bluuebunny/crossref_metadata_2025_split huggingface dataset:
TAP‐translocated peptides specifically bind proteins in the endoplasmic reticulum, including gp96, protein disulfide isomerase and calreticulin
Authors: Spee Pieter , Neefjes Jacques 
Published: March 2007

AbstractThe endoplasmic reticulum (ER) membrane‐embedded transporter associated with antigen processing (TAP) associates with peptides in the cytosol and translocates these into the ER lumen. Here, MHC class I molecules bind a subset of these peptides and the remainder is either removed or degraded, or may be retained in the ER in association with other proteins. We have visualized peptide‐binding proteins in the ER using radioactive peptides with a photoreactive group. Besides TAP, two proteins were identified as gp96 and protein disulfide isomerase (PDI). Calreticulin, previously found in complex with TAP, only binds glycosylated peptides. In addition, two as yet unidentified, ER luminal glycoproteins (gp120 and gp170) were visualized. The effects of peptide size and sequence on binding to the ER‐resident proteins were studied by using partially degenerated peptides with photoreactive side chains. All identified proteins were able to bind peptides within the size range of peptides translocated by TAP, from 8 to more than 20 amino acids. Whereas PDI associated with all peptides tested, gp96 and gp120 showed a clear sequence preference for non‐charged amino acids at positions 2 and 9 in 9mer peptides. Thus various ER proteins, other than the MHC class I heterodimer and TAP, are able to interact with peptides albeit with a different substrate selectivity.
Trypanosoma cruzi infection does not impair major histocompatibility complex class I presentation of antigen to cytotoxic T lymphocytes
Authors: Buckner Frederick S. , Wipke Brian T. , Van Voorhis Wesley C. 
Published: March 2007

AbstractTrypanosoma cruzi (T. cruzi), the etiological agent of Chagas' disease, lives free within the cytoplasm of infected host cells. This intracellular niche suggests that parasite antigens may be processed and presented on major histocompatibility complex (MHC) class I molecules for recognition by CD8+ T cells. However, the parasite persists indefinitely in the mammalian host, indicating its success at evading immune clearance. It has been shown that T. cruzi interferes with processing and presentation of antigenic peptides in the MHC class II pathway. This investigation sought to determine whether interference in MHC class I processing and presentation occurs with T. cruzi infection. Surface expression of MHC class I molecules was found to be unaffected or up‐regulated by T. cruzi infection in vitro. A model system employing a β‐galactosidase (β‐gal)‐specific murine cytotoxic T lymphocyte (CTL) line (0805B) showed: (i) in vitro infection of mouse peritoneal macrophages or J774 cells with T. cruzi did not inhibit MHC class I presentation of exogenous peptide (a nine‐amino acid epitope of β‐gal) to the CTL line, (ii) in vitro infection of a β‐gal‐expressing 3T3 cell line (LZEJ) with T. cruzi did not inhibit MHC class I presentation of the endogenous protein to the CTL line and (iii) mouse renal adenocarcinoma cells infected with T. cruzi and subsequently infected with adenovirus expressing β‐gal were able to present antigen to the β‐gal‐specific CTL line. These findings indicate that the failure of the immune response to clear T. cruzi does not result from global interference by the parasite with MHC class I processing and presentation. Parasites engineered to express β‐gal were unable to sensitize infected antigen‐presenting cells in vitro to lysis by the CTL 0805B line. This was probably due to the intracellular localization of the β‐gal within the parasite and its inaccessibility to the host cell cytoplasm.
Impaired spontaneous endocytosis of HLA‐G
Authors: Davis Daniel M. , Reyburn Hugh T. , Pazmany Laszlo , Chiu Isaac , Mandelboim Ofer , Strominger Jack L. 
Published: March 2007

AbstractHLA‐G is a class Ib (non‐classical) major histocompatibility complex (MHC) protein expressed at the maternal‐fetal interface that inhibits natural killer (NK) cell‐mediated lysis in an allotype‐independent manner. Here we report that the spontaneous endocytosis of HLA‐G is severely reduced because of its short cytoplasmic tail. Class I (classical) MHC proteins on the surface of B cell trans‐fectants detected by primary and secondary antibodies underwent endocytosis at a moderate rate, whereas HLA‐G, chimeric proteins consisting of the extracellular domains of HLA‐C with the C‐terminal sequence of HLA‐G, or glycophosphatidylinositol‐tailed HLA‐C proteins, were not efficiently internalized. In addition, a mutant of β2‐microglobulin (Ser88Cys) that could be specifically labeled with Texas red (or other fluorescent probes) and exchanged into class I or class Ib MHC proteins was employed to study spontaneous internalization of MHC proteins by a non‐perturbative method independent of an antibody ligand. These data are discussed in terms of both the role of HLA‐G expressed on the fetal trophoblast and the function of the cytoplasmic tail in class I MHC proteins.
Major histocompatibility complex class I molecules interact with both subunits of the transporter associated with antigen processing, TAP1 and TAP2
Authors: Powis Simon J. 
Published: March 2007

AbstractPrior to loading antigenic peptides, assembled major histocompatibility complex (MHC) class I molecules associate with the transporter associated with antigen processing (TAP) in a complex which also includes calreticulin and a recently described component, tapasin. The interaction of MHC class I molecules has been characterized as occurring exclusively with the TAP1 chain of the TAP heterodimer. In contrast, as described here, in the TAP‐deficient human cell line T2, MHC class I molecules interact with a transfected rat TAP2 polypeptide in addition to rat TAP1. Furthermore, this interaction with TAP2 also involves calreticulin and tapasin. An association with both TAP polypeptides would presumably further enhance the efficiency of peptide loading of MHC class I molecules by allowing more than one MHC class I allele proximity to the site of peptide supply on each TAP complex.
A role for the VLA‐4 integrin in the activation of human memory B cells
Authors: Silvy Anne , Altevogt Peter , Mondière Paul , Bella Chantal , Defrance Thierry 
Published: March 2007

AbstractIt is generally recognized that activation through membrane effector molecules such as CD40 or the B cell receptor (BCR) is mandatory to allow B cells to proliferate and differentiate into antibody (Ab)‐secreting cells in response to cytokines. We show here that purified tonsillar B cells can be stimulated directly by a cytokine combination to proliferate and secrete immunoglobulins when cultures are performed at high cell density. The contact‐mediated activation of B cells in this experimental system is strongly inhibited both by anti‐very late antigen (VLA)‐4 monoclonal Ab and by a peptide containing the LDV sequence specifically recognized by the α4 integrin binding site. These reagents also significantly suppressed the B cell responses elicited by engagement of the BCR or CD40. Our data reveal that memory B cells but not virgin or germinal center B cells are sensitive to the direct stimulatory effect of cytokines in high‐density cultures. Finally, we found that the dual expression of the α and β chains of VLA‐4 is a distinctive feature of the memory B cell population. Collectively, our findings support the notion that VLA‐4‐dependent homotypic B cell interactions can mediate a co‐stimulatory signal to human memory B cells and might participate in the B cell activation triggered through the BCR and CD40.
Involvement of nuclear factor‐xB in platelet‐activating factor‐mediated tumor necrosis factor‐α expression
Authors: Im Suhn Young , Han Su Ji , Ko Hyun Mi , Choi Jung Hwa , Chun Soon Bai , Lee Dong Geun , Ha Tai You , Lee Hern‐Ku 
Published: March 2007

AbstractTumor necrosis factor (TNF)‐α and platelet‐activating factor (PAF) are important mediators of inflammatory reactions, and their release is controlled by a positive feedback network. However, the regulatory mechanisms underlying the interaction of these two molecules are unknown. Within 10 min of the injection of lipopolysaccharide (LPS) into C57BL/6 mice, effects inducible by PAF such as anaphylactic shock‐like symptoms, disseminated intravascular coagulation, and hemorrhage in renal medullae were observed, and all these pathological changes were prevented by the PAF antagonist, BN 50739. The plasma level of PAF after LPS injection reached a peak at 5 min. TNF‐α gene expression was evident 20 min after LPS injection and was maximal at 40 min, and the level of serum TNF‐α reached a peak at 1 h. Pretreatment with BN 50739 inhibited LPS‐induced TNF‐α gene expression and protein synthesis in a dose‐dependent manner. Injection of PAF or treatment of the macrophage cell line, J774A.1, with PAF activated the transcription factor, nuclear factor (NF)‐xB, which is essential for inducible TNF‐α transcription. The activation of NF‐xB by PAF preceded the LPS‐mediated TNF‐α gene expression. Pretreatment with BN 50739 inhibited LPS‐induced mobilization of NF‐xB in a dose‐dependent manner in vivo as well as in vitro. These data suggest that PAF, which is released immediately or shortly after LPS injection, induces the expression of TNF‐α through the activation of NF‐xB.
Structural analysis of human γ3 intervening regions and switch regions: Implication for the low frequency of switching in IgG3‐deficient patients
Authors: Pan Qiang , Lindersson Ylva , Sideras Paschalis , Hammarström Lennart 
Published: March 2007

AbstractHigh and low serum concentrations of IgG3 are associated with the human G3m(b) and G3m(g) allotypes, respectively. In the present study, we analyzed the structure of the Sγ3 and Iγ3, the switch frequency, switch breakpoints and the levels and initiation sites of Iγ3 transcripts both in normal blood donors expressing (b) or (g) allotypes as well as IgG3‐deficient (D) patients. A low switch frequency to γ3 was found in the (g) allotype IgG3D patients which may be caused in part by the allotype‐associated mutations in the Sγ3 region and in part by additional individual mutations observed in the A (SNAP) and B (SNIP/NF‐xB) sites in the Sγ3 repeat region. A higher Iγ3 germ‐line (GL) transcriptional rate was seen in cells from the IgG3D patient, suggesting that low levels of GL Iγ3 transcripts are not a major contributing factor to the defect. However, individual mutations in the Iγ3 region and differential splicing of GL Iγ3 transcripts were found which may affect the switching process.
Thymic T cell export is not influenced by the peripheral T cell pool
Authors: Gabor Melinda J. , Scollay Roland , Godfrey Dale I. 
Published: March 2007

AbstractThe peripheral T cell pool is maintained both by export of naive T cells from the thymus and by post‐thymic expansion of activated/memory T cells. However, it is not known whether the thymus can alter its output following peripheral T cell depletion. Using intrathymic injection of fluorescein isothiocyanate to detect recent thymic emigrants (RTE), we directly tested whether the thymus is able to alter the number of RTE or the CD4:CD8 ratio of RTE emigrating to the periphery in response to in vivo depletion of total peripheral T cells or CD4 T cells, respectively. Depletion of peripheral T cells was achieved with anti‐Thy‐1 or anti‐CD4, at doses that did not affect thymocyte numbers. Depletion of greater than 70% of peripheral T cells by treatment with anti‐Thy‐1 in vivo did not alter the number or cell cycle status of RTE trafficking to lymph nodes or spleen during the peripheral reconstitution phase (6, 9, 12 days). Similarly, depletion of the majority of CD4 T cells, which significantly reduced the peripheral CD4:CD8 T cell ratio, did not alter the total number or the proportion of CD4+ CD8− RTE in peripheral lymphoid organs. These data clearly indicate that thymic output is not influenced by downstream alterations in peripheral T cell pool size or CD4:CD8 ratio. Rather we contend that thymic T cell export is internally regulated by as yet undefined mechanisms.
Immune complexes are potent inhibitors of interleukin‐12 secretion by human monocytes
Authors: Berger Stefan , Chandra Ramon , Balló Hilmar , Hildenbrand Ralf , Stutte Hans Jochen 
Published: March 2007

AbstractWe have studied the effect of immune complexes (IC) on interleukin (IL)‐12 secretion by human monocytes in vitro. Two experimental models of IC were used. IC formed of tetanus toxoid and polyclonal anti‐tetanus toxoid antiserum as well as heat‐aggregated human serum IgG almost completely inhibited IL‐12 (p70 and p40) secretion induced by interferon‐γ and lipopolysaccharide in human blood‐derived monocytes. Neutralizing anti‐IL‐10 antibodies plus indomethacin restored IL‐12 secretion in the presence of IC to a high extent, indicating that IL‐10 and prostaglandin (PG) partially mediate the IC‐induced inhibition of IL‐12 secretion. However, neutralization of tumor necrosis factor (TNF)‐α by specific antibodies also incompletely restored IL‐12 secretion. Indeed, monocytes secrete high levels of TNF‐α upon stimulation by IC. We found that exogenously added TNF‐α caused a profound inhibition of monocytic IL‐12 secretion in the absence of IC, again mediated via the induction of IL‐10 and PG. In summary, IC inhibit IL‐12 secretion via TNF‐α‐induced IL‐10 and PG synthesis. We conclude that IC, typically appearing in the course of chronic inflammatory processes, may influence the balance between Th1 and Th2 responses and may thus contribute to a deprivation of cell‐mediated immune responses.
Role of amino acid position 70 in the binding affinity of p50.1 and p58.1 receptors for HLA‐Cw4 molecules
Authors: Biassoni Roberto , Pessino Anna , Malaspina Angela , Cantoni Claudia , Bottino Cristina , Sivori Simona , Moretta Lorenzo , Moretta Alessandro 
Published: March 2007

AbstractIn an attempt to identify the amino acid position(s) of the HLA‐C‐specific p58.1/p50.1 natural killer cell receptors that determine the binding affinity for their ligand, we used soluble fusion proteins formed by the ectodomain of either receptor and the Fc portion of human IgG1. We show that the soluble p50.1 (activating) receptor binds weakly to 221‐Cw4 transfectants. In contrast, the soluble p58.1 (inhibitory) receptor binds with high affinity. A single amino acid mutation at position 70, obtained by site‐directed mutagenesis, was found to affect the binding affinity of both the p50.1 and the p58.1 receptors. Thus, sub‐stitution in p50.1 of lysine 70 by threonine (typical of the inhibitory p58.1 molecule) resulted in a dramatic increase in binding affinity, comparable to that of the p58.1 molecule. On the other hand, substitution of threonine 70 by lysine in p58.1 almost abolished binding to 221‐Cw4 cells. Our present data indicate that a single amino acid difference greatly influences the p58.1/p50.1 affinity for their HLA‐C ligand and suggests a possible role of position 70 as a contact site in the natural killer cell receptor/major histocompatibility complex class I interaction.
Identification of a T cell lineage‐specific RNA/DNA helicase and its cell surface expression during intrathymic education of αβ and γδ T cells
Authors: Miazek Arkadiusz , Brockhaus Manfred , Langen Hanno , Braun Andrea , Kisielow Pawel 
Published: March 2007

AbstractDespite ubiquitous expression of the gene, RNA/DNA helicase protein was found to be expressed specifically in all cells of the T cell lineage. Interestingly, immature thymocytes that are rearranging T cell receptor (TCR) genes express the helicase strongly on the cell surface and the surface expression is terminated upon engagement of functional TCR by positively selecting ligands. This provides the first evidence that a protein that binds nucleic acids can directly contact the extracellular environment in a developmentally controlled manner. Our discovery of a novel molecular link between the cell surface and nuclear events specific for thymocytes suggests that thymic education is supervised by a previously unknown molecular mechanism, which can now be experimentally explored.
CD28 can promote T cell survival through a phosphatidylinositol 3‐kinase‐independent mechanism
Authors: Collette Yves , Razanajaona D. , Ghiotto M. , Olive Daniel 
Published: March 2007

AbstractPhosphatidylinositol 3(Pl3)‐kinase is implicated in various biological responses, including protection from apoptosis, although its role in antigen‐induced T cell death and the molecular effectors it triggers remains ill‐defined. Here, we investigated the role of Pl3‐kinase activity in the prevention of T cell receptor/CD3‐induced cell death by CD28. Pl3‐kinase inhibitors blocked the up‐regulation of Bcl‐XL by CD28, without impairing the prevention of T cell receptor/CD3‐triggered apoptosis by CD28, hence showing the existence of a cell‐survival pathway independent of Pl3‐kinase activity and up‐regulation of Bcl‐XL. Instead, we show that up‐regulation of FasL which is instrumental in CD3‐induced apoptosis was prevented upon CD28 co‐stimulation. These results indicate that Pl3‐kinase couples CD28 to Bcl‐XL up‐regulation and provide a molecular basis for the role of CD28 in cell survival through a Pl3‐kinase‐independent mechanism including FasL down‐regulation.
Major role of the soluble interleukin‐6/interleukin‐6 receptor complex for the proliferation of interleukin‐6‐dependent human myeloma cell lines
Authors: Gaillard Jean‐Philippe , Liautard Janny , Klein Bernard , Brochier Jean 
Published: March 2007

AbstractInterleukin‐6 (IL‐6) is a proinflammatory cytokine which possesses a central growth factor activity for certain tumor cells such as plasma cells in multiple myeloma (MM). Upon binding of IL‐6, soluble IL‐6 receptor (sIL‐6R) has been shown to retain its affinity for IL‐6 and to associate with the signal‐transducing gp130 chain. Therefore, contrary to the majority of soluble cytokine receptors, it plays an agonist role in IL‐6 signaling. In order to test its physiological importance as compared to that of its membrane counterpart, we studied cells from two myeloma cell lines which need exogenous IL‐6 to proliferate and release sIL‐6R into their culture supernatant. Using a new culture system where the supernatant recirculated permanently through an anti‐IL‐6R affinity column, all sIL‐6R was removed from the culture medium throughout the culture period. Under these conditions IL‐6‐dependent cells were unable to grow in the presence of physiological concentrations of IL‐6, showing the major role of the sIL‐6R for sustaining the proliferation of these cell lines. Increasing IL‐6 concentrations well over the physiological values allowed the cells to proliferate again. No effect was seen when sIL‐6R was removed from the supernatant of an IL‐6‐independent myeloma cell line. These results show that the levels of circulating sIL‐6R (and thus those of IL‐6/sIL‐6R complex) are worth looking at in pathologies involving IL‐6 hyperactivity.
Endothelial cells in chorionic fetal vessels of first trimester placenta express HLA‐G
Authors: Blaschitz Astrid , Lenfant Françoise , Mallet Valérie , Hartmann Michaele , Bensussan Armand , Geraghty Daniel E. , Le Bouteiller Philippe , Dohr Gottfried 
Published: March 2007

AbstractUsing four different HLA‐G‐recognizing monoclonal antibodies (mAb), we investigated whether this nonclassical HLA class I molecule could be expressed in placental cell types other than extravillous cytotrophoblasts (evct) in which HLA‐G has already been detected. Immunohistochemical analysis was performed on serial cryosections of first trimester placenta as well as on maternal decidual tissue. In addition to some proliferative evct, the recently described BFL.1 mAb also slightly stained some villous cytotrophoblast (vct) stem cells located near cell columns and cell islands, which until now have been considered as HLA‐G negative. The same staining pattern was obtained with the 16G1 mAb raised against the soluble HLA‐G isoform, whereas neither 87G nor HCA2 reacted with vct but did strongly label the invasive populations of evct, including interstitial and endovascular trophoblasts. Surprisingly, BFL.1 strongly and reproducibly stained endothelial cells in the fetal capillaries present in the mesenchymal core of the chorionic villi, whereas none of the other surrounding cellular components were stained. The same specific labeling was obtained, although with less intensity, with the three other HLA‐G‐recognizing mAb. In contrast, maternal endothelial cells present in spiral arteries of the decidua parietalis remained unstained. This unexpected cellular localization suggests that HLA‐G may be present as a soluble form during the whole period of fetal vascularization and/or exert a nonimmunological function related to the endothelial cell type, in particular in the angiogenesis process which is highly active, until term, in chorionic villi.
Protein tyrosine kinase Syk is involved in Thy‐1 signaling in rat basophilic leukemia cells
Authors: Tolar Pavel , Dráberová Lubica , Dráber Petr 
Published: March 2007

AbstractThy‐1, a glycosyl‐phosphatidylinositol‐anchored surface glycoprotein, has been shown to possess transmembrane signaling capacity. In rat mast cells and rat basophilic leukemia cells (RBL) aggregation of surface Thy‐1 with antibodies triggers a series of intracellular events, resembling those induced by aggregation of the high‐affinity receptor for IgE (FcεRI), including tyrosine phosphorylation of multiple proteins and release of secretory components. Unlike the FcεRI‐mediated activation, where both the membrane‐associated protein tyrosine kinase (PTK) Lyn and the cytoplasmic PTK Syk are responsible for initiating the signaling cascade, only Lyn has been implicated in Thy‐1‐mediated activation in RBL cells. Here we report that Syk is also rapidly tyrosine phosphorylated upon Thy‐1 cross‐linking. Increased Syk tyrosine phosphorylation is observed only in cells in which extensive aggregation of Thy‐1 is induced by two layers of cross‐linking reagents. RBL‐derived mutant cells deficient in the expression of surface Thy‐1 and transfectants re‐expressing surface Thy‐1 were used to exclude the possibility that Syk activation reflects an interaction of the cross‐linking reagents with surface molecules other than Thy‐1. As FcεRI γ subunits are well known to promote activation of Syk and its recruitment to membrane complexes, we also investigated the role of these subunits in Thy‐1‐mediated Syk activation, using RBL‐derived mutant cells deficient in the expression of FcεRI γ subunits and their revertants. Consistent with the lack of FcεRI expression, no IgE‐induced response could be elicited, while Thy‐1‐inducible Syk phosphorylation was preserved. Our results suggest that Syk might be one of the kinases responsible for signal propagation upon Thy‐1 cross‐linking in a FcεRI‐independent pathway.
Four types of Ca2+ signals in naive CD8+ cytotoxic T cells after stimulation with T cell agonists, partial agonists and antagonists
Authors: Bachmann Martin F. , Mariathasan Sanjeev , Bouchard Denis , Speiser Daniel E. , Ohashi Pamela S. 
Published: March 2007

AbstractStimulation of T cells via the T cell receptor (TCR) leads to an increase intracellular in free Ca2+ levels ([Ca2+]i) and the activation of the MAP kinase signaling pathway. This study analyzes for the first time Ca2+ fluxes in naive cytotoxic T cells stimulated with full agonists, partial agonists, or antagonists. Four different types of Ca2+ responses could be observed. Full agonists triggered a strong and sustained increase in [Ca2+]i. In contrast, partial T cell agonists induced either a strong but transient Ca2+ flux or very low to no increases in [Ca2+]i, while T cell antagonists failed to induce any measurable Ca2+ flux. The ability of peptides to induce elevated [Ca2+]i perfectly paralleled their ability to trigger TCR internalization and T cell activation. Thus, stimulation of naive cytotoxic T cells with a panel of defined altered peptide ligands reveals a consistent picture, where Ca2+ fluxes predict agonist, partial agonist and antagonist properties of peptides.