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Infect. Immun., 02 1997, 758-766, Vol 65, No. 2
C van Ooij, G Apodaca and J Engel
Chlamydia trachomatis, an obligate intracellular parasite and a major human
pathogen, invades eukaryotic host cells and replicates within a
membrane-bound compartment (termed the vacuole or inclusion) in the
cytoplasm of the host cell. In this report, we describe in detail the
characteristics of the vacuole throughout the chlamydial life cycle in
terms of the endocytic pathway, as determined by epifluorescent and
confocal immunofluorescence microscopy. By indirect immunofluorescence, the
transferrin receptor (TfR), a component of early endosomes, and the
cation-independent mannose-6-phosphate receptor (CI-M6PR), a component of
late endosomes, were found in close association with the chlamydial vacuole
as early as 4 h postinfection (hpi) and as late as 20 hpi. Fluorescein
isothiocyanate (FITC)-labeled Tf was also found to colocalize with the
vacuole at 4, 12, and 20 hpi, indicating that exogenously added ligands can
be transported to the region of the vacuole. Antibodies to several
different lysosomal proteins failed to label the chlamydial vacuole at any
time point during the life cycle. Indirect immunofluorescence of cells
infected with chlamydiae stained with an antibody to the trans-Golgi
network (TGN) protein TGN38 demonstrated that in infected cells, the
integrity and structure of the TGN was altered. The rates of Tf recycling
in infected and uninfected cells were compared by fluorescence microscopy
and quantitated with 125I-Tf. While the rate of FITC-Tf recycling from
endocytic compartments in chlamydia-infected cells did not appear different
from that of uninfected cells, a small pool of FITC-Tf that had accumulated
adjacent to the chlamydial vacuole recycled at a slower rate. Quantitation
of Tf recycling with 125I-Tf showed that Tf was recycled more slowly in
infected cells than in uninfected cells. The altered distribution of
several endocytic pathway markers and the slowed Tf recycling are
consistent with the hypothesis that the chlamydial vacuole interacts with
the endocytic pathway of the host. These results furthermore suggest that
the chlamydial vacuole does not correspond to a canonical endocytic
compartment but that it is a unique and dynamic organelle that shares
several characteristics with recycling endosomes of the host cell.
Interactions with the early and/or late endosomal compartments, in addition
to the Golgi apparatus, may provide a source of membrane or nutrients for
the replicating organisms.
Copyright © 1997, American Society for Microbiology
Characterization of the Chlamydia trachomatis vacuole and its interaction with the host endocytic pathway in HeLa cells
Biomedical Sciences Program, University of California, San Francisco 94143-0654, USA.
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