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M L Thomas

Publications and source records attributed to M L Thomas.

At least 73 records · Page 4Linked to original sources
PubMed1997

Regulation of cell signaling by the protein tyrosine phosphatases, CD45 and SHP-1.

An equilibrium between positive and negative regulation of immunoreceptor signaling leads to the proper execution of lymphocyte activation. Tyrosine phosphorylation is the initial event in antigen receptor-induced lymphocyte activation. It is generally accepted that protein tyrosine kinases are involved in positive regulation, whereas protein tyrosine phosphatases are important for the negative regulation of tyrosine phosphorylation-dependent processes. However, the interaction between protein tyrosine kinases and protein tyrosine phosphatases is complex. This article discusses the role of two protein tyrosine phosphatases. CD45 and SHP-1, in the regulation of immunoreceptor signaling. SHP-1 acts as a negative regulator for several immunoreceptors, including those for T- and B-cell antigen receptors. The major role of CD45 is in the positive regulation of T- and B-cell antigen receptor signaling.

Animals↗
PubMed1997

Endoluminal brushing for detection of central venous catheter colonization--a comparison of daily vs. single brushing on removal.

The fibrin assay system (FAS) has been designed to address the problem of in-situ diagnosis of central venous catheter (CVC) colonization. The FAS was evaluated in 12 critically ill patients with daily brushings, comparing results with culture of the catheter tip and blood. Data analysis of the FAS showed a sensitivity of 0 with a specificity of 1.0. The study was repeated in a further 12 high-risk patients with a single terminal brushing on catheter removal. This gave a sensitivity of 0.14 and a specificity of 0.8. Differences in sensitivity may be due to daily disruption of the endoluminal fibrin clot. Our results do not support the routine use of the FAS to detect CVC colonization in the intensive care unit.

Adult↗
PubMed1997

Different nuclear signals are activated by the B cell receptor during positive versus negative signaling.

It is not known how immunogenic versus tolerogenic cellular responses are signaled by receptors such as the B cell antigen receptor (BCR). Here we compare BCR signaling in naive cells that respond positively to foreign antigen and self-tolerant cells that respond negatively to self-antigen. In naive cells, foreign antigen triggered a large biphasic calcium response and activated nuclear signals through NF-AT, NF-kappa B, JNK, and ERK/pp90rsk. In tolerant B cells, self-antigen stimulated low calcium oscillations and activated NF-AT and ERK/pp90rsk but not NF-kappa B or JNK. Self-reactive B cells lacking the phosphatase CD45 did not exhibit calcium oscillations or ERK/pp90rsk activation, nor did they repond negatively to self-antigen. These data reveal striking biochemical differences in BCR signaling to the nucleus during positive selection by foreign antigens and negative selection by self-antigens.

Animals↗
PubMed1997

Catch-up growth induced by growth hormone in the craniofacial skeleton of the Snell strain of the hypopituitary dwarf mouse.

Immature Snell strain dwarf mice were treated with human growth hormone for 20 and 40 days, between the ages of 22 and 41 days and 22 and 61 days, respectively. Mature dwarfs were similarly treated for 20 and 40 days between the ages of 62 and 81 days and 62 and 101 days, respectively. These groups of treated mice were compared with untreated dwarfs and normal mice reared under the same conditions. The catch-up growth effected by human growth hormone on the craniofacial and somatic development of the Snell strain dwarf mouse at both immature and mature ages was considerable, overall being approximately 14 per cent. Neurocranial parameters tended toward the values of normal mice achieving 89-98 per cent of normal growth. Viscerocranial parameters showed greater catch-up, from a lower start point, reaching 81-93 per cent of the control. This catch-up in mature mice (aged 82-102 days) was at a time when any substantial growth in either dwarf or normal mice has usually ceased.

Age Factors↗
PubMed1997

Sequential staining: the effects of sodium fluorescein, osmolarity, and pH on human corneal epithelium.

BACKGROUND: Previous reports have suggested that sequential applications of sodium fluorescein (NaF) to the ocular surface cause loss of epithelial cells. In those experiments the solutions were free of preservatives, but delivered a hypertonic and alkaline load. It is possible that either the hyperosmolarity, NaF, and/or alkalinity may have contributed to the epithelial cell loss. Our study explored the possible impact of these three factors on epithelial integrity. METHODS: We used a paradigm in which we designed four test solutions to isolate the cytotoxic effects of the three factors. Fifteen subjects were exposed to one of the solutions on separate visits. One solution was instilled in both eyes, every 3 min, for a total of seven applications, and a slitlamp examination was performed. Staining was graded on a scale of 0 to 3 for each of five corneal sectors. RESULTS: Application of solution 1 (NaF, hyperosmotic, and alkaline) resulted in staining for all subjects. For the other three solutions (without NaF), insignificant staining occurred. CONCLUSIONS: The epithelium tolerates changes in pH and osmolarity between 7.2 to 7.8 and 290 to 350, respectively. However, NaF when applied in multiple doses may be cytotoxic.

Administration, Topical↗
PubMed1997

Tracheal ring rupture and herniation during percutaneous dilatational tracheostomy identified by fibreoptic bronchoscopy.

We present a case of rupture and herniation of cartilaginous tracheal rings into the lumen of the trachea that was noticed as an incidental finding during bronchoscopy after percutaneous dilatational tracheostomy. While percutaneous methods of tracheostomy formation gain popularity in intensive care settings, the number of reported problems associated with this technique continue to grow. We propose that fibreoptic bronchoscopy used routinely with percutaneous tracheostomy formation will identify a number of complications involving the tracheal skeleton.

Aged↗
PubMed1996

Comparison of CD45 extracellular domain sequences from divergent vertebrate species suggests the conservation of three fibronectin type III domains.

Mammalian CD45 is a transmembrane protein tyrosine phosphatase expressed by all nucleated cells of hematopoietic origin. In lymphocytes, CD45 is required for Ag-induced signal transduction due to its ability to positively regulate Src family members. The mechanisms by which CD45 function is regulated are unknown. Indeed, the interactions of CD45 extracellular domains are largely undefined. To gain insight into potentially important regions of the extracellular domain, we sought to identify conserved features from divergent species. cDNAs encoding the putative CD45 homologue from Heterodontus francisci (horned shark) were isolated. The cDNA sequence predicts a protein of 1200 amino acids that contains a 452-amino acid extracellular domain, a 22-amino acid transmembrane region, and a 703-amino acid cytoplasmic domain. Alignment searches revealed that the Heterodontus cytoplasmic domain sequence was most identical to mammalian CD45 and a transmembrane protein tyrosine phosphatase sequence identified from chickens, ChPTP lambda. A dendrogram with other transmembrane protein tyrosine phosphatase sequences suggest that the Heterodontus and chicken sequences represents CD45 orthologues for their respective species. Analysis of vertebrate CD45 extracellular domain sequences indicates the conservation of three structural regions: a region containing potential O-linked carbohydrate sites, a cysteine-containing region, and a region containing three fibronectin type III domains. For each vertebrate species, multiple isoforms are generated by alternative splicing of three exons that encode a portion of the region containing potential O-linked glycosylation sites. These studies provide evidence for a conservation in CD45 extracellular domain structure between divergent species and provide a basis for understanding CD45 extracellular domain interactions.

Amino Acid Sequence↗
PubMed1996

Direct regulation of ZAP-70 by SHP-1 in T cell antigen receptor signaling.

The threshold at which antigen triggers lymphocyte activation is set by the enzymes that regulate tyrosine phosphorylation. Upon T cell activation, the protein tyrosine phosphatase SHP-1 was found to bind to the protein tyrosine kinase ZAP-70. This interaction resulted in an increase in SHP-1 phosphatase activity and a decrease in ZAP-70 kinase activity. Expression of a dominant negative mutant of SHP-1 in T cells increased the sensitivity of the antigen receptor. Thus, SHP-1 functions as a negative regulator of the T cell antigen receptor and in setting the threshold of activation.

Animals↗
PubMed1996

Regulation of B-lymphocyte negative and positive selection by tyrosine phosphatase CD45.

Elimination of self-reactive B cells must be balanced against the need for B-cell diversity for antibody responses to pathogens. To analyse factors that determine the extent of B-cell negative selection, we crossed CD45-deficient mice with mice carrying immunoglobulin transgenes specific for hen egg lysozyme (HEL). CD45 positively regulates antigen-receptor signalling and CD45-deficient HEL-specific B cells gave diminished signalling in response to HEL. Significantly, few mature CD45-/- B cells accumulated, despite normal immature B-cell production. Circulating HEL autoantigen mediates negative selection of mature CD45+/+ HEL-binding B cells but, in striking contrast, the autoantigen positively selected CD45-/- HEL-binding B cells, promoting their accumulation as long-lived IgD(hi) cells. These findings are consistent with a signal-threshold model for B-cell selection and demonstrate that changes in antigen receptor signalling can cause high-affinity self-reactive B cells to be actively retained instead of eliminated, thus revealing a potential mechanism for inherited susceptibility to autoimmune disease.

Animals↗
PubMed1996

Predictive values of species' identifications from the Vitek Gram-Positive Identification Card using clinical isolates of coagulase-negative staphylococci.

The Gram-Positive Identification Card (GPI, bioMerieux Vitek) was compared to conventional tests for identification of 616 clinical isolates of coagulase-negative staphylococci. All tests were inoculated with subcultures from single isolated colonies. The predictive values of GPI species' identifications (the number of the system's correct calls divided by the total number of calls for each species) were 100% (12 of 12) for Staphylococcus capitis, 100% (79 of 79) for S saprophyticus, 98.4% (246 of 250) for S epidermidis and 96.0% (120 of 125) for S haemolyticus, but only 64.5% (69 of 107) for the other species analyzed. When an infrequently encountered Staphylococcus species is named using the GPI, the identification should be confirmed using additional tests.

Bacteremia↗
PubMed1996

Portfolio-based learning and general practice vocational training.

This action research project developed a portfolio-based learning system, based around a 'log dairy,' with the trainers and general practitioner registrars of one training region in the UK. For those that found benefit from the system, the diary became an important way of holding all the events of a training year together; a way of looking back, in order to view the progress made, and looking forward, to view potential learning needs. Such portfolios were not found to be effective formal assessment mechanisms because the threat of assessment influenced the type of material collected. The enthusiasm of trainers was crucial in encouraging use of the model. The action research process was fundamental in stimulating explorations of ideas on reflective learning. There remains some resistance to the idea of reflective writing, and in this context, portfolios may be one educational tool for use by some, but which may not be universally applicable. Their development and implementation requires considerable local support through facilitation.

Family Practice↗
PubMed1996

Immunologic attributes of cytokine mobilized peripheral blood stem cells and recovery following transplantation.

The immunologic attributes of cytokine mobilized peripheral blood stem cell (PSC) products (n = 52) and the resulting reconstitution of the hematopoietic and immunologic system following autologous transplantation were examined in a consecutive population of non-Hodgkin lymphoma (NHL), or solid tumor patients at the University of Nebraska Medical Center. Granulocyte-monocyte colony stimulating factor (GM-CSF)-mobilized PSC products had a high frequency of monocytes (31%) and bands (15%) as compared to normal peripheral blood (PB) cells. The phenotypic analysis of the mobilized PSC product revealed that they had normal levels of CD4+ cells, an increased frequency of CD8+ cells and a corresponding decrease in the CD4+:CD8+ cell ratio as compared to the peripheral blood leukocytes (PBL) of normal individuals. PSC products also had an increase in CD34+ cells as compared to PB. Natural killer (NK) and T cell activity in the PSC products were also lower than that observed in PB. Post-transplantation there was an accelerated reconstitution of NK-cell function in the PB as compared to T cell function (PHA (phytohemagglutinin) mitogenesis) which did not return to normal by day 100 post-transplantation. We also report for the first time high levels of an irradiation resistant suppressor cell activity in the PSC product and in the PB post-transplantation. There was also a concomitant increase in CD4-, CD8-, TCR alpha/beta+ cells (phenotypic homolog of 'natural suppressor' (NS) cells) in the PB post-transplantation. The number of months of prior chemotherapy correlated with PHA response but the NS activity and frequency of CD4-, CD8- and TCR alpha/beta+ cells did not. Further, cytokine mobilization and apheresis appears to contribute to the loss of PHA responsiveness and the increased levels of suppressor cell activity.

Antigens, CD34↗
PubMed1995

CD45 protein-tyrosine phosphatase associates with the WW domain-containing protein, CD45AP, through the transmembrane region.

CD45 is a transmembrane protein-tyrosine phosphatase required for antigen receptor signaling in lymphocytes. CD45 activates the Src family protein-tyrosine kinases, p56lck and p59fyn, by dephosphorylating a negative regulatory tyrosine in the carboxyl terminus. Immunoprecipitation of CD45 precipitates p56lck and CD45AP. Although the function of CD45AP is unknown, it has been proposed to be an adapter between p56lck and CD45. To assess the ability of CD45AP to function as an adapter, we determined the regions required for the interaction with CD45 by expressing chimeric proteins in HeLa cells. CD45AP has a region similar to a potential protein-protein interaction domain, the WW domain. Surprisingly, this domain was not necessary for the association with CD45. Rather, a 40-amino acid sequence encompassing the putative transmembrane domain of CD45AP was sufficient to mediate binding to CD45. Similarly, a 39-amino acid sequence encompassing the CD45 transmembrane region was sufficient to direct the interaction with CD45AP. Expression of p56lck with CD45AP resulted in an interaction that could only be detected by in vitro kinase reaction, suggesting that the association of p56lck and CD45AP is weak. These data support a model in which CD45AP links CD45 with other proteins but not necessarily p56lck.

Amino Acid Sequence↗
PubMed1995

Comparison of the specificity of bacterially expressed cytoplasmic protein-tyrosine phosphatases SHP and SH-PTP2 towards synthetic phosphopeptide substrates.

SHP and SH-PTP2 are related cytoplasmic protein-tyrosine phosphatases having two tandem amino-terminal src homology 2 domains linked to a single catalytic domain. There is growing evidence that these two molecules may exhibit opposing effects within specific signaling pathways. However, the relative contributions of the src homology 2 domains or the catalytic domains to these opposing effects are not well known. To evaluate the potential contribution of the catalytic domains, we compared the substrate specificity of the two phosphatases. As seen previously, the catalytic activities of bacterially expressed SHP and SH-PTP2 were regulated by the presence of the linked src homology 2 domains. In addition, we characterized a cryptic thrombin cleavage site within the carboxy-terminus of SHP that led to a striking increase in the activity of the catalytic domain. Employing a panel of phosphopeptide substrates whose sequences were modeled after intracellular phosphorylation sites, both SHP and SH-PTP2 demonstrated a similar specificity pattern. Similar to SH-PTP2, SHP failed to elicit detectable phosphate release from several phosphopeptide substrates, while displaying catalytic efficiencies that ranged over approximately 40-1.6 x 10(3) M-1 s-1 towards other substrates. In contrast, the PTP-1B phosphatase dephosphorylated all of the phosphopeptide substrates tested with approximately equal ease. The overall similarity demonstrated by the catalytic domains of SHP and SH-PTP2 suggested that differences in the in vivo behavior of these two molecules might not stem from differences in the substrate specificity of the catalytic domains, suggesting instead that the specificity of the src homology 2 domains is more important in this regard.

Amino Acid Sequence↗
PubMed1995

A role in B cell activation for CD22 and the protein tyrosine phosphatase SHP.

CD22 is a membrane immunoglobulin (mIg)-associated protein of B cells. CD22 is tyrosine-phosphorylated when mIg is ligated. Tyrosine-phosphorylated CD22 binds and activates SHP, a protein tyrosine phosphatase known to negatively regulate signaling through mIg. Ligation of CD22 to prevent its coaggregation with mIg lowers the threshold at which mIg activates the B cell by a factor of 100. In secondary lymphoid organs, CD22 may be sequestered away from mIg through interactions with counterreceptors on T cells. Thus, CD22 is a molecular switch for SHP that may bias mIg signaling to anatomic sites rich in T cells.

Amino Acid Sequence↗
PubMed1995

Characterization of a protein tyrosine phosphatase (RIP) expressed at a very early stage of differentiation in both mouse erythroleukemia and embryonal carcinoma cells.

From our previous studies, several protein tyrosine phosphatases (PTPase) are implicated in the early events leading to in vitro differentiation of both mouse erythroleukemia (MEL) and embryonal carcinoma (F9) cells. Among the PTPases, recent experiments suggest that a new PTPase (RIP) plays a critical role in differentiation processes, particularly at their early stages. We isolated cDNA clones for RIP from a RNA preparation isolated from differentiating MEL cells, and determined the total 7932 bp base sequence for RIP cDNA. The cDNA codes for a putative 269.8 kDa (2450 amino acids) protein with a PTPase catalytic domain. We have demonstrated that the transcripts exist in multiple forms, and among mouse tissues they were found predominantly in kidney and, to a lesser extent, in lung, heart, brain and testis. The RIP gene was mapped between D5Mit90 and D5Mit25 on mouse chromosome 5.

Amino Acid Sequence↗
PubMed1995

Positive and negative regulation of leukocyte activation by protein tyrosine phosphatases.

Many of the initial signal transduction events essential for eliciting an immune response are controlled by the concerted action of protein tyrosine kinases and protein tyrosine phosphatases. However, positive or negative regulation of the cellular response does not fall exclusively into the domain of either class of enzymes. Rather, distinct enzymes can be either positive or negative regulators of a molecular reaction and in certain circumstances, it is conceivable that a single enzyme may have both functions. The biological functions of two protein tyrosine phosphatases, SHP and CD45, serve to illustrate the dichotomy by which this class of enzymes regulate immune responses.

Animals↗