Evasion of Legionella pneumophila from the bactericidal system by reactive oxygen species (ROS) in macrophages.
We demonstrated that the production of reactive oxygen species (ROS) by U937 macrophage-like cells was suppressed upon infection with a wild type Legionella pneumophila strain, whereas such suppression was not observed in the case of infection with intracellular growth-deficient mutants. This was supported not only by measuring ROS released into the supernatants of cell cultures by chemiluminescence assaying but also by detecting intracellular ROS with a fluorescent probe, 2-[6-(4'-amino)phenoxy-3H-xanthen-3-on-9-yl]benzoic acid (APF), under a confocal laser scanning microscope. Furthermore, more than 60% of the phagosomes containing intracellular growth-deficient mutants were colocalized with p47(phox), which is the cytosolic subunit of NADPH oxidase, consistently throughout the observation period in an early stage of bacterial infection. In contrast, the colocalization of p47(phox) was suppressed after infection with the wild type strain. These results suggest that the interference with ROS production by U937 cells infected with wild type L. pneumophila is due to a failure of NADPH oxidase activation through inhibition of p47(phox) recruitment to phagosomes harboring bacteria. The results also highlighted the difference in the nature of phagosomes between ones harboring the wild type and ones the intracellular growth-deficient strains.
Harada
Toshihiko
T
Laboratory of Microbiology and Immunology and the Global COE Program, School of Pharmaceutical Sciences, University of Shizuoka, Suruga-ku, Shizuoka-shi, Japan.
Miyake
Masaki
M
Imai
Yasuyuki
Y
D002460:Cell Line; D015169:Colony Count, Microbial; D006801:Humans; D016952:Legionella pneumophila / Q000235:genetics / Q000276:immunology* / Q000472:pathogenicity*; D008264:Macrophages / Q000737:chemistry / Q000276:immunology* / Q000382:microbiology*; D018613:Microscopy, Confocal; D019255:NADPH Oxidases / Q000032:analysis; D010588:Phagosomes / Q000737:chemistry / Q000382:microbiology; D017382:Reactive Oxygen Species / Q000032:analysis / Q000276:immunology*; D013481:Superoxides / Q000032:analysis
D017382:Reactive Oxygen Species; D013481:Superoxides; D019255:NADPH Oxidases; C060505:neutrophil cytosolic factor 1