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Infect. Immun., May 1995, 1876-1886, Vol 63, No. 5
S Inoue, S Itagaki and F Amano
Listeria monocytogenes is a facultative intracellular pathogen and survives
within phagocytic cells by escaping from phagosomes into the cytoplasm. It
has been reported that, in vivo, L. monocytogenes is effectively eliminated
through cell-mediated immunity, especially by macrophages which have been
immunologically activated by cytokines such as gamma interferon
(IFN-gamma). However, this killing mechanism for L. monocytogenes and the
role of macrophage activation in this bacterial killing are unclear. We
demonstrated the listericidal effect of oxidative radicals induced by
lipopolysaccharide (LPS) and IFN-gamma, using a macrophage-like cell line,
J774.1, and a mutant cell line, LPS1916. LPS1916 cells do not exhibit
normal generation of O2- and H2O2 after treatment with 0.1 microgram of LPS
per ml, although J774.1 cells generate 100 times the normal level of
oxidative radicals with the same LPS treatment. The growth of L.
monocytogenes was strongly inhibited in J774.1 cells pretreated with 0.1
microgram of LPS per ml or the combination of 0.1 microgram of LPS per ml
and 10 U of IFN-gamma per ml. On the other hand, in LPS1916 cells, the
growth of L. monocytogenes was not inhibited by treatment with LPS only,
although LPS1916 cells pretreated with the combination of LPS and IFN-gamma
showed moderate inhibition of listerial growth. This killing was not
influenced by treatment with NG-monomethyl-L-arginine, which is a strong
inhibitor of nitrite oxide generation. Interestingly, J774.1 cells treated
with LPS did not show enhanced intraphagosomal killing of a nonhemolytic
strain of avirulent L. monocytogenes that lacks the ability to escape from
phagosomes, and this killing was not influenced by treatment with NG-
monomethyl-L-arginine either. These results suggest that the reactive
oxygen radicals are more important than nitric oxide in the mechanism
underlying the intracellular killing of virulent L. monocytogenes and that
there seem to be different killing mechanisms for virulent and avirulent
strains of L. monocytogenes in activated-macrophage cell lines.
Copyright © 1995, American Society for Microbiology
Intracellular killing of Listeria monocytogenes in the J774.1 macrophage-like cell line and the lipopolysaccharide (LPS)-resistant mutant LPS1916 cell line defective in the generation of reactive oxygen intermediates after LPS treatment
Department of Veterinary Science, National Institute of Health, Tokyo, Japan.
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