Experimental basis for the clinical epidemiology of fungal infections. A review

Cytokine release in healthy donors and patients with chronic granulomatous disease upon stimulation with Aspergillus fumigatus

The release of tumour necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6) and IL-10 upon stimulation with non-viable conidia and hyphal fragments from Aspergillus fumigatus was investigated in an ex vivo whole-blood model. In healthy volunteers, high numbers of conidia (between 10(6) and 3 x 10(8)/ml) induced a moderate release of TNF-alpha and IL-6. Hyphal fragments (2.5 x 10(5)/ml) were more potent in stimulating the release of these pro-inflammatory cytokines. Although some IL-10 release was observed upon stimulation with either conidia or hyphal fragments, it was not significantly different from that in unstimulated controls. In comparison, in whole blood obtained from 4 patients with chronic granulomatous disease (CGD), a high release of pro-inflammatory cytokines together with a significantly higher IL-10 release than in the healthy controls was seen after stimulation with A. fumigatus. In conclusion, A. fumigatus can trigger the release of pro-inflammatory cytokines in a human whole-blood system, which is likely to be central to the activation of antifungal defence mechanisms. In contrast, A. fumigatus stimulates a higher release of anti-inflammatory cytokines in CGD patients, which may suggest that a dysregulation between pro- and anti-inflammatory cytokines contributes to the increased susceptibility to invasive aspergillosis in this patient group.

Aspergillus fumigatus and aspergillosis

Aspergillus fumigatus is one of the most ubiquitous of the airborne saprophytic fungi. Humans and animals constantly inhale numerous conidia of this fungus. The conidia are normally eliminated in the immunocompetent host by innate immune mechanisms, and aspergilloma and allergic bronchopulmonary aspergillosis, uncommon clinical syndromes, are the only infections observed in such hosts. Thus, A. fumigatus was considered for years to be a weak pathogen. With increases in the number of immunosuppressed patients, however, there has been a dramatic increase in severe and usually fatal invasive aspergillosis, now the most common mold infection worldwide. In this review, the focus is on the biology of A. fumigatus and the diseases it causes. Included are discussions of (i) genomic and molecular characterization of the organism, (ii) clinical and laboratory methods available for the diagnosis of aspergillosis in immunocompetent and immunocompromised hosts, (iii) identification of host and fungal factors that play a role in the establishment of the fungus in vivo, and (iv) problems associated with antifungal therapy.

Significance of fungal evolution for the understanding of their pathogenicity, illustrated with agents of phaeohyphomycosis

Phaeohyphomycosis is an umbrella term for all those mycoses where the fungus is present in tissue with melanized filaments. It is surmised that some groups of species within the ascomycete family Herpotrichiellaceae exhibit an evolutionary tendency towards pathogenicity on vertebrate hosts. Such a tendency is not observed in the families Pleosporaceae and Dothideaceae. Mycoses provoked by members of the three families thus may be fundamentally different. Phaeohyphomycosis should be regarded as an artificial descriptor without biological significance.

Amphotericin B refractory aspergillosis after itraconazole: evidence for significant antagonism

Failure of amphotericin B to halt aspergillosis in a patient previously treated with itraconazole raised the question of whether amphotericin B lost its activity as a result of antagonism between the two antifungal drugs. Azoles exhaust the target of amphotericin B on the fungal cell membrane. Accordingly amphotericin B in vitro lost its activity against six isolates of Aspergillus fumigatus after exposure to subfungicidal concentrations of itraconazole. Prior treatment of mice with itraconazole abolished the protective effect of amphotericin B, even when itraconazole was stopped before starting amphotericin B therapy. These observations raise concern about sequential therapy of aspergillosis with itraconazole followed by amphotericin B.

Pathogenic fungi in human dwellings

Airborne invasive fungal infections in various risk groups of people suffering from immunodeficiencies are an increasing problem for modern medicine. Because of the acute and rapid course of invasive infections, prevention is of principal significance. Such prevention mainly concerns the control of fungal spores in indoor air. In this connection the immediate environment offering ecological niches for growth and morphogenesis of infective particles of Aspergillus spp., Mucoraceae, Cryptococcus neoformans and some other yeast-like fungi is of main interest. The current problems of indoor air mycology, i.e. the epidemiology and ecology of pathogenic fungi in indoor air, can only be recognized and interpreted by centres routinely performing mycological diagnosis for all the various risk groups of patients. Models of specific surveillance of the most important fungal pathogens (e.g. Aspergillus spp. and Cryptococcus neoformans) in indoor air will be outlined and discussed.