Infections caused by Aspergillus fumigatus are a leading cause of death in immune compromised individuals. A. fumigatus is also a threat to those lacking a functional NADPH oxidase system, a defensive oxidant-generating system of phagocytic immune cells. Alveolar macrophages (AM) are phagocytes known to be important in the early innate defense against A. fumigatus conidia, and have been reported to produce oxidants to kill engaged pathogens. However, many details about the molecular mechanisms by which AM kill A. fumigatus are not well understood. With conflicting data about the antifungal mechanisms of AM, and the role of NADPH oxidase in this process, we proposed to better define the microbicidal mechanism of AM that protects from infections by A. fumigatus. The overall hypothesis being investigated is that the AM-derived resistance to A. fumigatus conidia is mediated by NADPH oxidase-independent microbicidal mechanisms that involve nutrient sequestration, leading to conidial killing.
Three aims proposed to address this goal are: 1) to compare the conidiacidal activity of AM from normal and gp91phox-/- mice that lack a functional phagocyte oxidase, using both in vitro and in vivo analyses. Reports on the role of NADPH oxidase of AM in protecting humans from IPA are conflicting, and our data do not indicate the respiratory burst in AM is necessary for a resistance to aspergillosis, as we have shown it is in neutrophils. This information will provide a better understanding of how the NADPH oxidase is applied in aspergillosis immunity. 2) to compare NADPH oxidase-dependent superoxide liberation by AM from normal C57Bl/6 and gp91phox-/- mice to describe the capabilities of oxidant production of AM in these mouse strains. Our preliminary data suggest that oxidant production in AM from normal and gp91phox-/- mice is not significantly different when triggered by oxidant-triggering stimulants, or by phagocytosis of fungal particles. This information will provide a better understanding of the capacity of oxidant generation by AM, and 3) to compare transcriptional responses of conidia exposed to AM from normal C57Bl/6 mice, to those in conidia subjected to low nutrient conditions.
This aim will test whether nutrient sequestration is a conidiacidal mechanism of AM. If oxidative killing of conidia is not utilized by AM, then the use of A. fumigatus conidia as a bioprobe of the conidiacidal environment of the AM should be suggested by transcriptional responses of internalized conidia. This information will provide a better understanding of the antifungal mechanism of AM that kills A. fumigatus conidia. The long-term goal of these approaches is to identify potential therapeutic targets to augment the natural immunity that protects from infections by A. fumigatus.
Aspergillus fumigatus is an inhaled fungus that can infect human patients with various types if immune suppression. At this time, most individuals that become infected by this organism do not survive, despite aggressive medical management. The long- term goal of this work is to identify molecular mechanisms that enable alveolar macrophages to kill the spore-like conidial form of A. fumigatus, so that natural immunity can be augmented in those at risk.