Human genetic susceptibility to invasive aspergillosis

Validating genetic variants in innate immunity linked to infectious events in acute myeloid leukemia post-induction chemotherapy

Infectious events, such as sepsis and invasive fungal disease (IFD), pose significant risks in patients with acute myeloid leukemia (AML). Previous studies, including our own, have suggested a potential role of single nucleotide polymorphisms (SNPs) within the innate immune system in influencing individual infection susceptibility. However, many of these associations lack validation in independent cohorts. This study sought to validate the impact of 11 candidate SNPs across 6 genes (TLR2, TLR4, Dectin-1, DC-SIGN, PTX3, L-Ficolin) in an independent cohort of patients. Two cohorts with newly diagnosed AML patients receiving intensive induction chemotherapy were analyzed: a stratification cohort comprising 186 patients and a validation cohort consisting of 138 patients. Multiple SNPs in each cohort were found to be associated to infectious complications, notably the DC-SIGN SNP rs4804800 demonstrated a significant association with sepsis in both cohorts. SNPs within the PTX3 and Dectin-1 genes were linked to IFD development in one cohort each. This study represents the first validation study of candidate genes associated with infectious events in AML patients after intensive induction chemotherapy. Identifying genetic predispositions to infections could significantly impact the management of antimicrobial prophylaxis and treatment in AML patients.

Pathogenicity and virulence of Aspergillus fumigatus

Pulmonary infections caused by the mould pathogen Aspergillus fumigatus are a major cause of morbidity and mortality globally. Compromised lung defences arising from immunosuppression, chronic respiratory conditions or more recently, concomitant viral or bacterial pulmonary infections are recognised risks factors for the development of pulmonary aspergillosis. In this review, we will summarise our current knowledge of the mechanistic basis of pulmonary aspergillosis with a focus on emerging at-risk populations.

Genetic Susceptibility to Fungal Infections

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

Loss of the mammalian G-protein coupled receptor, G2A, modulates severity of invasive pulmonary aspergillosis

Background

Aspergillus fumigatus is a well-known opportunistic pathogen that causes a range of diseases including the often-fatal disease, invasive pulmonary aspergillosis (IPA), in immunocompromised populations. The severity of IPA is dependent on both host- and pathogen-derived signaling molecules that mediate host immunity and fungal growth. Oxylipins are bioactive oxygenated fatty acids known to influence host immune response and Aspergillus developmental programs. Aspergillus synthesizes 8-HODE and 5,8-diHODE that have structural similarities to 9-HODE and 13-HODE, which are known ligands of the host G-protein-coupled receptor G2A (GPR132).

Materials and methods

Oxylipins were extracted from infected lung tissue to assess fungal oxylipin production and the Pathhunter β-arrestin assay was used to assess agonist and antagonist activity by fungal oxylipins on G2A. An immunocompetent model of A. fumigatus infection was used to assess changes in survival and immune responses for G2A-/- mice.

Results

Here we report that Aspergillus oxylipins are produced in lung tissue of infected mice and in vitro ligand assays suggest 8-HODE is a G2A agonist and 5,8-diHODE is a partial antagonist. To address the hypothesis that G2A could be involved in the progression of IPA, we assessed the response of G2A-/- mice to A. fumigatus infection. G2A-/- mice showed a survival advantage over wild-type mice; this was accompanied by increased recruitment of G2A-/- neutrophils and increased levels of inflammatory markers in A. fumigatus-infected lungs.

Conclusions

We conclude that G2A suppresses host inflammatory responses to Aspergillus fumigatus although it remains unclear if fungal oxylipins are involved in G2A activities.

Genomic and Phenotypic Trait Variation of the Opportunistic Human Pathogen Aspergillus flavus and Its Close Relatives

Fungal diseases affect millions of humans annually, yet fungal pathogens remain understudied. The mold Aspergillus flavus can cause both aspergillosis and fungal keratitis infections, but closely related species are not considered clinically relevant. To study the evolution of A. flavus pathogenicity, we examined genomic and phenotypic traits of two strains of A. flavus and three closely related species, Aspergillus arachidicola (two strains), Aspergillus parasiticus (two strains), and Aspergillus nomiae (one strain). We identified >3,000 orthologous proteins unique to A. flavus, including seven biosynthetic gene clusters present in A. flavus strains and absent in the three nonpathogens. We characterized secondary metabolite production for all seven strains under two clinically relevant conditions, temperature and salt concentration. Temperature impacted metabolite production in all species, whereas salinity did not affect production of any species. Strains of the same species produced different metabolites. Growth under stress conditions revealed additional heterogeneity within species. Using the invertebrate fungal disease model Galleria mellonella, we found virulence of strains of the same species varied widely; A. flavus strains were not more virulent than strains of the nonpathogens. In a murine model of fungal keratitis, we observed significantly lower disease severity and corneal thickness for A. arachidicola compared to other species at 48 h postinfection, but not at 72 h. Our work identifies variations in key phenotypic, chemical, and genomic attributes between A. flavus and its nonpathogenic relatives and reveals extensive strain heterogeneity in virulence that does not correspond to the currently established clinical relevance of these species. IMPORTANCE Aspergillus flavus is a filamentous fungus that causes opportunistic human infections, such as aspergillosis and fungal keratitis, but its close relatives are considered nonpathogenic. To begin understanding how this difference in pathogenicity evolved, we characterized variation in infection-relevant genomic, chemical, and phenotypic traits between strains of A. flavus and its relatives. We found extensive variation (or strain heterogeneity) within the pathogenic A. flavus as well as within its close relatives, suggesting that strain-level differences may play a major role in the ability of these fungi to cause disease. Surprisingly, we also found that the virulence of strains from species not considered to be pathogens was similar to that of A. flavus in both invertebrate and murine models of disease. These results contrast with previous studies on Aspergillus fumigatus, another major pathogen in the genus, for which significant differences in infection-relevant chemical and phenotypic traits are observed between closely related pathogenic and nonpathogenic species.

MAVS Expression in Alveolar Macrophages Is Essential for Host Resistance against Aspergillus fumigatus

Our recent data demonstrate a critical role of the RIG-I-like receptor family in regulating antifungal immunity against Aspergillus fumigatus in a murine model. However, the importance of this pathway in humans and the cell types that use this innate immune receptor family to detect A. fumigatus remain unresolved. In this study, using patients who underwent hematopoietic stem cell transplantation, we demonstrate that a polymorphism in human MAVS present in the donor genome was associated with the incidence of invasive pulmonary aspergillosis. Moreover, in a separate cohort of confirmed invasive pulmonary aspergillosis patients, polymorphisms in the IFIH1 gene alter the inflammatory response, including IFN-responsive chemokines. Returning to our murine model, we now demonstrate that CD11c+ Siglec F+ alveolar macrophages require Mavs expression to maintain host resistance against A. fumigatus. Our data support the role of MAVS signaling in mediating antifungal immunity in both mice and humans at least in part through the role of MAVS-dependent signaling in alveolar macrophages.

Prevalence of COVID-19-Associated Pulmonary Aspergillosis: Critical Review and Conclusions

First reports of cases and case series of COVID-19-associated pulmonary aspergillosis (CAPA) emerged during the first months of the pandemic. Prevalence rates varied widely due to the fact that CAPA was, and still remains, challenging to diagnose in patients with COVID-19-associated acute respiratory failure (ARF). The clinical picture and radiological findings of CAPA are unspecific and can resemble those of severe COVID-19. Hence, mycological evidence became a key component in establishing a diagnosis. However, blood tests lack sensitivity in early treatable phases of CAPA and once positive, mortality has been shown to exceed 80% despite systemic antifungal therapy. The primarily airway invasive growth in non-neutropenic patients and the late occurrence of angioinvasion in the course of disease may mainly account for these diagnostic obstacles. Testing of bronchoalveolar lavage (BAL) is therefore crucial in the diagnostic process, but was rarely performed during the early phase of the pandemic, which potentially interfered with the accuracy of reported prevalence. Current guidelines recommend treatment of CAPA during its early airway invasive phase, which may result in some overtreatment (i.e., treatment in patients that may not develop angioinvasive infection) and adverse drug events, yet there is no viable alternative approach. Timely treatment of cases needs to be ensured for patients with mycological evidence of CAPA in the lower respiratory tract given the independent contribution of CAPA to devastating mortality rates of around 50% that have been shown in multiple studies. Here, we review the evolution of reported CAPA prevalence and the role of CAPA as an important opportunistic infection affecting COVID-19 patients in intensive care units (ICUs).

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.

Pathogenesis of Respiratory Viral and Fungal Coinfections

Individuals suffering from severe viral respiratory tract infections have recently emerged as "at risk" groups for developing invasive fungal infections. Influenza virus is one of the most common causes of acute lower respiratory tract infections worldwide. Fungal infections complicating influenza pneumonia are associated with increased disease severity and mortality, with invasive pulmonary aspergillosis being the most common manifestation. Strikingly, similar observations have been made during the current coronavirus disease 2019 (COVID-19) pandemic. The copathogenesis of respiratory viral and fungal coinfections is complex and involves a dynamic interplay between the host immune defenses and the virulence of the microbes involved that often results in failure to return to homeostasis. In this review, we discuss the main mechanisms underlying susceptibility to invasive fungal disease following respiratory viral infections. A comprehensive understanding of these interactions will aid the development of therapeutic modalities against newly identified targets to prevent and treat these emerging coinfections.

Cytokine and Chemokine Responses in Invasive Aspergillosis Following Hematopoietic Stem Cell Transplantation: Past Evidence for Future Therapy of Aspergillosis

Invasive pulmonary aspergillosis is a frequent complication in immunocompromised individuals, and it continues to be an important cause of mortality in patients undergoing hematopoietic stem cell transplantation. In addition to antifungal therapy used for mycoses, immune-modulatory molecules such as cytokines and chemokines can modify the host immune response and exhibit a promising form of antimicrobial therapeutics to combat invasive fungal diseases. Cytokine and chemokine profiles may also be applied as biomarkers during fungal infections and clinical research has demonstrated different activation patterns of cytokines in invasive mycoses such as aspergillosis. In this review, we summarize different aspects of cytokines that have been described to date and provide possible future directions in research on invasive pulmonary aspergillosis following hematopoietic stem cell transplantation. These findings suggest that cytokines and chemokines may serve as useful biomarkers to improve diagnosis and monitoring of infection.

Genetic Variation in PFKFB3 Impairs Antifungal Immunometabolic Responses and Predisposes to Invasive Pulmonary Aspergillosis

Activation of immune cells in response to fungal infection involves the reprogramming of their cellular metabolism to support antimicrobial effector functions. Although metabolic pathways such as glycolysis are known to represent critical regulatory nodes in antifungal immunity, it remains undetermined whether these are differentially regulated at the interindividual level. In this study, we identify a key role for 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3) in the immunometabolic responses to Aspergillus fumigatus. A genetic association study performed in 439 recipients of allogeneic hematopoietic stem cell transplantation (HSCT) and corresponding donors revealed that the donor, but not recipient, rs646564 variant in the PFKFB3 gene increased the risk of invasive pulmonary aspergillosis (IPA) after transplantation. The risk genotype impaired the expression of PFKFB3 by human macrophages in response to fungal infection, which was correlated with a defective activation of glycolysis and the ensuing antifungal effector functions. In patients with IPA, the risk genotype was associated with lower concentrations of cytokines in the bronchoalveolar lavage fluid samples. Collectively, these findings demonstrate the important contribution of genetic variation in PFKFB3 to the risk of IPA in patients undergoing HSCT and support its inclusion in prognostic tools to predict the risk of fungal infection in this clinical setting. IMPORTANCE The fungal pathogen Aspergillus fumigatus can cause severe and life-threatening forms of infection in immunocompromised patients. Activation of glycolysis is essential for innate immune cells to mount effective antifungal responses. In this study, we report the contribution of genetic variation in the key glycolytic activator 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3) to the risk of invasive pulmonary aspergillosis (IPA) after allogeneic hematopoietic stem cell transplantation. The PFKFB3 genotype associated with increased risk of infection was correlated with an impairment of the antifungal effector functions of macrophages in vitro and in patients with IPA. This work highlights the clinical relevance of genetic variation in PFKFB3 to the risk of IPA and supports its integration in risk stratification and preemptive measures for patients at high risk of IPA.

Polymorphisms within the TNFSF4 and MAPKAPK2 Loci Influence the Risk of Developing Invasive Aspergillosis: A Two-Stage Case Control Study in the Context of the aspBIOmics Consortium

Here, we assessed whether 36 single nucleotide polymorphisms (SNPs) within the TNFSF4 and MAPKAPK2 loci influence the risk of developing invasive aspergillosis (IA). We conducted a two-stage case control study including 911 high-risk patients diagnosed with hematological malignancies that were ascertained through the aspBIOmics consortium. The meta-analysis of the discovery and replication populations revealed that carriers of the TNFSF4 _rs7526628T/T genotype had a significantly increased risk of developing IA (p = 0.00022). We also found that carriers of the TNFSF4 _rs7526628T allele showed decreased serum levels of TNFSF14 protein (p = 0.0027), and that their macrophages had a decreased fungicidal activity (p = 0.048). In addition, we observed that each copy of the MAPKAPK2 _rs12137965G allele increased the risk of IA by 60% (p = 0.0017), whereas each copy of the MAPKAPK2 _rs17013271T allele was estimated to decrease the risk of developing the disease (p = 0.0029). Mechanistically, we found that carriers of the risk MAPKAPK2 _rs12137965G allele showed increased numbers of CD38+IgM-IgD- plasmablasts in blood (p = 0.00086), whereas those harboring two copies of the allele had decreased serum concentrations of thymic stromal lymphopoietin (p = 0.00097). Finally, we also found that carriers of the protective MAPKAPK2 _rs17013271T allele had decreased numbers of CD27-IgM-IgD- B cells (p = 0.00087) and significantly lower numbers of CD14+ and CD14+CD16- cells (p = 0.00018 and 0.00023). Altogether, these results suggest a role of the TNFSF4 and MAPKAPK2 genes in determining IA risk.

Revised Transcriptome-Based Gene Annotation for Aspergillus flavus Strain NRRL 3357

Aspergillus flavus is an agriculturally and medically important filamentous fungus that produces mycotoxins, including aflatoxins, which are potent carcinogens. Here, we generated short- and long-read transcript sequence data from the growth of A. flavus strain NRRL 3357 under both typical and stress conditions to produce a new annotation of its genome.

Aspergillus flavus is an agriculturally and medically important filamentous fungus that produces mycotoxins, including aflatoxins, which are potent carcinogens. Here, we generated short- and long-read transcript sequence data from the growth of A. flavus strain NRRL 3357 under both typical and stress conditions to produce a new annotation of its genome.

Association between dectin-1 gene single nucleotide polymorphisms and fungal infection: a systemic review and meta-analysis

Objectives: To investigate the association between dectin-1 gene single nucleotide polymorphisms (SNPs) and susceptibility to fungal infection (FI). Methods: Databases were searched electronically and manually to identify case–control studies concerning dectin-1 SNPs and FI, which were published up to 12 November 2018. The Newcastle–Ottawa Quality Assessment Scale was used to determine the study quality and bias. The SNP frequencies of the B (the variant or minor allele) and A (the wild or major allele) alleles of the dectin-1 gene in both cases and controls were analyzed with regard to FI susceptibility. Results: Eight high-quality studies were included in the review. Systemic review of the included studies demonstrated that dectin-1 SNPs rs3901533 and rs7309123 might be associated with susceptibility to invasive pulmonary aspergillosis infection; moreover, rs16910527 SNP can possibly increase the susceptibility to oropharyngeal candidiasis in HIV-positive patients. The meta-analysis identified significant associations between dectin-1 SNPs and overall FI risk in the homozygote model (pooled odds ratio (OR) 1.77, P=0.04). When classified by subtypes, significant associations were also found for deep FI in the homozygote model (pooled OR 2.46, P=0.01) and the recessive model (pooled OR 2.85, P=0.002). There appeared to be no significant association between dectin-1 SNPs and superficial FI. Conclusion: Systemic review of the included studies suggested that dectin-1 SNPs rs3901533, rs7309123, and rs16910527 might play a role in FI susceptibility. The meta-analysis provided convincing evidence that dectin-1 SNPs might have an important role in FI susceptibility, especially for deep FI.

Genetic Risk Surveillance for Invasive Aspergillosis in Hematology Patients: A Prospective Observational Study

INTRODUCTION

The association between genetic background and the risk of invasive aspergillosis (IA) has not been addressed in Thailand. We conducted genetic risk surveillance for IA among Thai hematologic patients.

METHODS

We conducted a prospective observational cohort study including moderate- to high-risk hematology patients at Ramathibodi Hospital. IA occurrence, relevant clinical data, and genetic analyses were assessed. Odds ratios (ORs) of IA were assessed for the presence of the selected single nucleotide polymorphism genotype using logistic regression.

RESULTS

A total of 357 patients were enrolled. The most common hematologic disease was non-Hodgkin lymphoma (45.1%). IA was diagnosed in 36 patients (10.10%). The C allele of IL10_rs1800896 was associated with an increased risk of IA (adjusted OR 5.297; 95% confidence interval [CI] 2.032-13.809, p = 0.001). In multivariate Cox regression analysis, prolonged neutropenia and the C allele of IL10_rs1800896 were associated with IA (hazard ratio [HR] 12.585; 95% CI 3.866-40.967, p < 0.001 and HR 2.449; 95% CI 1.097-5.468, p = 0.042, respectively).

CONCLUSIONS

Carrying the C allele of IL10_rs1800896 was associated with an increased risk of IA among moderate- to high-risk Thai patients with hematologic diseases. This finding can potentially lead to a novel risk stratification scheme to further prevent IA in resource-limited settings.

Defining standards of CARE for invasive fungal diseases in adult haematology patients: antifungal prophylaxis versus treatment

Despite the availability of four different classes of antifungal agents, invasive fungal infections, in particular mould diseases, continue to have a high crude mortality rate in adult haematology patients, especially when diagnosed late. Early diagnosis, resulting in prompt and adequate antifungal intervention, is of great importance when trying to improve the overall outcome of these infections, but depends on the availability of rapid and sensitive diagnostic tools. The medical community has developed and continues to evaluate a continuum of antifungal strategies (starting with prophylaxis followed by empirical therapy and more recently a diagnostic-driven or pre-emptive approach) to better tackle these life-threatening diseases. While the empirical approach seems to have lost some of its popularity, the jury is still out about the pros and cons of universal antifungal prophylaxis in at-risk adult haematology patients compared with an approach that uses radiological and mycological diagnostic methods with good to excellent negative predictive values (also erroneously called pre-emptive), trying to exclude the presence of an invasive fungal disease. Whilst awaiting the results of comparative clinical studies, believers and non-believers around the globe continue to argue about the advantages and shortcomings of both strategies. The debate presented here provides a rationale for both prophylaxis for 'high-risk' haematology patients as well as for a more targeted approach based on the appropriate use of mycological, radiological, immunological (and genetic) methods for the diagnosis of invasive fungal diseases.

Host genetic susceptibility to mycetoma

Mycetoma is one of the badly neglected tropical diseases, characterised by subcutaneous painless swelling, multiple sinuses, and discharge containing aggregates of the infecting organism known as grains. Risk factors conferring susceptibility to mycetoma include environmental factors and pathogen factors such as virulence and the infecting dose, in addition to host factors such as immunological and genetic predisposition. Epidemiological evidence suggests that host genetic factors may regulate susceptibility to mycetoma and other fungal infections, but they are likely to be complex genetic traits in which multiple genes interact with each other and environmental factors, as well as the pathogen, to cause disease. This paper reviews what is known about genetic predisposition to fungal infections that might be relevant to mycetoma, as well as all studies carried out to explore host genetic susceptibility to mycetoma. Most studies were investigating polymorphisms in candidate genes related to the host immune response. A total of 13 genes had allelic variants found to be associated with mycetoma, and these genes lie in different pathways and systems such as innate and adaptive immune systems, sex hormone biosynthesis, and some genes coding for host enzymes. None of these studies have been replicated. Advances in genomic science and the supporting technology have paved the way for large-scale genome-wide association and next generation sequencing (NGS) studies, underpinning a new strategy to systematically interrogate the genome for variants associated with mycetoma. Dissecting the contribution of host genetic variation to susceptibility to mycetoma will enable the identification of pathways that are potential targets for new treatments for mycetoma and will also enhance the ability to stratify ‘at-risk’ individuals, allowing the possibility of developing preventive and personalised clinical care strategies in the future.

Polymorphisms within the ARNT2 and CX3CR1 Genes Are Associated with the Risk of Developing Invasive Aspergillosis

Invasive aspergillosis (IA) is a life-threatening infection that affects an increasing number of patients undergoing chemotherapy or allo-transplantation, and recent studies have shown that genetic factors contribute to disease susceptibility. In this two-stage, population-based, case-control study, we evaluated whether 7 potentially functional single nucleotide polymorphisms (SNPs) within the ARNT2 and CX3CR1 genes influence the risk of IA in high-risk hematological patients. We genotyped selected SNPs in a cohort of 500 hematological patients (103 of those had been diagnosed with proven or probable IA), and we evaluated their association with the risk of developing IA. The association of the most interesting markers of IA risk was then validated in a replication population, including 474 subjects (94 IA and 380 non-IA patients). Functional experiments were also performed to confirm the biological relevance of the most interesting markers. The meta-analysis of both populations showed that carriers of the ARNT2 _rs1374213G, CX3CR1 _rs7631529A, and CX3CR1 _rs9823718G alleles (where the RefSeq identifier appears as a subscript) had a significantly increased risk of developing IA according to a log-additive model (P value from the meta-analysis [P _Meta] = 9.8 · 10^-5, P _Meta = 1.5 · 10^-4, and P _Meta =7.9 · 10^-5, respectively). Haplotype analysis also confirmed the association of the CX3CR1 haplotype with AG CGG with an increased risk of IA (P = 4.0 · 10^-4). Mechanistically, we observed that monocyte-derived macrophages (MDM) from subjects carrying the ARNTR2 _rs1374213G allele or the GG genotype showed a significantly impaired fungicidal activity but that MDM from carriers of the ARNT2 _rs1374213G and CX3CR1 _rs9823718G or CX3CR1 _rs7631529A alleles had deregulated immune responses to Aspergillus conidia. These results, together with those from expression quantitative trait locus (eQTL) data browsers showing a strong correlation of the CX3CR1 _rs9823718G allele with lower levels of CX3CR1 mRNA in whole peripheral blood (P = 2.46 · 10^-7) and primary monocytes (P = 4.31 · 10^-7), highlight the role of the ARNT2 and CX3CR1 loci in modulating and predicting IA risk and provide new insights into the host immune mechanisms involved in IA development.

The Role of Pentraxin 3 in Aspergillosis: Reality and Prospects

Pentraxin 3 (PTX3) is a soluble pattern recognition receptor (PRR), which is produced by several kinds of cells, such as neutrophils, dendritic cells, macrophages, and epithelial cells. PTX3 is known to play an important protective effect against Aspergillus. Genetic linkage in gene-targeted mice and human PTX3 plays a non-redundant role in the immune protection against specific pathogens, especially Aspergillus. Recent studies have shown that the polymorphism of PTX3 is associated with increased susceptibility to invasive aspergillosis (IA). In this review, we provide an overview of these studies that underline the potential of PTX3 in diagnosis and therapy of IA.

Dectin-1 rs3901533 and rs7309123 Polymorphisms Increase Susceptibility to Pulmonary Invasive Fungal Disease in Patients with Acute Myeloid Leukemia from a Chinese Han Population

This study aimed to assess whether genetic variants of dendritic cell-associated C-type lectine-1 (Dectin-1), Toll-like receptor 2 (TLR2), Toll-like receptor 4 (TLR4), and myeloid differentiation primary response 88 (MyD88) influence the susceptibility to pulmonary invasive fungal disease (IFD) in patients with acute myeloid leukemia (AML) from a Chinese Han population. Eight single nucleotide polymorphisms (SNPs) of Dectin-1 (rs16910526, rs3901533, and rs7309123), TLR2 (rs5743708), TLR4 (rs4986790 and rs4986791) and MyD88 (rs4988453 and rs4988457) in the genomic DNA of 172 adult AML patients were genotyped. Pulmonary IFD was diagnosed as proven or probable according to the 2008 European Organization for Research and Treatment of Cancer/Invasive Fungal Infections Cooperative Group and the National Institute of Allergy and Infectious Diseases Mycoses Study Group (EORTC/MSG) consensus guidelines. SNPs that were significant in the univariate analysis were further analyzed using the multiple logistic regression analysis to determine their association with the occurrence of pulmonary IFD. The mRNA expression of Dectin-1 was detected according to the genotype by quantitative realtime PCR (qRT-PCR), and the correlation of this expression with the occurrence of pulmonary IFD in AML patients was analyzed. Two Dectin-1 intron SNPs (rs3901533 and rs7309123) were found to be significantly associated with the susceptibility to pulmonary IFD in AML patients in a Chinese Han population. Significant associations were noted between pulmonary IFD and Dectin-1 rs3901533 dominant model (G/T+G/G vs. T/T, OR: 2.158; 95% CI: 1.109-4.2, P=0.02), Dectin-1 rs3901533 G allele (OR: 2.201; 95% CI: 1.206-4.019, P=0.01), or Dectin-1 rs7309123 C allele (OR: 1.919; 95% CI: 1.047-3.518, P=0.03). There were no significant associations between pulmonary IFD and the remaining Dectin-1 SNPs (rs16910526), TLR2 (rs5743708), TLR4 (rs4986790 and rs4986791) or MyD88 (rs4988453 and rs4988457). In conclusion, two Dectin-1 SNPs (rs3901533 and rs7309123) are associated with increased susceptibility to pulmonary IFD in AML patients in a Chinese Han population.

Immune Parameters for Diagnosis and Treatment Monitoring in Invasive Mold Infection

Infections caused by invasive molds, including Aspergillus spp., can be difficult to diagnose and remain associated with high morbidity and mortality. Thus, early diagnosis and targeted systemic antifungal treatment remains the most important predictive factor for a successful outcome in immunocompromised individuals with invasive mold infections. Diagnosis remains difficult due to low sensitivities of diagnostic tests including culture and other mycological tests for mold pathogens, particularly in patients on mold-active antifungal prophylaxis. As a result, antifungal treatment is rarely targeted and reliable markers for treatment monitoring and outcome prediction are missing. Thus, there is a need for improved markers to diagnose invasive mold infections, monitor response to treatment, and assist in determining when antifungal therapy should be escalated, switched, or can be stopped. This review focuses on the role of immunologic markers and specifically cytokines in diagnosis and treatment monitoring of invasive mold infections.

Immunomodulatory effect of ibrutinib: Reducing the barrier against fungal infections

The Bruton tyrosine kinase (BTK) inhibitor ibrutinib is increasingly used in the treatment of chronic lymphocytic leukemia (CLL). Moreover, very promising results have been reported in other B-cell malignancies, including primary central nervous system lymphoma (PCNSL). Although well-tolerated in the majority of patients, ibrutinib demonstrates in some cases troublesome toxicities, including invasive fungal infections (IFIs). In the present review, we summarize clinical manifestations of IFIs in patients treated with ibrutinib, generally characterized by an early onset, mild clinical manifestations, asymptomatic/low symptomatic pulmonary localization and high incidence of central nervous system (CNS) involvement. IFI risk appears particularly increased in patients receiving ibrutinib associated with other immune modulator agents, especially with steroids or immune-chemotherapy. Moreover, the immunomodulatory effect of ibrutinib is described, pointing the attention on the involvement of specific molecules targeted by ibrutinib in innate and adaptive response to fungal infection. Overall, the findings indicate the ibrutinib may rapidly impair innate immune cell functions, while concomitantly restoring an effective protective potential of adaptive immune compartment. A correct awareness, especially when other predisposing factors are present, is warranted about the potential risk of IFIs in ibrutinib-treated patients.

Genetic defects in fungal recognition and susceptibility to invasive pulmonary aspergillosis

The interindividual variability in the onset and clinical course of invasive pulmonary aspergillosis (IPA) raises fundamental questions about its actual pathogenesis. Clinical and epidemiological studies have reported only a few examples of monogenic defects, however an expanding number of common polymorphisms associated with IPA has been identified. Understanding how genetic variation regulates the immune response to Aspergillus provides critical insights into the human immunobiology of IPA by pinpointing directly relevant immune molecules and interacting pathways. Most of the genetic defects reported to increase susceptibility to infection were described or suggested to impair fungal recognition by the innate immune system. In this review, we discuss the contribution of host genetic variation in pattern recognition receptors to the development of IPA. An improved understanding of the molecular and cellular processes that regulate human susceptibility to IPA is ultimately expected to pave the way toward personalized medical interventions based on host-directed risk stratification and individualized immunotherapy.

Polymorphisms in Receptors Involved in Opsonic and Nonopsonic Phagocytosis, and Correlation with Risk of Infection in Oncohematology Patients

High-risk hematological malignancies are a privileged setting for infection by opportunistic microbes, with invasive mycosis being one of the most serious complications. Recently, genetic background has emerged as an unanticipated risk factor. For this reason, polymorphisms for genes encoding archetypal receptors involved in the opsonic and nonopsonic clearance of microbes, pentraxin-3 (PTX3) and Dectin-1, respectively, were studied and correlated with the risk of infection. Fungal, bacterial, and viral infections were registered for a group of 198 patients with high-risk hematological malignancies. Polymorphisms for the pentraxin-3 gene (PTX3) showed a significant association with the risk of fungal infection by Candida spp. and, especially, by Aspergillus spp. This link remained even for patients undergoing antifungal prophylaxis, thus demonstrating the clinical relevance of PTX3 in the defense against fungi. CLEC7A polymorphisms did not show any definite correlation with the risk of invasive mycosis, nor did they influence the expression of Dectin-1 isoforms generated by alternative splicing. The PTX3 mRNA expression level was significantly lower in samples from healthy volunteers who showed these polymorphisms, although no differences were observed in the extents of induction elicited by bacterial lipopolysaccharide and heat-killed Candida albicans, thus suggesting that the expression of PTX3 at the start of infection may influence the clinical outcome. PTX3 mRNA expression can be a good biomarker to establish proper antifungal prophylaxis in immunodepressed patients.

Preparations for Invasion: Modulation of Host Lung Immunity During Pulmonary Aspergillosis by Gliotoxin and Other Fungal Secondary Metabolites

Pulmonary aspergillosis is a severe infectious disease caused by some members of the Aspergillus genus, that affects immunocompetent as well as immunocompromised patients. Among the different disease forms, Invasive Aspergillosis is the one causing the highest mortality, mainly, although not exclusively, affecting neutropenic patients. This genus is very well known by humans, since different sectors like pharmaceutical or food industry have taken advantage of the biological activity of some molecules synthetized by the fungus, known as secondary metabolites, including statins, antibiotics, fermentative compounds or colorants among others. However, during infection, in response to a hostile host environment, the fungal secondary metabolism is activated, producing different virulence factors to increase its survival chances. Some of these factors also contribute to fungal dissemination and invasion of adjacent and distant organs. Among the different secondary metabolites produced by Aspergillus spp. Gliotoxin (GT) is the best known and better characterized virulence factor. It is able to generate reactive oxygen species (ROS) due to the disulfide bridge present in its structure. It also presents immunosuppressive activity related with its ability to kill mammalian cells and/or inactivate critical immune signaling pathways like NFkB. In this comprehensive review, we will briefly give an overview of the lung immune response against Aspergillus as a preface to analyse the effect of different secondary metabolites on the host immune response, with a special attention to GT. We will discuss the results reported in the literature on the context of the animal models employed to analyse the role of GT as virulence factor, which is expected to greatly depend on the immune status of the host: why should you hide when nobody is seeking for you? Finally, GT immunosuppressive activity will be related with different human diseases predisposing to invasive aspergillosis in order to have a global view on the potential of GT to be used as a target to treat IA.

Genetic deficiency of NOD2 confers resistance to invasive aspergillosis

Invasive aspergillosis (IA) is a severe infection that can occur in severely immunocompromised patients. Efficient immune recognition of Aspergillus is crucial to protect against infection, and previous studies suggested a role for NOD2 in this process. However, thorough investigation of the impact of NOD2 on susceptibility to aspergillosis is lacking. Common genetic variations in NOD2 has been associated with Crohn's disease and here we investigated the influence of these  genetic variations on the anti-Aspergillus host response. A NOD2 polymorphism reduced the risk of IA after hematopoietic stem-cell transplantation. Mechanistically, absence of NOD2 in monocytes and macrophages increases phagocytosis leading to enhanced fungal killing, conversely, NOD2 activation reduces the antifungal potential of these cells. Crucially, Nod2 deficiency results in resistance to Aspergillus infection in an in vivo model of pulmonary aspergillosis. Collectively, our data demonstrate that genetic deficiency of NOD2 plays a protective role during Aspergillus infection.

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 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.

Risk stratification for invasive fungal infections in patients with hematological malignancies: SEIFEM recommendations

Invasive fungal infections (IFIs) are an important cause of morbidity and mortality in immunocompromised patients. Patients with hematological malignancies undergoing conventional chemotherapy, autologous or allogeneic hematopoietic stem cell transplantation are considered at high risk, and Aspergillus spp. represents the most frequently isolated micro-organisms. In the last years, attention has also been focused on other rare molds (e.g., Zygomycetes, Fusarium spp.) responsible for devastating clinical manifestations. The extensive use of antifungal prophylaxis has reduced the infections from yeasts (e.g., candidemia) even though they are still associated with high mortality rates. This paper analyzes concurrent multiple predisposing factors that could favor the onset of fungal infections. Although neutropenia is common to almost all hematologic patients, other factors play a key role in specific patients, in particular in patients with AML or allogeneic HSCT recipients. Defining those patients at higher risk of IFIs may help to design the most appropriate diagnostic work-up and antifungal strategy.

MyD88 Shapes Vaccine Immunity by Extrinsically Regulating Survival of CD4+ T Cells during the Contraction Phase

Soaring rates of systemic fungal infections worldwide underscore the need for vaccine prevention. An understanding of the elements that promote vaccine immunity is essential. We previously reported that Th17 cells are required for vaccine immunity to the systemic dimorphic fungi of North America, and that Card9 and MyD88 signaling are required for the development of protective Th17 cells. Herein, we investigated where, when and how MyD88 regulates T cell development. We uncovered a novel mechanism in which MyD88 extrinsically regulates the survival of activated T cells during the contraction phase and in the absence of inflammation, but is dispensable for the expansion and differentiation of the cells. The poor survival of activated T cells in Myd88^-/- mice is linked to increased caspase3-mediated apoptosis, but not to Fas- or Bim-dependent apoptotic pathways, nor to reduced expression of the anti-apoptotic molecules Bcl-2 or Bcl-xL. Moreover, TLR3, 7, and/or 9, but not TLR2 or 4, also were required extrinsically for MyD88-dependent Th17 cell responses and vaccine immunity. Similar MyD88 requirements governed the survival of virus primed T cells. Our data identify unappreciated new requirements for eliciting adaptive immunity and have implications for designing vaccines.

Despite several million new systemic fungal infections annually worldwide, there are no commercial vaccines available. The development of effective vaccines requires a fundamental understanding of how protective immune responses are induced. Using experimental vaccine strains, we previously demonstrated that populations of T helper cells producing interleukin 17 (Th17 cells) and interferon gamma (Th1 cells) mediate vaccine resistance to systemic dimorphic fungi of North America. Here, we report how the immune system recognizes the fungal vaccines and induces the development of protective T cells. We delineate the role of pathogen recognition receptors (PRRs) and their common signaling pathway in host immune cells that recognize the fungal vaccine. While the signaling pathway studied is essential for the development of vaccine-induced T cells, the mechanism of action is novel and included T cell death after activation. The findings could be extended to virus-specific T cells suggesting that the mechanism is conserved among the microbial kingdom. Our work sheds new light on how protective T cells are induced and can be harnessed by vaccine strategies tailored against fungal and other microbial infections.

Baseline cytokine profiling identifies novel risk factors for invasive fungal disease among haematology patients undergoing intensive chemotherapy or haematopoietic stem cell transplantation

BACKGROUND

Invasive fungal disease (IFD) is a disease of immunocompromised hosts. Cytokines are important mediators of innate and adaptive immune system. The aim of this study was to identify cytokine profiles that correlate with increased risk of IFD.

METHODS

We prospectively enrolled 172 adult haematology patients undergoing intensive chemotherapy, immunosuppressive therapy, and haematopoietic stem cell transplantation. Pro-inflammatory cytokine profiling using 30-plex Luminex assay was performed at baseline and during treatment. Nine single nucleotide polymorphisms (TLR1, TLR2, TLR3, TLR4.1, TLR4.2, TLR6, CLEC7A, CARD9, and INFG) were investigated among transplant recipients and donors.

FINDINGS

The incidence of IFD in this cohort was 16.9% (29/172). Median baseline serum concentrations of IL-15, IL-2R, CCL2, and MIP-1α were significantly higher whilst IL-4 was lower in patients with proven/probable IFD compared to those with no evidence of IFD. Baseline high IL-2R and CCL2 were associated with increased risk of IFD in the multivariate analysis (adjusted hazard ratio 2.3 [95% CI 1.1-5.1; P = 0.037], and hazard ratio 2.7 [95% CI 1.2-6.1; P = 0.016], respectively). However, these differences were not significant in follow up measurements. Similarly, no significant independent prognostic value was associated with baseline cytokine profile.

INTERPRETATION

High baseline IL-2R and CCL2 concentrations were independent indicators of the risk of developing IFD and could be used to identify patients for enhanced prophylaxis and early antifungal therapy.

Polymorphisms of Dectin-1 and TLR2 Predispose to Invasive Fungal Disease in Patients with Acute Myeloid Leukemia

BACKGROUND

Patients with acute myeloid leukemia (AML) who undergo induction chemotherapy are at high risk for invasive fungal disease (IFD). Dectin-1, a C-type lectin family member represents one of the most important pattern recognition receptors of the innate immune system and single nucleotide polymorphisms (SNPs) in the Dectin-1 gene have been associated with an increased risk of infectious complications. We sought to investigate the impact of three different Dectin-1 SNPs and one TLR2 SNP on developing IFD in 186 adult patients with newly diagnosed AML following anthracycline-based induction chemotherapy.

PATIENTS AND METHODS

Genotyping of Dectin-1 SNPs (rs16910526, rs3901533 and rs7309123) and TLR2 SNP (rs5743708) was performed by TaqMan method and pyrosequencing. IFD was defined according to the EORTC/MSG consensus guidelines. Multiple logistic regression analyses were applied to evaluate the association between the polymorphisms and the occurrence of pulmonary infections. Dectin-1 expression studies with SNP genotyped human monocytes were performed to elucidate susceptibility to IFD following chemotherapy.

RESULTS

We could demonstrate that patients carrying the Dectin-1 SNP rs7309123 G/G (n = 47) or G/G and C/G (n = 133) genotype revealed a significant higher risk for developing both pneumonia in general (adjusted odds ratio (OR): 2.5; p = 0.014 and OR: 3.0, p = 0.004) and pulmonary IFD (OR: 2.6; p = 0.012 and OR: 2.4, p = 0.041, respectively). Patients carrying the TLR2 SNP rs5743708 (R753Q, GA/AA genotype, n = 12) also revealed a significantly higher susceptibility to pneumonia including IFD. Furthermore, Dectin-1 mRNA expression in human monocytes was lower following chemotherapy.

CONCLUSION

To our best knowledge, this study represents the first analysis demonstrating that harbouring polymorphisms of Dectin-1 (rs7309123) or TLR2 (rs5743708) represents an independent risk factor of developing IFD in patients with AML undergoing induction chemotherapy.

Asexual sporulation facilitates adaptation: The emergence of azole resistance in Aspergillus fumigatus

Understanding the occurrence and spread of azole resistance in Aspergillus fumigatus is crucial for public health. It has been hypothesized that asexual sporulation, which is abundant in nature, is essential for phenotypic expression of azole resistance mutations in A. fumigatus facilitating subsequent spread through natural selection. Furthermore, the disease aspergilloma is associated with asexual sporulation within the lungs of patients and the emergence of azole resistance. This study assessed the evolutionary advantage of asexual sporulation by growing the fungus under pressure of one of five different azole fungicides over seven weeks and by comparing the rate of adaptation between scenarios of culturing with and without asexual sporulation. Results unequivocally show that asexual sporulation facilitates adaptation. This can be explained by the combination of more effective selection because of the transition from a multicellular to a unicellular stage, and by increased mutation supply due to the production of spores, which involves numerous mitotic divisions. Insights from this study are essential to unravel the resistance mechanisms of sporulating pathogens to chemical compounds and disease agents in general, and for designing strategies that prevent or overcome the emerging threat of azole resistance in particular.

Intrinsic MyD88-Akt1-mTOR Signaling Coordinates Disparate Tc17 and Tc1 Responses during Vaccine Immunity against Fungal Pneumonia

Fungal infections have skyrocketed in immune-compromised patients lacking CD4⁺ T cells, underscoring the need for vaccine prevention. An understanding of the elements that promote vaccine immunity in this setting is essential. We previously demonstrated that vaccine-induced IL-17A⁺ CD8⁺ T cells (Tc17) are required for resistance against lethal fungal pneumonia in CD4⁺ T cell-deficient hosts, whereas the individual type I cytokines IFN-γ, TNF-α and GM-CSF, are dispensable. Here, we report that T cell-intrinsic MyD88 signals are crucial for these Tc17 cell responses and vaccine immunity against lethal fungal pneumonia in mice. In contrast, IFN-γ⁺ CD8⁺ cell (Tc1) responses are largely normal in the absence of intrinsic MyD88 signaling in CD8⁺ T cells. The poor accumulation of MyD88-deficient Tc17 cells was not linked to an early onset of contraction, nor to accelerated cell death or diminished expression of anti-apoptotic molecules Bcl-2 or Bcl-xL. Instead, intrinsic MyD88 was required to sustain the proliferation of Tc17 cells through the activation of mTOR via Akt1. Moreover, intrinsic IL-1R and TLR2, but not IL-18R, were required for MyD88 dependent Tc17 responses. Our data identify unappreciated targets for augmenting adaptive immunity against fungi. Our findings have implications for designing fungal vaccines and immune-based therapies in immune-compromised patients.

Patients with AIDS, cancer or immune suppressive treatments are vulnerable to infection with invasive fungi. We have found that even when helper CD4 T cells are profoundly reduced in a mouse model that mimics this defect in AIDS, other remaining T cells are capable of mounting vaccine immunity against a deadly fungal infection, and they do so by producing the powerful, soluble product, IL-17. It has been widely believed that the activation and instruction of such cells, called Tc17 cells, is governed by another population of immune cells in the body, but we have found here that pathways within these Tc17 cells themselves mediate their activation and ability to produce the IL-17 needed for resistance to infection. We have also identified elements of the circuitry controlling this pathway—elements called MyD88, Akt1 and mTOR—and found that they control the production of IL-17 and not other products such as IFN-γ often produced by these cells. Further, we determined that this circuitry controls the development of Tc17 cells by regulating their ability to divide and expand. Thus, in a mouse model of vaccination against lethal fungal pneumonia caused by Blastomyces dermatitidis, we uncovered an important cellular arsenal that can be recruited to bolster resistance against a fungal infection, and identified novel ways in which the cells develop and expand into potent killers of fungi.

Epidemiology and risk factors for invasive fungal diseases in hematopoietic stem cell transplantation

PURPOSE OF REVIEW

Knowledge of the epidemiology and the risk factors of invasive fungal diseases (IFDs) in hematopoietic stem cell transplant (HSCT) recipients is a critical determinant of the prevention, diagnosis and therapeutic antifungal strategy. Transplant procedures are characterized by a continuous evolution; therefore, an update of the epidemiological findings of IFDs in HSCT populations is needed.

RECENT FINDINGS

In the last few years, the incidence and the clinical risk factors of IFD, mainly in allogeneic HSCT populations, have been investigated in prospective, multicenter studies. New findings in the different types and phases of transplant may be considered for a redefinition of the level of risk of IFD after HSCT. Furthermore, recent studies have uncovered associations between host's and/or donor's genetic variants and immunological risk for IFDs, in particular invasive aspergillosis.

SUMMARY

Evolution of the transplant procedures was followed by an important change in the epidemiology and clinical risk of IFD after allogeneic HSCT. A new stratification of subpopulations according to different clinical infectious risk and genetic susceptibility may be considered to predict those patients most vulnerable to IFD and update tailored antifungal strategies.

Paving the way for predictive diagnostics and personalized treatment of invasive aspergillosis

Invasive aspergillosis (IA) is a life-threatening fungal disease commonly diagnosed among individuals with immunological deficits, namely hematological patients undergoing chemotherapy or allogeneic hematopoietic stem cell transplantation. Vaccines are not available, and despite the improved diagnosis and antifungal therapy, the treatment of IA is associated with a poor outcome. Importantly, the risk of infection and its clinical outcome vary significantly even among patients with similar predisposing clinical factors and microbiological exposure. Recent insights into antifungal immunity have further highlighted the complexity of host-fungus interactions and the multiple pathogen-sensing systems activated to control infection. How to decode this information into clinical practice remains however, a challenging issue in medical mycology. Here, we address recent advances in our understanding of the host-fungus interaction and discuss the application of this knowledge in potential strategies with the aim of moving toward personalized diagnostics and treatment (theranostics) in immunocompromised patients. Ultimately, the integration of individual traits into a clinically applicable process to predict the risk and progression of disease, and the efficacy of antifungal prophylaxis and therapy, holds the promise of a pioneering innovation benefiting patients at risk of IA.

Host response to Candida albicans bloodstream infection and sepsis

Candida albicans is a major cause of bloodstream infection which may present as sepsis and septic shock - major causes of morbidity and mortality world-wide. After invasion of the pathogen, innate mechanisms govern the early response. Here, we outline the models used to study these mechanisms and summarize our current understanding of innate immune responses during Candida bloodstream infection. This includes protective immunity as well as harmful responses resulting in Candida induced sepsis. Neutrophilic granulocytes are considered principal effector cells conferring protection and recognize C. albicans mainly via complement receptor 3. They possess a range of effector mechanisms, contributing to elimination of the pathogen. Neutrophil activation is closely linked to complement and modulated by activated mononuclear cells. A thorough understanding of these mechanisms will help in creating an individualized approach to patients suffering from systemic candidiasis and aid in optimizing clinical management.

Compartment-specific and sequential role of MyD88 and CARD9 in chemokine induction and innate defense during respiratory fungal infection

Aspergillus fumigatus forms ubiquitous airborne conidia that humans inhale on a daily basis. Although respiratory fungal infection activates the adaptor proteins CARD9 and MyD88 via C-type lectin, Toll-like, and interleukin-1 family receptor signals, defining the temporal and spatial pattern of MyD88- and CARD9-coupled signals in immune activation and fungal clearance has been difficult to achieve. Herein, we demonstrate that MyD88 and CARD9 act in two discrete phases and in two cellular compartments to direct chemokine- and neutrophil-dependent host defense. The first phase depends on MyD88 signaling because genetic deletion of MyD88 leads to delayed induction of the neutrophil chemokines CXCL1 and CXCL5, delayed neutrophil lung trafficking, and fatal pulmonary damage at the onset of respiratory fungal infection. MyD88 expression in lung epithelial cells restores rapid chemokine induction and neutrophil recruitment via interleukin-1 receptor signaling. Exogenous CXCL1 administration reverses murine mortality in MyD88-deficient mice. The second phase depends predominately on CARD9 signaling because genetic deletion of CARD9 in radiosensitive hematopoietic cells interrupts CXCL1 and CXCL2 production and lung neutrophil recruitment beyond the initial MyD88-dependent phase. Using a CXCL2 reporter mouse, we show that lung-infiltrating neutrophils represent the major cellular source of CXCL2 during CARD9-dependent recruitment. Although neutrophil-intrinsic MyD88 and CARD9 function are dispensable for neutrophil conidial uptake and killing in the lung, global deletion of both adaptor proteins triggers rapidly progressive invasive disease when mice are challenged with an inoculum that is sub-lethal for single adapter protein knockout mice. Our findings demonstrate that distinct signal transduction pathways in the respiratory epithelium and hematopoietic compartment partially overlap to ensure optimal chemokine induction, neutrophil recruitment, and fungal clearance within the respiratory tract.

Our understanding of how epithelial and hematopoietic cells in the lung coordinate immunity against inhaled fungal conidia (spores) remains limited. The mold Aspergillus fumigatus is a major cause of infectious mortality in immune compromised patients. Host defense against A. fumigatus involves the activation of two host signal transducers, MyD88 and CARD9, leading to neutrophil recruitment to the infection site. In this study, we define how MyD88- and CARD9-coupled signals operate in epithelial and hematopoietic compartments to regulate neutrophil-mediated defense against A. fumigatus. Our studies support a two-stage model in which MyD88 activation in epithelial cells, via the interleukin-1 receptor, supports the rapid induction of neutrophil-recruiting chemokines. This process is essential for the first phase of neutrophil recruitment. Mortality observed in MyD88-deficient mice can be significantly reversed by administration of a chemokine termed CXCL1 to infected airways. The second phase of neutrophil recruitment is initiated by CARD9 signaling in hematopoietic cells. Loss of both phases of chemokine induction and neutrophil recruitment dramatically increases murine susceptibility to tissue-invasive disease. In sum, our study defines a temporal sequence of events, initiated by interleukin-1 receptor/MyD88 signaling in the pulmonary epithelium and propagated by CARD9 signaling in hematopoietic cells, that induces protective immunity against inhaled fungal conidia.