Generation of hydrogen peroxide by Candida albicans and influence on murine polymorphonuclear leukocyte activity

Iodide fixation by murine polymorphonuclear leukocytes (PMN) incubated with viable Candida albicans blastoconidia increases directly with yeast cell concentration up to about 3 x 10(6) cells per ml, but above this concentration bound activity declines dramatically. To understand the basis for this decline, we examined the oxidative metabolism of fungi and stimulated PMN and found some remarkable similarities between these cell types. Both produced 14CO2 when incubated with [1-14C]glucose, both reduced cytochrome c, and both fixed radiolabeled iodide, although the fungi required exogenous lactoperoxidase. In dose-response experiments, iodination by fungi with lactoperoxidase was identical to that with PMN, i.e., the maximum bound activity occurred in cultures with 10(6) to 3 x 10(6) blastoconidia per ml. Iodination by fungi with lactoperoxidase was reduced when blastoconidia were incubated at 25 degrees C or in the presence of catalase and the metabolic inhibitors rotenone, antimycin A, and 2-deoxyglucose. Results from assays for oxidation of scopoletin and o-dianisidine showed that 10(6) blastoconidia in 1.0 ml of medium released 0.5 to 0.7 nmol of H2O2 after 1 h, but 3 X 10(6) and 10(7) cells released significantly less H2O2. These results suggest that iodide fixation by PMN and low numbers of fungal cells may reflect a cooperative effort, with fungi generating some H2O2 that reacts with the myeloperoxidase released from the PMN. With high concentrations of blastoconidia, H2O2 activity appeared to be specifically inhibited, possibly to protect fungal cells from damage.