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Biomedical subjects

M L Thomas

Publications and source records attributed to M L Thomas.

At least 19 recordsLinked to original sources
PubMed2005

Impact of the European Working Time Directive on the training of paediatric anaesthetists.

The European Working Time Directive and the New Deal have decreased the number of hours worked by anaesthetic trainees. We implemented the Working Time Directive in May 2004 and evaluated the effect of its implementation on training. During two 6-month periods, one before and one after the change, we determined the number of operating lists undertaken by each Specialist Registrar in Anaesthesia. After implementation of the Working Time Directive, the mean number of lists performed by Specialist Registrars decreased from 24 to 21 lists per registrar per month, a 13% decrease. Exposure to subspecialty lists was the same in both periods, but this was at the expense of general lists and those in remote locations. We conclude that the Working Time Directive has had a measurable impact on the training of paediatric anaesthetists, but that the significance of this change for clinical practice has not yet been measured.

Anesthesiology↗
PubMed2001

Development of intestinal intraepithelial lymphocytes, NK cells, and NK 1.1+ T cells in CD45-deficient mice.

The transmembrane protein tyrosine phosphatase CD45 is differentially required for the development and function of B, T, and NK cells, with mice partially deficient for CD45 having a significant inhibition of T cell, but not NK or B cell, development. CD45-mediated signaling has also been implicated in the development of intrathymic, but not extrathymic, intestinal intraepithelial T lymphocytes (iIELs) in the CD45ex6(-/-) mouse. As NK1.1(+) CD3(+) (NK-T) cells can also develop through extrathymic pathways, we have investigated the role of CD45 in NK-T cell development. In mice with a complete absence of CD45 expression (CD45ex9(-/-)) the NK-T cell population was maintained in the iIEL compartment, but not in the spleen. Functionally, CD45-deficient NK-T cells were unable to secrete IL-4 in response to TCR-mediated signals, a phenotype similar to that of CD45-deficient iIELs, in which in vitro cytokine production was dramatically reduced. Using the CD45ex9(-/-) mouse strain, we have also demonstrated that only one distinct population of NK-T cells (CD8(+)) appears to develop normally in the absence of CD45. Interestingly, although an increase in cytotoxic NK cells is seen in the absence of CD45, these NK calls are functionally unable to secrete IFN-gamma. In the absence of CD45, a significant population of extrathymically derived CD8alphaalpha(+) iIELs is also maintained. These results demonstrate that in contrast to conventional T cells, CD45 is not required during the development of CD8(+) NK-T cells, NK cells, or CD8alphaalpha(+) iIELs, but is essential for TCR-mediated function and cytokine production.

Animals↗
PubMed2001

Molecular cloning of MIS, a myeloid inhibitory siglec, that binds protein-tyrosine phosphatases SHP-1 and SHP-2.

We describe the molecular cloning and characterization of a novel myeloid inhibitory siglec, MIS, that belongs to the family of sialic acid-binding immunoglobulin-like lectins. A full-length MIS cDNA was obtained from murine bone marrow cells. MIS is predicted to contain an extracellular region comprising three immunoglobulin-like domains (V-set amino-terminal domain followed by two C-set domains), a transmembrane domain and a cytoplasmic tail with two immunoreceptor tyrosine-based inhibitory motif (ITIM)-like sequences. The closest relative of MIS in the siglec family is human siglec 8. Extracellular regions of these two siglecs share 47% identity at the amino acid level. Southern blot analysis suggests the presence of one MIS gene. MIS is expressed in the spleen, liver, heart, kidney, lung and testis tissues. Several isoforms of MIS protein exist due to the alternative splicing. In a human promonocyte cell line, MIS was able to bind Src homology 2-containing protein-tyrosine phosphatases, SHP-1 and SHP-2. This binding was mediated by the membrane-proximal ITIM of MIS. Moreover, MIS exerted an inhibitory effect on FcgammaRI receptor-induced calcium mobilization. These data suggest that MIS can play an inhibitory role through its ITIM sequences.

Alternative Splicing↗
PubMed2001

Role of adhesion molecules in recruitment of Vdelta1 T cells from the peripheral blood to the tumor tissue of esophageal cancer patients.

The mechanism responsible for tissue specific localization of gammadelta T cell subsets is not well understood. In order to explain the sequestration of specific gammadelta T cell subsets in the peripheral blood and tumor tissue of patients with esophageal cancer, we examined the function and expression of adhesion molecules on these cells. A hierarchy in the expression of adhesion molecules was observed. In vitro activated gammadelta T cells showed dominant expression of LFA-1 (CD11a), VLA-alpha4 (CD49d), intermediate expression of VLA-alpha5 (CD49e) and L-selectin (CD62L), but low expression of CD44v6 and alphaEbeta7 (CD103). It was observed that the gammadelta T cells use LFA-1, L-selectin and CD44v6 to bind to squamous cell carcinoma (SCC) cells, whereas they adhere to fibroblast cells using LFA-1, VLA-alpha4 and VLA-alpha5. Vdelta1 T cell subsets from the peripheral blood gammadelta T cells utilize a larger array of adhesion molecules, namely LFA-1, VLA-alpha4, VLA-alpha5, L-selectin and alphaEbeta7, to bind to SCC cells compared to the restricted usage of LFA-1, L-selectin and CD44v6 by the Vdelta2 T cells. Flow cytometric analysis of tumor infiltrating lymphocytes from the esophageal tumors confirmed the selective accumulation of Vdelta1+ gammadelta T cells in the tumor compartment. It thus appears that adhesion molecules expressed on these lymphocytes play an important role in the recruitment and retention of Vdelta1 T cells in the tumor milieu.

Antibodies, Monoclonal↗
PubMed2001

Oesophageal diverticula.

BACKGROUND: Oesophageal pulsion diverticula, excluding pharyngeal types, are uncommon sequelae of oesophageal dysmotility. Current opinion favours myotomy as effective therapy, but the role of diverticulectomy, myotomy selection and placement, and the need for fundoplication remain unresolved. METHODS: A Medline search and review of references identified relevant English language articles. Data on epidemiology, aetiology, oesophageal motility, pathology, symptomatology, investigations, surgical management and outcome were examined. RESULTS: Data were largely retrospective. Significant morbidity and mortality were associated with pulmonary aspiration and diverticulectomy site leaks. Surgical outcome was similar whether or not a diverticulectomy was added to a myotomy, but a myotomy clearly reduced the risk of leaks. Fundoplication reduced the incidence of postcardiomyotomy reflux symptoms. Results from minimally invasive techniques were similar to those of open surgery. CONCLUSION: Surgery should be reserved for symptomatic patients; asymptomatic patients may benefit from surveillance. Pulmonary aspiration mandates surgical intervention. Myotomy remains the mainstay of treatment and an adequate subdiverticular extension is crucial in relieving obstruction. A partial fundoplication is preferred in selected patients. Minimally invasive techniques should become the routine approach for oesophageal pulsion diverticula.

Diverticulum, Esophageal↗
PubMed2001

Evaluation of a transdermal fentanyl system in yucatan miniature pigs.

Of 18 pigs used on a coronary stent experimental protocol, 6 each received a transdermal fentanyl patch to document the patterns of transdermal fentanyl absorption in swine. This approach was taken to reduce animal use and potentially refine the surgical regimen. The objective of the fentanyl portion of the study was to demonstrate that transdermal fentanyl may be useful in the management of postoperative analgesia in swine. This study sought to document that demonstrable levels of fentanyl are achievable in swine plasma via a transdermal system and to compare the magnitude of these levels to data in other species. This study does not directly correlate plasma fentanyl levels with analgesic efficacy. Plasma fentanyl concentration peaked within 42 h in five pigs and within 48 h in the remaining pig. All pigs had similar absorption patterns; the only difference was in magnitude. One pig reached 0.99 ng/ml at 42 h; the next highest concentration was 0.77 ng/ml at 48 h in a different animal. The peak concentration in the others ranged from 0.38 to 0.71 ng/ml.

Administration, Cutaneous↗
PubMed2001

The effect of magnesium deficiency on volatile anaesthetic requirement in the rat: the role of central noradrenergic neuronal activity.

Volatile anaesthetic minimum alveolar concentration (MAC, a measure of anaesthetic requirement) increased in a time-dependent manner in rats fed a Mg2+-deficient diet. MAC values in hypomagnesemic rats were 22-30 per cent greater than those in age-matched controls at 12 and 17 days after starting the diet (p < 0.01). Noradrenergic neuronal activity, as assessed from the ratio of the concentration of 3,4-dihydroxyphenylethylene-glycol (DHPG) to that of norepinephrine (NE), decreased in the brain stem and cerebrum-cerebellum in hypomagnesemic rats owing to an increase in NE concentration in both regions of the brain (p < 0.025). We conclude that prolonged hypomagnesemia (> or = 12 days) increases volatile anaesthetic MAC in the rat. The concomitant decrease in the ratio of DHPG/NE suggests that this increase in MAC cannot be attributed to an increase in noradrenergic neuronal activity in brain.

Anesthetics, Inhalation↗
PubMed2000

Dopamine D5 receptors in nucleus accumbens contribute to the detection of cocaine in rats.

Dopamine D(1)/D(5) receptor antagonism has been shown to block the euphoric and stimulatory effects of cocaine in humans and rats. In the present study, rats trained to discriminate the presence of cocaine (10 mg/kg) from its absence were used to analyze the functional contribution of D(1) (D(1)R) versus D(5) (D(5)R) receptors in the nucleus accumbens, an important neural site for the actions of cocaine. Bilateral microinfusion into the nucleus accumbens of an antisense oligonucleotide directed at the D(5)R (0. 75 nmol/0.3 microl per side, two times per day for 3 d) elicited a downward shift in the dose-effect curve for cocaine with a suppression of peak efficacy; the dose of cocaine estimated to elicit 50% drug-lever responding (ED(50)) was 6.71 mg/kg when assessed 12 hr after the D(5)R antisense oligonucleotide compared to the control ED(50) of 1.83 mg/kg and to the ED(50) of 1.75 mg/kg established 7 d after the last D(5)R antisense oligonucleotide infusion. The D(1)R antisense and scrambled oligonucleotide (0.75 nmol/0.3 microl per side, two times per day for 3 d) were both ineffective. Thus, using drug discrimination techniques that model the subjective effects of cocaine, we show that responsiveness to cocaine is dramatically attenuated after interference with the process of translation of the D(5)R mRNA to its protein product. These findings suggest that D(5)R is a functionally important target site for the indirect actions of cocaine and that rigorous investigations of the function of D(5)R may help guide the discovery of strategies for pharmacotherapy in cocaine dependence.

Analysis of Variance↗
PubMed2000

A supramolecular basis for CD45 tyrosine phosphatase regulation in sustained T cell activation.

Transmembrane protein tyrosine phosphatases, such as CD45, can act as both positive and negative regulators of cellular signaling. CD45 positively modulates T cell receptor (TCR) signaling by constitutively priming p56lck through the dephosphorylation of the C-terminal negative regulatory phosphotyrosine site. However, CD45 can also exert negative effects on cellular processes, including events triggered by integrin-mediated adhesion. To better understand these opposing actions of tyrosine phosphatases, the subcellular compartmentalization of CD45 was imaged by using laser scanning confocal microscopy during functional TCR signaling of live T lymphocytes. On antigen engagement, CD45 was first excluded from the central region of the interface between the T cell and the antigen-presenting surface where CD45 would inhibit integrin activation. Subsequently, CD45 was recruited back to the center of the contact to an area adjacent to the site of sustained TCR engagement. Thus, CD45 is well positioned within a supramolecular assembly in the vicinity of the engaged TCR, where CD45 would be able to maintain src-kinase activity for the duration of TCR engagement.

Animals↗
PubMed2000

Entry of B cell receptor into signaling domains is inhibited in tolerant B cells.

Signal transduction through the B cell antigen receptor (BCR) is altered in B cells that express a receptor that recognizes self-antigen. To understand the molecular basis for the change in signaling in autoreactive B cells, a transgenic model was used to isolate a homogeneous population of tolerant B lymphocytes. These cells were compared with a similar population of naive B lymphocytes. We show that the BCR from naive B cells enters a detergent-insoluble domain of the cell within 6 s after antigen binding, before a detectable increase in BCR phosphorylation. This fraction appears to be important for signaling because it is enriched for lyn kinase but lacks CD45 tyrosine phosphatase and because the BCR that moves into this domain becomes more highly phosphorylated. Partitioning of the BCR into this fraction is unaffected by src family kinase inhibition. Tolerant B cells do not efficiently partition the BCR into the detergent-insoluble domain, providing an explanation for their reduced tyrosine kinase activation and calcium flux in response to antigen. These results identify an early, regulated step in antigen receptor signaling and self-tolerance.

Animals↗
PubMed2000

gammadelta T cells lyse autologous and allogenic oesophageal tumours: involvement of heat-shock proteins in the tumour cell lysis.

T cells expressing gammadelta receptors were isolated from the peripheral blood of oesophageal cancer patients and analysed for their potential to lyse tumour targets. Immunophenotyping by flow cytometry showed that the dominant population of gammadelta T cells expressed the Vgamma9 and the Vdelta2 T cell receptor, and a minor population expressed the Vdelta1 receptor. Cytotoxicity assays revealed that activated gammadelta T cells lysed Daudi Burkitt's lymphoma and K562 cells. Lysis of autologous oesophageal tumours was higher than of allogenic tumours. Anti-hsp60 and anti-hsp70 mAb significantly inhibited the cytotoxicity of gammadelta T cells to both autologous and allogenic oesophageal tumours. Surface expression of hsp60 and hsp70 on oesophageal tumours and Daudi cells was demonstrated by flow cytometry. In conclusion, gammadelta T cells isolated from the peripheral blood of oesophageal cancer patients have the ability of kill oesophageal tumour cells. The lysis of tumour targets by the gammadelta T cells is brought about via recognition of heat-shock proteins expressed on the surface of tumour cells. gammadelta T cells isolated from the peripheral blood may have applications in adoptive immunotherapy of oesophageal cancer.

Antigens, Neoplasm↗
PubMed2000

Mutations in the tyrosine phosphatase CD45 gene in a child with severe combined immunodeficiency disease.

The hematopoietic-specific transmembrane protein tyrosine phosphatase CD45 functions to regulate Src kinases required for T- and B-cell antigen receptor signal transduction. So far, there have been no reports to our knowledge of a human deficiency in a tyrosine-specific phosphatase. Here, we identified a male patient with a deficiency in CD45 due to a large deletion at one allele and a point mutation at the other. The point mutation resulted in the alteration of intervening sequence 13 donor splice site. The patient presented at 2 months of age with severe combined immunodeficiency disease. The population of peripheral blood T lymphocytes was greatly diminished and unresponsive to mitogen stimulation. Despite normal B-lymphocyte numbers, serum immunoglobulin levels decreased with age. Thus, CD45 deficiency in humans results in T- and B-lymphocyte dysfunction.

Antigens, CD↗