Biomedical subjects

L Zhang

Publications and source records attributed to L Zhang.

At least 217 records · Page 12Linked to original sources

PubMed2002

The cyclooxygenase inhibitor ibuprofen and the FLAP inhibitor MK886 inhibit pancreatic carcinogenesis induced in hamsters by transplacental exposure to ethanol and the tobacco carcinogen NNK.

PURPOSE: Pancreatic cancer is the fourth leading cause of cancer death in men and women. Smoking is a documented risk factor for pancreatic cancer, and the risk is increased in smokers who also consume alcohol. Arachidonic acid (AA)-metabolizing enzymes have been implicated in aggressive clinical behavior of pancreatic cancer while mutations in the Ki- ras gene have been associated with prolonged survival and responsiveness to therapy. Using a hamster model of exocrine pancreatic cancer induced by transplacental exposure to ethanol and the tobacco-carcinogen NNK, we have analyzed these tumors for mutations in the ras and p53 genes and tested the modulating effects of the COX inhibitor, ibuprofen, and the FLAP inhibitor, MK886, on the development of pancreatic cancer in this animal model. METHODS: Hamsters were given 10% ethanol in the drinking water from the fifth to the last day of their pregnancy and a single dose of NNK on the last day. Starting at 4 weeks of age, groups of offspring were given either the COX inhibitor ibuprofen (infant Motrin oral suspension) or the FLAP-inhibitor MK886 (dissolved in carboxymethylcellulose orally) for life while a group of offspring not receiving any treatment served as positive controls. RESULTS: None of the induced pancreatic cancers demonstrated mutations in the Ki-, N-, or H- ras or p53 genes. The development of pancreatic cancer in offspring who had been given ibuprofen or MK886 was reduced by 50% or 30%, respectively. CONCLUSION: In conjunction with the documented over-expression of COX-2 and LOX in human pancreatic cancer, our findings suggest an important role of the AA-cascade in the genesis of this cancer type and indicate that pharmacological or dietary measures that reduce AA-metabolism may be useful for the prevention and clinical management of pancreatic cancer.

Adenocarcinoma↗

PubMed2002

D1 dopamine receptor regulation of microtubule-associated protein-2 phosphorylation in developing cerebral cortical neurons.

This study addresses the hypothesis that the previously described capacity of D1 dopamine receptors (D1Rs) to regulate dendritic growth in developing cortical neurons may involve alterations in the phosphorylation state of microtubule-associated protein-2 (MAP2). The changes in phosphorylation of this protein are known to affect its ability to stabilize the dendritic cytoskeleton. The study involved two systems: primary cultures of mouse cortical neurons grown in the presence of the D1R agonists, SKF82958 or A77636, and the cortex of neonatal transgenic mice overexpressing the D1A subtype of D1R. In both models, a decrease in dendritic extension corresponded with an elevation in MAP2 phosphorylation. This phosphorylation occurred on all three amino acid residues examined in this study: serine, threonine, and tyrosine. In cultured cortical neurons, D1R stimulation-induced increase in MAP2 phosphorylation was blocked by the protein kinase A (PKA) inhibitor, H-89, and mimicked by the PKA activator, S(p)-cAMPS. This indicates that D1Rs modulate MAP2 phosphorylation through PKA-associated intracellular signaling pathways. We also observed that the elevations in MAP2 phosphorylation in neuronal cultures in the presence of D1R agonists (or S(p)-cAMPS) were maintained for a prolonged time (up to at least 96 hr). Moreover, MAP2 phosphorylation underwent a substantial increase between 24 and 72 hr of exposure to these drugs. Our findings are consistent with the idea that D1Rs can modulate growth and maintenance of dendrites in developing cortical cells by regulating the phosphorylation of MAP2. In addition, our observations suggest that MAP2 phosphorylation by long-term activation of D1Rs (and PKA) can be divided into two phases: the initial approximately 24-hr-long phase of a relatively weak elevation in phosphorylation and the delayed phase of a much more robust phosphorylation increase taking place during the next approximately 48 hr.

Animals↗

PubMed2002

Absolute rate constants of alkene addition reactions of a fluorinated radical in water.

Absolute rate constants of *R(f)SO(3)(-) radical addition to a series of water-soluble alkenes containing ionic, carboxylate substituents were measured by laser flash photolysis experiments in water. The observed rate constants were all considerably larger than those of structurally similar analogues in a nonpolar organic solvent, with rate factors of 3-9-fold being observed. It is concluded that such rate enhancements derive at least in part from stabilization of the polar transition state for addition of the electrophilic fluorinated radical to alkenes by the polar solvent water.

Journal Article↗

PubMed2002

Clinical evaluation of safety and human tolerance of electrical sensation induced by electric fields with non-invasive electrodes.

This paper reports the first clinical safety study of human tolerance of electrical sensation using non-invasive, flexible surface-type electrodes and exponentially decaying electric pulses. The study evaluated the effect of electric fields in the absence of a drug and an anesthetic, and was performed in light of potential applications in the field of erectile dysfunction (ED). Twenty impotent patients who had previously received injection or intraurethral therapies were enrolled in the study. Voltage escalations from 50 to 80 V (in 10-V increments) with a single pulse of 3-ms duration were performed with meander-type electrodes placed on the shaft and part of the glans of the penis. The electric fields-induced sensation was assessed via a pain scale from 0 to 10. All 20 patients, who were free to withdraw from the study at any point, completed the voltage escalation study. No clinical safety concerns were apparent and no skin irritation was observed after electric treatment. Our initial study indicates that the pulses in the tested voltage range were well tolerated by most patients. In previous animal experiments under analogous experimental conditions, the application of 50 V has been found effective for transdermal drug delivery into the penis.

Adaptation, Physiological↗

PubMed2002

Vulvar squamous cell carcinoma in young women: a clinicopathologic study of 21 cases.

OBJECTIVES: Invasive squamous cell carcinoma (ISCC) of the vulva occurs most often in older women and the clinical, pathological, and immunohistochemical features of vulvar ISCC in young women are poorly characterized. The aim of this study was to examine clinical and pathological features of ISCC presenting in women younger than 40 years of age. METHODS: Patients younger than 40 years of age who presented with vulvar ISCC were identified in the population-based tumor registry of the British Columbia Cancer Agency (BCCA) for the period 1970-1998. Clinical data and follow-up were obtained. The pathologic material was reviewed and morphologic features assessed. Immunohistochemical staining for MIB-1 and p53 proteins was done and the presence of human papillomavirus (HPV) DNA was assessed by microdissection/PCR. RESULTS: Twenty-one cases, accounting for 5% of all cases of vulvar ISCC encountered at BCCA during this period, were identified, with patient's ages ranging from 17 to 39 years (mean 33). The number of cases of vulvar ISCC in young women, as a percentage of all cases of vulvar ISCC, increased significantly over the study period. Lichen sclerosus was seen in 3 cases. Vulvar intraepithelial neoplasia (VIN) was present in 20 of 21 cases and was multifocal in 4 of them. VIN was subclassified as warty in 7 cases, mixed warty and basaloid in 6, basaloid in 4, and differentiated in 3. There was MIB-1 immunostaining throughout the full thickness of warty and basaloid VIN. Only basal cells stained for MIB-1 in differentiated VIN. Increased p53 expression was present in only 2 cases; both were differentiated-type VIN. HPV DNA was detected in 17 of 20 cases. The tumors were staged as follows: stage IA, 3 cases; stage IB, 13 cases; stage II, 3 cases; stage III, 2 cases. Depth of invasion ranged from <1 to 8.5 mm. The definitive surgical procedure was vulvectomy with lymph node dissection in 14 cases, wide local excision in 6, and excisional biopsy in 1. Clinical follow-up of 1 to 28 years (median, 5 years) showed that 5 patients had local recurrence and 2 died of disease. Of the 21 patients in this study, 1 had concurrent HIV infection and 1 patient with Crohn's disease was treated with corticosteroids; the remaining patients had no clinical evidence of depressed immune function. CONCLUSIONS: The incidence of vulvar ISCC in young women has increased over time; this increase cannot be accounted for by ISCC in immunocompromised patients. The overall disease outcome was excellent, with 2 of 21 patients dead of disease. Most tumors were associated with HPV, but cases of ISCC in the absence of HPV, and associated with differentiated VIN, were encountered. p53 staining of the basal layer can aid in recognition of differentiated VIN while MIB-1 staining within the upper layers of the squamous epithelium is consistently present in warty and basaloid VIN, but not in differentiated VIN.

Adolescent↗

PubMed2002

No impact of repeated endoscopic screens on gastric cancer mortality in a prospectively followed Chinese population at high risk.

BACKGROUND: Gastric cancer (GC) is the leading cause of cancer deaths in China. Our study prospectively evaluated the impact of repeated endoscopic screens on GC mortality in a high-risk population in China. METHODS: Between 1989 and 1999, a population-based gastroscopic screening was conducted in 4,394 residents of Linqu County, China, a region with the highest rates of GC worldwide. Residents ages 35 to 64 years received initial gastroscopies with biopsies in 1989. Repeated endoscopies were performed in 1994 and 1999. Cancer occurrences and deaths were actively monitored throughout the entire period until July 2000. Mortality from GC was compared with expected values based on mortality rates obtained for Linqu in the 1990-1992 Chinese Cancer Mortality Survey. RESULTS: Between March 1989 and July 2000, 39,303 person-years were accumulated; 85 new GCs occurred, 29 (34.5%) were in early stage. Fifty-eight cases (68%) were identified at one of the screens. The number of observed deaths from GC (37) was close to the expected (36.8). The standardized mortality ratio was 1.01 (95% CI 0.72-1.37) for the entire cohort, 1.13 (95% CI 0.77-1.57) for males, and 0.65 (95% CI 0.26-1.32) for females. CONCLUSIONS: Despite high population coverage with repeated screens, no reduction in GC mortality was observed in this high-risk population in China.

Adult↗

PubMed2002

Advances in micro-calcification clusters detection in mammography.

A new mixed feature multistage false positive (FP) reduction method for micro-calcification clusters (MCCs) detection has been developed for improving the FP reduction performance. Eleven features were extracted from both spatial and morphology domains in order to describe MCCs from different perspectives. These features are grouped into three categories: gray-level description, shape description and clusters description. Two feature sets that focus on describing MCCs on every single calcification and on clustered calcifications, respectively, were combined with a back-propagation (BP) neural network with Kalman filter to obtain the best performance of FP reduction. First, nine of the eleven gray-level description and shape description features were employed with BP neural network to eliminate all the obvious FP calcifications in the image. Second, the remaining MCCs were classified into several clusters by a widely used criterion in clinical practice and then two cluster description features were added to the first feature set to eliminate the FP clusters from the remaining MCCs. The performance results of this approach were obtained using an image database of 67 real-patients mammogram images in H. Lee Moffitt Cancer Center imaging program. The proposed method successfully reduced the FP to 3.15/image, while the detection sensitivity or true positive rate improved to 97%.

Algorithms↗

PubMed2002

Environmental enrichment attenuates cognitive deficits, but does not alter neurotrophin gene expression in the hippocampus following lateral fluid percussion brain injury.

Environmental enrichment attenuates neurological deficits associated with experimental brain injury. The molecular events that mediate these environmentally induced improvements in function after injury are largely unknown, but neurotrophins have been hypothesized to be a neural substrate because of their role in cell survival and neural plasticity. Furthermore, exposure to complex environments in normal animals increases neurotrophin gene expression. However, following an ischemic injury, environmental enrichment decreases neurotrophin mRNA levels. Whether these contrasting findings are attributable to differences between injured and uninjured animals or are dependent upon the specific type of brain injury has not been determined. We examined the effects of 14 days of environmental enrichment following a lateral fluid percussion brain injury on behavior and gene expression of brain-derived neurotrophic factor, its high-affinity receptor, TrkB, and neurotrophin-3 in the rat hippocampus. Environmental enrichment attenuated learning deficits in the injured animals, but neither the injury nor housing conditions influenced neurotrophin/receptor mRNA levels. From these data we suggest that following brain trauma, improvements in learning associated with environmental enrichment are not mediated by alterations in brain-derived neurotrophic factor, TrkB or neurotrophin-3 gene expression.

Animals↗

PubMed2002

Angiopoietin-1 reduces cerebral blood vessel leakage and ischemic lesion volume after focal cerebral embolic ischemia in mice.

Angiopoietin-1 (Ang1) is a ligand for the endothelial specific receptor tyrosine kinase, Tie2, that protects the adult peripheral vasculature from vascular leakage. We tested the hypothesis that increases in levels of Ang1 reduce blood-brain barrier (BBB) leakage in ischemic brain. Mice were subjected to embolic middle cerebral artery (MCA) occlusion. Recombinant adenoviruses expressing Ang1 (Ad-Ang1) or a control gene encoding green fluorescent protein (Ad-GFP), or recombinant Ang1 protein, BowAng1, was administered to mice before MCA occlusion. Regional cerebral blood flow (rCBF), the brain tissue content of Evans Blue, and ischemic lesion volume were measured. Serum levels of Ang1 (183+/-31.9 microg/ml, n=4) were detected in mice receiving Ad-Ang1 or in mice treated with BowAng1 (262+/-35.4 microg/ml, n=7) but not in the control mice (n=11). Six hours after MCA occlusion, mice receiving Ad-GFP (n=8) or control protein (n=7) showed large Evans Blue leakage in the ipsilateral hemisphere (0.46+/-0.05 or 0.55+/-0.16 ng/mg tissue) whereas mice receiving Ad-Ang1 (n=6) or BowAng1 (n=7) had significantly (P<0.05) less Evans Blue leakage (0.26+/-0.07 or 0.14+/-0.03 ng/mg tissue). Infusion of recombinant human vascular endothelial growth factor (rhVEGF(165)) to ischemic mice resulted in significant (P<0.05) increases in Evans Blue leakage (1.24+/-0.34 ng/mg tissue, n=7) compared with the control mice. In contrast, infusion of rhVEGF(165) in ischemic mice receiving Ad-Ang1 did not significantly increase Evans Blue dye in the ipsilateral hemisphere (0.22+/-0.06 ng/mg tissue, n=6). Moreover, 24 h after ischemia mice receiving Ad-Ang1 had a significantly smaller ischemic lesion volume (22.6+/-2.7%, n=8) than the lesion volume in mice receiving Ad-GFP (44.7+/-3.7%, n=8), although rCBF reduced to approximately 20% of the contralateral levels in both groups of mice 10 min after ischemia. Our data demonstrate that Ang1 reduces BBB leakage in ischemic brain and consequently decreases ischemic lesion volume.

Angiogenesis Inducing Agents↗

PubMed2002

Expression and function of A1 adenosine receptors in the rat hippocampus following transient forebrain ischemia.

We investigated how transient cerebral ischemia affects the gene expression, immunoreactive protein levels, and the function of the A1 subtype of adenosine receptor in the rat hippocampus at different times following reperfusion. A1 receptor mRNA levels were altered significantly in different hippocampal subfields as early as 6 h following insult. However, these changes in mRNA levels were not paralleled at the protein level, as western blotting with A1 receptor-specific antibodies revealed that hippocampal A1 adenosine receptor prevalence did not differ from sham control at either 6 or 24 h following insult. The lack of change in A1 receptor prevalence was consistent with functional examinations, as only marginal changes were observed in the ability of A1 receptors to attenuate excitatory post-synaptic potentials in the CA1 subfield at 24 h following reperfusion. These data illustrate that although the mRNA expression levels of the A1 adenosine receptor are altered by transient cerebral ischemia, the immunoreactive prevalence and function of this receptor are maintained in the post-ischemic hippocampus at times preceding the death of the vulnerable neurons.

Animals↗

PubMed2002

The interaction of Cu2 + ions and NaDC micelles.

By mixing an aqueous solution of CuCl2 with an NaDC aqueous solution of various concentration and initial molar ratio, seven coordinated samples with distinct appearances and characters were obtained. Their structures and components were investigated by FT-IR spectroscopy, EXAFS (the extended X-ray absorption fine structure), thermal analysis, X-ray diffraction, laser light scattering, TEM (transmission electron micrograph), element analysis and ICP (inductively coupled plasma) analysis. The following conclusions were given: (1) The complexes of Cu2+-NaDC with distinct appearances and properties were synthesized. (2) After Cu(DC)2 dissolved in NaDC aqueous solution, larger micelles (30-90 nm diameter) formed in the supernate, it is a mixed micelle with Cu(DC)2 and NaDC. So these micelles are a new kind of micelle containing two kinds of metal ions. This is a new result using metal ions as bridges to form micelle. (3) According to the different concentration of Cu2+ to NaDC, the complexes formed as gel or poly-crystals. Both the composition of gel complexes and the coordination structure of carboxyl groups with metal ions varied with the initial molar ratio of Cu2+ to Na+. The gel complexes exhibits the non-stoichiometric character. (4) These results are in agreement with physiological condition. All the different states such as gel, precipitate, micelles of various structures are present in bile of gallbladder. We can suggest an ideal model of the interaction between Cu2+ and bile salts in vivo.

Biophysical Phenomena↗

PubMed2002

Comparison of HPV infection, p53 mutation and allelic losses in post-transplant and non-posttransplant oral squamous cell carcinomas.

BACKGROUND: Oral squamous cell carcinoma (SCC) is increasingly found in transplant recipients, although little is known of the natural history of the disease or the mechanism underlying this increase. METHODS: In this article we describe the history of development of 5 oral post-transplant SCCs (PSCCs) and compare their genetic profiles to 34 non-posttransplant SCCs (NPSCCs). RESULTS: Of the five patients with PSCCs, 3 had bone marrow transplants and two, kidney. All three PSCCs from bone marrow recipients were preceded locally by graft-vs.-host disease (GVHD). Two of the GVHD were biopsied and demonstrated dysplasia. Similar frequencies of loss of heterozygosity (LOH) occurred in PSCCs and NPSCCs at 3p, 9p, 17p and 8p, with lower frequencies in PSCCs at 4q (39% vs. 0%), 11q (53% vs. 20%) and 13q (45% vs. 20%), although the latter were not significantly different. Only 1 PSCC had a p53 mutation, compared to historical values of 40-60% for NPSCC. Interestingly, human papillomavirus (HPV) DNA was detected in 3 (60%) PSCCs, in comparison to only 4 (12%) of the 34 NPSCCs (P = 0.0346). CONCLUSIONS: Dysplasia in oral GVHD may be a strong indicator of cancer risk and should not be regarded as reactive changes to lichenoid mucosites. The low level of p53 mutation and increased HPV infection support the involvement of HPV in the development of PSCC, while the similarity in LOH patterns suggests that other aspects of carcinogenesis may be comparable in these two types of SCCs.

Adult↗

PubMed2002

Association of low-density lipoprotein receptor polymorphisms and outcome of hepatitis C infection.

The low-density lipoprotein receptor (LDLR) has been proposed to promote hepatitis C virus endocytosis and the cell membrane protein CD81 may also promote HCV host cell entry. The CD81 gene was sequenced to screen for novel polymorphisms, but no SNPs were identified. Polymorphisms within the LDLR gene are associated with the pathogenesis of familial hypercholesterolemia, atherosclerosis and obesity. We therefore studied genetic variation within the LDLR gene and clinical features of hepatitis C infection. An amino acid change in exon 8 was associated with severity of fibrosis; a SNP in exon 10 correlated with viral clearance and overall inflammation, and a SNP in the 3'UTR appeared to influence treatment response. There were no other significant associations between any of the SNPs studied and the clinical measures of hepatitis C infection. We furthermore report on linkage disequilibrium within the gene and haplotype frequencies in our population. Our findings support a possible role for the LDLR in the modulation of disease progression by affecting immune responses, rather than functioning as receptor for HCV.

Adolescent↗

PubMed2002

Mechanisms involved in development of resistance to adenovirus-mediated proapoptotic gene therapy in DLD1 human colon cancer cell line.

To evaluate resistance that develops in cancer cells during treatment with adenoviral vectors expressing proapoptotic genes, we repeatedly treated the human colon cancer cell line DLD1 with adenoviral vectors expressing the human Bax gene and the human tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) gene. DLD1 cells resistant to the Bax- or TRAIL-expressing adenoviral vectors were then selected and designated as DLD1/Bax-R or DLD1/TRAIL-R cells, respectively. Further study showed that resistance in DLD1/Bax-R cells was caused by resistance to adenoviral infection, which can be overcome by dose escalation of the adenoviral vectors. However, resistance in DLD1/TRAIL-R cells was caused by resistance to the TRAIL gene. Therefore, different mechanisms are involved in the development of resistance during adenovirus-mediated proapoptotic gene therapy. A survey of molecules involved in TRAIL- or Bax-mediated apoptotic pathways showed no significant change in expression of death receptors, death decoy receptors; FLIP; Bcl-2; Bcl-xS; Bax; Bak; XIAP or caspase-2, -7, -8, or -9 in either DLD1/Bax-R or DLD1/TRAIL-R cells. Bcl-xL expression detected in both mRNA and protein level assays was three times higher in DLD1/TRAIL-R cells than in parental or DLD1/Bax-R cells. However, transfection of DLD1 cells with the Bcl-xL gene showed that overexpression of Bcl-xL is not sufficient for the resistance. Moreover, DLD1/Bax-R cells were sensitive to adenoviral vectors that expressed the TRAIL gene, but resistant to adenoviral vectors that expressed the Bak gene. In contrast, DLD1/TRAIL-R cells were sensitive to adenoviral vectors that expressed either Bax or Bak gene. Thus, alternative application of adenoviral vectors that expressed proapoptotic genes in different pathways or different cell killing models may delay or prevent development of resistance in adenovirus-mediated proapoptotic gene therapy.

Adenoviridae↗

PubMed2002

Combined TRAIL and Bax gene therapy prolonged survival in mice with ovarian cancer xenograft.

We evaluated the antitumor activity of the Bax gene and green fluorescent protein/tumor necrosis factor-related apoptosis-inducing ligand (GFP/TRAIL) fusion gene driven by the human telomerase reverse transcriptase promoter both separately and combined in the human ovarian cancer lines SKOV3ip and DOV13 and human lung cancer line H1299. In vitro study showed that both TRAIL- and Bax-expressing vectors elicited significant cell killing in H1299 and SKOV3ip cells, but only the GFP/TRAIL gene elicited significant cell killing in DOV13 cells. Combined TRAIL and Bax therapy also produced more profound cell killing in SKOV3ip and H1299 cells, but not DOV13 cells without escalation of the vector doses. To further evaluate the combined effects of Bax and TRAIL, abdominally spread tumors were established in nude mice via intraperitoneal inoculation of SKOV3ip cells followed by that of adenoviral vectors. Tumor growth, ascites formation, survival duration and toxicity were evaluated after treatment. We found that treatment using the Bax- or TRAIL-expressing vector alone significantly suppressed tumor growth and ascites formation, and prolonged animal survival when compared with that of using PBS or a control vector. Combined TRAIL and Bax therapy further prolonged survival significantly when compared with therapy using the TRAIL or Bax gene alone. Transgene expression and apoptosis induction were not detected in normal human ovarian epithelial cells in vitro or normal mouse tissues in vivo after intraperitoneal vector administration. Also, liver toxicity was not detected after either treatment. Thus, combined TRAIL and Bax gene therapy may be useful for treatment of abdominally spread tumors.

Animals↗

PubMed2002

Transcription factors acting on the promoter of the rat fatty acid synthase gene.

Fatty acid synthase (FAS), one of the main lipogenic enzymes, converts dietary calories into a storage form of energy. The transcription factors, stimulatory proteins 1 and 3 (Sp1 and Sp3), nuclear factor Y (NF-Y), upstream stimulatory factor (USF) and sterol regulatory element binding protein-1 (SREBP-1) have cognate binding sites on the promoter of the FAS gene. It was shown that Sp1 and NF-Y interact co-operatively at the diet-induced DNase I-hypersensitive site at position -500. Adjacent binding sites for NF-Y and Sp1 have also been found between -71 and -52, and -91 and -83. cAMP regulation is mediated via the inverted CAAT element (ICE) at -99 to -92, which binds NF-Y. The FAS insulin-responsive element 3 (FIRE3)-binding site at -71 to -52 is capable of binding NF-Y, USF and SREBP-1, and is required for the sterol response in conjunction with the co-activator NF-Y around -100. Surprisingly, both FIRE3 and ICE are also necessary for the response to retinoic acid that plays a role in development and is an essential component of the diet.

Animals↗

PubMed2002

Thymic re-entry of mature activated T cells and increased negative selection in vascularized allograft recipients.

Transplantation tolerance is a dynamic state that involves several homeostatic mechanisms intrinsic to the host. One of these mechanisms is activation-induced T cell death (AICD). However, it is unclear where AICD takes place during alloreactive responses. Since activated T cells can re-enter the thymus, we hypothesized that mature T cells activated by an allograft could be deleted upon re-entry into the thymus. To test this hypothesis, we used wild-type or 2C TCR transgenic mice receiving syngeneic or allogeneic heterotopic, vascularized heart grafts. First, we demonstrated that ex vivo CFSE-labelled T cells re-entered the thymus when transferred into allograft recipients but not when transferred into isograft recipients. Next, we compared the changes in cell subset numbers and incidence of apoptosis in the thymi and spleens of allograft or isograft recipients. Seven days after transplantation, at a time in which all the allografts were undergoing rejection, cells expressing donor-MHC class II molecules had migrated to the thymus and to the spleen. In the thymus of allograft recipients, overall cellularity was significantly reduced by 40% and associated with an increase in the number of double negative (CD4-CD8-) thymocytes and a decrease in double positive (CD4+CD8+) thymocytes, consistent with increased negative selection of thymocytes. Additionally, thymi of allograft recipients showed an increase in the number of recently activated, mature T cells (TCRhi, CD25+, CD44+) and a significant increase in the number of apoptotic cells, especially in the thymic medulla, that involved mature T cells as indicated by the TCRhi, CD44+, CD4 or CD8 single positive phenotype. Spleens of allograft recipients were increased in size and cellularity but did not show any of the changes in cell subsets seen in the thymi. Our data show that after allografting there is an increase in apoptotic cell death that is associated with negative selection of developing thymocytes as well as of alloreactive mature T cells that have re-entered the thymus upon activation in the periphery. This may occur upon migration of graft-derived antigen-presenting cells to the thymus.

Animals↗

PubMed2002

Cloning and sequencing of quail and pigeon prion genes.

Quail and pigeon PrP genes were cloned and sequenced. Like mammalian PrP genes, quail and pigeon genes are encoded by a single exon of a single copy gene in the genome. All of the structural features of mammalian PrP genes were found in the quail and pigeon PrP gene. Compared with the nucleotide sequences of mammalian PrP, they display generally 30% similarity. When compared with chicken PrP's DNA sequence, they show a higher homology (90%), and an even higher homology (99%) when compared to each other. A phylogenetic tree was constructed to trace the evolution of the prion gene in animals.

Animals↗