bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thymic and Extrathymic T Cell Development Pathways Follow Different Rules
Authors: Terra Rafik , Labrecque Nathalie , Perreault Claude 
Published: April 2014

Abstract
Separation between primary and secondary lymphoid organs is a universal feature in jawed vertebrates. Strikingly, oncostatin M (OM)-transgenic mice present massive extrathymic T cell development, localized exclusively in the lymph nodes (LN). According to the prevailing paradigm, the thymus is the main source of T lymphocytes in gnathostomes mainly because thymic epithelial cells have a unique ability to support early steps in T cell development. It is therefore remarkable that productive T cell development occurs in the OM+ LN, despite the absence of epithelial cells. The present study shows that in the OM+ LN: 1) MHC class I expression strictly on hemopoietic cells is sufficient to support the development of a diversified repertoire of CD8 T cells; 2) the efficiency of positive selection of specific TCR-transgenic T cells is not the same as in the thymus; 3) negative selection is very effective, despite the lack of an organized thymic-like medulla. Furthermore, our data suggest that extrathymic T lymphocytes developing in the OM+ LN undergo extensive postselection expansion because they live in the microenvironment in which they were positively selected. This work illustrates how the division of labor between primary and secondary lymphoid organs influences the repertoire and homeostasis of T lymphocytes.
Induction of CD4 T Cell Changes in Murine AIDS Is Dependent on Costimulation and Involves a Dysregulation of Homeostasis
Authors: Yen Michael H. , Lepak Nancy , Swain Susan L. 
Published: April 2014

Abstract
Strong CD4 T cell activation and proliferation are seen in susceptible mice infected with the murine retroviral inoculum, LP-BM5, which produces an immunodeficiency syndrome called murine AIDS (MAIDS). We developed a short term adoptive transfer model of MAIDS to examine the requirements for the CD4 T cell response. Naive CD4 T cells from uninfected donors responded quickly after adoptive transfer into MAIDS-infected hosts, becoming activated and proliferating within several days. Using blocking mAbs to costimulatory ligands and CD4 T cells deficient in expression of their receptors, we found that the CD4 T cell response requires CD28:B7.1/B7.2 interactions, but not CTLA4 or CD40-CD40 ligand interactions. Naive CD4 T cells did not respond in H-2M-deficient mice with MAIDS, suggesting that disease requires recognition of self peptide-MHC complexes. The self MHC-dependent division and accumulation of large numbers of CD4 T cells suggest that MAIDS involves a disruption of the balance of homeostatic signals. Supporting this hypothesis, CD4 T cells from mice with MAIDS failed to regulate the homeostatic division of naive CD4 T cells in a cotransfer model. Thus, a combination of up-regulation of costimulatory ligands and disruption of homeostatic control may be responsible for CD4 lymphoproliferation in MAIDS.
Regulation of Retinoid X Receptor Responsive Element-Dependent Transcription in T Lymphocytes by Ser/Thr Phosphatases: Functional Divergence of Protein Kinase C (PKC)θ and PKCα in Mediating Calcineurin-Induced Transactivation
Authors: Ishaq Mohammad , Fan Ming , Wigmore Kip , Gaddam Arunasri , Natarajan Ven 
Published: April 2014

Abstract
T lymphocyte activation signals regulate the expression and transactivation function of retinoid X receptor (RXR) α through an interplay of complex signaling cascades that are not yet fully understood. We show that cellular Ser/Thr protein phosphatases (PPs) play an important role in mediating these processes. Inhibitors specific for PP1 and PP2A decreased basal expression of RXRα RNA and protein in T lymphocyte leukemia Jurkat cells and prevented activation-induced RXRα accumulation in these cells. In addition, these inhibitors attenuated the RXR responsive element (RXRE)-dependent transcriptional activation in transient transfection assays. Inhibitors of calcineurin (CN), by contrast, did not have any effect on the basal RXRα expression and even augmented activation-induced RXRα expression. Expression of a dominant-active (DA) mutant of CN together with a DA mutant of protein kinase C (PKC)θ, a novel PKC isoform, significantly increased RXRE-dependent transcription. Expression of catalytically inactive PKCθ or a dominant-negative mutant of PKCθ failed to synergize with CN and did not increase RXRE-dependent transcription. Expression of a DA mutant of PKCα or treatment with PMA was found to attenuate PKCθ and CN synergism. We conclude that PP1, PP2A, and CN regulate levels and transcriptional activation function of RXRα in T cells. In addition, CN synergizes with PKCθ to induce RXRE-dependent activation, a cooperative function that is antagonized by the activation of the conventional PKCα isoform. Thus, PKCθ and PKCα may function as positive and negative modulators, respectively, of CN-regulated RXRE-dependent transcription during T cell activation.
The Majority of Immunogenic Epitopes Generate CD4+ T Cells That Are Dependent on MHC Class II-Bound Peptide-Flanking Residues
Authors: Arnold Paula Y. , La Gruta Nicole L. , Miller Tim , Vignali Kate M. , Adams P. Scott , Woodland David L. , Vignali Dario A. A. 
Published: April 2014

AbstractPeptides bind to MHC class II molecules with a defined periodicity such that the peptide-flanking residues (PFRs) P-1 and P11, which lie outside the core binding sequence (P1–P9), are solvent exposed and accessible to the TCR. Using a novel MHC class II:peptide binding assay, we defined the binding register for nine immunogenic epitopes to formally identify the flanking residues. Seven of the nine epitopes, restricted by H-2Ak, H-2Ag7, or H-2Ek, were found to generate T cells that were completely dependent on either P-1 or P11, with dependency on P-1 favored over P11. Such PFR dependency appears to be influenced by the type of amino acid exposed, in that residues that can form salt bridges or hydrogen bonds are favored over small or hydrophobic residues. Peptides containing alanine substitutions at P-1 or P11 in place of PFRs that mediate dependency were considerably less immunogenic and mediated a substantially reduced in vitro recall response to the native protein, inferring that PFR recognition increases immunogenicity. Our data suggest that PFR recognition is a common event characteristic of all MHC class II-restricted T cell responses. This key feature, which is not shared by MHC class I-restricted responses, may underlie the broad functional diversity displayed by MHC class II-restricted T cells.
Modulation of Fas-Dependent Apoptosis: A Dynamic Process Controlling Both the Persistence and Death of CD4 Regulatory T Cells and Effector T Cells
Authors: Banz Alice , Pontoux Christiane , Papiernik Martine 
Published: April 2014

Abstract
We have previously shown that regulatory CD25+CD4+ T cells are resistant to clonal deletion induced by viral superantigen in vivo. In this work we report that isolated CD25+CD4+ T cells activated in vitro by anti-CD3 Ab are resistant to Fas-induced apoptosis, in contrast to their CD25−CD4+ counterparts. Resistance of CD25+CD4+ T cells to Fas-dependent activation-induced cell death is not linked to their inability to produce IL-2 or to their ability to produce IL-10. The sensitivity of both populations to Fas-induced apoptosis can be modulated in vitro by changing the CD25+CD4+:CD25−CD4+ T cell ratio. The sensitivity of CD25−CD4+ T cells to apoptosis can be reduced, while the sensitivity of CD25+CD4+ T cells can be enhanced. Modulation of Fas-dependent apoptosis is associated with changes in cytokine production. However, while CD25−CD4+ T cell apoptosis is highly dependent on IL-2 (production of which is inhibited by CD25+CD4+ T cells in coculture), modulation of CD25+CD4+ T cell apoptosis is IL-2 independent. Taken together, these results suggest that CD25+CD4+ and CD25−CD4+ T cell sensitivity to Fas-dependent apoptosis is dynamically modulated during immune responses; this modulation appears to help maintain a permanent population of regulatory T cells required to control effector T cells.
The B Cell Antigen Receptor Regulates the Transcriptional Activator β-Catenin Via Protein Kinase C-Mediated Inhibition of Glycogen Synthase Kinase-3
Authors: Christian Sherri L. , Sims Peter V. , Gold Michael R. 
Published: April 2014

Abstractβ-Catenin is a transcriptional activator that is regulated by glycogen synthase kinase-3 (GSK-3). GSK-3 is constitutively active in unstimulated cells where it phosphorylates β-catenin, targeting β-catenin for rapid degradation. Receptor-induced inhibition of GSK-3 allows β-catenin to accumulate in the cytoplasm and then translocate to the nucleus where it promotes the transcription of genes such as c-myc and cyclin D1. Wnt hormones, the best known regulators of β-catenin, inhibit GSK-3 via the Disheveled protein. However, GSK-3 is also inhibited when it is phosphorylated by Akt, a downstream target of phosphatidylinositol 3-kinase (PI3K). We have previously shown that B cell Ag receptor (BCR) signaling leads to activation of PI3K and Akt as well as inhibition of GSK-3. Therefore, we hypothesized that BCR engagement would induce the accumulation of β-catenin via a PI3K/Akt/GSK-3 pathway. We now show that BCR ligation causes an increase in the level of β-catenin in the nuclear fraction of B cells as well as an increase in β-catenin-dependent transcription. Direct inhibition of GSK-3 by LiCl also increased β-catenin levels in B cells. This suggests that GSK-3 keeps β-catenin levels low in unstimulated B cells and that BCR-induced inhibition of GSK-3 allows the accumulation of β-catenin. Surprisingly, we found that the BCR-induced phosphorylation of GSK-3 on its negative regulatory sites, as well as the subsequent up-regulation of β-catenin, was not mediated by Akt but by the phospholipase C-dependent activation of protein kinase C. Thus, the BCR regulates β-catenin levels via a phospholipase C/protein kinase C/GSK-3 pathway.
Rapid Chromatin Remodeling of Toll-Like Receptor 2 Promoter During Infection of Macrophages withMycobacterium avium
Authors: Wang Tianyi , Lafuse William P. , Takeda Kiyoshi , Akira Shizuo , Zwilling Bruce S. 
Published: April 2014

AbstractWe have previously reported that NF-κB and stimulating factor 1 elements within the proximal mouse Toll-like receptor 2 (TLR2) promoter region are required for the transcriptional activation of TLR2 expression following infection with Mycobacterium avium. In the present study, we found that a rapid increase in both DNase I sensitivity and restriction enzyme accessibility at the TLR2 promoter region occurred following infection with M. avium. Increase in restriction enzyme accessibility at the TLR2 promoter region covering the NF-κB and stimulating factor 1 elements was associated with the induction of TLR2 expression at the mRNA level. Furthermore, the increase in restriction enzyme accessibility at the TLR2 promoter region did not appear to result from binding of NF-κB, but rather depended on a TLR2-myeloid differentiation factor 88 signaling pathway. Together our results indicate that chromatin remodeling occurs at TLR2 promoter region following infection with M. avium, allowing the access of transcription factors to initiate the transcription of TLR2.
Effect of Environmental Antigens on the Ig Diversification and the Selection of Productive V-J Joints in the Bursa
Authors: Arakawa Hiroshi , Kuma Kei-ichi , Yasuda Masahiro , Ekino Shigeo , Shimizu Akira , Yamagishi Hideo 
Published: April 2014

Abstract
In chickens, a single set of unique functional segments of both Ig H and L chain genes is rearranged during early embryogenesis to generate a pool of B cell progenitors that will be diversified in the bursa by gene conversion, forming the preimmune repertoire. After hatching, bursal cells are exposed to environmental Ags in the bursal lumen. We prepared B cells from each single bursal follicle and used PCR-directed Ig L chain gene analysis to study the differentiation of B cells and the effect of antigenic stimulation from the bursal lumen on the neonatal chicken B cell repertoire formation. Selective amplification of B cell clones with a productive V-J joint was observed during the late embryonic stage, possibly by the interaction with ligands expressed on the bursal stroma and further accelerated in the neonatal chicken. Administration of the artificial Ags into the bursal lumen before the isolation of bursa by bursal duct ligation in the embryo caused a significant increase in lymphocytes with a productive V-J joint in the neonatal chicken bursa compared with the isolated bursa. Intra- and interclonal diversity of a complementarity-determining region measured by an evolutionary distance increased during bursal development. Clonal diversification did not require stimulation by artificial Ags from the bursal lumen. Thus, the preimmune repertoire in the bursa is generated by gene conversion during Ag-independent B cell proliferation, and antigenic stimulation from the bursal epithelium to bursal B cells plays roles in the selection of clones with a productive V-J joint.
A Putative Silencer Element in the IL-5 Gene Recognized by Bcl6
Authors: Arima Masafumi , Toyama Hirochika , Ichii Hirohito , Kojima Satoko , Okada Seiji , Hatano Masahiko , Cheng Gang , Kubo Masato , Fukuda Takeshi , Tokuhisa Takeshi 
Published: April 2014

Abstract
The Bcl6 gene is ubiquitously expressed in adult murine tissues and its product functions as a sequence-specific transcriptional repressor. Bcl6-deficient mice displayed eosinophilic inflammation caused by overproduction of Th2 cytokines. The regulatory mechanism of those cytokine productions by Bcl6 is controversial. When CD4+ T cells from Bcl6-deficient and lck-Bcl6-transgenic mice were stimulated with anti-CD3 Abs, production of IL-5 among Th2 type cytokines was preferentially affected by the amount of Bcl6 in the T cells. We found a putative Bcl6-binding sequence (IL5BS) on the 3′ untranslated region in the murine and human IL-5 genes, and specific binding of Bcl6 protein to the sequence was confirmed by gel retardation assay and chromatin immunoprecipitation assay. The binding activity of endogenous Bcl6 was transiently diminished in Th2 but not in Th1 clones after anti-CD3 stimulation. The exogenous Bcl6 repressed expression of the reporter gene with the IL5BS in K562 cells and the repressor activity was lost by a point mutation of the IL5BS. Furthermore, the IL5BS was required for Bcl6 to repress expression of the IL-5 cDNA. Thus, the IL5BS may act as a silencer element for Bcl6 to repress expression of the IL-5 gene.
Immunogenically Fit Subunit Vaccine Components Via Epitope Discovery from Natural Peptide Libraries
Authors: Matthews Leslie J. , Davis Robert , Smith George P. 
Published: April 2014

Abstract
Antigenic peptides that bind pathogen-specific Abs are a potential source of subunit vaccine components. To be effective the peptides must be immunogenically fit: when used as immunogens they must elicit Abs that cross-react with native intact pathogen. In this study, antigenic peptides obtained from phage display libraries through epitope discovery were systematically examined for immunogenic fitness. Peptides selected from random peptide libraries, in which the phage-displayed peptides are encoded by synthetic degenerate oligonucleotides, had marginal immunogenic fitness. In contrast, 50% of the peptides selected from a natural peptide library, in which phage display segments of actual pathogen polypeptides, proved very successful. Epitope discovery from natural peptide libraries is a promising route to subunit vaccines.
Bivalent Ligands with Rigid Double-Stranded DNA Spacers Reveal Structural Constraints on Signaling by FcεRI
Authors: Paar Jodi M. , Harris Nancie T. , Holowka David , Baird Barbara 
Published: April 2014

Abstract
Degranulation of mast cells and basophils during the allergic response is initiated by Ag-induced cross-linking of cell surface IgE-FcεRI receptor complexes. To investigate how separation distances between cross-linked receptors affect the competency of signal transduction, we synthesized and characterized bivalent dinitrophenyl (DNP)-modified dsDNA oligomers with rigid spacing lengths of ∼40–100 Å. All of these bivalent ligands effectively bind and cross-link anti-DNP IgE with similar affinities in the nanomolar range. The 13-mer (dsDNA length of 44 Å), 15-mer (51 Å), and flexible 30-mer ligands stimulate similar amounts of cellular degranulation, about one-third of that with multivalent Ag, whereas the 20-mer (68 Å) ligand is less effective and the rigid 30-mer (102 Å) ligand is ineffective. Surprisingly, all stimulate tyrosine phosphorylation of FcεRI β, Syk, and linker for activation of T cells to similar extents as multivalent Ag at optimal ligand concentrations. The magnitudes of Ca2+ responses stimulated by these bivalent DNP-dsDNA ligands are small, implicating activation of Ca2+ mobilization by stimulated tyrosine phosphorylation as a limiting process. The results indicate that structural constraints on cross-linked IgE-FcεRI complexes imposed by these rigid DNP-dsDNA ligands prevent robust activation of signaling immediately downstream of early tyrosine phosphorylation events. To account for these results, we propose that activation of a key downstream target is limited by the spacing between cross-linked, phosphorylated receptors and their associated components.
A Role for Inducible Costimulator Protein in the CD28- Independent Mechanism of Resistance to Toxoplasma gondii
Authors: Villegas Eric N. , Lieberman Linda A. , Mason Nicola , Blass Sarah L. , Zediak Valerie P. , Peach Robert , Horan Tom , Yoshinaga Steve , Hunter Christopher A. 
Published: April 2014

Abstract
Long-term resistance to Toxoplasma gondii is dependent on the development of parasite-specific T cells that produce IFN-γ. CD28 is a costimulatory molecule important for optimal activation of T cells, but CD28−/− mice are resistant to T. gondii, demonstrating that CD28-independent mechanisms regulate T cell responses during toxoplasmosis. The identification of the B7-related protein 1/inducible costimulator protein (ICOS) pathway and its ability to regulate the production of IFN-γ suggested that this pathway may be involved in the CD28-independent activation of T cells required for resistance to T. gondii. In support of this hypothesis, infection of wild-type or CD28−/− mice with T. gondii resulted in the increased expression of ICOS by activated CD4+ and CD8+ T cells. In addition, both costimulatory pathways contributed to the in vitro production of IFN-γ by parasite-specific T cells and when both pathways were blocked, there was an additive effect that resulted in almost complete inhibition of IFN-γ production. Although in vivo blockade of the ICOS costimulatory pathway did not result in the early mortality of wild-type mice infected with T. gondii, it did lead to increased susceptibility of CD28−/− mice to T. gondi associated with reduced serum levels of IFN-γ, increased parasite burden, and increased mortality compared with the control group. Together, these results identify a critical role for ICOS in the protective Th1-type response required for resistance to T. gondii and suggest that ICOS and CD28 are parallel costimulatory pathways, either of which is sufficient to mediate resistance to this intracellular pathogen.
Identification of T Cell Epitopes on the 33-kDa Fragment of Plasmodium yoelii Merozoite Surface Protein 1 and Their Antibody-Independent Protective Role in Immunity to Blood Stage Malaria
Authors: Wipasa Jiraprapa , Hirunpetcharat Chakrit , Mahakunkijcharoen Yuvadee , Xu Huji , Elliott Salenna , Good Michael F. 
Published: April 2014

Abstract
Merozoite surface protein 1 (MSP1) of malaria parasites undergoes proteolytic processing at least twice before invasion into a new RBC. The 42-kDa fragment, a product of primary processing, is cleaved by proteolytic enzymes giving rise to MSP133, which is shed from the merozoite surface, and MSP119, which is the only fragment carried into a new RBC. In this study, we have identified T cell epitopes on MSP133 of Plasmodium yoelii and have examined their function in immunity to blood stage malaria. Peptides 20 aa in length, spanning the length of MSP133 and overlapping each other by 10 aa, were analyzed for their ability to induce T cell proliferation in immunized BALB/c and C57BL/6 mice. Multiple epitopes were recognized by these two strains of mice. Effector functions of the dominant epitopes were then investigated. Peptides Cm15 and Cm21 were of particular interest as they were able to induce effector T cells capable of delaying growth of lethal P. yoelii YM following adoptive transfer into immunodeficient mice without inducing detectable Ab responses. Homologs of these epitopes could be candidates for inclusion in a subunit vaccine.
Segregation of B and T Cell Epitopes of Treponema pallidum Repeat Protein K to Variable and Conserved Regions During Experimental Syphilis Infection
Authors: Morgan Cecilia A. , Molini Barbara J. , Lukehart Sheila A. , Van Voorhis Wesley C. 
Published: April 2014

Abstract
Robust immune responses clear millions of treponemes to resolve lesions of primary and secondary syphilis, but cannot clear the treponemes that lead to debilitating and sometimes fatal tertiary syphilis. It is also known that the rabbit model and humans can be reinfected with heterologous isolates. How some treponemes are able to escape the immune system is unknown. In our laboratories rabbits immunized with the Seattle Nichols strain Treponema pallidum repeat protein K (TprK) were previously shown to have attenuated lesion development following challenge. In other isolates, TprK was shown to have seven discrete variable regions, with sequence variation among and within isolates. Using overlapping synthetic 20-aa peptides, we demonstrate that during experimental infection with the Nichols strain, the T cell responses are directed to conserved regions, while the Ab responses are directed primarily to variable regions. Abs from rabbits immunized with recombinant TprK recognized conserved and variable regions, suggesting that the conserved regions are inherently as immunogenic as the variable regions. TprK variability may allow some treponemes to escape recognition from Abs. The variable region heterogeneity may help explain the lack of protection against heterologous isolates.