Aspergillus fumigatus antigens activate innate immune cells via toll-like receptors 2 and 4

Natural Killer Cells and Cytotoxic T Cells: Complementary Partners against Microorganisms and Cancer

Natural killer (NK) cells and cytotoxic T (CD8+) cells are two of the most important types of immune cells in our body, protecting it from deadly invaders. While the NK cell is part of the innate immune system, the CD8+ cell is one of the major components of adaptive immunity. Still, these two very different types of cells share the most important function of destroying pathogen-infected and tumorous cells by releasing cytotoxic granules that promote proteolytic cleavage of harmful cells, leading to apoptosis. In this review, we look not only at NK and CD8+ T cells but also pay particular attention to their different subpopulations, the immune defenders that include the CD56+CD16dim, CD56dimCD16+, CD57+, and CD57+CD16+ NK cells, the NKT, CD57+CD8+, and KIR+CD8+ T cells, and ILCs. We examine all these cells in relation to their role in the protection of the body against different microorganisms and cancer, with an emphasis on their mechanisms and their clinical importance. Overall, close collaboration between NK cells and CD8+ T cells may play an important role in immune function and disease pathogenesis. The knowledge of how these immune cells interact in defending the body against pathogens and cancers may help us find ways to optimize their defensive and healing capabilities with methods that can be clinically applied.

Pathogenicity and virulence of Aspergillus fumigatus

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

Role of toll-like receptors and nod-like receptors in acute lung infection

The respiratory system exposed to microorganisms continuously, and the pathogenicity of these microbes not only contingent on their virulence factors, but also the host's immunity. A multifaceted innate immune mechanism exists in the respiratory tract to cope with microbial infections and to decrease tissue damage. The key cell types of the innate immune response are macrophages, neutrophils, dendritic cells, epithelial cells, and endothelial cells. Both the myeloid and structural cells of the respiratory system sense invading microorganisms through binding or activation of pathogen-associated molecular patterns (PAMPs) to pattern recognition receptors (PRRs), including Toll-like receptors (TLRs) and NOD-like receptors (NLRs). The recognition of microbes and subsequent activation of PRRs triggers a signaling cascade that leads to the activation of transcription factors, induction of cytokines/5chemokines, upregulation of cell adhesion molecules, recruitment of immune cells, and subsequent microbe clearance. Since numerous microbes resist antimicrobial agents and escape innate immune defenses, in the future, a comprehensive strategy consisting of newer vaccines and novel antimicrobials will be required to control microbial infections. This review summarizes key findings in the area of innate immune defense in response to acute microbial infections in the lung. Understanding the innate immune mechanisms is critical to design host-targeted immunotherapies to mitigate excessive inflammation while controlling microbial burden in tissues following lung infection.

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

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

Stimulation of surfactant exocytosis in primary alveolar type II cells by A. fumigatus

Aspergillus fumigatus is an opportunistic fungal pathogen with small airborne spores (conidia) that may escape clearance by upper airways and directly impact the alveolar epithelium. Consequently, innate alveolar defense mechanisms are being activated, including professional phagocytosis by alveolar macrophages, recruitment of circulating neutrophils and probably enhanced secretion of pulmonary surfactant by the alveolar type II (AT II) cells. However, no data are available in support of the latter hypothesis. We therefore used a coculture model of GFP-Aspergillus conidia with primary rat AT II cells and studied fungal growth, cellular Ca2+ homeostasis, and pulmonary surfactant exocytosis by live cell video microscopy. We observed all stages of fungal development, including reversible attachment, binding and internalization of conidia as well as conidial swelling, formation of germ tubes and outgrowth of hyphae. In contrast to resting conidia, which did not provoke immediate cellular effects, metabolically active conidia, fungal cellular extracts (CE) and fungal culture filtrates (CF) prepared from swollen conidia caused a Ca2+-independent exocytosis. Ca2+ signals of greatly varying delays, durations and amplitudes were observed by applying CE or CF obtained from hyphae of A. fumigatus, suggesting compounds secreted by filamentous A. fumigatus that severely interfere with AT II cell Ca2+ homeostasis. The mechanisms underlying the stimulatory effects, with respect to exocytosis and Ca2+ signaling, are unclear and need to be identified.

Rapidly expanded partially HLA DRB1-matched fungus-specific T cells mediate in vitro and in vivo antifungal activity

Invasive fungal infections are a major cause of disease and death in immunocompromised hosts, including patients undergoing allogeneic hematopoietic stem cell transplant (HSCT). Recovery of adaptive immunity after HSCT correlates strongly with recovery from fungal infection. Using initial selection of lymphocytes expressing the activation marker CD137 after fungal stimulation, we rapidly expanded a population of mainly CD4+ T cells with potent antifungal characteristics, including production of tumor necrosis factor α, interferon γ, interleukin-17, and granulocyte-macrophage colony stimulating factor. Cells were manufactured using a fully good manufacturing practice-compliant process. In vitro, the T cells responded to fungal antigens presented on fully and partially HLA-DRB1 antigen-matched presenting cells, including when the single common DRB1 antigen was allelically mismatched. Administration of antifungal T cells lead to reduction in the severity of pulmonary and cerebral infection in an experimental mouse model of Aspergillus. These data support the establishment of a bank of cryopreserved fungus-specific T cells using normal donors with common HLA DRB1 molecules and testing of partially HLA-matched third-party donor fungus-specific T cells as a potential therapeutic in patients with invasive fungal infection after HSCT.

The sino-nasal warzone: transcriptomic and genomic studies on sino-nasal aspergillosis in dogs

We previously showed that each dog with chronic non-invasive sino-nasal aspergillosis (SNA) was infected with a single genotype of Aspergillus fumigatus. Here, we studied the transcriptome of this fungal pathogen and the canine host within the biofilm resulting from the infection. We describe here transcriptomes resulting from natural infections in animal species with A. fumigatus. The host transcriptome showed high expression of IL-8 and alarmins, uncontrolled inflammatory reaction and dysregulation of the Th17 response. The fungal transcriptome showed in particular expression of genes involved in secondary metabolites and nutrient acquisition. Single-nucleotide polymorphism analysis of fungal isolates from the biofilms showed large genetic variability and changes related with adaptation to host environmental factors. This was accompanied with large phenotypic variability in in vitro stress assays, even between isolates from the same canine patient. Our analysis provides insights in genetic and phenotypic variability of Aspergillus fumigatus in biofilms of naturally infected dogs reflecting in-host adaptation. Absence of a Th17 response and dampening of the Th1 response contributes to the formation of a chronic sino-nasal warzone.

Triple RNA-Seq Reveals Synergy in a Human Virus-Fungus Co-infection Model

High-throughput RNA sequencing (RNA-seq) is routinely applied to study diverse biological processes; however, when performed separately on interacting organisms, systemic noise intrinsic to RNA extraction, library preparation, and sequencing hampers the identification of cross-species interaction nodes. Here, we develop triple RNA-seq to simultaneously detect transcriptomes of monocyte-derived dendritic cells (moDCs) infected with the frequently co-occurring pulmonary pathogens Aspergillus fumigatus and human cytomegalovirus (CMV). Comparing expression patterns after co-infection with those after single infections, our data reveal synergistic effects and mutual interferences between host responses to the two pathogens. For example, CMV attenuates the fungus-mediated activation of pro-inflammatory cytokines through NF-κB (nuclear factor κB) and NFAT (nuclear factor of activated T cells) cascades, while A. fumigatus impairs viral clearance by counteracting viral nucleic acid-induced activation of type I interferon signaling. Together, the analytical power of triple RNA-seq proposes molecular hubs in the differential moDC response to fungal/viral single infection or co-infection that contribute to our understanding of the etiology and, potentially, clearance of post-transplant infections.

Interactions between immune response to fungal infection and microRNAs: The pioneer tuners

Due to their physiological and biological characteristics, numerous fungi are potentially emerging pathogens. Active dynamicity of fungal pathogens causes life-threatening infections annually impose high costs to the health systems. Although immune responses play crucial roles in controlling the fate of fungal infections, immunocompromised patients are at high risk with high mortality. Tuning the immune response against fungal infections might be an effective strategy for controlling and reducing the pathological damages. MicroRNAs (miRNAs) are known as the master regulators of immune response. These single-stranded tuners (18-23 bp non-coding RNAs) are endogenously expressed by all metazoan eukaryotes and have emerged as the master gene expression controllers of at least 30% human genes. In this review article, following the review of biology and physiology (biogenesis and mechanism of actions) of miRNAs and immune response against fungal infections, the interactions between them were scrutinised. In conclusion, miRNAs might be considered as one of the potential goals in immunotherapy for fungal infections. Undoubtedly, advanced studies in this field, further identifying of miRNA roles in governing the immune response, pave the way for inclusion of miRNA-related immunotherapeutic in the treatment of life-threatening fungal infections.

Microbial killing by NK cells

It is now evident that NK cells kill bacteria, fungi, and parasites in addition to tumor and virus-infected cells. In addition to a number of recent publications that have identified the receptors and ligands, and mechanisms of cytotoxicity, new insights are reflected in the reports from researchers all over the world at the 17th Meeting of the Society for Natural Immunity held in San Antonio, TX, USA from May 28 through June 1, 2018. We will provide an overview of the field and discuss how the presentations at the meeting might shape our knowledge and future directions in the field.

TLR3 Is a Negative Regulator of Immune Responses Against Paracoccidioides brasiliensis

Toll-like receptors (TLRs) comprise the best-characterized pattern-recognition receptor (PRR) family able to activate distinct immune responses depending on the receptor/adaptor set assembled. TLRs, such as TLR2, TLR4 and TLR9, and their signaling were shown to be important in Paracoccidioides brasiliensis infections. However, the role of the endosomal TLR3 in experimental paracoccidioidomycosys remains obscure. In vitro assays, macrophages of the bone marrow of WT or TLR3^−/− mice were differentiated for evaluation of their microbicidal activity. In vivo assays, WT or TLR3^−/− mice were infected intratracheally with Paracoccidioides brasiliensis yeasts for investigation of the lung response type induced. The cytotoxic activity of CD8⁺ T cells was assessed by cytotoxicity assay. To confirm the importance of CD8⁺ T cells in the control of infection in the absence of tlr3, a depletion assay of these cells was performed. Here, we show for the first time that TLR3 modulate the infection against Paracoccidioides brasiliensis by dampening pro-inflammatory response, NO production, IFN⁺CD8⁺T, and IL-17⁺CD8⁺T cell activation and cytotoxic function, associated with granzyme B and perforin down regulation. As conclusion, we suggest that TLR3 could be used as an escape mechanism of the fungus in an experimental paracoccidioidomycosis.

Defects in intracellular trafficking of fungal cell wall synthases lead to aberrant host immune recognition

The human fungal pathogen, Cryptococcus neoformans, dramatically alters its cell wall, both in size and composition, upon entering the host. This cell wall remodeling is essential for host immune avoidance by this pathogen. In a genetic screen for mutants with changes in their cell wall, we identified a novel protein, Mar1, that controls cell wall organization and immune evasion. Through phenotypic studies of a loss-of-function strain, we have demonstrated that the mar1Δ mutant has an aberrant cell surface and a defect in polysaccharide capsule attachment, resulting in attenuated virulence. Furthermore, the mar1Δ mutant displays increased staining for exposed cell wall chitin and chitosan when the cells are grown in host-like tissue culture conditions. However, HPLC analysis of whole cell walls and RT-PCR analysis of cell wall synthase genes demonstrated that this increased chitin exposure is likely due to decreased levels of glucans and mannans in the outer cell wall layers. We observed that the Mar1 protein differentially localizes to cellular membranes in a condition dependent manner, and we have further shown that the mar1Δ mutant displays defects in intracellular trafficking, resulting in a mislocalization of the β-glucan synthase catalytic subunit, Fks1. These cell surface changes influence the host-pathogen interaction, resulting in increased macrophage activation to microbial challenge in vitro. We established that several host innate immune signaling proteins are required for the observed macrophage activation, including the Card9 and MyD88 adaptor proteins, as well as the Dectin-1 and TLR2 pattern recognition receptors. These studies explore novel mechanisms by which a microbial pathogen regulates its cell surface in response to the host, as well as how dysregulation of this adaptive response leads to defective immune avoidance.

Prospects for adoptive T-cell therapy for invasive fungal disease

PURPOSE OF REVIEW

Invasive fungal disease (IFD) is a cause of morbidity and mortality in allogeneic hematopoietic stem cell transplant (HSCT) recipients. As more potent broad-spectrum antifungal agents are used in prophylaxis, drug resistance and less common fungal species have increased in frequency. Here we review current treatments available for IFD and examine the potential for adoptive T-cell treatment to enhance current therapeutic choices in IFD.

RECENT FINDINGS

There is growing evidence supporting the role of T cells as well as phagocytes in antifungal immunity. T cells recognizing specific antigens expressed on fungal morphotypes have been identified and the role of T-cell transfer has been explored in animal models. The clinical efficacy of adoptive transfer of antigen-specific T cells for prophylaxis and treatment of viral infections post-HSCT has raised interest in developing good manufacturing practice (GMP)-compliant methods for manufacturing and testing fungus-specific T cells after HSCT.

SUMMARY

As the outcomes of IFD post-HSCT are poor, reconstitution of antifungal immunity offers a way to correct the underlying deficiency that has caused the infection rather than simply pharmacologically suppress fungal growth. The clinical development of fungus specific T cells is in its early stages and clinical trials are needed in order to evaluate safety and efficacy.

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.

Human and Murine Innate Immune Cell Populations Display Common and Distinct Response Patterns during Their In Vitro Interaction with the Pathogenic Mold Aspergillus fumigatus

Aspergillus fumigatus is the main cause of invasive fungal infections occurring almost exclusively in immunocompromised patients. An improved understanding of the initial innate immune response is key to the development of better diagnostic tools and new treatment options. Mice are commonly used to study immune defense mechanisms during the infection of the mammalian host with A. fumigatus. However, little is known about functional differences between the human and murine immune response against this fungal pathogen. Thus, we performed a comparative functional analysis of human and murine dendritic cells (DCs), macrophages, and polymorphonuclear cells (PMNs) using standardized and reproducible working conditions, laboratory protocols, and readout assays. A. fumigatus did not provoke identical responses in murine and human immune cells but rather initiated relatively specific responses. While human DCs showed a significantly stronger upregulation of their maturation markers and major histocompatibility complex molecules and phagocytosed A. fumigatus more efficiently compared to their murine counterparts, murine PMNs and macrophages exhibited a significantly stronger release of reactive oxygen species after exposure to A. fumigatus. For all studied cell types, human and murine samples differed in their cytokine response to conidia or germ tubes of A. fumigatus. Furthermore, Dectin-1 showed inverse expression patterns on human and murine DCs after fungal stimulation. These specific differences should be carefully considered and highlight potential limitations in the transferability of murine host–pathogen interaction studies.

Modulation of Immune Signaling and Metabolism Highlights Host and Fungal Transcriptional Responses in Mouse Models of Invasive Pulmonary Aspergillosis

Incidences of invasive pulmonary aspergillosis, an infection caused predominantly by Aspergillus fumigatus, have increased due to the growing number of immunocompromised individuals. While A. fumigatus is reliant upon deficiencies in the host to facilitate invasive disease, the distinct mechanisms that govern the host-pathogen interaction remain enigmatic, particularly in the context of distinct immune modulating therapies. To gain insights into these mechanisms, RNA-Seq technology was utilized to sequence RNA derived from lungs of 2 clinically relevant, but immunologically distinct murine models of IPA on days 2 and 3 post inoculation when infection is established and active disease present. Our findings identify notable differences in host gene expression between the chemotherapeutic and steroid models at the interface of immunity and metabolism. RT-qPCR verified model specific and nonspecific expression of 23 immune-associated genes. Deep sequencing facilitated identification of highly expressed fungal genes. We utilized sequence similarity and gene expression to categorize the A. fumigatus putative in vivo secretome. RT-qPCR suggests model specific gene expression for nine putative fungal secreted proteins. Our analysis identifies contrasting responses by the host and fungus from day 2 to 3 between the two models. These differences may help tailor the identification, development, and deployment of host- and/or fungal-targeted therapeutics.

Impact of human mesenchymal stromal cells on antifungal host response against Aspergillus fumigatus

Mesenchymal stromal cells (MSCs) are increasingly given as immunotherapy to hematopoietic stem cell transplant (HSCT) recipients with refractory graft-versus-host disease (GvHD). Whereas the immunosuppressive properties of MSCs seem to be beneficial in GvHD, there is, at the same time, major concern that MSCs increase the risk for infection. We therefore investigated the interplay of human MSCs with Aspergillus fumigatus and the impact of MSCs on different arms of the anti-Aspergillus host response in vitro. Although A. fumigatus hyphae increase mRNA levels of IL6 in MSCs, the extracellular availability of IL-6 and other pro-inflammatory cytokines remains unaffected. Human MSCs are able to phagocyte Aspergillus conidia, but phagocytosis of conidia is not associated with an alteration of the cytokine production by MSCs. In addition, human MSCs do not affect activation and function of A. fumigatus specific CD4+ T cells, and MSCs do not negatively impact the oxidative burst activity of phagocytes. Our in vitro data indicate that administration of human MSCs is not associated with a negative impact on the host response against A. fumigatus and that the fungus does not stimulate MSCs to increase the release of those cytokines which play a central role in the pathophysiology of GvHD.

Aspergillus fumigatus morphology and dynamic host interactions

Aspergillus fumigatus is an environmental filamentous fungus that can cause life-threatening disease in immunocompromised individuals. The interactions between A. fumigatus and the host environment are dynamic and complex. The host immune system needs to recognize the distinct morphological forms of A. fumigatus to control fungal growth and prevent tissue invasion, whereas the fungus requires nutrients and needs to adapt to the hostile environment by escaping immune recognition and counteracting host responses. Understanding these highly dynamic interactions is necessary to fully understand the pathogenesis of aspergillosis and to facilitate the design of new therapeutics to overcome the morbidity and mortality caused by A. fumigatus. In this Review, we describe how A. fumigatus adapts to environmental change, the mechanisms of host defence, and our current knowledge of the interplay between the host immune response and the fungus.

CD56 Is a Pathogen Recognition Receptor on Human Natural Killer Cells

Aspergillus (A.) fumigatus is an opportunistic fungal mold inducing invasive aspergillosis (IA) in immunocompromised patients. Although antifungal activity of human natural killer (NK) cells was shown in previous studies, the underlying cellular mechanisms and pathogen recognition receptors (PRRs) are still unknown. Using flow cytometry we were able to show that the fluorescence positivity of the surface receptor CD56 significantly decreased upon fungal contact. To visualize the interaction site of NK cells and A. fumigatus we used SEM, CLSM and dSTORM techniques, which clearly demonstrated that NK cells directly interact with A. fumigatus via CD56 and that CD56 is re-organized and accumulated at this interaction site time-dependently. The inhibition of the cytoskeleton showed that the receptor re-organization was an active process dependent on actin re-arrangements. Furthermore, we could show that CD56 plays a role in the fungus mediated NK cell activation, since blocking of CD56 surface receptor reduced fungal mediated NK cell activation and reduced cytokine secretion. These results confirmed the direct interaction of NK cells and A. fumigatus, leading to the conclusion that CD56 is a pathogen recognition receptor. These findings give new insights into the functional role of CD56 in the pathogen recognition during the innate immune response.

Effects of Aspergillus fumigatus on glucocorticoid receptor and β2-adrenergic receptor expression in a rat model of asthma

PURPOSE

Conventional inhaled corticosteroids or β2-adrenergic receptor agonists do not work well in some asthmatic populations while empirical antifungal therapy has obvious impact on those patients. The study was designed to investigate whether short-term exposure to Aspergillus fumigatus (A. fumigatus) could decrease glucocorticoid receptor (GCR) and β2-adrenergic receptor (ADRB2) expression in lung tissue of asthmatic rats.

MATERIALS AND METHODS

A rat model of chronic asthma was first established by ovalbumin sensitization and challenge. Rats with chronic asthma were then exposed to short-term application of A. fumigatus spores. Airway hyper-responsiveness, eosinophil ratio in bronchoalveolar lavage (BAL) fluid and total IgE in serum were counted in these experimental animals. GCR and ADRB2 expression in the lung were detected and analyzed. Furthermore, the levels of toll-like receptors (TLRs) 2, 3 and 4 in lung tissue were measured.

RESULTS

Short-term exposure to A. fumigatus could down-regulate the expression of GCR, aggravate airway hyper-responsiveness and increase the level of TLR2 in rats with asthma. There were no obvious changes in the levels of ADRB2 expression, recruited eosinophils, total IgE, TLR3 and TLR4 after application of A. fumigatus in asthmatic rats.

CONCLUSIONS

These findings indicate that A. fumigatus exposure may be involved in glucocorticoids unresponsiveness by down-regulating the expression of GCR in asthmatics. The possibility of A. fumigatus colonization or infection should not be ignored in patients of steroid-resistant asthma.

Impact of Mycotoxins Secreted by Aspergillus Molds on the Inflammatory Response of Human Corneal Epithelial Cells

Exposure to molds and mycotoxins not only contributes to the onset of respiratory disease, it also affects the ocular surface. Very few published studies concern the evaluation of the effect of mycotoxin exposure on ocular cells. The present study investigates the effects of aflatoxin B₁ (AFB₁) and gliotoxin, two mycotoxins secreted by Aspergillus molds, on the biological activity of the human corneal epithelial (HCE) cells. After 24, 48, and 72 h of exposure, cellular viability and inflammatory response were assessed. Both endpoint cell viability colorimetric assays and continuous cell impedance measurements, providing noninvasive real-time assessment of the effect on cells, were performed. Cytokine gene expression and interleukin-8 release were quantified. Gliotoxin appeared more cytotoxic than AFB₁ but, at the same time, led to a lower increase of the inflammatory response reflecting its immunosuppressive properties. Real-time cell impedance measurement showed a distinct profile of cytotoxicity for both mycotoxins. HCE cells appeared to be a well-suited in vitro model to study ocular surface reactivity following biological contaminant exposure. Low, but persistent inflammation, caused by environmental factors, such as fungal toxins, leads to irritation and sensitization, and could be responsible for allergic manifestations which, in turn, could lead to mucosal hyper-reactivity.

NK Cells and Their Role in Invasive Mold Infection

There is growing evidence that Natural Killer (NK) cells exhibit in vitro activity against both Aspergillus and non-Aspergillus molds. Cytotoxic molecules such as NK cell-derived perforin seem to play an important role in the antifungal activity. In addition, NK cells release a number of cytokines upon stimulation by fungi, which modulate both innate and adaptive host immune responses. Whereas the in vitro data of the antifungal activity of NK cells are supported by animal studies, clinical data are scarce to date.

PU.1 serves a critical role in the innate defense against Aspergillus fumigatus via dendritic cell-associated C-type lectin receptor-1 and toll-like receptors-2 and 4 in THP-1-derived macrophages

Aspergillus fumigatus (A. fumigatus) is one of the most common fungal pathogens of invasive pulmonary aspergillosis (IPA), which may be life threatening in immunocompromised individuals. The dendritic cell-associated C-type lectin receptor (Dectin-1), toll-like receptor (TLR)-2 and TLR-4 are major pattern recognition receptors in alveolar macrophages that recognize A. fumigatus components. The PU.1 transcription factor is known to be important for the transcriptional control of these three receptors in mature macrophages. The present study investigated whether alterations of PU.1 expression may affect the innate defense against A. fumigatus in the human monocyte THP-1 cell line. THP-1-derived macrophages were transduced with PU.1 adenoviral vectors and transfected with PU.1 small interfering RNA, and the mRNA and protein expression levels of Dectin-1, TLR-2 and TLR-4 were measured. In addition, the levels of tumor necrosis factor (TNF)-α and interleukin (IL)-1β were ascertained, and fungal phagocytosis and killing were assessed. The results demonstrated that overexpression of PU.1 by recombinant adenoviral vectors resulted in a significant upregulation of Dectin-1, TLR-2 and TLR-4 at the transcriptional and translational levels. In response to A. fumigatus stimulation, PU.1 overexpression increased TNF-α and IL-1β production. In addition, Dectin-1, TLR-2 and TLR-4 upregulation may have enhanced the phagocytosis and killing ability of THP-1-derived macrophages. As expected, silencing of PU.1 led to downregulation of Dectin-1, TLR-2, TLR-4 and the expression of pro-inflammatory cytokines, as well as decreased phagocytosis and the killing ability of THP1-derived macrophages. In conclusion, the results indicate that PU.1 may be a critical factor for the innate defense against A. fumigatus, and may therefore be a potential target for the prophylaxis and treatment of IPA.

The Role of Phagocytes and NETs in Dermatophytosis

Innate immunity is the host first line of defense against pathogens. However, only in recent years, we are beginning to better understand the ways it operates. A key player is this branch of the immune response that are the phagocytes, as macrophages, dendritic cells and neutrophils. These cells act as sentinels, employing specialized receptors in the sensing of invaders and host injury, and readily responding to them by production of inflammatory mediators. They afford protection not only by ingesting and destroying pathogens, but also by providing a suitable biochemical environment that shapes the adaptive response. In this review, we aim to present a broad perspective about the role of phagocytes in dermatophytosis, focusing on the mechanisms possibly involved in protective and non-protective responses. A full understanding of how phagocytes fit in the pathogenesis of these infections may open the venue for the development of new and more effective therapeutic approaches.

Current Concepts and Controversies in Innate Immunity of Cystic Fibrosis Lung Disease

Cystic fibrosis (CF) lung disease is characterized by chronic infection and inflammation. The inflammatory response in CF is dominated by the activation of the innate immune system. Bacteria and fungi represent the key pathogens chronically colonizing the CF airways. In response, innate immune pattern recognition receptors, expressed by airway epithelial and myeloid cells, sense the microbial threat and release chemoattractants to recruit large numbers of neutrophils into CF airways. However, neutrophils fail to efficiently clear the invading pathogens, but instead release harmful proteases and oxidants and finally cause tissue injury. Here, we summarize and discuss current concepts and controversies in the field of innate immunity in CF lung disease, facing the ongoing questions of whether inflammation is good or bad in CF and how innate immune mechanisms could be harnessed therapeutically.

Filamentous Fungi

Filamentous mycoses are often associated with significant morbidity and mortality. Prompt diagnosis and aggressive treatment are essential for good clinical outcomes in immunocompromised patients. The host immune response plays an essential role in determining the course of exposure to potential fungal pathogens. Depending on the effectiveness of immune response and the burden of organism exposure, fungi can either be cleared or infection can occur and progress to a potentially fatal invasive disease. Nonspecific cellular immunity (i.e., neutrophils, natural killer [NK] cells, and macrophages) combined with T-cell responses are the main immunologic mechanisms of protection. The most common potential mold pathogens include certain hyaline hyphomycetes, endemic fungi, the Mucorales , and some dematiaceous fungi. Laboratory diagnostics aimed at detecting and differentiating these organisms are crucial to helping clinicians make informed decisions about treatment. The purpose of this chapter is to provide an overview of the medically important fungal pathogens, as well as to discuss the patient characteristics, antifungal-therapy considerations, and laboratory tests used in current clinical practice for the immunocompromised host.

Genetic Susceptibility to Fungal Infections: What is in the Genes?

The development of severe fungal infections has long been associated with traditional risk factors such as profound immunosuppression, yet it remains challenging to understand why under similar conditions only some patients will develop these infections while others will not. Recent studies have demonstrated the importance of host genetic variation in influencing the severity and susceptibility to invasive fungal infections (IFIs). In this review, we examine selected primary immunodeficiencies characterized by their vulnerability to a narrow range of fungal pathogens, and then focus on recently identified genetic polymorphisms associated with an increased susceptibility to IFIs.

Adoptive T-cell therapy for fungal infections in haematology patients

The prolonged immune deficiency resulting from haematopoietic stem cell transplant and chemotherapy predisposes to a high risk of invasive fungal infections. Despite the recent advances in molecular diagnostic testing, early initiation of pre-emptive antifungal therapy and the use of combination pharmacotherapy, mortality from invasive mould infections remain high among recipients of allogeneic stem cell transplant. The increasing incidences of previously rare and drug-resistant strains of fungi present a further clinical challenge. Therefore, there is a need for novel strategies to combat fungal infections in the immunocompromised. Adoptive therapy using in vitro-expanded fungus-specific CD4 cells of the Th-1 type has shown clinical efficacy in murine studies and in a small human clinical study. Several techniques for the isolation and expansion of fungus-specific T cells have been successfully applied. Here we discuss the incidence and changing patterns of invasive fungal diseases, clinical evidence supporting the role of T cells in fungal immunity, methods to expand fungus-specific T cells in the laboratory and considerations surrounding the use of T cells for fungal immunotherapy.

Human Neutrophils Are Primed by Chemoattractant Gradients for Blocking the Growth of Aspergillus fumigatus

The contribution of human neutrophils to the protection against fungal infections by Aspergillus fumigatus is essential but not fully understood. Whereas healthy people can inhale spores of A. fumigatus without developing disease, neutropenic patients and those receiving immunosuppressive drugs have a higher incidence of invasive fungal infections. To study the role of neutrophils in protection against A. fumigatus infections, we developed an in vitro assay in which the interactions between human neutrophils and A. fumigatus were observed in real time, at single-cell resolution, in precisely controlled conditions. We measured the outcomes of neutrophil-fungus interactions and found that human neutrophils have a limited ability to migrate toward A. fumigatus and block the growth of A. fumigatus conidia (proportion with growth blocked, 69%). The blocking ability of human neutrophils increased to 85.1% when they were stimulated by uniform concentrations of fMLP and was enhanced further, to 99.4%, in the presence of chemoattractant gradients. Neutrophils from patients receiving immunosuppressive treatment after transplantation were less effective against the fungus than those from healthy donors, and broader heterogeneity exists between patients, compared with healthy individuals. Further studies using this microfluidic platform will help understand the relevance of innate immune deficiencies responsible for the higher risk of fungal infections in patients with immunosuppressive disease.

Dendritic cell interactions with Histoplasma and Paracoccidioides

Fungi are among the most common microbes encountered by humans. More than 100, 000 fungal species have been described in the environment to date, however only a few species cause disease in humans. Fungal infections are of particular importance to immunocompromised hosts in whom disease is often more severe, especially in those with impaired cell-mediated immunity such as individuals with HIV infection, hematologic malignancies, or those receiving TNF-α inhibitors. Nevertheless, environmental disturbances through natural processes or as a consequence of deforestation or construction can expose immunologically competent people to a large number of fungal spores resulting in asymptomatic acquisition to life-threatening disease. In recent decades, the significance of the innate immune system and more importantly the role of dendritic cells (DC) have been found to play a fundamental role in the resolution of fungal infections, such as in dimorphic fungi like Histoplasma and Paracoccidioides. In this review article the general role of DCs will be illustrated as the bridge between the innate and adaptive immune systems, as well as their specific interactions with these 2 dimorphic fungi.

The innate immune response to Aspergillus fumigatus at the alveolar surface

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

Trichophyton rubrum conidia modulate the expression and transport of Toll-like receptor 2 in HaCaT cell

Trichophyton rubrum (T. rubrum) represents the most important agent of dermatophytosis in humans. T. rubrum infection causes slight inflammation, and tends to be chronic and recurrent. It is suggested that T. rubrum can modulate the innate immune responses of host cells, which result in the failure of host cells to recognize T. rubrum and initiate effective immune responses. In this study we show how T. rubrum conidia modulate the expression and transport of Toll-like receptor 2 in HaCaT cell. Flow cytometric analysis showed that the surface and total expression of Toll-like receptor 2 were upregulated at the very early stage when keratinocytes were exposed to T. rubrum conidia regardless of the dose, and the upregulation of surface TLR2 was much more significant than that of total TLR2. Moreover, TLR2 expression was suppressed after upregulation in the initial stage of T. rubrum exposure, and the decrease of total TLR2 was earlier than that of surface TLR2. Our results suggest that in the early stage, TLR2 of keratinocytes were upregulated and transported to the cell surface. After then, the expression of TLR2 was suppressed by T. rubrum conidia.

Toll-like receptor polymorphisms in allogeneic hematopoietic cell transplantation

To assess the impact of the genetic variation in toll-like receptors (TLRs) on outcome after allogeneic myeloablative conditioning hematopoietic cell transplantation (HCT), we investigated 29 single nucleotide polymorphisms across 10 TLRs in 816 patients and donors. Only donor genotype of TLR8 rs3764879, which is located on the X chromosome, was significantly associated with outcome at the Bonferroni-corrected level P ≤ .001. Male hemizygosity and female homozygosity for the minor allele were significantly associated with disease-free survival (hazard ratio [HR], 1.47 [95% confidence interval {CI}, 1.16 to 1.85]; P = .001). Further analysis stratified by donor sex due to confounding by sex was suggestive for associations with overall survival (male donor: HR, 1.41 [95% CI, 1.09 to 1.83], P = .010; female donor: HR, 2.78 [95% CI, 1.43 to 5.41], P = .003), disease-free survival (male donor: HR, 1.45 [95% CI, 1.12 to 1.87], P = .005; female donor: HR, 2.34 [95% CI, 1.18 to 4.65], P = .015), and treatment-related mortality (male donor: HR, 1.49 [95% CI, 1.09 to 2.04], P = .012; female donor: HR, 3.12 [95% CI, 1.44 to 6.74], P = .004). In conclusion, our findings suggest that the minor allele of TLR8 rs3764879 of the donor is associated with outcome after myeloablative conditioned allogeneic HCT.

Interference of Aspergillus fumigatus with the immune response

Aspergillus fumigatus is a saprotrophic filamentous fungus and also the most prevalent airborne fungal pathogen of humans. Depending on the host’s immune status, the variety of diseases caused by A. fumigatus ranges from allergies in immunocompetent hosts to life-threatening invasive infections in patients with impaired immunity. In contrast to the majority of other Aspergillus species, which are in most cases nonpathogenic, A. fumigatus features an armory of virulence determinants to establish an infection. For example, A. fumigatus is able to evade the human complement system by binding or degrading complement regulators. Furthermore, the fungus interferes with lung epithelial cells, alveolar macrophages, and neutrophil granulocytes to prevent killing by these immune cells. This chapter summarizes the different strategies of A. fumigatus to manipulate the immune response. We also discuss the potential impact of recent advances in immunoproteomics to improve diagnosis and therapy of an A. fumigatus infection.

Human dendritic cell subsets display distinct interactions with the pathogenic mould Aspergillus fumigatus

The mould Aspergillus fumigatus is primarily an opportunistic pathogen of immunocompromised patients. Once fungal spores have been inhaled they encounter cells of the innate immune system, which include dendritic cells (DCs). DCs are the key antigen-presenting cells of the immune system and distinct subtypes, which differ in terms of origin, morphology and function. This study has systematically compared the interactions between A. fumigatus and myeloid DCs (mDCs), plasmacytoid DCs (pDCs) and monocyte-derived DCs (moDCs). Analyses were performed by time-lapse video microscopy, scanning electron microscopy, plating assays, flow cytometry, 25-plex ELISA and transwell assays. The three subsets of DCs displayed distinct responses to the fungus with mDCs and moDCs showing the greatest similarities. mDCs and moDCs both produced rough convolutions and occasionally phagocytic cups upon exposure to A. fumigatus whereas pDCs maintained a smooth appearance. Both mDCs and moDCs phagocytosed conidia and germ tubes, while pDCs did not phagocytose any fungi. Analysis of cytokine release and maturation markers revealed specific differences in pro- and anti-inflammatory patterns between the different DC subsets. These distinct characteristics between the DC subsets highlight their differences and suggest specific roles of moDCs, mDCs and pDCs during their interaction with A. fumigatus in vivo.

Assessment of Toll-like receptor 2, 4 and 9 SNP genotypes in canine sino-nasal aspergillosis

Background

The exact aetiology of canine sino-nasal aspergillosis (SNA) is unknown. In man, dysfunction in innate immunity, particularly in the function of pattern recognition receptors, is implicated in the pathogenesis of inflammatory sino-nasal disease and in fungal diseases. Associations between single nucleotide polymorphisms (SNPs) in Toll-like receptors (TLRs) and these diseases have been identified. Similarly, in dogs SNPs in genes encoding TLRs may be important in the pathogenesis of SNA. The aims of the present study were (1) to identify the presence of non-synonymous SNPs in the coding regions of the TLR2, 4 and 9 genes in dogs suffering from SNA, and (2) to investigate the SNP genotypes in dogs with SNA compared with a control population.

Results

Direct sequencing of nine dogs of various breeds with SNA revealed two non-synonymous SNPs in the coding region of TLR2, eight in TLR4 and four in TLR9. These non-synonymous SNPs were further evaluated in a case-control study of affected Golden Retrievers, Labrador Retrievers, Rottweilers and Beaucerons. Genotyping was performed using a combination of allele-specific primers and hydrolysis probe assays in 31 dogs with SNA and 31controls. No significant difference in minor allele frequency was identified between these groups, for all studied SNPs, in any of the four breeds.

Conclusions

These findings do not support a role for non-synonymous SNPs in the TLR 2, 4 and 9 coding regions in the pathogenesis of canine SNA, but do not exclude a role for innate immunity in the pathogenesis of the disease.

Neutrophil responses to aspergillosis: new roles for old players

Neutrophils are professional phagocytic cells that play a crucial role in innate immunity. Through an assortment of antifungal effector mechanisms, neutrophils are essential in controlling the early stages of fungal infection. These mechanisms range from the production of reactive oxygen intermediates and release of antimicrobial enzymes to the formation of complex extracellular traps that aid in the elimination of the fungus. Their importance in antifungal immunity is supported by the extreme susceptibility to infection of patients with primary (e.g., chronic granulomatous disease) or acquired (e.g., undergoing immunosuppressive therapy) neutrophil deficiency. More recently, common genetic variants affecting neutrophil antifungal capacity have also been disclosed as major risk factors for aspergillosis in conditions of generalized immune deficiency. The present review revisits the role of neutrophils in the host response against Aspergillus and highlights the consequences of their deficiency in susceptibility to aspergillosis.

Hyphal growth of phagocytosed Fusarium oxysporum causes cell lysis and death of murine macrophages

Fusarium oxysporum is an important plant pathogen and an opportunistic pathogen of humans. Here we investigated phagocytosis of F. oxysporum by J774.1 murine cell line macrophages using live cell video microscopy. Macrophages avidly migrated towards F. oxysporum germlings and were rapidly engulfed after cell-cell contact was established. F. oxysporum germlings continued hyphal growth after engulfment by macrophages, leading to associated macrophage lysis and escape. Macrophage killing depended on the multiplicity of infection. After engulfment, F. oxysporum inhibited macrophages from completing mitosis, resulting in large daughter cells fused together by means of a F. oxysporum hypha. These results shed new light on the initial stages of Fusarium infection and the innate immune response of the mammalian host.

Fever-range temperature modulates activation and function of human dendritic cells stimulated with the pathogenic mould Aspergillus fumigatus

In immunocompromised patients, invasive aspergillosis (IA) is the most frequent disease caused by the pathogenic mould Aspergillus fumigatus. Fever is one of the most common yet nonspecific clinical symptoms of IA. To evaluate the role of hyperthermia in the innate immune response to A. fumigatus in vitro, human monocyte-derived dendritic cells (DCs) were stimulated with germ tubes of A. fumigatus or the fungal cell wall component zymosan at 37°C or 40°C, followed by characterization of specific DC functions. While maturation of DCs was enhanced and DC phagocytic capacity was reduced at 40°C, we observed that DC viability and cytokine release were unaffected. Thus, our results suggest that hyperthermia has substantial impacts on DC function in vitro, which might also influence the course and outcome of IA in immunocompromised patients.

Immunosuppressive compounds exhibit particular effects on functional properties of human anti-Aspergillus Th1 cells

Allogeneic hematopoietic stem cell transplant (HSCT) recipients are at high risk for invasive aspergillosis. Whereas adoptive immunotherapy transferring donor-derived anti-Aspergillus TH1 cells has been shown to be beneficial for HSCT recipients suffering from invasive aspergillosis, little is known about the impact of commonly used immunosuppressants on the functional properties of anti-Aspergillus TH1 cells. Anti-Aspergillus TH1 cells were coincubated with different concentrations of methylprednisolone, cyclosporine (CsA), mycophenolic acid (MPA), the active component of mycophenolate mofetil, and rapamycin. Immunosuppressants were tested in concentrations reflecting common target levels in serum and in significantly lower and higher concentrations. Apoptosis of anti-Aspergillus TH1 cells, as well as proliferation and production of gamma interferon (IFN-γ) and CD154 upon restimulation, was evaluated in the presence and absence of immunosuppressive compounds. All dosages of CsA, MPA, and methylprednisolone significantly decreased the number of viable anti-Aspergillus TH1 cells in the cell culture, which was due partly to an impaired proliferative capacity of the cells and partly to an increased rate of apoptosis. In addition, CsA significantly decreased the number of IFN-γ-producing cells and had the highest impact of all immunosuppressants on IFN-γ levels in the supernatant. CsA also significantly decreased the expression of CD154 by anti-Aspergillus TH1 cells. Variant dosages of immunosuppressants exhibit particular effects on essential functional properties of anti-Aspergillus TH1 cells. Our findings may have an important impact on the design of clinical trials evaluating the therapeutic benefit of anti-Aspergillus TH1 cells in allogeneic HSCT recipients suffering from invasive aspergillosis.

Influence of TLR-2 in the immune response in the infection induced by fungus Sporothrix schenckii

Toll-like receptors (TLRs) play an important role in immunity, since they bind to pathogen surface antigens and initiate the immune response. However, little is known about the role of TLR-2 in the recognition of S. schenckii and in the subsequent immune response. Therefore, the aim of this study was to evaluate the involvement of TLR-2 in the immune response induced by S. schenckii. C57BL/6 mice (WT) and C57BL/6 TLR-2 knockout (TLR-2-/-) were used to evaluate, over a period of 10 weeks of sporotrichotic infection, the influence of TLR-2 over macrophages production of IL-1β, IL-12 and TNF-α, their stimulation level by NO release and the production of IFN -γ, IL-6, IL-17 and TGF-β by spleen cells. The results showed that the production of pro-inflammatory mediators and NO, TLR-2 interference is striking, since its absence completely inhibited it. IL-17 production was independent of TLR-2. The absence of Th1 response in TLR2-/- animals was concomitant with IL-17 production. Therefore, it can be suggested that TLR-2 absence interferes with the course of the infection induced by the fungus S. schenckii.

Activated mouse eosinophils protect against lethal respiratory virus infection

Eosinophils are recruited to the airways as a prominent feature of the asthmatic inflammatory response where they are broadly perceived as promoting pathophysiology. Respiratory virus infections exacerbate established asthma; however, the role of eosinophils and the nature of their interactions with respiratory viruses remain uncertain. To explore these questions, we established acute infection with the rodent pneumovirus, pneumonia virus of mice (PVM), in 3 distinct mouse models of Th2 cytokine-driven asthmatic inflammation. We found that eosinophils recruited to the airways of otherwise naïve mice in response to Aspergillus fumigatus, but not ovalbumin sensitization and challenge, are activated by and degranulate specifically in response to PVM infection. Furthermore, we demonstrate that activated eosinophils from both Aspergillus antigen and cytokine-driven asthma models are profoundly antiviral and promote survival in response to an otherwise lethal PVM infection. Thus, although activated eosinophils within a Th2-polarized inflammatory response may have pathophysiologic features, they are also efficient and effective mediators of antiviral host defense.

Gene Expression Profiling of Polymorphonuclear Leukocytes Treated with the Culture Filtrate ofAspergillus fumigatusand Gliotoxin

Pathogens of the Aspergillus species are frequently seen in deep-seated mycoses. We previously demonstrated that the culture filtrate of Aspergillus fumigatus (CF) has immunosuppressive effects on polymorphonuclear leukocytes (PMNs), which act as the main phagocytes to hyphae of Aspergillus fumigatus (A. fumigatus). But little is known about the gene expression profiles involved in it. Therefore we investigated the changes in gene expression in human PMNs treated with CF or gliotoxin at two time points, using microarray analysis. CF and gliotoxin changed the expression of 548 and 381 genes, respectively. Only 51 genes showed the same expression patterns with the two stimulants, and CF-induced changes in gene expression occurred comparatively earlier than those induced by gliotoxin. Among 31 genes encoding apoptosis, which were up- or down-regulated in this assay, only 3 genes were similarly changed by both kinds of stimulation. Apoptosis was detected and quantified using two apoptosis assays. CF and gliotoxin changed the expessions of only 3 out of 19 regulated genes related to inflammatory mediators and receptors similarly. The up-regulation of the gene encoding annexin 1 (ANXA1), which is known to be involved in extravasation and apoptosis of neutrophils, may play a role in the immunosuppressive effect of A. fumigatus. The difference in expression changes between CF and gliotoxin is presumed to be caused by the interaction among the components of CF and therefore the interaction is an area of interest for further investigation.

Clinical-scale generation of multi-specific anti-fungal T cells targeting Candida, Aspergillus and mucormycetes

BACKGROUND AIMS

Invasive fungal infections, in particular, infections caused by Candida, Aspergillus and mucormycetes, are a major cause of morbidity and mortality in patients undergoing allogeneic hematopoietic stem cell transplantation. Adoptive transfer of donor-derived anti-fungal T cells shows promise to restore immunity and to offer a cure. Because T cells recognize only specific epitopes, the low rate of patients in which the causal fungal pathogen can be identified and the considerable number of patients with co-infection with several genera or species of fungi significantly limit the application of adoptive immunotherapy.

METHODS

Using the interferon-γ secretion assay, we isolated multi-specific human anti-fungal T cells after simultaneous stimulation with cellular extracts of Aspergillus fumigatus, Candida albicans and Rhizopus oryzae. Cells were phenotypically and functionally characterized by flow cytometry.

RESULTS

Of a total of 1.1 × 10(9) peripheral blood mononuclear cells, a median number of 5.2 × 10(7) CD3+ CD4+ T cells was generated within 12 days. This cell population consisted of activated memory TH1 cells and reproducibly responded to a multitude of Aspergillus spp., Candida spp. and mucormycetes with interferon-γ production. On re-stimulation, the generated T cells proliferated and enhanced anti-fungal activity of phagocytes and showed reduced alloreactivity compared with the original cell fraction.

CONCLUSIONS

Our rapid and simple method of simultaneously generating functionally active multi-specific T cells that recognize a wide variety of medically relevant fungi may form the basis for future clinical trials investigating adoptive immunotherapy in allogeneic hematopoietic stem cell transplantation recipients with invasive fungal infection.

TLR9 activation dampens the early inflammatory response to Paracoccidioides brasiliensis, impacting host survival

BACKGROUND

Paracoccidioides brasiliensis causes paracoccidioidomycosis, one of the most prevalent systemic mycosis in Latin America. Thus, understanding the characteristics of the protective immune response to P. brasiliensis is of interest, as it may reveal targets for disease control. The initiation of the immune response relies on the activation of pattern recognition receptors, among which are TLRs. Both TLR2 and TLR4 have been implicated in the recognition of P. brasiliensis and regulation of the immune response. However, the role of TLR9 during the infection by this fungus remains unclear.

METHODOLOGY/PRINCIPAL FINDINGS

We used in vitro and in vivo models of infection by P. brasiliensis, comparing wild type and TLR9 deficient ((-/-)) mice, to assess the contribution of TLR9 on cytokine induction, phagocytosis and outcome of infection. We show that TLR9 recognizes either the yeast form or DNA from P. brasiliensis by stimulating the expression/production of pro-inflammatory cytokines by bone marrow derived macrophages, also increasing their phagocytic ability. We further show that TLR9 plays a protective role early after intravenous infection with P. brasiliensis, as infected TLR9(-/-) mice died at higher rate during the first 48 hours post infection than wild type mice. Moreover, TLR9(-/-) mice presented tissue damage and increased expression of several cytokines, such as TNF-α and IL-6. The increased pattern of cytokine expression was also observed during intraperitoneal infection of TLR9(-/-) mice, with enhanced recruitment of neutrophils. The phenotype of TLR9(-/-) hosts observed during the early stages of P. brasiliensis infection was reverted upon a transient, 48 hours post-infection, neutrophil depletion.

CONCLUSIONS/SIGNIFICANCE

Our results suggest that TLR9 activation plays an early protective role against P. brasiliensis, by avoiding a deregulated type of inflammatory response associated to neutrophils that may lead to tissue damage. Thus modulation of TLR9 may be of interest to potentiate the host response against this pathogen.