Biomedical subjects

M Egerton

Publications and source records attributed to M Egerton.

48 records · Page 3Linked to original sources

PubMed1990

Kinetics of mature T-cell development in the thymus.

We have reexamined the balance between cell birth, cell maturation, and cell death in the thymus by labeling dividing thymocytes and their progeny in vivo with [3H]-thymidine, isolating clearly defined subpopulations by fluorescence-activated cell sorting, and determining the distribution of label by autoradiography. When mature thymocytes were precisely defined (as CD4+CD8- CD3+ or CD4-CD8+ CD3+) and separated from immature single positives (CD4+CD8- CD3- and CD4-CD8+ CD3-), a lag was observed in the rate of entry of [3H]thymidine into mature cells. Thus, many of the mature thymocytes appear to derive from a small nondividing cortical thymocyte pool, rather than originating directly from the earliest dividing CD4+CD8+ blasts. There was little evidence for cell division during or after mature thymocyte formation, suggesting a one-for-one differentiation from cortical cells rather than selective clonal expansion. The rate of production of mature single positive thymocytes agreed closely with estimates of the rate of export of mature T cells from the thymus and was only 3% of the rate of production of double-positive cortical thymocytes. This was compatible with a stringent selection process and extensive intrathymic cell death and suggested that no extensive negative selection occurred after the mature cells were formed.

Animals↗

PubMed1990

CD4-CD8- thymocytes that express the T cell receptor may have previously expressed CD8.

Amongst CD4-CD8- (double negative) thymocytes there is a sizeable population (variable from strain to strain) of cells expressing surface T cell receptor (TCR). These TCR+ double negatives are predominantly non-cycling, have very little precursor activity, and, unlike the TCR-CD4-CD8- thymocytes, appear not to be part of the mainstream of thymocyte development. A unique feature of this population is the biased V beta-gene region usage. In CBA mice, 60-70% of TCR+ CD4-CD8- cells express receptors that utilize V beta 8 gene products, compared with peripheral T cells from the same strain which are only 20-30% V beta 8+. This suggests that the high V beta 8 usage may be the result of some selective process. A growing body of experimental data suggests that TCR specificity selection occurs at the CD4+CD8+ stage of thymocyte development. In order to gain some insight into the previous history of the TCR+ double negatives, in particular whether or not they have previously expressed CD8 and therefore been eligible for selection, we have determined the methylation state of the CD8 gene and compared it to other thymocyte populations. We show that the TCR+ CD4-CD8- thymocytes are demethylated at some sites in the CD8 gene, consistent with previous CD8 expression. However, the demethylation pattern is distinct from that seen on typical peripheral T cells or on mature thymocytes, suggesting that the TCR+ CD4-CD8- thymocytes are not derived from mature thymocytes or peripheral T cells which have returned to the thymus and downregulated CD8 expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Intrathymic selection of murine TCR alpha beta+CD4-CD8- thymocytes.

The CD4-CD8- thymocyte population contains the precursors of all other thymocytes. However, it also contains a significant proportion of cells which express surface TCR alpha beta, and have little or no precursor activity. Like peripheral T cells, but unlike most other thymocytes, these TCR alpha beta+CD4-CD8- thymocytes do not express heat stable antigen. Both the origin and developmental status of these cells are unclear, and are the subject of this report. We have measured the proportion of V beta 8.1+ cells amongst TCR+HSA-CD4-CD8- thymocytes in MIs-1a versus MIs-1b mice, in order to determine whether they have undergone negative selection. The proportions were similar in both strains, in contrast to mature T cells, indicating that neither they nor their precursors had undergone clonal deletion. We also measured the accumulation of these cells over the early life of the animal and found that it was extremely slow. Our data also show that although TCR-V beta 8.1+ cells are reactive to MIs-1a in association with MHC class II, most mature TCR-V beta 8.1+ cells in MIs-1b mice are CD8+, suggesting an additional reactivity with MHC class I. We raise the possibility that TCR-V beta 8.1+CD4-CD8- thymocytes are derived from TCR-V beta 8.1+CD4+CD8+ thymocytes, and that the reactivity of TCR-V beta 8.1 with both MHC classes I and II has resulted in the down-regulation of both CD4 and CD8.

Animals↗

PubMed1990

The kinetics of immature murine thymocyte development in vivo.

The dynamics of cell generation and turnover in the young adult murine thymus has been studied by in vivo administration of [6-3H]deoxythymidine, isolation of thymocyte subpopulations by negative depletion and cell sorting procedures, and assessment of dividing cells and their products by autoradiography. The flow of label through subpopulations of CD4-CD8- thymocytes defined by the markers heat stable antigen (HSA), phagocyte glycoprotein 1 (Pgp-1), interleukin 2 receptor (p55) (IL-2R), and CD3 was determined, to check the developmental sequence deduced from intrathymic transfer and molecular approaches. In addition, the flow of label 'downstream' into the CD4+CD8+ cortical populations was followed to check if cells expressing CD8 alone were obligatory intermediates. The main findings were: (i) support for the following sequence within the CD4-CD8- group: HSA++Pgp-1+IL-2R(-)----HSA++Pgp-1-IL-2R(+)----HSA++Pgp-1-IL- 2R-; (ii) the majority of cell generation and cell turnover within the CD4-CD8- population was due to the HSA++IL-2R-Pgp-1- subpopulation; (iii) the rate of cell output from the proposed intermediate CD3-CD4-CD8+ subpopulation was equivalent to only 55% of the cell output from its proposed precursor, the most mature CD4-CD8- subpopulation, suggesting that many double negatives differentiate directly (or via CD3-CD4+CD8- intermediates) into double positives; and (iv) the CD4-CD8-HSA- (and CD3+) thymic subpopulation contained very few cycling cells and turned over extremely slowly, indicating that these slowly accumulating product cells are off the mainstream of T cell development.

Animals↗

PubMed1990

The generation and fate of thymocytes.

In the adult thymus the majority of thymocytes are at a non-proliferating end stage, during which 3% of all CD4+CD8+ cortical thymocytes are selected on the basis of appropriate T-cell antigen-receptor (TcR) specificity to become CD4-CD8+ or CD4+CD8- mature thymocytes. The selected mature cells gradually emigrate to the periphery. The 97% unselected, or positively rejected, CD4+CD8+ thymocytes die in the thymus. This 3-day end stage is, however, the product of around 2 weeks of proliferation by less mature thymocytes, which gives about a 10(5)-fold expansion from the hundred prothymocytes estimated to seed the thymus each day. Rearrangement and expression of TcR genes and a sequence of changes in surface antigens occurs during this prolonged period. Two sequential waves of expansion and differentiation appear to be involved. The first, about 1 week long, involves the less than 0.1% of thymocytes which still resemble the prothymocyte; this leads via a non-dividing interval to the second 1-week stage involving the 3% of CD4-CD8- thymocytes and then the CD4+CD8+ blasts.

Animals↗

PubMed1989

A murine early thymocyte developmental sequence is marked by transient expression of the interleukin 2 receptor.

Precursors of all T-lineage cells are found in the population of thymocytes that lacks the CD4 and CD8 surface markers. These "double-negative" thymocytes are heterogeneous and can be divided into discrete subpopulations based on their expression of other surface markers. We have determined the relative maturity of these subpopulations based on the extent of rearrangement and expression of their T-cell receptor genes, their cell cycle status, and their thymus reconstitution capacity. Within the subpopulation of double negatives expressing high levels of the heat-stable antigen, the additional markers phagocytic glycoprotein 1 (Pgp-1) and interleukin 2 receptor (IL-2R) can be used to define the sequence IL-2R- Pgp-1+----IL-2R+ Pgp-1-----IL-2R- Pgp-1-, which occurs before the expression of CD4 and CD8. Transient expression of the IL-2R marks an important developmental point in the sequence just prior to a burst of cell proliferation and a loss of thymus reconstitution ability. The earliest cells in this sequence are already partially rearranged for genes in the C beta 1 region. IL-2R expression marks a second wave of T-cell antigen receptor of beta-chain gene rearrangement and the initiation of T-cell antigen receptor alpha- and beta-chain gene expression.

Animals↗

PubMed1989

Risk factors for cataract in Oxfordshire: diabetes, peripheral neuropathy, myopia, glaucoma and diarrhoea.

423 cataract patients and 608 controls between the ages of 50 and 79 were interviewed in a case-control study in Oxfordshire. Diabetes, myopia, glaucoma, peripheral neuropathy and severe diarrhoea were identified as risk factors. The excess risk experienced by females with diabetes was confirmed. The trauma of surgery for glaucoma may be largely responsible for the appearance of glaucoma as a risk factor. Severe diarrhoea has now been identified as a risk factor in England and in India. The risk associated with peripheral neuropathy may indicate a common aetiology at least for some proportions of the two conditions.

Aged↗

PubMed1989

Protection against cataract by aspirin, paracetamol and ibuprofen.

Results of a case-control of 423 cataract patients and 608 controls in Oxfordshire shows that the protective effect against cataract associated with consumption of aspirin-like analgesics (aspirin, paracetamol and ibuprofen family) is manifest even at low doses. Less than 150 g total dose was associated with a halving of the risk of cataract extraction.

Acetaminophen↗

PubMed1988

Subpopulations of CD4- CD8- murine thymocytes: differences in proliferation rate in vivo and proliferative responses in vitro.

Cell sorting and cytotoxic depletion procedures were used to subdivide the population of CD4- CD8- ("double-negative") thymocytes from adult CBA mice on the basis of expression of Ly-1, HSA (the "heat-stable antigen" M1/69 or B2A2), Pgp-1 glycoprotein, Thy-1, MEL-14 and the PC61 antigenic determinant on the IL2 receptor (IL2R). The level of dividing cells within these subsets was assessed by brief in vivo administration of [3H]-thymidine, followed by radioautography, or by flow cytometric cell cycle analysis after DNA staining. The capacity of the subsets to proliferate in culture, in response to stimulation with concanavalin A (Con A), or with phorbol myristate acetate (PMA) and the calcium ionophore ionomycin, was assessed in high cloning efficiency single-cell culture systems. In general, the proliferative response in culture was inversely related to the rate of cell division in vivo. Response of the double-negative subsets to Con A correlated with expression of the T cell antigen receptor complex; although a high cloning efficiency was obtained from the receptor-positive fractions, very few of the clones were cytotoxic. In particular, a major Ly-1+ HSA- Pgp-1+ double-negative subset, as well as minor Ly-1- HSA- Pgp-1+ subsets, contained very few cells in cycle in vivo, but showed a high cloning efficiency in both culture systems. Conversely, the other major double-negative subset, Ly-1- HSA+ Pgp-1-, included most of the cells in cycle, but showed a reduced cloning efficiency in response to PMA and ionomycin and failed to respond to Con A. The dividing cells within the Ly-1- HSA+ Pgp-1- group were strongly enriched in the IL2R- rather than in the IL2R+ subset, suggesting IL2 was not the growth factor maintaining their proliferation in vivo.

Animals↗

PubMed1988

Immature CD4- CD8+ murine thymocytes.

Mature thymocytes are usually defined and separated from other less mature thymocytes on the basis of their mutually exclusive expression of either CD4 or CD8. However, such murine "single positives" include a subpopulation of immature cells with properties resembling CD4- CD8- thymocytes or CD4+ CD8+ cortical blasts. Most of these immature single positives are CD4- CD8+, some expressing relatively low levels of CD8. They are large, dividing cortisone-sensitive cells found in the outer cortex. They express high levels of the heat-stable antigen (recognized by the monoclonals M1/69, B2A2, and J11d) but they are MEL-14-. The absence of detectable surface CD3, the absence of alpha-chain messenger RNA, and the predominance of the truncated form of the beta-chain messenger RNA all indicate that they do not express the T-cell antigen-receptor complex. Strategies for eliminating such immature cells from preparations of mature thymocytes are given, and their developmental significance is discussed.

Animals↗

PubMed1988

Developmental status and reconstitution potential of subpopulations of murine thymocytes.

In this chapter we have summarized our view of the subsets of murine CD4- CD8- thymocytes which can be identified with a range of monoclonal antibodies. We have shown the division rate and turnover time of the main subsets and have listed what we know of the TcR gene rearrangement, and expression at the RNA and protein levels. We have been unable to completely segregate gamma delta-TcR-expressing cells from alpha beta-TcR-expressing cells by any of the markers we have used, although the proportions of the two receptor forms vary widely in the different subsets. Experiments involving intrathymic transfer of the CD4- CD8- subsets are described, which indicate that all the TcR- subsets of the CD4- CD8- thymocytes display some precursor activity and which suggest a progression of at least five stages through the TcR- subpopulations of CD4- CD8- cells. The earliest precursor is a Thy 1 low, HSA low, Pgp-1 high cell which has unrearranged C beta and is non-dividing and which closely resembles the bone marrow prothymocyte. The later precursors are Thy 1 high, HSA high, Pgp-1 low, have rearranged C beta and are rapidly dividing. We tentatively conclude that none of the TcR+ CD4- CD8- cells are precursors of the major thymocyte subsets or of typical peripheral T cells, and we have found no evidence so far of separate precursors for the different mature subsets of thymocytes or peripheral T cells.

Animals↗

PubMed1988

Passionate women and passionate men: sex differences in accounting for angry and weeping episodes.

This experiment tests a rule-role model of accounting for angry aggression. The hypothesis, derived from Averill's (1984) rule model of anger, is that people with stronger norms against aggression will account for their own angry aggression by interpreting it as passion, that is as externally caused and uncontrollable, more than people with weaker norms against aggression. It was also hypothesized that sex role would affect interpretations. Women are believed to have stronger norms against aggression. Would they therefore account for angry aggression by presenting it as externally caused and uncontrollable more than men. Subjects (n = 45, 23F and 22M), were asked to evaluate an angry incident as if they had taken part in it themselves. Women judged more normative conflict about the episode than men, but had low consensus in using passion schemas (identified by multiple regression). Men had high consensus in using passion schemas. A control condition in which the protagonist wept was carried out (n = 43, 21F and 22M). In this condition there was some consensus among women in using a passion scheme but none among men. It must be concluded that sex role constrains the appropriateness of the accounting strategy used.

Adult↗