Role of neutrophils in invasive aspergillosis

The Inflammatory Response Induced by Aspergillus fumigatus Conidia Is Dependent on Complement Activation: Insight from a Whole Blood Model

INTRODUCTION

We aimed to elucidate the inflammatory response of Aspergillus fumigatus conidia in a whole-blood model of innate immune activation and to compare it with the well-characterized inflammatory reaction to Escherichia coli.

METHODS

Employing a human lepirudin whole-blood model, we analyzed complement and leukocyte activation by measuring the sC5b-9 complex and assessing CD11b expression. A 27-multiplex system was used for quantification of cytokines. Selective cell removal from whole blood and inhibition of C3, C5, and CD14 were also applied.

RESULTS

Our findings demonstrated a marked elevation in sC5b-9 and CD11b post-A. fumigatus incubation. Thirteen cytokines (TNF, IL-1β, IL-1ra, IL-4, IL-6, IL-8, IL-17, IFNγ, MCP-1, MIP-1α, MIP-1β, FGF-basic, and G-CSF) showed increased levels. A generally lower level of cytokine release and CD11b expression was observed with A. fumigatus conidia than with E. coli. Notably, monocytes were instrumental in releasing all cytokines except MCP-1. IL-1ra was found to be both monocyte and granulocyte-dependent. Pre-inhibiting with C3 and CD14 inhibitors resulted in decreased release patterns for six cytokines (TNF, IL-1β, IL-6, IL-8, MIP-1α, and MIP-1β), with minimal effects by C5-inhibition.

CONCLUSION

A. fumigatus conidia induced complement activation comparable to E. coli, whereas CD11b expression and cytokine release were lower, underscoring distinct inflammatory responses between these pathogens. Complement C3 inhibition attenuated cytokine release indicating a C3-level role of complement in A. fumigatus immunity.

Activation of leukotriene B4 receptor 1 is a prerequisite for complement receptor 3-mediated antifungal responses of neutrophils

Invasive fungal infections are life-threatening, and neutrophils are vital cells of the innate immune system that defend against them. The role of LTA4H-LTB4-BLT1 axis in regulation of neutrophil responses to fungal infection remains poorly understood. Here, we demonstrated that the LTA4H-LTB4-BLT1 axis protects the host against Candida albicans and Aspergillus fumigatus, but not Cryptococcus neoformans infection, by regulating the antifungal activity of neutrophils. Our results show that deleting Lta4h or Blt1 substantially impairs the fungal-specific phagocytic capacity of neutrophils. Moreover, defective activation of the spleen tyrosine kinase (Syk) and extracellular signal-related kinase (ERK1/2) pathways in neutrophils accompanies this impairment. Mechanistically, BLT1 regulates CR3-mediated, β-1,3-glucan-induced neutrophil phagocytosis, while a physical interaction with CR3 with slight influence on its dynamics is observed. Our findings thus demonstrate that the LTA4H-LTB4-BLT1 axis is essential for the phagocytic function of neutrophils in host antifungal immune response against Candida albicans and Aspergillus fumigatus.

Cutting Edge: Neutrophils License the Maturation of Monocytes into Effective Antifungal Effectors

Neutrophils are critical for the direct eradication of Aspergillus fumigatus conidia, but whether they mediate antifungal defense beyond their role as effectors is unclear. In this study, we demonstrate that neutrophil depletion impairs the activation of protective antifungal CCR2+ inflammatory monocytes. In the absence of neutrophils, monocytes displayed limited differentiation into monocyte-derived dendritic cells, reduced formation of reactive oxygen species, and diminished conidiacidal activity. Upstream regulator analysis of the transcriptional response in monocytes predicted a loss of STAT1-dependent signals as the potential basis for the dysfunction seen in neutrophil-depleted mice. We find that conditional removal of STAT1 on CCR2+ cells results in diminished antifungal monocyte responses, whereas exogenous administration of IFN-γ to neutrophil-depleted mice restores monocyte-derived dendritic cell maturation and reactive oxygen species production. Altogether, our findings support a critical role for neutrophils in antifungal immunity not only as effectors but also as important contributors to antifungal monocyte activation, in part by regulating STAT1-dependent functions.

Neutrophil-Specific Knockdown of β2 Integrins Impairs Antifungal Effector Functions and Aggravates the Course of Invasive Pulmonal Aspergillosis

β2-integrins are heterodimeric surface receptors that are expressed specifically by leukocytes and consist of a variable α (CD11a-d) and a common β-subunit (CD18). Functional impairment of CD18, which causes leukocyte adhesion deficiency type-1 results in an immunocompromised state characterized by severe infections, such as invasive pulmonary aspergillosis (IPA). The underlying immune defects have largely been attributed to an impaired migratory and phagocytic activity of polymorphonuclear granulocytes (PMN). However, the exact contribution of β2-integrins for PMN functions in-vivo has not been elucidated yet, since the mouse models available so far display a constitutive CD18 knockout (CD18^-/- or CD18^hypo). To determine the PMN-specific role of β2-integrins for innate effector functions and pathogen control, we generated a mouse line with a Ly6G-specific knockdown of the common β-subunit (CD18^Ly6G cKO). We characterized CD18^Ly6G cKO mice in-vitro to confirm the PMN-specific knockdown of β2-integrins. Next, we investigated the clinical course of IPA in A. fumigatus infected CD18^Ly6G cKO mice with regard to the fungal burden, pulmonary inflammation and PMN response towards A. fumigatus. Our results revealed that the β2-integrin knockdown was restricted to PMN and that CD18^Ly6G cKO mice showed an aggravated course of IPA. In accordance, we observed a higher fungal burden and lower levels of proinflammatory innate cytokines, such as TNF-α, in lungs of IPA-infected CD18^Ly6G cKO mice. Bronchoalveolar lavage revealed higher levels of CXCL1, a stronger PMN-infiltration, but concomitantly elevated apoptosis of PMN in lungs of CD18^Ly6G cKO mice. Ex-vivo analysis further unveiled a strong impairment of PMN effector function, as reflected by an attenuated phagocytic activity, and a diminished generation of reactive oxygen species (ROS) and neutrophil-extracellular traps (NET) in CD18-deficient PMN. Overall, our study demonstrates that β2-integrins are required specifically for PMN effector functions and contribute to the clearance of A. fumigatus by infiltrating PMN, and the establishment of an inflammatory microenvironment in infected lungs.

PLB-985 Neutrophil-Like Cells as a Model To Study Aspergillus fumigatus Pathogenesis

Fungal infections remain a major global concern. Emerging fungal pathogens and increasing rates of resistance mean that additional research efforts and resources must be allocated to advancing our understanding of fungal pathogenesis and developing new therapeutic interventions. Neutrophilic granulocytes are a major cell type involved in protection against the important fungal pathogen Aspergillus fumigatus, where they employ numerous defense mechanisms, including production of antimicrobial extracellular vesicles. A major drawback to work with neutrophils is the lack of a suitable cell line system for the study of fungal pathogenesis. To address this problem, we assessed the feasibility of using differentiated PLB-985 neutrophil-like cells as an in vitro model to study A. fumigatus infection. We find that dimethylformamide-differentiated PLB-985 cells provide a useful recapitulation of many aspects of A. fumigatus interactions with primary human polymorphonuclear leukocytes. We show that differentiated PLB-985 cells phagocytose fungal conidia and acidify conidia-containing phagolysosomes similar to primary neutrophils, release neutrophil extracellular traps, and also produce antifungal extracellular vesicles in response to infection. In addition, we provide an improved method for the isolation of extracellular vesicles produced during infection by employing a size exclusion chromatography-based approach. Advanced liquid chromatography-tandem mass spectrometry (LC-MS/MS) proteomics revealed an enrichment of extracellular vesicle marker proteins and a decrease of cytoplasmic proteins in extracellular vesicles isolated using this improved method. Ultimately, we find that differentiated PLB-985 cells can serve as a genetically tractable model to study many aspects of A. fumigatus pathogenesis. IMPORTANCE Polymorphonuclear leukocytes are an important defense against human fungal pathogens, yet our model systems to study this group of cells remain very limited in scope. In this study, we established that differentiated PLB-985 cells can serve as a model to recapitulate several important aspects of human polymorphonuclear leukocyte interactions with the important human fungal pathogen Aspergillus fumigatus. The proposed addition of a cultured neutrophil-like cell line to the experimental toolbox to study fungal pathogenesis will allow for a more mechanistic description of neutrophil antifungal biology. In addition, the easier handling of the cell line compared to primary human neutrophils allowed us to use PLB-985 cells to provide an improved method for isolation of neutrophil-derived extracellular vesicles using size exclusion chromatography. Together, these results provide significant tools and a baseline knowledge for the future study of neutrophil-derived extracellular vesicles in the laboratory.

Chronic Pulmonary Aspergillosis: Disease Severity Using Image Analysis and Correlation with Systemic Proinflammation and Predictors of Clinical Outcome

(1) Background: The presentation of chronic pulmonary aspergillosis (CPA) ranges from single granuloma to fibrosis in the affected lung. CPA can be divided into five categories according to European Respirology Society (ERS) guidance but is usually assessed by clinical physicians. Computer-based quantitative lung parenchyma analysis in CPA and its correlation with clinical manifestations, systemic inflammation, and angiogenesis have never been investigated. (2) Method: Forty-nine patients with CPA and 36 controls were prospectively enrolled. Pulmonary function tests (forced vital capacity (FVC), forced expiratory volume in one second (FEV₁), and FEV₁/FCV) and biomarkers in the peripheral blood (the chemokines interleukin (IL)-1B, IL-6, IL-10, IL-8, CRP, ESR, MMP1, MMP7, MMP8, TNF-α, calprotectin, SDF-1α, and VEGFA) were measured before antifungal treatment. The disease severity was categorized into mild, moderate, and severe based on chest computed tomography (CT) images. The oxygen demand and overall mortality until the end of the study were recorded. Quantitative parenchyma analysis was performed using the free software 3Dslicer. (3) Results: The results of quantitative parenchyma analysis concorded with the visual severity from the chest CT, oxygen demand, FVC, and FEV₁ in the study subjects. The decrease in kurtosis and skewness of the lung density histograms on CT, increase in high attenuation area (HAA), and reduced lung volume were significantly correlated with increases in the PMN %, CRP, IL-1B, SDF-1α, MMP1, and Calprotectin in peripheral blood in the multivariable regression analysis. TNF-α and IL-1B at study entry and the CPA severity from either a visual method or computer-based evaluation were predictors of long-term mortality. (4) Conclusion: The computer-based parenchyma analysis in CPA agreed with the categorization on a visual basis and was associated with the clinical outcomes, chemokines, and systemic proinflammation profiles.

Diagnostic value of serum human Galactomannan aspergillus antigen and 1,3-beta-D-glucan in immunocompromised patient suspected fungal infection

BACKGROUND

The prevalence of fungal infection (FI) in developing countries is high, but the diagnosis of FI is still challenging to determine, so it is needed evaluation of biomarkers other than microbiological culture, because the culture has low sensitivity, high cost, not available in every laboratory and needs a long time. The detection of human galactomannan Aspergillus antigen (GAL) and 1,3-beta-D-glucan (BDG) on the fungal cell wall could be the promising biomarkers for fungal infection. Neutropenia, lymphopenia and CD4T cells in the immunocompromised patients are essential factors, but these cell associations with BDG and GAL levels have not been evaluated yet. The study aimed to evaluate GAL and BDG for detecting fungal infection and their association with total leucocyte count, neutrophil, monocyte, lymphocyte and CD4T cells.

METHOD

A cross-sectional study was conducted among 86 patient with suspected FI. Fungal infection established using EORTC/MSG criteria. Serology test performed using ELISA. Leucocyte cells were measured using a haematology autoanalyser, and CD4T cells were analysed using BD FACSPresto. Statistical analysis obtained using Spearman's correlation coefficient, ROC curve analysis and 2 × 2 contingency table.

RESULTS

Serum Galactomannan and BDG had a significant correlation with CD4T cells and total lymphocyte count (p < 0.05). The cut-off OD GAL >0.3 had sensitivity 54.6%, specificity 87.5% and AUC 0.71; meanwhile, the BDG cut-off >115.78 pg/ mL had sensitivity 71.2%, specificity 52.4% and AUC 0.63 for detecting fungal infection.

CONCLUSIONS

The immunocompromised patients can undergo GAL for determining the diagnose of FI. The lower the CD4T cells and total lymphocyte count, the higher the GAL and BDG serum levels.

Cellular and molecular insights on the regulation of innate immune responses to experimental aspergillosis in chicken and turkey poults

Across the world, many commercial poultry flocks and captive birds are threatened by infection with Aspergillus fumigatus. Susceptibility to aspergillosis varies among birds; among galliform birds specifically, morbidity and mortality rates seem to be greater in turkeys than in chickens. Little is known regarding the features of avian immune responses after inhalation of Aspergillus conidia, and to date, scarce information on inflammatory responses during aspergillosis exists. Thus, in the present study, we aimed to improve our understanding of the interactions between A. fumigatus and economically relevant galliform birds in terms of local innate immune responses. Intra-tracheal aerosolization of A. fumigatus conidia in turkey and chicken poults led to more severe clinical signs and lung lesions in turkeys, but leukocyte recovery from lung lavages was higher in chickens at 1dpi only. Interestingly, only chicken CD8+ T lymphocyte proportions increased after infection. Furthermore, the lungs of infected chickens showed an early upregulation of pro-inflammatory cytokines, including IL-1β, IFN-γ and IL-6, whereas in turkeys, most of these cytokines showed a downregulation or a delayed upregulation. These results confirmed the importance of an early pro-inflammatory response to ensure the development of an appropriate anti-fungal immunity to avoid Aspergillus dissemination in the respiratory tract. In conclusion, we show for the first time that differences in local innate immune responses between chickens and turkeys during aspergillosis may determine the outcome of the disease.

Influenza Suppresses Neutrophil Recruitment to the Lung and Exacerbates Secondary Invasive Pulmonary Aspergillosis

Aspergillus fumigatus is an environmental fungus that can cause invasive pulmonary aspergillosis when spores are inhaled into the respiratory tract and invade airway or lung tissue. Influenza is a common respiratory virus that can cause severe respiratory disease, and postinfluenza invasive pulmonary aspergillosis, which is becoming a well-recognized clinical problem, typically occurs in critically ill patients. Mice challenged with influenza A PR/8/34 H1N1 and subsequently challenged with A. fumigatus had increased fungal burden, viral burden, inflammation, and mortality compared with single infected mice. Neutrophil recruitment in the lung of superinfected mice was decreased; however, mice were not neutropenic, and there was no difference in absolute blood neutrophils between groups. Additionally, CXCL1 and CXCL2 were decreased in lungs of superinfected mice compared with controls. IFN levels were increased in mice that received influenza, and deletion of STAT1 resulted in decreased fungal burden, increased airway and lung neutrophils, and increased CXCL1 compared with wild-type mice, whereas deletion of STAT2 did not change fungal burden or airway neutrophilia compared with wild-type mice. These data demonstrate a mechanism by which influenza A-induced STAT1 signaling inhibits neutrophil recruitment and increases susceptibility to postinfluenza invasive pulmonary aspergillosis.

Response of Human Neutrophil Granulocytes to the Hyphae of the Emerging Fungal Pathogen Curvularia lunata

Curvularia lunata is an ascomycete filamentous fungus causing local and invasive phaeohyphomycoses in both immunocompromised and immunocompetent patients. Neutrophils are crucial participants of the first line host defense against fungal infections. They migrate to the infected site and eliminate the infectious agents by various mechanisms including phagocytoses, oxidative damage, or formation of neutrophil extracellular trap (NET). Neutropenia may be a risk factor for phaeohyphomycoses, and restoration of the neutrophil function can improve the outcome of the infection. In the present study, interaction of primary human neutrophil granulocytes with the hyphae C. lunata was examined and compared to that with the well characterized filamentous fungal pathogen Aspergillus fumigatus. Neutrophils could recognize the serum opsonized hyphae of C. lunata and attach to them. Myeloperoxidase release was also activated by a soluble factor present in the culture supernatant of the fungus. Induction of the oxidative burst was found to depend on serum opsonization of the hyphae. Although extracellular hydrogen peroxide production was induced, the fungus efficiently blocked the oxidative burst by acidifying the reaction environment. This blockage also affected the NET forming ability of the neutrophils.

[Invasive aspergillosis in the patient with oncohematologic disease]

Invasive aspergillosis is the most common invasive fungal infection in patients with acute hematological malignancies or treated with hematopoietic stem cell transplantation due to the marked alteration of the physiological mechanisms of antifungal immunity that takes place in these situations. For this reason, antifungal prophylaxis has a relevant role in these patients. The introduction of new antifungal agents has motivated the updating of recommendations for prophylaxis and treatment in different guidelines. The objectives of this chapter are a brief review of the mechanisms of immunity against fungi, the definition of risk for developing an invasive fungal infection and an update of the prophylaxis recommendations and treatment of invasive aspergillosis in the group of patients with hematological diseases.

A transgenic zebrafish line for in vivo visualisation of neutrophil myeloperoxidase

The neutrophil enzyme myeloperoxidase (MPO) is a major enzyme made by neutrophils to generate antimicrobial and immunomodulatory compounds, notably hypochlorous acid (HOCl), amplifying their capacity for destroying pathogens and regulating inflammation. Despite its roles in innate immunity, the importance of MPO in preventing infection is unclear, as individuals with MPO deficiency are asymptomatic with the exception of an increased risk of candidiasis. Dysregulation of MPO activity is also linked with inflammatory conditions such as atherosclerosis, emphasising a need to understand the roles of the enzyme in greater detail. Consequently, new tools for investigating granular dynamics in vivo can provide useful insights into how MPO localises within neutrophils, aiding understanding of its role in preventing and exacerbating disease. The zebrafish is a powerful model for investigating the immune system in vivo, as it is genetically tractable, and optically transparent. To visualise MPO activity within zebrafish neutrophils, we created a genetic construct that expresses human MPO as a fusion protein with a C-terminal fluorescent tag, driven by the neutrophil-specific promoter lyz. After introducing the construct into the zebrafish genome by Tol2 transgenesis, we established the Tg(lyz:Hsa.MPO-mEmerald,cmlc2:EGFP)sh496 line, and confirmed transgene expression in zebrafish neutrophils. We observed localisation of MPO-mEmerald within a subcellular location resembling neutrophil granules, mirroring MPO in human neutrophils. In Spotless (mpxNL144) larvae-which express a non-functional zebrafish myeloperoxidase-the MPO-mEmerald transgene does not disrupt neutrophil migration to sites of infection or inflammation, suggesting that it is a suitable line for the study of neutrophil granule function. We present a new transgenic line that can be used to investigate neutrophil granule dynamics in vivo without disrupting neutrophil behaviour, with potential applications in studying processing and maturation of MPO during development.

Transcriptomic and proteomic host response to Aspergillus fumigatus conidia in an air-liquid interface model of human bronchial epithelium

Aspergillus fumigatus (A. fumigatus) is a wide-spread fungus that is a potent allergen in hypersensitive individuals but also an opportunistic pathogen in immunocompromised patients. It reproduces asexually by releasing airborne conidiospores (conidia). Upon inhalation, fungal conidia are capable of reaching the airway epithelial cells (AECs) in bronchial and alveolar tissues. Previous studies have predominantly used submerged monolayer cultures for studying this host-pathogen interaction; however, these cultures do not recapitulate the mucocililary differentiation phenotype of the in vivo epithelium in the respiratory tract. Thus, the aim of this study was to use well-differentiated primary human bronchial epithelial cells (HBECs) grown at the air-liquid interface (ALI) to determine their transcriptomic and proteomic responses following interaction with A. fumigatus conidia. We visualized conidial interaction with HBECs using confocal laser scanning microscopy (CLSM), and applied NanoString nCounter and shotgun proteomics to assess gene expression changes in the human cells upon interaction with A. fumigatus conidia. Western blot analysis was used to assess the expression of top three differentially expressed proteins, CALR, SET and NUCB2. CLSM showed that, unlike submerged monolayer cultures, well-differentiated ALI cultures of primary HBECs were estimated to internalize less than 1% of bound conidia. Nevertheless, transcriptomic and proteomic analyses revealed numerous differentially expressed host genes; these were enriched for pathways including apoptosis/autophagy, translation, unfolded protein response and cell cycle (up-regulated); complement and coagulation pathways, iron homeostasis, nonsense mediated decay and rRNA binding (down-regulated). CALR and SET were confirmed to be up-regulated in ALI cultures of primary HBECs upon exposure to A. fumigatus via western blot analysis. Therefore, using transcriptomics and proteomics approaches, ALI models recapitulating the bronchial epithelial barrier in the conductive zone of the respiratory tract can provide novel insights to the molecular response of bronchial epithelial cells upon exposure to A. fumigatus conidia.

Antifungal activities of surfactant protein D in an environment closely mimicking the lung lining

At the lung lining innate defenses protect our lungs against inhaled fungal cells that could pose a threat to our health. These defenses are comprised of mucociliary clearance, soluble effector molecules and roaming phagocytic cells, such as macrophages and neutrophils. How important each of these defenses is during fungal clearance depends on the specific fungal pathogen in question and on the stage of infection. In this study the localization and antifungal activity of the lung surfactant protein D (SP-D) was studied in an environment mimicking the lung lining. To this end Calu-3 cells were grown on an air-liquid interface allowing them to polarize and to produce mucus at their apical surface. Additionally, neutrophils were added to study their role in fungal clearance. Two fungal pathogens were used for these experiments: Candida albicans and Aspergillus fumigatus, both of clinical relevance. During fungal infection SP-D localized strongly to both fungal surfaces and stayed bound through the different stages of infection. Furthermore, SP-D decreased fungal adhesion to the epithelium and increased fungal clearance by neutrophils from the epithelial surface. These findings suggest that SP-D plays an important role at the different stages of pulmonary defense against fungal intruders.

A case of invasive pulmonary aspergillosis during treatment for acute exacerbation of interstitial lung disease

Prolonged immunosuppressive therapy is a risk factor for invasive pulmonary aspergillosis. We report a case of a 79-yearold man who underwent immunosuppressive therapy with methylprednisolone and cyclosporine for an acute exacerbation of interstitial lung disease. Ten days after initiation of immunosuppressive therapy, the patient reported night sweats and purulent sputum, and chest computed tomography scan revealed consolidation. He was diagnosed with invasive pulmonary aspergillosis, and required vasopressor support with oxygen therapy. After the administration of voriconazole and the modulation of immunosuppressive therapy, his condition improved. Short-term immunosuppressive therapy can also induce invasive pulmonary aspergillosis.

The spectrum of pulmonary aspergillosis

Notable progress has been made in the past years in the classification, diagnosis and treatment of pulmonary aspergillosis. New criteria were proposed by the Working Group of the International Society for Human and Animal Mycology (ISHAM) for the diagnosis of allergic bronchopulmonary aspergillosis (ABPA). The latest classification of chronic pulmonary aspergillosis (CPA) suggested by the European Society for Clinical Microbiology and Infectious Diseases (ESCMID) has become widely accepted among clinicians. Subacute invasive pulmonary aspergillosis is now considered a type of CPA, yet it is still diagnosed and treated similarly to invasive pulmonary aspergillosis (IPA). Isavuconazole, an extended-spectrum triazole, has recently been approved by the Food and Drug Administration (FDA) and the European Medicines Agency (EMA) for the treatment of IPA. The most recent Infectious Diseases Society of America (IDSA) guidelines strongly recommend reducing mold exposure to patients at high risk for pulmonary aspergillosis. The excessive relapse rate following discontinuation of therapy remains a common reality to all forms of this semi-continuous spectrum of diseases. This highlights the need to continuously reassess patients and individualize therapy accordingly. Thus far, the duration of therapy and the frequency of follow-up have to be well characterized.

A Multimodal Imaging Approach Enables In Vivo Assessment of Antifungal Treatment in a Mouse Model of Invasive Pulmonary Aspergillosis

Aspergillus fumigatus causes life-threatening lung infections in immunocompromised patients. Mouse models are extensively used in research to assess the in vivo efficacies of antifungals. In recent years, there has been an increasing interest in the use of noninvasive imaging techniques to evaluate experimental infections. However, single imaging modalities have limitations concerning the type of information they can provide. In this study, magnetic resonance imaging and bioluminescence imaging were combined to obtain longitudinal information on the extent of developing lesions and fungal load in a leukopenic mouse model of invasive pulmonary aspergillosis (IPA). This multimodal imaging approach was used to assess changes occurring within lungs of infected mice receiving voriconazole treatment starting at different time points after infection. The results showed that IPA development depends on the inoculum size used to infect animals and that disease can be successfully prevented or treated by initiating intervention during early stages of infection. Furthermore, we demonstrated that a reduction in fungal load is not necessarily associated with the disappearance of lesions on anatomical lung images, especially when antifungal treatment coincides with immune recovery. In conclusion, multimodal imaging allows an investigation of different aspects of disease progression or recovery by providing complementary information on dynamic processes, which are highly useful for assessing the efficacy of (novel) therapeutic compounds in a time- and labor-efficient manner.

Neutrophil extracellular traps in fungal infection

Fungal infections are a continuously increasing problem in modern health care. Understanding the complex biology of the emerging pathogens and unraveling the mechanisms of host defense may form the basis for the development of more efficient diagnostic and therapeutic tools. Neutrophils play a pivotal role in the defense against fungal pathogens. These phagocytic hunters migrate towards invading fungal microorganisms and eradicate them by phagocytosis, oxidative burst and release of neutrophil extracellular traps (NETs). In the last decade, the process of NET formation has received unparalleled attention, with numerous studies revealing the relevance of this neutrophil function for control of various mycoses. Here, we describe NET formation and summarize its role as part of the innate immune defense against fungal pathogens. We highlight factors influencing the formation of these structures and molecular mechanisms employed by fungi to impair the formation of NETs or subvert their antifungal effects.

Exogenous Stimulation of Type I Interferon Protects Mice with Chronic Granulomatous Disease from Aspergillosis through Early Recruitment of Host-Protective Neutrophils into the Lung

Invasive aspergillosis (IA) remains the primary cause of morbidity and mortality in chronic granulomatous disease (CGD) patients, often due to infection by Aspergillus species refractory to antifungals. This motivates the search for alternative treatments, including immunotherapy. We investigated the effect of exogenous type I interferon (IFN) activation on the outcome of IA caused by three Aspergillus species, A. fumigatus, A. nidulans, and A. tanneri, in CGD mice. The animals were treated with poly(I):poly(C) carboxymethyl cellulose poly-l-lysine (PICLC), a mimetic of double-stranded RNA, 24 h preinfection and postinfection. The survival rates and lung fungal burdens were markedly improved by PICLC immunotherapy in animals infected with any one of the three Aspergillus species. While protection from IA was remarkable, PICLC induction of type I IFN in the lungs surged 24 h posttreatment and returned to baseline levels by 48 h, suggesting that PICLC altered early events in protection against IA. Immunophenotyping of recruited leukocytes and histopathological examination of tissue sections showed that PICLC induced similar cellular infiltrates as those in untreated-infected mice, in both cases dominated by monocytic cells and neutrophils. However, the PICLC immunotherapy resulted in a marked earlier recruitment of the leukocytes. Unlike with conidia, infection with A. nidulans germlings reduced the protective effect of PICLC immunotherapy. Additionally, antibody depletion of neutrophils totally reversed the protection, suggesting that neutrophils are crucial for PICLC-mediated protection. Together, these data show that prophylactic PICLC immunotherapy prerecruits these cells, enabling them to attack the conidia and thus resulting in a profound protection from IA.IMPORTANCE Patients with chronic granulomatous disease (CGD) are highly susceptible to invasive aspergillosis (IA). While Aspergillus fumigatus is the most-studied Aspergillus species, CGD patients often suffer IA caused by A. nidulans, A. tanneri, and other rare species. These non-fumigatus Aspergillus species are more resistant to antifungal drugs and cause higher fatality rates than A. fumigatus Therefore, alternative therapies are needed to protect CGD patients. We report an effective immunotherapy of mice infected with three Aspergillus species via PICLC dosing. While protection from IA was long lasting, PICLC induction of type I IFN surged but quickly returned to baseline levels, suggesting that PICLC was altering early events in IA. Interestingly, we found responding immune cells to be similar between PICLC-treated and untreated-infected mice. However, PICLC immunotherapy resulted in an earlier recruitment of the leukocytes and suppressed fungal growth. This study highlights the value of type I IFN induction in CGD patients.

The Interface between Fungal Biofilms and Innate Immunity

Fungal biofilms are communities of adherent cells surrounded by an extracellular matrix. These biofilms are commonly found during infection caused by a variety of fungal pathogens. Clinically, biofilm infections can be extremely difficult to eradicate due to their resistance to antifungals and host defenses. Biofilm formation can protect fungal pathogens from many aspects of the innate immune system, including killing by neutrophils and monocytes. Altered immune recognition during this phase of growth is also evident by changes in the cytokine profiles of monocytes and macrophages exposed to biofilm. In this manuscript, we review the host response to fungal biofilms, focusing on how these structures are recognized by the innate immune system. Biofilms formed by Candida, Aspergillus, and Cryptococcus have received the most attention and are highlighted. We describe common themes involved in the resilience of fungal biofilms to host immunity and give examples of biofilm defenses that are pathogen-specific.

Innate and adaptive immune response to chronic pulmonary infection of hyphae of Aspergillus fumigatus in a new murine model

PURPOSE

The pathogenesis of chronic pulmonary aspergillosis (CPA) has seldom been studied due partly to a lack of animal models. Since hypha is the main morphology colonizing the airway in CPA, it's critical to study the immune reaction to chronic pulmonary infection of hyphae of Aspergillus fumigatus, which also has seldom been studied in vivo before.

METHODOLOGY

We established a novel murine model of chronic pulmonary infection of hyphae by challenging immunocompetent mice with tightly-structured hyphae balls intratracheally, and described the ensuing immunoreaction to hyphae and conidia, and the pathogenesis of CPA.

RESULTS

Our experiment proved that the hyphae balls could induce a chronic pulmonary infection for 28 days with a considerable recrudescence at day 28 post-infection. Lungs infected with hyphae balls were remarkable for the many neutrophils and macrophages that flooded into airway lumens, with peribronchiolar infiltration of leukocytes. There was a transient increase of Th2 cells and Th17 cells at day 7 post-infection in the lung tissue. In contrast, lungs infected with conidia showed no peribronchiolar infiltration of leukocytes, but an influx of a great number of macrophages, and a much less number of neutrophils in the lumen. Besides, conidia activated the co-response of Th1, Th2 and Th17 cells with an increase of Treg cells in the lung tissue (quite different from most previous studies).

CONCLUSION

We established a new murine model of chronic infection of hyphae to mimic the formation of CPA, and provide a new marker for different immune responses to hyphae and conidia.

The NADPH Oxidase and Microbial Killing by Neutrophils, With a Particular Emphasis on the Proposed Antimicrobial Role of Myeloperoxidase within the Phagocytic Vacuole

This review is devoted to a consideration of the way in which the NADPH oxidase of neutrophils, NOX2, functions to enable the efficient killing of bacteria and fungi. It includes a critical examination of the current dogma that its primary purpose is the generation of hydrogen peroxide as substrate for myeloperoxidase-catalyzed generation of hypochlorite. Instead, it is demonstrated that NADPH oxidase functions to optimize the ionic and pH conditions within the vacuole for the solubilization and optimal activity of the proteins released into this compartment from the cytoplasmic granules, which kill and digest the microbes. The general role of other NOX systems as electrochemical generators to alter the pH and ionic composition in compartments on either side of a membrane in plants and animals will also be examined.

Dynamic Immune Cell Recruitment After Murine Pulmonary Aspergillus fumigatus Infection under Different Immunosuppressive Regimens

Humans are continuously exposed to airborne spores of the saprophytic fungus Aspergillus fumigatus. However, in healthy individuals pulmonary host defense mechanisms efficiently eliminate the fungus. In contrast, A. fumigatus causes devastating infections in immunocompromised patients. Host immune responses against A. fumigatus lung infections in immunocompromised conditions have remained largely elusive. Given the dynamic changes in immune cell subsets within tissues upon immunosuppressive therapy, we dissected the spatiotemporal pulmonary immune response after A. fumigatus infection to reveal basic immunological events that fail to effectively control invasive fungal disease. In different immunocompromised murine models, myeloid, notably neutrophils, and macrophages, but not lymphoid cells were strongly recruited to the lungs upon infection. Other myeloid cells, particularly dendritic cells and monocytes, were only recruited to lungs of corticosteroid treated mice, which developed a strong pulmonary inflammation after infection. Lymphoid cells, particularly CD4⁺ or CD8⁺ T-cells and NK cells were highly reduced upon immunosuppression and not recruited after A. fumigatus infection. Moreover, adoptive CD11b⁺ myeloid cell transfer rescued cyclophosphamide immunosuppressed mice from lethal A. fumigatus infection but not cortisone and cyclophosphamide immunosuppressed mice. Our findings illustrate that CD11b⁺ myeloid cells are critical for anti-A. fumigatus defense under cyclophosphamide immunosuppressed conditions.

First Line of Defense: Innate Cell-Mediated Control of Pulmonary Aspergillosis

Mycotic infections and their effect on the human condition have been widely overlooked and poorly surveilled by many health organizations even though mortality rates have increased in recent years. The increased usage of immunosuppressive and myeloablative therapies for the treatment of malignant as well as non-malignant diseases has contributed significantly to the increased incidence of fungal infections. Invasive fungal infections have been found to be responsible for at least 1.5 million deaths worldwide. About 90% of these deaths can be attributed to Cryptococcus, Candida, Aspergillus, and Pneumocystis. A better understanding of how the host immune system contains fungal infection is likely to facilitate the development of much needed novel antifungal therapies. Innate cells are responsible for the rapid recognition and containment of fungal infections and have been found to play essential roles in defense against multiple fungal pathogens. In this review we summarize our current understanding of host-fungi interactions with a focus on mechanisms of innate cell-mediated recognition and control of pulmonary aspergillosis.

Challenges and Strategies for Proteome Analysis of the Interaction of Human Pathogenic Fungi with Host Immune Cells

Opportunistic human pathogenic fungi including the saprotrophic mold Aspergillus fumigatus and the human commensal Candida albicans can cause severe fungal infections in immunocompromised or critically ill patients. The first line of defense against opportunistic fungal pathogens is the innate immune system. Phagocytes such as macrophages, neutrophils and dendritic cells are an important pillar of the innate immune response and have evolved versatile defense strategies against microbial pathogens. On the other hand, human-pathogenic fungi have sophisticated virulence strategies to counteract the innate immune defense. In this context, proteomic approaches can provide deeper insights into the molecular mechanisms of the interaction of host immune cells with fungal pathogens. This is crucial for the identification of both diagnostic biomarkers for fungal infections and therapeutic targets. Studying host-fungal interactions at the protein level is a challenging endeavor, yet there are few studies that have been undertaken. This review draws attention to proteomic techniques and their application to fungal pathogens and to challenges, difficulties, and limitations that may arise in the course of simultaneous dual proteome analysis of host immune cells interacting with diverse morphotypes of fungal pathogens. On this basis, we discuss strategies to overcome these multifaceted experimental and analytical challenges including the viability of immune cells during co-cultivation, the increased and heterogeneous protein complexity of the host proteome dynamically interacting with the fungal proteome, and the demands on normalization strategies in terms of relative quantitative proteome analysis.

The innate immune response to Aspergillus fumigatus at the alveolar surface

Aspergillus fumigatus is an ubiquitous, saprophytic mould that forms and releases airborne conidia which are inhaled by humans on a daily basis. When the immune system is compromised (e.g. immunosuppressive therapy prior to organ transplantation) or there is pre-existing pulmonary malfunction (e.g. asthma, cystic fibrosis, TB lesions), A. fumigatus exploits weaknesses in the host defenses which can result in the development of saphrophytic, allergic or invasive aspergillosis. If not effectively eliminated by the innate immune response, conidia germinate and form invasive hyphae which can penetrate pulmonary tissues. The innate immune response to A. fumigatus is stage-specific and various components of the host's defenses are recruited to challenge the different cellular forms of the pathogen. In immunocompetent hosts, anatomical barriers (e.g. the mucociliary elevator) and professional phagocytes such as alveolar macrophages (AM) and neutrophils prevent the development of aspergillosis by inhibiting the growth of conidia and hyphae. The recognition of inhaled conidia by AM leads to the intracellular degradation of the spores and the secretion of proinflammatory mediators which recruit neutrophils to assist in fungal clearance. During the later stages of infection, dendritic cells activate a protective A. fumigatus-specific adaptive immune response which is driven by Th1 CD4(+) T cells.

Alkalinity of neutrophil phagocytic vacuoles is modulated by HVCN1 and has consequences for myeloperoxidase activity

The NADPH oxidase of neutrophils, essential for innate immunity, passes electrons across the phagocytic membrane to form superoxide in the phagocytic vacuole. Activity of the oxidase requires that charge movements across the vacuolar membrane are balanced. Using the pH indicator SNARF, we measured changes in pH in the phagocytic vacuole and cytosol of neutrophils. In human cells, the vacuolar pH rose to ~9, and the cytosol acidified slightly. By contrast, in Hvcn1 knock out mouse neutrophils, the vacuolar pH rose above 11, vacuoles swelled, and the cytosol acidified excessively, demonstrating that ordinarily this channel plays an important role in charge compensation. Proton extrusion was not diminished in Hvcn1^-/- mouse neutrophils arguing against its role in maintaining pH homeostasis across the plasma membrane. Conditions in the vacuole are optimal for bacterial killing by the neutral proteases, cathepsin G and elastase, and not by myeloperoxidase, activity of which was unphysiologically low at alkaline pH.

Axl receptor blockade protects from invasive pulmonary aspergillosis in mice

Aspergillus fumigatus is a sporulating fungus found ubiquitously in the environment, which is quickly contained in the immunocompetent host but can cause lethal invasive aspergillosis in the immunocompromised host. We have recently demonstrated that Axl (one member of the Tyro3, Axl, Mertk receptor family) is a key regulator of antiviral immune responses in the lung. In this study, we investigated the role of Axl in antifungal immunity in a model of invasive pulmonary aspergillosis (IPA). In this model, Aspergillus fumigatus conidia were administered into the lungs of neutrophil-depleted mice, and the mice were monitored for survival, lung inflammatory response, and fungal clearance. The lethal effect of IPA was significantly reduced in anti-Axl mAb-treated mice compared with IgG control-treated mice. Targeting Axl significantly inhibited pulmonary inflammation, including the expression of IL-1β, IL-6, TNF-α, and chitinase-like proteins in whole lung. Further, anti-Axl mAb treatment significantly increased M1 macrophages that highly expressed inducible NO synthase and decreased M2 macrophages that expressed Arginase 1 and were found in inflammatory zone protein (Fizz1). More importantly, anti-Axl mAb treatment significantly increased the number of IFN-γ-producing T cells and NK cells compared with the IgG control group during IPA. Together, our results demonstrate that the Axl mAb treatment is protective during invasive aspergillosis in neutropenic mice. Collectively, these data suggest a potential deleterious role for Axl during primary immune responses directed against A. fumigatus and novel therapeutic strategy for IPA.

Inflammatory monocytes orchestrate innate antifungal immunity in the lung

Aspergillus fumigatus is an environmental fungus that causes invasive aspergillosis (IA) in immunocompromised patients. Although -CC-chemokine receptor-2 (CCR2) and Ly6C-expressing inflammatory monocytes (CCR2⁺Mo) and their derivatives initiate adaptive pulmonary immune responses, their role in coordinating innate immune responses in the lung remain poorly defined. Using conditional and antibody-mediated cell ablation strategies, we found that CCR2⁺Mo and monocyte-derived dendritic cells (Mo-DCs) are essential for innate defense against inhaled conidia. By harnessing fluorescent Aspergillus reporter (FLARE) conidia that report fungal cell association and viability in vivo, we identify two mechanisms by which CCR2⁺Mo and Mo-DCs exert innate antifungal activity. First, CCR2⁺Mo and Mo-DCs condition the lung inflammatory milieu to augment neutrophil conidiacidal activity. Second, conidial uptake by CCR2⁺Mo temporally coincided with their differentiation into Mo-DCs, a process that resulted in direct conidial killing. Our findings illustrate both indirect and direct functions for CCR2⁺Mo and their derivatives in innate antifungal immunity in the lung.

Despite the significant impact of fungal infections to human health our understanding of immunity to these pathogens remains incomplete. Human mycoses are associated with high morbidity and mortality, even with modern antifungal therapies. Aspergillus fumigatus is the most common etiologic agent of invasive aspergillosis (IA), a serious infection that develops in immunodeficient patients. In this study we employ a combination of cell ablation strategies to examine the role of CCR2⁺Ly6C⁺ inflammatory monocytes (CCR2⁺Mo) in innate responses against a pulmonary infection with A.fumigatus conidia. We find that CCR2⁺Mo and their derivative dendritic cells (Mo-DCs) are required for defense against IA and that mice lacking these cells succumb to infection with A.fumigatus. Our studies indicate that CCR2⁺Mo and Mo-DCs exert crucial innate antifungal defense by two main mechanisms: 1) CCR2⁺Mo and Mo-DCs are a significant source of inflammatory mediators that augment the killing capacity of neutrophils and 2) conidial uptake by CCR2⁺Mo is coincident with their differentiation into Mo-DCs that directly kill fungal conidia via partially NADPH oxidase-dependent mechanisms. In aggregate, our studies find a novel essential function for CCR2⁺Mo in innate defense against a pulmonary fungal pathogen by mediating indirect and direct containment of fungal cells at the portal of infection.

Protective Effector Cells of the Recombinant Asp f3 Anti-Aspergillosis Vaccine

An Aspergillus fumigatus vaccine based on recombinant Asp f3-protein has the potential to prevent aspergillosis in humans, a devastating fungal disease that is the prime obstacle to the success of hematopoietic cell transplantation. This vaccine protects cortisone acetate (CA)-immunosuppressed mice from invasive pulmonary aspergillosis via CD4(+) T cell mediators. Aside from these mediators, the nature of downstream fungicidal effectors is not well understood. Neutrophils and macrophages protect immunocompetent individuals from invasive fungal infections, and selective neutrophil depletion rendered mice susceptible to aspergillosis whereas macrophage depletion failed to increase fungal susceptibility. We investigated the effect of neutrophil depletion on rAsp f3-vaccine protection, and explored differences in pathophysiology and susceptibility between CA-immunosuppression and neutrophil depletion. In addition to being protective under CA-immunosuppression, the vaccine also had a protective effect in neutrophil-depleted mice. However, in non-immunized mice, a 10-fold higher conidial dose was required to induce similar susceptibility to infection with neutrophil depletion than with CA-immunosuppression. The lungs of non-immunized neutrophil-depleted mice became invaded by a patchy dense mycelium with highly branched hyphae, and the peribronchial inflammatory infiltrate consisted mainly of CD3(+) T cells and largely lacked macrophages. In contrast, lungs of non-immunized CA-immunosuppressed mice were more evenly scattered with short hyphal elements. With rAsp f3-vaccination, the lungs were largely clear of fungal burden under either immunosuppressive condition. We conclude that neutrophils, although important for innate antifungal protection of immunocompetent hosts, are not the relevant effectors for rAsp f3-vaccine derived protection of immunosuppressed hosts. It is therefore more likely that macrophages represent the crucial effectors of the rAsp f3-based vaccine.

Systems biology of fungal infection

Elucidation of pathogenicity mechanisms of the most important human-pathogenic fungi, Aspergillus fumigatus and Candida albicans, has gained great interest in the light of the steadily increasing number of cases of invasive fungal infections. A key feature of these infections is the interaction of the different fungal morphotypes with epithelial and immune effector cells in the human host. Because of the high level of complexity, it is necessary to describe and understand invasive fungal infection by taking a systems biological approach, i.e., by a comprehensive quantitative analysis of the non-linear and selective interactions of a large number of functionally diverse, and frequently multifunctional, sets of elements, e.g., genes, proteins, metabolites, which produce coherent and emergent behaviors in time and space. The recent advances in systems biology will now make it possible to uncover the structure and dynamics of molecular and cellular cause-effect relationships within these pathogenic interactions. We review current efforts to integrate omics and image-based data of host-pathogen interactions into network and spatio-temporal models. The modeling will help to elucidate pathogenicity mechanisms and to identify diagnostic biomarkers and potential drug targets for therapy and could thus pave the way for novel intervention strategies based on novel antifungal drugs and cell therapy.

The proteomic signature of Aspergillus fumigatus during early development

Aspergillus fumigatus is a saprophytic fungus that causes a range of diseases in humans including invasive aspergillosis. All forms of disease begin with the inhalation of conidia, which germinate and develop. Four stages of early development were evaluated using the gel free system of isobaric tagging for relative and absolute quantitation to determine the full proteomic profile of the pathogen. A total of 461 proteins were identified at 0, 4, 8, and 16 h and fold changes for each were established. Ten proteins including the hydrophobin rodlet protein RodA and a protein involved in melanin synthesis Abr2 were found to decrease relative to conidia. To generate a more comprehensive view of early development, a whole genome microarray analysis was performed comparing conidia to 8 and 16 h of growth. A total of 1871 genes were found to change significantly at 8 h with 1001 genes up-regulated and 870 down-regulated. At 16 h, 1235 genes changed significantly with 855 up-regulated and 380 down-regulated. When a comparison between the proteomics and microarray data was performed at 8 h, a total of 22 proteins with significant changes also had corresponding genes that changed significantly. When the same comparison was performed at 16 h, 12 protein and gene combinations were found. This study, the most comprehensive to date, provides insights into early pathways activated during growth and development of A. fumigatus. It reveals a pathogen that is gearing up for rapid growth by building translation machinery, generating ATP, and is very much committed to aerobic metabolism.

Local phagocytic responses after murine infection with different forms of Fonsecaea pedrosoi and sclerotic bodies originating from an inoculum of conidiogenous cells

Fonsecaea pedrosoi is an important causative agent of chromoblastomycosis (CBM) especially in humid areas of the world; however, little is known about the infective forms of this agent that cause CBM. The aim of this study was to investigate the murine tissue response to inoculation with different forms of F. pedrosoi and the morphological changes of the fungal cells in vivo. BALB/c mice were inoculated intraperitoneally with hyphae, conidia or conidiogenous cells and conidia (CCC) at a single site. In addition, the abdomen and footpads were infected subcutaneously with CCC. Fungal forms were inoculated at a final concentration of 1 × 10(6) cells. Hyphae and ungerminated conidia inocula could not be transformed into parasitic forms. In tissue, a great number of conidiogenous cells underwent transformation into sclerotic bodies, which were more resistant to phagocytes in vivo than conidia and hyphae. Clinical and mycological cure of animals infected with CCC was observed from the fourth to the sixth week of infection, while conidia and hyphae infections were faster and generally lasted 2 to 3 weeks. A high number of destructed conidia was observed intracellularly in macrophages. The migration of neutrophils to the inflammatory site seems important for microbicidal activity, particularly against hyphae. Our observations suggest that inocula with conidiogenous cells are associated with in vivo transformation into sclerotic bodies and that local immune response involved with host resistance to experimental F. pedrosoi-infection is primarily mediated by neutrophils as observed in histological sections.

Phagocyte responses towards Aspergillus fumigatus

The saprophytic fungus Aspergillus fumigatus is a mold which is ubiquitously present in the environment. It produces large numbers of spores, called conidia that we constantly inhale with the breathing air. Healthy individuals normally do not suffer from true fungal infections with this pathogen. A normally robust resistance against Aspergillus is based on the presence of a very effective immunological defense system in the vertebrate body. Inhaled conidia are first encountered by lung-resident alveolar macrophages and then by neutrophil granulocytes. Both cell types are able to effectively ingest and destroy the fungus. Although some responses of the adaptive immune system develop, the key protection is mediated by innate immunity. The importance of phagocytes for defense against aspergillosis is also supported by large numbers of animal studies. Despite the production of aggressive chemicals that can extracellularly destroy fungal pathogens, the main effector mechanism of the innate immune system is phagocytosis. Very recently, the production of extracellular neutrophil extracellular traps (NETs) consisting of nuclear DNA has been added to the armamentarium that innate immune cells use against infection with Aspergillus. Phagocyte responses to Aspergillus are very broad, and a number of new observations have added to this complexity in recent years. To summarize established and newer findings, we will give an overview on current knowledge of the phagocyte system for the protection against Aspergillus.

Risk factors for Aspergillus colonization and allergic bronchopulmonary aspergillosis in children with cystic fibrosis

BACKGROUND

The annual prevalence of Aspergillus colonization (AC) and allergic bronchopulmonary aspergillosis (ABPA) has recently increased in pediatric patients with cystic fibrosis (CF). The reasons remain unclear although a number of factors have been suggested to be involved. This study was set up to investigate the association between potential predisposing factors, including new therapies recommended in CF, and the occurrence of AC or ABPA in children with CF.

METHODS

The medical records of 85 children monitored regularly in the Pediatric Reference Centre for Cystic Fibrosis Care (RCCFC) of the University Hospital of Marseille (France) were analyzed from the first time they attended the RCCFC until either the occurrence of an end event, or their last visit to the RCCFC. Risk factors for AC or ABPA were analyzed by univariate and multivariate logistic regression.

RESULTS

Eight children developed ABPA and 18 had AC. In univariate analysis, ABPA was significantly associated with RhDNase therapy, sensitization to Alternaria and Candida, and a low body mass index (BMI). Multivariate analysis identified an independent association between low BMI and ABPA (OR = 10.6, 95% CI [2.2-51.8], P = 0.004), and for the first time, between long-term azithromycin therapy and AC (OR = 6.4, 95% CI [2.1-19.5], P = 0.001). This latter association might be explained by the inhibitory effect of azithromycin on both the recruitment and the activation of neutrophils, which represent the first-line defenses against Aspergillus.

CONCLUSIONS

The risk factors associated with AC and ABPA in children with CF identified in this comprehensive exploratory study now need to be confirmed in further prospective studies.

Invasive aspergillosis in patients with acute myeloid leukemia: a SEIFEM-2008 registry study

BACKGROUND

The aim of this study was to evaluate prognostic factors, treatments and outcome of invasive aspergillosis in patients with acute myeloid leukemia based on data collected in a registry.

DESIGN AND METHODS

The registry, which was activated in 2004 and closed in 2007, collected data on patients with acute myeloid leukemia, admitted to 21 hematologic divisions in tertiary care centers or university hospitals in Italy, who developed proven or probable invasive aspergillosis.

RESULTS

One hundred and forty cases of invasive aspergillosis were collected, with most cases occurring during the period of post-induction aplasia, the highest risk phase in acute myeloid leukemia. The mortality rate attributable to invasive aspergillosis was 27%, confirming previous reports of a downward trend in this rate. Univariate and multivariate analyses revealed that the stage of acute myeloid leukemia and the duration of, and recovery from, neutropenia were independent prognostic factors. We analyzed outcomes after treatment with the three most frequently used drugs (liposomal amphotericin B, caspofungin, voriconazole). No differences emerged in survival at day 120 or in the overall response rate which was 71%, ranging from 61% with caspofungin to 84% with voriconazole.

CONCLUSIONS

Our series confirms the downward trend in mortality rates reported in previous series, with all new drugs providing similar survival and response rates. Recovery from neutropenia and disease stage are crucial prognostic factors. Efficacious antifungal drugs bridge the period of maximum risk due to poor hematologic and immunological reconstitution.

Human polymorphonuclear leukocytes inhibit Aspergillus fumigatus conidial growth by lactoferrin-mediated iron depletion

Aspergillus fumigatus, a common mold, rarely infects humans, except during prolonged neutropenia or in cases of chronic granulomatous disease (CGD), a primary immunodeficiency caused by mutations in the NADPH oxidase that normally produces fungicidal reactive oxygen species. Filamentous hyphae of Aspergillus are killed by normal, but not CGD polymorphonuclear leukocytes (PMN); however, the few studies on PMN-mediated host defenses against infectious conidia (spores) of this organism have yielded conflicting results, some showing that PMN do not inhibit conidial growth, with others showing that they do, most likely using reactive oxygen species. Given that CGD patients are exposed daily to hundreds of viable A. fumigatus conidia, yet considerable numbers of them survive years without infection, we reasoned that PMN use ROS-independent mechanisms to combat Aspergillus. We show that human PMN from both normal controls and CGD patients are equipotent at arresting the growth of Aspergillus conidia in vitro, indicating the presence of a reactive oxygen species-independent factor(s). Cell-free supernatants of degranulated normal and CGD neutrophils both suppressed fungal growth and were found to be rich in lactoferrin, an abundant PMN secondary granule protein. Purified iron-poor lactoferrin at concentrations occurring in PMN supernatants (and reported in human mucosal secretions in vivo) decreased fungal growth, whereas saturation of lactoferrin or PMN supernatants with iron, or testing in the presence of excess iron in the form of ferritin, completely abolished activity against conidia. These results demonstrate that PMN lactoferrin sequestration of iron is important for host defense against Aspergillus.