Biomedical subjects

S R Webb

Publications and source records attributed to S R Webb.

At least 19 recordsLinked to original sources

PubMed2002

Stability of green fluorescent protein using luminescence spectroscopy: is GFP applicable to field analysis of contaminants?

Green fluorescent protein (GFP) was first isolated in the early 1970s for experimental use from coelenterates or the Pacific jellyfish. Aequorea victoria (Morin and Hastings, 1971). GFP has since become a favored biomarker in the photophysical analysis of molecular and cell biology because of its strong intrinsic visible fluorescence and the feasibility of fusing it to other proteins without affecting their normal functions (Creemers et al., 2000). Here we report using Bacillus subtilis expressing GFP to evaluate the influence of different environmental pH conditions on GFP fluorescence. Emission acquisitions were configured to excite at 471 nm and detect at an emission from 490 to 650 nm at 1-nm increments. Fluorescence intensity was significantly better at pH 7 (4.2 x 105 cps; P-value < 0.01) than at acid or alkaline conditions. GFP is a good biomarker for environments near netural conditions: however, GFP may be unsuitable where soils or waters are below or above pH 7 because of loss in fluorescence intensity. Alternative fluorescent markers and delivery systems must be examined in different environments to optimize responses from bioreporter molecules.

Bacillus subtilis↗

PubMed2001

Costimulation via lymphocyte function-associated antigen 1 in the absence of CD28 ligation promotes anergy of naive CD4+ T cells.

The mechanisms controlling induction of anergy at the level of naive CD4+ T cells are poorly understood but thought to reflect limited contact with costimulatory molecules during T cell antigen receptor (TCR) ligation. To clarify this question, naive TCR transgenic CD4+ cells were exposed to specific peptide presented by transfected antigen-presenting cells (APC) expressing MHC class II molecules with defined accessory molecules. Significantly, culturing CD4(+) cells with APC expressing MHC II plus peptide alone elicited early TCR signaling but failed to induce either proliferation or anergy. Culture with APC expressing MHC II plus B7 molecules led to strong proliferation and T cell priming but no anergy. In marked contrast, conspicuous induction of anergy occurred after T cell culture with APC expressing MHC class II and intercellular adhesion molecule-1 (ICAM-1). Thus, at the level of naive CD4(+) cells, anergy induction appears to reflect selective contact with APC expressing ICAM-1 in the absence of B7.

Animals↗

PubMed2001

Vaccination with glutamic acid decarboxylase plasmid DNA protects mice from spontaneous autoimmune diabetes and B7/CD28 costimulation circumvents that protection.

The nonobese diabetic (NOD) mouse develops spontaneous T-cell-dependent autoimmune diabetes. We tested here whether vaccination of NOD mice with a plasmid DNA encoding glutamic acid decarboxylase (GAD), an initial target islet antigen of autoimmune T cell repertoire, would modulate their diabetes. Our results showed that vaccination of young or old female NOD mice with the GAD-plasmid DNA, but not control-plasmid DNA, effectively prevented their diabetes, demonstrating that GAD-plasmid DNA vaccination is quite effective in abrogating diabetes even after the development of insulitis. The prevention of diabetes did not follow the induction of immunoregulatory Th2 cells but was dependent upon CD28/B7 costimulation. Our results suggest a potential for treating spontaneous autoimmune diabetes via DNA vaccination with plasmids encoding self-Ag.

Animals↗

PubMed2001

A key role for ICAM-1 in generating effector cells mediating inflammatory responses.

We investigated how the accessory molecule interactions encountered during T cell priming influence T cell-mediated destruction of insulin-producing beta cells and lead to type 1 diabetes. T cell receptor (TCR)-transgenic CD4+ T cells were primed under controlled conditions in vitro before being adoptively transferred into transgenic recipients expressing membrane ovalbumin under the control of the rat insulin promoter (RIP-mOVA). During priming, antigen-presenting cell expression of B7-1 without intracellular adhesion molecule 1 (ICAM-1) led to the generation of effector cells that migrated to the pancreata of RIP-mOVA recipients but did not cause diabetes. In contrast, when T cells were primed with APCs expressing both B7-1 and ICAM-1, pronounced destruction of beta cells and a rapid onset of diabetes were observed. Pathogenicity was associated with T cell production of the macrophage-attracting chemokines CCL3 and CCL4. Thus, interactions of lymphocyte function-associated antigen 1 with ICAM-1 during priming induce both qualitative and quantitative alterations in T effector function and induce potentially autodestructive responses.

Animals↗

PubMed2000

Monoclonal-based ELISA for the identification of herbicidal cyclohexanedione analogues that inhibit graminaceous acetyl coenzyme-A carboxylase.

Cyclohexanediones are one of four known structural classes of herbicides that inhibit graminaceous acetyl coenzyme-A carboxylase (ACCase; EC 6.4.1.2). Five monoclonal antibodies were raised against cyclohexanediones conjugated to bovine serum albumin. Cross-reactivity studies using a homologous competitive indirect enzyme-linked immunosorbent assay (ciELISA) against 24 cyclohexanedione analogues revealed that two monoclonal antibodies (mAb A and mAb B) could segregate the analogues into active and inactive ACCase inhibitors on the basis of the analogue concentration required to inhibit 50% of antibody binding to the coating conjugate (IC(50)). Both mAb A and mAb B were also found to cross-react with various members of the indolizidinedione structural class of ACCase inhibitors in ciELISA, suggesting that both cyclohexanediones and indolizidinediones possess features recognized by monoclonal antibodies important for the inhibition of ACCase activity. In conclusion, pharmacophore-specific antibodies may be potentially valuable screening tools for the identification of new lead chemistries in a pesticide discovery program.

Acetyl-CoA Carboxylase↗

PubMed2000

Development and evaluation of an immunological approach for the identification of novel acetyl coenzyme-A carboxylase inhibitors: assay optimization and pilot screen results.

Cyclohexanediones, aryloxyphenoxypropionates, indolizidinediones, and triazinediones are four known structural classes of herbicides that inhibit acetyl coenzyme-A carboxylase (ACCase; EC 6.4.1.2). An immunological study to determine the potential of ACCase inhibitor-specific monoclonal antibodies as screening tools to identify novel lead chemistry was undertaken. Using two cyclohexanedione-specific monoclonal antibodies (mAb A and mAb B; Webb, S. R.; Hall, J. C. J. Agric. Food Chem. 2000, 48, 1210-1218) and three different cyclohexanedione hapten coating conjugates, competitive indirect enzyme-linked immunosorbent assays (ciELISA) were developed. Cross-reactivity of the monoclonal antibodies with four structural classes of ACCase inhibitors revealed that the ciELISA using mAb A and a modified cyclohexanedione hapten coating conjugate detected analogues from all four known classes of ACCase inhibitors. A pilot screen using this ciELISA format identified two novel ACCase inhibitors, demonstrating the potential for antibodies as rapid and cost-effective screening tools for identifying novel lead chemistry in pesticide discovery programs.

Acetyl-CoA Carboxylase↗

PubMed2000

Interaction of cyclohexanediones with acetyl coenzyme-A carboxylase and an artificial target-site antibody mimic: a comparative molecular field analysis.

Similarities and differences between steric and electrostatic potentials of a monoclonal-antibody-based surrogate of a herbicide target-site and its in vitro enzyme target were investigated using three-dimensional quantitative structure-activity relationship comparative molecular field analysis (3D-QSAR CoMFA). Two separate, five-component, partial least squares CoMFA models were developed to compare the interaction of cyclohexanedione herbicides with their target site, acetyl coenzyme-A carboxylase (ACCase; EC 6.4.1.2) and a cyclohexanedione pharmacophore-specific monoclonal antibody (mAb A). On the basis of CoMFA models, similarities in steric and electrostatic requirements around position 2 of the binding site for the oxime functional group of the cyclohexanedione molecule appear to be crucial for interaction of the herbicide with both ACCase and mAb A. These similarities explain the observed quantitative relationship between binding of cyclohexandedione herbicides to ACCase mAb A. Furthermore, these results support the production and use of mAb-based surrogates of pesticide targets as screening tools in pesticide discovery programs.

Acetyl-CoA Carboxylase↗

PubMed2000

Controlling mature CD4+ T cell responses.

Immune responses are by necessity highly regulated to achieve the appropriate balance of aggression and restraint. Among the many factors involved in maintaining this balance are the interactions between accessory molecule receptors expressed on T cells and their ligands on antigen-presenting cells. Our studies during the past several years have focused on defining how particular accessory molecule interactions influence the activation of naïve CD4+ T cells and the subsequent development of effector function. In this article, we discuss our findings on the effects of distinct accessory molecules with particular attention to the unique roles of LFA-1 and CD28 during different phases of the naïve CD4+ cell response.

Animals↗

PubMed1999

CD4+ T cell responses to CD40-deficient APCs: defects in proliferation and negative selection apply only with B cells as APCs.

During T-APC interactions in vivo, interfering with CD40-CD154 interactions leads to reduced T cell priming, defects in effector function, and, in some cases, T cell tolerance. As shown here, however, presentation of conventional peptide Ags by CD40-deficient spleen APC in vitro leads to normal CD4+ T cell proliferative responses. By contrast, responses to the same peptides presented by purified B cells were markedly reduced in the absence of CD40. Thus, the requirement for CD40-CD154 interactions appears to be strongly influenced by the type of APC involved. Analysis of responses to endogenous superantigens, which are known to be strongly dependent on B cells for presentation, indicated that CD4+ responses to strong Ags are less dependent on CD40 than are responses to weak Ags. Similar findings applied to negative selection in the thymus. Thus, deletion of potentially autoreactive cells depended on CD40 expression when B APC were involved, and this requirement was most pronounced when negative selection was directed to weak Ags.

Animals↗

PubMed1999

Intercellular adhesion molecule-1 inhibits interleukin 4 production by naive T cells.

The type of cytokines produced during T cell responses determines susceptibility or resistance to many pathogens and influences the development of autoimmunity and allergy. To define the role of individual accessory molecules in cytokine production during primary immune responses, Drosophila cell lines expressing murine major histocompatibility complex class II molecules with defined combinations of accessory molecules were used to present peptide antigen to naive T cell receptor transgenic T cells. Significantly, expression of B7.1 or B7.2 without additional accessory molecules led to very high production of interleukin (IL)-4, which contrasted with minimal IL-4 production elicited by conventional antigen presenting cells (APC). However, coexpression of ICAM-1 and B7 on Drosophila APC induced little IL-4, suggesting an inhibitory role for intercellular adhesion molecule-1 (ICAM-1). In support of this idea, stimulation of T cell receptor transgenic T cells with peptide presented by splenic APC devoid of ICAM-1 (from ICAM-1-deficient mice) led to high IL-4 production. Thus, the level of IL-4 production by naive CD4(+) T cells during typical primary responses appears to be controlled, at least in part, by T-APC interactions involving ICAM-1.

Animals↗

PubMed1998

Normal fetal cardiac dimensions obtained by perpendicular imaging.

This study provides normal fetal cardiac dimensional data in a large patient group over a wide range of gestational ages. Perpendicular imaging decreased lateral resolution error, resulting in normal values with narrower confidence limits than in prior studies.

Aorta, Thoracic↗

PubMed1997

CD40 and IL-4 regulate murine CD27L expression.

It is well known that interactions between accessory molecules on T cells and their ligands on APC play a key role in regulating T cell effector activity. The factors controlling the expression of these molecules are thus important determinants in the outcome of T cell activation. We have examined the expression of the murine ligand for CD27, a costimulatory molecule on T cells. Evidence is shown that CD27L is expressed at a low level on resting B cells but not on T cells, and that activation of B cells by culture with LPS or anti-IgM Ab increases the expression of CD27L. Interestingly, coligation of CD40 down-regulates CD27L on LPS-activated B cells but not on anti-Ig-activated cells. These findings suggest that costimulation via the CD27-CD27L pathway may be limited to interactions involving Ag-specific B cells, i.e., B cells specifically activated via their Ig receptors. In addition, testing a spectrum of different cytokines indicated that IL-4 and TGF, but not IL-2, IL-10, or IFN-gamma, prevented up-regulation of CD27L expression on activated B cells even when activation was induced by Ig signaling. The capacity of IL-4 to prevent CD27L expression could thus serve to limit CD27-CD27L interactions to Th1-type T cell responses.

Animals↗

PubMed1997

Antigen specificity of dual reactive T hybridomas determines the requirement for CD40 ligand-CD40 interactions.

CD40 ligand (CD40L) expression on T cells is known to play a crucial role in B cell responses. Some evidence also supports a role for CD40L-CD40 interactions in T cell responses, at least in vivo. Whether the T cell requirement for these interactions is an invariable finding, however, is less clear. Here, we provide evidence that the Ag specificity of T cells influences the requirement for CD40L. T cell hybridomas with dual reactivity for two different Ags, allo-H2-Ap and Mls(a) superantigens, display a differential requirement for CD40L expression. Whereas the response to splenic APC expressing Mls(a) Ags requires CD40L expression, the response to alloantigen-bearing APC does not. The requirement for CD40L expression for the Mls(a) response appears to reflect a strong dependence of this response on ICAM-1 (intercellular adhesion molecule-1) and the ability of CD40-mediated signals to regulate ICAM-1 expression. These findings demonstrate that CD40L-CD40-mediated cross-talk is important for some but not all T cell responses and is influenced by both the type of Ag recognized and the type of APC.

Animals↗

PubMed1997

Cross talk between T and B cells generates B antigen-presenting cells able to induce inositol phosphate production in T cells responding to Mls(a) superantigens.

Previous studies showed that activation of CD4+ T cells with mouse mammary tumor virus-encoded Mls(a) superantigens induces strong proliferative responses and interleukin-2 production but fails to elicit typical early T cell receptor (TCR)-mediated signal transduction events, such as hydrolysis of polyphosphoinositides (PI) or an increase in intracellular calcium. Here we show that the failure of Mls(a) antigen to activate PI hydrolysis applies when resting B cells are used as antigen-presenting cells (APC). By contrast, when Mls(a)-bearing B cells are activated for 24 h by exposure to lipopolysaccharide or, more importantly, to Mls(a)-reactive T cells or anti-CD40 antibodies the cells develop the capacity to elicit easily detectable PI turnover. These studies demonstrate that, for B cells as APC, the initiation of certain TCR-associated signal transduction pathways can depend on activation of the APC. The data suggest that cross talk between T cells and resting B cells can suffice to generate competent B APC and lead to the delayed initiation of signaling pathways important in T cell responses.

Animals↗

PubMed1996

Antigen presentation and T cell development in H2-M-deficient mice.

HLA-DM (DM) facilitates peptide loading of major histocompatibility complex class II molecules in human cell lines. Mice lacking functional H2-M, the mouse equivalent of DM, have normal amounts of class II molecules at the cell surface, but most of these are associated with invariant chain-derived CLIP peptides. These mice contain large numbers of CD4+ T cells, which is indicative of positive selection in the thymus. Their CD4+ cells were unresponsive to self H2-M-deficient antigen-presenting cells (APCs) but were hyperreactive to wild-type APCs. H2-M-deficient APCs failed to elicit proliferative responses from wild-type T cells.

Animals↗

PubMed1996

In vivo response of mature T cells to Mlsa antigens. Long-term progeny of dividing cells include cells with a naive phenotype.

To characterize T cells surviving elimination following strong in vivo responses, bromodeoxyuridine (BrdU) was used to mark the V beta 6+ CD4+ T cells proliferating after exposure to MLsa superantigens. Though a portion of the surviving V beta 6+ cells failed to label with BrdU, many were BrdU+, indicating that some proliferating cells escape elimination. Both the portion of V beta 6+ cells responding to MLs Ag in vivo and the number of responding cells that escaped elimination were influenced by the MHC haplotype; weaker responses correlated with enhanced survival of BrdU+ V beta 6+ cells. As expected, some of these cells expressed cell surface markers generally associated with an activated/memory phenotype. Significantly, however, a large proportion of BrdU+ V beta 6+ cells were phenotypically indistinguishable from naive cells.

Animals↗

PubMed1995

Intrathymic and extrathymic clonal deletion of T cells.

Clonal elimination accounts for self-tolerance induction in the thymus and also affects mature T cells responding to exogenous antigens in the periphery. Recent evidence on the microenvironments, cell-cell interactions and signalling requirements for clonal deletion of immature and mature T cells is discussed.

Animals↗

PubMed1995

Physical and chemical characterization of airbag effluents.

OBJECTIVE: This paper describes a study aimed at characterizing the exposure to physical and chemical by-products from the deployment of airbag restraint systems. DESIGN, MATERIALS AND METHODS: Specifically, the levels of particulates and the composition of gases and bag fabric speed were measured in the passenger compartment following deployment of either a driver's side or driver's side/passenger's side airbag system. MEASUREMENTS: A Fourier transform infrared analyzer (FTIR) and chemiluminescence analyzers were used for gas analysis, a cascade impactor and gravimetric filter measurements for aerosol determination and high-speed films to determine fabric speed. MAIN RESULTS AND CONCLUSIONS: The measured gases were found to be within the recommended guidelines for human exposures, but no guidelines exist for particle exposures of this magnitude (150-220 mg/m3) but short duration. High-speed films were also taken of the deployments to obtain an estimate of the fabric speed as it leaves the module. The maximum average speed for both types of airbag was approximately 100 mph and in both cases average speeds ranged from lows near 50 mph to highs of over 200 mph.

Air↗