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Journal of Virology, April 1999, p. 3273-3283, Vol. 73, No. 4
Department of Pathology and Center for
Immunology, Washington University School of Medicine, St. Louis,
Missouri 63110
Received 5 October 1998/Accepted 23 December 1998
B cells have previously been identified as the major hematopoietic
cell type harboring latent gammaherpesvirus 68 (
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Macrophages Are the Major Reservoir of Latent
Murine Gammaherpesvirus 68 in Peritoneal Cells
HV68) (N. P. Sunil-Chandra, S. Efstathiou, and A. A. Nash, J. Gen. Virol. 73:3275-3279, 1992). However, we have shown that
HV68 efficiently establishes latency in B-cell-deficient mice (K. E. Weck, M. L. Barkon, L. I. Yoo, S. H. Speck, and H. W. Virgin,
J. Virol. 70:6775-6780, 1996), demonstrating that B cells are not
required for
HV68 latency. To understand this dichotomy, we
determined whether hematopoietic cell types, in addition to B cells,
carry latent
HV68. We observed a high frequency of cells that
reactivate latent
HV68 in peritoneal exudate cells (PECs) derived
from both B-cell-deficient and normal C57BL/6 mice. PECs were composed
primarily of macrophages in B-cell-deficient mice and of macrophages
plus B cells in normal C57BL/6 mice. To determine which cells in PECs
from C57BL/6 mice carry latent
HV68, we developed a
limiting-dilution PCR assay to quantitate the frequency of cells
carrying the
HV68 genome in fluorescence-activated cell sorter-purified cell populations. We also quantitated the contribution of individual cell populations to the total frequency of cells carrying
latent
HV68. At early times after infection, the frequency of PECs
that reactivated
HV68 correlated very closely with the frequency of
PECs carrying the
HV68 genome, validating measurement of the
frequency of viral-genome-positive cells as a measure of latency in
this cell population. F4/80-positive macrophage-enriched, lymphocyte-depleted PECs harbored most of the
HV68 genome and efficiently reactivated
HV68, while CD19-positive, B-cell-enriched PECs harbored about a 10-fold lower frequency of
HV68
genome-positive cells. CD4-positive, T-cell-enriched PECs contained
only a very low frequency of
HV68 genome-positive cells, consistent
with previous analyses indicating that T cells are not a reservoir for
HV68 latency (N. P. Sunil-Chandra, S. Efstathiou, and A. A. Nash, J. Gen. Virol. 73:3275-3279, 1992). Since macrophages are bone marrow derived, we determined whether elicitation of a large
inflammatory response in the peritoneum would recruit additional latent
cells into the peritoneum. Thioglycolate inoculation increased the
total number of PECs by about 20-fold but did not affect the frequency
of cells that reactivate
HV68, consistent with a bone marrow
reservoir for latent
HV68. These experiments demonstrate
HV68
latency in two different hematopoietic cell types, F4/80-positive
macrophages and CD19-positive B cells, and argue for a bone marrow
reservoir for latent
HV68.
*
Corresponding author. Mailing address: Department of
Pathology, Box 8118, 660 S. Euclid Ave., St. Louis, MO 63110. Phone: H.W.V. (314) 362-9223; S.H.S. (314) 362-0367. Fax: (314) 362-4096. E-mail: virgin{at}pathology.wustl.edu or
speck{at}pathology.wustl.edu.
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