Innate antifungal immunity: the key role of phagocytes

Recent developments in Aspergillus fumigatus research: diversity, drugs, and disease

SUMMARYAdvances in modern medical therapies for many previously intractable human diseases have improved patient outcomes. However, successful disease treatment outcomes are often prevented due to invasive fungal infections caused by the environmental mold Aspergillus fumigatus. As contemporary antifungal therapies have not experienced the same robust advances as other medical therapies, defining mechanisms of A. fumigatus disease initiation and progression remains a critical research priority. To this end, the World Health Organization recently identified A. fumigatus as a research priority human fungal pathogen and the Centers for Disease Control has highlighted the emergence of triazole-resistant A. fumigatus isolates. The expansion in the diversity of host populations susceptible to aspergillosis and the complex and dynamic A. fumigatus genotypic and phenotypic diversity call for a reinvigorated assessment of aspergillosis pathobiological and drug-susceptibility mechanisms. Here, we summarize recent advancements in the field and discuss challenges in our understanding of A. fumigatus heterogeneity and its pathogenesis in diverse host populations.

Cadmium-induced augmentation of fungal translocation promotes systemic infection in mice via gut barrier disruption and immune dysfunction

Cadmium (Cd) disrupts the immune system and intestinal barrier, increasing infection risk and gut dysbiosis. Its impact on intestinal fungi, particularly the opportunistic pathogen Candida albicans, which can cause systemic infections in immunocompromised patients, is not well understood. Our study revealed that C. albicans exhibited high tolerance and maintained its morphogenetic switching in response to Cd. As C. albicans is not naturally found in the mouse gut, we attempted intestinal colonization of C. albicans-SC5314 strain using standard procedures. However, the intestinal fungal load decreased and was undetectable by 15th day. To assess the effects of sub-chronic Cd exposure, both oral and intravenous methods were used. Oral exposure to C. albicans (105 CFU/ml) resulted in a 10-fold increase in intestinal translocation in Cd-exposed mice (0.98 mg/kg) compared to controls. Cd exposure also downregulated intestinal tight junction proteins and increased FITC-dextran permeability, indicating that Cd disrupts the intestinal barrier and facilitates C. albicans translocation. Moreover, Cd-exposed mice showed significant morbidity and higher fungal loads in organs after intravenous non-lethal dose of C. albicans, along with a subdued cytokine response. These findings highlight the significant impact of Cd on fungal pathogenicity and immune response, pointing to the broader health risks of Cd exposure.

Pichia pastoris-Derived β-Glucan Capsules as a Delivery System for DNA Vaccines

BACKGROUND/OBJECTIVES

DNA vaccines are rapidly produced and adaptable to different pathogens, but they face considerable challenges regarding stability and delivery to the cellular target. Thus, effective delivery methods are essential for the success of these vaccines. Here, we evaluated the efficacy of capsules derived from the cell wall of the yeast Pichia pastoris as a delivery system for DNA vaccines.

METHODS

The capsules were extracted from the yeast Pichia pastoris strain GS115, previously grown in a YPD medium. pVAX1 expression vector was adopted to evaluate the DNA vaccine insertion and delivery. Three encapsulation protocols were tested to identify the most effective in internalizing the plasmid. The presence of plasmids inside the capsules was confirmed by fluorescence microscopy, and the encapsulation efficiency was calculated by the difference between the initial concentration of DNA used for insertion and the concentration of unencapsulated DNA contained in the supernatant. The capsules were subjected to different temperatures to evaluate their thermostability and were co-cultured with macrophages for phagocytosis analysis. HEK-293T cells were adopted to assess the cytotoxicity levels by MTT assay.

RESULTS

The microscopy results indicated that the macrophages successfully phagocytosed the capsules. Among the protocols tested for encapsulation, the one with 2% polyethylenimine for internalization showed the highest efficiency, with an encapsulation rate above 80%. However, the vaccine capsules obtained with the protocol that used 5% NaCl showed better thermal stability and encapsulation efficiency above 63% without induction of cell viability loss in HEK 293T.

CONCLUSIONS

We successfully described a vaccine delivery system using yeast capsules derived from Pichia pastoris, demonstrating its potential for DNA vaccine delivery for the first time. Additional studies will be needed to characterize and improve this delivery strategy.

H3K4 Methylation and Demethylation in Fungal Pathogens: The Epigenetic Toolbox for Survival and Adaptation in the Host

Pathogenic fungi represent a diverse group of eukaryotic microorganisms that significantly impact human health and agriculture. In recent years, the role of epigenetic modifications, particularly histone modifications, in fungal pathobiology has emerged as a prominent area of interest. Among these modifications, methylation of histone H3 at lysine-4 (H3K4) has garnered considerable attention for its implications in regulating gene expression associated with diverse cellular processes. A body of literature has uncovered the pivotal roles of H3K4 methylation in multiple biological processes crucial for pathogenic adaptation in a wide range of fungal pathogens of humans and food crops. This review delves into the recent advancements in understanding the impact of H3K4 methylation/demethylation on fungal pathogenesis. We explore the roles of H3K4 methylation in various cellular processes, including fungal morphogenesis and development, genome stability and DNA repair, metabolic adaptation, cell wall maintenance, biofilm formation, antifungal drug resistance, and virulence. We also discuss the conservation of H3K4 methylation regulators and their potential as therapeutic targets to prevent fungal diseases. Collectively, this review underscores the intricate links between H3K4 methylation, fungal pathogenesis, and potential avenues for novel antifungal strategies.

β-1,6-Glucan plays a central role in the structure and remodeling of the bilaminate fungal cell wall

The cell wall of human fungal pathogens plays critical roles as an architectural scaffold and as a target and modulator of the host immune response. Although the cell wall of the pathogenic yeast Candida albicans is intensively studied, one of the major fibrillar components in its cell wall, β-1,6-glucan, has been largely neglected. Here, we show that β-1,6-glucan is essential for bilayered cell wall organization, cell wall integrity, and filamentous growth. For the first time, we show that β-1,6-glucan production compensates the defect in mannan elongation in the outer layer of the cell wall. In addition, β-1,6-glucan dynamics are also coordinated by host environmental stimuli and stresses with wall remodeling, where the regulation of β-1,6-glucan structure and chain length is a crucial process. As we point out that β-1,6-glucan is exposed at the yeast surface and modulate immune response, β-1,6-glucan must be considered a key factor in host-pathogen interactions.

Functional characterization of macrophages and change of Th1/Th2 balance in patients with pythiosis after Pythium insidiosum antigen immunotherapy

There has been limited research into the role of the Pythium insidiosum antigen (PIA) in modulating immune response in patients with pythiosis. This study investigated the balance of T helper type 2 (Th2) and T helper type 1 (Th1) responses after receiving PIA immunotherapy in patients with pythiosis. Next, the phagocytic activity and phagocytic index of IFN-γ primed PIA-treated macrophages were examined. Furthermore, the phagocytosis of infective P. insidiosum zoospores by macrophages was investigated. This work showed that the PIA vaccine induced Th1 response and M1 macrophages in patients with vascular pythiosis who survived and those with localized pythiosis. Phagocytic activity and phagocytic index were increased considerably in localized pythiosis patients compared to vascular pythiosis patients with hematological diseases. IFN-γ priming of PIA-treated macrophages against P. insidiosum zoospores enhanced the phagocytic activity and phagocytic index in vascular and localized pythiosis patients. Macrophages engulfed P. insidiosum zoospores, but the zoospores continued germination, resulting in macrophage death. Overall, our results suggest that PIA can modulate the immune responses, contributing to higher levels of Th1-type cytokine and potentially improving the survival of patients with vascular pythiosis. This study is the first to uncover that P. insidiosum zoospores can survive within macrophages.

Trim72 is a major host factor protecting against lethal Candida albicans infection

Candida albicans is the most common aetiologic pathogen of fungal infections associated with high mortality in immunocompromised patients. There is an urgent need to develop new antifungal therapies owing to the poor efficacy and resistance of current antifungals. Here, we report that Trim72 positively regulates antifungal immunity during lethal fungal infection. Trim72 levels are significantly increased after Candida albicans infection. In vivo, Trim72 knockout significantly increases mortality, organ fungal burden and kidney damage in mice after lethal Candida albicans infection. Whereas recombinant Trim72 protein treatment protects mice against invasive candidiasis. Mechanistically, Trim72 facilitates macrophage infiltration and CCL2 production, which mediates Trim72-elicited protection against lethal Candida albicans infection. Furthermore, Trim72 may enhance macrophage migration and CCL2 production via NF-κB and ERK1/2 signaling. Inhibition of NF-κB and ERK1/2 signaling abrogates Trim72-mediated protection against lethal Candida albicans infection. Therefore, these data imply that Trim72 may be developed as a host-directed therapy for treating severe systemic candidiasis.

BLNK negatively regulates innate antifungal immunity through inhibiting c-Cbl-mediated macrophage migration

B cell linker protein (BLNK) is crucial for orchestrating B cell receptor-associated spleen tyrosine kinase (Syk) signaling. However, the role of BLNK in Syk-coupled C-type lectin receptor (CLR) signaling in macrophages remains unclear. Here, we delineate that CLRs govern the Syk-mediated activation of BLNK, thereby impeding macrophage migration by disrupting podosome ring formation upon stimulation with fungal β-glucans or α-mannans. Mechanistically, BLNK instigates its association with casitas B-lineage lymphoma (c-Cbl), competitively impeding the interaction between c-Cbl and Src-family kinase Fyn. This interference disrupts Fyn-mediated phosphorylation of c-Cbl and subsequent c-Cbl-associated F-actin assembly. Consequently, BLNK deficiency intensifies CLR-mediated recruitment of the c-Cbl/phosphatidylinositol 3-kinase complex to the F-actin cytoskeleton, thereby enhancing macrophage migration. Notably, mice with monocyte-specific BLNK deficiency exhibit heightened resistance to infection with Candida albicans, a prominent human fungal pathogen. This resistance is attributed to the increased infiltration of Ly6C+ macrophages into renal tissue. These findings unveil a previously unrecognized role of BLNK for the negative regulation of macrophage migration through inhibiting CLR-mediated podosome ring formation during fungal infections.

Temporal transcriptional response of Candida glabrata during macrophage infection reveals a multifaceted transcriptional regulator CgXbp1 important for macrophage response and fluconazole resistance

Candida glabrata can thrive inside macrophages and tolerate high levels of azole antifungals. These innate abilities render infections by this human pathogen a clinical challenge. How C. glabrata reacts inside macrophages and what is the molecular basis of its drug tolerance are not well understood. Here, we mapped genome-wide RNA polymerase II (RNAPII) occupancy in C. glabrata to delineate its transcriptional responses during macrophage infection in high temporal resolution. RNAPII profiles revealed dynamic C. glabrata responses to macrophages with genes of specialized pathways activated chronologically at different times of infection. We identified an uncharacterized transcription factor (CgXbp1) important for the chronological macrophage response, survival in macrophages, and virulence. Genome-wide mapping of CgXbp1 direct targets further revealed its multi-faceted functions, regulating not only virulence-related genes but also genes associated with drug resistance. Finally, we showed that CgXbp1 indeed also affects fluconazole resistance. Overall, this work presents a powerful approach for examining host-pathogen interaction and uncovers a novel transcription factor important for C. glabrata's survival in macrophages and drug tolerance.

Understanding the clinical and environmental drivers of antifungal resistance in the One Health context

Antifungal drugs have had a tremendous impact on human health and the yields of crops. However, in recent years, due to usage both in a health setting and in agriculture, there has been a rapid emergence of antifungal drug resistance that has outpaced novel compound discovery. It is now globally recognized that new strategies to tackle fungal infection are urgently needed, with such approaches requiring the cooperation of both sectors and the development of robust antifungal stewardship rationales. In this review, we examine the current antifungal regimes in clinical and agricultural settings, focusing on two pathogens of importance, Candida auris and Aspergillus fumigatus, examining their drivers of antifungal resistance, the impact of dual-use azoles and the impact agricultural practices have on driving the emergence of resistance. Finally, we postulate that a One Health approach could offer a viable alternative to prolonging the efficacy of current antifungal agents.

Immunogenicity and efficacy of CNA25 as a potential whole-cell vaccine against systemic candidiasis

Disseminated fungal infections account for ~1.5 million deaths per year worldwide, and mortality may increase further due to a rise in the number of immunocompromised individuals and drug-resistance fungal species. Since an approved antifungal vaccine is yet to be available, this study explored the immunogenicity and vaccine efficacy of a DNA polymerase mutant strain of Candida albicans. CNA25 is a pol32ΔΔ strain that exhibits growth defects and does not cause systemic candidiasis in mice. Immunized mice with live CNA25 were fully protected against C. albicans and C. parapsilosis but partially against C. tropicalis and C. glabrata infections. CNA25 induced steady expression of TLR2 and Dectin-1 receptors leading to a faster recognition and clearance by the immune system associated with the activation of protective immune responses mostly mediated by neutrophils, macrophages, NK cells, B cells, and CD4+ and CD8+ T cells. Molecular blockade of Dectin-1, IL-17, IFNγ, and TNFα abolished resistance to reinfection. Altogether, this study suggested that CNA25 collectively activates innate, adaptive, and trained immunity to be a promising live whole-cell vaccine against systemic candidiasis.

Impact of secreted glucanases upon the cell surface and fitness of Candida albicans during colonisation and infection

Host recognition of the pathogen-associated molecular pattern (PAMP), β-1,3-glucan, plays a major role in antifungal immunity. β-1,3-glucan is an essential component of the inner cell wall of the opportunistic pathogen Candida albicans. Most β-1,3-glucan is shielded by the outer cell wall layer of mannan fibrils, but some can become exposed at the cell surface. In response to host signals such as lactate, C. albicans shaves the exposed β-1,3-glucan from its cell surface, thereby reducing the ability of innate immune cells to recognise and kill the fungus. We have used sets of barcoded xog1 and eng1 mutants to compare the impacts of the secreted β-glucanases Xog1 and Eng1 upon C. albicans in vitro and in vivo. Flow cytometry of Fc-dectin-1-stained strains revealed that Eng1 plays the greater role in lactate-induced β-1,3-glucan masking. Transmission electron microscopy and stress assays showed that neither Eng1 nor Xog1 are essential for cell wall maintenance, but the inactivation of either enzyme compromised fungal adhesion to gut and vaginal epithelial cells. Competitive barcode sequencing suggested that neither Eng1 nor Xog1 strongly influence C. albicans fitness during systemic infection or vaginal colonisation in mice. However, the deletion of XOG1 enhanced C. albicans fitness during gut colonisation. We conclude that both Eng1 and Xog1 exert subtle effects on the C. albicans cell surface that influence fungal adhesion to host cells and that affect fungal colonisation in certain host niches.

The yeast-human coevolution: Fungal transition from passengers, colonizers, and invaders

Fungi are the cause of more than a billion infections in humans every year, although their interactions with the host are still neglected compared to bacteria. Major systemic fungal infections are very unusual in the healthy population, due to the long history of coevolution with the human host. Humans are routinely exposed to environmental fungi and can host a commensal mycobiota, which is increasingly considered as a key player in health and disease. Here, we review the current knowledge on host-fungi coevolution and the factors that regulate their interaction. On one hand, fungi have learned to survive and inhabit the host organisms as a natural ecosystem, on the other hand, the host immune system finely tunes the response toward fungi. In turn, recognition of fungi as commensals or pathogens regulates the host immune balance in health and disease. In the human gut ecosystem, yeasts provide a fingerprint of the transient microbiota. Their status as passengers or colonizers is related to the integrity of the gut barrier and the risk of multiple disorders. Thus, the study of this less known component of the microbiota could unravel the rules of the transition from passengers to colonizers and invaders, as well as their dependence on the innate component of the host's immune response. This article is categorized under: Infectious Diseases > Environmental Factors Immune System Diseases > Environmental Factors Infectious Diseases > Molecular and Cellular Physiology.

β-Glucan fragmentation by microfluidization and TNF-α-immunostimulating activity of fragmented β-glucans

Fragmentation of β-glucans secreted by the fungus Ophiocordyceps dipterigena BCC 2073 achieved by microfluidization was investigated. The degree of β-glucan fragmentation was evaluated based on the average number of chain scissions (α). The effects on the α value of experimental variables like solid concentration of the β-glucan suspension, interaction chamber pressure, and number of passes through the microfluidizer were examined. Kinetic studies were conducted using the relationships of the α and suspension viscosity values with the number of passes. Evidence indicated that α increases with the interaction chamber pressure and the number of passes, whereas the solid concentration shows the inverted effect. Kinetic data indicated that the fragmentation rate increases with β-glucan solid concentration and interaction chamber pressure. Furthermore, since β-glucan molecular weight is a key factor determining its biological activity, the effect of β-glucans of different molecular weights produced by fragmentation on tumor necrosis factor (TNF)-α-stimulating activity in THP-1 human macrophage cells was investigated. Evidence suggested that β-glucans have an immunostimulating effect on macrophage function, in the absence of cytotoxic effects. Indeed, β-glucans characterized by a range of molecular weights produced via microfluidization exhibited promise as immunostimulatory agents.

Proteome and Dihydrorhodamine Profiling of Bronchoalveolar Lavage in Patients with Chronic Pulmonary Aspergillosis

Neutrophil and (alveolar) macrophage immunity is considered crucial for eliminating Aspergillus fumigatus. Data derived from bronchoalveloar lavage (BAL) characterizing the human immuno-pulmonary response to Aspergillus fumigatus are non-existent. To obtain a comprehensive picture of the immune pathways involved in chronic pulmonary aspergillosis (CPA), we performed proteome analysis on AL of 9 CPA patients and 17 patients with interstitial lung disease (ILD). The dihydrorhodamine (DHR) test was also performed on BAL and blood neutrophils from CPA patients and compared to blood neutrophils from healthy controls (HCs). BAL from CPA patients primarily contained neutrophils, while ILD BAL was also characterized by a large fraction of lymphocytes; these differences likely reflecting the different immunological etiologies underlying the two disorders. BAL and blood neutrophils from CPA patients displayed the same oxidative burst capacity as HC blood neutrophils. Hence, immune evasion by Aspergillus involves other mechanisms than impaired neutrophil oxidative burst capacity per se. CPA BAL was enriched by proteins associated with innate immunity, as well as, more specifically, with neutrophil degranulation, Toll-like receptor 4 signaling, and neutrophil-mediated iron chelation. Our data provide the first comprehensive target organ-derived immune data on the human pulmonary immune response to Aspergillus fumigatus.

Interplay of Cytokines and Chemokines in Aspergillosis

Aspergillosis is a fungal infection caused by various species of Aspergillus, most notably A. fumigatus. This fungus causes a spectrum of diseases, including allergic bronchopulmonary aspergillosis, aspergilloma, chronic pulmonary aspergillosis, and invasive aspergillosis. The clinical manifestations and severity of aspergillosis can vary depending on individual immune status and the specific species of Aspergillus involved. The recognition of Aspergillus involves pathogen-associated molecular patterns (PAMPs) such as glucan, galactomannan, mannose, and conidial surface proteins. These are recognized by the pathogen recognition receptors present on immune cells such as Toll-like receptors (TLR-1,2,3,4, etc.) and C-type lectins (Dectin-1 and Dectin-2). We discuss the roles of cytokines and pathogen recognition in aspergillosis from both the perspective of human and experimental infection. Several cytokines and chemokines have been implicated in the immune response to Aspergillus infection, including interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α), CCR4, CCR17, and other interleukins. For example, allergic bronchopulmonary aspergillosis (ABPA) is characterized by Th2 and Th9 cell-type immunity and involves interleukin (IL)-4, IL-5, IL-13, and IL-10. In contrast, it has been observed that invasive aspergillosis involves Th1 and Th17 cell-type immunity via IFN-γ, IL-1, IL-6, and IL-17. These cytokines activate various immune cells and stimulate the production of other immune molecules, such as antimicrobial peptides and reactive oxygen species, which aid in the clearance of the fungal pathogen. Moreover, they help to initiate and coordinate the immune response, recruit immune cells to the site of infection, and promote clearance of the fungus. Insight into the host response from both human and animal studies may aid in understanding the immune response in aspergillosis, possibly leading to harnessing the power of cytokines or cytokine (receptor) antagonists and transforming them into precise immunotherapeutic strategies. This could advance personalized medicine.

Contribution to the study of inflammasome and programmed cell death in paracoccidioidomycosis oral lesions

BACKGROUND

Paracoccidioidomycosis is the most prevalent systemic mycosis in Latin America, with a high incidence in Brazil, Colombia and Venezuela, and constitutes a serious public health problem, a frequent cause of morbidity and disability for work. Some mechanisms of cell death are described as important tools in infectious processes. When apoptosis is blocked, RIPK (Receptor-interacting protein kinase) 3 dependent, a caspase-independent form of cell death, can limit the replication and spread of pathogens. Some molecules that mediate necroptosis include RIPK3 and have been extensively studied due to their signalling mechanism and pathological function. RIPK3 activates NLRP1 and NLRP3-mediated inflammasome formation. Caspase-1 has an important role in processing the cytokines ILβ and IL18 to their active form. Such molecules are part of the inflammasome characterization, whose caspase-1-dependent activation promotes the death of pyroptotic cells and the secretion of proinflammatory cytokines. Knowledge about the mechanisms of pathogen-mediated cell death can be useful for understanding of the pathogenesis of infections and inflammatory conditions.

OBJECTIVE

The objective of this work was to identify the mechanisms of programmed cell death and inflammasome components in human oral mucosal lesions of paracoccidioidomycosis through immunohistochemical methods and identification of RIPK-3, IL1β, IL18, NLRP-1 and caspase-1. Thirty specimens were included, and a histopathological analysis of the lesions was performed using haematoxylin-eosin staining.

RESULTS

Our results on in situ expression of inflammasome elements and programmed cell death showed increased expression of IL-1β, NLRP-1, caspase-1 and RIPK-3. We suggest that inflammasome complex participate in the immunopathogenesis in paracoccidioidomycosis oral lesions in an interplay with RIPK3.

Glutathione is required for growth and cadmium tolerance in the amphibian chytrid fungus, Batrachochytrium dendrobatidis

Batrachochytrium dendrobatidis (Bd) is a lethal amphibian pathogen, partly due to its ability to evade the immune system of susceptible frog species. In many pathogenic fungi, the antioxidant glutathione is a virulence factor that helps neutralise oxidative stressors generated from host immune cells, as well as other environmental stressors such as heavy metals. The role of glutathione in stress tolerance in Bd has not been investigated. Here, we examine the changes in the glutathione pool after stress exposure and quantify the effect of glutathione depletion on cell growth and stress tolerance. Depletion of glutathione repressed growth and release of zoospores, suggesting that glutathione is essential for life cycle completion in Bd. Supplementation with <2 mM exogenous glutathione accelerated zoospore development, but concentrations >2 mM were strongly inhibitory to Bd cells. While hydrogen peroxide exposure lowered the total cellular glutathione levels by 42 %, glutathione depletion did not increase the sensitivity to hydrogen peroxide. Exposure to cadmium increased total cellular glutathione levels by 93 %. Glutathione-depleted cells were more sensitive to cadmium, and this effect was attenuated by glutathione supplementation, suggesting that glutathione plays an important role in cadmium tolerance. The effects of heat and salt were exacerbated by the addition of exogenous glutathione. The impact of glutathione levels on Bd stress sensitivity may help explain differences in host susceptibility to chytridiomycosis and may provide opportunities for synergistic therapeutics.

Genetic Susceptibility to Fungal Infections

Reports of fungal infections have increased over the past decades, making them a major threat to human health. In this study, we review the effects of genetic defects on susceptibility to fungal diseases. To identify all relevant literature, we searched Google Scholar, PubMed, and Scopus and profiled studies published between 2008 and 2021. The results of several studies conducted on this subject have shown the significant effects of genetic variations such as hyper-IgE syndrome, Autoimmune polyendocrinopathy candidiasis ectodermal dystrophy syndrome, dectin-1 deficiency, CARD9 mutations, STAT1 mutations, and IL17 mutationson the host immune system's response, which has an important impact on susceptibility to fungal infections. The underlying immune system-related genetic profile affects the susceptibility of individuals to different fungal infections; therefore, this subject should be further studied for better treatment of fungal diseases.

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

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

Targeting tumor-associated macrophage: an adjuvant strategy for lung cancer therapy

The emergence of immunotherapy has revolutionized the treatment landscape for various types of cancer. Nevertheless, lung cancer remains one of the leading causes of cancer-related mortality worldwide due to the development of resistance in most patients. As one of the most abundant groups of immune cells in the tumor microenvironment (TME), tumor-associated macrophages (TAMs) play crucial and complex roles in the development of lung cancer, including the regulation of immunosuppressive TME remodeling, metabolic reprogramming, neoangiogenesis, metastasis, and promotion of tumoral neurogenesis. Hence, relevant strategies for lung cancer therapy, such as inhibition of macrophage recruitment, TAM reprograming, depletion of TAMs, and engineering of TAMs for drug delivery, have been developed. Based on the satisfactory treatment effect of TAM-targeted therapy, recent studies also investigated its synergistic effect with current therapies for lung cancer, including immunotherapy, radiotherapy, chemotherapy, anti-epidermal growth factor receptor (anti-EGFR) treatment, or photodynamic therapy. Thus, in this article, we summarized the key mechanisms of TAMs contributing to lung cancer progression and elaborated on the novel therapeutic strategies against TAMs. We also discussed the therapeutic potential of TAM targeting as adjuvant therapy in the current treatment of lung cancer, particularly highlighting the TAM-centered strategies for improving the efficacy of anti-programmed cell death-1/programmed cell death-ligand 1 (anti-PD-1/PD-L1) treatment.

Retrovirus-Derived RTL9 Plays an Important Role in Innate Antifungal Immunity in the Eutherian Brain

Retrotransposon Gag-like (RTL) genes play a variety of essential and important roles in the eutherian placenta and brain. It has recently been demonstrated that RTL5 and RTL6 (also known as sushi-ichi retrotransposon homolog 8 (SIRH8) and SIRH3) are microglial genes that play important roles in the brain's innate immunity against viruses and bacteria through their removal of double-stranded RNA and lipopolysaccharide, respectively. In this work, we addressed the function of RTL9 (also known as SIRH10). Using knock-in mice that produce RTL9-mCherry fusion protein, we examined RTL9 expression in the brain and its reaction to fungal zymosan. Here, we demonstrate that RTL9 plays an important role, degrading zymosan in the brain. The RTL9 protein is localized in the microglial lysosomes where incorporated zymosan is digested. Furthermore, in Rtl9 knockout mice expressing RTL9ΔC protein lacking the C-terminus retroviral GAG-like region, the zymosan degrading activity was lost. Thus, RTL9 is essentially engaged in this reaction, presumably via its GAG-like region. Together with our previous study, this result highlights the importance of three retrovirus-derived microglial RTL genes as eutherian-specific constituents of the current brain innate immune system: RTL9, RTL5 and RTL6, responding to fungi, viruses and bacteria, respectively.

Humoral Immunity Against Aspergillus fumigatus

Aspergillus fumigatus is one the most ubiquitous airborne opportunistic human fungal pathogens. Understanding its interaction with host immune system, composed of cellular and humoral arm, is essential to explain the pathobiology of aspergillosis disease spectrum. While cellular immunity has been well studied, humoral immunity has been poorly acknowledge, although it plays a crucial role in bridging the fungus and immune cells. In this review, we have summarized available data on major players of humoral immunity against A. fumigatus and discussed how they may help to identify at-risk individuals, be used as diagnostic tools or promote alternative therapeutic strategies. Remaining challenges are highlighted and leads are given to guide future research to better grasp the complexity of humoral immune interaction with A. fumigatus.

Targeted removal of macrophage-secreted interleukin-1 receptor antagonist protects against lethal Candida albicans sepsis

Invasive fungal infections are associated with high mortality rates, and the lack of efficient treatment options emphasizes an urgency to identify underlying disease mechanisms. We report that disseminated Candida albicans infection is facilitated by interleukin-1 receptor antagonist (IL-1Ra) secreted from macrophages in two temporally and spatially distinct waves. Splenic CD169+ macrophages release IL-1Ra into the bloodstream, impeding early neutrophil recruitment. IL-1Ra secreted by monocyte-derived tissue macrophages further impairs pathogen containment. Therapeutic IL-1Ra neutralization restored the functional competence of neutrophils, corrected maladapted hyper-inflammation, and eradicated the otherwise lethal infection. Conversely, augmentation of macrophage-secreted IL-1Ra by type I interferon severely aggravated disease mortality. Our study uncovers how a fundamental immunoregulatory mechanism mediates the high disease susceptibility to invasive candidiasis. Furthermore, interferon-stimulated IL-1Ra secretion may exacerbate fungal dissemination in human patients with secondary candidemia. Macrophage-secreted IL-1Ra should be considered as an additional biomarker and potential therapeutic target in severe systemic candidiasis.

RNA Vaccines: Yeast as a Novel Antigen Vehicle

In the last decades, technological advances for RNA manipulation enabled and expanded its application in vaccine development. This approach comprises synthetic single-stranded mRNA molecules that direct the translation of the antigen responsible for activating the desired immune response. The success of RNA vaccines depends on the delivery vehicle. Among the systems, yeasts emerge as a new approach, already employed to deliver protein antigens, with efficacy demonstrated through preclinical and clinical trials. β-glucans and mannans in their walls are responsible for the adjuvant property of this system. Yeast β-glucan capsules, microparticles, and nanoparticles can modulate immune responses and have a high capacity to carry nucleic acids, with bioavailability upon oral immunization and targeting to receptors present in antigen-presenting cells (APCs). In addition, yeasts are suitable vehicles for the protection and specific delivery of therapeutic vaccines based on RNAi. Compared to protein antigens, the use of yeast for DNA or RNA vaccine delivery is less established and has fewer studies, most of them in the preclinical phase. Here, we present an overview of the attributes of yeast or its derivatives for the delivery of RNA-based vaccines, discussing the current challenges and prospects of this promising strategy.

Mass Spectrometry Analysis Reveals Lipids Induced by Oxidative Stress in Candida albicans Extracellular Vesicles

Candida albicans is a commensal fungus in healthy humans that causes infection in immunocompromised individuals through the secretion of several virulence factors. The successful establishment of infection is owing to elaborate strategies to cope with defensive molecules secreted by the host, including responses toward oxidative stress. Extracellular vesicle (EV) release is considered an alternative to the biomolecule secretory mechanism that favors fungal interactions with the host cells. During candidiasis establishment, the host environment becomes oxidative, and it impacts EV release and cargo. To simulate the host oxidative environment, we added menadione (an oxidative stress inducer) to the culture medium, and we explored C. albicans EV metabolites by metabolomics analysis. This study characterized lipidic molecules transported to an extracellular milieu by C. albicans after menadione exposure. Through Liquid Chromatography coupled with Mass Spectrometry (LC-MS) analyses, we identified biomolecules transported by EVs and supernatant. The identified molecules are related to several biological processes, such as glycerophospholipid and sphingolipid pathways, which may act at different levels by tuning compound production in accordance with cell requirements that favor a myriad of adaptive responses. Taken together, our results provide new insights into the role of EVs in fungal biology and host-pathogen interactions.

C5a-licensed phagocytes drive sterilizing immunity during systemic fungal infection

Systemic candidiasis is a common, high-mortality, nosocomial fungal infection. Unexpectedly, it has emerged as a complication of anti-complement C5-targeted monoclonal antibody treatment, indicating a critical niche for C5 in antifungal immunity. We identified transcription of complement system genes as the top biological pathway induced in candidemic patients and as predictive of candidemia. Mechanistically, C5a-C5aR1 promoted fungal clearance and host survival in a mouse model of systemic candidiasis by stimulating phagocyte effector function and ERK- and AKT-dependent survival in infected tissues. C5ar1 ablation rewired macrophage metabolism downstream of mTOR, promoting their apoptosis and enhancing mortality through kidney injury. Besides hepatocyte-derived C5, local C5 produced intrinsically by phagocytes provided a key substrate for antifungal protection. Lower serum C5a concentrations or a C5 polymorphism that decreases leukocyte C5 expression correlated independently with poor patient outcomes. Thus, local, phagocyte-derived C5 production licenses phagocyte antimicrobial function and confers innate protection during systemic fungal infection.

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

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

Candida albicans Hyphal Morphogenesis within Macrophages Does Not Require Carbon Dioxide or pH-Sensing Pathways

The opportunistic fungal pathogen Candida albicans has evolved a variety of mechanisms for surviving inside and escaping macrophages, including the initiation of filamentous growth. Although several distinct models have been proposed to explain this process at the molecular level, the signals driving hyphal morphogenesis in this context have yet to be clarified. Here, we evaluate the following three molecular signals as potential hyphal inducers within macrophage phagosomes: CO2, intracellular pH, and extracellular pH. Additionally, we revisit previous work suggesting that the intracellular pH of C. albicans fluctuates in tandem with morphological changes in vitro. Using time-lapse microscopy, we observed that C. albicans mutants lacking components of the CO2-sensing pathway were able to undergo hyphal morphogenesis within macrophages. Similarly, a rim101Δ strain was competent in hyphal induction, suggesting that neutral/alkaline pH sensing is not necessary for the initiation of morphogenesis within phagosomes either. Contrary to previous findings, single-cell pH-tracking experiments revealed that the cytosolic pH of C. albicans remains tightly regulated both within macrophage phagosomes and under a variety of in vitro conditions throughout the process of morphogenesis. This finding suggests that intracellular pH is not a signal contributing to morphological changes.

Exploiting antifungal immunity in the clinical context

The continuous expansion of immunocompromised patient populations at-risk for developing life-threatening opportunistic fungal infections in recent decades has helped develop a deeper understanding of antifungal host defenses, which has provided the foundation for eventually devising immune-based targeted interventions in the clinic. This review outlines how genetic variation in certain immune pathway-related genes may contribute to the observed clinical variability in the risk of acquisition and/or severity of fungal infections and how immunogenetic-based patient stratification may enable the eventual development of personalized strategies for antifungal prophylaxis and/or vaccination. Moreover, this review synthesizes the emerging cytokine-based, cell-based, and other immunotherapeutic strategies that have shown promise as adjunctive therapies for boosting or modulating tissue-specific antifungal immune responses in the context of opportunistic fungal infections.

Candidalysin amplifies the immune inflammatory response in Candida albicans keratitis through the TREM-1/DAP12 pathway

Candidalysin is a fungal peptide toxin secreted by Candida albicans hyphae during invasion into epithelial cells. In Candida albicans-infected mucosa, candidalysin causes epithelial cell damage and activates downstream inflammatory responses, especially the release of inflammatory cytokines. However, the role of candidalysin in Candida albicans corneal keratitis remains unexplored. Moreover, it remains unclear whether candidalysin regulates the inflammatory response through the TREM-1/DAP12 pathway in Candida albicans corneal keratitis. In this study, we determined the expression pattern of TREM-1 in a mouse model of Candida albicans corneal keratitis and investigated the molecular mechanism underlying the inflammatory response regulation by candidalysin. The corneal keratitis model was established in C57BL/6 mice. In the GF9 group, mice were pretreated and then treated with the TREM-1 inhibitor GF9; in the candidalysin group, mice were treated with peptide candidalysin; and in the PD98059 group, mice were pretreated with the ERK inhibitor PD98059. Slit-lamp photography, clinical scoring, PCR, western blotting and immunofluorescence assay were performed to observe disease response and GF9 therapeutic efficacy. Pretreatment with candidalysin or PD98059 was performed before Candida albicans infection. GF9 treatment reduced the expression of TREM-1 and cytokines in the infected mouse cornea, whereas candidalysin treatment increased the expression of TREM-1, p-ERK, and cytokines, and this increase was inhibited by GF9. The candidalysin-induced increment of TREM-1, p-ERK, and cytokines was inhibited by PD98059 pretreatment. These data suggest that candidalysin can initiate inflammatory response in Candida albicans corneal keratitis through the TREM-1/DAP12 pathway and can regulate cytokine expression by enhancing ERK phosphorylation.

C1q Confers Protection Against Cryptococcal Lung Infection by Alleviating Inflammation and Reducing Cryptococcal Virulence

Background

To define the role of C1qa in host defense against Cryptococcus neoformans lung infection, we investigated its susceptibility to cryptococcal lung infection in mice deficient in complement factor C1qa (C1qa^-/- ).

Methods

We established a wild-type (WT) and C1qa-deficient murine inhalation model with C. neoformans. We compared the host survival rate, inflammatory responses, and pathogenicity of C. neoformans during the infection course between WT and C1qa^-/- mice.

Results

The mortality rate of C1qa-deficient mice was significantly higher than that of wild-type mice. The increased formation of Titan cells in the lungs was associated with augmented inflammation in C1qa-deficient mice. The capacity of lung homogenate supernatant from C1qa-deficient mice to induce Titan formation in vitro was greater compared with that of wild-type mice. The C. neoformans isolated from the lungs of infected C1qa-deficient mice was more resistant to macrophage killing in vitro and caused significantly higher mortality after administration to mice compared with that isolated from WT mice.

Conclusions

These findings reveal a novel role of C1qa in host defense against C. neoformans infection by regulating host inflammation and pathogen virulence and provide new insight into the C1q-mediated lung environment underlying the transition from yeast to Titan cell.

Molecular study of feline dermatophytosis and Toll-like receptor 2 and 4 gene expression in their lesions

BACKGROUND

Pattern recognition receptors (PRRs) as the recognition of pathogenic fungal structures induce the secretion of cytokines by immune systems. Toll-like receptors (TLRs) 2 and 4 are the main PRRs that recognize fungal components.

AIM

The present study aimed to assess the presence of dermatophyte species in symptomatic cats in a region of Iran and to investigate the expression of TLR-2 and 4 in cat lesions with dermatophytosis.

METHODS

A total of 105 cats suspected of dermatophytosis with skin lesions were examined. Samples were analysed by direct microscopy using potassium hydroxide (20%) and culture on Mycobiotic agar. Dermatophytes strains were confirmed by the polymerase chain reaction (PCR) amplification and then sequencing of the Internal Transcribed Spacer rDNA region. Also, for pathology and real-time PCR studies, skin biopsies were taken by sterile single-use biopsy punch from active ringworm lesions.

RESULTS

Dermatophytes were found in 41 felines. Based on the sequencing of all strains, Microsporum canis (80.48%, p < 0.05), Microsporum gypseum (17.07%) and Trichophyton mentagrophytes (2.43%) were the dermatophytes isolated from cultures. Cats under 1 year (78.04%) revealed a statistically significantly higher prevalence of infection (p < 0.05). Gene expression by real-time PCR revealed the increased TLR-2 and 4 mRNA levels in skin biopsies of cats with dermatophytosis.

CONCLUSIONS

M. canis is the most prevalent dermatophyte species isolated from feline dermatophytosis lesions. Increased expression of TLR-2 and TLR-4 mRNAs in cat skin biopsies suggests that these receptors are involved in the immune response by recognizing dermatophytosis.

Fungal resilience and host-pathogen interactions: Future perspectives and opportunities

We are constantly exposed to the threat of fungal infection. The outcome-clearance, commensalism or infection-depends largely on the ability of our innate immune defences to clear infecting fungal cells versus the success of the fungus in mounting compensatory adaptive responses. As each seeks to gain advantage during these skirmishes, the interactions between host and fungal pathogen are complex and dynamic. Nevertheless, simply compromising the physiological robustness of fungal pathogens reduces their ability to evade antifungal immunity, their virulence, and their tolerance against antifungal therapy. In this article I argue that this physiological robustness is based on a 'Resilience Network' which mechanistically links and controls fungal growth, metabolism, stress resistance and drug tolerance. The elasticity of this network probably underlies the phenotypic variability of fungal isolates and the heterogeneity of individual cells within clonal populations. Consequently, I suggest that the definition of the fungal Resilience Network represents an important goal for the future which offers the clear potential to reveal drug targets that compromise drug tolerance and synergise with current antifungal therapies.

Cell Wall Mannan of Candida Attenuates Osteogenic Differentiation by Human Dental Pulp Cells

INTRODUCTION

Candida spp. has recently been introduced to interact with conventional carious bacteria, leading to dental caries progression and virulence ability. Evidence regarding the influence of Candida spp. on human dental pulp cell response remains unknown. This study aimed to investigate the effects of Candida albicans mannans on cytotoxicity, cell proliferation, osteogenic differentiation, and inflammatory-related gene expression in human dental pulp cells (hDPCs).

METHODS

hDPCs were treated with cell wall mannans isolated from C. albicans, Candida krusei, Candida glabrata, Candida tropocalis, Candida parapsilosis, and Candida dubliniensis. Cell viability was performed using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide assay. Osteogenic differentiation- and inflammatory-related gene expression were determined using a real-time polymerase chain reaction. Mineralization was examined using alizarin red S staining.

RESULTS

The treatment of mannans isolated from C. albicans, C. krusei, C. glabrata, C. tropocalis, C. parapsilosis, and C. dubliniensis at concentrations ranging from 10-100 μg/mL did not affect cytotoxicity or cell proliferation. Mannans isolated from C. albicans, C. glabrata, and C. tropocalis significantly attenuated mineralization. However, cell wall mannans isolated from C. krusei, C. parapsilosis, and C. dubliniensis did not significantly influence mineral deposition in hDPCs. C. albicans cell wall mannans significantly attenuated osteogenic differentiation-related gene expression (RUNX2, ALP, and ENPP1). Interestingly, IL12 messenger RNA expression was significantly upregulated when treated with C. albicans cell wall mannans. The addition of recombinant IL12 significantly decreased mineralization in hDPCs.

CONCLUSIONS

C. albicans cell wall mannans attenuated osteogenic differentiation in hDPCs and up-regulated inflammatory-related gene IL12 expression.

An artificial intelligence approach to classify pathogenic fungal genera of fungal keratitis using corneal confocal microscopy images

PURPOSE

Fungal keratitis is a common cause of blindness worldwide. Timely identification of the causative fungal genera is essential for clinical management. In vivo confocal microscopy (IVCM) provides useful information on pathogenic genera. This study attempted to apply deep learning (DL) to establish an automated method to identify pathogenic fungal genera using IVCM images.

METHODS

Deep learning networks were trained, validated, and tested using a data set of 3364 IVCM images that collected from 100 eyes of 100 patients with culture-proven filamentous fungal keratitis. Two transfer learning approaches were investigated: one was a combined framework that extracted features by a DL network and adopted decision tree (DT) as a classifier; another was a complete supervised DL model which used DL-based fully connected layers to implement the classification.

RESULTS

The DL classifier model revealed better performance compared with the DT classifier model in an independent testing set. The DL classifier model showed an area under the receiver operating characteristic curves (AUC) of 0.887 with an accuracy of 0.817, sensitivity of 0.791, specificity of 0.831, G-mean of 0.811, and F1 score of 0.749 in identifying Fusarium, and achieved an AUC of 0.827 with an accuracy of 0.757, sensitivity of 0.756, specificity of 0.759, G-mean of 0.757, and F1 score of 0.716 in identifying Aspergillus.

CONCLUSION

The DL model can classify Fusarium and Aspergillus by learning effective features in IVCM images automatically. The automated IVCM image analysis suggests a noninvasive identification of Fusarium and Aspergillus with clear potential application in early diagnosis and management of fungal keratitis.

Designing Functionally Substituted Pyridine-Carbohydrazides for Potent Antibacterial and Devouring Antifungal Effect on Multidrug Resistant (MDR) Strains

The emergence of multidrug-resistant (MDR) pathogens and the gradual depletion of available antibiotics have exacerbated the need for novel antimicrobial agents with minimal toxicity. Herein, we report functionally substituted pyridine carbohydrazide with remarkable antimicrobial effect on multi-drug resistant strains. In the series, compound 6 had potent activity against four MDR strains of Candida spp., with minimum inhibitory concentration (MIC) values being in the range of 16-24 µg/mL and percentage inhibition up to 92.57%, which was exceptional when compared to broad-spectrum antifungal drug fluconazole (MIC = 20 µg/mL, 81.88% inhibition). Substitution of the octyl chain in 6 with a shorter butyl chain resulted in a significant anti-bacterial effect of 4 against Pseudomonas aeruginosa (ATCC 27853), the MIC value being 2-fold superior to the standard combination of ampicillin/cloxacillin. Time-kill kinetics assays were used to discern the efficacy and pharmacodynamics of the potent compounds. Further, hemolysis tests confirmed that both compounds had better safety profiles than the standard drugs. Besides, molecular docking simulations were used to further explore their mode of interaction with target proteins. Overall results suggest that these compounds have the potential to become promising antimicrobial drugs against MDR strains.

Nature of β-1,3-Glucan-Exposing Features on Candida albicans Cell Wall and Their Modulation

Candida albicans exists as a commensal of mucosal surfaces and the gastrointestinal tract without causing pathology. However, this fungus is also a common cause of mucosal and systemic infections when antifungal immune defenses become compromised. The activation of antifungal host defenses depends on the recognition of fungal pathogen-associated molecular patterns (PAMPs), such as β-1,3-glucan. In C. albicans, most β-1,3-glucan is present in the inner cell wall, concealed by the outer mannan layer, but some β-1,3-glucan becomes exposed at the cell surface. In response to host signals, such as lactate, C. albicans induces the Xog1 exoglucanase, which shaves exposed β-1,3-glucan from the cell surface, thereby reducing phagocytic recognition. We show here that β-1,3-glucan is exposed at bud scars and punctate foci on the lateral wall of yeast cells, that this exposed β-1,3-glucan is targeted during phagocytic attack, and that lactate-induced masking reduces β-1,3-glucan exposure at bud scars and at punctate foci. β-1,3-Glucan masking depends upon protein kinase A (PKA) signaling. We reveal that inactivating PKA, or its conserved downstream effectors, Sin3 and Mig1/Mig2, affects the amounts of the Xog1 and Eng1 glucanases in the C. albicans secretome and modulates β-1,3-glucan exposure. Furthermore, perturbing PKA, Sin3, or Mig1/Mig2 attenuates the virulence of lactate-exposed C. albicans cells in Galleria. Taken together, the data are consistent with the idea that β-1,3-glucan masking contributes to Candida pathogenicity. IMPORTANCE Microbes that coexist with humans have evolved ways of avoiding or evading our immunological defenses. These include the masking by these microbes of their "pathogen-associated molecular patterns" (PAMPs), which are recognized as "foreign" and used to activate protective immunity. The commensal fungus Candida albicans masks the proinflammatory PAMP β-1,3-glucan, which is an essential component of its cell wall. Most of this β-1,3-glucan is hidden beneath an outer layer of the cell wall on these microbes, but some can become exposed at the fungal cell surface. Using high-resolution confocal microscopy, we examine the nature of the exposed β-1,3-glucan at C. albicans bud scars and at punctate foci on the lateral cell wall, and we show that these features are targeted by innate immune cells. We also reveal that downstream effectors of protein kinase A (Mig1/Mig2, Sin3) regulate the secretion of major glucanases, modulate the levels of β-1,3-glucan exposure, and influence the virulence of C. albicans in an invertebrate model of systemic infection. Our data support the view that β-1,3-glucan masking contributes to immune evasion and the virulence of a major fungal pathogen of humans.

Mucormycosis in Post Novel Corona Virus Patients: An Institutional Experience

Mucormycosis is an emerging angioinvasive fungal infection caused by ubiquitous saprophytic filamentous fungus that belongs to the class Zygomycosis. Mucormycosis or black fungus infections in patients with recent COVID-19 infections has given rise to a new epidemic during the second wave of this current COVID-19 pandemic in India. Steroid misuse, poor glycemic control, use of industrial grade oxygen, improper humidification and specific variants strains have resulted in profound immunosuppression and are attributed for the high incidence of COVID associated Mucormycosis (CAM) in India. The aims of the present study were to assess the age and gender specific incidence of CAM, the utility of special stains (PAS and GMS) for diagnosing mucormycosis (false negatives and sensitivity). In the present study emphasis was laid on identifying if there exists a correlation between host response, angioinvasion and bone invasion with mortality. The Present study is a retrospective, cross sectional analytical study taken up in the Department of Pathology, Guntur Medical College for a period of 2 months between 1st of May 2021 to 30th of June 2021. Results were tabulated in Microsoft excel 2016 and SPSS software version 14 was used for calculation of odds ratio and for performing multivariate analysis. All samples were routinely fixed using 10% buffered formalin, processed and sectioned. All the sections were stained with Haematoxylin and Eosin and also special stains for fungus like periodic acid Schiff (PAS) and Gomori Methenamine silver (GMS) were used wherever required. CAM is a serious complication after recovery from COVID-19 infection due to its high morbidity and mortality (13.7% in this series). CAM epidemiology and presentation is mostly similar to non-COVID mucormycosis seen in pre-COVID era.

Human Dectin-1 deficiency impairs macrophage-mediated defense against phaeohyphomycosis

Subcutaneous phaeohyphomycosis typically affects immunocompetent individuals following traumatic inoculation. Severe or disseminated infection can occur in CARD9 deficiency or after transplantation, but the mechanisms protecting against phaeohyphomycosis remain unclear. We evaluated a patient with progressive, refractory Corynespora cassiicola phaeohyphomycosis and found that he carried biallelic deleterious mutations in CLEC7A encoding the CARD9-coupled, β-glucan-binding receptor, Dectin-1. The patient's PBMCs failed to produce TNF-α and IL-1β in response to β-glucan and/or C. cassiicola. To confirm the cellular and molecular requirements for immunity against C. cassiicola, we developed a mouse model of this infection. Mouse macrophages required Dectin-1 and CARD9 for IL-1β and TNF-α production, which enhanced fungal killing in an interdependent manner. Deficiency of either Dectin-1 or CARD9 was associated with more severe fungal disease, recapitulating the human observation. Because these data implicated impaired Dectin-1 responses in susceptibility to phaeohyphomycosis, we evaluated 17 additional unrelated patients with severe forms of the infection. We found that 12 out of 17 carried deleterious CLEC7A mutations associated with an altered Dectin-1 extracellular C-terminal domain and impaired Dectin-1-dependent cytokine production. Thus, we show that Dectin-1 and CARD9 promote protective TNF-α- and IL-1β-mediated macrophage defense against C. cassiicola. More broadly, we demonstrate that human Dectin-1 deficiency may contribute to susceptibility to severe phaeohyphomycosis by certain dematiaceous fungi.

Innate Immune Responses to Sporothrix schenckii: Recognition and Elimination

Sporothrix schenckii (S. schenckii), a ubiquitous thermally dimorphic fungus, is the etiological agent of sporotrichosis, affecting immunocompromised and immunocompetent individuals. Despite current antifungal regimens, sporotrichosis results in prolonged treatment and significant mortality rates in the immunosuppressed population. The innate immune system forms the host's first and primary line of defense against S. schenckii, which has a bi-layered cell wall structure. Many components act as pathogen-associated molecular patterns (PAMPs) in pathogen-host interactions. PAMPs are recognized by pattern recognition receptors (PRRs) such as toll-like receptors, C-type lectin receptors, and complement receptors, triggering innate immune cells such as neutrophils, macrophages, and dendritic cells to phagocytize or produce mediators, contributing to S. schenckii elimination. The ultrastructure of S. schenckii and pathogen-host interactions, including PRRs and innate immune cells, are summarized in this review, promoting a better understanding of the innate immune response to S. schenckii and aiding in the development of protective and therapeutic strategies to combat sporotrichosis.

Impact of changes at the Candida albicans cell surface upon immunogenicity and colonisation in the gastrointestinal tract

The immunogenicity of Candida albicans cells is influenced by changes in the exposure of microbe-associated molecular patterns (MAMPs) on the fungal cell surface. Previously, the degree of exposure on the C. albicans cell surface of the immunoinflammatory MAMP β-(1,3)-glucan was shown to correlate inversely with colonisation levels in the gastrointestinal (GI) tract. This is important because life-threatening systemic candidiasis in critically ill patients often arises from translocation of C. albicans strains present in the patient's GI tract. Therefore, using a murine model, we have examined the impact of gut-related factors upon β-glucan exposure and colonisation levels in the GI tract. The degree of β-glucan exposure was examined by imaging flow cytometry of C. albicans cells taken directly from GI compartments, and compared with colonisation levels. Fungal β-glucan exposure was lower in the cecum than the small intestine, and fungal burdens were correspondingly higher in the cecum. This inverse correlation did not hold for the large intestine. The gut fermentation acid, lactate, triggers β-glucan masking in vitro, leading to attenuated anti-Candida immune responses. Additional fermentation acids are present in the GI tract, including acetate, propionate, and butyrate. We show that these acids also influence β-glucan exposure on C. albicans cells in vitro and, like lactate, they influence β-glucan exposure via Gpr1/Gpa2-mediated signalling. Significantly, C. albicans gpr1Δ gpa2Δ cells displayed elevated β-glucan exposure in the large intestine and a corresponding decrease in fungal burden, consistent with the idea that Gpr1/Gpa2-mediated β-glucan masking influences colonisation of this GI compartment. Finally, extracts from the murine gut and culture supernatants from the mannan grazing gut anaerobe Bacteroides thetaiotaomicron promote β-glucan exposure at the C. albicans cell surface. Therefore, the local microbiota influences β-glucan exposure levels directly (via mannan grazing) and indirectly (via fermentation acids), whilst β-glucan masking appears to promote C. albicans colonisation of the murine large intestine.

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.

T cell responses to control fungal infection in an immunological memory lens

In recent years, fungal vaccine research emanated significant findings in the field of antifungal T-cell immunity. The generation of effector T cells is essential to combat many mucosal and systemic fungal infections. The development of antifungal memory T cells is integral for controlling or preventing fungal infections, and understanding the factors, regulators, and modifiers that dictate the generation of such T cells is necessary. Despite the deficiency in the clear understanding of antifungal memory T-cell longevity and attributes, in this review, we will compile some of the existing literature on antifungal T-cell immunity in the context of memory T-cell development against fungal infections.

Circulating inflammatory cells in patients with metastatic breast cancer: Implications for treatment

Adaptive and innate immune cells play a crucial role as regulators of cancer development.

Inflammatory cells in blood flow seem to be involved in pro-tumor activities and contribute to breast cancer progression. Circulating lymphocyte ratios such as the platelet-lymphocytes ratio (PLR), the monocyte-lymphocyte ratio (MLR) and the neutrophil-lymphocyte ratio (NLR) are new reproducible, routinely feasible and cheap biomarkers of immune response. These indexes have been correlated to prognosis in many solid tumors and there is growing evidence on their clinical applicability as independent prognostic markers also for breast cancer.

In this review we give an overview of the possible value of lymphocytic indexes in advanced breast cancer prognosis and prediction of outcome. Furthermore, targeting the immune system appear to be a promising therapeutic strategy for breast cancer, especially macrophage-targeted therapies. Herein we present an overview of the ongoing clinical trials testing systemic inflammatory cells as therapeutic targets in breast cancer.

A Fun-Guide to Innate Immune Responses to Fungal Infections

Immunocompromised individuals are at high risk of developing severe fungal infections with high mortality rates, while fungal pathogens pose little risk to most healthy people. Poor therapeutic outcomes and growing antifungal resistance pose further challenges for treatments. Identifying specific immunomodulatory mechanisms exploited by fungal pathogens is critical for our understanding of fungal diseases and development of new therapies. A gap currently exists between the large body of literature concerning the innate immune response to fungal infections and the potential manipulation of host immune responses to aid clearance of infection. This review considers the innate immune mechanisms the host deploys to prevent fungal infection and how these mechanisms fail in immunocompromised hosts. Three clinically relevant fungal pathogens (Candida albicans, Cryptococcus spp. and Aspergillus spp.) will be explored. This review will also examine potential mechanisms of targeting the host therapeutically to improve outcomes of fungal infection.

In vitro and in vivo efficacies of Dectin-1-Fc(IgG)(s) fusion proteins against invasive fungal infections

Fungal infections have increased in the last years, particularly associated to an increment in the number of immunocompromised individuals and the emergence of known or new resistant species, despite the difficulties in the often time-consuming diagnosis. The controversial efficacy of the currently available strategies for their clinical management, apart from their high toxicity and severe side effects, have renewed the interest in the research and development of new broad antifungal alternatives. These encompass vaccines and passive immunization strategies with monoclonal antibodies (mAbs), recognizing ubiquitous fungal targets, such as fungal cell wall β-1,3-glucan polysaccharides, which could be used in early therapeutic intervention without the need for the diagnosis at species-level. As additional alternatives, based on the Dectin-1 great affinity to β-1,3-glucan, our group developed broad antibody-like Dectin1-Fc(IgG)(s) from distinct subclasses (IgG2a and IgG2b) and compared their antifungal in vitro and passive immunizations in vivo performances. Dectin1-Fc(IgG2a) and Dectin1-Fc(IgG2b) demonstrated high affinity to laminarin and the fungal cell wall by ELISA, flow cytometry and microscopy. Both Dectin-1-Fc(IgG)(s) inhibited H. capsulatum and C. neoformans growth in a dose-dependent fashion. For C. albicans, such inhibitory effect was observed with concentrations as low as 0.098 and 0.049 µg/mL, respectively, which correlated with the impairment of the kinetics and lengths of germ tubes in comparison to controls. Previous opsonization with Dectin-1-Fc(IgG)(s) enhanced considerably the macrophage antifungal effector functions, increasing the fungi macrophages-interactions and significantly reducing the intraphagosome fungal survival, as lower CFUs were observed. The administration of both Dectin1-Fc(IgG)(s) reduced the fungal burden and mortality in murine histoplasmosis and candidiasis models, in accordance with previous evaluations in aspergillosis model. These results altogether strongly suggested that therapeutic interventions with Dectin-1-Fc(IgG)(s) fusion proteins could directly impact the innate immunity and disease outcome in favor of the host, by direct neutralization, opsonization, phagocytosis, and fungal elimination, providing interesting information on the potential of these new strategies for the control of invasive fungal infections.

Mycobiota and C-Type Lectin Receptors in Cancers: Know thy Neighbors

Numerous studies have demonstrated the importance of gut bacteria in the development of malignancy, while relatively little research has been done on gut mycobiota. As a part of the gut microbiome, the percentage of gut mycobiota is negligible compared to gut bacteria. However, the effect of gut fungi on human health and disease is significant. This review systematically summarizes the research progress on mycobiota, especially gut fungi, in patients with head and neck cancer (HNC), esophageal cancer (EC), gastric cancer (GC), colorectal cancer (CRC), hepatocellular carcinoma (HCC), pancreatic cancer, melanoma, breast cancer, and lung carcinoma-induced cachexia. Moreover, we also describe, for the first time in detail, the role of the fungal recognition receptors, C-type lectin receptors (CLRs) (Dectin-1, Dectin-2, Dectin-3, and Mincle) and their downstream effector caspase recruitment domain-containing protein 9 (CARD9), in tumors to provide a reference for further research on intestinal fungi in the diagnosis and treatment of malignant tumors.