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Infection and Immunity, September 2001, p. 5423-5429, Vol. 69, No. 9
Department of Medical Microbiology and
Immunology, University of Wisconsin School of Medicine, Madison,
Wisconsin 537061; Department of
Immunology and Microbiology, Wayne State University School of
Medicine, Detroit, Michigan 482012; and
Department of Molecular Microbiology, Washington University
School of Medicine, St. Louis, Missouri 631103
Received 4 April 2001/Returned for modification 30 May
2001/Accepted 19 June 2001
Chlamydia pneumoniae causes community-acquired
pneumonia and is associated with several chronic diseases, including
asthma and atherosclerosis. The intracellular growth rate of C.
pneumoniae slows dramatically during chronic infection, and
such persistence leads to attenuated production of new elementary
bodies, appearance of morphologically aberrant reticulate bodies, and
altered expression of several chlamydial genes. We used an in vitro
system to further characterize persistent C. pneumoniae
infection, employing both ultrastructural and transcriptional activity
measurements. HEp-2 cells were infected with C.
pneumoniae (TW-183) at a multiplicity of infection of 3:1, and
at 2 h postinfection gamma interferon (IFN-
0019-9567/01/$04.00+0 DOI: 10.1128/IAI.69.9.5423-5429.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Chlamydia pneumoniae Expresses Genes
Required for DNA Replication but Not Cytokinesis during Persistent
Infection of HEp-2 Cells
) was added to the
medium at 0.15 or 0.50 ng/ml. Treated and untreated cultures were
harvested at several times postinfection. RNA was isolated and reverse
transcribed, and reverse transcription (RT)-PCR analyses targeting
primary transcripts from chlamydial rRNA operons as well as
dnaA, polA, mutS,
minD, ftsK, and ftsW mRNA
were done. Some cultures were fixed and stained for electron microscopic analysis, and a real-time PCR assay was used to assess relative chlamydial chromosome accumulation under each culture condition. The latter assays showed that bacterial chromosome copies
accumulated severalfold during IFN-
treatment of infected HEp-2
cells, although less accumulation was observed in cells treated with
the higher dose. Electron microscopy demonstrated that high-dose
IFN-
treatment elicited aberrant forms of the bacterium. RT-PCR
showed that chlamydial primary rRNA transcripts were present in all
IFN-
-treated and untreated cell cultures, indicating bacterial
metabolic activity. Transcripts from dnaA, polA, mutS, and minD, all
of which encode products for bacterial chromosome replication and
partition, were expressed in IFN-
-treated and untreated cells. In
contrast, ftsK and ftsW, encoding
products for bacterial cell division, were expressed in untreated
cells, but expression was attenuated in cells treated with low-dose
IFN-
and absent in cells given the high dose of cytokine. Thus, the development of persistence included production of transcripts for DNA
replication-related, but not cell division-related, genes. These
results provide new insight regarding molecular activities that
accompany persistence of C. pneumoniae, as well as
suggesting requirements for reactivation from persistent to productive growth.
*
Corresponding author. Mailing address: Department of
Medical Microbiology and Immunology, University of Wisconsin School of Medicine, 436 Service Memorial Institute, 1300 University Ave., Madison, WI 53706. Phone: (608) 263-2494. Fax: (608) 265-0683. E-mail:
gibyrne{at}facstaff.wisc.edu.
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