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X D Wu

Publications and source records attributed to X D Wu.

48 records · Page 3Linked to original sources
PubMed1991

Myasthenia gravis. T epitopes on the delta subunit of human muscle acetylcholine receptor.

Autoimmune T cell lines specific for muscle nicotinic acetylcholine receptor (AChR) were propagated from the blood of three myasthenia gravis patients by the use of a pool of synthetic peptides (delta-pool) corresponding to the complete sequence of the delta-subunit of human muscle AChR. Propagation of AChR-specific T cell lines was attempted unsuccessfully from four other myasthenia gravis patients and from four healthy controls. The lines had CD3+, CD4+, CD8- phenotype, strongly recognized the delta-pool, and cross-reacted vigorously with non-denatured AChR purified from mammalian muscle. They did not cross-react detectably with pools of similar overlapping synthetic peptides corresponding to the complete sequences of the alpha- and gamma-subunits of human muscle AChR. The sequence segments of the delta-subunit that contain T epitopes were identified by investigating the response of the three CD4+ T cell lines to the individual synthetic peptides forming the delta-pool. Each line had an individual pattern of peptide recognition. Although no immunodominant region, recognized in association with different DR haplotypes, could be identified, the sequence segments most strongly recognized by the CD4+ T cell lines were clustered within residues 121-290. One of the peptides more strongly recognized by the T cells corresponded to a sequence segment with high predicted propensity to form an amphipathic alpha-helix, a structural motif proposed to be typical of T epitopes.

Amino Acid Sequence↗
PubMed1991

Alpha-bungarotoxin and the competing antibody WF6 interact with different amino acids within the same cholinergic subsite.

In the nicotinic acetylcholine receptors (AChRs), the sequence segment surrounding two invariant vicinal cysteinyl residues at positions 192 and 193 of the alpha subunit contains important structural component(s) of the binding site for acetylcholine and high molecular weight cholinergic antagonists, like snake alpha-neurotoxins. At least a second sequence region contributes to the formation of the cholinergic site. Studying the binding of alpha-bungarotoxin and three different monoclonal antibodies, able to compete with alpha-neurotoxins and cholinergic ligands, to a panel of synthetic peptides as representative structural elements of the AChR from Torpedo, we recently identified the sequence segments alpha 181-200 and alpha 55-74 as contributing to form the cholinergic site (Conti-Tronconi et al., 1990). As a first attempt to elucidate the structural requirements for ligand binding to the subsite formed by the sequence alpha 181-200, we have now studied the binding of alpha-bungarotoxin and of antibody WF6 to the synthetic peptide alpha 181-200, and to a panel of peptide analogues differing from the parental sequence alpha 181-200 by substitution of a single amino acid residue. CD spectral analysis of the synthetic peptide analogues indicated that they all have comparable structures in solution, and they can therefore be used to analyze the influence of single amino acid residues on ligand binding. Distinct clusters of amino acid residues, discontinuously positioned along the sequence 181-200, seem to serve as attachment points for the two ligands studied, and the residues necessary for binding of alpha-bungarotoxin are different from those crucial for binding of antibody WF6. In particular, residues at positions 188-190 (VYY) and 192-194 (CCP) were necessary for binding of alpha-bungarotoxin, while residues W187, T191, and Y198 and the three residues at positions 193-195 (CPD) were necessary for binding of WF6. Comparison of the CD spectra of the toxin/peptide complexes, and those obtained for the same peptides and alpha-bungarotoxin in solution, indicates that structural changes of the ligand(s) occur upon binding, with a net increase of the beta-structure component. The cholinergic binding site is therefore a complex surface area, formed by discontinuous clusters of amino acid residues from different sequence regions. Such complex structural arrangement is similar to the "discontinuous epitopes" observed by X-ray diffraction studies of antibody/antigen complexes [reviewed in Davies et al. (1988)]. Within this relatively large structure, cholinergic ligands bind with multiple points of attachment, and ligand-specific patterns of the attachment points exist.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1991

Optimization of high dose-rate cervix brachytherapy; Part I: Dose distribution.

Computer controlled high dose-rate (HDR) brachytherapy afterloading machines are equipped with a single, miniaturized, high activity Ir-192 source that can be rapidly moved in fine increments among several channels. Consequently, by appropriate programming of source dwell positions and times, the dose distribution can be optimized as desired. We have explored the optimization potential of this new technology for two applications: (a) cervix brachytherapy, and (b) transvaginal irradiation. Cervix brachytherapy with a gynecologic ring applicator was simulated by 48 sources of relative activities ranging from 0.17 to 1.00 that were equally distributed between the tandem and the ring. The results confirmed that the optimized distribution of physical doses are superior to those achievable with standard brachytherapy sources and applicators. For example, with five-point optimization, the relative dose-rate in the rectum was only 47% of that in point A; for standard application the dose rate was 47% higher. For transvaginal application 27 sources of relative activities between 0.07-0.79 were placed in the ring and a single source of unit strength in the tandem. Using dose distribution homogeneity as an optimization criterion, the results (+/- 2.5%) were again superior to those obtained for commonly used double ovoid (+/- 15%), linear cylinder (+/- 27%), or a "T" source (31%).

Brachytherapy↗
PubMed1990

Identification of a brain acetylcholine receptor alpha subunit able to bind alpha-bungarotoxin.

Peptides corresponding to sequence segments homologous to an alpha-bungarotoxin (alpha-BGT) binding region on the alpha subunit of the Torpedo nicotinic cholinergic receptor (nAChR) were synthesized for each identified nAChR alpha subunit of the rat nervous system (alpha 1, which is expressed in muscle, and alpha 2, alpha 3, alpha 4, and alpha 5, which are expressed by neurons). The peptides were tested for their ability to directly bind 125I-alpha-BGT and to compete for 125I-alpha-BGT with Torpedo nAChR and with the alpha-BGT-binding component expressed by PC12, a sympathetic neuronal cell line. In addition to peptides of the muscle alpha 1 subunit, peptides corresponding to the sequence of a neuronal subunit, alpha 5, were able to bind 125I-alpha-BGT. Peptides containing the sequence segments 182-201 of the alpha 1 subunit and 180-199 of the alpha 5 subunit competed with Torpedo nAChR for 125I-alpha-BGT binding with IC50 values of 0.5 and 3.5 microM, respectively. Both of these peptides were also able to compete for 125I-alpha-BGT binding with native Torpedo nAChR and with the alpha-BGT-binding protein(s) expressed on PC12 cells. To determine if other sequence segments contribute to form the neuronal alpha-BGT-binding site, overlapping peptides corresponding to the putative extracellular domain of the alpha 5 subunit were synthesized and used both in direct binding assays and in competition experiments. Peptides corresponding to amino acids 16-35 and 180-199 of the alpha 5 subunit directly bound 125I-alpha-BGT and inhibited the binding of toxin to both Torpedo nAChR and PC12 cells. The results of these studies strongly support identification of the alpha 5 subunit as a component of a neuronal alpha-BGT-binding nAChR.

Amino Acid Sequence↗
PubMed1990

Use of synthetic peptides to establish anti-human acetylcholine receptor CD4+ cell lines from myasthenia gravis patients.

Acetylcholine receptor-(AcChR) specific T cell lines were propagated from the PBL of six myasthenia gravis (MG) patients by the use of a pool of synthetic peptides (alpha-pool) corresponding to the complete sequence of the alpha-subunit of the human AcChR. All the lines had CD4+ phenotype and strongly recognized the alpha-pool. Four lines cross-reacted with native Torpedo AcChR. Five lines showed, at certain stages of their propagation, some degree of reactivity to autologous or DR-matched APC. One of the CD4+ T lines was challenged with each one of the peptides present in the alpha-pool. Several peptides, corresponding to the sequence segments 48-67, 101-120, 304-322, 320-337, and 419-437 of the human alpha-subunit were recognized, indicating that different epitopes and multiple T cell clones are involved in the recognition of the autoantigen in MG. Human AcChR-specific CD4+ T cell lines will be useful to identify the repertoire of epitopes recognized by the autoreactive Th cells in MG, to investigate the TCR genes utilized by autoreactive Th cells and to develop specific immunosuppressive treatments using anti-T cell vaccination.

Amino Acid Sequence↗
PubMed1990

Regulation of insulin-like growth factor I messenger ribonucleic acid levels by serum in cultured rat fibroblasts.

Fibroblasts represent one of the in vivo sites of extrahepatic insulin-like growth factor I (IGF-I) production. In this study, cultured fibroblasts prepared from the skin of neonatal rats were used as a model to assess the role of serum in regulating IGF-I messenger RNA (mRNA) levels. IGF-I mRNA, as demonstrated by Northern blot analysis, was present in the cultured fibroblasts, and serum free media which was conditioned by fibroblasts for 20 h contained 108 pg/ml of immunoreactive IGF-I. Fetal calf serum (FCS) decreased steady state IGF-I mRNA levels, as measured by solution hybridization/RNase protection assay, in fibroblasts in a time- and dose-dependent fashion. Incubation of fibroblasts for 18 h in the presence of 0.3%, 0.6%, or 1% FCS decreased IGF-I mRNA levels to 76%, 56%, and 46% of the levels present in control cells which were maintained in serum free media with 0.25% BSA. Maximal inhibition to approximately 20% of control levels was seen with 4-10% FCS. In contrast, basic fibroblast growth factor and beta-actin mRNA levels increased 2- and 4-fold, respectively, with increasing concentrations of FCS. Treatment of the cells with 10 micrograms/ml cycloheximide resulted in partial abrogation of the inhibitory effect of FCS while protein synthesis in the cells was decreased to 6% of control levels. The addition of 2 micrograms/ml of insulin or 15-100 ng/ml of IGF-I to the fibroblasts did not reproduce the inhibitory effect of FCS. Finally, the inhibitory factor(s) present in the FCS was partially removed/inactivated by charcoal stripping or heat inactivating the serum, but delipidation of the FCS by chloroform extraction had no effect on the inhibitory effect of FCS. In summary, FCS contains a factor(s) that decreases IGF-I mRNA levels in cultured fibroblasts in a time- and dose-dependent fashion. The partial abrogation of the inhibitory effect of FCS with cycloheximide treatment suggests that this effect is at least partially dependent upon new protein synthesis. Furthermore, the studies using delipidated, heat-inactivated, and charcoal-stripped serum suggest that the inhibitory factor(s) is a peptide.

Actins↗
PubMed1989

[Comparison of actions of m-nifedipine and nifedipine on isolated guinea pig atria and rabbit aortic strips].

m-Nifedipine (m-Nif) had weaker inhibitory effects than nifedipine (Nif) on the staircase phenomenon, functional refractory period and contraction (IC50: m-Nif/Nif = 18) of isolated guinea pig left atria at concentrations of 0.1-1.0 mumol/L. At the same concentrations, both m-Nif and Nif could hardly change the post-rest potentiation, excitability and ectopic automaticity induced by epinephrine. m-Nif 0.05 mumol/L, had no effect on the automatic contractile force of isolated right atria but could slow down the automatic rhythm. On the contrary, Nif had little effect on the automatic rhythm but potently inhibited the contractile force. Furthermore, in isolated rabbit aorta strips, m-Nif had an equal or somewhat stronger inhibitory effect on the tension induced by KCl. These results suggest that m-Nif might be superior to Nif in treating myocardial ischemia, arterial hypertension and congestive heart failure.

Animals↗
PubMed1985

[Application of trichosanthin in 179 difficult cases of artificial abortion].

This article introduces the application of compound crystal trichosanthin to 179 difficult cases of artificial abortion including cases with extreme anteversion and anteflexion of uterus with a fine and long cervix, cases with uterine deformations, cases within 1 year after cesarotomy, and cases of recently induced abortion. Past experiences have indicated that there have been considerable difficulties in inducing abortion in such cases as the above, and that accidents have been liable to occur. The authors have recently employed compound crystal trichosanthin, composed of crystal trichosanthin, testosterone propionate and reserpine, and succeeded in bringing about drug expansion of uterus and abortion, and safe abortion at that. The success roles were as follows: 97.96% for the group with extreme anteversion and anteflexion of uterus with a fine and long cervix, 100% for the one with uterine deformations, 95.08% for the one with past cesarotomy and 96.72% for the one with recently induced abortion.

Abortifacient Agents↗
PubMedDate not supplied

Maternal-fetal transfer of metallic mercury via the placenta and milk.

To clarify the situation of trans-placental movement and milk screening of metallic mercury in human, the content of mercury was detected in the maternal blood, umbilical cord blood, milk, and placental tissues. In 18 parturient women, 9 had been occupationally exposed to metallic mercury whereas the other 9 had not. Mercury was detected by means of cold vapor atomic absorption spectrophotometry. Results showed that the concentrations of mercury of the umbilical cord blood and placental tissues were higher than that of maternal blood. The ratio of organic and total mercury of milk was markedly lower than that of maternal blood in the exposed group (P < 0.01). The ratio of inorganic to total mercury of milk was significantly higher than that of maternal blood (P < 0.01). Therefore, this study concluded that the metallic mercury can be transferred to the fetus via the placenta and secreted to a newborn via milk.

Adult↗