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Biomedical subjects

C A Smith

Publications and source records attributed to C A Smith.

At least 235 records · Page 13Linked to original sources
PubMed1995

X-ray structure of the magnesium(II)-pyrophosphate complex of the truncated head of Dictyostelium discoideum myosin to 2.7 A resolution.

The structure of the magnesium pyrophosphate complex of the truncated head of Dictyostelium myosin has been determined by molecular replacement at 2.7 A resolution and refined to a crystallographic R-factor of 16.0%. The crystals belong to the orthorhombic space group P2(1)2(1)2, where a = 105.2 A, b = 182.1 A, and c = 54.5 A. The conformation of the protein around the magnesium pyrophosphate is very similar to that seen when magnesium ADP-beryllium fluoride binds in the active site. The latter complex mimics the binding of ATP prior to hydrolysis. The pyrophosphate molecule occupies the beta- and gamma-phosphate sites, where the two phosphorus atoms are in the same positions as the beta-phosphate and the BeFx moiety of the beryllium fluoride-trapped ADP. The surrounding active site residues are almost perfectly superimposable in the two structures and the hydrogen-bonding interactions that the PPi makes with the protein are essentially identical. The similarity between the MgPPi and MgADP.BeFx complex with S1Dc suggests that the conformational change, which occurs when ATP binds to actomyosin and which reduces the affinity of myosin for actin, is caused by the binding of the gamma- and beta-phosphate groups of the nucleotide. This then implies that the role of the remainder of the substrate is to increase the binding affinity for myosin and thus to drive the equilibrium toward dissociation of myosin from actin.

Adenosine Diphosphate↗
PubMed1995

Fas antigen stimulation induces marked apoptosis of T lymphocytes in human immunodeficiency virus-infected individuals.

Apoptosis (programmed cell death) of T lymphocytes has been proposed as a mechanism which plays an important role in the pathogenesis of human immunodeficiency virus (HIV) disease. Activation of Fas (CD95) can either result in costimulation of proliferation and cytokine production or in the induction of apoptosis of T lymphocytes. This raises the possibility that Fas is involved in the observed T cell apoptosis during HIV disease. In this report we show that peripheral blood CD4+ and CD8+ T lymphocytes from HIV-infected individuals undergo apoptosis in vitro in response to antibody stimulation (cross-linking) of Fas at a much higher frequency than from uninfected controls. This anti-Fas-induced T cell apoptosis is markedly higher than spontaneous T cell apoptosis in HIV-infected individuals. Antibodies against other members of the tumor necrosis factor (TNF)/nerve growth factor receptor family such as CD27, CD30, CD40, 4-1BB, p55 TNF receptor, p75 TNF receptor, and TNF receptor-related protein did not result in any increase of T cell apoptosis above that spontaneously observed in HIV+ individuals. Anti-Fas-induced apoptosis was much higher in symptomatic HIV-infected individuals; and the magnitude of anti-Fas-induced CD4+ T cell apoptosis correlated inversely with peripheral blood CD4+ T cell absolute counts. Surface expression of Fas on T cells was also found to be higher in HIV-infected individuals. Resting and activated CD4+ and CD8+ T cells both underwent apoptosis in response to anti-Fas antibody. L-Selectin positive memory CD4+ T cells were especially susceptible to anti-Fas-induced apoptosis. These findings show that CD4+ and CD8+ T lymphocytes in HIV-infected individuals are primed in vivo to undergo apoptosis in response to Fas stimulation, suggesting that Fas signaling may be responsible for the T lymphocyte functional defects and depletion observed in HIV disease.

Antigens, CD↗
PubMed1995

Use of gene-modified virus-specific T lymphocytes to control Epstein-Barr-virus-related lymphoproliferation.

Reactivation of Epstein-Barr virus (EBV) after bone-marrow transplantation leads in many cases to lymphoproliferative disease that responds poorly to standard therapy and is usually fatal. To prevent or control this complication, we prepared EBV-specific cytotoxic T-lymphocyte (CTL) lines from donor leucocytes and infused them into ten allograft recipients. Three of the patients had shown signs of EBV reactivation, with or without overt lymphoproliferation, and the others received CTL infusions as prophylaxis. No patient developed any complication that could be attributed to the CTL infusions. In the three patients with EBV reactivation, EBV DNA concentrations (measured by semiquantitative polymerase chain reaction [PCR]), which had increased 1000-fold or more, returned to the control range within 3-4 weeks of immunotherapy. The most striking consequence was the resolution of immunoblastic lymphoma in a 17-year-old patient who received four CTL infusions (two 1 x 10(7)/m2 and two 5 x 10(7)/m2). Because the CTL had been genetically marked before infusion, we were able to show by PCR analysis that they persisted for 10 weeks after administration. EBV-specific donor-type T-cell lines seem to offer safe and effective therapy for control of EBV-associated lymphoproliferation.

Adolescent↗
PubMed1995

Fas ligand mediates activation-induced cell death in human T lymphocytes.

A significant proportion of previously activated human T cells undergo apoptosis when triggered through the CD3/T cell receptor complex, a process termed activation-induced cell death (AICD). Ligation of Fas on activated T cells by either Fas antibodies or recombinant human Fas-ligand (Fas-L) also results in cytolysis. We demonstrate that these two pathways of apoptosis are causally related. Stimulation of previously activated T cells resulted in the expression of Fas-L mRNA and lysis of Fas-positive target cells. Fas-L antagonists inhibited AICD of T cell clones and staphylococcus enterotoxin B (SEB)-specific T cell lines. The data indicate AICD in previously stimulated T cells is mediated by Fas/Fas-L interactions.

Antigens, Surface↗
PubMed1995

Immunodominance with progenitor B cell diversity in the neutralizing antibody repertoire to influenza infection.

We report striking immunodominance in the neutralizing antibody responses of major histocompatibility complex congenic mice to natural infection with influenza virus (H3N2 subtype), as deduced by sequencing the hemagglutinin (HA) genes of monoclonal antibody (mAb)-selected mutant viruses. A majority of mAb, established from individual BALB/c (H-2d) mice, select mutant viruses containing the same single amino acid substitution in the membrane distal ecto-domain, HA1 198 A-->E, whereas changes at either HA1 158 G-->E or HA1 198 A-->E are selected for by mAb from BALB.K (H-2k) donors. The structural basis for immunodominance, and potential diversity of progenitor B cells, was investigated by sequence analysis of H and L chain gene rearrangements in mAb specific for HA1 158 or HA1 198. No correlation was found between antibody specificity and VH or VL gene usage, and a minimum of three to six progenitor cells contributed to the individual's repertoire for a single antigenic site. However, in a further analysis of the HA1 158-specific antibody response of CBA/Ca (H-2k) donors, there was highly restricted light chain gene usage. Focusing of the immune repertoire to limited regions of the HA molecule during a primary viral infection may be a significant factor in immune pressure for antigenic variation, particularly since there is no evident restriction in the antibody response to immunization.

Animals↗
PubMed1995

Regulation of murine B cell growth and differentiation by CD30 ligand.

A ligand for CD30 has been recently cloned, and has been shown to have sequence homology with the tumor necrosis factor family of cytokines. CD30 ligand (CD30L) was found to be induced on helper T cell clones, and its receptor was expressed on freshly isolated and activated murine B cells. Recombinant murine CD30L was found to share many functional properties with CD40 ligand (CD40L) in the regulation of murine B cell growth and differentiation in vitro. CD30L stimulated B cell proliferation, antigen-specific antibody production, and polyclonal immunoglobulin secretion in a cytokine-dependent manner. In particular, the stimulation of B cell proliferation by CD30L required interleukin (IL)-4 and IL-5, induction of anti-sheep red blood cell antibody-secreting B cells by CD30L required IL-2 and IL-5, and optimal induction of polyclonal immunoglobulin secretion required IL-4 and IL-5. Under these conditions, the polyclonal secretion of IgG1, IgA, IgG3 and IgE was induced. The induction of immunoglobulin secretion by CD30L was independent of CD40L, as B cells from CD40L deficient-mice responded normally to CD30L treatment. We conclude that CD30L is a potent mediator of B cell growth and differentiation in vitro and may play a role in cognate T cell-B cell interactions.

Animals↗
PubMed1995

Regulation of NK cells through the 80-kDa TNFR (CD120b).

By using monoclonal antibody specific for tumor necrosis factor receptor80 (TNFR80) (CD120b) and TNFR60 (CD120a), we determined which receptor transduces the signals involved in activating natural killer (NK) cells. Purified CD56+CD3- large lymphocytes express TNFR80 but not TNFR60 and interleukin-2 (IL-2) up-regulates TNFR80 expression, consistent with NK cells being activated in vivo. Treatment of NK cells with anti-TNFR80 for 18 h enhanced the NK activity detected on K562 target cells mimicking the effect of TNF. In combination with IL-2, TNF enhanced the development of lymphokine-activated killing. However, only anti-TNFR80 abrogated IL-2 induction of lymphokine-activated killer cell activity. The activity of TNF or anti-TNFR80 was selective for NK cytotoxic function because they did not directly mimic IL-2 activation or induce significant proliferation, expression of cell surface activation antigens (CD25 or HLA-DR), or interferon-gamma secretion. These results indicate that TNFR80 is an important signal transducing receptor for the differentiation of NK cells induced by TNF and IL-2.

Antibodies, Monoclonal↗
PubMed1995

Functional involvement of Pax-1 in somite development: somite dysmorphogenesis in chick embryos treated with Pax-1 paired-box antisense oligodeoxynucleotide.

The metameric pattern of the vertebrate axial skeleton, defined by structures such as the vertebral bodies and ribs, is a result of segmentation events that occur during embryogenesis. The key event in axial segmentation is somite formation. This study examines the role of Pax-1, a member of the paired-box containing Pax gene family, in chick somite development. To investigate whether misexpression of Pax-1 during somite development is functionally related to abnormal axial patterning, antisense methodologies were used to perturb Pax-1 expression. An antisense, phosphorothioate-modified oligodeoxynucleotide (ODN) was designed based on the mouse Pax-1 paired-box sequence, and was either injected into or directly applied topically to early, somitic stage chick embryos. Abnormalities in somite structure and pattern were subsequently observed and scored, including loss of somites (18% of injected embryos, 35% of embryos treated by topical application), fusion of somites (25% of injected, 6% with topical application), and shortened body axis (0% of injected, 11% with topical application). Control embryos receiving sense ODN or non-sense ODN (a scrambled sequence with base composition identical to the antisense ODN) showed substantially fewer somite anomalies, indicating that the effects were sequence-specific. These developmental abnormalities were analyzed using standard histological methods. Whole mount in situ hybridization was carried out to analyze the three-dimensional pattern of Pax-1 expression in whole embryos. In control, untreated embryos, the expression was localized to the entire epithelial somite, and as the somite matured, the expression was limited to its ventromedial region. With Pax-1 antisense ODN treatment, embryos with fused somites retained expression over the entire fused somite, and embryos that had complete loss of somites had greatly reduced expression of Pax-1 transcript. The results presented here provide strong evidence that Pax-1 is functionally important during somitogenesis and morphogenesis of the vertebral column. The spatial pattern of gene expression appears to delineate different populations of cells in the developing embryo (i.e., somite from somite, sclerotome from dermomyotome), and is consistent with the hypothesis that Pax-1 is involved in forming or maintaining boundaries at specific times and locations during development.

Abnormalities, Drug-Induced↗
PubMed1995

Immune receptor repertoire for influenza haemagglutinin.

An extensive analysis was made of receptor specificity and gene usage in the neutralising antibody (mAb) and Class II-restricted T cell responses to influenza haemagglutinin (HA) following natural infection of MHC (H-2(k) or H-2(d)) congenic mice with X31 virus (H3N2 subtype). Despite the diversity of available antigenic sites on the HA1 subunit, there was striking immunodominance in the mAb response as deduced by sequencing the HA genes of escape mutants and the corresponding antibody H and L chain gene rearrangements. Similarly, Class II restricted T cell responses of individual donors focused on a single antigenic site, or immunodominant peptide; and PCR sequence analysis of T cell receptor (alpha beta) gene usage indicated that T cell memory was derived from a single progenitor cell. Focusing of the immune repertoire to limited regions of the HA molecule during a primary viral infection may be a significant factor in immune pressure for antigenic variation.

Amino Acid Sequence↗
PubMed1995

Cross-linking of CD30 induces HIV expression in chronically infected T cells.

CD30, a member of the tumor necrosis factor (TNF) receptor family, is expressed constitutively on the surface of the human T cell line ACH-2, which is chronically infected with human immunodeficiency virus type-1 (HIV)-1. We demonstrate that cross-linking CD30 with an anti-CD30-specific monoclonal antibody, which mimics the described biological activities of the CD30 ligand (CD30L), results in HIV expression. CD30 cross-linking does not alter proliferation of ACH-2 cells and the induction of HIV expression is not mediated by endogenous TNF alpha/beta. Furthermore, cross-linking of CD30 leads to NF-kappa B activation and enhanced HIV transcription. Thus, CD30-CD30L interactions mediate the induction of HIV expression by a kappa B-dependent pathway that is independent of TNF. This mechanism may be important in the activation of HIV expression from latently infected CD4+ T cells, especially in lymphoid organs where cell to cell contact is conducive to receptor-ligand interactions.

Antibodies, Monoclonal↗
PubMed1995

Identification and characterization of a new member of the TNF family that induces apoptosis.

A novel tumor necrosis factor (TNF) family member has been cloned and characterized. This protein, designated TNF-related apoptosis-inducing ligand (TRAIL), consists of 281 and 291 aa in the human and murine forms, respectively, which share 65% aa identity. TRAIL is a type II membrane protein, whose C-terminal extracellular domain shows clear homology to other TNF family members. TRAIL transcripts are detected in a variety of human tissues, most predominantly in spleen, lung, and prostate. The TRAIL gene is located on chromosome 3 at position 3q26, which is not close to any other known TNF ligand family members. Both full-length cell surface expressed TRAIL and picomolar concentrations of soluble TRAIL rapidly induce apoptosis in a wide variety of transformed cell lines of diverse origin.

Amino Acid Sequence↗
PubMed1995

A simple technique to measure body sway in normal subjects and patients with dizziness.

For many years vestibular testing has relied on measurements of the vestibulo-ocular reflex (VOR). More recently quantified assessment of balance, using fixed or moving force platforms and magnetometry have been applied to clinical research. These are objective attempts to quantify the vestibulospinal reflex (VSR). This study evaluates whether SwayWeigh, a simple device which measures lateral body sway, can provide an objective assessment of balance dysfunction. Forty patients with a balance disorder and 31 subjects with normal balance were tested with eyes opened and eyes closed whilst they were standing on a flat surface and then on an air bed. The lateral sway in patients with a balance disorder was compared to that in the normal subjects and highly significant differences (p < 0.0001) were observed. The results also confirmed the importance of vision and proprioception in the maintenance of posture. The SwayWeigh balance platform is a simple and economical device which objectively measures balance dysfunction.

Adult↗
PubMed1995

Objective measurement of the benefit of walking sticks in peripheral vestibular balance disorders, using the Sway Weigh balance platform.

Following a lesion in the vestibular system visual, proprioceptive and residual vestibular information is integrated by the brain, to enable a patient to attain equilibrium. The basis of vestibular rehabilitation is to encourage these adaptive and compensatory mechanisms. Another form of rehabilitation is to provide some form of mechanical aid, and walking sticks are often used for this purpose in patients with balance disorders. There are no reported studies objectively assessing the use of walking sticks in patients with balance disorders. In this study we used the Sway Weigh balance platform (Raymar) to determine the efficacy of a walking stick in 25 patients with peripheral vestibular balance disorders. Patients were tested with their eyes opened and eyes closed whilst they were standing on a flat surface and on an air-filled bed (to alter limb proprioception) on the Sway Weigh balance platform. All the tests were carried out with, and without, a walking stick. The results demonstrate that a walking stick significantly reduces lateral body sway in patients with peripheral vestibular balance disorders.

Aged↗