Volume 36, Issue 3
  • ISSN: 0002-9637
  • E-ISSN: 1476-1645



Human monocytes maintained in culture lose microbicidal activity against intracellular protozoa which has been correlated with attenuation of the respiratory burst. The granule enzyme myeloperoxidase, which can markedly amplify hydrogen peroxide-pendent antimicrobial activity, is also lost in vitro. Adherent monocytes were examined immediately, 3 and 10–14 days following explanation, for the magnitude of the stimulated respiratory burst and for cellular myeloperoxidase. Fresh cells generated 254 ± 38 nmol O /mg protein as compared to a peak of 782 ± 45 nmol O /mg at 3 days and < 100 nmol O /mg after 10–14 days. The myeloperoxidase content of the cells also decreased; over 85% was lost after 3 days. Fresh monocytes killed over 90% of ingested or . In contrast, 10–14 day explanted monocytes killed only 12% of ingested and 33% of , and surviving organisms replicated readily. The 3-day monocytes were significantly less able to kill protozoa than were fresh cells despite their nearly 3-fold greater generation of O . If peroxidase was reintroduced into 3-day monocytes by coating organisms with eosinophil peroxidase prior to phagocytosis, their antiprotozoa activity was nearly restored to that of freshly explanted cells.


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