The combination of platelets and anidulafungin at 0.03 g/ml significantly (P < 0.05) reduced the germination rate and hyphal elongation in Aspergillus fumigatus compared to those with either anidulafungin only or an untreated control. Platelets decreased the expression of the fks gene, which plays an important role in cell wall synthesis. Our results suggest that human platelets plus anidulafungin might contribute to defense against A. fumigatus.A n intact immune system is essential for the defense against fungal pathogens (1). Human platelets are known to primarily play a key role in hemostasis; however, they are considered to be part of the innate immunity (2-4). They exert antimicrobial effects against bacteria, such as Staphylococcus aureus, and several other microorganisms in vitro (4, 5). Christin et al. showed that platelets damage hyphae of Aspergillus fumigatus (6). Recently, we observed that platelets have the capacity to attenuate the virulence of Aspergillus spp. and zygomycetes in vitro by reducing hyphal germination and elongation (7-9). In addition, the polysaccharide galactomannan, which is released by growing and vital hyphae of A. fumigatus, was significantly reduced under platelet treatment (8). Previously, we have reported that human platelets act beneficially with amphotericin B against A. fumigatus and other Aspergillus spp. (10, 11). Here we investigated whether platelets and anidulafungin in combination have an added effect on fungal germination, hyphal elongation, and hyphal damage of A. fumigatus. In addition, we analyzed the effects of human platelets in combination with anidulafungin on expression levels of the fks gene, which encodes the 1,3-␤-D-glucan synthase. Echinocandins interfere with cell wall synthesis by inhibiting this enzyme, which forms glucan polymers, the major component of the fungal cell wall (12).Two clinical isolates of A. fumigatus were used, and the strains were obtained from patients suffering from invasive aspergillosis. Platelet concentrates (storage time Ͻ 24 h) were provided by the local Department of Immunology and Blood Transfusion at Innsbruck Medical University. The minimum effective concentration (MEC) was determined according to the Antifungal Susceptibility Testing (AFST) committee, EUCAST, broth microdilution method (13), and it was found to be 0.03 g/ml for both isolates tested. Subsequently, 0.03 g/ml and a subinhibitory MEC of 0.0078 g/ml of anidulafungin were applied for further tests. The determination of germination rate and hyphal elongation was performed as described elsewhere (7-9). Conidial suspensions were treated either with platelets or anidulafungin alone or with the combination of platelets and the drug. For investigation of hyphal elongation and the germination percentage, 100 l of platelets (1 ϫ 10 8 /ml) and 100 l of conidia (1 ϫ 10 6 /ml) suspended in RPMI 1640 (Sigma-Aldrich, Vienna, Austria) were mixed in an effector-to-target-cell (E:T) ratio of 100:1 and then anidulafungin was added and the mixture was incubated at 37°C. To calc...

Platelets are known to be part of haemostasis but they are also players in innate host defense. Recently, we observed that platelets attenuate the virulence of Aspergillus spp. in vitro. However, little is known about the antifungal effects of platelets in the presence of antimycotics against non-A. fumigatus Aspergillus species. We therefore investigated whether platelets increase the in vitro activity of amphotericin B, voriconazole, posaconazole and caspofungin against two clinical isolates each of Aspergillus flavus, Aspergillus terreus and Aspergillus niger. The antifungal activity was evaluated by assessing germination percentages, hyphal elongation and hyphal damage by use of XTT. The combination of platelets plus amphotericin B significantly (P < 0.05) enhanced the reduction of germination percentage compared to either substance alone. Among triazoles, voriconazole exhibited significant effects with platelets for all tested aspergilli. Overall, these findings suggest that among the tested antimycotic substances, amphotericin B in combination with platelets has enhancing effects in reducing germination and hyphal elongation in the tested non-A. fumigatus Aspergillus species. These data indicate that platelets act beneficially with antimycotics in an early stage of fungal growth by blocking and/or delaying fungal germination and hyphal elongation; both crucial mechanisms in the development of invasive fungal disease.