Production of cytokines by alveolar and peritoneal macrophages stimulated by Aspergillus fumigatus conidia or hyphae

Aspergillus fumigatus is an opportunistic pathogen responsible for severe, invasive infections in neutropenic hosts. Lung clearance of A. fumigatus conidia seems to be mediated by phagocytic cells and oxygen radicals. It is not known if cytokines or nitrogen radicals are also involved. We tested for the production of TNF alpha, IL-1 and nitric oxide (NO) after stimulation of mouse macrophages with the fungus. We found that both cytokines, but not NO, were produced in a dose-dependent manner during the first 24 h of culture. Except for a faster kinetic, no appreciable differences were seen between alveolar and peritoneal macrophages. Furthermore, both hyphae and conidia, either alive or killed, were capable of inducing cytokines production. However, among different Aspergillus spp. only A. fumigatus and A. flavus seemed to induce significant amount of TNF alpha and IL-1, whereas A. terreus and A. niger were less effective. In no case could we detect production of NO. Finally, macrophages from dexamethasone-treated mice failed to produce cytokines in response to A. fumigatus conidia. These results indicate that in normal hosts inflammatory cytokines contribute to the natural response against Aspergillus infections and suggest that the impairment of cytokine production, in immunodepressed patients, may favour the growth and spread of the fungus.