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Infection and Immunity, September 1998, p. 4503-4506, Vol. 66, No. 9
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Protective Effect of Vaccination with a Combination
of Recombinant Surface Antigen 1 and Interleukin-12 against
Toxoplasmosis in Mice
Valerie
Letscher-Bru,1
Odile
Villard,1,*
Bernhard
Risse,2
Michael
Zauke,2
Jean-Paul
Klein,3 and
Truong T.
Kien1
Institut de Parasitologie et de Pathologie
Tropicale, Inserm U392, Faculté de
Médecine,1 and
Faculté de
Pharmacie,3 67000 Strasbourg, France, and
Roche Diagnostics, Basel, Switzerland2
Received 17 February 1998/Returned for modification 27 March
1998/Accepted 5 June 1998
 |
ABSTRACT |
We studied the immune response induced in mice by recombinant
Toxoplasma gondii surface antigen 1 (rSAG1) protein, alone
or combined with interleukin-12 (IL-12) as an adjuvant, and the
protective effect against toxoplasmosis. Immunization with rSAG1 alone
induced a specific humoral type 2 immunity and did not protect the
animals from infection. In contrast, immunization with rSAG1 plus IL-12 redirected humoral and cellular immunity toward a type 1 pattern and
reduced the brain parasite load by 40%.
 |
TEXT |
Toxoplasma gondii
infection is usually asymptomatic or mild, but it can be life
threatening in immunodeficient patients and fetuses (17).
The immune response induced in immunocompetent subjects by primary
T. gondii infection protects throughout life. This
protection is associated with a type 1 response, the main effectors of
which are T lymphocytes (12) and gamma interferon (IFN-
)
(32). The following general mechanisms are widely accepted (11). Macrophages infected by T. gondii secrete
interleukin-12 (IL-12), which activates T cells and NK cells to produce
IFN-
. IFN-
, in the presence of cofactors such as tumor necrosis
factor alpha (TNF-
), in turn activates macrophage toxoplasmicidal
activity. Similarly, stimulated T cells secrete IL-2 and IFN-
,
leading to a type 1 cellular immune response. Nevertheless, a moderate type 2 immune response is not necessarily detrimental, because it would
counter immunopathologic phenomena linked to excessive inflammatory and
type 1 responses (13).
The molecular structure of T. gondii is complex. Several
antigens involved in these immunological mechanisms have been
identified (10), and these form the basis for work on
candidate vaccines. The 30-kDa surface antigen 1 (SAG1) protein is the
major surface antigen of tachyzoites (4, 19) and is highly
conserved among virulent strains of T. gondii
(35). It induces high antibody titers in humans and is
recognized by all sera from seropositive subjects (28). The
protective value of SAG1 has also been evaluated in vivo in animal
models of T. gondii infection and showed only partial
protection (3, 7, 8, 20, 24). The model developed in our
laboratory since 1995 is based on the rapid immunization protocol
designed by Khan et al. (20). Because the use of
experimental adjuvants in humans is not authorized, we chose the
cytokine IL-12, which is undergoing clinical trials in cancer patients
(33). Moreover, IL-12 rapidly and strongly orients the
immune response toward a type 1 pattern (34, 36) and plays
an essential role in the acute phase of toxoplasmosis (18,
21), and its value as a Th1-inducing immunoadjuvant has clearly
been shown in several experimental models of infection (1, 26,
27). These results led us to replace the natural protein with a
recombinant SAG1 (rSAG1) protein produced in Escherichia
coli and then renatured. This recombinant protein does not contain
the glycosyl phosphatidyl inositol anchor, the immunological role of
which is, at present, unknown (30). A study by Harning et
al. (16) showed that this rSAG1 was well recognized by the
serum of seropositive subjects and that it induced antibodies
recognizing the natural protein in mice, indicating that the B
conformational epitopes were present.
The aim of this work was to characterize, in mice, the immune response
induced by T. gondii rSAG1 protein administered alone or
combined with IL-12 as an adjuvant and to assess the protective effect
of this vaccination against T. gondii infection.
Parasites.
Cysts of the avirulent PRU strain of T. gondii were obtained from the brains of orally infected Swiss OF1
mice (CERJ, Le Genest St. Isle, France) and prepared as previously
described (2). Tachyzoites of the virulent RH strain of
T. gondii were harvested from peritoneal fluid of Swiss OF1
mice infected intraperitoneally and were used to prepare the T. gondii lysate antigen (TLA) as previously described
(31).
Mouse immunization.
Female inbred CBA/J mice (CERJ) were used
at 8 to 10 weeks of age. rSAG1 protein expressed in E. coli
was kindly provided by Roche-Diagnostics, Basel, Switzerland.
Recombinant murine IL-12 was from Genzyme, Cergy Saint-Christophe,
France. Mice were immunized twice a week for 2 weeks (days 1, 4, 8, and
13) with rSAG1 alone (cumulative dose, 4 µg) or with rSAG1 plus IL-12
(cumulative dose, 4 µg of each). Control groups were injected with
IL-12 alone (cumulative dose, 4 µg) or with the vehicle. Each dose of
100 µl was injected subcutaneously in sterile water. For
immunological studies, three mice per group were sacrificed on day 21. Blood was obtained by retro-orbital puncture, and the spleens were
removed under sterile conditions. Each experiment was repeated three
times, and the experiments were reproducible. The results shown here
are from one representative experiment.
Measurement of antibody responses.
Specific anti-rSAG1
immunoglobulin G1 (IgG1) and IgG2a were measured by using an
enzyme-linked immunosorbent assay (ELISA). Ninety-six-well Maxisorb
microtiter plates (Nunc, Roskilde, Denmark) were coated overnight at
4°C with rSAG1 at 5 µg/ml in 0.1 M carbonate sodium buffer (pH 9.6)
(100 µl/well). The plates were then saturated for 1 h at 37°C
with 200 µl of phosphate-buffered saline (PBS)-1% bovine serum
albumin. Serum samples diluted 1:20 in PBS-0.05% Tween 20 (100 µl/well) were added in duplicate, and the plates were incubated for
1 h at 37°C. Peroxidase-labelled anti-IgG1 (clone LO-MG 1-2;
Biosoft, Paris, France) and biotinylated anti-IgG2a (clone LO-MG 2a-3;
Sigma, St. Louis, Mo.) were added at a dilution of 1/1,000 (100 µl/well) and incubated for 1 h at 37°C. To detect IgG2a, 100 µl of streptavidin-peroxidase (Amersham, Les Ullis, France) was added
(dilution 1/1,000), and this mixture was then incubated for 30 min at
room temperature. ABTS [2,2'-azinobis(3-ethylbenzthiazolinesulfonic acid)] substrate solution (KPL, Gaithersburg, Md.) was then added (100 µl/well) for 20 min at room temperature, and the reaction was stopped
by addition of 1% SDS (100 µl/well). Plates were read for
A405 in a microplate reader (Dynex Thermobio
Analysis, Issy les Moulineaux, France). Results are expressed as
indices of antibody titers (optical density at 405 nm
[OD405] of the sample/mean OD405 of three
negative controls).
Measurement of cytokine production.
Spleen cells were prepared
as described before (5) and cultured at a density of 4 × 105 per well in 96-well flat-bottom plates (Nunc,
Roskilde, Denmark) in RPMI 1640-HEPES supplemented with 10% fetal calf
serum (FCS) and with penicillin (100 U/ml) plus streptomycin (100 µg/ml) plus amphotericin B (Fungizone) (0.25 µg/ml) solution (Life
Technology Ltd., Paisley, Scotland). Cells were stimulated with 1 µg
of TLA per ml. This optimal TLA concentration was determined in
preliminary experiments with a range of concentrations (0.1 to 10 µg/ml) (data not shown). Positive controls were assayed with
concanavalin A in all experiments (data not shown). Culture medium
alone was used for negative controls. Levels of IL-2, IFN-
, IL-4,
IL-6, and IL-10 were measured in the supernatant of spleen cells by using a double-monoclonal antibody (MAb) sandwich ELISA. All MAbs were
obtained from Pharmingen (San Diego, Calif.). Preliminary studies
showed that the optimal incubation times were 6 h for IL-4
measurement and 5 days for other cytokines (data not shown). Ninety-six-well microtiter plates (Nunc) were coated overnight at 4°C
with a capture antibody at a concentration of 2 µg/ml in 0.1 M
NaHCO3 buffer (pH 8.2) (50 µl/well) (anti-IL-2 MAb, clone JES6-1A12; anti-IFN-
MAb, clone R4-6A2; anti-IL-4 MAb, clone BVD4-1D11; anti-IL-6 MAb, clone MP5-20M3; and anti-IL-10 MAb, clone
JES5-2A5). The plates were then blocked overnight with PBS-10% FCS.
Samples diluted 1:2 in PBS-10% FCS (triplicate wells) and serial
dilutions of recombinant standards (duplicate wells) were incubated
overnight at 4°C (100 µl/well). Biotinylated conjugates were then
added at 1 µg/ml in PBS-10% FCS (100 µl/well), and the plates
were incubated for 45 min at room temperature (anti-IL-2 MAb, clone
JES6-5H4; anti-IFN-
MAb, clone XMG1.2; anti-IL-4 MAb, BVD6-24G2;
anti-IL-6 MAb, clone MP5-32C11; anti-IL-10 MAb, clone SXC-1).
Avidin-peroxidase (Sigma) was added at 25 µg/ml (100 µl/well) for
30 min at room temperature, and the ABTS substrate was added as
described above. A405 was measured, and the
cytokine concentrations were calculated with RMS software (Dynex
Thermobio Analysis, Issy les Moulineaux, France) by interpolation of
standard curves. TNF-
was assayed by using a commercial ELISA kit
(Duoset mouse TNF-
ELISA kit; Genzyme, Cambridge, Mass.) with the
supernatants of cells cultured for 5 days. IL-12 was assayed in cell
culture supernatants after 6 h, 48 h, and 5 days of culture,
with an antibody pair kindly provided by M. Gately, Hoffman-La Roche,
Nutley, N.J. (capture MAb, clone 9A5; peroxidase-labelled MAb, clone
5C3-POD). The detection limits of the assays were as follows: IL-2, 10 pg/ml; IFN-
, 150 pg/ml; IL-4, 8 pg/ml; IL-6, 10 pg/ml; IL-10, 15 pg/ml; TNF-
, 20 pg/ml; and IL-12, 5 pg/ml.
Challenge infection.
Four weeks after the last immunization,
five mice per group were infected orally with 20 cysts of the PRU
strain. The mice were killed, and the brains were recovered on day 21 postinfection. Each brain was weighed and homogenized in 1 ml of PBS.
The number of cysts was determined microscopically by counting four
samples of each homogenate (20 µl each) and was expressed per gram of brain tissue.
rSAG1 alone induces specific humoral type 2 immunity.
The
results obtained after immunization of mice by rSAG1 alone were
globally comparable to those obtained with the purified natural protein
(6). The presence of specific anti-rSAG1 IgG1 (titer,
3.8 ± 1.1) and the absence of IgG2a suggest that rSAG1 preferentially induces type 2 humoral immunity (Fig.
1). The cytokine pattern produced ex vivo
by splenocytes in response to TLA stimulation indicates a decreased
type 1 response with reduced IL-2 (P = 0.0011) and
IFN-
(P < 0.0001) production relative to that of
the vehicle-treated mice (Table 1).
However, IL-4 production by splenocytes was not significantly modified
by rSAG1 immunization. Addition of IL-12 as an adjuvant abolished the
IL-4 production. No IL-10 was detected. These results are reminiscent
of those reported by Godard et al., who fragmented SAG1 into five
peptides and found that four peptides induced type 2 humoral immunity
(exclusive IgG1 production) when they were administered subcutaneously
or intravenously to mice (15).

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FIG. 1.
Specific anti-rSAG1 IgG1 and IgG2a titers after
immunization. Results are mean antibody titers (n = 3) ± standard deviation, expressed as the indices of triplicate wells.
The indices were calculated as mean OD405 of triplicate
samples/mean OD405 of three vehicle controls.
|
|
The rSAG1-IL-12 combination reorients the immune response toward
the type 1 pattern.
In response to TLA stimulation, splenocytes of
mice treated with rSAG1 plus IL-12 produced significantly more IL-2
(P = 0.048) and IFN-
(P = 0.0002)
than the vehicle control group (Table 1). In contrast, the production
of the type 2 cytokine IL-4 was totally abolished in both control mice
treated with IL-12 alone and mice treated with the combination rSAG1
plus IL-12. In the IL-12 control group, the production of IL-2 was
unchanged relative to that in the vehicle control group, whereas
IFN-
production was curiously reduced. Similar intriguing results
have been observed by Afonso et al. in an experimental immunization
model with an antigen from Leishmania major in combination
with IL-12 (1). In response to in vitro TLA stimulation, we
did not observe any exacerbated inflammatory response in the
rSAG1-IL-12-treated group, because IL-6 and TNF-
production
remained unchanged relative to that in the vehicle control group
(P = 0.056 and P = 0.060, respectively). No IL-12 production was detected under our experimental
conditions, even when a short incubation time (6 h) and different TLA
concentrations (0.1 to 10 µg/ml) were used. Nevertheless, this does
not rule out very early production after initial contact with the
antigen. Some observations indeed suggest that this cytokine is
produced within the first few hours of infection, and then production
ceases (22). This orientation toward a type 1 immune
response in the presence of a type 2 response-inducing antigen has been
documented in other models of infection by parasites (1,
26), bacteria (27), and fungi (25).
The precise mechanisms underlying the Th1 reorientation are uncertain.
IL-12 would act very rapidly on NK cells and undifferentiated naive Th0
T cells, orienting them towards a Th1 secretory phenotype with IFN-
production (36). IL-12 itself and the IFN-
thereby produced would then have an inhibitory effect on the production and
effects of IL-4 (29, 34).
The study of specific anti-rSAG1 antibody subclasses (Fig.
1) showed
that IgG1 titers were halved in the rSAG1-IL-12 group
relative to that
in the rSAG1 group (2.0 ± 0.4 and 3.8 ± 1.1,
respectively),
although the difference was not significant (
P = 0.055), probably because of the large standard deviation relative
to
the sample size. The persistence of IgG1 despite the absence
of
measurable IL-4 production and the presence of IFN-

can be
explained
in several ways. IL-4 concentrations may be below the
detection limit
but adequate to maintain IgG1 production despite
the inhibitory action
of IFN-

. Conversely, IgG1 production may
be at least partially
independent of IL-4, as suggested by the
persistence of IgG1 production
in IL-4 gene-deficient mice (
23).
Surprisingly, we observed no detectable production of IgG2a, although
most published data suggest that IL-12 induces the synthesis
of this
isotype (
14), mainly via IFN-

(
9). Our
previous
studies with natural SAG1 combined with IL-12 have shown IgG2a
production; however, the dose of IL-12 injected was double that
used
with the recombinant SAG1. In the present experiment, the
absence of
detectable IgG2a would therefore seem to show an imbalance,
in favor of
IL-4, between the inhibitory effects of IL-4 and the
activation effects
of IFN-

on IgG2a synthesis.
rSAG1 plus IL-12 immunization reduces brain parasite load after
peroral infection.
Immunization with rSAG1 alone did not modify
the number of cysts compared with that in control mice (1,777 ± 112 and 1,817 ± 536 cysts/g of brain, respectively;
P = 0.875) (Fig. 2). In contrast, in the group treated with rSAG1 plus IL-12, parasite load was
significantly reduced by 40% (1,083 ± 309 cysts/g of brain;
P = 0.029). Our results are difficult to compare with
those from published data, because most authors used either survival models or very different models of infection to evaluate the protective effect of their vaccine protocols. Nevertheless, our previous experiments with purified natural SAG1 protein showed similar results
with a brain parasite load significantly lower in the SAG1-IL-12 group
than that in the SAG1 group despite identical survival rates
(6). Debard et al. confirmed the lack of protection provided
by the natural SAG1 protein in terms of brain parasite load
(8).

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FIG. 2.
Brain cyst count on day 21 postinfection. Results are
expressed as the mean number of cysts per gram of brain
(n = 5) ± standard deviation. *, P < 0.05 (Student's t test for comparisons between the
vehicle control group and the rSAG1 or the rSAG1-IL-12 treatment
groups).
|
|
In conclusion, this study shows that rSAG1 protein administered
subcutaneously at a total dose of 4 µg induces specific immunity
characterized by a predominantly humoral type 2 pattern and does
not
protect the animals against infection by a cyst-forming strain
of
T. gondii. In contrast, combined immunization with IL-12 and
rSAG1 protein redirects immunity toward a predominantly humoral
and
cellular type 1 pattern and reduces the brain parasite load
by 40%.
Because this protocol protected mice only partially against
infection,
other injection time points (one injection every 2
weeks for 2 months
and one injection monthly for 4 months) were
evaluated and showed
identical results. Other adjuvants are now
under investigation.
 |
ACKNOWLEDGMENTS |
We are grateful to E. Candolfi for his helpful advice and many
suggestions during the course of this work.
 |
FOOTNOTES |
*
Corresponding author. Mailing address: Institut de
Parasitologie et de Pathologie Tropicale, Faculté de
Médecine de Strasbourg, 3, rue Koeberlé, 67000 Strasbourg,
France. Phone: 33-3-88-35-35-55. Fax: 33-3-88-36-42-02.
Editor:
S. H. E. Kaufmann
 |
REFERENCES |
| 1.
|
Afonso, L. C. C.,
T. M. Scharton,
L. Q. Vieira,
M. Wysocka,
G. Trinchieri, and P. Scott.
1994.
The adjuvant effect of IL-12 in a vaccine against Leishmania major.
Science
263:235-237[Abstract/Free Full Text].
|
| 2.
|
Brinkmann, V.,
J. S. Remington, and S. D. Sharma.
1987.
Protective immunity in toxoplasmosis: correlation between antibody response, brain cyst formation, T-cell activation, and survival in normal and B-cell-deficient mice bearing the H-2k haplotype.
Infect. Immun.
55:990-994[Abstract/Free Full Text].
|
| 3.
|
Bülow, R., and J. C. Boothroyd.
1991.
Protection of mice from fatal Toxoplasma gondii infection by immunization with P30 antigen in liposomes.
J. Immunol.
147:3496-3500[Abstract].
|
| 4.
|
Burg, J. L.,
D. Perelman,
L. H. Kasper,
P. L. Ware, and J. C. Boothroyd.
1988.
Molecular analysis of the gene encoding the major surface antigen of Toxoplasma gondii.
J. Immunol.
141:3584-3591[Abstract].
|
| 5.
|
Candolfi, E.,
C. A. Hunter, and J. S. Remington.
1994.
Mitogen- and antigen-specific proliferation of T cells in murine toxoplasmosis is inhibited by reactive nitrogen intermediates.
Infect. Immun.
62:1995-2001[Abstract/Free Full Text].
|
| 6.
|
Candolfi, E.,
R. Robert,
E. Antoni, and T. Kien.
1996.
The use of IL-12 as an adjuvant of a SAG-1 based vaccine enhances protective immunity to Toxoplasma gondii, abstr. C202.
In
VII European Multicolloquium of Parasitology (EMOP VII).
|
| 7.
|
Darcy, F.,
P. Maes,
H. Gras-Masse,
C. Auriault,
M. Bossus,
D. Deslée,
I. Godard,
M. F. Cesbron,
A. Tartar, and A. Capron.
1992.
Protection of mice and nude rats against toxoplasmosis by a multiple antigenic peptide construction derived from Toxoplasma gondii P30 antigen.
J. Immunol.
149:3636-3641[Abstract].
|
| 8.
|
Debard, N.,
D. Buzoni-Gatel, and D. Bout.
1996.
Intranasal immunization with SAG1 protein of Toxoplasma gondii in association with cholera toxin dramatically reduces development of cerebral cysts after oral infection.
Infect. Immun.
64:2158-2166[Abstract].
|
| 9.
|
Finkelman, F. D.,
I. M. Katona,
T. R. Mosmann, and R. L. Coffman.
1988.
IFN- regulates the isotypes of Ig secreted during in vivo humoral immune response.
J. Immunol.
140:1022-1027[Abstract].
|
| 10.
|
Fischer, H. G.,
G. Reichmann, and U. Hadding.
1996.
Toxoplasma proteins recognized by protective T lymphocytes.
Curr. Top. Microbiol. Immunol.
219:175-182[Medline].
|
| 11.
|
Gazzinelli, R. T.,
D. Amichay,
T. Sharton-Kersten,
E. Grunwald,
J. M. Farber, and A. Sher.
1996.
Role of macrophage derived cytokines in the induction and regulation of cell mediated immunity to Toxoplasma gondii.
Curr. Top. Microbiol. Immunol.
219:127-139[Medline].
|
| 12.
|
Gazzinelli, R. T.,
F. T. Hakim,
S. Hieny,
G. M. Shearer, and A. Sher.
1991.
Synergistic role of CD4+ and CD8+ T lymphocytes in IFN-gamma production and protective immunity induced by an attenuated Toxoplasma gondii vaccine.
J. Immunol.
146:286-292[Abstract].
|
| 13.
|
Gazzinelli, R. T.,
M. Wysocka,
S. Hieny,
T. Scharton-Kersten,
A. Cheever,
R. Kühn,
W. Müller,
G. Trinchieri, and A. Sher.
1996.
In the absence of endogenous IL-10, mice acutely infected with Toxoplasma gondii succumb to a lethal immune response dependent on CD4+ T cells and accompanied by overproduction of IL-12, IFN- and TNF- .
J. Immunol.
157:798-805[Abstract].
|
| 14.
|
Germann, T.,
M. Bongartz,
H. Dlugonska,
H. Hess,
E. Schmitt,
L. Kolbe,
E. Kölsch,
F. J. Podlaski,
M. K. Gately, and E. Rüde.
1995.
Interleukin-12 profoundly up-regulates the synthesis of antigen-specific complement-fixing IgG2a, IgG2b, IgG3 antibody subclasses in vivo.
Eur. J. Immunol.
25:823-829[Medline].
|
| 15.
|
Godard, I.,
J. Estaquier,
L. Zenner,
M. Bossus,
C. Auriault,
F. Darcy,
H. Gras-Masse, and A. Capron.
1994.
Antigenicity and immunogenicity of P30-derived peptides in experimental models of toxoplasmosis.
Mol. Immunol.
31:1353-1363[Medline].
|
| 16.
|
Harning, D.,
J. Spenter,
A. Metsis,
J. Vuust, and E. Petersen.
1996.
Recombinant Toxoplasma gondii surface antigen 1 (P30) expressed in Escherichia coli is recognized by human Toxoplasma-specific immunoglobulin M (IgM) and IgG antibodies.
Clin. Diagn. Lab. Immunol.
3:355-357[Abstract].
|
| 17.
|
Ho Yen, D. O., and A. W. L. Joss.
1992.
Human toxoplasmosis.
Oxford Medical Publications, Oxford, United Kingdom.
|
| 18.
|
Hunter, C. A.,
E. Candolfi,
C. Subauste,
V. van Cleave, and J. S. Remington.
1995.
Studies on the role of interleukin-12 in acute murine toxoplasmosis.
Immunology
84:16-20[Medline].
|
| 19.
|
Kasper, L. H.,
J. H. Crabb, and E. R. Pfefferkorn.
1983.
Purification of a major membrane protein of Toxoplasma gondii by immunoadsorption with a monoclonal antibody.
J. Immunol.
130:2407-2412[Abstract].
|
| 20.
|
Khan, I. A.,
K. H. Ely, and L. H. Kasper.
1991.
A purified parasite antigen (P30) mediates CD8+ T cell immunity against fatal Toxoplasma gondii infection in mice.
J. Immunol.
147:3501-3506[Abstract].
|
| 21.
|
Khan, I. A.,
T. Matsuura, and L. H. Kasper.
1994.
Interleukin-12 enhances murine survival against acute toxoplasmosis.
Infect. Immun.
62:1639-1642[Abstract/Free Full Text].
|
| 22.
|
Khan, I. A.,
J. D. Schwartzman,
S. Fonseka, and L. H. Kasper.
1997.
Neospora caninum: role for immune cytokines in host immunity.
Exp. Parasitol.
85:24-34[Medline].
|
| 23.
|
Kühn, R.,
K. Rajewsky, and W. Müller.
1991.
Generation and analysis of interleukin-4 deficient mice.
Science
254:707-710[Abstract/Free Full Text].
|
| 24.
|
Lundén, A.,
K. Lövgren,
A. Uggla, and F. G. Araujo.
1993.
Immune responses and resistance to Toxoplasma gondii in mice immunized with antigens of the parasite incorporated into immunostimulating complexes.
Infect. Immun.
61:2639-2643[Abstract/Free Full Text].
|
| 25.
|
Magee, D. M., and R. A. Cox.
1996.
Interleukin-12 regulation of host defenses against Coccidioides immitis.
Infect. Immun.
64:3609-3613[Abstract].
|
| 26.
|
Mountford, A. P.,
S. Anderson, and R. A. Wilson.
1996.
Induction of Th1 cell-mediated protective immunity to Schistosoma mansoni by co-administration of larval antigens and IL-12 as an adjuvant.
J. Immunol.
156:4739-4745[Abstract].
|
| 27.
|
Noll, A., and I. B. Autenrieth.
1996.
Immunity against Yersinia enterocolitica by vaccination with Yersinia HSP60 immunostimulating complexes or Yersinia HSP60 plus interleukin-12.
Infect. Immun.
64:2955-2961[Abstract].
|
| 28.
|
Potasman, I.,
F. G. Araujo,
G. Desmonts, and J. S. Remington.
1986.
Analysis of Toxoplasma gondii antigens recognized by human sera obtained before and after infection.
J. Infect. Dis.
154:650-657[Medline].
|
| 29.
|
Seder, R. A.,
R. T. Gazzinelli,
A. Sher, and W. E. Paul.
1993.
Interleukin-12 acts directly on CD4+ T cells to enhance priming for interferon- production and diminishes interleukin 4 inhibition of such priming.
Immunology
90:10188-10192.
|
| 30.
|
Seeber, F.,
J. F. Dubremetz, and J. C. Boothroyd.
1998.
Analysis of Toxoplasma gondii stably transfected with a transmembrane variant of its major surface protein, SAG1.
J. Cell Sci.
111:23-29[Abstract].
|
| 31.
|
Sharma, S. D.,
J. Mullenax,
F. G. Araujo,
H. A. Erlich, and J. S. Remington.
1983.
Western blot analysis of the antigens of Toxoplasma gondii recognized by human IgM and IgG antibodies.
J. Immunol.
131:977-983[Abstract].
|
| 32.
|
Suzuki, Y.,
M. A. Orellana,
R. D. Schreiber, and J. S. Remington.
1988.
Interferon- : the major mediator of resistance against Toxoplasma gondii.
Science
240:516-518[Abstract/Free Full Text].
|
| 33.
|
Trinchieri, G.
1997.
Function and clinical use of interleukin-12.
Curr. Opin. Hematol.
4:59-66[Medline].
|
| 34.
|
Trinchieri, G., and F. Gerosa.
1996.
Immunoregulation by interleukin-12.
J. Leukoc. Biol.
59:505-511[Abstract].
|
| 35.
|
Windeck, T., and U. Gross.
1996.
Toxoplasma gondii strain-specific transcript levels of SAG1 and their association with virulence.
Parasitol. Res.
82:715-719[Medline].
|
| 36.
|
Wolf, S. F.,
D. Sieburth, and J. Sypek.
1994.
Interleukin 12: a key modulator of immune function.
Stem Cells
12:154-168[Abstract].
|
Infection and Immunity, September 1998, p. 4503-4506, Vol. 66, No. 9
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
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