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Infection and Immunity, January 2000, p. 197-204, Vol. 68, No. 1
Departments of Internal
Medicine1 and
Pathology,2 Saint Louis University
Health Sciences Center, St. Louis, Missouri 63110
Received 24 March 1999/Returned for modification 18 May
1999/Accepted 11 October 1999
In general, gamma interferon (IFN-
0019-9567/0/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Involvement of CD4+ Th1 Cells in Systemic Immunity
Protective against Primary and Secondary Challenges with
Trypanosoma cruzi
)-producing CD4+
Th1 cells are important for the immunological control of
intracellular pathogens. We previously demonstrated an association
between parasite-specific induction of IFN-
responses and resistance
to the intracellular protozoan Trypanosoma cruzi. To
investigate a potential causal relationship between Th1 responses and
T. cruzi resistance, we studied the ability of Th1 cells to
protect susceptible BALB/c mice against virulent parasite challenges.
We developed immunization protocols capable of inducing polarized Th1
and Th2 responses in vivo. Induction of parasite-specific Th1
responses, but not Th2 responses, protected BALB/c mice against
virulent T. cruzi challenges. We generated T. cruzi-specific CD4+ Th1 and Th2 cell lines from
BALB/c mice that were activated by infected macrophages to produce
their corresponding cytokine response profiles. Th1 cells, but not
Th2 cells, induced nitric oxide production and inhibited
intracellular parasite replication in T. cruzi-infected macrophages. Despite the ability to inhibit parasite replication in
vitro, Th1 cells alone could not adoptively transfer protection against
T. cruzi to SCID mice. In addition, despite
the fact that the adoptive transfer of CD4+ T lymphocytes
was shown to be necessary for the development of immunity protective
against primary T. cruzi infection in our SCID mouse model,
protective secondary effector functions could be transferred to SCID
mice from memory-immune BALB/c mice in the absence of
CD4+ T lymphocytes. These results indicate that, although
CD4+ Th1 cells can directly inhibit intracellular parasite
replication, a more important role for these cells in T. cruzi systemic immunity may be to provide helper activity
for the development of other effector functions protective in vivo.
*
Corresponding author. Mailing address: Division of
Infectious Diseases and Immunology, Saint Louis University Health
Sciences Center, 3635 Vista Ave., St. Louis, MO 63110. Phone: (314)
577-8648. Fax: (314) 771-3816. E-mail: hoftdf{at}slu.edu.
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