Myeloperoxidase deficiency in mice exacerbates lung inflammation induced by nonviable Candida albicans.

Objective: This study aimed to evaluate the effect of myeloperoxidase (MPO) deficiency on lung inflammation induced by nonviable Candida albicans (nCA).

Methods: Mice were inoculated intranasally with nCA, and accumulation of neutrophils and macrophages in the bronchoalveolar lavage fluid was analyzed by flow cytometry. The levels of macrophage inflammatory protein 2 (MIP-2), keratinocyte-derived chemokine (KC), tumor necrosis factor (TNF)-α, and interleukin (IL)-1β in the lung were measured by ELISA. Production of MIP-2 and KC from neutrophils and macrophages was quantified in vitro. MIP-2 mRNA expression in the neutrophils was analyzed by real-time reverse transcription-PCR, and the extent of phosphorylation of ERK1/2 and Syk in the neutrophils was analyzed by Western blotting.

Results: The MPO(-/-) mice that received nCA showed more severe pneumonia than wild-type mice. Within 12 h of nCA administration, MPO(-/-) mice had significantly higher numbers of alveolar neutrophils and increased production of MIP-2 and KC relative to the responses seen in wild-type mice. Neutralization of MIP-2 and KC in vivo significantly reduced neutrophil infiltration. In vitro, production of MIP-2, but not that of KC, was enhanced in the nCA-stimulated neutrophils from MPO(-/-) mice, concomitant with up-regulation of Syk and ERK1/2. At 1 and 3 days after nCA administration, MPO(-/-) mice had significantly higher lung concentrations of TNF-α and IL-1β than wild-type mice.

Conclusion: Pulmonary administration of nCA produced an altered inflammatory response in MPO(-/-) mice relative to wild-type mice. Enhanced MIP-2 production by MPO(-/-) neutrophils may at least partly contribute to exacerbated inflammation in mutant mice.