Conditional knockout mice reveal distinct functions for the global transcriptional coactivators CBP and p300 in T-cell development

The global transcriptional coactivators CREB-binding protein (CBP) and the closely related p300 interact with over 312 proteins, making them among the most heavily connected hubs in the known mammalian protein-protein interactome. It is largely uncertain, however, if these interactions are important in specific cell lineages of adult animals, as homozygous null mutations in either CBP or p300 result in early embryonic lethality in mice. Here we describe a Cre/LoxP conditional p300 null allele (p300flox) that allows for the temporal and tissue-specific inactivation of p300. We used mice carrying p300flox and a CBP conditional knockout allele (CBPflox) in conjunction with an Lck-Cre transgene to delete CBP and p300 starting at the CD4- CD8- double-negative thymocyte stage of T-cell development. Loss of either p300 or CBP led to a decrease in CD4+ CD8+ double-positive thymocytes, but an increase in the percentage of CD8+ single-positive thymocytes seen in CBP mutant mice was not observed in p300 mutants. T cells completely lacking both CBP and p300 did not develop normally and were nonexistent or very rare in the periphery, however. T cells lacking CBP or p300 had reduced tumor necrosis factor alpha gene expression in response to phorbol ester and ionophore, while signal-responsive gene expression in CBP- or p300-deficient macrophages was largely intact. Thus, CBP and p300 each supply a surprising degree of redundant coactivation capacity in T cells and macrophages, although each gene has also unique properties in thymocyte development.

Mammalian Gene Expression Program Resiliency: The Roles of Multiple Coactivator Mechanisms in Hypoxia–Responsive Transcription

CBP and its paralog p300 (CBP/p300 collectively) are transcriptional coactivators that are among the most interconnected proteins in the mammalian protein-protein "interactome" with over 315 described interaction partners. CBP/p300 are protein/histone acetyltransferases, but most of the protein-binding domains of CBP/p300 are unique to these two coactivators, indicating that CBP/p300 should be highly limiting. The CH1 domain of CBP/p300 was considered essential for most, if not all, hypoxia-inducible transcription by binding to hypoxia-inducible-factor-1alpha (HIF-1alpha). Mutating CH1 had little effect, however, on the hypoxia-induced transcription of the HIF-target genes Higd1a, Egln1 (prolyl-hydroxylase), Bnip3 (Bcl2-interacting-protein-3), and Pfkl (phosphofructokinase). In contrast, HIF-targets Pgf (placental growth factor) and Egln3 were strongly affected by the CH1 mutation, while Stc1 (stanniocalcin-1) and Slc2a1 (glucose-transporter-1) were moderately affected. HIF targets were also dependent on coactivation mechanisms that are sensitive to trichostatin A (TSA(S)). Paradoxically, TSA inhibits histone deacetylases (HDACs) that are usually associated with transcriptional repression, implying that HDACs can also function as coactivators. Thus, activator-specific transcription in mammals requires seemingly unrelated coactivator mechanisms, and individual target genes vary in their requirements for each mechanism. Gene expression program resiliency is therefore coupled with gene specific regulation by avoiding uniform reliance on a "keystone" coactivator interaction.

Two transactivation mechanisms cooperate for the bulk of HIF-1-responsive gene expression

The C-terminal activation domain (C-TAD) of the hypoxia-inducible transcription factors HIF-1alpha and HIF-2alpha binds the CH1 domains of the related transcriptional coactivators CREB-binding protein (CBP) and p300, an oxygen-regulated interaction thought to be highly essential for hypoxia-responsive transcription. The role of the CH1 domain in vivo is unknown, however. We created mutant mice bearing deletions in the CH1 domains (DeltaCH1) of CBP and p300 that abrogate their interactions with the C-TAD, revealing that the CH1 domains of CBP and p300 are genetically non-redundant and indispensable for C-TAD transactivation function. Surprisingly, the CH1 domain was only required for an average of approximately 35-50% of global HIF-1-responsive gene expression, whereas another HIF transactivation mechanism that is sensitive to the histone deacetylase inhibitor trichostatin A (TSA(S)) accounts for approximately 70%. Both pathways are required for greater than 90% of the response for some target genes. Our findings suggest that a novel functional interaction between the protein acetylases CBP and p300, and deacetylases, is essential for nearly all HIF-responsive transcription.

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.

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.

A transcription-factor-binding surface of coactivator p300 is required for haematopoiesis

The coactivators CBP (Cre-element binding protein (CREB)-binding protein) and its paralogue p300 are thought to supply adaptor molecule and protein acetyltransferase functions to many transcription factors that regulate gene expression. Normal development requires CBP and p300, and mutations in these genes are found in haematopoietic and epithelial tumours. It is unclear, however, which functions of CBP and p300 are essential in vivo. Here we show that the protein-binding KIX domains of CBP and p300 have nonredundant functions in mice. In mice homozygous for point mutations in the KIX domain of p300 designed to disrupt the binding surface for the transcription factors c-Myb and CREB, multilineage defects occur in haematopoiesis, including anaemia, B-cell deficiency, thymic hypoplasia, megakaryocytosis and thrombocytosis. By contrast, age-matched mice homozygous for identical mutations in the KIX domain of CBP are essentially normal. There is a synergistic genetic interaction between mutations in c-Myb and mutations in the KIX domain of p300, which suggests that the binding of c-Myb to this domain of p300 is crucial for the development and function of megakaryocytes. Thus, conserved domains in two highly related coactivators have contrasting roles in haematopoiesis.

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.

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.

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.