Interaction of Aspergillus fumigatus Spores with Human Leukocytes and Serum

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Serum was necessary for optimal phagocytosis of Aspergillus fumigatus spores by human leukocytes, and its opsonic capacity was greatly diminished by heat inactivation (56 C, 30 min). A germination assay, described in this report, was developed to study the fate of phagocytized spores. After incubation for 3 hr with normal leukocytes and serum, spores ingested by peripheral blood neutrophils and monocytes remained viable. Since we had previously found that myeloperoxidase (MPO), a lysosomal enzyme of human neutrophils and monocytes, exerted fungicidal activity against Candida albicans when combined with H2O2 and chloride or iodide, the effects of these substances on A. fumigatus spores were examined. Spore viability was not impaired by MPO alone, H2O2 alone, or KI alone, but high concentrations of KI and H2O2 in combination caused marked inhibition of subsequent germination. MPO imparted fungicidal activity to concentrations of KI and H2O2 that lacked any effect in its absence. NaCl, in combination with MPO and H2O2, was far less effective than the iodide salt against A. fumigatus. The relative ineffectiveness of chloride in this system could underly the apparent inability of human neutrophils to kill ingested A. fumigatus spores, despite their competence to kill C. albicans.

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