β-Glucan Induces Distinct and Protective Innate Immune Memory in Differentiated Macrophages

Mesenchymal stromal cells can block palmitate training of macrophages via cyclooxygenase-2 and interleukin-1 receptor antagonist

Innate training of macrophages can be beneficial for the clearance of pathogens. However, for certain chronic conditions, innate training can have detrimental effects due to an excessive production of pro-inflammatory cytokines. Obesity is a condition that is associated with a range of increased pro-inflammatory training stimuli including the free fatty acid palmitate. Mesenchymal stromal cells (MSCs) are powerful immunomodulators and known to suppress inflammatory macrophages via a range of soluble factors. We show that palmitate training of murine bone-marrow-derived macrophages and human monocyte-derived macrophages (MDMs) results in an increased production of TNFα and IL-6 upon stimulation with lipopolysaccharide and is associated with epigenetic remodeling. Palmitate training led to metabolic changes, however, MSCs did not alter the metabolic profile of human MDMs. Using a transwell system, we demonstrated that human bone marrow MSCs block palmitate training in both murine and human macrophages suggesting the involvement of secreted factors. MSC disruption of the training process occurs through more than one pathway. Suppression of palmitate-enhanced TNFα production is associated with cyclooxygenase-2 activity in MSCs, while secretion of interleukin-1 receptor antagonist by MSCs is required to suppress palmitate-enhanced IL-6 production in MDMs.

Microbiota translocation following intestinal barrier disruption promotes Mincle-mediated training of myeloid progenitors in the bone marrow

Impairment of the intestinal barrier allows the systemic translocation of commensal bacteria, inducing a proinflammatory state in the host. Here, we investigated innate immune responses following increased gut permeability upon administration of dextran sulfate sodium (DSS) in mice. We found that Enterococcus faecalis translocated to the bone marrow following DSS treatment and induced trained immunity (TI) hallmarks in bone-marrow-derived mouse macrophages and human monocytes. DSS treatment or heat-killed E. faecalis reprogrammed bone marrow progenitors (BMPs), resulting in enhanced inflammatory responses in vitro and in vivo and protection against subsequent pathogen infections. The C-type lectin receptor Mincle (Clec4e) was essential for E. faecalis-induced TI in BMPs. Clec4e-/- mice showed impaired TI upon E. faecalis administration and reduced pathology following DSS treatment. Thus, Mincle sensing of E. faecalis induces TI that may have long-term effects on pathologies associated with increased gut permeability.

β-Glucan induced plasma B cells differentiation to enhance antitumor immune responses by Dectin-1

BACKGROUND

B lymphocytes, essential in cellular immunity as antigen-presenting cells and in humoral immunity as major effector cells, play a crucial role in the antitumor response. Our previous work has shown β-glucan enhanced immunoglobulins (Ig) secretion. But the specific mechanisms of B-cell activation with β-glucan are poorly understood. Here, we took advantage of β-glucan to improve the antitumor immune response of B cells.

RESULTS

In vitro experiments demonstrate that β-glucan enhance the differentiation of B220lo CD138+ B cells, up-regulate co-stimulatory molecules, and increase the production of cytokines and Ig in response to various antigens. Using the Dectin-1 knockout mice, we revealed that β-glucan modulate B cell immune responses dependent on Dectin-1 receptor. In mouse models of Lewis lung cancer (LLC) tumors, combining β-glucan with programmed death-1(PD-1) blocking antibodies led to increase recruitment of CD19+ B cells in the tumor microenvironment (TME), higher numbers of germinal centers B cells (GC B) in the spleen and draining lymph node (DLN), elevate Ig production, and delay tumor progression.

CONCLUSIONS

These findings reveal that β-glucan can serve as a potent adjuvant to modulate B cell immune responses in a Dectin-1 dependent manner and improve immune checkpoint blockade (ICB) therapy in antitumor.

CLINICAL TRIAL NUMBER

Not applicable.

β-Glucan reprograms neutrophils to promote disease tolerance against influenza A virus

Disease tolerance is an evolutionarily conserved host defense strategy that preserves tissue integrity and physiology without affecting pathogen load. Unlike host resistance, the mechanisms underlying disease tolerance remain poorly understood. In the present study, we investigated whether an adjuvant (β-glucan) can reprogram innate immunity to provide protection against influenza A virus (IAV) infection. β-Glucan treatment reduces the morbidity and mortality against IAV infection, independent of host resistance. The enhanced survival is the result of increased recruitment of neutrophils via RoRγt+ T cells in the lung tissue. β-Glucan treatment promotes granulopoiesis in a type 1 interferon-dependent manner that leads to the generation of a unique subset of immature neutrophils utilizing a mitochondrial oxidative metabolism and producing interleukin-10. Collectively, our data indicate that β-glucan reprograms hematopoietic stem cells to generate neutrophils with a new 'regulatory' function, which is required for promoting disease tolerance and maintaining lung tissue integrity against viral infection.

Levamisole, as a viral vaccine adjuvant, induces robust host defense through the modulation of innate and adaptive immune responses

Introduction

An effective vaccination policy must be implemented to prevent foot-and-mouth disease (FMD). However, the currently used vaccines for FMD have several limitations, including induction of humoral rather than cellular immune responses.

Methods

To overcome these shortcomings, we assessed the efficacy of levamisole, a small-molecule immunomodulator, as an adjuvant for the FMD vaccine. We conducted in vitro studies using murine peritoneal exudate cells (PECs) and porcine peripheral blood mononuclear cells (PBMCs) and in vivo studies using mice (experimental animals) and pigs (target animals). We evaluated levamisole-mediated modulation of the innate and adaptive immune responses; early, mid-term, and long-term immune-inducing effects; modes of action; and host defense against viral infection.

Results

Levamisole treatment promoted IFNγ secretion in murine PECs and porcine PBMCs. Additionally, it induced robust and long-lasting immune responses by eliciting high antibody titers and high virus-neutralizing antibody titers. By activating downstream signaling pathways of various pattern-recognition receptors, levamisole stimulated the expression of multiple cytokines and costimulatory molecules. Owing to these immunostimulatory effects, levamisole elicited host defense against viral infections in pigs. Our findings demonstrate the potential of levamisole as an immunostimulatory agent.

Discussion

The results also indicate that levamisole, as an adjuvant for animal vaccines, can elicit robust innate and adaptive immune responses, thereby enhancing host defense against viral infections. This study provides a promising approach for the development of improved FMD vaccine strategies in the future.

The effect of β-Glucan induced intestinal trained immunity against Trichinella spiralis infection

Parasitic helminth Trichinella spiralis (Ts) induce mixed Th1/Th2 response with predominant type 2 immune responses, with protective immunity mediated by interleukin (IL)-4, IL-5, and IL-13. β-Glucan (BG) has been shown to have the ability to induce trained immunity, confers non-specific protection from secondary infections. However, whether BG-induced trained immunity played a role in protective type 2 immunity against Ts infection is unclear. In this study, BG was administered five days before Ts infection to induce trained immunity. Our findings demonstrate that BG pretreatment effectively reduced the number of T. spiralis adults and muscle larvae, whereas inhibition of trained immunity abolished the effect of BG. Additionally, we observed a significant increase in goblet cells and mucus production as evidenced by Alcian blue periodic acid-Schiff staining. Furthermore, quantitative real-time PCR analysis revealed a significant upregulation of IL-4, IL-5, and IL-13 expression in response to BG. Conversely, the inhibitor of trained immunity reversed these effects, suggesting that BG-induced trained immunity confers strong protection against Ts infection. In conclusion, these findings suggest that BG-induced trained immunity may play a role in protection against infections caused by other helminths.

Candida albicans-Derived β-Glucan as a Novel Modulator of Tumor Microenvironment: Targeting Macrophage Polarization and Inducing Ferroptosis in Lung Cancer

Introduction

Tumor-associated macrophages (TAMs) play a crucial role in the tumor microenvironment (TME), and their polarization state significantly influences patient outcomes. This study investigates the inhibitory effects of β-glucan extracted from Candida albicans on lung cancer progression, focusing on its impact on TAM polarization and the induction of ferroptosis, a form of regulated cell death.

Methods

Utilizing both in vivo animal models and in vitro cellular assays, we assessed the impact of β-glucan on tumor growth, cellular proliferation, and migration. We evaluated TAM polarization by analyzing the expression of M1 and M2 markers and identified differentially expressed genes (DEGs) related to ferroptosis. The role of ferroptosis in TAM polarization was further confirmed by assessing the protein levels of ACSL4 and GPX4, intracellular ferrous ion levels, and lipid peroxides.

Results

β-glucan treatment significantly reduced tumor size and weight, along with cellular proliferation and migration, suggesting a potent suppressive effect on lung cancer cell growth. β-glucan promoted an M1-like phenotype in TAMs, as evidenced by increased CD86 expression and decreased CD206 expression, and modulated cytokine mRNA levels. RNA sequencing analysis post β-glucan treatment identified a substantial number of DEGs enriched in the ferroptosis pathway. The induction of ferroptosis by β-glucan was further confirmed through the significant upregulation of ACSL4 and downregulation of GPX4, alongside increased intracellular ferrous ion levels and lipid peroxides. The ferroptosis inhibitor Fer-1 abrogated these effects, highlighting the specificity of β-glucan-mediated polarization.

Conclusion

These results collectively provide novel insights into the immunotherapeutic potential of β-glucan from Candida albicans and its role in modulating TAM polarization and lung cancer growth, offering a promising avenue for cancer treatment strategies.

Biological evaluation of curdlan sulfate-based nanoparticles in trained immunity enhancement: In vitro and in vivo approaches

OBJECTIVES

Recently, more and more evidences suggest that β-glucans can induce trained immunity and non-specific protections against pathogens. However, most of the reports evaluated the immunological activities of β-glucans through injection route but no nasal inhalation. In this study, the effects of curdlan sulfate-based nanoparticles, CS/O-HTCC on trained immunity through intranasal administration were evaluated.

METHODS

Macrophages were treated with CS/O-HTCC and the metabolisms of the macrophages were detected. Mice were intranasal administered with CS/O-HTCC for 3 times with a 14 days interval, then the antitumor or infection prevention effects were assessed.

RESULTS

In vitro, CS/O-HTCC enhanced the macrophage metabolism significantly through upregulating glycolysis (26.1 ± 4.3 mpH/min) and oxidative phosphorylation (36.0 ± 9.0 pmol/min) compared with that of negative group (7.5 ± 2.3 mpH/min and 19.5 ± 4.9 pmol/min). In vivo, CS/O-HTCC inhibited lung metastasis of B16F10 tumor cells and improved the survival time (26.5 days) of the nmice compared with negative group (19.5 days). Moreover, CS/O-HTCC prevented the lung infections by Escherichia coli or Streptococcus pneumoniae (less bacterial residual) and reduced lung damages.

CONCLUSIONS

CS/O-HTCC can induce trained immunity through enhancing the metabolism of macrophages and enhance the non-specific protection against pathogens through intranasal immunization.

Immunoresponsive Gene 1 Facilitates TLR4-agonist-Induced Augmentation of Innate Antimicrobial Immunity

Treatment with the toll-like receptor (TLR) 4 agonist monophosphoryl lipid A (MPLA) conditions innate immunocytes to respond robustly to subsequent infection, a phenotype termed innate immune memory. Our published studies show that metabolic reprogramming of macrophages is a prominent feature of the memory phenotype. We undertook studies to define the functional contributions of tricarboxylic acid (TCA) cycle reprogramming to innate immune memory. We observed that priming of wild type (WT) mice with MPLA potently facilitated accumulation of the TCA cycle metabolite itaconate at sites of infection and enhanced microbial clearance. Augmentation of itaconate accumulation and microbial clearance was ablated in immuneresponsive gene 1 (Irg1) -deficient mice. We further observed that MPLA potently induces expression of Irg1 and accumulation of itaconate in macrophages. Compared to WT macrophages, the ability of Irg1-deficient macrophages to kill Pseudomonas aeruginosa was impaired. We further observed that itaconate is directly antimicrobial against P. aeruginosa at pH 5, which is characteristic of the phagolysosome, and is facilitated by reactive oxygen species. MPLA-induced augmentation of glycolysis, oxidative phosphorylation and accumulation of the TCA cycle metabolites succinate and malate was decreased in Irg1 KO macrophages compared to WT controls. RNA sequencing revealed suppressed transcription of genes associated with phagolysosome function and increased expression of genes associated with cytokine production and chemotaxis in Irg1 deficient macrophages. This study identifies a contribution of itaconate to MPLA-induced augmentation of innate antimicrobial immunity via facilitation of microbial killing as well as impact on metabolic and transcriptional adaptations.

Genomic investigation of innate sensing pathways in the tumor microenvironment

The innate immune system is the first responder to infectious agents, cellular debris, and cancerous growths. This system plays critical roles in the antitumor immune responses by boosting and priming T cell-mediated cytotoxicity but is understudied due to the complexity and redundancy of its various downstream signaling cascades. We utilized a mathematical tool to holistically quantify innate immune signaling cascades and immunophenotype over 8,000 tumors from The Cancer Genome Atlas (TCGA). We found that innate immune activation was predictive of patient mortality in a subset of cancers. Further analysis identified PHF genes as transcripts that were associated with genomic stability and innate activation. Knockdown of PHF gene transcripts in vitro led to an increase in cell death and IFNB1 expression in a cGAS-dependent manner, validating PHF genes as potential anti-tumor targets. We also found an association between innate immune activation and both tumor immunogenicity and intratumor microbes, which highlights the versatility of this model. In conclusion, interrogating activation of innate immune signaling cascades demonstrated the importance of studying innate signaling in cancer and broadened the search for new therapeutic adjuvants.

Weight loss-induced adipose macrophage memory improves local Staphylococcus aureus clearance in male mice

Different stimuli can induce innate immune memory to improve pathogen defense or worsen cardiometabolic disease. However, it is less clear if the same stimuli can induce both the protective and detrimental effects of innate immune memory. We previously showed that weight loss induces innate immune memory in adipose macrophages that correlates with worsened diabetes risk after weight regain. In this study, we investigated the effect of weight loss on macrophage cytokine production and overall survival in a mouse model of infection. Male C57Bl/6J mice were put on high-fat or low-fat diets over 18 weeks to induce weight gain or weight loss. Lean mice served as controls. All mice were then infected IV with 2.5×10^6 CFU Staphylococcus aureus . Tissues were collected from 10 mice/group at day 3 and the remaining animals were followed for survival. Weight gain mice had the highest blood neutrophils and the highest bacterial burden in the kidney. However, there was no significant difference in survival. The weight loss group had the highest plasma TNF-α and a significant reduction in bacterial burden in the adipose tissue that correlated with increased adipose macrophage cytokine production. Thus, weight loss-induced adipose macrophage memory may both improve local S.aureus clearance and worsen diabetes risk upon weight regain. Collectively, these findings support the notion that innate immune memory is an evolutionarily protective mechanism that also contributes to the development of cardiometabolic diseases.

Oat Beta-Glucan Dietary Intervention on Antioxidant Defense Parameters, Inflammatory Response and Angiotensin Signaling in the Testes of Rats with TNBS-Induced Colitis

Male infertility represents a significant public health concern. There is a negative impact of inflammatory bowel diseases (IBDs) on the male reproductive system. The aim of this study was to investigate whether oat beta-glucan (OBG) with different molar mass can modulate parameters of antioxidant defense and inflammatory response in the testes of adult Sprague-Dawley rats with TNBS-induced colitis and whether the OBG intervention can modulate the inflammatory response in association with the RAS system. Results: higher testicular superoxide dismutase (SOD), glutathione reductase (GR) activities and glutathione (GSH) concentration, and lower testosterone (T) level and glutathione peroxidase (GPx) activity, were observed in rats with colitis than in healthy control ones. TNBS-induced colitis resulted in decreased the angiotensin 1-7 (ANG 1-7) level in the testes of rats fed with low-molar mass OBG compared to control animals. Conclusions: although colitis induced moderate pro-oxidant changes in the gonads, it seems plausible that dietary intervention with different fractions of oat beta-glucans mass may support the maintenance of reproductive homeostasis via the stimulation of the local antioxidant defense system.

Exposure to structurally unique β-d-glucans differentially affects inflammatory responses in male mouse lungs

Pro-inflammatory fungal β-d-glucan (BDG) polysaccharides cause respiratory pathology. However, specific immunological effects of unique BDG structures on pulmonary inflammation are understudied. We characterized the effect of four unique fungal BDGs with unique branching patterns, solubility, and molecular weights in murine airways. Scleroglucan (1 → 3)(1 → 6)-highly branched BDG, laminarin (1 → 3)(1 → 6)-branched BDG, curdlan (1 → 3)-linear BDG, and pustulan (1 → 6)-linear BDG were assessed by nuclear magnetic resonance spectroscopy. Each BDG was tested by inhalation model with C3HeB/FeJ mice and compared to saline-exposed control mice and unexposed sentinels (n = 3-19). Studies were performed ±heat-inactivation (1 h autoclave) to increase BDG solubility. Outcomes included bronchoalveolar lavage (BAL) differential cell counts (macrophages, neutrophils, lymphocytes, eosinophils), cytokines, serum IgE, and IgG2a (multiplex and ELISA). Ex vivo primary cells removed from lungs and plated at monolayer were stimulated (BDG, lipopolysaccharide (LPS), anti-CD3), and cytokines compared to unstimulated cells. Right lung histology was performed. Inhalation of BDGs with distinct branching patterns exhibited varying inflammatory potency and immunogenicity. Lichen-derived (1 → 6)-linear pustulan was the most pro-inflammatory BDG, increasing inflammatory infiltrate (BAL), serum IgE and IgG2a, and cytokine production. Primed lung cells responded to secondary LPS stimulation with a T-cell-specific response to pustulan. Glucan source and solubility should be considered in exposure and toxicological studies.

The cholera toxin B subunit induces trained immunity in dendritic cells and promotes CD8 T cell antitumor immunity

Introduction

Innate immune training is a metabolic, functional, and epigenetic long-term reprogramming of innate cells triggered by different stimuli. This imprinting also reaches hematopoietic precursors in the bone marrow to sustain a memory-like phenotype. Dendritic cells (DCs) can exhibit memory-like responses, enhanced upon subsequent exposure to a pathogen; however, whether this imprinting is lineage and stimulus-restricted is still being determined. Nevertheless, the functional consequences of DCs training on the adaptive and protective immune response against non-infectious diseases remain unresolved.

Methods

We evaluated the effect of the nontoxic cholera B subunit (CTB), LPS and LTA in the induction of trained immunity in murine DCs revealed by TNFa and LDH expression, through confocal microscopy. Additionally, we obtained bone marrow DCs (BMDCs) from mice treated with CTB, LPS, and LTA and evaluated training features in DCs and their antigen-presenting cell capability using multiparametric cytometry. Finally, we design an experimental melanoma mouse model to demonstrate protection induced by CTB-trained DCs in vivo.

Results

CTB-trained DCs exhibit increased expression of TNFa, and metabolic reprogramming indicated by LDH expression. Moreover, CTB training has an imprint on DC precursors, increasing the number and antigen-presenting function in BMDCs. We found that training by CTB stimulates the recruitment of DC precursors and DCs infiltration at the skin and lymph nodes. Interestingly, training-induced by CTB promotes a highly co-stimulatory phenotype in tumor-infiltrating DCs (CD86+) and a heightened functionality of exhausted CD8 T cells (Ki67+, GZMB+), which were associated with a protective response against melanoma challenge in vivo.

Conclusion

Our work indicates that CTB can induce innate immune training on DCs, which turns into an efficient adaptive immune response in the melanoma model and might be a potential immunotherapeutic approach for tumor growth control.

Dietary Intake of Yeast-Derived β-Glucan and Rice-Derived Arabinoxylan Induces Dose-Dependent Innate Immune Priming in Mice

Beta-glucans and arabinoxylans are known for their immunostimulatory properties. However, in vivo these have been documented almost exclusively following parenteral administration, underemphasizing oral intake. C57BL/6 mice are fed either a control diet or a diet supplemented with yeast-derived whole β-glucan particle (yWGP) or with rice-derived arabinoxylan (rice bran-1) at a concentration of 1%, 2.5%, or 5% weight/weight (w/w) for 2 weeks. Thereafter, cells from blood, bone marrow, and spleen are collected for ex vivo stimulation with various microbial stimuli. Dietary intake of yWGP for 2 weeks at concentrations of 1% and 2.5% w/w increases ex vivo cytokine production in mouse blood and bone marrow, whereas 5% w/w yWGP shows no effect. In the spleen, cytokine production remains unaffected by yWGP. At a concentration of 1% w/w, rice bran-1 increases ex vivo cytokine production by whole blood, but 2.5% and 5% w/w cause inhibitory effects in bone marrow and spleen. This study demonstrates that dietary yWGP and rice bran-1 induce immune priming in mouse blood and bone marrow, with the strongest effects observed at 1% w/w. Future human trials should substantiate the efficacy of dietary β-glucans and arabinoxylans to bolster host immunity, focusing on dose optimization.

Endotoxin tolerance and trained immunity: breaking down immunological memory barriers

For decades, innate immune cells were considered unsophisticated first responders, lacking the adaptive memory of their T and B cell counterparts. However, mounting evidence demonstrates the surprising complexity of innate immunity. Beyond quickly deploying specialized cells and initiating inflammation, two fascinating phenomena - endotoxin tolerance (ET) and trained immunity (TI) - have emerged. ET, characterized by reduced inflammatory response upon repeated exposure, protects against excessive inflammation. Conversely, TI leads to an enhanced response after initial priming, allowing the innate system to mount stronger defences against subsequent challenges. Although seemingly distinct, these phenomena may share underlying mechanisms and functional implications, blurring the lines between them. This review will delve into ET and TI, dissecting their similarities, differences, and the remaining questions that warrant further investigation.

Epigenetic regulation of innate immune dynamics during inflammation

Innate immune cells play essential roles in modulating both immune defense and inflammation by expressing a diverse array of cytokines and inflammatory mediators, phagocytizing pathogens to promote immune clearance, and assisting with the adaptive immune processes through antigen presentation. Rudimentary innate immune "memory" states such as training, tolerance, and exhaustion develop based on the nature, strength, and duration of immune challenge, thereby enabling dynamic transcriptional reprogramming to alter present and future cell behavior. Underlying transcriptional reprogramming are broad changes to the epigenome, or chromatin alterations above the level of DNA sequence. These changes include direct modification of DNA through cytosine methylation as well as indirect modifications through alterations to histones that comprise the protein core of nucleosomes. In this review, we will discuss recent advances in our understanding of how these epigenetic changes influence the dynamic behavior of the innate immune system during both acute and chronic inflammation, as well as how stable changes to the epigenome result in long-term alterations of innate cell behavior related to pathophysiology.

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.

TGFβ macrophage reprogramming: a new dimension of macrophage plasticity

The August 2023 article in Science Signaling, "TGF-β uncouples glycolysis and inflammation in macrophages and controls survival during sepsis," challenges the traditional M1/M2 macrophage classification by investigating the impact of transforming growth factor β on macrophage metabolism and function. Despite its conventional anti-inflammatory role, transforming growth factor β-treated macrophages exhibit a distinct phenotype marked by heightened glycolysis, suppressed proinflammatory cytokines, and increased coagulation factor expression. The study identifies phosphofructokinase, liver type as a crucial glycolytic enzyme regulated by transforming growth factor β via the mTOR-c-MYC pathway. Epigenetic changes induced by transforming growth factor β, such as increased Smad3 activation and reduced proinflammatory transcription factor motif enrichment, contribute to the anti-inflammatory profile. The research extends its implications to sepsis, revealing the role of transforming growth factor β in exacerbating coagulation and reducing survival in mouse models. This effect involves upregulation of coagulation factor F13A1, dependent on phosphofructokinase, liver type activity and glycolysis in macrophages. Connections to COVID-19 pathology are drawn, as transforming growth factor β-treated macrophages and SARS-CoV-2 E protein-exposed cells display similar metabolic profiles. Bioinformatic analysis of COVID-19 patient data suggests correlations between myeloid expression of TGFβR1, PFKL, and F13A1 with disease severity. The study challenges the M1/M2 classification, emphasizing the complexity of macrophage responses influenced by transforming growth factor β, proposing transforming growth factor β as a potential therapeutic target for conditions like sepsis and COVID-19 where dysregulated coagulation is significant. Overall, the research provides valuable insights into transforming growth factor β-mediated immunometabolic regulation, paving the way for future investigations and potential therapeutic interventions.

β-glucans from Agaricus bisporus mushroom products drive Trained Immunity

Introduction

Macrofungi, such as edible mushrooms, have been used as a valuable medical resource for millennia as a result of their antibacterial and immuno-modulatory components. Mushrooms contain dietary fibers known as β-glucans, a class of polysaccharides previously linked to the induction of Trained Immunity. However, little is known about the ability of mushroom-derived β-glucans to induce Trained Immunity.

Methods & results

Using various powdered forms of the white button mushroom (Agaricus bisporus), we found that mouse macrophages pre-treated with whole mushroom powder (WMP) displayed enhanced responses to restimulation with TLR ligands, being particularly sensitive to Toll-like receptor (TLR)-2 stimulation using synthetic lipopeptides. This trained response was modest compared to training observed with yeast-derived β-glucans and correlated with the amount of available β-glucans in the WMP. Enriching for β-glucans content using either a simulated in-vitro digestion or chemical fractionation retained and boosted the trained response with WMP, respectively. Importantly, both WMP and digested-WMP preparations retained β-glucans as identified by nuclear magnetic resonance analysis and both displayed the capacity to train human monocytes and enhanced responses to restimulation. To determine if dietary incorporation of mushroom products can lead to Trained Immunity in myeloid cells in vivo, mice were given a regimen of WMP by oral gavage prior to sacrifice. Flow cytometric analysis of bone-marrow progenitors indicated alterations in hematopoietic stem and progenitor cells population dynamics, with shift toward myeloid-committed multi-potent progenitor cells. Mature bone marrow-derived macrophages derived from these mice displayed enhanced responses to restimulation, again particularly sensitive to TLR2.

Discussion

Taken together, these data demonstrate that β-glucans from common macrofungi can train innate immune cells and could point to novel ways of delivering bio-available β-glucans for education of the innate immune system.

A potential trade-off between offense and defense in honeybee innate immunity: Reduced phagocytosis in honeybee hemocytes correlates with a protective response after exposure to imidacloprid and amitraz

Phagocytosis "offense" is a crucial process to protect the organism from diseases and the effects of foreign particles. Insects rely on the innate immune system and thus any hindrance to phagocytosis may greatly affect their resistance to diseases and response to pathogens. The European honeybee, a valuable species due to its economic and environmental contribution, is being challenged by colony collapse disorder leading to its decline. Exposure to multiple factors including pesticides like imidacloprid and amitraz may negatively alter their immune response and ultimately make them more susceptible to diseases. In this study, we compare the effect of different concentrations and mixtures of imidacloprid and amitraz with different concentrations of the immune stimulant, zymosan A. Results show that imidacloprid and amitraz have a synergistic negative effect on phagocytosis. The lowered phagocytosis induces significantly higher hemocyte viability suggesting a negatively correlated protective mechanism "defense" from pesticide-associated damage but may not be protective from pathogens.

Polysaccharide of Asparagus cochinchinensis (Lour.) Merr regulates macrophage immune response and epigenetic memory through TLR4-JNK/p38/ERK signaling pathway and histone modification

BACKGROUND

Innate immune memory of macrophages is closely linked to histone modifications. While various studies have demonstrated that the polysaccharide of Asparagus cochinchinensis (Lour.) Merr (ACMP), extracted through alcohol-alkali extraction, enhances macrophages' non-specific immune function; no literature currently addresses whether ACMP's regulatory effect is related to innate immune memory and histone modification.

PURPOSE

This study aims to investigate if ACMP induces innate immune memory emergence in macrophages via pattern recognition receptor (PRR).

STUDY DESIGN

After co-incubating different doses of ACMP with RAW264.7 cells and BMDM cells, we observed changes in signaling pathways related to PRR and assessed the presence of innate immune memory phenomenon in the cells.

METHODS

We observed the morphological characteristics of the ACMP using a scanning electron microscope, infrared spectrum, and HPLC pre-column derivatization method. We used q-PCR, Western blot, RNA-seq, and CUT&Tag-seq methods to examine ACMP's regulation of macrophage immune response and innate immune memory and explored its specific mechanism.

RESULTS

ACMP, primarily composed of Man, GlcN, Rha, Fuc, GalA, Xyl, Glc, Gal, Ara, and, exhibited a molar ratio of each monosaccharide (1.41: 0.35: 0.49: 0.18: 1.00: 97.12: 0.36: 3.58: 1.14). ACMP regulated immunological function in macrophages through the TLR4-MAPK-JNK/p38/ERK pathway. ACMP induced elevated levels of chromosomal H3K4me1, enhancing TNF-α, IL-1β, and other genes' responsiveness, allowing macrophages to develop innate immune memory to ACMP stimulation.

CONCLUSION

This study first time demonstrates that ACMP regulates immunological function through the TLR4-MAPK-JNK/ERK/p38 signaling pathway, distinct from prior reports. ACMP induces innate immune memory in macrophages in response to its immune stimulation by promoting increased H3K4me1 on chromosomes. This mechanism may be crucial in how plant polysaccharides regulate macrophages and the body's immune function.

Bacteria- and fungus-derived PAMPs induce innate immune memory via similar functional, metabolic, and transcriptional adaptations

Exposure to pathogen-associated molecular patterns (PAMPs) induces an augmented, broad-spectrum antimicrobial response to subsequent infection, a phenomenon termed innate immune memory. This study examined the effects of treatment with β-glucan, a fungus-derived dectin-1 ligand, or monophosphoryl lipid A (MPLA), a bacteria-derived Toll-like receptor 4 ligand, on innate immune memory with a focus on identifying common cellular and molecular pathways activated by these diverse PAMPs. Treatment with either PAMP prepared the innate immune system to respond more robustly to Pseudomonas aeruginosa infection in vivo by facilitating mobilization of innate leukocytes into blood, recruitment of leukocytes to the site of infection, augmentation of microbial clearance, and attenuation of cytokine production. Examination of macrophages ex vivo showed amplification of metabolism, phagocytosis, and respiratory burst after treatment with either agent, although MPLA more robustly augmented these activities and more effectively facilitated killing of bacteria. Both agents activated gene expression pathways in macrophages that control inflammation, antimicrobial functions, and protein synthesis and suppressed pathways regulating cell division. β-glucan treatment minimally altered macrophage differential gene expression in response to lipopolysaccharide (LPS) challenge, whereas MPLA attenuated the magnitude of the LPS-induced transcriptional response, especially cytokine gene expression. These results show that β-glucan and MPLA similarly augment the innate response to infection in vivo. Yet, MPLA more potently induces alterations in macrophage metabolism, antimicrobial functions, gene transcription and the response to LPS.

CD115+ monocytes protect microbially experienced mice against E. coli-induced sepsis

Uropathogenic E. coli (UPEC) is a primary organism responsible for urinary tract infections and a common cause of sepsis. Microbially experienced laboratory mice, generated by cohousing with pet store mice, exhibit increased morbidity and mortality to polymicrobial sepsis or lipopolysaccharide challenge. By contrast, cohoused mice display significant resistance, compared with specific pathogen-free mice, to a monomicrobial sepsis model using UPEC. CD115+ monocytes mediate protection in the cohoused mice, as depletion of these cells leads to increased mortality and UPEC pathogen burden. Further study of the cohoused mice reveals increased TNF-α production by monocytes, a skewing toward Ly6ChiCD115+ "classical" monocytes, and enhanced egress of Ly6ChiCD115+ monocytes from the bone marrow. Analysis of cohoused bone marrow also finds increased frequency and number of myeloid multipotent progenitor cells. These results show that a history of microbial exposure impacts innate immunity in mice, which can have important implications for the preclinical study of sepsis.

Next Generation Mucosal Vaccine Strategy for Respiratory Pathogens

Inducing humoral and cytotoxic mucosal immunity at the sites of pathogen entry has the potential to prevent the infection from getting established. This is different from systemic vaccination, which protects against the development of systemic symptoms. The field of mucosal vaccination has seen fewer technological advances compared to nucleic acid and subunit vaccine advances for injectable vaccine platforms. The advent of the next-generation adenoviral vectors has given a boost to mucosal vaccine research. Basic research into the mechanisms regulating innate and adaptive mucosal immunity and the discovery of effective and safe mucosal vaccine adjuvants will continue to improve mucosal vaccine design. The results from clinical trials of inhaled COVID-19 vaccines demonstrate their ability to induce the proliferation of cytotoxic T cells and the production of secreted IgA and IgG antibodies locally, unlike intramuscular vaccinations. However, these mucosal vaccines induce systemic immune responses at par with systemic vaccinations. This review summarizes the function of the respiratory mucosa-associated lymphoid tissue and the advantages that the adenoviral vectors provide as inhaled vaccine platforms.

Prolonged Inhibition of the MEK1/2-ERK Signaling Axis Primes Interleukin-1 Beta Expression through Histone 3 Lysine 9 Demethylation in Murine Macrophages

Macrophages undergo different cellular states upon activation that can be hyporesponsive (tolerated) or hyperresponsive (primed or trained) to subsequent stimuli. Epigenetic modifications are known to play key roles in determining these cellular states. However, little is known about the role of signaling pathways that lead to these epigenetic modifications. Here, we examined the effects of various inhibitors targeting key signaling pathways induced by lipopolysaccharide (LPS) on tolerance and priming in murine macrophages. We found that a prolonged inhibition (>18 h) of the mitogen-activated protein kinase (MEK)1/2-extracellular signal-regulated kinase (ERK)1/2 signaling axis reversed tolerance and primed cells in expressing interleukin (IL)-1β and other inflammatory cytokines such as IL-6, tumor necrosis factor (TNF)α, and CXCL10. The ectopic expression of catalytically active and inactive MEK1 mutants suppressed and enhanced IL-1β expression, respectively. A transcriptomic analysis showed that cells primed by the MEK1/2 inhibitor U0126 expressed higher levels of gene sets associated with immune responses and cytokine/chemokine production, but expressed lower levels of genes with cell cycle progression, chromosome organization, and heterochromatin formation than non-primed cells. Of interest, the mRNA expressions of the histone 3 lysine 9 (H3K9) methyltransferase Suv39h1 and the H3K9 methylation reader Cbx5 were substantially suppressed, whereas the H3K9 demethylase Kdm7a was enhanced, suggesting a role of the MEK1/2-ERK signaling axis in H3K9 demethylation. The H3K9 trimethylation levels in the genomic regions of IL-1β, TNFα, and CXCL10 were decreased by U0126. Also, the H3K9 methyltransferase inhibitor BIX01294 mimicked the U0126 training effects and the overexpression of chromobox homolog (CBX)5 prevented the U0126 training effects in both RAW264.7 cells and bone-marrow-derived macrophages. Collectively, these data suggest that the prolonged inhibition of the MEK1/2-ERK signaling axis reverses tolerance and primed macrophages likely through decreasing the H3K9 methylation levels.

A clash on the Toll pathway: competitive action between pesticides and zymosan A on components of innate immunity in Apis mellifera

Background

The immune system of honeybees includes multiple pathways that may be affected by pesticide exposure decreasing the immune competencies of bees and increasing their susceptibility to diseases like the fungal Nosema spp. infection, which is detected in collapsed colonies.

Methods

To better understand the effect of the co-presence of multiple pesticides that interact with bees like imidacloprid and amitraz, we evaluated the expression of immune-related genes in honeybee hemocytes.

Results

Imidacloprid, amitraz, and the immune activator, zymosan A, mainly affect the gene expression in the Toll pathway.

Discussion

Imidacloprid, amitraz, and zymosan A have a synergistic or an antagonistic relationship on gene expression depending on the level of immune signaling. The presence of multiple risk factors like pesticides and pathogens requires the assessment of their complex interaction, which has differential effects on the innate immunity of honeybees as seen in this study.

Lipopolysaccharide Tolerance in Human Primary Monocytes and Polarized Macrophages

Innate immune memory allows macrophages to adequately respond to pathogens to which they have been pre-exposed. To what extent different pattern recognition receptors, cytokines and resolution signals influence innate immune memory needs further elucidation. The present study assessed whether lipopolysaccharide (LPS) tolerance in monocytes and macrophages is affected by these factors. Human CD14+ cells were isolated from peripheral blood, stimulated by LPS and re-stimulated after 3 days of resting. Hereafter, immune-responsive gene 1 (IRG-1), heme oxygenase 1 (HO-1), tumor necrosis factor α (TNF-α) and interleukin 6 (IL-6) expression were assessed. Our study revealed the following findings: (1) While pre-stimulation with the Toll-like receptor 4 ligand LPS inhibits the induction of IRG-1, TNF-α and IL-6 expression, pre-stimulation with TLR 1/2 ligands only affects cytokine production but not IRG-1 expression upon subsequent TLR4 engagement. (2) Prior TNF-α stimulation does not affect LPS tolerance but rather increases LPS-mediated cytokine expression. (3) Dimethyl itaconate (DMI) inhibits the expression of IRG-1 in a dose-dependent manner but does not affect TNF-α or IL-6 expression. (4) Docosahexaenoic acid (DHA) partly inhibits IRG-1 expression in monocytes but not in M(IFNγ) and M(IL-4) polarized macrophages. LPS tolerance is not affected in these cells by DHA. The data presented in this study partly corroborate and extend previous findings on innate immune memory and warrant further studies on LPS tolerance to gain a better understanding of innate immune memory at the molecular level.

Yeast cell wall extracts from Saccharomyces cerevisiae varying in structure and composition differentially shape the innate immunity and mucosal tissue responses of the intestine of zebrafish (Danio rerio)

With the rising awareness of antimicrobial resistance, the development and use of functional feed additives (FFAs) as an alternative prophylactic approach to improve animal health and performance is increasing. Although the FFAs from yeasts are widely used in animal and human pharma applications already, the success of future candidates resides in linking their structural functional properties to their efficacy in vivo. Herein, this study aimed to characterise the biochemical and molecular properties of four proprietary yeast cell wall extracts from S. cerevisiae in relation to their potential effect on the intestinal immune responses when given orally. Dietary supplementation of the YCW fractions identified that the α-mannan content was a potent driver of mucus cell and intraepithelial lymphocyte hyperplasia within the intestinal mucosal tissue. Furthermore, the differences in α-mannan and β-1,3-glucans chain lengths of each YCW fraction affected their capacity to be recognised by different PRRs. As a result, this affected the downstream signalling and shaping of the innate cytokine milieu to elicit the preferential mobilisation of effector T-helper cell subsets namely Th17, Th1, Tr1 and FoxP3⁺-Tregs. Together these findings demonstrate the importance of characterising the molecular and biochemical properties of YCW fractions when assessing and concluding their immune potential. Additionally, this study offers novel perspectives in the development specific YCW fractions derived from S. cerievisae for use in precision animal feeds.

β-Glucan Induces Training Immunity to Promote Antiviral Activity by Activating TBK1

Many studies have shown that β-glucan induces a trained immune phenotype in innate immune cells to defend against bacterial and fungal infections. The specific mechanism involves cellular metabolism and epigenetic reprogramming. However, it is unclear whether β-glucan plays a role in antiviral infection. Therefore, this study investigated the role of trained immunity induced by Candida albicans and β-glucan in antiviral innate immunity. It showed that C. albicans and β-glucan promoted the expression of interferon-β (IFN-β) and interleukin-6 (IL-6) in mouse macrophages triggered by viral infection. In addition, β-glucan pretreatment attenuated the pathological damage induced by the virus in mouse lungs and promoted the expression of IFN-β. Mechanistically, β-glucan could promote the phosphorylation and ubiquitination of TANK Binding Kinase 1 (TBK1), a key protein of the innate immune pathway. These results suggest that β-glucan can promote innate antiviral immunity, and this bioactive material may be a potential therapeutic target for antiviral treatment.

Polysaccharides-Naturally Occurring Immune Modulators

The prevention of disease and infection requires immune systems that operate effectively. This is accomplished by the elimination of infections and abnormal cells. Immune or biological therapy treats disease by either stimulating or inhibiting the immune system, dependent upon the circumstances. In plants, animals, and microbes, polysaccharides are abundant biomacromolecules. Due to the intricacy of their structure, polysaccharides may interact with and impact the immune response; hence, they play a crucial role in the treatment of several human illnesses. There is an urgent need for the identification of natural biomolecules that may prevent infection and treat chronic disease. This article addresses some of the naturally occurring polysaccharides of known therapeutic potential that have already been identified. This article also discusses extraction methods and immunological modulatory capabilities.

Differential Production of Nitric Oxide and Hydrogen Peroxide among Drosophila melanogaster, Apis mellifera, and Mamestra brassicae Immune-Activated Hemocytes after Exposure to Imidacloprid and Amitraz

Invertebrates have a diverse immune system that responds differently to stressors such as pesticides and pathogens, which leads to different degrees of susceptibility. Honeybees are facing a phenomenon called colony collapse disorder which is attributed to several factors including pesticides and pathogens. We applied an in vitro approach to assess the response of immune-activated hemocytes from Apis mellifera, Drosophila melanogaster and Mamestra brassicae after exposure to imidacloprid and amitraz. Hemocytes were exposed to the pesticides in single and co-exposures using zymosan A for immune activation. We measured the effect of these exposures on cell viability, nitric oxide (NO) production from 15 to 120 min and on extracellular hydrogen peroxide (H2O2) production after 3 h to assess potential alterations in the oxidative response. Our results indicate that NO and H2O2 production is more altered in honeybee hemocytes compared to D. melanogaster and M. brassicae cell lines. There is also a differential production at different time points after pesticide exposure between these insect species as contrasting effects were evident with the oxidative responses in hemocytes. The results imply that imidacloprid and amitraz act differently on the immune response among insect orders and may render honeybee colonies more susceptible to infection and pests.

Inducing trained immunity in pro-metastatic macrophages to control tumor metastasis

Metastasis is the leading cause of cancer-related deaths and myeloid cells are critical in the metastatic microenvironment. Here, we explore the implications of reprogramming pre-metastatic niche myeloid cells by inducing trained immunity with whole beta-glucan particle (WGP). WGP-trained macrophages had increased responsiveness not only to lipopolysaccharide but also to tumor-derived factors. WGP in vivo treatment led to a trained immunity phenotype in lung interstitial macrophages, resulting in inhibition of tumor metastasis and survival prolongation in multiple mouse models of metastasis. WGP-induced trained immunity is mediated by the metabolite sphingosine-1-phosphate. Adoptive transfer of WGP-trained bone marrow-derived macrophages reduced tumor lung metastasis. Blockade of sphingosine-1-phosphate synthesis and mitochondrial fission abrogated WGP-induced trained immunity and its inhibition of lung metastases. WGP also induced trained immunity in human monocytes, resulting in antitumor activity. Our study identifies the metabolic sphingolipid-mitochondrial fission pathway for WGP-induced trained immunity and control over metastasis.

Novel nutraceutical supplements with yeast β-glucan, prebiotics, minerals, and Silybum marianum (silymarin) ameliorate obesity-related metabolic and clinical parameters: A double-blind randomized trial

Purpose

It is known that obesity has a multifactorial etiology that involves genetic and environmental factors. The WHO estimates the worldwide prevalence of 1.9 billion overweight adults and more than 650 million people with obesity. These alarming data highlight the high and growing prevalence of obesity and represent a risk factor for the development and aggravation of other chronic diseases, such as nonalcoholic fatty liver disease (NAFLD) that is frequently considered the hepatic outcome of type 2 diabetes. The use of non-pharmacological therapies such as food supplements, nutraceuticals, and natural integrative therapies has grown as an alternative tool for obesity-related diseases compared to conventional medications. However, it is a still little explored research field and lacks scientific evidence of therapeutic effectiveness. Considering this, the aim is to evaluate whether a new nutraceutical supplement composition can improve and supply essential mineral nutrients, providing an improvement of obesity-related metabolic and endocrine parameters.

Methods

Sedentary volunteers (women and men) with body mass index (BMI) ≤34.9 kg/m2 were divided into two groups: Novel Nutraceutical Supplement_(S) (n = 30) and Novel Nutraceutical Supplement (n = 29), differing in the absence (S) or presence of silymarin, respectively. Volunteers were instructed to take two capsules in the morning and two capsules in the evening. No nutritional intervention was performed during the study period. The data (anthropometrics and anamneses) and harvest blood (biochemistry and hormonal exams) were collected at three different time points: baseline time [day 0 (T0)], day 90 (T90), and day 180 (T180) post-supplementation.

Results

In the anthropometric analysis, the waist circumference in middle abdomen (WC-mid) and waist circumference in iliac crest (WC-IC) were reduced. Also, the waist-to-height ratio (WHt R) and waist-to-hip ratio (WHR) seem to slightly decrease alongside the supplementation period with both nutraceutical supplements tested as well as transaminase enzyme ratio [aspartate aminotransferase (AST)/alanine aminotransferase (ALT) ratio (AAR)], a known as a biomarker of NAFLD, and endocrine hormones cortisol and thyroid-stimulating hormone (TSH) at 90 and 180 days post-supplementation.

Conclusions

In a condition associated with sedentary and no nutritional intervention, the new nutraceutical supplement composition demonstrated the ability to be a strong and newfangled tool to improve important biomarkers associated with obesity and its comorbidities.

Oral supplementation with yeast β-glucans improves the resolution of Escherichia coli-associated inflammatory responses independently of monocyte/macrophage immune training

Introduction

Confronted with the emerging threat of antimicrobial resistance, the development of alternative strategies to limit the use of antibiotics or potentiate their effect through synergy with the immune system is urgently needed. Many natural or synthetic biological response modifiers have been investigated in this context. Among them, β-glucans, a type of soluble or insoluble polysaccharide composed of a linear or branched string of glucose molecules produced by various cereals, bacteria, algae, and inferior (yeast) and superior fungi (mushrooms) have garnered interest in the scientific community, with not less than 10,000 publications over the last two decades. Various biological activities of β-glucans have been reported, such as anticancer, antidiabetic and immune-modulating effects. In vitro, yeast β-glucans are known to markedly increase cytokine secretion of monocytes/macrophages during a secondary challenge, a phenomenon called immune training.

Methods

Here, we orally delivered β-glucans derived from the yeast S. cerevisiae to mice that were further challenged with Escherichia coli.

Results

β-glucan supplementation protected the mice from E. coli intraperitoneal and intra-mammary infections, as shown by a lower bacterial burden and greatly diminished tissue damage. Surprisingly, this was not associated with an increased local immune response. In addition, granulocyte recruitment was transient and limited, as well as local cytokine secretion, arguing for faster resolution of the inflammatory response. Furthermore, ex-vivo evaluation of monocytes/macrophages isolated or differentiated from β-glucan-supplemented mice showed these cells to lack a trained response versus those from control mice.

Conclusion

In conclusion, dietary β-glucans can improve the outcome of Escherichia coli infections and dampen tissue damages associated to excessive inflammatory response. The mechanisms associated with such protection are not necessarily linked to immune system hyper-activation or immune training.

BG34-200 Immunotherapy of Advanced Melanoma

High levels of myeloid-derived cells are characteristic of the tumor microenvironment (TME) of advanced melanoma. These cells interact with tumor cells to suppress the development of antitumor immune responses, regulate tumor metastasis, and drive cancer's resistance to virtually all types of therapy. Therefore, methods to disrupt tumor-associated myeloid cell function are actively being sought to find a cure. Our team has recently developed a plant-derived carbohydrate molecule, BG34-200, that modulates tumor-associated myeloid cells by targeting the cell surface receptor CD11b. In this study, we found that BG34-200 IV administration could significantly inhibit tumor growth and improve survival in B16F10 mice with advanced melanoma. Our data supported a model that the entry of BG34-200 into circulating melanoma tumor-associated inflammatory monocytes (TAIMs) could trigger a sequential immune activation: the BG34-200⁺ TAIM subsets migrated to tumor and differentiated into monocyte-derived dendritic cells (mo-DCs); then, the BG34-200⁺ mo-DCs migrated to tumor draining lymph nodes, where they triggered the generation of tumor-antigen-specific T cells. Based upon these results, we combined BG34-200 treatment with adoptive transfer of TdLN-derived T cells to treat advanced melanoma, which significantly improved animal survival and helped tumor-free survivors be resistant to a second tumor-cell challenge. The scientific findings from this study will allow us to develop new technology and apply BG34-200-based immunotherapy to patients with advanced melanoma who have not responded to current standard of care therapies with and without immunotherapy.

MyD88-dependent signaling drives toll-like receptor-induced trained immunity in macrophages

Immunocompromised populations are highly vulnerable to developing life-threatening infections. Strategies to protect patients with weak immune responses are urgently needed. Employing trained immunity, whereby innate leukocytes undergo reprogramming upon exposure to a microbial product and respond more robustly to subsequent infection, is a promising approach. Previously, we demonstrated that the TLR4 agonist monophosphoryl lipid A (MPLA) induces trained immunity and confers broad resistance to infection. TLR4 signals through both MyD88- and TRIF-dependent cascades, but the relative contribution of each pathway to induction of trained immunity is unknown. Here, we show that MPLA-induced resistance to Staphylococcus aureus infection is lost in MyD88-KO, but not TRIF-KO, mice. The MyD88-activating agonist CpG (TLR9 agonist), but not TRIF-activating Poly I:C (TLR3 agonist), protects against infection in a macrophage-dependent manner. MPLA- and CpG-induced augmentation of macrophage metabolism and antimicrobial functions is blunted in MyD88-, but not TRIF-KO, macrophages. Augmentation of antimicrobial functions occurs in parallel to metabolic reprogramming and is dependent, in part, on mTOR activation. Splenic macrophages from CpG-treated mice confirmed that TLR/MyD88-induced reprogramming occurs in vivo. TLR/MyD88-triggered metabolic and functional reprogramming was reproduced in human monocyte-derived macrophages. These data show that MyD88-dependent signaling is critical in TLR-mediated trained immunity.

Trained Immunity Enhances Human Monocyte Function in Aging and Sepsis

Aging plays a critical role in the incidence and severity of infection, with age emerging as an independent predictor of mortality in sepsis. Trained immunity reprograms immunocytes to respond more rapidly and effectively to pathogens and serves as a potential approach to improve immune function in aging and/or sepsis. However, there is very little data on trained immunity in the aging immune system or in the presence of sepsis. We examined the impact of β-glucan induced innate immune training on monocytes from aging healthy humans (>60 years old) as well as sepsis patients. We observed increased metabolic capacity, upregulated cytokine secretion, increased H3K27 acetylation, and upregulation of crucial intracellular signaling pathways in trained monocytes from healthy aging subjects. The response to trained immunity in healthy aging monocytes was equivalent to the response of monocytes from younger, i.e., 18 – 59 years, individuals. Additionally, we found that trained immunity induced a unique expression pattern of cell surface markers in monocytes that was consistent across age groups. Trained monocytes from sepsis patients also displayed enhanced metabolic capacity and increased cytokine production. These results indicate that immune training can be induced in aging monocytes as well as monocytes from critically ill sepsis patients.

Trained Immunity Contribution to Autoimmune and Inflammatory Disorders

A dysregulated immune response toward self-antigens characterizes autoimmune and autoinflammatory (AIF) disorders. Autoantibodies or autoreactive T cells contribute to autoimmune diseases, while autoinflammation results from a hyper-functional innate immune system. Aside from their differences, many studies suggest that monocytes and macrophages (Mo/Ma) significantly contribute to the development of both types of disease. Mo/Ma are innate immune cells that promote an immune-modulatory, pro-inflammatory, or repair response depending on the microenvironment. However, understanding the contribution of these cells to different immune disorders has been difficult due to their high functional and phenotypic plasticity. Several factors can influence the function of Mo/Ma under the landscape of autoimmune/autoinflammatory diseases, such as genetic predisposition, epigenetic changes, or infections. For instance, some vaccines and microorganisms can induce epigenetic changes in Mo/Ma, modifying their functional responses. This phenomenon is known as trained immunity. Trained immunity can be mediated by Mo/Ma and NK cells independently of T and B cell function. It is defined as the altered innate immune response to the same or different microorganisms during a second encounter. The improvement in cell function is related to epigenetic and metabolic changes that modify gene expression. Although the benefits of immune training have been highlighted in a vaccination context, the effects of this type of immune response on autoimmunity and chronic inflammation still remain controversial. Induction of trained immunity reprograms cellular metabolism in hematopoietic stem cells (HSCs), transmitting a memory-like phenotype to the cells. Thus, trained Mo/Ma derived from HSCs typically present a metabolic shift toward glycolysis, which leads to the modification of the chromatin architecture. During trained immunity, the epigenetic changes facilitate the specific gene expression after secondary challenge with other stimuli. Consequently, the enhanced pro-inflammatory response could contribute to developing or maintaining autoimmune/autoinflammatory diseases. However, the prediction of the outcome is not simple, and other studies propose that trained immunity can induce a beneficial response both in AIF and autoimmune conditions by inducing anti-inflammatory responses. This article describes the metabolic and epigenetic mechanisms involved in trained immunity that affect Mo/Ma, contraposing the controversial evidence on how it may impact autoimmune/autoinflammation conditions.

Trained immunity: A Yin-Yang balance

Traditionally, immune memory is regarded as an exclusive hallmark of adaptive immunity. However, a growing body of evidence suggesting that innate immune cells show adaptive characteristics has challenged this dogma. In the past decade, trained immunity, a de facto innate immune memory, has been defined as a long-term functional reprogramming of cells of the innate immune system: the reprogramming is evoked by endogenous or exogenous insults, the cells return to a nonactivated state and subsequently show altered inflammatory responses against a second challenge. Trained immunity became regarded as a mechanism selected in evolution to protect against infection; however, a maladaptive effect might result in hyperinflammation. This dual effect is consistent with the Yin-Yang theory in traditional Chinese philosophy, in which Yang represents active, positive, and aggressive factors, whereas Yin represents passive, negative, and inhibitory factors. In this review, we give a brief overview of history and latest progress about trained immunity, including experimental models, inductors, molecular mechanisms, clinical application and so on. Moreover, this is the first time to put forward the theory of Yin-Yang balance to understand trained immunity. We envision that more efforts will be focused on developing novel immunotherapies targeting trained immunity in the coming years.

Innate Immune Memory and the Host Response to Infection

Unlike the adaptive immune system, the innate immune system has classically been characterized as being devoid of memory functions. However, recent research shows that innate myeloid and lymphoid cells have the ability to retain memory of prior pathogen exposure and become primed to elicit a robust, broad-spectrum response to subsequent infection. This phenomenon has been termed innate immune memory or trained immunity. Innate immune memory is induced via activation of pattern recognition receptors and the actions of cytokines on hematopoietic progenitors and stem cells in bone marrow and innate leukocytes in the periphery. The trained phenotype is induced and sustained via epigenetic modifications that reprogram transcriptional patterns and metabolism. These modifications augment antimicrobial functions, such as leukocyte expansion, chemotaxis, phagocytosis, and microbial killing, to facilitate an augmented host response to infection. Alternatively, innate immune memory may contribute to the pathogenesis of chronic diseases, such as atherosclerosis and Alzheimer's disease.