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Biomedical subjects

A H Liu

Publications and source records attributed to A H Liu.

At least 19 recordsLinked to original sources
PubMed2001

Metropolitan home living conditions associated with indoor endotoxin levels.

BACKGROUND: Household endotoxin exposure in allergy and asthma has been gaining attention for its dual potential to exacerbate these conditions in individuals with established disease and to abrogate atopy before disease onset. OBJECTIVE: We sought to better understand the home environmental and lifestyle factors influencing house dust endotoxin levels. METHODS: From the homes of 86 infants with wheeze in metropolitan Denver, Colorado, house dust endotoxin (detected with a standardized Limulus Amebocyte Lysate assay) and common indoor allergen (Fel d 1, Can f 1, Der p 1, Der f 1, and Bla g 1) contents were quantified. Comprehensive home environment and lifestyle questionnaires were completed during home visits by trained study staff and parents. RESULTS: House dust endotoxin levels were associated with only 2 home environmental features: animals in the home and the presence of central air conditioning. The strongest positive associations were found with animals in the home. Interestingly, the homes without cats or other animals revealed a negative correlation between house dust Fel d 1 and endotoxin (P =.03). Central air conditioning, especially during months of typical use, was associated with lower house dust endotoxin levels. No significant associations between house dust endotoxin levels and home dampness, number of household inhabitants or young children, cleaning frequency, or presence of tobacco smokers in the home were found. CONCLUSIONS: Indoor endotoxin exposure can be increased by the presence of animals in the home and decreased with central air conditioning. In some homes without animals, where allergen exposure adequate for sensitization still occurs, there are lower levels of house dust endotoxin. Therefore in homes without animals, factors that influence allergen and endotoxin levels in house dust probably differ. Households with detectable allergen levels but low endotoxin levels may provide a predisposing environment for animal allergen sensitization.

Air Conditioning↗
PubMed2000

Relation between house-dust endotoxin exposure, type 1 T-cell development, and allergen sensitisation in infants at high risk of asthma.

BACKGROUND: Bacterial endotoxin is known to induce interferon gamma and interleukin 12 production, and therefore has the potential to decrease allergen sensitisation. To find out the role of early chronic endotoxin exposure in the development of allergen sensitisation and asthma, we compared concentrations of endotoxin in house dust with allergen sensitisation in infants at high risk for developing asthma. METHODS: 61 infants 9-24 months old with at least three physician-documented episodes of wheezing were studied. Concentrations of house-dust endotoxin and allergens were measured in the infants' homes. Allergen sensitisation was measured by skin-prick testing with a panel of common inhalant and food allergens. In a subset of these infants, proportions of T lymphocytes producing interferon gamma, and interleukins 4, 5, and 13 were calculated by cell-surface and intracellular cytokine staining, with flow cytometry. FINDINGS: House-dust endotoxin concentrations ranged from 104 to 10,000 endotoxin units (EU) per mL (geometric mean 912 EU/mL). Concentrations did not vary significantly over a 6-month interval. Ten infants (16%) were sensitised to at least one allergen. The homes of allergen-sensitised infants contained significantly lower concentrations of house-dust endotoxin than those of non-sensitised infants (mean 468 vs 1035 EU/mL, respectively; p=0.01). Increased house-dust endotoxin concentrations correlated with increased proportions of interferon-gamma-producing CD4 T cells (p=0.01). Such concentrations did not correlate with proportions of cells that produced interleukins 4, 5, or 13. INTERPRETATION: This study may provide the first direct in-vivo evidence that indoor endotoxin exposure early in life may protect against allergen sensitisation by enhancing type 1 immunity.

Allergens↗
PubMed2000

Sequence heterogeneity in Ig kappa transcripts from single B lymphocytes.

Individually amplified kappa cDNA molecules from single B lymphocytes revealed sequence heterogeneity and aberrantly spliced products. The nature and frequency of the base changes and their absence from similarly amplified beta2 microglobulin transcripts indicate that they were not derived by Taq polymerase misincorporations or by a general infidelity in RNA polymerase. The trinucleotide sequences in which the base changes occurred are disfavored targets of the somatic hypermutation mechanism that modifies antibody variable (V) region genes during immunity. Taken together with the observation that the transcript alterations were absent from the kappa Ig gene, this suggests that somatic mutations were acquired by the kappa gene and rapidly repaired following limited transcription. Preferential repair of mutations located in specific trinucleotide contexts could be the basis for some of the microsequence-specific bias in mutation frequencies observed in antibody V region genes.

Animals↗
PubMed2000

The natural history of peanut allergy in young children and its association with serum peanut-specific IgE.

OBJECTIVES: To observe the nature and frequency of adverse reactions caused by accidental peanut exposure in young children with clinical peanut hypersensitivity and to determine the value of serum peanut-specific IgE levels during follow-up. STUDY DESIGN: Eighty-three children with clinical peanut hypersensitivity diagnosed before their fourth birthdays were contacted yearly to track adverse peanut reactions. Serum peanut-specific IgE levels were determined in 51 of 83 subjects. RESULTS: Fifty-eight percent (31/53) of subjects followed up for 5 years experienced adverse reactions from accidental peanut exposure. Regardless of the nature of their initial reaction, the majority with subsequent reactions (52%, 31/60) experienced potentially life-threatening symptoms. The group with isolated skin symptoms (11/51, 22%) had lower serum peanut-specific IgE levels than the group with respiratory and/or gastrointestinal symptoms (40/51, 78%) (median: 1.25 kU(A)/L vs 11. 65 kU(A)/L, P =.004, Wilcoxon rank sums test). Despite this, there was no threshold level below which only skin symptoms appeared to occur. Four selected subjects had negative double-blind placebo-controlled food challenge responses to peanuts during follow-up. CONCLUSIONS: The majority of children with clinical peanut hypersensitivity followed up for 5 years will have adverse reactions from accidental peanut exposure. Symptoms experienced during subsequent adverse peanut reactions may not be consistent with symptoms reported during initial reactions. Therefore proper education regarding peanut avoidance and treatment of adverse reactions is necessary in all cases of clinical peanut hypersensitivity. Young children who are allergic to peanuts can lose clinical hypersensitivity.

Allergens↗
PubMed1999

Clinical practice guidelines for the management of chronic sinusitis in children.

Chronic sinusitis in children is a common and vexing disease for clinicians and the public. There are insufficient data in the literature to develop an evidence-based clinical guideline. Experience in managing pediatric chronic sinusitis has been gained through a multidisciplinary clinic at our institution during the past 3 years. A panel of experts was formed, and with the guidance of a guideline methodologist, the development of a rigorous outcome-based guideline was undertaken. Symptom-improvement and recurrence estimates for a variety of medical and surgical treatments were assessed. Wide probability estimates were made by the panelists in most cases. Although we refrained from making specific recommendations, we developed a ranked series of practical treatment options taking into account side effects and costs.

Anti-Bacterial Agents↗
PubMed1999

Molecular pathogenesis of root dentin caries.

Human dentin has a higher content of organic matrix and more non-ideal hydroxyapatite than human enamel. Ultrastructural studies indicate that root caries involves both mineral dissolution and breakdown of the organic matrix. Factors involved in the root caries process seem more complicated than those in enamel caries. Moreover, the distinct roles of acids and enzymes and the sequence of events in the root caries process are not well-understood. Although Streptococcus mutans and Actinomyces viscosus are considered to be major pathogenic micro-organisms of root caries, their roles in degradation of the organic matrix components of root dentin need clarification. The purpose of this paper is to review the basic composition of root dentin and the roles of acids and both endogenous and bacterial enzymes in the root caries process.

Collagen↗
PubMed1998

Alterations in glycosyltransferases during myeloid and monocytoid differentiation of HL-60 cells.

HL-60, a human promyelocytic leukemia cell line, can be differentiated to myeloid lineage by all- trans retinoic acid (ATRA), dimethylsulfoxide (DMSO) and n -butyric acid (n -BA), or to monocytoid(monocytic/macrophagic) lineage by phorbol-12-myristate-13-acetate (PMA) and ganglioside GM(3). The activity alterations of N -acetylglucosaminyltransferase III and V (GnT-III, GnT-V) as well as alpha-1,6-fucosyl-tranferase (alpha1,6 Fuc T) were studied during the differentiation of HL-60 cells by the above-mentioned five inducers using the fluorescence (PA)-labeled glycan-HPLC method for GnT assays and biotin-labeled glycan-LCA affinity chromatography combined with the HRP-avidin colorimetric method for alpha1,6 Fuc T assay. It was observed that after 3 days, all three enzymes decreased in HL-60 cells induced by 1 micromol/l ATRA and 0.6 mmol/l n-BA, while GnT-III and alpha1,6 Fuc T increased, but GnT-V still decreased after induction by 1% DMSO. GnT-V and alpha1,6 Fuc T declined, while GnT-III was elevated after induction by 0.1 micromol/l PMA for 3 days. In contrast, GnT-III increased after the treatment with 50 micromol/l GM(3)for 3 or 6 days, but GnT-V was not appreciably changed and alpha1,6 FucT was elevated after 6 days of GM(3)treatment. It may be concluded that the decrease of GnT-V is the common change in myeloid differentiation and the increase of GnT-III is the general alteration in monocytoid differentiation. The changes in the activities of glycosyltransferases were consistent with the structural changes in surface N -glycans previously found in our laboratory, i.e. that the antennary number of N -glycans decreased during myeloid differentiation by ATRA, and the amount of bisecting GlcNAc in N -glycans increased during monocytoid differentiation by PMA.

Antineoplastic Agents↗
PubMed1998

Modification of pentasaccharide core of surface N-glycans during differentiation of HL-60 cells.

All-trans retinoic acid (ATRA) or phorbol-12-myristate-13-acetate (PMA) are two representative inducers which induce the differentiation of HL-60 cells to myelocytes and monocytes respectively. Structural modifications of the pentasaccharide core portion of N-glycans on cell surface glycoproteins during differentiation of HL-60 cells induced by these two agents and the enzymatic mechanism of the structural modifications were studied. Both ATRA and PMA enhanced the incorporation of [3H]-labeled mannose into N-glycans of glycoproteins from cell surface. By using E-PHA and WGA lectin affinity chromatography to analyze [3H]-N-glycans prepared from the surface of control, ATRA- and PMA-treated cells, it was found that the content of bisecting GlcNAc (bis-GlcNAc) attached to the core of N-glycans decreased in ATRA-treated cells, but increased in PMA-treated cells. Since GlcNAc T-III is the enzyme responsible for the synthesis of bis-GlcNAc, the change of bis-GlcNAc was consistent with the alteration of GlcNAc T-III activities in ATRA- and PMA-treated cells. Core alpha-1,6 fucose of surface N-glycans decreased during differentiation which was determined by AAL affinity chromatography. This was also compatible with the reduced activity of alpha-1,6 Fuc T. the enzyme catalyzing the synthesis of core Fuc, in ATRA- and PMA-treated cells. The increase of GlcNAc T-III activity and bis-GlcNAc content in N-glycans may be related to cell adhesion observed in monocytic differentiation.

Carbohydrate Sequence↗
PubMed1997

Influence of whey and purified whey proteins on neutrophil functions in sheep.

The effects of ruminant whey and its purified fractions on neutrophil chemotaxis and superoxide production in sheep were studied. Both colostral whey and milk whey were found to inhibit chemotaxis regardless of whether they were autologous or homologous, but the inhibitory effects were abolished by washing neutrophils with culture medium before their use in the chemotaxis assay. Colostral whey and milk whey also inhibited the chemotactic activity of zymosan-activated serum. Whey fractions of various degrees of purity such as lactoferrin, lactoperoxidase, lactoferrin-lactoperoxidase, alpha-lactalbumin, bovine serum albumin and whey protein concentrate were then studied. While none of these proteins showed any effects on chemotaxis, lactoferrin-lactoperoxidase and whey protein concentrate were found to have an enhancing effect on superoxide production in a dose-dependent manner. Our results provide information on the modulatory role of ruminant milk proteins in inflammatory responses and warrant future investigation.

Animals↗
PubMed1996

Tracing the development of single memory-lineage B cells in a highly defined immune response.

To study the development of B lymphocyte memory, we identified and isolated splenic B cells expressing a highly defined antibody variable region that constitutes a reproducible and predominant component of the memory antibody response to p-azophenylarsonate (Ars). Isolation was achieved during the primary immune response by surface staining and flow cytometry using a specific anti-idiotypic antibody called E4, which recognizes this canonical V region, encoded by one set of V gene segments. The isolated E4+ cells displayed all of the phenotypic characteristics of germinal center centrocytes, including a low level of surface Ig, a lack of surface IgD, a high level of receptor for peanut agglutinin, and expression of mutated antibody V genes. E4+ B cells were first detected in the spleen 7-8 d after primary immunization, reached peak numbers from days 10-13, and waned by day 16. Surprisingly, at their peak, E4+ cells comprised only 40,000 of all splenocytes, and half of these failed to bind Ars. Using this number, we estimate the total number of Ars-specific memory-lineage cells in the spleen to be no more than 50,000 (0.1%) at any one time, and presumably far fewer that are committed to the memory pool. Chromosomal copies of rearranged V genes from single E4+ cells were amplified by nested PCR, and the amplified products were sequenced directly without cloning, using standardized conditions that disclose virtually no Taq polymerase errors. V gene sequence analyses of E4+ cells isolated from single mice confirmed their canonical nature and revealed that they were derived from few precursors. In the average mouse, the E4+ pool was derived from fewer than five canonical precursors. Somatic mutations were found within the V genes of almost all cell isolates. At day 13, a significant fraction of E4+ cells had mutations known to increase antibody affinity for Ars, suggesting they were products of at least one cycle of post-mutational antigen-driven selection. However, the lack of shared mutations by clonally related cells indicated that the selective expansion of mutant subclones typical of memory responses had not yet taken place. This was supported by the observation that half of the E4+ cells failed to bind Ars. Collectively, our results indicate that the memory compartment is a highly selected entity, even at relatively early stages of the primary immune response when somatic mutation and clonal selection are still in progress. If germinal centers are the source of memory B cells, our data suggest that B cell memory may be derived from only a small fraction of all germinal centers.

Amino Acid Sequence↗
PubMed1996

Amplification of genes, single transcripts and cDNA libraries from one cell and direct sequence analysis of amplified products derived from one molecule.

We report a procedure to generate and amplify cDNA libraries and to amplify and sequence genes and single RNA transcript molecules from the same cell without cloning. An absence of cloning steps minimizes potential sources of contamination, which can be especially problematic when working at the single cell level. Potential contamination is further reduced by an absence of any purification step prior to PCR amplification. Amplifications are designed to minimize the production of aberrant molecules in favor of full-length products, which is especially advantageous when generating cDNA libraries. Genes are amplified from isolated single nuclei, which are segregated from cytoplasmic lysates by microcentrifugation. Specific cDNA, total cDNA or both are synthesized from aliquots of the cytoplasmic lysate, and single cDNA molecules are isolated from others of the same species by limiting dilution prior to PCR amplification. In this way, the frequency of amplified products provides for a direct calculation of cDNA copy number by a Poisson analysis. Incorporation errors by Taq DNA polymerase occur at a low frequency and can be eliminated by sequencing independently amplified cDNA molecules from the same cell. Single molecule amplifications provide sufficient material for numerous (approximately 150) direct DNA sequencing reactions. The limiting dilution approach also permits sequence information to be obtained from a single cDNA, when highly related transcripts derived from distinct genes are present in the same cell and simultaneously amplified with the same primers. In sum, this method provides for a maximum amount of nucleic acid information to be extracted from one cell. It has a wide range of applications to studies of the immune system where, to a first approximation, each lymphocyte has a unique receptor identity, where specific states of differentiation may be difficult to assess in a mixed cell population, and where cell immortalization procedures are not always possible nor practical.

Animals↗
PubMed1996

Modulation of immune responses by bovine beta-casein.

The present reports the influence of bovine beta-casein on in vitro and in vivo immune responses. Bovine beta-casein showed an inhibitory effect on ovine neutrophil chemotaxis but had an enhancing effect on superoxide production by neutrophils. In response to mitogenic stimulation, the proliferative response of both T and B lymphocytes was significantly enhanced by beta-casein. While beta-casein had no significant effects on IFN gamma production by ovine blood lymphocytes, and TNF alpha production and MCH Class II antigen expression by ovine bronchoalveolar macrophages, it enhanced IL-1 beta production by the macrophages, beta-casein also had no influence on bovine NK cell activity against a virally-infected cell line. Interestingly, beta-casein was found to reduce the adjuvant effect of matrix immune stimulating complexes (ISCOM) on anti-ovalbumin antibody response in mice when given intramuscularly. Taken together, the results suggest that bovine beta-casein had selective modulating effects in vitro on both innate and adaptive immune responses in ruminants, whereas systemic administration of beta-casein, that might have a depressive effect on adjuvant activity, requires further study.

Animals↗
PubMed1995

Phylogenetic relationships among two species of golden monkey and three species of leaf monkey inferred from rDNA variation.

Restriction maps of rDNA repeats of five species of Colobinae and three outgroup taxa, Hylobates leucogenys, Macaca mulatta, and Macaca irus, were constructed using 15 restriction endonucleases and cloned 18S and 28S rRNA gene probes. The site variation between Rhinopithecus roxellana and Rhinopithecus bieti is comparable to that between Presbytis françoisi and Preshytis phayrei, implying that R. bieti is a valid species rather than a subspecies of R. roxellana. Phylogenetic analysis on the 47 informative sites supports the case for Rhinopithecus being an independent genus and closely related to Presbytis. Furthermore, branch lengths of the tree seem to support the hypothesis that the leaf monkeys share some ancestral traits as well as some automorphic characters.

Animals↗