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Infection and Immunity, May 2000, p. 2728-2734, Vol. 68, No. 5
Parasitology Research Center, Department of
Pathology, Tufts University School of Medicine,1
and Department of Pathology, Tufts University School of
Veterinary Medicine, and New England Medical
Center,2 Boston, Massachusetts 02111;
Department of Biological Chemistry and Molecular
Pharmacology, Harvard Medical School, Boston, Massachusetts
021153; and Department of Molecular
Microbiology, Washington University School of Medicine, St. Louis,
Missouri 631104
Received 29 November 1999/Returned for modification 11 January
2000/Accepted 4 February 2000
Earlier studies showed that mice primed for a few hours with the
trans-sialidase (TS) of Trypanosoma cruzi, the
agent of Chagas' disease, become highly susceptible to trypanosomal
infection. These studies suggest that TS affects parasite virulence
independent of antigenic stimulation. Potentially, TS could enhance or
reduce the virulence of heterologous microbes depending on the
mechanism of TS action and on the type of immune response elicited by
the particular parasite. We tested this hypothesis by expressing
heterologous TS in Leishmania major, a protozoan parasite
that causes cutaneous leishmaniasis and lacks TS and the TS product
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Heterologous Expression of Trypanosoma cruzi
trans-Sialidase in Leishmania major Enhances
Virulence


2-3-linked sialic acid. Leishmania cells transfected
with a T. cruzi TS expression construct made high levels of
active enzyme, which was present in the promastigotes and shed into the
extracellular milieu. TS expression did not affect L. major
binding to and entry into cultured macrophages or its tropism for
macrophage infection in vivo. However, TS-expressing L. major exhibited elevated virulence in BALB/c mice, as determined
by lesion progression, parasite numbers, and macro- and microscopic
examination of cutaneous lesions. Several genetic tests proved that the
enhanced virulence was directly attributable to TS expression. The
results are consistent with TS functioning to sabotage the mouse immune
system to confer a growth advantage on T. cruzi and
transgenic L. major. These data suggest that heterologous
expression of T. cruzi virulence factors in
Leishmania may provide a new approach for dissecting their function in vivo.
*
Corresponding author. Mailing address: Department of
Pathology, Parasitology Research Center, Tufts Medical School, 136 Harrison Avenue, Boston, MA 02111. Phone: 617-636-2933. Fax:
617-636-6849. E-mail: maperrin{at}yahoo.com.
Present address: The Center for Blood Research, Department of
Pathology, Harvard Medical School, Boston, MA 02115.
Present address: Millennium Pharmaceuticals, Inc., Cambridge,
MA 02139.
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