Dectin-1 Stimulation by Candida albicans Yeast or Zymosan Triggers NFAT Activation in Macrophages and Dendritic Cells

Trained immunity causes myeloid cell hypercoagulability

The pathogenic basis for increased thrombotic risk in individuals with inflammatory diseases is poorly understood. Myeloid cell "trained immunity" describes persistent innate immune cell memory arising from prior exposure to an inflammatory stimulus, leading to an enhanced immune response to subsequent unrelated stimuli. We identify enhanced myeloid cell prothrombotic activity as a maladaptive consequence of trained immunity. Lipopolysaccharide (LPS) stimulation of macrophages trained previously with β-glucan or heme exhibited significantly enhanced procoagulant activity compared to macrophages stimulated with LPS alone, which was mediated by enhanced acid sphingomyelinase-mediated tissue factor decryption. Furthermore, splenic monocytes isolated from β-glucan-trained mice revealed enhanced procoagulant activity up to 4 weeks after β-glucan administration compared to monocytes from control mice over the same time period. Moreover, hematopoietic progenitor cells and bone marrow interstitial fluid from β-glucan-trained mice had enhanced procoagulant activity compared to control mice. Trained immunity and associated metabolic perturbations may therefore represent an opportunity for targeted intervention in immunothrombotic disease development.

NFATc1 in CD4+ T cells and CD11c+ dendritic cells drives TH2-mediated eosinophilic inflammation in allergic asthma

Background

Asthma, a chronic lung disease, is a significant public health problem worldwide. It is marked by increased TH2 response resulting in eosinophil accumulation. The pathophysiology of asthma involves various cell types, including epithelial cells, dendritic cells (DCs), innate lymphoid cells, B cells, and effector cells. Nuclear factor of activated T cells, cytoplasmic 1 (NFATc1), a critical transcription factor for immune regulation, is known for its role in T cells and, more recently, in myeloid cells. However, the specific contributions of NFATc1 in T cells and DCs in the context of asthma are not well understood.

Objective

We explored NFATc1's role in T cells and DCs in modulating TH2 immune responses within the pathophysiology of allergic asthma.

Methods

We induced asthma in mice lacking Nfatc1 in CD4+ T cells or CD11c+ DCs using house dust mite, thereby enabling investigation into NFATc1's role in both cell types in experimental allergic asthma. Additionally, we examined NFATc1 expression in these cell types and its correlation with blood eosinophil levels in an adult asthma cohort.

Results

In a house dust mite-induced asthma model, we found that Nfatc1 deficiency either in CD4+ T cells or CD11c+ DCs resulted in reduced TH2-driven eosinophilic inflammation, IgE levels, and mast cell presence in the lung of asthmatic mice. Nfatc1's absence in CD4+ T cells directly hampered TH2 cell polarization and functionality, whereas in CD11c+ DCs, it affected DC differentiation and maturation, thereby weakening T-cell priming, proliferation, and subsequent TH2 differentiation. Correspondingly, translational research indicated significant correlations between CD4+NFATc1+ and CD11c+NFATc1+ cell populations and eosinophil levels in asthmatic patients, but not in healthy controls.

Conclusion

NFATc1 in T cells and DCs modulates TH2-mediated eosinophilic inflammation in allergic asthma, thus offering insight into asthma pathogenesis and identifying NFATc1 as a potential target for therapeutic intervention.

Extracellular vimentin amplifies inflammation: Perspectives for immune injury and therapeutics for periodontitis

Periodontitis is an inflammatory disease triggered by microbial biofilms that promote immune dysfunction and tissue destruction of tooth-supporting tissues. The search for soluble mediators that amplify inflammatory responses and matrix degradation in periodontal tissues has implicated extracellular vimentin (ECV) as a signaling ligand and damage-associated molecular pattern in the pathogenesis of periodontitis. Intracellular vimentin filaments are essential for the structural integrity of cells and the preservation of matrix homeostasis. These are important determinants of health in the periodontium and many other organs. But in inflamed tissues, intracellular vimentin filaments are disassembled. Vimentin is subsequently released from cells into the extracellular space in a soluble form where it drives immune signaling and tissue destruction. We discuss the role of ECV as a signaling molecule in several tissues. We apply these data to understand how in inflammatory diseases like periodontitis, ECV amplifies immune responses that contribute to disease progression. Arising from these data, we consider novel therapeutic opportunities for limiting tissue destruction by targeting ECV for treatment of inflammatory disorders like periodontitis.

Adaptor protein 3BP2 regulates gene expression in addition to the ubiquitination and proteolytic activity of MALT1 in dectin-1-stimulated cells

Dectin-1, a C-type lectin, plays important roles in the induction of antifungal immunity. Caspase recruitment domain-containing protein 9 (CARD9) is essential for the dectin-1-induced production of cytokines through the activation of NF-κB. However, the molecular mechanisms underlying the dectin-1-mediated activation of CARD9 have not been fully elucidated. Recently, we reported that the adaptor protein SH3 domain-binding protein 2 (3BP2) is required for the dectin-1-induced production of cytokines and activation of NF-κB, although the relationship between 3BP2 and CARD9 in dectin-1-mediated signaling remains unclear. Here, we report that 3BP2 is required for dectin-1-induced expression of several genes that may contribute to antifungal immunity in bone marrow-derived dendritic cells (BMDCs). The results of reporter assays using HEK-293T cells indicate that 3BP2 induces CARD9-mediated activation of NF-κB through B-cell leukemia/lymphoma 10, mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1), and TNF receptor-associated factor 6-dependent mechanisms. In addition, we show that 3BP2 induces CARD9-mediated ubiquitination of cellular proteins and that MALT1 cleaves 3BP2 in a CARD9-dependent manner. Furthermore, we show that 3BP2 is required for the ubiquitination, in addition to the activation, of MALT1, which leads to MALT1-depenedent cleavage of 3BP2 in dectin-1-stimulated BMDCs. Finally, we identified hematopoietic cell-specific Lyn substrate 1 as a target of 3BP2, which is essential for dectin-1-induced expression of interleukin 10 in BMDCs. These results indicate that 3BP2 regulates gene expression and functions of MALT1 in dectin-1-stimulated cells and that 3BP2 plays an important role in the dectin-1-mediated antifungal immunity.

Exploration of the Dual Role of Dectin-1 in Tumor Development and Its Therapeutic Potential

Immunotherapy, particularly immune checkpoint inhibitors like PD-1, PD-L1, and CTLA-4, has revolutionized cancer treatment. However, the role of the innate immune system, especially pattern recognition receptors, in cancer development and immunity is gaining more and more attention. Dectin-1, a C-type lectin receptor primarily involved in antifungal immunity, has emerged as a significant player in cancer biology, exhibiting both pro-tumor and anti-tumor roles. This dual function largely depends on the tumor type and microenvironment. Dectin-1 can promote immune responses against tumors like melanoma and breast cancer by enhancing both innate and adaptive immunity. However, in tumors like pancreatic ductal adenocarcinoma and colorectal cancer, Dectin-1 activation suppresses T cell immunity, facilitating tumor progression. This review explores the complex mechanisms by which Dectin-1 modulates the tumor microenvironment and discusses its potential as a therapeutic target for cancer treatment.

Molecular and functional in vivo characterisation of murine Dectin-1 isoforms

Dectin-1 is a C-type lectin-receptor involved in sensing fungi by innate immune cells. Encoded by the Clec7a gene, Dectin-1 exists in two major splice isoforms, Dectin-1a and 1b, which differ in the presence of a membrane-proximal stalk domain. As reported previously, this domain determines degradative routes for Dectin-1a and 1b leading to the generation of a stable N-terminal fragment exclusively from Dectin-1a. Here, we narrow down the responsible part of the stalk and demonstrate the stabilisation of the Dectin-1a N-terminal fragment in tetraspanin-enriched microdomains. C57BL/6 and BALB/c mice show divergent Dectin-1 isoform expression patterns, which are caused by a single nucleotide polymorphism in exon 3 of the Clec7a gene, leading to a non-sense Dectin-1a mRNA in C57BL/6 mice. Using backcrossing, we generated mice with the C57BL/6 Clec7a allele on a BALB/c background and compared these to the parental strains. Expression of the C57BL/6 allele leads to the exclusive presence of the Dectin-1b protein. Furthermore, it was associated with higher Dectin-1 mRNA expression, but less Dectin-1 at the cell surface according to flow cytometry. In neutrophils, this altered ROS production induced by Dectin-1 model ligands, while cellular responses in macrophages and dendritic cells were not significantly influenced by the Dectin-1 isoform pattern.

Calcineurin-NFAT signaling controls neutrophils' ability of chemoattraction upon fungal infection

Calcineurin-nuclear factor of activated T cells (CN-NFAT) inhibitors are widely clinically used drugs for immunosuppression, but besides their required T cell response inhibition, they also undesirably affect innate immune cells. Disruption of innate immune cell function can explain the observed susceptibility of CN-NFAT inhibitor-treated patients to opportunistic fungal infections. Neutrophils play an essential role in innate immunity as a defense against pathogens; however, the effect of CN-NFAT inhibitors on neutrophil function was poorly described. Thus, we tested the response of human neutrophils to opportunistic fungal pathogens, namely Candida albicans and Aspergillus fumigatus, in the presence of CN-NFAT inhibitors. Here, we report that the NFAT pathway members were expressed in neutrophils and mediated part of the neutrophil response to pathogens. Upon pathogen exposure, neutrophils underwent profound transcriptomic changes with subsequent production of effector molecules. Importantly, genes and proteins involved in the regulation of the immune response and chemotaxis, including the chemokines CCL2, CCL3, and CCL4 were significantly upregulated. The presence of CN-NFAT inhibitors attenuated the expression of these chemokines and impaired the ability of neutrophils to chemoattract other immune cells. Our results amend knowledge about the impact of CN-NFAT inhibition in human neutrophils.

Pharmacologic Interventions to Immunologic and Immune-Mediated Conditions in Horses

Immunomodulators can stimulate, suppress, or regulate one or many aspects of the immune response. Use of a variety of immunostimulants, immunosuppressors, and anti-inflammatory drugs are described in horses, but the evidence supporting their efficacy is variable. Corticosteroids and nonsteroidal anti-inflammatory drugs are the best characterized immunomodulators in horses, but further study is needed to fully define their ideal dosing protocols and indications and to characterize the efficacy of other immunomodulators in equine medicine.

Myeloid C-type lectin receptors in innate immune recognition

C-type lectin receptors (CLRs) expressed by myeloid cells constitute a versatile family of receptors that play a key role in innate immune recognition. Myeloid CLRs exhibit a remarkable ability to recognize an extensive array of ligands, from carbohydrates and beyond, and encompass pattern-associated molecular patterns (PAMPs), damage-associated molecular patterns (DAMPs), and markers of altered self. These receptors, classified into distinct subgroups, play pivotal roles in immune recognition and modulation of immune responses. Their intricate signaling pathways orchestrate a spectrum of cellular responses, influencing processes such as phagocytosis, cytokine production, and antigen presentation. Beyond their contributions to host defense in viral, bacterial, fungal, and parasitic infections, myeloid CLRs have been implicated in non-infectious diseases such as cancer, allergies, and autoimmunity. A nuanced understanding of myeloid CLR interactions with endogenous and microbial triggers is starting to uncover the context-dependent nature of their roles in innate immunity, with implications for therapeutic intervention.

Decoding Toll-like receptors: Recent insights and perspectives in innate immunity

Toll-like receptors (TLRs) are an evolutionarily conserved family in the innate immune system and are the first line of host defense against microbial pathogens by recognizing pathogen-associated molecular patterns (PAMPs). TLRs, categorized into cell surface and endosomal subfamilies, recognize diverse PAMPs, and structural elucidation of TLRs and PAMP complexes has revealed their intricate mechanisms. TLRs activate common and specific signaling pathways to shape immune responses. Recent studies have shown the importance of post-transcriptional regulation in TLR-mediated inflammatory responses. Despite their protective functions, aberrant responses of TLRs contribute to inflammatory and autoimmune disorders. Understanding the delicate balance between TLR activation and regulatory mechanisms is crucial for deciphering their dual role in immune defense and disease pathogenesis. This review provides an overview of recent insights into the history of TLR discovery, elucidation of TLR ligands and signaling pathways, and their relevance to various diseases.

Fine tuning of the innate and adaptive immune responses by Interleukin-2

Novel immunotherapies for cancer and other diseases aim to trigger the immune system to produce durable responses, while overcoming the immunosuppression that may contribute to disease severity, and in parallel considering immunosafety aspects. Interleukin-2 (IL-2) was one of the first cytokines that the FDA approved as a cancer-targeting immunotherapy. However, in the past years, IL-2 immunotherapy is not actively offered to patients, due to limited efficacy, when compared to other novel immunotherapies, and the associated severe adverse events. In order to design improved in vitro and in vivo models, able to predict the efficacy and safety of novel IL-2 alternatives, it is important to delineate the mechanistic immunological events triggered by IL-2. Particularly, in this review we will discuss the effects IL-2 has with the bridging cell type of the innate and adaptive immune responses, dendritic cells. The pathways involved in the regulation of IL-2 by dendritic cells and T-cells in cancer and autoimmune disease will also be explored.

Recognition of yeast β-glucan particles triggers immunometabolic signaling required for trained immunity

Fungal β-glucans are major drivers of trained immunity which increases long-term protection against secondary infections. Heterogeneity in β-glucan source, structure, and solubility alters interaction with the phagocytic receptor Dectin-1 and could impact strategies to improve trained immunity in humans. Using a panel of diverse β-glucans, we describe the ability of a specific yeast-derived whole-glucan particle (WGP) to reprogram metabolism and thereby drive trained immunity in human monocyte-derived macrophages in vitro and mice bone marrow in vivo. Presentation of pure, non-soluble, non-aggregated WGPs led to the formation of the Dectin-1 phagocytic synapse with subsequent lysosomal mTOR activation, metabolic reprogramming, and epigenetic rewiring. Intraperitoneal or oral administration of WGP drove bone marrow myelopoiesis and improved mature macrophage responses, pointing to therapeutic and food-based strategies to drive trained immunity. Thus, the investment of a cell in a trained response relies on specific recognition of β-glucans presented on intact microbial particles through stimulation of the Dectin-1 phagocytic response.

Modulation of Dendritic Cell Function via Nanoparticle-Induced Cytosolic Calcium Changes

Calcium nanoparticles have been investigated for applications, such as drug and gene delivery. Additionally, Ca2+ serves as a crucial second messenger in the activation of immune cells. However, few studies have systematically studied the effects of calcium nanoparticles on the calcium levels and functions within immune cells. In this study, we explore the potential of calcium nanoparticles as a vehicle to deliver calcium into the cytosol of dendritic cells (DCs) and influence their functions. We synthesized calcium hydroxide nanoparticles, coated them with a layer of silica to prevent rapid degradation, and further conjugated them with anti-CD205 antibodies to achieve targeted delivery to DCs. Our results indicate that these nanoparticles can efficiently enter DCs and release calcium ions in a controlled manner. This elevation in cytosolic calcium activates both the NFAT and NF-κB pathways, in turn promoting the expression of costimulatory molecules, antigen-presenting molecules, and pro-inflammatory cytokines. In mouse tumor models, the calcium nanoparticles enhanced the antitumor immune response and augmented the efficacy of both radiotherapy and chemotherapy without introducing additional toxicity. Our study introduces a safe nanoparticle immunomodulator with potential widespread applications in cancer therapy.

Role of CARD9 in Cell- and Organ-Specific Immune Responses in Various Infections

The caspase recruitment domain-containing protein 9 (CARD9) is an intracellular adaptor protein that is abundantly expressed in cells of the myeloid lineage, such as neutrophils, macrophages, and dendritic cells. CARD9 plays a critical role in host immunity against infections caused by fungi, bacteria, and viruses. A CARD9 deficiency impairs the production of inflammatory cytokines and chemokines as well as migration and infiltration, thereby increasing susceptibility to infections. However, CARD9 signaling varies depending on the pathogen causing the infection. Furthermore, different studies have reported altered CARD9-mediated signaling even with the same pathogen. Therefore, this review focuses on and elucidates the current literature on varied CARD9 signaling in response to various infectious stimuli in humans and experimental mice models.

DECTIN-1: A modifier protein in CTLA-4 haploinsufficiency

Autosomal dominant loss-of-function (LoF) variants in cytotoxic T-lymphocyte associated protein 4 (CTLA4) cause immune dysregulation with autoimmunity, immunodeficiency and lymphoproliferation (IDAIL). Incomplete penetrance and variable expressivity are characteristic of IDAIL caused by CTLA-4 haploinsufficiency (CTLA-4h), pointing to a role for genetic modifiers. Here, we describe an IDAIL proband carrying a maternally inherited pathogenic CTLA4 variant and a paternally inherited rare LoF missense variant in CLEC7A, which encodes for the β-glucan pattern recognition receptor DECTIN-1. The CLEC7A variant led to a loss of DECTIN-1 dimerization and surface expression. Notably, DECTIN-1 stimulation promoted human and mouse regulatory T cell (Treg) differentiation from naïve αβ and γδ T cells, even in the absence of transforming growth factor-β. Consistent with DECTIN-1's Treg-boosting ability, partial DECTIN-1 deficiency exacerbated the Treg defect conferred by CTL4-4h. DECTIN-1/CLEC7A emerges as a modifier gene in CTLA-4h, increasing expressivity of CTLA4 variants and acting in functional epistasis with CTLA-4 to maintain immune homeostasis and tolerance.

Dectin-1/CARD9 induction of the TFEB and TFE3 gene network is dispensable for phagocyte anti-Aspergillus activity in the lung

Myeloid phagocytes of the respiratory immune system, such as neutrophils, monocytes, and alveolar macrophages, are essential for immunity to Aspergillus fumigatus, the most common etiologic agent of mold pneumonia worldwide. Following the engulfment of A. fumigatus conidia, fusion of the phagosome with the lysosome is a critical process for killing conidia. TFEB and TFE3 are transcription factors that regulate lysosomal biogenesis under stress and are activated by inflammatory stimuli in macrophages, but it is unknown whether TFEB and TFE3 contribute to anti-Aspergillus immunity during infection. We found that lung neutrophils express TFEB and TFE3, and their target genes were upregulated during A. fumigatus lung infection. In addition, A. fumigatus infection induced nuclear accumulation of TFEB and TFE3 in macrophages in a process regulated by Dectin-1 and CARD9. Genetic deletion of Tfeb and Tfe3 impaired macrophage killing of A. fumigatus conidia. However, in a murine immune-competent Aspergillus infection model with genetic deficiency of Tfeb and Tfe3 in hematopoietic cells, we surprisingly found that lung myeloid phagocytes had no defects in conidial phagocytosis or killing. Loss of TFEB and TFE3 did not impact murine survival or clearance of A. fumigatus from the lungs. Our findings indicate that myeloid phagocytes activate TFEB and TFE3 in response to A. fumigatus, and while this pathway promotes macrophage fungicidal activity in vitro, genetic loss can be functionally compensated in the lung, resulting in no measurable defect in fungal control and host survival.

IκBζ is an essential mediator of immunity to oropharyngeal candidiasis

Fungal infections are a global threat; yet, there are no licensed vaccines to any fungal pathogens. Th17 cells mediate immunity to Candida albicans, particularly oropharyngeal candidiasis (OPC), but essential downstream mechanisms remain unclear. In the murine model of OPC, IκBζ (Nfkbiz, a non-canonical NF-κB transcription factor) was upregulated in an interleukin (IL)-17-dependent manner and was essential to prevent candidiasis. Deletion of Nfkbiz rendered mice highly susceptible to OPC. IκBζ was dispensable in hematopoietic cells and acted partially in the suprabasal oral epithelium to control OPC. One prominent IκBζ-dependent gene target was β-defensin 3 (BD3) (Defb3), an essential antimicrobial peptide. Human oral epithelial cells required IκBζ for IL-17-mediated induction of BD2 (DEFB4A, human ortholog of mouse Defb3) through binding to the DEFB4A promoter. Unexpectedly, IκBζ regulated the transcription factor Egr3, which was essential for C. albicans induction of BD2/DEFB4A. Accordingly, IκBζ and Egr3 comprise an antifungal signaling hub mediating mucosal defense against oral candidiasis.

Eculizumab suppresses zymosan-induced release of inflammatory cytokines IL-1α, IL-1β, IFN-γ and IL-2 in autologous serum-substituted PBMC cultures: Relevance to cytokine storm in Covid-19

BACKGROUND AND OBJECTIVE

Cytokine storm (CS) is a major contributor to the fatal outcome of severe infectious diseases, including Covid-19. Treatment with the complement (C) C5 inhibitor eculizumab was beneficial in end-stage Covid-19, however, the mechanism of this effect is unknown. To clarify this, we analyzed the relationship between C activation and production of pro-inflammatory cytokines in a PBMC model.

METHODS

Human PBMC with or without 20 % autologous serum was incubated with C3a, C5a, zymosan or zymosan-pre-activated serum (ZAS) for 24 h with or without eculizumab or the C5a receptor antagonist, DF2593A. C activation (sC5b-9) and 9 inflammatory cytokines were measured by ELISA.

RESULTS

In serum-free unstimulated PBMC only IL-8 release could be measured during incubation. Addition of C5a increased IL-8 secretion only, ZAS induced both IL-2 and IL-8, while zymosan led to significant production of all cytokines, most abundantly IL-8. In the presence of serum the above effects were greatly enhanced, and the zymosan-induced rises of IL-1α, IL-1β IFN-γ and IL-2 were significantly attenuated by eculizumab but not by DF2593a.

CONCLUSIONS

These data highlight the complexity of interrelationships between C activation and cytokine secretion under different experimental conditions. The clinically relevant findings include the abundant formation of the chemokine IL-8, which was stimulated by C5a, and the suppression of numerous inflammatory cytokines by eculizumab, which explains its therapeutic efficacy in severe Covid-19. These data strengthen the clinical relevance of the applied PBMC model for drug screening against CS, enabling the separation of complex innate immune cross-talks.

The activation of CaN/NFAT signaling pathway in macrophages aggravated Lactobacillus casei cell wall extract-induced Kawasaki disease vasculitis

OBJECTIVES

By using GWAS(genome-wide association studies) and linkage disequilibrium analysis to investigate the susceptibility genes of KD(Kawasaki disease), previous studies have identified that the CaN(calcineurin)-NFAT(the nuclear factor of activated T cell) signal pathway were significantly associated with susceptibility to KD. However, little is known about the molecular basis of the CaN/NFAT pathway involved in KD. Therefore, in our study we investigate the role of Ca2+/CaN/NFAT signaling pathway in macrophages in vitro and in vivo on coronary artery lesions induced by LCWE (Lactobacillus casei cell wall extract).

METHODS AND RESULTS

We observed that LCWE could increase the expression of NFAT1 and NFAT2 in macrophages in vitro, and also enhance the transcriptional activity of NFAT by promoting the nucleus translocation. Similarly, in LCWE-induced mice model, the expression of NFAT1 and NFAT2 and associated proinflammatory factors were increased significantly. In addition, by knocking down or overexpressing NFAT1 or NFAT2 in macrophages, the results indicated that NFAT signaling pathway mediated LCWE-induced immune responses in macrophages and regulated the synthesis of IL(interleukin)-6, IL-1β and TNF(tumor necrosis factor)-α in LCWE-induced macrophage activation. As well, we found that this process could be suppressed by CaN inhibitor CsA(cyclosporinA).

CONCLUSIONS

Therefore, the CaN/NFAT signaling pathway mediated LCWE-induced immune responses in macrophages, and also participated in the LCWE-induced CALs(coronary artery lesions). And also the inhibitory effect of CsA in LCWE-induced cell model towards a strategy to modulate the CaN/NFAT pathway during the acute course of KD might be helpful in alleviate KD-induced CALs.

Dectin-1/CARD9-induction of the TFEB and TFE3 gene network is dispensable for phagocyte anti-Aspergillus activity in the lung

Myeloid phagocytes of the respiratory immune system, such as neutrophils, monocytes, and alveolar macrophages, are essential for immunity to Aspergillus fumigatus, the most common etiologic agent of mold pneumonia worldwide. Following engulfment of A. fumigatus conidia, fusion of the phagosome with the lysosome, is a critical process for killing conidia. TFEB and TFE3 are transcription factors that regulate lysosomal biogenesis under stress and are activated by inflammatory stimuli in macrophages, but it is unknown whether TFEB and TFE3 contribute to anti-Aspergillus immunity during infection. We found that lung neutrophils express TFEB and TFE3, and their target genes were upregulated during A. fumigatus lung infection. Additionally, A. fumigatus infection induced nuclear accumulation of TFEB and TFE3 in macrophages in a process regulated by Dectin-1 and CARD9 signaling. Genetic deletion of Tfeb and Tfe3 impaired macrophage killing of A. fumigatus conidia. However, in a murine immune competent Aspergillus infection model with genetic deficiency of Tfeb and Tfe3 in hematopoietic cells, we surprisingly found that lung myeloid phagocytes had no defects in conidial phagocytosis or killing. Loss of TFEB and TFE3 did not impact murine survival or clearance of A. fumigatus from the lungs. Our findings indicate that myeloid phagocytes activate TFEB and TFE3 in response to A. fumigatus, and while this pathway promotes macrophage fungicidal activity in vitro, genetic loss can be functionally compensated at the portal of infection in the lung, resulting in no measurable defect in fungal control and host survival.

Mycochemicals against Cancer Stem Cells

Since ancient times, mushrooms have been considered valuable allies of human well-being both from a dietary and medicinal point of view. Their essential role in several traditional medicines is explained today by the discovery of the plethora of biomolecules that have shown proven efficacy for treating various diseases, including cancer. Numerous studies have already been conducted to explore the antitumoural properties of mushroom extracts against cancer. Still, very few have reported the anticancer properties of mushroom polysaccharides and mycochemicals against the specific population of cancer stem cells (CSCs). In this context, β-glucans are relevant in modulating immunological surveillance against this subpopulation of cancer cells within tumours. Small molecules, less studied despite their spread and assortment, could exhibit the same importance. In this review, we discuss several pieces of evidence of the association between β-glucans and small mycochemicals in modulating biological mechanisms which are proven to be involved with CSCs development. Experimental evidence and an in silico approach are evaluated with the hope of contributing to future strategies aimed at the direct study of the action of these mycochemicals on this subpopulation of cancer cells.

β-glucans: a potential source for maintaining gut microbiota and the immune system

The human gastrointestinal (GI) tract holds a complex and dynamic population of microbial communities, which exerts a marked influence on the host physiology during homeostasis and disease conditions. Diet is considered one of the main factors in structuring the gut microbiota across a lifespan. Intestinal microbial communities play a vital role in sustaining immune and metabolic homeostasis as well as protecting against pathogens. The negatively altered gut bacterial composition has related to many inflammatory diseases and infections. β-glucans are a heterogeneous assemblage of glucose polymers with a typical structure comprising a leading chain of β-(1,4) and/or β-(1,3)-glucopyranosyl units with various branches and lengths as a side chain. β-glucans bind to specific receptors on immune cells and initiate immune responses. However, β-glucans from different sources differ in their structures, conformation, physical properties, and binding affinity to receptors. How these properties modulate biological functions in terms of molecular mechanisms is not known in many examples. This review provides a critical understanding of the structures of β-glucans and their functions for modulating the gut microbiota and immune system.

FK506 impairs neutrophil migration that results in increased polymicrobial sepsis susceptibility

OBJECTIVE

This study aimed to investigate the effects of FK506 on experimental sepsis immunopathology. It investigated the effect of FK506 on leukocyte recruitment to the site of infection, systemic cytokine production, and organ injury in mice with sepsis.

METHODS

Using a murine cecal ligation and puncture (CLP) peritonitis model, the experiments were performed with wild-type (WT) mice and mice deficient in the gene Nfat1 (Nfat1^-/-) in the C57BL/6 background. Animals were treated with 2.0 mg/kg of FK506, subcutaneously, 1 h before the sepsis model, twice a day (12 h/12 h). The number of bacteria colony forming units (CFU) was manually counted. The number of neutrophils in the lungs was estimated by the myeloperoxidase (MPO) assay. The expression of CXCR2 in neutrophils was determined using flow cytometry analysis. The expression of inflammatory cytokines in macrophage was determined using ELISA. The direct effect of FK506 on CXCR2 internalization was evaluated using HEK-293T cells after CXCL2 stimulation by the BRET method.

RESULTS

FK506 treatment potentiated the failure of neutrophil migration into the peritoneal cavity, resulting in bacteremia and an exacerbated systemic inflammatory response, which led to higher organ damage and mortality rates. Failed neutrophil migration was associated with elevated CXCL2 chemokine plasma levels and lower expression of the CXCR2 receptor on circulating neutrophils compared with non-treated CLP-induced septic mice. FK506 did not directly affect CXCL2-induced CXCR2 internalization by transfected HEK-293 cells or mice neutrophils, despite increasing CXCL2 release by LPS-treated macrophages. Finally, the CLP-induced response of Nfat1^-/- mice was similar to those observed in the Nfat1^+/+ genotype, suggesting that the FK506 effect is not dependent on the NFAT1 pathway.

CONCLUSION

Our data indicate that the increased susceptibility to infection of FK506-treated mice is associated with failed neutrophil migration due to the reduced membrane availability of CXCR2 receptors in response to exacerbated levels of circulating CXCL2.

Intestinal fungi and systemic autoimmune diseases

Nearly 20 years of studies have shown that fungi and the human immune system (non-specific immunity and specific immunity) and bacterial--fungal interactions maintain a balance that can't lead to diseases. Fungi--microorganism that lives in human intestine--may play an important role in human health and disease. Population studies and animal models in some diseases have found the changes in the diversity and composition of fungi. The dysregulation of the fungi can disrupt the normal "running" of the immune system and bacteria, which triggers the development of inflammatory diseases. The latest studies of fungi in inflammatory bowel disease, systemic lupus erythematosus, ankylosing spondylitis and type 1 diabetes mellitus were summarized. This review considers how the healthy host protect against the potential harm of intestinal fungi through the immune system and how fungal dysregulation alters host immunity.

Zymosan Particle-Induced Hemodynamic, Cytokine and Blood Cell Changes in Pigs: An Innate Immune Stimulation Model with Relevance to Cytokine Storm Syndrome and Severe COVID-19

Hemodynamic disturbance, a rise in neutrophil-to-lymphocyte ratio (NLR) and release of inflammatory cytokines into blood, is a bad prognostic indicator in severe COVID-19 and other diseases involving cytokine storm syndrome (CSS). The purpose of this study was to explore if zymosan, a known stimulator of the innate immune system, could reproduce these changes in pigs. Pigs were instrumented for hemodynamic analysis and, after i.v. administration of zymosan, serial blood samples were taken to measure blood cell changes, cytokine gene transcription in PBMC and blood levels of inflammatory cytokines, using qPCR and ELISA. Zymosan bolus (0.1 mg/kg) elicited transient hemodynamic disturbance within minutes without detectable cytokine or blood cell changes. In contrast, infusion of 1 mg/kg zymosan triggered maximal pulmonary hypertension with tachycardia, lasting for 30 min. This was followed by a transient granulopenia and then, up to 6 h, major granulocytosis, resulting in a 3-4-fold increase in NLR. These changes were paralleled by massive transcription and/or rise in IL-6, TNF-alpha, CCL-2, CXCL-10, and IL-1RA in blood. There was significant correlation between lymphopenia and IL-6 gene expression. We conclude that the presented model may enable mechanistic studies on late-stage COVID-19 and CSS, as well as streamlined drug testing against these conditions.

Macrophage NFATC2 mediates angiogenic signaling during mycobacterial infection

During mycobacterial infections, pathogenic mycobacteria manipulate both host immune and stromal cells to establish and maintain a productive infection. In humans, non-human primates, and zebrafish models of infection, pathogenic mycobacteria produce and modify the specialized lipid trehalose 6,6'-dimycolate (TDM) in the bacterial cell envelope to drive host angiogenesis toward the site of forming granulomas, leading to enhanced bacterial growth. Here, we use the zebrafish-Mycobacterium marinum infection model to define the signaling basis of the host angiogenic response. Through intravital imaging and cell-restricted peptide-mediated inhibition, we identify macrophage-specific activation of NFAT signaling as essential to TDM-mediated angiogenesis in vivo. Exposure of cultured human cells to Mycobacterium tuberculosis results in robust induction of VEGFA, which is dependent on a signaling pathway downstream of host TDM detection and culminates in NFATC2 activation. As granuloma-associated angiogenesis is known to serve bacterial-beneficial roles, these findings identify potential host targets to improve tuberculosis disease outcomes.

Dectin-1 signaling in neutrophils up-regulates PD-L1 and triggers ROS-mediated suppression of CD4+ T cells

Dectin-1 is known to drive proinflammatory cytokine production by macrophages and dendritic cells which promotes Th17 CD4+ T cell responses in the setting of fungal infection. However, the role of Dectin-1 signaling in neutrophils and its impact on CD4+ T cells is not well understood. In this study, we found that neutrophils stimulated with a Dectin-1 agonist diminish CD4+ T cell viability in a rapid and reactive oxygen species (ROS)-dependent manner. Furthermore, Dectin-1 promoted neutrophil PD-L1 expression via Syk and Card9 signaling, along with other immune-checkpoint factors in a neutrophil-biased manner. Although neutrophil PD-L1 did not significantly impact disease severity in experimental autoimmune encephalomyelitis (EAE), we found that CNS-infiltrated neutrophils potently up-regulate PD-L1 expression. Furthermore, a subset of PD-L1+ neutrophils was also found to express MHC-II during EAE. In summary, we found that Dectin-1 elicits a biphasic neutrophil response in which (1) T-cell suppressive ROS is followed by (2) up-regulation of PD-L1 expression. This response may serve to limit excess CD4+ T cell-driven inflammation in infection or autoimmunity while preserving host-defense functions of neutrophils. Summary sentence: Mechanisms by which Dectin-1 signaling in neutrophils promotes a cellular phenotype with T cell-suppressive properties.

Immunogenetics associated with severe coccidioidomycosis

Disseminated coccidioidomycosis (DCM) is caused by Coccidioides, pathogenic fungi endemic to the southwestern United States and Mexico. Illness occurs in approximately 30% of those infected, less than 1% of whom develop disseminated disease. To address why some individuals allow dissemination, we enrolled patients with DCM and performed whole-exome sequencing. In an exploratory set of 67 patients with DCM, 2 had haploinsufficient STAT3 mutations, and defects in β-glucan sensing and response were seen in 34 of 67 cases. Damaging CLEC7A and PLCG2 variants were associated with impaired production of β-glucan-stimulated TNF-α from PBMCs compared with healthy controls. Using ancestry-matched controls, damaging CLEC7A and PLCG2 variants were overrepresented in DCM, including CLEC7A Y238* and PLCG2 R268W. A validation cohort of 111 patients with DCM confirmed the PLCG2 R268W, CLEC7A I223S, and CLEC7A Y238* variants. Stimulation with a DECTIN-1 agonist induced DUOX1/DUOXA1-derived hydrogen peroxide [H2O2] in transfected cells. Heterozygous DUOX1 or DUOXA1 variants that impaired H2O2 production were overrepresented in discovery and validation cohorts. Patients with DCM have impaired β-glucan sensing or response affecting TNF-α and H2O2 production. Impaired Coccidioides recognition and decreased cellular response are associated with disseminated coccidioidomycosis.

Specific immunosuppressive role of nanodrugs targeting calcineurin in innate myeloid cells

Calcineurin (CN) inhibitors currently used to avoid transplant rejection block the activation of adaptive immune responses but also prevent the development of tolerance toward the graft, by directly inhibiting T cells. CN, through the transcription factors of the NFAT family, plays an important role also in the differentiation dendritic cells (DCs), the main cells responsible for the activation of T lymphocytes. Therefore, we hypothesized that the inhibition of CN only in DCs and not in T cells could be sufficient to prevent T cell responses, while allowing for the development of tolerance. Here, we show that inhibition of CN/NFAT pathway in innate myeloid cells, using a new nanoconjugate capable of selectively targeting phagocytes in vivo, protects against graft rejection and induces a longer graft acceptance compared to common CN inhibitors. We propose a new generation of nanoparticles-based selective immune suppressive agents for a better control of transplant acceptance.

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Calcineurin/NFATc2 pathway is required to enable DC migration to draining lymph nodes

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Calcineurin/NFATc2 pathway in DCs is required for type I immune responses activation

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Superparamagnetic iron oxide NPs can be used to efficiently target phagocytes in vivo

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Specific delivery of calcineurin inhibitor by NPs to phagocytes induce graft acceptance

Hematopoietic Stem and Progenitor Cell Maintenance and Multiple Lineage Differentiation Is an Integral Function of NFATc1

Hematopoietic stem and progenitor cell (HSPC) maintenance and the differentiation of various lineages is a highly complex but precisely regulated process. Multiple signaling pathways and an array of transcription factors influence HSPC maintenance and the differentiation of individual lineages to constitute a functional hematopoietic system. Nuclear factor of activated T cell (NFAT) family transcription factors have been studied in the context of development and function of multiple mature hematopoietic lineage cells. However, until now their contribution in HSPC physiology and HSPC differentiation to multiple hematopoietic lineages has remained poorly understood. Here, we show that NFAT proteins, specifically NFATc1, play an indispensable role in the maintenance of HSPCs. In the absence of NFATc1, very few HSPCs develop in the bone marrow, which are functionally defective. In addition to HSPC maintenance, NFATc1 also critically regulates differentiation of lymphoid, myeloid, and erythroid lineage cells from HSPCs. Deficiency of NFATc1 strongly impaired, while enhanced NFATc1 activity augmented, the differentiation of these lineages, which further attested to the vital involvement of NFATc1 in regulating hematopoiesis. Hematopoietic defects due to lack of NFATc1 activity can lead to severe pathologies such as lymphopenia, myelopenia, and a drastically reduced lifespan underlining the critical role NFATc1 plays in HSPC maintenance and in the differentaion of various lineages. Our findings suggest that NFATc1 is a critical component of the myriad signaling and transcriptional regulators that are essential to maintain normal hematopoiesis.

Recognition of Pathogens and Their Inflammatory Signaling Events

The innate immune system is the main and first line of defense mechanism present in the human body, which acts against a foreign antigen. To function it utilize several mechanisms, among those are the primary one is recognizing the foreign antigen which is accomplished via decidedly complicated group of molecules termed as pattern recognition receptors (PRRs), which perceive various diverse structures present on the pathogen known as pathogen-associated molecular patterns (PAMPs). PRPs include several classes of receptors’, functions, and nature of these receptors vary from each other depending upon the molecular composition of PAMPs they detect. However, the Toll-like receptors (TLRs) are among the class of PRPs, which are studied widely. In this review, we have presented the contemporary understanding of pathogens recognition by various receptor classes including PRRs. In addition, we also discuss PRPs associated signaling pathways associated with antimicrobial immune response triggering.

Physical activity in asthma control and its immune modulatory effect in asthmatic preschoolers

BACKGROUND

The impact of physical activity on immune response is a hot topic in exercise immunology, but studies involving asthmatic children are scarce. Our aims were to examine whether there were any differences in the level of physical activity and daily TV attendance, to assess its role on asthma control and immune responses to various immune stimulants.

METHODS

Weekly physical activity and daily television attendance were obtained from questionnaires at inclusion of the PreDicta study. PBMC cultures were stimulated with phytohemagglutinin (PHA), R848, poly I:C, and zymosan. A panel of cytokines was measured and quantified in cell culture supernatants using luminometric multiplex immunofluorescence beads-based assay.

RESULTS

Asthmatic preschoolers showed significantly more TV attendance than their healthy peers (58.6% vs. 41.5% 1-3 h daily and only 25.7% vs. 47.2% ≤1 h daily) and poor asthma control was associated with less frequent physical activity (PA) (75% no or occasional activity in uncontrolled vs. 20% in controlled asthma; 25% ≥3 times weekly vs. 62%). Asthmatics with increased PA exhibited elevated cytokine levels in response to polyclonal stimulants, suggesting a readiness of circulating immune cells for type 1, 2, and 17 cytokine release compared to subjects with low PA and high TV attendance. This may also represent a proinflammatory state in high PA asthmatic children. Low physical activity and high TV attendance were associated with a decrease in proinflammatory cytokines. Proinflammatory cytokines were correlating with each other in in vitro immune responses of asthmatic children, but not healthy controls, this correlation was more pronounced in children with sedentary behavior.

CONCLUSION

Asthmatic children show more sedentary behavior than healthy subjects, while poor asthma control is associated with a substantial decrease in physical activity. Our results suggest that asthmatic children may profit from regular exercise, as elevated cytokine levels in stimulated conditions indicate an immune system prepared for responding strongly in case of different types of infections. However, it has to be considered that a hyperinflammatory state in high PA may not be beneficial in asthmatic children.

Pathogen size alters C-type lectin receptor signaling in dendritic cells to influence CD4 Th9 cell differentiation

Dectin-1 recognizes β-glucan in fungal cell walls, and activation of Dectin-1 in dendritic cells (DCs) influences immune responses against fungi. Although many studies have shown that DCs activated via Dectin-1 induce different subsets of T helper cells according to different cytokine milieus, the mechanisms underlying such differences remain unknown. By harnessing polymorphic Candida albicans and polystyrene beads of different sizes, we find that target size influences production of cytokines that control differentiation of T helper cell subsets. Hyphal C. albicans and large beads activate DCs but cannot be phagocytosed due to their sizes, which prolongs the duration of Dectin-1 signaling. Transcriptomic analysis reveals that expression of Il33 is significantly increased by larger targets, and increased IL-33 expression promotes T_H9 responses. Expression of IL-33 is regulated by the Dectin-1-SYK-PLCγ-CARD9-ERK pathway. Altogether, our study demonstrates that size of fungi can be a determining factor in how DCs induce context-appropriate adaptive immune responses.

Oh et al. show that dendritic cells exposed to C. albicans hyphae more strongly induce IL-9-producing T cells compared with cells exposed to yeast. They find that this T_H9 response is driven in large part by Dectin-1 sensing microbe size, leading to elevated production of IL-33.

NFAM1 Promotes Pro-Inflammatory Cytokine Production in Mouse and Human Monocytes

NFAT activating protein with ITAM motif 1 (NFAM1) is an ITAM bearing-transmembrane receptor that has been reported to play a role in B cell signaling and development. We performed expression analysis of NFAM1 using publicly available gene expression data sets and found that NFAM1 expression is significantly induced in intestinal biopsies from Crohn’s disease (CD) and ulcerative colitis (UC) patients. At the cellular level, we further observed high expression of NFAM1 in monocytes and neutrophils, and low expression in B and T cells. To explore the role of NFAM1 in multiple immune cells and its potential role in IBD, we generated NFAM1^-/- mice. In contrast with previous reports using NFAM1-transgenic mice, NFAM1^-/- mice have no obvious defects in immune cell development, or B cell responses. Interestingly, NFAM1^-/- monocytes produce reduced levels of TNF-α in response to activation by multiple IBD-relevant stimuli, including CD40L, TLR ligands and MDP. Additional cytokines and chemokines such as IL-6, IL-12, CCL3 and CCL4 are also reduced in CD40L stimulated NFAM1^-/- monocytes. Collectively, these findings indicate that NFAM1 promotes monocyte activation, thereby amplifying the response to diverse stimuli. Similarly, we observed that deletion of NFAM1 in human monocytes reduces expression of CD40L-induced CCL4. Lastly, to assess the role of NFAM1 in IBD, we compared development of anti-CD40 induced colitis in NFAM1^+/+ and NFAM1^-/- mice. We found that although NFAM1 deletion had no impact on development of gut pathology, we did observe a decrease in serum TNF-α, confirming that NFAM1 promotes pro-inflammatory cytokine production in vivo. Taken together, we conclude that NFAM1 functions to amplify cytokine production and should be further evaluated as a therapeutic target for treatment of autoimmune disease.

Dectin-1 Signaling Update: New Perspectives for Trained Immunity

The C-type lectin receptor Dectin-1 was originally described as the β-glucan receptor expressed in myeloid cells, with crucial functions in antifungal responses. However, over time, different ligands both of microbial-derived and endogenous origin have been shown to be recognized by Dectin-1. The outcomes of this recognition are diverse, including pro-inflammatory responses such as cytokine production, reactive oxygen species generation and phagocytosis. Nonetheless, tolerant responses have been also attributed to Dectin-1, depending on the specific ligand engaged. Dectin-1 recognition of their ligands triggers a plethora of downstream signaling pathways, with complex interrelationships. These signaling routes can be modulated by diverse factors such as phosphatases or tetraspanins, resulting either in pro-inflammatory or regulatory responses. Since its first depiction, Dectin-1 has recently gained a renewed attention due to its role in the induction of trained immunity. This process of long-term memory of innate immune cells can be triggered by β-glucans, and Dectin-1 is crucial for its initiation. The main signaling pathways involved in this process have been described, although the understanding of the above-mentioned complexity in the β-glucan-induced trained immunity is still scarce. In here, we have reviewed and updated all these factors related to the biology of Dectin-1, highlighting the gaps that deserve further research. We believe on the relevance to fully understand how this receptor works, and therefore, how we could harness it in different pathological conditions as diverse as fungal infections, autoimmunity, or cancer.

Selective suppression of IL-10 transcription by calcineurin in dendritic cells through inactivation of CREB

Myeloid cells play a pivotal role in immune responses against bacterial and fungal infection. Among innate immune receptors, C-type lectin receptors (CLRs) can induce a wide spectrum of cytokines through immunoreceptor tyrosine-based activation motifs (ITAMs)-mediated signaling pathways. Dendritic cells (DCs) produce IL-10 through CLR stimulation; however, the regulatory mechanism of IL-10 expression has not been elucidated. In the current study, we report that calcium (Ca 2+) signaling-deficient DCs produced more IL-10 than wild type DCs. Mechanistically, Ca 2+-dependent phosphatase calcineurin directly inactivates cAMP response element binding protein (CREB), a transcription factor of Il10 in DCs, through dephosphorylating CREB at serine 133. In calcineurin-deficient DCs, CREB was highly phosphorylated and increased its binding to Il10 promoter. Elimination of MAPK signaling that phosphorylates CREB, deficiency of CREB, as well as deletion of CREB-binding site in Il10 promoter could diminish IL-10 production in DCs. Our findings identified a novel substrate of calcineurin as well as a mechanism through which Ca 2+ signaling regulates IL-10 expression downstream of CLRs. As IL-10 is a crucial immunosuppressive cytokine, this mechanism may counteract the over-activated IL-10 producing signals induced by CARD9 and MAPK pathways, preventing the ineffectiveness of immune system during bacterial and fungal infection.

Glycan Activation of Clec4b Induces Reactive Oxygen Species Protecting against Neutrophilia and Arthritis

Animal models for complex diseases are needed to position and analyze the function of interacting genes. Previous positional cloning identified Ncf1 and Clec4b to be major regulators of arthritis models in rats. Here, we investigate epistasis between Ncf1 and Clec4b, two major regulators of arthritis in rats. We find that Clec4b and Ncf1 exert an additive effect on arthritis given by their joint ability to regulate neutrophils. Both genes are highly expressed in neutrophils, together regulating neutrophil availability and their capacity to generate reactive oxygen species. Using a glycan array, we identify key ligands of Clec4b and demonstrate that Clec4b-specific stimulation triggers neutrophils into oxidative burst. Our observations highlight Clec4b as an important regulator of neutrophils and demonstrate how epistatic interactions affect the susceptibility to, and severity of, autoimmune arthritis.

β-Glucans Could Be Adjuvants for SARS-CoV-2 Virus Vaccines (COVID-19)

Waiting for an effective treatment against the SARS-CoV-2 virus (the cause of COVID-19), the current alternatives include prevention and the use of vaccines. At the moment, vaccination is the most effective strategy in the fight against pandemic. Vaccines can be administered with different natural biological products (adjuvants) with immunomodulating properties. Adjuvants can be taken orally, complementing vaccine action. Adjuvant compounds could play a key role in alleviating the symptoms of the disease, as well as in enhancing vaccine action. Adjuvants also contribute to an effective immune response and can enhance the protective effect of vaccines in immunocompromised individuals such as the elderly. Adjuvants must not produce adverse effects, toxicity, or any other symptoms that could alter immune system function. Vaccine adjuvants are substances of wide varying chemical structure that are used to boost the immune response against a simultaneously administered antigen. Glucans could work as adjuvants due to their immunomodulatory biological activity. In this respect, β-(1,3)-(1,6) glucans are considered the most effective and safe according to the list issued by the European Commission. Only glucans with a β-(1,3) bond linked to a β-(1,6) are considered modulators of certain biological responses. The aim of this review is to present the possible effects of β-glucans as adjuvants in the efficacy of vaccines against SARS-CoV-2 virus.

Immunosuppression Affects Neutrophil Functions: Does Calcineurin-NFAT Signaling Matter?

Neutrophils are innate immune cells with important roles in antimicrobial defense. However, impaired or dysregulated neutrophil function can result in host tissue damage, loss of homeostasis, hyperinflammation or pathological immunosuppression. A central link between neutrophil activation and immune outcomes is emerging to be the calcineurin-nuclear factor of activated T cells (NFAT) signaling pathway, which is activated by neutrophil detection of a microbial threat via pattern recognition receptors and results in inflammatory cytokine production. This potent pro-inflammatory pathway is also the target of several immunosuppressive drugs used for the treatment of autoimmune disorders, during solid organ and hematopoietic cell transplantations, and as a part of anti-cancer therapy: but what effects these drugs have on neutrophil function, and their broader consequences for immune homeostasis and microbial defense are not yet known. Here, we bring together the emerging literature describing pathology- and drug- induced neutrophil impairment, with particular focus on their effects on calcineurin-NFAT signaling in the innate immune compartment.

Emerging roles of Dectin-1 in noninfectious settings and in the CNS

Dectin-1 is a C-type lectin receptor (CLR) expressed on the surface of various mammalian myeloid cells. Dectin-1 recognizes β-glucans and elicits antifungal proinflammatory immune responses. Recent studies have begun to examine the biology of Dectin-1 in previously less explored settings, such as homeostasis, sterile inflammation, and in the central nervous system. Indeed, in certain contexts, Dectin-1 is now known to promote tolerance, and anti-inflammatory and neuroprotective responses. In this review, we provide an overview of the current understanding of the roles of Dectin-1 in immunology beyond the context of fungal infections, mainly focusing on in vivo neuroimmunology studies, which could reveal new therapeutic approaches to modify innate immune responses in neurologic disorders.

Identification and evolution of transcription factors RHR gene family (NFAT and RBPJ) involving lamprey (Lethenteron reissneri) innate immunity

Nuclear factor of activated T cells (NFAT) and recombination signal binding protein (RBP) belong to the family of Rel homology region (RHR) transcription factors which regulate the expression of genes involved in different aspects of the immune response. To gain insights into the evolution and characterisation of RHR genes in lampreys, a jawless vertebrate, four RHR genes, including nuclear factor of activated T cells (NFAT) and recombination signal binding protein for immunoglobulin kappa J region (RBPJ), have been identified and cloned from the lamprey (Lethenteron reissneri) database. Evolutionary relationships of NFAT and RBPJ genes among different species were determined through molecular phylogenetic analysis. Motif, genetic structure, and tertiary structure analyses showed that NFATs and RBPJ are conserved and contain RHD and IPT domains. Moreover, synteny analysis showed that the neighbourhood genes of Lr-NFATs and Lr-RBPJ have undergone significant changes compared to jawed vertebrates. Real-time quantitative results demonstrated that the RHR gene family plays a significant role in immune defence. This study provides a new understanding of the origin and evolution of the RHR gene family in different species.

NADPH Oxidase Limits Collaborative Pattern-Recognition Receptor Signaling to Regulate Neutrophil Cytokine Production in Response to Fungal Pathogen-Associated Molecular Patterns

Chronic granulomatous disease (CGD) is a primary immunodeficiency caused by genetic defects in leukocyte NADPH oxidase, which has both microbicidal and immunomodulatory roles. Hence, CGD is characterized by recurrent bacterial and fungal infections as well as aberrant inflammation. Fungal cell walls induce neutrophilic inflammation in CGD; yet, underlying mechanisms are incompletely understood. This study investigated the receptors and signaling pathways driving aberrant proinflammatory cytokine production in CGD neutrophils activated by fungal cell walls. Although cytokine responses to β-glucan particles were similar in NADPH oxidase-competent and NADPH oxidase-deficient mouse and human neutrophils, stimulation with zymosan, a more complex fungal particle, induced elevated cytokine production in NADPH oxidase-deficient neutrophils. The dectin-1 C-type lectin receptor, which recognizes β-glucans (1-3), and TLRs mediated cytokine responses by wild-type murine neutrophils. In the absence of NADPH oxidase, fungal pathogen-associated molecular patterns engaged additional collaborative signaling with Mac-1 and TLRs to markedly increase cytokine production. Mechanistically, this cytokine overproduction is mediated by enhanced proximal activation of tyrosine phosphatase SHP2-Syk and downstream Card9-dependent NF-κB and Card9-independent JNK-c-Jun. This activation and amplified cytokine production were significantly decreased by exogenous H₂O₂ treatment, enzymatic generation of exogenous H₂O₂, or Mac-1 blockade. Similar to zymosan, Aspergillus fumigatus conidia induced increased signaling in CGD mouse neutrophils for activation of proinflammatory cytokine production, which also used Mac-1 and was Card9 dependent. This study, to our knowledge, provides new insights into how NADPH oxidase deficiency deregulates neutrophil cytokine production in response to fungal cell walls.

NFAT signaling in human mesenchymal stromal cells affects extracellular matrix remodeling and antifungal immune responses

Mesenchymal stromal cells (MSCs) combined with calcineurin-nuclear factor of activated T cell (CN-NFAT) inhibitors are being tested as a treatment for graft-versus-host disease (GvHD). The immunosuppressive properties of MSCs seem beneficial; however, their response during fungal infection, which is an important cause of mortality in patients with GvHD , is unknown. We report that MSCs phagocytose the fungal component zymosan, resulting in phosphorylation of spleen tyrosine kinase (Syk), increase in cytosolic calcium levels, and ultimately, increase in NFAT1 nuclear translocation. RNA sequencing analysis of zymosan-treated MSCs showed that CN-NFAT inhibition affects extracellular matrix (ECM) genes but not cytokine expression that is under the control of the NF-κB pathway. When coculturing MSCs or decellularized MSC-ECM with human peripheral blood mononuclear cells (PBMCs), selective NFAT inhibition in MSCs decreased cytokine expression by PBMCs. These findings reveal a dual mechanism underlying the MSC response to zymosan: while NF-κB directly controls inflammatory cytokine expression, NFAT impacts immune-cell functions by regulating ECM remodeling.

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Stimulation of MSCs with zymosan activates NFAT and NF-kB via the dectin1-Syk axis

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Calcineurin-NFAT inhibition impacts the expression of extracellular matrix genes

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NF-kB pathway regulates cytokine expression in zymosan-stimulated MSCs

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Selective NFAT inhibition in MSCs impacts cytokine secretion of MSC-PBMC cocultures

Dectin-1-Mediated Production of Pro-Inflammatory Cytokines Induced by Yeast β-Glucans in Bovine Monocytes

Yeast-derived products containing β-glucans have long been used as feed supplements in domesticated animals in an attempt to increase immunity. β-glucans are mainly recognized by the cell surface receptor CLEC7A, also designated Dectin-1. Although the immune mechanisms elicited through Dectin-1 activation have been studied in detail in mice and humans, they are poorly understood in other species. Here, we evaluated the response of bovine monocytes to soluble and particulate purified β-glucans, and also to Zymosan. Our results show that particulate, but not soluble β-glucans, can upregulate the surface expression of costimulatory molecules CD80 and CD86 on bovine monocytes. In addition, stimulated cells increased production of IL-8 and of TNF, IL1B, and IL6 mRNA expression, in a dose-dependent manner, which correlated positively with CLEC7A gene expression. Production of IL-8 and TNF expression decreased significantly after CLEC7A knockdown using two different pairs of siRNAs. Overall, we demonstrated here that bovine monocytes respond to particulate β-glucans, through Dectin-1, by increasing the expression of pro-inflammatory cytokines. Our data support further studies in cattle on the induction of trained immunity using dietary β-glucans.

Mini-Factor H Modulates Complement-Dependent IL-6 and IL-10 Release in an Immune Cell Culture (PBMC) Model: Potential Benefits Against Cytokine Storm

Cytokine storm (CS), an excessive release of proinflammatory cytokines upon overactivation of the innate immune system, came recently to the focus of interest because of its role in the life-threatening consequences of certain immune therapies and viral diseases, including CAR-T cell therapy and Covid-19. Because complement activation with subsequent anaphylatoxin release is in the core of innate immune stimulation, studying the relationship between complement activation and cytokine release in an in vitro CS model holds promise to better understand CS and identify new therapies against it. We used peripheral blood mononuclear cells (PBMCs) cultured in the presence of autologous serum to test the impact of complement activation and inhibition on cytokine release, testing the effects of liposomal amphotericin B (AmBisome), zymosan and bacterial lipopolysaccharide (LPS) as immune activators and heat inactivation of serum, EDTA and mini-factor H (mfH) as complement inhibitors. These activators induced significant rises of complement activation markers C3a, C4a, C5a, Ba, Bb, and sC5b-9 at 45 min of incubation, with or without ~5- to ~2,000-fold rises of IL-1α, IL-1β, IL-5, IL-6, IL-7, IL-8, IL-10, IL-12, IL-13 and TNFα at 6 and 18 h later. Inhibition of complement activation by the mentioned three methods had differential inhibition, or even stimulation of certain cytokines, among which effects a limited suppressive effect of mfH on IL-6 secretion and significant stimulation of IL-10 implies anti-CS and anti-inflammatory impacts. These findings suggest the utility of the model for in vitro studies on CS, and the potential clinical use of mfH against CS.

Inositol 1,4,5-trisphosphate 3-kinase B promotes Ca2+ mobilization and the inflammatory activity of dendritic cells

Innate immune responses to Gram-negative bacteria depend on the recognition of lipopolysaccharide (LPS) by a receptor complex that includes CD14 and TLR4. In dendritic cells (DCs), CD14 enhances the activation not only of TLR4 but also that of the NFAT family of transcription factors, which suppresses cell survival and promotes the production of inflammatory mediators. NFAT activation requires Ca²⁺ mobilization. In DCs, Ca²⁺ mobilization in response to LPS depends on phospholipase C γ2 (PLCγ2), which produces inositol 1,4,5-trisphosphate (IP₃). Here, we showed that the IP₃ receptor 3 (IP₃R3) and ITPKB, a kinase that converts IP₃ to inositol 1,3,4,5-tetrakisphosphate (IP₄), were both necessary for Ca²⁺ mobilization and NFAT activation in mouse and human DCs. A pool of IP₃R3 was located on the plasma membrane of DCs, where it colocalized with CD14 and ITPKB. Upon LPS binding to CD14, ITPKB was required for Ca²⁺ mobilization through plasma membrane-localized IP₃R3 and for NFAT nuclear translocation. Pharmacological inhibition of ITPKB in mice reduced both LPS-induced tissue swelling and the severity of inflammatory arthritis to a similar extent as that induced by the inhibition of NFAT using nanoparticles that delivered an NFAT-inhibiting peptide specifically to phagocytic cells. Our results suggest that ITPKB may represent a promising target for anti-inflammatory therapies that aim to inhibit specific DC functions.

Dectin-1 limits autoimmune neuroinflammation and promotes myeloid cell-astrocyte crosstalk via Card9-independent expression of Oncostatin M

Pathologic roles of innate immunity in neurologic disorders are well described, but their beneficial aspects are less understood. Dectin-1, a C-type lectin receptor (CLR), is largely known to induce inflammation. Here, we report that Dectin-1 limited experimental autoimmune encephalomyelitis (EAE), while its downstream signaling molecule, Card9, promoted the disease. Myeloid cells mediated the pro-resolution function of Dectin-1 in EAE with enhanced gene expression of the neuroprotective molecule, Oncostatin M (Osm), through a Card9-independent pathway, mediated by the transcription factor NFAT. Furthermore, we find that the Osm receptor (OsmR) functioned specifically in astrocytes to reduce EAE severity. Notably, Dectin-1 did not respond to heat-killed Mycobacteria, an adjuvant to induce EAE. Instead, endogenous Dectin-1 ligands, including galectin-9, in the central nervous system (CNS) were involved to limit EAE. Our study reveals a mechanism of beneficial myeloid cell-astrocyte crosstalk regulated by a Dectin-1 pathway and identifies potential therapeutic targets for autoimmune neuroinflammation.

The role of dectin-1 in health and disease

Dendritic cell-associated C-type lectin-1 (Dectin-1), also known as β-glucan receptor is an emerging pattern recognition receptor (PRR) which belongs to the family of C-type lectin receptor (CLR). This CLR identifies ligands independently of Ca²⁺ and is majorly involved in coupling of innate with adaptive immunity. Formerly, Dectin-1 was best known for its role in anti-fungal defense only. However, recent explorations suggested its wider role in defense against variety of infectious diseases caused by pathogens including bacteria, parasites and viruses. In fact, Dectin-1 signaling axis has been suggested to be targeted as an effective therapeutic strategy for cancers. Dectin-1 has also been elucidated ascetically in the heart, respiratory, intestinal, neurological and developmental disorders. Being a defensive PRR, Dectin-1 results in optimal immune responses in collaboration with other PRRs, but the overall evaluation reinforces the hypothesis of disease development on dis-regulation of Dectin-1 activity. This underscores the impact of Dectin-1 polymorphisms in modulating protein expression and generation of non-optimal immune responses through defective collaborations, further underlining their therapeutic potential. To add on, Dectin-1 influence autoimmunity and severe inflammation accredited to recognition of self T cells and apoptotic cells through unknown ligands. Few reports have also testified its redundant role in infections, which makes it a complicated molecule to be fully resolved. Thus, Dectin-1 is a hub that runs a complex collaborative network, whose interactive wire connections to different PRRs are still pending to be revealed. Alternatively, so far focus of almost all the researchers was the two major cell surface isoforms of Dectin-1, despite the fact that its soluble functional intracellular isoform (Dectin-1E) has already been dissected but is indefinable. Therefore, this review intensely recommends the need of future research to resolve the un-resolved and treasure the comprehensive role of Dectin-1 in different clinical outcomes, before determining its therapeutic prospective.