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M A Sheard

Publications and source records attributed to M A Sheard.

15 recordsLinked to original sources
PubMed2001

Ionizing radiation as a response-enhancing agent for CD95-mediated apoptosis.

CD95 (Fas/APO-1) is a death receptor on the surface of a wide variety of cell types. In most cells examined, ionizing radiation acts as a response-enhancing agent for CD95-mediated cell death. Although DNA-damaging radiation appears to modulate CD95-mediated signals through multiple mechanisms, the only well-characterized mechanism is activation of the tumor-suppressor protein p53, which transcriptionally regulates the expression of CD95 on various cell types. The ligand for CD95 is expressed by activated lymphocytes and natural-killer cells, which produce factors that sensitize cells resistant to CD95-mediated cell death. Ligation of CD95 on irradiated tumor cells might be achievable using emerging modalities that reactivate the stalled anti-tumor immune response.

Animals↗
PubMed2001

Modulation of death receptor-mediated apoptosis in differentiating human myeloid leukemia HL-60 cells.

Differentiating myeloid cells may become resistant to various apoptotic stimuli. In the present study, dimethyl sulfoxide (DMSO) and all-trans retinoic acid (ATRA) were found to modulate the sensitivity of HL-60 cells to death receptor-mediated apoptosis in a time-dependent manner. During the early stages of differentiation, DMSO treatment increased the response of HL-60 cells to tumor necrosis factor alpha; (TNF-alpha), but enhanced responsiveness was lost during later differentiation stages. In contrast, ATRA treatment induced resistance to TNF-alpha-induced apoptosis. HL-60 cells were resistant to Fas-mediated apoptosis but were sensitized by culturing in serum-free conditions. Similar to its effect on TNF-alpha sensitivity, DMSO pretreatment augmented the response to Fas-mediated signaling, which coincided with increased expression of Fas on DMSO-pretreated cells. However, during the later stages of DMSO-induced differentiation, sensitivity to anti-Fas antibody-induced apoptosis declined significantly, although Fas expression was still elevated. The reduced sensitivity to anti-Fas treatment partially correlated with increased Fas-associated phosphatase-1 mRNA expression. Thus, regardless of either Fas up-regulation or potentiation of TNF-alpha-mediated apoptosis during early DMSO-induced differentiation, a slow increase in resistance to apoptosis mediated through these death receptors occurs during DMSO-induced differentiation, which contrasts with the rapid induction of resistance following treatment with ATRA.

Antibodies, Monoclonal↗
PubMed2000

Synchronous deletion of Mtv-superantigen-reactive thymocytes in the CD3(medium/high) CD4(+)CD8(+) subset.

Multiple model systems have demonstrated that negatively selected thymocytes can be deleted during the immature CD4(+)CD8(+) CD3(low) stage after high affinity interaction of T-cell receptors (TCRs) with antigen:major histocompatibility complex (MHC) complexes. Superantigens (SAGs) derived from endogenous mammary tumour viruses (Mtv) induce negative selection of Mtv-SAG-reactive thymocytes regardless of which peptide antigen is presented by MHC molecules. In this study, the timing of deletion of multiple subsets of Mtv-SAG-reactive CD4(+)CD8(+) thymocytes was investigated by a 4 colour flow cytometry in SJL x CBA/J cross-bred mice. Deletion of V beta 3(+), V beta 5(+), V beta 11(+), and V beta 17(+) Mtv-SAG-reactive thymocytes was found to occur synchronously in the most mature CD3(medium) and early CD3(high) subsets of CD4(+)CD8(+) thymocytes, in contrast with reports showing that the deletion of Mtv-SAG-reactive thymocytes can occur at different stages in particular model systems.

Animals↗
PubMed1999

A mathematical model for bacterial inactivation.

The first order kinetic model, the Buchanan model and Cerf's model, can model a linear survival curve, a survival curve with a shoulder and a survival curve with a tailing, respectively. However, they are not suitable for fitting a sigmoidal survival curve. The three models were integrated into a new model that was capable of fitting the four most commonly observed survival curves: linear curves, curves with a shoulder, curves with a tailing (biphasic curves) and sigmoidal curves. The new model was compared with the Whiting-Buchanan model using the survival curves of Staphylococcus aureus. The goodness-of-fit of the proposed model is practically as good as that of the Whiting-Buchanan model. Compared with the Whiting-Buchanan model, the proposed model has a more mechanistic background. Since for non-linear survival curves, such as biphasic and sigmoidal curves, the t(m-D) value (the time required for an m-log-cycle reduction of microorganisms under a given condition) cannot be estimated accurately by the existing or traditional method, a new method is also proposed to predict accurately the t(m-D) value for non-linear survival curves.

Food Microbiology↗
PubMed1999

Fractionated gamma-irradiation renders tumour cells more responsive to apoptotic signals through CD95.

Signals through the CD95 surface receptor can specifically induce apoptosis. Some tumour cell lines are sensitive to CD95 signals, and insensitive cells can be converted to a sensitive phenotype if given appropriate treatment. To determine whether the apoptotic response of tumour cells to signalling through CD95 might be enhanced by ionizing irradiation, carcinoma cells were treated with either single-dose or fractionated gamma-irradiation. The response to treatment with an agonist anti-CD95 antibody was enhanced by pretreatment with either a single large dose or daily fractionated radiation. Fractionated irradiation induced cumulative and prolonged up-regulation of CD95 expression in cell lines bearing functional p53. Since two of four cell lines exhibiting heightened responsiveness to CD95-mediated signals following fractionated irradiation express mutant p53 and displayed little or no up-regulation of CD95, enhanced responsiveness did not correlate with p53 status and CD95 up-regulation. Continuous inhibition of CD95/CD95-ligand interactions during fractionated irradiation provided no protective effect to cells, arguing that autologous CD95/CD95-ligand interactions did not contribute to the direct lethal effect of irradiation. We conclude that fractionated gamma-irradiation provides an extended period of time when carcinoma cells are more responsive to CD95-mediated signals in vitro.

Apoptosis↗
PubMed1997

Up-regulation of Fas (CD95) in human p53wild-type cancer cells treated with ionizing radiation.

Fas is a cell-surface protein which belongs to the tumor-necrosis-factor-receptor family. Signals through Fas are able to induce apoptosis in sensitive cells, and thus modalities for regulating the level of Fas expression on tumor cells are needed. We have studied cellular responses to gamma irradiation. The level of p53 tumor-suppressor protein was found to be elevated 3 hr after irradiation of p53wild-type MCF-7 breast-carcinoma cells. Interestingly, accumulation of p53 was followed by up-regulation of surface Fas levels between 4 and 8 hr after irradiation. The level of Fas up-regulation was dependent on dose and, whereas elevation in the level of p53 was transient, enhancement of Fas expression was stable. Fas up-regulation occurred coincidentally with induction of G1 cell-cycle arrest, a post-irradiation phenomenon known to be dependent on wild-type-p53 activity. We studied 9 other tumor lines, 2 with wild-type p53, 5 with mutant p53, and 2 expressing no p53. All lines expressing wild-type p53 were found to arrest in G1 and to up-regulate Fas after irradiation. In contrast, all 7 p53null and p53mutant lines failed not only to arrest their cell cycles in G1 phase, but also to up-regulate Fas levels in response to treatment. These findings demonstrate a direct correlation between wild-type-p53 activity and Fas up-regulation after treatment with ionizing radiation, strongly suggesting that post-irradiation Fas up-regulation is dependent on wild-type-p53 activity. Since low doses of radiation were sufficient to modulate Fas expression, up-regulation of the Fas death receptor may have clinical implications following radiotherapy.

Breast Neoplasms↗
PubMed1997

Apoptosis update: to be, or not to be, and how to arrange the latter. Meeting review.

It has become accepted that cell death is an essential mechanism for the maintenance of an animal's health. But how do cells know when they should die, and how do they do it? A recent conference titled "Programmed Cell Death" was held by the American Association For Cancer Research in Bolton Landing, New York state, USA, on October 19-23, 1996, which focused on the signals that push a cell towards its own self-destruction, and also on the biochemical tools used by these cells in making this ultimate sacrifice. The molecular vocabulary of programmed cell death is only recently being deciphered. At the heart of programmed cell death exists at least one intrinsic program for committing cell suicide, although it is still unclear if there is only one [3]. If only one program exists, it probably contains multiple branches, overlapping pathways, and redundant molecular interactions. One item is clear, however: there exist many mechanisms for inducing cells to suicide.

Animals↗
PubMed1994

Entry of CD4-CD8- immature thymocytes into the CD4/CD8 developmental pathway is controlled by tyrosine kinase signals that can be provided through TCR components.

Entry of thymus-migrated precursor cells into the CD4/CD8 developmental pathway was analyzed by using the short-term organ cultures of day 14 fetal mouse thymus lobes. Organ cultures of CD4-CD8- day 14 fetal thymocytes for 1-2 days resulted in the generation of CD4-CD8+ cells, which were mostly immediate precursor cells for CD4+CD8+ thymocytes. This differentiation of CD4-CD8- thymocytes into CD4-CD8+ cells was strongly enhanced by anti-CD3 antibodies. The anti-CD3- induced generation of CD4-CD8+ cells was even found in the immunodeficient scid fetal thymus cultures, and the cell surface CD3 expression on the scid fetal thymocytes could be directly visualized, indicating that functional CD3 could be expressed on CD4-CD8- immature thymocytes without being associated with rearranged TCR components. The anti-CD3-induced generation of CD4-CD8+ cells from scid and normal fetal thymus cultures was inhibited by tyrosine kinase inhibitors Herbimycin A and Tyrphostin. The generation of CD4-CD8+ cells in unstimulated normal fetal thymus cultures was also markedly inhibited by the tyrosine kinase inhibitors but not by Cyclosporin A, suggesting that tyrosine kinase-dependent but calcineurin-independent signals were essential for the differentiation of CD4-CD8- thymocytes. Interestingly, the generation of CD4-CD8+ cells from the normal fetal thymus cultures was modestly but consistently enhanced by anti-TCR beta antibody, suggesting that functional TCR beta in addition to CD3 was expressed on normal CD4-CD8- immature thymocytes. On the other hand, anti-TCR delta antibody did not affect this differentiation in the normal fetal thymus cultures and the generation of CD4-CD8+ cells from the fetal thymus cultures of TCR delta-deficient mice was still enhanced by anti-TCR beta or anti-CD3 antibodies, indicating that either TCR delta chains or TCR delta+ cells were not involved in the control of the differentiation into CD4-CD8+ cells. These results indicate that the entry of CD4-CD8- immature thymocytes into the CD4/CD8 developmental pathway is controlled by tyrosine kinase signals and that these signals can be provided through the engagement of TCR-CD3 complexes with or without TCR beta chains expressed on the CD4-CD8- immature thymocytes.

Animals↗
PubMed1993

T-cell regeneration after bone marrow transplantation: differential CD45 isoform expression on thymic-derived versus thymic-independent progeny.

To study the source of regenerated T cells after bone marrow transplantation (BMT), lethally irradiated thymectomized and thymus-bearing C57BL/6 (Thy 1.2+) mice were injected with syngeneic T-cell depleted bone marrow (TCD BM) cells and graded numbers of congenic B6/Thy 1.1+ lymph node (LN) cells. LN cell expansion was the predominant source for T-cell regeneration in thymectomized hosts but was minimal in thymus-bearing hosts. Analysis of T-cell receptor (TCR) expression on LN progeny showed a diverse V beta repertoire. Therefore, peripheral T-cell progenitors exist within V beta families, but expansion of these progenitors after BMT is downregulated in the presence of a functional thymus. CD4+ cells derived from BM versus LN in thymus-bearing hosts displayed differential CD44 and CD45 isoform expression. BM-derived cells were primarily CD45RB+CD44lo and LN derived cells were nearly exclusively CD45RB- CD44hi. In thymectomized hosts, BM, host, and LN CD4+ progeny were CD45RB- CD44hi. We conclude that T-cell regeneration via peripheral T-cell progenitors predominates in hosts lacking thymic function and gives rise to T cells that display a "memory" phenotype. In contrast, the ability to generate sizable populations of "naive" type T cells after BMT appears limited to the prethymic progenitor pool and could serve as a marker for thymic regenerative capacity.

Animals↗
PubMed1991

Characterization of a new minor lymphocyte stimulatory system. I. Cluster of self antigens recognized by "I-E-reactive" V beta s, V beta 5, V beta 11, and V beta 12 T cell receptors for antigen.

In the mouse, two sets of V beta gene products have been shown to be associated with T cell recognition of endogenous self Ag. One of these is the set of V beta associated with T cell reactivities to stimulatory Mls gene products, Mlsa (V beta 6, V beta 8.1, V beta 9) or Mlsc (V beta 3); another is the set of V beta, such as V beta 5, V beta 11, V beta 12, or V beta 17a, which were originally found to be related to I-E recognition. Although the Mls system has been well characterized, little is known about the nature of the ligands for the second set of V beta. In this work, we describe the evidence that the natural ligand or ligands of V beta 5, V beta 11, and V beta 12 may be novel Mls determinants that are recognized by naive T cells at a high precursor frequency and function as the ligand for clonal deletion of self-reactive T cells by negative selection. However, surprisingly, unlike the conventional Mls system, in which all V beta associated with Mlsa recognition or Mlsc recognition are uniformly deleted in those animals expressing the relevant Mls type, expression of these three V beta segregates independently among strains. Based on these observations, the nature of T cell recognition for this new Mls gene product(s) is discussed.

Animals↗
PubMed1991

Phenotypic characterization of murine tumor-infiltrating T lymphocytes.

Tumor infiltrating lymphocytes (TIL) can be isolated from solid tumors and selectively expanded in long term culture with IL-2 and autologous irradiated tumor. Such long term cultured cells express anti-tumor activity in vitro, mediate the regression of established tumor in murine models of cancer, and have been used for the treatment of cancer in humans. We have characterized freshly isolated mouse Thy-1+ TIL populations, as well as long term TIL cultures, from several different C57BL/6 (B6) tumors. Freshly isolated Thy-1+ TIL include both CD4+ and CD8+ cells, as well as cells bearing NK markers. These cells are predominantly TCR alpha beta+, with a smaller population of TCR gamma delta+ cells. The TCR alpha beta+ cells expressed a broad distribution of V beta phenotypes that was statistically different from that expressed in normal B6 splenic Thy-1+ cells or CD8+ cells, presumably reflecting in vivo selection in the host anti-tumor response. NK cells are present in these tumors at a greater frequency than noted in splenic T cells. Cultured TIL populations rapidly became exclusively Thy-1+/CD8+/CD4- and TCR alpha beta+/gamma delta-. Individual long term TIL populations initially expressed multiple V beta products, but rapidly restricted their V beta expression, frequently expressing a single dominant V beta. The identity of this dominant V beta varied among different TIL lines, but the overall representation of V beta phenotypes in these cultures was statistically different from that seen in Thy-1+ or CD8+ splenocytes. No statistical difference was noted between lines derived from antigenically distinct tumors. The selection of tumor specific T cells in vitro is therefore not reflected in any simple predominance of V beta usage. The complexity of TCR usage in the anti-tumor response may result from the involvement of multiple alpha- and beta-chain regions in the response to a single antigenic determinant, or may reflect multiple antigenic determinants expressed on a single syngeneic tumor.

Animals↗
PubMed1991

Intermittent vs maintenance medication in schizophrenia. Two-year results.

This is a 2-year, double-blind, placebo-controlled study of 101 patients, evaluating the relative efficacy of intermittent medication (given only when the patient shows early signs of relapse) compared with moderate doses of maintenance medication for stable schizophrenic outpatients. Patients were dropped from the study if they had three prodromal episodes in 1 year or if an episode lasted more than 9 weeks. Fourteen percent of patients given maintenance treatment were dropped from the study compared with 46% of intermittently treated patients. Relapse rates were 16% for patients given maintenance treatment and 30% for intermittently treated patients, a nonsignificant difference. Intermittently treated patients were receiving significantly less medication, but there were no differences found in drug side effects. There appears to be no advantage in using the intermittent approach, but we found that the use of an early intervention strategy reduced the relapse and rehospitalization rates for these patients.

Adult↗
PubMed1988

Graft-versus-host-related immunosuppression is induced in mixed chimeras by alloresponses against either host or donor lymphohematopoietic cells.

Graft-vs.-host (GVH)-related immunosuppression has previously been demonstrated in F1 rodent recipients of parental lymphoid cells, and has been thought to result from an immunologic attack of the donor against the host. Since all cells of such F1 recipients could potentially bear target class I MHC alloantigens, it has not previously been possible to determine precisely the target tissues responsible for development of GVH-related effects. In the present studies we have used mixed allogeneic chimeras as recipients of host or donor-strain lymphocyte inocula, and have made the surprising observation that "GVH-induced" immune unresponsiveness does not require GVH reactivity, per se, but develops in the presence of a one-way alloresponse against lymphohematopoietic cells in either the GVH or the host-versus-graft direction.

Animals↗
PubMed1988

Effects of T cell depletion in radiation bone marrow chimeras. II. Requirement for allogeneic T cells in the reconstituting bone marrow inoculum for subsequent resistance to breaking of tolerance.

The ability of normal recipient-type lymphocytes to break tolerance in long-term allogenic radiation chimeras has been investigated. Reconstitution of lethally irradiated mice with a mixture of syngeneic and allogeneic T cell-depleted (TCD) bone marrow (BM) has previously been shown to lead to mixed chimerism and permanent, specific tolerance to donor and host alloantigen (3-5). If allogeneic T cells are not depleted from the reconstituting inoculum, complete allogeneic chimerism results; however, no clinical evidence for GVHD is observed, presumably due to the protective effect provided by syngeneic TCD BM. This model has now been used to study the effects of allogenic T cells administered in reconstituting BM inocula on stability of long-term tolerance. We have attempted to break tolerance in long-term chimeras originally reconstituted with TCD or non-TCD BM by challenging them with inocula containing normal, nontolerant recipient strain lymphocytes. tolerance was broken with remarkable ease in recipients of mixed marrow inocula in which both original BM components were TCD. In contrast, tolerance in chimeras originally reconstituted with non-TCD allogeneic BM was not affected by such inocula. Susceptibility to loss of chimerism and tolerance was not related to initial levels of chimerism per se, but rather to T cell depletion of allogeneic BM, since chimeras reconstituted with TCD allogeneic BM alone (mean level of allogeneic chimerism 98%) were as susceptible as mixed chimeras to the tolerance-breaking effects of such inocula. The possible contribution of GVH reactivity to this resistance was investigated using an F1 into parent strain combination. In these animals, the use of non-TCD F1 BM inocula for reconstitution did not lead to resistance to the tolerance-breaking effects of recipient strain splenocytes. These results suggest that the ability of T cells in allogeneic BM inocula to confer resistance to late graft failure may be related to their graft-vs.-host reactivity, even in situations in which they do not cause clinical GVHD. These findings may have relevance to the mechanism whereby T cell depletion of allogeneic BM leads to an increased incidence of late graft failure in clinical BM transplantation situations.

Animals↗