Contribution of the myeloperoxidase-dependent oxidative system to host defence against Cryptococcus neoformans

Abstract

The in vivo contribution of reactive oxygen species produced by neutrophils against Cryptococcus infection is not widely recognized. Myeloperoxidase (MPO) is a neutrophil-specific enzyme that catalyses the production of hypohalous acids such as HOCl from H2O2. This study investigated the role of MPO in immunological defence against Cryptococcus neoformans in an MPO-deficient (MPO−/−) mouse model. The survival of MPO−/− mice infected either intranasally or intravenously with C. neoformans was lower than that of identically challenged wild-type mice. The MPO−/− mice that received intranasal injection of C. neoformans had significantly larger lung fungal burdens than wild-type mice. On day 7, MPO−/− mice had a significantly higher lung concentration of interleukin (IL)-4 and lower concentrations of IL-2, IL-12p70 and interferon (IFN)-γ than wild-type mice, suggesting a weak Th1 response in the MPO−/− mice to C. neoformans. Pathologically, the MPO−/− mice with intranasal infection showed more severe pneumonia than wild-type mice, which was associated with an increase in the levels of IL-1α/β in the lungs. In addition, in MPO−/− mice, the pulmonary infection disseminated to the brain with occasional meningitis. The keratinocyte-derived cytokine (KC) level in the brain of infected MPO−/− mice was higher than that of control mice. Both intranasal and intravenous infections resulted in a higher number of fungi in the spleen of MPO−/− mice compared to wild-type, suggesting decreased resistance to C. neoformans not only in the lungs but also in the spleen in the absence of MPO. Taken together, these data suggest a major role of MPO in the response to cryptococcal infection.