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Journal of Virology, August 2001, p. 7420-7428, Vol. 75, No. 16
Department of Neurology, Evanston
Hospital,1 and Departments of
Neurology,5
Microbiology-Immunology,4 and
Biochemistry, Molecular Biology and Cell
Biology,2 and Neuroscience Graduate
Program,3 Northwestern University, Evanston,
Illinois
Received 16 January 2001/Accepted 16 May 2001
The low-neurovirulence Theiler's murine encephalomyelitis viruses
(TMEV), such as BeAn virus, cause a persistent infection of the central
nervous system (CNS) in susceptible mouse strains that results in
inflammatory demyelination. The ability of TMEV to persist in the mouse
CNS has traditionally been demonstrated by recovering infectious virus
from the spinal cord. Results of infectivity assays led to the notion
that TMEV persists at low levels. In the present study, we analyzed the
copy number of TMEV genomes, plus- to minus-strand ratios, and
full-length species in the spinal cords of infected mice and infected
tissue culture cells by using Northern hybridization. Considering the
low levels of infectious virus in the spinal cord, a surprisingly large
number of viral genomes (mean of 3.0 × 109) was
detected in persistently infected mice. In the transition from the
acute (approximately postinfection [p.i.] day 7) to the persistent
(beginning on p.i. day 28) phase of infection, viral RNA copy numbers
steadily increased, indicating that TMEV persistence involves active
viral RNA replication. Further, BeAn viral genomes were full-length in
size; i.e., no subgenomic species were detected and the ratio of BeAn
virus plus- to minus-strand RNA indicated that viral RNA replication is
unperturbed in the mouse spinal cord. Analysis of cultured macrophages
and oligodendrocytes suggests that either of these cell types can
potentially synthesize high numbers of viral RNA copies if infected in
the spinal cord and therefore account for the heavy viral load.
A scheme is presented for the direct isolation of both cell types
directly from infected spinal cords for further viral analyses.
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.16.7420-7428.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
High Numbers of Viral RNA Copies in the Central Nervous
System of Mice during Persistent Infection with Theiler's
Virus
*
Corresponding author. Mailing address: Department of
Neurology, Multiple Sclerosis Research Center, Evanston Hospital,
Northwestern University, 2650 Ridge Ave., Evanston, IL 60201-1782. Phone: (847) 570-2168. Fax: (847) 570-1568. E-mail:
hllipton{at}merle.acns.nwu.edu.
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