Differential host susceptibility to pulmonary infections with bacteria andfungi in mice deficient in myeloperoxidase

Myeloperoxidase (MPO), which is located within neutrophils capable of produ cing hypochlorous acid, is active in vitro against bacteria and fungi. Howe ver, MPO-deficient persons are usually healthy. To define the in vivo contr ibution of MPO to early host defense against pulmonary infections, MPO-defi cient and control mice were intranasally infected with various fungi and ba cteria, and the number of residual microorganisms in lungs was compared 48 h later. MPO-deficient mice showed severely reduced cytotoxicity to Candida albicans, Candida tropicalis, Trichosporon asahii, and Pseudomonas aerugin osa. However, the mutant mice showed a slight but significantly delayed cle arance of Aspergillus fumigatus and klebsiella pneumoniae and had comparabl e levels of resistance to the wild type against Candida glabrata, Cryptococ cus neoformans, Staphylococcus aureus, and Streptococcus pneumoniae. These results suggest that the MPO-dependent oxidative system is important for ho st defense against fungi and bacteria, although the effect varies by pathog en species.