Suppression of host defences by Aspergillus fumigatus

An important feature of the microbicidal action of phagocytic cells is their ability to produce reactive oxygen intermediates. In an attempt to identify the mechanisms by which the fungus Aspergillus fumigatus resists normal host defences the effect of spores and spore diffusates of A fumigatus on the production of superoxide anion and hydrogen peroxide by primed rodent phagocytic cells has been measured. For comparison we have used the non-pathogenic fungus Penicillium ochrochloron. Production of these reactive oxygen intermediates in response to A fumigatus was significantly lower than that in response to P ochrochloron. A similar reduction was achieved by diffusate prepared from freshly washed spores. The inhibitory component was of low molecular weight (less than 14,000) and its effect was dose dependent. These results suggest that spores of A fumigatus fail to trigger and also inhibit the production of reactive oxygen intermediates by phagocytic cells.