Β-glucan Receptor Research Articles

Cordyceps militaris fruit body activates myeloid dendritic cells via a Dectin-1-mediated pathway

Cordyceps militaris, an entomopathogenic fungus, has been traditionally used in East Asian medicine. Recent research indicates that the fruit bodies of C. militaris are rich in bioactive compounds, such as polysaccharides and nucleosides, which may offer health benefits. However, the specific components responsible for its immunostimulatory effects and the mechanisms involved remain unclear. This study explored the immunomodulatory activity of a fruit body extract from C. militaris, named Ryukyu-kaso (RK), and examined the effect of the β-glucan receptor Dectin-1 on bone marrow-derived dendritic cells (BMDCs). Our results demonstrated that RK, which contains 1,3-β-glucan, effectively stimulated BMDCs to secrete pro-inflammatory and immunoregulatory cytokines and upregulated surface markers indicative of maturation and activation. Notably, these immunostimulatory effects were completely absent in BMDCs derived from Dectin-1-knockout mice, confirming that Dectin-1 is crucial for RK-induced immunomodulation. These findings provide new insights into the immunostimulatory mechanisms of C. militaris and underscore the potential of RK as a natural immunomodulatory agent for various therapeutic applications.

Long Prime-Boost Interval and Heightened Anti-GD2 Antibody Response to Carbohydrate Cancer Vaccine.

The carbohydrate ganglioside GD2/GD3 cancer vaccine adjuvanted by β-glucan stimulates anti-GD2 IgG1 antibodies that strongly correlate with improved progression-free survival (PFS) and overall survival (OS) among patients with high-risk neuroblastoma. Thirty-two patients who relapsed on the vaccine (first enrollment) were re-treated on the same vaccine protocol (re-enrollment). Titers during the first enrollment peaked by week 32 at 751 ± 270 ng/mL, which plateaued despite vaccine boosts at 1.2-4.5 month intervals. After a median wash-out interval of 16.1 months from the last vaccine dose during the first enrollment to the first vaccine dose during re-enrollment, the anti-GD2 IgG1 antibody rose to a peak of 4066 ± 813 ng/mL by week 3 following re-enrollment (p < 0.0001 by the Wilcoxon matched-pairs signed-rank test). Yet, these peaks dropped sharply and continually despite repeated boosts at 1.2-4.5 month intervals, before leveling off by week 20 to the first enrollment peak levels. Despite higher antibody titers, patients experienced no pain or neuropathic side effects, which were typically associated with immunotherapy using monoclonal anti-GD2 antibodies. By the Kaplan-Meier method, PFS was estimated to be 51%, and OS was 81%. The association between IgG1 titer during re-enrollment and β-glucan receptor dectin-1 SNP rs3901533 was significant (p = 0.01). A longer prime-boost interval could significantly improve antibody responses in patients treated with ganglioside conjugate cancer vaccines.

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.

One Step Purification-Vaccine Delivery System.

Glucan particles (GPs) are hollow, porous 3-5 µm microspheres derived from the cell walls of Baker's yeast (Saccharomyces cerevisiae). Their 1,3-β-glucan outer shell allows for receptor-mediated uptake by macrophages and other phagocytic innate immune cells expressing β-glucan receptors. GPs have been used for the targeted delivery of a wide range of payloads, including vaccines and nanoparticles, encapsulated inside the hollow cavity of GPs. In this paper, we describe the methods to prepare GP-encapsulated nickel nanoparticles (GP-Ni) for the binding of histidine (His)-tagged proteins. His-tagged Cda2 cryptococcal antigens were used as payloads to demonstrate the efficacy of this new GP vaccine encapsulation approach. The GP-Ni-Cda2 vaccine was shown to be comparable to our previous approach utilizing mouse serum albumin (MSA) and yeast RNA trapping of Cda2 in GPs in a mouse infection model. This novel GP-Ni approach allows for the one-step binding of His-tagged vaccine antigens and encapsulation in an effective delivery vehicle to target vaccines to antigen-presenting cells (APCs), antigen discovery, and vaccine development.

An efficient (nano) silica - In glucan particles protein encapsulation approach for improved thermal stability

Glucan particles (GPs) are hollow, porous microspheres derived from Saccharomyces cerevisiae (Baker's yeast). The hollow cavity of GPs allows for efficient encapsulation of different types of macromolecules and small molecules. The β-1,3-D-glucan outer shell provides for receptor-mediated uptake by phagocytic cells expressing β-glucan receptors and uptake of particles containing encapsulated proteins elicit protective innate and acquired immune responses against a wide range of pathogens. A limitation of the previously reported GP protein delivery technology is limited protection from thermal degradation. Here we present results of an efficient protein encapsulation approach using tetraethylorthosilicate (TEOS) to lock protein payloads in a thermostable silica cage formed in situ inside the hollow cavity of GPs. The methods for this improved, efficient GP protein ensilication approach were developed and optimized using bovine serum albumin (BSA) as model protein. The improved method involved controlling the rate of TEOS polymerization, such that the soluble TEOS-protein solution was able to be absorbed into the GP hollow cavity before the protein–silica cage polymerized and becomes too large to transverse across the GP wall. This improved method provided for >90% GP encapsulation efficiency, increased thermal stabilization of GP ensilicated BSA, and was shown to be applicable for encapsulation of proteins of different molecular weights and isoelectric points. To demonstrate the retention of bioactivity of this improved method of protein delivery, we evaluated the in vivo immunogenicity of two GP ensilicated vaccine formulations using (1) ovalbumin as a model antigen and (2) a protective antigenic protein from the fungal pathogen Cryptococcus neoformans. The results show that the GP ensilicated vaccines have a similar high immunogenicity as our current GP protein/hydrocolloid vaccines, as evidenced by robust antigen-specific IgG responses to the GP ensilicated OVA vaccine. Further, a GP ensilicated C. neoformans Cda2 vaccine protected vaccinated mice from a lethal pulmonary infection of C. neoformans.

Blocking Dectin-1 prevents colorectal tumorigenesis by suppressing prostaglandin E2 production in myeloid-derived suppressor cells and enhancing IL-22 binding protein expression

Dectin-1 (gene Clec7a), a receptor for β-glucans, plays important roles in the host defense against fungi and immune homeostasis of the intestine. Although this molecule is also suggested to be involved in the regulation of tumorigenesis, the role in intestinal tumor development remains to be elucidated. In this study, we find that azoxymethane-dextran-sodium-sulfate-induced and ApcMin-induced intestinal tumorigenesis are suppressed in Clec7a−/− mice independently from commensal microbiota. Dectin-1 is preferentially expressed on myeloid-derived suppressor cells (MDSCs). In the Clec7a−/− mouse colon, the proportion of MDSCs and MDSC-derived prostaglandin E2 (PGE2) levels are reduced, while the expression of IL-22 binding protein (IL-22BP; gene Il22ra2) is upregulated. Dectin-1 signaling induces PGE2-synthesizing enzymes and PGE2 suppresses Il22ra2 expression in vitro and in vivo. Administration of short chain β-glucan laminarin, an antagonist of Dectin-1, suppresses the development of mouse colorectal tumors. Furthermore, in patients with colorectal cancer (CRC), the expression of CLEC7A is also observed in MDSCs and correlated with the death rate and tumor severity. Dectin-1 signaling upregulates PGE2-synthesizing enzyme expression and PGE2 suppresses IL22RA2 expression in human CRC-infiltrating cells. These observations indicate a role of the Dectin-1-PGE2-IL-22BP axis in regulating intestinal tumorigenesis, suggesting Dectin-1 as a potential target for CRC therapy.

Human intestinal epithelial cells can internalize luminal fungi via LC3-associated phagocytosis.

Intestinal epithelial cells (IECs) are the first to encounter luminal microorganisms and actively participate in intestinal immunity. We reported that IECs express the β-glucan receptor Dectin-1, and respond to commensal fungi and β-glucans. In phagocytes, Dectin-1 mediates LC3-associated phagocytosis (LAP) utilizing autophagy components to process extracellular cargo. Dectin-1 can mediate phagocytosis of β-glucan-containing particles by non-phagocytic cells. We aimed to determine whether human IECs phagocytose β-glucan-containing fungal particles via LAP. Colonic (n=18) and ileal (n=4) organoids from individuals undergoing bowel resection were grown as monolayers. Fluorescent-dye conjugated zymosan (β-glucan particle), heat-killed- and UV inactivated C. albicans were applied to differentiated organoids and to human IEC lines. Confocal microscopy was used for live imaging and immuno-fluorescence. Quantification of phagocytosis was carried out with a fluorescence plate-reader. zymosan and C. albicans particles were phagocytosed by monolayers of human colonic and ileal organoids and IEC lines. LAP was identified by LC3 and Rubicon recruitment to phagosomes and lysosomal processing of internalized particles was demonstrated by co-localization with lysosomal dyes and LAMP2. Phagocytosis was significantly diminished by blockade of Dectin-1, actin polymerization and NAPDH oxidases. Our results show that human IECs sense luminal fungal particles and internalize them via LAP. This novel mechanism of luminal sampling suggests that IECs may contribute to the maintenance of mucosal tolerance towards commensal fungi.

The Lipid Raft-Associated Protein Stomatin Is Required for Accumulation of Dectin-1 in the Phagosomal Membrane and for Full Activity of Macrophages against Aspergillus fumigatus.

Alveolar macrophages belong to the first line of defense against inhaled conidia of the human-pathogenic fungus Aspergillus fumigatus. In lung alveoli, they contribute to phagocytosis and elimination of conidia. As a counterdefense, conidia have a gray-green pigment that enables them to survive in phagosomes of macrophages for some time. Previously, we showed that this conidial pigment interferes with the formation of flotillin-dependent lipid raft microdomains in the phagosomal membrane, thereby preventing the formation of functional phagolysosomes. Besides flotillins, stomatin is a major component of lipid rafts and can be targeted to the membrane. However, only limited information on stomatin is available, in particular on its role in defense against pathogens. To determine the function of this integral membrane protein, a stomatin-deficient macrophage line was generated by CRISPR/Cas9 gene editing. Immunofluorescence microscopy and flow cytometry revealed that stomatin contributes to the phagocytosis of conidia and is important for recruitment of the β-glucan receptor dectin-1 to both the cytoplasmic membrane and phagosomal membrane. In stomatin knockout cells, fusion of phagosomes and lysosomes, recruitment of the vATPase to phagosomes, and tumor necrosis factor alpha (TNF-α) levels were reduced when cells were infected with pigmentless conidia. Thus, our data suggest that stomatin is involved in maturation of phagosomes via fostering fusion of phagosomes with lysosomes. IMPORTANCE Stomatin is an integral membrane protein that contributes to the uptake of microbes, e.g., spores of the human-pathogenic fungus Aspergillus fumigatus. By generation of a stomatin-deficient macrophage line by advanced genetic engineering, we found that stomatin is involved in the recruitment of the β-glucan receptor dectin-1 to the phagosomal membrane of macrophages. Furthermore, stomatin is involved in maturation of phagosomes via fostering fusion of phagosomes with lysosomes. The data provide new insights on the important role of stomatin in the immune response against human-pathogenic fungi.

Effect of dietary β-glucan on intestinal microbial diversity and Salmonella vaccine immunogenicity and efficacy in pigs

Alternatives to antibiotics to improve animal performance, limit the negative impact of infectious disease, and/or reduce colonization with foodborne pathogens is a major focus of animal agricultural research. β-glucans, a generally-recognized-as-safe (GRAS) product derived from various sources, are used in swine and can serve as both a prebiotic and/or stimulant of the immune system given the expression of β-glucan receptors on immune cells. When supplied in the diet of nursery pigs, it is unclear how dietary additives, particularly those known to modulate immune status, impact immunogenicity and efficacy of mucosal-delivered vaccines. Salmonellosis is one of the most common bacterial foodborne infections in the United States, and consumption of contaminated pork is a major source of human infection. Reduction of foodborne Salmonella in pigs via vaccination is one strategy to reduce contamination risk and subsequently reduce human disease. We examined the ability of dietary β-glucan to modulate fecal microbial diversity, and immunogenicity and efficacy of a mucosally-delivered, live-attenuated Salmonella vaccine during the nursery period. While dietaryβ-glucan did modulate fecal alpha diversity, it did not alter the induction of peripheral Salmonella-specific IFN-γ secreting Tcells or Salmonella-specific IgA in oral fluids. In addition, vaccination reduced Salmonella enterica serovar Typhimurium fecal shedding and tissue colonization. Overall, addition of β-glucan to the nursery diet of pigs impacted the microbiota but did not alter mucosal vaccine immunogenicity and efficacy.

Effect of Oral β-Glucan on Antibody Response to Ganglioside Vaccine in Patients With High-Risk Neuroblastoma

Among patients with high-risk relapsed metastatic neuroblastoma, oral β-glucan adjuvant during GD2/GD3 ganglioside vaccine boost has stimulated IgG antibody response, which was associated with improved survival; however, the effectiveness of oral β-glucan during the vaccine priming phase remains unproven. To isolate the adjuvant effect of oral β-glucan on antibody response to GD2/GD3 ganglioside vaccine in patients with high-risk neuroblastoma. In this phase 2 randomized clinical trial, enrolled patients with high-risk neuroblastoma were randomized to 2 groups to receive the GD2/GD3 vaccine at a large cancer center in a major metropolitan area from October 2018 to September 2020. Data were analyzed from October 7, 2021, to February 28, 2022. Eligible patients receiving GD2/GD3 vaccine were randomly assigned to group 1 (n = 54) to receive no β-glucan or group 2 (n = 53) to receive an oral β-glucan regimen during the first 5 weeks of vaccine priming. From week 6 onwards, all 107 patients received oral β-glucan during vaccine boost for 1 year or until disease progression. Primary end point was comparison of anti-GD2 IgG1 response before vaccine injection 6 (week 32) in group 1 vs group 2. Seroconversion rate and the association of antibody titer with β-glucan receptor dectin-1 single nucleotide polymorphism (SNP) rs3901533 were also assessed. In all, 107 patients with high-risk neuroblastoma were randomized to the 2 groups: 54 patients (median [range] age, 5.2 [1.0-17.3] years; 28 [52%] male and 26 [48%] female) in group 1; and 53 patients (median [range] age, 6.2 [1.9-18.4] years; 25 [47%] male and 28 [53%] female) in group 2; both groups were also comparable in their first remission status at study entry (70% vs 70%). Adding oral β-glucan during the first 5 weeks of vaccine priming elicited a higher anti-GD2 IgG1 antibody response in group 2 (1.80; 90% CI, 0.12-3.39; P = .08; planned type I error, 0.10). Anti-GD2 IgG1 titer of 230 ng/mL or greater by week 8 was associated with statistically favorable PFS. Antibody titer correlated significantly with dectin-1 SNP. The genotype frequency, seroconversion rates, and vaccine-related toxic effects were similar in the 2 groups. This phase 2 randomized clinical trial found that adding oral β-glucan during vaccine priming increased anti-GD2 IgG1 titer among genetic responders without added toxic effects. Because responder dectin-1 SNP was identical in the 2 randomized groups, no difference was detected in seroconversion rates. Alternative or additional adjuvants may be needed to enhance seroconversion. ClinicalTrials.gov Identifier: NCT00911560.

IL-23 signaling prevents ferroptosis-driven renal immunopathology during candidiasis

During infection the host relies on pattern-recognition receptors to sense invading fungal pathogens to launch immune defense mechanisms. While fungal recognition and immune effector responses are organ and cell type specific, during disseminated candidiasis myeloid cells exacerbate collateral tissue damage. The β-glucan receptor ephrin type-A 2 receptor (EphA2) is required to initiate mucosal inflammatory responses during oral Candida infection. Here we report that EphA2 promotes renal immunopathology during disseminated candidiasis. EphA2 deficiency leads to reduced renal inflammation and injury. Comprehensive analyses reveal that EphA2 restrains IL-23 secretion from and migration of dendritic cells. IL-23 signaling prevents ferroptotic host cell death during infection to limit inflammation and immunopathology. Further, host cell ferroptosis limits antifungal effector functions via releasing the lipid peroxidation product 4-hydroxynonenal to induce various forms of cell death. Thus, we identify ferroptotic cell death as a critical pathway of Candida-mediated renal immunopathology that opens a new avenue to tackle Candida infection and inflammation.

Dectin-1 Reactivity to Paramylon Derived from &lt;i&gt;Euglena gracilis&lt;/i&gt; EOD-1

Euglena gracilis is a microalga that has recently attracted attention because of its bioactivities. Paramylon (PM), a major β-1,3-glucan, constitutes 70-80% of the cells of the E. gracilis EOD-1 strain. Dectin-1 is a pattern recognition receptor that recognizes β-glucan. However, it is unclear whether PM binds to dectin-1. In this study, we investigated the reactivity of EOD1PM with dectin-1 by analyzing the binding of soluble murine and human dectin-1-Fc fusion protein (m dectin-1 Fc, h dectin-1 Fc) to EOD1PM using flow cytometry and enzyme-linked immunosorbent assay (ELISA). m Dectin-1 Fc bound to EOD1PM particles when m dectin-1-Fc is added. Furthermore, the binding specificity was examined in a competitive reaction following addition of a soluble antigen. It was found that the binding of m dectin-1-Fc to EOD1PM was not inhibited by the addition of dextran or ovalbumin but by the addition of solubilized EOD1PM or Candida cell wall- solubilized β-glucan. In addition, the h dectin-1-Fc fusion protein was found to specifically bind to EOD1PM. These results suggest that dectin-1 recognizes and binds to the β-glucan structure of EOD1PM. Dectin-1 is expressed in leukocytes as a β-glucan receptor and is involved in the expression of various biological activities; therefore, the dectin-1 pathway may be involved in the biological activity of EOD1PM.

Macrophage‐inducible C‐type lectin (MINCLE): In silico characterization and its in vitro effects on head–kidney leukocytes from the fishLutjanus peru

MINCLE is a C-lectin receptor mainly expressed in macrophages to recognize carbohydrates enhanced by the innate immune response in mammals and fish. Toxin A (ToxA) from Vibrio parahaemolyticus N16 was evaluated as an antigenic protein; it was observed to induce IgM production, increase cytokine gene expression, and offer immunoprotection against bacterial challenges in fish. This study was aimed at analysing the MINCLE receptor from the Pacific red snapper (Lutjanus peru) through bioinformatics tools, and the stimulating effects of β-glucans from Sterygmatomyces halophilus 4 N16 (β-Glu/Sh) combined with an antigenic protein on head–kidney leukocytes (HKLs) before and on challenge with Vibrio parahaemolyticus N16. LpMincle was mainly expressed in the intestine, eyes and head–kidney tissues. Before and after V. parahaemolyticus challenge, an up-regulation of the receptors (Mincle, Marco and tlr2) and pro-inflammatory cytokines (il-1β and il-6) gene expression was observed in HKLs incubated with β-Glu/Sh. Respiratory burst activity was mainly enhanced in cells incubated with ToxA before and after V. parahaemolyticus infection. Nitric oxide (NO) production increased in leukocytes incubated with β-Glu/Sh or ToxA, whereas myeloperoxidase (MPO) activity augmented only after ToxA stimulation before the bacterial challenge. In conclusion, MINCLE from L. peru was characterized in silico and its effects on HKLs was identified. Receptors and pro-inflammatory cytokine genes up-regulated by β-Glu/Sh alone or in combination with ToxA can be elicitors of innate immune parameters. These findings evidence the function and recognition of novel β-glucans from yeast either alone or in combination with antigenic proteins by β-glucan receptors and their cytokines response.

Deletion of both Dectin-1 and Dectin-2 affects the bacterial but not fungal gut microbiota and susceptibility to colitis in mice

BackgroundInnate immunity genes have been reported to affect susceptibility to inflammatory bowel diseases (IBDs) and colitis in mice. Dectin-1, a receptor for fungal cell wall β-glucans, has been clearly implicated in gut microbiota modulation and modification of the susceptibility to gut inflammation. Here, we explored the role of Dectin-1 and Dectin-2 (another receptor for fungal cell wall molecules) deficiency in intestinal inflammation.DesignSusceptibility to dextran sodium sulfate (DSS)-induced colitis was assessed in wild-type, Dectin-1 knockout (KO), Dectin-2KO, and double Dectin-1KO and Dectin-2KO (D-1/2KO) mice. Inflammation severity, as well as bacterial and fungal microbiota compositions, was monitored.ResultsWhile deletion of Dectin-1 or Dectin-2 did not have a strong effect on DSS-induced colitis, double deletion of Dectin-1 and Dectin-2 significantly protected the mice from colitis. The protection was largely mediated by the gut microbiota, as demonstrated by fecal transfer experiments. Treatment of D-1/2KO mice with opportunistic fungal pathogens or antifungal agents did not affect the protection against gut inflammation, suggesting that the fungal microbiota had no role in the protective phenotype. Amplicon-based microbiota analysis of the fecal bacterial and fungal microbiota of D-1/2KO mice confirmed the absence of changes in the mycobiota but strong modification of the bacterial microbiota. We showed that bacteria from the Lachnospiraceae family were at least partly involved in this protection and that treatment with Blautia hansenii was enough to recapitulate the protection.ConclusionsDeletion of both the Dectin-1 and Dectin-2 receptors triggered a global shift in the microbial gut environment, affecting, surprisingly, mainly the bacterial population and driving protective effects in colitis. Members of the Lachnospiraceae family seem to play a central role in this protection. These findings provide new insights into the role of the Dectin receptors, which have been described to date as affecting only the fungal population, in intestinal physiopathology and in IBD.F446R2nzvxqjjpdjAkXVZkVideo

IL-23 signaling limits ferroptosis-driven immunopathology during systemic fungal infection

Abstract Pattern recognition receptors initiate antifungal immune responses during infection. Recently, we identified that the ephrin type-A receptor 2 (EphA2) is a fungal β-glucan receptor which orchestrates innate immune responses and prevents oral Candida infection. However, the role of EphA2 during invasive candidiasis (IC) remains unknown. Here we found that EphA2 induces renal inflammation and injury; thus, promoting immunopathology during IC. In Epha2−/− mice, dendritic cells migrated more efficient in infected tissues, while secreting more IL-23. Furthermore, Epha2−/− mice had reduced lipid peroxidation in kidneys, a marker of ferroptotic cell death. Pharmacological inhibtion of ferroptosis increased macrophage fungal killing, reduced inflammation, and increased disease outcomes during IC. Previously, IL-23 signaling has been associated with myeloid cell survival during candidiasis. Treatment of macrophages with IL-23 reduced ferroptotic macrophage cell death and excessive inflammation, while increasing killing capacity. Furthermore, IL-23 treatment of infected mice increased survival and reduced ferroptosis during IC. Collectively, our study demonstrates that ferroptotic host cell death is linked to immunopathology and can be targeted by recombinant cytokine therapy during fungal infection. This work was supported in part by NIH grant R00DE026856, an American Association of Immunologists Careers in Immunology Fellowship, and a TLI Seed grant to MS

The phagocytic receptors of β-glucan.

Phagocytosis is a cellular process maintaining tissue balance and plays an essential role in initiating the innate immune response. The process of phagocytosis was triggered by the binding of pathogen-associated molecular patterns (PAMP) with their cell surface receptors on the phagocytes. These receptors not only perform phagocytic functions, but also bridge the gap between extracellular and intracellular communication, leading to signal transduction and the production of inflammatory mediators, which are crucial for clearing the invading pathogens and maintaining cell homeostasis. For the past few years, the application of β-glucan comes down to immunoregulation and anti-tumor territory. As a well-known PAMP, β-glucan is one of the most abundant polysaccharides in nature. By binding to specific receptors on immune cells and activating intracellular signal transduction pathways, it causes phagocytosis and promotes the release of cytokines. Further retrieval and straightening out literature related to β-glucan phagocytic receptors will help better elucidate their immunomodulatory functions. This review attempts to summarize physicochemical properties and specific processes involved in β-glucan induced phagocytosis, its phagocytic receptors, and cascade events triggered by β-glucan at the cellular and molecular levels.

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.

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

Bacterial infections are a common and deadly threat to vulnerable patients. Alternative strategies to fight infection are needed. β-Glucan, an immunomodulator derived from the fungal cell wall, provokes resistance to infection by inducing trained immunity, a phenomenon that persists for weeks to months. Given the durability of trained immunity, it is unclear which leukocyte populations sustain this effect. Macrophages have a life span that surpasses the duration of trained immunity. Thus, we sought to define the contribution of differentiated macrophages to trained immunity. Our results show that β-glucan protects mice from Pseudomonas aeruginosa infection by augmenting recruitment of innate leukocytes to the site of infection and facilitating local clearance of bacteria, an effect that persists for more than 7 d. Adoptive transfer of macrophages, trained using β-glucan, into naive mice conferred a comparable level of protection. Trained mouse bone marrow-derived macrophages assumed an antimicrobial phenotype characterized by enhanced phagocytosis and reactive oxygen species production in parallel with sustained enhancements in glycolytic and oxidative metabolism, increased mitochondrial mass, and membrane potential. β-Glucan induced broad transcriptomic changes in macrophages consistent with early activation of the inflammatory response, followed by sustained alterations in transcripts associated with metabolism, cellular differentiation, and antimicrobial function. Trained macrophages constitutively secreted CCL chemokines and robustly produced proinflammatory cytokines and chemokines in response to LPS challenge. Induction of the trained phenotype was independent of the classic β-glucan receptors Dectin-1 and TLR-2. These findings provide evidence that β-glucan induces enhanced protection from infection by driving trained immunity in macrophages.

Deciphering of Candida parapsilosis induced immune response in Drosophila melanogaster

ABSTRACT Candida infections are the most prevalent cause of serious human mycoses and are the third most common pathogens isolated from bloodstream infections in hospitalized patients. C. parapsilosis is a member of the non-albicans spp., which have a predilection for causing life-threatening disease in neonates and hospitalized pediatric patients. In this study, we utilized a Drosophila melanogaster infection model to analyze the immunological responses to C. parapsilosis. Our results demonstrate that the Toll pathway in Drosophila controls C. parapsilosis proliferation as the Toll signaling mutant MyD88−/ − flies are highly susceptible to C. parapsilosis. We also confirmed that the MyD88−/ − fly is a convenient invertebrate animal model to analyze virulence properties of different species and strains from the C. parapsilosis sensu lato complex as C. orthopsilosis, C. metapsilosis proved to be less virulent than C. parapsilosis sensu stricto and the N-mannan deficient C. parapsilosis och1Δ/Δ strain showed attenuated pathogenicity in this immunodeficient Drosophila background. We also found that Persephone protease is not required for detection and activation of Toll pathway during C. parapsilosis infection. Furthermore, we observed that Drosophila β-glucan receptor deficient flies where more sensitive to C. parapsilosis compared to wild-type flies; however, we could not find a clear dependence on the recognition of this receptor and the cell wall β-glucan exposure-induced host response. These studies establish this D. melanogaster infection model as an efficient tool in deciphering immune responses to C. parapsilosis as well as for assessing virulence factors produced by this emerging fungal predator.

Candida albicans-induced EphA2 signaling promotes kidney injury and sepsis during invasive candidiasis

Abstract Pattern recognition receptors (PRRs) play key roles in fungal recognition and initiation of host immune responses. Recently, we identified that the ephrin type-A receptor 2 (EphA2) is a key β-glucan receptor on oral epithelial cells and neutrophils which orchestrates innate immune responses thereby preventing oral Candida infection. However, the contribution of this PRR in the pathogenesis of invasive candidiasis (IC) remains unknown. Although no differences in renal fungal burden could be observed, EphA2-deficient mice were more resistant to C. albicans infection suggesting that EphA2 deficiency enhances renal host tolerance to lethal fungal challenge. By testing renal cytokines, serum NGAL, a marker of renal injury, and the sepsis marker TREM-1, we found that EphA2 deficiency altered the pro- and anti-inflammatory response, reduced renal injury, and sepsis during IC. Epha2−/− mice decreased neutrophil and monocyte recruitment during IC. However, dendritic cells lacking EphA2 migrated more efficient to infected tissue. Since EphA2 is highly expressed on both, hematopoietic and stromal cells, we generated bone marrow chimeric mice. Both Epha2+/+ mice reconstituted with Epha2−/− BM and Epha2−/− mice reconstituted with Epha2+/+ BM were more resistant to IC compared to Epha2+/+ mice reconstituted with Epha2+/+BM. However, these chimeric mice were more susceptible than Epha2−/− mice reconstituted with Epha2−/− BM suggesting that EphA2 deficiency within cells of both compartments, the hematopoietic and the stromal, is required for full protection against IC. Collectively, our data highlight a detrimental role of EphA2 in promoting kidney injury and sepsis during lethal fungal infection.