Role of IL-10 in invasive aspergillosis: increased resistance of IL-10 gene knockout mice to lethal systemic aspergillosis

Interplay of Cytokines and Chemokines in Aspergillosis

Aspergillosis is a fungal infection caused by various species of Aspergillus, most notably A. fumigatus. This fungus causes a spectrum of diseases, including allergic bronchopulmonary aspergillosis, aspergilloma, chronic pulmonary aspergillosis, and invasive aspergillosis. The clinical manifestations and severity of aspergillosis can vary depending on individual immune status and the specific species of Aspergillus involved. The recognition of Aspergillus involves pathogen-associated molecular patterns (PAMPs) such as glucan, galactomannan, mannose, and conidial surface proteins. These are recognized by the pathogen recognition receptors present on immune cells such as Toll-like receptors (TLR-1,2,3,4, etc.) and C-type lectins (Dectin-1 and Dectin-2). We discuss the roles of cytokines and pathogen recognition in aspergillosis from both the perspective of human and experimental infection. Several cytokines and chemokines have been implicated in the immune response to Aspergillus infection, including interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α), CCR4, CCR17, and other interleukins. For example, allergic bronchopulmonary aspergillosis (ABPA) is characterized by Th2 and Th9 cell-type immunity and involves interleukin (IL)-4, IL-5, IL-13, and IL-10. In contrast, it has been observed that invasive aspergillosis involves Th1 and Th17 cell-type immunity via IFN-γ, IL-1, IL-6, and IL-17. These cytokines activate various immune cells and stimulate the production of other immune molecules, such as antimicrobial peptides and reactive oxygen species, which aid in the clearance of the fungal pathogen. Moreover, they help to initiate and coordinate the immune response, recruit immune cells to the site of infection, and promote clearance of the fungus. Insight into the host response from both human and animal studies may aid in understanding the immune response in aspergillosis, possibly leading to harnessing the power of cytokines or cytokine (receptor) antagonists and transforming them into precise immunotherapeutic strategies. This could advance personalized medicine.

Exploring the role of antioxidants in sepsis-associated oxidative stress: a comprehensive review

Sepsis is a potentially fatal condition characterized by organ dysfunction caused by an imbalanced immune response to infection. Although an increased inflammatory response significantly contributes to the pathogenesis of sepsis, several molecular mechanisms underlying the progression of sepsis are associated with increased cellular reactive oxygen species (ROS) generation and exhausted antioxidant pathways. This review article provides a comprehensive overview of the involvement of ROS in the pathophysiology of sepsis and the potential application of antioxidants with antimicrobial properties as an adjunct to primary therapies (fluid and antibiotic therapies) against sepsis. This article delves into the advantages and disadvantages associated with the utilization of antioxidants in the therapeutic approach to sepsis, which has been explored in a variety of animal models and clinical trials. While the application of antioxidants has been suggested as a potential therapy to suppress the immune response in cases where an intensified inflammatory reaction occurs, the use of multiple antioxidant agents can be beneficial as they can act additively or synergistically on different pathways, thereby enhancing the antioxidant defense. Furthermore, the utilization of immunoadjuvant therapy, specifically in septic patients displaying immunosuppressive tendencies, represents a promising advancement in sepsis therapy.

Risk Factors of Severe COVID-19: A Review of Host, Viral and Environmental Factors

The clinical course and outcome of COVID-19 are highly variable, ranging from asymptomatic infections to severe disease and death. Understanding the risk factors of severe COVID-19 is relevant both in the clinical setting and at the epidemiological level. Here, we provide an overview of host, viral and environmental factors that have been shown or (in some cases) hypothesized to be associated with severe clinical outcomes. The factors considered in detail include the age and frailty, genetic polymorphisms, biological sex (and pregnancy), co- and superinfections, non-communicable comorbidities, immunological history, microbiota, and lifestyle of the patient; viral genetic variation and infecting dose; socioeconomic factors; and air pollution. For each category, we compile (sometimes conflicting) evidence for the association of the factor with COVID-19 outcomes (including the strength of the effect) and outline possible action mechanisms. We also discuss the complex interactions between the various risk factors.

T cell responses to control fungal infection in an immunological memory lens

In recent years, fungal vaccine research emanated significant findings in the field of antifungal T-cell immunity. The generation of effector T cells is essential to combat many mucosal and systemic fungal infections. The development of antifungal memory T cells is integral for controlling or preventing fungal infections, and understanding the factors, regulators, and modifiers that dictate the generation of such T cells is necessary. Despite the deficiency in the clear understanding of antifungal memory T-cell longevity and attributes, in this review, we will compile some of the existing literature on antifungal T-cell immunity in the context of memory T-cell development against fungal infections.

Cytokine Profile of Invasive Pulmonary Aspergillosis in Severe COVID-19 and Possible Therapeutic Targets

During the SARS-CoV-2 pandemic, a higher incidence of invasive pulmonary aspergillosis was observed in patients affected by Coronavirus disease 2019 (COVID-19), leading to the delineation of a new entity named COVID-19 associated pulmonary aspergillosis (CAPA). A predisposition to invasive infection caused by Aspergillus spp. in SARS-CoV-2 infected patients can be ascribed either to the direct viral-mediated damage of the respiratory epithelium, as already observed in influenza H1N1 virus infections, or to the dysregulated immunity associated with COVID-19. This narrative review focuses on the impact of immune impairment, particularly due to cytokine dysregulation caused by Aspergillus spp. superinfection in COVID-19 for a more in-depth understanding of the molecular pathways implicated in CAPA. As immune competence has proven to be essential in protecting against CAPA onset, a role already threatened by SARS-CoV-2 infection itself, preventive strategies should focus on reducing factors that could further target the host immune system. We also aimed to focus on well-known and less-known risk factors for IPA in COVID-19 patients, related to the main causes of immune suppression, both virus-mediated and iatrogenic, including treatments currently indicated for COVID-19. Lastly, possible preventive strategies aimed at reducing morbidity and mortality due to CAPA could be implemented.

Cytomegalovirus viral interleukin-10 (cmvIL-10) in patients with Aspergillus infection and effects on clinical outcome

BACKGROUND

Human cytomegalovirus (CMV) is associated with aspergillosis, but the simultaneous presence of cytomegalovirus viral interleukin-10 (cmvIL-10) and aspergillosis has never been investigated. CmvIL-10 is produced by CMV-infected cells and acts as an immune modulator during CMV infection. The aim of this study was to evaluate cmvIL-10 levels in peripheral blood and its influence on the clinical outcomes of Aspergillus infection.

METHODS

Patients who visited or were admitted to the hospital with suspected Aspergillus infection, including invasive aspergillosis (IA) and chronic pulmonary aspergillosis (CPA), were prospectively enrolled. The cmvIL-10, human IL-10 (hIL-10), IL-1B, IL-6, IL-8, IFN-γ, and TNF-α levels in peripheral blood were measured.

RESULTS

Patients with Aspergillus infection had a higher level of cmvIL-10 than the control group (158±305 vs. 27.9±30.4 pg/mL, p<0.05). The level of cmvIL-10 was not correlated with CMV viremia or end-organ disease. The cmvIL-10 but not hIL-10 level was positively correlated with the IFN-γ level (p<0.05) and marginally negatively correlated with IL-1B and IL-8 levels (p<0.1). In patients with CPA, a high level of cmvIL-10 (≥100 pg/mL) was a poor prognostic factor for long-term survival (p<0.05). In contrast, CMV viremia or end-organ disease was associated with poor survival in patients with IA (p=0.05).

CONCLUSIONS

Aspergillus infection was associated with CMV coinfection with cmvIL-10 in blood. A cmvIL-10 concentration ≥100 pg/mL was a predictor for unfavourable outcome in CPA patients.

Post-COVID syndrome: pulmonary complications

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has infected millions of people worlwide and caused a pandemic that is still ongoing. The virus can cause a disease named as COVID-19, which is composed of multi systemic manifestations with a pulmonary system predominance. As the time passes, we are dealing more and more with a wide variety of effects and complications of the disease in survivors as far as with concerns about the clinical outcome and the timeline of symptoms in different patients. Since the lungs are the most involved organs and the post-COVID prolonged and persistent effects are mainly related to the pulmonary system, it is crucial to define and predict the outcome and to determine the individuals that can progress to fibrosis and loss of function of lungs. This review summarizes the current literature regarding the pulmonary complications in post-COVID syndrome and the management of these conditions.

Experimental Models of Infectious Pulmonary Complications Following Hematopoietic Cell Transplantation

Pulmonary infections remain a major cause of morbidity and mortality in hematopoietic cell transplantation (HCT) recipients. The prevalence and type of infection changes over time and is influenced by the course of immune reconstitution post-transplant. The interaction between pathogens and host immune responses is complex in HCT settings, since the conditioning regimens create periods of neutropenia and immunosuppressive drugs are often needed to prevent graft rejection and limit graft-versus-host disease (GVHD). Experimental murine models of transplantation are valuable tools for dissecting the procedure-related alterations to innate and adaptive immunity. Here we review mouse models of post-HCT infectious pulmonary complications, primarily focused on three groups of pathogens that frequently infect HCT recipients: bacteria (often P. aeruginosa), fungus (primarily Aspergillus fumigatus), and viruses (primarily herpesviruses). These mouse models have advanced our knowledge regarding how the conditioning and HCT process negatively impacts innate immunity and have provided new potential strategies of managing the infections. Studies using mouse models have also validated clinical observations suggesting that prior or occult infections are a potential etiology of noninfectious pulmonary complications post-HCT as well.

Blockade Of PD-1 Attenuated Postsepsis Aspergillosis Via The Activation of IFN-γ and The Dampening of IL-10

BACKGROUND

Nosocomial aspergillosis in patients with sepsis has emerged in the past few years. Blockade of PD-1/PD-L pathway has tended to become a promising therapeutic strategy as it improved the outcome of bacterial sepsis and postsepsis secondary fungal infection. Recently, the controversial effects of PD-1 blockade on infectious diseases, including aspergillosis, have been demonstrated; therefore, the efficacy of anti-PD-1 drug still remains to be elucidated.

METHODS

Cecal ligation and puncture (CLP) was conducted as a mouse sepsis model. Aspergillus fumigatus spores were intravenously inoculated on day 5 post-CLP, when the immune cells succumbed to exhaustion. Amphotericin B was medicated together with or without anti-PD-1 treatment after Aspergillus infection.

RESULTS

Amphotericin B alone was not effective to treat the CLP-mice with secondary aspergillosis. In contrast, antifungal medication with the adjunctive anti-PD-1 treatment attenuated the fungal burdens in blood and internal organs, and improved the survival rate of the mice with secondary aspergillosis. These outcomes of PD-1 blockade were concurring with the enhanced CD86 expression on splenocytes, the augmented serum IFN-γ, and the dampened IL-10. Activated T cells from anti-PD-1-treated mice also highly increased IFN-γ and diminished IL-10 production.

CONCLUSION

The blockade of PD-1 on postsepsis aspergillosis presumably reinvigorated exhausted antigen-presenting cells and T cells by upregulating CD86 expression and IFN-γ production, and dampened IL-10 production, which consequently leaded to the attenuation of secondary aspergillosis. The adjunctive anti-PD-1 therapy may become a promising strategy for the advanced immunotherapy against lethal fungal infection.

COVID-19 associated with pulmonary aspergillosis: A literature review

Bacterial or virus co-infections with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have been reported in many studies, however, the knowledge on Aspergillus co-infection among patients with coronavirus disease 2019 (COVID-19) was limited. This literature review aims to explore and describe the updated information about COVID-19 associated with pulmonary aspergillosis. We found that Aspergillus spp. can cause co-infections in patients with COVID-19, especially in severe/critical illness. The incidence of IPA in COVID-19 ranged from 19.6% to 33.3%. Acute respiratory distress syndrome requiring mechanical ventilation was the common complications, and the overall mortality was high, which could be up to 64.7% (n = 22) in the pooled analysis of 34 reported cases. The conventional risk factors of invasive aspergillosis were not common among these specific populations. Fungus culture and galactomannan test, especially from respiratory specimens could help early diagnosis. Aspergillus fumigatus was the most common species causing co-infection in COVID-19 patients, followed by Aspergillus flavus. Although voriconazole is the recommended anti-Aspergillus agent and also the most commonly used antifungal agent, aspergillosis caused by azole-resistant Aspergillus is also possible. Additionally, voriconazole should be used carefully in the concern of complicated drug-drug interaction and enhancing cardiovascular toxicity on anti-SARS-CoV-2 agents. Finally, this review suggests that clinicians should keep alerting the possible occurrence of pulmonary aspergillosis in severe/critical COVID-19 patients, and aggressively microbiologic study in addition to SARS-CoV-2 via respiratory specimens should be indicated.

Transcriptional Profiling of Immune and Inflammatory Responses in the Context of SARS-CoV-2 Fungal Superinfection in a Human Airway Epithelial Model

An increasing amount of evidence indicates a relatively high prevalence of superinfections associated with coronavirus disease 2019 (COVID-19), including invasive aspergillosis, but the underlying mechanisms remain to be characterized. In the present study, to better understand the biological impact of superinfection, we determine and compare the host transcriptional response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) versus Aspergillus superinfection, using a model of reconstituted human airway epithelium. Our analyses reveal that both simple infection and superinfection induce strong deregulation of core components of innate immune and inflammatory responses, with a stronger response to superinfection in the bronchial epithelial model compared to its nasal counterpart. Our results also highlight unique transcriptional footprints of SARS-CoV-2 Aspergillus superinfection, such as an imbalanced type I/type III IFN, and an induction of several monocyte and neutrophil associated chemokines, that could be useful for the understanding of Aspergillus-associated COVID-19 and also the management of severe forms of aspergillosis in this specific context.

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.

Advances in Understanding Human Genetic Variations That Influence Innate Immunity to Fungi

Fungi are ubiquitous. Yet, despite our frequent exposure to commensal fungi of the normal mammalian microbiota and environmental fungi, serious, systemic fungal infections are rare in the general population. Few, if any, fungi are obligate pathogens that rely on infection of mammalian hosts to complete their lifecycle; however, many fungal species are able to cause disease under select conditions. The distinction between fungal saprophyte, commensal, and pathogen is artificial and heavily determined by the ability of an individual host's immune system to limit infection. Dramatic examples of commensal fungi acting as opportunistic pathogens are seen in hosts that are immune compromised due to congenital or acquired immune deficiency. Genetic variants that lead to immunological susceptibility to fungi have long been sought and recognized. Decreased myeloperoxidase activity in neutrophils was first reported as a mechanism for susceptibility to Candida infection in 1969. The ability to detect genetic variants and mutations that lead to rare or subtle susceptibilities has improved with techniques such as single nucleotide polymorphism (SNP) microarrays, whole exome sequencing (WES), and whole genome sequencing (WGS). Still, these approaches have been limited by logistical considerations and cost, and they have been applied primarily to Mendelian impairments in anti-fungal responses. For example, loss-of-function mutations in CARD9 were discovered by studying an extended family with a history of fungal infection. While discovery of such mutations furthers the understanding of human antifungal immunity, major Mendelian susceptibility loci are unlikely to explain genetic disparities in the rate or severity of fungal infection on the population level. Recent work using unbiased techniques has revealed, for example, polygenic mechanisms contributing to candidiasis. Understanding the genetic underpinnings of susceptibility to fungal infections will be a powerful tool in the age of personalized medicine. Future application of this knowledge may enable targeted health interventions for susceptible individuals, and guide clinical decision making based on a patient's individual susceptibility profile.

Autocrine IL-10 Signaling Promotes Dendritic Cell Type-2 Activation and Persistence of Murine Cryptococcal Lung Infection

The substantial morbidity and mortality caused by invasive fungal pathogens, including Cryptococcus neoformans, necessitates increased understanding of protective immune responses against these infections. Our previous work using murine models of cryptococcal lung infection demonstrated that dendritic cells (DCs) orchestrate critical transitions from innate to adaptive immunity and that IL-10 signaling blockade improves fungal clearance. To further understand interrelationships among IL-10 production, fungal clearance, and the effect of IL-10 on lung DCs, we performed a comparative temporal analysis of cryptococcal lung infection in wild type C57BL/6J mice (designated IL-10^+/+) and IL-10^-/- mice inoculated intratracheally with C. neoformans (strain 52D). Early and sustained IL-10 production by lung leukocytes was associated with persistent infection in IL-10^+/+ mice, whereas fungal clearance was improved in IL-10^-/- mice during the late adaptive phase of infection. Numbers of monocyte-derived DCs, T cells, and alveolar and exudate macrophages were increased in lungs of IL-10^-/- versus IL-10^+/+ mice concurrent with evidence of enhanced DC type-1, Th1/Th17 CD4 cell, and classical macrophage activation. Bone marrow-derived DCs stimulated with cryptococcal mannoproteins, a component of the fungal capsule, upregulated expression of IL-10 and IL-10R, which promoted DC type-2 activation in an autocrine manner. Thus, our findings implicate fungus-triggered autocrine IL-10 signaling and DC type-2 activation as important contributors to the development of nonprotective immune effector responses, which characterize persistent cryptococcal lung infection. Collectively, this study informs and strengthens the rationale for IL-10 signaling blockade as a novel treatment for fungal infections.

mTOR Modulates CD8+ T Cell Differentiation in Mice with Invasive Pulmonary Aspergillosis

CD8⁺ T cells are a vital component of the adaptive immune system and important for eliminating intracellular pathogens. Notably, mTOR activity is associated with CD8⁺ T effector memory (Tem) cell differentiation in fungal infections. This study investigates the molecular mechanisms of CD8⁺ Tem cell proliferation and differentiation mediated by the mTOR pathway in immunosuppressed mice with invasive pulmonary aspergillosis (IPA). We first established the immunosuppressed IPA mouse model, then mice were subjected to rapamycin treatment daily or interleukin (IL)-12 treatment every other day. Lung tissues and blood samples were obtained seven days later. Aspergillus fumigatus was cultured from the lung tissue of mice inoculated with A. fumigatus spores. After IL-12 treatment, the expression of mTOR and its downstream signaling molecule S6 kinase, number of CD8⁺ Tem cells and interferon-γ expression were significantly increased, while they were significantly decreased after treatment with rapamycin. Additionally, IL-12 treatment induced T-bet but inhibited Eomesodermin expression, while the opposite was seen when the mTOR pathway was blocked by rapamycin. In conclusion, we found that the mTOR pathway induced CD8⁺ T cell proliferation and differentiation by regulating T-bet and Eomesodermin expression, which significantly influenced immune regulation during IPA and enhanced the immune response against fungal infection.

Animal Models of Aspergillosis

Aspergillosis is an airborne fungal disease caused by Aspergillus spp., a group of ubiquitous molds. This disease causes high morbidity and mortality in both humans and animals. The growing importance of this infection over recent decades has created a need for practical and reproducible models of aspergillosis. The use of laboratory animals provides a platform to understand fungal virulence and pathophysiology, assess diagnostic tools, and evaluate new antifungal drugs. In this review, we describe the fungus, various Aspergillus-related diseases in humans and animals and various experimental animal models. Overall, we highlight the advantages and limitations of the animal models, the experimental variables that can affect the course of the disease and the reproducibility of infection, and the critical need for standardization of the species, immunosuppressive drugs, route of infection, and diagnostic criteria to use.

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.

Genetic susceptibility to severe asthma with fungal sensitization

Severe asthma is problematic and its pathogenesis poorly understood. Fungal sensitization is common, and many patients with severe asthma with fungal sensitization (SAFS), used to denote this subgroup of asthma, respond to antifungal therapy. We have investigated 325 haplotype-tagging SNPs in 22 candidate genes previously associated with aspergillosis in patients with SAFS, with comparisons in atopic asthmatics and healthy control patients, of whom 47 SAFS, 279 healthy and 152 atopic asthmatic subjects were genotyped successfully. Significant associations with SAFS compared with atopic asthma included Toll-like receptor 3 (TLR3) (p = .009), TLR9 (p = .025), C-type lectin domain family seven member A (dectin-1) (p = .043), interleukin-10 (IL-10) (p = .0010), mannose-binding lectin (MBL2) (p = .007), CC-chemokine ligand 2 (CCL2) (2 SNPs, p = .025 and .041), CCL17 (p = .002), plasminogen (p = .049) and adenosine A2a receptor (p = .024). These associations differ from those found in ABPA in asthma, indicative of contrasting disease processes. Additional and broader genetic association studies in SAFS, combined with experimental work, are likely to contribute to our understanding of different phenotypes of problematic asthma.

IL-12 Influence mTOR to Modulate CD8+ T Cells Differentiation through T-bet and Eomesodermin in Response to Invasive Pulmonary Aspergillosis

Objective: To investigate whether mTOR signaling pathway regulate the proliferation and differentiation of CD8⁺ T cells by transcription factors T-bet and Eomes, and explore the role of IL-12 in this biological procedure. Methods: Aspergillus fumigatus spore suspension nasal inhalation was used to establish the invasive pulmonary aspergillosis (IPA) mouse model. After inoculation, rapamycin (2mg/kg) each day or IL-12 (5ug/kg) every other day was given for 7 days. The blood samples were obtained before the mice sacrificed and lung specimens were taken. Pathological sections were stained with hematoxylin and eosin (HE). The number of CD8⁺effective memory T cells (Tem) and the expression of IFN-γ, mTOR, ribosomal protein S6 kinase (S6K), T-bet and EOMES were measured by flow cytometry. The levels of IL-6, IL-10 and Galactomannan (GM) were determined by ELISA. Results: After IL-12 treatment, the number of CD8⁺ Tem and the expression of IFN-γ increased significantly; while quite the opposite results were observed when the mTOR pathway was blocked by rapamycin. The expression of mTOR and S6K as well as the level of IFN-γ of the IL-12 treatment group were significantly higher than those in IPA and IPA + rapamycin groups. In addition, IL-12 promoted increasing T-bet and down regulating Eomes to make the Tem transformation. The final immune effector was high level of inflammatory cytokines (IL-6) and low level of anti-inflammatory factors (IL-10) and this strengthened immune response to the Aspergillus infection. Conclusions: The biological effects of Tem could significantly affect IPA infection host immune regulation, which depended on the activation of mTOR signaling pathway by IL-12.

Heat-Killed Yeast as a Pan-Fungal Vaccine

Fungal infections continue to rise worldwide. Antifungal therapy has long been a mainstay for the treatment of these infections, but often can fail for a number of reasons. These include acquired or innate drug resistance of the causative agent, poor drug penetration into the affected tissues, lack of cidal activity of the drug and drug toxicities that limit therapy. In some instances, such as coccidioidal meningitis, therapy is life-long. In addition, few new antifungal drugs are under development. In light of this information a preventative vaccine is highly desirable. Although numerous investigators have worked toward the development of fungal vaccines, none have become commercially available for use in humans. In the course of our studies, we have discovered that heat-killed yeast (HKY) of Saccharomyces cerevisiae can be used as a vaccine and have shown that it has efficacy in the prevention and reduction of five different fungal infections when used experimentally in mice, which raises the possibility of a pan-fungal vaccine preparation. In our studies we grow S. cerevisiae in broth and heat-kill the organism at 70 ° C for 3 h. The number of dead yeast cells is adjusted and mice are vaccinated subcutaneously beginning 3-7 weeks prior to infection. After infection, efficacy is assessed on the basis of survival and residual burden of the fungus in the target organs. Alternatively, efficacy can be assessed solely on fungal burden at a predetermined time postinfection. Although itself it is unlikely to be moved toward commercialization, HKY can be used a positive control vaccine for studies on specific molecular entities as vaccines, and as a guidepost for the key elements of potential, more purified, pan-fungal vaccine preparations.

Aspergillosis and stem cell transplantation: An overview of experimental pathogenesis studies

Invasive aspergillosis is a life-threatening infection caused by the opportunistic filamentous fungus Aspergillus fumigatus. Patients undergoing haematopoietic stem cell transplant (HSCT) for the treatment of hematological malignancy are at particularly high risk of developing this fatal infection. The susceptibility of HSCT patients to infection with A. fumigatus is a consequence of a complex interplay of both fungal and host factors. Here we review our understanding of the host-pathogen interactions underlying the susceptibility of the immunocompromised host to infection with A. fumigatus with a focus on the experimental validation of fungal and host factors relevant to HSCT patients. These include fungal factors such as secondary metabolites, cell wall constituents, and metabolic adaptations that facilitate immune evasion and survival within the host microenvironment, as well as the innate and adaptive immune responses involved in host defense against A. fumigatus.

Polymorphisms in Host Immunity-Modulating Genes and Risk of Invasive Aspergillosis: Results from the AspBIOmics Consortium

Recent studies suggest that immune-modulating single-nucleotide polymorphisms (SNPs) influence the risk of developing cancer-related infections. Here, we evaluated whether 36 SNPs within 14 immune-related genes are associated with the risk of invasive aspergillosis (IA) and whether genotyping of these variants might improve disease risk prediction. We conducted a case-control association study of 781 immunocompromised patients, 149 of whom were diagnosed with IA. Association analysis showed that the IL4Rrs2107356 and IL8rs2227307 SNPs (using dbSNP numbering) were associated with an increased risk of IA (IL4Rrs2107356 odds ratio [OR], 1.92; 95% confidence interval [CI], 1.20 to 3.09; IL8rs2227307 OR, 1.73; 95% CI, 1.06 to 2.81), whereas the IL12Brs3212227 and IFNγrs2069705 variants were significantly associated with a decreased risk of developing the infection (IL12Brs3212227 OR, 0.60; 95% CI, 0.38 to 0.96; IFNγrs2069705 OR, 0.63; 95% CI, 0.41 to 0.97). An allogeneic hematopoietic stem cell transplantation (allo-HSCT)-stratified analysis revealed that the effect observed for the IL4Rrs2107356 and IFNγrs2069705 SNPs was stronger in allo-HSCT (IL4Rrs2107356 OR, 5.63; 95% CI, 1.20 to 3.09; IFNγrs2069705 OR, 0.24; 95% CI, 0.10 to 0.59) than in non-HSCT patients, suggesting that the presence of these SNPs renders patients more vulnerable to infection, especially under severe and prolonged immunosuppressive conditions. Importantly, in vitro studies revealed that carriers of the IFNγrs2069705C allele showed a significantly increased macrophage-mediated neutralization of fungal conidia (P = 0.0003) and, under stimulation conditions, produced higher levels of gamma interferon (IFNγ) mRNA (P = 0.049) and IFNγ and tumor necrosis factor alpha (TNF-α) cytokines (P value for 96 h of treatment with lipopolysaccharide [PLPS-96 h], 0.057; P value for 96 h of treatment with phytohemagglutinin [PPHA-96 h], 0.036; PLPS+PHA-96 h = 0.030; PPHA-72 h = 0.045; PLPS+PHA-72 h = 0.018; PLPS-96 h = 0.058; PLPS+PHA-96 h = 0.0058). Finally, we also observed that the addition of SNPs significantly associated with IA to a model including clinical variables led to a substantial improvement in the discriminatory ability to predict disease (area under the concentration-time curve [AUC] of 0.659 versus AUC of 0.564; P-2 log likehood ratio test = 5.2 · 10(-4) and P50.000 permutation test = 9.34 · 10(-5)). These findings suggest that the IFNγrs2069705 SNP influences the risk of IA and that predictive models built with IFNγ, IL8, IL12p70, and VEGFA variants can used to predict disease risk and to implement risk-adapted prophylaxis or diagnostic strategies.

Adoptive transfer of Aspergillus-specific T cells as a novel anti-fungal therapy for hematopoietic stem cell transplant recipients: Progress and challenges

Although newer antifungal drugs have substantially altered the natural history of invasive aspergillosis, the disease still accounts for significant morbidity and mortality in hematopoietic stem cell transplant recipients. Both the evidence supporting a protective role of T cells against this fungal pathogen and the documented efficacy of adoptive transfer of antigen-specific T cells for prophylaxis and treatment of viral infections post-transplant have stimulated much interest towards development of Aspergillus-specific T cells (Asp-STs) for adoptive immunotherapy in the allogeneic transplant setting. In contrast to the remarkable progress with virus-specific T cells, clinical development of fungus-specific T cells is still in its infancy. Several groups have characterized Asp-STs in healthy individuals and patients with malignant hematological diseases, while others sought to develop GMP-compliant methods of expanding or bioengineering Asp-STs ex vivo as immunotherapy. This review highlights the recent advances in this field, and discusses critical issues involved in development and protocol design of Asp-ST immunotherapy.

Whole glucan particles as a vaccine against systemic coccidioidomycosis

We reported previously that yeast-derived whole glucan particles (WGPs), with or without conjugation to BSA, used as a vaccine protected against systemic aspergillosis in mice. Here, we examined their utility as a potential vaccine against coccidioidomycosis. WGPs were prepared from Saccharomyces cerevisiae; conjugation with BSA (WGP-BSA) was done using 1-cyano-4-dimethylaminopyridinium tetrafluoroborate-mediated conjugation. Heat-killed S. cerevisiae (HKY) was used as a positive-control vaccine. CD-1 mice were vaccinated with WGPs or WGP-BSA, HKY or PBS once weekly, beginning 21 days prior to infection. Mice were infected intravenously with arthroconidia of Coccidioides posadasii. In the low-mortality study, 50 % of PBS-treated controls died. Only WGP-BSA at 0.6 mg per dose induced significant protection compared with PBS treatment. All surviving mice were infected in all three organs examined. Those given WGP-BSA at 0.6 mg per dose had fewer c.f.u. in liver and lungs (P = 0.04), and those given WGPs at 6 mg per dose had fewer in lungs (P < 0.02), compared with PBS. In the high-mortality study, 90 % of PBS mice died. Vaccination with HKY, and WGPs or WGP-BSA at 6 or 12 mg per dose significantly prolonged survival (P ≤ 0.05). No surviving mice were free of infection. HKY and WGP-BSA at 12 mg per dose reduced c.f.u. in the liver and lungs (P < 0.05) and WGP-BSA at 6 mg per dose reduced c.f.u. in the lungs (P < 0.05); unconjugated WGPs did not reduce infection. WGPs or WGP-BSA acted as a vaccine that protected against mortality caused by coccidioidomycosis. Thus, WGP protection against coccidioidomycosis and aspergillosis provides the basis for development of a pan-fungal vaccine.

Comparison of efficacy of the disease-specific LOX1- and constitutive cytomegalovirus-promoters in expressing interleukin 10 through adeno-associated virus 2/8 delivery in atherosclerotic mice

The development of gene therapy vectors for treating diseases of the cardiovascular system continues at a steady pace. Moreover, in the field of gene therapy the utility of "disease-specific promoters" has strong appeal. Many therapeutic genes, including transforming growth factor beta 1 or interleukin 10, are associated to adverse effects. The use of a disease-specific promoter might minimize toxicity. The lectin-like oxidized low density lipoprotein receptor 1 is a marker of cardiovascular disease and a potential therapeutic target. The lectin-like oxidized low density lipoprotein receptor 1 is known to be up-regulated early during disease onset in a number of cell types at the sites where the disease will be clinically evident. In this study an adeno-associated virus-2 DNA vector (AAV2) using the AAV8 capsid, and containing the full length The lectin-like oxidized low density lipoprotein receptor 1 promoter, was generated and assayed for its ability to express human interleukin 10 in low density lipoprotein receptor knockout mice on high cholesterol diet. The cytomegalovirus early promoter was used for comparison in a similarly structured vector. The two promoters were found to have equal efficacy in reducing atherogenesis as measured by aortic systolic blood velocity, aortic cross sectional area, and aortic wall thickness. This is the first head-to-head comparison of a constitutive with a disease-specific promoter in a therapeutic context. These data strongly suggest that the use of a disease-specific promoter is appropriate for therapeutic gene delivery.

Vaccinated C57BL/6 mice develop protective and memory T cell responses to Coccidioides posadasii infection in the absence of interleukin-10

High concentrations of lung tissue-associated interleukin-10 (IL-10), an anti-inflammatory and immunosuppressive cytokine, correlate with susceptibility of mice to Coccidioides spp. infection. In this study, we found that macrophages, dendritic cells, neutrophils, and both CD8(+) and CD4(+) T cells recruited to Coccidioides posadasii-infected lungs of nonvaccinated and vaccinated mice contributed to the production of IL-10. The major IL-10-producing leukocytes were CD8(+) T cells, neutrophils, and macrophages in lungs of nonvaccinated mice, while both Foxp3(+) and Foxp3(-) subsets of IL-10(+) CD4(+) T cells were significantly elevated in vaccinated mice. Profiles of the recruited leukocytes in lungs revealed that only CD4(+) T cells were significantly increased in IL-10(-/-) knockout mice compared to their wild-type counterparts. Furthermore, ex vivo recall assays showed that CD4(+) T cells isolated from vaccinated IL-10(-/-) mice compared to vaccinated wild-type mice produced significantly higher amounts of IL-2, gamma interferon (IFN-γ), IL-4, IL-6, and IL-17A in the presence of a coccidioidal antigen, indicating that IL-10 suppresses Th1, Th2, and Th17 immunity to Coccidioides infection. Analysis of absolute numbers of CD44(+) CD62L(-) CD4(+) T effector memory T cells (TEM) and IFN-γ- and IL-17A-producing CD4(+) T cells in the lungs of Coccidioides-infected mice correlated with better fungal clearance in nonvaccinated IL-10(-/-) mice than in nonvaccinated wild-type mice. Our results suggest that IL-10 suppresses CD4(+) T-cell immunity in nonvaccinated mice during Coccidioides infection but does not impede the development of a memory response nor exacerbate immunopathology of vaccinated mice over at least a 4-month period after the last immunization.

In pulmonary paracoccidioidomycosis IL-10 deficiency leads to increased immunity and regressive infection without enhancing tissue pathology

Background

Cellular immunity is the main defense mechanism in paracoccidioidomycosis (PCM), the most important systemic mycosis in Latin America. Th1 immunity and IFN-γ activated macrophages are fundamental to immunoprotection that is antagonized by IL-10, an anti-inflammatory cytokine. Both in human and experimental PCM, several evidences indicate that the suppressive effect of IL-10 causes detrimental effects to infected hosts. Because direct studies have not been performed, this study was aimed to characterize the function of IL-10 in pulmonary PCM.

Methodology/Principal Findings

Wild type (WT) and IL-10^−/− C57BL/6 mice were used to characterize the role of IL-10 in the innate and adaptive immunity against Paracoccidioides brasiliensis (Pb) infection. We verified that Pb-infected peritoneal macrophages from IL-10^−/− mice presented higher phagocytic and fungicidal activities than WT macrophages, and these activities were associated with elevated production of IFN-γ, TNF-α, nitric oxide (NO) and MCP-1. For in vivo studies, IL-10^−/− and WT mice were i.t. infected with 1×10⁶ Pb yeasts and studied at several post-infection periods. Compared to WT mice, IL-10^−/− mice showed increased resistance to P. brasiliensis infection as determined by the progressive control of pulmonary fungal loads and total clearance of fungal cells from dissemination organs. This behavior was accompanied by enhanced delayed-type hypersensitivity reactions, precocious humoral immunity and controlled tissue pathology resulting in increased survival times. In addition, IL-10^−/− mice developed precocious T cell immunity mediated by increased numbers of lung infiltrating effector/memory CD4⁺ and CD8⁺ T cells. The inflammatory reactions and the production of Th1/Th2/Th17 cytokines were reduced at late phases of infection, paralleling the regressive infection of IL-10^−/− mice.

Conclusions/Significance

Our work demonstrates for the first time that IL-10 plays a detrimental effect to pulmonary PCM due to its suppressive effect on the innate and adaptive immunity resulting in progressive infection and precocious mortality of infected hosts.

Paracoccidioidomycosis, the most important deep mycosis from Latin America, is acquired by inhalation of fungal spores. The pulmonary infection can remain as a quiescent infection or evolve to overt, life-threatening disease. Immunoprotection is mainly mediated by Th1 lymphocytes secreting IFN- γ, the most important macrophage activating cytokine. It is well established that the severe forms of infection are associated with elevated production of anti-inflammatory or suppressive cytokines such as IL-10. However, direct approaches investigating the role of this cytokine in pulmonary paracoccidioidomycosis were never employed. This led us to investigate the innate and adaptive aspects of immunity in pulmonary paracoccidioidomycosis using IL-10-deficient mice in comparison with their IL-10-normal counterparts. We verified that IL-10 absence leads to a regressive disease, resulting in reduced mortality rates of infected mice. This better disease outcome was associated with precocious and enhanced mechanisms of innate and adaptive immunity that allow the control of fungal growth without excessive inflammatory reactions and harmful tissue pathology. These evidences on the detrimental effects of IL-10 to pulmonary paracoccidioidomycosis suggest that therapeutic measures aimed to control IL-10 production or activity could exert a protective effect to this severe fungal pathology.

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.

Evaluation of the in vitro activity of voriconazole as predictive of in vivo outcome in a murine Aspergillus fumigatus infection model

We have evaluated the in vitro activity of voriconazole against 61 strains of Aspergillus fumigatus by using broth microdilution, disk diffusion, and minimal fungicidal concentration procedures. We observed an excellent correlation between the results obtained with the three methods. Five percent of the strains showed MICs greater than or equal to the epidemiological cutoff value (ECV; 1 μg/ml). To assess whether MICs were predictive of in vivo outcome, we tested the efficacy of voriconazole at 25 mg/kg of body weight daily in an immunosuppressed murine model of disseminated infection using 10 strains representing various patterns of susceptibility to the drug as determined by the in vitro study. Voriconazole prolonged survival and reduced fungal load in the kidneys and brain in those mice infected with strains with MICs of ≤0.25 μg/ml, while in mice infected with strains with MICs of 0.5 to 2 μg/ml, the efficacy was varied and strain dependent and in mice infected with the strain with a MIC of 4 μg/ml, the antifungal did not show efficacy. Voriconazole reduced galactomannan antigenemia against practically all strains with a MIC of <4 μg/ml. Our results demonstrate that some relationship exists between voriconazole MICs and in vivo efficacy; however, further studies testing additional strains are needed to better ascertain which MIC values can predict clinical outcome.

Host immune defense against Aspergillus fumigatus: insight from experimental systemic (disseminated) infection

Model of systemic Aspergillus fumigatus infection induced by intravenous application of conidia is suitable for studying important aspects of invasive aspergillosis including relationship between infection and mortality, dissemination of infection and immune mechanisms involved in host resistance to this fungus. Use of this model allows the investigation of both innate and adaptive immune response characteristics in resistant/susceptible host, and investigating the contribution of genetic background and cytokine gene deficiency improves the knowledge of the diversity of mechanisms of immune response to Aspergillus infection. Studying of various aspects of systemic aspergillosis contributes to development of antifungal drugs.

Differential strain-related tissue immune response to sublethal systemic Aspergillus fumigatus infection in mice

Using a nonlethal systemic Aspergillus fumigatus infection, we have recently shown that similarly efficient elimination of fungus from spleens of prototypic Th1 (C57BL/6) and prototypic Th2 (BALB/c) mice is associated with differential immune responses. In light of these data and given the disseminated character of infection, the aim of the present study is to explore whether there are also strain-dependent differences in antifungal responses in peripheral tissues of infected mice. Although similar efficiency of conidia removal was noted in liver and kidneys of both strains, BALB/c mice seemed more prone to tissue injury. Compared with other nonlymphoid organs, lungs proved immunologically the most responsive in systemic aspergillosis. Lower numbers of neutrophils and macrophages in the lungs of infected BALB/c mice, delayed and lower (compared with C57BL/6 mice) expression of their oxidative activity, along with late IFN-γ and upregulated IL-4 production by lung cells might be responsible for slower elimination of A. fumigatus from the lungs of this mouse strain. The data obtained imply that lungs should be viewed as mandatory organ in evaluation of immune-mediated antifungal potential of drugs in models of systemic/disseminated infection and that strain differences noted in tissue responses should be taken into account in these settings.

Murine infection models for Aspergillus terreus pulmonary aspergillosis reveal long-term persistence of conidia and liver degeneration

Aspergillus terreus is emerging as a causative agent of life-threatening invasive aspergillosis. Prognosis for affected patients is often worse than for A. fumigatus infections. To study A. terreus-mediated disease, we developed 3 infection models. In embryonated hen's eggs and leucopenic mice, the outcome of invasive aspergillosis was similar to that described for A. fumigatus. However, 10(2)- and 10(3)-fold higher conidia concentrations were required for 100% lethality. In corticosteroid-treated mice, only 50% mortality was observed, although bioluminescence imaging revealed transient disease in all infected animals. In surviving animals, we observed persistence of ungerminated but viable conidia. Cytokine levels in these mice were comparable to uninfected controls. In contrast to A. fumigatus infections, all mice infected with A. terreus developed fatty liver degeneration, suggesting the production of toxic secondary metabolites. Thus, at least in mice, persistence and subclinical liver damage are unique features of A. terreus infections.

Vaccination with mannan protects mice against systemic aspergillosis

Invasive aspergillosis is a major cause of mortality in immunocompromised patients and therapeutic options are often limited, thus a vaccine would be desirable. We presently studied acid-stable cell-wall mannan (α-1, 6-linked backbone highly branched with α-1, 2; α-1, 3; and β-1, 2-linked manno-oligomers) derived from C. albicans, with or without conjugation to bovine serum albumin (BSA), as a vaccine against systemic aspergillosis. Mice were vaccinated subcutaneously with mannan or mannan-BSA conjugate weekly 3 times, ending 2 weeks prior to infection with A. fumigatus conidia. Results showed that the protection induced by mannan is dose-dependent; 12 mg unconjugated mannan alone or > 0.3 mg mannan-BSA consistently enhanced survival (P < 0.05). Fungal burdens in brains and kidneys were reduced after > 0.3 mg of mannan-BSA (all P < 0.05). Mannan-induced protection was improved about 40-fold by conjugation of BSA to mannan. Mannan-BSA (500 kDa) was more protective than 40 kDa mannan-BSA. Mannan is a candidate for a cross-protective conjugate fungal vaccine.

Repeated exposure to Aspergillus fumigatus conidia results in CD4+ T cell-dependent and -independent pulmonary arterial remodeling in a mixed Th1/Th2/Th17 microenvironment that requires interleukin-4 (IL-4) and IL-10

Pulmonary arterial remodeling is a pathological process seen in a number of clinical disease states, driven by inflammatory cells and mediators in the remodeled artery microenvironment. In murine models, Th2 cell-mediated immune responses to inhaled antigens, such as purified Aspergillus allergen, have been reported to induce remodeling of pulmonary arteries. We have previously shown that repeated intranasal exposure of healthy C57BL/6 mice to viable, resting Aspergillus fumigatus conidia leads to the development of chronic pulmonary inflammation and the coevolution of Th1, Th2, and Th17 responses in the lungs. Our objective was to determine whether repeated intranasal exposure to Aspergillus conidia would induce pulmonary arterial remodeling in this mixed Th inflammatory microenvironment. Using weekly intranasal conidial challenges, mice developed robust pulmonary arterial remodeling after eight exposures (but not after two or four). The process was partially mediated by CD4+ T cells and by interleukin-4 (IL-4) production, did not require eosinophils, and was independent of gamma interferon (IFN-γ) and IL-17. Furthermore, remodeling could occur even in the presence of strong Th1 and Th17 responses. Rather than serving an anti-inflammatory function, IL-10 was required for the development of the Th2 response to A. fumigatus conidia. However, in contrast to previous studies of pulmonary arterial remodeling driven by the A. fumigatus allergen, viable conidia also stimulated pulmonary arterial remodeling in the absence of CD4+ T cells. Remodeling was completely abrogated in IL-10-/- mice, suggesting that a second, CD4+ T cell-independent, IL-10-dependent pathway was also driving pulmonary arterial remodeling in response to repeated conidial exposure.

Triggering receptor expressed on myeloid cells-1 (TREM-1) modulates immune responses to Aspergillus fumigatus during fungal asthma in mice

Triggering receptor expressed on myeloid cells-1 (TREM-1) expression is increased during pulmonary fungal infection suggesting that this receptor might be involved in anti-fungal immune responses. To address the role of TREM-1 in a murine model of fungal allergic airway disease, A. fumigatus-sensitized CBA/J mice received by intratracheal injection a mixture of live A. fumigatus conidia and one of a control adenovirus vector (Ad70), an adenovirus containing a gene encoding for the extracellular domain of mouse TREM-1 and the F(c) portion of human IgG (AdTREM-1Ig; a soluble inhibitor of TREM-1 function), or an adenovirus containing mouse DAP12 (AdDAP12; DAP12 is an intracellular adaptor protein required for TREM-1 signaling), and examined at various days after challenge. Whole lung TREM-1 levels peaked at day 3 whereas circulating TREM-1 levels peaked at day 30 in this fungal asthma model. AdTREM-1Ig-treated mice exhibited significantly higher airway hyperresponsiveness following methacholine challenge compared with Ad70- and AdDAP12-treated mice. Whole lung analysis of AdTREM-1Ig treated mice revealed markedly higher amounts of fungal material compared with the other groups. ELISA analysis of whole lung and bronchoalveolar lavage samples indicated that several pro-allergic cytokine and chemokines including CCL17 and CCL22 were significantly increased in the AdTREM-1Ig group compared with the other groups. Finally, Pam3Cys and soluble Aspergillus antigens induced TREM-1 transcript expression in macrophages in a TLR2 dependent manner. In conclusion, TREM-1 modulates the immune response directed against A. fumigatus during experimental fungal asthma.

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.

A role for macrophage migration inhibitory factor in protective immunity against Aspergillus fumigatus

Inflammation plays an important role in protective immunity against fungi, including the opportunistic pathogen, Aspergillus fumigatus. The balance between pro-inflammatory and anti-inflammatory cytokines is a key determinant of infection outcome. Since macrophage migration inhibitory factor (MIF) is an upstream regulator of many cytokines, we analyzed herein the role of endogenous MIF in the host control of hematogenously disseminated aspergillosis using MIF⁻/⁻ mice. As revealed by their mortality rate, MIF⁻/⁻ mice were more susceptible to disseminated infection than WT mice. Moreover, pharmacologic inhibition of MIF with (S,R)-3-(4-hydroxyphenyl)-4,5-dihydro-5-isoxazole acetic acid methyl ester, (ISO-1) increased the susceptibility of WT mice to lethal infection. The higher tissue fungal burden early in sublethal infection indicated increased susceptibility of MIF⁻/⁻ mice to sublethal infection as well. Substantial down-regulation of innate and acquired antifungal responses, characterized by decreased production of IL-1β, IL-6, TNF-α, IFN-γ and IL-17 in the spleen was noted in sublethally infected MIF⁻/⁻ mice. In contrast, IL-4 was higher in MIF⁻/⁻ than in WT mice. Taken together, our findings show that MIF contributes to host resistance against progressive invasive A. fumigatus infection by controlling downstream pro-inflammatory versus anti-inflammatory cytokine production thus determining the outcome of infection.

Differential transcriptional profiles induced by amphotericin B formulations on human monocytes during response to hyphae of Aspergillus fumigatus

Amphotericin B formulations possess diverse immunomodulatory properties that may contribute to the activity of phagocytes against invasive aspergillosis. In this work we provide a novel set of data on different gene transcriptional profiles of monocytes exposed to the combination of Aspergillus fumigatus and amphotericin B formulations. We used pathway-specific microarray analysis, RT-PCR analysis and enzyme-linked immunosorbent assays to compare the effects of amphotericin B deoxycholate (DAMB) at 1 μg/ml and amphotericin B lipid complex (ABLC) at 5 μg/ml to assess gene expression of immune molecules of THP-1 cells exposed to A. fumigatus hyphae (AF) for 4 h. A. fumigatus hyphae at effector/target ratio 10/1 induced mostly chemotactic factors for monocyte recruitment. DAMB at 1 μg/ml in the presence or absence of AF induced the most pronounced changes in pro-inflammatory and chemokine gene expression, while ABLC under the same conditions caused less dramatic effect. There was a reciprocal response of increased expression of the genes encoding IL-1β and IL-20 and decreased expression of IL-10, IL-2 and IL-3 in response of monocytes to both the hyphae and antifungal agents. These results demonstrate that amphotericin B formulations exert differential effects on genes encoding pro-inflammatory molecules, immunoregulatory molecules and chemokines by human monocytes during response to A. fumigatus and that these molecules may affect antifungal activity.

Differential mechanisms of resistance to sublethal systemic Aspergillus fumigatus infection in immunocompetent BALB/c and C57BL/6 mice

Studies of systemic and pulmonary Aspergillus fumigatus infection demonstrated differential susceptibility of inbred mice of various genetic background to lethal outcome, with an opposite pattern of Th1 cytokine interferon-γ (IFN-γ) and Th2 cytokine interleukin-4 (IL-4) in susceptible vs resistant mice. We have shown recently reciprocal IFN-γ and IL-4 expression in spleens of Th1-prone C57BL/6 mice in sublethal systemic aspergillosis. In this study, resistance to systemic (i.v.) A. fumigatus infection was investigated in Th2-prone BALB/c mice by survival rate at different fungal inocula, efficiency of reduction of visceral organ and spleen fungal burden at sublethal conidia dose and splenic immune response to this dose and compared to C57BL/6 mice. No strain differences in survival were noted at three A. fumigatus doses, with similar extent and dynamics of fungal eradication from all organs following sublethal conidia dose injection. Progressive decrease in spleen fungal burden was associated with different dynamics and quality of changes in spleen activity of BALB/c and C57BL/6 mice. Increased spleen mass and cellularity was noted in both strains, with higher values in BALB/c mice at some time points what might be ascribed to peripheral blood cell recruitment, as well as hematopoietic activity and red pulp upgrowth. Infection tipped the balance towards pro-inflammatory antifungal splenic response by a highly increasing IFN-γ and without changing the IL-4 expression in BALB/c mice, in contrast to down-regulating anti-inflammatory (IL-4) and a moderately increasing IFN-γ response in C57BL/6 mice. Jointly, stimulation of IL-17 expression noted in both strains provided an optimal inflammatory milieu in the spleen of infected mice that might have contributed to efficient removal of conidia.

Susceptibility of mice genetically deficient in SP-A or SP-D gene to invasive pulmonary aspergillosis

Pulmonary surfactant proteins, SP-A and SP-D, are carbohydrate pattern recognition molecules of innate immunity, which significantly enhance phagocytosis and killing of Aspergillus fumigatus, a pathogenic fungus, by neutrophils and macrophages. The present study examined the susceptibility of immunosuppressed SP-A gene deficient (SP-A(-/-)) or SP-D gene deficient (SP-D(-/-)) mice to A. fumigatus conidia challenge compared to wild-type (WT) mice. A. fumigatus-challenged SP-A(-/-) (SP-A(-/-) IPA) mice showed less mortality (40%) than the WT-IPA mice (100%) and increased mortality (60%) following administration of SP-A with decreased TNF-alpha and IFN-gamma to IL-4 ratio than SP-A(-/-) IPA mice. The SP-D(-/-) IPA mice (57.14%) showed similar mortality as WT-IPA mice (60%). However, the SP-D (-/-) IPA mice (42.86% mortality on day 2) died earlier than the WT-IPA mice (20% mortality on day 2), showed a higher hyphal density and tissue injury in lungs. Treatment with SP-D or a recombinant fragment of human SP-D rhSP-D reduced the mortality to 50% and 33%, respectively, concomitant with higher IFN-gamma to IL-4 ratios in treated SP-D(-/-) mice, compared to untreated control group. The results showed that SP-D gene deficient mice are more susceptible to IPA while SP-A gene deficient mice acquire resistance to IPA.

Interleukin-10 but not Transforming Growth Factor beta inhibits murine activated macrophages Paracoccidioides brasiliensis killing: effect on H2O2 and NO production

Paracoccidioidomycosis is caused by the thermally dimorphic fungus Paracoccidioides brasiliensis (P. brasiliensis). Most often, this mycosis runs as a chronic progressive course affecting preferentially the lungs. In vitro fungicidal activity against a high virulent strain of P. brasiliensis by murine peritoneal macrophages preactivated with IFN-gamma or TNF-alpha is high and correlates with increased NO and H2O2 production. Within this context, the purpose of this work was to study the role of suppressor cytokines, such as IL-10 and TGF-beta, in this process. Incubation of either IFN-gamma or TNF-alpha with IL-10 inhibits fungicidal activity of these cells. However, TGF-beta had no effect on fungicidal activity of IFN-gamma or TNF-alpha-activated macrophages. The suppression of fungicidal activity by IL-10 correlated with the inhibition of NO and H2O2 production supporting the involvement of these metabolites in P. brasiliensis killing. These results suggest that IL-10 production in vivo could represent an evasion mechanism of the fungus to avoid host immune response.

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.

Resistance of MBL gene-knockout mice to experimental systemic aspergillosis

Mannose binding lectin (MBL) is a protein of the collectin family that appears important in resistance to invasive pulmonary aspergillosis. We assessed the role of MBL in experimental systemic aspergillosis. MBL-sufficient C57BL/6 (WT) mice and B6.129S4--Mb11(tm1Kata) Mb12(tm1Kata)/J MBL A and C gene-knockout (KO) mice were infected intravenously with different inocula of Aspergillus fumigatus conidia. WT and KO mice were dose-responsively susceptible. In no instance were the KO mice more susceptible than WT. At the highest inoculum, all WT and 90% of KO mice died on day 4 (P>0.05). Reduction of the inoculum to 5.5 x 10(6) conidia was lethal, but comparison showed KO mice less susceptible to lethal infection (P<0.015). At the lowest inoculum used, deaths of KO mice were delayed, but survival was not significantly different than WT (P>0.05). These results suggest MBL may play a deleterious role in systemic aspergillosis.

Aberrant tissue localization of fungus-specific CD4+ T cells in IL-10-deficient mice

Aspergillus fumigatus, a common environmental fungus, can cause lethal invasive infections in immunocompromised hosts. In immunocompetent individuals, however, inhaled A. fumigatus spores prime CD4(+) T cells and activate immune responses that prevent invasive infection. Calibration of inflammatory responses to levels that prevent fungal invasion without inducing collateral tissue damage is essential for host survival, but the underlying regulatory mechanisms remain undefined. Although IL-10 is a validated regulatory cytokine that suppresses immune responses, and IL-10 deficiency or blockade generally enhances immune responses, we find that A. fumigatus-specific T cell frequencies are markedly reduced in airways of IL-10-deficient mice. T cell priming, proliferation, and survival were unaffected by IL-10 deficiency and did not account for decreased frequencies of A. fumigatus-specific T cells in the airways of IL-10-deficient mice. Instead, IL-10 deficiency results in redistribution of A. fumigatus-specific T cells from infected lungs to the gut, a process that is reversed by antibiotic-mediated depletion of intestinal microbes. Our studies demonstrate that disregulated immune responses in the gut can result in dramatic redistribution of pathogen-specific T cells within the host.