Human Anti-fungal Th17 Immunity and Pathology Rely on Cross-Reactivity against Candida albicans

The Double Game Played by Th17 Cells in Infection: Host Defense and Immunopathology

T-helper 17 (Th17) cells represent a subpopulation of CD4+ T lymphocytes that play an essential role in defense against pathogens. Th17 cells are distinguished from Th1 and Th2 cells by their ability to produce members of the interleukin-17 (IL-17) family, namely IL-17A and IL-17F. IL-17 in turn induces several target cells to synthesize and release cytokines, chemokines, and metalloproteinases, thereby amplifying the inflammatory cascade. Th17 cells reside predominantly in the lamina propria of the mucosa. Their main physiological function is to maintain the integrity of the mucosal barrier against the aggression of infectious agents. However, in an appropriate inflammatory microenvironment, Th17 cells can transform into immunopathogenic cells, giving rise to inflammatory and autoimmune diseases. This review aims to analyze the complex mechanisms through which the interaction between Th17 and pathogens can be on the one hand favorable to the host by protecting it from infectious agents, and on the other hand harmful, potentially generating autoimmune reactions and tissue damage.

Fungal sensing by dectin-1 directs the non-pathogenic polarization of TH17 cells through balanced type I IFN responses in human DCs

The non-pathogenic T_H17 subset of helper T cells clears fungal infections, whereas pathogenic T_H17 cells cause inflammation and tissue damage; however, the mechanisms controlling these distinct responses remain unclear. Here we found that fungi sensing by the C-type lectin dectin-1 in human dendritic cells (DCs) directed the polarization of non-pathogenic T_H17 cells. Dectin-1 signaling triggered transient and intermediate expression of interferon (IFN)-β in DCs, which was mediated by the opposed activities of transcription factors IRF1 and IRF5. IFN-β-induced signaling led to integrin αvβ8 expression directly and to the release of the active form of the cytokine transforming growth factor (TGF)-β indirectly. Uncontrolled IFN-β responses as a result of IRF1 deficiency induced high expression of the IFN-stimulated gene BST2 in DCs and restrained TGF-β activation. Active TGF-β was required for polarization of non-pathogenic T_H17 cells, whereas pathogenic T_H17 cells developed in the absence of active TGF-β. Thus, dectin-1-mediated modulation of type I IFN responses allowed TGF-β activation and non-pathogenic T_H17 cell development during fungal infections in humans.

Mycobiota and diet-derived fungal xenosiderophores promote Salmonella gastrointestinal colonization

The fungal gut microbiota (mycobiota) has been implicated in diseases that disturb gut homeostasis, such as inflammatory bowel disease. However, little is known about functional relationships between bacteria and fungi in the gut during infectious colitis. Here we investigated the role of fungal metabolites during infection with the intestinal pathogen Salmonella enterica serovar Typhimurium, a major cause of gastroenteritis worldwide. We found that, in the gut lumen, both the mycobiota and fungi present in the diet can be a source of siderophores, small molecules that scavenge iron from the host. The ability to use fungal siderophores, such as ferrichrome and coprogen, conferred a competitive growth advantage to Salmonella strains expressing the fungal siderophore receptors FhuA or FhuE in vitro and in a mouse model. Our study highlights the role of inter-kingdom cross-feeding between fungi and Salmonella and elucidates an additional function of the gut mycobiota, revealing the importance of these understudied members of the gut ecosystem during bacterial infection.

Pathogenesis and virulence of Candida albicans

Candida albicans is a commensal yeast fungus of the human oral, gastrointestinal, and genital mucosal surfaces, and skin. Antibiotic-induced dysbiosis, iatrogenic immunosuppression, and/or medical interventions that impair the integrity of the mucocutaneous barrier and/or perturb protective host defense mechanisms enable C. albicans to become an opportunistic pathogen and cause debilitating mucocutaneous disease and/or life-threatening systemic infections. In this review, we synthesize our current knowledge of the tissue-specific determinants of C. albicans pathogenicity and host immune defense mechanisms.

The gut mycobiome in health, disease, and clinical applications in association with the gut bacterial microbiome assembly

The gut mycobiome (fungi) is a small but crucial component of the gut microbiome in humans. Intestinal fungi regulate host homoeostasis, pathophysiological and physiological processes, and the assembly of the co-residing gut bacterial microbiome. Over the past decade, accumulating studies have characterised the gut mycobiome in health and several pathological conditions. We review the compositional and functional diversity of the gut mycobiome in healthy populations from birth to adulthood. We describe factors influencing the gut mycobiome and the roles of intestinal fungi-especially Candida and Saccharomyces spp-in diseases and therapies with a particular focus on their synergism with the gut bacterial microbiome and host immunity. Finally, we discuss the underappreciated effects of gut fungi in clinical implications, and highlight future microbiome-based therapies that harness the tripartite relationship among the gut mycobiome, bacterial microbiome, and host immunity, aiming to restore a core gut mycobiome and microbiome and to improve clinical efficacy.

Long-term exposure to PM2.5 aggravates pulmonary fibrosis and acute lung injury by disrupting Nrf2-mediated antioxidant function

Epidemiological studies have indicated that exposure to ambient air-borne fine particulate matter (PM2.5) is associated with many cardiopulmonary diseases; however, the underlying pathological mechanisms of PM2.5-induced lung injury remain unknown. In this study, we aimed to assess the impact of acute or prolonged exposure to water-insoluble fractions of PM2.5 (PM2.5 particulate) on lung injury and its molecular mechanisms. Balb/c mice were randomly exposed to PM2.5 once (acute exposure) or once every three days for a total of 6 times (prolonged exposure). Lung, BALF and blood samples were collected, and pulmonary pathophysiological alterations were analyzed. Nrf2 knockout mice were adapted to assess the involvement of Nrf2 in lung injury, and transcriptomic analysis was performed to delineate the mechanisms. Through transcriptomic analysis and validation of Nrf2 knockout mice, we found that acute exposure to PM2.5 insoluble particulates induced neutrophil infiltration-mediated airway inflammation, whereas prolonged exposure to PM2.5 insoluble particulate triggered lung fibrosis by decreasing the transcriptional activity of Nrf2, which resulted in the downregulated expression of antioxidant-related genes. In response to secondary LPS exposure, prolonged PM2.5 exposure induced more severe lung injury, indicating that prolonged PM2.5 exposure induced Nrf2 inhibition weakened its antioxidative defense capacity against oxidative stress injury, leading to the formation of pulmonary fibrosis and increasing its susceptibility to secondary bacterial infection.

Deep tissue infection by an invasive human fungal pathogen requires lipid-based suppression of the IL-17 response

Candida albicans is the most common cause of fungal infection in humans. IL-17 is critical for defense against superficial fungal infections, but the role of this response in invasive disease is less understood. We show that C. albicans secretes a lipase, Lip2, that facilitates invasive disease via lipid-based suppression of the IL-17 response. Lip2 was identified as an essential virulence factor in a forward genetic screen in a mouse model of bloodstream infection. Murine infection with C. albicans strains lacking Lip2 display exaggerated IL-17 responses that lead to fungal clearance from solid organs and host survival. Both IL-17 signaling and lipase activity are required for Lip2-mediated suppression. Lip2 inhibits IL-17 production indirectly by suppressing IL-23 production by tissue-resident dendritic cells. The lipase hydrolysis product, palmitic acid, similarly suppresses dendritic cell activation in vitro. Thus, C. albicans suppresses antifungal IL-17 defense in solid organs by altering the tissue lipid milieu.

Alterations of bacteriome, mycobiome and metabolome characteristics in PCOS patients with normal/overweight individuals

To characterize the gut bacteriome, mycobiome and serum metabolome profiles in polycystic ovary syndrome (PCOS) patients with normal/overweight individuals and evaluate a potential microbiota-related diagnostic method development for PCOS, 16S rRNA and ITS2 gene sequencing using 88 fecal samples and 87 metabolome analysis from serum samples are conducted and PCOS classifiers based on multiomics markers are constructed. There are significant bacterial, fungal community and metabolite differences among PCOS patients and healthy volunteers with normal/overweight individuals. Healthy individuals with overweight/obesity display less abnormal metabolism than PCOS patients and uniquely higher abundance of the fungal genus Mortierella. Nine bacterial genera, 4 predicted pathways, 11 fungal genera and top 30 metabolites are screened out which distinguish PCOS from healthy controls, with AUCs of 0.84, 0.64, 0.85 and 1, respectively. The metabolite-derived model is more accurate than the microbe-based model in discriminating normal BMI PCOS (PCOS-LB) from normal BMI healthy (Healthy-LB), PCOS-HB from Healthy-HB. Featured bacteria, fungi, predicted pathways and serum metabolites display higher associations with free androgen index (FAI) in the cooccurrence network. In conclusion, our data reveal that hyperandrogenemia plays a central role in the dysbiosis of intestinal microecology and the change in metabolic status in patients with PCOS and that its effect exceeds the role of BMI. Healthy women with high BMI showed unique microbiota and metabolic features.The priority of predictive models in discriminating PCOS from healthy status in this study were serum metabolites, fungal taxa and bacterial taxa.

Checkpoint inhibitors as immunotherapy for fungal infections: Promises, challenges, and unanswered questions

Opportunistic fungal infections have high mortality in patients with severe immune dysfunction. Growing evidence suggests that the immune environment of invasive fungal infections and cancers share common features of immune cell exhaustion through activation of immune checkpoint pathways. This observation gave rise to several preclinical studies and clinical case reports describing blockade of the Programmed Cell Death Protein 1 and Cytotoxic T-Lymphocyte Antigen 4 immune checkpoint pathways as an adjunct immune enhancement strategy to treat opportunistic fungal infections. The first part of this review summarizes the emerging evidence for contributions of checkpoint pathways to the immunopathology of fungal sepsis, opportunistic mold infections, and dimorphic fungal infections. We then review the potential merits of immune checkpoint inhibitors (ICIs) as an antifungal immunotherapy, including the incomplete knowledge of the mechanisms involved in both immuno-protective effects and toxicities. In the second part of this review, we discuss the limitations of the current evidence and the many unknowns about ICIs as an antifungal immune enhancement strategy. Based on these gaps of knowledge and lessons learned from cancer immunology studies, we outline a research agenda to determine a "sweet spot" for ICIs in medical mycology. We specifically discuss the importance of more nuanced animal models, the need to study ICI-based combination therapy, potential ICI resistance, the role of the immune microenvironment, and the impact of ICIs given as part of oncological therapies on the natural immunity to various pathogenic fungi.

A gut-oral microbiome-driven axis controls oropharyngeal candidiasis through retinoic acid

A side effect of antibiotics is outgrowth of the opportunistic fungus Candida albicans in the oropharynx (oropharyngeal candidiasis, OPC). IL-17 signaling is vital for immunity to OPC, but how the microbiome impacts antifungal immunity is not well understood. Mice in standard specific pathogen-free (SPF) conditions are resistant to OPC, whereas we show that germ-free (GF) or antibiotic-treated mice are susceptible. Oral type 17 cells and IL-17-dependent responses were impaired in antibiotic-treated and GF mice. Susceptibility could be rescued in GF mice by mono-colonization with segmented filamentous bacterium (SFB), an intestine-specific constituent of the microbiota. SFB protection was accompanied by restoration of oral IL-17+CD4+ T cells and gene signatures characteristic of IL-17 signaling. Additionally, RNA-Seq revealed induction of genes in the retinoic acid (RA) and RA receptor-α (RARα) pathway. Administration of RA rescued immunity to OPC in microbiome-depleted or GF mice, while RAR inhibition caused susceptibility in immunocompetent animals. Surprisingly, immunity to OPC was independent of serum amyloids. Moreover, RAR inhibition did not alter oral type 17 cytokine levels. Thus, mono-colonization with a component of the intestinal microflora confers protection against OPC by type 17 and RA/RARα, which act in parallel to promote antifungal immunity. In principle, manipulation of the microbiome could be harnessed to maintain antifungal immunity.

What Is Candida Doing in My Food? A Review and Safety Alert on Its Use as Starter Cultures in Fermented Foods

The use of yeasts as starter cultures was boosted with the emergence of large-scale fermentations in the 20th century. Since then, Saccharomyces cerevisiae has been the most common and widely used microorganism in the food industry. However, Candida species have also been used as an adjuvant in cheese production or as starters for coffee, cocoa, vegetable, meat, beer, and wine fermentations. A thorough screening of candidate Candida is sometimes performed to obtain the best performing strains to enhance specific features. Some commonly selected species include C. pulcherrima (teleomorph Metschnikowia pulcherrima) (wine), C. parapsilosis (teleomorph Monilia parapsilosis) (coffee), C. famata (teleomorph Debaryomyces hansenii) (cheese), and C. zeylanoides (teleomorph Kurtzmaniella zeylanoides) and C. norvegensis (teleomorph Pichia norvegensis) (cocoa). These species are associated with the production of key metabolites (food aroma formation) and different enzymes. However, safety-associated selection criteria are often neglected. It is widely known that some Candida species are opportunistic human pathogens, with important clinical relevance. Here, the physiology and metabolism of Candida species are addressed, initially emphasizing their clinical aspects and potential pathogenicity. Then, Candida species used in food fermentations and their functional roles are reported. We recommended that Candida not be used as food cultures if safety assessments are not performed. Some safety features are highlighted to help researchers choose methods and selection criteria.

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.

Malassezia: A Commensal, Pathogen, and Mutualist of Human and Animal Skin

Identified in the late nineteenth century as a single species residing on human skin, Malassezia is now recognized as a diverse genus comprising 18 species inhabiting not only skin but human gut, hospital environments, and even deep-sea sponges. All cultivated Malassezia species are lipid dependent, having lost genes for lipid synthesis and carbohydrate metabolism. The surging interest in Malassezia results from development of tools to improve sampling, culture, identification, and genetic engineering, which has led to findings implicating it in numerous skin diseases, Crohn disease, and pancreatic cancer. However, it has become clear that Malassezia plays a multifaceted role in human health, with mutualistic activity in atopic dermatitis and a preventive effect against other skin infections due to its potential to compete with skin pathogens such as Candida auris. Improved understanding of complex microbe-microbe and host-microbe interactions will be required to define Malassezia's role in human and animal health and disease so as to design targeted interventions.

Friendly fungi: symbiosis with commensal Candida albicans

Mucosal tissues are constitutively colonized by a wide assortment of host-adapted microbes. This includes the polymorphic fungus Candida albicans which is a primary target of human adaptive responses. Immunogenicity is replicated after intestinal colonization in preclinical models with a surprising array of protective benefits for most hosts, but harmful consequences for a few. The interaction between fungus and host is complex, and traditionally, the masking of antigenic fungal ligands has been viewed as a tactic for fungal immune evasion during invasive infection. However, we propose that dynamic expression of cell wall moieties, host cell lysins, and other antigenic C. albicans determinants is necessary during the more ubiquitous context of intestinal colonization to prime immunogenicity and optimize mammalian host symbiosis.

The long term vaccine-induced anti-SARS-CoV-2 immune response is impaired in quantity and quality under TNFα blockade

The humoral immune response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination in patients with chronic inflammatory disease (CID) declines more rapidly with tumor necrosis factor-α (TNF-α) inhibition. Furthermore, the efficacy of current vaccines against Omicron variants of concern (VOC) including BA.2 is limited. Alterations within immune cell populations, changes in IgG affinity, and the ability to neutralize a pre-VOC strain and the BA.2 virus were investigated in these at-risk patients. Serum levels of anti-SARS-CoV-2 IgG, IgG avidity, and neutralizing antibodies (NA) were determined in anti-TNF-α patients (n = 10) and controls (n = 24 healthy individuals; n = 12 patients under other disease-modifying antirheumatic drugs, oDMARD) before and after the second and third vaccination by ELISA, immunoblot and live virus neutralization assay. SARS-CoV-2-specific B- and T cell subsets were analysed by multicolor flow cytometry. Six months after the second vaccination, anti-SARS-CoV-2 IgG levels, IgG avidity and anti-pre-VOC NA titres were significantly reduced in anti-TNF-α recipients compared to controls (healthy individuals: avidity: p ≤ 0.0001; NA: p = 0.0347; oDMARDs: avidity: p = 0.0012; NA: p = 0.0293). The number of plasma cells was increased in anti-TNF-α patients (Healthy individuals: p = 0.0344; oDMARDs: p = 0.0254), while the absolute number of SARS-CoV-2-specific plasma cells 7 days after 2nd vaccination were comparable. Even after a third vaccination, these patients had lower anti-BA.2 NA titres compared to both other groups. We show a reduced SARS-CoV-2 neutralizing capacity in patients under TNF-α blockade. In this cohort, the plasma cell response appears to be less specific and shows stronger bystander activation. While these effects were observable after the first two vaccinations and with older VOC, the differences in responses to BA.2 were enhanced.

COVID-19 patients share common, corticosteroid-independent features of impaired host immunity to pathogenic molds

Patients suffering from coronavirus disease-2019 (COVID-19) are susceptible to deadly secondary fungal infections such as COVID-19-associated pulmonary aspergillosis and COVID-19-associated mucormycosis. Despite this clinical observation, direct experimental evidence for severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2)-driven alterations of antifungal immunity is scarce. Using an ex-vivo whole blood stimulation assay, we challenged blood from twelve COVID-19 patients with Aspergillus fumigatus and Rhizopus arrhizus antigens and studied the expression of activation, maturation, and exhaustion markers, as well as cytokine secretion. Compared to healthy controls, T-helper cells from COVID-19 patients displayed increased expression levels of the exhaustion marker PD-1 and weakened A. fumigatus- and R. arrhizus-induced activation. While baseline secretion of proinflammatory cytokines was massively elevated, whole blood from COVID-19 patients elicited diminished release of T-cellular (e.g., IFN-γ, IL-2) and innate immune cell-derived (e.g., CXCL9, CXCL10) cytokines in response to A. fumigatus and R. arrhizus antigens. Additionally, samples from COVID-19 patients showed deficient granulocyte activation by mold antigens and reduced fungal killing capacity of neutrophils. These features of weakened anti-mold immune responses were largely decoupled from COVID-19 severity, the time elapsed since diagnosis of COVID-19, and recent corticosteroid uptake, suggesting that impaired anti-mold defense is a common denominator of the underlying SARS-CoV-2 infection. Taken together, these results expand our understanding of the immune predisposition to post-viral mold infections and could inform future studies of immunotherapeutic strategies to prevent and treat fungal superinfections in COVID-19 patients.

The pre-exposure SARS-CoV-2-specific T cell repertoire determines the quality of the immune response to vaccination

SARS-CoV-2 infection and vaccination generates enormous host-response heterogeneity and an age-dependent loss of immune-response quality. How the pre-exposure T cell repertoire contributes to this heterogeneity is poorly understood. We combined analysis of SARS-CoV-2-specific CD4⁺ T cells pre- and post-vaccination with longitudinal T cell receptor tracking. We identified strong pre-exposure T cell variability that correlated with subsequent immune-response quality and age. High-quality responses, defined by strong expansion of high-avidity spike-specific T cells, high interleukin-21 production, and specific immunoglobulin G, depended on an intact naive repertoire and exclusion of pre-existing memory T cells. In the elderly, T cell expansion from both compartments was severely compromised. Our results reveal that an intrinsic defect of the CD4⁺ T cell repertoire causes the age-dependent decline of immune-response quality against SARS-CoV-2 and highlight the need for alternative strategies to induce high-quality T cell responses against newly arising pathogens in the elderly.

Microbiota and COVID-19: Long-term and complex influencing factors

The coronavirus disease 2019 (COVID-19) is an infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). According to the World Health Organization statistics, more than 500 million individuals have been infected and more than 6 million deaths have resulted worldwide. Although COVID-19 mainly affects the respiratory system, considerable evidence shows that the digestive, cardiovascular, nervous, and reproductive systems can all be involved. Angiotensin-converting enzyme 2 (AEC2), the target of SARS-CoV-2 invasion of the host is mainly distributed in the respiratory and gastrointestinal tract. Studies found that microbiota contributes to the onset and progression of many diseases, including COVID-19. Here, we firstly conclude the characterization of respiratory, gut, and oral microbial dysbiosis, including bacteria, fungi, and viruses. Then we explore the potential mechanisms of microbial involvement in COVID-19. Microbial dysbiosis could influence COVID-19 by complex interactions with SARS-CoV-2 and host immunity. Moreover, microbiota may have an impact on COVID-19 through their metabolites or modulation of ACE2 expression. Subsequently, we generalize the potential of microbiota as diagnostic markers for COVID-19 patients and its possible association with post-acute COVID-19 syndrome (PACS) and relapse after recovery. Finally, we proposed directed microbiota-targeted treatments from the perspective of gut microecology such as probiotics and prebiotics, fecal transplantation and antibiotics, and other interventions such as traditional Chinese medicine, COVID-19 vaccines, and ACE2-based treatments.

Lung and gut microbiomes in pulmonary aspergillosis: Exploring adjunctive therapies to combat the disease

Species within the Aspergillus spp. cause a wide range of infections in humans, including invasive pulmonary aspergillosis, chronic pulmonary aspergillosis, and allergic bronchopulmonary aspergillosis, and are associated with high mortality rates. The incidence of pulmonary aspergillosis (PA) is on the rise, and the emergence of triazole-resistant Aspergillus spp. isolates, especially Aspergillus fumigatus, limits the efficacy of mold-active triazoles. Therefore, host-directed and novel adjunctive therapies are required to more effectively combat PA. In this review, we focus on PA from a microbiome perspective. We provide a general overview of the effects of the lung and gut microbiomes on the growth of Aspergillus spp. and host immunity. We highlight the potential of the microbiome as a therapeutic target for PA.

Gut microbiota in systemic lupus erythematosus: A fuse and a solution

Gut commensals help shape and mold host immune system and deeply influence human health. The disease spectrum of mankind that gut microbiome may associate with is ever-growing, but the mechanisms are still enigmas. Characterized by loss of self-tolerance and sustained self-attack, systemic lupus erythematosus (SLE) is labeled with chronic inflammation, production of autoantibodies and multisystem injury, which so far are mostly incurable. Gut microbiota and their metabolites, now known as important environmental triggers of local/systemic immune responses, have been proposed to be involved in SLE development and progression probably through the following mechanisms: translocation beyond their niches; molecular mimicry to cross-activate immune response targeting self-antigens; epitope spreading to expand autoantibodies spectrum; and bystander activation to promote systemic inflammation. Gut microbiota which varies between individuals may also influence the metabolism and bio-transformation of disease-modifying anti-rheumatic drugs, thus associated with the efficacy and toxicity of these drugs, adding another explanation for heterogenic therapeutic responses. Modulation of gut microbiota via diet, probiotics/prebiotics, antibiotics/phages, fecal microbiota transplantation, or helminth to restore immune tolerance and homeostasis is expected to be a promising neoadjuvant therapy for SLE. We reviewed the advances in this territory and discussed the application prospect of modulating gut microbiota in controlling SLE.

IL-17A aggravates asthma-induced intestinal immune injury by promoting neutrophil trafficking

With the concept of the gut-lung axis reinforced in recent years, emerging evidence has shown that intestinal homeostasis is vital for lung health. Nevertheless, the impacts of lung homeostasis on intestinal tracts and their mechanism are rarely studied. Our results showed that papain-induced asthmatic mice exhibited apparent colonic injuries compared with controls, including increased intestinal permeability, neutrophil and Th17 infiltration in the colonic lamina propria. Moreover, the intranasal administration of papain aggravated such colonic injuries in mice with dextran sulfate sodium-induced colitis, as evidenced by increased occult blood scores, shortened colon length, and accumulated neutrophils. The level of IL-17A was also higher in the serum of asthmatic mice than wild-type mice. Interestingly, the pathologic scores, the proportion of Th17 cells, and neutrophil infiltration in the colon were markedly reduced after IL-17A blocking. Similarly, longer length, lower pathologic scores, and fewer neutrophils were also observed in the colon of IL-17-deficient asthmatic mice. More importantly, we demonstrated that severe gastrointestinal symptoms could accompany clinical asthmatics. The frequencies of Th17 cells and the mRNA expression of IL-17A in the peripheral blood of these patients were significantly enhanced. Besides, the gastrointestinal symptom rating scale scores positively correlated with the frequencies of Th17 in asthmatics. These findings enlighten that IL-17A aggravates asthma-induced intestinal immune injury by promoting neutrophil trafficking, which facilitates the exploration of new potential biomarkers to treat asthma.

Reciprocal Interactions Between Regulatory T Cells and Intestinal Epithelial Cells

It has been well established that Foxp3+ regulatory T cells (Treg cells) play a crucial role for immune repression and tolerance, protecting the body from autoimmunity and inflammation. Previous studies indicate that intestinal Treg cells are one specialized population of Treg cells, distinct from those in other organ compartments, both functionally and phenotypically. Specific external and internal signals, particularly the presence of microbiota, shape these Treg cells to better cooperate with the gut ecosystem, controlling intestinal physiology. The integrity of intestinal epithelial barrier represents a key feature of gut immune tolerance, which can be regulated by multiple factors. Emerging evidence suggests that bidirectional interactions between gut epithelium and resident T cells significantly contribute to intestinal barrier function. Understanding how Treg cells regulate intestinal barrier integrity provides insights into immune tolerance-mediated mucosal homeostasis, which can further illuminate potential therapeutic strategies for treating inflammatory bowel disease and colon cancer.

Interleukin-17A and interleukin-22 production by conventional and non-conventional lymphocytes in three different end-stage lung diseases

Objectives

The contribution of adaptive vs. innate lymphocytes to IL-17A and IL-22 secretion at the end stage of chronic lung diseases remains largely unexplored. In order to uncover tissue- and disease-specific secretion patterns, we compared production patterns of IL-17A and IL-22 in three different human end-stage lung disease entities.

Methods

Production of IL-17A, IL-22 and associated cytokines was assessed in supernatants of re-stimulated lymphocytes by multiplex assays and multicolour flow cytometry of conventional T cells, iNKT cells, γδ T cells and innate lymphoid cells in bronchial lymph node and lung tissue from patients with emphysema (n = 19), idiopathic pulmonary fibrosis (n = 14) and cystic fibrosis (n = 23), as well as lung donors (n = 17).

Results

We detected secretion of IL-17A and IL-22 by CD4⁺ T cells, CD8⁺ T cells, innate lymphoid cells, γδ T cells and iNKT cells in all end-stage lung disease entities. Our analyses revealed disease-specific contributions of individual lymphocyte subpopulations to cytokine secretion patterns. We furthermore found the high levels of microbial detection in CF samples to associate with a more pronounced IL-17A signature upon antigen-specific and unspecific re-stimulation compared to other disease entities and lung donors.

Conclusion

Our results show that both adaptive and innate lymphocyte populations contribute to IL-17A-dependent pathologies in different end-stage lung disease entities, where they establish an IL-17A-rich microenvironment. Microbial colonisation patterns and cytokine secretion upon microbial re-stimulation suggest that pathogens drive IL-17A secretion patterns in end-stage lung disease.

Systemic Candidiasis in Mice: New Insights From an Old Model

Animal models are essential to understand the pathophysiology of infections, to test novel antifungal compounds, and to determine the potential of adjunctive therapies, e.g. immune modulation. The murine model of systemic candidiasis induced by intravenous infection is technically straightforward, highly reproducible, and well-characterized. However, intravenous inoculation circumvents the necessity for the fungus to translocate across mucosal barriers, and the use of SPF mice that are immunologically naïve to Candida does not reflect the situation in human patients, in whom adaptive immune responses have been induced by mucosal colonization prior to infection. Therefore, mouse models that combine intestinal colonization and systemic infection have been developed, resulting in novel insights into host-fungal interactions and immunity. In this review, we summarize the main findings, current questions, and discuss how these might impact the translatability of results from mice to humans.

The Mediating Effect of Cytokines on the Association between Fungal Sensitization and Poor Clinical Outcome in Asthma

Sensitization to fungal allergens is one of the proposed phenotypes in asthma. An association between fungal sensitization and worse clinical outcomes is apparent. Moreover, fungal sensitization in asthma that is associated with different type of immunological mechanism has been reported. How the role of cytokines mediates the association between fungal sensitization and poorer asthmatic outcomes remains unclear. We aimed to determine role of cytokines in the relationship between fungal sensitization and worse clinical outcomes in asthma.

METHOD

We conducted a prospective study to recruit adult patients with asthma. Data including age, sex, height, weight, smoking history, medication, emergency visit and admission, pulmonary function testing result, and Asthma Control Test (ACT) scores were collected. We used the automated BioIC method to measure fungal allergen sIgE in sera. Serum levels of Interleukin (IL) -4, IL-13, IL-6, IL-9, IL-10, IL-17 A, IL-22, Interferon (IFN) -γ, Immunoglobulin E (IgE), Tumor necrosis factor-α (TNF-α), and Transforming growth factor-β (TGF-β) were measured using ELISA.

RESULT

IL-6 and IL-17A had a significant positive correlation between sensitization and most fungi species compared to IgE. Sensitization to Candida albicans had strongly positive association both with IL-6 and IL-17A. However, only IL-17A had significant relationship with ED visit times. The mediation analysis result indicates that IL-17A had a significant positively mediating effect (ME) on the association between Candida albicans and ED visit times.

CONCLUSION

IL-17A is a potential mediator to link Candida albicans sensitization and ED visits for asthma. We suggest that patients with fungal sensitization, such as Candida albicans, have poorer outcomes associated with Th17-mediated immune response rather than Th2.

Mycobiota composition and changes across pregnancy in patients with gestational diabetes mellitus (GDM)

The gut mycobiota has never been studied either during pregnancy or in patients with gestational diabetes (GDM). This study aimed to analyze the fecal mycobiota of GDM patients during the second (T2) and third (T3) trimester of pregnancy and to compare it with the mycobiota of pregnant normoglycemic women (controls). Forty-one GDM patients and 121 normoglycemic women were studied. GDM mycobiota was composed almost exclusively by the Ascomycota phylum; Basidiomicota accounted for 43% of the relative frequency of the controls. Kluyveromyces (p < 0.001), Metschnikowia (p < 0.001), and Pichia (p < 0.001) showed a significantly higher frequency in GDM patients, while Saccharomyces (p = 0.019), were more prevalent in controls. From T2 to T3, a reduction in fungal alpha diversity was found in GDM patients, with an increase of the relative frequency of Candida, and the reduction of some pro-inflammatory taxa. Many associations between fungi and foods and nutrients were detected. Finally, several fungi and bacteria showed competition or co-occurrence. Patients with GDM showed a predominance of fungal taxa with potential inflammatory effects when compared to normoglycemic pregnant women, with a marked shift in their mycobiota during pregnancy, and complex bacteria-fungi interactions.

Could gut mycobiome play a role in NAFLD pathogenesis? Insights and therapeutic perspectives

The entire spectrum of nonalcoholic fatty liver disease (NAFLD) ranging from fatty liver to cirrhosis has been considered as the result of specific metabolic pathways and mediators, gut barrier function alterations and inflammatory responses. Previous studies have associated intestinal microbiota with NAFLD pathogenesis, focusing mostly on bacteria. In a recent study by Demir et al. in the Journal of Hepatology, researchers characterized the fecal mycobiome of patients with NAFLD and controls. NAFLD severity was linked to a specific fecal mycobiome signature, particularly in patients without obesity, highlighting previously undescribed aspects of the non obese phenotype of NAFLD. There has recently been a growing interest in the pathophysiology and progression of non obese NAFLD, as its actual incidence seems to be higher than previously described. Moreover, the authors demonstrated that in subjects with NAFLD and advanced fibrosis, there was an augmented systemic immune response to Candida albicans. Amphotericin B, which has been widely regarded as an antifungal with a good safety profile, low rate of resistance and high efficacy, has already been shown to prevent liver injury and steatosis in mice. Similarly in this study when germ-free mice colonized with feces from patients with NASH were fed with a Western diet, treatment with amphotericin B protected against steatohepatitis and liver fibrosis. In conclusion, this study has provided novel insights into the fecal mycobiome composition in advanced NAFLD especially in the non obese population while suggesting a role for antifungal therapy in the management of NAFLD.

Efficacy, T cell activation and antibody responses in accelerated Plasmodium falciparum sporozoite chemoprophylaxis vaccine regimens

Repeated direct venous inoculation of Plasmodium falciparum sporozoites (PfSPZ) together with antimalarial chemoprophylaxis (PfSPZ-CVac) is the most potent way to induce sterile immunity against P. falciparum infection in malaria-naive volunteers. However, established schedules are complex and long. Here, we tested two accelerated three-dose schedules (28- and 10-day regimen) assessing efficacy by controlled human malaria infection (CHMI) against placebo, comparing vaccine-specific T cell and antibody responses by antigen-reactive T cell enrichment (ARTE) and protein microarray, respectively. Both regimens were similarly efficacious (67 and 63% vaccine efficacy) but different in the induction of vaccine-specific T cells and antibodies. The 10-day regimen resulted in higher numbers of antigen-specific CD4+ effector memory pro-inflammatory T cells and a broader antibody response compared with the 28-day regimen. Usually in nature, P. falciparum liver stage lasts about 6.5 days. The short vaccination-interval of the 10-day regimen prolongs the time of continuous exposure to liver-stage parasites, which may explain the stronger response. Besides dose and number of vaccinations, duration of liver-stage exposure is a factor to optimize PfSPZ-CVac immunogenicity.

Candida albicans oscillating UME6 expression during intestinal colonization primes systemic Th17 protective immunity

Systemic immunity is stringently regulated by commensal intestinal microbes, including the pathobiont Candida albicans. This fungus utilizes various transcriptional and morphological programs for host adaptation, but how this heterogeneity affects immunogenicity remains uncertain. We show that UME6, a transcriptional regulator of filamentation, is essential for intestinal C. albicans-primed systemic Th17 immunity. UME6 deletion and constitutive overexpression strains are non-immunogenic during commensal colonization, whereas immunogenicity is restored by C. albicans undergoing oscillating UME6 expression linked with β-glucan and mannan production. In turn, intestinal reconstitution with these fungal cell wall components restores protective Th17 immunity to mice colonized with UME6-locked variants. These fungal cell wall ligands and commensal C. albicans stimulate Th17 immunity through multiple host pattern recognition receptors, including Toll-like receptor 2 (TLR2), TLR4, Dectin-1, and Dectin-2, which work synergistically for colonization-induced protection. Thus, dynamic gene expression fluctuations by C. albicans during symbiotic colonization are essential for priming host immunity against disseminated infection.

Candida albicans evades NK cell elimination via binding of Agglutinin-Like Sequence proteins to the checkpoint receptor TIGIT

Candida albicans is the most common fungal pathogen and a prevalent cause of deadly bloodstream infections. Better understanding of the immune response against it, and the ways by which it evades immunity, are crucial for developing new therapeutics against it. Natural Killer (NK) cells are innate lymphocytes best known for their role against viruses and tumors. In recent years it became clear that NK cells also play an important role in anti-fungal immunity. Here we show that while NK cells recognize and eliminate C. albicans, the fungal cells inhibit NK cells by manipulating the immune checkpoint receptor TIGIT (T cell immunoreceptor with Ig and ITIM domains) in both humans and mice. We identify the responsible fungal ligands as members of the Als (Agglutinin-Like Sequences) protein family. Furthermore, we show that blocking this interaction using immunotherapy with a TIGIT-blocking antibody can re-establish anti-Candida immunity and serve as a potential therapeutic tool.

Natural killer cells have emerged as critical immune cells in the response to fungal infection. Here the authors identify how Candida albicans evades the natural killer cell response via expression of ligands that directly modify the natural killer cell response and can be therapeutically targeted to restore the anti-Candida immunity.

Wild herbivorous mammals (genus Neotoma) host a diverse but transient assemblage of fungi

Fungi are often overlooked in microbiome research and, as a result, little is known about the mammalian mycobiome. Although frequently detected in vertebrate guts and known to contribute to digestion in some herbivores, whether these eukaryotes are a persistent part of the mammalian gut microbiome remains contentious. To address this question, we sampled fungi from wild woodrats (Neotoma spp.) collected from 25 populations across the southwestern United States. For each animal, we collected a fecal sample in the wild, and then re-sampled the same individual after a month in captivity on a controlled diet. We characterized and quantified fungi using three techniques: ITS metabarcoding, shotgun metagenomics and qPCR. Wild individuals contained diverse fungal assemblages dominated by plant pathogens, widespread molds, and coprophilous taxa primarily in Ascomycota and Mucoromycota. Fungal abundance, diversity and composition differed between individuals, and was primarily influenced by animal geographic origin. Fungal abundance and diversity significantly declined in captivity, indicating that most fungi in wild hosts came from diet and environmental exposure. While this suggests that these mammals lack a persistent gut mycobiome, natural fungal exposure may still impact fungal dispersal and animal health.

Immunosurveillance of Candida albicans commensalism by the adaptive immune system

The fungal microbiota (mycobiota) is an integral part of the microbial community colonizing the body surfaces and is involved in many key aspects of human physiology, while an imbalance of the fungal communities, termed fungal dysbiosis, has been described in pathologies ranging from infections to inflammatory bowel disease. Commensal organisms, such as the fungus Candida albicans, induce antigen-specific immune responses that maintain immune homeostasis. Adaptive immune mechanisms are vital in this process, while deficiencies in adaptive immunity are linked to fungal infections. We start to understand the mechanisms by which a shift in mycobiota composition, in particular in C. albicans abundance, is linked to immunopathological conditions. This review discusses the mechanisms that ensure continuous immunosurveillance of C. albicans during mucosal colonization, how these protective adaptive immune responses can also promote immunopathology, and highlight therapeutic advances against C. albicans-associated disease.

Effective Regulation of Gut Microbiota With Probiotics and Prebiotics May Prevent or Alleviate COVID-19 Through the Gut-Lung Axis

Coronavirus disease 2019 (COVID-19) can disrupt the gut microbiota balance, and patients usually have intestinal disorders. The intestine is the largest immune organ of the human body, and gut microbes can affect the immune function of the lungs through the gut-lung axis. Many lines of evidence support the role of beneficial bacteria in enhancing human immunity, preventing pathogen colonization, and thereby reducing the incidence and severity of infection. In this article, we review the possible approach of modulating microbiota to help prevent and treat respiratory tract infections, including COVID-19, and discuss the possibility of using probiotics and prebiotics for this purpose. We also discuss the mechanism by which intestinal micro-flora regulate immunity and the effects of probiotics on the intestinal micro-ecological balance. Based on this understanding, we propose the use of probiotics and prebiotics to modulate gut microbiota for the prevention or alleviation of COVID-19 through the gut-lung axis.

The Fungal Gut Microbiome Exhibits Reduced Diversity and Increased Relative Abundance of Ascomycota in Severe COVID-19 Illness and Distinct Interconnected Communities in SARS-CoV-2 Positive Patients

Clinical and experimental studies indicate that the bacterial and fungal gut microbiota modulates immune responses in distant organs including the lungs. Immune dysregulation is associated with severe SARS-CoV-2 infection, and several groups have observed gut bacterial dysbiosis in SARS-CoV-2 infected patients, while the fungal gut microbiota remains poorly defined in these patients. We analyzed the fungal gut microbiome from rectal swabs taken prior to anti-infective treatment in 30 SARS-CoV-2 positive (21 non-severe COVID-19 and 9 developing severe/critical COVID-19 patients) and 23 SARS-CoV-2 negative patients by ITS2-sequencing. Pronounced but distinct interconnected fungal communities distinguished SARS-CoV-2 positive and negative patients. Fungal gut microbiota in severe/critical COVID-19 illness was characterized by a reduced diversity, richness and evenness and by an increase of the relative abundance of the Ascomycota phylum compared with non-severe COVID-19 illness. A dominance of a single fungal species with a relative abundance of >75% was a frequent feature in severe/critical COVID-19. The dominating fungal species were highly variable between patients even within the groups. Several fungal taxa were depleted in patients with severe/critical COVID-19.The distinct compositional changes of the fungal gut microbiome in SARS-CoV-2 infection, especially in severe COVID-19 illness, illuminate the necessity of a broader approach to investigate whether the differences in the fungal gut microbiome are consequences of SARS-CoV-2 infection or a predisposing factor for critical illness.

Two sides of the same coin: Protective versus pathogenic CD4+ resident memory T cells

The ability of the adaptive immune system to form memory is key to providing protection against secondary infections. Resident memory T cells (T_RM) are specialized T cell populations that reside within tissue sites where they await reencounter with their cognate antigen. T_RM are distinct from circulating memory cells, including central and effector memory T cells, both functionally and transcriptionally. Since the discovery of T_RM, most research has focused on CD8⁺ T_RM, despite that CD4⁺ T_RM are also abundant in most tissues. In the past few years, more evidence has emerged that CD4⁺ T_RM can contribute both protective and pathogenic roles in disease. A complexity inherent to the CD4⁺ T_RM field is the ability of CD4⁺ T cells to polarize into a multitude of distinct subsets and recognize not only viruses and intracellular bacteria but also extracellular bacteria, fungi, and parasites. In this review, we outline the key features of CD4⁺ T_RM in health and disease, including their contributions to protection against SARS-CoV-2 and potential contributions to immunopathology associated with COVID-19.

Roles for the mycobiome in liver disease

Liver disease, a major cause of global mortality, has been associated with dysbiosis of the intestinal microbiota (bacteria, fungi, viruses, and other microbes). Studies have associated changes in gut bacteria with pathogenesis and severity of liver disease, but the contributions of the mycobiome (the fungal populations of the gut) to health and disease have not been well studied. We review recent findings of alterations in the composition of the mycobiota in patients with liver disease and discuss the mechanisms by which these might affect pathogenesis and disease progression. Strategies to manipulate the gut mycobiota might be developed to treat or prevent liver disease.

The role of A Disintegrin and Metalloproteinase (ADAM)-10 in T helper cell biology

A Disintegrin and Metalloproteinases (ADAM)-10 is a member of a family of membrane-anchored proteinases that regulate a broad range of cellular functions with central roles within the immune system. This has spurred the interest to modulate ADAM activity therapeutically in immunological diseases. CD4 T helper (Th) cells are the key regulators of adaptive immune responses. Their development and function is strongly dependent on Notch, a key ADAM-10 substrate. However, Th cells rely on a variety of additional ADAM-10 substrates regulating their functional activity at multiple levels. The complexity of both, the ADAM substrate expression as well as the functional consequences of ADAM-mediated cleavage of the various substrates complicates the analysis of cell type specific effects. Here we provide an overview on the major ADAM-10 substrates relevant for CD4 T cell biology and discuss the potential effects of ADAM-mediated cleavage exemplified for a selection of important substrates.

The Polarity and Specificity of Antiviral T Lymphocyte Responses Determine Susceptibility to SARS-CoV-2 Infection in Patients with Cancer and Healthy Individuals

Vaccination against coronavirus disease 2019 (COVID-19) relies on the in-depth understanding of protective immune responses to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). We characterized the polarity and specificity of memory T cells directed against SARS-CoV-2 viral lysates and peptides to determine correlates with spontaneous, virus-elicited, or vaccine-induced protection against COVID-19 in disease-free and cancer-bearing individuals. A disbalance between type 1 and 2 cytokine release was associated with high susceptibility to COVID-19. Individuals susceptible to infection exhibited a specific deficit in the T helper 1/T cytotoxic 1 (Th1/Tc1) peptide repertoire affecting the receptor binding domain of the spike protein (S1-RBD), a hotspot of viral mutations. Current vaccines triggered Th1/Tc1 responses in only a fraction of all subject categories, more effectively against the original sequence of S1-RBD than that from viral variants. We speculate that the next generation of vaccines should elicit Th1/Tc1 T-cell responses against the S1-RBD domain of emerging viral variants.

SIGNIFICANCE

This study prospectively analyzed virus-specific T-cell correlates of protection against COVID-19 in healthy and cancer-bearing individuals. A disbalance between Th1/Th2 recall responses conferred susceptibility to COVID-19 in both populations, coinciding with selective defects in Th1 recognition of the receptor binding domain of spike. See related commentary by McGary and Vardhana, p. 892. This article is highlighted in the In This Issue feature, p. 873.

"Molding" immunity-modulation of mucosal and systemic immunity by the intestinal mycobiome in health and disease

Fungi are important yet understudied contributors to the microbial communities of the gastrointestinal tract. Starting at birth, the intestinal mycobiome undergoes a period of dynamic maturation under the influence of microbial, host, and extrinsic influences, with profound functional implications for immune development in early life, and regulation of immune homeostasis throughout life. Candida albicans serves as a model organism for understanding the cross-talk between fungal colonization dynamics and immunity, and exemplifies unique mechanisms of fungal-immune interactions, including fungal dimorphism, though our understanding of other intestinal fungi is growing. Given the prominent role of the gut mycobiome in promoting immune homeostasis, emerging evidence points to fungal dysbiosis as an influential contributor to immune dysregulation in a variety of inflammatory and infectious diseases. Here we review current knowledge on the factors that govern host-fungi interactions in the intestinal tract and immunological outcomes in both mucosal and systemic compartments.

The Effect of Antibiotics on the Infant Gut Fungal Microbiota

Antibiotics are commonly used drugs in infants, causing disruptions in the developing gut microbiota with possible detrimental long-term effects such as chronic inflammatory diseases. The focus has been on bacteria, but research shows that fungi might have an important role as well. There are only a few studies on the infant gut fungal microbiota, the mycobiota, in relation to antibiotic treatment. Here, the aim was to investigate the impact of antibiotics on the infant gut mycobiota, and the interkingdom associations between bacteria and fungi. We had 37 antibiotic-naïve patients suffering from respiratory syncytial virus, of which 21 received one to four courses of antibiotics due to complications, and 16 remained antibiotic-naïve throughout the study. Fecal samples were collected before, during and after antibiotic treatment with a follow-up period of up to 9.5 months. The gut mycobiota was studied by Illumina MiSeq sequencing of the ITS1 region. We found that antibiotic use affected the gut mycobiota, most prominently seen as a higher relative abundance of Candida (p < 0.001), and a higher fungal diversity (p = 0.005−0.04) and richness (p = 0.03) in the antibiotic-treated infants compared to the antibiotic-naïve ones at multiple timepoints. This indicates that the gut mycobiota could contribute to the long-term consequences of antibiotic treatments.

Recent Advances in Fungal Infections: From Lung Ecology to Therapeutic Strategies With a Focus on Aspergillus spp

Fungal infections are estimated to be the main cause of death for more than 1.5 million people worldwide annually. However, fungal pathogenicity has been largely neglected. This is notably the case for pulmonary fungal infections, which are difficult to diagnose and to treat. We are currently facing a global emergence of antifungal resistance, which decreases the chances of survival for affected patients. New therapeutic approaches are therefore needed to face these life-threatening fungal infections. In this review, we will provide a general overview on respiratory fungal infections, with a focus on fungi of the genus Aspergillus. Next, the immunological and microbiological mechanisms of fungal pathogenesis will be discussed. The role of the respiratory mycobiota and its interactions with the bacterial microbiota on lung fungal infections will be presented from an ecological perspective. Finally, we will focus on existing and future innovative approaches for the treatment of respiratory fungal infections.

Insights into the Role of Commensal-Specific T Cells in Intestinal Inflammation

Trillions of microorganisms exist in the human intestine as commensals and contribute to homeostasis through their interactions with the immune system. In this review, we use previous evidence from published papers to elucidate the involvement of commensal-specific T cells (CSTCs) in regulating intestinal inflammatory responses. CSTCs are generated centrally in the thymus or peripherally at mucosal interfaces and present as CD4+ or CD8+ T cells. Bacteria, fungi, and even viruses act commensally with humans, warranting consideration of CSTCs in this critical relationship. Dysregulation of this immunological balance can result in both intestinal inflammation or damaging autoimmune responses elsewhere in the body. Given the relative novelty of CSTCs in the literature, we aim to introduce the importance of their role in maintaining immune homeostasis at barrier sites such as the intestine.

Fungi make fun guys

In a recent Cell study, Leonardi et al. show that commensal mucosa-associated gut fungi profoundly impact host immunity, epithelial barrier function, and, unexpectedly, neuroimmune modulation of social behavior. All of these events are controlled by fungal-induced activation of type 17 cytokines that act on both epithelial cells and neurons.

Mucosal fungi promote gut barrier function and social behavior via Type 17 immunity

Fungal communities (the mycobiota) are an integral part of the gut microbiota, and the disruption of their integrity contributes to local and gut-distal pathologies. Yet, the mechanisms by which intestinal fungi promote homeostasis remain unclear. We characterized the mycobiota biogeography along the gastrointestinal tract and identified a subset of fungi associated with the intestinal mucosa of mice and humans. Mucosa-associated fungi (MAF) reinforced intestinal epithelial function and protected mice against intestinal injury and bacterial infection. Notably, intestinal colonization with a defined consortium of MAF promoted social behavior in mice. The gut-local effects on barrier function were dependent on IL-22 production by CD4⁺ T helper cells, whereas the effects on social behavior were mediated through IL-17R-dependent signaling in neurons. Thus, the spatial organization of the gut mycobiota is associated with host-protective immunity and epithelial barrier function and might be a driver of the neuroimmune modulation of mouse behavior through complementary Type 17 immune mechanisms.

Informatic analysis of the pulmonary microecology in non-cystic fibrosis bronchiectasis at three different stages

This study explored the impact of pulmonary microecological changes on disease progression in non-cystic fibrosis bronchiectasis (nCFB). A careful search of the NCBI BioProject database revealed the 16S rRNA-based microbiological testing results of 441 pulmonary sputum samples from patients in the relatively stable (baseline), acute exacerbation, or recovery stage. After preliminary analysis and screening, we selected 152 samples for further analyses, including determination of the operational taxonomic unit (OTU) distribution at the phylum, class, order, family and genus levels, community structure, alpha diversity, beta diversity, microbial multivariables, correlations, and community structure after the abundances of intragroup samples were averaged. The recovery group showed significant differences in pulmonary microbiological changes (P < 0.05) compared with the other groups. There were 30 differentially abundant OTUs, with 27 and 7 at the genus and phylum levels, respectively. The Chao1 value of the recovery group was comparable to that of the baseline group, and the Shannon and Simpson values of the recovery group were the highest. Rhodococcus in Actinobacteria was positively correlated with Ochrobactrum in Firmicutes. The differences in pulmonary microecological changes at different nCFB stages may serve as a biologically predictive indicator of nCFB progression.

Immune Response of an Oral Enterococcus faecalis Phage Cocktail in a Mouse Model of Ethanol-Induced Liver Disease

Cytolysin-positive Enterococcus faecalis (E. faecalis) cause more severe alcohol-associated hepatitis, and phages might be used to specifically target these bacteria in a clinical trial. Using a humanized mouse model of ethanol-induced liver disease, the effect of cytolytic E. faecalis phage treatment on the intestinal and liver immune response was evaluated. The observed immune response was predominantly anti-inflammatory and tissue-restoring. Besides, live phages could be readily recovered from the serum, spleen, and liver following oral gavage in ethanol-fed mice. We also isolated 20 new phages from the sewage water; six of them exhibited a relatively broad host range. Taken together, the oral administration of cytolytic E. faecalis phages leads to the translocation of phages to the systemic circulation and appears to be safe, following chronic-binge ethanol administration. A cocktail of three phages covers the majority of tested cytolysin-positive E. faecalis strains and could be tested in a clinical trial.

Metaproteomic profiling of fungal gut colonization in gnotobiotic mice

BACKGROUND

Eukaryotic microbes can modulate mammalian host health and disease states, yet the molecular contribution of gut fungi remains nascent. We previously showed that mice exclusively colonised with fungi displayed increased sensitivity to allergic airway inflammation and had fecal metabolite profiles similar to germ-free mice. This marginal effect on the host metabolome suggested that fungi do not primarily use metabolites to modulate the host immune system.

METHODS

To describe functional changes attributed to fungal colonisation, we performed mass spectrometry-based analyses of feces (Label-Free Quantitative; LFQ) and the small intestine (labeling with Tandem Mass Tag; TMT) of gnotobiotic mice colonised with defined consortia of twelve bacterial species, five fungal species, or both. We also evaluated the effect of microbiome perturbances on the metaproteome by analysing feces from mouse pups treated with an antibiotic or antifungal.

RESULTS

We detected 6675 proteins in the mice feces, of which 3845 had determined LFQ levels. Analysis of variance showed changes in the different gnotobiotic mouse groups; specifically, 46% of 2860 bacterial, 15% of 580 fungal, and 76% of 405 mouse quantified proteins displayed differential levels. The antimicrobial treatments resulted in lasting changes in the bacterial and fungal proteomes, suggesting that the antimicrobials impacted the entire community. Fungal colonisation resulted in changes in host proteins functional in innate immunity as well as metabolism, predicting specific roles of gut fungi on host systems during early developmental stages. Several of the detected fungal proteins (3% of 1492) have been previously reported as part of extracellular vesicles and having immunomodulating properties. Using an isobaric labelling TMT approach for profiling low abundant proteins of the jejunal tissue, we confirmed that the five fungal species differentially impacted the host intestinal proteome compared to the bacterial consortium. The detected changes in mouse jejunal proteins (4% of 1514) were mainly driven by metabolic proteins.

CONCLUSIONS

We used quantitative proteomic profiling of gnotobiotic conditions to show how colonisation with selected fungal species impacts the host gut proteome. Our results suggest that an increased abundance of certain gut fungal species in early life may affect the developing intracellular attributes of epithelial and immune cells.

Fungal Colonization and Infections-Interactions with Other Human Diseases

Candida albicans is a commensal fungus that asymptomatically colonizes the skin and mucosa of 60% of healthy individuals. Breaches in the cutaneous and mucosal barriers trigger candidiasis that ranges from asymptomatic candidemia and mucosal infections to fulminant sepsis with 70% mortality rates. Fungi influence at least several diseases, in part by mechanisms such as the production of pro-carcinogenic agents, molecular mimicking, and triggering of the inflammation cascade. These processes impact the interactions among human pathogenic and resident fungi, the bacteriome in various organs/tissues, and the host immune system, dictating the outcomes of invasive infections, metabolic diseases, and cancer. Although mechanistic investigations are at stages of infancy, recent studies have advanced our understanding of host-fungal interactions, their role in immune homeostasis, and their associated pathologies. This review summarizes the role of C. albicans and other opportunistic fungi, specifically their association with various diseases, providing a glimpse at the recent developments and our current knowledge in the context of inflammatory-bowel disease (IBD), cancers, and COVID-19. Two of the most common human diseases where fungal interactions have been previously well-studied are cancer and IBD. Here we also discuss the emerging role of fungi in the ongoing and evolving pandemic of COVID-19, as it is relevant to current health affairs.

Fungal commensalism modulated by a dual-action phosphate transceptor

Successful host colonization by fungi in fluctuating niches requires response and adaptation to multiple environmental stresses. However, our understanding about how fungal species thrive in the gastrointestinal (GI) ecosystem by combing multifaceted nutritional stress with respect to homeostatic host-commensal interactions is still in its infancy. Here, we discover that depletion of the phosphate transceptor Pho84 across multiple fungal species encountered a substantial cost in gastrointestinal colonization. Mechanistically, Pho84 enhances the gastrointestinal commensalism via a dual-action activity, coordinating both phosphate uptake and TOR activation by induction of the transcriptional regulator Try4 and downstream commensalism-related transcription. As such, Pho84 promotes Candida albicans commensalism, but this does not translate into enhanced pathogenicity. Thus, our study uncovers a specific nutrient-dependent dual-action regulatory pathway for Pho84 on fungal commensalism.