Detection of apoptosis of immature CD4+8+ thymocytes by flow cytometry

Lovastatin inhibits G1/S transition of normal human B-lymphocytes independent of apoptosis

Lovastatin is a potent inhibitor of protein prenylation, and it has been reported to have pleiotropic cellular effects. In the present study we have elucidated the effects of lovastatin on cell cycle progression and apoptosis of normal human B-lymphocytes. When added to B-lymphocytes stimulated with anti-immunoglobulin (anti-mu) and SAC, lovastatin (20 microM) inhibited the cells in the late G1 phase of the cell cycle. Thus, no early activation parameters such as Ca(2+) flux or MYC induction were affected by lovastatin, whereas progression of cells into the second cell cycle as well as DNA synthesis was markedly reduced. We therefore examined the effects of lovastatin on components of the cell cycle machinery responsible for regulating the G1/S transition. We demonstrated that pRB phosphorylation, cdk2 activity needed for this phosphorylation, and the levels of cyclin A, D, and E were inhibited after 24 h of lovastatin treatment, while the levels of p27(Kip1) were elevated. There was no effect on p21(Cip1), cyclin D2, cdk4, and cdk6. These data are consistent with the cells being inhibited by lovastatin between 24 and 32 h into G1. Lovastatin added to stimulated B-cells in late G1 still inhibited the DNA synthesis by 60%, but at this point only minor effects were noted on the cell cycle machinery. We therefore looked for induced apoptosis as an explanation for reduced S-phase entry of the cells. However, despite the ability to enhance the apoptosis of unstimulated B-cells from 48 to 61% as judged by the TUNEL method, lovastatin only marginally affected apoptosis when administered to stimulated B-cells. Thus, it appears that accelerated apoptosis cannot account for the effect of lovastatin on cell cycle progression.

Establishment of a human thymic myoid cell line. Phenotypic and functional characteristics

The subset of myoid cells is a normal component of the thymic stroma. To characterize these cells, we immortalized stromal cells from human thymus by using a plasmid vector encoding the SV40 T oncogene. Among the eight cell lines obtained, one had myoid characteristics including desmin and troponin antigens. This new line was designated MITC (myoid immortalized thymic cells). These cells expressed both the fetal and adult forms of muscle acetylcholine receptor (AChR) at the mRNA level, as well as the myogenic transcription factor MyoD1. alpha-Subunit AChR protein expression was detected by flow cytometry and the AChR was functional in patch-clamp studies. In addition, AChR expression was down-modulated by myasthenia gravis sera or by monoclonal antibody anti-AChR on MITC line similarly to TE671 rhabdomyosarcoma cells, making the MITC line an interesting tool for AChR antigenic modulation experiments. Finally, the MITC line expressed LFA-3, produced several cytokines able to act on T cells, and protected total thymocytes from spontaneous apoptosis in vitro. These results are compatible with a role of thymic myoid cells in some steps of thymocyte development. Therefore MITC line appears to be a useful tool to investigate the physiological role of thymic myoid cells.

Negative Selection of T Cells Occurs Throughout Thymic Development

Thymic positive and negative selections govern the development of a self-MHC-reactive, yet self-tolerant, T cell repertoire. Whether these processes occur independently or sequentially remains controversial. To investigate these issues, we have employed tetrameric peptide-MHC complexes to fluorescently label and monitor polyclonal populations of thymocytes that are specific for moth cytochrome c (MCC)/I-Ek. In TCR β mice tetramer-positive thymocytes are detectable even in the most immature TCR-expressing cells. In the presence of MCC peptide, thymocytes that bind strongly to MCC/I-Ek tetramers are deleted earlier in development and more extensively than cells that bind weakly. This negative selection of the MCC/I-Ek-specific cells occurs continuously throughout development and before any evidence of positive selection. Thus, positive and negative selections are independent processes that need not occur sequentially.

The lack of chromosomal protein Hmg1 does not disrupt cell growth but causes lethal hypoglycaemia in newborn mice

High mobility group 1 (HMG1) protein is an abundant component of all mammalian nuclei, and related proteins exist in all eukaryotes. HMG1 binds linear DNA with moderate affinity and no sequence specificity, but bends the double helix significantly on binding through the minor groove. It binds with high affinity to DNA that is already sharply bent, such as linker DNA at the entry and exit of nucleosomes; thus, it is considered a structural protein of chromatin. HMG1 is also recruited to DNA by interactions with proteins required for basal and regulated transcriptions and V(D)J recombination. Here we generate mice harbouring deleted Hmg1. Hmg1-/- pups are born alive, but die within 24 hours due to hypoglycaemia. Hmg1-deficient mice survive for several days if given glucose parenterally, then waste away with pleiotropic defects (but no alteration in the immune repertoire). Cell lines lacking Hmg1 grow normally, but the activation of gene expression by the glucocorticoid receptor (GR, encoded by the gene Grl1) is impaired. Thus, Hmg1 is not essential for the overall organization of chromatin in the cell nucleus, but is critical for proper transcriptional control by specific transcription factors.

Activation of the cAMP signaling pathway increases apoptosis in human B-precursor cells and is associated with downregulation of Mcl-1 expression

During B- and T-cell ontogeny, extensive apoptosis occurs at distinct stages of development. Agents that increase intracellular levels of cAMP induce apoptosis in thymocytes and mature B cells, prompting us to investigate the role of cAMP signaling in human CD10+ B-precursor cells. We show for the first time that forskolin (which increases intracellular levels of cAMP) increases apoptosis in the CD10- cells in a dose-dependent manner (19%-94% with 0-1,000 microM forskolin after 48 hours incubation, IC50 = 150 microM). High levels of apoptosis were also obtained by exposing the cells to the cAMP analogue 8-chlorophenylthio-cAMP (8-CPT-cAMP). Specific involvement of cAMP-dependent protein kinase (PKA) was demonstrated by the ability of a cAMP antagonist, Rp-isomer of 8-bromo-adenosine- 3', 5'- monophosphorothioate (Rp-8-Br-cAMPS), to reverse the apoptosis increasing effect of the complementary cAMP agonist, Sp-8-Br-cAMPS. Furthermore, we investigated the expression of Bcl-2 family proteins. We found that treatment of the cells with forskolin or 8-CPT-cAMP for 48 hours resulted in a fourfold decline in the expression of Mcl-1 (n = 6, P = 0.002) compared to control cells. The expression of Bcl-2, Bcl-xL, or Bax was largely unaffected. Mature peripheral blood B cells showed a smaller increase in the percentage of apoptotic cells in response to 8-CPT-cAMP (1.3-fold, n = 6, P = 0.045) compared to B-precursor cells, and a smaller decrease in Mcl-1 levels (1.5-fold, n = 4, P = 0.014). Taken together, these findings show that cAMP is important in the regulation of apoptosis in B-progenitor and mature B cells and suggest that cAMP-increased apoptosis could be mediated, at least in part, by a decrease in Mcl-1 levels.

Immune regulatory properties of corticosteroids: prednisone induces apoptosis of human T lymphocytes following the CD3 down-regulation

Glucocorticoid hormones (GCH) induce apoptosis in PHA-primed peripheral blood T lymphocytes (PBL) and down-regulate membrane-bound proteins involved in the immune response. We have analyzed whether GCH are able to affect the expression of the TCR-associated molecules CD3, CD4, and CD8 on PBL-PHA, and whether the modulation of those receptors is related to the GCH-driven apoptosis of the PBL-PHA. Lymphocytes were cultured with PHA or with PHA plus prednisone (PDN) 10(-3), 10(-6), and 10(-9) M. Then expression of CD2, CD3, CD4, CD8, and CD56 antigens was studied by cytofluorimetric assay using propidium iodide (PI) staining and annexin procedure, and by gel electrophoresis of low molecular weight DNA. PDN, at a pharmacological concentration (10(-6) M), was able to inhibit the CD3 expression on T cells. The kinetics of CD3 decrement and of apoptosis show that the down-regulation of CD3 molecules precedes DNA fragmentation and that the cells lacking CD3 are those prone to PDN-induced apoptosis. The inhibition of CD3 is not related to a transcriptional or posttranscriptional phenomenon, because both PBL-PHA and PBL-PHA-PDN expressed the same amount of intracytoplasmic CD3 molecule. PDN also induced a down-regulation of the CD4 and CD8 molecules that resulted sooner in more intense CD8. In vitro PDN is able to induce apoptosis in PBL-PHA through a down-regulation of CD3 molecules.

Functional and phenotypic analysis of thymic B cells: role in the induction of T cell negative selection

The phenotype of mouse thymic B cells and their capacity to induce T cell negative selection in vitro were analyzed. Thymic B cells expressed B cell markers such as IgM, Fc gamma receptor, CD44, heat-stable antigen, LFA-1 and CD40. In addition, they were positive for the activation molecule CD69 and displayed high levels of B7-2. Although thymic B cells expressed CD5 on their surface, no CD5-specific mRNA was detected. Moreover, thymic B cells induced a stronger deletion of TCR-transgenic (TG) thymocytes than splenic B cells, which had low CD69 and B7-2 levels. Interestingly, CD40-activated splenic B cells up-regulated CD69 and B7-2 and acquired a capacity to induce T cell deletion comparable to that of thymic B cells. Moreover, thymic B cells from CD40-deficient mice displayed lower CD69 and B7-2 levels than control thymic B cells, and lower capacity to induce the deletion of TCR TG thymocytes. These results support the hypothesis that CD40-mediated activation of thymic B cells determines a high efficiency of antigen presentation, suggesting that within the thymus B cells may play an important role in the elimination of autoreactive thymocytes.

Apoptotic human lymphocytes have diminished CD4 and CD8 receptor expression

We used quantitative multiparameter flow cytometric assays to simultaneously detect viable, apoptotic, and necrotic human peripheral blood mononuclear cells (PBMC) and immunophenotyped lymphocyte subsets within the PBMC. Apoptosis was induced by a spectrum of treatments, including camptothecin, cisplatin, dexamethasone, hyperthermia, staurosporine, and etoposide in anti-CD3 mAb-stimulated cells and by cyclohexamide in both quiescent and stimulated cells; apoptosis in the latter was augmented by anti-fas mAb. We found that CD4(+) and CD8(+) cells were significantly underrepresented in the apoptotic PBMC and that the percentage of CD4(+) and CD8(+) PBMC each markedly decreased as apoptosis increased. This suggested that surface expression of these receptors was lessened on apoptotic CD4(+) and CD8(+) cells. This was directly confirmed by observation of sorted CD4(+) PBMC. This analysis of a wide variety of apoptotic stimuli demonstrates that diminished CD4 and CD8 surface receptor expression is a common feature of human T lymphocyte apoptosis.

A rapid single-laser flow cytometric method for discrimination of early apoptotic cells in a heterogenous cell population

A recently reported cytometric method described the possibility of discriminating apoptotic from necrotic cells using FITC-labelled annexin V and propidium iodide (PI). Nevertheless, the brightness of PI-staining and its extensive spectral emission overlap with phycoerythrin (PE) does not permit the study of a subset of a heterogenous cell population with single laser instrumentation. The surface staining of a subset with PE in a heterogenous cell population therefore requires another exclusion dye to detect necrotic cells. We used 7-amino-actinomycin D (7-AAD) that can be excited by the 488 nm argon laser line. 7-AAD emits in the far red range of the spectrum and 7-AAD spectral emission can be separated from the emissions of FITC and PE. The fluorescence parameters allow characterization of necrotic (7-AAD+ annexin V-FITC+ cells), apoptotic (7-AAD-annexin V-FITC+ cells) and viable cells (7-AAD- annexin V-FITC- cells) in a subset of PE+ cells. The value of this method was demonstrated by measuring apoptosis and necrosis in a model of HL-60 cells exposed to different inducers of cell death. The method was validated by fluorescent cell sorting in combination with morphologic examination of the sorted cells. The technique we present is particularly valuable in a clinical setting because it enables rapid multiparameter analysis of necrosis and early apoptosis in combination with cell surface phenotyping with a single laser. We present the effects of haemopoietic growth factor deprivation on myeloid progenitor CD34+ cells as an example of its application.

Upregulated Expression of Fibronectin Receptors Underlines the Adhesive Capability of Thymocytes to Thymic Epithelial Cells During the Early Stages of Differentiation: Lessons From Sublethally Irradiated Mice

A 250-cGy whole-body γ-radiation dose was used to induce thymus regression in mice, and to study the expression and function of extracellular matrix (ECM) receptors in distinct thymocyte subsets emerging during repopulation of the organ. The onset of regeneration was detected from day 2 to 3 postirradiation (P-Ir), when a remarkable increase in the absolute counts of CD3−CD25hiCD44+ and CD3−CD25in/hiCD44−cells occurred. Enhanced expression of L-selectin, 4, and 5 integrin chains (L-selhi 4hi5hi) was also exhibited by these cells. This pattern of expression was maintained until the CD4+CD8+ (DP) young stage was achieved. Afterward, there was a general downregulation of these ECM receptors in DP as well as in CD4+ or CD8+ single positive (SP) thymocytes (L-selin 4in5in). In some recently generated SP cells, 4 expression was downregulated before the 5 chain, and L-selectin was upregulated in half of more mature cells. The expression of the 6 integrin chain was downregulated only in maturing CD4+cells. Importantly, the increased expression of L-selectin and 4 and 5 chains in thymocytes was strongly correlated with their adhesiveness to thymic epithelial cells (TEC) in vitro. Blocking experiments with monoclonal antibody or peptides showed the following: (1) that the LDV rather than the REDV cell attachment motif in the IIIC segment of fibronectin is targeted by the 4 integrin during thymocyte/TEC adhesion; (2) that the RGD motif of the 120-kD fragment of fibronectin, a target for 5 integrin, has a secondary role in this adhesion; and (3) that the YIGSR cell attachment motif of the β1 chain of laminin/merosin recognized by a nonintegrin receptor is not used for thymocyte adherence. In conclusion, our results show that an upregulated set of receptors endows CD25+ precursors and cells up to the young DP stage with a high capability of interacting with thymic ECM components.

Upregulated Expression of Fibronectin Receptors Underlines the Adhesive Capability of Thymocytes to Thymic Epithelial Cells During the Early Stages of Differentiation: Lessons From Sublethally Irradiated Mice

A 250-cGy whole-body γ-radiation dose was used to induce thymus regression in mice, and to study the expression and function of extracellular matrix (ECM) receptors in distinct thymocyte subsets emerging during repopulation of the organ. The onset of regeneration was detected from day 2 to 3 postirradiation (P-Ir), when a remarkable increase in the absolute counts of CD3−CD25hiCD44+ and CD3−CD25in/hiCD44−cells occurred. Enhanced expression of L-selectin, 4, and 5 integrin chains (L-selhi 4hi5hi) was also exhibited by these cells. This pattern of expression was maintained until the CD4+CD8+ (DP) young stage was achieved. Afterward, there was a general downregulation of these ECM receptors in DP as well as in CD4+ or CD8+ single positive (SP) thymocytes (L-selin 4in5in). In some recently generated SP cells, 4 expression was downregulated before the 5 chain, and L-selectin was upregulated in half of more mature cells. The expression of the 6 integrin chain was downregulated only in maturing CD4+cells. Importantly, the increased expression of L-selectin and 4 and 5 chains in thymocytes was strongly correlated with their adhesiveness to thymic epithelial cells (TEC) in vitro. Blocking experiments with monoclonal antibody or peptides showed the following: (1) that the LDV rather than the REDV cell attachment motif in the IIIC segment of fibronectin is targeted by the 4 integrin during thymocyte/TEC adhesion; (2) that the RGD motif of the 120-kD fragment of fibronectin, a target for 5 integrin, has a secondary role in this adhesion; and (3) that the YIGSR cell attachment motif of the β1 chain of laminin/merosin recognized by a nonintegrin receptor is not used for thymocyte adherence. In conclusion, our results show that an upregulated set of receptors endows CD25+ precursors and cells up to the young DP stage with a high capability of interacting with thymic ECM components.

Identification of nuclei from apoptotic, necrotic, and viable lymphoid cells by using multiparameter flow cytometry

BACKGROUND

Methods widely used to detect apoptosis do not allow us to easily distinguish between nuclei from viable or necrotic cells. Even if apoptosis and necrosis seem to occur as alternatives at the single cell level, they could be present simultaneously in a cell population much more frequently than expected. For this reason, attention was focused on attempting to recognize, by multiparameter flow cytometry, the characteristics of viable cells and of apoptotic or necrotic dead cells.

METHODS

Apoptosis and necrosis were induced in vitro in murine thymocytes and lymphocytes from adult peripheral blood by using dexamethasone or prostaglandin E2 treatment and heat shock at 60 degrees C or hydrogen peroxide, respectively. Traditional methods, such as DNA gel electrophoresis and propidium iodide staining followed by single-fluorescence analysis or annexin-V-fluorescein isothiocyanate plus propidium iodide staining by using flow cytometry, were compared with a new method. This method consisted of combined light-scatter and red fluorescence analysis by flow cytometry after isolation of nuclei by hypotonic solution as well as high-dose detergent treatment and DNA staining with propidium iodide.

RESULTS

Results showed that, although traditional methods such as DNA-gel electrophoresis and single-parameter fluorescence flow cytometry analysis were unable, as expected, to discriminate among viability, apoptosis, and necrosis, our new method has enabled us to easily identify nuclei from viable, apoptotic, and necrotic cells. Results obtained by using our method were comparable to those obtained by using two-color analysis of cells after propidium iodide/annexin V staining.

CONCLUSIONS

A highly reproducible, inexpensive, rapid, and easily accessible method of analysis has been developed for simultaneously detecting apoptosis and necro sis.

Type I interferons keep activated T cells alive

Antigen injection into animals causes antigen-specific T cells to become activated and, rapidly thereafter, die. This antigen-induced death is inhibited by inflammation. To find out how inflammation has this effect, various cytokines were tested for their ability to interfere with the rapid death of activated T cells. T cells were activated in vivo, isolated, and cultured with the test reagents. Two groups of cytokines were active, members of the interleukin 2 family and the interferons (IFNs) alpha and beta. This activity of IFN-alpha/beta has not been described previously. It was due to direct effects of the IFNs on the T cells and was not mediated by induction of a second cytokine such as interleukin 15. IFN-gamma did not slow the death of activated T cells, and therefore the activity of IFN-alpha/beta was not mediated only by activation of Stat 1, a protein that is affected by both classes of IFN. IFN-alpha/beta did not raise the levels of Bcl-2 or Bcl-XL in T cells. Therefore, their activity was distinct from that of members of the interleukin 2 family or CD28 engagement. Since IFN-alpha/beta are very efficiently generated in response to viral and bacterial infections, these molecules may be among the signals that the immune system uses to prevent activated T cell death during infections.

A necessary role for cell shrinkage in apoptosis

The loss of cell volume is a fundamental and universal characteristic of programmed cell death. However, what was once thought to be a passive, secondary feature of the cell death process has now become an area of research interest. Recent studies have integrated cell volume regulation and the movement of ions with the activation of apoptosis. A dramatic reduction of potassium and sodium concentration has been shown to occur in apoptotic cells that exhibit a shrunken morphology. Furthermore, maintaining the normal physiological intracellular concentration of monovalent ions, particularly potassium, inhibits the activation and activity of the death cascades. Thus, the role ions play during apoptosis is more extensive than just facilitation of the loss of cell volume. In this article, we will review the concepts of cell volume regulation and the loss of volume during apoptosis. Additionally, we will underscore our current understanding of ion movement as it relates to the activation of the cell death process.

Evaluation of GM1 ganglioside-mediated apoptosis in feline thymocytes

Cats with inherited GM1 gangliosidosis (GM1 mutant cats) have premature thymic involution characterized by decreased total thymocytes primarily affecting the CD4+ CD8+ subpopulation. While GM1 mutant cats have increased cell surface GM1 gangliosides, as determined by cholera toxin B binding, on both thymocytes and peripheral lymph node cells only thymocytes show increased apoptosis. To determine if GM1 gangliosides can increase the occurrence of apoptosis in feline thymocytes directly, we added exogenous GM1 ganglioside (GM1) to feline thymocyte primary cultures and compared the results to apoptotic changes seen in untreated cells or in cells treated with dexamethasone (Dex), a known inducer of thymocyte apoptosis in other species. Incorporation of exogenous GM1 into thymocyte cytoplasmic membranes was confirmed by flow cytometric analyses of cholera toxin B labelling. Apoptosis in feline thymocytes was analyzed by electron microscopy, spectrophotometric evaluation of DNA fragmentation, flow cytometric enumeration of apoptotic nuclei, and gel electrophoretic analysis of degraded DNA. Alterations in percentages of thymocyte immunophenotype following GM1 incorporation were determined by flow cytometric analyses of labelled cell surface markers for feline CD4 and CD8. Because in vitro addition of GM1 gangliosides has been reported in other species to decrease surface expression of CD4 on both thymocytes and peripheral lymphocytes, we evaluated GM1-associated down-regulation of CD4 on the surface of feline thymocytes and peripheral lymph node cells by flow cytometry. Additionally, we compared the apoptotic response of the more mature peripheral lymph node cells to the less mature thymocytes. Our results indicate that incorporation of exogenous GM1 into feline thymocyte cell membranes produces a dose-dependent increase of apoptotic cell death. Although, CD4 expression on both feline thymocyte and lymph node cell membranes was abruptly decreased after introducing exogenous GM1, enhanced apoptotic death was observed only in thymocytes, not in lymph node cells at the same GM1 concentration. Enhancement of thymocyte apoptosis appears to be age-related since cells derived from cats <3 months of age were more vulnerable than those from cats >3 months of age.

Role of superoxide in apoptosis induced by growth factor withdrawal

We have examined the role of reactive oxygen species (ROS) in apoptosis induced by growth factor deprivation in primary cultures of mouse proximal tubular (MPT) cells. When confluent monolayers of MPT cells are deprived of all growth factors, the cells die by apoptosis over a 10- and 14-day period. Both epidermal growth factor (EGF) and high-dose insulin directly inhibit apoptosis of MPT cells deprived of growth factors. Growth factor deprivation results in an increase in the cellular levels of superoxide anion while apoptosis of MPT cells induced by growth factor withdrawal is inhibited by a number of antioxidants and scavengers of ROS. Growth factor deprivation also results in activation of caspase activity, which is inhibited by EGF and high-dose insulin as well as by the ROS scavengers and antioxidants that inhibit apoptosis. The cell-permeant caspase inhibitor, z-Val-Ala-Asp-CH2F (zVAD-fmk), prevents the increase in caspase activity and markedly inhibits apoptosis induced by growth factor deprivation. However, zVAD-fmk had no effect on the increased levels of superoxide associated with growth factor deprivation. Thus we provide novel evidence that ROS play an important role in mediating apoptosis associated with growth factor deprivation. ROS appear to act upstream of caspases in the apoptotic pathway. We hypothesize that oxidant stress, induced by growth factor withdrawal, represents a signaling mechanism for the default pathway of apoptosis.

Regulation of anti-DNA B cells in recombination-activating gene-deficient mice

Anti-DNA antibodies are regulated in normal individuals but are found in high concentration in the serum of systemic lupus erythematosus (SLE) patients and the MRL lpr/lpr mouse model of SLE. We previously studied the regulation of anti-double-stranded (ds)DNA and anti-single-stranded (ss)DNA B cells in a nonautoimmune background by generating mice carrying immunoglobulin transgenes coding for anti-DNAs derived from MRL lpr/lpr. Anti-dsDNA B cells undergo receptor editing, but anti-ssDNA B cells seem to be functionally silenced. Here we have investigated how anti-DNA B cells are regulated in recombination- activating gene (RAG)-2-/- mice. In this setting, anti-dsDNA B cells are eliminated by apoptosis in the bone marrow and anti-ssDNA B cells are partially activated.

Measurement of apoptosis

The cell dying by apoptosis undergoes a sequence of morphological, biochemical, and molecular changes which are characteristic, and often unique, to this mode of cell death. Specific features of apoptotic cells resulting from these changes, which serve as markers used to reveal the apoptotic mode of cell death and to quantify the extent of apoptosis in cultures or in tissue, are reviewed. Analysis of these features by flow or image cytometry is the most commonly used approach to detect, quantify, and study various aspects of apoptosis. Flow or laser scanning cytometry also offer all the advantages of rapid, accurate and multiparametric measurements to investigate the biological processes associated with cell death. Numerous methods have been developed to identify apoptotic and necrotic cells, which are widely used in various disciplines, particularly in oncology and immunology. The methods based on changes in cell morphology, plasma membrane molecular structure and transport function, function of cell organelles, DNA stability to denaturation and endonucleolytic DNA degradation are reviewed and their applicability in the research laboratory and in the clinical setting is discussed. The most common pitfalls and improper use of the methodology in analysis of cell death and in data interpretation are also discussed.

Selective apoptosis of neoplastic cells by the HLA-DR-specific monoclonal antibody

The human major histocompatibility complex (MHC) class II molecule-specific monoclonal antibody (mAb) 8D1 can induce apoptosis of tumor cells expressing HLA-DR molecules on their surface. This effect is associated with a cross-linking of HLA-DR, since monovalent Fab fragments of 8D1 cannot mediate cytotoxicity unless they are anchored to a solid support. Anti-neoplastic activity of 8D1 is highly selective, i.e. the mAb affects neither the viability nor the function of non-malignant HLA-DR+ cells. These findings raise the possibility of a selective antibody-based anti-tumor therapy of class II positive blood cell neoplasm.

RAR-, not RXR, ligands inhibit cell activation and prevent apoptosis in B-lymphocytes

We have previously shown that retinoids inhibit activation of human peripheral blood B-lymphocytes. In the present paper, we wished to explore the involvement of nuclear retinoid-specific receptors in this process by using ligands specific for the retinoic acid receptors (RARs) and retinoid X receptors (RXRs). We found that the RAR-specific ligand TTAB reduced anti-IgM-induced B-cell activation in a dose-dependent manner. Thus, at 100 nM of TTAB, DNA synthesis was reduced by approximately 60%. In contrast, the RXR-selective ligand SR11217 had no effect on DNA synthesis. Similar findings were obtained when the expression of the activation antigen CD71 (appears late in G1) was examined. The role of retinoids in apoptosis of resting peripheral blood B-lymphocytes was examined using the same receptor-selective ligands. Again, we found that the RAR-selective ligands were more potent effectors than were the RXR-selective ligands. In spite of the inhibitory effects of retinoids on B-cell proliferation, the same retinoids significantly promoted the survival of the cells. Thus, 10 nM TTAB significantly reduced spontaneous apoptosis of in vitro cultured B-cells at day 3 from 45% to 30%, as determined by vital dye staining and DNA end-labeling. Again, the RXR-specific ligand SR11217 had no effect. Interestingly, we found that CD40 ligand was able to potentiate the retinoid-mediated inhibition of apoptosis. By reverse transcriptase polymerase chain reaction (PCR), we found that peripheral blood B-lymphocytes expressed RARalpha, RARgamma, and RXRalpha, but not RARbeta, RXRbeta, or RXRgamma. Hence, the lack of effect of the RXR-specific ligand SR11217 on growth and apoptosis was not due to absence of RXRs. In conclusion, the ability of retinoids to inhibit growth and prevent apoptosis of normal human B-lymphocytes indicates a dual role of retinoids in this cell compartment, and it appears that both effects of retinoids are mediated via RARs and not RXRs.

Expression of B220 on activated T cell blasts precedes apoptosis

Superantigens are bacterial or viral products that polyclonally activate T cells bearing certain TCR beta chain variable elements. For instance, Vbeta8+ T cells proliferate in response to staphylococcal enterotoxin B (SEB) in vivo and then undergo Fas- and/or TNF-mediated apoptosis. We have recently shown that apoptotic SEB-reactive T cells express the B cell marker B220. Here we report the identification of a novel subset of CD4+ B220+ T cell blasts that are the precursors of these apoptotic cells in SEB-immunized mice. Moreover, we show that the CD4- CD8- B220+ T cells that accumulate in the lymphoid organs of Fas ligand-defective gld mice stably express a form of the B220 molecule which exhibits biochemical similarities to that expressed by activated wild-type T cells, but is distinct from that displayed on the surface of B cells. Surprisingly, we also find a population of CD4+ B220+ pre-apoptotic T cells in FasL-defective gld mice, arguing that these cells can be generated in a Fas-independent fashion. Collectively, our data support a general model whereby upon activation, T cells up-regulate B220 before undergoing apoptosis. When the apoptotic mechanisms are defective, T cells presumably down-regulate their coreceptor molecules but retain expression of B220 as they accumulate in lymphoid organs.

Gangliosides enhance apoptosis of thymocytes

Monosialogangliosides, normal components of cell membranes, regulate cell development and differentiation in several organs. Our previous observation of dramatic premature thymic involution in cats with feline GM1 gangliosidosis, whose thymocytes have abnormally high cell surface gangliosides, suggested that excess GM1 ganglioside (GM1) could modulate thymocyte apoptosis in this disease (Cox et al., "Thymic Alterations in Feline GM1 Gangliosidosis," submitted). In these studies, we added exogenous GM1 to murine primary thymocyte cultures and demonstrated enhanced apoptosis in treated cells by DNA fragmentation, apoptotic body, and electrophoretic analyses. GM1-enhanced apoptosis was blocked by common apoptotic pathway inhibitors including aurintricarboxylic acid (inhibitor of endonuclease activity), actinomycin D (inhibitor of RNA transcription), and cycloheximide (inhibitor of protein synthesis). GM1 treatment primarily affected the immature CD4+ CD8+ subset, as shown by flow cytometric evaluation of fetal thymic organ culture and primary thymocyte cultures. Apoptosis also could be induced by GM2, GM3, and GT1b, whereas asialo-GM1 failed to do so, suggesting that the sialic acid moiety may play an important role in the induction of thymocyte apoptosis.

Apoptosis of CD4+ and CD8+ T cells isolated immediately ex vivo correlates with disease severity in human immunodeficiency virus type 1 infection

Apoptosis of CD4+ and CD8+ T cells has been shown in peripheral blood mononuclear cells (PBMCs) from HIV-infected adults analyzed after overnight culture. Because cell death may be an artifact of in vitro culture, and because there is little information on apoptosis in pediatric HIV disease, we undertook a cross-sectional analysis of apoptosis in PBMCs analyzed immediately ex vivo in HIV-infected children and adults. PBMCs from 22 children, four adolescents, and nine adults and seronegative age-matched control subjects were stained for CD4 and CD8 surface markers. Apoptotic cells were detected in a newly characterized flow cytometric assay by diminished forward and increased side scatter. Children with the most advanced disease had 9.9% (SEM 1.8) apoptotic CD4+ T cells above control, significantly higher than in asymptomatic patients [0.4% (SEM 2.3)], those with mild disease [2.2% (SEM 1.83)], and those with moderate disease [2.5 (SEM 3.6)] (p = 0.015). The percentages of both CD4+ and CD8+ T cell apoptosis were directly related to CD4+ T cell depletion (R2 = 0.23; p = 0.006; n = 32 and R2 = 0.2; p = 0.012; n = 30, respectively). Patients who responded to antiretroviral therapy with the greatest increase in CD4+ T cell percentage had the least CD4+ T cell apoptosis (R2 = 0.15; p = 0.1; n = 19). These findings show that the rate or extent of T cell death by apoptosis percentage of T cell apoptosis is significantly increased in HIV-infected children. The observed correlation of both CD4+ and CD8+ T cell apoptosis with CD4+ T cell depletion suggests that apoptosis plays a role in HIV pathogenesis and may be a useful marker of disease activity.

Lysophosphatidic acid: a novel growth and survival factor for renal proximal tubular cells

Lysophosphatidic acid (LPA) is the smallest and structurally simplest of all glycerophospholipids. LPA is a normal constituent of serum and binds with high affinity to albumin while retaining its biological activity. The effects of LPA are pleiotropic and range from mitogenesis to stress fiber formation. In this report, we demonstrate two novel functions for LPA. LPA acts as a survival factor to inhibit apoptosis of primary cultures of mouse renal proximal tubular (MPT) cells. LPA also acts as a potent mitogen for MPT cells. The ability of LPA to act as both a survival factor and a mitogen is mediated by the lipid kinase phosphatidylinositol 3-kinase (PI3K), since these activities were completely blocked by wortmannin or LY-294002, two structurally dissimilar inhibitors of PI3K. The identification of LPA as a proliferative and anti-apoptotic factor suggests a potential role for this lipid mediator during the injury and/or recovery phases following tubular damage.

Spontaneous programmed cell death (PCD) process of lymphocytes of FIV-infected cats: cellular targets and modulation

Unstimulated lymphocytes from FIV-infected cats undergo spontaneous apoptosis in vitro as indicated by internucleosomal DNA fragmentation and hypodiploid DNA content of nuclei. Unlike what is reported in HIV-infected individuals, we observed that cell death of cat lymphocytes was inhibited by activation. Spontaneous apoptosis was reduced by the addition of cat serum and after activation by phorbol ester (PMA), superantigens (SEB, SEA), and to a lesser extent by mitogens such as concanavalin A and pokeweed mitogen. In contrast, apoptosis of lymphocytes from FIV-infected, but not from control cats was increased in the presence of calcium ionophore (ionomycin). Analysis of the phenotype of cells undergoing apoptosis revealed that cell death is not restricted to a cell subpopulation but involved all lymphocyte subsets. These data suggest that the mature lymphocytes of FIV-infected cats appear programmed to die by apoptosis unless rescued by specific agents, such as protein kinase C activators or mitogens.

The use of Apostain in identifying early apoptosis

Irradiated human peripheral blood lymphoid cells undergo apoptosis and progressively exhibit typical changes in light scatter and plasma membrane integrity that can be easily tracked by flow cytometry. Using this model, we assessed the capacity of a newly developed fluorochrome, Apostain, in identifying early apoptosis in unfixed samples. This probe is a plasma membrane permeant DNA dye that can be conveniently excited at 488 nm and has an emission wavelength > 650 nm. To identify apoptotic cells, Apostain relies on the transient changes of chromatin texture that allow to accommodate more of a DNA dye occurring in early apoptosis. As early as 4 h after irradiation a proportion of cells showed an enhanced Apostain uptake. Consistent with their initial apoptotic nature, these cells had a still integer plasma membrane, as assessed by ethidium bromide, and unaltered light scatter. With time, cells showing the enhanced Apostain uptake started to bind dimly Annexin-V and, later, reduced their forward scatter. After 18 h from irradiation, cells exhibiting a reduced forward scatter exhibited a bright staining with Annexin-V with a concomitant reduction in Apostain uptake, reflecting the gross chromatin disruption characterising the endpoint of apoptosis.

Interleukin-13 in Combination With CD40 Ligand Potently Inhibits Apoptosis in Human B Lymphocytes: Upregulation of Bcl-xL and Mcl-1

Interleukin-13 (IL-13) is a novel T-cell–derived cytokine with IL-4–like effects on many cell types. In human B lymphocytes, IL-13 induces activation, stimulates proliferation in combination with anti-IgM or anti-CD40 antibodies, and directs Ig isotype switching towards IgE and IgG4 isotypes. We show here that IL-13 also regulates human B-cell apoptosis. IL-13 reduced spontaneous apoptosis of peripheral blood B cells in vitro, as shown by measurement of DNA fragmentation using the TUNEL and Nicoletti assays. The inhibition of cell death by IL-13 alone was significant but modest, but was potently enhanced in combination with CD40 ligand (CD40L), a survival stimulus for B cells by itself. Interestingly, IL-13 increased the expression of CD40 on peripheral blood B cells, providing a possible mechanism for the observed synergy. IL-13 alone was a less potent inhibitor of apoptosis than IL-4. Moreover, there was no additive effect of combining IL-4 and IL-13 at supraoptimal concentrations, which is consistent with the notion that the IL-4 and IL-13 binding sites share a common signaling subunit. The combination of IL-13 with CD40L augmented the expression of the Bcl-2 homologues Bcl-xL and Mcl-1, suggesting this as a possible intracellular mechanism of induced survival. By contrast, levels of Bcl-2, and two other Bcl-2 family members, Bax and Bak, remained unaltered. Given the importance of the CD40-CD40L interaction in B-cell responses, these results suggest a significant role of IL-13 in the regulation of B-cell apoptosis.

Susceptibility of different subsets of immature thymocytes to apoptosis

In the present study the susceptibility of different subsets of immature rat thymocytes to undergo apoptosis was examined. Unfractionated rat thymocytes were negatively enriched into immature double positive (CD4+ CD8+), immature single positive (CD4- CD8+ CD3-) and triple negative (CD4- CD8- CD3-) thymocytes. These enriched subsets of immature thymocytes were then exposed to various apoptotic stimuli such as dexamethasone, etoposide and thapsigargin which readily induced apoptosis in unfractionated rat thymocytes. We found that the double positive thymocytes and their precursor cells, i.e. the single positive immature thymocytes, were equally sensitive to apoptosis after treatment with the apoptotic stimuli. In sharp contrast, the early migrants or precursor-containing thymocytes which are triple negative have a lower spontaneous apoptosis rate and were relatively resistant to all the apoptotic stimuli. These findings showed a breakpoint in thymocyte sensitivity to apoptosis which occurs after the onset of CD8 expression, suggesting that susceptibility of thymocytes to apoptosis is developmentally regulated.

Down-regulation of actin genes precedes microfilament network disruption and actin cleavage during p53-mediated apoptosis

Inactivation of Simian Virus 40 large T antigen, in cells immortalized with conditional mutants, leads to activation of p53 and apoptosis. We used the mRNA differential display method to identify genes differentially expressed during this process. We found that steady-state levels of mRNA for cytoplasmic actins decreased early during apoptosis. We also showed that, although the steady-state level of the corresponding proteins is not profoundly affected, they are substrates for an interleukin 1-beta converting enzyme (ICE)-like protease activated during the process. However, only a very small fraction of actin is proteolysed during the early stages of apoptosis. The microfilament network is affected and non polymerized actin accumulates in apoptotic bodies after the decrease of mRNA levels, but before a significant amount of actin is cleaved. This suggests that down-regulation of actin genes may be involved in microfilament rearrangements during p53-mediated apoptosis.

Comparative analysis of flow cytometric methods for apoptosis quantitation in murine thymocytes and human peripheral lymphocytes from controls and HIV-infected persons. Evidence for interference by granulocytes and erythrocytes

The present article reports a multiparametric cytofluorimetric analysis of apoptosis in murine thymocytes and human PBMC from healthy donors or HIV-infected patients. We have evaluated four previously described cytofluorimetric methods of apoptosis quantification, each of them detecting distinct cellular alterations of the apoptosis process. Reduced DNA stainability was detected with the PI assay on nuclei and the AO/EB dual staining method was evaluated on entire and non-fixed cells. DNA strand breaks were detected following in situ nick translation, and alterations in membrane integrity were evaluated following 7-AAD incorporation. When apoptosis was quantified in murine thymocytes under various conditions of induction, the combined analysis of FSC/SSC criteria and 7-AAD or AO/EB staining on the same samples permitted the identification of distinct steps in the apoptosis process. Moreover these four methods proved to be reliable and gave statistically similar results both on murine thymocytes and PBMC from healthy donors. However, in HIV-infected persons, some discordant apoptosis determinations were observed with PI and 7-AAD staining assays. We found that after Ficoll isolation, PBMC from AIDS patients were enriched in erythrocytes and granulocytes. On the one hand, granulocytes were found to be responsible for a poor apoptosis estimation with the PI assay whereas erythrocytes were responsible for an underestimation rate of apoptosis in the 7-AAD assay. To prevent such interference, we propose some modifications which render these methods more suitable for application to PBMC from HIV-infected patients. Taken together these observations indicate that it is essential to assess critically the apoptosis quantification methods with respect to their applicability to complex lymphoid populations such as those from AIDS patients.

Apoptosis induction of ultraviolet light A and photochemotherapy in cutaneous T-cell Lymphoma: relevance to mechanism of therapeutic action

The anti-tumor action of many chemotherapeutic agents has recently been attributed to the induction of apoptosis in the malignant cell population. In this study, we investigated the ability of extracorporeal photopheresis (ExP) and in vitro PUVA (8-methoxy-psoralen + ultraviolet A) therapy to induce apoptosis in peripheral blood mononuclear cells from Sezary syndrome patients and normal controls. Flow cytometric analysis of ExP- or PUVA-treated peripheral blood lymphocytes demonstrated two distinct cell populations within 24 h of treatment. One population was similar to untreated controls with the other exhibiting characteristics of apoptotic cell death, i.e., a loss of cell volume and an accompanying increase in cell density. This latter population was comprised of cells with DNA strand breaks as determined by the Tdt-mediated deoxyuridine triphosphate-biotin nick end labeling assay. Apoptosis was also confirmed morphologically by fluorescent and electron microscopy as well as by demonstration of characteristic DNA strand breaks (laddering) using gel electrophoresis. Apoptosis was not observed with 8-methoxypsoralen (< or = 300 ng per ml) alone; however, ultraviolet A alone at doses > or = 2 J per cm2 induced apoptosis in lymphocytes. Peripheral blood T-cell subpopulations of Sezary syndrome patients, including the malignant clone, were equally susceptible to apoptosis subsequent to either photopheresis or PUVA treatment. In contrast, monocytes (CD14+/CD45+) appear to be resistant to apoptosis induction by ExP or PUVA treatment. Moreover, ExP-treated and untreated monocytes phagocytized apoptotic, but not untreated, peripheral blood mononuclear cells. ExP and PUVA have been shown to be efficacious and well-tolerated therapies in the treatment of dermatologic diseases and transplant rejection. These data suggest that induction of apoptosis may be an important event for therapeutic efficacy.

Calcitonin gene-related peptide enhances apoptosis of thymocytes

The effect of calcitonin gene-related peptide (CGRP), a neuropeptide, on the apoptosis of murine thymocytes was investigated. CGRP enhanced apoptosis of thymocytes beyond the spontaneous level at concentrations of 10(-11) M or higher, and the effect attained a plateau at 10(-9) M, mainly by stimulating cAMP formation. Implication of cAMP-independent mechanism was also suggested in the CGRP-induced apoptosis. Flow cytometric analysis revealed that CGRP caused apoptosis preferentially in CD4+8+ thymocytes. In addition, RNA and protein synthesis was required for apoptosis induced by CGRP.

Combined Hoechst 33342 and merocyanine 540 staining to examine murine B cell cycle stage, viability and apoptosis

A procedure is described for the dual staining of lymphocytes with Hoechst 33342 (Ho342) to examine cell cycle position, and merocyanine 540 (MC540) that allows for the analysis of cells entering the early stages of apoptosis. Ho342 is a DNA specific dye and MC540 detects membrane phospholipid domain changes, some of which are associated with apoptotic cells. Flow analysis of B cells dually stained with Ho342 and MC540 allows for the discrimination of five distinct subpopulations. Two of these subpopulations represent viable, MC540 negative/dull cells with either 2n or 4n DNA. As 2n and 4n DNA B cells become MC540 bright they move into two distinct subpopulations representing cells entering and progressing through the early stages of apoptosis. As the apoptotic, MC540 bright cells move into the latter stages of apoptosis, they localize into a fifth subpopulation displaying reduced staining with Ho342 indicative of late stage apoptotic cells in the process of fragmenting their DNA. This experimental approach enables the characterization of lymphocyte populations for percentages of viable, early apoptotic, and late apoptotic cells. The cells are not fixed during this procedure, and since both dyes are viable dyes there is an additional opportunity to obtain sorted cells from any of the defined subpopulations for reculturing and functional analysis.

Differential effects of staphylococcal toxic shock syndrome toxin-1 on B cell apoptosis

Superantigens, such as toxic shock syndrome toxin 1 (TSST-1), have been implicated in the pathogenesis of several autoimmune and allergic diseases associated with polyclonal B cell activation. In this report, we studied the in vitro effects of TSST-1 on B cell activation. We show herein that TSST-1 produced antagonistic effects on Ig synthesis by peripheral blood mononuclear cells (PBMC) from normal subjects, depending on the concentration used; Ig production was inhibited at 1000 pg/ml (P < 0.01) and enhanced at 1 and 0.01 pg/ml (P < 0.01) of toxin. Cultures of PBMC were then examined for morphologic features and DNA fragmentation characteristic for apoptosis. B cells exhibited a significantly higher (P < 0.01) incidence of apoptosis after stimulation with 1000 pg/ml of TSST-1 compared with 1 or 0.01 pg/ml of toxin or medium alone. Abundant expression of Fas, a cell surface protein that mediates apoptosis, was detected on B cells after stimulation with 1000 pg/ml of TSST-1 and was significantly higher on B cells undergoing apoptosis than on live cells (P = 0.01). Additionally, increased Fas expression and B cell death occurred at concentrations of TSST-1 inducing the production of high amounts of gamma interferon (IFN-gamma), and both events could be blocked by neutralizing anti-IFN-gamma antibody. These findings suggest that high concentrations of TSST-1 can induce IFN-gamma-dependent B cell apoptosis, whereas at low concentrations it stimulates Ig synthesis by PBMC from normal subjects. These findings support the concept that staphylococcal toxins have a role in B cell hyperactivity in autoimmunity and allergy.

Prednisone increases apoptosis in in vitro activated human peripheral blood T lymphocytes

Glucocorticoid hormones (GCH) regulate, through the apoptotic process, the negative selection of immature T cells in the thymus. Because apoptosis seems to occur also in the maintenance of peripheral tolerance, we have investigated whether GCH may induce apoptosis in human mature lymphocytes. Peripheral blood lymphocytes (PBL) or peripheral CD4(+) and CD8(+) T cell subsets were cultured in the presence of phytohaemaglutinin (PHA) or PHA and prednisone (PDN) at 10(-3)-10(-12)M concentrations for 72, 96 and 120h. Cell cycle and membrane antigen expression were evaluated by flow cytometry and DNA degradation was detected by agarose gel electrophoresis. PDN blocks PBL growth in the G1 phase of cell cycle and inhibits both IL-2 receptor (IL-2R) expression and IL-2 secretion. Apoptosis is clearly increased by PDN in PHA-activated human PBL, and the apoptotic effect of PDN is stronger on CD8(+) than on CD4(+) T lymphocytes. All these effects are dose- and time-dependent. The addition of exogenous IL-2 did not rescue lymphocytes from PDN-increased apoptosis. These results show that PDN increases apoptosis in mature activated human peripheral blood lymphocytes, suggesting a possible role of GCH in the maintenance of immune tolerance at post-thymic level.

Flow cytometric ratio analysis of the Hoechst 33342 emission spectrum: multiparametric characterization of apoptotic lymphocytes

The apoptotic response to various stimuli is an important part of immune regulation, and the ability to identify apoptotic lymphocytes within a complex population is a prerequisite to a more detailed understanding of its role in vivo, We described a flow cytometric technique which utilizes viable cells and enables simultaneous identification of apoptotic cells and analyses of immunophenotype, cell cycle progression, membrane integrity and light scatter properties. It is based upon analysis of two regions of the emission spectrum of the DNA-binding vital dye hoechst 33342. We established a precise correlation between the ratio of red to blue fluorescence emission and apoptosis based upon nuclear morphology and the presence of characteristic DNA degradation patterns. In human peripheral blood lymphocytes (PBL) and mouse thymocytes we incorporated light scatter properties, cell cycle stage, relevant cell surface immunophenotypic markers (CD25 or CD4) and CD8) and a marker of plasma membrane integrity (merocyanine 540) to enable multiparametric phenotyping of apoptotic cells. We show that staurosporine-induced apoptosis of ConA-stimulated PBL is not correlated with cell cycle stage but is selective for activated cells since the frequency of large, CD25+ cells is decreased by staurosporine. Dexamethasone and ionomycin differ in their ability to induce apoptosis selectively in murine thymocyte subsets. Dexamethasone kills a broad spectrum of the CD4/8 immunophenotypes with no selectively for cell cycle stage. Ionomycin selectively deplete CD4+8+ cells, especially those in the Go/G1 region of the cell cycle, and spared CD4-8+ cells. This technique is broadly advantageous for in vitro and ex vivo models of apoptosis in that it interrogates individual viable cells and correlates membrane and nuclear apoptotic changes with standard flow cytometric immunophenotyping.

Peripheral T cells undergoing superantigen-induced apoptosis in vivo express B220 and upregulate Fas and Fas ligand

Staphylococcal enterotoxin B (SEB) is a bacterial superantigen (SAg) that predominantly interacts with V(beta)8+ T cells. In vivo treatment of mice with SEB leads to an initial increase in the percentage of V(beta)8+ T cells, followed by a decrease in the numbers of these cells, eventually reaching lower levels than those found before treatment with the SAg. This decrease is due to apoptosis of the SEB-responding cells. In the present study, we use the distinct light scattering characteristics of apoptotic cells to characterize T cells that are being deleted in response to SEB in vivo. We show that dying, SEB-reactive T cells express high levels of Fas and Fas ligand (Fas-L), which are implicated in apoptotic cell death. In addition, the B cell marker B220 is upregulated on apoptotic cells. Moreover, we show that the generation of cells with an apoptotic phenotype is severely impaired in response to SEB in functional Fas-L-deficient mutant gld mice, confirming the role of the Fas pathway in SAg mediated peripheral deletion in vivo.

Thyroid hormone promotes BCL-2 expression and prevents apoptosis of early differentiating cerebellar granule neurons

Programmed cell death is a basic cellular process that has aroused much interest in recent years. Like immune cells, cultures of cerebellar granule neurons are very homogeneous and provide a unique opportunity for quantifying by flow cytometry one form of programmed cell death in the CNS, the apoptosis, and for studying its regulation by neurotrophic factors. We found that thyroid hormone promoted postmitotic survival by preventing the apoptosis of newly formed and early differentiated granule neurons in a dose-dependent manner. This regulation could be through the protein bcl-2, which is known to prevent cell death. This protein was present at all stages of granule neuron differentiation and appeared to be developmentally regulated. It was underexpressed in apoptotic granule neurons. The protein content of the cerebellum in hypothyroid rats was drastically reduced. In contrast, thyroid hormone caused a marked dose-dependent increase in the amounts of this protein in granule neuron cultures. The possibility that thyroid hormone may be directly or indirectly required to promote cell survival is discussed, in terms of the hormone control of the local delivery of neurotrophins, such as NGF and NT-3, as well as the expression of their low affinity receptors, gp75. We suggest that thyroid hormone has a permissive action on the developing CNS.

Use of wild-type p53 to achieve complete treatment sensitization of tumor cells expressing endogenous mutant p53

It is known that transfer of the wild-type p53 gene into p53-negative cells from transgenic mice increases their sensitivity to drug and radiation-induced apoptosis. However, unlike many human tumors, these transgenic cells do not express mutant p53, and it is not known from these earlier studies whether wild-type p53 dominates the effects of mutant p53 with respect to drug and radiation sensitivity. We addressed this question in glioblastoma, a disease characterized by an unusually high level of intrinsic resistance to therapy and poor prognosis: mean survival time from diagnosis is only about 1 yr. We introduced the gene for wild-type p53 into human T98G glioblastoma cells, which express endogenous mutant p53 but not wild-type p53. Stable transfectants that co-expressed mutant and wild-type p53 had enhanced sensitivity to cisplatin and gamma radiation, compared with parental cells, control vector-transduced cells, and transduced cells that had lost expression of wild-type p53. Transient wild-type p53 expression after high-efficiency gene transfer by a p53 adenovirus also sensitized the cells to cisplatin and correlated with the induction of apoptosis. The sensitization effect was also observed in p53 adenovirus-infected H23 small cell lung carcinoma cells, which express endogenous mutant p53. Therefore, wild-type p53 gene transfer has dominant effects over mutant p53 in sensitizing tumor cells to therapy, which supports the potential of p53 gene therapy to enhance the efficacy of traditional therapy.

Modulation of drug-induced apoptosis in a human B-lymphoma cell line (HT58)

The cytotoxic effect of etoposide (ETO), a topoisomerase II inhibitor, and staurosporine (STA), a non-selective protein kinase inhibitor, were studied on a human lymphoma cell line of B-cell origin (HT58). Apoptosis, induced dose dependently by both drugs, was accompanied with nucleosomal DNA fragmentation detected by flow cytometry. On the other hand, induction of cell death failed using phorbol ester (PMA), anti-IgM antibody (a-IgM) or dexamethasone (DEX), although, all of these agents arrested the cells in G1. Furthermore, PMA pretreatment retarded ETO-induced apoptosis, but enhanced STA cytotoxicity. DEX increased the sensitivity of cells to STA, but did not to ETO. Activity of STA or DEX was only slightly modified by a-IgM pretreatment. The results support the possibility that different apoptotic pathways exist in HT58 cells. The differences in pathways could be manifested either in the signaling routes, or in the molecular effectors of apoptosis.

Effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin on anti-CD3-induced changes in T-cell subsets and cytokine production

The influence of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure on the cytokine-dependent toxicity syndrome induced by the injection of 145-2C11 (anti-CD3), a hamster monoclonal antibody to the CD3 epsilon portion of the murine T-cell receptor, was studied. This syndrome has been attributed to the transient release of several cytokines including TNF-alpha, IFN-gamma, IL-2, IL-3, IL-6, and GM-CSF. Exposure of C57Bl/6 mice to TCDD (15 micrograms/kg) 2 days prior to anti-CD3 injection exacerbated anti-CD3-induced toxicity as evidenced by significantly enhanced and prolonged body weight loss and lymphoid tissue atrophy. Unexpectedly, TCDD exposure did not alter plasma levels of TNF or IL-2 at any time after anti-CD3 injection. However, plasma IFN-gamma was significantly reduced at 24 h and plasma IL-6 levels were elevated 48 h after anti-CD3 injection in TCDD-treated mice. In addition, TCDD exposure resulted in elevated levels of plasma GM-CSF at 24 and 48 h. Since the body weight of TCDD-treated mice diverged from vehicle-treated mice at 48 h, it suggests that the increased IL-6 and GM-CSF may have contributed to the prolonged loss of body weight. The ability of spleen cells from vehicle- and TCDD-treated mice to produce cytokines was evaluated in vitro at various times after anti-CD3 injection. TCDD treatment resulted in reduced IL-2 and GM-CSF production at 90 min but increased GM-CSF production at 48 h post-anti-CD3 injection. In contrast, TCDD exposure did not influence cytokine production by spleen cells from mice injected with a control IgG and activated in vitro with anti-CD3. Flow cytometric analysis showed that the percentage of CD4+ cells in the draining lymph nodes from TCDD-treated mice was reduced 48-144 h post-anti-CD3 injection. In contrast, the percentage of CD8+ cells was not affected by TCDD exposure. A high fraction of lymph node cells (LNC) from TCDD-treated animals showed decreased forward angle light scatter and increased 90 degrees light scatter following anti-CD3 injection, which is a pattern characteristic of cells undergoing apoptosis. In contrast, few LNC from vehicle-treated animals showed this light scatter profile. These data suggest that TCDD may be targeting T-helper cells during activation resulting in activation-driven cell death (apoptosis) rather than differentiation.

Kinetics of plasma membrane and mitochondrial alterations in cells undergoing apoptosis

Programmed cell death or apoptosis is characterized by typical morphological alterations. By transmission electron microscopy, apoptotic cells are identified by condensation of the chromatin in tight apposition to the nuclear envelope, alteration of the nuclear envelope and fragmentation of the nucleus, whereas integrity of the plasma membrane and organelles is preserved. Conversely cells undergoing necrosis display an early desintegration of cytoplasmic membrane and swelling of mitochondria. In this study we assessed by flow cytometry the sequential alterations of forward angle light scatter, 90 degrees light scatter, and fluorescence associated with fluorescein diacetate, rhodamine 123, and propidium iodide in two human B cell lines undergoing apoptosis induced by the topoisomerase II inhibitor VP-16. The kinetics of these modifications were compared to those of cells undergoing necrosis induced by sodium azide. At the same time intervals, cells were examined by transmission electron microscopy and by UV microscopy after staining with Hoechst 33342. We report that sequential changes in light scatters and fluorescein diacetate are similar in cells undergoing apoptosis or necrosis, whereas apoptosis is characterized by a slightly delayed decrease of mitochondrial activity as assessed by rhodamine 123 staining. Surprisingly a part of cells undergoing apoptosis displayed an early uptake of propidium iodide followed by a condensation and then a fragmentation of their nuclei. It is concluded that uptake of propidium iodide is a very early marker of cell death which does not discriminate between necrosis and apoptosis. Along with biochemical criteria, nuclear morphology revealed by staining with Hoechst 33342 would seem to be of the most simple and most discriminative assay of apoptosis.

Nucleic acid dyes for detection of apoptosis in live cells

Apoptotic thymocytes were found to be much dimmer than normal thymocytes when stained with several nucleic acid dyes. These dyes provide a quick and simple assay for apoptosis which works for live cells and does not require a UV laser. The collection of dyes giving this staining pattern includes reagents suitable for use in either the FL1, FL2, or FL3 channel of a standard FACScan. Cells identified by these reagents were identical to apoptotic thymocytes defined by several widely used criteria: (i) rapid uptake of Hoechst 33342 but exclusion of propidium iodide, (ii) merocyanin 540 bright, and (iii) sub-G1 DNA content when permeabilized in a buffer that elutes fragmented DNA. In addition, L3T4/Thy-1 dim thymocytes were included in the dyc dim population. The standard Hoechst 33342 and merocyanin 540 assays were not able to separate the normal and apoptotic populations in HL-60 cells treated with camptothecin. However, the dyes SYTO-16 and LDS-751 both gave adequate differentiation of apoptotic from nonapoptotic cells in this model system. Some of these dyes also emit very little in other fluorescence channels of the flow cytometer and can be used in multicolor assays on cytometers equipped with only a single argon-ion laser.

Increased T-cell apoptosis and terminal B-cell differentiation induced by inactivation of the Ets-1 proto-oncogene

The Ets-1 proto-oncogene is a member of a transcription factor family characterized by homology to the v-ets oncogene. In adult mice, Ets-1 is expressed predominantly in lymphoid cells where it has been implicated in regulating transcription of lymphocyte-specific genes. Following T-cell activation, the specific DNA binding activity of Ets-1 is inactivated by transient phosphorylation, suggesting a function in the transition from the resting to activated state. Ets-1 has also been suggested to cooperate with the AP-1 transcription factor complex to mediate cellular growth factor responses. Here we show, by using RAG-2-deficient blastocyst complementation, that Ets-1 deficiency has dramatic, but different, effects on development and function of T- and B-lineage cells. Ets-1-deficient T cells were present in reduced numbers and were highly susceptible to cell death in vitro. In contrast, Ets-1-deficient B cells were present in normal numbers but a large proportion were IgM plasma cells. Our data demonstrate that Ets-1 is essential for maintenance of the normal pool of resting T- and B-lineage cells.

Alterations in mitochondrial structure and function are early events of dexamethasone-induced thymocyte apoptosis

In this paper we used a multiparametric approach to analyze extensively the events occurring during apoptotic cell death of thymocytes, and furthermore, we asked whether alterations in mitochondrial structure and function are occurring in early stages of apoptosis. A multiparametric quantitative analysis was performed on normal or apoptotic thymocytes emerging from a few-hour culture performed in culture medium or in the presence of dexamethasone. Simultaneous detection of light scattering properties, integrity of plasma membrane (trypan blue exclusion), chromatin condensation (AO/EB staining of entire cells or PI staining of nuclei), and DNA fragmentation (in situ nick-translation in apoptotic cells) allowed a precise analysis of the preapoptotic and apoptotic stages. Moreover a thorough study of mitochondrial transmembrane potential (delta psi m) assessed following in a time course study the uptake by apoptotic cells of the cationic lipophilic dye DiOC6(3) or the J-aggregate-forming cation JC-1, indicates that a drop in delta psi m occurs very early in thymocyte apoptosis, before DNA fragmentation. This is associated with alteration in mitochondrial structure assessed by cytofluorimetric study of NAO uptake in apoptotic cells. Finally these dramatic alterations in mitochondrial structure and function occurring in early stages of apoptosis were confirmed by confocal and electron microscopy analysis.

A new flow cytometric method for discrimination of apoptotic cells and detection of their cell cycle specificity through staining of F-actin and DNA

Drug-initiated apoptosis of human leukemia HL-60, THP-1, and U-937 cells was studied via multiparameter flow cytometry and cell sorting. A new flow cytometric method that allows both identification and quantitation of apoptotic cells and estimation of their cell cycle specificity is presented. The method is based on paraformaldehyde fixation followed by staining of F-actin and DNA with fluorescein isothiocyanate (FITC)-phalloidin and propidium iodide (PI), respectively. Bivariate green fluorescence (F-actin) vs. side scatterplots of HL-60 cells treated with 10 microM etoposide for 4 h showed two cell populations, one with high green fluorescence and low side scatter and one with low green fluorescence and high side scatter. Sorting revealed cells with intact nuclei in the high green fluorescence/low side scatter population and cells with fragmented nuclei in the low green fluorescence/high side scatter population, demonstrating that the cells in the latter population were apoptotic. Exposure of HL-60 cells to 10 microM etoposide for 4 h resulted in S-phase selective apoptosis, whereas 5 micrograms/ml cycloheximide initiated apoptosis mainly in G0/G1-phase and S-phase cells. The apoptotic response of HL-60 cells to 20 GY gamma-irradiation was selective for S-phase and G2 + M-phase cells. The present method offers the opportunity to estimate the cell cycle distributions of both the apoptotic and the nonapoptotic cell populations, which is especially valuable when apoptosis occurs in association with cell cycle perturbations. A similar shift from one to two cell populations in green fluorescence vs. side scatter-plots, similar to that observed for HL-60 cells, was observed in the THP-1 and U-937 cell lines secondary to etoposide treatment.

Apoptosis in chicken embryos induced by the infectious bursal disease virus

Fifteen-day-old fertile eggs (specific pathogen-free) were inoculated with the infectious bursal disease virus (IBDV) by the allantoic route and were opened and examined 2, 4 or 6 days later. The bursas of Fabricius (BFs) were collected and processed for DNA extraction, flow cytometry, and light and electron microscopy. Cellular DNA was subjected to electrophoresis on 1.5% agarose gel and stained with ethidium bromide. Intense internucleosomal DNA fragmentation was detected in IBDV-infected bursas. Cytograms from cell suspensions derived from infected BFs displayed an increased population of cells with either high density and small size (apoptotic cells) or small size and high uptake of ethidium bromide (necrotic cells). Light and electron microscopical examination of the IBDV-infected BFs revealed death of lymphoid cells without surrounding inflammatory reaction, but with condensation of nuclear chromatin, crescent formation, and nuclear and cellular fragmentation. These data indicated that infection of chicken embryos with IBDV induced apoptosis in bursal lymphoid cells.

Detection and quantification of live, apoptotic, and necrotic human peripheral lymphocytes by single-laser flow cytometry

Regulation of peripheral lymphocyte number involves a poorly understood balance between cell renewal and loss. Disrupting this balance leads to a large number of disease states. Methods which allow qualitative and quantitative measurements of cell viability are increasingly valuable to studies directed at revealing the mechanisms underlying apoptotic and necrotic cell death. Here, we have characterized a method using single-laser flow cytometry that differentiates and quantifies the relative number of live, apoptotic, and late-stage apoptotic and necrotic peripheral lymphocytes. Following in vitro gamma irradiation and staining with acridine orange in combination with ethidium bromide, three distinct populations were seen by bivariate analysis of green versus red fluorescence. The identity of each distinct fluorescent population (whether live, apoptotic, or necrotic) was determined by sorting and examination of cellular morphology by electron microscopy. This flow cytometric method is directly compared with the techniques of trypan blue exclusion and DNA fragmentation to quantify cell death following exposure to various doses of in vitro gamma irradiation and postirradiation incubation times. We extend our findings to illustrate the utility of this method beyond analyzing radiation-induced apoptotic peripheral blood mononuclear cells (PBMC); similar fluorescent patterns are shown for radiation- and corticosteroid-treated murine thymocytes, activated human PBMC, and PBMC from human immunodeficiency virus-infected individuals. Our results demonstrate that dual-parameter flow cytometric analysis of acridine orange-ethidium bromide-stained lymphocytes is overall a superior method with increased sensitivity, greater accuracy, and decreased subjectivity in comparison with the other methods tested. By using standard laser and filter settings commonly available to flow cytometric laboratories, this method allows rapid measurement of a large number of cells from a heterogeneous sample.