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Infect. Immun., Sep 1995, 3609-3620, Vol 63, No. 9
MS Swanson and RR Isberg
Legionella pneumophila replicates within a membrane-bounded compartment
that is studded with ribosomes. In this study we investigated whether these
ribosomes originate from the cytoplasmic pool or are associated with host
endoplasmic reticulum (ER). Immunofluorescence and electron microscopic
localization studies of ER proteins in macrophages infected with L.
pneumophila indicated that the bacteria reside in a compartment surrounded
by ER. An L. pneumophila mutant that grows slowly in macrophages was slow
to associate with host ER, providing genetic evidence in support of the
hypothesis that this specialized vacuole is required for intracellular
bacterial growth. Ultrastructural studies, in which the ER luminal protein
BiP was labeled by immunoperoxidase cytochemistry, revealed that L.
pneumophila replication vacuoles resemble nascent autophagosomes.
Furthermore, short-term amino acid starvation of macrophages, which
stimulated host autophagosomes. Furthermore, short-term amino acid
starvation of macrophages, which stimulated host autophagy, increased
association of the bacteria with the ER and enhanced bacterial growth.
These results are compatible with the hypothesis that L. pneumophila
exploits the autophagy machinery of macrophages to establish an
intracellular niche favorable for replication.
Copyright © 1995, American Society for Microbiology
Association of Legionella pneumophila with the macrophage endoplasmic reticulum
Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111, USA.
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