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Infection and Immunity, April 2000, p. 2187-2195, Vol. 68, No. 4
Wadsworth Center, New York State Department
of Health, Albany, New York 12201-2002,1 and
Department of Biomedical Sciences, School of Public Health,
University at Albany, Albany, New York
12201-05092
Received 21 May 1999/Returned for modification 14 October
1999/Accepted 3 January 2000
It is generally accepted that cellular, but not humoral immunity,
plays an important role in host defense against intracellular bacteria.
However, studies of some of these pathogens have provided evidence that
antibodies can provide immunity if present during the initiation of
infection. Here, we examined immunity against infection by
Ehrlichia chaffeensis, an obligate intracellular bacterium
that causes human monocytic ehrlichiosis. Studies with mice have
demonstrated that immunocompetent strains are resistant to persistent
infection but that SCID mice become persistently and fatally infected.
Transfer of immune serum or antibodies obtained from immunocompetent
C57BL/6 mice to C57BL/6 scid mice provided significant
although transient protection from infection. Bacterial clearance was
observed when administration occurred at the time of inoculation or
well after infection was established. The effect was dose dependent,
occurred within 2 days, and persisted for as long as 2 weeks. Weekly
serum administration prolonged the survival of susceptible mice.
Although cellular immunity is required for complete bacterial
clearance, the data show that antibodies can play a significant role in
the elimination of this obligate intracellular bacterium during active
infection and thus challenge the paradigm that humoral responses are
unimportant for immunity to such organisms.
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Antibody-Mediated Elimination of the Obligate
Intracellular Bacterial Pathogen Ehrlichia chaffeensis
during Active Infection

*
Corresponding author. Mailing address: Wadsworth
Center, 120 New Scotland Ave., Albany, NY 12208. Phone: (518) 473-2795. Fax: (518) 486-4395. E-mail: gary.winslow{at}wadsworth.org.
Present address: Department of Pathology, Case Western Reserve
University, MetroHealth Medical Center, Cleveland, OH 44109.
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