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T Lam

Publications and source records attributed to T Lam.

53 records · Page 3Linked to original sources
PubMed1987

Development of active and passive transport of bile acids in rabbit intestine.

Previous studies have indicated that saturable, Na+-bile acid coupled transport is absent in the ileum throughout most of the suckling period and that the maturation of ileal bile acid uptake which occurs during weaning results primarily through an increase in functional bile acid carriers within the ileal brush border membrane. This study was undertaken in weanling and adult rabbits to establish the effect of maturation on the active ileal and passive jejunal and colonic uptake of 8 bile acids. The in vitro uptake of a range of concentrations of cholic (C), taurocholic (TC), glycocholic (GC), chenodeoxycholic (CDC), taurochenodeoxycholic (TCDC), glycochenodeoxycholic (GCDC), deoxycholic (DC) and taurodeoxycholic (TDC) acid was determined. Active ileal uptake of C, TC, GC, DC and TDC was greater in adult than in weanling animals, whereas uptake of CDC, TCDC and GCDC was similar in both groups. The relative permeability for passive uptake of bile acids into the jejunum and colon was similar in young and adult rabbits. Jejunal mucosal surface area was similar in the two groups, but was greater in the ileum in the adult than in the weanling rabbits due to an increase in villus height, width, and number of villi per unit serosal length. However, the age-associated differences in active bile acid uptake were not explained simply on the basis of these differences in ileal mucosal surface area or the concentration of bile acids in the intestinal lumen. Thus, maturation of the rabbit from weanling to adulthood does not influence the relative passive permeability of the jejunum or colon to bile acids, but does increase active ileal uptake of conjugated and unconjugated cholic acid and deoxycholic acid, but not chenodeoxycholic acid.

Aging↗
PubMed1987

Immunochemical observations of antigen 5, a major venom allergen of hornets, yellowjackets and wasps.

Antigen 5 is a venom protein of hornets, yellowjackets and wasps, and it is an important allergen for insect-sensitive patients. Antigen 5s from these insects are found to have similar amino-terminal sequences for their first 20 residues, and to have similar cyanogen bromide cleavage patterns. A partial sequence homology of antigen 5s and scorpion neurotoxins is observed. Antigen 5s from these insects show varying extents of cross reactivity when tested with mouse polyclonal antibodies by enzyme immunoassay and they show limited or no cross reactivity with mouse monoclonal antibodies. Chemically modified antigen 5s shown greatly decreased binding of antigen 5-specific mouse polyclonal antibodies. The modified antigen 5s include its reduced and carboxymethylated

Amino Acid Sequence↗
PubMed1986

Preparation of protein conjugates via intermolecular hydrazone linkage.

Proteins can be modified at their amino groups under gentle conditions to contain an average of three to six aryl aldehyde or acyl hydrazide groups. These two types of modified proteins at about 10 microM concentration condense with each other at pH approximately 5 to form conjugates linked by hydrazone bonds. Under proper conditions conjugates mainly of dimers and trimers in size or, if desired, higher oligomers can be obtained. The conjugates can be dissociated to their individual protein components by an exchange reaction with an excess of acetyl hydrazide. The reversible hydrazone bonds of conjugates can be reduced with NaCNBH3 to give stable hydrazide bonds. The stability of protein-hydrazone conjugates was found to be significantly greater than that of the model compound, the N-acetylhydrazone of p-carboxybenzaldehyde. This difference is believed to result from the presence of multiple hydrazone linkages in protein conjugates.

Aldehydes↗
PubMed1986

Studies on HSAG, a middle repetitive family of genetic elements which elicit a leukemia-related cellular surface antigen.

HSAG is a family of genetic elements capable of eliciting, in transfected cells, a cellular surface antigen which is correlated with human chronic lymphocytic leukemia (CLL). Its prototype member, HSAG-1, was cloned as a 3.4 kb insert and contains numerous Alu-related elements, including its left hand 1.4 kb antigen-eliciting end. These elements are present in mammalian cells with copy numbers varying from 7,000 to 200,000 per haploid genome, depending on how closely their sequence conforms to the Alu consensus sequence. They are present in the configuration found in HSAG-1, a 3.4 kb EcoRI fragment which is part of a larger unit of at least 12.7 kb, at a frequency of 20-50 per haploid genome, and dispersed around the genome. A second family member, HSAG-2, isolated using a functional assay, was cloned as a 9.5 kb insert and contained a 1.5 kb antigen-eliciting left hand end. As in HSAG-1, the antigen-eliciting portion of the insert also contained Alu-like elements, unlike most of the remainder of the insert. A number of HSAG family members were cloned from a library of human CLL genomic DNA by sequence homology with the antigen-eliciting portion of HSAG-1. Most of these members were also shown to be capable of eliciting antigen. Their only sequence similarity with HSAG-1 appeared to be in their content of numerous Alu-like elements. The evidence thus supports the view that the HSAG functional family consists of clusters of Alu-like elements.

Animals↗
PubMed1986

The structure of HSAG-1, a middle repetitive genetic element which elicits a leukemia-related cellular surface antigen.

HSAG-1 is a cloned member of a heterogeneous middle repetitive family of genetic elements which is capable of eliciting a leukemia-related surface antigen detected with a monoclonal antibody after DNA transformation of mouse cells. HSAG-1 was originally isolated from a Chinese hamster-human leukemia hybrid cell gene library both by sib-selection for antigen producing activity and by hybridization with labelled human genomic human DNA. We show here that the human labelled site is at the right hand end of the insert, while the antigen-eliciting portion is included in a 1450 bp fragment at the left hand end of the insert. We also present the complete nucleotide sequence of the 3369 bp insert. The sequence contains 12 elements which bear a significant resemblance to accepted consensus sequences for Alu repetitive elements. The right hand end contains adjacent elements with close sequence similarity to portions of the human and hamster type I and type II Alu consensus sequences. All of the other Alu-related elements have diverged relative to the Alu consensus sequences by additions, long deletions and substitutions. The left hand portion of the insert which has the antigen-producing activity contains four of these diverged elements representing a relatively high proportion (26%) of the nucleotide sequence. The sequence is thus consistent with our previous observations of a repetitive family with biological function.

Animals↗
PubMed1983

Recreational and social activities of orthognathic surgery patients.

The present study examined changes in recreational and social activities after orthognathic surgery. Because this is often an expectation of patients seeking surgery, it was hypothesized that activity levels would increase gradually after surgery, particularly for patients who become more extroverted and for unmarried patients. Information on the frequencies of recreational and social activities, and the persons with whom these activities were performed, were obtained from 53 patients in a self-administered questionnaire administered at least 2 days before surgery and again 3 weeks, 4 months, and 9 months after surgery. In addition, patients were assessed on introversion-extroversion before and after surgery. The results indicated that (1) for both married and single patients, recreational and social activities dropped immediately after surgery and gradually increased to a level similar to that prior to surgery at nine months after surgery; (2) contrary to expectations, the single patients over age 15 did not increase their recreational and social activities with friends of the opposite sex after surgery; and (3) the degree of change in introversion-extroversion after surgery was not associated with the degree of change in recreational and social activities performed with others. Implications for postsurgical adjustment of orthognathic patients and recommendations for future research are discussed.

Adolescent↗
PubMed1983

Requirement for human red blood cells in inactivation of C3b in immune complexes and enhancement of binding to spleen cells.

We showed previously that soluble immune complexes (IC) added to normal human serum and unseparated autologous blood cells bind predominantly to red blood cells (RBC) bearing C3b receptors. RBC-associated IC are processed both by C3b/C4b inactivator (I) cleavage of C3b and by alternative pathway-dependent C3b generation, and are returned to the serum in a modified form. In the present study, soluble IC were prepared by using 125I-BSA and guinea pig anti-BSA, and were treated with diluted human serum to optimize sustained C3b-dependent binding to human RBC. This binding to RBC could not be abrogated by preincubation of IC with heat-inactivated human serum or purified serum regulatory proteins, I and beta 1H (H), but after binding, pretreated IC dissociated. When IC were prepared with serum containing 125I-C3, treatment with I + H did not release labeled C3 from the complexes. Analysis by polyacrylamide gel electrophoresis in sodium dodecyl sulfate (SDS-PAGE) of 125I-C3b in IC showed similar labeled peaks whether IC were pretreated with buffer or with I + H or were bound to RBC without pretreatment. In contrast, when IC containing 125I-C3b were exposed to I + RBC, nearly 70% of the label was released from the IC. The released material analyzed by SDS-PAGE showed major 125I-C3 peaks corresponding in m.w. to free beta-chain and alpha 1 cleavage products of 30,000 to 33,000 daltons. IC in undiluted serum after incubation with RBC gave less binding to human polymorphonuclear leukocytes than after incubation without RBC, but notably more binding to guinea pig spleen cells and human lymphoblastoid cells. These findings argue that exposure to serum regulatory proteins does not prevent subsequent binding of experimental IC to RBC, that RBC binding promotes degradation of C3b in IC which proceeds beyond iC3b, and that this I-mediated breakdown renders IC reactive with spleen cells.

Animals↗
PubMed1981

Cloning of a functional gene responsible for the expression of a cell surface antigen correlated with human chronic lymphocytic leukemia.

A cell--cell hybrid of a Chinese hamster ovary (CHO) cell line and human peripheral blood lymphoblasts from a patient with B-cell chronic lymphocytic leukemia produces a surface antigen detectable by a monoclonal antibody. This surface antigen can be detected at significant levels on a fraction of chronic lymphocytic leukemia cells, but not on normal human lymphocytes from peripheral blood or bone marrow. Two different clones capable of transforming mouse cells to produce the surface antigen were isolated from a gene library of the hybrid cell by identification of small portions of the library containing functional genes, followed by detection of clones with human-specific reiterated sequences. Both clones also contain CHO-specific reiterated sequences and are therefore human--CHO recombinants. From the frequency of antigen-producing clones in the library, we estimate that they were present in the hybrid cell genome at a copy number of 100 to 1000.

Animals↗
PubMed1980

Mammalian cells do not have a stringent response.

A key attribute of the stringent response of bacteria is the rapid inhibition of ribosomal RNA synthesis mediated by unusual nucleotides in respnse to uncharged tRNA. The question as to whether mammalian cells show a stringent response analogous to that of bacteria was critically tested by the effective rapid amino acid starvation of both normal and transformed cells. Rapid starvation giving a high proportion of uncharged tRNA for leucine was produced within 7 minutes of expression of a nonleaky ts leucyl tRNA synthetase mutation in transformed CHO cells (tsH1) and in its normal growth control revertant (L-73). To control for the effect of temperature alone, ts revertants of tsH1 and L-73 were included in the study, and to control for effects due simply to the inhibition of protein synthesis, the translational elongation inhibitor cycloheximide was used. In addition, rapid starvation for histidine was effected by incubation of both the CHO cell lines and of freshly explanted normal Chinese hamster embryo fibroblasts in histidine-free medium containing high concentrations of histidinol. The rate of preribosomal RNA synthesis and the extent of its maturation to mature rRNA was measured using (3H-methyl) methionine as a donor of methyl groups during synthesis and methylation of pre-rRNA. There was no effect on pre-rRNA synthesis of the rapid generation of uncharged tRNA for 45 minutes for any of the cell types tested. A nonspecific inhibition of maturation of 18S rRNA and late (3 hour) inhibition of pre-rRNA synthesis was observed, but could be mimicked by the inhibition of protein synthesis to comparable levels with cycloheximide. Less severe amino acid starvation resulting in a more physiological inhibition of protein synthesis to 30% also had no specific effect on pre-rRNA synthesis and maturation. Intracellular nucleotide pools were also examined for the appearance of unusual nucleotides such as guanosine tetraphosphate or pentaphosphate and for changes in the levels of normal nucleotides after severe amino acid starvation. No such changes could be detected. We conclude that although mammalian cells may have some biochemical reactions which respond to uncharged tRNA, they do not possess a macromolecular control system analogous to the stringent response of bacteria.

Amino Acids↗
PubMed1977

Analysis of VSV mutant with attenuated cytopathogenicity: mutation in viral function, P, for inhibition of protein synthesis.

T1026, a ts mutant of VSV which is much less cytopathogenic than its parent, HR, and which can establish persistent infection under certain conditions, is a double mutant. In addition to its ts mutation in the virion RNA polymerase, T1026 has a second non-ts mutation in a viral function termed "P". This function is responsible for the inhibition of total protein synthesis in infected cells and acts chiefly at the level of translational initiation. In some cell systems, the inhibition of protein synthesis produced by P appears to be selective for cellular protein synthesis, whereas in other cell systems, both cellular and viral protein synthesis are inhibited. T1026 and its ts revertants are phenotypically P- -that is, cells infected with them show total protein synthesis rates equal to or greater than uninfected cells, while synthesizing viral proteins at the same or even greater rates than HR-infected cells. The P- mutation is correlated with failure to increase plaque size after 2-3 days of incubation. Since viral mutants obtained from persistently infected cultures in a variety of systems appear to be double mutants with a ts mutation in the virion RNA polymerase and a small plaque marker, we suggest that T1026 could represent a model for such mutants.

Animals↗
PubMedDate not supplied

Linkage and risk assessment in fragile X families using new DNA probes at Xq27.

Until recently few polymorphic loci had been genetically mapped close to the fragile X syndrome locus [FRAXA]. Six polymorphic loci, DXS369, DXS297, DXS296, DXS304, IDS and DXS374, have now been mapped closer to the fragile X FRAXA than in the present study. We report the results of genetic linkage analysis of 32 fragile X [fra(X)] families using 12 polymorphic loci including these new markers. Cytogenetic and molecular data were combined in two-point linkage analysis for the estimation of lod scores and carrier probabilities in potential carriers. Combined with results from previous studies, recombination fractions (0) corresponding to the maximum lod scores (Z max) were obtained for each of the 12 loci versus FRAXA. Recombination fractions between marker loci in the families were also calculated. The data were evaluated to determine the efficacy of using the strategy suggested by Suthers et al. (1991a) for molecular studies in fra(X) families. The large proportion of females heterozygous for at least one locus (83%) and of females heterozygous for flanking loci (60%) indicate that this is a very useful diagnostic strategy. Use of these new marker loci substantially changed the carrier risk estimates for members of 7 of the 32 families from the risk estimates previously calculated on the basis of less closely linked probes available prior to 1989.

DNA Probes↗
PubMedDate not supplied

Allograft ligament transplantation. A morphological and biochemical evaluation of a medial collateral ligament complex in a rabbit model.

Our purpose in this investigation was to describe and compare several morphological, histological, vascular, and biochemical healing processes of allograft and autograft bone-medial collateral ligament-bone complexes in a rabbit model. Forty-nine animals had their right medial collateral ligament complex replaced with a frozen allograft while 30 separate control animals each received a fresh autograft. Animals were sacrificed at 3, 6, 12, 24, or 48 weeks after transplantation for comparison of grafted with unoperated contralateral control complexes. Results demonstrate some recovery of both allografts and autografts over time. Allografts generally showed slower recovery than autografts with more persistent abnormalities in gross appearances, increased cellularity (corresponding to increased DNA content), and decreased collagen content. Allografts also showed aggressive remodeling of bone at insertions and they remained hypervascular throughout their substance as compared with contralateral controls. Autografts went through similar but less chronic increases in cellularity and DNA concentration with no changes in collagen content. While both types of grafts showed some signs of "healing" and some recovery of control ligament biology, results are also consistent with allograft encasement, infiltration, and at least partial replacement by host tissue. This was particularly true of insertions. Collectively, these results also demonstrate some differences between allografts and autografts in this extraarticular model. The causes, mechanisms, and longer-term consequences of these changes, including defining the qualities of these graft and host tissues, clearly requires further investigation.

Animals↗
PubMedDate not supplied

3-D components of a biological neural network visualized in computer generated imagery. I. Macular receptive field organization.

Computer-assisted, 3-dimensional reconstructions of macular receptive fields and of their linkages into a neural network have revealed new information about macular functional organization. Both type I and type II hair cells are included in the receptive fields. The fields are rounded, oblong, or elongated, but gradations between categories are common. Cell polarizations are divergent. Morphologically, each calyx of oblong and elongated fields appears to be an information processing site. Intrinsic modulation of information processing is extensive and varies with the kind of field. Each reconstructed field differs in detail from every other, suggesting that an element of randomness is introduced developmentally and contributes to endorgan adaptability.

Acoustic Maculae↗
PubMedDate not supplied

3-D components of a biological neural network visualized in computer generated imagery. II. Macular neural network organization.

Computer-assisted reconstructions of small parts of the macular neural network show how the nerve terminals and receptive fields are organized in 3-dimensional space. This biological neural network is anatomically organized for parallel distributed processing of information. Processing appears to be more complex than in computer-based neural networks, because spatiotemporal factors figure into synaptic weighting. Serial reconstruction data show anatomical arrangements which suggest that 1) assemblies of cells analyse and distribute information with inbuilt redundancy, to improve reliability; 2) feedforward/feedback loops provide the capacity for presynaptic modulation of output during processing; 3) constrained randomness in connectivities contributes to adaptability; and 4) local variations in network complexity permit differing analyses of incoming signals to take place simultaneously. The last inference suggests that there may be segregation of information flow to central stations subserving particular functions.

Acoustic Maculae↗
PubMedDate not supplied

[Establishment of a blood transfusion center at Kabul (Afghanistan)].

Recent events concerning blood transfusion (BT) have led to the number of BT being drastically reduced and to more rigorous checking of blood donations before their use for transfusion. Very few developing countries have been able to set up BT organizations that are both self-sufficient and capable of ensuring a high quality of blood testing. A central blood bank (CBB) was set up in Kabul (Afghanistan) during the 1980s. From 1992 onwards, its activities were curtailed due to the political turmoil, lack of funds and the fact that no blood collection policy was being implemented. A partnership between a development aid agency (Avicen), French public institutions and the local authorities has resulted in the rebirth of this CBB by the injection of financial resources and technical and scientific expertise. An independent committee of BT specialists was responsible for assessing the scientific validity and ethical acceptability of the project. In 1996, the objectives of the project, which had been in operation for one year, were achieved as far as the renovation of the laboratories was concerned. Work has focused mostly on setting up a proper cold chain and on training laboratory technicians in standard biological methods for testing blood from donors (blood group, HIV screening, Ag Hbs, HCV and syphilis). However, due to the shortage of blood donors, it has been difficult to set up a minimum blood bank stock. The results of the first biological tests carried out on the blood of the first 1,281 donors have made it possible to define an appropriate, detailed policy for preventing and controlling the main risks of infection from BT, involving routine testing for HIV, Ag HBs and HCV (0.3% prevalence). BT is a major component of any health care system and it must be reconstructed. The measures proposed here are long-term and require the ongoing participation of all those involved in this project including the local authorities and sources of financial support.

Adult↗