Pharmacological inhibition of programmed lymphocyte death

Hypogammaglobulinemia in pediatric kidney transplant recipients

Infections remain the most common cause of hospitalization after kidney transplantation, contributing to significant post-transplant morbidity and mortality. There is a growing body of literature that suggests that immunoglobulins may have a significant protective role against post-transplant infections, although the literature remains sparse, inconsistent, and not well publicized among pediatric nephrologists. Of great concern are data indicating a high prevalence of immunoglobulin abnormalities following transplantation and a possible link between these abnormalities and poorer outcomes. Our educational review focuses on the epidemiology and risk factors for the development of immunoglobulin abnormalities after kidney transplantation, the outcomes in patients with low immunoglobulin levels, and studies evaluating possible interventions to correct these immunoglobulin abnormalities.

Does increasing immunoglobulin levels impact survival in solid organ transplant recipients with hypogammaglobulinemia?

BACKGROUND

Severe hypogammaglobulinemia (IgG < 400 mg/dL) has adverse impact on mortality during the first year post-transplantation. The aim of the study was to determine whether increasing IgG levels to ≥400 mg/dL improved outcomes.

METHODS

Kaplan-Meier analyses were performed to estimate survival, log-rank test to compare survival distributions between groups, and Fisher's exact test to determine the association between hypogammaglobulinemia and rejection or graft loss.

RESULTS

Thirty-seven solid organ transplant (SOT) recipients were included. Hypogammaglobulinemia was diagnosed at median of 5.6 months (range: 0-291.8 months) post-transplantation. Types of transplants: liver-small bowel (17); liver-small bowel-kidney (2); liver (5); small bowel (4); liver-kidney (1); kidney/kidney-pancreas (3); heart (3); heart-kidney (1); and heart-lung (1). The three-yr survival after the diagnosis of hypogammaglobulinemia was 49.5% (95% CI: 32.2-64.6%). Patients were dichotomized based upon IgG level at last follow-up: IgG ≥ 400 mg/dL (23 patients) and IgG < 400 mg/dL (14 patients). There was no evidence of a difference in survival (p = 0.44), rejection rate (p = 0.44), and graft loss censored for death (p = 0.99) at one yr between these two groups. There was no difference in survival between patients receiving or not immunoglobulin (p = 0.99) or cytomegalovirus hyperimmunoglobulin (p = 0.14).

CONCLUSION

Severe hypogammaglobulinemia after SOT is associated with high mortality rates, but increasing IgG levels to ≥400 mg/dL did not seem to translate in better patient or graft survival in this cohort.

What is the impact of hypogammaglobulinemia on the rate of infections and survival in solid organ transplantation? A meta-analysis

Hypogammaglobulinemia has been described after solid organ transplantation and has been associated with increased risk of infections. The aim of the study was to evaluate the rate of severe hypogammaglobulinemia and its relationship with the risk of infections during the first year posttransplantation. Eighteen studies (1756 patients) that evaluated hypogammaglobulinemia and posttransplant infections were included. The data were pooled using the DerSimonian and Laird random-effects model. Q statistic method was used to assess statistical heterogeneity. Within the first year posttransplantation, the rate of hypogammaglobulinemia (IgG < 700 mg/dL) was 45% (95% CI: 0.34-0.55; Q = 330.1, p < 0.0001), the rate of mild hypogammaglobulinemia (IgG = 400-700 mg/dL) was 39% (95% CI: 0.22-0.56; Q = 210.09, p < 0.0001) and the rate of severe hypogammaglobulinemia (IgG < 400 mg/dL) was 15% (95% CI: 0.08-0.22; Q = 50.15, p < 0.0001). The rate of hypogammaglobulinemia by allograft type: heart 49% (21%-78%; Q = 131.16, p < 0.0001); kidney 40% (30%-49%; Q = 24.55, p = 0.0002); liver 16% (0.001%-35%; Q = 14.31, p = 0.0002) and lung 63% (53%-74%; Q = 6.85, p = 0.08). The odds of respiratory infection (OR = 4.83; 95% CI: 1.66-14.05; p = 0.004; I(2) = 0%), CMV (OR = 2.40; 95% CI: 1.16-4.96; p = 0.02; I(2) = 26.66%), Aspergillus (OR = 8.19; 95% CI: 2.38-28.21; p = 0.0009; I(2) = 17.02%) and other fungal infections (OR = 3.69; 95% CI: 1.11-12.33; p = 0.03; I(2) = 0%) for patients with IgG < 400 mg/dL were higher than the odds for patients with IgG > 400 mg/dL. The odds for 1-year all-cause mortality for severe hypogammaglobulinemia group was 21.91 times higher than those for IgG > 400 mg/dL group (95% CI: 2.49-192.55; p = 0.005; I(2) = 0%). Severe hypogammaglobulinemia during the first year posttransplantation significantly increased the risk of CMV, fungal and respiratory infections, and was associated with higher 1-year all-cause mortality.

Hypogammaglobulinemia and infection risk in solid organ transplant recipients

PURPOSE OF REVIEW

Hypogammaglobulinemia may develop as a result of a number of immune deficiency syndromes that can be devastating. This review article explores the risk of infection associated with hypogammaglobulinemia in solid organ transplantation and discusses therapeutic strategies to alleviate such a risk.

RECENT FINDINGS

Hypogammaglobulinemia is associated with increased risk of opportunistic infections, particularly during the 6-month posttransplant period when viral infections are most prevalent. The preemptive use of immunoglobulin replacement results in a significant reduction of opportunistic infections in patients with moderate and severe hypogammaglobulinemia.

SUMMARY

Monitoring immunoglobulin G levels may aid in clinical management of solid organ transplant recipients. The preemptive use of immunoglobulin replacement may serve as a new strategy for managing solid organ transplant recipients with hypogammaglobulinemia.

BCL-XL regulates TNF-alpha-mediated cell death independently of NF-kappaB, FLIP and IAPs

Upon activation, tumor necrosis factor alpha (TNF-alpha) receptor can engage apoptotic or survival pathways. Inhibition of macromolecular synthesis is known to sensitize cells to TNF-alpha-induced cell death. It is believed that this sensitization is due to the transcriptional blockade of genes regulated by NF-kappaB. Nevertheless, such evidence has remained elusive in the nervous system. Here, we show that TNF-alpha cannot normally induce apoptosis in PC12 cells or cortical neurons. However, cells treated with Actinomycin D (ActD) become susceptible to TNF-alpha-induced cell death through the activation of caspase-8, generation of tBid and activation of caspase-9 and -3. Analysis of several proteins involved in TNF-alpha receptor signaling showed no significant downregulation of NF-kappaB target genes, such as IAPs or FLIP, under such conditions. However, Bcl-x(L) protein levels, but not those of Bcl-2, Bax and Bak, are reduced by ActD or TNF-alpha/ActD treatments. Moreover, Bcl-x(L) overexpression fully protects cells against TNF-alpha/ActD-induced cell death. When endogenous levels of Bcl-x(L) are specifically downregulated by lentiviral-based RNAi, cells no longer require ActD to be sensitive to TNF-alpha-triggered apoptosis. Furthermore, Bcl-x(L) downregulation does not affect TNF-alpha-mediated NF-kappaB activation. Altogether, our results demonstrate that Bcl-x(L), and not Bcl-2, FLIP or IAPs, acts as the endogenous regulator of neuronal resistance/sensitivity to TNF-alpha-induced apoptosis in an NF-kappaB-independent manner.

Biological therapy in the management of recent-onset Crohn's disease: why, when and how?

Crohn's disease is a chronic inflammatory bowel disease that may involve any part of the gastrointestinal tract. Conventional therapy consists of corticosteroids, azathioprine or methotrexate, but the clinical management of Crohn's disease is significantly hampered by adverse effects. With the introduction of biological agents (such as infliximab), the goals of therapy have advanced, including induction of remission with bowel healing as well as reduction in the rate of complications, surgeries and mortality. Current therapy for moderate to severe Crohn's disease is based on 'step-up' algorithms, which initiate treatment with corticosteroids followed by immunomodulatory agents, and defer therapy with biological agents until patients become refractory to conventional therapeutics. Recently, it has been shown that induction therapy with infliximab and azathioprine in recent-onset Crohn's disease (i.e. 'top-down' approach) is superior to current step-up algorithms to induce clinical remission. The underlying molecular mechanisms responsible for these differences in clinical outcome remain to be defined. Experimental studies have demonstrated that corticosteroids are able to induce impaired apoptosis of immune cells, including T cells and dendritic cells, resulting in loss of tolerance and subsequent autoimmunity. Further research will have to determine whether corticosteroid therapy augments the mechanism of loss of tolerance in Crohn's disease, which could complicate future clinical management.

Inhibition of death-receptor mediated apoptosis in human adipocytes by the insulin-like growth factor I (IGF-I)/IGF-I receptor autocrine circuit

Adipose tissue mass is reflected by the volume and the number of adipocytes and is subject to homeostatic regulation involving cell death mechanisms. In this study we have investigated the mechanisms of apoptosis in human preadipocytes and adipocytes that may play a role in the regulation of adipose tissue mass. We found that death receptors (CD95, TNF-related apoptosis-inducing ligand receptors 1 and 2, and TNF receptor 1) are expressed in human fat cells and that apoptosis can be induced by specific ligands. Sensitivity to apoptosis could be stimulated by an inhibitor of biosynthesis. In addition, inhibition of auto-/paracrine action of IGF-I dramatically sensitizes human adipocytes for death ligand-induced apoptosis. Phosphoinositide 3-kinase and, to a weaker extent, p38 MAPK are involved in IGF-I-mediated survival. IGF-I protects human fat cells from apoptosis by maintaining the expression of antiapoptotic proteins, Bcl-x(L) and Fas-associated death domain-like IL-1-converting enzyme inhibitory protein. In conclusion, we identified mechanisms of apoptosis induction in human fat cells. We furthermore demonstrate that human fat cells protect themselves from apoptosis by IGF-I in an auto-/paracrine manner.

The CB1/VR1 agonist arvanil induces apoptosis through an FADD/caspase-8-dependent pathway

1. Arvanil (N-arachidonoylvanillamine), a nonpungent capsaicin-anandamide hybrid molecule, has been shown to exert biological activities through VR1/CB1-dependent and -independent pathways. We have found that arvanil induces dose-dependent apoptosis in the lymphoid Jurkat T-cell line, but not in peripheral blood T lymphocytes. Apoptosis was assessed by DNA fragmentation through cell cycle and TUNEL analyses. 2. Arvanil-induced apoptosis was initiated independently of any specific phase of the cell cycle, and it was inhibited by specific caspase-8 and -3 inhibitors and by the activation of protein kinase C. In addition, kinetic analysis by Western blots and fluorimetry showed that arvanil rapidly activates caspase-8, -7 and -3, and induces PARP cleavage. 3. The arvanil-mediated apoptotic response was greatly inhibited in the Jurkat-FADDDN cell line, which constitutively expresses a negative dominant form of the adapter molecule Fas-associated death domain (FADD). This cell line does not undergo apoptosis in response to Fas (CD95) stimulation. 4. Using a cytofluorimetric approach, we have found that arvanil induced the production of reactive oxygen species (ROS) in both Jurkat-FADD+ and Jurkat-FADDDN cell lines. However, ROS accumulation only plays a residual role in arvanil-induced apoptosis. 5. These results demonstrate that arvanil-induced apoptosis is essentially mediated through a mechanism that is typical of type II cells, and implicates the death-inducing signalling complex and the activation of caspase-8. This arvanil-apoptotic activity is TRPV1 and CB-independent, and can be of importance for the development of potential anti-inflammatory and antitumoral drugs.

Synergism between rViscumin and cisplatin is not dependent on ERCC-1 expression

Interactions between recombinant mistletoe lectin (rViscumin) and anticancer drugs were investigated in vitro. rViscumin enhanced the cytotoxic effects of vincristine, mafosfamide, idarubicin and cisplatin in the human leukemia cell lines K562 and KG1a. In human marrow progenitor cells, rViscumin inhibited colony formation and did not exert any protective activity against cisplatin-induced inhibition of clonogenicity. Quantitative real-time reverse transcription polymerase chain reaction analysis revealed that cisplatin treatment of K562 cells resulted in a 1.9-fold increase in mRNA expression of the nucleotide excision repair gene ERCC-1. This upregulation was not prevented when cells were post-incubated with rViscumin. Our study provides evidence that rViscumin is capable of enhancing cytotoxicity of anticancer agents in vitro. This synergism appears to be independent of transcriptional activity of DNA repair relevant genes.

Alternative splicing variants of c-FLIP transduce the differential signal through the Raf or TRAF2 in TNF-induced cell proliferation

In human cancer, despite apoptotic activity, death-ligand promotes the cell cycle progression under certain conditions. In this study, we demonstrated that TNF-alpha-induced cell proliferation is achieved through the c-FLIP. In addition, alternative splicing variants (c-FLIP(L) and c-FLIP(S)) contribute the TNF-alpha-induced cell cycle promotion through distinct pathways. The long form of c-FLIP (c-FLIP(L)) activates the Raf, which enhance the activity of Erk and PI3K, whereas short form (c-FLIPS) are activated by c-jun-N-terminal Kinase (JNK) through the TNF receptor-associated factor (TRAF) 2. Since, however, recruitment of c-FLIP(L) into FADD is later than that of c-FLIP(S), the activation of PI3K and Erk show the late response to activation of JNK. We also show that each c-FLIP variant is regulated by a distinct molecular mechanism at the transcriptional level; c-FLIP(L) is induced by Erk, whereas c-FLIP(S), through the JNK activation, is like an autocrine regulatory loop. Therefore, the induction of c-FLIP(L) in response to TNF-alpha is achieved in a more delayed manner than that of c-FLIP(S). Our present study also implies that other alternative splicing variants perform differential roles in spite of the same pathway.

Reduced expression of flice-inhibitory protein (FLIP) and NFkappaB is associated with death receptor-induced cell death in human aortic endothelial cells (HAECs)

We investigated the effects of TNF receptor 1 (TNFR1) and 2 (TNFR2) modulation on the death of human aortic endothelial cells (HAECs) resistant to TNF-alpha-induced cell death. Alteration of the transcription of anti-apoptotic proteins, including inhibitor of apoptosis protein 1, 2 (cIAP1, 2), TNF receptor-associated factor 1 (TRAF1), nuclear factor kappa B1 protein (NFkappaB1), and FLICE-inhibitory protein (FLIP) was assessed by real-time reverse transcriptase-polymerase chain reaction (RT-PCR). TNF-alpha (200 ng/ml) or actinomycin D (ActD) (5 ng/ml) did not kill cells, while 5 ng/ml of TNF-alpha and 5 ng/ml of ActD increased expression of Fas (CD95) and FasL (CD95L), and 45% of cells died. TNFR2 blockade suppressed NFkappaB1 and FLIP expression and increased cell death. TNFR1 blockade enhanced FLIP expression and decreased cell death. Cells insensitive to TNF-alpha may respond to TNF-alpha through TNFR that induces transcription of NFkappaB1 and FLIP. Down-regulation of these proteins may facilitate death of cells insensitive to TNF-alpha-induced cell death.

Hypogammaglobulinemia following cardiac transplantation: a link between rejection and infection

BACKGROUND

Hypogammaglobulinemia (HGG) has been reported after solid organ transplantation and is noted to confer an increased risk of opportunistic infections.

OBJECTIVES

In this study, we sought to assess the relationship between severe HGG to infection and acute cellular rejection following heart transplantation.

METHODS

Between February 1997 and January 1999, we retrospectively analyzed the clinical outcome of 111 consecutive heart transplant recipients who had immunoglobulin G (IgG) level monitoring at 3 and 6 months post-transplant and when clinically indicated.

RESULTS

Eighty-one percent of patients were males, mean age 54 +/- 13 years, and the mean follow-up period was 13.8 +/- 5.7 months. Patients had normal IgG levels prior to transplant (mean 1137 +/- 353 mg/dl). Ten percent (11 of 111) of patients developed severe HGG (IgG < 350 mg/dl) post-transplant. The average time to the lowest IgG level was 196 +/- 125 days. Patients with severe HGG were at increased risk of opportunistic infections compared to patients with IgG > 350 mg/dl (55% [6 of 11] vs. 5% [5 of 100], odds ratio = 22.8, p < 0.001). Compared to patients with no rejection, patients who experienced three or more episodes of rejection had lower mean IgG (580 +/- 309 vs. 751 +/- 325, p = 0.05), and increased incidence of severe HGG (33% [7 of 21] vs. 2.8% [1 of 35], p = 0.001). The incidence of rejection episodes per patient at 1 year was higher in patients with severe HGG compared to patients with IgG >350 (2.82 +/- 1.66 vs. 1.36 +/- 1.45 episodes/patient, p = 0.02). The use of parenteral steroid pulse therapy was associated with an increased risk of severe HGG (odds ratio = 15.28, p < 0.001).

CONCLUSIONS

Severe HGG after cardiac transplantation may develop as a consequence of intensification of immunosuppressive therapy for rejection and hence, confers an increased risk of opportunistic infections. IgG level may be a useful marker for identifying patients at high risk.

Modulation of pro- and anti-apoptotic genes in lymphocytes exposed to bone cements

The ability of bone cements to modify the apoptotic program in activated immune cells and the mechanisms by which they act were evaluated. Mononuclear cells were collected from healthy individuals, cultured for 4 and 24 h with phytohemoagglutinina-P and cement extracts and then tested to assess: (a) cell viability; (b) early apoptotic events, by Annexin V/propidium iodide staining; and (c) the expression of pro- (p53, c-myc, ICE) and anti-apoptotic (bcl-2) genes. After 4 h three cements were able to increase significantly the percentage of apoptotic cells, while after 24 h no differences were found. The proportion of dead cells was not significantly changed at either culture time. The simultaneous expression of both pro-apoptotic (ICE, c-myc, p53) and antiapoptotic genes (bcl-2) was investigated only with regard to the materials which induced significant changes in apoptosis: two cements induced the p53 expression, while the third down-regulated bcl-2. As apoptosis regulates the balance of immune response, the authors recommend that the interaction between materials and immune cells should be assessed, so that the use of pro-apoptotic materials may be avoided in patients with immune defects.

Prevention of nitrogen mustard-induced apoptosis in normal and transformed lymphocytes by ebselen

The alkylating agent, nitrogen mustard (HN2), is thought to cause apoptosis through production of free oxygen radicals. To explore the mechanism of HN2-induced apoptosis, we utilized ebselen, a selenoorganic compound with potent antioxidant activity. We examined whether ebselen would inhibit apoptosis in BALB/c mouse spleen lymphocytes and human MOLT-4 leukemia cells treated with HN2 (2.5 microM) in vitro. Non-toxic concentrations (<50 microM) of ebselen were found to prevent HN2-induced apoptosis of murine lymphocytes in a dose-dependent manner, as measured by cell viability, hypodiploid DNA formation, and phosphatidylserine externalization. However, ebselen was ineffective at preventing spontaneous apoptosis in these cells, pointing to the selectivity of its action. Furthermore, pretreatment with ebselen at 1-10 microM for 72 hr protected MOLT-4 cells from HN2-induced apoptosis and maintained cell viability and proliferation as monitored by the above-mentioned parameters. This was accompanied by the preservation of mitochondrial transmembrane potential and elevated glutathione levels and by a blockage of caspase-3 and -9 activation. In vivo, ebselen also had a marked protective effect against spleen weight loss associated with lymphocyte apoptosis in mice treated by HN2. Therefore, ebselen provides an efficient protection against HN2-induced cell death in normal and tumoral lymphocytes and might prove useful as an antidote against alkylating agents.

Apoptosis inhibitory effect of the isothiourea compound, tri-(2-thioureido-S-ethyl)-amine

Sulfhydril compounds, some of them with immunomodulatory activity have also been shown to modulate the induction of apoptosis. This study was performed to assess the possible apoptosis inhibitory effect of the immunomodulatory compound tri-(2-thioureido-S-ethyl)-amine (K-1) in U-937 and HL-60 leukaemia cell lines as model systems. Treatment of U-937 and HL-60 cells with K-1 inhibited etoposide (ETO)-induced apoptosis in both cell lines in a dose-dependent manner, IC(50)=200 microg/ml. The results indicate that inhibition of ETO-induced apoptosis occurs downstream of ETO-mediated cleavable complex formation but early in, or at the level of the mitochondria events of the apoptotic pathway. Further, like other isothioureas, K-1 proved to be a potent inhibitor of nitric oxide synthase. This raises the possibility that where the activation of nitric oxide synthase is involved in apoptosis induction, K-1 might also be effective. These findings suggest that K-1 may serve as a potent inhibitor of apoptosis initiated by ETO or nitric oxide.

Evidence that apoptosis of activated T cells occurs in spontaneous tolerance of liver allografts and is blocked by manipulations which break tolerance

BACKGROUND

Fully allogeneic liver grafts from piebald virol glaxo to dark agouti rats are spontaneously tolerated, whereas kidney transplants between these strains are rejected. Liver tolerance is broken by donor irradiation or peritransplant corticosteroid treatment of recipient rats, both of which interfere with the activation of recipient cells.

METHODS

In this study we used a combination of immunohistochemical staining, reverse transcription-polymerase chain reaction, and terminal deoxynucleotide transferase-mediated dUTP nick end labeling and Annexin-V apoptosis assays to compare donor cell migration, cytokine profiles, and leukocyte apoptosis in grafts and lymphoid organs from tolerant liver and rejecting kidney recipients. We then examined the effect on apoptosis of treatments which abrogate liver tolerance.

RESULTS

Liver transplantation in this tolerant strain combination is accompanied by rapid migration of many passenger leukocytes to the recipient spleen and lymph node, concurrent with a marked but transient increase in the amount of mRNA for the cytokines interleukin-2 and interferon-gamma. Apoptotic cells appear promptly in the spleen, their numbers reaching a peak 2 days earlier than has been previously shown for the graft infiltrate. Both CD4+ and CD8+ T cells undergo apoptosis and apoptotic cells are most concentrated among CD25+ T cells. In contrast, renal transplant rejection is associated with limited donor cell migration to lymphoid tissues and significantly less up-regulation of interleukin-2 and interferon-gamma in the spleen. Few apoptotic cells are detected in spleen or graft infiltrate during rejection, whereas apoptotic renal tubular and glomerular cells are found from day 5. Either recipient steroid treatment or donor irradiation significantly reduced the number of apoptotic cells in liver graft infiltrates and recipient spleen.

CONCLUSIONS

Taken together, these findings suggest that a mechanism akin to activation-induced cell death, with apoptosis of alloreactive recipient cells may be responsible for the induction of spontaneous liver transplant tolerance.

Multiparametric assessment of bursal lymphocyte apoptosis

When bursal lymphocytes are placed in cell culture, they undergo an apoptotic form of cell death that can be inhibited by phorbol esters and protein synthesis inhibitors. The goal of the current study was to evaluate the time course of this process and the inhibition of this process using several different assays to detect apoptosis: (1) terminal deoxynucleotidyl transferase-mediated nick end labeling (TUNEL) of lymphocyte DNA strand breaks with dUTP-FITC; (2) propidium iodide (PI) staining of lymphocyte chromatin; (3) chloromethyl-x-rosamine (CMX-Ros) binding to lymphocyte mitochondria; (4) merocyanine-540 (MC-540) binding to the lymphocyte plasma membrane; (5) flow cytometric analysis of light scatter from lymphocytes; (6) analysis of genomic DNA from lymphocytes by agarose gel electrophoresis; and (7) cellular caspase-3 activity of lymphocytes. When bursal lymphocyte apoptosis was analyzed as a function of time, or inhibited by phorbol esters or cycloheximide, all of these assays corroborated the apoptotic process. However, treatment of lymphocytes with a cytotoxic level of the proteinase inhibitor, n-ethylmaleimide (NEM) resulted in a putative, necrotic form of cell death that revealed discrepancies among the various assays in the detection of apoptotic cells. Specifically, the CMX-Ros and MC-540 assays erroneously detected the necrotic cells as being apoptotic cells following NEM treatment. These findings indicate the need for additional assays and appropriate treatment controls to verify the apoptotic process when using the CMX-Ros and MC-540 assays.

Imuthiol inhibits the etoposide-induced apoptosis in HL-60 cells

Imuthiol (sodium-diethyl-dithiocarbamate, DTC) has been proven to possess immunomodulatory properties, this effect, however, varies in different model systems. This study was performed to assess the possible effect of imuthiol on etoposide-induced apoptosis in the human promyelocytic leukemia cell line, HL-60. In vitro pre-treatment with imuthiol at concentrations between 50 and 100 microM significantly inhibited etoposide-induced apoptosis of HL-60 cells, the inhibition appeared to be dose dependent. This effect may be associated with the immunomodulatory activity of imuthiol.

Pyruvate prevents hydrogen peroxide-induced apoptosis

Studies were carried out to investigate the protective effects of pyruvate, a key glycolytic intermediate and alpha-keto-monocarboxylate, against oxidative stress-induced apoptosis. Oxidative stress was induced by treating mouse thymocytes with 25 microM hydrogen peroxide for 15 min at 37 degrees C under 5% CO2 in air. Pre- and post-treatment of cells with 10 mM pyruvate inhibited morphological changes, internucleosomal DNA fragmentation, and translocation of phosphatidylserine to the plasma membrane surface, which are characteristic features of apoptosis. L-lactate (10 mM) and acetate (10 mM) were ineffective in inhibiting apoptosis and appeared to be toxic to the cells under similar conditions. The results suggest that pyruvate has therapeutic potential for use in the treatment of oxidative stress-induced disorders associated with increased apoptosis.

CD95 (Fas/APO-1) induces an increased phosphatidylserine synthesis that precedes its externalization during programmed cell death

CD95 (Fas, APO-1)-induced programmed cell death (apoptosis) in T cell lines is accompanied by a rapid flip-flop of phosphatidylserine (PtdSer). Externalization of this phospholipid has been previously recognized as one of the early detectable events of cells undergoing apoptosis. We show here that CD95 induces a rapid (detectable at time < 15 min), strong (2.5-fold) but transitory neosynthesis of PtdSer in the Jurkat cell line that precedes its externalization. PtdSer decarboxylation, a mitochondrial specific process, was strongly inhibited by CD95 suggesting that changes in mitochondrial activity take place in the early events of Fas-induced apoptosis and participate in the increased PtdSer synthesis observed. In cells undergoing apoptosis, newly synthesized PtdSer first exposed at the cell surface was in part shed with CD95-induced plasma membrane vesicles, a process that likely explains the transitory effect observed.

Kinetics of intragraft cytokine expression, cellular infiltration, and cell death in rejection of renal allografts compared with acceptance of liver allografts in a rat model: early activation and apoptosis is associated with liver graft acceptance

BACKGROUND

Liver transplants in the rat strain combination PVG-to-Dark Agouti are spontaneously tolerated, whereas kidney transplants in the same strain combination are rejected in 7-9 days.

METHODS

To identify organ-specific differences that might yield further information about the mechanism of tolerance induction in this strain combination, liver or kidney grafts, spleen, and draining lymph nodes were harvested at days 1, 3, 5, and 7, and examined by immunohistochemistry, terminal deoxynucleotide transferase-mediated dUTP nick end labeling assay, and reverse transcriptase-polymerase chain reaction for interferon-gamma, interleukin (IL)-2, IL-4, and IL-10.

RESULTS

Renal allograft rejection was associated with the progressive development of an intense mononuclear cell infiltrate. Markers of lymphocyte activation and cytokine up-regulation appeared from day 3, and many apoptotic parenchymal cells were noted on days 5-7, at the peak of rejection. Conversely, liver allograft tolerance was associated with more rapid infiltration by activated T cells and earlier increases in cytokine expression, but with a more limited degree of cellular infiltration. Concurrent with the early activation, high levels of apoptosis were found in areas of leukocyte infiltrate, paralleling the disappearance of activated T cells from the graft between days 3 and 5.

CONCLUSIONS

Apoptosis of infiltrating leukocytes in liver allografts may represent an important process in the induction of spontaneous liver transplant tolerance and may underlie the abortive nature of the effector response observed within tolerated livers. In contrast, activated cells in renal allografts in the same strain combination survive and proliferate, express high levels of cytokines, and are efficient in bringing about graft destruction.

Inhibition by dexamethasone of transforming growth factor beta1-induced apoptosis in rat hepatoma cells: a possible association with Bcl-xL induction

The authors previously reported that transforming growth factor beta1 (TGF-beta1) induces apoptosis in McA-RH7777 (7777) and McA-RH8994 (8994) rat hepatoma cell lines. Although these cell lines exhibit different responses to glucocorticoid treatment in various cellular functions and gene expression, dexamethasone (DEX) inhibited spontaneous and TGF-beta1-induced apoptosis in both. Analysis of analogous hormones in TGF-beta1-induced apoptosis in 8994 cells suggested the inhibitory effect to be glucocorticoid-specific. By cell-cycle analysis and DNA fragmentation assay using sodium butyrate, a G1-arrest-inducing reagent, regulation of apoptosis by TGF-beta1 and DEX was shown independent of the cell cycle. For elucidation of the mechanisms of anti-apoptotic action of DEX, the effects of various chemical probes on this apoptosis model were examined, and various reagents known to exhibit anti-apoptotic activity in other experimental systems were found to be ineffective. The effect of TGF-beta1 and DEX on cellular amounts of several apoptosis-related proteins, members of the Bcl-2 family, Bcl-2, Bcl-xL, Bcl-xS, Bad, and Bax was also examined. DEX drastically increased Bcl-xL in both cell lines irrespective of the presence of TGF-beta1. Bcl-2 and Bcl-xS proteins were not detected, and Bax and Bad content did not change by treatment with TGF-beta1 or DEX. Progesterone (Prog), a partial antagonist for glucocorticoid receptor, inhibited the effects of DEX on apoptosis and Bcl-xL expression in 8994 cells. Thus, Bcl-xL induction by DEX would appear closely associated with its inhibitory effect on spontaneous and TGF-beta1-induced apoptosis in the hepatoma cell lines.

A neuronal C5a receptor and an associated apoptotic signal transduction pathway

1. We report the first experimental evidence of a neuronal C5a receptor (nC5aR) in human cells of neuronal origin. Expression of nC5aR mRNA was demonstrated by the reverse transcriptase-polymerase chain reaction (RT-PCR) in TGW human neuroblastoma cells. 2. Expression of a functional C5aR was supported by the finding that C5a evoked a transient increase in the intracellular calcium level as measured by flow cytometry (FACS). 3. To analyse the function of the nC5aR, an antisense peptide fragment of the C5aR was used. Previous data showed that a C5aR fragment (a peptide termed PR226) has C5aR agonist and antagonist effects in U-937 cells depending on the concentration of the peptide. We found that a multiple antigenic peptide (MAP) form of the same peptide (termed PR226-MAP) induced rapid elevation of nuclear c-fos immunoreactivity and resulted in DNA fragmentation, a characteristic sign of apoptosis, in TGW cells. 4. Early electrophysiological events characteristic of apoptosis were also detected: intermittent calcium current pulses were recorded within 1-2 min of peptide administration. C5a pretreatment delayed the onset of this calcium influx. 5. We also demonstrated that the apoptotic pathway is linked to nC5aR via pertussis toxin-sensitive G-proteins. 6. Although the function of C5a and its receptor on neurons is unknown, these results suggest that an abnormal activation of this signal transduction pathway can result in apoptosis and, subsequently, in neurodegeneration.

[Significance of apoptotic processes in radiotherapy. I]

According to a considerable amount of publications apoptosis plays an important role for radio- and chemotherapy. The most important results related to this issue will be described in 2 independent articles, covering the following topics: Part I: I. definition, morphology, biochemical processes, II. clinical relevant detection assays, III. signal transduction. Part II: significance of apoptosis for radio- and chemotherapy.

Induction of apoptosis of lymphocytes in rat mucosal immune system

AIM: To undergo apoptosis during negative and positive selection processes in rat mucosal immune system which are implicated in the pathogenesis of various mucosal diseases.

METHODS: Female Sprague-Dawley rats were given protein synthesis inhibitor, cycloheximide, intravenously or intraperitoneally, an apoptosis was recognized by morphological hallmark under light and electronmicroscopy, and the expression of proliferating cell nuclear antigen was visualized immunohistochemically.

RESULTS: The apoptosis of mucosal lymphocytes in the digestive tract, as well as in trachea, uterus and lacrimal gland was induced by cycloheximide ( > 1.0 mg·kg^-1 body weight), which were located mainly in lamina propria and germinal centers of lymphoid nodules. At the same time, a portion of crypt epithelial cells of proliferating zone in small and large intestine, and the epithelial cells in genital tract were also found to undergo apoptosis. Immunostainings showed that apoptotic cells expressed proliferating cell nuclear antigen.

CONCLUSION: Apoptosis of lymphocytes in mucosal immune system can be induced by cycloheximide. This model will facilitate the understanding of normal mucosal immune system and its role in the pathogenesis of related diseases such as inflammatory bowel diseases.

Flow cytometry applications in pharmacodynamics and drug delivery

We highlight recent advances in flow cytometry that have potential applications in the pharmaceutical sciences, particularly in pharmacodynamics and drug delivery. These advances are discussed in the context of the preclinical development of anticancer agents, immunosuppressants and immunomodulators, and oligonucleotides and gene therapy.

Trypanosoma cruzi: T cell subpopulations in the Peyer's patches of BALB/c infected mice

The changes in the T cell subsets of the Peyer's patches and the thymus were analyzed in BALB/c mice infected with Trypanosoma cruzi, Tulahuén strain. During the acute stage of the infection both lymphoid organs drastically reduced their cellularity. This was mainly due to the decrease in the immature CD4+CD8+ T cell population in the thymus and in both T and B cells in the Peyer's patches. In the acute infection, few Peyer's patches were found and the histological studies revealed a depletion of the thymic-dependent areas, paralleling the decreased number of cells expressing CD4 and alpha beta T cell receptor. After 14 weeks, in the late stage of the infection, the cellularity and the levels of the T cell subsets studied returned to values similar to those of noninfected mice.

Abnormal differentiation of thymocytes induced by free cyclosporine is avoided when cyclosporine bound to N-(2-hydroxypropyl)methacrylamide copolymer carrier is used

BACKGROUND

The side effects of cyclosporine (CsA)-including nephrotoxicity and abnormal differentiation of thymocytes developing in the thymus-can be decreased or even avoided using targeted conjugates of CsA, where both targeting moiety and drug are bound to water-soluble polymeric carrier based on N-(2-hydroxypropyl) methacrylamide (HPMA).

METHODS

Irradiated, syngeneic bone marrow transplanted-mice (BALB/c and A/Ph) were treated intraperitoneally for 4 weeks with 20 mg/kg of free CsA, HPMA-conjugated CsA, or antibody-targeted HPMA-bound CsA. Immunohistology of the thymus was performed together with two-color flow cytometry to detect the effect of different forms of CsA on individual thymocyte subpopulations.

RESULTS

. We have shown that free CsA strongly abrogated T-cell development. The appearance of mature thymocytes expressing CD3(high) is almost completely inhibited (1.8%) after free CsA treatment, whereas these cells are well detectable in controls (22%) and HPMA polymer-bound CsA-treated animals (19%). Immunohistological studies have shown acellular rests of the medulla after free CsA treatment, whereas well-stained medullary thymocytes were detected in controls and after exposure to antibody-targeted HPMA. conjugated CsA.

CONCLUSIONS

HPMA-conjugates of CsA are generally more specific in their targeting to T lymphocytes. It was found that nonspecific binding of CsA to erythrocytes and plasma lipoproteins is significantly reduced using anti-CD3 targeted, HPMA polymer-bound CsA In addition, the entry of these macromolecules into the thymus is limited-probably due to the blood-thymus barrier-and HPMA conjugates of CsA, unlike free drug, do not abrogate T-cell development in bone marrow transplanted mice.

Induction of apoptosis in peripheral blood lymphocytes following treatment in vitro with hydroxychloroquine

OBJECTIVE

Defective regulation of apoptosis may be central to the development of autoimmune disorders. This study investigated the possibility that the antirheumatic effect of hydroxycholoroquine (HCQ) may be achieved by up-regulation of apoptosis.

METHODS

Peripheral blood lymphocytes collected from normal controls and patients with systemic lupus erythematosus (SLE) were cultured in the presence or absence of a range of concentrations of HCQ. Cells undergoing apoptosis were identified by several standard methods, including morphologic changes, DNA fragmentation, and flow cytometry. For some experiments, lymphocytes were simultaneously stained with antibodies to T cell surface markers and with propidium iodide for dual-stain flow cytometric studies.

RESULTS

HCQ was able to induce apoptosis in peripheral blood lymphocytes in a dose- and time-dependent manner. HCQ induced these changes in all T cell subpopulations studied. There was no significant difference between the controls and patients with SLE in terms of the percentage of apoptotic cells detected following treatment with HCQ.

CONCLUSION

The present study demonstrated that HCQ induces apoptosis in peripheral blood lymphocytes, which leads to the speculation that HCQ may exert its antirheumatic effect through this mechanism.

Spontaneous programmed cell death (PCD) process of lymphocytes of FIV-infected cats: pharmacological modulation in vitro

We previously reported that unstimulated lymphocytes in culture 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, interleukins [interleukin (IL)1, Il2, IL6 and interferon-gamma (IFN gamma)] and after activation by phorbol ester [phorbol myristyl acetate (PMA)], superantigens [staphylococcal enterotoxin B (SEB), staphylococcal enterotoxin A (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). In this study, we studied the spontaneous programmed cell death (PCD)-inducing pathways, and the mechanisms of action of PMA, SEB and SEA. Spontaneous lymphocyte apoptosis of FIV-infected cats was inhibited by cycloheximide, ZnSO4 and N-acetyl-cystein. The preventive effect of SEB and SEA was inhibited by actinomycin, but not by inhibitors of kinases. Calyculin, an inhibitor of phosphatase, had no effect either on spontaneous apoptosis, or on the action of PMA, SEB and SEA. Ionomycin-induced apoptosis was found sensitive to PMA and cytokines. In FIV-infected cats, these data suggest that the mature lymphocytes appear programmed to die by apoptosis, unless rescued by specific agents, such as protein kinase C activators or growth factors, and that spontaneous PCD seems to be dependent of de nove protein synthesis (see effect of cycloheximide). The effects of PMA, SEB and SEA are probably mediated by de novo proteins which for PMA, undergo a phosphorylation involving serine-threonine and/or tyrosine groups. Our data suggest a clear difference between lymphocytes from FIV-infected cats and lymphocytes from HIV-infected humans, with regard to their metabolic regulations.

Reduced glutathione and S-acetylglutathione as selective apoptosis-inducing agents in cancer therapy

The effect of reduced glutathione (GSH) and S-acetylglutathione (S-acglu) treatment on several tumor cell lines and normal cells in vitro was investigated. GSH and S-acglu applied at concentrations of 1 mM and 2 mM induced apoptosis in malignant cells as shown by DNA-fragmentation and staining of apoptotic cells with 7-amino-actinomycin D while viability and growth of normal cells were not significantly influenced by this treatment. The results demonstrated that GSH and S-acglu may be selective inducers of apoptosis in malignant cells.

Regulation of bcl-2 and fas expression in primary activation of human peripheral lymphocytes is not sensitive to dexamethasone or cyclosporin-A

The regulation of bcl-2 and fas (Apo-1/CD95) gene product expression plays a significant role in lymphocytes proliferation, survival, and apoptosis. Dexamethasone (Dex) and the immunosuppressive agent cyclosporin-A (CsA) inhibit primary activation of lymphocytes by distinct, though overlapping mechanisms that trigger undefined signals and can induce or prevent apoptosis in lymphoid cells in vitro. Here we demonstrate that Dex and CsA, at concentrations that markedly inhibit phytohemagglutinin (PHA)-induced proliferation of normal human peripheral blood lymphocytes, suppress the activation-dependent expression of interleukin 2 (IL-2) and the alpha-chain IL-2 receptor in a dose-dependent fashion without affecting the inducible accumulation and kinetics of either bcl-2 or fas mRNAs. Similar results were obtained when PHA-stimulated lymphocytes were cultured in the presence of the CsA analogue FK-506 or rapamycin. Moreover, the inducible maximal expression of either bcl-2 or fas protein levels on 48-h PHA-activated lymphocytes was not changed in the presence of either Dex or CsA. These findings show that the cell activation-induced biosynthesis of bcl-2 and fas proteins is not affected by immunosuppressive agents, suggesting that the expression of IL-2 and both bcl-2 and fas genes is regulated through independent mechanisms.

N-acetylcysteine protects lymphocytes from nitrogen mustard-induced apoptosis

The ability of the antioxidant N-acetylcysteine to prevent apoptosis induced in lymphocytes by nitrogen mustard (HN2) was investigated. HN2 caused a concentration-dependent induction of apoptosis on C3H murine spleen cells, as identified by two criteria: morphological features revealed by microscopical observations and DNA fragmentation visualized by the characteristic "ladder" pattern observed upon agarose gel electrophoresis, as well as by hypodiploid DNA-containing cells revealed by the flow cytometric analysis of propidium iodide labelled cells. The antioxidant N-acetylcysteine (NAC) was found to markedly reduce the occurrence of HN2-induced apoptosis in these cells. This protective effect will still obtained when NAC was added 30 min after HN2. In contrast, the pretreatment of spleen cells with this antioxidant did not provide any significant protection. We also showed that lymphocytes protected by NAC are still able to respond to a mitogenic stimulation. To gain some insight into the mechanisms underlying the cytoprotective action of NAC against HN2, we tested whether or not poly(ADP-ribose) polymerase (PARP, EC 2.4.2.30), a nuclear enzyme that participates in the triggering of apoptosis induced by alkylating agents, is involved. We report that 6(5H)-phenanthridinone, a potent PARP inhibitor, did not affect the ability of NAC to prevent HN2-induced apoptosis under our experimental conditions. Thus, the exact mechanism by which NAC protects lymphocytes from HN2 cytotoxicity has yet to be determined.

Modulation of apoptosis with cytokines in B-cell chronic lymphocytic leukaemia

In B chronic lymphocytic leukaemia (B-CLL) non-proliferating peripheral blood (PB) B cells have a long life span in vivo. In cultures, these cells die spontaneously by apoptosis. Interleukin (IL) 4 inhibits spontaneous apoptosis (SA) and promotes survival of B-CLL B cells in vitro. No such effect is observed in PB B cells from normal healthy donors. The anti-apoptotic effect of IL4 is independent of mitogen-induced cell activation but depends on the concentration of IL4. The protective effect of IL4 is specific and it is significantly reduced or abolished with anti-IL4 antibody. Interferon (IFN)-gamma and alpha- IFN also protect B-CLL B cells from apoptosis in vitro. Sera from B-CLL patients have increased levels of IFN-gamma when compared with sera from healthy donors. In addition, B-cells in B-CLL express detectable levels of IFN-gamma mRNA. Other cytokines, namely ILl, IL2, IL6 and IL7 do not affect SA of B-CLL B cells. By contrast, IL5 and antibody to apolipoprotein-1 (APO- 1) receptor increase SA significantly and in a dose-dependent manner. Interleukin 4 protects B-CLL B cells from IL5-, anti(alpha) APO-1- and steroid-induced apoptosis. The mode of action of the cytokines inducing apoptosis or protecting B-CLL B cells from dying is largely unknown. Recently the bcl-2 proto-oncogene has been associated with prolonged cell survival. However, the involvement of bel-2 in spontaneous, cytokine-induced or steroid-induced apoptosis in B-CLL has been controversial. Some authors have reported down-regulation of bcl-2 protein expression in B-CLL B-cells undergoing SA or in steroid-treated cells with IL4 preventing this down-regulation. By contrast, others observed no significant loss of bcl-2 protein expression in steroid-, alpha-APO-1 - and IL5-treated cells when compared with untreated or fresh cells. Also, no correlation between bcl-2 protein expression and protection with IL4 has been reported. In conclusion, in B-CLL IL4, IFN-gamma and alpha-IFN promote the survival of the leukaemic cells. These cytokines may therefore be involved in the pathogenesis of the B-CLL.

Apoptosis as a mechanism of keratinocyte death in toxic epidermal necrolysis

Toxic epidermal necrolysis (TEN) and Stevens-Johnson syndrome (SJS) are life-threatening diseases characterized by extensive epidermal destruction. The aim of our study was to investigate apoptosis in keratinocytes of patients with TEN and TEN/SJS overlap syndrome. Keratinocytes from TEN patients were found to undergo extensive apoptosis. These results suggest that cell destruction in TEN occurs as a result of apoptosis. Our findings suggest that apoptosis inhibitory agents may play an important part in the therapeutic strategy of TEN.

Uncontrolled triggering of programmed cell death (apoptosis) in haematopoietic stem cells: a new hypothesis for the pathogenesis of aplastic anaemia

The cause of bone marrow failure in aplastic anaemia (AA) is still unknown; however, it is clear that acquired AA is a heterogeneous disease including basically different pathophysiological conditions. Causative agents, clinically associated with AA, possibly exert their action through restricted pathways. Some theoretical and experimental data show that programmed cell death (PCD) or apoptosis is physiologically important in normal haematopoiesis and could be involved in the pathophysiological events responsible for the development of AA. Therefore, it is intriguing to hypothesize that the pathogenetic mechanism underlying most cases of acquired AA could be represented by an excessive and/or uncontrolled triggering of PCD in haematopoietic stem cells. Investigations to test this hypothesis are proposed.

RRR-alpha-tocopheryl succinate induces apoptosis in avian retrovirus-transformed lymphoid cells

The RRR-alpha-tocopheryl succinate form of vitamin E [vitamin E succinate (VES)] inhibits the proliferation of avian reticuloendotheliosis virus-transformed RECC-UTC4-1 (C4-1) lymphoblastoid cells in a dose-dependent manner, blocks the cells in the G2/M cell cycle phase, and induces the cells to undergo apoptosis. Apoptosis was documented by demonstrating changes that are characteristic of this type of cell death, including morphological analyses of chromatin condensation by 4',6-diamidine-2'-phenylindole dihydrochloride (DAPI) staining using scanning confocal and traditional fluorescent microscopy; flow cytometry analyses of propidium iodide-labeled DNA showing fragmented DNA as a pre-G1 peak; two-color flow cytometry analyses of intact cells labeled first by the TUNEL procedure (terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick-end-labeled DNA stained with fluorescein isothiocyanate-labeled avidin) and then by propidium iodide demonstrating fragmented DNA; and electrophoresis of DNA showing a DNA ladder created by internucleosomal DNA fragmentation. The percentage of apoptotic cells was determined by DAPI staining and showed 11%, 27%, and 49% of cells to be apoptotic after treatment with 10 micrograms/ml VES for one, two, and three days, respectively. Analyses of mRNA levels of genes that have been implicated in the apoptotic process, namely, bcl-2, c-myc, and c-jun, revealed no change in bcl-2, decreases in c-myc mRNA levels after 36 hours of treatment, and increases in c-jun mRNA levels within four hours after treatment. Western immunoblotting analyses of protein levels for the transcription factors c-Myc and c-Jun showed normal levels of c-Myc at early time points and decreased levels at 24 and 48 hours after treatment. c-Jun increased as early as 6 hours after treatment and returned to lower (yet still elevated over control) levels by 48 hours. To determine possible functional consequences of increased c-Jun expression, gel electrophoretic mobility assays were conducted that showed increased AP-1 binding at 24 and 48 hours after treatment. These data show that VES induces apoptosis in reticuloendotheliosis virus-transformed lymphoid cells and suggest that decreases of c-Myc protein and increases of c-Jun protein and DNA binding capacity may be playing a role in VES-mediated events leading to apoptosis in this cell type.

An 'antigenic ligand competition' model for antigen receptor-mediated lymphocyte selection

The 'antigenic ligand competition' model advanced herein represents a principally novel view on lymphocyte selection, postulating a leading role in this process of competition between different determinants expressed on self ligands for binding to antigen receptors. Based on the data indicating that cell viability and cell growth are separately regulated processes, it is speculated that the binding of antigenic receptors with monovalent determinants (MDs) expressed on soluble self ligands may be responsible for lymphocyte survival, whereas the moderate (but not hyper) cross-linking of antigenic receptors with polyvalent determinants (PDs) expressed on other or the same self ligands may provide signalling that is necessary to trigger lymphocyte proliferation. In the light of the model, the lymphocytes whose receptors bind with high affinity to self MDs survive, while not receiving a proliferative stimulus. On the other hand, those lymphocytes whose receptors interact with high affinity with self PDs and consequently undergo hypercross-linking die by apoptosis. Lastly, those lymphocytes whose receptors interact simultaneously with both MDs and PDs in a balanced competitive manner receive both viability and a proliferative stimulus and, as a consequence, it is only they which obtain selective advantage. The balanced competition between self MDs and self PDs for receptor binding seems likely when the receptors have relatively low affinity to such determinants inasmuch as the opposite, namely comparably high specificity (affinity) to structurally distinct determinants, is unlikely. Essentially, the model presented herein also suggests that a balance between distinct antigenic determinants occupying antigen receptors may determine not only self antigen-driven lymphocyte selection, but also immune reactivity of the functionally mature B- and T-cells which have passed through this selection.

The antiglucocorticoid action of mifepristone

Glucocorticoid hormones influence the physiological activity of almost all cell types in the mammal. This is accomplished via a soluble receptor that, in the presence of an appropriate steroid, modifies the activity of RNA polymerase by binding to the site where different factors assemble for the initiation of cell transcription. The development of antiglucocorticoids has permitted the molecular elucidation of a number of underlying events. Contrary to the classical view, it is now clear that the affinity, stability and activability of the glucocorticoid receptor in the presence of a steroid are cell- and/or tissue-dependent events. The antiglucocorticoid RU 38486 can even activate transcription by binding to sites distinct from those that process transactivation by the agonist. Furthermore, glucocorticoids can sometimes activate the mineralocorticoid receptor, whereas mineralocorticoids can bind the glucocorticoid receptor. Since mifepristone is devoid of adverse toxicity, it has been used for the paraclinical diagnosis of the hypothalamus-pituitary-adrenal axis in normal volunteers, subjects with disorders of the behaviour, and the treatment of Cushing's disease. However, the whole spectrum of cell-specific processes that are antagonized by RU 38486 suggests wide ranging possibilities in the eventual application of antigluco-corticoids.

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.

Sequential reduction of mitochondrial transmembrane potential and generation of reactive oxygen species in early programmed cell death

Programmed cell death (PCD) is a physiological process commonly defined by alterations in nuclear morphology (apoptosis) and/or characteristic stepwise degradation of chromosomal DNA occurring before cytolysis. However, determined characteristics of PCD such as loss in mitochondrial reductase activity or cytolysis can be induced in enucleated cells, indicating cytoplasmic PCD control. Here we report a sequential disregulation of mitochondrial function that precedes cell shrinkage and nuclear fragmentation. A first cyclosporin A-inhibitable step of ongoing PCD is characterized by a reduction of mitochondrial transmembrane potential, as determined by specific fluorochromes (5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolcarbocyanine++ + iodide; 3,3'dihexyloxacarbocyanine iodide). Cytofluorometrically purified cells with reduced mitochondrial transmembrane potential are initially incapable of oxidizing hydroethidine (HE) into ethidium. Upon short-term in vitro culture, such cells acquire the capacity of HE oxidation, thus revealing a second step of PCD marked by mitochondrial generation of reactive oxygen species (ROS). This step can be selectively inhibited by rotenone and ruthenium red yet is not affected by cyclosporin A. Finally, cells reduce their volume, a step that is delayed by radical scavengers, indicating the implication of ROS in the apoptotic process. This sequence of alterations accompanying early PCD is found in very different models of apoptosis induction: glucocorticoid-induced death of lymphocytes, activation-induced PCD of T cell hybridomas, and tumor necrosis factor-induced death of U937 cells. Transfection with the antiapoptotic protooncogene Bcl-2 simultaneously inhibits mitochondrial alterations and apoptotic cell death triggered by steroids or ceramide. In vivo injection of fluorochromes such as 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolcarbocyanine iodide; 3,3'dihexyloxacarbocyanine iodide; or HE allows for the detection of cells that are programmed for death but still lack nuclear DNA fragmentation. In particular, assessment of mitochondrial ROS generation provides an accurate picture of PCD-mediated lymphocyte depletion. In conclusion, alterations of mitochondrial function constitute an important feature of early PCD.

Involvement of cAMP in CD3 T cell receptor complex- and CD2-mediated apoptosis of human thymocytes

During intrathymic T cell development, elimination of autoreactive T cell clones by programmed cell death (PCD or apoptosis) is an essential mechanism for self tolerance. The precise intracellular second messengers that lead to this process remain to be determined. In the present work, we show that treatment of freshly isolated thymocytes with an antagonist of the cAMP pathway, the Rp-cAMP, significantly decreases spontaneous death by apoptosis of human thymocytes in vitro. Addition of Rp-cAMP also rescues thymocytes from activation-induced apoptosis following the ligation of surface CD3/T cell receptor complex or CD2 antigens. A cAMP analog, the dibutyryl(Dibut)-cAMP increases PCD of human thymocytes in a dose-dependent manner. Growth and rescue from PCD of thymocytes in the presence of interleukin (IL)-2 or IL-4 are also enhanced by Rp-cAMP and inhibited by Dibut-cAMP. Finally, we detect substantial levels of intracellular cAMP in freshly isolated thymocytes. This study reveals the involvement of cAMP as a second messenger during the apoptosis of normal human thymocytes.