Apoptosis in the immune system

Factor associated suicide ligand (FasL) participates in the intestinal immune response to muramyl dipeptide challenge in grass carp Ctenopharyngodon idella

Factor associated suicide ligand (FasL) is a multifunctional member of tumor necrosis factor ligand (TNF) superfamily, which exerts vital effects on maintaining homeostasis in the immune system. However, the functions of FasL in intestinal immunity of teleost fish are unknown. This study detected and characterized a fish FasL homolog (defined as CiFasL) in grass carp. The deduced CiFasL protein contained a conserved TNF homology domain (THD) and a representative transmembrane region. Expression profile analysis indicated that CiFasL was widely expressed in the tested tissues and developmental stages of grass carp, and that its mRNA level was significantly up-regulated after being challenged by Aeromonas hydrophila, A. veronii, and muramyl dipeptide (MDP) in vivo. Recombinant CisFasL (rCisFasL) was found to up-regulate pro-apoptotic genes (FasL, FADD, Caspase-8 and Caspase-3) expression in the intestine time-dependently. Moreover, rCisFasL protein effectively suppressed the expression of intestinal inflammatory cytokines (TNF-α, IL-1β, IL-6 and IL-8) and PepT1/NOD2 pathway signaling molecules (PepT1, NOD2, RIP2, p38MAPK and NF-κB) in response to MDP challenge. Finally, CiFasL silencing aggravated the MDP-mediated intestinal inflammation by inhibiting PepT1/NOD2 pathway activation in intestine of grass carp. Collectively, these findings provide the first experimental demonstration that CiFasL plays a negative regulatory role in MDP-induced intestinal inflammation.

Programmed cell death in African trypanosomes

Until recently it had generally been assumed that apoptosis and other forms of programmed cell death evolved during evolution of the metazoans to regulate growth and development in these multicellular organisms. However, recent research is adding strength to the original phenotypic observations described almost a decade ago which indicated that some parasitic protozoa may have evolved a cell death pathway analogous to the process described as apoptosis in metazoa. Here we explore the implications of a programmed cell death pathway in the African tsetse-transmitted trypanosomes.

Inverse relationship between the ratio of ICAM-1 expressing lymphocytes and serum TGF-β1 concentrations in acute rheumatic fever

Autoimmunity in acute rheumatic fever (ARF) is triggered by group-A beta hemolytic streptococci (GAS). Although most of the recent work has focused on the major impact of lymphocytes, the exact immunopathogenesis is still unresolved. Regulation of self-tolerance in response to GAS has been investigated in various animal experiments. This study aimed to associate the ratio of lymphocytes bearing adhesion/costimulatory molecules, Bcl-2/CD95 and serum TGF-beta1 concentrations with clinical stages of ARF. Thirty-five patients were assigned according to the clinical stages. Bcl-2 expression on CD19+ and CD3+ lymphocytes was similar within patient groups and controls. CD62p expression was higher in patients with carditis. The ratio of ICAM-1 bearing lymphocytes was significantly different between patient groups and controls and was increased through acute to remission stages longitudinally. In contrast, a gradual and significant decrease in TGF-beta1 concentrations was observed longitudinally from acute to chronic stages. A positive correlation has been documented between ICAM-1+ lymphocyte ratios and Fas+ cytotoxic T cell ratios supported by a prominent increase in CD95+ T cells. These data draw our attention to the role of ICAM-1, Fas and TGF-beta1 in ARF pathogenesis through the perspective of self-tolerance in a clinical setting.

Programmed cell death in trypanosomatids

It has generally been assumed that apoptosis and other forms of programmed cell death evolved to regulate growth and development in multicellular organisms. However, recent work has shown that some parasitic protozoa have evolved a cell suicide pathway analogous to the process described as apoptosis in metazoa. In this review, Susan Welburn, Marcello Barcinski and Gwyn Williams discuss the possible implications of a cell suicide pathway in the vector-borne Trypanosomatids.

The levels of serum-soluble Fas in patients with rheumatoid arthritis and systemic sclerosis

Different defects in Fas/APO-1 interaction with its ligand or in signaling of apoptosis may contribute to autoimmune disease. The aim of this study was to examine whether elevated serum-soluble Fas (sFas) levels are associated with rheumatoid arthritis (RA) or systemic sclerosis (SSc). sFas level was assayed using a sandwich ELISA in serum from 37 patients with RA, 30 patients with SSc and 20 healthy controls. The RA patients were classified according to disease activity, anatomical joint damage, and the presence of pulmonary involvement. Presence of pulmonary fibrosis, CO diffusion capacity (DLCO) and skin score were determined in patients with SSc. Serum sFas levels were not significantly different between study groups. Serum sFas level in the active RA patients was significantly higher than in the patients with inactive disease (p < 0.05). The untreated active RA patients had significantly higher sFas level than healthy controls (p < 0.05). In RA patients, sFas level was significantly correlated with rheumatoid factor titer (p = 0.01), C-reactive protein (p < 0.05), and erythrocyte sedimentation rate (p < 0.05). The RA patients with severe joint damage had significantly higher sFas level than those with mild joint damage (p < 0.05). The untreated SSc patients had significantly higher sFas levels than the treated SSc patients and healthy controls (p < 0.01). Serum sFas level was not correlated with presence of pulmonary fibrosis, DLCO or skin score. The soluble Fas molecule may provide a useful additional marker for assessment of disease activity and severity in patients with RA.

Apoptosis in the malaria protozoan, Plasmodium berghei: a possible mechanism for limiting intensity of infection in the mosquito

Death by apoptosis regulates cell numbers in metazoan tissues and it is mediated by activation of caspases and results in characteristic morphological and biochemical changes. We report here that the malaria protozoan, Plasmodium berghei, exhibits features typical of metazoan apoptotic cells including condensation of chromatin, fragmentation of the nuclear DNA and movement of phosphatidylserine from the inner to the outer lamellae of the cell membrane. In addition, proteins with caspase-like activity were identified in the cytoplasm of the ookinete suggesting that the cellular mechanism of cell death may be similar to that of multicellular eukaryotes. Our data show that more than 50% of the mosquito midgut stages of the parasite die naturally by apoptosis before gut invasion. Cell death was prevented by a caspase inhibitor, treatment resulting in a doubling of parasite intensity. All these features also occur in vitro. Cell suicide thus plays a major and hitherto unrecognised role in controlling parasite populations and could be a novel target for malaria control strategies.

Inhibitory effects of extracellular Mg2+ on intracellular Ca2+ dynamic changes and thapsigargin-induced apoptosis in human cancer MCF7 cells

The effects of extracellular Mg2+ on both dynamic changes of [Ca2+]i and apoptosis rate were analysed. The consequences of spatial and temporal dynamic changes of intracellular Ca2+ on apoptosis, in thapsigargin- and the calcium-ionophore 4BrA23187-treated MCF7 cells were first determined. Both 4BrA23187 and thapsigargin induced an instant increase of intracellular Ca2+ concentrations ([Ca2+]i) which remained quite elevated (> 150 nM) and lasted for several hours. [Ca2+]i increases were equivalent in the cytosol and the nucleus. The treatments that induced apoptosis in MCF7 cells were systematically associated with high and sustained [Ca2+]i (150 nM) for several hours. The initial [Ca2+]i increase was not determinant in the events triggering apoptosis. Thapsigargin-mediated apoptosis and [Ca2+]i rise were abrogated when cells were pretreated with the calcium chelator BAPTA. The role of the extracellular Mg2+ concentration has been studied in thapsigargin treated cells. High (10 mM) extracellular Mg2+, caused an increase in basal [Mg2+]i from 0.8+/-0.3 to 1.6+/-0.5 mM. As compared to 1.4 mM extracellular Mg2+, 1 microM thapsigargin induces, in 10 mM Mg2+, a reduced percentage from 22 to 11% of fragmented nuclei, a lower sustained [Ca2+]i and a lower Ca2+ influx through the plasma membrane. In conclusion, the cell death induced by thapsigargin was dependent on high and sustained [Ca2+]i which was inhibited by high extracellular and intracellular Mg2+.

Upregulation of Fas-signalling molecules in lung epithelial cells from patients with idiopathic pulmonary fibrosis

The caspase cascade is an executioner of apoptosis, mediated by Fas. Fas-associating protein with death domain (FADD) interacts with Fas and initiates apoptosis through activating caspase-8. It has previously been demonstrated that the Fas-Fas ligand pathway may be involved in the pathophysiology of idiopathic pulmonary fibrosis (IPF). The aim of this study was to investigate Fas-signalling molecules in epithelial cells in IPF. The immunohistochemistry for FADD and caspase-1 and -3 and terminal deoxynucleotidyl transferase-mediated deoxyuridinetriphosphate nick endlabelling (TUNEL) methods were performed in lung tissues from 10 patients with IPF obtained by thoracoscopic biopsy and in seven normal lung parenchyma specimens. The induction of caspases expression and activation by Fas-ligation on lung epithelial cell line A549 was also investigated. The immunoreactivity grade for FADD and caspase-1 and -3, and positive signals for TUNEL were significantly increased in epithelial cells of IPF compared with controls. Fas-ligation induced upregulation of caspase-1 and -3 expression in the nucleus and cytoplasm in A549 cells. Procaspase-1, -3, and -8 were activated in apoptotic cells, but not in viable cells. Although direct measurement of the caspase activity in lung epithelial cells of idiopathic pulmonary fibrosis could not be made, these results suggest that the Fas-signalling pathway is upregulated in lung epithelial cells of idiopathic pulmonary fibrosis.

Derangement of apoptosis-related lymphocyte homeostasis in systemic sclerosis

OBJECTIVES

Both increased and decreased apoptosis may be involved in generating autoimmunity. This study addressed the question of whether apoptosis and apoptosis-regulating proteins are altered in systemic sclerosis (SSc). Patients and methods. Peripheral lymphocytes of 39 SSc patients and 47 healthy control persons were studied for apoptosis, Bcl-2 and Bax levels, expression of Fas (CD95) and activation markers (CD25, HLA-DR) as determined by fluorocytometry. Serum Fas and Fas ligand were measured by ELISA.

RESULTS

SSc lymphocytes (mainly CD4(+)) expressed increased amounts of Bcl-2, while Bax was not elevated. Apoptosis rates of SSc lymphocytes were increased in unsupplemented medium, but returned to normal in the presence of autologous plasma. SSc patients had increased percentages of activated and CD95(+) lymphocytes and elevated soluble Fas and soluble FasL levels in serum. Activating anti-CD95 antibodies further increased the apoptosis rate.

CONCLUSIONS

Increased in vitro apoptosis, elevated lymphocytic Bcl-2 content and the increased number of Fas-positive T cells are not specific for peripheral blood from SSc patients, but indicate deregulation of lymphocyte homeostasis in this disease.

Increased incidence of apoptosis in non-labour-affected cytotrophoblast cells in term fetal membranes overlying the cervix

A regional reduction in the cellularity of the cytotrophoblastic and decidual layers occurs in the fetal membranes overlying the cervix in the lower uterine segment prior to labour. Although the mechanism(s) involved are not known it could result from regionally increased apoptosis, the histological manifestation of programmed cell death, or decreased proliferation. Apoptosis was assessed in regionally sampled fetal membranes from women undergoing elective Caesarean section (n = 14) by the presence of apoptotic bodies by light and electron microscopy. Cell proliferation was assessed by immunocytochemical detection of the protein Ki-67. Apoptotic bodies were identified in all regions of the fetal membrane with the highest incidence found within the cytotrophoblast layer. However, this layer in fetal membranes biopsied over the cervix contained significantly more apoptotic bodies (mean +/- SD 0.085 +/- 0.020%) compared to the layer in fetal membranes obtained from the mid-zone (0.020 +/- 0.008%) apoptotic bodies. Isolated Ki-67 positive cells were detected in the cytotrophoblast layer, but no regional differences in their incidence were seen. Fetal membranes also failed to exhibit significant immunoreactivity for BCL-2 but exhibited strong BAX immunoreactivity within the decidual layer. We conclude that the regionally increased incidence of apoptosis in the cytotrophoblastic layer in the membrane overlying the cervix may account for the reduction in its cellularity but not the relative decrease in the decidual layer. Given the consequence of the loss of local function in degrading uterotonins and stabilizing the fetal membrane, the study of the regulation of apoptosis in these cells may have important implications for fetal membrane rupture and parturition.

Application of a fluorometric assay to detect caspase activity in thymus tissue undergoing apoptosis in vivo

To date, in vivo apoptosis within the thymus has been assessed using morphological criteria and/or detection of a DNA ladder indicative of oligonucleosomal fragmentation of the DNA. Here, we have used a fluorometric method to investigate activation of the caspase protease family in the thymus following in vivo induction of apoptosis by injection of the synthetic glucocorticoid hydrocortisone. Cleavage of DEVD-MCA by caspase-3 and other group II caspases releases free MCA which can be detected fluorimetrically. We demonstrate a time-dependent increase in DEVD-MCA cleavage activity within this tissue indicating the activation of caspase-3 like enzymes. This activity was inhibited by the specific group II caspase inhibitor DEVD-CHO. The interpretation of increased caspase activity was confirmed by immunoblot analysis to reveal cleavage of the caspase-3 substrate, fodrin. In addition, agarose gel electrophoresis of the DNA yielded a ladder pattern, confirming the occurrence of apoptosis. This study demonstrates that DEVD-MCA cleavage activity may be a useful quantitative method for the analysis of apoptosis in thymus tissue. It is a relatively rapid procedure not requiring thymocyte isolation or gel electrophoresis and detects fairly early biochemical changes occurring during apoptosis. In the present study we have used this method to demonstrate the involvement of caspases in thymocyte apoptotic death induced in vivo by glucocorticoids. Thus, measurement of caspase activity in thymus tissue may have applications for studying the in vivo effects of immunotoxicants.

Cutaneous CD30+ lymphoproliferative disorders: expression of bcl-2 and proteins of the tumor necrosis factor receptor superfamily

The spectrum of CD30+ cutaneous lymphoproliferative disorders is characterized by the histology of a high-grade lymphoma but frequent clinical regression of skin lesions in lymphomatoid papulosis (LyP) and occasional regression in CD30+ large cell lymphomas (LCLs). A recent study shows that apoptosis may be a significant mechanism of regression of LyP (Arch Dermatol 133:828-833, 1997). Therefore, we studied expression of proteins that induce apoptosis, including CD27, CD40, CD95, and nerve growth factor receptor (NGF-R), as well as anti-apoptotic protein bcl-2 in skin lesions from 25 patients within the spectrum of CD30+ cutaneous lymphoma. Our results show consistent expression of CD95 (APO-1/Fas), but rare or absent expression of CD27, CD40, and NGF-R on tumor cells from both regressing LyP lesions and nonregressing CD30+ lymphomas. Bcl-2 was expressed at low levels in LyP and at high levels in pleomorphic CD30+ lymphomas. These results indicate that, in addition to CD30, CD95 expression is preferentially expressed at high levels in all cutaneous CD30+ lymphomas and suggest that CD95 may play a role in the regression of CD30+ skin lesions. Expression of bcl-2 appears to protect tumor cells from apoptosis in CD30+ lymphoproliferative disorders.

Nitric oxide synthase expression in macrophages of Histoplasma capsulatum-infected mice is associated with splenocyte apoptosis and unresponsiveness

Splenic macrophages from Histoplasma capsulatum-infected mice express inducible nitric oxide synthase (iNOS), and the iNOS expression correlates with severity of the infection. We examined whether production of NO is responsible for apoptosis and the anti-lymphoproliferative response of splenocytes from mice infected with H. capsulatum. In situ terminal deoxynucleotidyl transferase nick end labeling revealed apoptotic nuclei in cryosections of spleen from infected but not normal mice. Splenocytes of infected mice were unresponsive to stimulation by either concanavalin A or heat-killed H. capsulatum yeast cells. Splenocyte responsiveness was restored by addition to the medium of NG-monomethyl-L-arginine, a known inhibitor of NO production. The proliferative response of splenocytes from infected mice was also restored by depletion of macrophages or by replacement with macrophages from normal mice. In addition, expression of iNOS returned to its basal level when the animals had recovered from infection. These results suggest that suppressor cell activity of macrophages is associated with production of NO, which also appears to be an effector molecule for apoptosis of cultured splenocytes from infected mice.

Bcl-xS and Bad potentiate the death suppressing activities of Bcl-xL, Bcl-2, and A1 in yeast

Members of the Bcl-2 family can be grouped into three classes based upon their effects on cell death. The first class suppresses death and includes Bcl-2. A second group, which includes Bax, is lethal, whereas a third class, including Bcl-xS, potentiates killing, although the members are not lethal by themselves. The proteins in the last class are proposed to exert their activity by binding to anti-apoptotic family members, thereby making the cell more susceptible to killing by another agent. To test this hypothesis, an inducible yeast expression system is reported that permits the functional analysis of three Bcl-2 family members. In yeast, Bax is lethal, and this activity is suppressed by Bcl-xL, Bcl-2, and A1. Co-expression of Bcl-xS did not diminish the ability of any of the anti-apoptotic members to antagonize Bax. Rather, co-expression of Bcl-xS potentiated the anti-death activity of all three proteins. This effect was not the result of changes in either the levels or integrity of Bax or anti-apoptotic proteins. Thus, Bcl-xS can bind to anti-apoptotic family members, but this association does not result in loss of biological activity. Therefore, Bcl-xS may act downstream of Bax and in a pathway that is conserved in yeast.

Cadmium induces apoptosis differentially on immune system cell lines

We investigate the role of cadmium-induced apoptosis in the immune system, studying the apoptotic effect of Cd2+ in three human cell lines, the T-cell line CCRF-CEM, the B-cell line Raji and the lymphoblastoid cell line Molt-3. Cd2+ was found to be dose-dependently toxic for these cell lines, after 18 h incubation. The 50% lethal dose (LD50) for CCRF-CEM was 25 +/- 20 microM, for Molt-3 was 22.5 +/- 2.4 microM, and for Raji was 13.5 +/- 2.2 microM. DNA electrophoresis and quantitation of apoptosis after 18 h incubation with different Cd2+ concentrations was carried out. In CCRF-CEM cells, apoptosis was detected at 10 microM, reaching a maximum at 30 microM. In Molt-3, apoptosis was detected at 10 microM, increased thereafter and a plateau effect was observed from 30 to 50 microM Cd2+. In Raji, apoptosis was detected at 5 microM, while a plateau effect was observed from 20 to 30 microM Cd2+. The above results indicated that Raji cells were more sensitive to cadmium compared to both CCRF-CEM and Molt-3 cells, suggesting a differential Cd2+-induced apoptotic effect, which may disturb the immune system normal growth and development.

Regression of basal cell carcinoma by intralesional interferon-alpha treatment is mediated by CD95 (Apo-1/Fas)-CD95 ligand-induced suicide

Basal cell carcinoma (BCC) is the most common skin cancer in humans, and although metastasis rarely occurs, the tumor cells are nevertheless able to invade and destroy the surrounding tissue. Intralesional injection of IFN-alpha has been found to be highly effective in inducing BCC regression by an unknown mechanism. We show that in untreated patients, BCC cells express CD95 ligand, but not the receptor, which may allow tumor expansion by averting the attack of activated CD95 receptor-positive lymphoid effector cells. The CD95 ligand of BCC cells is functional as CD95-positive cells incubated on BCC cryosections become apoptotic and are lysed. In IFN-alpha-treated patients BCC cells express not only CD95 ligand but also CD95 receptor, whereas the peritumoral infiltrate that mainly consists of CD4+ T cells predominantly contains CD95 receptor and only few CD95 ligand-positive cells. Thus, in treated patients BCC most likely regresses by committing suicide through apoptosis induction via CD95 receptor-CD95 ligand interaction.

Ability of Early Acting Cytokines to Directly Promote Survival and Suppress Apoptosis of Human Primitive CD34+CD38− Bone Marrow Cells With Multilineage Potential at the Single-Cell Level: Key Role of Thrombopoietin

Purified primitive progenitor/stem cells from bone marrow represent likely target populations for ex vivo expansion of stem cells to be used in high-dose chemotherapy or gene therapy. Whereas such primitive progenitor cells require combined stimulation by multiple cytokines for growth, some cytokines selectively promote viability rather than growth when acting individually. We investigated here for the first time the direct effects of cytokines on survival of primitive CD34+CD38− human bone marrow progenitor cells at the single-cell level. Interleukin-3 (IL-3) and the ligands for c-kit (KL) and flt3 (FL) had direct and selective viability-promoting effects on a small fraction of CD34+CD38− but not CD34+CD38+ progenitor cells. Interestingly, the recently cloned thrombopoietin (Tpo), although stimulating little growth, kept most CD34+CD38− progenitors viable after prolonged culture, maintaining twofold and fourfold more progenitors viable than KL and IL-3, respectively. A high fraction of these progenitors had a combined myeloid and erythroid differentiation potential, as well as capacity for prolonged production of progenitor cells under stroma-independent conditions. In addition, Tpo promoted viability of CD34+CD38− long-term culture-initiating cells, further supporting the idea that Tpo promotes viability of primitive human progenitor cells. Finally, Tpo suppressed apoptosis of CD34+CD38− cells in culture. Thus, the present studies show a novel effect of Tpo, implicating a potential role of this cytokine in maintaining quiescent primitive human progenitor cells viable.

Ability of Early Acting Cytokines to Directly Promote Survival and Suppress Apoptosis of Human Primitive CD34+CD38− Bone Marrow Cells With Multilineage Potential at the Single-Cell Level: Key Role of Thrombopoietin

Purified primitive progenitor/stem cells from bone marrow represent likely target populations for ex vivo expansion of stem cells to be used in high-dose chemotherapy or gene therapy. Whereas such primitive progenitor cells require combined stimulation by multiple cytokines for growth, some cytokines selectively promote viability rather than growth when acting individually. We investigated here for the first time the direct effects of cytokines on survival of primitive CD34+CD38− human bone marrow progenitor cells at the single-cell level. Interleukin-3 (IL-3) and the ligands for c-kit (KL) and flt3 (FL) had direct and selective viability-promoting effects on a small fraction of CD34+CD38− but not CD34+CD38+ progenitor cells. Interestingly, the recently cloned thrombopoietin (Tpo), although stimulating little growth, kept most CD34+CD38− progenitors viable after prolonged culture, maintaining twofold and fourfold more progenitors viable than KL and IL-3, respectively. A high fraction of these progenitors had a combined myeloid and erythroid differentiation potential, as well as capacity for prolonged production of progenitor cells under stroma-independent conditions. In addition, Tpo promoted viability of CD34+CD38− long-term culture-initiating cells, further supporting the idea that Tpo promotes viability of primitive human progenitor cells. Finally, Tpo suppressed apoptosis of CD34+CD38− cells in culture. Thus, the present studies show a novel effect of Tpo, implicating a potential role of this cytokine in maintaining quiescent primitive human progenitor cells viable.

DNA fragmentation is not the primary event in glucocorticoid-induced thymocyte death in vivo

Thymocyte death has been recognized as one of the best models for studying apoptosis. Our recent study, however, indicated that most thymocytes die without DNA fragmentation and become terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end-labeling-positive (TUNEL+) only after being phagocytosed by macrophages. In this study, we used histological techniques using the TUNEL method, histochemistry, immunohistochemistry, and transmission electron microscopy as well as flow cytometry to examine in vivo the effect of glucocorticoid (GC), a well-known agent for inducing thymocyte apoptosis in vitro, on thymocyte death to determine whether or not DNA fragmentation was the first event of GC-induced thymocyte death. At 2 h and 4 h after GC injection, a large number of cortical thymocytes were TUNEL+. Most TUNEL+ cells were aggregated to form clusters. Double staining of the section showed that the TUNEL+ thymocytes were phagocytosed by acid phosphatase+ and Mac-2+ macrophages. An ultrastructural study indicated that a far greater number of small pyknotic thymocytes were present in the cortex of the GC-treated thymus than were observed in the control thymus, that all those pyknotic thymocytes were TUNEL-, and moreover, that at the electron microscopic level, TUNEL+ cells were all phagocytosed by macrophages. Flow cytometric analysis did not detect a single TUNEL+ thymocyte even 4 h after the GC treatment, suggesting that virtually no free dead thymocytes were present after DNA fragmentation. These results indicate that, consistent with our previous findings with normal thymocyte death and B cell death in the germinal centers, DNA fragmentation is not involved in the cell death process of the GC-induced rapid thymocyte death in vivo.

Key morphologic changes and DNA strand breaks in human lymphoid cells: discriminating apoptosis from necrosis

Apoptosis is an important form of physiologic cell death displayed by an enormous variety of tissues under divergent conditions. The recent attention toward apoptosis in virtually all aspects of modern biology indicates that rapid and accurate differentiation between apoptosis and necrotic death is of considerable interest. Apoptosis is distinguishable from necrosis on the basis of several criteria. In this study, we undertook to examine the effects of mild hyperthermia (43 degrees C leading to apoptotic death) and severe hyperthermia (50 degrees C leading to necrotic killing) on associated DNA fragmentation. Using laser scanning and fluorescent microscopic evaluation of DNA "comets" in the single cell gel assay, we compared necrotic and apoptotic DNA damage in a variety of human leukemia and lymphoma cell lines at the level of the individual cell. We show that necrotic cells do display detectable DNA damage. We confirm our preliminary report that comet "tail moment" is sufficient to distinguish between necrotic and apoptotic DNA damage, while comet tail length may confuse the two forms. We report that a recovery period is necessary for expression of increasing apoptotic but not necrotic DNA damage. We show that apoptosis increases with prolonged hyperthermia and confirm that the mode of death changes from apoptosis to necrosis with higher heat loads, producing a greater fraction of cells showing damage. In addition, we show that for necrotic cells, DNA tail moment reflects sensitivity to prolonged exposure without a concomitant change in tail length.

One step ahead of the game: viral immunomodulatory molecules

For decades cell biologists have relied on viruses to facilitate the study of complex cellular function. More recently, the tragedy of the AIDS epidemic has focused considerable human and financial resources on both virology and immunology, resulting in the generation of new information relating these disciplines. As the miracle of the mammalian immune system unfolds in the laboratory, the elegance of the mechanisms used by co-evolving viruses to circumvent detection and destruction by the host becomes inescapably obvious. Although many observation of virus-induced phenomena that likely contribute to the virus's escape of immune surveillance are still empirical, many other such phenomena have now been defined at the molecular level and confirmed in in vivo models. Immune modulators encoded within viral genomes include proteins that regulate antigen presentation, function as cytokines or cytokine antagonists, inhibit apoptosis, and interrupt the complement cascade. The identification of such gene products and the elucidation of their function have substantially strengthened our understanding of specific virus-host interactions and, unexpectedly, have contributed to the recognition of potent synergy between viruses, which can result in an unpredictable exacerbation of disease in co-infected individuals. Because many viral immune modulators clearly have host counterparts, viruses provide a valuable method for studying normal immune mechanisms. It is conceivable that an improved understanding of virus-encoded immunomodulators will enhance our ability to design reagents for use in therapeutic intervention in disease and in vaccine development.

Effect of interferon therapy on bone marrow morphology in chronic myeloid leukemia: a cytochemical and immunohistochemical study of trephine biopsies

The effect of interferon (IFN) therapy on bone marrow features in chronic myeloid leukemia (CML) has been studied on successive trephine biopsies (mean interval 13 +/- 8 months) by cytochemical and immunohistochemical methods in combination with morphometry and in comparison with a control group of patients who received monotherapy by busulfan (BU). Following IFN administration (IFN-alpha frequently in combination with IFN-gamma), there was a decrease in neutrophil granulopoiesis accompanied by a significant expansion of erythroid precursors and increased numbers of hemosiderin-laden macrophages. These changes corresponded with the hematologic response in 21 of the 25 patients investigated. Numbers of megakaryocytes and reticulin/collagen fiber density increased during treatment. Most conspicuously, in responding patients atypical micromegakaryocytes, usually characterizing CML, were partially replaced by normal-sized cells of this lineage. These features are in keeping with the assumption of a reappearance of the normal hematopoietic cell clone as the result of IFN therapy, which was not found in the BU-treated control group. On the other hand, a relevant subpopulation of micromegakaryocytes (about 30%) was still maintained. This result probably relates to the failure to improve myelofibrosis more effectively. Analysis of cell proliferation (proliferating cell nuclear antigen-PCNA) and apoptosis (in situ end labeling) revealed a reduction in PCNA labeling and increased numbers of cells undergoing programmed death. Identification of the activated subset of macrophages (alpha-D-galactosyl residues expression) by appropriate lectin histochemistry disclosed an increase in the number of GSA-I binding cells. These findings were exclusively limited to IFN administration and reflect an inhibitory effect of IFN on cell proliferation and stimulation of programmed cell death. The latter phenomenon probably results in increased phagocytosis of clonally transformed myeloid cells by GSA-I-positive (activated) macrophages.

Apoptosis: molecular regulation of cell death

The field of apoptosis is unusual in several respects. Firstly, its general importance has been widely recognised only in the past few years and its surprising significance is still being evaluated in a number of areas of biology. Secondly, although apoptosis is now accepted as a critical element in the repertoire of potential cellular responses, the picture of the intra-cellular processes involved is probably still incomplete, not just in its details, but also in the basic outline of the process as a whole. It is therefore a very interesting and active area at present and is likely to progress rapidly in the next two or three years. This review emphasises recent work on the molecular mechanisms of apoptosis and, in particular, on the intracellular interactions which control this process. This latter area is of crucial importance since dysfunction of the normal control machinery is likely to have serious pathological consequences, probably including oncogenesis, autoimmunity and degenerative disease. The genetic analysis of programmed cell death during the development of the nematode Caenorhabditis elegans has proved very useful in identifying important events in the cell death programme. Recently defined genetic connections between C. elegans cell death and mammalian apoptosis have emphasised the value of this system as a model for cell death in mammalian cells, which, inevitably, is more complex. The signals inducing apoptosis are very varied and the same signals can induce differentiation and proliferation in other situations. However, some pathways appear to be of particular significance in the control of cell death; recent analysis of the apoptosis induced through the cell-surface Fas receptor has been especially important for immunology. Two gene families are dealt with in particular detail because of their likely importance in apoptosis control. These are, first, the genes encoding the interleukin-1 beta-converting enzyme family of cysteine proteases and, second, those related to the proto-oncogene bcl-2. Both of these families are homologous to cell death genes in C. elegans. In mammalian cells the number of members of both families which have been identified is growing rapidly and considerable effort is being directed towards establishing the roles played by each member and the ways in which they interact to regulate apoptosis. Other genes with established roles in the regulation of proliferation and differentiation are also important in controlling apoptosis. Several of these are known proto-oncogenes, e.g. c-myc, or tumour suppressors, e.g. p53, an observation which is consistent with the importance of defective apoptosis in the development of cancer. Viral manipulation of the apoptosis of host cells frequently involves interactions with these cellular proteins. Finally, the biochemistry of the closely controlled cellular self-destruction which ensues when the apoptosis programme has been engaged is also very important. The biochemical changes involved in inducing phagocytosis of the apoptotic cell, for example, allow the process to be neatly integrated within the tissues, under physiological conditions. Molecular defects in this area too may have important pathological consequences.

The Epstein-Barr virus gene BHRF1, a homologue of the cellular oncogene Bcl-2, inhibits apoptosis induced by gamma radiation and chemotherapeutic drugs

Analysis of apoptosis, active and controllable cell death, has demonstrated that the size of a cell population can be regulated by changes in the cell death rate as well as in the rates of proliferation and differentiation. Factors which alter the rate of cell death, such as expression of the proto-oncogene bcl-2, can therefore directly affect the number of cells within a population. Bcl-2 has been shown to suppress apoptosis in response to a variety of stimuli and to act as a complementary survival signal for the random acquisition of other oncogenic mutations, such as deregulated c-myc. The Epstein Barr virus (EBV) gene BHRF1 was the first of a family of bcl-2 homologues now being identified. BHRF1 and bcl-2 share 25% primary amino acid sequence homology. Here we show that gamma radiation and several cytotoxic anticancer agents induce apoptosis in Burkitt's lymphoma (BL) cell lines, as has been found in several other systems. Using gene transfection studies we have also shown that expression of either BHRF1 or bcl-2 in BL cell lines significantly suppresses apoptosis in response to a variety of anticancer treatment. This has confirmed that BHRF1 is functionally homologous to bcl-2 in B-cells and suggests that BHRF1 may act to prevent apoptosis during EBV infection, maximising virus particle production, as has been suggested for other human and insect viral genes. Suppression of chemotherapeutic drug induced cell death by bcl-2 and BHRF1 as demonstrated in this cell system, results in resistance to a variety of different agents and may represent an alternative mechanism by which multidrug resistance arises during chemotherapy.

Activin A-induced apoptosis is suppressed by BCL-2

Activin A, a member of TGF beta superfamily has various activities including induction of apoptosis in mammalian cells. However, it remains unknown how activin A induces cell death. To clarify this, we investigated the expression of BCL-2 and BAX, and the effect of BCL-2 overexpression on activin A-induced apoptosis in B cell hybridoma cell lines. The activin A-sensitive cell lines expressed BAX but not BCL-2 and that activin A did not increase BAX levels. Overexpression of human BCL-2 suppressed activin A-induced apoptosis in these cells. Thus, activin A has been shown to induce apoptosis by a BCL-2-inhibitable mechanism without activating BAX.

Apoptosis: regulation and relevance to toxicology

1. Apoptosis is a remarkably stereotyped morphological event across all tissues in response to a vast array of damaging agents. 2. Our very existence depends upon a willing exchange of old life for new: apoptotic cell death is our guardian and saviour from genetic damage. 3. There is a close link between cell proliferation and apoptosis: When a cell picks up the machinery to proliferate it also acquires an abort pathway--'better dead than wrong'. 4. A wide variety of highly conserved genes have been implicated in triggering apoptosis. 5. The release of DNA loops from the nuclear scaffold is a more crucial intracellular event than DNA 'laddering' in apoptotic cells. 6. The manipulation of apoptotic rates in many of the common diseases in man will be a major therapeutic strategy in the future.

Redox signalling and the control of cell growth and death

Cells maintain a reduced intracellular state in the face of a highly oxidizing extracellular environment. Redox signalling pathways provide a link between external stimuli, through the flavoenzyme-mediated NADPH-dependent reduction of intracellular peptide thiols, such as glutathione, thioredoxin, glutaredoxin, and redox factor-1, to the posttranslational redox modification of certain intracellular proteins. This can affect the proteins' correct folding, assembly into multimeric complexes, enzymatic activity, and their binding as transcription factors to specific DNA sequences. Such changes have been linked to altered cell growth and death.

Inhibition of T lymphocyte activation and apoptotic cell death by cyclosporin A and tacrolimus (FK506). Its relevance to therapy of HIV infection

Theoretically, drugs that inhibit programmed cell death could be used to inhibit the increased apoptotic decay of lymphocyte populations in human immunodeficiency virus (HIV) infection. The concept that immunopathologic processes cause immune suppression provides a further rationale for the use of agents such as cyclosporin A (CsA) or tacrolimus (formerly known as FK506) early in HIV infection to reduce cytotoxic CD8+ T cell-mediated destruction of HIV-infected target cells.

Anal carcinoma--a histological review

Epidemiological evidence of an association between anal carcinoma and symptomatic HIV-related disease suggests that the number of cases of this disease may increase significantly over the next few years. The role of oncogenic HPV types in the pathogenesis of anal carcinoma is substantiated by both epidemiological evidence that tumours are associated with a past history of anal warts and by experimental evidence showing that over 85% of tumours contain HPV 16/18 DNA on PCR. The physical state of the virus in the tumour cell genome is currently under investigation, and cellular interactions between HPV, HIV and other sexually transmitted viruses require further research. Clinical studies have shown that patients with anal warts and those who are HIV positive also show an increased tendency to develop dysplasia within the anal epithelium. However, the malignant potential of dysplasia remains unclear and, it presents problems in management, particularly when multifocal and high grade. Problems in classification of anal carcinomas involve both the site of the tumours and the histological appearance. Despite the difficulties which exist in estimating the origin of a tumour from canal or margin, this information does appear to have clinical significance and should therefore continue to be assessed. Recent morphological and keratin studies have emphasized the heterogeneity of these tumours and have revealed a similar heterogeneous profile of keratin expression in the normal anal epithelium. These results support the body of opinion which suggests that, with the exception of small cell carcinoma and adenocarcinoma, anal carcinomas should be considered as squamous cell tumours which are able to display a range of further morphological characteristics within which ductal differentiation and mucin production appear to carry the worst prognosis. Although there is no universally accepted staging system for anal carcinoma, depth of invasion and extent of spread at the time of diagnosis are the most important clinical factors determining survival and response to therapy. Randomized clinical trials are now under way to compare the outcome of various combinations of radiotherapy and chemotherapy, which have replaced radical surgery as a first line treatment and resulted in a significant decrease in patient morbidity from this disease.