Brain injury was reduced in mice lacking a functional NADPH oxidase in both the central nervous system and peripheral leukocytes, suggesting a pivotal role for the NADPH oxidase in the pathogenesis of ischemia-reperfusion injury in the brain.

Gp91-phox is an integral component of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex that generates reactive oxygen species (ROS) in activated circulating phagocytes. The authors previously demonstrated that gp91-phox knockout (KO) mice show significant protection from neuronal injury after cerebral ischemia--reperfusion injury, suggesting a pivotal role for this enzyme. Moreover, results from chimeric mice suggested that elimination of gp91-phox from both circulating phagocytes and a putative central nervous system (CNS) source were required to confer neuroprotection. In the current study, the authors demonstrated gp91-phox-specific immunostaining of perivascular cells in the CNS of control rats. However, after transient cerebral ischemia, gp91-phox-positive phagocytes were observed within the core ischemic region and activated microglial cells were positive in the penumbra. Such activated microglial cells were also gp91-phox-positive in the CNS of a chimpanzee with mild meningitis. Finally, in humans, both normal adult CNS tissues and isolated fetal microglial cells expressed gp91-phox mRNA. These microglia also expressed mRNA for the five other known components that comprise the NADPH oxidase complex. These data strongly suggest that microglial cells may contain a functionally active NADPH oxidase capable of generating ROS during CNS inflammation.

Tyrosine phosphorylation is an important component of the signaling pathways responsible for the activation of the macrophage respiratory burst. Because the virulence plasmid of Yersinia enterocolitica encodes a phosphotyrosine phosphatase, YopH, it is possible that the pathogenic strategy of Y. enterocolitica involves the disruption of tyrosine phosphorylation in the macrophage leading to inhibition of respiratory burst activity. We have investigated the effects of Yersinia infection on tyrosine phosphorylation and respiratory burst activity in murine bone marrow-derived macrophages. Infection of macrophages with virulent [Ye(pYV+)] but not avirulent [Ye(pYV-)] strains of Y. enterocolitica was found to suppress both tyrosine phosphorylation and respiratory burst activity in response to zymosan. Mutational inactivation of YopH reversed the suppressive effect of Ye(pYV+) on zymosan-induced tyrosine phosphorylation, indicating that YopH is responsible for the dephosphorylation of macrophage phosphotyrosine-containing proteins observed in macrophages infected with the virulent strain of Y. enterocolitica. In contrast, mutational loss of YopH failed to reverse the inhibitory effect of Ye(pYV+) on the zymosan-triggered respiratory burst. We conclude that the inhibition of the macrophage respiratory burst by Y. enterocolitica involves a plasmid-encoded virulence protein(s) other than, or in addition to, YopH.

The capacity of neutrophils to generate superoxide (O 2 . ) can be enhanced by prior exposure to "priming"