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Biomedical subjects

L Davidson

Publications and source records attributed to L Davidson.

At least 73 records · Page 4Linked to original sources
PubMed1998

Ku70 is required for late B cell development and immunoglobulin heavy chain class switching.

Immunoglobulin (Ig) heavy chain (HC) class switch recombination (CSR) is a late B cell process that involves intrachromosomal DNA rearrangement. Ku70 and Ku80 form a DNA end-binding complex required for DNA double strand break repair and V(D)J recombination. Ku70(-/-) (K70T) mice, like recombination activating gene (RAG)-1- or RAG-2-deficient (R1T or R2T) mice, have impaired B and T cell development at an early progenitor stage, which is thought to result at least in part from defective V(D)J recombination (Gu, Y., K.J. Seidl, G.A. Rathbun, C. Zhu, J.P. Manis, N. van der Stoep, L. Davidson, H.L. Cheng, J.M. Sekiguchi, K. Frank, et al. 1997. Immunity. 7:653-665; Ouyang, H., A. Nussenzweig, A. Kurimasa, V.C. Soares, X. Li, C. Cordon-Cardo, W. Li, N. Cheong, M. Nussenzweig, G. Iliakis, et al. 1997. J. Exp. Med. 186:921-929). Therefore, to examine the potential role of Ku70 in CSR, we generated K70T mice that carry a germline Ig HC locus in which the JH region was replaced with a functionally rearranged VH(D)JH and Ig lambda light chain transgene (referred to as K70T/HL mice). Previously, we have shown that B cells from R1T or R2T mice carrying these rearranged Ig genes (R1T/HL or R2T/HL mice) can undergo CSR to IgG isotypes (Lansford, R., J. Manis, E. Sonoda, K. Rajewsky, and F. Alt. 1998. Int. Immunol. 10:325-332). K70T/HL mice had significant numbers of peripheral surface IgM+ B cells, which generated serum IgM levels similar to those of R2T/HL mice. However, in contrast to R2T/HL mice, K70T/HL mice had no detectable serum IgG isotypes. In vitro culture of K70T/HL B cells with agents that induce CSR in normal or R2T/HL B cells did lead to the induction of germline CH transcripts, indicating that initial signaling pathways for CSR were intact in K70T/HL cells. However, treatment with such agents did not lead to detectable CSR by K70T/HL B cells, and instead, led to cell death within 72 h. We conclude that Ku70 is required for the generation of B cells that have undergone Ig HC class switching. Potential roles for Ku70 in the CSR process are discussed.

Animals↗
PubMed1998

Defects in actin-cap formation in Vav-deficient mice implicate an actin requirement for lymphocyte signal transduction.

BACKGROUND: Antigen-receptor interactions on lymphocytes result in local clustering of actin, receptors and signaling molecules into an asymmetric membrane structure termed a cap. Although actin polymerization is known to be required, the mechanisms underlying cap formation are unclear. We have studied the events underlying cap formation using mice bearing a null mutation in vav (vav-/-), a gene that encodes a guanine-nucleotide exchange factor for the GTPase Rac. RESULTS: Lymphocytes from vav-/- mice failed to form T-cell receptor caps following activation and had a defective actin cytoskeleton. The vav-/- T cells were deficient in interleukin-2 (IL-2) production and proliferation, and the peak of Ca2+ mobilization was reduced although of normal duration. Activation of Jun N-terminal kinase or stress-activated kinase (JNK or SAPK) and mitogen-activated protein kinase (MAPK) and the induction of the transcription factor NF-ATc1 and egr-1 genes was normal. Despite the reduced Ca2+ mobilization, translocation of cytoplasmic NF-ATc to the nucleus was normal, reflecting that the lower levels of Ca2+ in vav-/- cells were still sufficient to activate calcineurin. Treatment of lymphocytes with cytochalasin D, which blocks actin polymerization, inhibited cap formation and produced defects in signaling and IL-2 transcriptional induction in response to antigen-receptor signaling that were nearly identical to those seen in vav-/- cells. In transfection studies, either constitutively active Vav or Rac could complement constitutively active calcineurin to activate NF-AT-dependent transcription. CONCLUSIONS: These results indicate that Vav is required for cap formation in lymphocytes. Furthermore, the correlation between cap formation, IL-2 production and proliferation supports the hypothesis that an actin-dependent pathway is a source of specialized growth regulatory signals.

Actins↗
PubMed1998

Is a mandatory general surgery rotation necessary in the surgical clerkship?

BACKGROUND: Changes in the spectrum of general surgery and the delivery of surgical care have placed the requirement for a mandatory general surgery rotation in the surgical clerkship in question. METHODS: We tested the hypothesis that equal mastery of surgical clerkship objectives can be obtained in a clerkship with and without general surgery. Students chose any two surgical rotations and were assessed by written examination, objective structured clinical examination (OSCE), ward evaluations, self-assessment objectives questionnaire, and satisfaction survey. RESULTS: Data for 54 students showed no differences in scores between groups on any parameter. No specific concerns related to the absence of general surgery were identified. CONCLUSIONS: Effective undergraduate surgical education can be offered in many specialty settings. Removal of the requirement for general surgery in clerkship may lead to a more effective use of all educational opportunities. A careful analysis of local programs and facilities is necessary before suggesting this change to other institutions.

Attitude↗
PubMed1998

Delayed lymphoid repopulation with defects in IL-4-driven responses produced by inactivation of NF-ATc.

The NF-AT family of transcription factors activates early immune response genes such as cytokines. In the adult, NF-ATc is expressed exclusively in the lymphoid system and is induced upon lymphocyte activation. NF-ATc null mutant mice die in utero of cardiac failure, precluding analysis of the role of NF-ATc in lymphocyte activation. By using RAG-2-deficient blastocyst complementation, we now demonstrate that young, highly chimeric mice lacking NF-ATc have impaired repopulation of both thymus and peripheral lymphoid organs. Furthermore, NF-ATc deficiency impaired T lymphocyte activation and secretion of IL-4. B lymphocytes displayed reduced proliferation and a selective loss of IL-4-driven immunoglobulin isotypes both in vivo and in vitro. Our data demonstrate that NF-ATc is essential for the optimal generation and function of mature T and B lineage cells, with an especially profound effect on IL-4-driven responses.

Alleles↗
PubMed1998

SEK1/MKK4 is required for maintenance of a normal peripheral lymphoid compartment but not for lymphocyte development.

SAPK is a member of the group of evolutionary conserved stress-activated kinases that mediate control of cellular death and proliferation. In lymphocytes, the SAPK pathway has been implicated in signaling from antigen, costimulatory, and death receptors; SEK1, which directly activates SAPK, is required for early embryonic development and has also been reported to be essential for normal lymphocyte development. In contrast to the latter findings, we have used RAG-2-deficient blastocyst complementation to show that SEK1-deficient embryonic stem cells support unimpaired T and B lymphocyte development. Moreover, mature SEK1-deficient lymphocytes are capable of SAPK activation. Surprisingly, however, aging SEK1-deficient chimeric mice frequently develop lymphadenopathy and polyclonal B and T cell expansions. Thus, SEK1 is not required for lymphocyte development, but is required for maintaining peripheral lymphoid homeostasis.

Animals↗
PubMed1998

Wiskott-Aldrich syndrome protein-deficient mice reveal a role for WASP in T but not B cell activation.

The Wiskott-Aldrich syndrome (WAS) is a human X-linked immunodeficiency resulting from mutations in a gene (WASP) encoding a cytoplasmic protein implicated in regulating the actin cytoskeleton. To elucidate WASP function, we disrupted the WASP gene in mice by gene-targeted mutation. WASP-deficient mice showed apparently normal lymphocyte development, normal serum immunoglobulin levels, and the capacity to respond to both T-dependent and T-independent type II antigens. However, these mice did have decreased peripheral blood lymphocyte and platelet numbers and developed chronic colitis. Moreover, purified WASP-deficient T cells showed markedly impaired proliferation and antigen receptor cap formation in response to anti-CD3epsilon stimulation. Yet, purified WASP-deficient B cells showed normal responses to anti-Ig stimulation. We discuss the implications of our findings regarding WASP function in receptor signaling and cytoskeletal reorganization in T and B cells and compare the effects of WASP deficiency in mice and humans.

Animals↗
PubMed1998

A targeted DNA-PKcs-null mutation reveals DNA-PK-independent functions for KU in V(D)J recombination.

The DNA-dependent protein kinase (DNA-PK) consists of Ku70, Ku80, and a large catalytic subunit, DNA-PKcs. Targeted inactivation of the Ku70 or Ku80 genes results in elevated ionizing radiation (IR) sensitivity and inability to perform both V(D)J coding-end and signal (RS)-end joining in cells, with severe growth retardation plus immunodeficiency in mice. In contrast, we now demonstrate that DNA-PKcs-null mice generated by gene-targeted mutation, while also severely immunodeficient, exhibit no growth retardation. Furthermore, DNA-PKcs-null cells are blocked for V(D)J coding-end joining, but retain normal RS-end joining. Finally, while DNA-PK-null fibroblasts exhibited increased IR sensitivity, DNA-PKcs-deficient ES cells did not. We conclude that Ku70 and Ku80 may have functions in V(D)J recombination and DNA repair that are independent of DNA-PKcs.

Animals↗
PubMed1998

An expressed neo(r) cassette provides required functions of the 1gamma2b exon for class switching.

Germline CH transcripts initiate from a promoter upstream of a non-coding I exon, proceed through the switch (S) region and terminate downstream of the associated CH exons. To elucidate the role of germline transcription in Ig heavy chain class switch recombination (CSR), we used gene targeting in embryonic stem (ES) cells to replace most of the Igamma2b exon from immediately 3' of the majority of transcription initiation sites to beyond its donor splice site with a PGK-neo(r)gene inserted in the same transcriptional orientation as the endogenous unit. The mutation was introduced into both alleles of ES cell lines (referred to as gamma2-b(N/N)) and the neo(r) gene was deleted (referred to as Igamma2b-/-) by the loxP/Cre method. These mutations were assayed for effects on CSR in B cells derived via RAG-2-deficient blastocyst complementation. Igamma2b-/- B cells lacked ability to switch to IgG2b both in vivo and in vitro, and, correspondingly, showed no germline transcription through the Igamma2b exon, Sgamma2b or the Cgamma2b region. In contrast, Igamma2b(N/N) B cells switched at normal levels to IgG2b and showed substantial transcription through the Sgamma2b and Cgamma2b regions. Taken together, these results show that the Igamma2b sequences, per se, are not necessary for mediating CSR since a transcribed PGK-neo(r) gene can replace its function. However, the deleted portion of the Igamma2b exon and splice donor site apparently contain sequences necessary for efficient germline gene transcription and thus for CSR to IgG2b.

ATP-Binding Cassette Transporters↗
PubMed1998

A method for determining patient oral care skills: The University of Mississippi Oral Hygiene Index.

The plaque control record (O'Leary index) appears to be a commonly used oral hygiene index for assessing oral health skills. This index provides sufficient information for patient education; however, the time involved in data collection reduces its value. Most other indices limit the number of teeth and surfaces and function well for researchers, but are limited for patient education. A new oral hygiene index was developed based on the concepts of the Periodontal Screening and Recording (PSR). The highest score obtained in each buccal and lingual sextant is recorded. In addition, proximal and gingival plaque are noted separately. This study assesses the index for inter- and intrarater reliability and validity. Two calibrated hygienists examined 47 patients 3 times. The University of Mississippi Oral Hygiene Index (UM-OHI) was recorded for times 1 and 3, the O'Leary for time 2. There was a strong positive correlation between scores obtained for both hygienists for each method and repetition. The intrarater reliability was high for the 2 methods and also over time for the UM-OHI. Pearson's correlation coefficients ranged from 0.79 to 0.92. Paired t-tests used to compare scores for the 2 hygienists over time showed significant differences. Despite observer bias, these data seem to indicate that the UM-OHI has sufficient reliability and validity to be used as a health education teaching tool.

Calibration↗
PubMed1997

The GTP effector site of ornithine decarboxylase from Lactobacillus 30a: kinetic and structural characterization.

A nucleotide effector site of the biodegradative form of ornithine decarboxylase from Lactobacillus 30a (OrnDC L30a) has been identified. OrnDC L30a activity at pH 8.0, where the enzyme is normally inactive, is stimulated by GTP and dGTP and to a lesser extent by GDP but not by ATP, CTP, or UTP. The pH profile indicates that activation by GTP is reflected by an increase in kcat/KM,orn (above pH 6.8), while Vmax remains constant over the pH range 4.0-9. 0. Scatchard plot analysis shows that GTP binds to OrnDC L30a at both pH 5.8 (KD = 0.11 microM) and pH 8.0 (KD = 1.6 microM), but unexpectedly, half-site binding is observed at the higher pH. The OrnDC L30a dodecamer dissociates into dimers at high pH in the presence or absence of GTP. The GTP binding site was located in difference electron density maps using low-resolution X-ray data. This represents a new type of GTP binding site. A model explaining the activation of OrnDC L30a by GTP is presented.

Bacterial Proteins↗
PubMed1997

Function of the TCR alpha enhancer in alphabeta and gammadelta T cells.

We have used gene targeted mutational approaches to assess the role of the T cell receptor alpha (TCR alpha) enhancer (E alpha) in the control of TCR alpha and TCR delta gene rearrangement and expression. We show that E alpha functions in cis to promote V alpha to J alpha rearrangement across the entire J alpha locus, a distance of greater than 70 kb. We also show that E alpha is required for normal alphabeta T cell development; in this lineage, E alpha is required for germline J alpha expression, for normal expression levels of rearranged V alpha J alpha genes, and for expression of a diverse V alpha repertoire. In gamma delta T cells, E alpha is not required for VdeltaDJdelta rearrangement, but, surprisingly, is required for normal expression levels of mature VdeltaDJdelta transcripts and for expression of germline J alpha transcripts. Our findings imply that E alpha function is not limited to the TCR alpha components of the TCRalpha/delta locus or to the alpha beta lineage; rather, E alpha function is important in both alphabeta and gammadelta lineage T cells.

Animals↗
PubMed1997

Growth retardation and leaky SCID phenotype of Ku70-deficient mice.

Ku70, Ku80, and DNA-PKcs are subunits of the DNA-dependent protein kinase (DNA-PK), an enzyme implicated in DNA double-stranded break repair and V(D)J recombination. Our Ku70-deficient mice were about 50% the size of control littermates, and their fibroblasts were ionizing radiation sensitive and displayed premature senescence associated with the accumulation of nondividing cells. Ku70-deficient mice lacked mature B cells or serum immunoglobulin but, unexpectedly, reproducibly developed small populations of thymic and peripheral alpha/beta T lineage cells and had a significant incidence of thymic lymphomas. In association with B and T cell developmental defects, Ku70-deficient cells were severely impaired for joining of V(D)J coding and recombination signal sequences. These unanticipated features of the Ku70-deficient phenotype with respect to lymphocyte development and V(D)J recombination may reflect differential functions of the three DNA-PK components.

Animals↗
PubMed1997

Free-living energy expenditure of adult men assessed by continuous heart-rate monitoring and doubly-labelled water.

Free-living energy expenditure was estimated by doubly-labelled water (DLW) and continuous heart-rate (HR) monitoring over nine consecutive days in nine healthy men with sedentary occupations but different levels of leisure-time physical activity. Individual calibrations of the HR-energy expenditure (EE) relationship were obtained for each subject using 30 min average values of HR and EE obtained during 24 h whole-body calorimetry with a defined exercise protocol, and additional data points for individual leisure activities measured with an Oxylog portable O2 consumption meter. The HR data were processed to remove spurious values and insert missing data before the calculation of EE from second-order polynomial equations relating EE to HR. After data processing, the HR-derived EE for this group of subjects was on average 0.8 (SEM 0.6) MJ/d, or 6.0 (SEM 4.2) % higher than that estimated by DLW. The diary-respirometer method, used over the same 9 d, gave values which were 1.9 (SEM 0.7) MJ/d, or -12.1 (SEM 4.0) % lower than the DLW method. The results suggest that HR monitoring can provide a better estimate of 24 h EE of groups than the diary-respirometer method, but show that both methods can introduce errors of 20% or more in individuals.

Adult↗
PubMed1997

Effects of crystalloid solutions on circulating lactate concentrations: Part 1. Implications for the proper handling of blood specimens obtained from critically ill patients.

OBJECTIVES: a) To test the hypothesis that circulating lactate concentrations are the same in simultaneously collected arterial and central venous blood specimens; b) to test the hypothesis that even small amounts of crystalloid solutions, which are inadequately "cleared" from these indwelling arterial and venous catheters, can lead to clinically important and misleading changes in the measured lactate values. DESIGN: A prospective, multiexperiment study. SETTING: A critical care research laboratory and a 20-bed intensive care unit (ICU). PATIENTS: Three hundred fifty-five patients. INTERVENTIONS: Blood samples were collected. MEASUREMENTS AND MAIN RESULTS: Experiment 1: Simultaneously collected arterial and central venous blood specimens were obtained on 148 occasions from 48 medical ICU patients receiving no lactated Ringer's solution (RL). Arterial and central venous lactate values were nearly identical in these patients. The correlation between the arterial and central venous lactate concentrations was excellent (r2 = .85; p < .0001) and the agreement between the arterial and central venous lactate concentrations was also excellent (bias and precision = 0.04 mmol/L and +/- 0.38 mmol/L, respectively). Experiment 2: Arterial and mixed venous blood samples were obtained from 100 percutaneous transluminal coronary angioplasty (PTCA) and 75 cardiac surgical patients immediately before the performance of these cardiac procedures. We found the central venous lactate concentrations to be higher than arterial lactate values in the cardiac surgical group, and there was a very poor correlation (r2 = .07) between arterial and central venous lactate values in the cardiac surgical group. The correlation between central venous and arterial lactate concentrations in the PTCA patients was excellent (r2 = .84) and similar to the findings of experiment 1. Since the cardiac surgical patients received RL and the PTCA patients received no RL, we speculated that the intravenous infusion of RL in the cardiac surgical group accounted for these discordant findings. To test this speculation, we performed experiments 3 and 4. Experiment 3: In a large bench study, blood specimens were divided into multiple 1-mL aliquot portions, to which 0.01, 0.05, 0.10, 0.50, or 1.0 mL of various crystalloid solutions, containing or not containing RL, were added. In a volume-dependent and linear manner, solutions containing RL increased the circulating lactate concentration from 10% to > 400% of the baseline lactate value. In a volume-dependent and linear fashion, the non-RL crystalloid solutions decreased the lactate concentration by 0 to 66% of the baseline nondiluted lactate concentration. Experiment 4: In 30 different cardiac surgical patients, we simultaneously obtained central venous and arterial blood specimens. Patients this time received no RL, and catheter lines were adequately cleared (removal > 5 mL) of crystalloid solutions. We found a correlation (r2 = .82; p < .0001) that was virtually identical to the findings of experiment 1 and to the findings in the PTCA group of experiment 2. CONCLUSIONS: a) Arterial and central venous lactate concentrations are similar in hemodynamically stable critically ill patients, b) Even small amounts of RL-containing solutions in catheters used for blood sampling may cause false increases in the circulating lactate concentration. c) Even small amounts of non-RL crystalloid solutions in catheters used for blood sampling may falsely decrease circulating lactate values. d) When blood specimens are drawn from indwelling catheters, all crystalloid solutions must be cleared from the line.

Blood Specimen Collection↗
PubMed1997

Normalizing acute care: a day hospital/crisis residence alternative to inpatient hospitalization.

Normalization is the use of culturally valued means to enable people with disabilities to live culturally valued lives. In this article, the authors describe an effort to bring normalization practices to acute psychiatric care. They describe a day hospital/crisis respite diversion program that serves as an alternative to acute inpatient hospitalization and sketch the research project that fostered it. The authors argue that a day hospital/ crisis respite provides effective clinical care comparable to inpatient hospitalization but achieves greater potential for recovery through a normalizing philosophy and practice. An implication of this finding is that such programs based on the principle of normalization may be both cost effective as well as more empowering for patients.

Acute Disease↗
PubMed1997

The varied outcomes of schizophrenia.

OBJECTIVE: To review variations in outcomes in schizophrenia across individual, historical, and cross-cultural boundaries, as well as within specific domains of functioning. METHOD: Research literature on the outcomes of schizophrenia appearing within the last 8 years was reviewed. RESULTS: First, a review of follow-up studies published in the developed world suggests that heterogeneity in outcome across individuals with schizophrenia remains the rule, with affective symptoms, later and acute onset, and responsiveness to biological treatments predictive of good outcome. Negative symptoms are associated with poor outcome, cognitive impairments, and incapacity in social and work domains. Deterioration appears to occur within the first few months of onset if not already in the prodrome, with recent early-course studies finding longer duration of untreated psychosis associated with insidious onset, negative symptoms, social and work incapacity, and poor outcome. Second, a review of recent cross-cultural and historical studies provides evidence that outcome varies across time and place, schizophrenia having a more favourable outcome in the developing world and becoming a more benign disorder over the course of this century. Third, a review of studies of the domains of functioning within individuals identifies 4 relatively independent dimensions of depression and negative, psychotic, and disorganized symptoms. Cognitive deficits, which are associated with negative symptoms, also constitute a relatively stable dimension over time, showing neither marked deterioration nor improvement once established early in the course of disorder. CONCLUSIONS: The early appearance and stability over time of negative symptoms and cognitive impairments call for assertive intervention efforts early in the course of disorder to prevent chronicity and prolonged disability.

Follow-Up Studies↗