Enhancement by Recombinant Human Interleukin 2 of Host Resistance to Toxoplasma gondii Infection in Pregnant Mice

The lymphokine production by pregnant mice infected with a lethal dose of Toxoplasma gondii was evaluated in comparison with that by virgin mice infected with a sublethal dose of this protozoan parasite. Splenocytes taken from mice before and on the day after infection produced considerable amounts of IL-2 in response to concanavalin A (Con A) stimulation, but the titers rapidly declined in both pregnant and virgin mice as infection progressed. A trace amount or undetectable level of IL-2 was produced by splenocytes from acutely infected mice when stimulated with Toxoplasma lysate antigen (TLA). In contrast to the kinetics of IL-2 production, the levels of IFN-γ produced by splenocytes cultured with Con A or TLA increased steadily in the later stage of infection in both pregnant and virgin mice. Thus, the response to Con A or TLA of splenocytes to produce IL-2 and IFN-γ differed strikingly in acute toxoplasmosis in mice. The administration of rHuIL-2 resulted in a significant decrease in the mortality of pregnant mice infected with a lethal dose of Toxoplasma. The combination of rHuIL-2 and rMuIFN-γ increased the survival rate slightly but not significantly compared with pregnant mice receiving either rHuIL-2 or rMuIFN-γ. Moreover, exogenously administered rHuIL-2 enhanced the production of both IFN-α and IFN-γ in the bloodstreams of pregnant mice, in accordance with the decreased mortality. These results indicate that IL-2 may play a significant role in modulating the host defense against Toxoplasma infection in pregnant mice.     

Protection against lethal toxoplasmosis in mice by an avirulent strain of Toxoplasma gondii: stimulation of IFN-gamma and TNF-alpha response

In this study, we examined whether the PTN strain (isolated from an AIDS patient) of Toxoplasma gondii could induce cross-protection in mice against infection with a lethal dose of the PLK strain. Mice were first infected with tachyzoites (5 x 10(5)) of PTN and 5 days later challenged with PLK (1 x 10(5), LD(90)) parasites. None of these mice succumbed to infection until day 21 after infection, whereas 100% of the mice given the same dose of PLK infection alone died between 5 and 11 days after infection. The protection was accompanied by an increased expansion of NK cells and CD4 + T cells. This condition was associated by increased production of IFN-gamma and an augmented number of IFN-gamma-producing cells in the spleen. Further, PTN + PLK-infected mice showed higher production of TNF-alpha and nitrite compared to PLK-infected mice. Mice infected with the PTN strain had an enhanced capacity to activate the immune system early in infection since they produced higher levels of IFN-gamma, TNF-alpha, and NO than PLK-infected mice. Administration of anti-IFN-gamma mAb or anti-asialo GM1 antibody resulted in 100 and 20% mortality, respectively, in PTN-infected mice but no death in PTN + PLK-infected mice. Together, these results suggest that early production of IFN-gamma and NK-cell activity is important in protection against PTN infection, whereas in PTN + PLK infection components of adaptive immunity rapidly developed following elaboration of an effective early innate immune response.     

Decreased resistance of B cell-deficient mice to infection with Toxoplasma gondii despite unimpaired expression of IFN-gamma, TNF-alpha, and inducible nitric oxide synthase

The role of B cells in resistance against Toxoplasma gondii was studied using B cell-deficient (muMT) mice. Following peroral infection with 10 cysts of the ME49 strain, all muMT mice survived the acute stage of the infection but died between 3 and 4 wk after infection. In contrast, all control mice were alive at 8 wk after infection. At the stage during which muMT animals succumbed to the infection, parasite replication and pathology were most evident in their brains; small numbers of tachyzoites were also detectable in their lungs. Significantly greater numbers of T. gondii cysts and areas of inflammation associated with tachyzoites were observed in brains of muMT than in control mice. Large areas of necrosis associated with numerous tachyzoites were observed only in brains of muMT mice. Anti-T. gondii IgG Abs were detected only in sera of control mice, whereas similar levels of IFN-gamma were detected in sera of both strains of mice. Amounts of mRNA for IFN-gamma, IL-10, and inducible NO synthase in the brain did not differ between infected muMT and control mice. Expression of mRNA for TNF-alpha was increased in brains of muMT mice. Administration of polyclonal rabbit anti-T. gondii IgG Ab prevented early mortality and pathology associated with tachyzoites in the brain in the infected muMT mice. These results indicate that B cells play an important role, most likely through their production of specific Abs, in resistance to persistent active (tachyzoite) infection with T. gondii in mice, especially in the brain and lung.     

Importance of endogenous IFN-gamma for prevention of toxoplasmic encephalitis in mice

The importance of endogenous IFN-gamma for prevention of toxoplasmic encephalitis was studied in mice chronically infected with Toxoplasma gondii by using a mAb to this lymphokine. Control mice chronically infected with the ME49 strain that received saline or normal IgG had slight inflammation in their brains whereas those that received the mAb developed severe encephalitis. In contrast to control mice, the mAb-treated mice had many areas of acute focal inflammation and infiltration of large numbers of inflammatory cells in the meninges and parenchyma of their brains. In the areas of acute focal inflammation, tachyzoites and Toxoplasma Ag were demonstrated by immunoperoxidase staining with the use of rabbit anti-Toxoplasma antibody, suggesting that the focal inflammation was induced by Toxoplasma organisms. Acute inflammation was also observed around cysts of Toxoplasma. Immunohistologic staining revealed tachyzoites and Toxoplasma Ag surrounding the periphery of these cysts suggesting cyst disruption had occurred. Mice treated with mAb against IFN-gamma had five times the numbers of cysts in their brains as did control mice. These results clearly indicate that endogenous IFN-gamma plays a significant and important role in prevention of encephalitis in mice chronically infected with Toxoplasma. The mAb-treated mice had the same Toxoplasma antibody titers and the same degree of macrophage killing of Toxoplasma as did untreated controls. These results suggest that IFN-gamma may have a direct role in preventing cyst rupture and toxoplasmic encephalitis.     

IFN-gamma overproduction and high level apoptosis are associated with high but not low virulence Toxoplasma gondii infection.

Toxoplasma gondii is an opportunistic intracellular parasite which induces a highly strong type 1 cytokine response. The present study focuses on defining the factors influencing the outcome of infection with tachyzoites of the type I, highly lethal RH strain, relative to the type II, low virulence strain ME49. Infection with the RH strain led to widespread parasite dissemination and rapid death of mice; in contrast, mice survived low virulence strain ME49 infection, and tachyzoite dissemination was much less extensive. Furthermore, massive apoptosis and disintegration of the splenic architecture was characteristic of RH, but not ME49, infection. In addition, hyperinduction of IFN-gamma and lack of NO production were found during RH, in contrast to ME49 infection. These data demonstrate that Toxoplasma strain characteristics exert a profound effect on the host immune response and that the latter itself is a crucial determinant in parasite virulence.     

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.     

Toxoplasma gondii and Schistosoma mansoni synergize to promote hepatocyte dysfunction associated with high levels of plasma TNF-alpha and early death in C57BL/6 mice.

To address the question of how the murine host responds to a prototypic type 1 cytokine inducer while concurrently undergoing a helminth-induced type 2 cytokine response, C57BL/6 strain animals with patent schistosomiasis mansoni were orally infected with the cystogenic Toxoplasma gondii strain ME49. Schistosoma mansoni infection resulted in a significantly higher mortality rate when mice were subsequently orally infected with ME49, and these animals displayed a defective IFN-gamma and NO response relative to animals infected with T. gondii alone. Plasma levels of TNF-alpha and aspartate transaminase in double-infected mice were greatly elevated relative to mice infected with either parasite alone. Consistent with the latter observation, these animals exhibited severe liver pathology, with regions of coagulative necrosis and hepatocyte vacuolization unapparent in mice carrying either infection alone. Interestingly, mean egg granuloma size was approximately 50% of that in mice with S. mansoni infection alone. The exacerbated liver pathology in coinfected mice did not appear to be a result of uncontrolled tachyzoite replication, because both parasite-specific RT-PCR analysis and immunohistochemical staining demonstrated a low number of tachyzoites in the liver. We hypothesize that mortality in these animals results from the high level of systemic TNF-alpha, which mediates a severe liver pathology culminating in death of the animal.     

Simultaneous depletion of CD4+ and CD8+ T lymphocytes is required to reactivate chronic infection with Toxoplasma gondii.

C57BL/6 mice chronically infected with an avirulent strain (ME-49) of Toxoplasma gondii were used to study the mechanisms by which T lymphocytes and IFN-gamma prevent reactivation of latent infection. Infected animals were treated with mAb, either anti-CD8, anti-CD4, anti-CD4 plus anti-CD8, anti-IFN-gamma, or anti-CD4 plus anti-IFN-gamma and the mice followed for survival, histopathology, cyst numbers, and spleen cell cytokine responses. In agreement with previously published findings, treatment with anti-IFN-gamma antibodies fully reactivated the asymptomatic infection, inducing massive necrotic areas in the brain with the appearance of free tachyzoites and death of all animals within 2 wk. Mice treated with the combination of anti-CD4 plus anti-CD8 antibodies showed augmented pathology and mortality nearly identical to the anti-IFN-gamma- treated animals. In contrast, treatment with anti-CD4 or anti-CD8 mAb alone failed to result in significantly enhanced brain pathology or mortality. In additional experiments, full reactivation of infection was observed in mice treated with anti-CD4 plus anti-IFN-gamma indicating that CD4+ lymphocytes are not required for the pathology resulting from IFN-gamma neutralization. Cytokine measurements on parasite Ag-stimulated spleen cells from mAb-treated mice indicated that both CD4+ and CD8+ cells produce IFN-gamma whereas only CD4+ cells contribute to parasite Ag-induced IL-2 synthesis. Together, these results suggest that CD4+ and CD8+ lymphocytes act additively or synergistically to prevent reactivation of chronic T. gondii infection probably through the production of IFN-gamma.     

Role of L3T4+ and Lyt-2+ T cell subsets in protective immune responses of mice against infection with a low or high virulent strain of Toxoplasma gondii

In order to elucidate the role of T cell subsets in protective immunity against infection with high virulent and low virulent strains of Toxoplasma gondii, monoclonal antibodies specific for T cell subsets were injected into mice before immunization or challenge infection. Treatment of mice with monoclonal antibody to either L3T4+ or Lyt-2+ T cells before they were immunized with Toxoplasma cell homogenate prepared from high virulent RH strain tachyzoites markedly reduced survival after mice were challenged with low virulent bradyzoites of the Beverley strain. Thus, induction of protective immunity against bradyzoites of the Beverley strain requires the presence of both L3T4+ and Lyt-2+ T cells. In contrast, mice injected with living bradyzoites of the low virulent Beverley strain after immunization with Toxoplasma cell homogenate acquired protective immunity against high virulent tachyzoites of the RH strain. Lyt-2+ T cells alone appear to be final effector cells for protection against the challenge with high virulent RH strain tachyzoites, since treatment of the bradyzoite-immune mice with anti-Lyt-2 antibody, but not anti-L3T4 antibody, before challenge significantly increased mortality.     

Toxoplasma gondii: detection of MIC10 antigen in sera of experimentally infected mice

We developed a sandwich ELISA for the detection of circulating Toxoplasma gondii MIC10 antigens. In T. gondii culture supernatant, MIC10 was detected in a growth dependent manner. Mice were infected with a lethal dose of either a virulent RH strain, an avirulent Beverley strain or a sub-lethal dose of a PLK strain of T. gondii. MIC10 appeared 2 days after infection and increased gradually in the sera of RH-infected mice. A detectable but significantly lower amount of MIC10 was observed in the sera of mice infected intraperitoneally with Beverley tachyzoites. In contrast, the MIC10 antigen in mice sera following oral infection with Beverley cysts was below detectable levels during the course of the experiment. In sera of PLK-infected mice, MIC10 was predominantly observed between late acute and early chronic phase. Our data show that the kinetics of circulating MIC10 differs depending on the strain and route of infection.     

Functional and quantitative analysis of splenic T cell immune responses following oral toxoplasma gondii infection in mice

Functional and quantitative analysis of splenic T cell immune responses following oral Toxoplasma gondii infection in mice. Experimental Parasitology 91, 212-221. Immunity to Toxoplasma gondii is mediated primarily by the host T cell response. Although there is considerable information regarding host immunity following intraperitoneal infection with tachyzoites, little information is available regarding naturally acquired infection following peroral infection with bradyzoites. In this study, a sequential quantitative analysis of the cell-mediated immune response was performed at the single cell level. To assess the kinetics of this response and parasitic loads, inbred mice were orally infected with the 76K strain bradyzoites of T. gondii. Within 24 h of infection, follicular hyperplasia followed by infiltration with histiocytes, macrophages, and apoptotic bodies was observed in the spleens of infected mice. T. gondii were detected from day 1, and counts increased gradually during the experimental period. Splenocyte DNA synthesis to antigen and mitogen was severely suppressed at days 7 and 10. The percentages of NK1.1(+) or delta gamma T cells were increased from day 1, whereas CD4(+) and CD8alpha+ T cells were signficantly increased after day 7 postinfection. CD25 expression and intracellular IFN-gamma production increased in NK1.1(+) cells on day 1 and by all other T cell subsets after day 4. Intracellular IL-4 did not increase until day 7, and IL-10 production was increased in all T cell subsets after day 4. Together, these findings indicate that oral infection with T. gondii stimulates a strong cellular immune response that appears to polarize toward an early Th1 response. However, within 7 days, a strong immune Th2 regulatory response as well as high parasitic loads can be observed, with a reduction in lymphoproliferation to mitogen stimulation, increased production of IL-4 and IL-10, and evidence of T cell apoptosis in the splenic immune compartment.     

Stage conversion of Toxoplasma gondii RH parasites in mice by treatment with atovaquone and pyrrolidine dithiocarbamate

The mouse-virulent RH strain of Toxoplasma gondii is generally considered to have lost its cyst-forming capacity, and conversion of RH tachyzoites into cysts in non-immune mice has previously been shown exclusively following early treatment with sulfadiazine (SDZ). We here describe the development of tissue cysts in mice infected with RH strain parasites and treated with atovaquone (ATO) combined with pyrrolidine dithiocarbamate (PDTC). Groups of Swiss-Webster mice infected intraperitoneally (i.p.) with 10(2) RH tachyzoites were treated with 5, 25 and 100 mg of ATO/kg per day alone or combined with PDTC at 250 mg/kg per day from day 1 postinfection (p.i.) for 14 days. A total of 19 mice survived the 6-week observation period. Of these, brain cysts were recovered in nine (47%), with burdens ranging from 50 to 3120 (mean +/- S.D. = 622 +/- 963). All cyst-harboring mice had high specific IgG antibody levels (1:10,240-1:40,960, corresponding to 500-2000 IU/ml), as did one mouse in which cysts were not demonstrated, which was therefore included in the group of mice with residual infection. Bioassay performed to test the infectivity of these cysts produced acute lethal toxoplasmosis following i.p. inoculation in all instances (100%), and importantly, following peroral inoculation in four (29%). The recovered tachyzoites were highly infectious. In addition, significantly elevated interferon gamma (IFN-gamma) in the treated mice which developed residual infection compared with any group of infection-free (treated or subinoculated) mice, indicates immunological control of the parasite in the latent form. In conclusion, early treatment of mice infected with T. gondii RH tachyzoites with ATO and PDTC induces conversion into tissue cysts, thus providing a new model for studying the mechanism(s) of T. gondii stage conversion.     

Changes in blastogenic responses and antibody titers of mice infected with Toxoplasma gondii]

This study was performed to observe the cell-mediated and humoral immune responses in mice which were infected with Beverley, Fukaya and ME49 strain of Toxoplasma gondii, respectively. The blastogenic responses of splenocytes using [3H]-thymidine and serum antibody titers were measured weekly up to 10 weeks after infection. The blastogenic responses of splenocytes treated with concanavalin A and Toxoplasma lysate were significantly declined in the 3 strain groups as compared with the non-infected group (p less than 0.05), however lipopolysaccharide-treated blastogenic responses were not significantly different between infected and non-infected groups. The serum IgG antibody titers in the three infected groups increased from 2 weeks after infection, and the serum IgM antibody titers increased until 4 weeks after infection. No significant differences were revealed in blastogenic responses and serum antibody titers among the 3 groups. The present study suggested that cell-mediated immune responses were involved in T. gondii infected mice and blastogenic responses of T lymphocytes were inhibited in acute T. gondii infection.     

Infection and immunity with the RH strain of Toxoplasma gondii in rats and mice.

Infection and immunity to toxoplasmosis induced by the RH strain of Toxoplasma gondii was compared in Sprague-Dawley (SD) and Wistar rats and in outbred Swiss Webster mice. All rats injected with up to 1,000,000 RH-strain tachyzoites remained clinically normal, whereas mice injected with only 1 live tachyzoite died of acute toxoplasmosis. Rats could be infected with 1 tachyzoite of the RH strain as shown by antibody development and by bioassay in mice. However, after 8 days, RH-strain organisms were recovered only inconsistently from SD and Wistar rat brains. Contrary to a report of sterile immunity to T. gondii infection in rats after immunization with live RH tachyzoites, we found infection immunity after challenge with the VEG strain. Toxoplasma gondii tissue cysts of the VEG strain could be recovered from most SD and Wistar rats, first injected with live RH-strain tachyzoites and then challenged with oocysts of the VEG strain. Our RH strain, and probably many others, passed for 50+ yr as tachyzoites has lost not only the capacity to form oocysts, but also shows a marked reduction or absence of tissue cyst (bradyzoites) formation.     

Human dendritic cells discriminate between viable and killed Toxoplasma gondii tachyzoites: dendritic cell activation after infection with viable parasites results in CD28 and CD40 ligand signaling that controls IL-12-dependent and -independent T cell production of IFN-gamma

We studied how the interaction between human dendritic cells (DC) and Toxoplasma gondii influences the generation of cell-mediated immunity against the parasite. We demonstrate that viable, but not killed, tachyzoites of T. gondii altered the phenotype of immature DC. DC infected with viable parasites up-regulated the expression of CD40, CD80, CD86, and HLA-DR and down-regulated expression of CD115. These changes are indicative of DC activation induced by T. gondii. Viable and killed tachyzoites had contrasting effects on cytokine production. DC infected with viable T. gondii rather than DC that phagocytosed killed parasites induced secretion of high amounts of IFN-gamma by T cells from T. gondii-seronegative donors. IFN-gamma production in response to DC infected with viable parasites required CD28 and CD40 ligand (CD40L) signaling. In addition, this IFN-gamma response was dependent in part on IL-12 secretion. Production of IL-12 p70 occurred after interaction between T cells and DC infected with viable T. gondii, but not after incubation of T cells with DC plus killed tachyzoites. IL-12 synthesis was inhibited by blockade of CD40L signaling. IL-12-independent IFN-gamma production required CD80/CD86-CD28 interaction and, to a lesser extent, CD40-CD40L signaling. Taken together, T. gondii-induced activation of human DC is associated with T cell production of IFN-gamma through CD40-CD40L-dependent release of IL-12 and through CD80/CD86-CD28 and CD40-CD40L signaling that mediate IFN-gamma secretion even in the absence of bioactive IL-12.     

Toxoplasma gondii Hsp70 as a danger signal in toxoplasma gondii-infected mice

Toxoplasma gondii Hsp70, T gondii Hsp30/bag1, and surface antigen 1 messenger RNAs were shown to be useful in analyzing stage conversion of T gondii between bradyzoites and tachyzoites. The high-level expression of T gondii Hsp70 was correlated with mortality in interferon-gamma knockout mice infected with T gondii. Tgondii Hsp70 inhibited the induction of nitric oxide release by peritoneal macrophages of T gondii-infected mice. These findings identify T gondii Hsp70 as a danger signal during lethal, acute T gondii infection.     

Toxoplasma gondii: blood and tissue kinetics during acute and chronic infections in mice

Acute lethal infections were obtained in mice by intraperitoneal (IP) injection of 10(2) or 10(4) tachyzoites of the virulent RH and C56 strains. Chronic infections were obtained by IP injection or peroral (PO) gavage of 20 cysts of the avirulent C strain. Mice were sacrificed at varying intervals after infection and parasite burdens were quantitated in blood, brain, and lungs using a tissue culture method. Acutely infected mice died within 6 to 10 days postinfection as a function of the strain and inoculum size. With either strain, tachyzoites were first detected in lungs on either Days 2 or 4 postinfection, according to the inoculum size, then in brain and blood at Days 4 or 6; parasitic loads remained constantly at a higher level in lungs than in brain until the date of death. Bradyzoites could only be detected in lungs, from Days 4 or 6 until death. In chronic infections, similar results were obtained for IP and PO infected mice. Both tachyzoites and bradyzoites were first detected in lungs and brain from Day 7 after infection; tachyzoites remained at a higher level in lungs than in brain until Day 10, then subsequently decreased in lungs. At Day 50, tachyzoites were not detectable in lungs, whereas bradyzoites remained at a constant level; in brain, both parasitic stages were detectable at a similar level throughout the follow-up period. These results indicate that infection with a virulent Toxoplasma strain is characterized by an early involvement of lungs, with pneumonia as the principal cause of death.(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of CD28 in the generation of effector and memory responses required for resistance to Toxoplasma gondii.

CD28 deficient (CD28-/-) mice were used to study the role of costimulation in the T cell-mediated, IFN-gamma-dependent mechanism of resistance to Toxoplasma gondii. These mice were resistant to infection with the ME49 strain of T. gondii. Analysis of the immune response of acutely infected CD28-/- mice revealed that IL-12 was required for T cell production of IFN-gamma and this was independent of the CD40/CD40 ligand interaction. A similar mechanism of IL-12-dependent, CD28/B7 independent production of IFN-gamma by T cells was also observed in wild-type mice. Interestingly, although chronically infected wild-type mice were resistant to rechallenge with the virulent RH strain of T. gondii, chronically infected CD28-/- mice were susceptible to rechallenge with the RH strain. This deficiency in the protective memory response by CD28-/- mice correlated with a lack of IL-2 and IFN-gamma in recall responses and reduced numbers of CD4+ T cells expressing a memory phenotype. Together, our findings demonstrate that CD28 is not required for the development of a protective T cell response to T. gondii, but CD28 is required for an optimal secondary immune response.     

Maternal-fetal transmission of Toxoplasma gondii in interferon-gamma deficient pregnant mice

Toxoplasma gondii infection is generally asymptomatic in immunocompetent persons but can be life-threatening in immunocompromised persons and for fetuses in the case of maternal-fetal transmission. The effect of interferon (IFN)-gamma, which plays a crucial role in the protective immunity against T. gondii infection, on maternal-fetal transmission of T. gondii was analyzed by quantitative competitive polymerase chain reaction targeting T. gondii-specific SAG1 gene. T. gondii loads were obvious in uterus and placenta of wild type (WT) C57BL/6 (B6, susceptible strain) but not BALB/c (resistant strain) pregnant mice. Higher levels of T. gondii were detected in uterus and placenta of IFN-gamma knock-out (GKO) B6 and BALB/c than in those of WT mice. Furthermore, T. gondii was detected in fetus of GKO B6 but not GKO BALB/c, WT B6, or WT BALB/c mice. Thus, not only IFN-gamma but also genetic susceptibility to T. gondii infection was important for the protective immunity of maternal-fetal transmission of T. gondii to fetus via placenta. T. gondii-infected WT mice displayed a low delivery rate with high IFN-gamma production, whereas infected GKO mice did not. Additionally, mean body weight of neonates from T. gondii-infected GKO BALB/c pregnant mice was significantly lower than that of unaborted neonates from WT BALB/c pregnant mice, suggesting the effects of T. gondii infection on intrauterine growth retardation of fetus in pregnant GKO mice.     

Depletion of CD4+ T cells but not inhibition of the protective activity of IFN-gamma prevents cure of toxoplasmosis mediated by drug therapy in mice.

Toxoplasmosis is a frequent opportunistic infection in patients with AIDS. In these patients the major immune deficiencies are a severe depletion of CD4+ T lymphocytes and an impaired capacity to produce IFN-gamma. A mouse model was developed and used to study the effects that depletion of CD4+ T cells and/or inhibition of the protective activity of IFN-gamma have on the effectiveness of the drug therapy for toxoplasmosis. Infection of mice with a lethal inoculum of Toxoplasma gondii cysts followed by treatment with the hydroxynaphthoquinone 566C80 or with sulfadiazine resulted in 100% survival whereas untreated controls had 100% mortality within 15 days of infection. Administration of antiserum to IFN-gamma resulted in early death of untreated mice and in 30% mortality in those treated. Administration of mAb to CD4+ T cells followed by infection with T. gondii prevented the development of both antibody and cell-mediated immune responses against the parasite. These mice resisted the acute infection while undergoing specific treatment. Discontinuation of the treatment, however, resulted in reactivation of the infection and the majority of the animals died within 17 days of suspension of the treatment. Administration of antiserum to IFN-gamma or to CD4+ T cells 24 h but not 15 days after conclusion of the treatment also resulted in mortality. These results indicate that successful treatment of toxoplasmosis depends on the status of the immune system, particularly of CD4+ T cells. Although it is speculative to compare results obtained in mice to the situation in humans, our work suggests that restoration of a competent immune response is of crucial importance for a successful treatment of toxoplasmosis in immunocompromised individuals.