Basic Studies On Aspergillus Species

National Institute Of Allergy And Infectious Diseases

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Abstract

Aspergillus is one of the most common fungal pathogens affecting neutropenic patients and other types of immunocompromised individuals such as those with Chronic Granulomatous Disease(CGD) of Childhood. Among a dozen species of Aspergillus reported to cause infection in humans, A. fumigatus is the most common species reported to cause invasive aspergillosis. All Aspergillus species propagate by conidia (spores), which humans encounter daily through inhalation. During 2006-2007, we determined that both laeA ko and glip ko strains lost their ability to synthesize gliotoxin and were significantly less virulent than the wild type or reconstituted strains in mice immunosuppressed with corticosteroids. The reduced virulence in these ko strains was in contrast to reports by other groups who used neutropenic mice treated with both cyclophosphamide and corticosteroids. We also found that the neutrophils from CGD patients and normal volunteers were equally efficient in blocking the growth of conidia indicating that neutrophils from both subjects exerted an antifungal mechanism independent from the oxidative burst since neutophils from CGD patients are defective in generating superoxide. We have determined that the antifungal compound is lactoferrin, a protein secreted during degranulation of neutrophils. The mycelium, in contrast,was effectively inhibited only by neutrophils from normal volunteers and not by neutrophils from CGD patients which, confirmed the previous studies.[unreadable] [unreadable] During 2007-2008,we investigated the Aspergillus response to host immune cells by studying the genes differentially expressed in conidia vs hyphae in response to neutrophils from healthy donors as well as from those with chronic granulomatous disease (CGD). To our knowledge, this is the first study that investigated the genes differentially expressed in conidia vs hyphae of A. fumigatus in response to neutrophils from healthy donors as well as from those with CGD which are defective in the production of reactive oxygen species.[unreadable] Upon exposure to either normal or CGD neutrophils, 244 genes were up-regulated in conidia but not in hyphae. Several of these genes are involved in the degradation of fatty acids, peroxisome function and the glyoxylate cycle which suggests that conidia exposed to neutrophils reprogram their metabolism to adjust to the host environment. In addition, the mRNA levels of four genes encoding proteins putatively involved in iron/copper assimilation were found to be higher in conidia and hyphae exposed to normal neutrophils compared to those exposed to CGD neutrophils. Deletants of several of these differentially expressed genes showed phenotypes related to the proposed functions, i.e. deletants of genes involved in fatty acid catabolism showed defective growth on fatty acids and the deletants of iron/copper assimilation showed a higher sensitivity to the oxidative agent menadione. None of these deletants, however, showed reduced resistance to neutrophil attack.