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R Tan

Publications and source records attributed to R Tan.

At least 19 recordsLinked to original sources
PubMed1992

B7 costimulates proliferation of CD4-8+ T lymphocytes but is not required for the deletion of immature CD4+8+ thymocytes.

In addition to TCR-derived signals, costimulatory signals derived from stimulation of the CD28 molecule by its natural ligand, B7, have been shown to be required for CD4+8- T cell activation. We investigate the ability of B7 to provide costimulatory signals necessary to drive proliferation and differentiation of virgin CD4-8+ T-cells that express a transgenic TCR specific for the male (H-Y) Ag presented by H-2Db class I MHC molecules. Virgin male-specific CD4-8+ T cells can be activated either with B7 transfected chinese hamster ovary (CHO) cells and T3.70, a mAb specific for the transgenic TCR-alpha chain that is associated with male-reactivity, or by male dendritic cells (DC). Activated CD4-8+ T cells proliferated in the absence of exogenously added IL-2. IL-2 activity was detected in supernatants of CD4-8+T3.70+ cells that were stimulated with T3.70 and B7+CHO cells. The response of CD4-8+T3.70+ cells to T3.70/B7+CHO or to male DC stimulation were inhibited by CTLA4Ig, a fusion protein comprising the extracellular portion of CTLA4 and human IgG C gamma 1. It has been previously shown that CTLA4Ig binds B7 with high affinity. Staining with CTLA4Ig revealed that DC express about 50 times more B7 than CD4-8+ T cells. CTLA4Ig also specifically blocked the proliferation of male-reactive cells in vivo. We have also used an in vitro deletion assay whereby immature CD4+8+ thymocytes expressing the transgenic male-specific TCR are deleted by overnight incubation with either immobilized T3.70 or male DC to investigate the participation of the CD28/B7 pathway in the negative selection of immature thymocytes. Staining with B7Ig established that both immature murine CD4+8+ and mature CD4-8+ thymocytes express a high level of CD28. However, despite the high expression of CD28 on CD4+8+ thymocytes, it was found that deletion of CD4+8+ thymocytes expressing the male-specific TCR by the T3.70 mAb was not inhibited by B7+CHO cells. Furthermore, the deletion of these thymocytes by DC also was not inhibited by CTLA4Ig. These findings provide evidence that although signaling through CD28 can costimulate a primary anti-male response in mature CD4-8+ T cells, the CD28/B7 pathway does not appear to participate in the negative selection of immature CD4+8+ thymocytes.

Animals↗
PubMed1992

Circular dichroism studies suggest that TAR RNA changes conformation upon specific binding of arginine or guanidine.

Short basic peptides from the HIV Tat protein bind specifically to a bulge region in TAR RNA, with a single arginine residue providing the only sequence-specific contact. The free amino acid arginine also binds specifically to TAR. Previous circular dichroism (CD) experiments suggested that peptide binding induces a conformational change in TAR. Here we confirm this observation using single arginine-containing peptides and show that arginine or guanidine binding also induces a conformational change in TAR. A peptide containing a single arginine within a stretch of histidines (CYHHHRHHHHHA) shows pH-dependent binding and a corresponding change in TAR conformation, as detected by a decrease in the CD signal at 265 nm. Arginine and guanidine, which bind to TAR with apparent Kd's of approximately 1.5 mM, induce similar CD changes. In contrast, lysine, which does not bind specifically to TAR, has no effect. Mutants of TAR that abolish specific binding (a U-->C substitution in the three-nucleotide bulge, a deletion of the bulge, or an A-U to U-A base pair change above the bulge) show no change in the CD signal upon binding of peptides, arginine, or guanidine. The results suggest that binding of a single guanidinium group to a specific site in TAR induces a change in RNA conformation.

Amino Acid Sequence↗
PubMed1992

Conformation of the TAR RNA-arginine complex by NMR spectroscopy.

The messenger RNAs of human immunodeficiency virus-1 (HIV-1) have an RNA hairpin structure, TAR, at their 5' ends that contains a six-nucleotide loop and a three-nucleotide bulge. The conformations of TAR RNA and of TAR with an arginine analog specifically bound at the binding site for the viral protein, Tat, were characterized by nuclear magnetic resonance (NMR) spectroscopy. Upon arginine binding, the bulge changes conformation, and essential nucleotides for binding, U23 and A27.U38, form a base-triple interaction that stabilizes arginine hydrogen bonding to G26 and phosphates. Specificity in the arginine-TAR interaction appears to be derived largely from the structure of the RNA.

Arginine↗
PubMed1992

Effects of human HSS on hepatocyte and hepatoma cell proliferation and D-GAL induced acute liver failure.

Human hepatic stimulator substance (HSS), an organ-specific and heat-stable factor which differs from insulin, glucagon and EGF, has been partially purified from aborted human fetal livers. It was found to stimulate DNA synthesis of human hepatocytes. AH22 hepatoma cells responded dose-dependently. HSS was also found to enhance the survival of D-GAL intoxicated rats as compared to control (62.5% vs. 26.1%). Our results suggest that human HSS is very similar to that in animals.

Animals↗
PubMed1992

Localization of the basement membrane heparan sulfate proteoglycan in islet amyloid deposits in type II diabetes mellitus.

Amyloid in the islets of Langerhans is the uniform pathologic feature in the pancreata of patients with type II diabetes mellitus. Although the mechanisms of islet amyloid fibrillogenesis are unknown, the presence of heparan sulfate proteoglycan in many other forms of amyloid suggests a role for this proteoglycan in amyloidogenesis in general. In this study, islet amyloid was evaluated for the presence of the basement membrane heparan sulfate proteoglycan using histochemical and immunohistochemical techniques. Staining with sodium sulfate-alcian blue identified highly sulfated glycosaminoglycans within all islet amyloid deposits, and anti-basement membrane heparan sulfate proteoglycan antisera localized this specific proteoglycan within the islet amyloid. The presence of the basement membrane heparan sulfate proteoglycan links islet amyloid to other disparate forms of amyloid and further supports the hypothesis that it has a role in a common pathway of amyloid fibrillogenesis.

Amyloid↗
PubMed1991

Radiotherapy for postoperative recurrent uterine cervical carcinoma.

From January 1980 to December 1985, a total of 110 patients with postoperative recurrent uterine cervical carcinoma were treated with radiotherapy. The mean age was 53 years. Ten patients were excluded due to incomplete treatment. The population was grouped according to the classification by Ciatto et al. into patients with central recurrence (n = 48), with peripheral limited recurrence (n = 43), and with peripheral massive recurrence (n = 9). The midpelvic dose given to patients with central recurrence was 40 to 45 Gy, followed by a boost given either by perineal teletherapy with 30 Gy or brachytherapy with 30 Gy at 0.5 cm. beneath the vaginal mucosa. For the peripheral group, the midpelvic dose was 50 Gy followed by a boost of 10 Gy through reduced portals. Further boost to the vaginal mucosa was given by either of the two methods mentioned above. The overall 5-year survival rate was 28%. In the group with central recurrence, it was 42% and in the group with peripheral recurrence 15%. Sixteen patients had persistent local tumor and 15 patients developed distant metastasis. Complications noted were proctitis (5%), cystitis (2%), vesicovaginal fistula (2%) and rectovaginal fistula (2%). Our data clearly indicate that radiotherapy was effective in controlling central recurrence, but for peripheral recurrence, control rate and prognosis were less favorable.

Adult↗
PubMed1991

Results of postoperative radiotherapy for clinical stage Ib uterine cervical carcinoma with evidence of microscopic involvement of surgical margin, parametrium and/or lymph node metastasis.

From January 1979 to September 1985, a total of 125 patients preoperatively staged as International Federation of Gynecology and Obstetrics (FIGO) Ib uterine cervical carcinoma were proven to have either microscopic involvement of the surgical margin, parametrium and/or regional lymph node metastasis histopathologically after radical hysterectomy and pelvic lymphadenectomy. All of these patients were treated postoperatively with radiotherapy because of the above indications. Based on indications of postoperative radiotherapy, patients were divided into 3 major subgroups according to the microscopic involvement: group A patients (50) with microscopic evidence of regional lymph node metastasis only; group B patients (59) with microscopic evidence of parametrial involvement; and group C patients (16) with microscopic infiltration of the surgical margin involving the vaginal cuff. All patients were treated with external irradiation using a Cobalt-60 teletherapy machine. The overall actuarial 5-year survival rate was 62% with a 77% 5-year survival rate for group A, a 50% rate for group B and a 75% rate for group C. Further analysis of the prognostic factors revealed that those with regional lymph node involvement of 4 or less had a better chance of survival than those with lymph node involvement of more than 4. Also those with poorly differentiated squamous cell carcinoma had a lower 5-year survival rate than those with moderately or well-differentiated squamous cell carcinoma. Univariate analysis revealed that hemoglobin values, age, and the time interval from surgery to radiotherapy were not significant prognostic factors.

Adenocarcinoma↗
PubMed1989

A technical note on diluting semen for the haemocytometric determination of sperm concentration.

A comparison was made of the use of either an SMI positive displacement pipette or an Eppendorf Varipette as the method of sampling 63 liquefied semen samples for volumetric dilution and haemocytometry to determine sperm concentration. The 95% range of the differences between the values obtained using the SMI and the Varipette with whole tips was from -46.9 to 63.8 x 10(6)/ml. With the Varipette tips cut off 12.5 mm from the end the 95% range was from -52.4 to 55.8 x 10(6)/ml. Previous work had shown that the 95% ranges of differences between duplicate determinations using the SMI pipette were from -7.2 to 6.9 x 10(6)/ml for two 1 + 19 dilutions, or from -16.0 to 12.1 x 10(6)/ml for 1 + 19 and 1 + 49 parallel dilutions. Therefore, since the Varipette had a far greater potential for error, a positive displacement pipette should be used when taking precise volume aliquots of human semen.

Humans↗
PubMed1989

The use of lithium carbonate to correct leukopenia during cancer treatment.

Leukopenia is a common complication noted in patients receiving radiotherapy and/or chemotherapy but no effective method has been reported so far to correct this complication. In the field of psychiatry, lithium carbonate used in treating depression has been noted to have induced leukocytosis as a side effect. From July 1985 to December 1987, a total of 111 patients receiving radiotherapy and/or chemotherapy with leukopenia were included in this study. There were sixty nine patients who received lithium carbonate and the remaining forty two patients served as control group were allowed to stop their primary treatment temporarily without medication during their period of leukopenia. For the group given lithium carbonate, 79% of the patients were able to recover their white blood count (WBC) above 3,000/cu.mm. within 5 days and finished their primary treatment smoothly. For the control group, it took them on the average about 11.8 days of rest in order to recover their WBC level to 3,000/cu.mm. and above. Reports in the recent literature indicates that the average toxic level is around 1.5 mEq/l to 2.0 mEq/l. In our study, the average serum lithium level before administration is 0.44 mEq/l, it reached 0.59 mEq/l and 1.08 mEq/l after the fifth and the 10th day of intake respectively. From this laboratory data, obviously no patient reached the toxic level and no side effects were noted clinically. Based on these figures, we can see clearly that lithium carbonate can shorten the period of leukopenia in comparison to the control group which was not given any medication.

Adolescent↗
PubMed1988

A reproducible model for the study of factor X kinetics in AA amyloidosis.

Factor X clearance was examined in a model of rapid AA amyloid deposition. Accelerated equilibration with extravascular compartments and accelerated removal postequilibration mimic features seen in patients with AL amyloidosis. The handling of Factor X was different from that of two other proteins, mouse albumin and IgG. Each protein had its own specific characteristic clearance properties, although in amyloidotic animals all proteins were cleared more rapidly in the postequilibration phase. The liver was by far the major site of Factor X clearance but this was true in all control groups as well. No significant difference was seen in tissue clearance site in any of the treatment groups, perhaps because the amount of AA amyloid in each tissue 3 days into the protocol was not yet large. Nevertheless, a reproducible model that possesses accelerated Factor X clearance is now available to study the mechanism of coagulation factor abnormalities in amyloidosis.

Albumins↗
PubMed1988

Direct evidence for circulating apoSAA as the precursor of tissue AA amyloid deposits.

A precursor product study was carried out using tritiated, undenatured murine high-density lipoprotein (HDL)-apoSAA, to assess whether circulating HDL-apoSAA is the precursor of tissue AA amyloid deposits. The quantity of label accumulating in AA over a 24-h period was determined per unit weight of spleen. In addition a mathematical assessment of the quantity of label that should have accumulated in splenic AA within 24 h was made, based on the half-life of circulating apoSAA, the rate of change of the specific activity of circulating apoSAA, and rate of deposition of splenic AA. The observed result was approximately 47% of the theoretically predicted value. The latter did not include extraction efficiencies of AA peptide from spleen nor losses which might have occurred during column fractionation of splenic extracts. The observed and predicted results are therefore in remarkably good agreement and indicate that circulating apoSAA is the major source of protein for splenic AA amyloid deposition.

Amyloidosis↗
PubMed1986

Standardization and quality control of sperm concentration and sperm motility counts in semen analysis.

The paper reports a study of standardization and quality control of sperm concentration counts and visual motility assessments in human semen analyses performed for infertility investigations and from internal quality control procedures. Sperm concentration determinations were performed in Improved Neubauer haemocytometers on volumetric dilutions made using a positive displacement pipettor for sampling the liquefied semen. In addition to a standard 1 + 19 dilution a second dilution of either 1 + 9, 1 + 19 or 1 + 49 was made according to whether the estimated sperm concentration was less than 20, 20-100 or greater than 100 X 10(6)/ml respectively. The duplicate determinations of sperm concentration were highly significantly correlated (P much less than 0.001) with less than 5% variability. Parallel visual sperm motility assessments were made by two pairs of technicians and showed highly significant correlations (P much less than 0.001) between technicians in the determination of the percentages of motile and progressive spermatozoa as well as the subjective rating of sperm progressivity. When these values were incorporated into a calculated motility index which gave added weight to the progressive spermatozoa and to their quality of progression the correlations between technicians remained highly significant (P much less than 0.001) with average differences of the order of 1.0%. Therefore, provided that sufficient attention is paid to technician training, regular standardization checks and the use of only proven reliable procedures, quantitatively accurate values for sperm concentration and motility can be obtained in routine semen analyses.

Humans↗
PubMed1985

Isolation of Japanese encephalitis virus from Anopheles annularis and Anopheles vagus in Lombok, Indonesia.

Three strains of Japanese encephalitis (JE) virus were recorded from mosquitoes collected in Lombok, Indonesia, during March 1979, from pools of Anopheles vagus, An. annularis and Culex tritaeniorhynchus respectively. This is believed to be the first report of isolation of JE virus from An. vagus. The frequencies of JE viral infection in zoophilic Anopheles species were higher than in Cx tritaeniorhynchus, the principle vector of JE virus in Asia. The low frequency of infection in Cx tritaeniorhynchus and the relatively infrequent raising of pigs may account for the low prevalence of JE neutralizing antibodies in the human populations of Lombok.

Animals↗
PubMed1985

Correlation of population indices of female Culex tritaeniorhynchus with Japanese encephalitis viral activity in Kapuk, Indonesia.

Nineteen consecutive monthly light trap collections of mosquitoes were made between October 1978 and April 1980 in Kapuk, Indonesia. Kapuk is a small suburb of Jakarta where pigs are raised in close proximity to rice paddies which are breeding sites for Culex tritaeniorhynchus. Japanese encephalitis (JE) virus is believed to be endemic and has been recovered from mosquitoes and pigs in the area on several occasions. A total of 18,435 female Cx. tritaeniorhynchus were allocated to 359 pools of approximately 50 per pool. Virus isolations were attempted in both Vero and BHK-21 cells and agents producing cytopathic effect were identified in a micro-neutralization test. Nineteen strains of JE were recovered from the 359 pools of Cx. tritaeniorhynchus tested. The light trap index of female Cx. tritaeniorhynchus (X) and the relative frequency of pools positive for JE (Y) for each month of the study were plotted and correlation coefficients (r) calculated after transforming the mosquito population data logarithmically and the relative frequencies of isolation by arcsine square root. The close fit of the data (p less than 0.001) to an inverse linear model (1/y = a + b log10X) suggests a close dependence of JE viral activity on the population dynamics of Cx. tritaeniorhynchus. Three additional strains of JE were recovered from other Culex spp. at the same study site. One strain each was isolated from individual pools of Cx. gelidus, Cx. vishnui and Cx. fuscocephala. Cx. tritaeniorhynchus was more frequently infected with JE than the other species tested.

Culex↗