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Biomedical subjects

L Tan

Publications and source records attributed to L Tan.

At least 163 records · Page 9Linked to original sources
PubMed1991

Regions of the T cell receptor alpha and beta chains that are responsible for interactions with CD3.

The T cell antigen receptor consists of the Ti alpha/beta heterodimer which recognizes antigen, and the associated CD3 chains, thought to be involved in signal transduction. To understand the nature of the interaction between Ti and CD3, chimeric molecules which included the COOH-terminal segments of Ti alpha or beta linked to the extracellular segment of CD8, were transfected into a mutant T cell deficient in Ti beta chain expression and cell surface CD3. Both chimeric chains were required to express the chimeric Ti and to restore CD3 surface expression. CD8/Ti and CD3 cointernalized and coimmunoprecipitated. Stimulation of the chimeric receptor induced transmembrane signaling events and cell activation. These results demonstrate that the Ti alpha and beta COOH termini containing the transmembrane domains are sufficient for structural and functional coupling of Ti to CD3.

Antigens, Differentiation, T-Lymphocyte↗
PubMed1991

Predicting recovery of facial nerve function following injury from a basilar skull fracture.

Twenty-five patients with posttraumatic facial nerve palsy were studied. Partial recovery of function had occurred in 95% of these patients by 18 months after injury. At 5 months posttrauma, there was some recovery in 92.5% of those with a partial lesion compared with 10% of those with a complete lesion. This difference attains statistical significance. Complete recovery of nerve function had occurred by 10.5 months in 53.5% of the patients; in 62% of patients with a partial lesion, complete recovery had occurred by 4 months compared with 0% in those with a complete lesion. This difference also attains statistical significance. There was no statistically significant difference in recovery of function between patients with an immediate as opposed to a delayed onset of facial nerve palsy. It was determined that the degree of palsy had a statistically significant influence on recovery of facial nerve function, whereas the time of onset did not. The data presented support a conservative approach to these injuries and it is recommended that the possibility of surgical treatment should be entertained in patients with complete facial palsy persisting for 12 to 18 months after injury.

Adolescent↗
PubMed1991

Comparison of the immune response against polio peptides covalently-surface-linked to and internally-entrapped in liposomes.

The adjuvanticity of liposomes on two different modes of presentation of polio virus subunit peptides was demonstrated by incorporating the poorly immunogenic synthetic polio peptides, W1 and W2, into the internal space of and covalently-linked to the surface of dehydration-rehydration vesicles (DRV). It was found that for both peptides, liposome association in either mode boosted the primary and secondary IgG1 responses against 5 micrograms peptide as compared to controls in which free peptide was administered. Surface-linkage of peptides (both W1 and W2) exhibited an initially more rapid rise in antibody levels, as compared to internal entrapment of the peptides, but elicited no observable secondary response. However, although encapsulated W1 showed a milder primary response when compared to the surface-linked formulation, it later elicited a strong secondary response. These results suggested that it may be advantageous to administer liposomal virus subunit vaccines in both surface-linked and internally entrapped formulations to achieve adequate initial antibody levels followed by an anamnestic response.

Adjuvants, Immunologic↗
PubMed1991

A novel positively-charged lipid 1,2-bis(hexadecylcycloxy)-3-trimethyl aminopropane (BisHOP) enhances the adjuvant effect of liposomes on encapsulated tetanus toxoid.

A novel positively charged lipid, 1,2-bis(hexadecylcycloxy)-3-trimethylaminopropane-HCl (BisHOP), when incorporated into the bilayers of phosphatidylcholine (PC) and distearoyl phosphatidylcholine (DSPC) dehydration-rehydration vesicles (DRV), was shown to have a powerful effect in enhancing the IgG1 response to tetanus toxoid encapsulated within the liposomes. The adjuvant effect was significantly greater when 20% BisHOP was incorporated as compared to 10% incorporation and to control PC and DSPC DRV. Plain, uncharged DSPC DRV were found to have a greater adjuvant effect than plain PC DRV on the entrapped tetanus toxoid after a single intramuscular injection. Even though antibody levels at 8 weeks post-injection were similar for 20% BisHOP PC and DSPC DRV, the rate of rise of antibody titres was more rapid for 20% BisHOP DSPC than for 20% BisHOP PC DRV. These results suggest that faster and higher titers of antibodies may be obtained by optimal manipulation of the charged and non-charged lipid components of liposomes.

Adjuvants, Immunologic↗
PubMed1991

A study of the efficacy of liposomes in comparison to new and established adjuvants in potentiating the antibody response against hepatitis B virus surface antigen.

The dehydration-rehydration vesicle (DRV) method was used to encapsulate hepatitis B surface antigen (HBsAg) in phosphatidylcholine (PC) and distearoyl phosphatidylcholine (DSPC) liposomes giving entrapment values of 31.7% and 33.1% respectively. A comparison of antibody levels, as determined by ELISA, in the primary and secondary immune responses in mice immunized twice with 1 microgram HBsAg free, or in formulations of PC DRV, DSPC DRV, Syntex Adjuvant Formulation (SAF), alum and Freund's Complete Adjuvant (FCA) showed that by far, FCA was the best adjuvant in both the primary and secondary IgG1, IgG2a and IgG2b responses. In the secondary response, apart from FCA, DSPC DRV and SAF were equally efficacious and better adjuvants than alum and PC DRV for the IgG2a and IgG2b subclasses. SAF was a better adjuvant for HBsAg than alum, DSPC DRV and PC DRV (in descending order of efficacy) in the secondary IgG1 response.

Alum Compounds↗
PubMed1990

Use of a nasal continuous positive airway pressure mask in the treatment of postoperative atelectasis in aortocoronary bypass surgery.

Pulmonary oxygen transfer, defined by PaO2/FIO2, and radiologic presence of atelectasis were measured pre-, intra-, and postoperatively to postoperative day 9 in elective cardiac aortocoronary bypass surgical patients, who were randomly allocated either to receive 18 h PEEP while on the ventilator followed by 12 h of nasal continuous positive airway pressure (nasal CPAP) or to be control subjects. The two groups were comparable in age, sex, forced expiratory volume in 1 sec (FEV1), the ratio of FEV1 over forced vital capacity (FVC), time on pump, units of blood transfused, New York Heart Association grading, and cardiac performance indices. The PaO2/FIO2 was significantly (p less than .05) better from half an hour after extubation until 24 h postextubation in the nasal CPAP group, but was decreased for the remainder of the study in both groups. Incidence of atelectasis/consolidation was not different in both groups during the study period. We conclude that nasal CPAP is well tolerated as a treatment of hypoxemia in the immediate postoperative period of aortocoronary bypass patients. CPAP does not change the course of postoperative atelectasis.

Aged↗
PubMed1990

Cytogenetic analysis of 147 cases of non-Hodgkin's lymphoma: non-random chromosomal abnormalities and histological correlations.

A prospective cytogenetic study of patients with non-Hodgkin's lymphoma (NHL) presenting to one institution was commenced in 1983 as part of a larger study including histology, immunophenotyping, cytokinetics and survival. 175 patients were studied over 5 years and G-banded karyotypes were successfully obtained in 147. Chromosome abnormalities were detected in 135 cases (92%) with the commonest abnormality being t(14;18)(q32;q21) in 69 cases. Other non-random translocations were much less frequent, i.e. t(11;14) in seven cases and t(8;14) in four cases. Other specific structural changes included partial deletions of 6q (breakpoints ranging within q13-q23), 3q (breakpoints ranging within q21-q27), 1q and 10q22. Chromosome regions highlighted as being frequently involved in structural abnormalities were 11q13-q25, 1p22-p36, 3q21-q27 and 6q13-q23. Several specific recurring breakpoints were identified and these included 14q32, 18q21, 1p36 and 6q21. Frequently occurring numerical abnormalities were gains of chromosomes 3, 7, X and 12. Correlation with histological type showed, as expected, that t(14;18) was present in 89% of follicular lymphoma but also occurred in 30% of diffuse lymphoma. Abnormalities of 11q were correlated with the diffuse histologies as a group, whereas both numerical and structural abnormalities of chromosome 3 correlated with the diffuse large cell lymphoma (DLCL) subtype, and t(11;14) with diffuse small cleaved cell lymphoma (DSCCL). Although not statistically significant, abnormalities of 6q occurred twice as frequently in DLCL than in any other variety. However, several other commonly occurring abnormalities, such as extra copies of chromosomes 7, X, 12 and most of the structural abnormalities of 1p, did not correlate with any histological type. Therefore this large cytogenetic study has confirmed some previously reported correlations between specific chromosome abnormalities and histological subtypes of non-Hodgkin's lymphoma and has also identified some new correlations which may prove useful in the investigation of the biological basis of the disease.

Chromosome Aberrations↗
PubMed1989

Adipose veno-lymphatic transfer for management of post-radiation lymphedema.

In a patient who had post-radiation lymphedema after excision of liposarcoma, a method is described that is called adipose veno-lymphatic transfer. The technique involves transferring adipose tissue containing lymphatic vessels that surround the long saphenous vein, from the normal, healthy leg to the irradiated leg, with the creation of an arteriovenous fistula.

Adipose Tissue↗
PubMed1989

Diurnal rhythm of beta-endorphin in neonates.

In an attempt to prove whether beta-endorphin diurnal rhythm existed in neonates, 17 infants with a mean (+/- SD) gestational age of 31.7 +/- 4.8 weeks and a birth weight of 1,790 +/- 898 g were studied at a mean postnatal age of 3.3 +/- 0.5 days. Plasma samples were obtained from a pre-existing umbilical arterial line at 09.00 h, noon and 15.00 h. Mean plasma concentrations of beta-endorphin were 68.3 +/- 27.7, 54.5 +/- 13.7, and 45.1 +/- 10.8 pg/ml, respectively. Highly significant (p = 0.0002) variation of plasma beta-endorphin concentration was observed in these neonates suggesting the presence of a diurnal rhythm of beta-endorphin in neonates. It is important to specify the time of collection of blood samples for determination of opiates in neonates.

Asphyxia Neonatorum↗
PubMed1989

Diurnal rhythms of cortisol, ACTH, and beta-endorphin levels in neonates and adults.

To determine whether a diurnal rhythm exists in neonates admitted to neonatal intensive care units where there is continuous artificial lighting and periodic nursing and medical care, plasma cortisol, adrenocorticotropin (ACTH), and beta-endorphin concentrations were measured in two groups of infants and in adult human volunteers. As expected, a diurnal rhythm was seen in adults. A diurnal rhythm was also found for cortisol and endorphin levels in neonates (3 to 4 days postnatally) with minimal stress and in infants who were clinically severely stressed. There was not a significant difference between the morning and afternoon concentrations of ACTH in these infants, but the afternoon concentrations were lower than the morning's, as would be expected. We found that a diurnal rhythm does exist in neonates within the first few days of postnatal life and that the continuous lighting and medical and nursing interventions do not interfere with this rhythm.

Adrenocorticotropic Hormone↗
PubMed1989

Chloral hydrate sedation in neonates and infants--clinical and pharmacologic considerations.

Chloral hydrate has been used clinically for over 100 years. There is significant paucity of information regarding chloral hydrate metabolism in neonates and infants. Chloral hydrate and its various metabolites were quantitated in 12 neonates and 2 infants at prescribed time intervals. The analysis of the data indicates accumulation of trichloroacetic acid and trichloroethanol in tissue of compromised infants. There is indirect evidence of competition for hepatic glucuronidation for bilirubin with trichloroethanol in ill preterm infants. Multiple dosing of chloral hydrate in preterm infants should be used with caution and frequent monitoring of serum bilirubin concentrations is indicated in such cases. The mechanism of chloral hydrate metabolism is discussed in detail.

Bilirubin↗
PubMed1988

The sequence specificity of bleomycin damage in three cloned DNA sequences that differ by a small number of base substitutions.

The DNA sequence specificity of the cancer chemotherapeutic agent, bleomycin, has been investigated in three clones of human alpha RI-DNA. The three 340-base pair alpha RI-DNA sequences were almost identical in their nucleotide sequence enabling the study of subtle effects of base substitutions on bleomycin cleavage. By utilizing densitometer scanning and statistical analysis of the degree of bleomycin DNA cleavage, we found 17 significant differences between the three DNA sequences. Eleven of these differences could be attributed to base substitutions close to the dinucleotide cleavage site. However, six of the differences were at positions two or more base pairs from the base substitution sites. The significant differences were up to 12 base pairs from base substitutions. It is proposed that these long range effects are due to base substitutions causing microvariation in the DNA structure to which bleomycin cleavage is sensitive.

Base Sequence↗