Polymorphonuclear leukocytes (PMN) or neutrophils have multiple systems available for killing ingested bacteria. Nearly each of these incorporates H2O2 indicating the essential nature of this reactive oxygen intermediate for microbicidal activity. Following ingestion of bacteria by PMN, H2O2 is formed by the respiratory burst which consumes O2 and generates H2O2 from O2 .-. H2O2 is deposited intracellularly near bacteria within phagocytic vacuoles where it can react with the MPO-H2O2-halide system to form toxic hyperchlorous acid (HOCl) and/or possibly singlet oxygen (1O2). H2O2 can also react with O2 .- and/or iron (Fe++) from lactoferrin or bacteria to form the highly toxic hydroxyl radical (.OH). These mechanisms appear important since deficiencies of H2O2 production, myeloperoxidase or lactoferrin frequently increases their owner's susceptibility to infection. In particular, examination of PMN from infection prone patients with chronic granulomatous disease (CGD) most clearly demonstrates the importance of H2O2 in killing of bacteria. CGD PMN lack the capacity to effectively generate H2O2 and subsequently have impaired ability to kill catalase positive (H2O2 producing) but not catalase negative (not H2O2 producing) bacteria. PMN also have catalase and glutathione peroxidase systems in their cytoplasms to protect themselves from the toxicity of H2O2. Finally, while H2O2 is critical for host defense, it can also be released extracellularly and thereby play a significant role in PMN mediated tissue injury.
Chemiluminescence was used to determine opsonic requirements for interaction of Cryptococcus neoformans with human peripheral blood polymorphonuclear leukocytes (PMNLs) and monocytes (MNs). Peak chemiluminescence (mean +/- SD) was 172 +/- 25 X 10(3) for PMNLs and 50 +/- 13 X 10(3) for MNs with 20% pooled normal human serum vs. 10 +/- 3 X 10(3) for PMNLs and 6 +/- 1 X 10(3) for MNs without serum (P less than 0.005 for each comparison). The nature of the serum requirement was investigated; alternative pathway serum complements were necessary. The alternative pathway was activated directly by C. neoformans without the need for specific antibody. Chemiluminescence provided a quantitative and reproducible assay of the interaction of human phagocytes with C. neoformans and may be useful in studying opsonic requirements of other fungi.
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