Biomedical subjects

S Buus

Publications and source records attributed to S Buus.

At least 55 records · Page 3Linked to original sources

PubMed1998

Comparisons of DNA-mediated immunization procedures directed against surface glycoproteins of human immunodeficiency virus type-1 and hepatitis B virus.

DNA vaccination methods were compared to examine the in vivo expression of HIV-1 gp160 and beta-galactosidase, and the resulting immune response. Beta-galactosidase plasmid showed expression rates of 2-5% of muscle fibers with or without pretreatments using bupivacaine or cardiotoxin facilitators 1 or 5 days earlier, respectively. In contrast, HIV gp160 expression was lower in untreated or bupivacaine-treated muscles, but was improved by pretreatment with cardiotoxin. Equal expression of beta-galactosidase and HIV gp160 was obtained using gene gun delivery to the epidermis. Unlike the i.m. in situ expression of gp160, the anti-HIV antibody response did not improve after muscle pretreatments but depended on the vaccination intervals. Gene gun delivery of pMN160 also resulted in a slow and low titered antibody response. In contrast, a single i.m. injection of plasmid encoding another viral envelope, HBsAg, resulted in earlier seroconversion to high titers without the need for pretreatments or boostings. Intradermal inoculation by gene gun using 100-fold less DNA resulted in the same anti-HBsAg antibody profile only after boostings. In contrast to the differences in antibody responses, a specific CTL response was obtained in all cases. Bupivacaine-treated muscles showed an extreme degree of edema with disruption of connective tissue (endo- and mesomysium) and was not well tolerated (4 of 19 mice died). Cardiotoxin created muscle necrosis and occasional (2 of 20 mice) development of fibrotic muscles. It is concluded that in vivo expression cannot be properly predicted using reporter gene experiments and that the resulting immune response does not follow directly with the expression rate. It is suggested that the antibody response may depend primarily on the nature of the antigen expressed rather than the DNA vaccination method. It is proposed that gene gun or i.m. injection be used without pretreatment in the case of DNA vaccination with plasmid encoding HIV MN gp160.

AIDS Vaccines↗

PubMed1998

On loudness at threshold.

Absolute thresholds for and loudness matches between pure tones and four- and ten-tone complexes were used to assess the form of the function relating loudness to sensation level, SL, at low and moderate levels. The components of the tone complexes had equal SLs and were separated by one, two, four, or six critical bands. Six listeners with normal hearing were tested. The thresholds for the multitone complexes indicate that they generally can be detected even when the level of a single component is a few dB below the threshold. The average detection advantage is consistent with predictions for multiple observations in independent, frequency-selective auditory channels, but differences among listeners are apparent. The loudness matches also vary somewhat among listeners. Five of the six listeners matched tone complexes composed of subthreshold components to a pure tone a few dB above threshold. This indicates that the loudness of tones at or even below threshold is greater than zero for these five listeners. A simple model of loudness summation was used to obtain loudness functions from the individual listeners' loudness matches. The slopes of the loudness functions [log(loudness) plotted as a function of log(intensity)] generally exceed unity at low levels and are near 0.2 at 40 dB SL. This shallow slope at moderate levels agrees with loudness functions derived from data on temporal integration of loudness. The average loudness function derived from the present data also is in good agreement with a variety of previous data obtained by magnitude estimation, magnitude production, ratio production, and measurements of binaural loudness summation.

Adolescent↗

PubMed1998

Temporal integration of loudness under partial masking.

This paper tests the hypothesis that the loudness ratio between equal-SPL tones with different durations is the same at all SPLs. Detection thresholds and levels required to produce equal loudness for 5- and 200-ms tones presented in quiet or in broadband noise were measured using adaptive, two-interval, two-alternative forced-choice procedures. Tone levels ranged from 5 dB SL to 90 dB SPL for the long tones and about 100 dB SPL for the short tones. Results from six listeners with normal hearing show that the amount of temporal integration, defined as the level difference between equally loud 5- and 200-ms tones, varies nonmonotonically with level and is greatest at moderate levels. The average amount of temporal integration in quiet is about 15 dB near threshold, increases to a peak of 27 dB when the 5-ms tone is about 58 dB SPL, and decreases to about 15 dB near 100 dB SPL. For masker levels of 40, 60, and 80 dB SPL, the amount of temporal integration near masked threshold remains near 15 dB. The maximum amount of temporal integration decreases as masker level increases and occurs at progressively higher levels. At high levels, the amount of temporal integration is nearly the same as in the quiet for all masker levels. Loudness functions derived by applying the equal-loudness-ratio hypothesis to the data yield excellent predictions of loudness matches between tones in the quiet and partially masked tones with the 40- and 60-dB maskers. For the 80-dB masker, clear deviations are present. These results support the equal-loudness-ratio hypothesis, but suggest that intense masking may alter the loudness ratio between 200- and 5-ms tones.

Adult↗

PubMed1997

Age of second-language acquisition and perception of speech in noise.

To determine how age of acquisition influences perception of second-language speech, the Speech Perception in Noise (SPIN) test was administered to native Mexican-Spanish-speaking listeners who learned fluent English before age 6 (early bilinguals) or after age 14 (late bilinguals) and monolingual American-English speakers (monolinguals). Results show that the levels of noise at which the speech was intelligible were significantly higher and the benefit from context was significantly greater for monolinguals and early bilinguals than for late bilinguals. These findings indicate that learning a second language at an early age is important for the acquisition of efficient high-level processing of it, at least in the presence of noise.

Adolescent↗

PubMed1997

Temporal integration of loudness, loudness discrimination, and the form of the loudness function.

Temporal integration for loudness of 5-kHz tones was measured as a function of level between 2 and 60 dB SL. Absolute thresholds and levels required to produce equal loudness were measured for 2-, 10-, 50-, and 250-ms tones using adaptive, two-interval, two-alternative forced-choice procedures. The procedure for loudness balances was new and employed ten interleaved tracks to obtain concurrent measurements for ten tone pairs. Each track converged at the level required to make the variable stimulus just louder than the fixed stimulus. Thus, the data yield estimates of the just-noticeable difference (jnd) for loudness level and temporal integration for loudness. Results for four listeners show that the amount of temporal integration, defined as the level difference between equally loud short and long tones, varies markedly with level and is largest at moderate levels. The effect of level increases as the duration of the short stimulus decreases and is largest for comparisons between the 2- and 250-ms tones. The loudness-level jnds are also largest at moderate levels and, contrary to traditional jnds for the level of two equal-duration tones, they do not appear to depend on duration. The latter finding indicates that loudness discrimination between stimuli that differ along multiple dimensions is not the same as level discrimination between stimuli that differ only in level. An equal-loudness-ratio model, which assumes that the ratio of loudnesses for a long and short tone at equal SPL is the same at all SPLs, can explain the level dependence of temporal integration and the loudness jnds. It indicates that the loudness function [log(loudness) versus SPL] is flatter at moderate levels than at low and high levels in agreement with earlier findings for 1-kHz tones [M. Florentine et al., J. Acoust. Soc. Am. 99, 1633-1644 (1996)].

Female↗

PubMed1996

Shared fine specificity between T-cell receptors and an antibody recognizing a peptide/major histocompatibility class I complex.

Cytotoxic T cells recognize mosaic structures consisting of target peptides embedded within self-major histocompatibility complex (MHC) class I molecules. This structure has been described in great detail for several peptide-MHC complexes. In contrast, how T-cell receptors recognize peptide-MHC complexes have been less well characterized. We have used a complete set of singly substituted analogs of a mouse MHC class I, Kk-restricted peptide, influenza hemagglutinin (Ha)255-262, to address the binding specificity of this MHC molecule. Using the same peptide-MHC complexes we determined the fine specificity of two Ha255-262-specific, Kk-restricted T cells, and of a unique antibody, pSAN, specific for the same peptide-MHC complex. Independently, a model of the Ha255-262-Kk complex was generated through homology modeling and molecular mechanics refinement. The functional data and the model corroborated each other showing that peptide residues 1, 3, 4, 6, and 7 were exposed on the MHC surface and recognized by the T cells. Thus, the majority, and perhaps all, of the side chains of the non-primary anchor residues may be available for T-cell recognition, and contribute to the stringent specificity of T cells. A striking similarity between the specificity of the T cells and that of the pSAN antibody was found and most of the peptide residues, which could be recognized by the T cells, could also be recognized by the antibody.

Amino Acid Sequence↗

PubMed1996

T cell responses affected by aminopeptidase N (CD13)-mediated trimming of major histocompatibility complex class II-bound peptides.

Endocytosed protein antigens are believed to be fragmented in what appears to be a balance between proteolysis and MHC-mediated epitope protection, and the resulting peptide-MHC complexes are transported to the surface of the antigen-presenting cells (APC) and presented to T cells. The events that lead to antigenic peptide generation and the compartments where antigen processing takes place remains somewhat enigmatic. The importance of intracellular antigen processing has been well established; however, it is unclear whether additional processing occurs at the APC surface. To follow antigen processing, we have identified a pair of T cell hybridomas that recognize a long vs. a short version of the same epitope. We have used prefixed APC and various protease inhibitors to demonstrate that the APC surface has a considerable potential for antigen processing. Specific antibodies further identified the exopeptidase Aminopeptidase N (APN, CD13) as one of the enzymes involved in the observed cell-surface antigen processing. The NH2-terminal end of the longer peptide could, even while bound to major histocompatibility complex (MHC) class II molecules, be digested by APN with dramatic consequences for T cell antigen recognition. This could be demonstrated both in cell-free systems using purified reagents and in cellular systems. Thus, MHC class II and APN may act in concert to generate the final T cell epitopes.

Amino Acid Sequence↗

PubMed1996

pH dependence of MHC class I-restricted peptide presentation.

The function of MHC class I molecules is to bind and present antigenic peptides to cytotoxic T cells. Here, we report that class I-restricted peptide presentation is strongly pH dependent. The presentation of some peptides was enhanced at acidic pH, whereas the presentation of others was inhibited. Biochemical peptide-MHC class I binding assays demonstrated that peptide-MHC class I complexes are more stable at neutral pH than at acidic pH. We suggest that acid-dependent peptide dissociation can generate empty class I molecules and that the resulting binding potential can be exploited by a subset of peptide-MHC class I combinations, in some cases leading to considerable peptide exchange. We further speculate that the relative instability of peptide-class I complexes under acidic conditions may affect the outcome of class I-restricted Ag presentation, as less stably associated peptides may dissociate from class I during passage of the acidic trans-Golgi network, and therefore may not be presented. Finally, our results may in part explain how endocytosed proteins can be presented by MHC class I molecules to cytotoxic T cells.

Amino Acid Sequence↗

PubMed1996

A recombinant antibody with the antigen-specific, major histocompatibility complex-restricted specificity of T cells.

Specific recognition of peptide/major histocompatibility complex (MHC) molecule complexes by the T-cell receptor is a key reaction in the specific immune response. Antibodies against peptide/MHC complexes would therefore be valuable tools in studying MHC function and T-cell recognition and might lead to novel approaches in immunotherapy. However, it has proven difficult to generate antibodies with the specificity of T cells by conventional hybridoma techniques. Here we report that the phage display technology is a feasible alternative to generate antibodies recognizing specific, predetermined peptide/MHC complexes.

Amino Acid Sequence↗

PubMed1996

Peptide binding specificity of major histocompatibility complex class I resolved into an array of apparently independent subspecificities: quantitation by peptide libraries and improved prediction of binding.

Considerable interest has focused on understanding how major histocompatibility complex (MHC) specificity is generated and characterizing the specificity of MHC molecules with the ultimate goal being to predict peptide binding. We have used a strategy where all possible peptides of a particular size are distributed into positional scanning combinatorial peptide libraries (PSCPL) to develop a highly efficient, universal and unbiased approach to address MHC specificity. The PSCPL approach appeared qualitatively and quantitatively superior to other currently used strategies. The average effect of any amino acid in each position was quantitated, allowing a detailed description of extended peptide binding motifs including primary and secondary anchor residues. It also identified disfavored residues which were found to be surprisingly important in shaping MHC class I specificity. Assuming that MHC class I specificity is the result of largely independently acting subsites, the binding of unknown peptides could be predicted. Conversely, this argues that MHC class I specificities consist of an array of subspecificities acting in a combinatorial mode.

Amino Acid Sequence↗

PubMed1996

Binding of peptides from the N-terminal region of alpha-gliadin to the celiac disease-associated HLA-DQ2 molecule assessed in biochemical and T cell assays.

Celiac disease (CD) is most probably an immunological disease, precipitated in susceptible individuals by ingestion of wheat gliadin and related proteins from other cereals. The disease shows a strong HLA association predominantly to the cis- or trans-encoded HLA-DQ(alpha1*0501, beta1*02) (i.e., DQ2) heterodimer. T cell recognition of gliadin peptides presented by DQ2 in the intestinal mucosa is central in the immunopathogenesis of CD. Here we describe a study where overlapping peptides from the N-terminal region of alpha-gliadin have been tested in biochemical assays for binding to affinity-purified DQ2 and DR3 (i.e., DR(alpha, beta1*0301)) molecules. The peptides were also tested for binding to DQ2 in a functional binding assay, where binding was measured as the capacity to inhibit the stimulation of a gliadin-specific, DQ2-restricted T lymphocyte clone RNnTalpha33. In both assay systems the overlapping gliadin peptides were found to bind with weak or intermediate affinity to DQ2. No or only very weak binding was found to DR3 in the biochemical binding assay. Overall, the results question the role of these peptides in the T-cell-mediated immunopathogenesis of CD. The in vitro assays described here provide new methods for the screening of potentially toxic peptides.

Amino Acid Sequence↗

PubMed1996

Temporal integration of loudness as a function of level.

Temporal integration of loudness for 1-kHz tones and broadband noises was compared over a wide range of levels. Absolute thresholds and levels required to produce equal loudness were measured for 5-, 30-, and 200-ms stimuli using an adaptive, two-interval, two-alternative forced-choice procedure. Levels ranged from 5 to 80 dB SL for noises and from 5 to 90 dB SL for tones. Results for six listeners with normal hearing show that the amount of temporal integration, defined as the level difference between equally loud 5- and 200-ms stimuli, varies nonmonotonically with level. The average amount of temporal integration varies from about 10-12 dB near threshold, to a peak of 18-19 dB when the 5-ms tone is about 56 dB and the 5-ms noise is about 76 dB SPL; the amount of temporal integration decreases to 10 dB for tones and 13 dB for noises with levels around 100 dB SPL. The data for tones are in good agreement with the majority of existing data. The data for noises are within the range of the few previous data, but the effect of level differs from that obtained in previous studies. The present results indicate that the growth of loudness may, at least in part, be consistent with the nonlinear input/output function of the basilar membrane.

Adult↗

PubMed1996

Stimulus-driven, time-varying weights for comodulation masking release.

This study tests the hypothesis that comodulation masking release (CMR) is mediated by "listening in the valleys" [S. Buus, J. Acoust. Soc. Am. 78, 1958-1965 (1985)]. Detectability was measured for signals consisting of six consecutive 25-ms, 1-kHz tone pulses presented in a 50-Hz-wide masker or in maskers consisting of seven 50-Hz-wide noises, one critical band apart, with either correlated or uncorrelated envelopes. The level of each signal pulse varied randomly around masked threshold according to Gaussian distributions with rms perturbations (standard deviations) of 3 or 6 dB. For each listener and condition, the responses from 5000 trials were sorted to construct conditional psychometric functions for d' as a function of signal-pulse intensity for ten ranges of short-term level of the on-frequency masker band during the pulse. The slopes of these functions for three normal listeners decrease markedly with increasing short-term masker level for the correlated multiband masker, but are largely constant for the other maskers. This indicates that the weight applied to the signal channel is high when the masker level is low and vice versa for the correlated masker, but is approximately constant for single-band and uncorrelated multiband maskers. These findings provide direct evidence that CMR is mediated by "listening in the valleys," but models based on direct envelope comparison may also account for the results if they are modified to include a compressive nonlinearity before the comparison.

Adult↗

PubMed1995

Receptor-ligand interactions measured by an improved spun column chromatography technique. A high efficiency and high throughput size separation method.

Size exclusion chromatography may under the right circumstances be an easy and powerful way to measure in solution the interaction between a receptor an dits ligand. Spun column chromatography is a fast size exclusion technique of increasing popularity, however, little information exists on the method development essential to obtain efficient separation in particular when used for analytical purposes. In this paper we describe a systematic approach to select the optimal parameters for spun column separation including a simple modification of the technique whereby the spun columns are eluted by high-speed gradient centrifugation. This modification is easy to implement and it considerably improves spun column performance. We hypothesize that the high-speed centrifugation step leads to the release of additional buffer which assists in the complete elution of excluded molecules while the gradient centrifugation helps to achieve equilibrium across the gel matrix during the elution. The new method has been used successfully for several different receptor-ligand interactions, and this paper describes a general approach on how to develop new applications of the technique.

Amino Acid Sequence↗

PubMed1995

The interaction of beta 2-microglobulin (beta 2m) with mouse class I major histocompatibility antigens and its ability to support peptide binding. A comparison of human and mouse beta 2m.

The function of major histocompatibility complex (MHC) class I molecules is to sample peptides derived from intracellular proteins and to present these peptides to CD8+ cytotoxic T lymphocytes. In this paper, biochemical assays addressing MHC class I binding of both peptide and beta 2-microglobulin (beta 2m) have been used to examine the assembly of the trimolecular MHC class I/beta 2m/peptide complex. Recombinant human beta 2m and mouse beta 2ma have been generated to compare the binding of the two beta 2m to mouse class I. It is frequently assumed that human beta 2m binds to mouse class I heavy chain with a much higher affinity than mouse beta 2m itself. We find that human beta 2m only binds to mouse class I heavy chain with slightly (about 3-fold) higher affinity than mouse beta 2m. In addition, we compared the effect of the two beta 2m upon peptide binding to mouse class I. The ability of human beta 2m to support peptide binding correlated well with its ability to saturate mouse class I heavy chains. Surprisingly, mouse beta 2m only facilitated peptide binding when mouse beta 2m was used in excess (about 20-fold) of what was needed to saturate the class I heavy chains. The inefficiency of mouse beta 2m to support peptide binding could not be attributed to a reduced affinity of mouse beta 2m/MHC class I complexes for peptides or to a reduction in the fraction of mouse beta 2m/MHC class I molecules participating in peptide binding. We have previously shown that only a minor fraction of class I molecules are involved in peptide binding, whereas most of class I molecules are involved in beta 2m binding. We propose that mouse beta 2m interacts with the minor peptide binding (i.e. the "empty") fraction with a lower affinity than human beta 2m does, whereas mouse and human beta 2m interact with the major peptide-occupied fraction with almost similar affinities. This would explain why mouse beta 2m is less efficient than human beta 2m in generating the peptide binding moiety, and identifies the empty MHC class I heavy chain as the molecule that binds human beta 2m preferentially.

Amino Acid Sequence↗

PubMed1995

Masked level discrimination: deterring profile listening.

Two experiments examined how level discrimination (also called intensity discrimination) between two successive three-tone complexes depends on the bandwidth and rove range of a notched-noise masker. The three-tone complex consisted of equally intense components at 0.84, 1, and 1.17 kHz set to 25, 55, or 85 dB SPL. The notch extended from 0.77 to 1.27 kHz for all masker bandwidths. The masker level changed randomly on each presentation to reduce profile cues. Results from five listeners showed that level-discrimination thresholds, delta L's (= 20 log([p + delta p]/p), where p is pressure), increased somewhat as the rove range increased. In contrast to profile-discrimination experiments, the delta L's did not decrease with increasing masker bandwidth. In addition, when the rove range was 10 dB or larger, discrimination was generally better than the best possible performance by a profile observer. The results indicate that profile analysis is not essential for reasonably good level discrimination in the presence of notched-noise maskers.

Adolescent↗

PubMed1995

Psychometric functions for level discrimination in cochlearly impaired and normal listeners with equivalent-threshold masking.

The purpose of this study was to determine whether the form of the psychometric functions for level discrimination (also known as intensity discrimination) measured in a two-interval, two-alternative forced-choice paradigm changes with hearing impairment. Measurements of sensitivity, d', as a function of delta L (= 20 log[(p+delta p)lp], where p is pressure) were obtained in six listeners with cochlear impairments, five normal listeners tested in the quiet, and two masked-normal listeners. Stimuli were chosen to encompass a wide range of conditions and difference limens. Results show that the d' is nearly proportional to delta L over the entire range of stimuli. This simple relationship is not changed by cochlear impairments or masking noise. These findings indicate that if the transformation from stimulus intensity to decision variable is affected by hearing impairment or masking, the change affects both the mean and the standard deviation in the same manner--i.e., the standard deviation may be proportional to the derivative of the transformation as was suggested by Zwislocki and Jordan [J. Acoust. Soc. Am. 79, 772-780 (1986)]. The results also lend support to the notion that delta L--plotted on a logarithmic scale--is an appropriate representation of level-discrimination performance.

Adult↗

PubMed1995

An excitation-pattern model for the starling (Sturnus vulgaris).

This paper develops and tests an excitation-pattern model for the starling. Like excitation-pattern models for humans [e.g., Zwicker, Acustica 6, 365-381 (1956); Florentine and Buus, J. Acoust. Soc. Am. 70, 1646-1654 (1981)], the model for starlings provides a unified account of a large body of data. The foundation of the model is a critical-band scale, which is derived as an equal-distance scale according to a cochlear-map function. The cochlear-map function is determined as a best-fitting function to physiological data relating characteristic frequency (CF) of auditory-nerve fibers to their place of innervation on the basilar papilla. Excitation patterns are derived from auditory-nerve measurements of levels at CF necessary to produce firing rates equal to those evoked by a test tone. The shape of these excitation patterns is independent of level and frequency when plotted on a cochlear-distance scale. The resulting model indicates that 10-dB bandwidths of auditory-nerve tuning curves and frequency DLs can be approximated as equal distances along the basilar papilla. Predictions of level discrimination are in good agreement with the data, except below 20 dB SL. Overall, the present work indicates that excitation-pattern models account for a wide range of auditory phenomena in both humans and starlings, when the models take into account differences in critical-band scales, absolute thresholds, excitation-pattern slopes, and growth of excitation, which is linear in starlings, but nonlinear in humans.

Animals↗