Fungal Components Research Articles

Conserved fungal effector suppresses PAMP-triggered immunity by targeting plant immune kinases

Plant pathogens have optimized their own effector sets to adapt to their hosts. However, certain effectors, regarded as core effectors, are conserved among various pathogens, and may therefore play an important and common role in pathogen virulence. We report here that the widely distributed fungal effector NIS1 targets host immune components that transmit signaling from pattern recognition receptors (PRRs) in plants. NIS1 from two Colletotrichum spp. suppressed the hypersensitive response and oxidative burst, both of which are induced by pathogen-derived molecules, in Nicotiana benthamianaMagnaporthe oryzae NIS1 also suppressed the two defense responses, although this pathogen likely acquired the NIS1 gene via horizontal transfer from Basidiomycota. Interestingly, the root endophyte Colletotrichum tofieldiae also possesses a NIS1 homolog that can suppress the oxidative burst in N. benthamiana We show that NIS1 of multiple pathogens commonly interacts with the PRR-associated kinases BAK1 and BIK1, thereby inhibiting their kinase activities and the BIK1-NADPH oxidase interaction. Furthermore, mutations in the NIS1-targeting proteins, i.e., BAK1 and BIK1, in Arabidopsis thaliana also resulted in reduced immunity to Colletotrichum fungi. Finally, M. oryzae lacking NIS1 displayed significantly reduced virulence on rice and barley, its hosts. Our study therefore reveals that a broad range of filamentous fungi maintain and utilize the core effector NIS1 to establish infection in their host plants and perhaps also beneficial interactions, by targeting conserved and central PRR-associated kinases that are also known to be targeted by bacterial effectors.

2036. Plasma (1→3)-β-D-Glucan Levels Correlate with Neurocognitive Functioning in HIV-Infected Adults

BackgroundAlthough antiretroviral therapy (ART) has improved survival and morbidity, HIV-infected adults still have higher rates of non-AIDS disorders, such as neurocognitive impairment, than HIV-uninfected adults. (1–3)-b-D-Glucan (BDG) is a fungal cell wall component which serves as a plasma biomarker for fungal infection and—in the absence of fungal infections—for gut barrier integrity failure and microbial translocation. The objective of this study was to determine whether higher plasma and cerebrospinal fluid (CSF) levels of BDG are associated with neurocognitive impairment [evaluated by global deficit score (GDS)] in HIV-infected adults.MethodsWe measured levels of BDG in paired plasma and CSF samples, and compared levels with GDS, soluble urokinase plasminogen activator receptor (suPAR; a marker of monocyte activation and chronic inflammation that has previously been associated with non-AIDS disorders) and plasma CD4/CD8 ratio in a cohort of 61 HIV+ adults on suppressive ART. Study samples were collected as part of the prospective CHARTER study between 2005 and 2015 at the University of California San Diego and were stored at −80°C on the day of collection. BDG testing of blood plasma and CSF supernatant was performed at the Associates of Cape Cod, Inc., research laboratories using the Fungitell assay.ResultsMedian plasma BDG level was 18 pg/mL (range: 2–60 pg/mL), median CSF BDG level was 20 pg/mL (range: 0–830 pg/mL). Higher levels of plasma BDG were associated with more severe cognitive impairment as measured by the GDS (Spearman r = 0.35; P = 0.006, Figure). Individuals with neurocognitive impairment (i.e., GDS > 0.5, n = 33) had higher plasma BDG levels compared with unimpaired individuals (P = 0.027). Plasma levels of BDG and suPAR correlated significantly (r = 0.31, P = 0.016), while all other correlations were nonsignificant (e.g., CSF BDG and GDS [r = 0.23], plasma suPAR and GDS [r = 0.19], CSF suPAR and GDS [r = −0.022], CD4/CD8 ratio and GDS [r = −0.028]).ConclusionElevated plasma levels of BDG may be an indicator of gut barrier integrity failure and an independent biomarker associated with neurocognitive functioning in HIV+ adults on suppressive ART. Disclosures M. Finkelman, Associated of Cape Cod: Employee, Salary.

C-Type Lectin Receptor CD23 Is Required for Host Defense against Candida albicans and Aspergillus fumigatus Infection.

Infection by invasive fungi, such as Candida albicans, Aspergillus fumigatus, and Cryptococcus neoformans, is one of the leading death causes for the increasing population of immunocompromised and immunodeficient patients. Several C-type lectin receptors (CLRs), including Dectin-1, -2, and -3 and Mincle can recognize fungal surface components and initiate the host antifungal immune responses. Nevertheless, it remains to be determined whether other CLRs are involved in antifungal immunity. Our recent study suggests that CD23 (CLEC4J), a CLR and also a well-known B cell surface marker, may function to sense C. albicans components in antifungal immunity. However, it is not clear how CD23 functions as a fungal pattern recognition receptor and whether the antifungal role of CD23 is specific to C. albicans or not. In this study, we show that CD23 can recognize both α-mannan and β-glucan from the cell wall of C. albicans or A. fumigatus but cannot recognize glucuronoxylomannan from Cryptococcus Through forming a complex with FcRγ, CD23 can induce NF-κB activation. Consistently, CD23-deficient mice were highly susceptible to C. albicans and A. fumigatus but not to C. neoformans infection. The expression of CD23 in activated macrophages is critical for the activation of NF-κB. CD23 deficiency results in impaired expression of NF-κB-dependent genes, especially iNOS, which induces NO production to suppress fungal infection. Together, our studies reveal the CD23-induced signaling pathways and their roles in antifungal immunity, specifically for C. albicans and A. fumigatus, which provides the molecular basis for designing potential therapeutic agents against fungal infection.

Fungal Component Coating Enhances Titanium Implant‐Bone Integration

AbstractBioactive coating on bone and dental implants is widely used to increase their integration with the host tissue, with millions of implantations performed globally each year. Numerous coating strategies focus on creating a cell‐adhesive surface by employing bone matrix components, but insufficient integration and its associated complications remain a substantial clinical challenge. Designing an implant coating to more comprehensively promote healing while appropriately modulating host immune response is still an unfulfilled promise. This study reports the development of a polysaccharide coating that can improve osseointegration by targeting and regulating inflammatory activity at the implant surface. Zymosan—a fungal component—is screened and covalently grafted onto titanium (Ti) substrates. The zymosan coating specifically stimulates macrophages through toll‐like receptors into a proregenerative phenotype, which produces abundant osteogenic/angiogenic cytokines to enhance osteogenic activities locally. Further assessment in a rat femur condyle defect indicates that zymosan coated at a medium dose (0.1 µg mm−2) remarkably increases the integration of Ti column with bone tissue, causing no abnormality to the host. This is the first demonstration that modulating inflammation with an immunoactive coating material can promote bone‐implant integration, which may inspire new strategies for the design of bone and dental implants.

Function and crystal structure of the dimeric P-loop ATPase CFD1 coordinating an exposed [4Fe-4S] cluster for transfer to apoproteins

Maturation of iron-sulfur (Fe-S) proteins in eukaryotes requires complex machineries in mitochondria and cytosol. Initially, Fe-S clusters are assembled on dedicated scaffold proteins and then are trafficked to target apoproteins. Within the cytosolic Fe-S protein assembly (CIA) machinery, the conserved P-loop nucleoside triphosphatase Nbp35 performs a scaffold function. In yeast, Nbp35 cooperates with the related Cfd1, which is evolutionary less conserved and is absent in plants. Here, we investigated the potential scaffold function of human CFD1 (NUBP2) in CFD1-depleted HeLa cells by measuring Fe-S enzyme activities or 55Fe incorporation into Fe-S target proteins. We show that CFD1, in complex with NBP35 (NUBP1), performs a crucial role in the maturation of all tested cytosolic and nuclear Fe-S proteins, including essential ones involved in protein translation and DNA maintenance. CFD1 also matures iron regulatory protein 1 and thus is critical for cellular iron homeostasis. To better understand the scaffold function of CFD1-NBP35, we resolved the crystal structure of Chaetomium thermophilum holo-Cfd1 (ctCfd1) at 2.6-Å resolution as a model Cfd1 protein. Importantly, two ctCfd1 monomers coordinate a bridging [4Fe-4S] cluster via two conserved cysteine residues. The surface-exposed topology of the cluster is ideally suited for both de novo assembly and facile transfer to Fe-S apoproteins mediated by other CIA factors. ctCfd1 specifically interacted with ATP, which presumably associates with a pocket near the Cfd1 dimer interface formed by the conserved Walker motif. In contrast, ctNbp35 preferentially bound GTP, implying differential regulation of the two fungal scaffold components during Fe-S cluster assembly and/or release.

First Insights in NK-DC Cross-Talk and the Importance of Soluble Factors During Infection With Aspergillus fumigatus.

Invasive aspergillosis (IA) is an infectious disease caused by the fungal pathogen Aspergillus fumigatus that mainly affects immunocompromised hosts. To investigate immune cell cross-talk during infection with A. fumigatus, we co-cultured natural killer (NK) cells and dendritic cells (DC) after stimulation with whole fungal structures, components of the fungal cell wall, fungal lysate or ligands for distinct fungal receptors. Both cell types showed activation after stimulation with fungal components and were able to transfer activation signals to the counterpart not stimulated cell type. Interestingly, DCs recognized a broader spectrum of fungal components and thereby initiated NK cell activation when those did not recognize fungal structures. These experiments highlighted the supportive function of DCs in NK cell activation. Furthermore, we focused on soluble DC mediated NK cell activation and showed that DCs stimulated with the TLR2/Dectin-1 ligand zymosan could maximally stimulate the expression of CD69 on NK cells. Thus, we investigated the influence of both receptors for zymosan, Dectin-1 and TLR2, which are highly expressed on DCs but show only minimal expression on NK cells. Specific focus was laid on the question whether Dectin-1 or TLR2 signaling in DCs is important for the secretion of soluble factors leading to NK cell activation. Our results show that Dectin-1 and TLR2 are negligible for NK cell activation. We conclude that besides Dectin-1 and TLR2 other receptors on DCs are able to compensate for the missing signal.

Immune synergistic oligodeoxynucleotide from Lactobacillus rhamnosus GG enhances the immune response upon co-stimulation by bacterial and fungal cell wall components.

Bacterial genomic DNA has recently been shown to elicit a highly evolved immune defense. This response can be selectively triggered for a wide range of therapeutic applications, including use as a vaccine adjuvant to immunotherapies for allergy, cancer, and infectious diseases. Previously, we identified a low-concentration immune synergistic oligodeoxynucleotide (iSN-ODN, named iSN34) from Lactobacillus rhamnosus GG that has immunosynergistic activity upon costimulation of target cells with ligands of Toll-like receptor 9 (TLR9). Here, we extend that observation by demonstrating the synergistic induction (in mouse splenocytes) of IL-6 by the combination of iSN34 with cell wall components of bacteria and fungi. We observed that splenocytes pretreated with iSN34 and then costimulated with agonists for TLR1/2 (Pam3 CSK4 ), TLR4 (lipopolysaccharide), or TLR2/6 (Zymosan) exhibited enhanced accumulation of IL-6. These results suggested that the combination of iSN34 with TLR1/2, TLR4, or TLR2/6 agonists may permit the induction of a potent immune response.

Experimental and molecular approximation to microbial niche: trophic interactions between oribatid mites and microfungi in an oligotrophic freshwater system.

Mite-fungal interactions play a key role in structuring core ecosystem processes such as nutrient dynamics. Despite their ecological relevance, these cross-kingdom interactions remain poorly understood particularly in extreme environments. Herein, we investigated feeding preferences of a novel genetic lineage of aquatic oribatids obtained from an oligotrophic freshwater system in the Cuatro Ciénegas Basin (CCB) within the Chihuahuan Desert, Mexico. During in vitro diet preference bioassays, transient aquatic microfungi (Aspergillus niger, Talaromyces sp., and Pleosporales sp.) recovered from the same mesocosm samples were offered individually and simultaneously to mites. Gut content was analyzed using classic plating and culture-independent direct PCR (focusing on the fungal barcoding region) methods. Our results indicated that oribatids fed on all tested fungal isolates, yet the profusely developing A. niger was preferentially consumed with all fungal components being digested. This feeding habit is particularly interesting since A. niger has been reported as an unsuitable dietary element for population growth, being consistently avoided by mites in previous laboratory experiments. It is possible that our mites from the CCB have adapted to exploit available resources within this oligotrophic site. This work confirms the trophic relationship between microfungi and mites, two rarely investigated major components of the microbial community, shedding light on the niche dynamics under low-nutrient conditions.

Paddy periphyton: Potential roles for salt and nutrient management in degraded mudflats from coastal reclamation

AbstractPeriphyton exists ubiquitously in paddy ecosystems of coastal mudflat area, playing significant roles in salt and nutrient cycling between the water and soil interface. However, the definition, composition, influenced factors, and potential function of paddy periphyton are still unclear. We attempt to define paddy periphyton as an integrated and independent microcosm, which is dominated by phototrophic communities, containing both biotic components, such as algal, fungal, bacterial, protozoan, and metazoan, and abiotic components, such as soil, extracellular polymeric substance, and detritus. They interact with each other such as predation and competition, co‐inhabiting in a common microhabitat. The development of paddy periphyton mainly includes three processes: growth stage, mature stage, and fading stage. Paddy periphyton has a significant influence on the salt migration in paddy ecosystem that was reclaimed from coastal mudflat by improving the soil structure, assimilating and adsorbing the salt like sodium chloride, and inhibiting the salt accumulation near the soil surface. As for nutrient management, the roles of paddy periphyton can be summarized as a slow‐released bio‐fertilizer, a nutrient‐removal agent, a nutrient mediator, and a nutrient indicator in mudflat‐reclaimed paddy ecosystem. All these imply that paddy periphyton may be a new and promising biotechnological tool for better salt and nutrient management in paddy ecosystems that degraded from mudflat land, which has a vast potential in the amelioration and fertility improvement of salt‐affected soils, as well as control of nonpoint agricultural pollution in coastal areas.

New insight into the effect of fungal mycelia present in the bio-pretreated paddy straw on their enzymatic saccharification and optimization of process parameters

Assessment of Pleurotus florida efficiency on paddy straw pretreatment and optimization of saccharification parameters were studied. P. florida growth was monitored by the estimation of fungal cell wall component (glucosamine). The control bio-pretreatment sample showed high glucosamine content by 397 mg/g in 28 days of incubation. But, the Inhibitor Mediated Biological (IMB) Pretreatment showed 29% lower result due to the inhibition of cellulase enzyme limits mycelial penetration rate inside the paddy straw. Fungal components present inside the pretreated straw renders nonspecific interactions with the hydrolytic enzymes during saccharification process and reducing the hydrolysis efficiency. IMB pretreated paddy straw showed maximum saccharification efficiency up to 75.3% with optimized condition (Biomass loading- 10% (w/v), Enzyme loading- 20 FPU/g and saccharification time – 72 h) than control pretreatment sample. Thus, the study brings out new insight into the effect of fungal residues inside the bio-pretreated paddy straw during enzymatic saccharification to improve the efficiency.

Conversion of Tibetan grasslands to croplands decreases accumulation of microbially synthesized compounds in soil

Conversion of grassland to cropland affects microbial transformation of plant derived organic substances and the accumulation of microbially synthesized products in soil. We investigated long-term effects of agricultural use [more than 50 years' rotation with barley (Hordeum vulgare) and rapeseed (Brassica rapa)] after conversion from grasslands (grazed in the winter season) on the contents and composition of non-cellulose sugars and amino sugars in a broad range of soils on the Tibetan Plateau. Soils from two types of croplands (barley or rapeseed) were compared to a reference grassland soil by detailed analysis of plant vs. microbial and bacterial vs. fungal biomarkers. Long-term cultivation decreased total soil organic matter (SOM), light SOM and total non-cellulose sugar contents in the 0–20 cm soil by 27%, 47–72% and 57%, respectively, reflecting decreased root biomass compared to grassland. The ratios of (galactose + mannose)/(arabinose + xylose) and (rhamnose + fucose)/(arabinose + xylose) were both 26% smaller in cropland than in grassland soils, while the ratios of hemicelluloses in shoots or roots were similar between native and cultivated plants. Consequently, net transformation of plant substances to microbially synthesized polysaccharides decreased in cultivated soils. The total amino sugars (muramic acid, glucosamine, mannosamine, galactosamine) in cropland soils decreased by 42% as did their contribution to the SOM pool by 22%, compared to grassland soils, but the ratio of glucosamine/muramic acid in cropland soils doubled when compared to the grassland soil. This shows a strong decrease in microbial residue under cultivation, with the magnitude of the decrease greater in the bacterial than in the fungal components. All the above results from the intensively sampled site were confirmed in seven other sites featuring lower sampling intensity. We concluded that the conversion of grassland to cropland strongly decreases microbial transformation of plant residues and accumulation of the resulting microbial compounds – necromass – in soil (i.e., reduction of microbial input to stable SOM). The conversion also leads to a shift in the composition of microbial compounds towards a decreasing contribution of bacterial compared to fungal necromass.

Spondyloarthritis, Acute Anterior Uveitis, and Fungi: Updating the Catterall-King Hypothesis.

Spondyloarthritis is a common type of arthritis which affects mostly adults. It consists of idiopathic chronic inflammation of the spine, joints, eyes, skin, gut, and prostate. Inflammation is often asymptomatic, especially in the gut and prostate. The HLA-B*27 allele group, which presents intracellular peptides to CD8+ T cells, is by far the strongest risk factor for spondyloarthritis. The precise mechanisms and antigens remain unknown. In 1959, Catterall and King advanced a novel hypothesis explaining the etiology of spondyloarthritis: an as-yet-unrecognized sexually acquired microbe would be causing all spondyloarthritis types, including acute anterior uveitis. Recent studies suggest an unrecognized sexually acquired fungal infection may be involved in prostate cancer and perhaps multiple sclerosis. This warrants reanalyzing the Catterall–King hypothesis based on the current literature. In the last decade, many links between spondyloarthritis and fungal infections have been found. Antibodies against the fungal cell wall component mannan are elevated in spondyloarthritis. Functional polymorphisms in genes regulating the innate immune response against fungi have been associated with spondyloarthritis (CARD9 and IL23R). Psoriasis and inflammatory bowel disease, two common comorbidities of spondyloarthritis, are both strongly associated with fungi. Evidence reviewed here lends credence to the Catterall–King hypothesis and implicates a common fungal etiology in prostate cancer, benign prostatic hyperplasia, multiple sclerosis, psoriasis, inflammatory bowel disease, and spondyloarthritis. However, the evidence available at this time is insufficient to definitely confirm this hypothesis. Future studies investigating the microbiome in relation to these conditions should screen specimens for fungi in addition to bacteria. Future clinical studies of spondyloarthritis should consider antifungals which are effective in psoriasis and multiple sclerosis, such as dimethyl fumarate and nystatin.

Endobronchial Topical Amphotericin B Instillation for Pulmonary Chromomycosis After Lung Transplantation: A Case Report

We report a very rare case of pulmonary chromomycosis caused by Scedosporium prolificans that developed after lung transplantation and was successfully treated with endobronchial topical amphotericin B instillation. The subject was a woman in her 50s with a history of bilateral lobar lung transplantation from living donors for idiopathic pulmonary hypertension. Eight years after the lung transplantation, chest radiography X-ray and computed tomography showed an abnormal shadow in the right lung. Bronchoscopic findings showed obstruction by a fungal component at the laterobasal bronchus B9. She was diagnosed with pulmonary chromomycosis after S. prolificans was detected in the bronchial aspirate. Systemic antifungal treatment with itraconazole was ineffective. Therefore, we administered topical amphotericin B weekly via endobronchial instillation and replaced oral itraconazole with voriconazole. The endobronchial procedure was safe and tolerable. Bronchial obstruction improved after three 3 instillations. We continued topical amphotericin B instillation once every 3 months for 2 years, and the abnormal shadow nearly disappeared. This case report describes infection by S. prolificans, which rarely becomes an etiologic agent in lung transplant patients, and shows that endobronchial topical amphotericin B instillation is a therapeutic option when systemic antifungal treatment is ineffective.

Candida albicans β-Glucan-Containing Particles Increase HO-1 Expression in Oral Keratinocytes via a Reactive Oxygen Species/p38 Mitogen-Activated Protein Kinase/Nrf2 Pathway.

Oral keratinocytes provide the first line of host defense against oral candidiasis. We speculated that interactions of fungal cell wall components with oral keratinocytes regulate the stress response against Candida infection and examined the expression of genes induced by heat-killed Candida albicans in oral immortalized keratinocytes using a cDNA microarray technique. Of 24,000 genes revealed by that analysis, we focused on HO-1, a stress-inducible gene, as its expression was increased by both heat-killed and live C. albicans In histological findings, HO-1 expression in the superficial layers of the oral epithelium following Candida infection was elevated compared to that in healthy epithelium. We then investigated fungal cell wall components involved in induction of HO-1 expression and found that β-glucan-containing particles (β-GPs) increased its expression. Furthermore, β-glucan was observed on the surface of both heat-killed C. albicans and Candida cells that had invaded the oral epithelium. Fungal β-GPs also promoted induction of intracellular reactive oxygen species (ROS), NADPH oxidase activation, and p38 mitogen-activated protein kinase (MAPK) phosphorylation, while those specific inhibitors inhibited the HO-1 expression induced by fungal β-GPs. Moreover, fungal β-GPs induced Nrf2 translocation into nuclei via p38 MAPK signaling, while the HO-1 expression induced by fungal β-GPs was inhibited by Nrf2-specific small interfering RNA (siRNA). Finally, knockdown of cells by HO-1- and Nrf2-specific siRNAs resulted in increased β-GP-mediated ROS production compared to that in the control cells. Our results show that the HO-1 induced by fungal β-GPs via ROS/p38 MAPK/Nrf2 from oral keratinocytes may have important roles in host defense against the stress caused by Candida infection in the oral epithelium.

Short-Course Antimicrobial Therapy Does Not Increase Treatment Failure Rate in Patients with Intra-Abdominal Infection Involving Fungal Organisms.

Fungi frequently are isolated in intra-abdominal infections (IAI). The Study to Optimize Peritoneal Infection Therapy (STOP-IT) recently suggested short-course treatment for patients with IAI. It remains unclear whether the presence of fungi in IAI affects the optimal duration of Antimicrobial therapy. We hypothesized that a shorter treatment course in IAI with fungal organisms would be associated with a higher rate of treatment failure. Patients enrolled in the STOP-IT trial were stratified according to the presence or absence of a fungal isolate. They were analyzed as a subgroup based on original randomization to either the control group or an experimental group that received a four-day course of Antimicrobial therapy and by comparison with those without a fungal component to their infection. Descriptive comparisons were performed using a χ2, Fisher exact, or Kruskal-Wallis test as appropriate. The primary outcome was a composite of recurrent IAI, surgical site infection, and death. A total of 411 patients in the study (79%) had available culture data, of which 58 (14%) had positive fungal cultures. The most common organisms were Candida albicans and C. glabrata. The treatment failure rate was equivalent in the experimental and control arms (29.6% vs. 22.6%; p = 0.54). Patients with fungal isolates were more likely to have malignant disease (25.9% vs. 9.6%; p = 0.0004) and coronary artery disease (22% vs. 12%; p = 0.04), but were otherwise similar to those without fungal isolates. Patients with fungal isolates had more hospital days (median 10 vs. 7; p < 0.0001) and more days to resumption of enteral intake (median 5 vs. 3; p = 0.0006), but there was no difference in the composite outcome. Patients with IAI involving fungal organisms randomized to a shorter course of Antimicrobial therapy had no difference in the rate of treatment failure. These results suggest that the presence of fungi in IAI may not indicate independently the need for a longer course of Antimicrobial therapy.

Targeting Mycobacterium tuberculosis Antigens to Dendritic Cells via the DC-Specific-ICAM3-Grabbing-Nonintegrin Receptor Induces Strong T-Helper 1 Immune Responses.

Tuberculosis remains a major global health problem and efforts to develop a more effective vaccine have been unsuccessful so far. Targeting antigens (Ags) to dendritic cells (DCs) in vivo has emerged as a new promising vaccine strategy. In this approach, Ags are delivered directly to DCs via antibodies that bind to endocytic cell-surface receptors. Here, we explored DC-specific-ICAM3-grabbing-nonintegrin (DC-SIGN) targeting as a potential vaccine against tuberculosis. For this, we made use of the hSIGN mouse model that expresses human DC-SIGN under the control of the murine CD11c promoter. We show that in vitro and in vivo delivery of anti-DC-SIGN antibodies conjugated to Ag85B and peptide 25 of Ag85B in combination with anti-CD40, the fungal cell wall component zymosan, and the cholera toxin-derived fusion protein CTA1-DD induces strong Ag-specific CD4+ T-cell responses. Improved anti-mycobacterial immunity was accompanied by increased frequencies of Ag-specific IFN-γ+ IL-2+ TNF-α+ polyfunctional CD4+ T cells in vaccinated mice compared with controls. Taken together, in this study we provide the proof of concept that the human DC-SIGN receptor can be efficiently exploited for vaccine purposes to promote immunity against mycobacterial infections.

The Mycobiome: A Neglected Component in the Microbiota-Gut-Brain Axis.

In recent years, the gut microbiota has been considered as a full-fledged actor of the gut–brain axis, making it possible to take a new step in understanding the pathophysiology of both neurological and psychiatric diseases. However, most of the studies have been devoted to gut bacterial microbiota, forgetting the non-negligible fungal flora. In this review, we expose how the role of the fungal component in the microbiota-gut-brain axis is legitimate, through its interactions with both the host, especially with the immune system, and the gut bacteria. We also discuss published data that already attest to a role of the mycobiome in the microbiota-gut-brain axis, and the impact of fungi on clinical and therapeutic research.

Fungal melanin stimulates surfactant protein D–mediated opsonization of and host immune response to Aspergillus fumigatus spores

Surfactant protein D (SP-D), a C-type lectin and pattern-recognition soluble factor, plays an important role in immune surveillance to detect and eliminate human pulmonary pathogens. SP-D has been shown to protect against infections with the most ubiquitous airborne fungal pathogen, Aspergillus fumigatus, but the fungal surface component(s) interacting with SP-D is unknown. Here, we show that SP-D binds to melanin pigment on the surface of A. fumigatus dormant spores (conidia). SP-D also exhibited an affinity to two cell-wall polysaccharides of A. fumigatus, galactomannan (GM) and galactosaminogalactan (GAG). The immunolabeling pattern of SP-D was punctate on the conidial surface and was uniform on germinating conidia, in accordance with the localization of melanin, GM, and GAG. We also found that the collagen-like domain of SP-D is involved in its interaction with melanin, whereas its carbohydrate-recognition domain recognized GM and GAG. Unlike un-opsonized conidia, SP-D-opsonized conidia were phagocytosed more efficiently and stimulated the secretion of proinflammatory cytokines by human monocyte-derived macrophages. Furthermore, SP-D-/- mice challenged intranasally with wildtype conidia or melanin ghosts (i.e. hollow melanin spheres) displayed significantly reduced proinflammatory cytokines in the lung compared with wildtype mice. In summary, SP-D binds to melanin present on the dormant A. fumigatus conidial surface, facilitates conidial phagocytosis, and stimulates the host immune response.

A Tyrosine Phosphorylation Cycle Regulates Fungal Activation of a Plant Receptor Ser/Thr Kinase

Plants initiate immunity by cell-surface pattern-recognition receptors (PRRs), which perceive non-self molecules. PRRs are predominantly receptor serine/threonine (Ser/Thr) kinases that are evolutionarily related to animal interleukin-1 receptor-associated kinase (IRAK)/Pelle-soluble kinases. However, how the activity of these receptor kinases is modulated remains poorly understood. We report that the Arabidopsis PRR chitin elicitor receptor kinase 1 (CERK1) is autophosphorylated in unstimulated cells at tyrosine428 (Tyr428), a modification that is required for CERK1 activation upon binding to the fungal cell wall component chitin. Upon chitin activation, CERK1 recruits the CERK1-interacting protein phosphatase 1 (CIPP1), a predicted Ser/Thr phosphatase, to dephosphorylate Tyr428 and dampen CERK1 signaling. CIPP1 subsequently dissociates from Tyr428-dephosphorylated CERK1, allowing CERK1 to regain Tyr428 autophosphorylation and return to a standby state. This work sheds light onto plant chitin signaling and shows that a receptor kinase and phosphatase can coordinately regulate signal transduction of a receptor kinase through a phosphorylation cycle.

Interleukin (IL)-23 Stimulates IFN-γ Secretion by CD56bright Natural Killer Cells and Enhances IL-18-Driven Dendritic Cells Activation.

Interleukin (IL)-23 is a member of the IL-12 family of cytokines that, as the other members of this family, is secreted by monocytes, macrophages, and dendritic cells (DC) upon recognition of bacterial, viral, and fungal components. IL-23 is critical during immunity against acute infections, and it is also involved in the development of autoimmune diseases. Although immunoregulatory effects of IL-23 on mouse natural killer (NK) cells have been described, the effect of IL-23 on human NK cells remains ill-defined. In this study, we observed that monocytes stimulated with LPS secreted IL-23 and that blockade of this cytokine during monocyte and NK cell coculture led to a diminished production of IFN-γ by NK cells. Accordingly, rIL-23-induced NK cell activation and stimulated IFN-γ production by CD56bright NK cells. This effect involved MEK1/MEK2, JNK, PI3K, mammalian target of rapamycin, and NF-κB, but not STAT-1, STAT-3, nor p38 MAPK pathways. Moreover, while NK cell-mediated cytotoxicity remained unaltered, antibody-dependent cellular cytotoxicity (ADCC) was enhanced after IL-23 stimulation. In addition, IL-23 displayed a synergistic effect with IL-18 for IFN-γ production by both CD56bright and CD56dim NK cells, and this effect was due to a priming effect of IL-23 for IL-18 responsiveness. Furthermore, NK cells pre-stimulated with IL-18 promoted an increase in CD86 expression and IL-12 secretion by DC treated with LPS, and IL-23 potentiated these effects. Moreover, IL-23-driven enhancement of NK cell “helper” function was dependent on NK cell-derived IFN-γ. Therefore, our results suggest that IL-23 may trigger NK cell-mediated “helper” effects on adaptive immunity, shaping T cell responses during different pathological situations through the regulation of DC maturation.