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About 225 million malaria cases have been reported worldwide in 2009, and one-third of the world's population is infected with parasitic helminths. As helminths and Plasmodium are co-endemic, concurrent infections frequently occur. Helminths have been shown to modulate the host's immune response; therefore, pre-existing helminth infections may interfere with the efficient immune response to Plasmodium. To study the interaction between helminths and Plasmodium, we established a murine model of co-infection using the gastrointestinal nematode Strongyloides ratti and Plasmodium yoelii. We show that a pre-existing Strongyloides infection slightly enhanced peak parasitemia and weight loss in P. yoelii-infected BALB/c mice, while disease progression was not altered in co-infected C57BL/6 mice. The Plasmodium-induced IFN-γ production and final clearance of Plasmodium infection were not affected by S. ratti co-infection in both C57BL/6 and BALB/c mice. Interestingly, the T helper cell (Th) 2 response induced by S. ratti was significantly suppressed upon P. yoelii co-infection. This suppressed Th2 response, however, was still sufficient to allow expulsion of S. ratti parasitic adults. Taken together, we provide evidence that simultaneous presence of helminth and protist parasites does not interfere with efficient host defence in our co-infection model although changes in Th responses were observed.

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The protozoan parasite Trypanosoma cruzi circulates in the blood as trypomastigotes and invades a variety of cells to multiply intracellularly as amastigotes. The acute phase triggers an immune response that restricts the proliferation of the parasite. However, parasites are able to persist in different tissues causing the pathology of Chagas' disease. Natural killer (NK) cells play an important role in innate resistance to a variety of pathogens. In the present study we demonstrate that NK cells trigger trypanocidal mechanisms in infected L929 cells that are critically dependent on inducible nitric oxide (NO) synthase (iNOS) induction which is, to a major degree, triggered by interferon (IFN)-gamma provided by NK cells. This work provides a more detailed analysis of how NK cells as a part of the innate immune system participate in the control of parasites that reside intracellularly in fibroblast-like L929 cells.

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CD83 is a marker molecule for mature dendritic cells (DCs) but is also substantially expressed on activated T cells in humans and mice. Its function is unknown, but CD83 knockout mice show an impaired thymic maturation of CD4-positive cells and soluble CD83 inhibits partially antigen-specific responses in vitro pointing to a role of CD83 in the immune system. Here we show that CD83-positive T cells produce strongly increased amounts of interferon-gamma and interleukin-2. In contrast, constitutive expression of CD83 on DCs alters neither the activation of DCs following addition of lipopolysaccharide nor the ability to present antigenic peptides. Thus, the expression of CD83 on T cells has direct functional consequences for tuning the activation threshold.

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Chagas' disease is caused by the protozoan parasite Trypanosoma cruzi and commonly modelled in inbred mice. Susceptibility of mouse strains to experimental infection varies considerably. We quantified parasite tissue burdens in resistant and susceptible strains by real time PCR and applied a backcross strategy to map the genomic loci linked to susceptibility in inbred mice. Resistant B6D2F1 mice were backcrossed with susceptible C57BL/6 mice, and 46 of a total 192 offspring died after infection. Their genomes were scanned with microsatellite markers. One region on chromosome 17 was significantly linked to susceptibility, while another on chromosome 5 was suggestive of linkage.

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T cells involved in autoimmune diseases have been characterized by the genetic elements used to construct their autoimmune TCR. In the present study, we sequenced the alpha and beta chains of the TCR expressed by a CD4(+) T cell clone, C9, functional in NOD mouse diabetes. Clone C9 can adoptively transfer diabetes or, when attenuated, C9 can be used to vaccinate NOD mice against diabetes. Clone C9 recognizes a peptide epitope (p277) of the 60 kDa heat shock protein (hsp60) molecule. We now report that the C9 TCR beta chain features a CDR3 peptide sequence that is prevalent among NOD mice. This CDR3 element is detectable by 2 weeks of age in the thymus, and later in the spleen and in the autoimmune insulitis. Thus, a TCR CDR3beta sequence appears to be a common idiotope associated with mouse diabetes.

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T lymphocytes can be activated via the T cell receptor (TCR) or by triggering through a number of other surface structures, including the CD2 co-receptor molecule. Signaling through the CD2 molecule was shown previously to be dependent on the TCR-associated zeta-chain. Here, we show that CD2-induced activation also functions in T cells which express zeta-chains lacking a functional immune-receptor tyrosine-based activation motif (ITAM). TCR-positive T cells that express only the transmembrane part of the zeta-chain protein and thus lack a functional zeta-derived ITAM readily produce interleukin (IL)-2 when cross-linked with CD2-specific monoclonal antibodies (mAb). TCR-negative T cell hybridomas expressing minimal receptors consisting of an extracellular CD25 and an intracellular zeta-chain-derived segment were effectively stimulated via CD2-specific mAb. For CD2-mediated co-stimulation of TCR-negative cells, two zeta-chain-derived ITAM were sufficient to induce IL-2 when the CD2 molecules were co-cross-linked with the chimeric CD25-zeta molecules. Taken together, our results show that CD2-induced signaling does not necessarily employ the zeta-chain in TCR-positive cells and that CD2-dependent co-stimulation in TCR-negative cells can be mediated via two functional zeta-chain-derived ITAM.

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CD26 or dipeptidylpeptidase IV (DPP IV) is a cell surface protease involved in T-cell activation. Triggering or costimulation of T-cells via CD26 was shown to be dependent on the expression of the T-cell receptor (TCR) associated zeta-chain with at least one functional immune receptor tyrosine based activation motif (ITAM). Here we tested T-cell lines expressing chimeric proteins (hCD25-zeta) consisting of human IL-2 receptor-alpha chain derived extracellular sequences (hCD25) fused to mouse-specific zeta-chain segments, for their capacity to transfer CD26 mediated signals. Although these 'minimal receptor' expressing T-cell lines were capable of transmitting signals from other costimulatory molecules (e.g. CD2), crosslinking of CD26 did not induce IL-2 secretion. Co-cross-linking of hCD25 and CD26 molecules, however, resulted in the stimulation of the T-cells. Thus, although the zeta-chain is a prerequisite for CD26 mediated signaling events, the sole expression of zeta-protein as a signaling molecule is not sufficient for CD26 mediated triggering but permits CD26 induced costimulation in TCR negative cells.

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CD26 is a proteolytic enzyme (dipeptidylpeptidase IV) that defines an alternative activation signal for human T lymphocytes. Crosslinking of CD26 via monoclonal antibodies triggers proliferation and cytotoxicity in CD26-positive T cells or provides costimulatory signals for these cells. Because there is some debate about whether the enzymatic activity plays a role in activation via CD26 we have here generated a mutant CD26 molecule devoid of enzymatic activity. After transfection into T cell receptor-positive recipient T cells, such mutant molecules were tested for their signaling capacity compared to that in the wildtype molecules. The response of transfected clones to direct stimulation with anti-CD26 antibodies and to costimulation via CD26 was variable and not solely dependent on the amount of CD26 and T cell receptor expressed on the T cells. Several mutant transfectants were more easily triggered via CD26 than cells transfected with the wildtype molecule. These data demonstrate that the enzymatic activity of CD26 is not required for its T cell activating or costimulating properties.

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The protease dipeptidylpeptidase IV (CD26) provides an alternative activation pathway for T lymphocytes and is involved in several aspects of T cell function. Activation via CD26 requires the expression of the T cell receptor (TcR)/CD3 complex. Here we have investigated the role of the TcR zeta chain for T cell activation via CD26. T cell hybridomas expressing TcR with various deletions in the CD3 zeta chain were transfected with a CD26 cDNA and the response of the transfected cells to anti-CD26 monoclonal antibodies was tested. Our data show that the zeta chain is essential and that at least one YXXL motif in the cytoplasmic tail of the zeta chain is required for CD26-mediated signaling. Other TcR components do not replace the zeta chain.

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We have introduced two specific point mutations, located 20 base pairs apart, into the endogenous murine gene that encodes the largest subunit of RNA polymerase II (RPII215). The first mutation conferred resistance to the mushroom toxin alpha-amanitin (amar), and the second mutation generated a restriction fragment length polymorphism without altering the protein sequence. Targeted amar clones were generated at a frequency of 1 in 30 totipotent embryonic stem cells that expressed stably integrated DNA vectors after electroporation. Thirty to 40% of these clones had acquired both mutations, whereas, surprisingly, the remaining clones had acquired the specific amar point mutation but lacked the restriction fragment length polymorphism. We suggest that the latter clones were generated by independent DNA mismatch repair rather than by double crossover or gene conversion. These results demonstrate that it is possible to introduce specific point mutations into an endogenous gene in embryonic stem cells. Thus it should be possible to introduce single base substitutions into other cellular genes, including nonselectable genes, by optimizing the efficiency of gene transfer and/or the sensitivity of screening for targeted clones.

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We have reinvestigated the ability of the matrix protein (MA) (p19gag) of avian sarcoma and leukemia viruses to interact with RNA. Previous reports claimed on the one hand that MA can bind tightly and with a high degree of specificity to avian sarcoma and leukemia virus RNA in vitro and on the other that it cannot bind to RNA at all. We found that MA purified by any of several methods does bind to RNA, as measured by its ability to cause retention of radioactive RNA on nitrocellulose membranes in a filtration assay. However, this interaction is weak and lacks specificity. The interaction of MA with RNA was barely detectable by classical sedimentation analysis, and from this observation we estimate that the intrinsic MA-RNA association constant is ca. 10(3) M-1, at least 3 orders of magnitude smaller than the constant describing the interaction of the viral nucleocapsid protein (NC) (p12gag) with RNA, ca. 10(6) M-1. Separately purified phosphorylated and nonphosphorylated MA species bound RNA equally. We also found that MA can bind to DNA with an affinity similar to that for RNA. The large quantitative discrepancy between our results and earlier published reports can be traced in part to methods of data analysis.

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Myelin basic protein (MBP)-specific T cell lines and clones have been established from rats of the major histocompatibility complex (MHC)-compatible Lewis and BS strains. All lines and clones are MHC class II restricted and share the CD4+ phenotype. The cells proliferate specifically in response to either a peptide representing amino acids #68-88 of guinea pig MBP, to residues #47-67 or to an unidentified myelin antigen which is distinct from MBP. All lines and clones specific for MBP express the same T cell receptor (TcR) variable (V) beta chain element, which is homologous to the mouse V beta 8.2 gene segment. Three lines/clones with the same antigen fine specificity have identical V beta D beta J beta junctions on the protein level, a region which represents part of the potential antigen-binding portion of the TcR; two of the lines express members of the V alpha 2 family. These results suggest biased usage of TcR V beta elements in rat T cells specific for MBP. Our findings broaden the basis for a rational therapeutic strategy to specifically intervene in the rodent model system of experimental allergic encephalomyelitis.

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Forty-one children, 20 boys and 21 girls, aged 11 days to 19 years (mean 9.9 years) at initial pacemaker implant, were followed 1 to 248 months (mean 90 months). Ten (mean age 8.2 years) were implanted between 1966 and 1972 (Group I), 14 (mean age 9.9 years) between 1973 and 1980 (Group II) and 17 (mean age 10.9 years) from 1981 through April 1988 (Group III). Arrhythmias were congenital complete heart block in 19, postoperative heart block in 15, acquired heart block in 3, sick sinus syndrome in 3, and bradycardia-induced ventricular fibrillation in 1. Twenty-eight of 41 children had a transvenous implant: 40% of Group I, 71% of Group II and 82% of Group III. Thirteen were cephalic, four subclavian and 11 jugular. Generator site was pectoral in 19, abdominal in 12, intrathoracic in one, and retromammary in nine of 12 girls aged 10 years or more at implant. In Groups I, II and III, 5, 14 and 6 had VOO or VVI units; 5, 0 and 8 dual chamber (VAT, VDD and DDD) pacemakers; 0, 0 and 1 AAI; and 0, 0 and 2 rate-modulated (VVIR) units at initial implant. The average interval between pacer-related hospitalizations in Groups I, II and III was 20, 42, and 39 months. Complications included infection in six, hemothorax in one, and impending pacemaker erosion in one. Six patients died, one of pacer infection, four from primary cardiac disease, and one suddenly without apparent reason. Follow-up continues in 31: 14 are employed full-time, three are homemakers, eight are full-time students, and six are active pre-schoolers.(ABSTRACT TRUNCATED AT 250 WORDS)

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The effect of various physical or chemical treatments of splenic stimulator cells on their endogenous, mitogen-inducible IL-2 production and on their ability to induce IL-2 production in clonally developing helper T lymphocytes was investigated. While most methods (T cell depletion by monoclonal antibodies plus complement, glutaraldehyde fixation, heat inactivation and high-dose irradiation) effectively suppressed the endogenous IL-2 production of splenic stimulator cells, only T cell depletion and high-dose (6000-10,000 R) irradiation sustained their stimulatory capacity. High-dose irradiated stimulator cells induced high numbers of clonally developing helper T lymphocytes to secrete IL-2. Moreover, this induction was found to be antigen-specific. Hence, high-dose irradiation is a simple, rapid and reliable method for the treatment of stimulator cells, especially when large numbers of cultures are to be screened.

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