T(H)17 cells promote microbial killing and innate immune sensing of DNA via interleukin 26.

Interleukin 17-producing helper T cells (T(H)17 cells) have a major role in protection against infections and in mediating autoimmune diseases, yet the mechanisms involved are incompletely understood. We found that interleukin 26 (IL-26), a human T(H)17 cell-derived cytokine, is a cationic amphipathic protein that kills extracellular bacteria via membrane-pore formation. Furthermore, T(H)17 cell-derived IL-26 formed complexes with bacterial DNA and self-DNA released by dying bacteria and host cells. The resulting IL-26-DNA complexes triggered the production of type I interferon by plasmacytoid dendritic cells via activation of Toll-like receptor 9, but independently of the IL-26 receptor. These findings provide insights into the potent antimicrobial and proinflammatory function of T(H)17 cells by showing that IL-26 is a natural human antimicrobial that promotes immune sensing of bacterial and host cell death.

A carbapenem-focused antimicrobial stewardship programme implemented during the COVID-19 pandemic in a setting of high endemicity for multidrug-resistant Gram-negative bacteria.

BACKGROUND: Greece is among the countries characterized by high rates of antimicrobial resistance and high consumption of antibiotics, including carbapenems. OBJECTIVES: To measure the impact of a carbapenem-focused antimicrobial stewardship programme (ASP) on the antibiotic consumption and patient outcomes in a Greek tertiary hospital during the COVID-19 pandemic. METHODS: A quasi-experimental, before-after study, comparing a 12 month pre-intervention period with a 12 month intervention period in which a carbapenem-focused ASP was implemented. RESULTS: A total of 1268 patients were enrolled. The proportion of admitted patients who received carbapenems decreased from 4.1% (842 of 20 629) to 2.3% (426 of 18 245) (-1.8%; P < 0.001). A decrease of -4.9 DDD/100 patient-days (PD) (95% CI -7.3 to -2.6; P = 0.007) in carbapenem use and an increase in the use of piperacillin/tazobactam [+2.1 DDD/100 PD (95% CI 1.0-3.3; P = 0.010)] were observed. Thirty-day mortality following initiation of carbapenem treatment and all-cause in-hospital mortality remained unaltered after ASP implementation. In contrast, length of hospital stay increased (median 17.0 versus 19.0 days; P < 0.001), while the risk of infection-related readmission within 30 days of hospital discharge decreased (24.6% versus 16.8%; P = 0.007). In the post-implementation period, acceptance of the ASP intervention was associated with lower daily hazard of in-hospital death [cause-specific HR (csHR) 0.49; 95% CI 0.30-0.80], lower odds of 30 day mortality (OR 0.36; 95% CI 0.18-0.70) and higher rate of treatment success (csHR 2.45; 95% CI 1.59-3.77). CONCLUSIONS: Implementing and maintaining a carbapenem-focused ASP is feasible, effective and safe in settings with high rates of antimicrobial resistance, even during the COVID-19 pandemic.

The Cell Wall of the Human Fungal Pathogen Aspergillus fumigatus: Biosynthesis, Organization, Immune Response, and Virulence.

More than 90% of the cell wall of the filamentous fungus Aspergillus fumigatus comprises polysaccharides. Biosynthesis of the cell wall polysaccharides is under the control of three types of enzymes: transmembrane synthases, which are anchored to the plasma membrane and use nucleotide sugars as substrates, and cell wall-associated transglycosidases and glycosyl hydrolases, which are responsible for remodeling the de novo synthesized polysaccharides and establishing the three-dimensional structure of the cell wall. For years, the cell wall was considered an inert exoskeleton of the fungal cell. The cell wall is now recognized as a living organelle, since the composition and cellular localization of the different constitutive cell wall components (especially of the outer layers) vary when the fungus senses changes in the external environment. The cell wall plays a major role during infection. The recognition of the fungal cell wall by the host is essential in the initiation of the immune response. The interactions between the different pattern-recognition receptors (PRRs) and cell wall pathogen-associated molecular patterns (PAMPs) orientate the host response toward either fungal death or growth, which would then lead to disease development. Understanding the molecular determinants of the interplay between the cell wall and host immunity is fundamental to combatting Aspergillus diseases.

Are All Patients with Cancer at Heightened Risk for Severe Coronavirus Disease 2019 (COVID-19)?

Cancer patients are traditionally considered at high risk for complicated respiratory viral infections, due to their underlying immunosuppression. In line with this notion, early case series reported high mortality rates of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in patients with malignancy. However, subsequent large, prospective, epidemiological surveys indicate that the risk for severe coronavirus disease 2019 (COVID-19) may be largely attributed to the multiple confounders operating in this highly heterogeneous population of patients, rather than the cancer or its treatment per se. We critically discuss the conundrums of SARS-CoV-2 infection in cancer patients and underscore mechanistic insights on the outcome of COVID-19 as it relates to cancer therapy and the type and status of the underlying malignancy. Not all cancer patients are similarly at risk for a complicated COVID-19 course. A roadmap is needed for translational and clinical research on COVID-19 in this challenging group of patients.

Aspergillus fumigatus DHN-Melanin.

Dihydroxynaphthalene melanin (DHN-melanin) is an integral component of the conidial cell wall surface, which has a central role in the pathogenicity of the major human airborne fungal pathogen Aspergillus fumigatus. Although the biosynthetic pathway for A. fumigatus DHN-melanin production has been well characterized, the molecular interactions of DHN-melanin with the immune system have been incompletely understood. Recent studies demonstrated that apart from concealing immunostimulatory cell wall polysaccharides, calcium sequestration by DHN-melanin inhibits essential host effector pathways regulating phagosome biogenesis and prevents A. fumigatus conidia killing by phagocytes. From the host perspective, DHN-melanin is specifically recognized by a C-type lectin receptor (MelLeC) present in murine endothelia and in human myeloid cells. Furthermore, DHN-melanin activates platelets and facilitates opsonophagocytosis by macrophages via binding to soluble pattern recognition receptors. Dissecting the dynamics of DHN-melanin organization on the fungal cell wall and the molecular interplay with the immune system will lead to a better understanding of A. fumigatus pathophysiology.

Selective inhibition of Rhizopus eumelanin biosynthesis by novel natural product scaffold-based designs caused significant inhibition of fungal pathogenesis.

Melanin is a dark color pigment biosynthesized naturally in most living organisms. Fungal melanin is a major putative virulence factor of Mucorales fungi that allows intracellular persistence by inducing phagosome maturation arrest. Recently, it has been shown that the black pigments of Rhizopus delemar is of eumelanin type, that requires the involvement of tyrosinase (a copper-dependent enzyme) in its biosynthesis. Herein, we have developed a series of compounds (UOSC-1-14) to selectively target Rhizopus melanin and explored this mechanism therapeutically. The compounds were designed based on the scaffold of the natural product, cuminaldehyde, identified from plant sources and has been shown to develop non-selective inhibition of melanin production. While all synthesized compounds showed significant inhibition of Rhizopus melanin production and limited toxicity to mammalian cells, only four compounds (UOSC-1, 2, 13, and 14) were selected as promising candidates based on their selective inhibition to fungal melanin. The activity of compound UOSC-2 was comparable to the positive control kojic acid. The selected candidates showed significant inhibition of Rhizopus melanin but not human melanin by targeting the fungal tyrosinase, and with an IC50 that are 9 times lower than the reference standard, kojic acid. Furthermore, the produced white spores were phagocytized easily and cleared faster from the lungs of infected immunocompetent mice and from the human macrophages when compared with wild-type spores. Collectively, the results suggested that the newly designed derivatives, particularly UOSC-2 can serve as promising candidate to overcome persistence mechanisms of fungal melanin production and hence make them accessible to host defenses.

Aspergillus fumigatus and Aspergillosis in 2019.

Aspergillus fumigatus is a saprotrophic fungus; its primary habitat is the soil. In its ecological niche, the fungus has learned how to adapt and proliferate in hostile environments. This capacity has helped the fungus to resist and survive against human host defenses and, further, to be responsible for one of the most devastating lung infections in terms of morbidity and mortality. In this review, we will provide (i) a description of the biological cycle of A. fumigatus; (ii) a historical perspective of the spectrum of aspergillus disease and the current epidemiological status of these infections; (iii) an analysis of the modes of immune response against Aspergillus in immunocompetent and immunocompromised patients; (iv) an understanding of the pathways responsible for fungal virulence and their host molecular targets, with a specific focus on the cell wall; (v) the current status of the diagnosis of different clinical syndromes; and (vi) an overview of the available antifungal armamentarium and the therapeutic strategies in the clinical context. In addition, the emergence of new concepts, such as nutritional immunity and the integration and rewiring of multiple fungal metabolic activities occurring during lung invasion, has helped us to redefine the opportunistic pathogenesis of A. fumigatus.

The puzzling construction of the conidial outer layer of Aspergillus fumigatus.

If the mycelium of Aspergillus fumigatus is very short-lived in the laboratory, conidia can survive for years. This survival capacity and extreme resistance to environmental insults is a major biological characteristic of this fungal species. Moreover, conidia, which easily reach the host alveola, are the infective propagules. Earlier studies have shown the role of some molecules of the outer conidial layer in protecting the fungus against the host defense. The outer layer of the conidial cell wall, directly in contact with the host cells, consists of α-(1,3)-glucan, melanin, and proteinaceous rodlets. This study is focused on the global importance of this outer layer. Single and multiple mutants without one to three major components of the outer layer were constructed and studied. The results showed that the absence of the target molecules resulting from multiple gene deletions led to unexpected phenotypes without any logical additivity. Unexpected compensatory cell wall surface modifications were indeed observed, such as the synthesis of the mycelial virulence factor galactosaminogalactan, the increase in chitin and glycoprotein concentration or particular changes in permeability. However, sensitivity of the multiple mutants to killing by phagocytic host cells confirmed the major importance of melanin in protecting conidia.

Call for Action: Invasive Fungal Infections Associated With Ibrutinib and Other Small Molecule Kinase Inhibitors Targeting Immune Signaling Pathways.

Opportunistic infections caused by Pneumocystis jirovecii, Cryptococcus neoformans, and ubiquitous airborne filamentous fungi have been recently reported in patients with hematological cancers historically considered at low risk for invasive fungal infections (IFIs), after receipt of the Bruton tyrosine kinase inhibitor ibrutinib. The spectrum and severity of IFIs often observed in these patients implies the presence of a complex immunodeficiency that may not be solely attributed to mere inhibition of Bruton tyrosine kinase. In view of the surge in development of small molecule kinase inhibitors for treatment of malignant and autoimmune diseases, it is possible that there would be an emergence of IFIs associated with the effects of these molecules on the immune system. Preclinical assessment of the immunosuppressive effects of kinase inhibitors and human studies aimed at improving patient risk stratification for development of IFIs could lead to prevention, earlier diagnosis, and better outcomes in affected patients.

IL-1 receptor blockade restores autophagy and reduces inflammation in chronic granulomatous disease in mice and in humans.

Patients with chronic granulomatous disease (CGD) have a mutated NADPH complex resulting in defective production of reactive oxygen species; these patients can develop severe colitis and are highly susceptible to invasive fungal infection. In NADPH oxidase-deficient mice, autophagy is defective but inflammasome activation is present despite lack of reactive oxygen species production. However, whether these processes are mutually regulated in CGD and whether defective autophagy is clinically relevant in patients with CGD is unknown. Here, we demonstrate that macrophages from CGD mice and blood monocytes from CGD patients display minimal recruitment of microtubule-associated protein 1 light chain 3 (LC3) to phagosomes. This defect in autophagy results in increased IL-1ß release. Blocking IL-1 with the receptor antagonist (anakinra) decreases neutrophil recruitment and T helper 17 responses and protects CGD mice from colitis and also from invasive aspergillosis. In addition to decreased inflammasome activation, anakinra restored autophagy in CGD mice in vivo, with increased Aspergillus-induced LC3 recruitment and increased expression of autophagy genes. Anakinra also increased Aspergillus-induced LC3 recruitment from 23% to 51% (P < 0.01) in vitro in monocytes from CGD patients. The clinical relevance of these findings was assessed by treating CGD patients who had severe colitis with IL-1 receptor blockade using anakinra. Anakinra treatment resulted in a rapid and sustained improvement in colitis. Thus, inflammation in CGD is due to IL-1-dependent mechanisms, such as decreased autophagy and increased inflammasome activation, which are linked pathological conditions in CGD that can be restored by IL-1 receptor blockade.

Cationic antimicrobial peptides in psoriatic skin cooperate to break innate tolerance to self-DNA.

Psoriasis is a T-cell-mediated skin autoimmune disease characterized by the aberrant activation of dermal dendritic cells (DCs) and the sustained epidermal expression of antimicrobial peptides. We have previously identified a link between these two events by showing that the cathelicidin antimicrobial peptide LL37 has the ability to trigger self-nucleic acid mediated activation of plasmacytoid DCs (pDCs) in psoriatic skin. Whether other cationic antimicrobial peptides exert similar activities is unknown. By analyzing heparin-binding HPLC fractions of psoriatic scales, we found that human beta-defensin (hBD)2, hBD3, and lysozyme are additional triggers of pDC activation in psoriatic skin lesions. Like LL37, hBD2, hBD3, and lysozyme are able to condense self-DNA into particles that are endocytosed by pDCs, leading to activation of TLR9. In contrast, other antimicrobial peptides expressed in psoriatic skin including elafin, hBD1, and psoriasin (S100A7) did not show similar activities. hBD2, hBD3, and lysozyme were detected in psoriatic skin lesions in the vicinity of pDCs and found to cooperate with LL37 to induce high levels of IFN production by pDCs, suggesting their concerted role in the pathogenesis of psoriasis.

Autophagy controls BCG-induced trained immunity and the response to intravesical BCG therapy for bladder cancer.

The anti-tuberculosis-vaccine Bacillus Calmette-Guérin (BCG) is the most widely used vaccine in the world. In addition to its effects against tuberculosis, BCG vaccination also induces non-specific beneficial effects against certain forms of malignancy and against infections with unrelated pathogens. It has been recently proposed that the non-specific effects of BCG are mediated through epigenetic reprogramming of monocytes, a process called trained immunity. In the present study we demonstrate that autophagy contributes to trained immunity induced by BCG. Pharmacologic inhibition of autophagy blocked trained immunity induced in vitro by stimuli such as ß-glucans or BCG. Single nucleotide polymorphisms (SNPs) in the autophagy genes ATG2B (rs3759601) and ATG5 (rs2245214) influenced both the in vitro and in vivo training effect of BCG upon restimulation with unrelated bacterial or fungal stimuli. Furthermore, pharmacologic or genetic inhibition of autophagy blocked epigenetic reprogramming of monocytes at the level of H3K4 trimethylation. Finally, we demonstrate that rs3759601 in ATG2B correlates with progression and recurrence of bladder cancer after BCG intravesical instillation therapy. These findings identify a key role of autophagy for the nonspecific protective effects of BCG.

Albumin Enhances Caspofungin Activity against Aspergillus Species by Facilitating Drug Delivery to Germinating Hyphae.

The modest in vitro activity of echinocandins against Aspergillus implies that host-related factors augment the action of these antifungal agents in vivo. We found that, in contrast to the other antifungal agents (voriconazole, amphotericin B) tested, caspofungin exhibited a profound increase in activity against various Aspergillus species under conditions of cell culture growth, as evidenced by a ≥4-fold decrease in minimum effective concentrations (MECs) (P = 0. 0005). Importantly, the enhanced activity of caspofungin against Aspergillus spp. under cell culture conditions was strictly dependent on serum albumin and was not observed with the other two echinocandins, micafungin and anidulafungin. Of interest, fluorescently labeled albumin bound preferentially on the surface of germinating Aspergillus hyphae, and this interaction was further enhanced upon treatment with caspofungin. In addition, supplementation of cell culture medium with albumin resulted in a significant, 5-fold increase in association of fluorescently labeled caspofungin with Aspergillus hyphae (P < 0.0001). Collectively, we found a novel synergistic interaction between albumin and caspofungin, with albumin acting as a potential carrier molecule to facilitate antifungal drug delivery to Aspergillus hyphae.

Corticosteroids block autophagy protein recruitment in Aspergillus fumigatus phagosomes via targeting dectin-1/Syk kinase signaling.

Aspergillus fumigatus is the predominant airborne fungal pathogen in immunocompromised patients. Genetic defects in NADPH oxidase (chronic granulomatous disease [CGD]) and corticosteroid-induced immunosupression lead to impaired killing of A. fumigatus and unique susceptibility to invasive aspergillosis via incompletely characterized mechanisms. Recent studies link TLR activation with phagosome maturation via the engagement of autophagy proteins. In this study, we found that infection of human monocytes with A. fumigatus spores triggered selective recruitment of the autophagy protein LC3 II in phagosomes upon fungal cell wall swelling. This response was induced by surface exposure of immunostimulatory ß-glucans and was mediated by activation of the Dectin-1 receptor. LC3 II recruitment in A. fumigatus phagosomes required spleen tyrosine kinase (Syk) kinase-dependent production of reactive oxygen species and was nearly absent in monocytes of patients with CGD. This pathway was important for control of intracellular fungal growth, as silencing of Atg5 resulted in impaired phagosome maturation and killing of A. fumigatus. In vivo and ex vivo administration of corticosteroids blocked LC3 II recruitment in A. fumigatus phagosomes via rapid inhibition of phosphorylation of Src and Syk kinases and downstream production of reactive oxygen species. Our studies link Dectin-1/Syk kinase signaling with autophagy-dependent maturation of A. fumigatus phagosomes and uncover a potential mechanism for development of invasive aspergillosis in the setting of CGD and corticosteroid-induced immunosupression.

Cytosolic sensing of extracellular self-DNA transported into monocytes by the antimicrobial peptide LL37.

The intracellular location of nucleic acid sensors prevents recognition of extracellular self-DNA released by dying cells. However, on forming a complex with the endogenous antimicrobial peptide LL37, extracellular DNA is transported into endosomal compartments of plasmacytoid dendritic cells, leading to activation of Toll-like receptor-9 and induction of type I IFNs. Whether LL37 also transports self-DNA into nonplasmacytoid dendritic cells, leading to type I IFN production via other intracellular DNA receptors is unknown. Here we found that LL37 very efficiently transports self-DNA into monocytes, leading the production of type I IFNs in a Toll-like receptor-independent manner. This type I IFN induction was mediated by double-stranded B form DNA, regardless of its sequence, CpG content, or methylation status, and required signaling through the adaptor protein STING and TBK1 kinase, indicating the involvement of cytosolic DNA sensors. Thus, our study identifies a novel link between the antimicrobial peptides and type I IFN responses involving DNA-dependent activation of cytosolic sensors in monocytes.

Distinct trafficking routes of polarized and non-polarized membrane cargoes in Aspergillus nidulans.

Membrane proteins are sorted to the plasma membrane (PM) via Golgi-dependent trafficking. However, our recent studies challenged the essentiality of Golgi in the biogenesis of specific transporters. Here, we investigate the trafficking mechanisms of membrane proteins by following the localization of the polarized R-SNARE SynA versus the non-polarized transporter UapA, synchronously co-expressed in wild-type or isogenic genetic backgrounds repressible for conventional cargo secretion. In wild-type, the two cargoes dynamically label distinct secretory compartments, highlighted by the finding that, unlike SynA, UapA does not colocalize with the late-Golgi. In line with early partitioning into distinct secretory carriers, the two cargoes collapse in distinct ERES in a sec31ts background. Trafficking via distinct cargo-specific carriers is further supported by showing that repression of proteins essential for conventional cargo secretion does not affect UapA trafficking, while blocking SynA secretion. Overall, this work establishes the existence of distinct, cargo-dependent, trafficking mechanisms, initiating at ERES and being differently dependent on Golgi and SNARE interactions.

Epidemiology of Invasive Fungal Diseases: A 10-Year Experience in a Tertiary Pediatric Hematology-Oncology Department in Greece.

Although advances in the management of pediatric neoplasms have profoundly improved infectious disease outcomes, invasive fungal diseases (IFDs) remain a major cause of morbidity and mortality in children and adolescents with high-risk hematological malignancies. A retrospective study was conducted in the Pediatric Hematology-Oncology Department of the University General Hospital of Heraklion for 2013-2022 to estimate the prevalence and describe the clinical and epidemiological characteristics of IFDs for pediatric and adolescent patients with neoplasia. Demographic, clinical, and laboratory parameters were analyzed to identify risk factors for the development of IFD. The overall prevalence of IFDs was estimated to be 7.8% (12/154 patients) throughout the study. The mean age at IFD diagnosis was 9.8 years (SD 6.4 years). The most common IFD was possible/probable invasive pulmonary aspergillosis (IPA; in ≈50%), followed by candidemia/invasive candidiasis (in 44%). Candida parapsilosis was the most prevalent Candida species (4/6 events). Of interest, the majority (75%) of IFDs were breakthrough infections. Patients with increased risk for IFDs were those who were colonized by fungi in sites other than the oral cavity, hospitalized in the intensive care unit for >7 days, received >7 different antimicrobials in the last 3 months, or had severe neutropenia for >44 days. Two children out of a total of 12 with IFD died due to refractory disease or relapse (16.7%). More detailed and prospective epidemiological studies on fungal infections in pediatric patients with hematological or solid neoplasms can contribute to the optimization of prevention and treatment.

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.

Damping excessive viral-induced IFN-γ rescues the impaired anti-Aspergillus host immune response in influenza-associated pulmonary aspergillosis.

BACKGROUND: Influenza-associated pulmonary aspergillosis (IAPA) is a severe fungal superinfection in critically ill influenza patients that is of incompletely understood pathogenesis. Despite the use of contemporary therapies with antifungal and antivirals, mortality rates remain unacceptably high. We aimed to unravel the IAPA immunopathogenesis as a means to develop adjunctive immunomodulatory therapies. METHODS: We used a murine model of IAPA to investigate how influenza predisposes to the development of invasive pulmonary aspergillosis. Immunocompetent mice were challenged with an intranasal instillation of influenza on day 0 followed by an orotracheal inoculation with Aspergillus 4 days later. Mice were monitored daily for overall health status, lung pathology with micro-computed tomography (µCT) and fungal burden with bioluminescence imaging (BLI). At endpoint, high parameter immunophenotyping, spatial transcriptomics, histopathology, dynamic phagosome biogenesis assays with live imaging, immunofluorescence staining, specialized functional phagocytosis and killing assays were performed. FINDINGS: We uncovered an early exuberant influenza-induced interferon-gamma (IFN-γ) production as the major driver of immunopathology in IAPA and delineated the molecular mechanisms. Specifically, excessive IFN-γ production resulted in a defective Th17-immune response, depletion of macrophages, and impaired killing of Aspergillus conidia by macrophages due to the inhibition of NADPH oxidase-dependent activation of LC3-associated phagocytosis (LAP). Markedly, mice with partial or complete genetic ablation of IFN-γ had a restored Th17-immune response, LAP-dependent mechanism of killing and were fully protected from invasive fungal infection. INTERPRETATION: Together, these results identify exuberant viral induced IFN-γ production as a major driver of immune dysfunction in IAPA, paving the way to explore the use of excessive viral-induced IFN-γ as a biomarker and new immunotherapeutic target in IAPA. FUNDING: This research was funded by the Research Foundation Flanders (FWO), project funding under Grant G053121N to JW, SHB and GVV; G057721N, G0G4820N to GVV; 1506114 N to KL and GVV; KU Leuven internal funds (C24/17/061) to GVV, clinical research funding to JW, Research Foundation Flanders (FWO) aspirant mandate under Grant 1186121N/1186123 N to LS, 11B5520N to FS, 1SF2222N to EV and 11M6922N/11M6924N to SF, travel grants V428023N, K103723N, K217722N to LS. FLvdV was supported by a Vidi grant of the Netherlands Association for Scientific Research. FLvdV, JW, AC and GC were supported by the Europeans Union's Horizon 2020 research and innovation program under grant agreement no 847507 HDM-FUN. AC was also supported by the Fundação para a Ciência e a Tecnologia (FCT), with the references UIDB/50026/2020, UIDP/50026/2020, PTDC/MED-OUT/1112/2021 (https://doi.org/10.54499/PTDC/MED-OUT/1112/2021), and 2022.06674.PTDC (http://doi.org/10.54499/2022.06674.PTDC); and the "la Caixa" Foundation under the agreement LCF/PR/HR22/52420003 (MICROFUN).

BTK drives neutrophil activation for sterilizing antifungal immunity.

We describe a previously-unappreciated role for Bruton's tyrosine kinase (BTK) in fungal immune surveillance against aspergillosis, an unforeseen complication of BTK inhibitors (BTKi) used for treating B-cell lymphoid malignancies. We studied BTK-dependent fungal responses in neutrophils from diverse populations, including healthy donors, BTKi-treated patients, and X-linked agammaglobulinemia patients. Upon fungal exposure, BTK was activated in human neutrophils in a TLR2-, Dectin-1-, and FcγR-dependent manner, triggering the oxidative burst. BTK inhibition selectively impeded neutrophil-mediated damage to Aspergillus hyphae, primary granule release, and the fungus-induced oxidative burst by abrogating NADPH oxidase subunit p40phox and GTPase RAC2 activation. Moreover, neutrophil-specific Btk deletion in mice enhanced aspergillosis susceptibility by impairing neutrophil function, not recruitment or lifespan. Conversely, GM-CSF partially mitigated these deficits by enhancing p47phox activation. Our findings underline the crucial role of BTK signaling in neutrophils for antifungal immunity and provide a rationale for GM-CSF use to offset these deficits in susceptible patients.