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Biomedical subjects

R L Allen

Publications and source records attributed to R L Allen.

At least 19 recordsLinked to original sources
PubMed2006

Consistent patterns of expression of HLA class I free heavy chains in healthy individuals and raised expression in spondyloarthropathy patients point to physiological and pathological roles.

OBJECTIVES: Major histocompatibility complex class I (MHC-I) proteins exist at the cell surface in antigen presenting forms and as beta2m-independent free heavy chains (FHCs). FHCs have been implicated in spondyloarthritis, but little is known about their expression in healthy individuals. We studied FHC expression on various human cell types, comparing spondyloarthropathy patients with healthy and rheumatoid arthritis (RA) patient controls. METHODS: MHC-I expression was analysed by flow cytometry. FHC levels were normalized for overall MHC-I to generate a relative expression level. Relative FHC levels were analysed for peripheral blood and trophoblast samples from healthy volunteers, RA and spondyloarthropathy patients. Macrophages and dendritic cells were cultured in vitro to analyse changes following activation. Peripheral blood leucocytes from patients with ankylosing spondylitis (AS) and RA were treated with inflammatory stimuli and subsequent alterations in their relative FHC levels were analysed. RESULTS: We found consistent patterns of differential relative FHC expression across lymphocyte subpopulations and particularly high expression on extravillous trophoblast. FHCs were present at higher levels in a reactive arthritis (ReA) population than in healthy controls and RA patients; differences not merely due to the presence of Human Leucocyte Antigen (HLA) B27. Treatment of leucocytes from arthritic patients with bacterial lipopolysaccharide resulted in significant up-regulation of FHC compared with an HLA B27+ control population. CONCLUSIONS: Our findings define normal levels and tissue expression of FHCs, and support the hypothesis that disregulation of heavy chain expression may play a pathogenic role in spondyloarthropathy.

Adult↗
PubMed2002

The subventricular zone: new molecular and cellular developments.

The subventricular zone (SVZ), which lines the lateral walls of the lateral ventricle, persists as a neurogenic zone into adulthood and functions as the largest site of neurogenesis in the adult brain. In recent years, with the acceptance of the concept of postembryonic mammalian neurogenesis, neurogenesis in the adult SVZ has been an area of active research. With the rapid accumulation of new information on the SVZ, some of which is contradictory, summarizing existing knowledge on the SVZ and outlining future research directions in this area become important. In this review, we will cover recent molecular and cellular investigations that characterize the SVZ niche, SVZ neurogenesis, and SVZ cell migration within the adult brain.

Animals↗
PubMed2001

Leukocyte receptor complex-encoded immunomodulatory receptors show differing specificity for alternative HLA-B27 structures.

We studied recognition of the disease-associated HLA-B27 allele by immunomodulatory receptors encoded within the leukocyte receptor complex. HLA class I are ligands for members of the killer Ig receptor (KIR) and Ig-like transcript (ILT)/LIR/LILR families (the new LILR nomenclature is described at www. gene.ucl.ac.uk/nomenclature/genefamily/lilr.html). Members of these families bound HLA-B27 in both classical and beta(2) microglobulin-independent forms. Classical complexes bound ILT2, ILT4, and LIR6 transfectants but not ILT1, ILT3, or ILT5. A free H chain form of HLA-B27 bound ILT4 and LIR6. Both forms of HLA-B27 bound KIR3DL1 transfectants. HLA-B27 free H chain bound CD14(+) cells in PBL from healthy controls, consistent with ILT4 expression on monocytes. Alternative recognition of different forms of HLA-B27 by KIR or ILT could influence their immunomodulatory function and may imply a role in inflammatory disease.

Antigens, CD↗
PubMed2001

Clustered mutations in HIV-1 gag are consistently required for escape from HLA-B27-restricted cytotoxic T lymphocyte responses.

The immune response to HIV-1 in patients who carry human histocompatibility leukocyte antigen (HLA)-B27 is characterized by an immunodominant response to an epitope in p24 gag (amino acids 263-272, KRWIILGLNK). Substitution of lysine (K) or glycine (G) for arginine (R) at HIV-1 gag residue 264 (R264K and R264G) results in epitopes that bind to HLA-B27 poorly. We have detected a R264K mutation in four patients carrying HLA-B27. In three of these patients the mutation occurred late, coinciding with disease progression. In another it occurred within 1 yr of infection and was associated with a virus of syncytium-inducing phenotype. In each case, R264K was tightly associated with a leucine to methionine change at residue 268. After the loss of the cytotoxic T lymphocyte (CTL) response to this epitope and in the presence of high viral load, reversion to wild-type sequence was observed. In a fifth patient, a R264G mutation was detected when HIV-1 disease progressed. Its occurrence was associated with a glutamic acid to aspartic acid mutation at residue 260. Phylogenetic analyses indicated that these substitutions emerged under natural selection rather than by genetic drift or linkage. Outgrowth of CTL escape viruses required high viral loads and additional, possibly compensatory, mutations in the gag protein.

Arginine↗
PubMed2000

Defying death after DNA damage.

DNA damage frequently triggers death by apoptosis. The irreversible decision to die can be facilitated or forestalled through integration of a wide variety of stimuli from within and around the cell. Here we address some fundamental questions that arise from this model. Why should DNA damage initiate apoptosis in the first place? In damaged cells, what are the alternatives to death and why should they be selected in some circumstances but not others? What signals register DNA damage and how do they impinge on the effector pathways of apoptosis? Is there a suborganellar apoptosome complex effecting the integration of death signals within the nucleus, just as there is in the cytoplasm? And what are the consequences of failure to initiate apoptosis in response to DNA damage?

Animals↗
PubMed2000

Direct visualization of HIV-1-specific cytotoxic T lymphocytes during primary infection.

OBJECTIVE: HIV-specific cytotoxic T lymphocytes (CTL) are believed to play an important role in containing viral replication throughout HIV-1 infection. Previous studies have attempted to quantify the HIV-1-specific CTL precursor frequency during primary HIV infection by using limiting dilution analysis, which almost certainly underestimates the true CTL frequency. Here we use a relatively new technique to quantify HIV-specific CD8 T cells in primary HIV infection. METHODS: We have used soluble tetrameric complexes of HLA class I molecules complexed with HIV epitope peptides to study the dynamics and frequency of HIV-specific CD8 T cells in relation to plasma viral load in early HIV infection, in three patients with a highly focused HIV-specific CTL response. RESULTS: We show that the frequencies of HIV-1-specific CD8 T cells in acute infection are significantly higher than previously documented and can be demonstrated well before full seroconversion. These studies also confirm the immunodominance of the B27-restricted response in HIV infection and demonstrate a close temporal relationship between the numbers of circulating HIV-specific CD8 T cells and viral load. CONCLUSIONS: These findings strongly suggest that HIV-1-specific CD8 T cells are responding directly to the level of viral replication in early HIV infection and are a major factor in its control. In addition, the data indicate that immunodominance for CD8 T-cell responses is established in the acute phase of HIV infection.

Adult↗
PubMed2000

Three years survival in patients with a clinical diagnosis of dementia with Lewy bodies.

The majority of information available on the prognosis of dementia with Lewy bodies (DLB) is based on retrospective data from autopsy series, which are subject to selection bias due to the specific reasons patients are referred for post-mortem studies. The earlier studies comparing DLB patients with patients with Alzheimer's disease (AD) suggest that the mean duration of illness is shorter in DLB patients than in patients with AD. However, more recent studies have not observed significant differences between DLB and AD in age of onset, age at death or duration of illness. We report a 3 year follow-up of a cohort of 114 consecutive patients with dementia, referred to an old age psychiatric service and diagnosed using ICD 10 criteria and the McKeith and Byrne DLB criteria. The case notes of all patients were reviewed to determine the date of onset of symptoms and the date of first presentation to the psychiatric services. Information about outcome was gathered from case notes, hospital files and general practitioner (GP) records. Of the original sample of 114 patients, 106 could be traced. Sixty-four had died and 42 were still alive at the time of the follow-up. Thirty-two patients had originally been assigned the diagnosis of DLB, 43 the diagnosis of AD, 31 vascular dementia and other diagnoses. There were no differences between the AD and DLB group in age at onset, age at death or survival. We have not found any evidence that the prognosis of clinically diagnosed DLB patients is worse than that of patients with a clinical diagnosis of AD.

Aged↗
PubMed2000

The effects of preventive vocal hygiene education on the vocal hygiene habits and perceptual vocal characteristics of training singers.

The purpose of the present study was to determine the effects of vocal hygiene education on the vocal hygiene behaviors and perceptual vocal characteristics of untrained singers. Eleven adult untrained singers served as subjects. They attended four 1-hour class sessions on vocal hygiene, including anatomy and physiology of the phonatory mechanism, vocally abusive behaviors, voice disorders commonly seen in singers, and measures to prevent voice disorders. Pre- and postinstruction surveys were used to record subjects' vocal abuses and their perceptions of their speaking and singing voice. They also rated their perceived value of vocal hygiene education. Results revealed minimal changes in vocal hygiene behaviors and perceptual voice characteristics. The subjects did report a high degree of benefit and learning, however.

Adolescent↗
PubMed2000

Investigation of binaural interference in normal-hearing and hearing-impaired adults.

When speech recognition testing is performed under diotic conditions, some elderly persons with asymmetric hearing loss exhibit a phenomenon in which the performance of the poorer ear interferes with that of the better ear. This binaural interference phenomenon has been estimated to occur in 8 to 10 percent of elderly hearing aid users. The purpose of the present study was to investigate the prevalence of this phenomenon in groups (n = 12) of young and elderly listeners with normal hearing, plus groups of elderly listeners with hearing loss who were aided or unaided. Of 48 subjects tested, only 2 exhibited significant evidence of binaural interference, a result that is close to that expected by chance. Although both of these subjects were elderly, one had normal hearing and the other was aided binaurally. A third elderly unaided subject exhibited a significant binaural advantage. Further studies are needed to determine the prevalence of binaural interference in normal-hearing or hearing-impaired listeners in any decade of life.

Adult↗
PubMed1999

Cutting edge: HLA-B27 can form a novel beta 2-microglobulin-free heavy chain homodimer structure.

HLA-B27 has a striking association with inflammatory arthritis. We show that free HLA-B27 heavy chains can form a disulfide-bonded homodimer, dependent on residue Cys67 in their extracellular alpha 1 domain. Despite the absence of beta 2-microglobulin, HLA-B27 heavy chain homodimers (termed HC-B27) were stabilized by a known peptide epitope. HC-B27 complexes were recognized by the conformation-specific Ab W6/32, but not the ME1 Ab. Surface labeling and immunoprecipitation demonstrated the presence of similar W6/32-reactive free heavy chains at the surface of HLA-B27-transfected T2 cells. HC-B27 homodimer formation might explain the ability of HLA-B27 to induce spondyloarthropathy in beta 2-microglobulin-deficient mice.

Antibody Specificity↗
PubMed1999

The role of HLA-B27 in spondyloarthritis.

The human major histocompatibility complex (MHC) class I allele HLA-B27 bears a striking association with the spondylolarthritic group of inflammatory arthritides, yet despite extensive studies its role in the disease process remains obscure. As an MHC class I protein, the primary function of HLA-B27 is to complex with beta(2)-microglobulin forming a structure that presents short antigenic peptides for recognition by cytotoxic T lymphocytes (CTL). It has been proposed that the role of HLA-B27 in spondyloarthropathy involves this process of antigen presentation, and of the numerous theories proposed to explain the association, the most popular have involved the binding and presentation of "arthritogenic" peptides. Transgenic rodent studies directly implicate HLA-B27 heavy chains in disease pathogenesis, but suggest that the mechanism may be distinct from their primary function. The recent demonstration that HLA-B27 heavy chains can form stable homodimers may thus be of relevance. This review summarizes the evidence supporting current theories of disease association and proposes an alternative model of disease based on recent findings.

Alleles↗
PubMed1999

Disassembly of nuclear inclusions in the dividing cell--a novel insight into neurodegeneration.

Spinocerebellar ataxias and Huntington's disease are examples of neurodegenerative diseases caused by a trinucleotide repeat expansion. One hallmark of such diseases is the formation of inclusion bodies (IBs) within neuronal tissue. Although these inclusions may play a pivotal role in the disease process, the reasons underlying their specific accumulation remain obscure. By studying intranuclear IBs in dividing cells we demonstrate for the first time that inclusions such as those of ataxin-1 disperse during mitosis, thus reducing the nuclear aggregate burden. IBs reform in the interphase nucleus. By high-resolution confocal microscopy we also show that inclusions comprise ordered structures capable of homotypic interactions. Unlike those of a non-pathologic protein, ataxin-1 inclusions were shown to be capable of non-specific protein sequestration. Our studies indicate that the specific accumulation of inclusions in terminally differentiated cells such as neurons is a direct consequence of their inability to divide and therefore provides a key to explaining their persistence in neurodegenerative disease.

Amino Acid Sequence↗
PubMed1998

Oligoclonal expansions of CD8(+) T cells in chronic HIV infection are antigen specific.

Acute HIV infection is associated with a vigorous immune response characterized by the proliferation of selected T cell receptor V beta (BV)-expressing CD8(+) T cells. These 'expansions', which are commonly detected in the peripheral blood, can persist during chronic HIV infection and may result in the dominance of particular clones. Such clonal populations are most consistent with antigen-driven expansions of CD8(+) T cells. However, due to the difficulties in studying antigen-specific T cells in vivo, it has been hard to prove that oligoclonal BV expansions are actually HIV specific. The use of tetrameric major histocompatibility complex-peptide complexes has recently enabled direct visualization of antigen-specific T cells ex vivo but has not provided information on their clonal composition. We have now made use of these tetrameric complexes in conjunction with anti-BV chain-specific monoclonal antibodies and analysis of cytotoxic T lymphocyte lines/clones to show that chronically clonally expanded CD8(+) T cells are HIV specific in vivo.

CD8-Positive T-Lymphocytes↗
PubMed1998

Human myelomonocytic cells express an inhibitory receptor for classical and nonclassical MHC class I molecules.

Leukocyte activation can be negatively regulated by inhibitory receptors specific for MHC class I molecules. While one inhibitory receptor, Ig-like transcript 2 (ILT2), is expressed by all lymphoid and myelomonocytic cell types, other receptors display a more selective tissue distribution. Here we characterize an inhibitory receptor, termed ILT4, which is selectively expressed in monocytes, macrophages, and dendritic cells (DCs), binds classical class I molecules and the nonclassical class I molecules HLA-G, and transduces negative signals that can inhibit early signaling events triggered by stimulatory receptors. ILT4 may control inflammatory responses and cytotoxicity mediated by myelomonocytic cells and may modulate their Ag-presenting functions, focusing immune responses to microbial challenges and avoiding autoreactivity.

Animals↗
PubMed1998

Importance of a conserved TCR J alpha-encoded tyrosine for T cell recognition of an HLA B27/peptide complex.

Human HLA B27-restricted cytotoxic T lymphocytes (CTL) specific for the influenza A epitope NP383-391 use similar TCR alpha and beta chains, with two closely related J alpha segments used by six of nine CTL clones from three unrelated donors (Bowness et al., Eur J. Immunol. 1993. 23: 1417-1421). The role of TCR complementarity-determining region (CDR)3alpha residues 93 and 100-102 was examined by site-directed mutagenesis, following expression of the TCR alpha and beta extracellular domains from one clone as a TCR zeta fusion heterodimer in rat basophil leukemia (RBL) cells. For the first time we have measured direct binding of tetrameric HLA B*2705/NP383-391 complexes to transfected TCR. Independently peptide-pulsed antigen-presenting cells (APC) were used to induce TCR-mediated degranulation of RBL transfectants. Our results show a key role for the conserved TCRalpha CDR3 J alpha-encoded residue Y102 in recognition of HLA B27/NP383-391. Thus the Y102D mutation abolished both tetramer binding and degranulation in the presence of peptide-pulsed APC. Even the Y102F mutation, differing only by a single hydroxyl group from the native TCR, abolished detectable degranulation. Further mutations F93A and S100R also abolished recognition. Interestingly, the N101A mutation recognized HLA B27/NP in functional assays despite having significantly reduced tetramer binding, a finding consistent with "kinetic editing" models of T cell activation. Modeling of the GRb TCR CDR3alpha loop suggests that residue Y102 contacts the HLA B*2705 alpha1 helix. It is thus possible that selection of germ-line TCRAJ-encoded residues at position 102 may be MHC driven.

Amino Acid Sequence↗