Macrophages and neutrophils kill the airborne fungal pathogen Aspergillus fumigatus. The dependency of this killing process on reactive oxygen intermediates (ROI) has been strongly suggested. Therefore, we investigated the enzymatic ROI detoxifying system by proteome analysis of A. fumigatus challenged by H 2 O 2 . Since many of the identified proteins and genes are apparently regulated by a putative Saccharomyces cerevisiae Yap1 homolog, the corresponding gene of A. fumigatus was identified and designated Afyap1. Nuclear localization of a functional AfYap1-eGFP fusion was stress dependent. Deletion of the Afyap1 gene led to drastically increased sensitivity of the deletion mutant against H 2 O 2 and menadione, but not against diamide and NO radicals. Proteome analysis of the ⌬Afyap1 mutant strain challenged with 2 mM H 2 O 2 indicated that 29 proteins are controlled directly or indirectly by AfYap1, including catalase 2. Despite its importance for defense against reactive agents, the Afyap1 deletion mutant did not show attenuated virulence in a murine model of Aspergillus infection. These data challenge the hypothesis that ROI such as superoxide anions and peroxides play a direct role in killing of A. fumigatus in an immunocompromised host. This conclusion was further supported by the finding that killing of A. fumigatus wild-type and ⌬Afyap1 mutant germlings by human neutrophilic granulocytes worked equally well irrespective of whether the ROI scavenger glutathione or an NADPH-oxidase inhibitor was added to the cells.In the last few decades Aspergillus fumigatus has become the most important airborne fungal pathogen of humans. Diseases caused by A. fumigatus can be divided into three categories: allergic reactions and colonization with restricted invasiveness are observed in immunocompetent individuals, while systemic infections with high mortality rates occur in immunocompromised patients. Due to the improvement in transplant medicine and the therapy of hematological malignancies, the number of cases of invasive aspergillosis has increased. Specific diagnostics are still limited, as are the possibilities of therapeutic intervention, leading to a high mortality rate of 30 to 98% for invasive aspergillosis (8). The genome of the A. fumigatus isolate Af293 was fully sequenced. It consists of a haploid set of eight chromosomes with a total size of 29.4 Mb, of which 9,926 protein-encoding sequences were identified (44). With the genome data available the regulation of genes and the expression profile of proteins of A. fumigatus can be analyzed on a global scale, including the conditions that are related to infection.The infectious agent of A. fumigatus are conidia, which are inhaled during routine daily activities (8). Therefore, in immunocompromised patients, the lung is the site of infection of A. fumigatus. In immunocompetent individuals, mucociliary clearance and phagocytic defense normally prevent the disease. Alveolar macrophages are the major resident cells of the lung alveoli; they, along with neutrophils ...

Dectin-1 was identified as an important receptor for A. fumigatus and C. albicans on human iDCs and was found to be involved in the induction of a proinflammatory cytokine response.

SummaryCandida albicans is among the most important fungal pathogens in humans. Morphological plasticity has been linked to its pathogenic potential as filamentous forms are associated with tissue invasion and infection. Here we show that human neutrophils discriminate between yeasts and filaments of C. albicans. Whereas filaments induced targeted motility, resulting in the establishment of close contact between neutrophils and fungal cells, yeast forms were largely ignored during coincubation. In transwell assays, C. albicans filaments induced significantly higher migratory activity in neutrophils than yeasts. Neutrophil motility based on actin rearrangement was essential for killing of C. albicans filaments but not involved in killing of yeast forms. Using inhibitors for MAP-kinase cascades, it was shown that recognition of C. albicans filaments by neutrophils is mediated via the MEK/ERK cascade and independent of JNK or p38 activation. Inhibition of the ERK signalling pathway abolished neutrophil migration induced by C. albicans filaments and selectively impaired the ability to kill this morphotype. These data show that invasive filamentous forms of C. albicans trigger a morphotype-specific activation of neutrophils, which is strongly dependent on neutrophil motility. Therefore, human neutrophils are capable of sensing C. albicans invasion and initiating an appropriate early immune response.

Mycophenolic acid (MPA) is used clinically to prevent graft rejection but may increase the risk of fungal infection. We observed that MPA enhanced the Aspergillus fumigatus-induced oxidative burst of polymorphonuclear neutrophils, but without a corresponding increase in fungal killing. Furthermore, MPA inhibited the proinflammatory cytokine response and maturation of dendritic cells.Mycophenolate mofetil is an antimetabolite immunosuppressant used in stem cell and solid organ transplant regimens for graft rejection and graft-versus-host disease prophylaxis and for treatment of acute or chronic graft-versus-host disease. Mycophenolic acid (MPA) is the active drug moiety and is a potent, selective, and reversible inhibitor of IMP dehydrogenase, leading to arrest of T-and B-lymphocyte proliferation (1, 2). The increasing application of immunosuppressive drugs is one reason for the growing incidence of invasive aspergillosis (6, 9). In this study, the impact of MPA on the functionality of polymorphonuclear neutrophils (PMN) and dendritic cells (DCs) in the immune response to Aspergillus fumigatus was analyzed.To quantify reactive oxygen intermediates (ROI), PMN were separated from blood of healthy volunteers by dextran sedimentation (Nycomed, Norway) (15). ROI were quantified by measuring the conversion of dichlorofluorescein acetate (2.5 M; Sigma-Aldrich, Germany) to green fluorescent dichlorofluorescein (15). PMN were stimulated at 37°C in a fluorescence reader (GENios; Tecan, Germany) recording in 5-min intervals (excitation wavelength, 485 nm; emission wavelength, 520 nm). Phorbol myristate acetate (PMA) (23 ng/ml; Sigma-Aldrich) was used as a positive control.Killing assays with A. fumigatus germlings (ATCC 9197) (8 ϫ 10 4 ; multiplicity of infection [MOI] ϭ 1) were performed as described previously (12). MPA (10 M; Novartis, Germany) was administered for 3 h at 37°C. Serial dilutions were plated on Sabouraud agar and incubated for 24 h to quantify viable fungi. A two-tailed unpaired t test was used for statistical analyses.To analyze the viability of PMN under MPA treatment, apoptosis and necrosis rates were determined by flow cytometry (FACSCalibur; Becton Dickinson), using a dual-color protocol quantifying phosphatidylserine by fluorescein isothiocyanate (FITC)-annexin V staining (Roche) and DNA of dead cells by propidium iodide staining (Sigma) (16).For immature DC (iDC) generation, monocytes were isolated by magnet-associated cell sorting using anti-human CD14 antibodies (Miltenyi,

Toll-like receptors (TLRs) play a crucial role for detecting conserved pathogen-associated molecular patterns comprising fungal structures. Activation of polymorphonuclear granulocytes (PMNs) as well as mobilization of antigen presenting cells is important for successful clearance of fungal infections. Here, the role of TLR2 and TLR4 for activation of PMNs and immature dendritic cells (iDCs) through Aspergillus fumigatus was analyzed. Generation of iDCs was achieved by cultivating monocytes in the presence of GM-CSF and IL-4. PMNs were obtained from fresh blood. In blocking studies, cells were preincubated with anti-TLR2 and / or anti-TLR4 antibody before stimulation with Aspergillus fumigatus germinating conidia. For RNA interference (RNAi) experiments, iDCs were transfected with short-interfering RNA (siRNA) via electroporation and gene expression was controlled by quantitative real-time PCR. Oxidative burst of PMNs was induced after contact with Aspergillus or TLR2 ligand zymosan. Release of oxygen intermediates could be significantly reduced if PMNs were preincubated with anti-TLR2 antibody. In contrast to monocytes, cytokine secretion (IL-12 and TNF-α) of iDCs was not altered if anti-TLR antibodies were used. To study the role of TLR2 and TLR4 more detailed, an RNAi system for iDCs was established to downregulate gene expression. Determination of siRNA transfection rate revealed an efficiency of about 85% and allowed significant downregulation of TLR2 and TLR4 (> 90%). In accordance to blocking studies, expression of IL-10, IL-12 and TNF-a was not reduced after TLR2 or TLR4 siRNA transfection and stimulation with Aspergillus. We conclude that TLR2 plays an important role in the induction of the oxidative burst of PMNs whereas cytokine release of iDCs seems to be independent of TLR2 / TLR4 signalling. The established siRNA system allows the detection of receptors responsible for activation of iDCs.