NKT cells are critical for the initiation of an inflammatory bowel response against Toxoplasma gondii

We demonstrated in this study the critical role of NKT cells in the lethal ileitis induced in C57BL/6 mice after infection with Toxoplasma gondii. This intestinal inflammation is caused by overproduction of IFN-gamma in the lamina propria. The implication of NKT cells was confirmed by the observation that NKT cell-deficient mice (Jalpha281(-/-)) are more resistant than C57BL/6 mice to the development of lethal ileitis. Jalpha281(-/-) mice failed to overexpress IFN-gamma in the intestine early after infection. This detrimental effect of NKT cells is blocked by treatment with alpha-galactosylceramide, which prevents death in C57BL/6, but not in Jalpha281(-/-), mice. This protective effect is characterized by a shift in cytokine production by NKT cells toward a Th2 profile and correlates with an increased number of mesenteric Foxp3 lymphocytes. Using chimeric mice in which only NKT cells are deficient in the IL-10 gene and mice treated with anti-CD25 mAb, we identified regulatory T cells as the source of the IL-10 required for manifestation of the protective effect of alpha-galactosylceramide treatment. Our results highlight the participation of NKT cells in the parasite clearance by shifting the cytokine profile toward a Th1 pattern and simultaneously to immunopathological manifestation when this Th1 immune response remains uncontrolled.

Experimental ocular toxoplasmosis in genetically susceptible and resistant mice

Genetic factors determining the pathogenesis and course of ocular toxoplasmosis are poorly understood. In this study, we explored the development of experimental ocular pathogenesis in genetically dissimilar mice infected with either the RH strain, the PLK strain, or the immunodominant surface antigen 1 (SAG1 [P30])-deficient mutant of the RH strain of Toxoplasma gondii. At 11 days postinfection, ocular infection of C57BL/6 mice with all of the strains of parasites resulted in severe inflammatory lesions and high numbers of parasites in eye tissue; less severe ocular lesions at earlier histopathology and prolonged survival were observed in this mouse strain infected with either the major surface antigen 1-deficient SAG1(-/-) strain or the less virulent PLK strain compared with RH infection. In contrast, both BALB/c and CBA/J mice had less severe lesions and low numbers of parasites in their eye tissue, and infection developed into the chronic stage in these mice. There were significantly higher serum levels of gamma interferon and tumor necrosis factor alpha in C57BL/6 mice than in BALB/c and CBA/J mice following ocular infection. These observations confirm earlier reports on systemic immunity to these parasites that the route of Toxoplasma infection markedly influences survival of mice. Our data indicate that genetic factors of the host as well as the parasite strain are critical in determining susceptibility to experimental ocular toxoplasmosis in murine models.

Attachment and invasion of host cells by Toxoplasma gondii

Recent studies indicate that Toxoplasma gondii attachment is mediated via a parasite ligand-host cell receptor interaction. Lloyd Kosper and Jose Mineo here survey factors involved in the attachment to and penetration and invasion of host cells by T. gondii.

FLAIR lesion volume in multiple sclerosis: relation to processing speed and verbal memory

Information processing speed and episodic memory are two commonly affected cognitive abilities in MS. Insights into the mechanisms of and relationships between these abilities have recently come from structural neuroimaging techniques, but few studies have used fluid-attenuated inversion recovery (FLAIR), a neuroimaging sequence known to be sensitive to cortical and juxtacortical lesions in MS. We hypothesized that a volumetric index of FLAIR total lesion volume (TLV) would be associated with slowed processing speed and verbal memory dysfunction in MS. Twenty MS patients underwent FLAIR imaging and were administered measures of verbal memory and processing speed. Correlational and regression analyses indicated that TLV was directly and independently related to measures of processing speed and verbal memory, and TLV accounted for 56% of the variance in cognitive performance. These findings, considered in the context of prior work, suggest that FLAIR TLV is a useful predictor of commonly impaired cognitive functions in MS, and shows promise as a functionally relevant biomarker for disease status.

Brain activation patterns associated with working memory in relapsing-remitting MS

BACKGROUND

Patients with multiple sclerosis (MS) show changes in brain activation patterns during visual and motor tasks that include decreases in the typical local network for a function and increases in other brain regions.

OBJECTIVE

To determine whether brain activation patterns associated with working memory are affected by MS.

METHODS

Activation of working memory circuitry was examined using an fMRI n-back task in adults with mild relapsing-remitting MS (RRMS; n = 10) and demographically matched healthy controls (n = 10).

RESULTS

Group differences in brain activation emerged during both low- and high-demand conditions (p < 0.001). Overall, patients showed less activation than controls in core prefrontal and parietal regions of working memory circuitry, and greater activation in other regions within and beyond typical working memory circuitry, including bilateral medial frontal, cingulate, parietal, bilateral middle temporal, and occipital regions.

CONCLUSIONS

Relative to controls, patients with mild RRMS showed shifts in brain activation patterns within and beyond typical components of working memory circuitry.

Co-infection of malaria and gamma-herpesvirus: exacerbated lung inflammation or cross-protection depends on the stage of viral infection

In order to study the interaction between a gamma-herpesvirus and malaria we established a co-infection model that involves infection of mice with murine gamma-herpesvirus (MHV-68) and Plasmodium yoelii non-lethal strain (PYNL). To investigate the interaction between acute malaria and the lytic stage of MHV-68, the timing of infections was chosen such that the peak virus and parasite burdens would be present at the same time. Under this condition, we observed significant mortality in co-infected mice and aggressive lung inflammation with a marked influx of neutrophils and megakaryocytes. If mice were latently infected with MHV-68 and then co-infected with malaria we noticed significantly less viral load and parasitaemia. Using MHC/peptide tetramer staining we found that acute malaria reduces the anti-MHV-68 CD8+ T cell response in the animals that develop severe disease. Our study provides important fundamental information, which will be of use when devising strategies to combat infections with more than one agent, a situation that often occurs naturally.

The induction of acute ileitis by a single microbial antigen of Toxoplasma gondii

The role of specific microbial Ags in the induction of experimental inflammatory bowel disease is poorly understood. Oral infection of susceptible C57BL/6 mice with Toxoplasma gondii results in a lethal ileitis within 7-9 days postinfection. An immunodominant Ag of T. gondii (surface Ag 1 (SAG1)) that induces a robust B and T cell-specific response has been identified and a SAG1-deficient parasite (Deltasag1) engineered. We investigated the ability of Deltasag1 parasite to induce a lethal intestinal inflammatory response in susceptible mice. C57BL/6 mice orally infected with Deltasag1 parasites failed to develop ileitis. In vitro, the mutant parasites replicate in both enterocytes and dendritic cells. In vivo, infection with the mutant parasites was associated with a decrease in the chemokine and cytokine production within several compartments of the gut-associated cell population. RAG-deficient (RAG1(-/-)) mice are resistant to the development of the ileitis after T. gondii infection. Adoptive transfer of Ag-specific CD4(+) effector T lymphocytes isolated from C57BL/6-infected mice into RAG(-/-) mice conferred susceptibility to the development of the intestinal disease. In contrast, CD4(+) effector T lymphocytes from mice infected with the mutant Deltasag1 strain failed to transfer the pathology. In addition, resistant mice (BALB/c) that fail to develop ileitis following oral infection with T. gondii were rendered susceptible following intranasal presensitization with the SAG1 protein. This process was associated with a shift toward a Th1 response. These findings demonstrate that a single Ag (SAG1) of T. gondii can elicit a lethal inflammatory process in this experimental model of pathogen-driven ileitis.

CD4+ T cells in the pathogenesis of murine ocular toxoplasmosis

The role of CD4(+) T cells in the pathogenesis of ocular toxoplasmosis was investigated in murine models utilizing inbred C57BL/6 mice deficient either in CD4(+), CD8(+), or B cells (microMT). Severe necrosis and inflammation with replicating parasites were observed in the eyes of control mice after primary ocular infection, and near-normal histology with few tachyzoites was observed in the eyes of mice immunized intraperitoneally with the avirulent ts-4 strain followed by intraocular challenge with the RH strain of Toxoplasma gondii. In contrast, mild inflammation without evidence of necrosis associated with increased parasite burdens were observed in the eyes of CD4 knockout (KO) mice after both primary ocular infection and challenge with RH tachyzoites. CD8 KO mice, as well as microMT mice, demonstrated increased ocular necrosis in response to either primary ocular infection or challenge. The parasite burden was increased in the eyes of both CD8 KO and microMT mice in which the parasite load was even higher. As expected, there were no increases in the levels of immunoglobulin G in serum or aqueous humor in microMT mice, and there was no increase in the levels of gamma interferon and tumor necrosis factor alpha in the sera of CD4 KO mice after both infection and challenge. These results suggest that the ocular inflammatory response to the parasite is mediated primarily by the CD4(+)-T-cell response. CD8(+) T cells and B cells may play an important role in limiting tachyzoite proliferation in the eyes. Mice deficient in CD8(+) CD4(+) T cells or B cells exhibit diminished vaccine-induced resistance and increased ocular parasite burden after challenge.

Novel approaches and cutting edge immunotherapies in multiple sclerosis

MS is a chronic inflammatory disease of the central nervous system (CNS). MS is a predominantly CD4+ T cell mediated autoimmune disorder. Recent studies have challenged this existing paradigm by supporting the role of other immune cells and factors (even non-immune) including CNS antigen-driven clonally expanded B cells, autoantibodies, complement and mediators of the innate immune responses in MS lesions. Further expansion of this global CNS dysfunction includes oligodendroglial cell (OGC) loss, attenuated remyelination, axonopathy, and gliosis. The recognition of new "players" directing effector and regulatory functions and further insight into reparative mechanisms occurring at various stages of the disease within a given individual will influence ongoing and future therapeutic trials. The following discussion will encompass evolving concepts in the pathogenesis of MS with a focus on novel immunotherapies. These new approaches reflect targeting of a multifaceted spectrum of immune activity. The immunotherapies will be characterized by their intervening role of specific and/or multiple pathogenic steps including initiation, peripheral activation, molecular co-stimulation and immune effector responses during early, transitional and late phases of disease. Emerging strategies for the enhancement of neuroprotection and reparative mechanisms will also be reviewed. Classification of novel approaches will include the following main types of immunotherapies: (1) targeting of myelin specific T cells: antigen-specific therapies (2) targeting of B cell and autoantibody responses (3) targeting of immunologic steps of disease pathology (4) targeting of reparative stages of disease: neurotrophic and neuroprotective, (5) global therapies: broad-based polydirectional strategies.

A novel triterpenoid induces transforming growth factor beta production by intraepithelial lymphocytes to prevent ileitis

BACKGROUND & AIMS

The loss of homeostasis is a hallmark of inflammatory bowel disease. Oral infection of susceptible mice with Toxoplasma gondii results in an acute lethal ileitis characterized by increased interferon gamma, tumor necrosis factor alpha, and inducible nitric oxide synthase; homeostasis results from transforming growth factor beta production by intraepithelial lymphocytes. The synthetic oleanane triterpenoid 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO) is a potent anti-inflammatory molecule previously shown in vitro to suppress the de novo synthesis of inducible nitric oxide synthase and to induce the transcription and activation of genes from the transforming growth factor beta signaling pathway.

METHODS

We evaluated the immune response in the small intestine and by intraepithelial lymphocytes after a single intraperitoneal dose of CDDO at the time of T. gondii oral infection. We abrogated the homeostatic effects of CDDO by blocking transforming growth factor beta in vivo.

RESULTS

CDDO acid prevented ileitis development through the global down-regulation of inflammatory cytokines and chemokines. Total transforming growth factor beta(1) production by the intraepithelial lymphocytes increased, as did Smad2 expression. Blocking transforming growth factor beta reversed CDDO-induced protection and prevented the up-regulation of Smad2 in the small intestine.

CONCLUSIONS

CDDO acid is a novel anti-inflammatory molecule capable of preventing ileitis by activating the transforming growth factor beta signaling pathway in a pathogen-driven ileitis model. This could represent a new treatment of inflammatory bowel disease.

Intestinal intraepithelial lymphocytes prevent pathogen-driven inflammation and regulate the Smad/T-bet pathway of lamina propria CD4+ T cells

Intraepithelial lymphocytes (IEL) play a key role in gut homeostasis and are critical effector cells preventing the inflammatory intestinal lesions induced in mice following oral infection with Toxoplasma gondii. In this intestinal inflammatory model, CD4(+) T lymphocytes from the lamina propria (LP) synergize with the infected enterocytes to secrete pro-inflammatory chemokines and cytokines. In this study, we assessed the mechanisms accounting for the ability of IEL to modulate the inflammatory activity of these cells. Adoptive transfer of IEL purified from wild-type mice, or CD154-,CD95L- or IL-10-deficient mice infected with T. gondii completely impairs the development of the lethal ileitis in recipient mice orally infected with T. gondii. Compared with unprimed IEL isolated from naive mice, the CD8 alpha beta TCR alpha beta subset of primed IEL, isolated from T. gondii-infected mice, secretes increased amount of TGF-beta. IEL interact with the LP CD4(+) T lymphocytes, down-regulate their production of inflammatory cytokines such as IFN-gamma and reduce their proliferative activity. These effects are linked to the secretion of TGF-beta and are correlated with a shift in the balance between Smad7/T-bet down-regulation and Smad2/Smad3 up-regulation in LP CD4(+) T lymphocytes.

Interleukin-10 and pathogenesis of murine ocular toxoplasmosis

To understand the role of interleukin-10 (IL-10) in ocular toxoplasmosis, we compared C57BL/6 (B6) and BALB/c background mice lacking a functional IL-10 gene (IL-10(-/-)) and B6 transgenic mice expressing IL-10 under the control of the IL-2 promoter. Increased cellular infiltration and necrosis were observed in the eye tissue of IL-10(-/-) mice of both the B6 and BALB/c backgrounds with associated changes in the levels of cytokines in serum. In contrast, there was no evidence of necrosis in the eye tissue from IL-10 transgenic mice following parasite exposure. Our results demonstrate that IL-10 is important in the regulation of inflammation during acute ocular toxoplasmosis.

CCR5 mediates specific migration of Toxoplasma gondii-primed CD8 lymphocytes to inflammatory intestinal epithelial cells

BACKGROUND & AIMS

Toxoplasma gondii, an obligate intracellular parasite, can invade intestinal epithelial cells and elicit a robust Th1 immune response. In this model of intestinal inflammation, CD8(+) intraepithelial lymphocytes (IELs) secrete transforming growth factor (TGF)-beta, which appears necessary for the maintenance of homeostasis in the intestine. However, the mechanism responsible for the IEL migration to the inflamed intestine is still unclear.

METHODS

An in vitro coculture cell system was used to quantify the IEL attraction by an infected intestinal epithelial cell line (m-IC(cl2)). We used CCR5-deficient mice to determine which chemokine receptor-chemokine interaction could be responsible for the recruitment of antigen-specific CD8(+) IELs to the small intestine for the promotion of parasite clearance and host recovery.

RESULTS

We observed increased expression of several chemokine receptors (CCR1, CCR2, CCR5, CXCR3) in the infected ileum. In particular, CCR5 expression was markedly increased in antigen-primed CD8(+) IELs. Experiments using recombinant chemokines as well as blocking antibodies showed that macrophage inflammatory protein (MIP)-1alpha and MIP-1beta were critical for their homing. CD8(+) IELs isolated from CCR5-deficient mice (CCR5-/-), despite their high production of TGF-beta and overexpression of activation markers, were impaired in their ability to migrate in vitro to the m-IC(cl2) monolayer or in vivo to the inflamed intestine after adoptive transfer.

CONCLUSIONS

Our data emphasize the biologic role of CCR5 as an important component in the migration of intraepithelial CD8(+) T cells and the regulation of the inflammatory response following parasite infection.

Toxoplasma gondii induces granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor secretion by human fibroblasts: implications for neutrophil apoptosis

Human neutrophils are rescued from apoptosis following incubation with once-washed, fibroblast-derived Toxoplasma gondii tachyzoites. Both infected and uninfected neutrophils are rescued, implicating a soluble mediator. In this study we investigated the origin and identity of this soluble mediator. Neutrophils were incubated either with purified tachyzoites or with conditioned medium derived from T. gondii-infected human fibroblasts. Conditioned medium was found to be a potent stimulus that delayed neutrophil apoptosis up to 72 h, whereas purified and extensively washed tachyzoites had no effect. Delayed apoptosis correlated with up-regulation of the neutrophil antiapoptotic protein, Mcl-1, and the neutrophil interleukin 3 receptor alpha subunit (IL-3Ralpha), suggesting a role for granulocyte-macrophage colony-stimulating factor (GM-CSF). GM-CSF and granulocyte colony-stimulating factor (G-CSF) were measurable in conditioned medium by enzyme-linked immunosorbent assay. Neutralizing antibodies to GM-CSF and G-CSF were additive in abrogating delayed neutrophil apoptosis induced by conditioned medium. Inhibitors of Src family tyrosine kinases, G(i) proteins, phosphatidylinositol 3-kinase, p44(erk1) and p42(erk2) mitogen-activated protein kinases, and Jak2 kinases partially attenuated the effect of conditioned medium, consistent with a role for G-CSF and/or GM-CSF. Hence, delayed neutrophil apoptosis is mediated by GM-CSF and G-CSF secreted by T. gondii-infected human fibroblasts. This enhanced neutrophil survival may contribute to the robust proinflammatory response elicited in the T. gondii-infected host.

Lamina propria CD4+ T lymphocytes synergize with murine intestinal epithelial cells to enhance proinflammatory response against an intracellular pathogen

Acute and lethal ileitis can be elicited in certain strains of inbred mice after oral infection with the intracellular protozoan parasite Toxoplasma gondii. The development of this inflammatory process is dependent upon the induction of a robust Th1 response, including overproduction of IFN-gamma, TNF-alpha, and NO, as has been reported in other experimental models of human inflammatory bowel disease. In this study we have investigated the role of CD4(+) T cells from the lamina propria (LP) in the early inflammatory events after T. gondii infection using isolated and primary cultured intestinal cells from infected mice and immortalized mouse mIC(cl2) intestinal epithelial cells. Primed LP CD4(+) T cells isolated from parasite-infected mice produce substantial quantities of both IFN-gamma and TNF-alpha. IFN-gamma- and TNF-alpha-producing LP CD4(+) T cells synergize with infected mIC(cl2) and enhance the production of several inflammatory chemokines including macrophage-inflammatory protein-2, monocyte chemoattractant protein-1, monocyte chemoattractant protein-3, macrophage-inflammatory protein-1alphabeta, and IFN-gamma-inducible protein-10. Furthermore, primed LP CD4(+) T cells cocultured with infected mIC(cl2) inhibited replication of the parasite in the intestinal epithelial cells. Thus, LP CD4(+) T cells can interact with parasite-infected intestinal epithelial cells and alter the expression of several proinflammatory products that have been associated with the development of intestinal inflammation. The interaction between these two components of the gut mucosal compartment (CD4(+) T cells and enterocytes) may play a role in the immunopathogenesis of this pathogen-driven experimental inflammatory bowel disease model.

CD40/CD154 ligation is required for the development of acute ileitis following oral infection with an intracellular pathogen in mice

BACKGROUND & AIMS

Acute inflammatory ileitis occurs in C57BL/6 mice after oral infection with Toxoplasma gondii. We evaluated the role of CD40/CD154 interaction in the development of acute ileitis in this experimental model.

METHODS

CD154-/- and anti-CD154 antibody-treated mice as well as chimeric mice, either C57BL/6 or CD40-/- reconstituted with bone marrow from C57BL/6 or CD40-/- mice, were orally infected with cysts. Inflammation was assessed by qualitative histologic and phenotypic analysis of the intestinal compartment at day 7 after infection. Intestinal chemokine and cytokine production was assayed by ribonuclease protection assay.

RESULTS

CD154-/- and anti-CD154 monoclonal antibody-treated mice failed to develop an acute, lethal ileitis after oral infection and survived. Chimeric mice reconstituted with bone marrow from C57BL/6 mice developed ileitis and died, whereas those recipient mice deficient in CD40 survived. CD40 expression in the intestine after infection was found principally within the B-cell compartment. A modest increase in CD40 expression in both the macrophage and dendritic cell compartments was also observed. Both chemokine and cytokine expression was up-regulated in those recipients of wild-type bone marrow. Impairment of CD40/CD154 interaction abrogated the production of these proinflammatory productions.

CONCLUSIONS

CD40/CD154 interaction is essential to the development of inflammation in this pathogen-driven experimental model of acute ileitis.

Detection of IgG antibodies to Neospora caninum and Toxoplasma gondii in dogs examined in a veterinary hospital from Brazil

A total of 163 dogs with neuromuscular, respiratory and/or gastrointestinal disorders, was admitted at the Veterinary Hospital, Federal University of Uberlândia, Brazil, and submitted to serology for Toxoplasma gondii and Neospora caninum. Assays for T. gondii included indirect haemagglutination (IHA), indirect fluorescent antibody (IFAT-Tg), immunoenzymatic (ELISA), and immunoblotting (IB-Tg). Assays for N. caninum included IFAT-Nc and immunoprecipitation (IP-Nc). Based on concordant results by three serological tests (IHA, IFAT-Tg and ELISA) for T. gondii, and divergent results further confirmed by IB-Tg for reactivity to TgSAG1, the 163 sera were divided into two groups: 59 (36%) Tg-seropositive samples and 104 (64%) Tg-seronegative samples. Antibodies to Neospora were detected in 11 (6.7%) out of 163 analyzed dog sera, with 5 (3.1%) samples reactive to both parasites (Tg+/Nc+), and 6 (3.7%) reactive only to Neospora (Tg-/Nc+). Antibodies only to T. gondii were found in 54 (33%) samples. Among the 11 Neospora-positive sera analyzed by IB-Tg, the five sera Tg+/Nc+ showed strong reactivity to Toxoplasma antigens, especially to TgSAG1 (p30). No reactivity was observed to TgSAG1 in the six samples Tg-/Nc+. By IP-Nc, two highly immunodominant antigens (29 and 35kDa proteins) were recognized by all 11 IFAT-Nc positive sera. Our results suggest that the infection by N. caninum can be concomitantly present in dogs from this area, although less common, and therefore should be considered in the differential clinical diagnosis with T. gondii in dogs presenting neuromuscular, respiratory and/or gastrointestinal disorders.

Identification and role of thiols in Toxoplasma gondii egress

The nucleoside triphosphate hydrolase of Toxoplasma gondii is a potent apyrase that is secreted into the parasitophorous vacuole where it appears to be essentially inactive in an oxidized form. Recent evidence shows that nucleoside triphosphate hydrolase can be activated by dithiothreitol in vivo. On reduction of the enzyme, there is a rapid depletion of host cell ATP. Previous results also demonstrate a dithiothreitol induced egress of parasites from the host cell with a concurrent Ca2+ flux, postulated to be a consequence of the release of ATP-dependent Ca2+ stores within the tubulovesicular network of the parasitophorous vacuole. Reduction of the nucleoside triphosphate hydrolase appears crucial for its activation; however, the exact mechanism of reduction/activation has not been determined. Using a variety of techniques, we show here that glutathione promoters activate a Ca2+ flux and decrease ATP levels in infected human fibroblasts. We further show the in vitro activation of nucleoside triphosphate hydrolase by endogenous reducing agents, one of which we postulate might be secreted into the PV by T. gondii. Our findings suggest that the reduction of the parasite nucleoside triphosphate hydrolase, and ultimately parasite egress, is under the control of the parasites themselves.

Apoptosis within mouse eye induced by Toxoplasma gondii

OBJECTIVE

To investigate apoptosis induced by Toxoplasma gondii (T. gondii) in eyes of C57BL/6 (B6) mice.

METHODS

Apoptosis was detected by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labeling (TUNEL) technique and pathological changes within eyes were analyzed at different time points after intraocular inoculation of either 50 or 500 of tachyzoites.

RESULTS

In eyes that received 50 tachyzoites, a few apoptotic inflammatory cells in the anterior chamber and keratocytes in the cornea were seen at days 1 and 2, but no apoptosis was detected 4 days after inoculation. Significantly greater apoptosis of inflammatory cells was observed in the anterior chamber and in the vitreous of eyes injected with 500 parasites. Apoptosis of inflammatory cells in the anterior chamber and of keratocytes in the cornea was seen at day 1. The apoptotic stromal keratocytes strikingly increased at day 4. There were a number of apoptotic inflammatory cells in the vitreous at day 2, and a few apoptotic retinal cells along the internal limiting membrane and the nerve fiber layer of the retina 4 days after inoculation.

CONCLUSION

These results suggest that apoptosis of inflammatory cells infiltrated eye infected with this parasite may be a mechanism of eliminating the organism.

Disruption of the FG nucleoporin NUP98 causes selective changes in nuclear pore complex stoichiometry and function

The NUP98 gene encodes precursor proteins that generate two nucleoplasmically oriented nucleoporins, NUP98 and NUP96. By using gene targeting, we have selectively disrupted the murine NUP98 protein, leaving intact the expression and localization of NUP96. We show that NUP98 is essential for mouse gastrulation, a developmental stage that is associated with rapid cell proliferation, but dispensable for basal cell growth. NUP98-/- cells had an intact nuclear envelope with a normal number of embedded nuclear pore complexes. Typically, NUP98-deficient cells contained on average approximately 5-fold more cytoplasmic annulate lamellae than control cells. We found that a set of cytoplasmically oriented nucleoporins, including NUP358, NUP214, NUP88, and p62, assembled inefficiently into nuclear pores of NUP98-/- cells. Instead, these nucleoporins were prominently associated with the annulate lamellae. By contrast, a group of nucleoplasmically oriented nucleoporins, including NUP153, NUP50, NUP96, and NUP93, had no affinity for annulate lamellae and assembled normally into nuclear pores. Mutant pores were significantly impaired in transport receptor-mediated docking of proteins with a nuclear localization signal or M9 import signal and showed weak nuclear import of such substrates. In contrast, the ability of mutant pores to import ribosomal protein L23a and spliceosome protein U1A appeared intact. These observations show that NUP98 disruption selectively impairs discrete protein import pathways and support the idea that transport of distinct import complexes through the nuclear pore complex is mediated by specific subsets of nucleoporins.

Cryptogenic epilepsy: an infectious etiology?

PURPOSE

Cryptogenic epilepsy, the group of epilepsy syndromes for which an etiology is unknown, comprises approximately 20% of all epilepsy syndromes. We selected patients in this subgroup of epilepsy and tested them for evidence of Toxoplasma gondii IgG antibodies by the enzyme-linked immunosorbent assay. T. gondii is found in up to 20% of the U.S. population forming dormant brain cysts in the latent bradyzoite form. We investigated the hypothesis that dormant T. gondii infection might be associated with cryptogenic epilepsy.

METHODS

We selected patients with cryptogenic epilepsies and tested them for evidence of T. gondii IgG antibodies by the enzyme-linked immunosorbent assay. A control group was also tested for comparison.

RESULTS

We have found a statistically-significant elevation of T. gondii antibodies among cryptogenic epilepsy patients as compared to controls [59% increase in optical density (OD), p = 0.013]. This association persisted after adjustment for subjects' gender and age in a multiple logistic regression model; however, it was no longer as statistically significant.

CONCLUSIONS

Our results suggest that chronic T. gondii infection with brain cysts may be a cause of cryptogenic epilepsy.

Murine ileitis after intracellular parasite infection is controlled by TGF-beta-producing intraepithelial lymphocytes

BACKGROUND & AIMS

Acute inflammatory ileitis occurs in susceptible (C57BL/6) mice after oral infection with Toxoplasma gondii. Overproduction of interferon (IFN)-gamma and synthesis of nitric oxide mediate the inflammation. We evaluated the role of transforming growth factor (TGF)-beta produced by intraepithelial lymphocytes (IELs) in this process.

METHODS

We analyzed the histologic and immunologic consequences of adoptive transfer of antigen-primed IELs into susceptible mice treated with anti-TGF-beta before oral challenge with T. gondii cysts. An in vitro coculture of enterocytes and IELs assessed the production of chemokines and cytokines in the presence of anti-TGF-beta.

RESULTS

Antigen-primed IELs prevent acute ileitis in susceptible mice that is reversed with anti-TGF-beta. Resistant mice (CBA/J) develop ileitis after treatment with anti-TGF-beta. Antigen-primed IELs can induce systemic immunosuppression as measured by depressed IFN-gamma production. In vitro, primed IELs reduce the production of inflammatory chemokines by infected enterocytes and IFN-gamma by splenocytes.

CONCLUSIONS

Regulation of the ileal inflammatory process resulting from T. gondii is dependent on TGF-beta-producing IELs. The IELs are an essential component in gut homeostasis after oral infection with this parasite.

Cerebral malaria in mice: interleukin-2 treatment induces accumulation of gammadelta T cells in the brain and alters resistant mice to susceptible-like phenotype

In this study, we report that infection with Plasmodium yoelii 17XL, a lethal strain of rodent malaria, does not result in death in the DBA/2 strain of mice. In contrast to BALB/c mice, DBA/2 mice developed significantly less parasitemia and never manifested symptoms of cerebral malaria (CM) on infection with this parasite. Moreover, the histological changes evident in the brain of susceptible BALB/c were absent in DBA/2 mice. Interestingly, the resistant DBA/2 mice when treated with recombinant interleukin (IL)-2, were found to develop CM symptoms and the infection became fatal by 6 to 8 days after infection. This condition was associated with an augmented interferon-gamma and nitric oxide production. Unexpectedly, IL-10 levels were also elevated in IL-2-treated DBA/2 mice during late stage of infection (at day 6 of infection) whereas the inverse relationship between IL-10 and interferon-gamma or nitric oxide was maintained in the early stage of infection (at day 3 after infection). The level of tumor necrosis factor-alpha production was moderately increased in the late phase of infection in these mice. Histology of brain from IL-2-treated mice demonstrated the presence of parasitized erythrocytes and infiltration of lymphocytes in cerebral vessels, and also displayed some signs of endothelial degeneration. Confocal microscopical studies demonstrated preferential accumulation of gammadelta T cells in the cerebral vessels of IL-2-treated and -infected mice but not in mice treated with IL-2 alone. The cells recruited in the brain were activated because they demonstrated expression of CD25 (IL-2R) and CD54 (intercellular adhesion molecule 1) molecules. Administration of anti-gammadelta mAb prevented development of CM in IL-2-treated mice until day 18 after infection whereas mice treated with control antibody showed CM symptoms by day 6 after infection. The information concerning creating pathological sequelae and death in an otherwise resistant mouse strain provides an interesting focus for the burden of pathological attributes on death in an infectious disease.

Attachment of Toxoplasma gondii to a specific membrane fraction of CHO cells

We have observed previously that attachment of Toxoplasma gondii to synchronized host cells is considerably increased at the mid-S phase (4 h postrelease). Synchronized CHO host cells at the mid-S phase were fractionated by molecular weight, and the antigens were used to produce a panel of polyclonal mouse antisera. The polyclonal antisera raised against fraction 4 with molecular mass ranging approximately from 18 to 40 kDa significantly reduced attachment to mid-S-phase host cells. Immunofluorescence assays demonstrated strong reactivity to mid-S-phase host cells and identified a number of potential receptors on Western blots. These data indicate that there is a specific host membrane receptor for parasite attachment that is upregulated during the mid-S phase of the host cell cycle.

Production of macrophage-activated killer cells for targeting of glioblastoma cells with bispecific antibody to FcgammaRI and the epidermal growth factor receptor

OBJECTIVE

The aim was to determine the ability of macrophage-activated killer cells (MAK cells) obtained from peripheral blood of normal volunteers to kill glioblastoma multiforme (GBM) cell lines. Another goal was to investigate whether a bispecific antibody (bsAb) MDX-447, recognizing the high-affinity Fc receptor for IgG (FcgammaRI) and epidermal growth factor receptor (EGFR), would enhance MAK cell tumoricidal activity.

METHODS

Monocytes, from leukapheresis product, were isolated by countercurrent elutriation and differentiated into MAK cells by culture with granulocyte/macrophage-colony-stimulating factor, vitamin D3 and interferon gamma. Cells were checked for sterility, endotoxin and phenotypic markers. MAK cell functional activity was measured by a flow-cytometric phagocytosis assay. Target cells, a carcinoma cell line and two glioma cell lines expressing EGFR, were stained with PKH-26. MAK cells were labeled with fluorescein-conjugated anti-CD14. Combined effectors, targets and bsAb were incubated and the percentage of MAK cells with phagocytosed targets was determined by flow cytometry.

CONCLUSION

We demonstrate that a large number of highly purified monocytes, isolated from peripheral blood, can be differentiated into MAK cells for use as an adjuvant for cancer treatment. After culture these cells are sterile, endotoxin-free and comprise more than 95% MAK cells. Increased amounts of CD14, CD64 and HLA-DR, which are characteristics of macrophage activation, were expressed. MAK cells were extremely phagocytic in comparison to monocytes, even in the absence of bsAb. Moreover, bsAb enhanced the tumoricidal activity of elutriated MAK cells targeted against GBM cell lines. Therefore, intracavity MAK cells armed with MDX-447 could be an effective adoptive immunotherapy for EGFR-positive GBM.

Differential infectivity and division of Toxoplasma gondii in human peripheral blood leukocytes

When tachyzoites were incubated with human peripheral blood leukocytes in vitro, more monocytes and dendritic cells than neutrophils or lymphocytes were infected. Although tachyzoites were able to divide in each of these cell types, monocytes and dendritic cells were more permissive to rapid tachyzoite division than neutrophils or lymphocytes.

Sequential analysis of cell differentials and IFN-gamma production of splenocytes from mice infected with Toxoplasma gondii

To assess the relationship between the changes of cellular components and the production of Th1 cytokine in the immune tissue, inbred C57BL/6 mice were orally infected with 40 cysts of 76K strain of Toxoplasma gondii. The sequential change of cell differentials and IFN-gamma production of splenocytes were analyzed by Diff-Quik stain and RT-PCR. There were no significant proportional changes of cellular components of splenocytes until day 4 postinfection (PI) as compared to those of day 0, and the relative percentage of macrophages and neutrophils/eosinophils increased significantly (p < 0.01) thereafter. The expression of IFN-gamma mRNA of CD3- cells was observed from day 1 PI at a low level. However, IFN-gamma production of CD3+ cells increased significantly from day 4 PI (p < 0.01) which progressively increased thereafter. These findings provide the relative percentages of granulocytes and macrophages were increased in conjunction with increase of total number of splenocytes after oral infection with T. gondii in the susceptible murine hosts, and lymphocytes were the major cellular components and the important source of IFN-gamma.

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.

Detection of Toxoplasma gondii soluble antigen, SAG-1(p30), antibody and immune complex in the cerebrospinal fluid of HIV positive or negative individuals

Active infection by T. gondii was evaluated by immunoassay for soluble SAG-1 (p30), the major surface antigen from T. gondii, specific antibodies and immune complexes in human cerebrospinal fluid (CSF) samples. A total of 263 samples of CSF were collected from hospitalized patients presenting neurological disorders and analyzed for antibodies to HIV. Patients were divided into two groups: HIV positive (n = 96) or HIV negative (n =167). The results of the assays showed that 45% of all samples were positive for soluble SAG-1. Toxoplasma Ag/Ab immune complexes were detected in 19% of the CSF samples and 62% were positive for T. gondii- specific IgG. A combination of these assays in the presence of clinical findings consistent with active Toxoplasma infection may predict the presence of toxoplasmic encephalitis. Moreover, detection of soluble SAG-1 in the CSF of these individuals appears consistent with active infection.

Immune CD8(+) T cells prevent reactivation of Toxoplasma gondii infection in the immunocompromised host

Toxoplasma gondii remains a serious cause of morbidity and mortality in individuals that are immunosuppressed, patients with AIDS in particular. The cellular immune response, especially by gamma interferon (IFN-gamma)-producing CD8(+) T cells, is an essential component of protective immunity against the parasite. In the present study the role of CD8(+) T cells during the reactivation of Toxoplasma infection in an immunocompromised murine model was evaluated. Chronically infected mice were challenged with LP-BM5 virus, and the kinetics of CD8(+) T-cell function was studied. At 10 weeks after viral infection, mice showed obvious signs of systemic illness and began to die. At this stage, CD8(+) T cells were unresponsive to antigenic stimulation and unable to kill Toxoplasma-infected targets. IFN-gamma production by the CD8(+) T cells from dual-infected animals reached background levels, and a dramatic fall in the frequency of precursor cytotoxic T lymphocytes was observed. Histopathological analysis of the tissues demonstrated signs of disseminated toxoplasmosis as a result of reactivation of infection. However, treatment of the dual-infected animals with immune CD8(+) T cells at 5 weeks post-LP-BM5 challenge prevented the reactivation of toxoplasmosis, and mice continued to live. Our study for the first time demonstrates a therapeutic role for CD8(+) T cells against an opportunistic infection in an immunocompromised state.

Immunization with heat-killed Toxoplasma gondii stimulates an early IFN-gamma response and induces protection against virulent murine malaria

In this study, we describe protection of BALB/c mice by immunization with heat-killed T. gondii tachyzoites against infection with Plasmodium yoelii 17XL which causes cerebral malaria and death in mice by day 7-8 post infection. Immunization resulted significant reduction in parasitemia at the peak period of infection. Protection induced by heat-killed T. gondii was associated with marked increase in NK cell number and IFN-gamma mRNA expression early in the infection. The level of IFN-gamma or TNF-alpha was found to diminish in T. gondii-treated mice as the infection progressed to the late stage. This declined response of IFN-gamma or TNF-alpha was associated with marked increase in the expression of IL-10, a counterregulatory cytokine. Pretreatment of mice with live T. gondii induced poor level of protection as compared with that of heat-killed parasites. Mice that received P. yoelii infection alone, had an elevated IFN-gamma response in the late stage of infection. Development of cerebral malaria in untreated mice was accompanied by an augmented production of TNF-alpha and nitric oxide (NO), the proinflammatory mediators. These findings suggest that nonspecific immunization with T. gondii leads to restoration of an early IFN-gamma response in P. yoelii-infected mice and in the establishment of an immunoregulatory mechanism that effectively antagonizes the disease-promoting effects of proinflammatory cytokines in the late phase of infection.

Interleukin-15 enhances host protection against acute Toxoplasma gondii infection in T-cell receptor alpha-/-deficient mice

A potential role for T-cell receptor (TCR)-gamma(delta) cells in response to Toxoplasma gondii has been described. This study was undertaken to evaluate whether exogenous rIL-15 can enhance the production of gamma(delta) T cells in response to infection with T. gondii. For this, C57BL/6 and TCR alpha-gene deficient mice (alpha-/-) were vaccinated with Toxoplasma lysate antigen (TLA) in combination with interleukin (IL)-15. The cellular and humoral immune response was assessed following immunization. Administration of IL-15/TLA to alpha-/-mice lengthened survival time post lethal challenge. Several immunological parameters were increased in the alpha-/-mice following immunization with IL-15/TLA including serum immunoglobulin (Ig)G1 and IgG2a antibody titres and splenocyte lymphoproliferation in response to parasite antigen. Further, the CTL response to parasite infected target cells as well as the production of interferon gamma was enhanced by IL-15/TLA administration in the alpha-/-mice. These observations indicate that the gamma(delta) T cells response to this parasite can be enhanced by the administration of exogenous IL-15 in the presence of parasite lysate antigen.

Intraepithelial Lymphocytes Traffic to the Intestine and Enhance Resistance to Toxoplasma gondii Oral Infection

Toxoplasma gondii Ag-primed intraepithelial lymphocytes (IEL) from the mouse intestine have been shown to be protective against an lethal parasite challenge when adoptively transferred into recipient mice. In the present study, we observed that Ag-primed IEL traffic to the intestine of naive mice following i.v. administration. Primed and CD8β+ IEL were the most efficient cells at homing to the host organ. In congenic mice, IEL migrated from intestine within several hours posttransfer. On Ag reexposure, the primed IEL return to the intestine where they enhance resistance as determined by reduction in the number of brain cysts. Treatment of recipient mice with anti-α4 and anti-αE Abs partially inhibited IEL intestinal homing. The Ab treatment dramatically impaired resistance to a subsequent oral infection. These finding indicate that lymphocyte homing is an important parameter in establishing long term immunity to recurrent infection with this parasite.

CD8+ CTLs Are Essential for Protective Immunity Against Encephalitozoon cuniculi Infection

Encephalitozoon cuniculi is a protozoan parasite that has been implicated recently as a cause of opportunistic infection in immunocompromised individuals. Protective immunity in the normal host is T cell-dependent. In the present study, the role of individual T cell subtypes in immunity against this parasite has been studied using gene knockout mice. Whereas CD4−/− animals resolved the infection, mice lacking CD8+ T cells or perforin gene succumbed to parasite challenge. The data obtained in these studies suggest that E. cuniculi infection induces a strong and early CD8+ T response that is important for host protection. The CD8+ T cell-mediated protection depends upon the CTL activity of this cell subset, as the host is rendered susceptible to infection in the absence of this function. This is the first report in which a strong dependence upon the cytolytic activity of host CD8+ T cells has been shown to be important in a parasite infection.

CD8+ CTLs are essential for protective immunity against Encephalitozoon cuniculi infection

Encephalitozoon cuniculi is a protozoan parasite that has been implicated recently as a cause of opportunistic infection in immunocompromised individuals. Protective immunity in the normal host is T cell-dependent. In the present study, the role of individual T cell subtypes in immunity against this parasite has been studied using gene knockout mice. Whereas CD4-/- animals resolved the infection, mice lacking CD8+ T cells or perforin gene succumbed to parasite challenge. The data obtained in these studies suggest that E. cuniculi infection induces a strong and early CD8+ T response that is important for host protection. The CD8+ T cell-mediated protection depends upon the CTL activity of this cell subset, as the host is rendered susceptible to infection in the absence of this function. This is the first report in which a strong dependence upon the cytolytic activity of host CD8+ T cells has been shown to be important in a parasite infection.

Intraepithelial lymphocytes traffic to the intestine and enhance resistance to Toxoplasma gondii oral infection

Toxoplasma gondii Ag-primed intraepithelial lymphocytes (IEL) from the mouse intestine have been shown to be protective against an lethal parasite challenge when adoptively transferred into recipient mice. In the present study, we observed that Ag-primed IEL traffic to the intestine of naive mice following i.v. administration. Primed and CD8beta+ IEL were the most efficient cells at homing to the host organ. In congenic mice, IEL migrated from intestine within several hours posttransfer. On Ag reexposure, the primed IEL return to the intestine where they enhance resistance as determined by reduction in the number of brain cysts. Treatment of recipient mice with anti-alpha4 and anti-alphaE Abs partially inhibited IEL intestinal homing. The Ab treatment dramatically impaired resistance to a subsequent oral infection. These finding indicate that lymphocyte homing is an important parameter in establishing long term immunity to recurrent infection with this parasite.

Attachment ligands of viable Toxoplasma gondii induce soluble immunosuppressive factors in human monocytes

Previous studies have demonstrated that surface antigen proteins, in particular SAG-1, of Toxoplasma gondii are important to this parasite as attachment ligands for the host cell. An in vitro assay was developed to test whether these ligands and other secretory proteins are involved in the immune response of human cells to toxoplasma. Human monocytes were infected with tachyzoites in the presence of antiparasite antibodies, and their effect on mitogen-induced lymphoproliferation was examined. The presence of antibody to either parasite-excreted proteins (MIC-1 and MIC-2) or surface proteins (SAG-1 and SAG-2) during infection neutralized the marked decrease seen in mitogen-induced lymphoproliferation in the presence of infected monocytes. Conversely, antibodies to other secreted proteins (ROP-1) and cytoplasmic molecules had no effect on parasite-induced, monocyte-mediated downregulation. Fluorescence microscope analysis detected microneme and surface antigen proteins on the monocyte cell surface during infection. These results suggest that microneme and surface antigen proteins trigger monocytes to downregulate mitogen-induced lymphoproliferation.

Augmentation of the CD8+ T Cell Response by IFN-γ in IL-12-Deficient Mice During Toxoplasma gondii Infection

The importance of IFN-γ in regulating the host CD8+ T cell response during microbial infection has not been delineated. Mice deficient for the p40 chain of the IL-12 heterodimer have impaired IFN-γ production and are susceptible to infection with the intracellular parasite Toxoplasma gondii. The administration of exogenous IFN-γ to parasite-infected p40−/− mice increases survival and up-regulates the depressed CD8+ T cell response following infection. CD8+ T cells isolated from cytokine-treated p40−/− mice exhibit an increase in both precursor CTL frequency and IFN-γ production compared with untreated controls. The enhancement of the CD8+ T cell response is independent of CD4+ T cell help. These CD8+ T cells induce protective immunity against a lethal challenge when adoptively transferred into naive p40−/− and IFN-γ−/− mice. These observations indicate that IFN-γ can regulate the CD8+ T cell response during T. gondii infection.

Augmentation of the CD8+ T cell response by IFN-gamma in IL-12-deficient mice during Toxoplasma gondii infection

The importance of IFN-gamma in regulating the host CD8+ T cell response during microbial infection has not been delineated. Mice deficient for the p40 chain of the IL-12 heterodimer have impaired IFN-gamma production and are susceptible to infection with the intracellular parasite Toxoplasma gondii. The administration of exogenous IFN-gamma to parasite-infected p40-/- mice increases survival and up-regulates the depressed CD8+ T cell response following infection. CD8+ T cells isolated from cytokine-treated p40-/- mice exhibit an increase in both precursor CTL frequency and IFN-gamma production compared with untreated controls. The enhancement of the CD8+ T cell response is independent of CD4+ T cell help. These CD8+ T cells induce protective immunity against a lethal challenge when adoptively transferred into naive p40-/- and IFN-gamma-/- mice. These observations indicate that IFN-gamma can regulate the CD8+ T cell response during T. gondii infection.

RAE1 is a shuttling mRNA export factor that binds to a GLEBS-like NUP98 motif at the nuclear pore complex through multiple domains

Gle2p is implicated in nuclear export of poly(A)+ RNA and nuclear pore complex (NPC) structure and distribution in Saccharomyces cerevisiae. Gle2p is anchored at the nuclear envelope (NE) via a short Gle2p-binding motif within Nup116p called GLEBS. The molecular mechanism by which Gle2p and the Gle2p-Nup116p interaction function in mRNA export is unknown. Here we show that RAE1, the mammalian homologue of Gle2p, binds to a GLEBS-like NUP98 motif at the NPC through multiple domains that include WD-repeats and a COOH-terminal non-WD-repeat extension. This interaction is direct, as evidenced by in vitro binding studies and chemical cross-linking. Microinjection experiments performed in Xenopus laevis oocytes demonstrate that RAE1 shuttles between the nucleus and the cytoplasm and is exported from the nucleus in a temperature-dependent and RanGTP-independent manner. Docking of RAE1 to the NE is highly dependent on new mRNA synthesis. Overexpression of the GLEBS-like motif also inhibits NE binding of RAE1 and induces nuclear accumulation of poly(A)+ RNA. Both effects are abrogated either by the introduction of point mutations in the GLEBS-like motif or by overexpression of RAE1, indicating a direct role for RAE1 and the NUP98-RAE1 interaction in mRNA export. Together, our data suggest that RAE1 is a shuttling transport factor that directly contributes to nuclear export of mRNAs through its ability to anchor to a specific NUP98 motif at the NPC.

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.

Experimental ocular toxoplasmosis induced in naive and preinfected mice by intracameral inoculation

We have developed a murine model to investigate the pathogenesis of acquired ocular toxoplasmosis. Tachyzoites of PLK strain of Toxoplasma gondii were intracamerally inoculated under anesthesia into the right eyes of naive or perorally preinfected C57BL/6 and MRL-MpJ mice. Clinical and histopathological observations of responses to intraocular infection were analyzed. Ocular inflammation from Toxoplasma gondii is dose-dependent in both strains of mice. After inoculation of fifty parasites, no evidence of inflammation was observed in the eyes of naive mice. The eyes of naive mice that received 500 or 5,000 parasites developed inflammatory changes by day 6 post challenge. By day 8, the changes progressed to moderate to severe intraocular inflammation. Histologic analysis of the ocular lesions demonstrated mononuclear cell infiltration and necrosis predominantly in the anterior segment of the eyes of the naive mice. Inoculation of 50,000 tachyzoites induced a destructive ocular inflammatory response and was uniformly lethal to the mice by approximately one week after challenge. In contrast, eyes from mice previously orally infected with Toxoplasma gondii and that received a 50 or 500 parasite intracameral challenge revealed no inflammation, but the eyes receiving 5,000 parasites demonstrated necrotic focal retinochoroiditis with vitreitis by day 8 after challenge. The murine model reproduces some features of ocular toxoplasmosis in humans and may be suitable for large-scale controlled studies of the pathogenesis and therapeutics of acquired ocular toxoplasmosis as well as for study of the mechanisms of immune privilege in the eye.

Fas-FasL interaction involved in pathogenesis of ocular toxoplasmosis in mice

Ocular toxoplasmosis is a potentially blinding intraocular inflammation. The intent of this study was to investigate the role of Fas-FasL interaction in a murine model of acquired ocular toxoplasmosis induced by intracameral inoculation of Toxoplasma gondii. Intraocular inflammation, Fas and FasL expression on lymphocytes and on ocular tissues, the occurrence of apoptosis, and the frequency of CD8(+) and CD4(+) T cells in the infected eyes were analyzed in C57BL/6 (B6) mice. Susceptibility to parasite-induced intraocular inflammation was observed in Fas-deficient (B6-lpr) and FasL-deficient (B6-gld) mice. Inoculation of 5,000 T. gondii tachyzoites induced significant intraocular inflammation associated with increase of Fas and FasL expression in the inoculated eyes of wild-type B6 mice. Flow cytometry demonstrated a significant increase of Fas and FasL expression on the splenocytes from naive mice incubated in vitro with the parasite and on the splenocytes harvested from the infected mice at day 8 after parasite inoculation. Apoptosis of inflammatory cells and cells in ocular tissues was seen, and a greater frequency of CD8(+) than CD4(+) T cells was observed in the infected eyes. The intensity of intraocular inflammation was greater in B6-lpr and B6-gld mice than in wild-type B6 mice (P < 0.05). The results suggest that Fas-FasL interaction associated with apoptosis is involved in the pathogenesis of acquired ocular toxoplasmosis in mice.

Sensitized lymphocytes and CD40 ligation augment interleukin-12 production by human dendritic cells in response to Toxoplasma gondii

Dendritic cells (DC) are potent antigen-presenting cells that can stimulate T cell responses by secreting cytokines. During Toxoplasma gondii infection, host immunity is mediated by interferon-gamma, which is induced by interleukin-12 (IL-12). Whether T. gondii infection would stimulate human DC to produce IL-12 was determined. DC were generated from human peripheral blood mononuclear cells cultured with recombinant human granulocyte-macrophage colony-stimulating factor and recombinant human IL-4. DC secreted high levels of IL-12 in response to lipopolysaccharide but not to either live T. gondii tachyzoites or soluble antigen. However, IL-12 production in response to T. gondii was observed when DC were cocultured in contact with lymphocytes isolated from seropositive donors. Ligation of CD40:CD154 was partially essential for IL-12 secretion. These data demonstrate that signals obtained from contact with sensitized lymphocytes are critical for human DC to secrete IL-12 in response to T. gondii.

CREB binding protein interacts with nucleoporin-specific FG repeats that activate transcription and mediate NUP98-HOXA9 oncogenicity

Genes encoding the Phe-Gly (FG) repeat-containing nucleoporins NUP98 and CAN/NUP214 are at the breakpoints of several chromosomal translocations associated with human acute myeloid leukemia (AML), but their role in oncogenesis is unclear. Here we demonstrate that the NUP98-HOXA9 fusion gene encodes two nuclear oncoproteins with either 19 or 37 NUP98 FG repeats fused to the DNA binding and PBX heterodimerization domains of the transcription factor HOXA9. Both NUP98-HOXA9 chimeras transformed NIH 3T3 fibroblasts, and this transformation required the HOXA9 domains for DNA binding and PBX interaction. Surprisingly, the FG repeats acted as very potent transactivators of gene transcription. This NUP98-derived activity is essential for transformation and can be replaced by the bona fide transactivation domain of VP16. Interestingly, FG repeat-containing segments derived from the nucleoporins NUP153 and CAN/NUP214 functioned similarly to those from NUP98. We further demonstrate that transactivation by FG repeat-rich segments of NUP98 correlates with their ability to interact functionally and physically with the transcriptional coactivators CREB binding protein (CBP) and p300. This finding shows, for the first time, that a translocation-generated fusion protein appears to recruit CBP/p300 as an important step of its oncogenic mechanism. Together, our results suggest that NUP98-HOXA9 chimeras are aberrant transcription factors that deregulate HOX-responsive genes through the transcriptional activation properties of nucleoporin-specific FG repeats that recruit CBP/p300. Indeed, FG repeat-mediated transactivation may be a shared pathogenic function of nucleoporins implicated human AML.

Alteration of Intracellular Calcium Flux and Impairment of Nuclear Factor-AT Translocation in T Cells During Acute Toxoplasma gondii Infection in Mice

Down-regulation of host immune response to Toxoplasma gondii is associated with the expression of specific cytokines, in particular IL-10, and the induction of CD4+ T cell anergy. In the present study we report that the expression of both CD4 and CD2 antigen is down-regulated during the acute phase of infection. A decrease in the expression of CD2 was apparent during the acute phase of T. gondii infection in three genetically distinct strains of mice, CBA/J, C57BL/6, and BALB/c. The lymphoproliferative response induced by cross-linked anti-CD3 mAb or by Con A was markedly depressed. This suppressed response was associated with a reduction in the influx of Ca2+. We have examined whether lymphocytes from T. gondii mice maintain NF-AT transcription factors in the nucleus where they participate in the Ca2+-dependent induction of genes required for lymphocyte activation and proliferation. Immunofluorescence with confocal microscopy using an Ab to NF-ATc demonstrates a decrease in translocation of NF-ATc in T lymphocytes from acutely infected mice. Together, these results suggest that the defect in T cell expansion that occurs during acute murine toxoplasmosis is related to reduced activity of NF-AT, a calcium-dependent transcription factor required for T cell proliferation.

Alteration of intracellular calcium flux and impairment of nuclear factor-AT translocation in T cells during acute Toxoplasma gondii infection in mice

Down-regulation of host immune response to Toxoplasma gondii is associated with the expression of specific cytokines, in particular IL-10, and the induction of CD4+ T cell anergy. In the present study we report that the expression of both CD4 and CD2 antigen is down-regulated during the acute phase of infection. A decrease in the expression of CD2 was apparent during the acute phase of T. gondii infection in three genetically distinct strains of mice, CBA/J, C57BL/6, and BALB/c. The lymphoproliferative response induced by cross-linked anti-CD3 mAb or by Con A was markedly depressed. This suppressed response was associated with a reduction in the influx of Ca2+. We have examined whether lymphocytes from T. gondii mice maintain NF-AT transcription factors in the nucleus where they participate in the Ca2+-dependent induction of genes required for lymphocyte activation and proliferation. Immunofluorescence with confocal microscopy using an Ab to NF-ATc demonstrates a decrease in translocation of NF-ATc in T lymphocytes from acutely infected mice. Together, these results suggest that the defect in T cell expansion that occurs during acute murine toxoplasmosis is related to reduced activity of NF-AT, a calcium-dependent transcription factor required for T cell proliferation.

Gut-Derived Intraepithelial Lymphocytes Induce Long Term Immunity Against Toxoplasma gondii

Intraepithelial lymphocytes (IEL) of the intestine represent an important barrier in the prevention of infection against orally acquired pathogens. Adoptive transfer of Ag-primed IEL into a naive host can protect against challenge. Using a murine model, we demonstrate in two genetically distinct mouse strains (C57BL/6 and CBA/J) that protective IEL can be isolated at specific times after oral infection with cysts containing bradyzoites. Adoptive transfer of IEL obtained from the intestine of infected mice at these specific times can provide long term protection, as determined by mortality and cyst number against challenge. The protective IEL appear to be CD8+, TCR-α/β and are at least partially dependent upon the presence of TCR-γ/δ T cells in the host. Endogenous production of the pivotal cytokine, IFN-γ, is essential for host immunity. These findings demonstrate that gut-derived IEL represent a potentially important mechanism to provide long term immunity to the host.