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Biomedical subjects

B Baird

Publications and source records attributed to B Baird.

At least 55 records · Page 3Linked to original sources
PubMed1995

Alteration of lipid composition modulates Fc epsilon RI signaling in RBL-2H3 cells.

We have used sonicated liposomes of phosphatidylcholine (PC), sphingomyelin (SM), or a mixture of cholesterol (chol) and PC to investigate the role of cellular lipid composition in Fc epsilon RI-mediated stimulation of RBL-2H3 cells. Overnight treatment with either PC or SM liposomes causes a substantial enhancement of antigen-stimulated degranulation and phospholipase A2 activity, whereas treatment with a PC/chol mixture results in partial inhibition of the antigen-stimulated response. The most consistent change in the cellular lipid composition that results from the PC and SM liposome treatments is an approximate 40% decrease in the chol/phospholipid (PL) ratio. The lipid treatments do not alter degranulation stimulated by AlF4- or by Ca2+ ionophore in the presence or absence of PMA, suggesting that lipid alteration affects a receptor-specific signaling process. The lipid treatments do not appear to alter antigen-stimulated tyrosine phosphorylation or Ca2+ mobilization. Possible involvement of protein kinase C (PKC) activation in the signal-enhancing effect of the PL treatments was investigated by using calphostin C and phorbol-12-myristol-13-acetate (PMA) to inhibit PKC activity and degranulation in RBL-2H3 cells. Both SM and PC treatment restore the antigen-mediated degranulation response that is inhibited by long-term treatment (> or = 16 h) with 100 nM PMA or short-term treatment (10 min) with 5 microM calphostin C. The results indicate that a decreased chol/PL ratio facilitates or enhances the receptor-mediated activation of a PKC-like pathway that plays an important role in Fc epsilon RI-stimulated degranulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Antigens↗
PubMed1995

Computing with dynamic attractors in neural networks.

In this paper we report on some new architectures for neural computation, motivated in part by biological considerations. One of our goals is to demonstrate that it is just as easy for a neural net to compute with arbitrary attractors--oscillatory or chaotic--as with the more usual asymptotically stable fixed points. The advantages (if any) of such architectures are currently being investigated; but it seems reasonable that the much richer dynamics of recurrent networks, so obvious in recordings of brain activity, must be useful for something. On the other hand, the constraints of computing with biological wet-ware may make chaotic dynamics unavoidable in complex nervous systems. We hypothesize also that the as yet unrivaled capabilities of the human brain derive from an ability to integrate both analog intuitive pattern recognition operations, and digital symbolic logical operations at the ground level of its hardware. To investigate these possibilities, we have constructed a parallel distributed processing architecture inspired by the structure and dynamics of cerebral cortex. The construction assumes that cortex is a set of coupled associative memories with dynamic attractors. It is guided also by a particular concept of the physical structure required of macroscopic computational systems in general for reliable computation in the presence of noise. Our challenge is to accomplish real tasks that brains can do, using ordinary differential equations, in networks that are as faithful as possible to the known anatomy and dynamics of cortex.

Algorithms↗
PubMed1994

Large-scale co-aggregation of fluorescent lipid probes with cell surface proteins.

Large scale aggregation of fluorescein-labeled immunoglobulin E (IgE) receptor complexes on the surface of RBL cells results in the co-aggregation of a large fraction of the lipophilic fluorescent probe 3,3'-dihexadecylindocarbocyanine (diI) that labels the plasma membranes much more uniformly in the absence of receptor aggregation. Most of the diI molecules that are localized in patches of aggregated receptors have lost their lateral mobility as determined by fluorescence photobleaching recovery. The diI outside of patches is mobile, and its mobility is similar to that in control cells without receptor aggregates. It is unlikely that the co-aggregation of diI with IgE receptors is due to specific interactions between these components, as two other lipophilic probes of different structures are also observed to redistribute with aggregated IgE receptors, and aggregation of two other cell surface antigens also results in the coredistribution of diI at the RBL cell surface. Quantitative analysis of CCD images of labeled cells reveals some differences in the spatial distributions of co-aggregated diI and IgE receptors. The results indicate that cross-linking of specific cell surface antigens causes a substantial change in the organization of the plasma membrane by redistributing pre-existing membrane domains or causing their formation.

Carbocyanines↗
PubMed1994

Effect of do-not-resuscitate orders on the nursing care of critically ill patients.

BACKGROUND: The effect of a do-not-resuscitate order on the standard of care of critically ill patients is of concern to practitioners, patients, and their families. Because "do not resuscitate" may be misconstrued to include more than "no cardiopulmonary resuscitation," it may influence the aggressiveness with which some patients are managed. Nurses play a central role in determining standards of care. Hence, confusion on their part as to the meaning of this term can have a significant impact on patient care. OBJECTIVES: To compare nurses' attitudes about standards of care for critically ill patients with and without a do-not-resuscitate order. METHOD: A quasi-experimental design using simulation measurement was used for this study. RESULTS: Nurses reported that they would be significantly less likely to perform a variety of physiologic monitoring modalities and interventions for patients with a do-not-resuscitate order than for patients without such an order. Patients with a do-not-resuscitate order were more likely to receive psychosocial interventions including assessment of their spiritual needs and more flexible visiting practices. CONCLUSIONS: Our findings suggest that "do-not-resuscitate" may be misinterpreted to include more than "no cardiopulmonary resuscitation" even if the patient is receiving aggressive medical management. Misinterpretation of orders not to resuscitate may be related to a variety of factors including lack of understanding about hospital policy and ethical and moral values of the staff. We suggest replacing orders such as "Do not resuscitate" with clearly defined resuscitation plans that are jointly determined by the multidisciplinary team, patient, and family.

Adult↗
PubMed1994

Solvents and color discrimination ability. Nonreplication of previous findings.

Previous research has shown exposure-related increases in the prevalence of acquired color vision deficits among printers. We administered the Lanthony D-15 desaturated test of color vision to 82 print shop workers. Two tests of cognitive function, Trails A and B and the Symbol Digit Modalities Test, were also administered. Personal air sampling indicated that current exposure to organic solvents was highest among printers and lowest among bindery workers. In contrast to previous studies, the age-adjusted quantitative Lanthony D-15 desaturated test error scores did not differ significantly between exposure groups, and the proportion of subjects with > or = 1 error was greater in the lower-exposure, rather than higher-exposure, groups (P = .03). Of note, the proportion of subjects with > or = 2 errors did not differ significantly between groups (P = .24). Cognitive tests showed no significant association with exposure. These results are discussed in the context of methodological issues related to lighting sources, reliability of test results, and establishment of criteria for identifying deficits.

Adult↗
PubMed1993

Heterologous desensitization of the high affinity receptor for IgE (Fc epsilon R1) on RBL cells.

To study the properties of Fc epsilon RI desensitization induced by aggregation of that receptor, RBL cells were sensitized with a mixture of two different IgE mAb to create two different populations of IgE-receptor complexes. Cross-linking of one receptor population containing anti-dinitrophenyl (DNP) IgE with a bivalent Ag, 1-DNP-amino-12-biotinamidododecane)2-avidin ((DNP)2-avidin), results in desensitization of a subsequent response, both of the same receptor population (homologous desensitization) and of the second receptor population containing anti-5-dimethylaminonaphthalene-1-sulfonyl (dansyl) IgE (heterologous desensitization). The extent of heterologous desensitization is dependent on several parameters, including the concentration of both the first and the second Ag and the densities of the respective IgE populations. Heterologous desensitization of the Ca2+ response is more sensitive to the concentration of the second stimulus (dansyl-BSA) than heterologous desensitization of the degranulation response. AlF4-, which activates GTP-binding proteins, can effectively replace (DNP)2-avidin as the initial stimulant and desensitizing agent. Other agents that mobilize intracellular Ca2+ including thrombin and a Ca2+ ionophore are less effective at replacing (DNP)2-avidin. Because prestimulation with Ag does not desensitize subsequent responses to AlF4- or Ca2+ ionophore, it appears that signal transduction via Fc epsilon RI is impaired at an early step. Addition of monovalent DNP hapten within approximately 10 min after cross-linking by (DNP)2-avidin completely prevents the desensitization of the subsequent Ca2+ or degranulation response to dansyl-BSA. After longer times of incubation with DNP Ag, the DNP hapten becomes increasingly less effective at preventing the desensitization of the dansyl-BSA response, even though ongoing signal transduction by the DNP Ag is halted. These results suggest a form of cellular memory for the desensitized state.

Aluminum↗
PubMed1993

Fc epsilon RI and the T cell receptor for antigen activate similar signalling pathways in T cell-RBL cell hybrids.

In order to investigate the functional similarities of the high affinity receptor for IgE (Fc epsilon RI) and the T cell receptor for antigen, we have developed a high efficiency polyethylene glycol-mediated fusion method to make somatic hybrids between cells from a mast cell line (RBL-2H3) and cells from T lymphoma cell lines (Jurkat and HPB-ALL). Using flow cytometry to select for the heterologously fused cells, we demonstrated that aggregation of the T cell receptor results in the efficient secretion of [3H]5-hydroxytryptamine from RBL cell-derived granules. In addition, both receptors mediate Ca2+ mobilization in the hybrid cells that is insensitive to inhibition by the protein kinase C activator phorbol-12-myristoyl-13-acetate (PMA). In contrast, Ca2+ mobilization caused by aggregation of Fc epsilon RI in the parent RBL cells is completely inhibited by PMA. The results indicate that these two different receptors for foreign antigen can substitute for each other to trigger responses in the hybrid cells that are unique to each cell type. The methodology employed has general utility for studying signal transduction mediated by mammalian cell surface receptors.

Calcium↗
PubMed1992

Dynamic conformations compared for IgE and IgG1 in solution and bound to receptors.

Dynamic conformations of two distinct immunoglobulin (Ig) isotypes, murine IgE and human IgG1, were examined with fluorescence resonance energy transfer measurements. The IgE mutant epsilon/C gamma 3* and the IgG1 mutant gamma/C gamma 3* each bind [5-(dimethylamino)naphthalen-1-yl]sulfonyl (DNS) in two identical antigen binding sites at the amino (N)-terminal ends of the Ig in the Fab segments. Eosin-DNS bound in these Fab sites served as the acceptor probe in these studies. Both Ig have a carboxy (C)-terminal domain (C gamma 3*) which contains genetically introduced cysteine residues. Modification of these cysteine sulfhydryls with fluorescein maleimide provided donor probes near the C-terminal ends of the Ig in the Fc segment. Energy transfer between the C-terminal and N-terminal ends was compared for these two Ig in solution and when they were found to their respective high-affinity receptors on plasma membranes: IgE-Fc epsilon RI on RBL cell membranes and IgG1-Fc gamma RI on U937 cell membranes. Previous energy-transfer measurements with these probes yielded an average end-to-end distance of 71 A for IgE in solution and 69 A for IgE bound to Fc epsilon RI, indicating that in both situations IgE is bent such that the axes of the Fab segments and the axis of the Fc segment do not form a planar Y-shape [Zheng, Shopes, Holowka, & Baird (1991) Biochemistry 30, 9125]. In the current study we found the average end-to-end distance for IgG1 in solution is 75 A and greater than or equal to 85 A for IgG1 bound to Fc gamma RI, suggesting an average bend conformation for IgG1 as well. The contributions of segmental flexibility to the average distances were assessed directly by measuring the efficiency of energy transfer as a function of variations in donor quantum yield caused by a collisional quencher and using these data to extract a Gaussian distribution of end-to-end distances. The distribution average (rho) and half-width (hw) were determined to be as follows: rho = 75 A, hw = 24 A for IgE in solution; rho = 71 A, hw = 12 A for IgE bound to Fc epsilon RI; and rho = 100 A, hw = 88 A for IgG in solution.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Aggregation of IgE-receptor complexes on rat basophilic leukemia cells does not change the intrinsic affinity but can alter the kinetics of the ligand-IgE interaction.

The aggregation of IgE anchored to high-affinity Fc epsilon receptors on rat basophilic leukemia (RBL) cells by multivalent antigens initiates transmembrane signaling and ultimately cellular degranulation. Previous studies have shown that the rate of dissociation of bivalent and multivalent DNP ligands from RBL cells sensitized with anti-DNP IgE decreases with increasing ligand incubation times. One mechanism proposed for this effect is that when IgE molecules are aggregated, a conformational change occurs that results in an increase in the intrinsic affinity of IgE for antigen. This possibility was tested by measuring the equilibrium constant for the binding of monovalent DNP-lysine to anti-DNP IgE under two conditions, where the cell-bound IgE is dispersed and where it has been aggregated into visible patches on the cell surface using anti-IgE and a secondary antibody. No difference in the equilibrium constant in these two cases was observed. We also measured the rate of dissociation of a monovalent ligand from cell surface IgE under these two conditions. Whereas the affinity for monovalent ligand is not altered by IgE aggregation, we observe that the rate of ligand dissociation from IgE in clusters is slower than the rate of ligand dissociation from unaggregated IgE. These results are discussed in terms of recent theoretical developments concerning effects of receptor density on ligand binding to cell surfaces.

Animals↗
PubMed1992

Rotational motion of monomeric and dimeric immunoglobulin E-receptor complexes.

Erythrosin 5'-thiosemicarbazide labeled immunoglobulin E (IgE) was used to monitor the rotational dynamics of monomeric and dimeric Fc epsilon RI receptors for IgE on rat basophilic leukemia (RBL) basophilic leukemia (RBL) cells using time-resolved phosphorescence anisotropy. Receptors were studied both on living RBL cells and on membrane vesicles derived from RBL cell plasma membrane. The un-cross-linked IgE-receptor complexes on cells and vesicles exhibit rotational correlation times that are consistent with those expected for freely rotating monomers, but a small fraction of these complexes on cells may be rotationally immobile. A comparison of the initial phosphorescence anisotropy values for erythrosin-labeled IgE-receptor complexes on cells and vesicles reveals a fast component of rotational motion that is greater on the vesicles and may be due to a site of segmental flexibility in the receptor itself. Dimers of IgE-receptor complexes formed with anti-IgE monoclonal antibodies appear to be largely immobile on cells, but they are mobile on vesicles with a 2-fold larger rotational correlation time than the monomeric complexes. The results suggest that dimeric IgE-receptor complexes undergo interactions with other membrane components on intact cells that do not occur on the membrane vesicles. The possible significance of these interactions to receptor function is discussed.

Animals↗
PubMed1991

Conformations of IgE bound to its receptor Fc epsilon RI and in solution.

Previous resonance energy transfer studies suggested that murine immunoglobulin E (IgE) is bent near the junction of its Fc and Fab segments when bound to its high-affinity receptor (Fc epsilon RI) on RBL cells. To examine further the conformations of IgE, both bound to this receptor and in solution, a mutant recombinant IgE (epsilon/C gamma 3*) was prepared that has a cysteine replacing a serine near the C-terminal ends of the heavy chain. The introduced cysteine residues provide a means for specific modification of IgE, and the sulfhydryl groups were selectively labeled with fluorescein-5-maleimide (FM-epsilon/C gamma 3*). This IgE also binds a 5-(dimethylamino)naphthalene-1-sulfonyl (DNS) group in the antigen-binding sites. Resonance energy transfer experiments carried out on receptor-bound FM-epsilon/C gamma 3* yielded a distance of 53 A between fluorescein near the C-terminal end of the Fc segment and amphipathic acceptor probes at the membrane surface. The average distance between this C-terminal fluorescein and acceptor eosin-DNS in the antigen-binding sites at the N-terminal ends of the Fab segments was found to be 69 A. These results combine with those from previous structural studies to provide an unprecedented detailed description of the bent geometry of IgE bound to its receptor on the membrane. Energy transfer measured for FM-epsilon/C gamma 3* in solution between fluorescein near the C-terminal end of the Fc segment and eosin-DNS at the N-terminal ends of the Fab segments indicates that the average distance between these probes is about 71 A.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Characterization of increased K+ permeability associated with the stimulation of receptors for immunoglobulin E on rat basophilic leukemia cells.

Aggregation of immunoglobulin E-receptor complexes on the surface of rat basophilic leukemia cells stimulates an increase in plasma membrane K+ permeability that is monitored as an increase in the rate of efflux of preloaded 86Rb+. A major component of this stimulated 86Rb+ efflux appears to be due to a Ca(2+)-activated K+ channel because it is inhibited by quinidine in parallel with the inhibition of degranulation and membrane potential repolarization, it is blocked by 0.1 mM La3+, and it is dependent on external Ca2+. Depolarization of the plasma membrane by carbonyl cyanide 3-chlorophenylhydrazone inhibits stimulated Ca2+ influx and prevents antigen-induced 86Rb+ efflux, and increased external Ca2+ partially restores 86Rb+ efflux under these conditions. In addition, potentiation of antigen-stimulated Ca2+ influx by pretreatment with cholera toxin increases the initial rate of stimulated 86Rb+ efflux. Another component of antigen-stimulated K+ efflux appears to be mediated by a guanine nucleotide-binding protein because pretreatment of rat basophilic leukemia cells with pertussis toxin decreases the initial rate of antigen-stimulated 86Rb+ efflux to 40% of that for the untreated cells. Stimulated 86Rb+ efflux is also observed when ionomycin is used to increase cytoplasmic Ca2+ and to trigger membrane depolarization. The efflux stimulated by ionomycin is inhibited by quinidine but not by pertussis toxin pretreatment; thus, it appears to occur through the Ca(2+)-activated K+ efflux pathway. It is proposed that these K+ efflux pathways serve to sustain the Ca2+ influx that is necessary for receptor-mediated triggering of cellular degranulation.

Animals↗
PubMed1991

Dissociation kinetics of bivalent ligand-immunoglobulin E aggregates in solution.

We study the dissociation of preformed bivalent ligand-bivalent receptor aggregates in solution, where the ligand is a symmetric bivalent hapten with two identical 2,4-dinitrophenyl (DNP) groups and the receptor is a fluorescein-labeled monoclonal anti-DNP IgE. We promote dissociation in two ways: by the addition of high concentrations of a monovalent hapten that competes for IgE binding sites with the bivalent hapten and by the addition of high concentrations of unlabeled IgE that binds almost all ligand binding sites that dissociate from labeled IgE. We investigate both theoretically and experimentally the two types of dissociation and find them to be quite different. Theory predicts that their kinetics will depend differently on the fundamental rate constants that characterize binding and aggregation. Using monovalent ligand to promote dissociation, we find that the fraction of labeled IgE sites bound to bivalent ligand decays with a slow and fast component. The fast decay corresponds to the dissociation of a singly bound DNP hapten. The interpretation of the slow decay depends on the detailed way in which ligand-receptor aggregates break up. We show that one possible explanation of these data is that small stable rings form before the addition of monovalent ligand. Other possible explanations are also presented.

Animals↗
PubMed1991

Bivalent ligand dissociation kinetics from receptor-bound immunoglobulin E: evidence for a time-dependent increase in ligand rebinding at the cell surface.

The bivalent ligand N,N'-bis[[epsilon-[(2,4- dinitrophenyl)amino]caproyl]-L-tyrosyl]cystine [(DCT)2-Cys] binds and cross-links anti-dinitrophenyl (DNP) immunoglobulin E (IgE)-receptor complexes on the cell surface of rat basophilic leukemia cells. The rate of dissociation of this bound ligand was monitored by using a fluorescence method under two different conditions. In one case the monovalent ligand DCT was added in large excess to prevent the dissociating ligand from rebinding to unoccupied antibody combining sites. Under these conditions, dissociation of the bivalent ligand from IgE-sensitized cells proceeds to completion with kinetics that are well described by two rate constants that are independent of the time of preincubation of the bivalent ligand with the cells. In the second case, dissociation of (DCT)2-Cys from cell-bound anti-DNP IgE was monitored in the presence of a large excess of anti-DNP IgE in solution that acts as a sink to absorb the dissociated ligand. Under these conditions, the bivalent ligand becomes more resistant to dissociation as the preincubation time of the bivalent ligand with the cells is increased. An increasing fraction of the bound ligand does not dissociate on a measurable time scale in the presence of this sink. The results indicate that cell-associated IgE-receptor complexes undergo a time-dependent change that facilitates the reformation of the cross-linked state when one end of the ligand dissociates to break up the existing cross-link. The possible physical basis and functional implications of these results are discussed.

Animals↗
PubMed1991

Characterization of new rat anti-mouse IgE monoclonals and their use along with chimeric IgE to further define the site that interacts with Fc epsilon RII and Fc epsilon RI.

Three rat monoclonal antibodies specific for mouse IgE (C12B9, 23G3, and B1E3) were established by using monoclonal anti-DNP mouse IgE (mIgE) as immunogen. These antibodies, as well as a fourth, (R1E4) were characterized. It was found that one antibody (C12B9) recognizes an allotypic determinant (Igh-7a) found on the C epsilon chain of mIgE. Antibody cross-blocking studies and epitope mapping studies using recombinant mIgE indicated that 3 antibodies (C12B9, R1E4 and 23G3) were directed against the C epsilon 3 domain while one (B1E3) was directed against the C epsilon 4 domain. A highly specific sandwich RIA for mIgE was developed using these antibodies. Use of these monoclonal anti-mIgE antibodies in conjunction with recombinant chimeric mIgE-human IgG1 molecules, demonstrated that the C epsilon 3 domain is important in the binding of mIgE to the murine B cell Fc epsilon RII as well as to the murine mast cell F epsilon RI. The presence of the C epsilon 4 domain influenced the binding of the recombinant IgE to the Fc epsilon RII; in contrast to the C epsilon 4 domain had no effect on binding to the Fc epsilon RI.

Animals↗
PubMed1990

Recombinant human IgG1-murine IgE chimeric Ig. Construction, expression, and binding to human Fc gamma receptors.

We have constructed a set of chimeric Ig by exchanging corresponding H chain C domains between human (hu) IgG1 and murine (m) IgE. We used this set of Ig to dissect the interaction of individual Ig domains with human Fc gamma receptors. Only one of the chimeras, epsilon/C gamma 2,3 (an mIgE with C epsilon 3 and C epsilon 4 replaced by C gamma 2 and C gamma 3 from huIgG1), binds tightly to the human Fc gamma RI on U937 cells. We found that epsilon/C gamma 2,3 has only twofold lower affinity for Fc gamma RI as compared to huIgG1. The gamma/C epsilon 4 (huIgG1 with C epsilon 4 replacing C gamma 3) binds weakly to Fc gamma RI. The other chimeric Ig, epsilon/C gamma 3, epsilon/C gamma 2, and gamma/C epsilon 3, as well as mIgE do not bind detectably to Fc gamma RI. From these data we conclude that the C gamma 2 domain is crucial for binding and contains the majority of the binding site for Fc gamma RI on IgG1. The C gamma 3 domain makes a smaller contribution to the binding, and the C gamma 1 domain and the hinge region have very little effect on the Fc gamma RI-IgG1 interaction. The chimeric epsilon/C gamma 2,3 and huIgG1 both mediate the formation of rosettes between K562 cells and antigen-sensitized E with similar concentration dependences. These results suggest similar ability to bind to Fc gamma RII. The other chimeric Ig do not cause rosettes in this assay system. Hence, both C gamma 2 and C gamma 3 seem to be required for binding to Fc gamma RII, but the C gamma 1-hinge region has no detectable effect.

Animals↗