OxyFile #133

Molecular and Cellular Biochemistry, 49
143-149 (1982)

Hydrogen Peroxide Mediated Killing of Bacteria

D.P. Clifford and J.E. Repine

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.  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) 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.