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PubMed2005

Toxoplasma gondii infections in chickens from Venezuela: isolation, tissue distribution, and molecular characterization.

The prevalence of Toxoplasma gondii, in free-ranging chickens is a good indicator of the prevalence of T. gondii oocysts in the soil because chickens feed from the ground. The prevalence of T. gondii in 46 free-range chickens (Gallus domesticus) from Venezuela was determined. Antibodies to T. gondii were assayed by the modified agglutination test (MAT). Antibodies were found in 16 (32%) chickens with titers of 1:5 in 1, 1:10 in 2, 1:40 in 2, 1:80 in 2, 1:160 in 2, 1:320 in 3, 1: 640 in 2, and 1:1,280 or higher in 2. Hearts, pectoral muscles, and brains of 13 chickens with MAT titers of 1:40 or more were bioassayed individually in mice. Tissues of each of 3 chickens with titers of 1:5 or 1:10 were pooled and bioassayed in mice. Tissues from the remaining 30 seronegative chickens were pooled and fed to 1 T. gondii-free cat. Feces of the cat were examined for oocysts; it did not shed oocysts. Toxoplasma gondii was isolated from 12 of 13 chickens with MAT titers of 1:40 or more. Toxoplasma gondii was isolated from pooled tissues of 1 of 2 chickens with titers of 1:10. Eight of these 13 isolates were virulent for mice. Genotyping of 13 of these isolates using the SAG2 locus indicated that 10 were type III, and 3 were type II. Phenotypically and genetically these isolates were different from T. gondii isolates from North America and Brazil. This is the first report of isolation of T. gondii from chickens from Venezuela.

Agglutination Tests↗
PubMed2005

Characterization of Toxoplasma gondii isolates in free-range chickens from Argentina.

The prevalence of Toxoplasma gondii in free-ranging chickens is a good indicator of the prevalence of T. gondii oocysts in the soil because chickens feed from the ground. The prevalence of T. gondii in 61 free-range chickens (Gallus domesticus) from provinces of Santiago del Estero and Entre Rios, Argentina was determined. Antibodies to T. gondii were assayed by the modified agglutination test (MAT) and were found in 25 chickens; titers were 1:5 in 6 chickens, 1:10 in 1 chicken, 1:20 in 2 chickens, 1:40 in 1 chicken, 1:80 in 2 chickens, 1:60 in 4 chickens, 1:120 in 2 chickens, 1:640 in 3 chickens, and 1: 1,280 or higher in 4 chickens. Hearts, pectoral muscles, and brains of 22 seropositive (MAT 1:10 or higher) chickens were bioassayed individually in mice. Tissue from 39 chickens with titers of 1:5 or less were pooled and fed to 3 T. gondii-free cats. Feces of cats were examined for oocysts, but none was found. Toxoplasma gondii was isolated from 17 of 22 chickens with MAT titers of 1:10 or higher. Genotyping of these 17 isolates using polymorphisms at the SAG2 locus indicated that 4 were Type I, 3 were Type II, and 10 were Type III. Toxoplasma gondii isolates (2 Type I and I Type III) from 3 chickens were virulent for mice and 1 Type I was not mouse virulent. Prevalence of T. gondii antibodies in chickens varied among regions, being 3 times greater in the humid Pampeana region (61.2%) than in the semiarid plain of Santiago del Estero (20%).

Animals↗
PubMed2005

Prevalence of viable Toxoplasma gondii in beef, chicken, and pork from retail meat stores in the United States: risk assessment to consumers.

The prevalence of viable Toxoplasma gondii was determined in 6,282 samples (2,094 each of beef, chicken, and pork) obtained from 698 retail meat stores from 28 major geographic areas of the United States. Each sample consisted of a minimum of 1 kg of meat purchased from the retail meat case. To detect viable T. gondii, meat samples were fed to T. gondii-free cats and feces of cats were examined for oocyst shedding. Initially, 100 g of meat from 6 individual samples of a given species were pooled (total, 600 g), fed to a cat over a period of 3 days, and feces were examined for oocysts for 14 days; the remaining meat samples were stored at 4 C for 14 days (until results of the initial cat fecal examination were known). When a cat fed pooled samples had shed oocysts, 6 individual meat samples from each pool were bioassayed for T. gondii in cats and mice. Toxoplasma gondii isolates were then genetically characterized using the SAG2 locus and 5 hypervariable microsatellite loci. In all, 7 cats fed pooled pork samples shed oocysts. Toxoplasma gondii oocysts were detected microscopically in the feces of 2 of the cats; 1 isolate was Type II and the second was Type III. Analyzed individually, T. gondii was detected by bioassay in 3 of the 12 associated samples with genetic data indicating T. gondii isolates present in 2. The remaining 5 pooled pork samples had so few oocysts that they were not initially detected by microscopic examination, but rather by mouse bioassay of cat feces. Two were Type I, 1 was Type II, and 2 were Type III. None of the cats fed chicken or beef samples shed oocysts. Overall, the prevalence of viable T. gondii in retail meat was very low. Nevertheless, consumers, especially pregnant women, should be aware that they can acquire T. gondii infection from ingestion of undercooked meat, and in particular, pork. Cooking meat to an internal temperature of 66 C kills T. gondii.

Animals↗
PubMed2005

Seroprevalence of Toxoplasma gondii antibodies in clinically ill cats in the United States.

OBJECTIVE: To determine regional seroprevalence estimates of Toxoplasma gondi-specific IgM and IgG in clinically ill cats throughout the United States. Sample Population-Sera from 12,628 clinically ill, client-owned cats. PROCEDURE: Toxoplasma gondii-specific IgM and IgG antibodies were detected by use of ELISAs. Sera from clinically ill cats previously submitted for T. gondii antibody testing were sequentially selected from our serum bank and the sample submission paperwork reviewed. The country was divided into 12 geographic regions. Overall prevalence as well as prevalence for each region, age group, season, sex (male vs female), and breed (domestic shorthair vs other) was calculated. Data were analyzed by logistic regression analysis. RESULTS: Overall, 31.6% of the cats were seropositive for T. gondii-specific IgM, IgG, or both. Percentage of cats seropositive for T. gondii antibodies ranged from 16.1% (southwestern United States) to 43.5% (northeastern United States). As age increased, odds of positive T. gondii antibody assay results (IgM alone, IgG alone, and any combination of IgM or IgG) increased. Males were more likely than females to be seropositive for T. gondii antibodies (IgG alone and any combination of IgM or IgG). Domestic shorthair cats were more likely than other breeds to be seropositive for T. gondii antibodies (IgM alone, IgG alone, and any combination of IgM or IgG). CONCLUSIONS AND CLINICAL RELEVANCE: Toxoplasma gondii-specific antibodies are common in serum samples of clinically ill cats from all regions of the United States. Seroprevalence increases as cats age and is higher in male and domestic shorthair cats, compared with females and other breeds.

Age Factors↗
PubMed1975

Experimental Toxoplasma gondii infection in mice: the role of the fifth component of complement.

Experiments performed to determine the influence of the C5 component of complement in experimental Toxoplasma infection revealed that mice deficient in C5 had reduced mortality due to acute toxoplasmosis. Similar results were noted when inbred congenic mice of known complement type, as well as random-bred mice selected for complement type, were used. In both, mice with high complement activity were less resistant to Toxoplasma than were mice deficient in C5. However, many factors must interact in susceptibility to infection with T. gondii. Thus, lower resistance to Toxoplasma was noted in C5-deficient DBA/2J mice, whereas a high degree of resistance was noted in DBA/1J mice, which are not related to DBA/2J mice and which possess a normal sequence of complement. This accentuates the importance of using both random-bred and where possible cogenic lines in assessing the importance of individual factors in infectious immunity.

Animals↗
PubMed1994

[Antigen analysis of Toxoplasma gondii lysate and excretory-secretory materials by enzyme-linked immunoelectrotransfer blot (EITB)].

Recently, the importance of toxoplasmosis is raised as a complication in immunosuppressed or AIDS patients. Our study focused on the identification of a variety of Toxoplasma antigens by immunoblotting. Rabbits and BALB/c mice were immunized with Toxoplasma lysate (RH strain), frozen tachyzoites (RH strain) or cysts (Beverly and Fukaya strain). Blood were collected from ear vein, heart or orbital plexus for detecting the serum antibody levels. For excretory-secretory (E.S) antigens, T. gondii (RH) tachyzoite were cultured in CHL (Chinese hamster lung) cells with MEM containing of 5% FCS. After 72 hrs, culture supernatant was collected. BALB/c mice were inoculated with RH tachyzoite intraperitoneally and peritoneal fluids were extracted three days later. E.S antigens were detected in culture supernatant and infected mouse peritoneal fluid by EITB. Serum IgG levels in rabbit were 1:512 of 10 days after primary immunization, 1:2,048 of 10 days after secondary immunization, 1:1,024 of 20 days after secondary immunization by IFAT, respectively. Serum IgG levels of immunized mice were 1:128 after 7 weeks. Tachyzoite antigens of the RH strain were detected 25 protein bands ranging 10 kDa-220 kDa of molecular weights with Coomassie blue stain. Toxoplasma major antigens corresponding to MW of 24 kDa, 27 kDa, 30 kDa, 35 kDa, 38 kDa were recognized by IgG and IgM antibodies. Excretory-secretory antigens present in culture supernatant with M. W. of 20, 30 kDa and in infected mouse peritoneal fluid with M.W. of 33 (P30), 45 kDa. When RH tachyzoite antigen was probed with different mice sera immunized with 2 strains of T. gondii, the IgG antibody band of Fukaya and Beverly strain (8 week-serum) is identical to those of RH strain. It is considered that the 30 kDa polypeptide detected in excretory-secretory materials and lysate was important major antigen of T. gondii (RH).

Animals↗
PubMed1997

Partially purified Toxoplasma gondii antigens by immunoaffinity chromatography.

Tachyzoite antigens of Toxoplasma gondii (RH) were partially purified by immunoaffinity chromatography. The cultivated Toxoplasma in vivo (mouse) and in vitro (Hep-2 cell) and peritoneal fluid of T. gondii infected mice were collected for antigen analysis. Tachyzoite antigens collected from infected mouse showed positive bands of 76 kDa, 70 kDa, 64 kDa, 53 kDa, 46 kDa, 44 kDa, 41 kDa, 35 kDa, 25 kDa, 18 kDa, and 13 kDa on immunoblot with anti-Toxoplasma rabbit sera, and those from infected Hep-2 cells revealed reactive bands of 70 kDa, 64 kDa, 53 kDa, 35 kDa 28 kDa, and 13-10 kDa. After applying to an IgG-Sepharose column, two elution peaks, E-1 and E-2 fractions, were obtained from both soluble antigen of T. gondii and the peritoneal fluid of infected mice, respectively. Immunoblots of soluble antigen with immunized rabbit sera revealed positive bands of 97 kDa, 63 kDa, 53 kDa, and 35 kDa from E-1 fraction and 53 kDa and 35 kDa from E-2. In the case of the eluted peaks from mice peritoneal fluid, E-1 showed protein bands of 84 kDa, 76 kDa, 53 kDa, and 29 kDa bands and 53 kDa and 45 kDa from E-2 on immunoblots. Serum IgG antibody titer of mice immunized with T. gondii tachyzoites was increased on 1 week after booster immunization when analysed by ELISA using crude antigen, while it was elevated on 3 weeks after booster immunization by ELISA using purified antigen.

Animals↗
PubMed2003

Anti-Toxoplasma gondii antibodies in haemodialysis patients with chronic renal failure.

UNLABELLED: This study aimed to determine the prevalence of anti- Toxoplasma gondii antibodies in haemodialysis patients with chronic renal failure (CRF). METHODS: One hundred and seventy three haemodialysis patients, and 40 healthy controls, were studied for the prevalence of anti-Toxoplasma gondii antibodies by a micro enzyme-linked immunosorbent assay (ELISA). Anti-T. gondii IgG antibodies were detected in 97 (56.06%) haemodialysis patients and 8 (20%) controls with a statistical significance. In addition, anti-T. gondii IgM antibodies were detected in 1.73% of patients, but none of the controls. In conclusion, a high percentage of positivity for Toxoplasma antibodies in patients with CRF undergoing haemodialysis was noticed, thus parasitological surveys of CRF patients should be periodically performed to prevent the possible dissemination of toxoplasmosis through the dialysis procedure.

Adolescent↗
PubMed2004

Toxoplasma gondii triggers myeloid differentiation factor 88-dependent IL-12 and chemokine ligand 2 (monocyte chemoattractant protein 1) responses using distinct parasite molecules and host receptors.

Toll-like receptors (TLR) that signal through the common adaptor molecule myeloid differentiation factor 88 (MyD88) are essential in proinflammatory cytokine responses to many microbial pathogens. In this study we report that Toxoplasma gondii triggers neutrophil IL-12 and chemokine ligand 2 (CCL2; monocyte chemoattractant protein 1) production in strict dependence upon functional MyD88. Nevertheless, the responses are distinct. Although we identify TLR2 as the receptor triggering CCL2 production, parasite-induced IL-12 release did not involve this TLR. The production of both IL-12 and CCL2 was increased after neutrophil activation with IFN-gamma. However, the synergistic effect of IFN-gamma on IL-12, but not CCL2, was dependent upon Stat1 signal transduction. Although IL-10 was a potent down-regulator of Toxoplasma-triggered neutrophil IL-12 release, the cytokine had no effect on parasite-induced CCL2 production. Soluble tachyzoite Ag fractionation demonstrated that CCL2- and IL-12 inducing activities are biochemically distinct. Importantly, Toxoplasma cyclophilin-18, a molecule previously shown to induce dendritic cell IL-12, was not involved in neutrophil IL-12 production. Our results show for the first time that T. gondii possesses multiple molecules triggering distinct MyD88-dependent signaling cascades, that these pathways are independently regulated, and that they lead to distinct profiles of cytokine production.

Adaptor Proteins, Signal Transducing↗
PubMed2004

T cell-intrinsic expression of c-Rel regulates Th1 cell responses essential for resistance to Toxoplasma gondii.

The ability of many microbial and inflammatory stimuli to activate members of the Rel/NF-kappaB family of transcription factors is associated with the regulation of innate and adaptive responses required to control infection. Individual family members play distinct roles during different infectious and inflammatory responses. For example, c-Rel is essential for the production of IL-12 in response to LPS, but dispensable for IL-12 production in response to Toxoplasma Ag. To assess the role of c-Rel during immunity to the intracellular pathogen Toxoplasma gondii, wild-type (WT) and c-Rel(-/-) mice were infected with Toxoplasma and the immune response was analyzed. c-Rel(-/-) mice developed severe toxoplasmic encephalitis with increased numbers of parasites compared with WT controls and succumbed to infection within 5-8 wk. Although increased susceptibility of c-Rel(-/-) mice was associated with decreased T cell activation, proliferation, and production of IFN-gamma, these mice were able to generate Th1 effector cells that were present in the brain during chronic infection. In vitro mixing studies using WT and c-Rel(-/-) dendritic cells and WT and c-Rel(-/-) TCR transgenic T cells indicated that c-Rel(-/-) dendritic cells are defective in their ability to stimulate T cell responses. However, when c-Rel(-/-) T cells were transferred into T cell-deficient hosts, early defects in T cell activation, proliferation, and IFN-gamma production persisted, and these mice remained susceptible to infection. Together, these studies indicate that although c-Rel is an important regulator of innate immune responses, it also plays an important role in optimization and maintenance of adaptive T cell responses during infection.

Animals↗
PubMed1975

Soil survival of toxoplasma oocysts in Kansas and Costa Rica.

Toxoplasma oocysts in cat feces were marked with a tracer amount of strontium-85 (85-SR), and were superficially buried simulating the natural disposal of feces by cats. Oocyst infectivity in Costa Rica was followed qualitatively and persisted for 1 year in three shaded sites, two moist, and one relatively dry site. Oocyst infectivity was quantitated in the Kansas deposit over a period of 18 months, including two winters. After initial mixing in soil, the level of infectivity remained fairly stable. Infectivity was recovered, probably from the surface on one Musca, several isopods, and earthworms. These data on persistence of Toxoplasma oocysts in soil support the concept that Toxoplasma infectivity in nature may be increased logarithmically by cats.

Animals↗
PubMed1979

The effect of trimethoprim and sulfamethoxazole on Toxoplasma gondii in vitro and in vivo.

Trimethoprim (TMP) and sulfamethoxazole (SMZ) were studied alone and in combination to determine their effect in vitro on intracellular Toxoplasma gondii and in vivo against murine toxoplasmosis. In the in vitro experiments, whereas 1 and 2 microgram/ml TMP had no demonstrable effect on intracellular T. gondii, 10-20 microgram/ml TMP resulted in death of the intracellular organisms; concentrations as high as 100 microgram/ml SMZ had no demonstrable effect against the intracellular organisms. When used in combination, a significant synergistic effect was noted with 2 microgram/ml TMP-50 microgram/ml SMZ. Studies on the kinetics of inhibition and/or killing of Toxoplasma revealed that 18 hours of treatment with 2 microgram/ml TMP-50 microgram/ml SMZ resulted in irreversible inhibition of the intracellular organisms. When used in vivo against a 50,000 LD100 dose of Toxoplasma, TMP fed by gavage or mixed in the diet had no effect in murine toxoplasmosis at doses as high as 200 mg/kg a day. SMZ administered by gavage had no effect at doses up to 200 mg/kg a day; but at 300 and 400 mg/kg SMZ, protection was 47% and 83%, respectively. Treatment of infected mice was continued for 14 consecutive days, whether the drugs were administered alone or in combination. The combination 200 mg/kg TMP-200 mg/kg SMZ, when administered by gavage, protected 87% of mice. Survival after 14 days of SMZ mixed in the diet was 0% at 100 mg/kg, 47% at 200 mg/kg, and 100% at 300 mg/kg. Survival with the combination was 40% for 200 mg/kg TMP-100 mg/kg SMZ and 100% for 100 mg/kg TMP-200 mg/kg SMZ. The half-life of TMP in serum of Swiss Webster mice was calculated to be 24 min. The results obtained in vivo were inferior to those obtainable with the combination of pyrimethamine plus sulfadiazine. The problems of interpretation of results obtained in the murine model using TMP-SMZ and in their extrapolation to the treatment of the infection in man are discussed.

Administration, Oral↗
PubMed1999

Macrophage responses to Toxoplasma antigens in vitro: a possible role in inflammatory lesions in toxoplasmosis.

Toxoplasma antigen and Toxoplasma immune complex were shown to induce increased production and release of acid hydrolases from macrophage cell line P388D in a concentration-dependent manner. Antigen concentrations of 10-50 microg/ml gave a 2-4-fold increase in the activities of acid proteinase, acid phosphatase, and phospholipase A2 compared with control cells without antigen. Results were similar for immune complex concentrations of 30-80 microg/ml compared with controls. No significant lactate dehydrogenase activity was detected in the culture medium, indicating that enzyme release was selective and not due to cell death. These results suggest that increased release of acid hydrolases may play a role in the inflammatory lesions observed in Toxoplasma encephalitis.

Acid Anhydride Hydrolases↗
PubMed2000

Proportion positive for Epstein-Barr virus, cytomegalovirus, human herpesvirus 6, Toxoplasma, and human immunodeficiency virus types 1 and 2 in heterophile-negative patients with an absolute lymphocytosis or an instrument-generated atypical lymphocyte flag.

OBJECTIVES: To determine the proportion of patients with evidence of an acute infection due to Epstein-Barr virus (EBV), cytomegalovirus (CMV), human herpesvirus 6 (HHV-6), Toxoplasma, or human immunodeficiency virus types 1 and 2 (HIV-1 and HIV-2) in heterophile-negative patients with an absolute lymphocytosis or an instrument-generated atypical lymphocyte flag, and to develop a cost-effective testing algorithm for managing such heterophile-negative patients. DESIGN: We conducted a prospective investigation of 70 selected outpatients who tested negative for heterophile antibody in association with an absolute lymphocytosis or instrument-generated atypical lymphocyte flag. The control population consisted of 50 patients who were heterophile negative and had a normal absolute lymphocyte count and no instrument-generated atypical lymphocyte flag. SETTING: A large outpatient laboratory system. INTERVENTION: Viral serology for HHV-6 was performed by immunofluorescence, and all other serologies were performed by enzyme-linked immunoassay. All testing was for immunoglobulin (Ig) M antibodies, except in the case of HIV. RESULTS: The proportion of study patients positive for EBV was 40% (28/70); for CMV, 39% (27/70); for HHV-6, 25% (16/65); for Toxoplasma, 3% (2/70); and for HIV, 0% (0/70). All 50 control patients were negative for EBV IgM antibodies. When patients with more than 1 positive viral test were excluded from analysis, positivity was 20% (9/45) for EBV, 22% (10/45) for CMV, 9% (4/45) for HHV-6, and 2% (1/45) for Toxoplasma. Utilizing hypothesis-generating logistic regression models, Downey type II atypical lymphocytes were significantly associated with EBV positivity (P =.006), while Downey type III lymphocytes were significantly associated with HHV-6 positivity (P =.016), and there was a trend for the association of Downey type I lymphocytes with CMV positivity (P =.097). CONCLUSIONS: A positive viral serology was identified in 70% of study patients. Multiple positive serologies complicate establishing a definitive diagnosis. Potential cost savings may be associated with the use of an appropriate testing algorithm.

Adolescent↗
PubMed1976

Prevalence of antibodies to Toxoplasma gondii in wild and domestic animals of New Mexico, Arizona and Colorado.

Using the Sabin-Feldman dye test, sera from wild and domestic animals in New Mexico, Arizona and Colorado were tested for the prevalence of antibodies to Toxoplasma gondii. The prevalence of positive titers (greater than or equal to 1:8) in animals from these areas was: New Mexico (178 of 569, 31%), Arizona (11 of 56, 20%), and Colorado (2 of 7, 29%). The overall prevalence of antibodies to Toxoplasma was 30% (191 of 632). Nine of 17 fecal samples from wild zoo felines contained Toxoplasma-like oocysts which were inoculated per os and intraperitoneally into mice. Mice from six of these nine inoculations later showed positive dye test titers and tissues from five of these six groups had tissue cysts when examined histologically.

Animals↗
PubMed1995

Prevalence of antibodies to Toxoplasma gondii in wild mammals of Missouri and east central Kansas: biologic and ecologic considerations of transmission.

Sera from 273 wild mammals from Missouri and Kansas (USA), collected between December 1974 and December 1987, were tested for the presence of antibodies to Toxoplasma gondii using the Sabin-Feldman dye test. Sixty-five (24%) had antibodies at titers of > or = 1:8, including 38 (66%) of 58 carnivores, 14 (15%) of 94 omnivores, 13 (11%) of 117 herbivores, and none of four insectivores. The prevalence of antibodies in mice (Mus musculus and Peromyscus spp.) and rats (Rattus norvegicus and Sigmodon hispidus) was low (3%), while medium sized herbivores such as squirrels (Sciurus spp.), rabbits (Sylvilagus floridanus), and muskrats (Ondatra zibethicus) had prevalences of about 18%. Red foxes (Vulpes fulva) and mink (Mustela vison) had the highest prevalence of antibodies with frequencies of 90 and 66%, respectively. In 32 attempts to isolate Toxoplasma gondii from wild mammals with positive (> or = 1:4) titers, only six (19%) were successful: a gray squirrel (Sciurus carolinensis), a beaver (Castor canadensis), an opossum (Didelphis marsupialis), a red fox and two mink. These findings are consistent with the hypothesis that the probability of infection with Toxoplasma gondii, and therefore prevalence of antibodies in wildlife, is greatest in carnivores.

Animals↗
PubMed2005

Prevalence of Toxoplasma gondii and Neospora caninum in sika deer from eastern Hokkaido, Japan.

Brain and serum were collected from 120 and 12 free-ranging sika deer (Cervus nippon yesoensis), respectively, from six regions in eastern Hokkaido during controlled hunts in the autumn of 2003. Brains were tested for Neospora caninum and Toxoplasma gondii DNA by polymerase chain reaction (PCR) assays. Antibodies to Toxoplasma gondii were measured by means of a latex agglutination test. No brain tested positive for either type of DNA, and no antibody to Toxoplasma gondii was detected in serum, suggesting a low prevalence of infection with these organisms in free-ranging sika deer from eastern Hokkaido. Further examination of multiple tissues by PCR and serologic surveys will be necessary to confirm this.

Animals↗
PubMed1999

IL-15 prolongs the duration of CD8+ T cell-mediated immunity in mice infected with a vaccine strain of Toxoplasma gondii.

Immunization of mice with a vaccine (ts-4) strain of Toxoplasma gondii is known to induce complete protection against subsequent lethal infection. Ts-4-mediated protection has been reported to be primarily dependent on IFN-gamma-producing CD8+ T cells. However, duration of CD8+ T cell-mediated immunity in the ts-4-vaccinated animals is not known. In the present study, the kinetics of the CD8+ T cell response in mice immunized with the ts-4 strain of T. gondii was evaluated. Optimal CD8+ T cell immunity persisted at least 6 mo after vaccination, and mice at this time point continued to overcome lethal challenge with a more virulent strain. However, at 9 mo postimmunization, CD8+ T cell immunity was severely diminished and the mice succumbed to Toxoplasma challenge. Pretreatment of animals, vaccinated 9 mo earlier, with rIL-15 prevented the mortality induced by Toxoplasma challenge. The protective effect of IL-15 treatment was due to a rise in the frequency of Ag-specific CD8+ T cells. CD8+ T cells from IL-15-administered animals showed increased proliferation and IFN-gamma production in response to antigenic restimulation. These findings suggest that rIL-15 can reverse the decline in the long-term CD8+ T cell immune response in mice immunized with vaccine strain of T. gondii.

Adjuvants, Immunologic↗