bluuebunny/crossref_metadata_2025_split huggingface dataset:
Inducible nuclear factors binding the IgM heavy chain pre‐mRNA secretory poly(A) site
Authors: Phillips Cathy , Schimpl Anneliese , Dietrich‐Goetz Walter , Clements J. Barklie , Virtanen Anders 
Published: March 2007

AbstractTwo alternative forms of IgM heavy‐chain mRNA are produced from a common precursor mRNA as a result of competition between cleavage/poly(A) addition at the upstream (secretory) poly(A) site and cleavage/poly(A) addition at the downstream (membrane) poly(A) site coupled with splicing. The efficiency of cleavage at the secretory poly(A) site is thought to play a crucial role in this alternative processing. We therefore examined RNA binding factors recognizing the secretory poly(A) site, in the absence of the splicing option, to look for transacting factors that may play a role in cleavage/polyadenylation efficiency at this site. Purified primary B cells produce the secretory form of μ mRNA when stimulated with lipopolysaccharide (LPS) and the membrane form of μ mRNA when their antigen receptors are ligated by anti‐μ antibodies. We compared RNA binding factors in nuclear extracts from cells produced by these different stimulatory conditions and show that induction of the secretory form of μ mRNA by LPS correlates with the induction of a 28–32‐kDa secretory poly(A) site‐specific polypeptide which is also present in the plasmacytoma cell line J558L. Visualization of the 28–32‐kDa polypeptide in UV cross‐linking assays depends on a GU‐rich element downstream of the secretory poly (A) site. We show that this GU‐rich region enhances polyadenylation efficiency in vivo by transfection of luciferase reporter constructs into the plasmacytoma J558L. We also examined nuclear extracts from B cells doubly stimulated with LPS and anti‐μ antibodies in which expression of the secretory form of μ mRNA is selectively inhibited. This inhibition may be due to a down‐regulation of polyadenylation at the secretory poly(A) site or an up‐regulation of the competitive splicing process. This form of stimulation does not lead to the disappearance of the 28–32‐kDa polypeptide, but to an enhanced binding of a 50–55‐kDa factor which binds both the secretory and membrane poly(A) site. We report the first detection of changes in RNA binding factors taking place at the secretory poly(A) site which correlate with the expression of different forms of μ mRNA produced by primary B cells under different stimulation conditions.
Antigen presentation by Leishmania mexicana‐infected macrophages: activation of helper T cells by a model parasite antigen secreted into the parasitophorous vacuole or expressed on the amastigote surface
Authors: Wolfram Markus , Fuchs Manuela , Wiese Martin , Stierhof York‐Dieter , Overath Peter 
Published: March 2007

AbstractLeishmania are protozoan parasites which invade mammalian macrophages and multiply as amastigotes in phagolysosomes (parasitophorous vacuoles). Using L. mexicana and bone marrow‐derived macrophages (BMM), the question is addressed whether infected BMM induced to express major histocompatibility complex class II molecules can present defined antigens to specific T helper type 1 cells. As a model antigen, a membrane‐bound acid phosphatase (MAP), a minor protein associated with intracellular vesicles in amastigotes, was either overexpressed at the surface of the parasites or overexpressed in a soluble form leading to antigen secretion into the parasitophorous vacuole. Presentation of MAP epitopes by these three types of amastigotes was then compared for macrophages containing live parasites or amastigotes inactivated by drug treatment. It is shown that surface‐exposed and secreted MAP can be efficiently presented to T cells by macrophages harboring live amastigotes. Therefore, the parasitophorous vacuole communicates by vesicular membrane traffic with the plasmalemma of the host cell. The intracellular MAP of wild‐type cells or the abundant lysosomal cysteine proteinases are not or only inefficiently presented, respectively. After killing of the parasites, abundant proteins such as overexpressed MAP and the cysteine proteinases efficiently stimulate T cells, while wild‐type MAP levels are not effective. We conclude that intracellular proteins of intact amastigotes are not available for presentation, while after parasite inactivation, presentation depends on antigen abundance and possibly stability. The cell biological and possible immunological consequences of these results are discussed.
Leishmania‐infected macrophages sequester endogenously synthesized parasite antigens from presentation to CD4+ T cells
Authors: Kima Peter E. , Soong Lynn , Chicharro Carmen , Ruddle Nancy H. , McMahon‐Pratt Diane 
Published: March 2007

AbstractCD4+ T cell lines raised against the protective leishmanial antigens GP46 and P8 were used to study the presentation of endogenously synthesized Leishmania antigens by infected cells. Using two different sources of macrophages, the 14.07 macrophage cell line (H‐2k) which constitutively expresses major histocompatibility complex (MHC) class II molecules, and elicited peritoneal exudate cells, we found that cells infected with Leishmania amastigotes presented little, if any endogenously synthesized parasite antigens to CD4+ T cells. In contrast, promastigote‐infected macrophages did present endogenous parasite molecules to CD4+ T cells, although only for a limited time, with maximal presentation occurring within 24 h of infection and decreasing to minimal antigen presentation at 72 h post‐infection. These observations suggest that once within the macrophage, Leishmania amastigote antigens are sequestered from the MHC class II pathway of antigen presentation. This allows live parasites to persist in infected hosts by evading the activation of CD4+ T cells, a major and critical anti‐leishmanial component of the host immune system. Studies with drugs that modify fusion patterns of phagosomes suggest that the mechanism of this antigen sequestration includes targeted fusion of the parasitophorous vacuole with certain endocytic compartments.
B lymphocytes are impaired in mice lacking the transcriptional co‐activator Bob1/OCA‐B/OBF1
Authors: Nielsen Peter J. , Georgiev Oleg , Lorenz Barbara , Schaffner Walter 
Published: March 2007

AbstractThe protein Bob1 (also called OCA‐B or OBF‐1) is a B lymphocyte‐specific transcriptional co‐activator which can stimulate transcription by interaction with Oct‐1 or Oct‐2 and the octamer sequence found in the promoter and most enhancer regions of the immunoglobulin genes. The role that Bobl plays in the maturation and function of B cells was investigated in mice deficient for Bobl1. Although early stages of B cell development in the bone marrow do not appear to be affected, these mice show reduced numbers of B cells in peripheral lymph‐oid organs. Based on staining for B220, heat‐stable antigen, and IgD, this reduction is particularly strong in those cells representing the more mature B cell stages. Probably as a consequence of this reduction in mature B cells, Bobl1‐deficient mice show reduced serum titers of the immunoglobulin isotypes IgG1, IgG2a, IgG2b and IgA, but not IgM. Histological examination of sections from spleen and lymph nodes reveal that while Bob‐1‐deficient mice have primary follicles, they lack well‐developed germinal centers. Interestingly, B1 (Ly1) B cells in the peritoneum do not appear to be affected by the lack of Bobl1. Taken together, these results suggest that, at least in conventional B cells, Bob1 plays in important role in the antigen‐driven stages of B cell activation and maturation.
Major histocompatibility complex class I‐dependent cell binding to isolated Ly‐49A: evidence for high‐avidity interaction
Authors: Chang Chew Shun , Shen Lianjun , Gong Dong‐Er , Kane Kevin P. 
Published: March 2007

AbstractLy‐49A molecules negatively regulate a subset of mouse natural killer (NK) cells, preventing lysis of H‐2Dd‐expressing target cells. In the present report, we immunoaffinity‐purified Ly‐49A from the EL4 lymphoma using the A1 monoclonal antibody (mAb) and examined cell adhesion to immobilized Ly‐49A. Adhesion was observed by cells expressing relatively high levels of H‐2Dd, but not cells expressing very low or no cell surface Dd, while antibodies specific for Dd or Ly‐49A inhibited the cell binding, indicating that Dd and Ly‐49A mediate the observed adhesion. The density of immobilized Ly‐49A was varied and confirmed by ELISA. Cell binding exhibited a threshold Ly‐49A density requirement, and above this threshold, increases in Ly‐49A density resulted in substantial increases in cell adhesion to a high maximum cell binding. The density of Ly‐49A homodimers required to mediate cell adhesion was found to be quite low: 140–250 molecules/μm2. These results suggest that the avidity of Ly‐49A for Dd is relatively high and indicate that small changes in Ly‐49A density near the threshold result in large changes in stable Ly‐49A receptor engagement. The relatively sharp threshold and marked density dependence presented here for Ly‐49A receptor engagement may explain the observation that relatively small differences in Ly‐49A expression level on NK cells result in significant differences in functional outcome, i.e. whether a target cell expressing a low level of Dd is spared from lysis or not.
Migratory response of human natural killer cells to lymphotactin
Authors: Giancarlo Bianchi , Silvano Sozzani , Albert Zlotnik , Alberto Mantovani , Paola Allavena 
Published: March 2007

AbstractLymphotactin (Lptn) is a new protein belonging to the C or γ subfamily of chemokines with only two of the four cysteine residues. Lptn was reported to act specifically on T lymphocytes and not on monocytes and neutrophils. To understand better the spectrum of action of Lptn we have examined its ability to induce natural killer (NK) cell migration. Freshly isolated human NK cells as well as long‐term cultured NK cells propagated in interleukin‐2 (IL‐2)‐containing medium migrated in response to Lptn. Optimal activity was observed at concentrations ranging from 50 to 200 ng/ml, and the efficacy was comparable to that of MCP‐1, the prototype of C‐C chemokines. Migration in response to Lptn was chemotaxis rather than chemokinesis as determined in a checkerboard analysis. Migration of NK cells was comparable to that observed with T lymphocytes from the same donor, under the same experimental conditions. Finally, in contrast to other cytokines (IL‐2 and IL‐12) which in addition to chemotaxis augment NK cell adhesion to endothelial cells in vitro, Lptn did not affect the adhesiveness of NK cells to vascular endothelium.
Human T lymphocytes bind to germinal centers of human tonsils via integrin α4/VCAM‐1 and LFA‐1/ICAM−1 and −2
Authors: Schriever Folke , Korinth Dirk , Salahi André , Lefterova Petja , Schmidt‐Wolf Ingo G. H. , Behr Susanne I. 
Published: March 2007

AbstractBinding of T lymphocytes within the different compartments of the secondary lymphoid organs is crucial for the function of the cellular and the humoral immune response. It is still not known which adhesion molecules guide T cells to the distinct areas of the lymphoid microenvironment. In the current study an in situ adhesion assay was used to define the receptors for binding of T cells to human tonsils. The T cell lines Jurkat and MOLT‐4 and normal, activated T cells were found to bind exclusively to germinal centers. Jurkat cells used the receptor pair integrin‐α4 (VLA‐4α)/VCAM‐1, whereas activated MOLT‐4 cells and normal T cells bound via both adhesion pathways, namely via integrin‐α4/VCAM‐1 and LFA‐1/ICAM‐1 and ‐2. It is suggested that these adhesion mechanisms are involved in the migration of T cells into the germinal centers of secondary lymphoid organs and that they influence the selection of B cells by apoptosis.
Integrin α chain cytoplasmic tails regulate “antibody‐redirected” cell adhesion, independently of ligand binding
Authors: Weitzman Jonathan B. , Pujades Cristina , Hemler Martin E. 
Published: March 2007

AbstractHere we describe a novel “antibody‐redirected cell adhesion” (ARCA) assay. This assay measures heterotypic cell‐cell adhesion, resulting from antibody bridging between Fcγ receptors type II (CD32) on leukocytes, and clustered intergrins on adherent cell monolayers. This ARCA activity, facilitated by integrins αβ1 or α4β1, required an intact cytoskeleton, but did not involve typical integrin ligand binding sites or divalent cations. Furthermore, deletion of the α4 cytoplasmic tail almost completely abrogated integrin ARCA activity, suggesting an alteration of integrin recruitment into adhesive sites. If two or more tail residues were present after the conserved GFFKR motif, then ARCA activity was largely restored. Although α4 tail deletion caused loss of ARCA activity, it had no effect on the binding of VCAM‐1 to intact α4‐transfected K562 cells. In conclusion, the integrin α chain tail can positively regulate integrin‐dependent cell adhesion by a receptor recruitment/clustering mechanism independent of conventional integrin ligand‐binding considerations.
Regulated production of the interferon‐γ‐inducible protein−10 (IP‐10) chemokine by human neutrophils
Authors: Cassatella Marco A. , Gasperini Sara , Calzetti Federica , Bertagnin Anna , Luster Andrew D. , McDonald Patrick P. 
Published: March 2007

AbstractInterferon‐γ (IFN‐γ)‐inducible protein‐10 (IP‐10), a member of the C‐X‐C sub‐family of chemokines, is known to be produced by monocytes, lymphocytes, keratinocytes and endothelial cells in response to IFN‐γ Here, we show that human polymorphonuclear neutrophils (PMN) also have the ability to produce IP‐10. IFN‐γ alone had a modest effect on IP‐10 mRNA accumulation, whereas tumor necrosis factor‐α (TNF‐α), yeast particles opsonized with IgG (Y‐IgG), lipopolysaccharide (LPS), and formyl‐methionyl‐leucyl‐phenylalanine (fMLP) all failed to up‐regulate IP‐10 gene expression. However, stimulation of neutrophils with IFN‐γ in combination with either TNF‐α or LPS (but not with Y‐IgG or fMLP) resulted in a considerable induction of IP‐10 mRNA transcripts, as well as in the extracellular release of the protein. In contrast, the best inducer of IP‐10 release from peripheral blood mononuclear cells was IFN‐γ alone. Furthermore, mRNA stabilization analyses demonstrated that IP‐10 mRNA isolated from PMN stimulated with IFN‐γ only, or with IFN‐γ plus either TNF‐α or LPS, had similar half‐lives. Finally, we found that interleukin‐10, a known inhibitor of chemokine production in PMN, moderatley suppressed the extracellular production of IP‐10 in neutrophils stimulated with IFN‐γ plus either LPS or TNF‐α. Since IP‐10 is a potent chemoattractant for activated T lymphocytes, the ability of neutrophils to produce IP‐10 might contribute to the evolution and progression of the inflammatory response.
Pattern of usage and somatic hypermutation in the VH5 gene segments of a patient with asthma: Implications for IgE
Authors: Snow Rachel E. , Chapman Caroline J. , Frew Anthony J. , Holgate Stephen T. , Stevenson Freda K. 
Published: March 2007

AbstractThe VH5 family contains two functional genes, V5–51 and VH32, and appears to be over‐represented in IgE antibodies from patients with allergic disease. Previous sequence analysis of VH5 gene segments in IgE has revealed a substantial level of somatic hypermutation, with evidence for hotspots. To assess characteristics of VH5 gene behavior, VH5 gene segments in combination with Cμ, Cγ, Cα, and Cε have been amplified from blood B lymphocytes of a patient with atopic asthma. Sequence analysis revealed strong preferential usage of one of the two VH5 gene segments (V5–51) by IgM, IgG, and IgA. In contrast, IgE used both genes equally. Levels of somatic mutation were higher following all isotype switches, particularly to IgA. Mutational hotspots were identifiable in all isotypes, leading to several common replacement amino acids. The dominant mutational site in IgM was a common hotspot at Ser31. IgG, IgA, and IgE‐derived sequences had mainly common hotspots, with few distinct sites. The results indicate that mutational hotspots are a feature of the VH5 gene, are identifiable at an early stage of somatic hypermutation, and are not a unique feature of IgE. Generation of IgE antibodies appears to involve three processes: the preferential use of VH5 genes, consistent with superantigen stimulation; the accumulation of somatic mutations in common hotspots, some of which are in complementarity‐determining regions (CDR); and the acquisition of non‐hotspot mutations in CDR, accounting for ∼ 50% of replacement amino acids in these sites, and presumably contributing to affinity maturation.
Major histocompatibility complex recognition by immune receptors: Differences among T cell receptor versus antibody interactions with the VSV8/H‐2Kb complex
Authors: Witte Torsten , Smolyar Alex , Spoerl Rebecca , Goyarts Earl C. , Nathenson Stanley G. , Reinherz Ellis L. , Chang Hsiu‐Ching 
Published: March 2007

AbstractThe surface residues of the VSV8/Kb complex important for recognition by N15 and N26 αβ T cell receptors (TCR) were mapped by mutational analysis and compared to each other and with epitopes of well‐characterized Kb specific monoclonal antibodies (mAb). Three features of immune receptor recognition emerge. First, the footprints of the two TCR on VSV8/Kb are similar with more than 80% overlap between sites. Given that only 8 of 14 surface exposed VSV8/Kb residues identified as critical for TCR interaction are in common, the chemical basis of the N15 and N26 interactions is nevertheless distinct. Second, the cognate peptide is a major focus of TCR recognition: mutation at any of the three exposed side chains (at p1, p4 or p6) abrogates interaction of both TCR as measured by functional T cell activation. Third, in contrast to TCR, mAb bind to discrete segments on the periphery of the α1 and/or α2 helices without orientational restriction. These findings suggest that unlike soluble antibodies, surface membrane receptor‐ligand interactions on opposing cells (i.e. TCR‐peptide/MHC, CD8‐MHC) limit the orientational freedom of the TCR in the immune recognition process.
CD28‐mediated induction of proliferation in resting T cells in vitro and in vivo without engagement of the T cell receptor: Evidence for functionally distinct forms of CD28
Authors: Tacke Michael , Hanke Gabriele , Hanke Thomas , Hünig Thomas 
Published: March 2007

AbstractJJ316 and JJ319 are rat CD28‐specific monoclonal antibodies (mAb) of the γ1χ isotype with identical co‐stimulatory potency. At a concentration 100–1000‐fold higher than that required for co‐stimulation, JJ316, but not JJ319 induces massive proliferation of all T cell subsets in vitro without T cell receptor (TCR) triggering. “Direct” stimulation by JJ316 is fully blocked by JJ319, indicating that it is not due to cross‐reactivity of JJ316 with the TCR complex or other activating receptors. JJ316 binds much more slowly to primary T cells than JJ319, whereas both antibodies bind with similar kinetics to CD28‐transfected L‐929 cells, suggesting that JJ316 binding to T cells requires redistribution or a conformational change of CD28. In vivo, JJ316 but not JJ319 induces rapid and transient proliferation of most CD4 T cells and, indirectly, of B cells. These data show that TCR engagement is not an absolute prerequisite either in vitro or in vivo for the induction of T cell proliferation through CD28 and suggest that mAb JJ316 is able to stimulate resting T cells directly by recruiting CD28 molecules from an inactive to an active form.
Accumulation of somatic hypermutation and antigen‐driven selection in rapidly cycling surface Ig+ germinal center (GC) B cells which occupy GC at a high frequency during the primary antihapten response in mice
Authors: Kimoto Hiroshi , Nagaoka Hitoshi , Adachi Yoshihiro , Mizuochi Toshiaki , Azuma Takachika , Yagi Takenori , Sata Tetsutaro , Yonehara Shin , Tsunetsugu‐Yokota Yasuko , Taniguchi Masaru , Takemori Toshitada 
Published: March 2007

AbstractWell‐developed germinal centers (GC) contain rapidly dividing surface immunoglobulin‐negative (sIg‐) B cells (centroblasts), and most of their progeny are sIg+ B cells (centrocytes) in a resting state. It has been predicted that somatic hypermutation occurs in centroblasts, whereas antigen‐driven selection takes place in centrocytes. The present analysis indicates that murine GC B cells bearing sIg with specificity for an immunizing antigen are in a rapidly cycling state and increase exponentially in number to occupy spleen GC at high frequency during the 1st week after primary immunization; however, the number of these cells is significantly reduced in the 2nd week of immunization. During that period, these proliferating sIg+ GC B cells accumulate somatic hypermutations with nucleotide exchanges indicative of affinity maturation. These sIg+ GC B cells co‐express B7‐2, ICAM‐1, and LFA‐1, and have potent antigen‐presenting activity which results in T cell activation in vitro. These observations indicate that the sIg+ GC B cells accumulate somatic hypermutations and undergo antigen‐driven selection through proliferation, probably upon activation by T cells. This sIg+ GC B cell population may represent cell cycling centrocytes; however, the possibility that these may represent centroblasts undergoing re‐expression of sIg could not be excluded.
Redox regulation of apoptosis: Impact of thiol oxidation status on mitochondrial function
Authors: Marchetti Philippe , Decaudin Didier , Macho Antonio , Zamzami Naoufal , Hirsch Tamara , Susin Santos A. , Kroemer Guido 
Published: March 2007

AbstractThe probability that a cell will undergo apoptosis is in part dictated by the cellular redox potential, which is mainly determined by the reduction and oxidation of thiol residues on glutathione and proteins. We and others have recently shown that mitochondria play a critical role in the apoptotic cascade. Here, we address the question as to whether thiol modification regulates apoptosis and in which cellular compartment apoptosis‐regulatory thiols are localized. To resolve this problem, we employed the divalent thiol‐reactive agent diamide, which causes thiol cross‐linking and thus mimics disulfide bridge formation, and a panel of monovalent thiol‐reactive compounds (which impede disulfide bridge formation due to thiol oxidation), one of which is specifically targeted to the mitochondrial matrix. Our data indicate that thymocyte apoptosis induced by diamide mimics natural apoptosis in the sense that mitochondrial transmembrane potential (ΔΨm) disruption precedes nuclear chromatin degradation: that monovalent thiol‐reactive compounds inhibit apoptosis induced by diamide, glucocorticoids, irradiation, and topoisomerase inhibition; that the critical thiols determining cell fate after exposure to diamide, glucocorticoids, or DNA damage are likely to be located in the mitochondrial matrix; and that thiol oxidation and reduction are critical for apoptosis induction by some stimuli (glucocorticoids. DNA damage), but not by Fas/CD95 cross‐linking. Taken together, these findings suggest that, at least in some pathways of apoptosis, mitochondrial thiols constitute a critical sensor of the cellular redox potential.