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Biomedical subjects

L A Hart

Publications and source records attributed to L A Hart.

48 records · Page 3Linked to original sources
PubMed1988

Generation of high-rate ovalbumin-specific antibody-secreting cells in cultures of human peripheral blood B cells obtained from non-immunized blood donors.

When human peripheral blood B cells are cultured for 6 days with the T cell-dependent peptide antigen ovalbumin (OA) in the presence of antigen-presenting cells and helper T cells, plaque-forming cells (PFC) are generated. These OA-induced PFC differ from the conventional high-rate antibody-secreting PFC formed after stimulation of B cells with recall antigens (e.g. tetanus toxoid) in that they secrete antibody at a very low level. Previous studies have shown that OA-induced PFC are B lymphocytes in an early activation state rather than cells that have differentiated into plasmablasts. The apparent arrest in the maturation of OA-induced PFC in an early activation phase can be overcome by simultaneous stimulation with interleukin 2 (IL-2) and gamma interferon (IFN-gamma). The isotype of the OA-specific antibodies secreted, however, are only of the IgM class, demonstrating that an isotype switch does not occur.

Antibody-Producing Cells↗
PubMed1988

Ovalbumin-specific human B-cell activation and maturation. The absence of final maturation is due to the incapacity of ovalbumin-activated T cells to produce maturation factors.

By means of a panel of monoclonal antibodies it is demonstrated that, in cultures of human peripheral blood mononuclear cells (PBMC) with the T-cell-dependent (TD) antigen ovalbumin (OA), responding B cells are activated from the resting state. The differentiation of the activated B cells to high rate-secreting plasma blasts, however, is arrested in an early activation phase, in which they can be detected as low rate-secreting plaque-forming cells. The arrest does not occur when stimulation with OA occurs in the presence of antigen-nonspecific activation and maturation factors, which are provided in the culture by the anamnestic response to the TD antigen tetanus toxoid.

Adjuvants, Immunologic↗
PubMed1987

Premature temporal theta (PT theta).

A distinctive pattern called premature temporal theta (PT theta) was studied in 436 infants, ranging in age from 24 to 46 weeks. The pattern is seen in early prematurity, maximizes at 29-31 weeks and then diminishes and disappears near term. Usually the pattern is found independently on both temporal areas, but with a right-sided preference. Patients without PT theta or with a significantly low amount had either neurological or non-neurological (medical) conditions. With age there is a tendency for an increase in frequency and a decrease in amplitude. Five different peaks in the amount of this pattern are seen at approximately every month. Unilateral PT theta tends to be seen in older babies, more often on the right side and with an abnormal EEG. An abnormal EEG is usually associated with a delay in both the appearance and disappearance of this wave form. PT theta is also associated mainly with REM or active sleep. A polynomial rather than an exponential or power function best describes these data with changes of age. PT theta may arise from the inferior temporal gyrus and/or especially the transverse gyrus.

Electroencephalography↗
PubMed1987

Usefulness of different stimuli in visual evoked potentials.

The goal of this study was to determine the relative usefulness of the flash (FL), pattern reversal (PR) of 56', and PR of 28' in 62 patients (pts) with either MS (34) or non-MS (28) compared with normals (19). An abnormal visual evoked potential was found in 58%, 69%, and 81% of the eyes tested in possible, probable, and definite MS and in 88% of the non-MS group. The 28' PR produced the most abnormal responses, the greatest number with either greater than 3 standard deviations (SD) from the mean or greater than 2 SD in both MS and non-MS groups. The FL was second best at producing the most abnormal responses, but more often produced the only abnormality (29), compared with 28' PR (11). The 56' PR produced the only abnormality in none of the MS pts and in only one of the non-MS pts. In all categories (most abnormal, greater than 3 SD, greater than 2 SD, the only abnormality of greater than 3 SD or greater than 2 SD, and other peaks abnormal), the 28' PR was usually by far the best stimulus for definite (and probable) MS, but equally as effective was the FL in the possible MS pts Our data suggest the usefulness of 28' and not 56' PR, but the FL is especially useful in pts with possible MS.

Adolescent↗
PubMed1985

Selecting pet dogs on the basis of cluster analysis of breed behavior profiles and gender.

Using a computer-generated data base of rankings of 56 breeds of dogs on 13 behavioral traits, a factor analysis was performed to determine the extent to which a few general underlying behavioral tendencies are manifested in specific characteristics. Three factors, referred to as reactivity, aggression, and trainability, accounted for 81% of the variance in the 13 behavioral traits. Subsequently, a cluster analysis was performed to generate 7 clusters of dog breeds on the basis of similarity in scores for each of the 3 main factors. The clusters reflected to some degree the conventional groupings of dogs into working, sporting, hound, and terrier breeds. A quantitative analysis of the ranking of male dogs vs female dogs for the 13 characteristics revealed that males differed from females on 10 traits. It was concluded that these gender and cluster profiles will allow people to select a breed or gender of dog that is most likely to match the emotional and physical needs of the person who will provide a home for the pet.

Animals↗
PubMed1985

The relationship between visual seizures and visual evoked potentials.

We have studied a patient (pt) in status epilepticus with visual seizures (szs) arising focally from the right occipital area and have recorded the visual evoked potential (VEP) to three different stimuli under three different conditions (during, between and with no szs). The pt experienced "sparkling" in the contralateral visual field as the sz and the intensity of the "sparkling" was directly related to the frequency of the ictal activity recorded on the EEG. During the szs the VEPs could still be recorded, but the amplitude of the P100 was higher on the contralateral side with pattern reversal (PR) stimuli, and with flashes (FL) the positive peak after the P100 was less evident on the ipsilateral side. Latencies to these latter two positivities were generally shorter than in normals, with much greater standard deviations ipsilaterally with FL and contralaterally with PR, especially during the actual szs. The relationship between VEP generation and visual sz phenomena is discussed.

Adult↗
PubMed1985

The significance of the negativities in the brainstem auditory evoked potential (BAEP).

This study was designed to investigate the negativities of the brainstem auditory evoked potential (BAEP), especially to determine if they represented a part of a composite waveform together with a given positivity. Subjects (10) and patients (56) provided the data, mainly in the form of correlation coefficients of latency and amplitude values, trace by trace comparisons of multiple responses from the same subject and the specific grouping of abnormal waves from the patient population. The results show that the strongest relationships of latency and amplitude involved completely different pairs of waves, that the negative and positive values often changed in opposite directions, and that no pair of waves of opposite polarity were typically abnormal together. Thus, the negativities are not generally associated with given positivities and likely have their own generators.

Adult↗
PubMed1985

Analysis of the antigen-induced in vitro differentiation of human peripheral blood B cells: stimulation with ovalbumin induces the transition from the resting state into the excited state.

Human peripheral blood B lymphocytes, when cultured for 6 days with ovalbumin in the presence of T cells and monocytes, can differentiate into plaque-forming cells (PFC) secreting small amounts of antigen-specific IgM. Phenotype analysis using Ig-isotype and B-cell specific monoclonal antibodies revealed that the PFC precursor is a sIgM+ IgD+IgG- B lymphocyte. The PFC itself also carries the B-cell specific membrane antigens B1 and BA-1; it expresses only IgM on its surface. When apart from the antigen a Concanavalin A-induced, T-cell derived growth factor preparation was added to the cultures, we observed the disappearance of sIgM from the membrane. Furthermore, it was demonstrated by means of density gradient centrifugation that the differentiation of the PFC-precursor into a PFC is accompanied by a decrease in cellular density. Finally, it was shown using hydroxyurea as an inhibitor of DNA-synthesis, that the PFC-precursor passes several cycles of cell division during the process of differentiation into a PFC.

Antibody-Producing Cells↗
PubMed1984

The effect of light sleep on the brainstem auditory evoked potential (BAEP).

This study dealt with the latency and amplitude changes in the brainstem auditory evoked potential (BAEP) measured during periods from wake to light sleep, after stimulating both ears of 16 subjects. All 13 latencies (positive and negative) increased from the central vertex electrode (referred C7 vertebra) with statistical significance from peak VI (and II), and 8 of 13 latencies increased from the (ipsilateral) ear electrode with statistical significance from negative peak V. Furthermore, a significant decrease in amplitude occurred in peak V (ear) and in peak VIII (Cz and ear). Finally, the more typical recording of vertex to ipsilateral ear showed all 13 latencies increasing in the sleep state and nonparametric statistics showed significance in 6 of these latencies. The assumption that the latencies and amplitudes do not change from the waking to the sleeping state should be reconsidered.

Brain Stem↗
PubMedDate not supplied

Two functionally and chemically distinct immunomodulatory compounds in the gel of Aloe vera.

An aqueous extract of Aloe vera gel was analyzed guided by modulatory activity with regard to the in vitro activation of human complement and of human polymorphnuclear leucocytes (PMN). Upon ultrafiltration a high (h-Mr) and a low (l-Mr) molecular mass fraction were obtained. Pre-incubation of human pooled serum with the h-Mr fraction resulted in a depletion of classical and alternative pathway complement activity. In contrast, only the l-Mr fraction could inhibit the production of free oxygen radicals by activated PMNs. The latter activity cannot be attributed to non-specific effects like toxicity, interference with stimulant binding or scavenger activity.

Adjuvants, Immunologic↗
PubMedDate not supplied

Selective predictive value of rapid automatized naming in poor readers.

This study considers the differential predictive value of rapid naming tests for various aspects of later reading, where the differential is between nondisabled and poor readers. Two large-N longitudinal samples of students who have been evaluated from third through eighth grades are studied: (a) a randomly accessed, normally distributed group including students with varying degrees of reading ability (N = 154), and (b) a group of poor readers whose single-word reading in third grade is at or below the population 10th percentile (N = 64). Outcomes in fifth and eighth grade were measured in both groups. Single-word reading in both grades was strongly predicted from third-grade rapid naming only within the poor readers, even when IQ, socioeconomic status, and third-grade single-word reading were statistically controlled. Although rapid naming had predictive value within the large, normally distributed group, its predictive power was entirely absent in the average-reading nondisabled students who were between the 10th and 90th percentiles (n = 122). The fact that rapid naming has predictive power only for poor readers but not for average readers is interpreted as suggesting that impaired readers are qualitatively different from the normal-reading population and are not simply the "tail" of a normal distribution of reading ability. It also seems that it is the automaticity of retrieval, not the knowledge of names itself (as in confrontational naming tasks), that gives the predictive power in rapid naming. These data are considered in light of the one- and two-factor theories of the underlying processes involved in reading disability or dyslexia.

Anomia↗