Search PubMed⌕ Search

Biomedical subjects

J E Calvert

Publications and source records attributed to J E Calvert.

49 records · Page 3Linked to original sources
PubMed1987

Activation of B chronic lymphocytic leukaemia cells by Branhamella catarrhalis.

Cells from the blood of patients with chronic lymphocytic leukaemia were cultured in the presence of two polyclonal activators of human B cells, the bacteria Branhamella catarrhalis (Bc) and Staphylococcus aureus Cowan 1 (SAC). Although the magnitude of the responses varied, cells from seven of the eight patients studied were induced to proliferate in response to Bc. In contrast, the response to SAC was low or negligible in seven of the eight patients, and only one patient responded well to this mitogen. Bc was also effective in inducing secretion of IgM in cells from seven of the eight patients, and this was unaffected by removal of T cells. Fractionation of CLL cells on density gradients showed that the highest level of IgM production was induced in cells with a low buoyant density, whilst cells with a high buoyant density secreted little or no immunoglobulin in response to Bc. Together, these results demonstrate that Bc is an effective, T-independent activator of both DNA synthesis and immunoglobulin production in CLL cells.

Aged↗
PubMed1986

Modification of visual orientation illusions by drugs which influence dopamine and GABA neurones: differential effects on simultaneous and successive illusions.

The effects of haloperidol, nomifensine and lorazepam on the visual tilt illusion were studied in normal volunteers. Haloperidol and nomifensine produced no significant changes in the illusion, although in previous work they had been found to reduce and enhance, respectively, a closely related illusion, the tilt aftereffect. By contrast, lorazepam produced a dose-related increment in the size of the tilt illusion, but had no effect on the tilt aftereffect. The results are discussed in relation to proposed mechanisms which may underlie the two kinds of illusion. The differential effects of individual drugs on the two illusions may reflect their differing actions on two processes: lateral inhibition and adaptation in visual channels.

Adolescent↗
PubMed1986

Characteristics of human B cells responsive to the T-independent mitogen Branhamella catarrhalis.

Non-T cells from tonsil or blood were fractionated according to buoyant density, isotype of surface immunoglobulin, or the ability to form rosettes with mouse erythrocytes. Each fraction was tested for the ability to proliferate in response to B. catarrhalis (Bc) and, for comparison, Staphylococcus aureus Cowan 1 (SAC) or an MLR supernatant (TF). Cells in all density fractions responded to Bc, the greatest response occurring in the high-density cell fraction. SAC could similarly induce proliferation in high-density cells, in contrast to TF which preferentially activated cells in the low-density fraction. When cells were fractionated by rosetting with mouse erythrocytes, both fractions (MRBC-R+ and MRBC-R-) responded to Bc and to SAC, whereas the greatest response to TF occurred in the MRBC-R- cell fraction. Depletion of sIgD+ sIgM+ cells almost completely abolished the response to Bc, suggesting that responsive cells express both these classes of immunoglobulin on their membrane. Furthermore inclusion of anti-delta antibodies in cultures resulted in failure to proliferate in response to Bc. These data strongly suggest that Bc, like SAC but in contrast to TF, is able to stimulate proliferation in cells with the characteristics of resting B cells, i.e., high-density, sIgD+ cells which form rosettes with MRBC. This may be related to the fact that Bc, like SAC, is able to bind to human immunoglobulins.

Antigens, Surface↗
PubMed1985

The tilt after-effect: changes with stimulus size and eccentricity.

Previous evidence that the tilt after-effect (TAE) is larger when the stimuli are viewed peripherally rather than centrally was confirmed. An increase in viewing distance also increased TAE size. However, the increase in the TAE in peripheral vision was abolished if stimuli were increased in size to compensate for the change in the cortical magnification factor. Both the decrease in field diameter and increase in spatial frequency with viewing distance were found to influence the size of the TAE. When the data were expressed in cortical terms, the TAE was found to increase with spatial frequency, and decrease with field diameter, regardless of retinal position. The functional significance of these effects is discussed.

Adaptation, Ocular↗
PubMed1984

Use of a programmable calculator for rapid, low-cost processing of echocardiographic records.

A comparative study was performed to determine the accuracy of a programmable calculator with supplemental digitizer in echocardiographic analysis. Twenty separate measurements were collected per heart beat from five different dogs, taking five heart beats from each dog. The measurements were made by an echocardiographic technician (ET), echocomputer (EC), and by a programmable calculator (HP). In a triple comparison (ET-HP, ET-EC, HP-EC) there were no significant differences in the values obtained, suggesting that the programmable calculator can provide a highly accurate and rapid means of processing echocardiographic measurements, thereby providing the advantages of the echocomputer without the cost of such a device.

Animals↗
PubMed1983

Differentiation of B lineage cells from liver of neonatal mice: generation of immunoglobulin isotype diversity in vitro.

The development and differentiation of B cells expressing different immunoglobulin (Ig) isotypes was studied in cultures of murine neonatal liver cells. Before culture, 5 to 15% of the liver cells were mu + pre-B cells; 1 to 3% had surface IgM and less than 0.1% had slgG. During 4 days in culture the number of pre-B cells declined, whereas the number of IgM B cells increased greater than 20-fold; IgG B cells also increased in number. Of the four subclasses, IgG3+ and IgG2b+ cells predominated, each representing 3 to 10% of the total B cells at day 4. IgG1+ and IgG2a+ cells were present in lower numbers, representing 1 to 5% and 0.3 to 2.5% of B cells, respectively. Most IgG+ cells also expressed sIgM. Only a minority (less than 10%) of the sIgM+ cells were sIgD+, and most sIgG+ cells were sIgD-. Few T cells were present in these cultures (less than 0.5% in newborn liver), and sIgG+ cells were generated in normal frequencies in cultures of cells from nude mice. The numbers of B cells expressing each IgG subclass were similar in cultures from athymic nu/nu mice, nu/+ heterozygous littermates, and normal BALB/c mice. Plasmablasts and plasma cells appeared over a 14-day culture interval, and these expressed cytoplasmic IgM, IgG3, IgG1, IgG2b, IgG2a, and IgA. Measurable amounts of the first four isotypes were detected in the culture supernatants by radioimmunoassay. These results indicate that neonatal B cells can undergo isotype switching in the absence of T cell help, and that the expression of sIgD may not be a prerequisite for cells to switch Ig isotypes.

Animals↗
PubMed1981

Study of proteolytic removal of Fab delta and Fe delta determinants of lymphocyte membrane IgD using a direct rosette assay.

Proteolysis of lymphocyte surface membrane immunoglobulin (SIg) by trypsin, papain and pronase was investigated. Cleavage in the hinge region resulting in removal of Fab delta was distinguished from removal of the whole SIgD molecule using antisera specific for c delta l and Fc delta. Using the sensitive direct rosette assay SIgD determinants were detected after digestion under conditions previously thought to remove IgD from the membrane. By increasing digestion times is was shown that whilst papain and pronase remove the whole IgD molecule, Fc delta but not Fab delta determinants survive trypsin. The implications of the results for structural differences between membrane and serum IgD and for models of insertion of SIgD into the plasma membrane are discussed.

Epitopes↗
PubMedDate not supplied

The synthesis and in vivo assembly of functional antibodies in yeast.

The yeast Saccharomyces cerevisiae can synthesize, process and secrete higher eukaryotic proteins. We have investigated the expression of immunoglobulin chains in yeast and demonstrate here the synthesis, processing and secretion of light and heavy chains, the glycosylation of heavy chain, the intracellular localization of these foreign proteins by immunofluorescence, and the detection of functional antibodies in cells co-expressing both chains. This may provide the basis of a microbial fermentation process for the production of monoclonal antibodies. The co-expression of light and heavy chains in Escherichia coli has been reported but functional antibodies were not assembled in vivo. Furthermore, only low-level assembly of these chains was found in vitro.

Antibodies, Fungal↗
PubMedDate not supplied

Early visual processing over the menstrual cycle: the tilt aftereffect.

We have previously shown that the tilt aftereffect (TAE) appears to respond to changes in central dopaminergic function. In this study, the TAE was investigated during the preovulatory and the premenstrual phases of the menstrual cycle. Results in the preovulatory phase mimicked those previously found associated with increased dopaminergic function, compared to data produced in the premenstrual phase, suggesting changes in dopamine function over the cycle.

Adult↗
PubMedDate not supplied

B cell differentiation and lymphocyte surface phenotype in late onset hypogammaglobulinaemia.

Lymphocyte function and cell surface phenotype were examined in fifteen patients with late onset hypogammaglobulinaemia. The percentage of surface immunoglobulin-positive B cells in fourteen of the fifteen patients was in the normal range. Patients' B cells expressed MHC class II antigens at normal levels. For one patient, there was relatively high sIgD and low sIgM expression on B cells; the rest of the patients did not differ from controls in surface immunoglobulin density. The proportion of B cells positive for CD5 in patients was comparable to normal controls, and considerably less than in cord blood. However, the pattern of immunoglobulin isotype secretion in vitro by patients' B cells closely paralleled responses of cord blood B cells. Spontaneous secretion of IgM and IgG by patients' B cells was very low. Following polyclonal activation in the presence of autologous T cells, cells from thirteen patients secreted IgM within the normal range in response to at least one activator. The response of patients' purified B cells to IL-2 and gamma-IFN was variable. For four of six tested, B cells cultured with IL-2 and gamma-IFN together with polyclonal activators secreted normal levels of IgM. B cells from the other two patients secreted little or no IgM in response to these cytokines. For fourteen patients, IgG secretion following polyclonal activation remained low both when B cells were cultured with T cells or with a combination of IL-2 and gamma-IFN. IgG subclass imbalance was seen in one patient, whose cells secreted an unusually high proportion of IgG3, and undetectable IgG2 and IgG4; this pattern was consistent whether T cell help was provided by autologous or allogeneic T cells. Similarly purified B cells from this patient showed deficient IgG2 and IgG4 production in response to IL-2 and gamma-IFN.

Adult↗