Transient lung-specific expression of the chemokine KC improves outcome in invasive aspergillosis

Detailed characterisation of invasive aspergillosis in a murine model of X-linked chronic granulomatous disease shows new insights in infections caused by Aspergillus fumigatus versus Aspergillus nidulans

Introduction

Invasive aspergillosis (IA) is the most prevalent infectious complication in patients with chronic granulomatous disease (CGD). Yet, understanding of fungal pathogenesis in the CGD host remains limited, particularly with regards to A. nidulans infection.

Methods

We have used a murine model of X-linked CGD to investigate how the pathogenesis of IA varies between A. fumigatus and A. nidulans, comparing infection in both X-linked CGD (gp91-/-) mice and their parent C57BL/6 (WT) mice. A 14-colour flow cytometry panel was used to assess the cell dynamics over the course of infection, with parallel assessment of pulmonary cytokine production and lung histology.

Results

We observed a lack of association between pulmonary pathology and infection outcome in gp91-/- mice, with no significant mortality in A. nidulans infected mice. An overwhelming and persistent neutrophil recruitment and IL-1 release in gp91-/- mice following both A. fumigatus and A. nidulans infection was observed, with divergent macrophage, dendritic cell and eosinophil responses and distinct cytokine profiles between the two infections.

Conclusion

We have provided an in-depth characterisation of the immune response to pulmonary aspergillosis in an X-linked CGD murine model. This provides the first description of distinct pulmonary inflammatory environments in A. fumigatus and A. nidulans infection in X-linked CGD and identifies several new avenues for further research.

Evaluation of Host Constitutive and Ex Vivo Coccidioidal Antigen-Stimulated Immune Response in Dogs with Naturally Acquired Coccidioidomycosis

The early innate immune response to coccidioidomycosis has proven to be pivotal in directing the adaptive immune response and disease outcome in mice and humans but is unexplored in dogs. The objectives of this study were to evaluate the innate immune profile of dogs with coccidioidomycosis and determine if differences exist based on the extent of infection (i.e., pulmonary or disseminated). A total of 28 dogs with coccidioidomycosis (pulmonary, n = 16; disseminated, n = 12) and 10 seronegative healthy controls were enrolled. Immunologic testing was performed immediately, without ex vivo incubation (i.e., constitutive), and after coccidioidal antigen stimulation of whole blood cultures. Whole blood cultures were incubated with a phosphate-buffered solution (PBS) (negative control) or a coccidioidal antigen (rCTS1 (105-310); 10 µg/mL) for 24 h. A validated canine-specific multiplex bead-based assay was used to measure 12 cytokines in plasma and cell culture supernatant. Serum C-reactive protein (CRP) was measured with an ELISA assay. Leukocyte expression of toll-like receptors (TLRs)2 and TLR4 was measured using flow cytometry. Dogs with coccidioidomycosis had higher constitutive plasma keratinocyte chemotactic (KC)-like concentrations (p = 0.02) and serum CRP concentrations compared to controls (p < 0.001). Moreover, dogs with pulmonary coccidioidomycosis had higher serum CRP concentrations than those with dissemination (p = 0.001). Peripheral blood leukocytes from dogs with coccidioidomycosis produced higher concentrations of tumor necrosis factor (TNF)-α (p = 0.0003), interleukin (IL)-6 (p = 0.04), interferon (IFN)-γ (p = 0.03), monocyte chemoattractant protein (MCP)-1 (p = 0.02), IL-10 (p = 0.02), and lower IL-8 (p = 0.003) in supernatants following coccidioidal antigen stimulation when compared to those from control dogs. There was no detectable difference between dogs with pulmonary and disseminated disease. No differences in constitutive or stimulated leukocyte TLR2 and TLR4 expression were found. These results provide information about the constitutive and coccidioidal antigen-specific stimulated immune profile in dogs with naturally acquired coccidioidomycosis.

Aspergillus fumigatus and Aspergillosis in 2019

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

MicroRNA-142-3p inhibits IFN-γ production via targeting of RICTOR in Aspergillus fumigatus activated CD4+ T cells

Background

Aspergillus fumigatus (AFE) is a well-adapted, opportunistic fungus that causes a severe and commonly fatal disease, wherein IFN-γ is one of the most important protective cytokines. The aim of this study was to investigate the microRNA expression profile and explore the underlying mechanism during infection with AFE.

Methods

CD4⁺ T cells were activated by co-culturing with dendritic cells (DCs), which were pre-treated with AFE. Next, we performed microRNA microarray expression profiles of activated and control T cells, following which, miRNA-142-3P was selected. To explore the effect of miR-142-3P on T cell activation, miRNA-142-3P expression was disrupted by transient transfection with miR-142-3P mimic or inhibitor. Then, levels of RICTOR, phosphorylated AKT and IFN-γ were detected via Western blotting and qPCR respectively. We further used siRNA to decrease RICTOR expression and determined the role played by RICTOR in miR-142-3P mediated-IFN-γ expression by qPCR following AFE-mediated T cell activation.

Results

The heat-map of miRNA expression profiles showed that 54 microRNAs (miRNAs) were filtered, the levels of which, were significantly different between CD4⁺ T cells activated by AFE and control T cells, in which microRNA-142-3 was involved. Forced expression of miRNA-142-3P dramatically suppressed RICTOR levels, phosphorylated AKT and IFN-γ in AFE activated T cells. Conversely, loss of miRNA-142-3P elevated RICTOR levels, phosphorylated AKT and IFN-γ. Notably, RICTOR deficiency decreased AKT phosphorylation levels and IFN-γ secretion.

Conclusions

Observations indicated that down-regulation of microRNA-142-3p enhanced IFN-γ expression, and did so by promoting RICTOR expression in CD4⁺ T cells activated by AFE.

Pathogenic Fungal Infection in the Lung

Respiratory fungal infection is a severe clinical problem, especially in patients with compromised immune functions. Aspergillus, Cryptococcus, Pneumocystis, and endemic fungi are major pulmonary fungal pathogens that are able to result in life-threatening invasive diseases. Growing data being reported have indicated that multiple cells and molecules orchestrate the host's response to a fungal infection in the lung. Upon fungal challenge, innate myeloid cells including macrophages, dendritic cells (DC), and recruited neutrophils establish the first line of defense through the phagocytosis and secretion of cytokines. Natural killer cells control the fungal expansion in the lung via the direct and indirect killing of invading organisms. Adaptive immune cells including Th1 and Th17 cells confer anti-fungal activity by producing their signature cytokines, interferon-γ, and IL-17. In addition, lung epithelial cells (LEC) also participate in the resistance against fungal infection by internalization, inflammatory cytokine production, or antimicrobial peptide secretion. In the host cells mentioned above, various molecules with distinct functions modulate the immune defense signaling: Pattern recognition receptors (PRRs) such as dectin-1 expressed on the cell surface are involved in fungal recognition; adaptor proteins such as MyD88 and TRAF6 are required for transduction of signals to the nucleus for transcriptional regulation; inflammasomes also play crucial roles in the host's defense against a fungal infection in the lung. Furthermore, transcriptional factors modulate the transcriptions of a series of genes, especially those encoding cytokines and chemokines, which are predominant regulators in the infectious microenvironment, mediating the cellular and molecular immune responses against a fungal infection in the lung.

Organ Failure Due to Systemic Injury in Acute Pancreatitis

Acute pancreatitis may be associated with both local and systemic complications. Systemic injury manifests in the form of organ failure, which is seen in approximately 20% of all cases of acute pancreatitis and defines "severe acute pancreatitis." Organ failure typically develops early in the course of acute pancreatitis, but also may develop later due to infected pancreatic necrosis-induced sepsis. Organ failure is the most important determinant of outcome in acute pancreatitis. We review here the current understanding of the risk factors, pathophysiology, timing, impact on outcome, and therapy of organ failure in acute pancreatitis. As we discuss the pathophysiology of severe systemic injury, the distinctions between markers and mediators of severity are highlighted based on evidence supporting their causality in organ failure. Emphasis is placed on clinically relevant end points of organ failure and the mechanisms underlying the pathophysiological perturbations, which offer insight into potential therapeutic targets to treat.

CXCL1 regulates neutrophil homeostasis in pneumonia-derived sepsis caused by Streptococcus pneumoniae serotype 3

Neutrophil migration to the site of bacterial infection is a critical step in host defense. Exclusively produced in the bone marrow, neutrophil release into the blood is tightly controlled. Although the chemokine CXCL1 induces neutrophil influx during bacterial infections, its role in regulating neutrophil recruitment, granulopoiesis, and neutrophil mobilization in response to lung infection-induced sepsis is unclear. Here, we used a murine model of intrapulmonary Streptococcus pneumoniae infection to investigate the role of CXCL1 in host defense, granulopoiesis, and neutrophil mobilization. Our results demonstrate that CXCL1 augments neutrophil influx to control bacterial growth in the lungs, as well as bacterial dissemination, resulting in improved host survival. This was shown in Cxcl1 ^-/- mice, which exhibited defective amplification of early neutrophil precursors in granulocytic compartments, and CD62L- and CD49d-dependent neutrophil release from the marrow. Administration of recombinant CXCL2 and CXCL5 after infection rescues the impairments in neutrophil-dependent host defense in Cxcl1 ^-/- mice. Taken together, these findings identify CXCL1 as a central player in host defense, granulopoiesis, and mobilization of neutrophils during Gram-positive bacterial pneumonia-induced sepsis.

Tissue-Resident Macrophages in Fungal Infections

Invasive fungal infections result in high morbidity and mortality. Host organs targeted by fungal pathogens vary depending on the route of infection and fungal species encountered. Cryptococcus neoformans infects the respiratory tract and disseminates throughout the central nervous system. Candida albicans infects mucosal tissues and the skin, and systemic Candida infection in rodents has a tropism to the kidney. Aspergillus fumigatus reaches distal areas of the lung once inhaled by the host. Across different tissues in naïve hosts, tissue-resident macrophages (TRMs) are one of the most populous cells of the innate immune system. Although they function to maintain homeostasis in a tissue-specific manner during steady state, TRMs may function as the first line of defense against invading pathogens and may regulate host immune responses. Thus, in any organs, TRMs are uniquely positioned and specifically programmed to function. This article reviews the current understanding of the roles of TRMs during major fungal infections.

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

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

Rodent Models of Invasive Aspergillosis due to Aspergillus fumigatus: Still a Long Path toward Standardization

Invasive aspergillosis has been studied in laboratory by the means of plethora of distinct animal models. They were developed to address pathophysiology, therapy, diagnosis, or miscellaneous other concerns associated. However, there are great discrepancies regarding all the experimental variables of animal models, and a thorough focus on them is needed. This systematic review completed a comprehensive bibliographic analysis specifically-based on the technical features of rodent models infected with Aspergillus fumigatus. Out the 800 articles reviewed, it was shown that mice remained the preferred model (85.8% of the referenced reports), above rats (10.8%), and guinea pigs (3.8%). Three quarters of the models involved immunocompromised status, mainly by steroids (44.4%) and/or alkylating drugs (42.9%), but only 27.7% were reported to receive antibiotic prophylaxis to prevent from bacterial infection. Injection of spores (30.0%) and inhalation/deposition into respiratory airways (66.9%) were the most used routes for experimental inoculation. Overall, more than 230 distinct A. fumigatus strains were used in models. Of all the published studies, 18.4% did not mention usage of any diagnostic tool, like histopathology or mycological culture, to control correct implementation of the disease and to measure outcome. In light of these findings, a consensus discussion should be engaged to establish a minimum standardization, although this may not be consistently suitable for addressing all the specific aspects of invasive aspergillosis.

Hepcidin-mediated iron sequestration protects against bacterial dissemination during pneumonia

Gram-negative pneumonia is a dangerous illness, and bacterial dissemination to the bloodstream during the infection is strongly associated with death. Antibiotic resistance among the causative pathogens has resulted in diminishing treatment options against this infection. Hepcidin is the master regulator of extracellular iron availability in vertebrates, but its role in the context of host defense is undefined. We hypothesized that hepcidin-mediated depletion of extracellular iron during Gram-negative pneumonia protects the host by limiting dissemination of bacteria to the bloodstream. During experimental pneumonia, hepcidin was induced in the liver in an IL-6-dependent manner and mediated a rapid decline in plasma iron. In contrast, hepcidin-deficient mice developed a paradoxical increase in plasma iron during infection associated with profound susceptibility to bacteremia. Incubation of bacteria with iron-supplemented plasma enhanced bacterial growth in vitro, and systemic administration of iron to WT mice similarly promoted increased susceptibility to bloodstream infection. Finally, treatment with a hepcidin analogue restored hypoferremia in hepcidin-deficient hosts, mediated bacterial control, and improved outcomes. These data show hepcidin induction during pneumonia to be essential to preventing bacterial dissemination by limiting extracellular iron availability. Hepcidin agonists may represent an effective therapy for Gram-negative infections in patients with impaired hepcidin production or signaling.

CXCL1, but not IL-6, significantly impacts intraocular inflammation during infection

During intraocular bacterial infections, the primary innate responders are neutrophils, which may cause bystander damage to the retina or perturb the clarity of the visual axis. We hypothesized that cytokine IL-6 and chemokine CXCL1 contributed to rapid neutrophil recruitment during Bacillus cereus endophthalmitis, a severe form of intraocular infection that is characterized by explosive inflammation and retinal damage that often leads to rapid vision loss. To test this hypothesis, we compared endophthalmitis pathogenesis in C57BL/6J, IL-6^-/-, and CXCL1^-/- mice. Bacterial growth in eyes of CXCL1^-/-, IL-6^-/-, and C67BL/6J mice was similar. Retinal function retention was greater in eyes of IL-6^-/- and CXCL1^-/- mice compared with that of C57BL/6J, despite these eyes having similar bacterial burdens. Neutrophil influx into eyes of CXCL1^-/- mice was reduced to a greater degree compared with that of eyes of IL6^-/- mice. Histology confirmed significantly less inflammation in eyes of CXCL1^-/- mice, but similar degrees of inflammation in IL6^-/- and C57BL/6J eyes. Because inflammation was reduced in eyes of infected CXCL1^-/- mice, we tested the efficacy of anti-CXCL1 in B. cereus endophthalmitis. Retinal function was retained to a greater degree and there was less overall inflammation in eyes treated with anti-CXCL1, which suggested that anti-CXCL1 may have therapeutic efficacy in limiting inflammation during B. cereus endophthalmitis. Taken together, our results indicate that absence of IL-6 did not affect overall pathogenesis of endophthalmitis. In contrast, absence of CXCL1, in CXCL1^-/- mice or after anti-CXCL1 treatment, led to an improved clinical outcome. Our findings suggest a potential benefit in targeting CXCL1 to control inflammation during B. cereus and perhaps other types of intraocular infections.

Interactions of Aspergillus fumigatus Conidia with Airway Epithelial Cells: A Critical Review

Aspergillus fumigatus is an environmental filamentous fungus that also acts as an opportunistic pathogen able to cause a variety of symptoms, from an allergic response to a life-threatening disseminated fungal infection. The infectious agents are inhaled conidia whose first point of contact is most likely to be an airway epithelial cell (AEC). The interaction between epithelial cells and conidia is multifaceted and complex, and has implications for later steps in pathogenesis. Increasing evidence has demonstrated a key role for the airway epithelium in the response to respiratory pathogens, particularly at early stages of infection; therefore, elucidating the early stages of interaction of conidia with AECs is essential to understand the establishment of infection in cohorts of at-risk patients. Here, we present a comprehensive review of the early interactions between A. fumigatus and AECs, including bronchial and alveolar epithelial cells. We describe mechanisms of adhesion, internalization of conidia by AECs, the immune response of AECs, as well as the role of fungal virulence factors, and patterns of fungal gene expression characteristic of early infection. A clear understanding of the mechanisms involved in the early establishment of infection by A. fumigatus could point to novel targets for therapy and prophylaxis.

Peripancreatic fat necrosis worsens acute pancreatitis independent of pancreatic necrosis via unsaturated fatty acids increased in human pancreatic necrosis collections

BACKGROUND AND AIMS

Peripancreatic fat necrosis occurs frequently in necrotising pancreatitis. Distinguishing markers from mediators of severe acute pancreatitis (SAP) is important since targeting mediators may improve outcomes. We evaluated potential agents in human pancreatic necrotic collections (NCs), pseudocysts (PCs) and pancreatic cystic neoplasms and used pancreatic acini, peripheral blood mononuclear cells (PBMC) and an acute pancreatitis (AP) model to determine SAP mediators.

METHODS

We measured acinar and PBMC injury induced by agents increased in NCs and PCs. Outcomes of caerulein pancreatitis were studied in lean rats coadministered interleukin (IL)-1β and keratinocyte chemoattractant/growth-regulated oncogene, triolein alone or with the lipase inhibitor orlistat.

RESULTS

NCs had higher fatty acids, IL-8 and IL-1β versus other fluids. Lipolysis of unsaturated triglyceride and resulting unsaturated fatty acids (UFA) oleic and linoleic acids induced necro-apoptosis at less than half the concentration in NCs but other agents did not do so at more than two times these concentrations. Cytokine coadministration resulted in higher pancreatic and lung inflammation than caerulein alone, but only triolein coadministration caused peripancreatic fat stranding, higher cytokines, UFAs, multisystem organ failure (MSOF) and mortality in 97% animals, which were prevented by orlistat.

CONCLUSIONS

UFAs, IL-1β and IL-8 are elevated in NCs. However, UFAs generated via peripancreatic fat lipolysis causes worse inflammation and MSOF, converting mild AP to SAP.

Tumor driven by gain-of-function HER2 H878Y mutant is highly sensitive to HER2 inhibitor

HER2, a well established oncogenic member of EGFR family, is among the most intensely investigated kinase drug targets. In contrast to hotspot mutations of EGFR, few mutations of HER2 locate in activation loop within kinase domain. We previously reported the molecular mechanism underlying hyper kinase activity of HER2^H878Y, a mutation located in activation loop. However, its tumorigenicity in vivo and relevant therapeutics remain to be determined. Here, we report for the first time that HER2^H878Y was tumorigenic in vivo in lung adenocarcinoma transgenic mouse model. Induced expression of HER2^H878Y in lung epithelial compartments resulted in formation of poorly differentiated lung adenocarcinoma with bronchioloalveolar carcinoma (BAC) features. Strikingly, we found that these tumors depended on continuous expression of HER2^H878Y for maintenance. Typical HER2 downstream signaling mediators, including PLCγ1, STAT5 and AKT, were hyperactivated in HER2^H878Y driven lung tumors. More importantly, administration of HKI-272, a tyrosine kinase inhibitor (TKI), efficiently shrank HER2^H878Y driven tumors in transgenic mouse model. Moreover, we found that combinational treatment with HKI272 and mTOR inhibitor, Rapamycin, showed a superior cytotoxicity to H878Y mutant transformed cells and enhanced activity to elicit apoptosis and inhibit growth in situ in tumorous area. Our work therefore showed that HER2^H878Y mutant was a reasonable drug target. Hence, our work supported the assessment of HKI-272/rapamycin treatment in clinical trials.

IL-1α signaling is critical for leukocyte recruitment after pulmonary Aspergillus fumigatus challenge

Aspergillus fumigatus is a mold that causes severe pulmonary infections. Our knowledge of how A. fumigatus growth is controlled in the respiratory tract is developing, but still limited. Alveolar macrophages, lung resident macrophages, and airway epithelial cells constitute the first lines of defense against inhaled A. fumigatus conidia. Subsequently, neutrophils and inflammatory CCR2+ monocytes are recruited to the respiratory tract to prevent fungal growth. However, the mechanism of neutrophil and macrophage recruitment to the respiratory tract after A. fumigatus exposure remains an area of ongoing investigation. Here we show that A. fumigatus pulmonary challenge induces expression of the inflammasome-dependent cytokines IL-1β and IL-18 within the first 12 hours, while IL-1α expression continually increases over at least the first 48 hours. Strikingly, Il1r1-deficient mice are highly susceptible to pulmonary A. fumigatus challenge exemplified by robust fungal proliferation in the lung parenchyma. Enhanced susceptibility of Il1r1-deficient mice correlated with defects in leukocyte recruitment and anti-fungal activity. Importantly, IL-1α rather than IL-1β was crucial for optimal leukocyte recruitment. IL-1α signaling enhanced the production of CXCL1. Moreover, CCR2+ monocytes are required for optimal early IL-1α and CXCL1 expression in the lungs, as selective depletion of these cells resulted in their diminished expression, which in turn regulated the early accumulation of neutrophils in the lung after A. fumigatus challenge. Enhancement of pulmonary neutrophil recruitment and anti-fungal activity by CXCL1 treatment could limit fungal growth in the absence of IL-1α signaling. In contrast to the role of IL-1α in neutrophil recruitment, the inflammasome and IL-1β were only essential for optimal activation of anti-fungal activity of macrophages. As such, Pycard-deficient mice are mildly susceptible to A. fumigatus infection. Taken together, our data reveal central, non-redundant roles for IL-1α and IL-1β in controlling A. fumigatus infection in the murine lung.

Aspergillus spp. are ubiquitous in the environment, and even though individuals are regularly exposed to fungal spores clinical invasive disease is a rare manifestation. In contrast, individuals with weakened immune systems develop severe disease, such as invasive pulmonary aspergillosis (IPA). IPA is associated with extremely poor prognoses and unacceptably high mortality rates. Knowledge gained from understanding how immunocompetent mammals control Aspergillus challenge will help develop new immunomodulatory strategies aimed at improving patient outcomes. It is well known that neutrophils and monocytes are crucial immune cells that act to limit fungal growth. Our work demonstrates a central role for the cytokine IL-1α in orchestrating the optimal recruitment of neutrophils and monocytes, whereas IL-1β and the inflammasome are more important in activation of anti-fungal activity of the monocytes. Moreover, our studies indicate that CCR2⁺ monocytes are required for optimal production of IL-1α in the lungs of A. fumigatus challenged mice. Thus, our data highlight a crucial role of the IL-1 cytokine in mediating anti-fungal immunity which might be harnessed to treat clinical cases of IPA.

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.

Myeloid derived hypoxia inducible factor 1-alpha is required for protection against pulmonary Aspergillus fumigatus infection

Hypoxia inducible factor 1α (HIF1α) is the mammalian transcriptional factor that controls metabolism, survival, and innate immunity in response to inflammation and low oxygen. Previous work established that generation of hypoxic microenvironments occurs within the lung during infection with the human fungal pathogen Aspergillus fumigatus. Here we demonstrate that A. fumigatus stabilizes HIF1α protein early after pulmonary challenge that is inhibited by treatment of mice with the steroid triamcinolone. Utilizing myeloid deficient HIF1α mice, we observed that HIF1α is required for survival and fungal clearance early following pulmonary challenge with A. fumigatus. Unlike previously reported research with bacterial pathogens, HIF1α deficient neutrophils and macrophages were surprisingly not defective in fungal conidial killing. The increase in susceptibility of the myeloid deficient HIF1α mice to A. fumigatus was in part due to decreased early production of the chemokine CXCL1 (KC) and increased neutrophil apoptosis at the site of infection, resulting in decreased neutrophil numbers in the lung. Addition of recombinant CXCL1 restored neutrophil survival and numbers, murine survival, and fungal clearance. These results suggest that there are unique HIF1α mediated mechanisms employed by the host for protection and defense against fungal pathogen growth and invasion in the lung. Additionally, this work supports the strategy of exploring HIF1α as a therapeutic target in specific immunosuppressed populations with fungal infections.

Aspergillus-associated airway disease, inflammation, and the innate immune response

Aspergillus moulds exist ubiquitously as spores that are inhaled in large numbers daily. Whilst most are removed by anatomical barriers, disease may occur in certain circumstances. Depending on the underlying state of the human immune system, clinical consequences can ensue ranging from an excessive immune response during allergic bronchopulmonary aspergillosis to the formation of an aspergilloma in the immunocompetent state. The severest infections occur in those who are immunocompromised where invasive pulmonary aspergillosis results in high mortality rates. The diagnosis of Aspergillus-associated pulmonary disease is based on clinical, radiological, and immunological testing. An understanding of the innate and inflammatory consequences of exposure to Aspergillus species is critical in accounting for disease manifestations and preventing sequelae. The major components of the innate immune system involved in recognition and removal of the fungus include phagocytosis, antimicrobial peptide production, and recognition by pattern recognition receptors. The cytokine response is also critical facilitating cell-to-cell communication and promoting the initiation, maintenance, and resolution of the host response. In the following review, we discuss the above areas with a focus on the innate and inflammatory response to airway Aspergillus exposure and how these responses may be modulated for therapeutic benefit.

The biology of chemokines and their receptors

This article summarizes the work done by our laboratory and by our collaborators on the biological role of chemokines and their receptors. Using both gain-of-function and loss of function genetic approaches, we have demonstrated that chemokines are important for the homeostatic distribution of leukocytes in tissues and for their mobilization from the bone marrow. We have also shown that chemokines are important players in inflammation and autoimmunity and that they contribute to lymphoid organogenesis, angiogenesis, and immune regulation. Together, our results and those of the literature suggest an important role for chemokines in homeostasis and disease and characterize chemokines as important targets for therapeutic intervention.

Effect of combined nitrogen dioxide and carbon nanoparticle exposure on lung function during ovalbumin sensitization in Brown Norway rat

The interaction of particulate and gaseous pollutants in their effects on the severity of allergic inflammation and airway responsiveness are not well understood. We assessed the effect of exposure to NO₂ in the presence or absence of repetitive treatment with carbon nanoparticle (CNP) during allergen sensitization and challenges in Borwn-Norway (BN) rat, in order to assess their interactions on lung function and airway responses (AR) to allergen and methacholine (MCH), end-expiratory lung volume (EELV), bronchoalveolar lavage fluid (BALF) cellular content, serum and BALF cytokine levels and histological changes. Animals were divided into the following groups (n = 6): Control; CNP (Degussa-FW2): 13 nm, 0.5 mg/kg instilled intratracheally ×3 at 7-day intervals; OVA: ovalbumin-sensitised; OVA+CNP: both sensitized and exposed to CNP. Rats were divided into equal groups exposed either to air or to NO₂, 10 ppm, 6 h/d, 5d/wk for 4 weeks. Exposure to NO₂, significantly enhanced lung inflammation and airway reactivity, with a significantly larger effect in animals sensitized to allergen, which was related to a higher expression of TH1 and TH2-type cytokines. Conversely, exposure to NO₂ in animals undergoing repeated tracheal instillation of CNP alone, increased BALF neutrophilia and enhanced the expression of TH1 cytokines: TNF-α and IFN-γ, but did not show an additive effect on airway reactivity in comparison to NO₂ alone. The exposure to NO₂ combined with CNP treatment and allergen sensitization however, unexpectedly resulted in a significant decrease in both airway reactivity to allergen and to methacholine, and a reduction in TH2-type cytokines compared to allergen sensitization alone. EELV was significantly reduced with sensitization, CNP treatment or both. These data suggest an immunomodulatory effect of repeated tracheal instillation of CNP on the proinflammatory effects of NO₂ exposure in sensitized BN rat. Furthermore, our findings suggest that NO₂, CNP and OVA sensitization may significantly slow overall lung growth in parenchymally mature animals.

In vivo hypoxia and a fungal alcohol dehydrogenase influence the pathogenesis of invasive pulmonary aspergillosis

Currently, our knowledge of how pathogenic fungi grow in mammalian host environments is limited. Using a chemotherapeutic murine model of invasive pulmonary aspergillosis (IPA) and (1)H-NMR metabolomics, we detected ethanol in the lungs of mice infected with Aspergillus fumigatus. This result suggests that A. fumigatus is exposed to oxygen depleted microenvironments during infection. To test this hypothesis, we utilized a chemical hypoxia detection agent, pimonidazole hydrochloride, in three immunologically distinct murine models of IPA (chemotherapeutic, X-CGD, and corticosteroid). In all three IPA murine models, hypoxia was observed during the course of infection. We next tested the hypothesis that production of ethanol in vivo by the fungus is involved in hypoxia adaptation and fungal pathogenesis. Ethanol deficient A. fumigatus strains showed no growth defects in hypoxia and were able to cause wild type levels of mortality in all 3 murine models. However, lung immunohistopathology and flow cytometry analyses revealed an increase in the inflammatory response in mice infected with an alcohol dehydrogenase null mutant strain that corresponded with a reduction in fungal burden. Consequently, in this study we present the first in vivo observations that hypoxic microenvironments occur during a pulmonary invasive fungal infection and observe that a fungal alcohol dehydrogenase influences fungal pathogenesis in the lung. Thus, environmental conditions encountered by invading pathogenic fungi may result in substantial fungal metabolism changes that influence subsequent host immune responses.

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.

Neutropenia enhances lung dendritic cell recruitment in response to Aspergillus via a cytokine-to-chemokine amplification loop

Current understanding of specific defense mechanisms in the context of neutropenic infections is limited. It has previously been reported that invasive aspergillosis, a prototypic opportunistic infection in neutropenic hosts, is associated with marked accumulation of inflammatory dendritic cells (DCs) in the lungs. Given recent data indicating that neutrophils can modulate immune responses independent of their direct microbial killing, we hypothesized that neutropenia impacts the host response to Aspergillus by determining the migration and phenotype of lung DCs. Inflammatory DCs, but not other DC subsets, were found to accumulate in the lungs of neutropenic hosts challenged with killed or live-attenuated Aspergillus as compared with nonneutropenic hosts, indicating that the accumulation was independent of neutrophil microbicidal activity. The mechanism of this accumulation in neutropenic hosts was found to be augmented influx of DCs, or their precursors, from the blood to the lungs. This effect was attributable to greatly elevated lung TNF expression in neutropenic as compared with nonneutropenic animals. This resulted in greater lung expression of the chemokine ligands CCL2 and CCL20, which, in turn, mediated enhanced recruitment of TNF-producing inflammatory DCs, resulting in a positive feedback cycle. Finally, in the context of neutropenic invasive aspergillosis, depletion of DCs resulted in impaired fungal clearance, indicating that this mechanism is protective for the host. These observations identify what we believe is a novel defense mechanism in invasive aspergillosis that is the result of alterations in DC traffic and phenotype and is specific to neutropenic hosts.

Immunogenetics of invasive aspergillosis

Invasive aspergillosis is one of the most important infections in hematopoietic stem cell transplant recipients, with an incidence rate of 5-15% and an associated mortality of 30-60%. It remains unclear why certain patients develop invasive aspergillosis while others, undergoing identical transplant regimen and similar post transplant immunosuppression, do not. Over the last decade, pattern recognition receptors such as Toll-like receptors (TLRs) and the C-type lectin receptors (CLRs) have emerged as critical components of the innate immune system. By detecting specific molecular patterns from invading microbes and initiating inflammatory and subsequent adaptive immune responses, pattern recognition receptors are strategically located at the molecular interface of hosts and pathogens. Polymorphisms in pattern recognition receptors and downstream signaling molecules have been associated with increased or decreased susceptibility to infections, suggesting that their detection may have an increasing impact on the treatment and prevention of infectious diseases in the coming years. Infectious risk stratification may be particularly relevant for patients with hematologic malignancies, because of the high prevalence and severity of infections in this population. This review summarizes the innate immune mechanisms involved in Aspergillus fumigatus detection and the role of host genetic polymorphisms in susceptibility to invasive aspergillosis.

Cytokine networks in the infected lung

The generation of an innate immune response is essential for rapid clearance of microbes from the respiratory tract, whereas acquired immunity is required for the generation of cellular immunity necessary for the killing of certain intracellular pathogens and the development of immunological memory. Cytokines play an integral role in host defense by serving as leukocyte chemoattractants, leukocyte-activating factors or afferent signals in the induction or regulation of other effector molecules. This review assesses the contribution of cytokine networks to the generation of antimicrobial host defenses in the lung, with an emphasis on cytokines/cytokine networks that are instrumental in innate antibacterial responses, including mucosal immunity, and also introduces networks that instruct the development of adaptive immunity.

Embryonated eggs as an alternative infection model to investigate Aspergillus fumigatus virulence

Infection models are essential tools for studying microbial pathogenesis. Murine models are considered the "gold standard" for studying in vivo infections caused by Aspergillus species, such as A. fumigatus. Recently developed molecular protocols allow rapid construction of high numbers of fungal deletion mutants, and alternative infection models based on cell culture or invertebrates are widely used for screening such mutants to reduce the number of rodents in animal experiments. To bridge the gap between invertebrate models and mice, we have developed an alternative, low-cost, and easy-to-use infection model for Aspergillus species based on embryonated eggs. The outcome of infections in the egg model is dose and age dependent and highly reproducible. We show that the age of the embryos affects the susceptibility to A. fumigatus and that increased resistance coincides with altered chemokine production after infection. The progress of disease in the model can be monitored by using egg survival and histology. Based on pathological analyses, we hypothesize that invasion of embryonic membranes and blood vessels leads to embryonic death. Defined deletion mutant strains previously shown to be fully virulent or partially or strongly attenuated in a mouse model of bronchopulmonary aspergillosis showed comparable degrees of attenuation in the egg model. Addition of nutrients restored the reduced virulence of a mutant lacking a biosynthetic gene, and variations of the infectious route can be used to further analyze the role of distinct genes in our model. Our results suggest that embryonated eggs can be a very useful alternative infection model to study A. fumigatus virulence and pathogenicity.

Use of a new-generation reverse tetracycline transactivator system for quantitative control of conditional gene expression in the murine lung

Conditional regulation of gene expression by the combined use of a lung-specific promoter and the tetracycline-regulated system provides a powerful tool for studying gene function in lung biology and disease pathogenesis in a development-independent fashion. However, the original version of the reverse tetracycline-dependent transactivator (rtTA) exhibited limited doxycycline sensitivity and residual affinity to its promoter (P(tet)), producing leaky transgene expression in the absence of doxycycline. These limitations impeded the use of this system in studying gene dosage effects in pulmonary pathogenesis and repair mechanisms in the diseased lung. Therefore, we used a new-generation rtTA, rtTA2(s)-M2, with no basal activity and increased doxycycline sensitivity, and the rat Clara cell secretory protein (CCSP) promoter to target its expression to pulmonary epithelia in mice. Novel CCSP-rtTA2(s)-M2 founder lines were crossed, with bi-transgenic reporter mice expressing luciferase and Cre recombinase. Background activity, doxycycline sensitivity, tissue and cell-type specificity, inducibility, and reversibility of doxycycline-dependent gene expression were determined by luciferase activity, immunohistochemistry, morphometry, and bioluminescence measurements in neonatal and adult lungs. We generated two distinct novel CCSP-rtTA2(s)-M2 activator mouse lines that confer tight and doxycycline dose-dependent regulation of transgene expression, with high inducibility, complete reversibility, and no background activity, in airway and alveolar epithelia. We conclude that rtTA2(s)-M2 enables quantitative control of conditional gene expression in respiratory epithelia of the murine lung, and that the new CCSP-rtTA2(s)-M2 activator mouse lines will be useful in the further elucidation of the pathogenesis of complex lung diseases and in studies of lung repair.

Innate immunity to Aspergillus species

All humans are continuously exposed to inhaled Aspergillus conidia, yet healthy hosts clear the organism without developing disease and without the development of antibody- or cell-mediated acquired immunity to this organism. This suggests that for most healthy humans, innate immunity is sufficient to clear the organism. A failure of these defenses results in a uniquely diverse set of illnesses caused by Aspergillus species, which includes diseases caused by the colonization of the respiratory tract, invasive infection, and hypersensitivity. A key concept in immune responses to Aspergillus species is that the susceptibilities of the host determine the morphological form, antigenic structure, and physical location of the fungus. In this review, we summarize the current literature on the multiple layers of innate defenses against Aspergillus species that dictate the outcome of this host-microbe interaction.

The power of reversibility regulating gene activities via tetracycline-controlled transcription

Tetracycline-controlled transcriptional activation systems are widely used to control gene expression in transgenic animals in a truly conditional manner. By this we refer to the capability of these expression systems to control gene activities not only in a tissue specific and temporal defined but also reversible manner. This versatility has made the Tet regulatory systems to a preeminent tool in reverse mouse genetics. The development of the technology in the past 15 years will be reviewed and guidelines will be given for its implementation in creating transgenic rodents. Finally, we highlight some recent exciting applications of the Tet technology as well as its foreseeable combination with other emerging technologies in mouse transgenesis.

DARC on RBC limits lung injury by balancing compartmental distribution of CXC chemokines

The Duffy antigen receptor for chemokines (DARC) has a high affinity for CC and CXC chemokines. However, it lacks the ability to induce cell responses that are typical for classical chemokine receptors. The role of DARC in inflammatory conditions remains to be elucidated. We studied the role of DARC in a murine model of acute lung injury. We found that in Darc-gene-deficient (Darc(-/-)) mice, LPS-induced PMN migration into the alveolar space was elevated more than twofold. In contrast, PMN adhesion to endothelial cells and within the interstitial space was reduced in Darc(-/-) mice. Darc(-/-) mice also exhibited increased microvascular permeability. Elevated PMN migration in Darc(-/-) mice was associated with increased concentrations of two essential CXCR2 ligands, CXCL1 and CXCL2/3 in the alveolar space. In the blood, CXCL1 was mostly associated with RBC in WT mice and with plasma in Darc(-/-) mice. We found that DARC on RBC prevented excessive PMN migration into the alveolar space. In contrast, DARC on non-hematopoietic cells appeared to have only minor effects on leukocyte trafficking in this model. These findings show how DARC regulates lung inflammation by controlling the distribution and presentation of chemokines that bind CXCR2.

Early NK cell-derived IFN-{gamma} is essential to host defense in neutropenic invasive aspergillosis

Invasive aspergillosis is among the most common human fungal infections and occurs in patients with severe and complex defects in immune responses. NK cells have previously been found to be important in host defense against this infection, but the mechanism of this effect is not known. We hypothesized that NK cells mediate their protective effect in invasive aspergillosis by acting as the major source of IFN-gamma during early infection. We found that, in the lungs of neutropenic mice with invasive aspergillosis, NK cells were the major population of cells capable of generating IFN-gamma during early infection. Depletion of NK cells resulted in reduced lung IFN-gamma levels and increased lung fungal load that was independent of T and B cell subsets. Depletion of NK cells and absence of IFN-gamma resulted in a similar increase in susceptibility to the infection, but depletion of NK cells in IFN-gamma-deficient hosts did not result in further increase in severity of the infection. NK cell-derived IFN-gamma caused enhanced macrophage antimicrobial effects in vitro and also resulted in greater expression of IFN-inducible chemokines in the lungs. Finally, transfer of activated NK cells from wild-type, but not IFN-gamma-deficient hosts, resulted in greater pathogen clearance from the lungs of both IFN-gamma-deficient and wild-type recipients. Taken together, these data indicate that NK cells are the main source of early IFN-gamma in the lungs in neutropenic invasive aspergillosis, and this is an important mechanism in the defense against this infection.

Aspergillus fumigatus-induced interleukin-8 synthesis by respiratory epithelial cells is controlled by the phosphatidylinositol 3-kinase, p38 MAPK, and ERK1/2 pathways and not by the toll-like receptor-MyD88 pathway

Previous studies have established that phagocytes are key cells of the pulmonary innate immune defense against A. fumigatus, an opportunistic fungus responsible of invasive pulmonary aspergillosis. Macrophages detect A. fumigatus via Toll-like receptors 2 and 4 (TLR2 and -4) and respond by the MyD88-NF-kappaB-dependent synthesis of inflammatory mediators. In the present study, we demonstrate that respiratory epithelial cells also sense A. fumigatus and participate in the host defense. Thus, the interaction of respiratory epithelial cells with germinating but not resting conidia of A. fumigatus results in interleukin (IL)-8 synthesis that is controlled by phosphatidylinositol 3-kinase, p38 MAPK, and ERK1/2. Using MyD88-dominant negative transfected cells, we also show that IL-8 production is not dependent on the TLR-MyD88 pathway, although the MyD88 pathway is activated by A. fumigatus and leads to NF-kappaB activation. Thus, our results provide evidence for the existence of two independent signaling pathways activated in respiratory epithelial cells by A. fumigatus, one that is MyD88-dependent and another that is My88-independent and involved in IL-8 synthesis.

Mice deficient in the CXCR2 ligand, CXCL1 (KC/GRO-alpha), exhibit increased susceptibility to dextran sodium sulfate (DSS)-induced colitis

The role of TLRs and MyD88 in the maintenance of gut integrity in response to dextran sodium sulfate (DSS)-induced colitis was demonstrated recently and led to the conclusion that the innate immune response to luminal commensal flora provides necessary signals that facilitate epithelial repair and permits a return to homeostasis after colonic injury. In this report, we demonstrate that a deficit in a single neutrophil chemokine, CXCL1/KC, also results in a greatly exaggerated response to DSS. Mice with a targeted mutation in the gene that encodes this chemokine responded to 2.5% DSS in their drinking water with significant weight loss, bloody stools, and a complete loss of gut integrity in the proximal and distal colon, accompanied by a predominantly mononuclear infiltrate, with few detectable neutrophils. In contrast, CXCL1/KC(- /-) and wild-type C57BL/6J mice provided water showed no signs of inflammation and, at this concentration of DSS, wild-type mice showed only minimal histopathology, but significantly more infiltrating neutrophils. This finding implies that neutrophil infiltration induced by CXCL1/KC is an essential component of the intestinal response to inflammatory stimuli as well as the ability of the intestine to restore mucosal barrier integrity.

Role of neutrophils in preventing and resolving acute fungal sinusitis

Acute fungal sinusitis (AFS) is a devastating disease of the paranasal sinuses afflicting immunocompromised individuals. Knowledge about this disease is limited to clinical observations because there are no animal models in which to study the pathogenesis of the infection. Our goal was to develop a murine model of AFS and examine the role of neutrophils in host defense within the nasal cavity. Female C57BL/6 mice were depleted of neutrophils using anti-Gr-1 monoclonal antibody from day -1 to day 5 postinfection to initiate a transient neutropenia within the mice. At day 0, Aspergillus fumigatus conidia were administered intranasally. The untreated Aspergillus-exposed group had significant neutrophil recruitment by day 3, but by day 7 the leukocyte numbers had returned to unexposed levels. There was not a significant influx of mononuclear cells at either time point. In contrast, beginning at day 3 postinfection and continuing through day 7, anti-Gr-1-treated mice had increased cellular recruitment consisting of banded neutrophils at day 3 and mature neutrophils at day 7. Hyphal masses developed only in the anti-Gr-1-treated mice (25 to 36%) but only during the period of treatment. When the treatment was discontinued, hyphal masses could no longer be detected in the nasal cavities of these mice. In contrast, cyclophosphamide treatment did not induce neutropenia, and the nasal cavity remained free of hyphal masses. These studies demonstrate the feasibility of using this model to study AFS and implicate neutrophils in protection of the sinuses against acute Aspergillus infection and in clearance of established hyphal masses.

The role of CC chemokine receptor 6 in host defense in a model of invasive pulmonary aspergillosis

RATIONALE

Invasive aspergillosis is a severe fungal infection afflicting immunocompromised patients, particularly patients with neutrophil defects. CCR6, a beta-chemokine receptor, mediates migration of dendritic cells (DCs) and several lymphocyte subsets to sites of epithelial inflammation, but its role in infections has not been examined extensively.

OBJECTIVES

To test the hypothesis that CCR6-mediated leukocyte recruitment is necessary for effective host defense in neutropenic hosts with invasive pulmonary aspergillosis.

METHODS

Neutropenic wild-type mice and mice with targeted deletion of CCR6 were infected with Aspergillus fumigatus. The host responses to the infection were compared in vivo and leukocyte responses to the fungus were examined in vitro.

MEASUREMENTS AND MAIN RESULTS

In the context of infection, immature myeloid DCs were the major population of CCR6-expressing cells in the lungs. As compared with wild-type animals, CCR6-deficient mice developed a more severe infection when challenged with A. fumigatus conidia, as documented by a higher mortality rate and greater lung fungal burden. This was associated with reduced accumulation of DCs in the lungs. CCR6-deficient and wild-type DCs did not differ in their phagocytosis of conidia, cytokine response, or maturation in vitro. In adoptive transfer experiments, however, DCs from CCR6-deficient donors showed lesser accumulation in the lungs of infected mice as compared with wild-type cells, and transfer of wild-type, but not CCR6-deficient, DCs resulted in attenuated severity of infection in CCR6-deficient recipients.

CONCLUSIONS

Taken together, these results implicate CCR6-mediated DC influx into the lung in the initial host defense in invasive aspergillosis.

Early neutrophil recruitment and aggregation in the murine lung inhibit germination of Aspergillus fumigatus Conidia

Several types of polymorphonuclear neutrophil (PMN) deficiency are a predisposing condition for fatal Aspergillus fumigatus infection. In order to study the defensive role of PMNs in the lungs, with particular reference to PMN recruitment and antimicrobial oxidant activity, responses to pulmonary instillation of A. fumigatus conidia were examined. Responses in BALB/c and C57BL/6 mice were compared with those in CXCR2(-/-) and gp91(phox-/-) mice, which are known to have delayed recruitment of PMN to the lungs in response to inflammatory stimuli and inactive NADPH oxidase, respectively. In BALB/c mice, PMNs were recruited to the lungs and formed oxidase-active aggregates with conidia, which inhibited germination. In C57BL/6, gp91(phox-/-), and CXCR2(-/-) mice, PMN recruitment was slower and there was increased germination compared to that in BALB/c mice at 6 and 12 h. In gp91(phox-/-) mice, germination was extensive in PMN aggregates but negligible in alveolar macrophages (AM). Lung sections taken at 6 and 48 h from BALB/c mice showed PMN accumulation at peribronchiolar sites but no germinating conidia. Those from C57BL/6 and CXCR2(-/-) mice showed germinating conidia at 6 h but not at 48 h and few inflammatory cells. In contrast, those from gp91(phox-/-) mice showed germination at 6 h with more-extensive hyphal proliferation and tissue invasion at 48 h. These results indicate that when the lungs are exposed to large numbers of conidia, in addition to the phagocytic activity of AM, early PMN recruitment and formation of oxidative-active aggregates are essential in preventing germination of A. fumigatus conidia.

Neutrophils regulate airway responses in a model of fungal allergic airways disease

Neutrophils infiltrate airway walls in patients with allergic airway diseases and in animal models of these illnesses, but their contribution to the pathogenesis of airway allergy is not established. We hypothesized that, in a mouse model of airway allergy to the ubiquitous environmental mold, Aspergillus fumigatus, airway neutrophils contribute to disease severity. Ab-mediated neutrophil depletion resulted in reduced airway hyperresponsiveness and remodeling, whereas conditional transgenic overexpression of the neutrophil chemotactic molecule, CXCL1, in airway walls resulted in worsened allergic responses. This worsened phenotype was associated with a marked increase in the number of airway neutrophils but not other lung leukocytes, including eosinophils and lymphocyte subsets, and depletion of neutrophils in sensitized mice with transgenic overexpression of CXCL1 resulted in attenuated airway responses. The number of lung neutrophils correlated with lung matrix metalloproteinase 9 (MMP-9) activity both in the context of neutrophil depletion and with augmented neutrophil recruitment to the airways. Although wild-type and MMP-9-deficient neutrophils homed to the inflamed airways to a similar extent, transfer of wild-type, but not MMP-9-deficient, neutrophils to MMP-9-deficient animals resulted in augmented allergic airway responses. Taken together, these data implicate neutrophils in the pathogenesis of fungal allergic airway disease.

Transient overexpression of gamma interferon promotes Aspergillus clearance in invasive pulmonary aspergillosis

Cytokines are critical molecules necessary for normal lung pathogen host defences. Gamma interferon (IFN-gamma) and T1-phenotype immune responses are important components of host defence against Aspergillus. Therefore, we hypothesized that transient overexpression of IFN-gamma within the lung could augment host immunity against Aspergillus. Here it was showed that intranasal administration of 5 x 10(7) colony-forming units (CFU) of Aspergillus fumigatus (Af ) induced the expression of IFN-gamma. Mice were intranasally (i.n) administrated with 5 x 10(8) PFU of a recombinant adenovirus vector containing the murine IFN-gamma cDNA (AdmIFN-gamma), and challenged 24 h later with Af. We observed that i.n. administration of AdmIFN-gamma resulted in about a fourfold increase in levels of IFN-gamma and IL-12 within the lung, about a 75% reduction in lung fungal contents at day 2 and a more than threefold higher survival rate in the AdmIFN-gamma-treated group compared to the controls (P < 0.01). This protection effect was not found when AdmIFN-gamma was i.p. administrated. Alveolar macrophages and lung leucocytes isolated from i.n. AdmIFN-gamma-treated animals displayed enhanced killing of intracellular Aspergillus organisms ex vivo. These results demonstrate that transient overexpression of IFN-gamma could augment host defence against Aspergillus.

Immunosuppressive effects of CCL17 on pulmonary antifungal responses during pulmonary invasive aspergillosis

Aspergillus fumigatus-sensitized CCR4-deficient (CCR4-/-) mice exhibit an accelerated clearance of conidia during fungal asthma. In the present study, we examined the roles of CCL17 and CCL22, two CCR4 ligands, during pulmonary invasive aspergillosis in neutropenic mice. Kaplan-Meier survival curve analysis revealed that wild-type C57BL/6 (CCR4+/+) mice were significantly protected from the lethal effects of Aspergillus compared with their wild-type controls following systemic neutralization with anti-CCL17 but not anti-CCL22 antibodies. Systemic neutralization of CCL17 significantly increased whole-lung CCL2 levels. Mouse survival and histological analysis revealed that the receptor mediating the deleterious effects of CCL17 was CCR4 since mice genetically deficit in CCR4 (CCR4-/-) did not develop invasive aspergillosis. Enzyme-linked immunosorbent assay analysis of whole-lung samples at day 2 after conidial challenge in neutrophil-depleted CCR4-/- and CCR4+/+ mice revealed that whole-lung IL-12 levels were significantly increased in the CCR4-/- group compared with the wild-type group. Also at day 2 after conidial challenge, significantly greater numbers of CD11c+ F4/80+ and CD11c+/CD86+ but fewer CD3/NK1.1+ cells were present in the lungs of CCR4-/- mice compared with their wild-type counterparts. Thus, CCL17-CCR4 interactions dramatically impair the pulmonary antifungal response against A. fumigatus in neutropenic mice.

Therapeutic targeting of CCR1 attenuates established chronic fungal asthma in mice

CC chemokine receptor 1 (CCR1) represents a promising target in chronic airway inflammation and remodeling due to fungus-associated allergic asthma. The present study addressed the therapeutic effect of a nonpeptide CCR1 antagonist, BX-471, in a model of chronic fungal asthma induced by Aspergillus fumigatus conidia. BX-471 treatment of isolated macrophages inhibited CCL22 and TNF-alpha and promoted IL-10 release. BX-471 also increased toll like receptor-9 (TLR9) and decreased TLR2 and TLR6 expression in these cells. When administered daily by intraperitoneal injection, from days 15 to 30 after the initiation of chronic fungal asthma, BX-471 (3, 10, or 30 mg kg(-1)) dose-dependently reduced airway inflammation, hyper-responsiveness, and remodeling at day 30 after conidia challenge. The maximal therapeutic effect was observed at the 10 mg kg(-1) dose. In summary, the therapeutic administration of BX-471 significantly attenuated experimental fungal asthma via its effects on both innate and adaptive immune processes.

Role of CXCR2/CXCR2 ligands in vascular remodeling during bronchiolitis obliterans syndrome

Angiogenesis and vascular remodeling support fibroproliferative processes; however, no study has addressed the importance of angiogenesis during fibro-obliteration of the allograft airway during bronchiolitis obliterans syndrome (BOS) that occurs after lung transplantation. The ELR(+) CXC chemokines both mediate neutrophil recruitment and promote angiogenesis. Their shared endothelial cell receptor is the G-coupled protein receptor CXC chemokine receptor 2 (CXCR2). We found that elevated levels of multiple ELR(+) CXC chemokines correlated with the presence of BOS. Proof-of-concept studies using a murine model of BOS not only demonstrated an early neutrophil infiltration but also marked vascular remodeling in the tracheal allografts. In addition, tracheal allograft ELR(+) CXC chemokines were persistently expressed even in the absence of significant neutrophil infiltration and were temporally associated with vascular remodeling during fibro-obliteration of the tracheal allograft. Furthermore, in neutralizing studies, treatment with anti-CXCR2 Abs inhibited early neutrophil infiltration and later vascular remodeling, which resulted in the attenuation of murine BOS. A more profound attenuation of fibro-obliteration was seen when CXCR2(-/-) mice received cyclosporin A. This supports the notion that the CXCR2/CXCR2 ligand biological axis has a bimodal function during the course of BOS: early, it is important for neutrophil recruitment and later, during fibro-obliteration, it is important for vascular remodeling independent of neutrophil recruitment.

The pathogenesis of fatal outcome in murine pulmonary aspergillosis depends on the neutrophil depletion strategy

Aspergillus fumigatus causes invasive disease in severely immunocompromised hosts but is readily cleared when host innate defenses are intact. Animal models for evaluation of therapeutic strategies to combat invasive aspergillosis that closely mimic human disease are desirable. We determined optimal dosing regimens for neutrophil depletion and evaluated the course of infection following aerosol infection in mice by determining survival, organ fungal burden, and histopathology in mice in which neutropenia was induced by three methods, administration of granulocyte-depleting monoclonal antibody RB6-8C5 (MAb RB6), administration of cyclophosphamide, and administration of both agents. Administration of either individual agent resulted in a requirement for relatively high conidial inocula to achieve 100% mortality in both BALB/c and C57BL/6 mice, although the infection appeared to be somewhat more lethal in C57BL/6 mice. Death following induction of neutropenia with MAb RB6 occurred when a relatively low fungal burden was present in the lung and may have been related to the inflammatory response associated with neutrophil recovery. In contrast, administration of both agents reduced the lethal inoculum in each mouse strain by approximately 1 log(10), and C57BL/6 mice that received both agents had a higher fungal burden and less inflammation in the lung at the time of death than BALB/c mice or mice of either strain that received MAb RB6 alone. Our data suggest that the relationship among fungal burden, inflammation, and death is complex and can be influenced by the immunosuppression regimen, the mouse strain, and the inoculum.

Cytokines in host defense againstAspergillus: recent advances

Many aspects of antimicrobial host responses are orchestrated by a complex network of cytokines and their receptors. This review focuses on recent progress in our understanding of the function of cytokines in innate immune responses to Aspergillus. TNF, a recognition cytokine, has been shown to be required for initiation of the innate response in the mouse model of invasive aspergillosis. Several recruitment cytokines play critical roles in mediating influx of specific leukocytes to the site of infection in invasive aspergillosis. Among these, the ELR + subset of CXC chemokines and their receptor CXCR2 are critical to neutrophil recruitment, while CCL3/macrophage inflammatory protein (MIP)-1alpha and CCL2/ monocyte chemoattractant protein (MCP)-1 are critical to recruitment of monocyte-lineage leukocytes and NK cells, respectively. Of the activation cytokines, those associated with the Th-1 phenotype, including interleukin (IL)-12, IL-18, and interferon-gamma (IFN-gamma), are critical to protective responses to the infection. Conversely, the Th2-phenotype cytokines IL-4 and IL-10 contribute to progression of infection. Modulation of the immune response to Aspergillus by manipulating these mediators remains intriguing as a potential adjunctive treatment in patients with invasive aspergillosis.

[Pulmonary anti-Aspergillus defences]

The lung, constantly exposed to inhaled infectious particles, uses a very efficient immune system to insure sterility of the airways. It has to be tightly regulated for the tissues to be kept from its potentially deleterious effects. Pulmonary anti-Aspergillus defences are based upon the concurrent action of innate immunity, non specific but rapidly mobilisable, and of adaptative immunity. The former first consists in natural barriers, namely the respiratory epithelium and its antimicrobial peptides (complement, defensins, collectins). Then come the phagocytic cells (macrophages and neutrophils), but also the dendritic cells, able to stimulate adaptative responses through the presentation of antigens they have phagocytised ans processed. The Toll-like receptors are among the key ones involved in the recognition of fungal components. Chemokines have a crucial role for the recruitment, maturation and activation of neutrophils, while anti-inflammatory cytokines tightly influence T lymphocytes functional differentiation. These latter, cornerstones of the adaptative immunity, differentiate into two mutually exclusive pathways according to the type of cytokines which they produce. The Th1 one is largely protective in the context of Aspergillus, while the Th2 one is deleterious. However, a good cooperation between these 2 pathways is required for an efficient protection. Pulmonary anti-Aspergillus defences are multifactorial. Innate immunity is crucial but a capacity of the host to generate specific responses is also warranted.