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S Britton

Publications and source records attributed to S Britton.

At least 37 records · Page 2Linked to original sources
PubMed2000

The third human FER-1-like protein is highly similar to dysferlin.

Dysferlin, the protein product of the gene mutated in patients with an autosomal recessive limb-girdle muscular dystrophy type 2B (LGMD2B) and a distal muscular dystrophy, Miyoshi myopathy, is homologous to a Caenorhabditis elegans spermatogenesis factor, FER-1. Analysis of fer-1 mutants and of sequence predictions of the FER-1 and dysferlin ORFs has predicted a role in membrane fusion. Otoferlin, another human FER-1-like protein (ferlin), has recently been shown to be responsible for autosomal recessive nonsyndromic deafness (DFNB9). In this report we describe the third human ferlin gene, FER1L3, which maps to chromosome 10q23.3. Expression analysis of the orthologous mouse gene shows ubiquitous expression but predominant expression in the eye, esophagus, and salivary gland. All the ferlins are characterized by sequences corresponding to multiple C2 domains that share the highest level of homology with the C2A domain of rat synaptotagmin III. They are predicted to be Type II transmembrane proteins, with the majority of the protein facing the cytoplasm anchored by the C-terminal transmembrane domain. Sequence and predicted structural comparisons have highlighted the high degree of similarity of dysferlin and FER1L3, which have sequences corresponding to six C2 domains and which share more than 60% amino acid sequence identity.

Amino Acid Sequence↗
PubMed2000

HIV-1 alters T helper cytokines, interleukin-12 and interleukin-18 responses to the protozoan parasite Leishmania donovani.

OBJECTIVE: To investigate the in vitro and in vivo effect of HIV-1 on lymphoproliferative and T helper (Th) cytokine responses in leishmaniasis. METHODS: Th1 [interleukin (IL)-2 and interferon (IFN)-gamma] and Th2 (IL-4 and IL-10) as well as IFN-gamma-inducing cytokines (IL-12 and IL-18) were measured in antigen and mitogen-stimulated culture supernatants of peripheral blood mononuclear cells (PBMC) of healthy donors, HIV-infected and visceral leishmaniasis (VL) patients with or without HIV co-infection. RESULTS: Proliferative responses to phytohaemagglutinin (PHA) were significantly lower in PBMC from VL and asymptomatic HIV-infected persons compared with responses in healthy individuals. VL-HIV co-infected patients showed the lowest responses. Although there was no significant difference in the Leishmania-induced proliferative responses among the healthy group and those infected with HIV only, VL patients (with or without HIV) exhibited very low proliferation. When cultured with PHA or Leishmania, PBMC from healthy donors produced high levels of a Th1 cytokine (IFN-gamma) and low levels of Th2 cytokines (IL-4 and IL-10). In addition, co-culturing PBMC from healthy donors with a killed HIV preparation abrogated the production of IFN-gamma induced by Leishmania and augmented IL-4 and IL-10 production. Cells from HIV-infected patients produced low levels of IFN-gamma, but high levels of IL-10. The addition of anti-IL-10 did not increase Leishmania-induced proliferative responses or IFN-gamma production. Both IL-12 and/or IL-18 responses were lower in VL patients, HIV-infected, or VL-HIV co-infected patients as compared with those of healthy donors. CONCLUSION: The data suggest that the inhibitory effect of HIV and VL on proliferation and IFN-gamma production is not due to IL-10 alone, but that the defect induced by HIV and VL probably operates at the level of regulation of IFN-gamma-inducing factors, such as IL-12 and IL-18.

Animals↗
PubMed2000

A postgenomic approach to identification of Mycobacterium leprae-specific peptides as T-cell reagents.

To identify Mycobacterium leprae-specific human T-cell epitopes, which could be used to distinguish exposure to M. leprae from exposure to Mycobacterium tuberculosis or to environmental mycobacteria or from immune responses following Mycobacterium bovis BCG vaccination, 15-mer synthetic peptides were synthesized based on data from the M. leprae genome, each peptide containing three or more predicted HLA-DR binding motifs. Eighty-one peptides from 33 genes were tested for their ability to induce T-cell responses, using peripheral blood mononuclear cells (PBMC) from tuberculoid leprosy patients (n = 59) and healthy leprosy contacts (n = 53) from Brazil, Ethiopia, Nepal, and Pakistan and 20 United Kingdom blood bank donors. Gamma interferon (IFN-gamma) secretion proved more sensitive for detection of PBMC responses to peptides than did lymphocyte proliferation. Many of the peptides giving the strongest responses in leprosy donors compared to subjects from the United Kingdom, where leprosy is not endemic, have identical, or almost identical, sequences in M. leprae and M. tuberculosis and would not be suitable as diagnostic tools. Most of the peptides recognized by United Kingdom donors showed promiscuous recognition by subjects expressing differing HLA-DR types. The majority of the novel T-cell epitopes identified came from proteins not previously recognized as immune targets, many of which are cytosolic enzymes. Fifteen of the tested peptides had > or =5 of 15 amino acid mismatches between the equivalent M. leprae and M. tuberculosis sequences; of these, eight gave specificities of > or =90% (percentage of United Kingdom donors who were nonresponders for IFN-gamma secretion), with sensitivities (percentage of responders) ranging from 19 to 47% for tuberculoid leprosy patients and 21 to 64% for healthy leprosy contacts. A pool of such peptides, formulated as a skin test reagent, could be used to monitor exposure to leprosy or as an aid to early diagnosis.

Amino Acid Sequence↗
PubMed2000

High dose prednisolone treatment of leprosy patients undergoing reactions is associated with a rapid decrease in urinary nitric oxide metabolites and clinical improvement.

Evidence is accumulating that nitric oxide (NO) produced by macrophages has a role in the pathogenesis of reactions in leprosy. We followed the urinary levels of the metabolites of NO [nitrite (NO2-) and nitrate (NO3-)] and the clinical response to prednisolone treatment in leprosy patients (n = 9) admitted to ALERT leprosy hospital Addis Ababa, Ethiopia, because of reversal reaction (RR) or erythema nodosum leprosum (ENL). In untreated reactional leprosy patients, the levels of urinary NO metabolites (1645 +/- 454 microM, n = 9, ENL = 4, RR = 5) decreased significantly 2 weeks after high dose prednisolone treatment (1075 +/- 414 microM, P < 0.05), and remained stable 4 (895 +/- 385 microM, P < 0.02) and 6 weeks following treatment initiation (1048 +/- 452 microM, P < 0.02). This decrease was also present when the reactional patients were subdivided according to the type of reaction (ENL, RR) and coincided with a clinical improvement. In patients showing a poor clinical response to steroids, no or minor effects on the urinary NO metabolite levels were observed. We conclude that there is a correlation between the decrease in urinary NO metabolites and a favourable clinical response after high dose prednisolone treatment of reactional leprosy patients.

Adolescent↗
PubMed2000

Diagnostic assays for leprosy based on T-cell epitopes.

To date, only a limited number of antigens have been described as specific for Mycobacterium leprae, and in many cases, homologues have subsequently been shown to exist in mycobacteria such as M. avium and M. intracellulare. A Leprosy Synthetic Peptide Skin Test Initiative was established by the Steering Committee on the Immunology of Mycobacteria of the UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases, to investigate the potential of synthetic peptides that encode T-cell epitopes as diagnostic tools, which could be used to develop a skin-test reagent specific for leprosy. Such M. leprae-specific peptides should have unique amino acid sequences, or significant sequence-dissimilarity from those in other mycobacteria. Synthetic peptides, 15 amino acids long, were synthesised from 33 genes or open reading frames within the M. leprae genome. Tuberculoid leprosy patients from four leprosy-endemic countries, Brazil, Ethiopia, Nepal and Pakistan, were tested as subjects known to have been infected with M. leprae, and to make good T-cell responses to antigens of M. leprae; UK blood donors were used as non-exposed or non-infected subjects. Peptides inducing potentially specific responses in leprosy patients and not in UK controls, and those inducing cross-reaction responses, present in both leprosy patients and non-exposed, non-infected controls, were identified. A difference from the equivalent M. tuberculosis sequence of five or more amino acid residues did not, by itself, identify peptides that were M. leprae-specific, suggesting that many of these peptides may have homologues in environmental mycobacteria. To date, this approach has identified a number of peptides with greater than 90% specificity and 19-47% sensitivity, which are undergoing further specificity-testing. Such peptides would have great potential as T-cell reagents with which to monitor exposure to M. leprae within communities, formulated either as skin-test reagents, or as antigens for tests in vitro.

Epitopes, T-Lymphocyte↗
PubMed1999

Telomere loss in peripheral blood mononuclear cells may be moderately accelerated during highly active antiretroviral therapy (HAART).

It has been speculated that infection with HIV-1 may lead to a significant increase in turnover, and subsequent exhaustion, of immune repopulation. Given that telomeric DNA is lost on mitotic replication, telomere lengths can be used as an indirect gauge of this rate. We have analyzed the mean telomere restriction fragment lengths in peripheral blood mononuclear cells (PBMC) from 31 patients with established, though mainly untreated, HIV infection and found them to be no different than those among healthy controls. Our results are in line with several findings in CD4+ cell fractions but contradict a previous report suggesting that telomere shortening contributes to immune failure. Interestingly, after approximately 2 years of subsequent aggressive antiretroviral treatment we found a telomere reduction corresponding to a loss of about 250 base pairs per year; this is roughly tenfold above that predicted from healthy individuals. This could partly result from nucleoside analogue inhibition of the natural telomere replacement enzyme, telomerase-a reverse transcriptase inducible in certain hematopoietic cells. However, this may also indicate accelerated cell replacement on initiation of optimal therapeutic regimes or result from changes in the composition of the PBMC pool. These results suggest careful monitoring of telomere lengths during long-term HAART.

Adult↗
PubMed1999

Dose-response resistance to HIV-1/MuLV pseudotype virus ex vivo in a hairpin ribozyme transgenic mouse model.

We have investigated the efficacy of a hairpin ribozyme targeting the 5' leader sequence of HIV-1 RNA in a transgenic model system. Primary spleen cells derived from transgenic or control mice were infected with HIV-1/MuLV pseudotype virus. A significantly reduced susceptibility to infection in ribozyme-expressing transgenic spleen cells (P = 0.01) was shown. Variation of transgene-expression levels between littermates revealed a dose response between ribozyme expression and viral resistance, with an estimated cut off value below 0.2 copies of hairpin ribozyme per cell. These findings open up possibilities for studies on ribozyme efficacy and anti-HIV-1 gene therapy.

Animals↗
PubMed1999

HIV viral load and response to antileishmanial chemotherapy in co-infected patients.

OBJECTIVE: To investigate whether clearance of Leishmania parasites from tissue aspirate smears in patients with HIV and visceral leishmaniasis (VL) co-infection treated with pentavalent antimonials is influenced by initial HIV viral load and to assess the effect of active VL on HIV viral load and replication in vivo. METHODS: Leishmania parasites were identified in Giemsa-stained smears prepared from tissue aspirates. Parasite index was determined by quantifying Leishmania donovani bodies in smears. HIV-1 RNA was quantitated by using the nucleic acid sequence-based amplification technique with a limit of detection of 500 copies/ml. All patients were treated with pentavalent antimonials at 20 mg pentavalent antimony (Sb(V))/kg daily for a total of 28 days. None of the patients received specific anti-retroviral therapy. RESULTS: Seventeen patients (73.9%) showed good initial response to anti-leishmanial treatment and the remaining six (26.1%) had very poor response. Among the good responders, 11 (64.7%) had no demonstrable Leishmania donovani bodies in post-therapy tissue aspirate smear preparations, and in the remaining six (35.3%) their parasite loads were reduced to very low levels. Patients with poor response had persistently high parasite index despite completion of anti-leishmanial chemotherapy. Poor responders had pre-treatment median HIV viral load that was >160-fold higher than responders to anti-leishmanial chemotherapy; [410000 copies/ml (quartile range, 33000-530000) and 2500 copies/ml (quartile range 500-297500), respectively]. Furthermore, compared with pre-treatment viral concentrations, patients with good response showed marked reduction in post-treatment viral load. In contrast, post-treatment HIV viral concentrations were markedly increased among patients with poor response to anti-leishmanial therapy. CONCLUSIONS: The results suggest that pre-treatment HIV viral load influences response to anti-leishmanial chemotherapy and active VL is associated with increased viral replication in vivo, supporting the notion that dual infection plays an important role in the pathogenesis and disease progression of either infection.

AIDS-Related Opportunistic Infections↗
PubMed1999

[30 years of successful mycobacteriology research, The AHRI in Addis Abeba--a unique research environment in a developing country].

The Armauer Hansen Research Institute (AHRI) in Addis Abeba, Ethiopia, was established by the Swedish and Norwegian Save the Children organisations in collaboration with the University of Bergen, with the principal objective of pursuing basic research in leprosy. The institute has a commendable record of achievement, and has made significant contributions to our understanding of leprosy and its control, and to the training of scientists from Ethiopia and other African countries. Recently, the Ethiopian, Swedish and Norwegian governments agreed to continue supporting the AHRI as an autonomous research centre. Its main objectives will be to conduct research in mycobacterial diseases, particularly tuberculosis, and to promote the enhancement of human resources in health research through instruction, supervision, and scientific collaboration.

Clinical Competence↗
PubMed1999

Leishmania-HIV interaction: immunopathogenic mechanisms.

Both Leishmania and the human immunodeficiency virus (HIV) can infect and multiply in macrophages, and both can dysregulate the immune system. Recent studies indicate that Leishmania can induce the activation of HIV in latently infected monocytic and T cells. Moreover, HIV can enhance intracellular growth of Leishmania in macrophages. Here, Dawit Wolday and colleagues examine the mechanisms that might be involved in the immunopathogenesis of Leishmania- HIV co-infection.

AIDS-Related Opportunistic Infections↗
PubMed1999

Effects of HIV co-infection and chemotherapy on the urinary levels of nitric oxide metabolites in patients with pulmonary tuberculosis.

The presence of nitric oxide (NO) and its role as a factor in host defence against intracellular pathogens in human macrophages is controversial. We measured the metabolites of NO (nitrite (NO2-) and nitrate (NO3-)) in urine from Ethiopian patients suffering from tuberculosis. The urinary level of NO2-/NO3- in a group of healthy Ethiopians was 1020+/-471 microM (n = 22). Untreated HIV negative patients with active pulmonary tuberculosis (1574+/-588 microM, p<0.01, n = 12) and household contacts to tuberculosis patients (1949+/-812 microM, p = 0.006, n = 7) had significantly higher levels of urinary NO2-/NO3- than the control group. Untreated HIV positive patients with pulmonary tuberculosis did not have increased levels of urinary NO2-/NO3- (1101+/-614 microM, n = 6). Some of the HIV negative untreated patients with pulmonary tuberculosis (1710+/-519 microM, n = 6) were followed up after treatment and showed a reduction in the levels of urinary NO2-/NO3- 1 week after treatment (945+/-599 microM, p<0.05). We conclude that HIV negative patients with active pulmonary tuberculosis have increased urinary levels of nitric oxide metabolites with a reduction following specific anti-tuberculous chemotherapy.

Adolescent↗
PubMed1999

Dysferlin is a plasma membrane protein and is expressed early in human development.

Recently, a single gene, DYSF, has been identified which is mutated in patients with limb-girdle muscular dystrophy type 2B (LGMD2B) and with Miyoshi myopathy (MM). This is of interest because these diseases have been considered as two distinct clinical conditions since different muscle groups are the initial targets. Dysferlin, the protein product of the gene, is a novel molecule without homology to any known mammalian protein. We have now raised a monoclonal antibody to dysferlin and report on the expression of this new protein: immunolabelling with the antibody (designated NCL-hamlet) demonstrated a polypeptide of approximately 230 kDa on western blots of skeletal muscle, with localization to the muscle fibre membrane by microscopy at both the light and electron microscopic level. A specific loss of dysferlin labelling was observed in patients with mutations in the LGMD2B/MM gene. Furthermore, patients with two different frameshifting mutations demonstrated very low levels of immunoreactive protein in a manner reminiscent of the dystrophin expressed in many Duchenne patients. Analysis of human fetal tissue showed that dysferlin was expressed at the earliest stages of development examined, at Carnegie stage 15 or 16 (embryonic age 5-6 weeks). Dysferlin is present, therefore, at a time when the limbs start to show regional differentiation. Lack of dysferlin at this critical time may contribute to the pattern of muscle involvement that develops later, with the onset of a muscular dystrophy primarily affecting proximal or distal muscles.

Amino Acid Sequence↗
PubMed1999

Identical mutation in patients with limb girdle muscular dystrophy type 2B or Miyoshi myopathy suggests a role for modifier gene(s).

Limb girdle muscular dystrophy type 2B (LGMD2B) and Miyoshi myopathy (MM), a distal muscular dystrophy, are both caused by mutations in the recently cloned gene dysferlin, gene symbol DYSF. Two large pedigrees have been described which have both types of patient in the same families. Moreover, in both pedigrees LGMD2B and MM patients are homozygous for haplotypes of the critical region. This suggested that the same mutation in the same gene would lead to both LGMD2B or MM in these families and that additional factors were needed to explain the development of the different clinical phenotypes. In the present paper we show that in one of these families Pro791 of dysferlin is changed to an Arg residue. Both the LGMD2B and MM patients in this kindred are homozygous for this mutation, as are four additional patients from two previously unpublished families. Haplotype analyses suggest a common origin of the mutation in all the patients. On western blots of muscle, LGMD2B and MM patients show a similar abundance in dysferlin staining of 15 and 11%, respectively. Normal tissue sections show that dysferlin localizes to the sarcolemma while tissue sections from MM and LGMD patients show minimal staining which is indistinguishable between the two types. These findings emphasize the role for the dysferlin gene as being responsible for both LGMD2B and MM, but that the distinction between these two clinical phenotypes requires the identification of additional factor(s), such as modifier gene(s).

Base Sequence↗
PubMed1999

Role of Leishmania donovani and its lipophosphoglycan in CD4+ T-cell activation-induced human immunodeficiency virus replication.

Chronic immune activation by coinfecting pathogens has been suggested as a cofactor in human immunodeficiency virus (HIV) disease progression, particularly in the setting of developing countries. Here, we used in vivo-infected mononuclear cells to examine the role of the protozoan parasite Leishmania donovani and its major membrane constituent, lipophosphoglycan (LPG), in mediating CD4+ T-lymphocyte activation-induced HIV replication and CD4+ T-cell death. We found that Leishmania antigens upregulated HIV replication in CD8-depleted peripheral blood mononuclear cells from asymptomatic HIV-infected donors compared to unstimulated cells. L. donovani-induced viral replication was associated with cellular proliferation, increased expression of the cellular immune activation markers CD25 and HLA-DR within the CD4+ subpopulation, and enhanced secretion of tumor necrosis factor alpha (TNF-alpha), interleukin 2 (IL-2), and IL-6. LPG induced TNF-alpha secretion in the absence of increased expression of cellular activation markers. Moreover, in a few cases we observed that L. donovani induced HIV replication without significant cellular activation but with cytokine secretion. The rate of apoptosis was accelerated in these latently infected CD4+ T cells primed with Leishmania antigens compared to controls, and TNF-alpha production appeared to be the central event necessary for this effect. Furthermore, we demonstrate that thalidomide inhibited Leishmania-induced virus replication coupled with abrogated Leishmania-induced TNF-alpha secretion but not IL-2 or IL-6 production. Furthermore, thalidomide did not affect Leishmania-induced apoptosis. The results suggest that Leishmania and its product, LPG, up-regulate HIV replication in latently infected cells through distinct antigen-specific and non-antigen-specific cellular immune activation mechanisms and that TNF-alpha secretion is pivotal in this process. The immunomodulatory role of thalidomide raises interest as a potential adjuvant to reduce HIV disease progression in Leishmania-HIV coinfected individuals.

Adult↗
PubMed1999

T-cell recognition of Mycobacterium tuberculosis culture filtrate fractions in tuberculosis patients and their household contacts.

We examined the immune responses of patients with active pulmonary tuberculosis (TB) and their healthy household contacts to short-term culture filtrate (ST-CF) of Mycobacterium tuberculosis or molecular mass fractions derived from it. Our goal was to identify fractions strongly recognized by donors and differences among the donor groups of possible relevance for vaccine development. The study population consisted of 65 human immunodeficiency virus-negative donors from the Hossana Regional Hospital, Hossana, Ethiopia. Peripheral blood leukocytes from the donors were stimulated with different antigens and immune responses were determined. Household contacts produced significantly higher levels of gamma interferon (IFN-gamma) than the TB patients in response to antigens present in ST-CF and the 10 narrow-molecular-mass fractions. A similar difference in leukocyte proliferative responses to the antigens between the two groups was also found. In general, while all fractions stimulated immune responses, the highest activity was seen with the low-molecular-mass fractions, which include well-defined TB antigens such as ESAT-6. Leukocytes from contacts of TB patients with severe disease produced higher levels of antigen-specific IFN-gamma than those from contacts of patients with minimal disease. Both groups of contacts exhibited higher cell-mediated responses than the patients themselves. The enhanced immune response of healthy contacts, especially those of patients with severe disease, to secreted mycobacterial antigens is suggestive of an early stage of infection by M. tuberculosis, which could in time result in overt disease or containment of the infection. This possibility is currently being investigated by follow-up studies of the household contacts.

Antigens, Bacterial↗
PubMed1999

Increased levels of nitric oxide metabolites in urine from leprosy patients in reversal reaction.

We measured the metabolites of NO [nitrite (NO2-) and nitrate (NO3-)] in urine from Ethiopian patients suffering from leprosy. The urinary level of NO2-/NO3- in a group of healthy Ethiopians was 1020 +/- 471 microM (n = 22). Leprosy patients in reversal reaction had significantly higher levels of NO2-/NO3- (1817 +/- 492 microM, p < 0.001, n = 12) than both the control group and leprosy patients who were not in reversal reaction (1079 +/- 446 microM, n = 12). We conclude that the reversal reaction in leprosy in associated with increased urinary levels of nitric oxide metabolites.

Adult↗