Search

Invasive aspergillosis (IA) is an infectious disease caused by the fungal pathogen Aspergillus fumigatus that mainly affects immunocompromised hosts. To investigate immune cell cross-talk during infection with A. fumigatus , we co-cultured natural killer (NK) cells and dendritic cells (DC) after stimulation with whole fungal structures, components of the fungal cell wall, fungal lysate or ligands for distinct fungal receptors. Both cell types showed activation after stimulation with fungal components and were able to transfer activation signals to the counterpart not stimulated cell type. Interestingly, DCs recognized a broader spectrum of fungal components and thereby initiated NK cell activation when those did not recognize fungal structures. These experiments highlighted the supportive function of DCs in NK cell activation. Furthermore, we focused on soluble DC mediated NK cell activation and showed that DCs stimulated with the TLR2/Dectin-1 ligand zymosan could maximally stimulate the expression of CD69 on NK cells. Thus, we investigated the influence of both receptors for zymosan, Dectin-1 and TLR2, which are highly expressed on DCs but show only minimal expression on NK cells. Specific focus was laid on the question whether Dectin-1 or TLR2 signaling in DCs is important for the secretion of soluble factors leading to NK cell activation. Our results show that Dectin-1 and TLR2 are negligible for NK cell activation. We conclude that besides Dectin-1 and TLR2 other receptors on DCs are able to compensate for the missing signal. [ABSTRACT FROM AUTHOR]

Aspergillus fumigatus is an opportunistic fungal pathogen causing detrimental infections in immunocompromised individuals. Dendritic cells (DCs) are potent antigen-presenting cells and recognize the A. fumigatus cell wall component β-1,3 glucan via Dectin-1, followed by DCmaturation and cytokine release. Here, we demonstrate that human primary myeloid DCs (mDCs) interact with different morphotypes of A. fumigatus. Dectin-1 is expressed on mDCs and is down-regulated after contact with A. fumigatus, indicating that mDCs recognize A. fumigatus via this receptor. Blocking of Dectin-1, followed by stimulation with depleted zymosan diminished the up-regulation of the T-cell co-stimulatory molecules CD40, CD80, HLA-DR and CCR7 on mDCs and led to decreased release of the cytokines TNF-α, IL-8, IL-1β and IL-10. [ABSTRACT FROM AUTHOR]

Aspergillus fumigatus is an opportunistic mould that causes invasive pulmonary aspergillosis ( IPA), a life-threatening infection in immunocompromised patients. During the course of IPA, localised areas of tissue hypoxia occur. Bacterial infection models revealed that hypoxic microenvironments modulate the function of host immune cells. However, the influence of hypoxia on anti-fungal immunity has been largely unknown. We evaluated the impact of hypoxia on the human anti- A. fumigatus immune response. Human monocyte-derived dendritic cells ( DCs) were stimulated in vitro with germ tubes of A. fumigatus under normoxia or hypoxia (1% O2), followed by analysis of DC viability, maturation and cytokine release. While DC viability was unaffected, hypoxia attenuated cytokine release from DCs and maturation of DCs upon stimulation with A. fumigatus. These data suggest that hypoxia at the site of A. fumigatus infection inhibits full activation and function of human DCs. Thereby, this study identified hypoxia as a crucial immune-modulating factor in the human anti-fungal immune response that might influence the course and outcome of IPA in immunocompromised patients. [ABSTRACT FROM AUTHOR]

Invasive aspergillosis (IA) is a devastating opportunistic infection and its treatment constitutes a considerable burden for the health care system. Immunocompromised patients are at an increased risk for IA, which is mainly caused by the species Aspergillus fumigatus. An early and reliable diagnosis is required to initiate the appropriate antifungal therapy. However, diagnostic sensitivity and accuracy still needs to be improved, which can be achieved at least partly by the definition of new biomarkers. Besides the direct detection of the pathogen by the current diagnostic methods, the analysis of the host response is a promising strategy toward this aim. Following this approach, we sought to identify new biomarkers for IA. For this purpose, we analyzed gene expression profiles of hematological patients and compared profiles of patients suffering from IA with non-IA patients. Based on microarray data, we applied a comprehensive feature selection using a random forest classifier. We identified the transcript coding for the S100 calcium-binding protein B (S100B) as a potential new biomarker for the diagnosis of IA. Considering the expression of this gene, we were able to classify samples from patients with IA with 82.3% sensitivity and 74.6% specificity. Moreover, we validated the expression of S100B in a real-time reverse transcription polymerase chain reaction (RT-PCR) assay and we also found a down-regulation of S100B in A. fumigatus stimulated DCs. An influence on the IL1B and CXCL1 downstream levels was demonstrated by this S100B knockdown. In conclusion, this study covers an effective feature selection revealing a key regulator of the human immune response during IA. S100B may represent an additional diagnostic marker that in combination with the established techniques may improve the accuracy of IA diagnosis. [ABSTRACT FROM AUTHOR]

Aspergillus fumigatus is responsible for severe and often fatal infections in immunocompromised patients. The human immune response against this pathogenic mould is still not fully understood. Recently, microRNAs (miRNAs) have been characterized as regulators of inflammation and immune response in various diseases. MiRNAs specifically bind to mRNA target sequences, thereby leading to gene silencing by target degradation and/or translational repression. To investigate the possible role of miRNAs during A. fumigatus infection, we studied the expression of two major immune relevant miRNAs, miR-132 and miR-155, in human monocytes and dendritic cells (DCs). Both cell types are crucial for the immune response against A. fumigatus. Here, we demonstrate for the first time that miR-132 and miR-155 are differentially expressed in monocytes and DCs upon stimulation with A. fumigatus or bacterial lipopolysaccharide (LPS). Interestingly, miR-132 was induced by A. fumigatus but not by LPS in both cell types. Our data suggest that miR-132 may be a relevant regulator of the immune response directed against A. fumigatus. [ABSTRACT FROM AUTHOR]

The initial stages of the interaction between the host and Aspergillus fumigatus at the alveolar surface of the human lung are critical in the establishment of aspergillosis. Using an in vitro bilayer model of the alveolus, including both the epithelium (human lung adenocarcinoma epithelial cell line, A549) and endothelium (human pulmonary artery epithelial cells, HPAEC) on transwell membranes, it was possible to closely replicate the in vivo conditions. Two distinct sub-groups of dendritic cells (DC), monocyte-derived DC (moDC) and myeloid DC (mDC), were included in the model to examine immune responses to fungal infection at the alveolar surface. RNA in high quantity and quality was extracted from the cell layers on the transwell membrane to allow gene expression analysis using tailored custom-made microarrays, containing probes for 117 immune-relevant genes. This microarray data indicated minimal induction of immune gene expression in A549 alveolar epithelial cells in response to germ tubes of A. fumigatus. In contrast, the addition of DC to the system greatly increased the number of differentially expressed immune genes. moDC exhibited increased expression of genes including CLEC7A, CD209 and CCL18 in the absence of A. fumigatus compared to mDC. In the presence of A. fumigatus, both DC subgroups exhibited up-regulation of genes identified in previous studies as being associated with the exposure of DC to A. fumigatus and exhibiting chemotactic properties for neutrophils, including CXCL2, CXCL5, CCL20, and IL1B. This model closely approximated the human alveolus allowing for an analysis of the host pathogen interface that complements existing animal models of IA. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]