Biomedical subjects

D J Barrett

Publications and source records attributed to D J Barrett.

At least 19 recordsLinked to original sources

PubMed2006

A study of dry cow therapy and effects on SCC in 10 Irish dairy herds.

Somatic cell count (SCC) data for 480 cows in 10 Irish dairy herds from January 2001 until June 2002 were analysed. Herds were selected on the basis of a recent or ongoing history of clinical or subclinical mastitis. An individual cow SCC of 200 000 cells per ml was used as the threshold for elevation of SCC. The duration of elevated SCC prior to drying-off and the magnitude of the elevation in SCC were found to have an impact on the response to dry cow therapy (DCT). A trend also emerged indicating that increasing parity had a negative influence on the response to DCT.

Animals↗

PubMed2001

Reflexive shifts of covert attention operate in an egocentric coordinate frame.

Covert shifts of attention have been shown to improve detection and discrimination thresholds for a range of visual stimuli. Although there is some evidence to suggest that the allocation of attention to a particular region of interest occurs in a retinotopic frame of reference, the importance of an allocentric, or object-based, framework has gained widespread empirical support. The current experiment investigates the nature of the spatial representation in which covert shifts of attention occur in response to a reflexive prime. Primes and targets were presented in four conditions designed to vary systematically the validity of the spatial relationship between the prime and target in egocentric or allocentric coordinate frameworks. A significant advantage, in terms of reaction time and correct identification, was found for targets located in positions previously primed in an egocentric (but not allocentric) framework whereas there was no advantage for locations primed in an allocentric (but not egocentric) framework. These results suggest that the allocation of covert spatial attention within an egocentric framework may be more important than previously thought.

Attention↗

PubMed1999

Analysis of intensive care populations to select possible candidates for high dependency care.

OBJECTIVES: To identify the proportion, and range across intensive care units, of intensive care patients who might potentially be managed on a high dependency unit (HDU) using three different classification systems. METHODS: 8095 adult patients admitted to 15 intensive care units in the south of England between 1 April 1993 and 31 December 1994 were studied. Patients were identified as potential HDU admissions if their APACHE III derived risk of hospital mortality was < or =10%, if they were categorised as a low risk monitor (LRM) patient using the Wagner risk stratification method, or if they did not require advanced respiratory support (ARS). RESULTS: 4146 patients (51.2%) had an APACHE III derived risk of hospital death of < or =10%, 1687 (20.8%) were classified as LRM, and 3860 (47.7%) did not receive ARS. The values for each intensive care unit ranged from 32.8-63.3% (APACHE III group), 7.2-29.9% (LRM group), and 14.4-68.2% (ARS group). No matter which of the three methods was used, there were significant differences between the 15 units (p<0.0001) with regard to the number of potential HDU patients identified within the scored population. CONCLUSIONS: The percentage of intensive care patients who might be more appropriately managed in a HDU varies considerably between hospitals, and depends upon both local circumstances and the method used to define a high dependency patient. However, whichever method is used, it appears that significant numbers of patients of low dependency status currently fill intensive care beds in the units studied. If these analyses are correct, the perceived national shortage in intensive care beds might be improved by the development of HDUs.

APACHE↗

PubMed1997

Sensitization of multidrug-resistant human leukemia cells with MDR1-targeted antisense and inhibition of drug-mediated MDR1 induction.

Increased expression of MDR1 is strongly implicated in the appearance of chemotherapeutic drug resistance in cancer, especially hematological malignancies. We therefore examined the potential of antisense oligonucleotides to inhibit MDR1 and restore sensitivity to drug-resistant human lymphoblastic cells (CCRF-CEM). Treatment with two different phosphorothioate-modified antisense sequences as well as a DNA-RNA hybrid sequence resulted in a 30 to 45% decrease in MDR1 expression as determined by staining with the monoclonal antibody MRK16 followed by flowcytometry (FCM) analysis. Further, inhibition of MDR1 expression persisted for 3 days after removal of oligonucleotides. Increased accumulation of rhodamine 123 and nearly a three-fold sensitization of cells to vincristine paralleled the reduction in staining with MRK16. Reversed or scrambled control sequences had no effect in any of the assays. During the course of these studies, we observed a 25 to 75% increase in MRK16 staining of cells treated with the chemotherapeutic agents daunorubicin and vincristine as well as by the resistance reversal agents verapamil and cyclosporin. Treatment of cells with antisense oligonucleotides prior to exposure to daunorubicin or cyclosporin reduced the increase in MRK16 staining. These results indicate that antisense targeted to MDR1 can sensitize drug-resistant leukemia cells and suggest that antisense treatment may prevent the emergence of MDR1-mediated drug resistance.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1996

Hsp90-mediated folding of the lymphoid cell kinase p56lck.

Several lines of evidence suggest that members of the 90-kDa family of heat shock proteins (hsp90) may support the folding of various homologues of the src kinase family. In this work, we utilized pulse-chase analyses in rabbit reticulocyte lysate to demonstrate that hsp90-bound intermediates existed for the majority of newly synthesized p56lck molecules. The hsp90-binding drug geldanamycin disrupted the association of p56lck with hsp90, prevented the kinase from demonstrating a protease-resistant conformation, and caused decreases in kinase specific activity. Requirements for geldanamycin-inhibitable hsp90 function and physical interactions between hsp90 and p56lck persisted during chase periods. Consistent with the effects observed in rabbit reticulocyte lysate, application of geldanamycin to fibroblasts caused specific reversion of lck-mediated transformation concomitant with loss of p56lck activity and protein. However, geldanamycin had no direct effect on purified p56lck. Also consistent with functional linkages between hsp90 and p56lck, physical interactions between these proteins were detected in cytoplasmic, but not membrane, fractions of LSTRA cells. Although hsp90 functions in both the initial de novo folding and the reiterative support of p56lck structure in rabbit reticulocyte lysate, the specific occurrence of complexes between hsp90 and p56lck in the cytoplasm of T cells suggests that hsp90 primarily folds nascent molecules of p56lck in vivo.

Animals↗

PubMed1996

The outcome of poliovirus infections in K562 cells is cytolytic rather than persistent after hemin-induced differentiation.

K562-Mu erythroleukemia cells readily establish a long-term persistent poliovirus infection characterized by continuous virus production in the absence of complete p220 cleavage and host translation shutoff (R. E. Lloyd and M. Bovee, Virology 194:200-209, 1993). The mechanism of resistance appears to be modulated at the intracellular level and to be related to decreased virus-mediated cytopathic effects (P. A. Benton, J. W. Murphy, and R. E. Lloyd Virology 213:7-18, 1995). It is well documented that hemin induces the differentiation of K562 cells and alters the expression of several host proteins. We report here that growth of K562 cells in hemin prior to poliovirus infection results in a dose-dependent increase in virus-induced cell lysis and thereby alters the normally persistent outcome of infection to a more lytic phenotype. K562 cells infected after hemin treatment displayed increased host translation shutoff, p220 cleavage, viral protein synthesis, and viral RNA accumulation compared with nontreated cells. Since hemin treatment of K562 cells also induced the increased expression of several heat shock proteins (Hsp70, Hsc70, Hsp90, and cohort p60), we tested the hypothesis that their increased expression may play a role in altering poliovirus infection in hemin-treated K562 cells. However, neither heat stress nor oxidative stress, inducers of heat shock protein synthesis, altered the outcome (of virus infections. In addition, we report the novel finding that subunits of two translation initiation factors, p220 (eIF-4G) and eIF-2alpha, are cleaved as a result of hemin treatment of K562 cells. It is proposed that hemin alters the expression of specific host proteins in K562 cells, probably other than heat shock proteins, which changes the initial response to poliovirus infections from persistent to lytic.

Cell Differentiation↗

PubMed1994

Arrested rearrangement of TCR V beta genes in thymocytes from children with X-linked severe combined immunodeficiency disease.

Human X-linked severe combined immunodeficiency disease (SCID) is an immunodeficiency disorder in which T cell development is arrested in the thymic cortex. B lymphocytes in children with X-linked SCID seem to differentiate normally. X-linked SCID is associated with a mutation in the gene that encodes the IL-2R gamma-chain. Because TCR-beta gene recombination is a pivotal initial event in T lymphocyte ontogeny within the thymus, we hypothesized that a failure to express normal IL-2R gamma could lead to impaired TCR-beta gene recombination in early thymic development. PCR was used to determine the status of TCR-beta gene-segment rearrangements in thymic DNA that had been obtained from children with X-linked SCID. The initial step in TCR-beta gene rearrangement, that of D beta to J beta recombination, was readily detected in all thymus samples from children with X-linked SCID; in contrast, V beta to DJ beta gene rearrangements were undetectable in the same samples. Both D beta to J beta and V beta to DJ beta TCR genes were rearranged in the thymic tissues obtained from immunologically normal children. We conclude that TCR beta-chain gene rearrangement is arrested in children with X-linked SCID. Our results suggest a causative relationship between the failure of TCR beta-chain gene rearrangements to proceed beyond DJ beta rearrangements and the production of a nonfunctional IL-2R gamma-chain.

Base Sequence↗

PubMed1994

Persistence of multiple maternal genotypes of human immunodeficiency virus type I in infants infected by vertical transmission.

The extent of nucleotide variation within the HIV-1 env hypervariable domains serves as a marker of virus genotypes within infected individuals and as a means to track transmission of the virus between individuals. We analyzed env V1 and V2 sequences in longitudinal samples from two HIV-1-infected mothers, each with three children infected by maternal transmission of the virus. Sequences in samples that were obtained from two infants at 2 d and 4 wk after birth displayed more variation in V1 and V2 than maternal samples obtained at the same times. Multiple HIV-1 genotypes were identified in each mother. In each family, multiple maternal HIV-1 genotypes were transmitted to the infants. Specific amino acid residues in the hypervariable domains were conserved within sequences from each family producing a family-specific amino acid signature pattern in V1 and V2. Viruses that were highly related to maternal viruses in signature pattern persisted for as long as 4 yr in the older children. Results support a model of transmission involving multiple HIV-1 genotypes with development of genetic variation from differential outgrowth and accumulation of genetic changes within each individual.

Acquired Immunodeficiency Syndrome↗

PubMed1993

Ocular manifestations of the lacrimo-auriculo-dento-digital syndrome.

We studied a mother and daughter with an extremely rare constellation of signs and symptoms. One or both had absent lacrimal puncta, nasolacrimal duct obstruction, chronic dacryocystitis, dry eyes, and epiphora. Systemic findings included salivary gland hyposecretion, dental hypoplasia and dysplasia, cup-shaped ears with hearing loss, and digital anomalies. These findings are consistent with those of the lacrimo-auriculo-dento-digital syndrome, a genetic disorder. Our study supports the autosomal dominant inheritance of this syndrome, delineates the ophthalmic manifestations, and provides evidence that renal anomalies are part of the disorder.

Abnormalities, Multiple↗

PubMed1993

Corticosteroids improve survival of children with AIDS and Pneumocystis carinii pneumonia.

OBJECTIVE: To determine if corticosteroids administered in addition to antimicrobials improve survival in children with acquired immunodeficiency syndrome and severe Pneumocystis carinii pneumonia (PCP). DESIGN: Before-after, nonrandomized, case-comparison study. SETTING: Pediatric intensive care unit of a tertiary care teaching hospital in Florida. PARTICIPANTS: Eleven children infected with the human immunodeficiency virus (HIV) with confirmed PCP. SELECTION PROCEDURE: Infants with HIV infection and acute respiratory failure due to PCP were studied sequentially. INTERVENTION: The first seven infants were treated with antimicrobials alone while the next four received a 2-week course of methylprednisolone sodium succinate in addition to antimicrobials. MEASUREMENTS AND RESULTS: The two groups were similar with respect to age, route of HIV infection, stage of HIV disease, CD4 T-cell count, antiretroviral therapy, and respiratory parameters at intubation. All children treated with antimicrobials alone died while receiving mechanical ventilation. Survival of the children who received corticosteroid therapy was significantly improved (P < .05), and all were weaned from the ventilator. CONCLUSIONS: Corticosteroids administered in addition to antimicrobials and supportive care improve the short-term survival of HIV-infected children who have acute respiratory failure due to PCP.

AIDS-Related Opportunistic Infections↗

PubMed1993

The temporal association between gamma delta T cells and the natural history of insulin-dependent diabetes.

We previously reported a significant increase in percentages of peripheral blood gamma delta+ T cells in islet cell antibody (ICA) positive relatives of patients with insulin-dependent diabetes (IDD). In the present study, we further characterized this T cell abnormality in a larger group of ICA+ subjects and report that (1) Percentages of gamma delta+ T lymphocytes were significantly increased only in subjects with high ICA titers (> or = 20 JDF units) (P = 0.005) and resulted from an increase in absolute numbers of gamma delta+ T lymphocytes. (2) In these subjects, the increase in gamma delta+ T lymphocytes was associated with an increase in the V gamma 9 V delta 2 subpopulation (r = 0.99). (3) In these same subjects, high percentages of gamma delta+ T lymphocytes were associated with normal beta cell function while low percentages were associated with diminished insulin response. Using 65 microU/ml as the threshold of abnormal intravenous glucose tolerance test (IVGTT) response, percentages of gamma delta+ T lymphocytes could significantly predict IVGTT status in these subjects (P < 0.01). A longitudinal follow-up further suggested that the development of an abnormal IVGTT response and progression to diabetes was associated with a decrease in percentages of gamma delta+ T lymphocytes while patients whose gamma delta+ T cell percentages remained high retained normal beta cell function. Our data therefore suggest that gamma delta+ T lymphocytes and more specifically V gamma 9 V delta 2 T cells are implicated in the autoimmune process leading to diabetes and may have a regulatory role. The monitoring of their percentages in the blood of patients at risk for diabetes may be useful as an additional predictor of diabetes development.

Adolescent↗

PubMed1993

Independent variation and positive selection in env V1 and V2 domains within maternal-infant strains of human immunodeficiency virus type 1 in vivo.

Multiple targets for immune recognition and cellular tropism are localized to the V1 and V2 hypervariable regions in the amino portion of human immunodeficiency virus type 1 (HIV-1) gp120env. We have assessed genetic diversity in env V1 and V2 hypervariable domains in vivo within epidemiologically related strains of HIV-1. Our strategy was to analyze longitudinal samples from two seropositive mothers and multiple children infected by perinatal transmission. Although the V1 and V2 domains are closely linked in the HIV-1 genome, nucleotide sequences in V1 and in V2 evolved independently in maternal-infant viruses in vivo. A high proportion of the nucleotide substitutions would introduce amino acid diversity in V1 and in V2. A significant excess of nonsynonymous over synonymous substitutions was identified in HIV-1 env V1 and V2 peptides in the mothers and in two older children but was not generally apparent in HIV-1 sequences in infants. An excess of nonsynonymous over synonymous substitutions indicated that there is positive selection for independent genetic variation in the V1 and V2 domains in vivo. It is likely that there are host responses to complex determinants in the V1 or V2 hypervariable domain of HIV-1 gp120.

Amino Acid Sequence↗

PubMed1992

Human anti-pneumococcal polysaccharide antibodies are secreted by the CD5- B cell lineage.

To determine whether human antibody responses to T cell-independent pneumococcal polysaccharide antigens are derived from CD5+ or CD5- B cells, we utilized an ELISPOT assay to detect individual anti-polysaccharide antibody-secreting cells. Human anti-type IV pneumococcal polysaccharide antibody-secreting cells were found in the CD5- B cell subpopulation. An EBV transformed anti-pneumococcal antibody-secreting B cell line was also CD5-. The ontogeny of CD5 expressing B cells correlated with the age at which polysaccharide responsiveness is acquired (generally around age 2 years in humans). The CD5- B cell subset represents only 25-30% of the B cells in young children, but this fraction increases throughout childhood to a plateau of 70-80% of the B cells in adults. These results support the hypothesis that the developmental change in responsiveness to T cell-independent polysaccharide antigens in humans is associated with maturation of the CD5- B cell subset.

Adolescent↗

PubMed1991

Con A-induced suppressor cell function depends on the activation of the CD4+CD45RA inducer T cell subpopulation.

Human T cells incubated for 48 hr with Con A suppress B cell Ig production. We sought to define the interactions between CD4+ T cells and CD8+ T cells in the generation of suppressor cell activity following Con A stimulation. Con A-activated CD4+ inducer T cells suppressed Ig production in autologous cocultures of T cells and B cells by 84%, while PHA-activated CD4+ T cells could not. However, Con A-activated CD4+ T cells are not themselves suppressors. When Con A-activated CD4+ T cells were added to coculture of B cells plus T cells depleted of CD8+ T cells, no suppression of Ig production was observed. Furthermore, these Con A-activated CD4+ T cells were able to provide excellent help for Ig production. Therefore, Con A-induced suppressor cell function requires a CD4+ suppressor/inducer acting on a CD8+ suppressor/effector ultimately resulting in the down regulation of B cell Ig synthesis. Human CD4+ inducer T cells can be functionally dissected into helper/inducer or suppressor/inducer T lymphocytes based on their expression of either the CDw29 or CD45RA surface molecules, respectively. Following incubation with Con A the expression of CD45RA on CD4+ T cells increased from 34 to 80% (P = 0.001) while CDw29 expression was unchanged. Incubating lymphocytes with PHA resulted in a non-specific increase in both CD45RA and CDw29 expression by CD4+ T cells. The increase in CD4+CD45RA expression was a result of active proliferation by the Con A-stimulated T cells. Suppression of Ig secretion was directly correlated with the enhanced CD45RA expression following Con A activation. We demonstrate that enhanced suppressor/inducer function is unique to Con A stimulation and was not observed following activation by PHA. Furthermore, short-term culture with Con A results in the selective expansion of the CD4+CD45RA T cell subpopulation.

Antigens, CD↗

PubMed1991

Defective inducer T-cell function before the onset of insulin-dependent diabetes mellitus.

To investigate the possible role of CD4+ T lymphocyte immunoregulatory abnormalities in the pathogenesis of human insulin-dependent diabetes mellitus (IDD), we studied the in vitro function of CD4+ helper/inducer and suppressor/inducer T-cell subpopulations in 25 high risk non-diabetic individuals who tested positive for islet-cell antibodies (ICA). Helper-inducer T-cell function, as measured in the pokeweed mitogen T-B co-culture system, was decreased in the ICA+ subjects in comparison to controls. This abnormality in helper/inducer T-cell function was present for both IgG (P = 0.0001) and IgM (P = 0.004) secretion by B cells. Diminished helper/inducer function correlated with ICA titer (Pearson correlation coefficient -0.44) with subjects having an ICA titer greater than or equal to 40 JDF units demonstrating the most significant disturbances in function (P = 0.01). The helper/inducer T-cell subset percentage was also decreased in ICA+ subjects when compared to matched controls (30 +/- 3% vs 39 +/- 2%; P = 0.02). The abnormality in helper/inducer function was intrinsic to the CD4+ CD45RA+ subset and was not simply due to diminished numbers of helper/inducer T-cells added in the co-culture experiments, since the defect persisted when CD4+ CD45RA+ helper/inducer T-cells were purified and added to B cells as the only source of T-cell help. Our results indicate that ICA+ subjects have functional defects in the helper/inducer subpopulation of CD4+ T-cells. This abnormality may contribute to the pathogenesis of IDD and may provide a novel marker for identifying persons at risk for developing IDD.

Adolescent↗

PubMed1991

Increased T lymphocytes bearing the gamma-delta T cell receptor in subjects at high risk for insulin dependent diabetes.

The effector mechanisms responsible for autoimmune beta cell destruction in insulin dependent (type 1) diabetes (IDD) remain elusive. In order to investigate whether T lymphocytes bearing the gamma-delta T cell receptor (gamma delta+ T cells) could be involved in this process, we measured percentages of peripheral blood gamma delta+ T cells in IDD patients, relatives of IDD probands and controls. High levels of gamma delta+ T cells strongly differentiated 23 relatives at high risk for IDD on the basis of positive islet cell autoantibodies (ICA positive relatives) from 59 controls (P = 0.0013), whereas 26 ICA negative relatives, 14 recent-onset and nine long term IDD patients could not be distinguished from controls on the basis of percentages of gamma delta+ T cells. These data suggest that increased levels of circulating gamma delta+ T cells correlate with the ongoing autoimmune process in pancreatic islets of subjects at high risk for IDD and may thus represent an additional marker for the development of the disease.

Adolescent↗

PubMed1991

CD5+ B lymphocytes in high-risk islet cell antibody-positive and newly diagnosed IDDM subjects.

Human CD5+ B lymphocytes produce autoantibodies that bind to self- and exogenous antigens. Extremely high percentages of CD5+ B lymphocytes are present in the fetal and newborn periods, whereas they constitute only a minority of B lymphocytes in healthy adults. Increased percentages of circulating CD5+ lymphocytes have previously been demonstrated in several autoimmune diseases, including rheumatoid arthritis, progressive systemic sclerosis, Graves' disease, and Sjögren's syndrome. We measured the percentages of B lymphocytes that expressed the CD5 determinant in 93 control subjects (age range 1 day to 59 yr, mean +/- 22.6 +/- 17.7 yr), 17 subjects with newly diagnosed insulin-dependent diabetes mellitus (IDDM; range 5-29 yr, mean +/- SD 13 +/- 5.9 yr), 31 high-risk islet cell antibody (ICA)-positive nondiabetic subjects (range 4-45 yr, mean +/- SD 19.8 +/- 14.1 yr), and 13 subjects with IDDM of greater than 5 yr duration (range 10-43 yr, mean +/- SD 24.2 +/- 9.9 yr). We report that CD5+ B-lymphocyte percentages are strikingly age dependent in healthy control subjects, declining progressively from the newborn period to the middle-age years (r = -0.75, P = 0.0001). In ICA+ nondiabetic and recent-onset IDDM subjects less than 29 yr of age, the percentage of circulating CD5+ B lymphocytes fell within the 95% confidence intervals established for control subjects. However, the age-dependent rate of decline in the percentage of CD5+ B lymphocytes within the control range was slower in ICA+ and newly diagnosed IDDM subjects than in control subjects.

Adolescent↗

PubMed1990

Combined immunodeficiency due to the selective absence of CD4 inducer T lymphocytes.

Selective congenital deficiency of the CD4 inducer T lymphocyte subset is a recently described variant of combined immunodeficiency. To further characterize the cellular and molecular mechanisms which lead to the profound T and B cell immunodeficiency in this condition, we examined in vitro immunoregulatory T lymphocyte activation and effector function, interleukin-2 (IL-2) synthesis, IL-2 receptor generation, and CD4 gene structure. Immunophenotyping of T lymphocytes demonstrated a selective deficiency of CD4+ cells, with normal numbers of CD2+ and CD3+ T cells, nearly all of which expressed the CD8+ determinant. Mitogen- and alloantigen-induced blastogenesis was profoundly decreased. B lymphocytes were present in normal numbers but there was a functional dysgammaglobulinemia (low IgG, normal IgM, low IgA) with no antibody response to in vivo immunization. T cells from the patient did not provide help to normal B cells for in vitro immunoglobulin synthesis; however, the patient's B cells were capable of synthesizing normal amounts of IgG when provided help from normal T cells. Concanavalin A failed to activate suppressor-inducer function in the patient's T cells. However, CD8+ T cell-mediated suppression was expressed if the patients T cells were cocultured with normal CD4+ T cells in a pokeweed mitogen-stimulated IgG secretion assay. IL-2 secretion and IL-2 receptor expression were both markedly reduced. Southern blot analysis of genomic DNA revealed no obvious abnormality in CD4 gene structure. The global defects in T cell activation, effector function, immunoregulation, and lymphokine generation observed in CD4+ inducer lymphocyte deficiency emphasizes the central role that the CD4 T lymphocyte plays in the activation and regulation in vivo immune responses.

B-Lymphocytes↗