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Infection and Immunity, March 2000, p. 1026-1033, Vol. 68, No. 3
Trudeau Institute, Inc., Saranac Lake, New
York 12983
Received 28 June 1999/Returned for modification 5 August
1999/Accepted 29 November 1999
T lymphocytes and gamma interferon (IFN-
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
B Cells Are Essential for Vaccination-Induced
Resistance to Virulent Toxoplasma gondii
and
) are known mediators of
immune resistance to Toxoplasma gondii infection, but
whether B cells also play an important role is not clear. We have
investigated this issue using B-cell-deficient (µMT) mice. If
vaccinated with attenuated T. gondii tachyzoites, µMT
mice are susceptible to a challenge intraperitoneal infection with
highly virulent tachyzoites that similarly vaccinated B-cell-sufficient
mice resist. Susceptibility is evidenced by increased numbers of
parasites at the challenge infection site and by extensive mortality.
The susceptibility of B-cell-deficient mice does not appear to be
caused by deficient T-cell functions or diminished capacity of
vaccinated and challenged B-cell-deficient mice to produce IFN-
.
Administration of Toxoplasma-immune serum, but not
nonimmune serum, to vaccinated B-cell-deficient mice significantly
prolongs their survival after challenge with virulent tachyzoites.
Vaccinated mice lacking Fc receptors or the fifth component of
complement resist a challenge infection, suggesting that neither
Fc-receptor-dependent phagocytosis of antibody-coated tachyzoites nor
antibody-dependent cellular cytotoxicity nor
antibody-and-complement-dependent lysis of tachyzoites is a crucial
mechanism of resistance. However, Toxoplasma-immune serum
effectively inhibits the infection of host cells by tachyzoites in
vitro. Together, the results support the hypothesis that B cells are
required for vaccination-induced resistance to virulent tachyzoites in
order to produce antibodies and that antibodies may function
protectively in vivo by blocking infection of host cells by tachyzoites.
*
Corresponding author. Mailing address: Trudeau
Institute, Inc., P.O. Box 59, Saranac Lake, NY 12983. Phone: (518)
891-3084. Fax: (518) 891-5126. E-mail:
ljohnson{at}trudeauinstitute.org.
Present address: Procter and Gamble Pharmaceuticals, Cincinnati, OH
45253-8707.
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