bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel p62dok family members, dok-4 and dok-5, are substrates of the c-Ret receptor tyrosine kinase and mediate neuronal differentiation
Authors: Grimm Jan , Sachs Martin , Britsch Stefan , Di Cesare Silvana , Schwarz-Romond Thomas , Alitalo Kari , Birchmeier Walter
Published: July 2002

Docking proteins are substrates of tyrosine kinases and function in the recruitment and assembly of specific signal transduction molecules. Here we found that p62dok family members act as substrates for the c-Ret receptor tyrosine kinase. In addition to dok-1, dok-2, and dok-3, we identified two new family members, dok-4 and dok-5, that can directly associate with Y1062 of c-Ret. Dok-4 and dok-5 constitute a subgroup of dok family members that is coexpressed with c-Ret in various neuronal tissues. Activated c-Ret promotes neurite outgrowth of PC12 cells; for this activity, Y1062 in c-Ret is essential. c-Ret/dok fusion proteins, in which Y1062 of c-Ret is deleted and replaced by the sequences of dok-4 or dok-5, induce ligand-dependent axonal outgrowth of PC12 cells, whereas a c-Ret fusion containing dok-2 sequences does not elicit this response. Dok-4 and dok-5 do not associate with rasGAP or Nck, in contrast to p62dok and dok-2. Moreover, dok-4 and dok-5 enhance c-Ret–dependent activation of mitogen-activated protein kinase. Thus, we have identified a subclass of p62dok proteins that are putative links with downstream effectors of c-Ret in neuronal differentiation.
Cytoplasmic tail–dependent internalization of membrane-type 1 matrix metalloproteinase is important for its invasion-promoting activity
Authors: Uekita Takamasa , Itoh Yoshifumi , Yana Ikuo , Ohno Hiroshi , Seiki Motoharu
Published: July 2002

Membrane-type 1 matrix metalloproteinase (MT1-MMP) is an integral membrane proteinase that degrades the pericellular extracellular matrix (ECM) and is expressed in many migratory cells, including invasive cancer cells. MT1-MMP has been shown to localize at the migration edge and to promote cell migration; however, it is not clear how the enzyme is regulated during the migration process. Here, we report that MT1-MMP is internalized from the surface and that this event depends on the sequence of its cytoplasmic tail. Di-leucine (Leu571–572 and Leu578–579) and tyrosine573 residues are important for the internalization, and the μ2 subunit of adaptor protein 2, a component of clathrin-coated pits for membrane protein internalization, was found to bind to the LLY573 sequence. MT1-MMP was internalized predominantly at the adherent edge and was found to colocalize with clathrin-coated vesicles. The mutations that disturb internalization caused accumulation of the enzyme at the adherent edge, though the net proteolytic activity was not affected much. Interestingly, whereas expression of MT1-MMP enhances cell migration and invasion, the internalization-defective mutants failed to promote either activity. These data indicate that dynamic turnover of MT1-MMP at the migration edge by internalization is important for proper enzyme function during cell migration and invasion.
In vivo dissection of the chromosome condensation machinery
Authors: Lavoie Brigitte D. , Hogan Eileen , Koshland Douglas
Published: July 2002

The machinery mediating chromosome condensation is poorly understood. To begin to dissect the in vivo function(s) of individual components, we monitored mitotic chromosome structure in mutants of condensin, cohesin, histone H3, and topoisomerase II (topo II). In budding yeast, both condensation establishment and maintenance require all of the condensin subunits, but not topo II activity or phospho-histone H3. Structural maintenance of chromosome (SMC) protein 2, as well as each of the three non-SMC proteins (Ycg1p, Ycs4p, and Brn1p), was required for chromatin binding of the condensin complex in vivo. Using reversible condensin alleles, we show that chromosome condensation does not involve an irreversible modification of condensin or chromosomes. Finally, we provide the first evidence of a mechanistic link between condensin and cohesin function. A model discussing the functional interplay between cohesin and condensin is presented.
Polarization of Chemokine Receptors to the Leading Edge during Lymphocyte Chemotaxis
Authors: Nieto Marta , Frade José M.R. , Sancho David , Mellado Mario , Martinez-A Carlos , Sánchez-Madrid Francisco
Published: July 2002

Leukocyte migration in response to cell attractant gradients or chemotaxis is a key phenomenon both in cell movement and in the inflammatory response. Chemokines are quite likely to be the key molecules directing migration of leukocytes that involve cell polarization with generation of specialized cell compartments. The precise mechanism of leukocyte chemoattraction is not known, however. In this study, we demonstrate that the CC chemokine receptors CCR2 and CCR5, but not cytokine receptors such as interleukin (IL)-2Rα, IL-2Rβ, tumor necrosis factor receptor 1, or transforming growth factor βR, are redistributed to a pole in T cells that are migrating in response to chemokines. Immunofluorescence and confocal microscopy studies show that the chemokine receptors concentrate at the leading edge of the cell on the flattened cell-substratum contact area, induced specifically by the signals that trigger cell polarization. The redistribution of chemokine receptors is blocked by pertussis toxin and is dependent on cell adhesion through integrin receptors, which mediate cell migration. Chemokine receptor expression on the leading edge of migrating polarized lymphocytes appears to act as a sensor mechanism for the directed migration of leukocytes through a chemoattractant gradient.
Cloning and Characterization of TRAIL-R3, a Novel Member of the Emerging TRAIL Receptor Family
Authors: Degli-Esposti Mariapia A. , Smolak Pamela J. , Walczak Henning , Waugh Jennifer , Huang Chang-Pin , DuBose Robert F. , Goodwin Raymond G. , Smith Craig A.
Published: July 2002

TRAIL-R3, a new member of the TRAIL receptor family, has been cloned and characterized. TRAIL-R3 encodes a 299 amino acid protein with 58 and 54% overall identity to TRAIL-R1 and -R2, respectively. Transient expression and quantitative binding studies show TRAIL-R3 to be a plasma membrane–bound protein capable of high affinity interaction with the TRAIL ligand. The TRAIL-R3 gene maps to human chromosome 8p22-21, clustered with the genes encoding two other TRAIL receptors. In contrast to TRAIL-R1 and -R2, this receptor shows restricted expression, with transcripts detectable only in peripheral blood lymphocytes and spleen. The structure of TRAIL-R3 is unique when compared to the other TRAIL receptors in that it lacks a cytoplasmic domain and appears to be glycosyl-phosphatidylinositol–linked. Moreover, unlike TRAIL-R1 and -R2, in a transient overexpression system TRAIL-R3 does not induce apoptosis.
Physical and Functional Association of the Src Family Kinases Fyn and Lyn with the Collagen Receptor Glycoprotein VI-Fc Receptor γ Chain Complex on Human Platelets
Authors: Ezumi Yasuharu , Shindoh Keisuke , Tsuji Masaaki , Takayama Hiroshi
Published: July 2002

We have previously shown that uncharacterized glycoprotein VI (GPVI), which is constitutively associated and coexpressed with Fc receptor γ chain (FcRγ) in human platelets, is essential for collagen-stimulated tyrosine phosphorylation of FcRγ, Syk, and phospholipase Cγ2 (PLCγ2), leading to platelet activation. Here we investigated involvement of the Src family in the proximal signals through the GPVI–FcRγ complex, using the snake venom convulxin from Crotalus durissus terrificus, which specifically recognizes GPVI and activates platelets through cross-linking GPVI. Convulxin-coupled beads precipitated the GPVI–FcRγ complex from platelet lysates. Collagen and convulxin induced tyrosine phosphorylation of FcRγ, Syk, and PLCγ2 and recruited tyrosine-phosphorylated Syk to the GPVI–FcRγ complex. Using coprecipitation methods with convulxin-coupled beads and antibodies against FcRγ and the Src family, we showed that Fyn and Lyn, but not Yes, Src, Fgr, Hck, and Lck, were physically associated with the GPVI–FcRγ complex irrespective of stimulation. Furthermore, Fyn was rapidly activated by collagen or cross-linking GPVI. The Src family–specific inhibitor PP1 dose-dependently inhibited collagen- or convulxin-induced tyrosine phosphorylation of proteins including FcRγ, Syk, and PLCγ2, accompanied by a loss of aggregation and ATP release reaction. These results indicate that the Src family plays a critical role in platelet activation via the collagen receptor GPVI–FcRγ complex.
Major Histocompatibility Complex Class I–restricted Cross-presentation Is Biased towards High Dose Antigens and Those Released during Cellular Destruction
Authors: Kurts Christian , Miller Jacques F.A.P. , Subramaniam Rathan M. , Carbone Francis R. , Heath William R.
Published: July 2002

Naive T cells recirculate mainly within the secondary lymphoid compartment, but once activated they can enter peripheral tissues and perform effector functions. To activate naive T cells, foreign antigens must traffic from the site of infection to the draining lymph nodes, where they can be presented by professional antigen presenting cells. For major histocompatibility complex class I–restricted presentation to CD8+ T cells, this can occur via the cross-presentation pathway. Here, we investigated the conditions allowing antigen access to this pathway. We show that the level of antigen expressed by peripheral tissues must be relatively high to facilitate cross-presentation to naive CD8+ T cells. Below this level, peripheral antigens did not stimulate by cross-presentation and were ignored by naive CD8+ T cells, although they could sensitize tissue cells for destruction by activated cytotoxic T lymphocytes (CTLs). Interestingly, CTL-mediated tissue destruction facilitated cross-presentation of low dose antigens for activation of naive CD8+ T cells. This represents the first in vivo evidence that cellular destruction can enhance access of exogenous antigens to the cross-presentation pathway. These data indicate that the cross-presentation pathway focuses on high dose antigens and those released during tissue destruction.
Uptake of Leishmania major Amastigotes Results in Activation and Interleukin 12 Release from Murine Skin–derived Dendritic Cells: Implications for the Initiation of Anti-Leishmania Immunity
Authors: von Stebut Esther , Belkaid Yasmine , Jakob Thilo , Sacks David L. , Udey Mark C.
Published: July 2002

Epidermal Langerhans cells (LC) are immature dendritic cells (DC) located in close proximity to the site of inoculation of infectious Leishmania major metacyclic promastigotes by sand flies. Using LC-like DC expanded from C57BL/6 fetal skin, we characterized interactions involving several developmental stages of Leishmania and DC. We confirmed that L. major amastigotes, but not promastigotes, efficiently entered LC-like DC. Parasite internalization was associated with activation manifested by upregulation of major histocompatibility complex (MHC) class I and II surface antigens, increased expression of costimulatory molecules (CD40, CD54, CD80, and CD86), and interleukin (IL)-12 p40 release within 18 h. L. major–induced IL-12 p70 release by DC required interferon γ and prolonged (72 h) incubation. In contrast, infection of inflammatory macrophages (Mφ) with amastigotes or promastigotes did not lead to significant changes in surface antigen expression or cytokine production. These results suggest that skin Mφ and DC are infected sequentially in cutaneous leishmaniasis and that they play distinct roles in the inflammatory and immune response initiated by L. major. Mφ capture organisms near the site of inoculation early in the course of infection after establishment of cellular immunity, and kill amastigotes but probably do not actively participate in T cell priming. In contrast, skin DC are induced to express increased amounts of MHC antigens and costimulatory molecules and to release cytokines (including IL-12 p70) by exposure to L. major amastigotes that ultimately accumulate in lesional tissue, and thus very likely initiate protective T helper cell type 1 immunity.
Freshly Isolated Peyer's Patch, but Not Spleen, Dendritic Cells Produce Interleukin 10 and Induce the Differentiation of T Helper Type 2 Cells
Authors: Iwasaki Akiko , Kelsall Brian Lee
Published: July 2002

Orally administered antigens often generate immune responses that are distinct from those injected systemically. The role of antigen-presenting cells in determining the type of T helper cell response induced at mucosal versus systemic sites is unclear. Here we examine the phenotypic and functional differences between dendritic cells (DCs) freshly isolated from Peyer's patches (PP) and spleen (SP). Surface phenotypic analysis of CD11c+ DC populations revealed that PP DCs expressed higher levels of major histocompatibility complex class II molecules, but similar levels of costimulatory molecules and adhesion molecules compared with SP DCs. Freshly isolated, flow cytometrically sorted 98–100% pure CD11c+ DC populations from PP and SP were compared for their ability to stimulate naive T cells. First, PP DCs were found to be much more potent in stimulating allogeneic T cell proliferation compared with SP DCs. Second, by using naive T cells from ovalbumin peptide–specific T cell receptor transgenic mice, these ex vivo DCs derived from PP, but not from SP, were found to prime for the production of interleukin (IL)-4 and IL-10 (Th2 cytokines). In addition, PP DCs were found to prime T cells for the production of much lower levels of interferon (IFN)-γ (Th1) compared with SP DCs. The presence of neutralizing antibody against IL-10 in the priming culture dramatically enhanced IFN-γ production by T cells stimulated with PP DCs. Furthermore, stimulation of freshly isolated PP DCs via the CD40 molecule resulted in secretion of high levels of IL-10, whereas the same stimulus induced no IL-10 secretion from SP DCs. These results suggest that DCs residing in different tissues are capable of inducing distinct immune responses and that this may be related to the distinct cytokines produced by the DCs from these tissues.
Immunoglobulin A1 Protease, an Exoenzyme of Pathogenic Neisseriae, Is a Potent Inducer of Proinflammatory Cytokines
Authors: Lorenzen Dirk R. , Düx Frank , Wölk Uwe , Tsirpouchtsidis Anastasios , Haas Gaby , Meyer Thomas F.
Published: July 2002

A characteristic of human pathogenic Neisseriae is the production and secretion of an immunoglobulin (Ig)A1-specific serine protease (IgA1 protease) that cleaves preferentially human IgA1 and other target proteins. Here we show a novel function for native IgA1 protease, i.e., the induction of proinflammatory cytokines such as tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, and IL-8 from peripheral blood mononuclear cells. The capacity of IgA1 protease to elicit such cytokine responses in monocytes was enhanced in the presence of T lymphocytes. IgA1 protease did not induce the regulatory cytokine IL-10, which was, however, found in response to lipopolysaccharide and phytohemagglutinin. The immunomodulatory effects caused by IgA1 protease require a native form of the enzyme, and denaturation abolished cytokine induction. However, the proteolytic activity is not required for the cytokine induction by IgA1 protease. Our results indicate that IgA1 protease exhibits important immunostimulatory properties and may contribute substantially to the pathogenesis of neisserial infections by inducing large amounts of TNF-α and other proinflammatory cytokines. In particular, IgA1 protease may represent a key virulence determinant of bacterial meningitis.
Type I Interferon as a Powerful Adjuvant for Monocyte-Derived Dendritic Cell Development and Activity in Vitro and in Hu-Pbl-Scid Mice
Authors: Santini Stefano M. , Lapenta Caterina , Logozzi Mariantonia , Parlato Stefania , Spada Massimo , Di Pucchio Tiziana , Belardelli Filippo
Published: July 2002

Type I interferons (IFNs) are cytokines exhibiting antiviral and antitumor effects, including multiple activities on immune cells. However, the importance of these cytokines in the early events leading to the generation of an immune response is still unclear. Here, we have investigated the effects of type I IFNs on freshly isolated granulocyte/macrophage colony-stimulating factor (GM-CSF)–treated human monocytes in terms of dendritic cell (DC) differentiation and activity in vitro and in severe combined immunodeficiency mice reconstituted with human peripheral blood leukocytes (hu-PBL-SCID) mice. Type I IFNs induced a surprisingly rapid maturation of monocytes into short-lived tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)–expressing DCs endowed with potent functional activities, superior with respect to the interleukin (IL)-4/GM-CSF treatment, as shown by FACS® analyses, mixed leukocyte reaction assays with allogeneic PBLs, and lymphocyte proliferation responses to HIV-1–pulsed autologous DCs. Type I IFN induced IL-15 production and strongly promoted a T helper cell type 1 response. Notably, injection of IFN-treated HIV-1–pulsed DCs in SCID mice reconstituted with autologous PBLs resulted in the generation of a potent primary immune response, as evaluated by the detection of human antibodies to various HIV-1 antigens. These results provide a rationale for using type I IFNs as vaccine adjuvants and support the concept that a natural alliance between these cytokines and monocytes/DCs represents an important early mechanism for connecting innate and adaptive immunity.
Critical Role for Cd8 in T Cell Receptor Binding and Activation by Peptide/Major Histocompatibility Complex Multimers
Authors: Daniels Mark A. , Jameson Stephen C.
Published: July 2002

Recent data using MHC/peptide tetramers and dimers suggests that the T cell coreceptors, CD4 and CD8, although important for T cell activation, do not play a direct role in facilitating T cell receptor (TCR) binding to multivalent MHC/peptide ligands. Instead, a current model proposes that coreceptors are recruited only after a stable TCR–MHC/peptide complex has already formed and signaled. In contrast, we show using multimeric class I MHC/peptide ligands that CD8 plays a critical (in some cases obligatory) role in antigen-specific TCR binding. T cell activation, measured by calcium mobilization, was induced by multimeric but not monomeric ligands and also showed CD8 dependency. Our analysis using anti-CD8 antibodies revealed that binding to different epitopes of CD8 can either block or augment TCR–MHC/peptide interaction. These effects on TCR binding to high-affinity agonist ligands were even more pronounced when binding to multimeric low-affinity ligands, including TCR antagonists, was studied. Our data have important implications for the role of CD8 in TCR binding to MHC/peptide ligands and in T cell activation. In addition, our results argue against the view that multimeric MHC/peptide ligands bind directly and solely to the TCR; rather, our data highlight a pivotal contribution of CD8 for this association.
Alymphoplasia (aly)-Type Nuclear Factor κB–Inducing Kinase (Nik) Causes Defects in Secondary Lymphoid Tissue Chemokine Receptor Signaling and Homing of Peritoneal Cells to the Gut-Associated Lymphatic Tissue System
Authors: Fagarasan Sidonia , Shinkura Reiko , Kamata Tadashi , Nogaki Fumiaki , Ikuta Koichi , Tashiro Kei , Honjo Tasuku
Published: July 2002

Alymphoplasia (aly) mice, which carry a point mutation in the nuclear factor κB–inducing kinase (NIK) gene, are characterized by the systemic absence of lymph nodes and Peyer's patches, disorganized splenic and thymic architectures, and immunodeficiency. Another unique feature of aly/aly mice is that their peritoneal cavity contains more B1 cells than normal and aly/+ mice. Transfer experiments of peritoneal lymphocytes from aly/aly mice into recombination activating gene (RAG)-2−/− mice revealed that B and T cells fail to migrate to other lymphoid tissues, particularly to the gut-associated lymphatic tissue system. In vivo homing defects of aly/aly peritoneal cells correlated with reduction of their in vitro chemotactic responses to secondary lymphoid tissue chemokine (SLC) and B lymphocyte chemoattractant (BLC). The migration defect of aly/aly lymphocytes was not due to a lack of expression of chemokines and their receptors, but rather to impaired signal transduction downstream of the receptors for SLC, indicating that NIK is involved in the chemokine signaling pathway known to couple only with G proteins. The results showed that the reduced serum levels of immunoglobulins (Igs) and the absence of class switch to IgA in aly/aly mice are due, at least in part, to a migration defect of lymphocytes to the proper microenvironment where B cells proliferate and differentiate into Ig-producing cells.
Ras Mediates Effector Pathways Responsible for Pre-B Cell Survival, Which Is Essential for the Developmental Progression to the Late Pre-B Cell Stage
Authors: Nagaoka Hitoshi , Takahashi Yoshimasa , Hayashi Reiko , Nakamura Tohru , Ishii Kumiko , Matsuda Junichiro , Ogura Atsuo , Shirakata Yumiko , Karasuyama Hajime , Sudo Tetsuo , Nishikawa Shin-Ichi , Tsubata Takeshi , Mizuochi Tsuguo , Asano Toshihiko , Sakano Hitoshi , Takemori Toshitada
Published: July 2002

Ras is essential for the transition from early B cell precursors to the pro-B stage, and is considered to be involved in the signal cascade mediated by pre-B cell antigen receptors. To examine the role of p21ras in the late stage of B cell differentiation, we established transgenic mice (TG) expressing a dominant-inhibitory mutant of Ha-ras (Asn-17 Ha-ras) in B lineage cells at high levels after the early B cell precursor stage. Expression of p21Asn-17 Ha-ras was associated with a prominent reduction in the number of late pre-B cells, but had little effect on proliferation of early pre-B cells. Inhibition of p21ras activity markedly reduced the life span of pre-B cells, due, at least in part, to downregulation of the expression of an antiapoptotic protein, Bcl-xL. Thus, the apparent role for p21ras activity in pre-B cell survival may explain the decreased numbers of late pre-B cells in Asn-17 Ha-ras TG. Consistent with this possibility, overexpression of Bcl-2 in Asn-17 Ha-ras TG reversed the reduction in the number of late pre-B cells undergoing immunoglobulin light chain gene (IgL) rearrangement and progressing to immature B cells. These results suggest that p21ras mediates effector pathways responsible for pre-B cell survival, which is essential for progression to the late pre-B and immature B stages.
A Second Leukotriene B4 Receptor, Blt2
Authors: Yokomizo Takehiko , Kato Kazuhiko , Terawaki Kan , Izumi Takashi , Shimizu Takao
Published: July 2002

Leukotriene B4 (LTB4) is a potent chemoattractant and activator of both granulocytes and macrophages. The actions of LTB4 appear to be mediated by a specific G protein–coupled receptor (GPCR) BLT1, originally termed BLT (Yokomizo, T., T. Izumi, K. Chang, Y. Takuwa, and T. Shimizu. 1997. Nature. 387:620–624). Here, we report the molecular cloning of a novel GPCR for LTB4, designated BLT2, which binds LTB4 with a Kd value of 23 nM compared with 1.1 nM for BLT1, but still efficiently transduces intracellular signaling. BLT2 is highly homologous to BLT1, with an amino acid identity of 45.2%, and its open reading frame is located in the promoter region of the BLT1 gene. BLT2 is expressed ubiquitously, in contrast to BLT1, which is expressed predominantly in leukocytes. Chinese hamster ovary cells expressing BLT2 exhibit LTB4-induced chemotaxis, calcium mobilization, and pertussis toxin–insensitive inhibition of adenylyl cyclase. Several BLT1 antagonists, including U 75302, failed to inhibit LTB4 binding to BLT2. Thus, BLT2 is a pharmacologically distinct receptor for LTB4, and may mediate cellular functions in tissues other than leukocytes. BLT2 provides a novel target for antiinflammatory therapy and promises to expand our knowledge of LTB4 function. The location of the gene suggests shared transcriptional regulation of these two receptors.
Pathogen-specific T Regulatory 1 Cells Induced in the Respiratory Tract by a Bacterial Molecule that Stimulates Interleukin 10 Production by Dendritic Cells
Authors: McGuirk Peter , McCann Chantelle , Mills Kingston H.G.
Published: July 2002

Antigen-specific T helper type 1 (Th1) cells mediate protective immunity against a range of infectious diseases, including that caused by Bordetella pertussis. Distinct T cell subtypes that secrete interleukin (IL)-10 or tumor growth factor (TGF)-β are considered to play a role in the maintenance of self-tolerance. However, the antigens recognized by these regulatory T cells in vivo have not been defined. Here we provide the first demonstration of pathogen-specific T regulatory type 1 (Tr1) cells at the clonal level and demonstrate that these cells are induced at a mucosal surface during an infection where local Th1 responses are suppressed. Tr1 clones specific for filamentous hemagglutinin (FHA) and pertactin were generated from the lungs of mice during acute infection with B. pertussis. The Tr1 clones expressed T1/ST2 and CC chemokine receptor 5, secreted high levels of IL-10, but not IL-4 or interferon (IFN)-γ, and suppressed Th1 responses against B. pertussis or an unrelated pathogen. Furthermore, FHA inhibited IL-12 and stimulated IL-10 production by dendritic cells (DCs), and these DCs directed naive T cells into the regulatory subtype. The induction of Tr1 cells after interaction of a pathogen-derived molecule with cells of the innate immune system represents a novel strategy exploited by an infectious pathogen to subvert protective immune responses in vivo.
An Immune Evasion Mechanism for Spirochetal Persistence in Lyme Borreliosis
Authors: Liang Fang Ting , Jacobs Mary B. , Bowers Lisa C. , Philipp Mario T.
Published: July 2002

Borrelia burgdorferi, the Lyme disease spirochete, persistently infects mammalian hosts despite the development of strong humoral responses directed against the pathogen. Here we describe a novel mechanism of immune evasion by B. burgdorferi. In immunocompetent mice, spirochetes that did not express ospC (the outer-surface protein C gene) were selected within 17 d after inoculation, concomitantly with the emergence of anti-OspC antibody. Spirochetes with no detectable OspC transcript that were isolated from immunocompetent mice reexpressed ospC after they were either cultured in vitro or transplanted to naive immunocompetent mice, but not in OspC-immunized mice. B. burgdorferi persistently expressed ospC in severe combined immune-deficient (SCID) mice. Passive immunization of B. burgdorferi–infected SCID mice with an anti-OspC monoclonal antibody selectively eliminated ospC-expressing spirochetes but did not clear the infection. OspC-expressing spirochetes reappeared in SCID mice after the anti-OspC antibody was eliminated. We submit that selection of surface-antigen nonexpressers is an immune evasion mechanism that contributes to spirochetal persistence.
Altered Ionic Selectivity of the Sodium Channel Revealed by Cysteine Mutations within the Pore
Authors: Tsushima Robert G. , Li Ronald A. , Backx Peter H.
Published: July 2002

To explore the role of pore-lining amino acids in Na+ channel ion-selectivity, pore residues were  replaced serially with cysteine in cloned rat skeletal muscle Na+ channels. Ionic selectivity was determined by measuring permeability and ionic current ratios of whole-cell currents in Xenopus oocytes. The rSkM1 channels displayed an ionic selectivity sequence Na+>Li+>NH4+>>K+>>Cs+ and were impermeable to divalent cations.  Replacement of residues in domain IV showed significantly enhanced current and permeability ratios of NH4+ and K+, and negative shifts in the reversal potentials recorded in the presence of external Na+ solutions when compared to cysteine mutants in domains I, II, and III (except K1237C). Mutants in domain IV showed altered selectivity sequences: W1531C (NH4+>K+>Na+≥Li+≈Cs+), D1532C, and G1533C (Na+>Li+≥NH4+>K+>Cs+). Conservative replacement of the aromatic residue in domain IV (W1531) with phenylalanine or tyrosine retained Na+ selectivity of the channel while the alanine mutant (W1531A) reduced ion selectivity. A single mutation within the third pore forming region (K1237C) dramatically altered the selectivity sequence of the rSkM1 channel (NH4+>K+>Na+≥Li+≈Cs+) and was permeable to divalent cations having the selectivity sequence Ca2+≥Sr2+>Mg2+>Ba2+. Sulfhydryl modification of K1237C, W1531C or D1532C with methanethiosulfonate derivatives that introduce a positively charged ammonium group, large trimethylammonium moiety, or a negatively charged sulfonate group within the pore was ineffective in restoring Na+ selectivity to these channels. Selectivity of D1532C mutants could be largely restored by increasing extracellular pH suggesting altering the ionized state at this position influences selectivity. These data suggest that K1237 in domain III and W1531, D1532, and G1533 in domain IV play a critical role in determining the ionic selectivity of the Na+ channel.
An investigation of the structure near the L2,3edges of argon, the M4,5edges of krypton and the N4,5edges of xenon, using electron impact with high resolution
Authors: G C King  , M Tronc  , F H Read  , R C Bradford
Published: July 2002

The authors have investigated structure near the L2,3edges of argon, the M4,5edges of krypton and the N4,5edges of xenon, using electron impact at an incident energy of 1.5 keV and with an energy resolution of typically 70 meV. The structure observed corresponds to the promotion, via an optically allowed or optically forbidden transition, of an electron from an inner shell of the atom to an unoccupied Rydberg orbital. The energies of these excited states have been obtained, enabling the accurate determination of the Rydberg series limits. The effective quantum numbers of the excited states have been found to be closely related to those of the 'equivalent-core' atoms K I, Rb I and Cs I.
R-matrix theory of electron-molecule scattering
Authors: P G Burke  , I Mackey  , I Shimamura
Published: July 2002

A general R-matrix theory of low-energy electron scattering by diatomic molecules is developed. The theory is based on the frame-transformation approach of Chang and Fano (1972) in which different representations are used for different ranges of the electron-molecule distance coordinate. Particular emphasis is given to short distances where exchange and correlation effects between the electron and the molecule are strong, and it is shown in detail how the R matrix on the surface of this region can be expressed in terms of a multi-centre configuration-interaction wavefunction. Finally, a description is given of the numerical procedures which are used in the calculation of electron collision cross sections for an arbitrary diatomic molecule.
Vacuum-ultraviolet fluorescence under monochromatic excitation and collision processes in gaseous Kr and Xe
Authors: R Brodmann  , G Zimmerer
Published: July 2002

The vacuum-ultraviolet fluorescence of Kr and Xe and its dependence on gas pressure (10 to 500 Torr) was studied under monochromatic excitation in the vicinity of the first (3P1) and second (1P1) resonance states. For excitation synchrotron radiation was used. Excitation in the long-wavelength wing of the3P1states directly results in excited molecules (e.g. 2Kr+h(cross) omega to Kr2*). The radiative decay of these molecules results in the first (Kr: 1250 AA, Xe: 1500 AA) and second (Kr: 1470 AA, Xe: 1700 AA) continua. Under resonant3P1excitation, molecule formation via three-body collisions (e.g. Kr*+2Kr to Kr2*+Kr) is established. Excitation of1P1states results in1P1emission and the continua. The1P1emission contains molecular components. In Xe, it is strongly quenched by collisional interaction between the1P1state and a near-lying atomic p state.
The hollow cathode as a source for diatomic platinum molecules
Authors: R Scullman  , P Cederbalk
Published: July 2002

In a hollow-cathode discharge, molecules such as diatomic platinum hydride and platinum oxide have been obtained. The cathode was made of aluminium lined with a platinum foil which was sputtered by a discharge in argon gas. By studying the emission spectrum from the hollow cathode, it was found that, with oxygen in the argon, PtO was easily formed and that the experiments with PtO were easily reproducible. However, the formation of PtH and the isotopic molecule PtD was more sensitive to the experimental conditions. A new band spectrum was also observed, probably originating from the hitherto unknown molecule PtAl.
The polarization of electrons elastically scattered from xenon at energies between 150 and 1200 eV
Authors: J Kessler  , C B Lucas  , L Vuskovic
Published: July 2002

The spin polarization of electrons elastically scattered by a xenon atomic beam has been measured between scattering angles of 20 degrees and 155 degrees for electron energies of 150, 200, 300, 400, 550, 700, 900 and 1200 eV. The pressure dependence of the depolarization due to multiple scattering was investigated, and the influence of the angular resolution on the measurements is discussed. Comparison is made at all energies with Walker's calculations (1971) based on the solution of the relativistic Dirac equation with and without electron exchange. The agreement between theory and experiment is improved when exchange is fully included, but the importance of exchange decreases towards higher energies, although it makes a significant contribution at 700 eV.
Elastic scattering of electrons by molecular and atomic hydrogen
Authors: B van Wingerden  , F J de Heer  , E Weigold  , K J Nygaard
Published: July 2002

Absolute experimental cross sections are presented for elastic differential scattering of electrons by molecular hydrogen at impact energies between 100 and 2000 eV and at scattering angles between 5 and 50 degrees . The results are compared with the relative experimental cross sections of previous experiments and with the data of different theoretical calculations. Total elastic cross sections are considered as well. The present absolute molecular hydrogen cross sections, together with the 100 and 200 eV ratio measurements of the differential elastic cross sections of H2and H of Lloyd et al. (1974) were used to obtain a new set of absolute elastic cross sections for atomic hydrogen. These experimental data are compared with the absolute experimental sections obtained by Williams (1975) and with theory.
A non-perturbative open-shell theory for ionisation potential and excitation energies using HF ground state as the vacuum
Authors: A Mukhopadhyay  , R K Moitra  , D Mukherjee
Published: July 2002

The authors' recently developed (1975) non-perturbative open-shell theory is adapted for direct evaluation of ionisation potential and excitation energies. Separating the 'core' contribution from the 'valence' part through the use of a multiple-cluster-expansion operator, the method provides a systematic way of including various core-valence interaction and core relaxation components. HF orbitals have been used as the basis for facilitating detailed comparison of the method with perturbative and propagator techniques. It has been shown that the method encompasses all the important second-order contributions of the latter formalisms and certain other classes of diagrams in a compact manner. An application to a simple 4 pi electronic problem is discussed to illustrate how this method works for real systems.
MCDF calculation of argon Auger process
Authors: J Bruneau
Published: July 2002

The Auger transitions in argon are computed with a multiconfiguration Dirac-Fock (MCDF) program using Slater's transition state approximation. All the transitions are investigated with the smallest possible basis of configurations; then some of them are improved using a larger basis set. Fairly good agreement is obtained with other theoretical calculations and with experimental data.
Steady state of a laser-cooled trapped ion in the Lamb-Dicke limit
Authors: M Lindberg
Published: July 2002

The author formulates the problem of the steady state for a laser-cooled trapped ion using a generalisation of the method of moments. The problem is solved using a perturbation expansion and he obtains a steady-state solution which is exact in the Lamb-Dicke limit. The stead-state energy is compared with earlier results. The populations of the occupation number eigenstates of the harmonic trap are also obtained.
Singlet-triplet mixing in Hg 6s photoionisation via autoionising transitions
Authors: G Schonhense  , F Schafers  , Ch Heckenkamp  , U Heinzmann  , M A Baig
Published: July 2002

New experimental photoabsorption cross section and angle-resolved photoelectron spin polarisation data for mercury are presented. For the first three autoionisation resonances above the Hg 6s threshold an analysis is performed in terms of transition amplitudes to the singlet and triplet continua. These quantities reveal that photoionisation dynamics is largely influenced by a rather complicated spectral behaviour of the triplet matrix element, including three changes of sign. Results are compared with quantum defect differences and ratios of oscillator strengths from the discrete spectrum.
Relativistic perturbation theory method for investigating the radiation decay of highly excited many electron atomic states. Application to the Tm atom
Authors: E Vidolova-Angelova  , L N Ivanov  , E P Ivanova  , D A Angelov
Published: July 2002

The transition probabilities and radiation widths of the 4f136snRlR(nR=10-50, lR=0; 1) Rydberg states of the Tm atom have been calculated in the electric dipole approximation. Special attention has been paid to the manifestation of non-Coulombic properties of the Rydberg states considered. The calculation has been carried out using relativistic perturbation theory with a model zero-order approximation. The formalism of the energy approach to the atomic processes theory has been used. The contributions of the one- and two-quasiparticle effects to the complex energy matrix have evidently been taken into account. The three-quasiparticle effects have been effectively accounted for.
A molecular description of molecular collisions
Authors: J Robert  , J Baudon
Published: July 2002

A molecular description of molecular collisions is given in which Eckart coordinates are used for the nuclei and the principal inertia axes are used to define the rotating frame to which the electrons are referred. Coupled equations for the nuclear motion in the Born-Oppenheimer basis are established. Dynamical coupling terms appear as a natural generalisation of those occurring in the diatomic case. Collision channels are straightforwardly defined from the asymptotic properties. The case of reactive collisions is also examined. It is shown that binary dissociation channels correspond to a single continuum and are governed by a single vector or 'chemical pointer'.
The ionization potentials of clustered alkali metal atoms
Authors: P J Foster  , R E Leckenby  , E J Robbins
Published: July 2002

Small clusters of alkali metal atoms produced in the expansion of near-saturated vapours through a small orifice have been ionized by ultra-violet light and detected with a mass spectrometer. Ionization potentials were determined by measuring the threshold wavelength for the formation of the corresponding ion species. The experimental technique is described in detail. Results are presented for clusters of up to four atoms in sodium, potassium, caesium, a sodium/potassium mixture and for the double molecule of lithium. The values for clusters of three and four potassium and caesium atoms are the lowest of any molecular species yet reported. There are no theoretical values with which to compare these results but comparison is made with previous experimental values for double molecules. The ionization potential for clusters of three and four atoms approximates to the expected work function of a corresponding metal drop. These clusters can have a dominant effect on the electrical conductivity of a metal vapour.
Photoabsorption spectrum of atomic sulphur
Authors: Y N Joshi  , M Mazzoni  , A Nencioni  , W H Parkinson  , A Cantu
Published: July 2002

The photoabsorption spectrum of atomic sulphur was obtained in the 1220-840 AA wavelength region on a 3m normal incidence spectrograph using the flash pyrolysis technique. The previously known photoionisation cross section in the 1200-940 AA range has been extended and confirmed on the relative scale. The new discrete line absorption data have enabled the authors to extend the principal series limiting on4S to n=23. Of the seven Rydberg series limiting on2D and2P of S II reported recently, six could be identified on the plates. They have been revised and confirmed. Four additional Rydberg series limiting on2D and2P have been observed and interpreted. All lines below 1220 AA assigned to S I have been reported.
New quadrupole and forbidden lines in the L emission spectrum of neodymium 60
Authors: B G Gokhale  , S N Shukla
Published: July 2002

A detailed study, using a 40 cm curved crystal transmission (Cauchois-type) spectrograph, has revealed for the first time the existence of four new diagram lines at 1745.5 x.u., 1765.6 x.u., 1841.2 x.u. and 1994.0 x.u. in the L emission spectrum of neodymium. The lines have been ascribed, in that order, to the forbidden transition L1O1and the quadrupole transitions LINIV.V( gamma11), LIINVI.VII( gamma8') and LIIINVI.VII( beta7'). The presence of three more lines gamma4.4'(LIOII,III), eta (LIIMI) and gamma8(LiiOi) has been confirmed, the first two having been hitherto measured only by Coster and the third only by Dauvillier. The measurements of previously known dipole and quadrupole lines have been compared with those of earlier workers.
The Pople-Schofield approximation in the calculation of polarizabilities and polarization potentials
Authors: A L Sinfailam  , D G Thompson
Published: July 2002

Theory and results are given for the polarizability of the nitrogen molecule using the method introduced by Pople and Schofield. Previous work in the application of the method to atoms is discussed and it is shown shown that the method can be easily extended to provide polarization potentials of the Temkin type.
Quenching of photoluminescence of solutions by electronic excitation transfer
Authors: A Kawski  , J Kaminski  , E Kuten
Published: July 2002

Based on the shell model of a luminescent centre and on the Forster theory of intermolecular energy transfer, an expression for the decrease in sensitizer S quantum yield with increasing acceptor A concentration is derived. The dependence of the probability of resonance excitation energy transfer on mutual orientation of the transition moments of the interacting molecules S and A, as well as the fluctuations of the concentration of the acceptor molecules A was taken into account. The quenching of electronic excitation energy of fluorescein, acting as sensitizer, by rhodamine B, action as acceptor, and 2,5-diphenyloxazole by 9,10-dibromoanthracene in glycerol and cylohexane respectively, was investigated and compared with the theory. Fair agreement was found between the experimental data and the values calculated according to theoretical treatment.
Electron temperature and ionization state in laser produced plasmas
Authors: T P Donaldson  , R J Hutcheon  , M H Key
Published: July 2002

Neodymium glass laser pulses of up to 2 GW power, 10 ns duration and focused flux densities up to 2*1013W cm-2have been used to form plasmas at temperatures up to 450 eV. Plane solid plastic targets with atoms of hydrogen, nitrogen, carbon, oxygen and fluorine were used. The relation between laser flux density and electron temperature was studied and found to be of the form temperature varies as (flux density)xwhere x=0.40+or-0.05. Both the power law and absolute temperature are consistent with steady state hydrodynamical theories predicting x=4/9. Temperatures were deduced from soft X-ray continuum emission using both relative and absolute intensities. The spatial features of the X-ray emission were observed with a pinhole camera. Grazing incidence XUV photographic spectra were used to identify the highest degree of ionization in the plasma. The results were correlated with steady state and transient ionization theories and with the measured electron temperature. Satisfactory agreement was found when self-absorption of resonance radiation was taken into account.
A quantitative analysis of ion-molecule reactions occurring within the extraction orifice of a mass-spectrometric sampling probe
Authors: H Helm  , F Howorka  , F Handle  , F Egger  , W Lindinger
Published: July 2002

Ion-molecule reactions occurring within a sampling probe orifice are studied with the help of a hollow cathode discharge. The change in intensity of a particular ion due to reactions in and behind the orifice will be negligible only if the radius and the length of the opening are kept small. A relation is given for the probability of orifice reactions as a function of orifice dimensions, reaction cross section and pressure. The effect was demonstrated and the relation was studied for the reaction H2O++H2O to H3O++OH in a pure water vapour discharge and the reactions N2
++H2O to N2H++OH and N2H++H2O to H3O++N2 in a nitrogen-water vapour mixture.
Production of Lyman-α radiation in H(2S)-H2collisions
Authors: V Dose  , W Hett
Published: July 2002

Relative cross sections for the production of Lyman-alpha radiation in collisions of atomic metastable hydrogen with molecular hydrogen have been measured at twenty-five velocities between 6*105and 3*106cms-1. The measurements were carried out using time of flight techniques in combination with a recently developed target pressure modulation. Results for the Lyman-alpha emission cross section exhibit the same velocity dependence as the total destruction cross section (see abstr. A78529 of 1973) and are in complete disagreement with earlier measurements of Comes and Wenning (see abstr. A7068 of 1970).
Dissociative ionization by electron impact. III. O+, CO+and C+from CO2
Authors: A Crowe  , J W McConkey
Published: July 2002

For pt. II, see abstr. A75105 of 1973. It is demonstrated that anisotropies can exist in the angular distributions of dissociative ions produced from a polyatomic molecule by electron impact. In particular, the distributions of O+and CO+ions from CO2are found to exhibit anisotropies for incident electron energies close to their respective production thresholds. The same symmetry arguments previously used to qualitatively explain similar anisotropies in the case of diatomic molecules can also be used in this case. The C+angular distribution is found to be essentially isotropic. The cross sections for the production of CO2+, CO+, O+and C+are obtained for incident electron energies up to 300 eV. Large discrepancies exist between these cross section values and those obtained in other recent experiments. It is shown that predissociation via the C state is not a dominant mechanism for the production of fragment ions.
New electronic states of N2+
Authors: D C Cartwright  , T H Dunning Jr
Published: July 2002

Eleven new bound electronic states within 12 eV of the ground state of N2+have been identified from detailed configuration interaction calculations. Certain of the new states offer explanations for the recent photoabsorption experiments in N2.
Differential cross sections for the scattering of electrons by atomic hydrogen at intermediate energies
Authors: B H Bransden  , C J Noble
Published: July 2002

The four-state coupled-channel second-order-potential model of Bransden and Coleman (1972) is employed to calculate differential cross sections for the elastic scattering of electrons by atomic hydrogen and for the excitation of the n=2 levels, allowing comparison with recent absolute measurements by Lloyd et al. (1974), and by Williams and Willis (1975), and with other theoretical models.
On the theory of the Franz-Keldysh effect
Authors: H I Ralph
Published: July 2002

The excitonic optical absorption in the presence of a static electric field has been evaluated by solving the effective mass equation numerically. The results are compared with a previous approximate calculation and some experimental measurements. A certain degree of agreement has been found with experiment.