Integrating genetic and immune factors to uncover pathogenetic mechanisms of viral-associated pulmonary aspergillosis

Invasive pulmonary aspergillosis is a severe fungal infection primarily affecting immunocompromised patients. Individuals with severe viral infections have recently been identified as vulnerable to developing invasive fungal infections. Both influenza-associated pulmonary aspergillosis (IAPA) and COVID-19-associated pulmonary aspergillosis (CAPA) are linked to high mortality rates, emphasizing the urgent need for an improved understanding of disease pathogenesis to unveil new molecular targets with diagnostic and therapeutic potential. The recent establishment of animal models replicating the co-infection context has offered crucial insights into the mechanisms that underlie susceptibility to disease. However, the development and progression of human viral-fungal co-infections exhibit a significant degree of interindividual variability, even among patients with similar clinical conditions. This observation implies a significant role for host genetics, but information regarding the genetic basis for viral-fungal co-infections is currently limited. In this review, we discuss how genetic factors known to affect either antiviral or antifungal immunity could potentially reveal pathogenetic mechanisms that predispose to IAPA or CAPA and influence the overall disease course. These insights are anticipated to foster further research in both pre-clinical models and human patients, aiming to elucidate the complex pathophysiology of viral-associated pulmonary aspergillosis and contributing to the identification of new diagnostic and therapeutic targets to improve the management of these co-infections.

Lower respiratory tract single-cell RNA sequencing and neutrophil extracellular trap profiling of COVID-19-associated pulmonary aspergillosis: a single centre, retrospective, observational study

BACKGROUND

COVID-19-associated pulmonary aspergillosis (CAPA) is a severe superinfection with the fungus Aspergillus affecting patients who are critically ill with COVID-19. The pathophysiology and the role of neutrophil extracellular traps (NETs) in this infection are largely unknown. We aimed to characterise the immune profile, with a focus on neutrophils and NET concentrations, of critically ill patients with COVID-19, with or without CAPA.

METHODS

We conducted a single-centre, retrospective, observational study in two patient cohorts, both recruited at University Hospitals Leuven, Belgium. We included adults aged 18 years or older who were admitted to the intensive care unit because of COVID-19 between March 31, 2020, and May 18, 2021, and who were included in the previous Contagious trial (NCT04327570). We investigated the immune cellular landscape of CAPA versus COVID-19 only by performing single-cell RNA sequencing (scRNA-seq) on bronchoalveolar lavage fluid. Bronchoalveolar lavage immune cell fractions were compared between patients with CAPA and patients with COVID-19 only. Additionally, we determined lower respiratory tract NET concentrations using biochemical assays in patients aged 18 years and older who were admitted to the intensive care unit because of severe COVID-19 between March 15, 2020, and Dec 31, 2021, for whom bronchoalveolar lavage was available in the hospital biobank. Bronchoalveolar lavage NET concentrations were compared between patients with CAPA and patients with COVID-19 only and integrated with existing data on immune mediators in bronchoalveolar lavage and 90-day mortality.

FINDINGS

We performed scRNA-seq of bronchoalveolar lavage on 43 samples from 39 patients, of whom 36 patients (30 male and six female; 14 with CAPA) were included in downstream analyses. We performed bronchoalveolar lavage NET analyses in 59 patients (46 male and 13 female), of whom 26 had CAPA. By scRNA-seq, patients with CAPA had significantly lower neutrophil fractions than patients with COVID-19 only (16% vs 33%; p=0·0020). The remaining neutrophils in patients with CAPA preferentially followed a hybrid maturation trajectory characterised by expression of genes linked to antigen presentation, with enhanced transcription of antifungal effector pathways. Patients with CAPA also showed depletion of mucosal-associated invariant T cells, reduced T helper 1 and T helper 17 differentiation, and transcriptional defects in specific aspects of antifungal immunity in macrophages and monocytes. We observed increased formation of NETs in patients with CAPA compared with patients with COVID-19 only (DNA complexed with citrullinated histone H3 median 15 898 ng/mL [IQR 4588-86 419] vs 7062 ng/mL [775-14 088]; p=0·042), thereby explaining decreased neutrophil fractions by scRNA-seq. Low bronchoalveolar lavage NET concentrations were associated with increased 90-day mortality in patients with CAPA.

INTERPRETATION

Qualitative and quantitative disturbances in monocyte, macrophage, B-cell, and T-cell populations could predispose patients with severe COVID-19 to develop CAPA. Hybrid neutrophils form a specialised response to CAPA, and an adequate neutrophil response to CAPA is a major determinant for survival in these patients. Therefore, measuring bronchoalveolar lavage NETs could have diagnostic and prognostic value in patients with CAPA. Clinicians should be wary of aspergillosis when using immunomodulatory therapy that might inhibit NETosis to treat patients with severe COVID-19.

FUNDING

Research Foundation Flanders, KU Leuven, UZ Leuven, VIB, the Fundação para a Ciência e a Tecnologia, the European Regional Development Fund, la Caixa Foundation, the Flemish Government, and Horizon 2020.

Glutamine Metabolism Supports the Functional Activity of Immune Cells against Aspergillus fumigatus

The reprogramming of cellular metabolism of immune cells is an essential process in the regulation of antifungal immune responses. In particular, glucose metabolism has been shown to be required for protective immunity against infection with Aspergillus fumigatus. However, given the intricate cross talk between multiple metabolic networks and signals, it is likely that cellular metabolic pathways other than glycolysis are also relevant during fungal infection. In this study, we demonstrate that glutamine metabolism is required for the activation of macrophage effector functions against A. fumigatus. Glutamine metabolism was found to be upregulated early after fungal infection and glutamine depletion or the pharmacological inhibition of enzymes involved in its metabolism impaired phagocytosis and the production of both proinflammatory and T-cell-derived cytokines. In an in vivo model, inhibition of glutaminase increased susceptibility to experimental aspergillosis, as revealed by the increased fungal burden and inflammatory pathology, and the defective cytokine production in the lungs. Moreover, genetic variants in glutamine metabolism genes were found to regulate cytokine production in response to A. fumigatus stimulation. Taken together, our results demonstrate that glutamine metabolism represents an important component of the immunometabolic response of macrophages against A. fumigatus both in vitro and in vivo. IMPORTANCE The fungal pathogen Aspergillus fumigatus can cause severe and life-threatening forms of infection in immunocompromised patients. The reprogramming of cellular metabolism is essential for innate immune cells to mount effective antifungal responses. In this study, we report the pivotal contribution of glutaminolysis to the host defense against A. fumigatus. Glutamine metabolism was essential both in vitro as well as in in vivo models of infection, and genetic variants in human glutamine metabolism genes regulated cytokine production in response to fungal stimulation. This work highlights the relevance of glutaminolysis to the pathogenesis of aspergillosis and supports a role for interindividual genetic variation influencing glutamine metabolism in susceptibility to infection.

S3.3d Influenza versus COVID-19-associated pulmonary aspergillosis: Profiling lower respiratory tract epithelial and myeloid innate immunity in patient samples

 

S3.3 Innate immune responses to pathogenic fungi, September 21, 2022, 4:45 PM - 6:15 PM

Objectives

Up to 20% and 15% of critically ill influenza and coronavirus disease 2019 (COVID-19) patients are affected by influenza- and COVID-19-associated pulmonary aspergillosis (IAPA and CAPA) respectively. These viral-fungal coinfections are difficult to diagnose and are associated with increased mortality. Mechanistic insights into the development of IAPA and CAPA are a prerequisite for the development of new biomarkers and novel immunomodulatory therapeutic targets. However, data on the pathophysiology are scarce. With this study, we aimed at expanding our knowledge of IAPA and CAPA pathophysiology in an explorative way, resorting to lower respiratory tract samples and focusing on the epithelial and myeloid innate immunity components of the antifungal host response.

Methods

We performed nCounter gene expression analyses of 755 genes linked to innate immunity, and determined protein levels of 47 cytokines, chemokines, growth factors, and other inflammatory mediators on bronchoalveolar lavage (BAL) fluid samples from 166 ICU-admitted influenza and COVID-19-patients with or without aspergillosis. Additionally, we performed spatial transcriptomics and RNAscope on in vivo tracheobronchial biopsies from four IAPA and CAPA patients.

Results

Several genes encoding proteins with important effector functions in antifungal immunity are downregulated in BAL fluid of IAPA and CAPA patients compared with influenza-only or COVID-19-only patients. Cellular deconvolution of the gene expression data reveals a significantly lower BAL neutrophil fraction in CAPA patients compared to COVID-19-only patients.

IAPA and CAPA patients have high BAL fluid levels of pro-inflammatory cytokines, but these are not significantly different from the levels seen in influenza-only and COVID-19-only patients. By integrating the BAL fluid cytokine levels with their respective transcriptional responses, we show that IAPA patients, and to a lesser extent CAPA patients, have an aberrant transcriptional response to pro-inflammatory cytokines as well as type I and type II interferons, which may result in poor cellular effector functions (Fig. 1a). Interferon-gamma signaling is abrogated in both IAPA and CAPA patients when compared with influenza-only and COVID-19-only patients.

We observe significantly higher levels of growth factors associated with lung fibrosis in both IAPA and CAPA BAL fluid, which may contribute to the higher mortality seen in these coinfections (Fig. 1b).

Using spatial transcriptomics, we show that different epithelial defense mechanisms are at play in IAPA and CAPA (Fig. 2a).

Finally, using RNAscope ultrasensitive single-molecule RNA in situ hybridization, we visualize fungal and viral co-localization in CAPA tracheobronchial tissue, proving that virus-induced epithelial barrier disruption paves the way for tissue-invasive aspergillosis (Fig. 2b).

Conclusion

Using state-of-the-art techniques in lower respiratory tract samples obtained from a large representative patient cohort, we provide arguments for a three-level breach in antifungal immunity in IAPA and CAPA. A hampered ability to phagocytize and kill fungal spores enables Aspergillus germination and growth, leading to hyphae that are not contained because of restrained extracellular defense mechanisms. These hyphae may easily become tissue-invasive through an epithelium that is weakened by the viral infection, causing detrimental damage to the respiratory system. Functional studies will be necessary to further unravel the pathophysiology of IAPA and CAPA.

Genetic determinants of fungi-induced ROS production are associated with the risk of invasive pulmonary aspergillosis

Reactive oxygen species (ROS) are an essential component of the host defense against fungal infections. However, little is known about how common genetic variation affects ROS-mediated antifungal host defense. In the present study, we investigated the genetic factors that regulate ROS production capacity in response to the two human fungal pathogens: Candida albicans and Aspergillus fumigatus. We investigated fungal-stimulated ROS production by immune cells isolated from a population-based cohort of approximately 200 healthy individuals (200FG cohort), and mapped ROS-quantitative trait loci (QTLs). We identified several genetic loci that regulate ROS levels (P < 9.99 × 10-6), with some of these loci being pathogen-specific, and others shared between the two fungi. These ROS-QTLs were investigated for their influence on the risk of invasive pulmonary aspergillosis (IPA) in a disease relevant context. We stratified hematopoietic stem-cell transplant (HSCT) recipients based on the donor's SNP genotype and tested their impact on the risk of IPA. We identified rs4685368 as a ROS-QTL locus that was significantly associated with an increased risk of IPA after controlling for patient age and sex, hematological malignancy, type of transplantation, conditioning regimen, acute graft-versus-host-disease grades III-IV, and antifungal prophylaxis. Collectively, this data provides evidence that common genetic variation can influence ROS production capacity, and, importantly, the risk of developing IPA among HSCT recipients. This evidence warrants further research for patient stratification based on the genetic profiling that would allow the identifications of patients at high-risk for an invasive fungal infection, and who would benefit the most from a preventive strategy.

Lung epithelial and myeloid innate immunity in influenza-associated or COVID-19-associated pulmonary aspergillosis: an observational study

BACKGROUND

Influenza-associated pulmonary aspergillosis (IAPA) and COVID-19-associated pulmonary aspergillosis (CAPA) affect about 15% of critically ill patients with influenza or COVID-19, respectively. These viral-fungal coinfections are difficult to diagnose and are associated with increased mortality, but data on their pathophysiology are scarce. We aimed to explore the role of lung epithelial and myeloid innate immunity in patients with IAPA or CAPA.

METHODS

In this observational study, we retrospectively recruited patients who had been admitted to the intensive care unit (ICU) of University Hospitals Leuven, Belgium, requiring non-invasive or invasive ventilation because of severe influenza or COVID-19, with or without aspergillosis, between Jan 1, 2011, and March 31, 2021, whose bronchoalveolar lavage samples were available at the hospital biobank. Additionally, biobanked in vivo tracheobronchial biopsy samples from patients with IAPA or CAPA and invasive Aspergillus tracheobronchitis admitted to ICUs requiring invasive ventilation between the same dates were collected from University Hospitals Leuven, Hospital Network Antwerp (Belgium), and Amiens-Picardie University Hospital (France). We did nCounter gene expression analysis of 755 genes linked to myeloid innate immunity and protein analysis of 47 cytokines, chemokines, and growth factors on the bronchoalveolar lavage samples. Gene expression data were used to infer cell fractions by use of CIBERSORTx, to perform hypergeometric enrichment pathway analysis and gene set enrichment analysis, and to calculate pathway module scores for the IL-1β, TNF-α, type I IFN, and type II IFN (IFNγ) pathways. We did RNAScope targeting influenza virus or SARS-CoV-2 RNA and GeoMx spatial transcriptomics on the tracheobronchial biopsy samples.

FINDINGS

Biobanked bronchoalveolar lavage samples were retrieved from 166 eligible patients, of whom 40 had IAPA, 52 had influenza without aspergillosis, 33 had CAPA, and 41 had COVID-19 without aspergillosis. We did nCounter gene expression analysis on bronchoalveolar lavage samples from 134 patients, protein analysis on samples from 162 patients, and both types of analysis on samples from 130 patients. We performed RNAScope and spatial transcriptomics on the tracheobronchial biopsy samples from two patients with IAPA plus invasive Aspergillus tracheobronchitis and two patients with CAPA plus invasive Aspergillus tracheobronchitis. We observed a downregulation of genes associated with antifungal effector functions in patients with IAPA and, to a lesser extent, in patients with CAPA. We found a downregulated expression of several genes encoding proteins with functions in the opsonisation, recognition, and killing of conidia in patients with IAPA versus influenza only and in patients with CAPA versus COVID-19 only. Several genes related to LC3-associated phagocytosis, autophagy, or both were differentially expressed. Patients with CAPA had significantly lower neutrophil cell fractions than did patients with COVID-19 only. Patients with IAPA or CAPA had downregulated IFNγ signalling compared with patients with influenza only or COVID-19 only, respectively. The concentrations of several fibrosis-related growth factors were significantly elevated in the bronchoalveolar lavage fluid from patients with IAPA versus influenza only and from patients with CAPA versus COVID-19 only. In one patient with CAPA, we visualised an active or very recent SARS-CoV-2 infection disrupting the epithelial barrier, facilitating tissue-invasive aspergillosis.

INTERPRETATION

Our results reveal a three-level breach in antifungal immunity in IAPA and CAPA, affecting the integrity of the epithelial barrier, the capacity to phagocytise and kill Aspergillus spores, and the ability to destroy Aspergillus hyphae, which is mainly mediated by neutrophils. The potential of adjuvant IFNγ in the treatment of IAPA and CAPA should be investigated.

FUNDING

Research Foundation Flanders, Coronafonds, the Max Planck Society, the Fundação para a Ciência e a Tecnologia, the European Regional Development Fund, "la Caixa" Foundation, and Horizon 2020.

Targeting immunometabolism in host-directed therapies to fungal disease

Fungal infections affect over a billion people and are responsible for more than 1.5 million deaths each year. Despite progress in diagnostic and therapeutic approaches, the management of severe fungal infections remains a challenge. Recently, the reprogramming of cellular metabolism has emerged as a central mechanism through which the effector functions of immune cells are supported to promote antifungal activity. An improved understanding of the immunometabolic signatures that orchestrate antifungal immunity, together with the dissection of the mechanisms that underlie heterogeneity in individual immune responses, may therefore unveil new targets amenable to adjunctive host-directed therapies. In this review, we highlight recent advances in the metabolic regulation of host-fungus interactions and antifungal immune responses, and outline targetable pathways and mechanisms with promising therapeutic potential.

Understanding the genetic basis of immune responses to fungal infection

INTRODUCTION

Fungal infections represent a global public health problem that affect millions of people. Despite remarkable advances achieved over the last decades, available diagnostic and therapeutic tools remain insufficient for the optimal management of these diseases. The clinical course of fungal infection is highly variable, and evidence accumulated from patients with rare mutations and cohort-based studies suggests that the trajectory of disease is largely defined by patient genetics and its impact on immune responses. Therefore, there is an urgent need to elucidate the precise mechanisms by which which genetic variants influence the risk, progression, and outcome of fungal infection.

AREAS COVERED

In this review, we highlight recent advances in our understanding of the genetic factors that influence antifungal immune responses based on candidate gene studies and genome-wide approaches performed in different experimental and clinical models.

EXPERT OPINION

Research on genetics of susceptibility to infection is expected to lead to a detailed knowledge framework for the pathogenesis of human fungal infections and unveil novel targets and pathways amenable to clinical intervention.

Lung microbiota predict invasive pulmonary aspergillosis and its outcome in immunocompromised patients

Rationale

Recent studies have revealed that the lung microbiota of critically ill patients is altered and predicts clinical outcomes. The incidence of invasive fungal infections, namely, invasive pulmonary aspergillosis (IPA), in immunocompromised patients is increasing, but the clinical significance of variations in lung bacterial communities is unknown.

Objectives

To define the contribution of the lung microbiota to the development and course of IPA.

Methods and measurements

We performed an observational cohort study to characterise the lung microbiota in 104 immunocompromised patients using bacterial 16S ribosomal RNA gene sequencing on bronchoalveolar lavage samples sampled on clinical suspicion of infection. Associations between lung dysbiosis in IPA and pulmonary immunity were evaluated by quantifying alveolar cytokines and chemokines and immune cells. The contribution of microbial signatures to patient outcome was assessed by estimating overall survival.

Main results

Patients diagnosed with IPA displayed a decreased alpha diversity, driven by a markedly increased abundance of the Staphylococcus, Escherichia, Paraclostridium and Finegoldia genera and a decreased proportion of the Prevotella and Veillonella genera. The overall composition of the lung microbiome was influenced by the neutrophil counts and associated with differential levels of alveolar cytokines. Importantly, the degree of bacterial diversity at the onset of IPA predicted the survival of infected patients.

Conclusions

Our results reveal the lung microbiota as an understudied source of clinical variation in patients at risk of IPA and highlight its potential as a diagnostic and therapeutic target in the context of respiratory fungal diseases.

TREM1 regulates antifungal immune responses in invasive pulmonary aspergillosis

Pattern recognition receptors (PRRs) are responsible for Aspergillus fumigatus recognition by innate immunity and its subsequent immune signaling. The triggering receptor expressed on myeloid cells 1 (TREM1) is a recently characterized pro-inflammatory receptor constitutively expressed on the surface of neutrophils and macrophages. A soluble form (sTREM1) of this protein that can be detected in human body fluids has been identified. Here we investigated the role of TREM1 during invasive pulmonary aspergillosis (IPA). IPA patients displayed significantly higher levels of sTREM1 in bronchoalveolar lavages when compared to control patients. Functional analysis in TREM1 showed that the levels of sTREM1 and TREM1 pathway-related cytokines were influenced by single nucleotide polymorphisms in TREM1. In addition, we confirmed a role of TREM1 on antifungal host defense against A. fumigatus in a murine model of IPA. TREM1 deficiency increased susceptibility to infection in the immunosuppressed murine host. Deletion of TREM1 showed delayed innate and adaptive immune responses and impaired pro-inflammatory cytokine responses. The absence of TREM1 in primary macrophages attenuated the TLR signaling by altering the expression of both receptor and effector proteins that are critical to the response against A. fumigatus. In this study, and for the first time, we demonstrate the key role for the TREM1 receptor pathway during IPA.

Microbiota-derived metabolites as diagnostic markers for respiratory fungal infections

An emerging body of evidence has highlighted the significant role of the pulmonary microbiota during respiratory infections. The individual microbiome is nowadays recognized to supervise the outcome of the host-pathogen interaction by orchestrating mechanisms of immune regulation, inflammation, metabolism, and other physiological processes. A shift in the normal flora of the respiratory tract is associated with several lung inflammatory disorders including asthma, chronic obstructive pulmonary disease, or cystic fibrosis. These diseases are characterized by a lung microenvironment that becomes permissive to infections caused by the opportunistic fungal pathogen Aspergillus fumigatus. Although the role of the lung microbiota in the pathophysiology of respiratory fungal diseases remains elusive, microbiota-derived components have been proposed as important biomarkers to be considered in the diagnosis of these severe infections. Here, we review this emerging area of research and discuss the potential of microbiota-derived products in the diagnosis of respiratory fungal diseases.

Phagosomal removal of fungal melanin reprograms macrophage metabolism to promote antifungal immunity

In response to infection, macrophages adapt their metabolism rapidly to enhance glycolysis and fuel specialized antimicrobial effector functions. Here we show that fungal melanin is an essential molecule required for the metabolic rewiring of macrophages during infection with the fungal pathogen Aspergillus fumigatus. Using pharmacological and genetic tools, we reveal a molecular link between calcium sequestration by melanin inside the phagosome and induction of glycolysis required for efficient innate immune responses. By remodeling the intracellular calcium machinery and impairing signaling via calmodulin, melanin drives an immunometabolic signaling axis towards glycolysis with activation of hypoxia-inducible factor 1 subunit alpha (HIF-1α) and phagosomal recruitment of mammalian target of rapamycin (mTOR). These data demonstrate a pivotal mechanism in the immunometabolic regulation of macrophages during fungal infection and highlight the metabolic repurposing of immune cells as a potential therapeutic strategy.

Host Genetic Signatures of Susceptibility to Fungal Disease

Our relative inability to predict the development of fungal disease and its clinical outcome raises fundamental questions about its actual pathogenesis. Several clinical risk factors are described to predispose to fungal disease, particularly in immunocompromised and severely ill patients. However, these alone do not entirely explain why, under comparable clinical conditions, only some patients develop infection. Recent clinical and epidemiological studies have reported an expanding number of monogenic defects and common polymorphisms associated with fungal disease. By directly implicating genetic variation in the functional regulation of immune mediators and interacting pathways, these studies have provided critical insights into the human immunobiology of fungal disease. Most of the common genetic defects reported were described or suggested to impair fungal recognition by the innate immune system. Here, we review common genetic variation in pattern recognition receptors and its impact on the immune response against the two major fungal pathogens Candida albicans and Aspergillus fumigatus. In addition, we discuss potential strategies and opportunities for the clinical translation of genetic information in the field of medical mycology. These approaches are expected to transfigure current clinical practice by unleashing an unprecedented ability to personalize prophylaxis, therapy and monitoring for fungal disease.

Evaluation of Bronchoalveolar Lavage Fluid Cytokines as Biomarkers for Invasive Pulmonary Aspergillosis in At-Risk Patients

Background: Invasive pulmonary aspergillosis (IPA) is an infection that primarily affects immunocompromised hosts, including hematological patients and stem-cell transplant recipients. The diagnosis of IPA remains challenging, making desirable the availability of new specific biomarkers. High-throughput methods now allow us to interrogate the immune system for multiple markers of inflammation with enhanced resolution.

Methods: To determine whether a signature of alveolar cytokines could be associated with the development of IPA and used as a diagnostic biomarker, we performed a nested case-control study involving 113 patients at-risk.

Results: Among the 32 analytes tested, IL-1β, IL-6, IL-8, IL-17A, IL-23, and TNFα were significantly increased among patients with IPA, defining two clusters able to accurately differentiate cases of infection from controls. Genetic variants previously reported to confer increased risk of IPA compromised the production of specific cytokines and impaired their discriminatory potential toward infection. Collectively, our data indicated that IL-8 was the best performing cytokine, with alveolar levels ≥904 pg/mL predicting IPA with elevated sensitivity (90%), specificity (73%), and negative predictive value (88%).

Conclusions: These findings highlight the existence of a specific profile of alveolar cytokines, with IL-8 being the dominant discriminator, which might be useful in supporting current diagnostic approaches for IPA.

The Cell Biology of the Trichosporon-Host Interaction

Fungi of the genus Trichosporon are increasingly recognized as causative agents of superficial and invasive fungal disease in humans. Although most species are considered commensals of the human skin and gastrointestinal tract, these basidiomycetes are an increasing cause of fungal disease among immunocompromised hosts, such as hematological patients and solid organ transplant recipients. The initiation of commensal or pathogenic programs by Trichosporon spp. involves the adaptation to the host microenvironment and its immune system. However, the exact virulence factors activated upon the transition to a pathogenic lifestyle, including the intricate biology of the cell wall, and how these interact with and subvert the host immune responses remain largely unknown. Here, we revisit our current understanding of the virulence attributes of Trichosporon spp., particularly T. asahii, and their interaction with the host immune system, and accommodate this knowledge within novel perspectives on fungal diagnostics and therapeutics.

The microbiome-metabolome crosstalk in the pathogenesis of respiratory fungal diseases

Filamentous fungi of the genus Aspergillus are responsible for several superficial and invasive infections and allergic syndromes. The risk of infection and its clinical outcome vary significantly even among patients with similar predisposing clinical factors and pathogen exposure. There is increasing evidence that the individual microbiome supervises the outcome of the host-fungus interaction by influencing mechanisms of immune regulation, inflammation, metabolism, and other physiological processes. Microbiome-mediated mechanisms of resistance allow therefore the control of fungal colonization, preventing the onset of overt disease, particularly in patients with underlying immune dysfunction. Here, we review this emerging area of research and discuss the contribution of the microbiota (and its dysbiosis), including its immunoregulatory properties and relationship with the metabolic activity of commensals, to respiratory fungal diseases. Finally, we highlight possible strategies aimed at decoding the microbiome-metabolome dialog and at its exploitation toward personalized medical interventions in patients at high risk of infection.

Sevelamer decreases systemic inflammation in parallel to a reduction in endotoxemia

INTRODUCTION

Uremic toxins play a pivotal role in the development of systemic complications of chronic kidney disease (CKD), which are largely mediated by the activation of the immune system. Triggers of inflammation in CKD are largely unknown and strategies aiming to reduce circulating ligands that could start the inflammatory response are potentially important. In the present study, we investigated the impact of sevelamer hydrochloride treatment in reducing endotoxemia and inflammation in a group of hemodialysis (HD) patients.

MATERIAL AND METHODS

HD patients, who were converted from calcium carbonate treatment to sevelamer according to KDOQI guidelines, were included and prospectively followed for 6 months. Systemic inflammation was evaluated by serum ultra-high-sensitivity C-reactive protein (hsCRP) using an automated immunoturbidimetric assay. Endotoxin was measured using Limulus amebocyte lysate chromogenic endpoint assay. All the analyses were performed immediately before conversion and after 6 months of treatment.

RESULTS

After the exclusion of patients discontinuing the treatment, 20 patients (mean dialysis time 12 +/- 4 months on HD, age 52 +/- 2 years, 38% males, 11% diabetics) were included in the analysis. No significant changes were observed in Ca, P and PTH levels, while a reduction in cholesterol levels was seen. Plasma concentration of hsCRP and endotoxin significantly decreased after 6 months of conversion to sevelamer compared with baseline.

CONCLUSION

We conclude that sevelamer treatment leads to a decrease in hsCRP levels, which was accompanied by a parallel decrease in endotoxemia, suggesting that endotoxemia may contribute to the systemic inflammation in HD patients, which was partially reduced by the use of sevelamer.