PubMed Health⌕ Search

Biomedical subjects

O Williams

Publications and source records attributed to O Williams.

At least 37 records · Page 2Linked to original sources
PubMed1998

Altered peptide ligands induce quantitatively but not qualitatively different intracellular signals in primary thymocytes.

Interaction of the T cell receptor (TCR) with peptide/major histocompatibility complexes (MHC) in the thymus is of critical importance for developing thymocytes. In a previous study, we described an antagonist peptide that inhibited negative selection of transgenic thymocytes induced by an agonist peptide. In this study we show that this antagonist peptide can induce positive selection of CD8(+) thymocytes more efficiently than the agonist or the weak agonist peptides, whereas the opposite is true for their ability to cause negative selection. The intracellular signals induced in thymocytes by such peptides after TCR ligation was examined in CD4(+)8(+) double-positive thymocytes from F5/beta2mo/Rag-1(o) transgenic mice. TCR ligation with either the agonist, weak agonist, or antagonist peptide variants resulted in hyperphosphorylation of CD3zeta, CD3epsilon, ZAP-70, Syk, Vav, SLP-76, and pp36-38. The extent of phosphorylation of these intracellular proteins correlated with the efficiency with which the peptide analogs induced apoptosis of immature thymocytes. Unexpectedly, there was no correlation between the upstream TCR signaling pathways analyzed and the capacity of the different peptides to induce positive selection.

Animals↗
PubMed1998

Susceptibility and resistance to antigen-induced apoptosis in the thymus of transgenic mice.

Injection of TCR transgenic mice with antigenic peptide results in the deletion of immature thymocytes expressing the transgenic TCR. We have analyzed this process in mice transgenic for a TCR (F5) that recognizes a peptide from the influenza nucleoprotein (NP68). To determine whether deletion of immature thymocytes is the result of specific recognition of the antigenic peptide by the thymocytes or mature T cell activation, bone marrow chimeric mice were generated using a mixture of cells from F5 transgenic and nontransgenic mice. Injection of these mice with antigenic peptide leads to the preferential depletion of F5 transgenic thymocytes, whereas nontransgenic thymocytes remain largely unaffected. Furthermore, exposure of F5 fetal thymic lobes to peptide leads to thymocyte deletion even though no mature single positive T cells are present at this stage. These data suggest that Ag-induced death of immature thymocytes is due to peptide-specific recognition, although activated mature T cells appear to potentiate such deletion. Further administration of antigenic peptide to F5 mice results in the appearance of double-positive thymocytes that are resistant to Ag or anti-CD3-induced apoptosis. These data suggest a change in the ability of the cells to signal through the TCR-CD3 complex, resembling the state of anergy induced in peripheral T cells following chronic exposure to Ag.

Animals↗
PubMed1998

Interactions with multiple peptide ligands determine the fate of developing thymocytes.

Thymocytes are positively or negatively selected depending on interactions between their T cell receptors (TCR) and peptides presented by major histocompatibility complex molecules. We have previously shown that apoptosis of thymocytes from an alpha beta TCR-transgenic mouse (F5), induced by antigenic peptide, can be inhibited specifically by an antagonist peptide variant in an in vitro culture model. We have now extended these experiments by demonstrating that the antagonist peptide can inhibit natural negative selection of maturing thymocytes, induced by endogenously expressed antigen, in fetal thymic organ cultures (FTOC). This inhibition resulted in the rescue and maturation of thymocytes that would otherwise have been deleted. Mature T cells generated in these cultures were able to respond to antigen by producing limited quantities of interferon-gamma, but unlike T cells from control FTOC, they required exogenous interleukin-2 to generate cytolytic effector cells. Interestingly, the antagonist peptide also accelerated the development of F5 thymocytes in the absence of the negatively selecting ligand. These data suggest that the developmental fate of a thymocyte may be determined by the recognition of multiple distinct peptide ligands during thymic selection. Alterations in the profiles of selecting peptides presented in the thymus would thus have profound effects on the size and autoreactive potential of the T cell repertoire generated.

Animals↗
PubMed1998

Tempo of hematologic recovery correlates with peripheral blood CD34+ cell level in patients undergoing stem cell mobilization.

This study was undertaken to evaluate the relationship between the time to recovery of peripheral blood counts and CD34+ cells in the peripheral blood (PB) and apheresis collections of patients undergoing intensive chemotherapy followed by rhG-CSF. Twenty-three patients with a median age of 42 years (range 17-64) with malignancies underwent peripheral blood stem cell (PBSC) collection after cyclophosphamide (CY) 4 g/m2 and etoposide (600 mg/m2) followed by rhG-CSF (10 microg/kg/day). The WBC, platelet counts, CD34+ cell counts per ml of PB, and CD34+ cells in apheresis products were followed in all patients. The relationship of the time to recovery of WBC > 1,000/microl, >3,000/microl, >10,000/microl and platelets >20,000/microl and 50,000/microl was compared to the average daily CD34+ cells/ml in each patient using the Spearman Correlation test. The tempo of recovery of WBC and platelets were highly correlated with the average CD34+ cell count in blood. In order to derive some useful guidelines for the timing of apheresis, the patients were divided into two groups, early recover (ER) and late recover (LR) based on the median time (day 10) to reach WBC count greater than 1,000/microl. ER patients had an average daily PB CD34+ cell count of 9.04 x 10(4)/ml (range 0.44-17.5) and a median yield of CD34+ cells of 10.43 x 10(6)/kg (range 0.60-25.95) compared to LR patients, who had 1.87 x 10(4)/ml (range 0.32-5.44) in the PB (P = .001) and a yield 3.20 x 10(6)/kg CD34+ cells (range 0.037-9.39) (P = .001). Patients recovering their WBC to 1,000/ml within 10 days of completing this regimen may undergo PBSC collection and achieve minimum-target cell doses of >2.5 x 10(6) CD34+ cells/kg--100% of the time.

Adolescent↗
PubMed1998

The management of chlamydial infection: setting standards at a regional level.

Between 1993 and 1997, clinicians from 9 departments of genitourinary medicine (GUM) and one department of sexual health in East Anglia met to audit the process of contact tracing in chlamydial infection. After defining the target group, standards were set for discussion of the diagnosis with the index patient, appropriate treatment of the condition and documented notification of partners. Data were collected for all patients with confirmed chlamydial infection during the periods January to March 1995 and 1996. Considering the combined data for both years, overall 97% of patients were informed of the diagnosis and 100% received appropriate treatment. Notification of partners was addressed at the initial consultation in 99% of cases and again at follow-up in 87%. Where contacts were traceable, there was confirmation that assessment had occurred in 65%, and the index cases reported that 66% had undergone assessment. The achievements and also the problems associated with this audit are discussed.

Chlamydia Infections↗
PubMed1997

A CD8 genomic fragment that directs subset-specific expression of CD8 in transgenic mice.

Helper and cytotoxic T cell subsets require the expression of different coreceptors (CD4 and CD8, respectively) for their development and function. We have cloned the CD8 gene locus from genomic cosmid and P1 libraries and analyzed the region around the CD8alpha and CD8beta genes for gene expression regulatory elements. DNase I (DNase I) hypersensitivity analysis of 80 kb in the CD8 locus identified four clusters of putative regulatory regions, three of which are thymocyte specific. Transgenic mice carrying the cloned CD8alphabeta genomic locus and containing the identified DNase I-hypersensitive site clusters express the transgenic CD8 in a developmentally regulated, tissue-specific, and CD8 T cell subset-specific manner.

Animals↗
PubMed1997

Noncontinent urinary diversion.

When the need for urinary diversion arises, whether from carcinoma of the urinary tract, malfunction, or malformation, a decision must be made about the type of diversion to be performed. Currently, the patient and surgeon must decide on continent versus noncontinent versus neobladder, and on the type of intestinal segment to be used.

History, 19th Century↗
PubMed1997

The agonist-antagonist balance in positive selection.

Peptide antigens expressed in the thymus, in combination with self major histocompatibility complex molecules play a crucial role in thymocyte selection and shaping of the mature T-cell repertoire. Here, it is proposed that a single thymocyte may be exposed to numerous different peptide ligands as it matures, such that its fate is determined by the sum of signals produced by these interactions.

Animals↗
PubMed1997

Evidence for B cell participation in the in vitro and in vivo maintenance of in vivo staphylococcal enterotoxin B-induced T cell anergy.

The mechanisms involved in the maintenance of staphylococcal enterotoxin B (SEB)-induced T cell anergy are poorly understood. Here, we demonstrate that CD4+ T cell anergy induced by SEB treatment is under partial B cell control. This effect is not mediated by anti-SEB antibodies or any in vitro B cell-produced suppresser factor. At day 13 after SEB immunization, T cells from B cell-deficient mice proliferate upon in vitro stimulation with SEB. These results suggest that SEB-induced T cell anergy is reversible and that B cells have an important function in anergy maintenance in CD4+ T cells, both in vivo and in vitro.

Animals↗
PubMed1997

In vitro positive selection of alpha beta TCR transgenic thymocytes by a conditionally immortalized cortical epithelial clone.

Development of mature CD4 and CD8 single-positive T cells requires a process known as positive selection, which depends on the specific recognition of self-peptide-MHC complexes on thymic stromal cells by immature CD4+CD8+ thymocytes. We have used an in vitro reaggregate system to study the positive selection of thymocytes by conditionally immortalized thymic epithelial clones. Thymocytes from mice transgenic for the F5 alpha beta TCR, specific for a peptide from the influenza nucleoprotein in the context of H-2Db, are positively selected in the H-2b MHC background, but fail to mature in mice expressing the H-2q haplotype. Development of embryonic day 15 F5 H-2q transgenic thymocytes was followed in reaggregate cultures supplemented with H-2b-expressing epithelial clones. A conditionally immortalized cortical epithelial clone, derived from H-2Kb-tsA58 transgenic mice, was found to be as efficient as freshly isolated thymic stromal cells in positively selecting CD8 transgenic thymocytes. In contrast, an H-2b-expressing kidney epithelial clone did not augment positive selection above background levels, implying that the effect of the thymic epithelial clone was not merely the presentation of selecting MHC molecules. Mature transgenic thymocytes generated in reaggregate cultures were able to differentiate into functionally competent cytotoxic T cells. This model provides an important in vitro system for the detailed study of the specific molecular interactions leading to positive selection of developing thymocytes.

Animals↗
PubMed1996

Inhibition of thymocyte negative selection by T cell receptor antagonist peptides.

The T cell receptor (TCR) recognizes antigenic peptide presented by major histocompatibility complex (MHC) molecules. Analogs of antigenic peptides have been shown to inhibit antigen-specific T cell responses, a phenomenon described as TCR antagonism. We have examined the effect of a natural variant of an antigenic peptide and a synthetic peptide analog, on the responses of mature T cells and immature thymocytes from an alpha-beta TCR-transgenic mouse (F5), the TCR of which recognizes a nonamer peptide from the nucleoprotein (NP) of influenza virus in the context of the H-2Db MHC molecule. Both peptides were shown to antagonize specifically the T cells cytolytic response without being able directly to stimulate mature T cells from these transgenic mice. Furthermore, a negative selection assay in vitro was used to demonstrate for the first time that antagonistic peptides are capable of antagonizing thymocyte deletion induced by antigenic peptides. These data suggest that the final selection of a T cell could be the result of a balance between the positive and negative influences of endogenous peptide ligands.

Amino Acid Sequence↗
PubMed1996

Direct visualization of thymocyte apoptosis in neglect, acute and steady-state negative selection.

During thymocyte differentiation, the majority of the developing cells die in situ by apoptosis and are subsequently removed by macrophages. DNA fragmentation is one of the hallmarks of apoptosis and can be detected in situ by TdT-mediated dUTP-biotin nick end labeling (TUNEL). We used TUNEL combined with immunohistology to determine the sites of thymocyte apoptosis in mice transgenic for a TCR (F5) which recognizes a peptide (NP68) of the influenza virus nucleoprotein (NP) presented on the MHC class I H-2Db molecule. Apoptosis due to neglect was studied in F5 mice expressing a neutral MHC haplotype (F5/H-2q) and in beta 2-microglobulin-deficient F5 mice (F5/ beta 2m+). In both cases, the frequency of apoptotic cells was similar to that seen in F5/H-2b mice and non-transgenic C57BI/10 mice. Antigen-induced apoptosis was studied in F5 mice after i.p. Injection of the cognate NP68 peptide and in F5/NP double-transgenic mice. Three hours after peptide injection, apoptosis was high throughout the thymus cortex and clusters of apoptotic cells formed due to tissue macrophage uptake, whereas the thymic medulla remained unaffected. Massive recruitment of inflammatory cells into the thymus was seen as early as 1 h after peptide injection. Nine hours after peptide injection changes were apparent in the cortical epithelium and, by 4 days, the cortical network had collapsed to give scattered, compacted epithelial cells. In contrast, in F5/NP double-transgenic mice, thymocyte apoptosis induced by cognate self-peptide was localized at the cortico-medullary junction with little change seen in the epithelium of the cortex.

Animals↗
PubMed1996

The effect of zidovudine dose on the formation of intracellular phosphorylated metabolites.

OBJECTIVES: Zidovudine (ZDV) requires intracellular phosphorylation to ZDV triphosphate (ZDV-TP) prior to the inhibition of HIV replication. The effect of ZDV dose on the formation of intracellular phosphorylated metabolites may help define the optimum daily dose of ZDV, which is still unknown. DESIGN AND METHODS: The plasma and intracellular phosphorylated metabolite concentrations of ZDV were determined over a 12 h period following oral administration of 100 and 300 mg ZDV to 10 HIV-seropositive patients at steady state during two dosing regimens (i.e., 100 mg three times daily and 300 mg twice daily). The intracellular ZDV phosphates, ZDV monophosphate (ZDV-MP), ZDV diphosphate (ZDV-DP) and ZDV-TP were measured in peripheral blood mononuclear cells using a combination of high-performance liquid chromatography and radioimmunoassay. RESULTS: There was a greater than threefold increase in maximum plasma concentration (Cmax) following 300 mg ZDV when compared with 100 mg ZDV (mean +/- SD, 2.59 +/- 0.52 versus 0.70 +/- 0.14 mumol/l). The area under the concentration time curve (AUC0-12 h) was also significantly increased (4.59 +/- 0.79 versus 1.42 +/- 0.51 mumol/l x h) following 300 mg ZDV dose. For total intracellular ZDV phosphate metabolites the AUC0-12 h was doubled (7.64 +/- 3.67 versus 3.71 +/- 1.83 pmol/10(6) cells x h) in patients taking 300 mg ZDV compared with 100 mg. The AUC0-12 h for ZDV-MP was significantly increased at the higher dose (6.47 +/- 3.14 versus 2.77 +/- 1.70 pmol/10(6) cells x h), whereas the active moiety ZDV-TP was variable and not significantly different (0.42 +/- 0.42 versus 0.61 +/- 0.81 pmol/10(6) cells x h) following 100 and 300 mg ZDV. CONCLUSIONS: Administration of 100 mg ZDV orally produces significantly less of the potentially toxic metabolite, ZDV-MP, and comparative, although variable, concentrations of the active metabolite ZDV-TP when compared with 300 mg ZDV orally. This finding supports clinical data indicating the efficacy of low-dose (300 mg daily) ZDV. The measurement of intracellular phosphorylated metabolites advances our understanding of the clinical pharmacology of ZDV.

Adult↗
PubMed1996

What is clinical audit?

The emphasis of clinical audit should be on improvement in care. Audit can only improve healthcare if it includes a mechanism for change. The fact that information about outcomes is collected does not necessarily mean that care is being audited, nor that improved care will result. Audit must be distinguished from data collection, surgical epidemiology, and research.

Data Collection↗