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Biomedical subjects

L S Walker

Publications and source records attributed to L S Walker.

At least 19 recordsLinked to original sources
PubMed2001

The relation of daily stressors to somatic and emotional symptoms in children with and without recurrent abdominal pain.

Prior investigations of the relation between stressors and symptoms in children with recurrent abdominal pain (RAP) have focused on major negative life events. This study used consecutive daily telephone interviews to assess daily stressors and symptoms in 154 pediatric patients with RAP and 109 well children. Results showed that patients with RAP reported more frequent daily stressors than well children reported both at home and at school. Idiographic (within-subject) analyses indicated that the association between daily stressors and somatic symptoms was significantly stronger for patients with RAP than for well children. In contrast, the relation between daily stressors and negative affect did not differ between the groups. The relation between daily stressors and somatic symptoms was stronger for patients with RAP who had higher levels of trait negative affectivity.

Abdominal Pain↗
PubMed2000

Co-stimulation and selection for T-cell help for germinal centres: the role of CD28 and OX40.

Given the importance of responding to infections with the right defensive strategy, much interest has focused on cytokine differentiation in CD4+ T cells. However, relatively little is known of the logistics of T-cell help for B cells. Here, Lucy Walker and colleagues propose key roles for CD28 and OX40 in coordinating the selection, expansion and migration of CD4+ T cells to B-cell follicles.

Animals↗
PubMed1999

Compromised OX40 function in CD28-deficient mice is linked with failure to develop CXC chemokine receptor 5-positive CD4 cells and germinal centers.

Mice rendered deficient in CD28 signaling by the soluble competitor, cytotoxic T lymphocyte-associated molecule 4-immunoglobulin G1 fusion protein (CTLA4-Ig), fail to upregulate OX40 expression in vivo or form germinal centers after immunization. This is associated with impaired interleukin 4 production and a lack of CXC chemokine receptor (CXCR)5 on CD4 T cells, a chemokine receptor linked with migration into B follicles. Germinal center formation is restored in CTLA4-Ig transgenic mice by coinjection of an agonistic monoclonal antibody to CD28, but this is substantially inhibited if OX40 interactions are interrupted by simultaneous injection of an OX40-Ig fusion protein. These data suggest that CD28-dependent OX40 ligation of CD4 T cells at the time of priming is linked with upregulation of CXCR5 expression, and migration of T cells into B cell areas to support germinal center formation.

Abatacept↗
PubMed1999

IL-2-independent activation and proliferation in human T cells induced by CD28.

Although the role of CD28 in T cell costimulation is firmly established, the mechanisms by which it exerts its costimulatory actions are less clear. In many circumstances it is difficult to distinguish the effects of CD28 from subsequent actions of cytokines, such as IL-2, on T cell proliferation. Here, we report a model of CD28 costimulation using PMA plus the natural ligand CD80 that resulted in very limited stimulation of IL-2, as evidenced by both cytokine production and IL-2 promoter stimulation. Promoter assays revealed CD28-dependent effects on both NF-kappaB and AP-1, but not on NF-AT or the intact IL-2 promoter. In addition, T cell proliferation was completely resistant to the actions of the immunosuppressant cyclosporin A (CsA). Moreover T cell proliferation was unaffected by the addition of blocking Abs to both IL-2 and the IL-2 receptor, demonstrating that this form of costimulation by CD28 was independent of IL-2. We also investigated the effects of stimulating T cell blasts with CD80 alone and found that there was a limited requirement for IL-2 in this system. We conclude that CD28 costimulation can cause substantial T cell proliferation in the absence of IL-2, which is driven by a soluble factor independent of NF-AT transactivation.

Animals↗
PubMed1999

Lack of activation induced cell death in human T blasts despite CD95L up-regulation: protection from apoptosis by MEK signalling.

The generation of effective immunity requires that antigen-specific T cells are activated, clonally expanded and ultimately eliminated by apoptosis. The involvement of CD95-mediated apoptosis in T-cell elimination is well established, but the conditions which regulate the death pathway under normal circumstances are still emerging. Using superantigen-activated human T cells, we found that whilst T-cell receptor (TCR) signalling triggered up-regulation of CD95 ligand (CD95L), the majority of T cells were resistant to apoptosis induction, despite co-expressing high levels of CD95. Resistance was maintained following direct antibody-mediated cross-linking of CD95 and was not confined to early time periods following activation. Our data implicate TCR-derived signals in protection from apoptosis and reveal a role for the mitogen-activated protein (MAP) kinase pathway by use of a MAP kinase kinase (MEK) inhibitor. Collectively these data demonstrate that resistance to activation-induced cell death in human T cells is prolonged rather than transient, is not attributable to a lack of CD95L up-regulation and is due, at least in part, to signalling via the MEK pathway.

Antibodies, Monoclonal↗
PubMed1999

Functional disability in adolescents and young adults with symptoms of irritable bowel syndrome: the role of academic, social, and athletic competence.

OBJECTIVE: To examine perceived academic, social, and athletic competence as potential moderators of the relation between symptoms of irritable bowel syndrome (IBS) and functional disability in adolescents and young adults with a history of recurrent abdominal pain (RAP). METHODS: We assessed IBS symptoms, competence, and disability by telephone interview in RAP patients five years following their medical evaluation. RESULTS: For both male and female subjects, the relation between symptoms and disability was stronger at lower levels of perceived academic competence. Furthermore, among females, the relation between symptoms and disability was stronger at lower levels of perceived social competence; among males, the relation was stronger at lower levels of perceived athletic competence. CONCLUSIONS: Perceived competence moderated the relation between IBS symptoms and functional disability. Interventions designed to enhance patient competence in various roles may be useful in reducing disability among adolescents and young adults with symptoms of IBS.

Adolescent↗
PubMed1999

Maternal attributions for the causes and remedies of their children's abdominal pain.

OBJECTIVE: To examine mothers' attributions for the causes and remedies of their children's abdominal pain, specifically whether attributions differed according to child diagnosis, reflected a dualistic or multidimensional view of pain, and changed following medical evaluation. METHODS: Mothers of children whose medical evaluation indicated peptic disease (n = 55) or unexplained pain without identifiable organic disease (n = 98) participated in telephone interviews prior to their children's medical evaluations and one year later. RESULTS: About half of the mothers in each group endorsed both psychosocial and physical factors as important in the etiology of their children's abdominal pain. Following medical evaluation, mothers in both groups tended to maintain their attributions regarding the importance of psychosocial factors. CONCLUSIONS: Many mothers acknowledged the contribution of psychosocial factors to their children's abdominal pain. They may be receptive to behavioral interventions if physicians present these remedies as an integral component of treatment.

Abdominal Pain↗
PubMed1999

Children with recurrent abdominal pain: issues in the selection and description of research participants.

Research criteria proposed by Apley for identification of children with recurrent abdominal pain (RAP) have been widely adopted, but many researchers have deviated from the original definition. Ambiguities in Apley's criteria and problems caused by departures from his definition are discussed in this article. Many inconsistencies in research results may have been created by the decision of some researchers to exclude children with presumed organic causes for their pain from RAP study samples. Further precision and comparability of research results may be gained by using the two-stage approach to classification that is proposed in this article. The first stage requires no medical evaluation but is based strictly on the correspondence of RAP symptoms to temporal and severity criteria. At the second stage, subgroups of RAP are specified by using results from medical assessments or detailed patterns of symptoms. It is also suggested that researchers specify the temporal features of RAP and provide measures of impairment. Like Apley's criteria, the revised approach to classification allows the comparison of community- and school-based samples with children who have undergone medical evaluation for RAP.

Abdominal Pain↗
PubMed1998

Positive and negative regulation of human T cell activation mediated by the CTLA-4/CD28 ligand CD80.

CD28 and CTLA-4 are related receptors that differentially regulate T cell activation. Despite the fact that they bind the same ligands, CD28 is a classical costimulator enhancing proliferation whereas CTLA-4 appears to perform negative regulatory functions. In this study, we have utilized the natural ligand for CD28 and CTLA-4 (CD80) to determine under what circumstances positive and negative effects are operative. We show here that the stimulation of purified human T cells with phorbol ester and ionomycin is inhibited in the presence of Chinese hamster ovary (CHO) cells expressing CD80. This inhibition is reversed by blocking with both anti-CD80 or Fab fragments of anti-CTLA-4 but also requires CD28 engagement. Furthermore, we show that the inhibitory function of CD80 requires elevated intracellular calcium since inhibition was observed only in the presence of ionomycin. In the absence of intracellular calcium elevation, CTLA-4 was not expressed at the cell surface, and CD80 acted positively as a costimulator of T cells, via CD28. These results demonstrate that the natural ligand CD80 can either costimulate or inhibit T cell responses depending on the conditions of T cell stimulation.

Abatacept↗
PubMed1998

Activation of human T cells with superantigen (staphylococcal enterotoxin B) and CD28 confers resistance to apoptosis via CD95.

Ag recognition is an essential component for an effective T cell response. However, T cell activation is also subject to additional regulation by accessory molecules. CD28 provides essential costimulatory signals that allow T cells to proliferate, whereas molecules such as CTLA-4 and CD95 (Fas) appear to be negative regulators. Currently, which outcome predominates under conditions of antigenic challenge is poorly understood. In particular it has been suggested that one consequence of antigenic activation of T cells is the up-regulation of both CD95 and CD95 ligand, thereby exposing activated T cells to apoptotic death. We have investigated this possibility in normal human peripheral blood T cells triggered by the superantigen SEB either in the presence of endogenous APCs or transfectants expressing DR4 and CD80. In either case, we find that such activation does not expose the majority of T cells to anti-CD95-induced apoptosis as detected by annexin V externalization and DNA fragmentation. Furthermore, by phenotypically identifying, by flow cytometry, those cells that received both antigenic and costimulatory signals from those cells that did not, we observed that CD95-induced apoptosis was not seen in activated T cells receiving Ag and costimulatory signals via CD28. However, while not all T cells were stimulated by superantigen, CD95 expression was found to be homogeneously up-regulated, suggesting a mechanism whereby bystander cells might be made susceptible to CD95-induced death. We conclude that antigenic activation of T cells via the TCR and CD28 engagement provides protection from CD95-induced apoptosis.

Animals↗
PubMed1998

Recurrent abdominal pain: a potential precursor of irritable bowel syndrome in adolescents and young adults.

OBJECTIVES: To assess symptoms of irritable bowel syndrome (IBS) in patients with recurrent abdominal pain (RAP) 5 years after their initial evaluation, to identify the relation of IBS symptoms to functional disability and health service use, and to determine the extent to which IBS symptoms are associated with life stress and poor psychosocial adjustment. METHODS: Patients with RAP (n = 76) and control subjects (n = 49) completed a telephone interview; measures included the Bowel Disease Questionnaire, the Functional Disability Inventory, the Life Events Questionnaire, the Family Inventory of Life Events, the Center for Epidemiological Studies Depression Scale, the Self-Perception Profile for Adolescents, and the Health Resources Inventory. RESULTS: Five years after the initial evaluation, patients with RAP reported significantly more episodes of abdominal pain than did control subjects, as well as significantly higher levels of functional disability, school absence, and clinic visits for abdominal distress. Female patients with RAP were more likely than female control subjects to meet the Manning criteria for IBS. Among patients with RAP, higher levels of IBS symptoms were associated with significantly greater functional disability, more clinic visits, more life stress, higher levels of depression, and lower academic and social competence. CONCLUSION: Female patients with a history of RAP may be at increased risk of IBS during adolescence and young adulthood. Among adolescents and young adults with a history of RAP, IBS symptoms are likely to be associated with high levels of disability and health service use.

Abdominal Pain↗
PubMed1998

Concordance between mothers' and children's reports of somatic and emotional symptoms in patients with recurrent abdominal pain or emotional disorders.

Mother-child concordance regarding children's somatic and emotional symptoms was assessed in children with recurrent abdominal pain (n = 88), emotional disorders (n = 51), and well children (n = 56). Children between 6 and 18 years of age and their mothers completed questionnaires assessing the children's somatic symptoms, functional disability, and depression. Mothers of children with recurrent abdominal pain reported more child somatic and depressive symptoms than did their children, and mothers of children with emotional disorders reported more child depressive symptoms than did their children. Higher levels of maternal distress were associated with greater mother-child discordance in the direction of mothers reporting more child symptoms than did their children. No significant child age or sex differences were found in concordance patterns.

Abdominal Pain↗
PubMed1998

Down-regulation of CD28 via Fas (CD95): influence of CD28 on T-cell apoptosis.

Following antigen engagement of the T-cell receptor (TCR), T-cell survival is largely dictated by the provision of additional signals, such as those from costimulatory receptors and cytokine receptors. Whilst CD28-mediated signalling is increasingly associated with survival, ligation of alternative T-cell antigens, such as Fas (CD95), can trigger apoptosis. The T-cell response following antigen engagement may therefore be influenced by the relative expression levels of these coreceptors as well as by the availability of their ligands (CD80/86 and Fas-L). In this study we demonstrate functional interplay between the death receptor Fas and the costimulatory receptor CD28 in human T cells. In Jurkat T cells, we show that Fas signalling leads to rapid and selective CD28 down-regulation, and that this is associated with a specific decrease in mRNA for CD28, indicating that mechanisms exist which target CD28 at a transcriptional level. Moreover, cells that down-regulate CD28 also undergo apoptosis. Studies on activated human peripheral blood T cells demonstrate that cells expressing high levels of CD28 are resistant to Fas-mediated apoptosis whereas cells expressing low levels are more susceptible, implicating CD28 in the provision of anti-apoptotic signals. Consistent with this hypothesis, direct ligation of CD28 using B7 transfectants concomitant with anti-Fas challenge protects from apoptosis. Since antigen-presenting cells may express Fas-L under certain circumstances, the maintenance of T-cell CD28 expression may be crucial for the prevention of Fas-mediated apoptosis during the course of antigen engagement.

Apoptosis↗
PubMed1998

Chromium picolinate effects on body composition and muscular performance in wrestlers.

PURPOSE: The purpose of this study was to assess the effects of 14 wk of chromium picolinate supplementation during the final 16 wk of a preseason resistance and conditioning program on body composition and neuromuscular performance in NCAA Division I wrestlers. During this phase of training, wrestlers are primarily interested in trying to improve physical performance and wrestling technique and are not engaged in severe, acute weight loss practices commonly employed before competition. METHODS: This double-blinded, randomized placebo-controlled study involved 20 wrestlers from the University of Oklahoma assigned to either a treatment group (Cr+3; N = 7; 20.4 yr +/- 0.1) receiving 200 micrograms chromium picolinate daily, a placebo group (P; N = 7; 19.9 yr +/- 0.2), or a control group (C; N = 6; 20.2 yr +/- 0.1) using a stratified random sampling technique based on weight classification. Body composition, neuromuscular performance, metabolic performance, and serum insulin and glucose were measured before and immediately following the supplementation and training period. RESULTS: Repeated measures ANOVA indicated no significant changes in body composition for any of the groups. Aerobic power increased significantly (P < 0.002) in all groups, independent of supplementation. There were significant trial and group x trial interactions for upper body endurance (P = 0.038) and relative bench press power (P = 0.050). Post-hoc analyses revealed that the C group increased upper body endurance (P = 0.006), but none of the pre- to post-test changes in bench press power were significant. CONCLUSIONS: These results suggest that chromium picolinate supplementation coupled with a typical preseason training program does not enhance body composition or performance variables beyond improvements seen with training alone.

Adolescent↗
PubMed1997

Psychosomatic problems and stress in adolescence.

Psychosomatic problems are common in adolescents, and stress frequently plays a role in their development and maintenance. Armed with an understanding of the stressors experienced by adolescents, the individual's vulnerabilities and competencies and their level of social support, the physician can systematically assess each of these factors. Once the assessment is complete, a management plan can be formulated to address the particular psychosomatic problem. Symptom relief, stress reduction, and promotion of competence are important interventions that can be initiated by the primary care physician. When referrals are made for counseling and other stress management techniques, the primary care physician should maintain contact with the patient and family and remain an integral part of the management team. Incorporating brief discussions about the potential role of stress in health and illness into anticipatory guidance sessions may also help prevent the development of psychosomatic problems in adolescents.

Abdominal Pain↗