Biomedical subjects

H Shen

Publications and source records attributed to H Shen.

At least 91 records · Page 5Linked to original sources

PubMed2001

Activation of the Rap1 guanine nucleotide exchange gene, CalDAG-GEF I, in BXH-2 murine myeloid leukemia.

Here we report the recurrent proviral activation of the Rap1-specific guanine nucleotide exchange factor CalDAG-GEF I (Kawasaki, H., Springett, G. M., Toki, S., Canales, J. J., Harlan, P., Blumenstiel, J. P., Chen, E. J., Bany, I. A., Mochizuki, N., Ashbacher, A., Matsuda, M., Housman, D. E., and Graybiel, A. M. (1998) Proc. Natl. Acad. Sci. U. S. A. 95, 13278-13283; Correction (1999) Proc. Natl. Acad. Sci. U. S. A. 96, 318) gene in BXH-2 acute myeloid leukemia. We also show that CalDAG-GEF I encodes two protein isoforms, a full-length isoform (CalDAG-GEF Ia) and a C-terminally truncated isoform (CalDAG-GEF Ib). Expression of the full-length CalDAG-GEF Ia isoform in Rat2 fibroblasts enhances growth in low serum, whereas expression in Swiss 3T3 cells causes morphological transformation and increased saturation density. In FDCP1 myeloid cells, CalDAG-GEF Ia expression increases growth and saturation density in the presence of the diacylglycerol analogs phorbol 12-myristate 13-acetate (PMA), which activates CalDAG-GEF Ia exchange activity. Likewise, in 32Dcl3 myeloblast cells, CalDAG-GEF Ia expression increases cell adherence to fibronectin in response to PMA and calcium ionophore and allows higher saturation densities and prolonged growth on fibronectin-coated plates. These effects were correlated with increased Rap1, but not Ras, protein activation following PMA and calcium ionophore treatment. Our results suggest that Rap1-GTP delivers signals that favor progression through the cell cycle and morphological transformation. The identification of CalDAG-GEF I as a proto-oncogene in BXH-2 acute myeloid leukemia is the first evidence implicating Rap1 signaling in myeloid leukemia.

Amino Acid Sequence↗

PubMed2001

Effects of exercise on gene-expression profile in the rat hippocampus.

Exercise has beneficial effects on brain function, including the promotion of plasticity and the enhancement of learning and memory performance. Previously we found that exercise increases the expression of certain neurotrophic factors including brain derived neurotrophic factor in the rat hippocampus. To further explore the molecular mechanisms underlying these changes, we used high-density oligonucleotide microarrays containing probe sets representing approximately 5000 genes to analyze the level of gene transcripts in the hippocampus of rats voluntary running for 3 weeks in comparison with sedentary animals. An improved statistical approach for the analysis of DNA microarray data, Cyber-T, was utilized in data analysis. Here we show that exercise leads to changes in the level of a large number of gene transcripts, many of which are known to be associated with neuronal activity, synaptic structure, and neuronal plasticity. Our data indicate that exercise elicits a differential gene expression pattern with significant changes in genes of relevance for brain function.

Aging↗

PubMed2001

Physical activity modulates the combined effect of a common variant of the lipoprotein lipase gene and smoking on serum triglyceride levels and high-density lipoprotein cholesterol in men.

Physical activity has been identified as a protective factor against the occurrence and progression of coronary heart disease. The lipoprotein lipase (LPL) HindIII polymorphism has been associated with changes in triglyceride and high density lipoprotein (HDL)-cholesterol levels. We have investigated whether the association between the LPL HindIII genetic polymorphism and lipid levels is modified by physical activity. We have also tested the hypothesis that physical activity may interact with smoking and the LPL HindIII polymorphism to determine an individual's plasma lipid concentrations. A total of 520 men were selected from a representative sample used in a population study conducted in Gerona, Spain. The median value (291 kcal/day) of energy expenditure in leisure-time physical activity of the studied sample was selected as a cut-off to define sedentary or active subjects. Serum HDL-cholesterol was positively and significantly associated with the amount of daily energy expenditure in physical activity, whereas inverse associations were seen between physical activity and triglyceride concentration and with the triglyceride to HDL-cholesterol ratio. These effects were consistent across LPL HindIII genotypes. There was a statistically significant interaction between LPL genotype and smoking on lipid concentrations. No statistically significant differences were observed in lipid levels of active or sedentary non-smokers between H- carriers and H+H+ homozygotes for the LPL HindIII polymorphism. In smokers, sedentary H+H+ homozygotes showed significantly higher triglyceride and lower HDL-cholesterol concentrations than sedentary H- carriers. These differences were smaller and not statistically significant when lipid values of active H+H+ homozygotes were compared with active H- carriers. Among all subgroups, sedentary smokers with the H+H+ genotype had the most adverse lipid profile, which was considerably less adverse in H+H+ smokers who were physically active. These findings suggest that the presence of the H+H+ genotype has a deleterious effect on lipid profile in an adverse environment such as smoking, and that the expenditure of more than 291 kcal/day in physical activity attenuates this effect.

Cholesterol, HDL↗

PubMed2001

Micron-scale positioning of features influences the rate of polymorphonuclear leukocyte migration.

Microfabrication technology was used to create regular arrays of micron-size holes (2 microm x 2 microm x 210 nm) on fused quartz and photosensitive polyimide surfaces. The patterned surfaces, which possessed a basic structural element of a three-dimensional (3-D) network (i.e., spatially separated mechanical edges), were used as a model system for studying the effect of substrate microgeometry on neutrophil migration. The edge-to-edge spacing between features was systematically varied from 6 microm to 14 microm with an increment of 2 microm. In addition, collagen was used to coat the patterned quartz surfaces in an attempt to change the adhesive properties of the surfaces. A radial flow detachment assay revealed that cell adhesion was the strongest on the quartz surface (approximately 50% cell attached), whereas it was relatively weaker on polyimide and collagen-coated quartz (approximately 25% cell attached). Cell adhesion to each substrate was not affected either by the presence of holes or by the spacing between holes. A direct visualization assay showed that neutrophil migration on each patterned surface could be characterized as a persistent random walk; the dependence of the random motility coefficient (mu) as a function of spacing was biphasic with the optimal spacing at approximately 10 microm on each substrate. The presence of evenly distributed holes at the optimal spacing of 10 microm enhanced mu by a factor of 2 on polyimide, a factor of 2.5 on collagen-coated quartz, and a factor of 10 on uncoated quartz. The biphasic dependence on the mechanical edges of neutrophil migration on 2-D patterned substrate was strikingly similar to that previously observed during neutrophil migration within 3-D networks, suggesting that microfabricated materials provide relevant models of 3-D structures with precisely defined physical characteristics. In addition, our results demonstrate that the microgeometry of a substrate, when considered separately from adhesion, can play a significant role in cell migration.

Cell Adhesion↗

PubMed2001

Genetic deletions of NCAM and PSA impair circadian function in the mouse.

The adult suprachiasmatic nuclei (SCN) express neural cell adhesion molecule (NCAM) that carries polysialic acid (PSA), a carbohydrate polymer which controls plastic cell-cell interactions in neural tissues. Expression of the three major isoforms of NCAM [180 (principal PSA carrier), 140, and 120 kDa) varies with developmental and physiological state. The requirements for NCAM and PSA in circadian timekeeping function were assessed among three transgenic mutant strains with differing expressions of PSA and NCAM. These included: NCAM(tm3Ciw) mice lacking only NCAM 180; NCAM(tm1Cwr) mice lacking NCAM 180, 140, and PSA; and NCAM(tm1Cgn) mice lacking all NCAM isoforms and PSA. Locomotor activity was stably entrained to a 12-h light/dark cycle (LD) in the NCAM(tm3Ciw) and NCAM(tm1Cwr) mutants, but not in NCAM(tm1Cgn) mutants, where the daily onset and offset of activity were irregular or lost. Under constant darkness (DD), the free-running rhythmicity of the NCAM(tm3Ciw) mutants expressing PSA was similar to wild-type controls, but was markedly disrupted in the majority of the NCAM(tm1Cwr) and NCAM(tm1Cgn) mutants lacking PSA. This analysis indicates that PSA and its NCAM carrier are necessary for stable free-running circadian rhythmicity under DD, and that NCAM, but not PSA, is needed for synchronization to LD. Notably, when NCAM 180 is deleted, NCAM 140 compensates as the PSA carrier, and may assume other SCN-related functions of the NCAM 180 isoform.

Animals↗

PubMed2001

Electron microscopic observations of a marine fish iridovirus isolated from brown-spotted grouper, Epinephelus tauvina.

The morphogenesis and the ultrastructure of a marine fish iridovirus isolated from diseased grouper, Epinephelus tauvina were studied by electron microscopy. The virus was grown on a marine fish cell line (GP) at 25 degrees C. After appearance of advanced cytopathic effect (CPE), various morphogenetic stages of virus amplification, maturation and assembly were detected in the cytoplasm of virus-infected cells. The matured nucleocapsids were probably formed by insertion of electron-dense core material into a partly forming empty capsid just before completely sealed. The nucleocapsids were located at the assembly sites as pseudocrystalline arrays or scattered individually. In the late phase of infection, the nucleocapsids were enveloped and released by budding from the plasma membrane. The budding virus particles could directly enter neighbouring cells by endocytosis to start the next round infection. Ultrastructure of the grouper iridovirus was studied using the methods of enzymatic digestions and detergent degradations. The purified iridovirus particles showed a three-layered membrane including an external lipoprotein envelope, an inner periodic protein capsid and a lipid-containing membrane. The regular array of surface capsid subunits was observed after degradation with detergent.

Animals↗

PubMed2001

Upregulation of gap junction connexin 32 with epileptiform activity in the isolated mouse hippocampus.

Gap junctions, which serve as intercellular channels providing direct cytoplasmic continuity and ionic current flow between adjacent cells, are constituted by connexin proteins. Using an in vitro model of bicuculline-induced epileptiform activity, we asked whether increased connexin levels occur during epileptiform activity in the intact whole hippocampus, freshly isolated from young (15-day-old) mouse brain. Exposure to bicuculline (10 microM), for 2-10 h, induced persistent changes in electrical activities that included enhanced spontaneous field activity (4 h), an epileptiform response to single electrical stimulation (6 h), and spontaneous epileptiform activity (6 h). These electrophysiological changes were not reversed by up to 60 min perfusion with normal artificial cerebrospinal fluid, but were greatly depressed by the gap junction uncoupler, carbenoxolone (120 microM, 10 min). Data from RNase protection assay and immunoblotting showed that among several detected gap junctions, only connexin 32 was affected. After 2-6 h exposure to bicuculline, the connexin 32 mRNA expression was upregulated to 2-3-fold control (P < 0.01), and its protein level was significantly elevated the following 6 h (P < 0.01), at which time electrophysiologically measured evidence of clearly epileptiform activity was apparent. In addition, the transcription factor, c-fos protein, but not the cAMP response element-binding protein, was also found to be increased at the early stage of bicuculline exposure (2 h) compared to control (P < 0.05).Thus, we have found that exposing the acutely isolated hippocampus to bicuculline, induced increased c-fos protein, followed by increased connexin 32 transcript and protein, and concurrently, persistent epileptiform activity that was depressed by carbenoxolone.

Action Potentials↗

PubMed2001

Physical activity elicits sustained activation of the cyclic AMP response element-binding protein and mitogen-activated protein kinase in the rat hippocampus.

To elucidate molecular mechanisms involved in physical activity-induced beneficial effects on brain function, we studied in rats the influence of voluntary running on the activation in the hippocampus of cyclic AMP response element-binding protein (CREB) and mitogen-activated protein kinase (MAPK)/extracellular signal-regulated protein kinase (ERK). These are signaling molecules that play critical roles in synaptic plasticity, including learning and memory. Exercise resulted in an increase in the level of the activated transcription factor, CREB phosphorylated at Ser-133. The amount of the activated transcription factor about doubled already after 1 night of running and remained elevated for at least a week, although control levels were restored after 1 month of exercise. In addition, binding activity in nuclear extracts to cyclic AMP response element (CRE) motif containing oligonucleotides increased significantly in the hippocampus after 3 nights of exercise, although the total amount of the immunochemically identified CREB remained unaltered. Electrophoretic mobility supershift assays indicated that the increased binding was due to the recruitment of members of this transcription factor family, in addition to the CREB proper. Voluntary running also resulted in an increase in the level of phosphorylated MAPK (both p42 and p44). The time-courses of the increases in the level of the phosphorylated protein kinase and the activated transcription factor were different. In comparison with the activated CREB, the increase in the phosphorylated MAPK was delayed, but lasted longer, being detectable even after 1 month of exercise. These observations are consistent with the view that the relatively long-lasting activation of these signaling molecules participates in the regulation of genes, such as the neurotrophin genes, and contributes to the beneficial effects of physical exercise on brain function.

Animals↗

PubMed2001

Electroconvulsive shock regulates serotonin transporter mRNA expression in rat raphe nucleus.

The antidepressive actions of electroconvulsive shock (ECS) therapy are considered to involve altered neurotransmission of serotonin. In this study, we investigated the effects of acute and chronic ECS on 5-hydroxytryptamine (5-HT) transporter mRNA expression in rat raphe nucleus. We found that serotonin transporter (5-HTT) mRNA expression was decreased in 9 and 24 h after acute ECS and in 3, 9, 24 h and 2 weeks after chronic ECS in rat raphe nucleus. We presume that the adaptive change in 5-HTT mRNA expression is possibly related to the therapeutic efficacy of electroconvulsive therapy (ECT) on medication-resistant depression.

Animals↗

PubMed2001

Preferential expression of antioxidant response element mediated gene expression in astrocytes.

Transcriptional control of target genes by antioxidant/electrophile response elements has been well described in peripheral tissues. Genes that are regulated by this mechanism include the antioxidant enzymes NAD(P)H:quinone oxidoreductase, gamma-glutamyl cystine synthetase and glutathione-S-transferase. Antioxidant/electrophile response elements within a gene's promoter confer induction by low-molecular-weight electrophilic compounds such as tert-butylhydroquinone and dimethyl fumarate. We have now examined the ability of antioxidant/electrophile response elements to elicit gene expression in neurons and astrocytes in both brain slices and primary cultures using transient transfection of promoter reporter constructs. Our results using a heat-stable human placental alkaline phosphatase reporter indicate that antioxidant/electrophile response element mediated gene expression is largely restricted to astrocyte cell populations. Placental alkaline phosphatase expression was significantly elevated in astrocytes treated with the antioxidant/electrophile response element inducer dimethyl fumarate. Mutant constructs lacking a functional antioxidant/electrophile response element abolished all placental alkaline phosphatase expression in astrocytes. We suggest that astrocytic metabolic processes that normally aid and/or protect neurons may be controlled via this inducible system.

Animals↗

PubMed2001

Activation of 5-HT(1A) but not 5-HT(1B) receptors attenuates an increase in extracellular dopamine derived from exogenously administered L-DOPA in the striatum with nigrostriatal denervation.

In order to determine whether L-DOPA-derived extracellular dopamine (DA) in the striatum with dopaminergic denervation is affected by activation of serotonin autoreceptors (5-HT(1A) and 5-HT(1B) receptors), we applied in vivo brain microdialysis technique to 6-hydroxydopamine-lesioned rats and examined the effects of the selective 5-HT(1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and the selective 5-HT(1B) receptor agonist CGS-12066 A on L-DOPA-derived extracellular DA levels. Single L-DOPA injection (50 mg/kg i.p.) caused a rapid increase and a following decrease of extracellular DA, with a peak value at 100 min after L-DOPA injection. Pretreatment with both 0.3 mg/kg and 1 mg/kg 8-OH-DPAT (i.p.) significantly attenuated an increase in L-DOPA-derived extracellular DA and the times of peak DA levels were prolonged to 150 min and 225 min after L-DOPA injection, respectively. These 8-OH-DPAT-induced changes in L-DOPA-derived extracellular DA were antagonized by further pretreatment with WAY-100635, a selective 5-HT(1A) antagonist. In contrast, intrastriatal perfusion with the 5-HT(1B) agonist CGS-12066 A (10 nM and 100 nM) did not induce any changes in L-DOPA-derived extracellular DA. Thus, stimulation of 5-HT(1A) but not 5-HT(1B) receptors attenuated an increase in extracellular DA derived from exogenous L-DOPA. These results support the hypothesis that serotonergic neurons are primarily responsible for the storage and release of DA derived from exogenous L-DOPA in the absence of dopaminergic neurons.

Animals↗

PubMed2001

1H-MRS detected lipolysis in diabetic rat hearts requires neutral lipase.

PURPOSE: Triacylglycerol (TAG) lipolysis increases in diabetic hearts. However, it is not known which pathway for lipolysis catalyzes this process. Thus, using 1H-magnetic resonance spectroscopy (MRS), we determined whether TAG lipolysis in diabetic rat hearts requires acid lipase or neutral lipase activity. METHODS: Rats were given IP injections of 110 mg streptozotocin (STZ)/kg. Forty-eight to 72 h after this treatment, all rats exhibited ketotic diabetes. The hearts of these ketotic rats were isolated, perfused isovolumically, and analyzed using 1H-MRS. RESULTS: The content of methylene protons (CH2)n--and otherfatty acid protons, measured using 1H-MRS, increased in hearts isolatedfrom STZ-treated compared to untreated rats. This increase in heart--(CH2)n--was directly related to the chemical content of heart TAGs. If isolated diabetic hearts were perfused with either glucose or glucose plus the acid lipase inhibitor methylamine, then heart content of TAG, measured as (CH2)n, decreased at rates of approximately 130 nmol TAG/gdw/min throughout a 55-min perfusion. If diabetic hearts were pretreated with the neutral lipase inhibitor diethyl-p-nitro-phenylphosphate (DNPP) and perfused with glucose, then heart TAG content, measured as (CH2)n, did not change during perfusion. CONCLUSIONS: 1H-MRS can detect the TAG and the net lipolysis of TAG in diabetic rat hearts. Net TAG lipolysis in diabetic rat hearts requires neutral lipase.

Animals↗

PubMed2001

Polymorphic hCHK2/hCds1 codon 84 allele and risk of squamous cell carcinoma of the head and neck--a case-control analysis.

Checkpoint kinase 2 (hCHK2/hCds1) is a tumor suppressor gene involved in cell-cycle control. A hCHK2/hCds1 polymorphism in codon 84 (A-->G at nucleotide 252) was recently identified in Li-Fraumeni syndrome patients. Because cell cycle regulates DNA repair that is associated with cancer risk, we hypothesized that this new polymorphism exists in the general population and is associated with cancer risk. To test this hypothesis, we evaluated the role of this polymorphism in a case-control study of 215 non-Hispanic white patients with newly diagnosed squamous cell carcinoma of the head and neck (SCCHN) and 229 frequency-matched cancer-free controls. We found that the hCHK2/hCds1 codon 84 variant was rare and less frequent in non-Hispanic white cases (0.0186) than in controls (0.0437; P = 0.033). Although no variant homozygotes were detected in these cases and controls, heterozygosity protected against SCCHN, representing a 60% reduction of risk (adjusted odds ratio = 0.40; 95% confidence intervals, 0.17-0.93) compared with wild-type homozygotes. The variant allele was also rare in other ethnic groups (0.0487, 0.0095 and 0.0541 in 115 African Americans, 105 Hispanic Americans and 111 native Chinese, respectively), and only one variant homozygous individual (a Chinese subject) was identified. These results suggest that this hCHK2/hCds1 codon 84 polymorphism is rare and may have a protective role in the aetiology of SCCHN in non-Hispanic whites. Larger studies are warranted to confirm this finding and further mechanistic studies are needed to understand biological relevance of this polymorphism.

Aged↗

PubMed2001

Cyclin D1 polymorphism and risk for squamous cell carcinoma of the head and neck: a case-control study.

A G-->A polymorphism (G870A) in exon 4 of the cyclin D1 (CCND1) gene creates an alternative splice site in its mRNA, encoding a protein with an altered C-terminal domain. It has been suggested that DNA damage in cells with the A allele bypasses the G(1)/S checkpoint of the cell cycle more easily than damage in cells without the A allele. Because CCND1 plays a critical role in cell cycle control and reduced DNA repair capacity is associated with an increased risk for squamous cell carcinoma of the head and neck (SCCHN), we hypothesize that this CCND1 polymorphism modulates individual susceptibility to SCCHN. To test this hypothesis we evaluated the frequency of the polymorphism in a hospital-based case-control study of 233 newly diagnosed SCCHN patients and 248 non-cancer controls. The cases and controls were frequency matched by age (+/-5 years), sex and tobacco use. All subjects were non-Hispanic whites. We found that the A allele frequency was slightly higher in the cases (0.485) than in the controls (0.425), but the difference was borderline statistically significant (P = 0.064). The frequencies of the CCND1 AA, GA and GG genotypes were 23.6, 49.8 and 26.6%, respectively, in cases and 16.5, 52.5 and 31.5%, respectively, in controls. Multivariate logistic regression analysis adjusting for age (in years), sex, smoking and alcohol use was performed to calculate odds ratios (OR) and 95% confidence intervals (CI). Compared with the wild-type CCND1 GG, the CCND1 A G genotype was associated with a non-significantly increased risk (adjusted OR 1.15, 95% CI 0.75-1.76), but the CCND1 AA genotype was associated with a significantly increased risk (adjusted OR 1.77, 95% CI 1.04-3.02) for SCCHN. Results from a trend test using a logistic regression model were statistically significant (P = 0.044). Among the cases the mean age of onset was 59.0, 56.8 and 55.5 years for the GG, GA and AA genotypes, respectively. In the stratification analysis the CCND1 AA variant genotype was associated with a >3-fold increased risk in individuals who were </=50 years old (OR 3.18, 95% CI 1.19-8.46), females (3.57, 1.26-10.0), non-smokers (3.71, 1.37-10.1) and non-alcohol users (4.76, 1.61-14.0). These results suggest that the CCND1 polymorphism is associated with early onset of SCCHN and contributes to susceptibility to SCCHN in this population.

Carcinoma, Squamous Cell↗

PubMed2001

Long-term pharmacologic doses of vitamin E only moderately affect the erythrocytes of patients with type 1 diabetes mellitus.

In erythrocytes from diabetic patients, increased membrane lipid peroxidation might lead to abnormalities in composition and function. To study this relationship, we investigated the effects of a moderate pharmacologic dose of vitamin E for 1 y on erythrocyte membrane peroxidation in vitro and on its fatty acid composition, antioxidant capacity and rheological function. In a random and double-blind manner, type 1 diabetic patients (n = 44) were assigned to the following two groups: Group S received 250 IU (168 mg) d-alpha tocopherol 3 times daily for 1 y. Group P received placebo for 6 mo followed by d-alpha-tocopherol for an additional 6 mo. Variables were monitored every 3 mo. After 3 mo of supplementation, serum vitamin E doubled (P < 0.0005), thiobarbituric acid reactive substances in erythrocyte membranes incubated with tert-butyl hydroperoxide decreased by 25% (P = 0.006) and the lagtime of fluorescence increased from 28 +/- 16 to 41 +/- 28 min (P = 0.028). Patients who did not respond to supplementation (13 of 44) had lower serum lipids (P = 0.017) and body mass index (P = 0.024). We did not detect any significant effects of vitamin E supplementation on membrane lipid composition, antioxidant capacity or blood viscosity. Continuing supplementation for up to 1 y did not further affect serum vitamin E or membrane peroxidation. Stopping supplementation was followed by a return to inclusion values. These results show that the decrease in erythrocyte membrane peroxidation after vitamin E supplementation is moderate, saturable, reversible, restricted to some individuals and has no detectable effect on erythrocyte composition and function.

Adult↗

PubMed2001

Hematopoietic stem cells in HIV disease.

The hematopoietic stem cell has long been hypothesized to be a target of human immunodeficiency virus type-1 (HIV) infection that limits the potential for compensatory immune cell production. Data have recently emerged documenting stem cell dysfunction in HIV disease and indicating that immune recovery from potent antiretroviral therapy is partly driven by new T-cell generation. Effects of HIV on stem cell physiology, however, appear to be indirect, as stem cells are highly resistant to HIV infection. Despite the presence of surface receptors for HIV, the hematopoietic stem cell is not infectible with HIV. However, stem transduction can be achieved with HIV constructs in which the envelope glycoproteins have been replaced by vesicular stomatitis virus G protein. Therefore, hematopoietic stem cells are likely participants in HIV-related cytopenias, but they are spared direct infection and can serve as a resource for cellular therapies for AIDS.

3T3 Cells↗

PubMed2001

Optimal scheduling of tracing computations for real-time vascular landmark extraction from retinal fundus images.

Recently, this group published fast algorithms for automatic tracing (vectorization) of the vasculature in live retinal angiograms, and for the extraction of visual landmarks formed by vascular bifurcations and crossings. These landmarks are used for feature-based image matching for controlling a computer-assisted laser retinal surgery instrument currently under development. This paper describes methods to schedule the vascular tracing computations to maximize the rate of growth of quality of the partial tracing results within a frame cycle. There are two main advantages. First, progressive image matching from partially extracted landmark sets can be faster, and provide an earlier indication of matching failure. Second, the likelihood of successful image matching is greatly improved since the extracted landmarks are of the highest quality for the given computational budget. The scheduling method is based on quantitative measures for the computational work and the quality of landmarks. A coarse grid-based analysis of the image is used to generate seed points for the tracing computations, along with estimates of local edge strengths, orientations, and vessel thickness. These estimates are used to define criteria for real-time preemptive scheduling of the tracing computations. It is shown that the optimal schedule can only be achieved in perfect hindsight, and is thus unrealizable. This leads to scheduling heuristics that approximate the behavior of the optimal algorithm. One such approximation produced approximately 400% improvement in the quality of the partial results at a defined milestone, as compared to random scheduling. The resulting algorithm can be readily implemented on conventional and multiple-processor systems, and is being applied to computer-assisted laser retinal surgery.

Algorithms↗

PubMed2001

Effector differentiation is not prerequisite for generation of memory cytotoxic T lymphocytes.

The lineage relationship between short-lived effector T cells and long-lived memory cells is not fully understood. We have described T-GFP mice previously, in which naive and early activated T cells express GFP uniformly, whereas cells that have differentiated into effector cytotoxic T cells selectively lose GFP expression. Here we studied antigen-specific CD8 T cell differentiation using T-GFP mice crossed to the TCR transgenic (Tg) mice P14 (specific for the lymphocytic choriomeningitis virus glycoprotein peptide, gp33-41). After activation with antigenic peptide, P14XT-GFP CD8(+) T cells cultured in high-dose IL-2 developed into cells with effector phenotype and function: they were blastoid, lost GFP expression, expressed high levels of activation and effector markers, and were capable of immediate cytotoxic function. In contrast, cells cultured in IL-15 or low-dose IL-2 never developed into full-fledged effector cells. Rather, they resembled memory cells: they were smaller, were GFP(+), did not express effector markers, and were incapable of immediate cytotoxicity. However, they mediated rapid-recall responses in vitro. After adoptive transfer, they survived in vivo for at least 10 weeks and mounted a secondary immune response after antigen rechallenge that was as potent as endogenously generated memory cells. In addition to providing a simple means to generate memory cells in virtually unlimited numbers, our results suggest that effector differentiation is not a prerequisite for memory cell generation.

Animals↗