Research Group Heussler (Malaria I) - Bernhard-Nocht-Institut für ...

our 10 to 100 fold more parasites within various organs
such as heart muscle or the spleen. IL-12 is expressed
by activated macrophages and augments the
generation of Th1 cells, the production of IFN-γ and the
activation of NK cells. IL-18 has been shown to augment
IFN-γ expression and NK cell activation in the presence
of IL-12. We used C57BL/6 mice deficient of IL-
12p40 or of IL-18 to determine differential requirements
for these Th1 inducing cytokines in the implementation
of a protective immune response. We analysed trypanocidal
effector functions of NK cells and their contribution
to innate resistance to the parasite.
Project Description and Results
IL-12-/- mice were highly susceptible to T.cruzi infection
and succumbed to low infective doses, displaying high
parasitemia and tissue parasite burdens on day 14 of
infection (fig. 1). IL-18-/- mice were found to resist low
infective doses to the same extent as wildtype mice.
Tissue burdens were not significantly increased in
these mice. IFN-γ levels in the sera of infected mice, as
well as in supernatants of splenic T cell cultures, were
decreased in IL-18-/- mice, and diminished in IL-12-/mice.
IL-4 levels were significantly increased in supernatants
from IL-12-/- mice but not from IL-18-/- mice, indicating
that the deficiency of IL-18 did not reverse the
strong Th1 biased immune response of C57BL/6 mice
to T. cruzi infection, while IL-12 was required to mount a
Th1 response. These results imply that other than IL-12,
IL-18 is dispensable in the generation of a protective
pro-inflammatory immune response to experimental T.
cruzi infection in mice.
The role of NK cells in murine Chagas’ disease was
further analysed. Splenic NK cells from naive mice were
found to be activated by co-culture with trypanosomes.
T. cruzi-infected mice displayed increased levels of parasitaemia
when NK cells were depleted, but tissue parasite
burdens and mortality rates were not affected.
NK cells isolated from spleen displayed intimate interaction
with epimastigotes in vitro (fig. 2) and exhibited
a contact-dependent trypanocidal activity. Cytotoxic
granules of NK cells were found to be required, but the
effect was perforin-independent, since it was also seen
with NK cells from perforin knockout mice. These results
imply that NK cells primarily act on extracellular
trypanosomes by a contact-dependent, perforin-independent
mechanism that contributes to restricting parasitaemia.
55
Selected Publications
• Graefe SEB, Wiesgigl M, Gaworski I, Macdonald A,
Clos J (2002).
Inhibition of HSP90 in Trypanosoma cruzi induces a
stress response but no stage differentiation.
Eukaryotic Cell 1: 936-43
• Graefe SEB, Meyer BS, Müller-Myhsok B, Drosten C,
Laue T, Steeg C, Nürnberg P, Fleischer B (2003).
Murine susceptibility to Chagas’ disease maps to
chromosomes 5 and 17. Genes Immun 4: 321-5
• Graefe SEB, Jacobs J, Gaworski I, Klauenberg U,
Steeg C, Fleischer B (2003).
Interleukin-12 but not interleukin-18 is required for
immunity to Trypanosoma cruzi in mice.
Microbes Infect 5: 833-9
• Lieke T, Graefe SEB, Klauenberg U, Fleischer B,
Jacobs T (2004): NK cells contribute to the control of
Trypanosoma cruzi infection by killing free parasites
by perforin-independent mechanisms.
Infect Immun, submitted
Cooperating Partners
• Birgit S. Meyer, Peter Nürnberg
Max-Delbrück-Center, Berlin
Investigators
• Sebastian Graefe
• Bernhard Fleischer
• Thomas Jacobs
• Ulricke Klauenberg
• Thorsten Lieke
• Christiane Steeg
Medical Microbiology Section
Figure 2.
Scanning electron micrograph
showing intimate interaction
between splenic
DX5 + NK cells (purified by
magnetic cell sorting) and
epimastigotes of T. cruzi
(12000x).