bluuebunny/crossref_metadata_2025 huggingface dataset:
In vitro selection of Plasmodium falciparum 3D7 for expression of variant surface antigens associated with severe malaria in African children
Authors: Staalsoe Trine , Nielsen Morten A. , Vestergaard Lasse S. , Jensen Anja T. R. , Theander Thor G. , Hviid Lars
Published: December 2003

P. falciparum‐infected red blood cells (IRBC) can adhere to endothelial host receptors through parasite‐encoded, clonally variant surface antigens (VSA). The VSA‐mediated IRBC adhesion and the acquired VSA‐specific antibody response have both been linked to IRBC organ tropism and disease severity. Parasites isolated from young children with severe malaria (SM) tend to express a limited and conserved set of VSA (VSASM) that are both stronger and more commonly recognized by IgG in the plasma of malaria‐exposed individuals than VSA (VSAUM) expressed by parasites causing uncomplicated malaria (UM) in older semi‐immune children.

Establishment of the genetic mechanism underlying changes in VSA expression in response to in vitro selective pressure is now possible because of the availability of the entire genomic sequence of the P. falciparum clone 3D7. As a first step towards direct molecular identification of VSASM‐encoding genes in 3D7, we report here a method of enforcing expression of VSASM‐like antigens in this parasite clone by a novel selection method using plasma from semi‐immune children with low VSAUM‐specific, but high VSASM‐specific, IgG reactivity. In addition to the resulting increase in VSA‐specific IgG recognition, VSASM‐expressing 3D7(3D7‐Dodowa1) showed reduced adhesion to CD36. Finally, levels of IgG specific for the VSA expressed by 3D7‐Dodowa1 were uniformly higher than those of IgG with specificity for VSA expressed by the unselected 3D7 in plasma samples from geographically and epidemiologically diverse areas of endemic parasite transmission. The described selection method appears a useful tool in the identification of genes encoding VSA involved in severe and life‐threatening P. falciparum malaria.
Humoral immune responses induced by Kudoa sp. (Myxosporea: Multivalvulida) in BALB/c mice: oral administration, immunization and cross‐reactions with Myxobolus aeglefini (Myxosporea: Bivalvulida)
Authors: Martínez De Velasco Gonzalo , Cuéllar Carmen
Published: December 2003

The majority of Kudoa species infect the somatic muscle of fish, establishing cysts. Because there is no effective method to detect infected fish without destroying them, these parasitized fish reach the consumer. The elevated humoral responses detected previously by us in BALB/c mice immunized with Kudoa sp. pseudocyst extracts showed the possible immunopathological effects in man from the ingestion of Kudoa‐infected fish. In this work, the high IgG1 and IgE levels induced by the oral administration of Kudoa pseudocysts to BALB/c mice confirmed the allergenic nature of some of their components. An alternative way of preparing the soluble extract by using a FastPrep‘ shaker indicated the inconvenience of using sonication to prepare the Kudoa sp. extract. IgG+M, IgG, IgG3 and IgA cross‐reactions of Kudoa sp. with another myxosporean, Myxobolus aeglefini, were found.
Adrenocortical hormones and interleukin patterns in leprosy
Authors: Leal Ângela M. O. , Magalhães Patrícia K. R. , Souza Cacilda S. , Foss Norma T.
Published: December 2003

The functional status of adrenocortical hormones and their relationship to the pattern of inflammatory cytokines in the lepromatous and tuberculoid poles of leprosy were investigated. Interleukin (IL)‐1β, IL‐6 and tumour necrosis factor (TNF)‐α plasma levels, C‐reactive protein (CRP) concentrations and erythrocyte sedimentation rates (ESR) were significantly higher in LL/BL (lepromatous) leprosy patients than in control subjects. There was a significant positive correlation between IL‐6 and TNF‐α plasma levels and ESR and CRP concentrations. IL‐1β was positively correlated with ESR but not with CRP. Both baseline and stimulated adrenocorticotropic hormone and cortisol plasma levels were not different between patients and control subjects. In contrast, adrenal androgen dehydroepiandrosterone sulphate (DHEA‐S) plasma levels were significantly lower in leprosy patients than in sex‐matched control subjects. There was a significant inverse correlation between DHEA‐S and IL‐6, TNF‐α, and CRP concentrations. This finding may be of pathogenetic significance in this disease and in other inflammatory states.
Factors influencing Leishmania major infection in IL‐4‐deficient BALB/c mice
Authors: Kropf P. , Herath S. , Weber V. , Modolell M. , Müller I.
Published: December 2003

The outcome of Leishmania major infection in IL‐4‐deficient BALB/c mice has been a controversial subject. We have shown that IL‐4‐deficient BALB/c mice infected with Leishmania major developed progressive lesions and could not contain the replication of the parasites, whereas other studies have reported that IL‐4‐deficient mice were able to resist infection. Therefore, we examined different factors that can influence the course of Leishmania major infection. We tested different lines of IL‐4‐deficient BALB/c mice and show that the reported differences in the outcome of infection were not due to the different genetic origin of the embryonic stem cells used to disrupt the IL‐4 gene. In addition, we infected IL‐4‐deficient mice with different isolates of L. major parasites and show that none of the parasite strains tested were cleared, although some of them caused milder pathology. Interestingly, this milder pathology was paralleled by a reduced arginase activity of the parasites. We also tested the influence of age on the course of Leishmania major infection in IL‐4‐deficient BALB/c mice and show that older mice express a transient resistance. Thus, we conclude that differences in the age of the mice and in the arginase activity of the different isolates of parasites are factors that can influence the non‐healing phenotype of IL‐4‐/‐ BALB/c mice.
Trade, Technical Change, and Labour Market Adjustment
Authors: Heitger Bernhard , Stehn Jürgen
Published: December 2003

This paper empirically examines three possible reasons for the high and rising unemployment of low‐skilled employees in Germany: (i) an upsurge in inter‐industry trade, (ii) a skill‐biased technical change, and (iii) a failure of labour market adjustment. The empirical analyses indicate that an exogenous wage‐setting process as well as a bundle of factors, including a skill‐biased technical and structural change, have contributed to the decline in relative demand for low‐skilled employees in Germany. Thus, economic policy in Germany should focus on improving the employability of workers in the lower segment of the labour market and on raising the adjustment flexibility, above all the flexibility of the wage structure, of the German labour market.
B‐cell development in the amphibian Xenopus
Authors: Du Pasquier Louis , Robert Jacques , Courtet Michèle , Mußmann Rainer
Published: December 2003

Summary: The amphibian Xenopus and mammals have similar organization and usage of their immunoglobulin gene loci with combinatorial joining of V, D and J elements. The differences in B‐cell development between mammals and this amphibian are due to major differences in developmental kinetics, cell number and lymphoid organ architecture. Unlike mammals, the immune system of Xenopus develops early under pressure to develop quickly and to produce a heterogeneous repertoire before lymphocyte numbers reach 5,000, thereby imposing a limitation on clonal amplification. In addition, it is submitted to metamorphosis. Thus, during the early antigen‐independent period, several features of B‐cell development related to immune diversification are under strict genetically preprogramed control: 1) D reading frames contribute complementary determining region 3 with features that occur in mammals by somatic selection, 2) the temporal stepwise utilization of VH genes in Xenopus occur in families probably because of structural DNA features rather than their position in the locus. Larval and adult immune responses differ in heterogeneity. Larval rearrangements lack N diversity. During the course of immune responses, somatic mutants are generated at the same rate as in other vertebrates but are not optimally selected, probably due to the simpler organization of the lymphoid organs, with neither lymph nodes nor germinal centers resulting in poor affinity maturation. Switch from IgM to other isotypes is mediated by loop‐excision deletion of the IgM constant region gene via switch regions which, unlike their mammalian counterpart, are A‐T rich and reveal conserved microsites for the breakpoints.
Early B‐lymphocyte precursors and their regulation by sex steroids
Authors: Kincade Paul W. , Medina Kay L. , Payne Kimberly J. , Rossi Maria Isabel D. , Tudor Kim‐Sue R. S. , Yamashita Yoshio , Xx Taku
Published: December 2003

Summary: This review describes an improved characterization of early B‐lymphocyte precursors in mice and the remarkable sensitivity of the same cells to hormones. The nuclear enzyme terminal deoxynucleotidyl transferase (TdT) was used as a marker to image and characterize bone marrow cells lacking all lineage‐associated markers. Most early TdT+ precursors have a distinctive density of c‐kit and express the interleukin‐7Ra chain, as well as flt‐3/flk2, but lack CD34. An understanding of those cell surface properties made it possible to obtain highly enriched, viable cells with the potential to give rise to CD19+ lymphocytes in culture. A series of other flow cytometry and culture experiments suggested a possible differentiation sequence for these early pro‐B cells. This new model was used to advantage in our studies of sex steroids. It appears that early precursors represent a hormone‐sensitive control point for determining numbers of new B lymphocytes that are produced within bone marrow. We also compare and contrast these findings with B lymphopoiesis in humans.
Transcriptional regulation of early B‐lymphocyte differentiation
Authors: O'Riordan* Mary , Grosschedl** Rudolf
Published: December 2003

Summary: Differentiation of hematopoietic progenitors into the B‐lymphocyte lineage requires co‐ordination of a complex network of transcriptional regulators. Lineage specificity is likely to result from combinatorial mechanisms of gene regulation. Four general functions are mediated by transcription factors in the differentiating pro‐B cell. First, a cascade of B‐cell‐restricted transcription factors is upregulated. Second, genes involved in the specification of other cell fates are repressed. Both activation and repression require the participation of different classes of transcriptional regulators, including proteins of the Ikaros family that can recruit chromatin‐modifying complexes. Third, the expression of genes that facilitate B‐cell proliferation and differentiation are activated. Lastly, genes required for recombination are expressed and targeted to the immunoglobulin loci, thus initiating the characteristic rearrangement of the immunoglobulin genes. The interactions and functions of transcription factors in pro‐B‐cell differentiation are discussed.
All B cells are progeny of endothelial cells: a new perspective
Authors: Nishikawa Shin‐Ichi , Fraser Stuart , Fujimoto Tetsuhiro , Endoh Mitsuhiro , Nishikawa Satomi , Ogawa Minetaro
Published: December 2003

Summary: We present here a speculative view of embryonic hematopoiesis. We do this with the hope of finding directions for future study, keeping in mind that our model may diverge from the real situation. However, we want to emphasize that previous models have neglected the possibility that endothelial cells (EC) represent a progenitor of hematopoietic cells (HPC). Emerging evidence, including our own, and previous histological studies argue for the presence of hemogenic EC. We discuss seemingly contradictory points of view of embryonic hematopoiesis, such as the origin of lymphogenic progenitors, and have shown that they may be resolved more satisfactorily by introducing this notion. Obviously, a good model should be a testable one, so we are currently developing experimental systems to demonstrate that all B cells are, indeed, the progeny of EC.
Apoptosis and its modulation during B lymphopoiesis in mouse bone marrow
Authors: Lu Liwei , Osmond Dennis G.
Published: December 2003

Summary: Studies in normal, gene‐deleted, transgenic and mutant mice have examined apoptotic cell death and its role in B lymphopoiesis in bone marrow. Apoptotic activity has been quantitated among phenotypically defined populations of precursor B cells using flow cytometry of apoptotic cells and an established model of B‐cell development. In normal mice, the frequencies of apoptotic cells (apoptotic index) and accumulation of apop­totic cells during short‐term culture (apoptotic rate) are maximal at around the pro/pre‐B‐cell transition and among immature B lymphocytes. The brief period between onset of apoptosis and clearance by macro­phages (apoptotic transit time) is similar for most precursor B‐cells. Apop­tosis‐modulating factors produce substantial changes in apoptotic activity among pro‐B and pre‐B cells, associated with altered expression of bcl‐2 family proteins. Pro‐B‐cell apoptosis, normally extensive, is markedly suppressed in the absence of p53. Complete pro‐B‐cell abortion in RAG‐2 deletion provides an assay for apoptotic fractions in other experimental systems. Pre‐B‐cell apoptosis is enhanced by deficiencies of interleukin (IL)‐7, Abl protooncogene or colony‐stimulating factor (CSF)‐1 and overexpression of heat‐stable antigen, and is inhibited by IL‐7 and p190bcr/abl transgenes. CSF‐1 and melatonin administration inhibit pre‐B‐cell apoptosis, probably via stromal cell stimulation. Such apoptotic modulation has implications for B‐cell homeostasis, quality control, immunodeficiency and neoplasia.
The chicken B‐cell receptor complex and its role in avian B‐cell development
Authors: Sayegh Camil E. , Demaries Sandra L. , Pike Kelly A. , Friedman Jennifer E. , Ratcliffe Michael J. H.
Published: December 2003

Summary: The bursa of Fabricius is critical to normal B‐lymphocyte development in birds. During embryonic life, B‐cell precursors migrate to the bursal rudiment and those which have undergone productive V(D)J recombination colonize lymphoid follicles and undergo immunoglobulin V gene diversification by gene conversion. The chicken surface IgM complex appears structurally and functionally equivalent to its mammalian counterpart, with homologs to CD79a and CD79b. Expression of a truncated Ig chain is sufficient to drive the early stages of B‐cell development in the embryo bursa. Bursal cells expressing the truncated receptor complex proliferate in bursal follicles, and those which contain V gene rearrangements undergo V gene diversification by gene conversion. The bursa is a gut‐associated organ and antigen is focused to bursal lymphoid follicles after hatch. While expression of the truncated chain is sufficient to support B‐cell development in the embryo, B cells expressing this receptor are rapidly eliminated after hatch. We suggest the possibility that B‐cell development in the bursa after hatch is driven by encounter with antigen leading to redistribution of B cells within the lymphoid follicle, B‐cell proliferation and V gene repertoire development by gene conversion.
B‐cell repertoire formation: role of the recombination signal sequence in non‐random V segment utilization
Authors: Feeney Ann J. , Tang Alan , Ogwaro Kisani M.
Published: December 2003

Summary: V, D, and J gene segments rearrange at different frequencies in vivo. Each rearranging gene segment is flanked by a recombination signal sequence (RSS), which is composed of a conserved heptamer and nona­mer, separated by a spacer of conserved length but not conserved sequence. We summarize data from our lab and other labs showing that in many cases, but not all, the RSS can account for differences in recombination frequencies observed in vivo. Our approach is to determine the initial frequency of rearrangement of the V genes in vivo, and then place the RSSs of two V genes into a competition recombination substrate to determine the relative frequency with which the two RSSs support recombination. In one example, we have shown that a polymorphism in the heptamer of a Vk gene can result in a significant reduction in recombination frequency. This particular allele is prevalent in Navajos and absent in other populations. We suggest that this single change may play a major role in the high susceptibility of Navajos to Haemophilus influenzae infection, since this Vk gene is important in the antibody response to this bacteria. We also describe experiments showing that the sequence of the spacer of the RSS can play an important role in relative recombination frequencies.
Pre‐B and pre‐T‐cell receptors: conservation of strategies in regulating early lymphocyte development
Authors: Muljo Stefan A , Schlissel Mark S.
Published: December 2003

Summary: Early lymphocyte development is characterized by the regulated activity of the V(D)J recombinase and the positive and negative selection of cells based on the structure of their assembled antigen receptor genes. Developing B and T cells use remarkably similar signaling complexes, the pre‐B‐cell receptor (pre‐BCR) and the pre‐T‐cell receptor (pre‐TCR) respectively, to monitor the progress of antigen receptor gene assembly. This review will compare and contrast the regulation and activities of the pre‐BCR and pre‐TCR signaling complexes. In addition, we will consider a number of critical but as yet unanswered questions prompted by such an analysis.
Repertoire selection by pre‐B‐cell receptors and B‐cell receptors, and genetic control of B‐cell development from immature to mature B cells
Authors: Melchers Fritz , Ten Boekel Edwin , Seidl Thomas , Kong Xian Chu , Yamagami Tamotsu , Onishi Kazuo , Shimizu Takeyuki , Rolink Antonius G. , Andersson Jan
Published: December 2003

Summary: During B‐cell development the surrogate light (SL) chain is selectively expressed in progenitor and precursor B cells during the developmental stages of DH to JH and VH to DH JH rearrangements. Approximately half of all H chains produced by these rearrangements cannot pair with SL chains and cannot form a pre‐B‐cell receptor (pre‐BCR). A spectrum of affinities between VpreB and individual VH domains generates preB cells with pre‐BCR of different fitness which, in turn, determines the extent of the pre‐B II‐cell proliferation and the fidelity of allelic exclusion of the H chain locus. Once pre‐BCR is expressed, SL chain expression is turned off. As pre‐B II cells proliferate, SL is diluted out, thus limiting pre‐BCR formation. As a consequence, pre‐B II cells stop proliferating, become small and resting and begin to rearrange the L chain loci. Multiple rearrangements of the k L chain alleles are often detected in wild‐type small pre‐B II cells. Around 20% of the H chain‐expressing small pre‐B II cells also express L chains but do not display the Ig on the surface. Hence, it is likely that not all L chains originally generated in resting pre‐B II cells can pair with the H chain previously present in that cell. The best fitting ones are selected preferentially to generate sIg+ B cells. Furthermore, the transition of immature B cells from the bone marrow to spleen and their development to mature cells appear as two separate steps controlled by different genes.
The role of the preBCR, the interleukin‐7 receptor, and homotypic interactions during B‐cell development
Authors: Stoddart Angela , Fleming Heather E. , Paige Christopher J.
Published: December 2003

Summary: Considerable progress has been made in defining intermediate stages in the process leading from stem cells to mature B cells. Cell‐bound and secreted molecules direct the progression through these stages and regulate the selection of clones from which the immune repertoire emerges. In fact, a myriad of signals derived from B‐cell progenitors themselves and the microenvironment in which they develop direct the differentiation process. These signals are provided by B‐cell antigen receptors (BCR) and their surrogates, and by adhesion and cytokine receptors. The co‐operation of these receptors to control survival, expansion, and differentiation of early B‐cell progenitors is the topic of this review. Specifically, we will summarize recent findings from our laboratory demonstrating that preBCR expression lowers the threshold for interleukin (IL)‐7 responsiveness. How signals initiated by these receptors may intersect at this critical point of B‐cell selection will be discussed. At the stage following IL‐7 responsiveness we have shown that interactions between B‐cell progenitors themselves promote their differentiation to immunoglobulin‐secreting B cells. We propose that one function of stromal cells, known to be central to B lymphopoiesis, is to promote critical preB–preB homotypic interactions and ensuing signals.
Microenvironmental influences on human B‐cell development
Authors: Bertrand F. E. , Eckfeldt C. E. , Fink J. R. , Lysholm A. S. , Pribyl J. A. R. , Shah N. , LeBien T. W.
Published: December 2003

Summary: Mammalian B‐cell development can be viewed as a developmental performance with several acts. The acts are represented by checkpoints centered around commitment to the B‐lineage and functional Ig gene rearrangement – culminating in expression of the pre‐B‐cell receptor (pre‐BCR) and the BCR. Progression of cells through these checkpoints is profoundly influenced by the fetal liver and adult bone marrow (BM) stromal cell microenvironments. Our laboratory has developed a model of human B‐cell development that utilizes freshly isolated/non‐transformed human BM stromal cells as an in vitro microenvironment. Human CD34+ hematopoietic stem cells plated in this human BM stromal cell microenvironment commit to the B lineage and progress through the pre‐BCR and BCR checkpoints. This human BM stromal cell microenvironment also provides survival signals that prevent apoptosis in human B‐lineage cells. Human B‐lineage cells exhibit differential expression of Notch receptors and human BM stromal cells express the Notch ligand Jagged‐1. These results suggest a potential role for Notch in regulating B‐lineage commitment and/or progression through the pre‐BCR and BCR checkpoints.
E2A proteins: essential regulators at multiple stages of B‐cell development
Authors: Kee Barbara L. , Quong Melanie W. , Murre Cornelis
Published: December 2003

Summary: The development of mature B lymphocytes from multipotent progenitor cells requires the co‐ordinated activities of a number of trans­criptional regulatory proteins. The transcription factors encoded by the E2A gene are required for the development of committed B‐lineage cells and regulate the expression of essential B‐lineage genes at multiple stages of differentiation and activation. In this review we discuss the evidence that the E2A gene products function in the regulation of 1) transcription factors required for B‐lineage determination, 2) essential proteins involved in pro‐B and pre‐B‐cell development, 3) accessibilty and recombination of the IgH and IgL chain loci, and 4) isotype switching in activated, mature B lymphocytes.
B‐cell subsets and the mature ­preimmune repertoire. Marginal zone and B1 B cells as part of a “natural immune memory”
Authors: Martin Flavius , Kearney John F.
Published: December 2003

Summary: The rate of elimination of a pathogenic agent is of critical importance for the host and determines the extent and consequences of the infection. Antibody production, along with the activity of other cells of the immune system, plays an important role early and late in the response and contributes to all containment and elimination of the organism. B‐cell clones reaching the mature long‐lived pool are heterogeneous: some belong to the B1 B‐cell subset, some are enriched in the CD21high compartment (mostly marginal zone (MZ)), whereas others recirculate primarily among the B‐cell follicles (FO). This segregation is a T‐independent, CD40L‐independent but BCR/CD19‐dependent process. Antigen encounter will recruit antigen‐specific cells from the pool of mature B‐lymphocytes and activate them to perform effector functions. CD21highCD23low B cells enriched in the MZ of the spleen initiate the early plasmablast wave during the first 3 days of an antibody response against particulate T‐independent bacterial antigens. These findings indicate a functional heterogeneity within the mature B‐lymphocyte population. MZ B cells and B1 B, in contrast to FO B cells, have the unique capacity to generate effector cells in early stages of the immune response against (particulate) antigens that are scavenged efficiently in these specialized anatomical sites.
Development of the antibody repertoire in rabbit: gut‐associated lymphoid tissue, microbes, and selection
Authors: Lanning Dennis , Zhu Xiaocui , Zhai Shi‐Kang , Knight Katherine L.
Published: December 2003

Summary: Rabbits generate their antibody repertoire in three stages. First, a neonatal repertoire is generated by B lymphopoiesis in fetal liver and bone marrow and is limited by preferential VH gene segment usage. Between 4 and 8 weeks after birth a complex primary antibody repertoire is developed by somatically diversifying the neonatal repertoire through somatic hypermutation and a somatic gene conversion‐like mechanism in gut‐associated lymphoid tissue (GALT). In rabbits, unlike other species, the development of the primary antibody repertoire through somatic diversification of Ig genes appears to be dependent on intestinal microbial flora. The primary antibody repertoire is subsequently modified during antigen‐dependent immune responses in which VDJ genes further diversify both by somatic hypermutation and by a gene conversion‐like mechanism (the secondary repertoire). During the various stages of development, the antibody repertoire is modified and shaped by selective processes. In this review, we discuss the roles of GALT, microbes, and B‐cell selection in generating antibody diversity in rabbits.
B‐cell commitment, development and selection
Authors: Hardy Richard R. , Li Yue‐Sheng , Allman David , Asano Masanao , Gui Ming , Hayakawa Kyoko
Published: December 2003

Summary: Here we review three areas in B‐cell development in the mouse, with a focus on relevance to B‐1/CD5+ B cells. Multiparameter flow cytometry has allowed the dissection of intermediate stages of developing B cells, both in fetal liver and bone marrow. In the first area, we present recent work that has delineated a fraction of pre‐pro‐B cells, committed to the B lineage, but lacking any immunoglobulin rearrangements. Next, the role of the pre‐B‐cell receptor in B‐cell repertoire selection has become clear in the past few years, but we present work suggesting that the action of this process during fetal life is different, resulting in selection of a very distinct repertoire compared with adult. Finally, we describe a new VH3609 antithymocyte Ig transgenic mouse model system that has provided the first definitive evidence for the role of self‐antigen in development and maintenance of natural autoreactive B cells.
Terminal deoxynucleotidyl transferase and repertoire development
Authors: Benedict Cindy L. , Gilfillan Susan , Thai To‐Ha , Kearney John F.
Published: December 2003

Summary: In mice, the absence of terminal deoxynucleotidyl transferase (Tdt) expression during fetal and neonatal life provides a window in development where clones of lymphocytes are generated that provide protective immunity. Introducing premature Tdt activity interferes with the development of these clones and results in an impaired ability to make protective antibodies. Conversely, gene‐targeted disruption of Tdt prevents N additions at all stages of T and B‐lymphocyte development and promotes the development of fetal‐like T and B‐cell clones into adulthood, with accompanying alterations in repertoire. The alternative splice forms of Tdt may be necessary to provide regulatory mechanisms to restrict N addition to appropriate stages of the developmental pathways, the details of which are being revealed. The evidence continues to build that Tdt is a key player in influencing the outcome of V(D)J recombination during lymphocyte and repertoire development.
B‐1 cells: the lineage question revisited
Authors: Herzenberg Leonore A.
Published: December 2003

Summary: The origins and functions of B‐1 cells have sparked a good deal of controversy, largely centered on whether these B cells are developmentally distinct from the principal B cell populations (B‐2) found in peripheral lymphoid organs. However, the prime criteria for assigning B‐1 and B‐2 cells to separate developmental lineages are satisfied by studies published some time ago that 1) identify distinct sources of progenitors for B‐1 and B‐2 cells; 2) show that these progenitors express their inherent commitment developing under the same conditions in co‐transfer recipients; and, 3) have distinctive developmental patterns revealed by analysis of cells at various stages along the B‐cell development pathway. I review these developmental studies here both to clarify the issue and to set the stage for presentation of evidence from more recent studies, which further define the functional differences between B‐1 and B‐2 cells and reveal intriguing complexities in the selective and other mechanisms that control the VH composition of the B‐1 antibody repertoire.
Heat Transfer Enhancement in Square Ducts With V-Shaped Ribs
Authors: Jia, Rongguang , Saidi, and Arash , Sunden Bengt
Published: December 2003

This paper concerns a numerical investigation of the heat and fluid flow in V-shaped ribbed ducts. The Navier-Stokes equations and the energy equation are solved in conjunction with a low Reynolds number k–ε turbulence model. The Reynolds turbulent stresses are computed with an explicit algebraic stress model (EASM) while the turbulent heat fluxes are calculated with a simple eddy diffusivity model (SED). Detailed velocity and thermal field results have been used to explain the effects of the V-shaped ribs and the mechanisms of the heat transfer enhancement.
Heat Transfer Coefficients and Film Cooling Effectiveness on the Squealer Tip of a Gas Turbine Blade
Authors: Kwak Jae Su , Han Je-Chin
Published: December 2003

Experimental investigations were performed to measure the detailed heat transfer coefficients and film cooling effectiveness on the squealer tip of a gas turbine blade in a five-bladed linear cascade. The blade was a two-dimensional model of a first stage gas turbine rotor blade with a profile of the GE-E3 aircraft gas turbine engine rotor blade. The test blade had a squealer (recessed) tip with a 4.22% recess. The blade model was equipped with a single row of film cooling holes on the pressure side near the tip region and the tip surface along the camber line. Hue detection based transient liquid crystals technique was used to measure heat transfer coefficients and film cooling effectiveness. All measurements were done for the three tip gap clearances of 1.0%, 1.5%, and 2.5% of blade span at the two blowing ratios of 1.0 and 2.0. The Reynolds number based on cascade exit velocity and axial chord length was 1.1×106 and the total turning angle of the blade was 97.9 deg. The overall pressure ratio was 1.2 and the inlet and exit Mach numbers were 0.25 and 0.59, respectively. The turbulence intensity level at the cascade inlet was 9.7%. Results showed that the overall heat transfer coefficients increased with increasing tip gap clearance, but decreased with increasing blowing ratio. However, the overall film cooling effectiveness increased with increasing blowing ratio. Results also showed that the overall film cooling effectiveness increased but heat transfer coefficients decreased for the squealer tip when compared to the plane tip at the same tip gap clearance and blowing ratio conditions.
Large Eddy Simulation of Film Cooling Flow From an Inclined Cylindrical Jet
Authors: Tyagi Mayank , Acharya Sumanta
Published: December 2003

Predictions of turbine blade film cooling have traditionally employed Reynolds-averaged Navier-Stokes solvers and two-equation models for turbulence. Evaluation of several versions of such models have revealed that the existing two-equation models fail to resolve the anisotropy and the dynamics of the highly complex flow field created by the jet-crossflow interaction. A more accurate prediction of the flow field can be obtained from large eddy simulations (LES) where the dynamics of the larger scales in the flow are directly resolved. In the present paper, such an approach has been used, and results are presented for a row of inclined cylindrical holes at blowing ratios of 0.5 and 1 and Reynolds numbers of 11,100 and 22,200, respectively, based on the jet velocity and hole diameter. Comparison of the time-averaged LES predictions with the flow measurements of Lavrich and Chiappetta (UTRC Report No. 90-04) shows that LES is able to predict the flow field with reasonable accuracy. The unsteady three-dimensional flow field is shown to be dominated by packets of hairpin-shaped vortices. The dynamics of the hairpin vortices in the wake region of the injected jet and their influence on the unsteady wall heat transfer are presented. Generation of “hot spots” and their migration on the film-cooled surface are associated with the entrainment induced by the hairpin structures. Several geometric properties of a “mixing interface” around hairpin coherent structures are presented to illustrate and quantify their impact on the entrainment rates and mixing processes in the wake region.
Nitrogen Control of Atrazine Utilization in
Pseudomonas
sp. StrainADP
Authors: García-González Vicente , Govantes Fernando , Shaw Liz J. , Burns Richard G. , Santero Eduardo
Published: December 2003

Pseudomonas
sp. strain ADP uses the herbicide atrazine as the sole nitrogen source.
We have devised a simple atrazine degradation assay to determine the
effect of other nitrogen sources on the atrazine degradation pathway.
The atrazine degradation rate was greatly decreased in cells grown on
nitrogen sources that support rapid growth of
Pseudomonas
sp.
strain ADP compared to cells cultivated on growth-limiting nitrogen
sources. The presence of atrazine in addition to the nitrogen sources
did not stimulate degradation. High degradation rates obtained in the
presence of ammonium plus the glutamine synthetase inhibitor MSX and
also with an Nas
−
mutant derivative grown on nitrate
suggest that nitrogen regulation operates by sensing intracellular
levels of some key nitrogen-containing metabolite. Nitrate amendment in
soil microcosms resulted in decreased atrazine mineralization by the
wild-type strain but not by the Nas
−
mutant. This
suggests that, although nitrogen repression of the atrazine catabolic
pathway may have a strong impact on atrazine biodegradation in
nitrogen-fertilized soils, the use of selected mutant variants may
contribute to overcoming this
limitation.
Useof Borate To Control the 5′-Position-Selective MicrobialGlucosylation ofPyridoxine
Authors: Wada Koichi , Asano Yasuhisa
Published: December 2003

Nearly
100% 5′-position selectivity of transglucosylation from
maltodextrin to pyridoxine (PN) by cells of
Verticillium
dahliae
TPU 4900 was observed when the reaction was carried out
with borate. The same effect of borate was observed not only during
synthesis of pyridoxine 5′-α-
d
-glucoside by
partially purified enzyme of this strain but also during synthesis of
this compound by other microorganisms and with other enzymes
(α-glucosidase and cyclomaltodextrin glucanotransferase). The
effect was thought to be caused by the formation of a borate complex
with 3- and 4′-position hydroxyl groups of PN. A decrease in
the formation of pyridoxine 5′-α-
d
-glucoside
was observed in the reaction with borate, but this decrease was
overcome by optimizing the pH and increasing the amount of cells in the
reaction
mixture.
Diversity of Bacteria Associated with Natural AphidPopulations
Authors: Haynes S. , Darby A. C. , Daniell T. J. , Webster G. , van Veen F. J. F. , Godfray H.C.J. , Prosser J. I. , Douglas A. E.
Published: December 2003

The bacterial communities of aphids were investigated by terminal restriction fragment length polymorphism and denaturing gradient gel electrophoresis analysis of 16S rRNA gene fragments generated by PCR with general eubacterial primers. By both methods, theγ -proteobacteriumBuchnerawas detected in laboratory cultures of six parthenogenetic lines of the pea aphidAcyrthosiphon pisumand one line of the black bean aphidAphis fabae, and one or more of four previously described bacterial taxa were also detected in all aphid lines except one ofA. pisum. These latter bacteria, collectively known as secondary symbionts or accessory bacteria, comprised three taxa of γ-proteobacteria (R-type [PASS], T-type [PABS], and U-type [PAUS]) and a rickettsia (S-type [PAR]). Complementary analysis of aphids from natural populations of four aphid species (A. pisum[n= 74],Amphorophora rubi[n= 109],Aphis sarothamni[n= 42], andMicrolophium carnosum[n= 101]) from a single geographical location revealedBuchneraand up to three taxa of accessory bacteria, but no other bacterial taxa, in each aphid. The prevalence of accessory bacterial taxa varied significantly among aphid species but not with the sampling month (between June and August 2000). These results indicate that the accessory bacterial taxa are distributed across multiple aphid species, although with variable prevalence, and that laboratory culture does not generally result in a shift in the bacterial community in aphids. Both the transmission patterns of the accessory bacteria between individual aphids and their impact on aphid fitness are suggested to influence the prevalence of accessory bacterial taxa in natural aphid populations.
Specific and Sensitive Detection of
Ralstoniasolanacearum
in Soil on the Basis of PCR Amplification of
fliC
Fragments
Authors: Schönfeld J. , Heuer H. , van Elsas J. D. , Smalla K.
Published: December 2003

Ralstonia
solanacearum
is the causative agent of bacterial wilt in many
important crops. A specific and sensitive PCR detection method that
uses primers targeting the gene coding for the flagella subunit,
fliC
, was established. Based on the first
fliC
gene
sequence of
R. solanacearum
strain K60 available at GenBank,
the Ral_
fliC
PCR primer system was designed; this
system yielded a single 724-bp product with the DNAs of all of the
R. solanacearum
strains tested. However,
R. pickettii
and four environmental
Ralstonia
isolates also yielded
amplicons. The Ral_
fliC
PCR products obtained with 12
strains (
R. solanacearum
,
R. pickettii
, and
environmental isolates) were sequenced. By sequence alignment,
Rsol_
fliC
primers specific for
R.
solanacearum
were designed. With this primer system, a specific
400-bp PCR product was obtained from all 82 strains of
R.
solanacearum
tested. Six strains of
R. pickettii
and
several closely related environmental isolates yielded no PCR product;
however, a product was obtained with one
Pseudomonas syzygii
strain. A GC-clamped 400-bp
fliC
product could be
separated in denaturing gradient gels and allowed us to distinguish
P. syzygii
from
R. solanacearum
. The
Rsol_
fliC
PCR system was applied to detect
R.
solanacearum
in soil. PCR amplification, followed by Southern blot
hybridization, allowed us to detect about one target DNA molecule per
PCR, which is equivalent to 10
3
CFU g of bulk
soil
−1
. The system was applied to survey soils from
different geographic origins for the presence of
R.
solanacearum
.
Variation in Biofilm Formation among Strains of
Listeriamonocytogenes
Authors: Borucki Monica K. , Peppin Jason D. , White David , Loge Frank , Call Douglas R.
Published: December 2003

Contamination
of food by
Listeria monocytogenes
is thought to occur most
frequently in food-processing environments where cells persist due to
their ability to attach to stainless steel and other surfaces. Once
attached these cells may produce multicellular biofilms that are
resistant to disinfection and from which cells can become detached and
contaminate food products. Because there is a correlation between
virulence and serotype (and thus phylogenetic division) of
L.
monocytogenes
, it is important to determine if there is a link
between biofilm formation and disease incidence for
L.
monocytogenes
. Eighty
L. monocytogenes
isolates were
screened for biofilm formation to determine if there is a robust
relationship between biofilm formation, phylogenic division, and
persistence in the environment. Statistically significant differences
were detected between phylogenetic divisions. Increased biofilm
formation was observed in Division II strains (serotypes 1/2a and
1/2c), which are not normally associated with food-borne outbreaks.
Differences in biofilm formation were also detected between persistent
and nonpersistent strains isolated from bulk milk samples, with
persistent strains showing increased biofilm formation relative to
nonpersistent strains. There were no significant differences detected
among serotypes. Exopolysaccharide production correlated with cell
adherence for high-biofilm-producing strains. Scanning electron
microscopy showed that a high-biofilm-forming strain produced a dense,
three-dimensional structure, whereas a low-biofilm-forming strain
produced a thin, patchy biofilm. These data are consistent with data on
persistent strains forming biofilms but do not support a consistent
relationship between enhanced biofilm formation and disease
incidence.
Comparative Sequence Analysis of the
tuf
and
recA
Genes and Restriction Fragment Length Polymorphism of the Internal Transcribed Spacer Region Sequences Supply Additional Tools for Discriminating
Bifidobacterium lactis
from
Bifidobacterium animalis
Authors: Ventura Marco , Zink Ralf
Published: December 2003

The
relationship between
Bifidobacterium lactis
and
Bifidobacterium animalis
was examined by comparative analysis
of
tuf
and
recA
gene sequences and by restriction
fragment length polymorphism analysis of their internal 16S-23S
transcribed spacer region sequences. The bifidobacterial strains
investigated could be divided into two distinct groups within a single
species based on the
tuf
,
recA
, and 16S-23S spacer
region sequence analysis. Therefore, all strains of
B. lactis
and
B. animalis
could be unified as the species
B.
animalis
and divided into two subspecies,
Bifidobacterium
animalis
subsp.
lactis
and
Bifidobacterium
animalis
subsp.
animalis
.
Effect of smokeless tobacco (snus) on smoking and public health in Sweden
Authors: Foulds J , Ramstrom L , Burke M , Fagerström K
Published: December 2003

Objective:To review the evidence on the effects of moist smokeless tobacco (snus) on smoking and ill health in Sweden.

Method:Narrative review of published papers and other data sources (for example, conference abstracts and internet based information) on snus use, use of other tobacco products, and changes in health status in Sweden.

Results:Snus is manufactured and stored in a manner that causes it to deliver lower concentrations of some harmful chemicals than other tobacco products, although it can deliver high doses of nicotine. It is dependence forming, but does not appear to cause cancer or respiratory diseases. It may cause a slight increase in cardiovascular risks and is likely to be harmful to the unborn fetus, although these risks are lower than those caused by smoking. There has been a larger drop in male daily smoking (from 40% in 1976 to 15% in 2002) than female daily smoking (34% in 1976 to 20% in 2002) in Sweden, with a substantial proportion (around 30%) of male ex-smokers using snus when quitting smoking. Over the same time period, rates of lung cancer and myocardial infarction have dropped significantly faster among Swedish men than women and remain at low levels as compared with other developed countries with a long history of tobacco use.

Conclusions:Snus availability in Sweden appears to have contributed to the unusually low rates of smoking among Swedish men by helping them transfer to a notably less harmful form of nicotine dependence.
No association of smoke-free ordinances with profits from bingo and charitable games in Massachusetts
Authors: Glantz S A , Wilson-Loots R
Published: December 2003

Background:Because it is widely played, claims that smoking restrictions will adversely affect bingo games is used as an argument against these policies. We used publicly available data from Massachusetts to assess the impact of 100% smoke-free ordinances on profits from bingo and other gambling sponsored by charitable organisations between 1985 and 2001.

Methods:We conducted two analyses: (1) a general linear model implementation of a time series analysis with net profits (adjusted to 2001 dollars) as the dependent variable, and community (as a fixed effect), year, lagged net profits, and the length of time the ordinance had been in force as the independent variables; (2) multiple linear regression of total state profits against time, lagged profits, and the percentage of the entire state population in communities that allow charitable gaming but prohibit smoking.

Results:The general linear model analysis of data from individual communities showed that, while adjusted profits fell over time, this effect was not related to the presence of an ordinance. The analysis in terms of the fraction of the population living in communities with ordinances yielded the same result.

Conclusion:Policymakers can implement smoke-free policies without concern that these policies will affect charitable gaming.
Tobacco use in India: prevalence and predictors of smoking and chewing in a national cross sectional household survey
Authors: Rani M , Bonu S , Jha P , Nguyen S N , Jamjoum L
Published: December 2003

Objective:To estimate the prevalence and the socioeconomic and demographic correlates of tobacco consumption in India.

Design:Cross sectional, nationally representative population based household survey.

Subjects:315 598 individuals 15 years or older from 91 196 households were sampled in National Family Health Survey-2 (1998–99). Data on tobacco consumption were elicited from household informants.

Measures and methods:Prevalence of current smoking and current chewing of tobacco were used as outcome measures. Simple and two way cross tabulations and multivariate logistic regression analysis were the main analytical methods.

Results:Thirty per cent of the population 15 years or older—47% men and 14% of women—either smoked or chewed tobacco, which translates to almost 195 million people—154 million men and 41million women in India. However, the prevalence may be underestimated by almost 11% and 1.5% for chewing tobacco among men and women, respectively, and by 5% and 0.5% for smoking among men and women, respectively, because of use of household informants. Tobacco consumption was significantly higher in poor, less educated, scheduled castes and scheduled tribe populations. The prevalence of tobacco consumption increased up to the age of 50 years and then levelled or declined. The prevalence of smoking and chewing also varied widely between different states and had a strong association with individual’s sociocultural characteristics.

Conclusion:The findings of the study highlight that an agenda to improve health outcomes among the poor in India must include effective interventions to control tobacco use. Failure to do so would most likely result in doubling the burden of diseases—both communicable and non-communicable—among India’s teeming poor. There is a need for periodical surveys using more consistent definitions of tobacco use and eliciting information on different types of tobacco consumed. The study also suggests a need to adjust the prevalence estimates based on household informants