Cellular immunopathogenesis in primary Toxoplasma gondii infection during pregnancy.

Congenital toxoplasmosis is caused by the vertical transmission of infection from mother to foetus through the placenta when a pregnant woman is infected with Toxoplasma gondii (T. gondii). Congenital infection can have serious consequences, such as intrauterine abortion, foetal death and severe neurological, ocular or other organ damage in the foetus. In this review, we focus on recent publications investigating vertical transmission of T. gondii infection, cellular immunopathogenesis and protective immunity in primary toxoplasmosis during pregnancy.

Interleukin-17A-Deficient Mice Are Highly Susceptible to Toxoplasma gondii Infection Due to Excessively Induced T. gondii HSP70 and Interferon Gamma Production.

Interleukin17A (IL-17A) is known to be involved in the host defense against pathogens and the pathogenesis of autoimmune diseases. Previously, we showed that excessive amounts of interferon gamma (IFN-γ) play an important role in the pathogenesis of the lethal effects of Toxoplasma gondii by inducing anaphylactic responses. In the study described in this report, we examined the effects of IL-17A deficiency on murine host defense against oral T. gondii infection. IL-17A-deficient C57BL/6 (B6) mice exhibited higher rates of mortality than wild-type (WT) mice during the acute phase of T. gondii infection. CD4+ T cells in the mesenteric lymph nodes (mLNs) and ileum of T. gondii-infected IL-17A-deficient mice produced higher levels of IFN-γ than did those of WT mice. In addition, the level of T. gondii HSP70 (T.gHSP70) expression was also significantly increased in the ileum, mLNs, liver, and spleen of infected IL-17A-deficient mice compared with that in WT mice. These elevated levels of expression of T.gHSP70 and IFN-γ in infected IL-17A-deficient mice were presumably linked to the IL-17A defect since they decreased to WT levels after treatment with recombinant IL-17A. Furthermore, IL-17A-deficient mice were highly susceptible to the anaphylactic effect of T.gHSP70, and the survival of IL-17A-deficient mice during the acute phase was improved by treatment with an anti-T.gHSP70 monoclonal antibody. These results suggest that IL-17A plays an important role in host survival against T. gondii infection by protecting the host from an anaphylactic reaction via the downregulation of T.gHSP70 and IFN-γ production.

Human wound myiasis caused by Phormia regina and Sarcophaga haemorrhoidalis in Minia Governorate, Egypt.

Myiasis is the parasitic infestation of human by the larvae (maggots) of dipterous fly that grow within the host while feeding on its tissue. Cutaneous myiasis is the most considerably encountered clinical form. Moreover, wound (traumatic) myiasis is the main clinical manifestation of cutaneous myiasis. In this research, we aimed to study the type of infesting larvae that are responsible for wound myiasis in the patients in Minia city, Egypt. Three cases of wound myiasis have been noticed among 280 patients with wounds at different parts of bodies. Two of them were diabetic patients. The third one had a history of hypertension with right side hemiplegia 2 years ago. All of them were elderly. The larvae removed from cases 1 and 3 were identified macroscopically and microscopically as the third-stage larvae of Sarcophaga haemorrhoidalis. The larvae removed from case 2 were the third-stage larvae of Phormia regina, which is very rare worldwide. In addition to the open and obsolete wound, diabetes mellitus and low socio-economic circumstances were shown to be attributed as important predisposing risk factors that led to the occurrence of myiasis in these patients.

Congenital toxoplasmosis from a mother with type 2 diabetes mellitus: a case report.

A 33-year-old woman with type 2 diabetes mellitus (DM) was suspected of being primarily infected with Toxoplasma gondii at 12 weeks of gestation (GW). Although acetylspiramycin was started at 17 GW, the T. gondii DNA gene was detected in the amniotic fluid at 18 GW. Chemotherapy was changed to pyrimethamine plus sulfadiazine from 20 GW, but was changed back to acetylspiramycin after 2 weeks because of vomiting. Acetylspiramycin was continued until her delivery. DM was controlled well during the pregnancy. An asymptomatic male baby was born by cesarean section at 37 GW, and was treated with acetylspiramycin for 4 weeks because the polymerase chain reaction results of umbilical cord blood were positive. He has developed normally until the present, that is, 6 months of age. Herein, we describe a case report in which symptomatic congenital toxoplasmosis was avoided in a pregnant woman with an immunosuppressive risk due to prompt chemotherapy.

Protective effect of arctiin against Toxoplasma gondii HSP70-induced allergic acute liver injury by disrupting the TLR4-mediated activation of cytosolic phospholipase A2 and platelet-activating factor.

Toxoplasma gondii (T. gondii)-derived heat shock protein 70 (T.g.HSP70) is a toxic protein that downregulates host defense responses against T. gondii infection. T.g.HSP70 was proven to induce fatal anaphylaxis in T. gondii infected mice through cytosolic phospholipase A2 (cPLA2) activated-platelet-activating factor (PAF) production via Toll-like receptor 4 (TLR4)-mediated signaling. In this study, we investigated the effect of arctiin (ARC; a major lignan compound of Fructus arctii) on allergic liver injury using T.g.HSP70-stimulated murine liver cell line (NCTC 1469) and a mouse model of T. gondii infection. Localized surface plasmon resonance, ELISA, western blotting, co-immunoprecipitation, and immunofluorescence were used to investigate the underlying mechanisms of action of ARC on T. gondii-induced allergic acute liver injury. The results showed that ARC suppressed the T.g.HSP70-induced allergic liver injury in a dose-dependent manner. ARC could directly bind to T.g.HSP70 or TLR4, interfering with the interaction between these two factors, and inhibiting activation of the TLR4/mitogen-activated protein kinase/nuclear factor-kappa B signaling, thereby inhibiting the overproduction of cPLA2, PAF, and interferon-γ. This result suggested that ARC ameliorates T.g.HSP70-induced allergic acute liver injury by disrupting the TLR4-mediated activation of inflammatory mediators, providing a theoretical basis for ARC therapy to improve T.g.HSP70-induced allergic liver injury.

Toxoplasma gondii infection inhibits Th17-mediated spontaneous development of arthritis in interleukin-1 receptor antagonist-deficient mice.

Interleukin 1 receptor antagonist (IL-1Ra)-deficient BALB/c mice develop spontaneous arthritis resembling human rheumatoid arthritis. We herein report that infection with Toxoplasma gondii, an intracellular protozoan, is capable of ameliorating the spontaneous development of arthritis in IL-1Ra-deficient mice. The onset of arthritis development was delayed and the severity score of arthritis was significantly suppressed in T. gondii-infected mice. Expression of IL-12p40 mRNA from CD11c(+) cells of mesenteric lymph nodes (mLN) and spleen markedly increased at 1 week after peroral infection. While CD11c(+) cells also produced IL-10, IL-1ß, and IL-6, CD4(+) T cells from T. gondii-infected mice expressed significantly high levels of T-bet and gamma interferon (IFN-γ) mRNA in both mLN and spleen. Levels of GATA-3/IL-4 mRNA or RORγt/IL-17 mRNA decreased in the infected mice, indicating Th1 cell polarization and the reduction of Th2 and Th17 cell polarization. The severity of arthritis was related to Th1 cell polarization accompanied by Th17 cell reduction, demonstrating the protective role of the T. gondii-derived Th1 response against Th17 cell-mediated arthritis in IL-1Ra-deficient mice.

Ginsenoside Rh2 attenuates microglial activation against toxoplasmic encephalitis via TLR4/NF-κB signaling pathway.

BACKGROUND: Ginsenoside Rh2 (GRh2) is a characterized component in red ginseng widely used in Korea and China. GRh2 exhibits a wide range of pharmacological activities, such as anti-inflammatory, antioxidant, and anticancer properties. However, its effects on Toxoplasma gondii (T. gondii) infection have not been clarified yet. METHODS: The effect of GRh2 against T. gondii was assessed under in vitro and in vivo experiments. The BV2 cells were infected with tachyzoites of T. gondii RH strain, and the effects of GRh2 were evaluated by MTT assay, morphological observations, immunofluorescence staining, a trypan blue exclusion assay, reverse transcription PCR, and Western blot analyses. The in vivo experiment was conducted with BALB/c mice inoculated with lethal amounts of tachyzoites with or without GRh2 treatment. RESULTS AND CONCLUSION: The GRh2 treatment significantly inhibited the proliferation of T. gondii under in vitro and in vivo studies. Furthermore, GRh2 blocked the activation of microglia and specifically decreased the release of inflammatory mediators in response to T. gondii infection through TLR4/NF-κB signaling pathway. In mice, GRh2 conferred modest protection from a lethal dose of T. gondii. After the treatment, the proliferation of tachyzoites in the peritoneal cavity of infected mice markedly decreased. Moreover, GRh2 also significantly decreased the T. gondii burden in mouse brain tissues. These findings indicate that GRh2 exhibits an anti-T. gondii effect and inhibits the microglial activation through TLR4/NF-κB signaling pathway, providing the basic pharmacological basis for the development of new drugs to treat toxoplasmic encephalitis.

Arctigenin protects against depression by inhibiting microglial activation and neuroinflammation via HMGB1/TLR4/NF-κB and TNF-α/TNFR1/NF-κB pathways.

BACKGROUND AND PURPOSE: Arctigenin, a major bioactive component of Fructus arctii, has been reported to have antidepressant-like effects. However, the mechanisms underlying these effects are still unclear. Neuroinflammation can be caused by excessive production of proinflammatory cytokines in microglia via high-mobility group box 1 (HMGB1)/TLR4/NF-κB and TNF-α/TNFR1/NF-κB signalling pathways, leading to depression. In this study, we have investigated the antidepressant mechanism of arctigenin by conducting in vitro and in vivo studies. EXPERIMENTAL APPROACH: The effects of chronic unpredictable mild stress (CUMS) on wild-type (WT) and TLR4-/- mice were examined. Antidepressant-like effects of arctigenin were tested using the CUMS-induced model of depression in WT mice. The effects of arctigenin were assessed on the HMGB1/TLR4/NF-κB and TNF-α/TNFR1/NF-κB signalling pathways in the prefrontal cortex (PFC) of mouse brain and HMGB1- or TNF-α-stimulated primary cultured microglia. The interaction between HMGB1 and TLR4 or TNF-α and TNFR1 with or without arctigenin was examined by localized surface plasmon resonance (LSPR) and co-immunoprecipitation assays. KEY RESULTS: The immobility times in the tail suspension test (TST) and forced swimming test (FST) were reduced in TLR4-/- mice, compared with WT mice. Arctigenin exhibited antidepressant-like effects. Arctigenin also inhibited microglia activation and inflammatory responses in the PFC of mouse brain. Arctigenin inhibited HMGB1 and TLR4 or TNF-α and TNFR1 interactions, and suppressed both HMGB1/TLR4/NF-κB and TNF-α/TNFR1/NF-κB signalling pathways. CONCLUSIONS AND IMPLICATIONS: Arctigenin has antidepressant-like effects by attenuating excessive microglial activation and neuroinflammation through the HMGB1/TLR4/NF-κB and TNF-α/TNFR1/NF-κB signalling pathways. This suggests that arctigenin has potential as a new drug candidate suitable for clinical trials to treat depression.

Arctigenin ameliorates depression-like behaviors in Toxoplasma gondii-infected intermediate hosts via the TLR4/NF-κB and TNFR1/NF-κB signaling pathways.

Toxoplasma gondii (T. gondii) is a known neurotropic protozoan that remains in the central nervous system and induces neuropsychiatric diseases in intermediate hosts. Arctigenin (AG) is one of the major bioactive lignans of the fruit Arctium lappa L. and has a broad spectrum of pharmacological activities such as neuroprotective, anti-inflammatory and anti-T. gondii effects. However, the effect of AG against depressive behaviors observed in T. gondii-infected hosts has not yet been clarified. In the present study, we analyzed the effects of AG against T. gondii-induced depressive behaviors in intermediate hosts using a microglia cell line (BV2 cells) and brain tissues of BALB/c mice during the acute phase of infection with the RH strain of T. gondii. AG attenuated microglial activation and neuroinflammation via the Toll-like receptor/nuclear factor-kappa B (NF-κB) and tumor necrosis factor receptor 1/NF-κB signaling pathways, followed by up-regulating the dopamine and 5-hydroxytryptamine levels and inhibiting the depression-like behaviors of hosts. AG also significantly decreased the T. gondii burden in mouse brain tissues. In conclusion, we elucidated the effects and underlying molecular mechanisms of AG against depressive behaviors induced by T. gondii infection.

Arctigenin exhibits hepatoprotective activity in Toxoplasma gondii-infected host through HMGB1/TLR4/NF-κB pathway.

Toxoplasmosis is a parasitic zoonosis with the highest incidence in humans. Severe lesions due to acute toxoplasmosis have been recorded in the visceral organs including the liver, where hepatocytes and Kupffer cells are important innate immune cells. Arctigenin (AG) is a bioactive ingredient of Arctium lappa L. and increasing evidence suggests that AG exhibits anti-oxidant, anti-inflammatory and anti-Toxoplasma gondii (T. gondii) effects. However, the role of AG in acute liver damage induced by T. gondii infection remains unclear. In this study, we analyzed the effects of AG against T. gondii-induced liver damage by establishing an in vitro infection model using a murine liver cell line (NCTC-1469 cells) and an in vivo mouse model with acute T. gondii infection of virulent RH strain. In the current study, AG effectively attenuated hepatocytes apoptosis and inhibited the reproduction of T. gondii. The results of in vitro and in vivo studies showed that AG significantly reduced alanine aminotransferase/aspartate aminotransferase activities and lessened pathological damage of liver. Moreover, AG suppressed T. gondii-induced inducible nitric oxide synthase production. AG also attenuated liver inflammation by inhibiting T. gondii-induced activation of the high-mobility group box1/toll-like receptor 4/nuclear factor-kappa B (HMGB1/TLR4/NF-κB) signaling pathway. These findings demonstrated that AG exhibited prominent hepatoprotective activities in toxoplasmic liver injury with anti-inflammatory effects by inhibiting the HMGB1/TLR4/NF-κB signaling axis. Thus, this study provides the basis for the development of new drugs to treat toxoplasmic hepatitis.

Infection dynamics of Toxoplasma gondii in gut-associated tissues after oral infection: The role of Peyer's patches.

Toxoplasma gondii is a common perorally transmitted parasite; however, its immunopathogenesis in gut-associated tissues remains unclear. Here, we compared disease manifestation in C57BL/6 immunocompetent wild type (WT) mice and immunocompromised interferon (IFN)-γ-deficient (GKO) mice after peroral infection (PI) with T. gondii cysts (Fukaya strain). Strong PI-induced Th1 cytokine expression was detected in WT mice. Moreover, bradyzoite-specific T.g.HSP30/bag1 mRNA was detected in the ileum parenchyma and Peyer's patches (PP), but not in the mesenteric lymph nodes, at 7 days post-infection in WT mice, and was significantly higher than that in GKO mice. Nested PCR showed that parasites existed in ileum parenchyma at days 1 and 1.5 post-PI in GKO and WT mice, respectively. In addition, quantitative competitive-PCR indicated that T. gondii first colonized the PP (day 3 post-PI), followed by the ileum parenchyma and mesenteric lymph nodes, spleen, and portal and aortic blood (day 7 post-PI). Although parasites were consistently more abundant in GKO mice, similar invasion and dissemination patterns were observed in the two hosts. Collectively, these data suggest that some zoites differentiate from tachyzoites to bradyzoites in the ileum and that T. gondii initially invades the ileum parenchyma, and then accumulates and proliferates in the PP before disseminating through the lymphatic systems of both GKO and WT hosts.

The clinical significance of anti-heat shock cognate protein 71 antibody in myasthenia gravis.

Anti-heat shock cognate protein 71 antibody (HSC71 Ab) formation in the sera of myasthenia gravis (MG) patients was measured, and the correlation between HSC71 Ab titers, clinical features and therapy efficacies for MG patients were examined. Clinical evaluations were performed according to the MG Foundation of America (MGFA) clinical classification. Therapy efficacies were measured using the MG activities of daily living (MG-ADL) score. Before treatment, 38 out of 48 serum samples (79%) from MG patients showed positive HSC71 Ab titers. In the "therapy-responsive group", HSC71 Ab titers significantly reduced, along with patient clinical improvements. Conversely, in the "therapy-resistant group", HSC71 Ab titers did not decline. The use of tacrolimus resulted in improvement in clinical manifestations together with a reduction in HSC71 Ab titers in the "therapy-resistant group". Thus, measurement of HSC71 Ab in the sera of MG patients seemed useful, as it appeared to reflect the effectiveness of treatment and allowed prediction of prognosis.

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.

Effects of sulfamethoxazole on murine ocular toxoplasmosis in interferon-gamma knockout mice.

PURPOSE: To evaluate the effects of sulfamethoxazole (SMX) on experimental ocular toxoplasmosis by quantitative competitive polymerase chain reaction (QC-PCR) assay. METHODS: Wild-type (WT) C57BL/6 and WT BALB/c mice and interferon-gamma knockout (GKO) mice were infected orally with Toxoplasma gondii of the Fukaya strain. Mice were classified into groups. The first group (G1) remained untreated, the second group (G2) had a short SMX treatment period, and the third group (G3) received treatment continuously. WT and GKO mice were divided into G1 and G3, and G1, G2, and G3, respectively. T. gondii burdens were evaluated by QC-PCR assay. The effect on stage distribution was analyzed by reverse transcription-PCR. RESULTS: SMX significantly decreased mortality among the infected WT C57BL/6 and GKO mice. In WT G1 mice, T. gondii DNA was detected in all organs and tissues, although in G3 mice it was detected only in the brain. In GKO C57BL/6 G1 mice, the protozoan proliferated much more actively than in the WT mice. In the GKO C57BL/6 G2 mice, the number of T. gondii was less than in G1 during the treatment, although the protozoan reappeared after cessation of treatment. In GKO C57BL/6 G3 mice, T. gondii DNA was detected in the brain, optic nerve, and retina, but not in the iris, choroid, sclera, and blood. In GKO BALB/c mice, the patterns of the kinetics of protozoan abundance in various organs were similar or were milder than those in GKO C57BL/6 mice. In SMX-treated GKO mice, the percentage of bradyzoites increased and that of tachyzoites decreased in the organs and tissues. CONCLUSIONS: SMX decreased the parasitic load in both WT and GKO mice. SMX decreased the tachyzoite load but did not completely eliminate bradyzoites in GKO mice. The present mouse model was used successfully to assess treatment effects in a quantitative fashion.

Toxoplasma gondii-derived heat shock protein 70 stimulates maturation of murine bone marrow-derived dendritic cells via Toll-like receptor 4.

Toxoplasma gondii-derived heat shock protein 70 (T.g.HSP70) induced maturation of bone marrow-derived dendritic cells (DCs) of wild-type (WT) C57BL/6 mice as evidenced by an increase in surface expression of MHC class I and II molecules and costimulatory molecules such as CD40, CD80, and CD86. Functionally, decreased phagocytic ability and increased alloreactive T cell stimulatory ability were observed in T.g.HSP70-stimulated DCs. These phenotypic and functional changes of T.g.HSP70-stimulated DCs were demonstrated in Toll-like receptor (TLR) 2- and myeloid differentiation factor 88 (MyD88)-deficient but not TLR4-deficient C57BL/6 mice. DCs from WT and TLR2-deficient but not TLR4-deficient mice produced IL-12 after T.g.HSP70 stimulation. T.g.HSP70-stimulated DCs from WT, TLR2-deficient, and MyD88-deficient, but not TLR4-deficient mice expressed IFN-beta mRNA. Thus, T.g.HSP70 stimulates murine DC maturation via TLR4 through the MyD88-independent signal transduction cascade.

Deterioration of visual function as examined by electroretinograms in Toxoplasma gondii-infected IFN-gamma-knockout mice.

PURPOSE: To investigate by ERG the effects of Toxoplasma gondii infection on the visual function of interferon gamma knockout (GKO) mice, as a model of immunocompromised hosts. METHODS: Susceptible wild-type (WT) C57BL/6 and GKO C57BL/6 mice were infected with five cysts of the avirulent T. gondii perorally. ERGs were recorded before and after the infection. The eyes of WT and GKO mice were enucleated and prepared for histologic studies 4 weeks and 12 days after infection, respectively. RESULTS: The a- and b-waves of ERGs did not change significantly up to 1 month after infection in WT mice, but those of GKO mice were significantly reduced 11 days after infection. Histopathology revealed focal retinitis and vasculitis in WT mice 4 weeks after infection. Mild inflammation and sludging of blood in the retina and choroid were found in GKO mice 12 days after infection, just before death. Cysts were found in the inner nuclear layer, with little disturbance of the surrounding retinal architecture in both WT and GKO mice. CONCLUSIONS: ERG clearly showed deterioration of visual function in GKO but not in WT mice after T. gondii infection. ERG is a sensitive and reliable method for observing activity in mice severely affected with experimental toxoplasmic retinochoroiditis.

IFN-gamma-regulated Toxoplasma gondii distribution and load in the murine eye.

PURPOSE: To establish a mouse model of ocular toxoplasmosis in both wild type (WT) and immunocompromised hosts and to clarify the effects of interferon (IFN)-gamma on the infectivity of Toxoplasma gondii in various parts of the eye. METHODS: Susceptible WT C57BL/6, resistant WT BALB/c, and IFN-gamma knockout (GKO) mice were infected with cysts of T. gondii perorally. The tissues were harvested for molecular and histopathologic studies. Analysis included a quantitative competitive polymerase chain reaction (QC-PCR) assay and reverse transcription (RT)-PCR for IFN-gamma and stage conversion markers. All animals underwent ophthalmic examinations including fluorescein angiography (FA). RESULTS: In WT C57BL/6 mice, T. gondii was detected in tissue in the following order: brain, retina, choroid, sclera, and optic nerve (ON). The highest T. gondii load was observed in the posterior retina, and was much greater than that in WT BALB/c mice. In GKO mice, disseminated infection was evident, and the T. gondii load was highest in the choroid and ON. IFN-gamma mRNA expression in WT C57BL/6 mice was higher than that in WT BALB/c mice after infection. Tachyzoites existed in GKO mice, whereas bradyzoites existed in WT C57BL/6 mice. FA showed dye leakage from the retinal capillaries of GKO mice. CONCLUSIONS: The T. gondii load in the retina in the susceptible WT strain continued to increase, unlike in the resistant WT strain. IFN-gamma was shown to regulate the T. gondii load and interconversion in the eye. A toxoplasmic vasculitis model was established with GKO mice and assay systems with QC-PCR and FA.

Roles of IFN-gamma on stage conversion of an obligate intracellular protozoan parasite, Toxoplasma gondii.

IFN-gamma downregulates the stage conversion of Toxoplasma gondii (T. gondii), from bradyzoites to tachyzoites, and the expression of heat shock protein 70 (HSP70) of T. gondii (T.g.HSP70) by tachyzoites. T.g.HSP70 has been shown to downregulate NO release from macrophages and also to induce auto-HSP70 antibody formation and IL-10 secretion by VH11-JH1 B-1 cells, resulting in the suppression of host defense responses to T. gondii infection. A novel category of virulent tachyzoite stage of T. gondii expressing T.g.HSP70 (virulent tachyzoite), which indirectly manifests its pathogenicity by downregulating host defense responses, has been proposed.

Toxoplasma gondii-derived heat shock protein HSP70 functions as a B cell mitogen.

We have investigated the role of Toxoplasma gondii-derived heat shock protein 70 (TgHSP70) as a B cell mitogen by measuring proliferative responses in vitro. TgHSP70 induced prominent proliferative responses in murine B cells derived not only from T gondii-infected but also from uninfected mice. Nude mice responded to TgHSP70; however, severe combined immunodeficiency, RAG1-/- B6, and microMT mice failed to respond. B220+ spleen cells showed marked proliferation after stimulation with TgHSP70, but neither CD4+ nor CD8+ population responded. This unresponsiveness of CD4+ and CD8- T cells to TgHSP70 was antigen presenting cells independent. These data indicate that TgHSP70 induced the proliferation of B cells but not T cells. Polymyxin B, a potent inhibitor of lipopolysaccharide (LPS), did not eliminate TgHSP70-induced proliferation. C3H/HeN mice responded well to TgHSP70 stimulation; however, C3H/HeJ mice carrying a point mutation in the Toll-like receptor (TLR) 4 failed to respond. This indicates that TLR4 is required for TgHSP70-induced B cell activation. The involvement of TLR4 in the TgHSP70-induced proliferative responses of spleen cells was also shown by the use of TLR4-/- mice. But TgHSP70-induced, but not LPS-induced, spleen cell proliferation was observed in MyD88-/- mice, indicating that the MyD88 molecule was involved in LPS-induced proliferation but not in TgHSP70-induced proliferation.