Killing of gram-negative bacteria by neutrophils: role of O2-independent system in intracellular killing and evidence of O2-dependent extracellular killing.

For many strains of these two bacterial species, ingested bacteria are efficiently killed by O2-independent mechanisms. Intracellular killing depends not on 2de novo generation of toxic products of the respiratory burst but rather on intracellular delivery to pre-existing cytotoxic proteins. The principal O2- independent bactericidal system toward these bacteria appears to be BPI which rapidly binds to ingested bacteria and whose discrete action closely resembles the initial lesions produced by the intact neutrophil. In addition, at least for one strain of E. coli (S15), extracellular bacteria can be killed in an O2- dependent fashion.