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[...]invasive aspergillosis has been linked with inborn errors in patients with chronic granulomatous disease, severe congenital neutropenia or leukocyte adhesion deficiency type I (31,32). [...]other less common congenital immunodeficiencies (e.g., CARD9 immunity, IL-12/interferon (IFN)-γ axis or IL-17 immunity) have been described to increase susceptibility risk to invasive candidiasis, dermatophytosis, chronic mucocutaneous candidiasis or endemic mycoses (Figure 1) (33–36). [...]implementation of host genetic screening in the diagnostic pipelines for fungal disease would require validation in large and well-characterised cohort of patients with different genetic backgrounds and the development of point of care testing approaches that would allow the transference of these technologies to those regions where the prevalence of fungal disease is particularly high. [...]in a recent publication using population genomics, it was observed that human infections caused by drug resistant A. fumigatus have their origin in the environment (46). (51) reported that long-term Aspergillus infection in patients with chronic granulomatous disease is driven by host microevolution (51). [...]recent analyses of fungal pangenomes has shown that A. fumigatus environmental isolates do not differ in their gene content (52).

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS) that is associated with demyelination and neuronal loss. Over recent years, the immunological and neuronal effects of tryptophan (Trp) metabolites have been largely investigated, leading to the hypothesis that these compounds and the related enzymes are possibly involved in the pathophysiology of MS. Specifically, the kynurenine pathway of Trp metabolism is responsible for the synthesis of intermediate products with potential immunological and neuronal effects. More recently, Trp metabolites, originating also from the host microbiome, have been identified in MS, and it has been shown that they are differently regulated in MS patients. Here, we sought to discuss whether, in MS patients, a specific urinary signature of host/microbiome Trp metabolism can be potentially identified so as to select novel biomarkers and guide toward the identification of specific metabolic pathways as drug targets in MS.

The chemical processes taking place in humans intersects the myriad of metabolic pathways occurring in commensal microorganisms that colonize the body to generate a complex biochemical network that regulates multiple aspects of human life. The role of tryptophan (Trp) metabolism at the intersection between the host and microbes is increasingly being recognized, and multiple pathways of Trp utilization in either direction have been identified with the production of a wide range of bioactive products. It comes that a dysregulation of Trp metabolism in either the host or the microbes may unbalance the production of metabolites with potential pathological consequences. The ability to redirect the Trp flux to restore a homeostatic production of Trp metabolites may represent a valid therapeutic strategy for a variety of pathological conditions, but identifying metabolic checkpoints that could be exploited to manipulate the Trp metabolic network is still an unmet need. In this review, we put forward the hypothesis that pyridoxal 5′-phosphate (PLP)-dependent enzymes, which regulate multiple pathways of Trp metabolism in both the host and in microbes, might represent critical nodes and that modulating the levels of vitamin B6, from which PLP is derived, might represent a metabolic checkpoint to re-orienteer Trp flux for therapeutic purposes.

T helper 9 (Th9) cells contribute to lung inflammation and allergy as sources of interleukin-9 (IL-9). However, the mechanisms by which IL-9/Th9 mediate immunopathology in the lung are unknown. Here we report an IL-9-driven positive feedback loop that reinforces allergic inflammation. We show that IL-9 increases IL-2 production by mast cells, which leads to expansion of CD25 + type 2 innate lymphoid cells (ILC2) and subsequent activation of Th9 cells. Blocking IL-9 or inhibiting CD117 (c-Kit) signalling counteracts the pathogenic effect of the described IL-9-mast cell-IL-2 signalling axis. Overproduction of IL-9 is observed in expectorates from cystic fibrosis (CF) patients, and a sex-specific variant of IL-9 is predictive of allergic reactions in female patients. Our results suggest that blocking IL-9 may be a therapeutic strategy to ameliorate inflammation associated with microbial colonization in the lung, and offers a plausible explanation for gender differences in clinical outcomes of patients with CF. In patients with cystic fibrosis, IL-9 signalling is increased. The authors describe an inflammatory loop in which IL-9 produced by Th9 cells drives mast cells to produce IL-2, resulting in ILC2 cell activation, and show inhibition of this loop with blocking antibodies to IL-9 in a mouse model of pulmonary infection.

Key role for superoxides In chronic granulomatous disease (CGD), phagocytes lack NADPH oxidase activity and are unable to generate superoxide, making sufferers susceptible to recurrent microbial infections. The precise mechanism involved — and the reasons for exaggerated inflammation in CGD — are unclear. Experiments in genetically engineered CGD mice infected with Aspergillus fumigatus , a frequent infection in CGD patients, supports the theory that superoxide-dependent conversion of tryptophan to kynurenine is defective in CGD, compromising antimicrobial resistance, inflammation, and T-cell homeostasis through a single, as yet unknown mechanism. The finding raises the possibility that replacement therapy with natural kynurenines might help control pathologic inflammation and susceptibility to infection in CGD patients. Chronic granulomatous disease is associated with lack of NADPH activity in phagocytes and characterized by recurrent bacterial and fungal infections as well as exagerated inflammation. This paper shows that the excessive inflammation can be attributed to the lack of NAPPH-derived reactive oxygen which is required for the conversion of tryptophan to kynurenine. Half a century ago, chronic granulomatous disease (CGD) was first described as a disease fatally affecting the ability of children to survive infections. Various milestone discoveries have since been made, from an insufficient ability of patients’ leucocytes to kill microbes to the underlying genetic abnormalities 1 . In this inherited disorder, phagocytes lack NADPH oxidase activity and do not generate reactive oxygen species, most notably superoxide anion, causing recurrent bacterial and fungal infections. Patients with CGD also suffer from chronic inflammatory conditions, most prominently granuloma formation in hollow viscera. The precise mechanisms of the increased microbial pathogenicity have been unclear 2 , and more so the reasons for the exaggerated inflammatory response 3 , 4 , 5 , 6 . Here we show that a superoxide-dependent step in tryptophan metabolism along the kynurenine pathway is blocked in CGD mice with lethal pulmonary aspergillosis, leading to unrestrained Vγ1 + γδ T-cell reactivity, dominant production of interleukin (IL)-17, defective regulatory T-cell activity and acute inflammatory lung injury. Although beneficial effects are induced by IL-17 neutralization or γδ T-cell contraction, complete cure and reversal of the hyperinflammatory phenotype are achieved by replacement therapy with a natural kynurenine distal to the blockade in the pathway. Effective therapy, which includes co-administration of recombinant interferon-γ (IFN-γ), restores production of downstream immunoactive metabolites and enables the emergence of regulatory Vγ4 + γδ and Foxp3 + αβ T cells. Therefore, paradoxically, the lack of reactive oxygen species contributes to the hyperinflammatory phenotype associated with NADPH oxidase deficiencies, through a dysfunctional kynurenine pathway of tryptophan catabolism. Yet, this condition can be reverted by reactivating the pathway downstream of the superoxide-dependent step.

Pathogenicity mechanisms of the yeast Candida albicans involve filamentous growth, adhesion, invasion, and toxin production. Interestingly, clinical isolates, and other Candida spp., can cause infection independent of filamentation or toxin production. These strains and species often are characterized as avirulent ex vivo, yet this does not correlate with their potential to cause infection. We hypothesized that specific host factors, which trigger pathogenicity in vivo, are absent in in vitro infection models and thereby clinical isolates can seem avirulent ex vivo. We investigated how albumin, the most abundant protein in humans, impacts infection and cytotoxic potential of C. albicans in vitro. The presence of albumin induces otherwise non-damaging and non-filamentous clinical isolates to cause host cell cytotoxicity. Moreover, avirulent deletion mutants deficient in filamentation, adhesion, or toxin production are restored in their cytotoxicity by albumin. This involves transcriptional and metabolic reprogramming of C. albicans , increasing biofilm formation and production of the oxylipin 13-hydroxyoctadecadienoic acid, driving host cell cytotoxicity. Collectively, our study uncoveres a pathogenicity mechanism by which C. albicans causes epithelial cytotoxicity independent of its conventional virulence mechanisms. This alternative pathogenicity strategy helps to explain the avirulence of clinical isolates ex vivo, when they are separated from the host environment. Candida albicans normally relies on specific pathogenicity mechanisms to cause tissue damage. This study reveals that when sensing host albumin, C. albicans , even avirulent strains, can trigger an alternative pathogenicity pathway via transcriptional and metabolic reprogramming.

is the most prevalent filamentous fungal pathogen of humans, causing either severe allergic bronchopulmonary aspergillosis or often fatal invasive pulmonary aspergillosis (IPA) in individuals with hyper- or hypo-immune deficiencies, respectively. Disease is primarily initiated upon the inhalation of the ubiquitous airborne conidia-the initial inoculum produced by -which are complete developmental units with an ability to exploit diverse environments, ranging from agricultural composts to animal lungs. Upon infection, conidia initially rely on their own metabolic processes for survival in the host's lungs, a nutritionally limiting environment. One such nutritional limitation is the availability of aromatic amino acids (AAAs) as animals lack the enzymes to synthesize tryptophan (Trp) and phenylalanine and only produce tyrosine from dietary phenylalanine. However, produces all three AAAs through the shikimate-chorismate pathway, where they play a critical role in fungal growth and development and in yielding many downstream metabolites. The downstream metabolites of Trp in include the immunomodulatory kynurenine derived from indoleamine 2,3-dioxygenase (IDO) and toxins such as fumiquinazolines, gliotoxin, and fumitremorgins. Host IDO activity and/or host/microbe-derived kynurenines are increasingly correlated with many diseases including IPA and infections of chronic granulomatous disease patients. In this review, we will describe the potential metabolic cross talk between the host and the pathogen, specifically focusing on Trp metabolism, the implications for therapeutics, and the recent studies on the coevolution of host and microbe IDO activation in regulating inflammation, while controlling infection.

Cystic fibrosis (CF) is an autosomal recessive disorder characterized by respiratory failure due to a vicious cycle of defective Cystic Fibrosis Transmembrane conductance Regulator (CFTR) function, chronic inflammation and recurrent bacterial and fungal infections. Although the recent introduction of CFTR correctors/potentiators has revolutionized the clinical management of CF patients, resurgence of inflammation and persistence of pathogens still posit a major concern and should be targeted contextually. On the background of a network-based selectivity that allows to target the same enzyme in the host and microbes with different outcomes, we focused on sphingosine-1-phosphate (S1P) lyase (SPL) of the sphingolipid metabolism as a potential candidate to uniquely induce anti-inflammatory and antifungal activities in CF. As a feasibility study, herein we show that interfering with S1P metabolism improved the immune response in a murine model of CF with aspergillosis while preventing germination of Aspergillus fumigatus conidia. In addition, in an early drug discovery process, we purified human and A. fumigatus SPL, characterized their biochemical and structural properties, and performed an in silico screening to identify potential dual species SPL inhibitors. We identified two hits behaving as competitive inhibitors of pathogen and host SPL, thus paving the way for hit-to-lead and translational studies for the development of drug candidates capable of restraining fungal growth and increasing antifungal resistance.

Humans inhale hundreds of Aspergillus conidia without adverse consequences. Powerful protective mechanisms may ensure prompt control of the pathogen and inflammation. Here we reveal a previously unknown mechanism by which the danger molecule S100B integrates pathogen- and danger-sensing pathways to restrain inflammation. Upon forming complexes with TLR2 ligands, S100B inhibited TLR2 via RAGE, through a paracrine epithelial cells/neutrophil circuit that restrained pathogen-induced inflammation. However, upon binding to nucleic acids, S100B activated intracellular TLRs eventually resolve danger-induced inflammation via transcriptional inhibition of S100B. Thus, the spatiotemporal regulation of TLRs and RAGE by S100B provides evidence for an evolving braking circuit in infection whereby an endogenous danger protects against pathogen-induced inflammation and a pathogen-sensing mechanism resolves danger-induced inflammation.

Organoids are complex multicellular three-dimensional (3D) in vitro models that are designed to allow accurate studies of the molecular processes and pathologies of human organs. Organoids can be derived from a variety of cell types, such as human primary progenitor cells, pluripotent stem cells, or tumor-derived cells and can be co-cultured with immune or microbial cells to further mimic the tissue niche. Here, we focus on the development of 3D lung organoids and their use as disease models and drug screening tools. We introduce the various experimental approaches used to model complex human diseases and analyze their advantages and disadvantages. We also discuss validation of the organoids and their physiological relevance to the study of lung diseases. Furthermore, we summarize the current use of lung organoids as models of host-pathogen interactions and human lung diseases such as cystic fibrosis, chronic obstructive pulmonary disease, or SARS-CoV-2 infection. Moreover, we discuss the use of lung organoids derived from tumor cells as lung cancer models and their application in personalized cancer medicine research. Finally, we outline the future of research in the field of human induced pluripotent stem cell-derived organoids.