Biology Reference
In-Depth Information
group bugs tested positive by ELISA for progesterone binding activity. This study established that
paratransgenic transformation of
R. prolixus
could result in constitutive and stable expression of a
functional single-chain antibody. It provided the basis for expression of single-chain antibodies that
target surface antigens of
T. cruzi
to inactivate the trypanosome within the gut of the reduviid bug.
T. cruzi
has a life cycle consisting of four major stages. The parasite multiplies as an epimas-
tigote within the gut of the insect host and differentiates into the trypomastigote in the hindgut.
The trypomastigotes are metacyclic, nondividing invasive forms that are transmitted to the mam-
malian host by fecal droplets released by the bug during a blood meal. In the mammalian host,
T. cruzi
invades the macrophages and multiplies as an amastigote that later differentiates into the
trypomastigote form. Many surface-speciÝc antigens of
T. cruzi
have been cloned and sequenced.
Gp72 is a 72-kd glycoprotein that was Ýrst identiÝed on epimastigote cells using a speciÝc
monoclonal antibody WIC29.26 (Haynes et al., 1996). The WIC29.26 epitope was characterized
on epimastigotes and insect-derived metacyclic trypomastigotes and to a lesser extent on trypo-
mastigotes that were derived from a culture of epimastigotes. The WIC 29.26 epitope is not present
in the amastigote form of
T. cruzi
.
Gp72 null mutant strains of
T. cruzi
are morphologically distinct from wild-type parasites,
predominantly due to detachment of the Þagellum from the Þagellar pocket. The exact function of
Gp72 is unclear, but it has been implicated to have a role in maintenance of morphology, to function
as an acceptor for complement factor C3, and to help in differentiation of
T. cruzi
. Gp72 null mutant
strains of
T. cruzi
are grossly misshapen, have impaired motility, and, in a
Triatoma infestans
model,
are incapable of maturation in the bug gut (Nozaki and Cross, 1994).
Studies involving the monoclonal anti-Gp72 antibody WIC29.26 are currently under way.
Trypanosoma cruzi
strains ÑYÒ and ÑTelhuenÒ that have been coated with WIC29.26
(Figure 6.5)
have been introduced into
R. prolixus
. Survival and maturation of the antibody-coated trypanosomes
will be determined. Ultimately, Vh-Kappa fragments that target the Gp72 epitope and, potentially,
other key surface epitopes of
T. cruzi
will be expressed in the gut of
R. prolixus
by engineered
Rhodococcus rhodnii
. Antibody-mediated disruption of the
T. cruzi
life cycle coupled with lytic
functions of immune peptides such as cecropin A may provide the necessary molecular armamen-
tarium for a successful paratransgenic strategy.
FIGURE 6.5
(Color Ýgure follows p. 206.)
ImmunoÞuorescence stain of ÑYÒ strain
Trypanosoma cruzi
coated with the anti-Gp72 antibody, WIC 29.26 at 400 magniÝcation.
