proof-of-concept that a bona fide ocular microbiome that tunes immunity can exist at the ocular surface, there remain numerous unanswered questions to be addressed before microbiome-modulating therapies may be successfully developed. Here, the authors will briefly outline what is currently known about the local ocular microbiome as well as microbiomes associated with other sites, and how those sites may play a role in ocular surface immunity. Understanding how commensal microbes affect the ocular surface immune homeostasis has the potential revolutionize how we think about treating ocular surface disease.

The Mast Cell-Aryl Hydrocarbon Receptor Interplay at the Host-Microbe Interface

Mast cells are increasingly being recognized as crucial cells in the response of the organism to environmental agents. Interestingly, the ability of mast cells to sense and respond to external cues is modulated by the microenvironment that surrounds mast cells and influences their differentiation. The scenario that is emerging unveils a delicate equilibrium that balances the effector functions of mast cells to guarantee host protection without compromising tissue homeostasis. Among the environmental components able to mold mast cells and fine-tune their effector functions, the microorganisms that colonize the human body, collectively known as microbiome, certainly play a key role. Indeed, microorganisms can regulate not only the survival, recruitment, and maturation of mast cells but also their activity by setting the threshold required for the exploitation of their different effector functions. Herein, we summarize the current knowledge about the mechanisms underlying the ability of the microorganisms to regulate mast cell physiology and discuss potential deviations that result in pathological consequences. We will discuss the pivotal role of the aryl hydrocarbon receptor in sensing the environment and shaping mast cell adaptation at the host-microbe interface.

Substance P and IL-33 administered together stimulate a marked secretion of IL-1β from human mast cells, inhibited by methoxyluteolin

Mast cells are critical for allergic and inflammatory responses in which the peptide substance P (SP) and the cytokine IL-33 are involved. SP (0.01-1 μM) administered together with IL-33 (30 ng/mL) to human cultured LAD2 mast cells stimulates a marked increase (P < 0.0001) in secretion of the proinflammatory cytokine IL-1β. Preincubation of LAD2 (30 min) with the SP receptor (NK-1) antagonists L-733,060 (10 μM) or CP-96345 (10 µM) inhibits (P < 0.001) secretion of IL-1β stimulated by either SP (1 μM) or SP together with IL-33 (30 ng/mL). Surprisingly, secretion of IL-1β stimulated by IL-33 is inhibited (P < 0.001) by each NK-1 antagonist. Preincubation with an antibody against the IL-33 receptor ST2 inhibits (P < 0.0001) secretion of IL-1β stimulated either by IL-33 or together with SP. The combination of SP (1 μM) with IL-33 (30 ng/mL) increases IL-1β gene expression by 90-fold in LAD2 cells and by 200-fold in primary cultured mast cells from human umbilical cord blood. The combination of SP and IL-33 increases intracellular levels of IL-1β in LAD2 by 100-fold and gene expression of IL-1β and procaspase-1 by fivefold and pro-IL-1β by twofold. Active caspase-1 is present even in unstimulated cells and is detected extracellularly. Preincubation of LAD2 cells with the natural flavonoid methoxyluteolin (1-100 mM) inhibits (P < 0.0001) secretion and gene expression of IL-1β, procaspase-1, and pro-IL-1β. Mast cell secretion of IL-1β in response to SP and IL-33 reveals targets for the development of antiinflammatory therapies.

Benzoxazole derivatives suppress lipopolysaccharide-induced mast cell activation

Mast cells are central regulators of allergic inflammation that function by releasing various proallergic inflammatory mediators, including histamine, eicosanoids and proinflammatory cytokines. Occasionally, bacterial infections may initiate or worsen allergic inflammation. A number of studies have indicated that activation of lipoxygenase in mast cells positive regulates allergic inflammatory responses by generating leukotrienes and proinflammatory cytokines. In the present study, the effects of benzoxazole derivatives on the lipopolysaccharide (LPS)‑induced expression of proinflammatory cytokines, production of histamine and surface expression of co‑stimulatory molecules on bone marrow-derived mast cells (BMMCs) were studied. The benzoxazole derivatives significantly reduced the expression of interleukin (IL)‑1β, IL‑6, IL‑13, tumor necrosis factor‑α, perilipin (PLIN) 2, and PLIN3 in BMMCs treated with LPS. Furthermore, histamine production was suppressed in BMMCs treated with LPS, or treated with phorbol-12-myristate-13-acetate/ionomycin. Benzoxazole derivatives marginally affected the surface expression of cluster of differentiation (CD)80 and CD86 on BMMCs in the presence of LPS, although LPS alone did not increase the expression of those proteins. Therefore, benzoxazole derivatives inhibited the secretion of proinflammatory cytokines in mast cells and may be potential candidate anti‑allergic agents to suppress mast cell activation.