Oxidative burst and neutrophil elastase contribute to clearance of Aspergillus fumigatus pneumonia in mice

Polymorphonuclear neutrophils (PMN) are important for the control of invasive aspergillosis (IA), a major threat to immunocompromised individuals. For clearance of Aspergillus fumigatus infections, PMN employ their potent oxidative and non-oxidative mechanisms. To clarify the relative contribution of these mechanisms, we analyzed p47phox−/−, gp91phox−/− and elastase (ELA) deficient mice (ELANE) after intratracheal infection with A. fumigatus. Infected p47phox−/− and gp91phox−/− mice died within 4 days and had a significant higher fungal burden in the lungs compared to wild-type controls. Interestingly, the survival of ELANE mice after infection was unimpaired suggesting that ELA is not essential here. Nevertheless, A. fumigatus clearance was delayed in ELANE mice indicating a partial contribution of ELA to fungal immunity. Comparing p47phox−/−, gp91phox−/− or ELANE mice for PMN activation and recruitment to the lungs, we were unable to detect significant differences in vitro or in vivo among mutant or wild-type strains suggesting intact PMN functionality of basic effector mechanisms. Fungal killing in vitro by ELA deficient PMN was comparably reduced as in p47phox−/− and gp91phox−/− deficient PMN corroborating the importance of oxidative and non-oxidative PMN mechanisms for the control of fungal outgrowth. Taken together, this suggests that intact oxidative as well as non-oxidative PMN effector functions are highly relevant for the control of A. fumigatus infections in vitro and in vivo. While ELA contributes to clearance of A. fumigatus, the oxidative functions are essential for survival.