Microvesicles: ROS scavengers and ROS producers

This review analyzes the relationship between microvesicles and reactive oxygen species (ROS). This relationship is bidirectional; on the one hand, the number and content of microvesicles produced by the cells are affected by oxidative stress conditions; on the other hand, microvesicles can directly and/or indirectly modify the ROS content in the extra- as well as the intracellular compartments. In this regard, microvesicles contain a pro-oxidant or antioxidant machinery that may produce or scavenge ROS: direct effect. This mechanism is especially suitable for eliminating ROS in the extracellular compartment. Endothelial microvesicles, in particular, contain a specific and well-developed antioxidant machinery. On the other hand, the molecules included in microvesicles can modify (activate or inhibit) ROS metabolism in their target cells: indirect effect. This can be achieved by the incorporation into the cells of ROS metabolic enzymes included in the microvesicles, or by the regulation of signaling pathways involved in ROS metabolism. Proteins, as well as miRNAs, are involved in this last effect.

Klotho Prevents Translocation of NFκB

Klotho protein is a β-glucuronidase capable of hydrolyzing steroid β-glucuronides. Two molecules are produced by the Klotho gene, a membrane bound form and a circulating form. This protein is recognized as an antiaging gene with pleiotropic functions. The activation of cellular systems is associated with the pathogenesis of several chronic and degenerative diseases associated with an inflammatory state. Inflammation is characterized by an activation of NFκB. Klotho suppresses nuclear factor NFκB activation and the subsequent transcription of proinflammatory genes. This review focuses on the current understanding of Klotho protein function and its relationship with NFκB regulation, emphasizing its potential involvement in the pathophysiologic process.

Home e-health system integration in the Smart Home through a common media server

Home e-health systems and services are revealed as one of the most important challenges to promote Quality of Life related to Health in the Information Society. Leading companies have worked on e-health systems although the majority of them are addressed to hospital or primary care settings. The solution detailed in this paper offers a personal health system to be integrated with Smart Home services platform to support home based e-care. Thus, the home e-health system and architecture detailed in this research work is ready to supply a seamless personal care solution both from the biomedical data analysis, service provision, security guarantee and information management s point of view. The solution is ready to be integrated within the Accessible Digital Home, a living lab managed by Universidad Politécnica de Madrid for R&D activities.

Microinflammation induces endothelial damage in hemodialysis patients: the role of convective transport

Cardiovascular complications are a major cause of mortality in hemodialysis patients. On-line hemofiltration combines convective clearance for removing large solutes with diffusion to remove small solutes and is associated with a significant reduction of inflammation and improved patient survival. We compared on-line hemofiltration to high-flux hemodialysis (HF-HD) in patients in a sequential manner. At baseline, 15 stable patients on HF-HD as compared with five control subjects showed significant increases in CD14+CD16+ cells, endothelial microparticles, and endothelial progenitor cells (EPCs). After 4 months of on-line hemofiltration, the number of CD14+CD16+ cells, microparticles, and EPCs decreased. After returning to HF-HD for 4 months, all measured parameters returned to their respective baseline values. The number of CD14+CD16+ cells correlated with both endothelial microparticles and EPCs. We conclude that on-line hemofiltration attenuates endothelial dysfunction possibly by decreasing microinflammation. This effect may be directly caused by a modulatory effect of on-line hemofiltration on proinflammatory cells or by a complex interaction that encompasses a wider removal of uremic toxins.

[Acute rejection of kidney transplant is associated with induction of replicative senescence in CD8+ T lymphocytes]

Acute renal rejection repeatedly activates immunocompromised CD8 + T cells. Maintained activation of CD8 + T cells can induce a process of replicative senescence. In the present study, we will evaluate in CD8 lymphocytes from patients undergoing acute renal rejection characteristics of replicative senescence such as: a) low expression of CD28 molecule; b) telomere shortening and c) increase production of proinflammatory cytokines. The study was carried out in CD8 + T cells from 14 patients transplanted without clinical evidences of acute renal rejection, 14 patients kidney transplanted with clinical and anatomopathological evidences of acute renal rejection, 8 healthy controls. The results shown that in peripheral blood and renal biopsy of patients with acute renal rejection there is a significant increment of the population of T cells CD28-CD8+, with short telomere length, as compared with healthy controls and patients without acute renal rejection. The presence of senescent cells was associated with high levels of IL-10 and IFN-Y in plasma and urine. In conclusion our study suggest that the CD8 + T cells of patients with acute renal rejection suffer a process of replicative senescence.

Antibody-mediated pure red-cell aplasia (PRCA): the Spanish experience

BACKGROUND

The incidence of antibody (Ab)-mediated pure red-cell aplasia (PRCA) in patients with chronic kidney disease (CKD) has increased between 1998 and 2002. After initially responding to treatment with recombinant human erythropoietic agents for CKD-associated anemia, patients became treatment-refractory and severely anemic. Although most PRCA cases have occurred in Europe, the varying epidemiologies among individual countries have not been well characterized.

METHODS

We investigated Ab-mediated PRCA in 12 Spanish patients treated with epoetin alfa alone or prior to treatment with epoetin beta (n=1) or darbepoetin alfa (n=1). Serum Abs against epoetin alfa were detected by radioimmunoprecipitation (RIP) assay or bioassay. Following diagnosis of PRCA, erythropoietic treatment was stopped and patients received immunosuppressive therapy alone (n=11) or in combination with renal transplant (n=1).

RESULTS

Treatments were administered for 16 months (average) before diagnosis of PRCA in bone marrow aspirates (n=8) or biopsies (n=4). At diagnosis, patients had an average of 0.68% blood reticulocytes and blood hemoglobin (Hb) level of 7.13 g/dL. Eight patients had anti-epoetin Abs detected by RIP, and 5 had neutralizing Abs measured in the bioassay. As of December 2003, 4 patients had died, 3 had no recovery, and 5 had recovered from anemia (blood Hb level, 9.9 g/dL). All 5 recovering patients received corticosteroid therapy alone, and 1 received a renal transplant as well as corticosteroids.

CONCLUSIONS

Sudden onset of treatment-refractory anemia in CKD patients suggests a course of treatment cessation followed by diagnostic procedures for Ab-mediated PRCA, and immunosuppressive therapy. This study may serve as a model for a centralized global PRCA registry.

Antithrombin III prevents early pulmonary dysfunction after lung transplantation in the dog

BACKGROUND

Ischemia-reperfusion injury with the resulting inflammatory response is a devastating complication of lung transplantation; much of the tissue damage could be diminished by control of the inflammatory response. Recent studies have show that antithrombin III (AT III) has an anti-inflammatory effect in addition to its established role in the regulation of blood coagulation. Thus, we hypothesized that the administration of AT III might help to prevent ischemia-reperfusion injury after lung transplantation.

METHODS AND RESULTS

The study was performed in a dog model of orthotopic lung transplantation. Dogs were randomly assigned to receive either vehicle (controls) or AT III. We observed that in control dogs, during the 180-minute period after lung transplantation, the arterial O(2) partial pressure decreased and both the alveolar-arterial O(2) difference and the pulmonary vascular resistance increased. By contrast, these parameters remained unchanged in the group of dogs receiving AT III. Dogs with transplants receiving AT III did not show an increase in cell adhesion molecules, and histological examination revealed almost an absence of inflammatory response. The administration of AT III produced a marked increase in serum prostacyclin (PGI(2)) levels, whereas in control dogs, the PGI(2) levels did not change. The beneficial effect of AT III was not observed when dogs received indomethacin to prevent the stimulation of PGI(2) release by AT III.

CONCLUSIONS

Our results demonstrate that AT III prevents ischemia-reperfusion injury in a dog model of lung transplantation and that this effect is conditioned by an increase in PGI(2) production.

Role of adhesion molecules in mononuclear cell apoptosis induced by cuprophan hemodialysis membranes

BACKGROUND/AIM

Hemodialysis with Cuprophan (CU) membranes induces mononuclear cell activation, leading to increased expression of adhesion molecules, formation of cell aggregates, and apoptosis. It is likely that structure(s) of the CU membrane interact with mononuclear cell surface molecules which transduce biochemical signals to the cell. Interactions between adhesion molecules and extracellular matrix have been implicated in cell activation, proliferation, and/or apoptosis. In the present work, we study whether adhesion molecules may be involved in CU-induced mononuclear cell aggregation and/or apoptosis.

METHODS

The present study was performed using THP-1 cells, a human monocytic cell line, cultured in the presence of the CU membrane. CD11b and CD54 expression was studied with fluorescent monoclonal antibodies. Cell aggregation was quantified using a phase-contrast microscope. Apoptosis was evaluated by either light microscopy or annexin V labeling.

RESULTS

The results show that incubation of CU membranes with the proteins CD11b, CD18, and CD54 or the blockade of these cell surface molecules with specific monoclonal antibodies inhibited the CU-induced aggregation and apoptosis in a dose-dependent manner.

CONCLUSION

These results suggest that CU membranes interact selectively with these specific proteins to induce cell activation which ultimately results in apoptosis.

TH2 lymphocytes from atopic patients treated with immunotherapy undergo rapid apoptosis after culture with specific allergens

BACKGROUND

In atopic patients treatment with specific immunotherapy (SIT) induced a shift in the balance of T-cell immune response away from a T(H)2-type (producing mostly IL-4) in favor of a T(H)1-type T-lymphocyte response (with the preferential production of IFN-gamma). However, the mechanisms through which SIT acts are less clear. We have recently shown that allergens may induce an activation-induced cell death process in lymphocytes from SIT-treated atopic patients.

OBJECTIVE

This study aimed to determine whether allergen-induced apoptosis can occur in a specific subset of cells.

METHODS

The study was performed in lymphocytes from normal subjects and atopic patients, some of whom were treated with SIT. Cells were cultured in the presence of gramineous pollen (Lolium perenne) allergenic extracts. Cell phenotype and intracellular cytokine expression were measured by means of fluorescent mAbs. Apoptosis was measured by using terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling. Fluorescence was analyzed in a FACScan flow cytometer, and the data were evaluated with Consort 30 software.

RESULTS

Our results showed that allergens induce apoptosis of lymphocytes in SIT-treated atopic patients. Apoptosis occurs mainly in T(H)2 lymphocytes with the IL-4+/CD4+ phenotype and subsequently increases the percentage of IFN-gamma(+) cells in the culture.

CONCLUSION

These results suggest that the shift from T(H)2 to T(H)1 induced by SIT in atopic patients may be mediated, at least in part, by the induction of an activation-induced cell death process in allergen-responder T(H)2 cells.

Allergens induce apoptosis in lymphocytes from atopic patients

Repeated stimulation of immune cells may induce an "activation-induced cell death" (AICD) program. Allergy is characterized by the cyclic activation of allergen-reactive immune cells. To study the effects of allergen stimulation in cell proliferation and apoptosis in atopic subjects, peripheral blood mononuclear cells (PBL) from 40 atopic patients with positive reactivity to the allergens Olea Europaea (OE) and Lollium Perenne (LP) (20 without immunotherapy and 20 with specific immunotherapy) and 10 normal subjects were cultured with the allergens OE and LP. PBL from atopic patients proliferate more vigorously than cells from normal subjects after culture in vitro with both allergens, although PBL from atopic subjects without immunotherapy proliferate more than PBL from atopic subjects with immunotherapy. The study of cell proliferation shows that in atopic patients PBL mainly exhibit the CD4/CD45RO phenotype. This preferential proliferation is more evident in PBL from atopic patients treated without immunotherapy. Cell culture with specific allergens induces apoptosis in PBL from atopic patients. The percentage of apoptosis increased when atopic patients had been previously treated with immunotherapy. In addition to the observed increase in cell proliferation, apoptosis mainly occurs in the CD45RO cells that support the involvement of these cells in allergy. Furthermore, results obtained in cells from immunized patients suggest that an AICD process may partly at least explain the mechanism of action of allergen immunotherapy.

NK phenotypic markers and IL2 response in NK cells from elderly people

Immunosenescence is a process that primarily affects the T cell compartment of the immune system, although age-associated immunological alterations have also been demonstrated in the NK cell phenotype and function. A significant expansion in the number of NK cells is found in aging. The NK cytotoxic capacity of total peripheral blood lymphocytes is also well preserved, not only in healthy elderly people but also in centenarians. However, NK cell killing of K562 is impaired when considered in a per-cell basis, and this defect is associated with defective signal transduction after activation more than a diminished conjugate formation or killing capacity. We have studied the phenotype of NK cells in elderly donors fulfilling the Senieur criteria. We have also studied the capacity of these cells to be activated by IL2 when different NK cell functions, other than cytotoxicity, are considered. Our results confirm the increased percentage of NK cells in the elderly due to the expansion of the CD56dim subset that also show an altered pattern of activation markers, whereas no differences were found in the CD56bright subset. The response of NK cells to IL2 was found to be impaired when proliferation, expression of CD69, and Ca2+ mobilization were considered, whereas TNF-alpha production was not significantly affected. These results suggest that human NK cells do not escape the aging process, although senescence have a differential effect on distinct NK cell biological functions, ranging from severe to negligible impairment, depending on the parameters considered.

Serum levels of intercellular adhesion molecule 1 (ICAM-1) in patients with colorectal cancer: inhibitory effect on cytotoxicity

A positive correlation between the level of ICAM-1 in serum and the stage of neoplastic processes has been demonstrated. We studied ICAM-1 serum concentration in 27 colorectal cancer patients and investigated the effect of this molecule on cellular aggregation and toxicity. ICAM-1 serum concentration in the group of patients was significantly higher (P < 0.01) than in normal controls and was related to tumour stage. Patient sera inhibited both the formation of cellular aggregates and the percentage of specific lysis, the effect being lost when the serum was depleted of ICAM-1. These results suggest that the release of soluble ICAM-1 may represent a mechanism of tumour escape.

Nonbiocompatible hemodialysis membranes induce apoptosis in mononuclear cells: the role of G-proteins

Mononuclear cells are activated during hemodialysis. In this study, we provide evidence that in vitro culture of mononuclear cells with Cuprophan, a nonbiocompatible hemodialysis membrane, increases the levels of protein phosphorylation in these cells as well as the expression of surface activation molecules. By contrast, culturing of mononuclear cells with AN69, a more biocompatible membrane, did not increase protein phosphorylation levels or expression of surface activation molecules in these cells. In addition, Cuprophan, but not the AN69 membrane, increased the percentage of mononuclear cell death by apoptosis. Inhibition of G-protein-mediated signal transduction decreased the apoptosis of cells cultured with the Cuprophan membrane. The GTP-binding protein involved in Cuprophan-induced apoptosis was sensitive to the ADP-ribosylating pertussis toxin (PTX). The inhibition of GTP-binding protein decreased apoptosis in the early stage of the activation-induced apoptosis, suggesting that G-proteins are implicated in the transmission of apoptosis-inducing signal(s) but do not interfere with the effector signals that mediate the late stages of apoptotic catabolism. Finally, PTX was capable of inhibiting apoptosis without affecting expression of activation molecules; thus, the inhibition of apoptosis by Cuprophan was not due to quenching of the stimulation signals, because monocytes were still able to be activated by Cuprophan despite the action of PTX. The results obtained in this study suggest that cell activation and apoptosis may be mediated by separate intracellular signals.

C1-esterase inhibitor prevents early pulmonary dysfunction after lung transplantation in the dog

The success of lung transplantation to a large extent depends on effective protection of the graft from ischemic injury after reperfusion. Although mechanisms have not been clarified, the pathologic findings of ischemic injury after reperfusion are similar to adult respiratory distress syndrome, a condition in which the blood coagulation contact system is activated. This study evaluates the effect of C1-esterase inhibitor (C1-INH), the main inhibitor of the blood coagulation contact system, on short-term lung function in a dog model of orthotopic lung transplantation. Twelve lung transplantations were performed after 24 h of ischemic time. Dogs were randomly assigned to receive either vehicle (Control) or C1-INH. After the lung transplantation in the control group, Pao2 decreased by 84% and both the AaPO2 and the Qs/Qt% increased (340 and 530%, respectively, p < 0.01); these parameters remained unchanged in the C1-INH group. The hypoxemia observed in control animals was associated with decreased blood coagulation contact factors, complement consumption, increased expression of adhesion glycoproteins in leukocytes, and extensive intraalveolar and interstitial neutrophil infiltration. In contrast, C1-INH administration prevented hypoxemia, the decrease in blood coagulation contact factors, the activation of the complement system, the increase in expression of leukocyte adhesion molecules, and inflammatory cell infiltrate. This study has demonstrated that in a dog model of lung transplantation, the administration of C1-INH prevents early pulmonary dysfunction, and it suggests that activation of blood coagulation contact system and complement are important mechanisms causing ischemic injury after reperfusion.

Mycobacterium tuberculosis induces apoptosis in gamma/delta T lymphocytes from patients with advanced clinical forms of active tuberculosis

Antigens from inactivated Mycobacterium tuberculosis H37Ra induce activation in a subpopulation of gamma/delta (gamma/delta) T lymphocytes in a manner that resembles that of superantigens from alpha/beta T cells. After culture in vitro with H37Ra proteins, gamma/delta T lymphocytes from patients with advanced clinical forms of active tuberculosis (ACF-TBC) display cytotoxic activity against homotypic target cells exposed to H37Ra. Cytotoxicity by gamma/delta T lymphocytes from ACF-TBC patients occurs in a range similar to that observed in healthy subjects. Following activation, H37Ra-stimulated gamma/delta T lymphocytes from healthy subjects did proliferate in the presence of exogenous recombinant human interleukin 2. However, under the same conditions, gamma/delta T lymphocytes from ACF-TBC patients not only did not proliferate but died by apoptosis. These results suggest that in gamma/delta T lymphocytes from patients with ACF-TBC, antigens from M. tuberculosis may induce cell activation that leads to apoptotic cell death.

Inhibition of apoptotic cell death in B-CLL by interferon gamma correlates with clinical stage

Apoptosis was evaluated in B cells from 41 patients with B-CLL and 20 healthy aged-matched controls. B cells were cultured with and without gamma-IFN and other cytokines; apoptosis was quantified at regular intervals throughout a 5-day culture period. According to Rai's criteria, 17 patients were classified as good risk, 16 as intermediate and eight as high risk. In vitro, purified B cells from B-CLL patients were evaluated for apoptosis. Maximal apoptosis (44.12%) was observed at day 5 in cells from patients with poor prognosis. The addition of gamma-IFN to the culture media prevented apoptosis in a dose-dependent manner. Maximal inhibition of apoptosis was achieved with 100 IU/ml of gamma-IFN. The degree of inhibition of apoptosis by gamma-IFN was greater in cells from the high-risk group patients than in those from the intermediate and good prognosis group (P < 0.0001). The expression of gamma-IFN receptors in B-CLL cells was evaluated using a MnAb against the extracellular domain of gamma-IFN receptor. After 4 days in culture with gamma-IFN, only cells from the intermediate- and high-risk groups showed an increase in the density of gamma-IFN receptors (P < 0.001). gamma-IFN was not detected in the sera of our study patients. However gamma-IFN was detectable in the media from both normal B cells and B-CLL cells in culture; there was no difference in the amount of gamma-IFN released by cells from the three groups of patients studied. Our results show that in vivo gamma-IFN inhibits apoptosis of B cells from B-CLL patients. The inhibitory effect of gamma-IFN on apoptosis correlates directly with the severity of the disease and this is likely explained by a marked upregulation of gamma-IFN receptors in cells from patients in the high-risk group.

CD69-induced monocyte apoptosis involves multiple nonredundant signaling pathways

Simultaneous stimulation of human monocytes/macrophages or THP1 cells with LPS and an antibody specific for the activation marker CD69 induces apoptosis. Here we demonstrate the involvement of multiple independent signals that are necessary for apoptosis induction. Thus, inhibitors of phospholipase A2 and lipoxygenase prevent apoptosis induction. Similarly, the ADP-ribosylating G-protein-reactive pertussis toxin (PTX) but not a mutant toxin lacking the ADP-ribosylating moiety (mPTX) prevents apoptosis induction. Furthermore, inhibition of NO generation abrogates completely the induction of apoptosis by LPS/CD69 ligation. These three pathways can be dissociated from each other in the sense that interventions on the arachidonic acid metabolism or G proteins do not inhibit the generation of NO and that exogenous NO cannot reverse the inhibition of cell death by inhibitors of phospholipase A2 or PTX. In addition, both PTX and mPTX affect arachidonic acid mobilization only partially, indicating that the apoptosis-inhibitory effect of PTX (which is not shared by mPTX) cannot be explained by its effect on phospholipase A2 activation. Both LPS and anti-CD69 are sufficient on their own to activate cells, as determined by TNF production, NO generation, or arachidonic acid metabolism, but neither LPS nor anti-CD69 can induce apoptosis on their own. Thus, apoptosis induction in this system involves at least three independent signal transduction systems--(i) arachidonic acid metabolism, (ii) NO, and (iii) PTX-sensitive events--each of which is necessary but insufficient to induce monocyte/macrophage apoptosis. These findings underline the complex control of activation-induced apoptosis in cells of the myelomonocytic lineage.

1 alpha, 25-dihydroxyvitamin D3 (calcitriol) induces apoptosis in stimulated T cells through an IL-2 dependent mechanism

The steroid hormone 1 alpha,25-dihydroxyvitamin D3 (calcitriol) has been shown to inhibit PHA-induced T-cell proliferation. In the present work we show that calcitriol caused a concentration-dependent decrease in the viability of PHA stimulated but not unstimulated T lymphocytes. Under microscopy, nonviable cells exhibit classic features of programmed cell death or apoptosis. In addition, the same concentration of calcitriol induces a blockage in the G1 phase of T cell cycle and decreased secretion of IL-2, which was correlated with the extent of apoptosis. Thus, addition of exogenous IL-2 reverted both the cell cycle block and the apoptotic cell death induced by calcitriol. This data indicates that calcitriol induced apoptosis in PHA-stimulated T cell, and suggests that this action is mediated through suppression of IL-2 secretion.

Cell aggregation and apoptosis induced by hemodialysis membranes

During hemodialysis, circulating mononuclear cells can be stimulated to different degrees, depending on membrane biocompatibility. Cell activation usually leads to aggregation and proliferation. It may also result in apoptosis if cells are subjected to abnormal activation. This may be the case of cells exposed to bioincompatible hemodialysis membranes. The study presented here evaluates the effects of two hemodialysis membranes, with different degrees of biocompatibility, (Cuprophan (CU; Lundia IC 5N; GAMBRO, Sweden) and polyacrylonitrile (AN69; Biospal 3000S, Hospal, France)) on aggregation and apoptosis of circulating human mononuclear cells and the human mononuclear cell line (THP-1). The results showed that 2-h incubation with CU, a bioincompatible membrane, produces cell aggregation of both peripheral mononuclear cells and THP-1 cells (35% and 54%, respectively). After 48 h of incubation with a CU membrane, apoptotic death was observed in 32% of THP-1 cells and in 45% of normal peripheral mononuclear cells. Neither cell aggregation nor apoptosis was observed after incubation with the AN69 membrane. CU membrane-induced apoptosis was inhibited by Staurosporrin (Sigma, St. Louis, MO) a protein kinase C (PKC)-inhibitor, suggesting that cell apoptosis induced by the CU membrane is mediated by a PKC-dependent cell activation. Furthermore, cell prestimulation with phorbol 12-myristate 13-acetate, an activator of PKC, results in a increase in the percentage of THP-1 cell death by apoptosis after CU exposure (53%). Our study indicates that CU membranes induce mononuclear cell activation, leading to cell apoptosis.

Pertussis toxin-sensitive GTP-binding proteins regulate activation-induced apoptotic cell death of human natural killer cells

Apoptosis of natural killer (NK) cells can be induced by non-specific physical damage (UV irradiation, heat shock) or by simultaneous ligation of the CD16 and the interleukin-2 receptor (IL-2R) molecules, but not with either anti-CD16 or IL-2 alone. Whereas blockade of GTP-binding protein (G protein)-mediated signal transduction using ADP-ribosylating bacterial toxins or the GTPase-resistant GTP analog guanosine 5'-0-(3-thiotriphosphate (GTP gamma S) does not affect non-specific induction of NK cell apoptosis, such interventions do inhibit induction of apoptosis by anti-CD16/IL-2. The G proteins involved in the regulation of activation-induced NK apoptosis are sensitive to pertussis toxin (PTX) and to the non-specific GTP analog GTP gamma S but not to cholera toxin, Pseudomonas exotoxin A or diphtheria toxin. A pertussis toxin mutant that lacks ADP-ribosylating activity, but conserves the membrane translocating and T cell-mitogenic effects of the native molecule, fails to inhibit NK apoptosis. To exert their apoptosis-inhibitory effect, PTX and GTP gamma S must be employed before cells are activated. Later addition has no effect, suggesting the implication of G proteins in the transmission of apoptosis-inducing signals, but not in the effector stage of apoptosis. Pre-incubation with PTX or GTP gamma S does not affect the activation of NK cells by CD16 cross-linking, IL-2 stimulation- or both, as assessed by the induction of CD69 expression, protein tyrosine phosphorylation and calcium mobilization. Moreover, neither PTX nor GTP gamma S compromise the effector function of NK cells or the susceptibility of target cells to NK-mediated lysis. These data suggest apoptosis as a novel mechanism by which NK responses may be controlled in vivo, as well as an experimental and therapeutical strategy to counteract endogenous down-regulation of NK responses.

Pertussis toxin inhibits activation-induced cell death of human thymocytes, pre-B leukemia cells and monocytes

Activation of human thymocytes and pre-B cells via the CD3/T cell receptor (TCR) complex or the IgM/B cell receptor complex, respectively, results in apoptotic cell death. Similarly, cross-linking of the activation marker CD69, which belongs to the natural killer complex, causes apoptosis of lipopolysaccharide-preactivated monocytes. Here we show that pertussis toxin (PTX) inhibits the activation-induced apoptosis of these three cell types, though it fails to prevent the programmed cell death that follows exposure of cells to the synthetic glucocorticoid dexamethasone (thymocytes, pre-B cells) or to interleukin 4 (monocytes). The capacity of pertussis toxin to suppress activation-induced death is not due to quenching of the activation signal, because thymocytes exposed to PTX are still capable of mobilizing Ca2+ after TCR-alpha/beta cross-linking and proliferate in response to costimulation with PTX and CD3/TCR ligation. The apoptosis-inhibitory effect of PTX depends on the presence of an intact adenosine diphosphate (ADP)-ribosylating moiety, since a mutant pertussis toxin molecule that lacks enzymatic activity, but still possesses the membrane translocating activity, fails to interfere with activation-induced cell death. A toxin that induces a different spectrum of ADP ribosylation than PTX, cholera toxin, fails to inhibit apoptosis. To suppress apoptosis, the intact PTX holotoxin must be added to cells before the lethal activation step; its addition 30 min after initial activation remains without effect on apoptosis. These data unravel a PTX sensitive signal transduction event that intervenes during an early step of activation-induced cell death of immune cells.

HLA class II-mediated aggregation is associated with the proliferation of B lymphocytes

We have studied the role of LFA-1 antigens in human B lymphocyte aggregation, proliferation, and Ig production induced by a short stimulation via class II antigens. Cell stimulation with either bacterial superantigens or anti-DR mAbs rapidly induced homotypic cell aggregation. In response to IL-4, an increase in cell proliferation and Ig production was observed only when aggregation preceded addition of IL-4. The involvement of LFA-1 molecules in class II-induced aggregation was supported as LFA-1-deficient cells or B cells incubated with anti-LFA-1/ICAM-1 mAbs failed to aggregate after stimulation. The association between aggregation and subsequent Ig production and proliferation was further supported as, after IL-4 stimulation, in both LFA-1-deficient cells and B cells incubated with anti-LFA-1 mAbs, class II-mediated signals failed to increase Ig production or cell proliferation. These data suggest that in class II-stimulated cells, LFA-1-dependent aggregation has a major role in IL-4-dependent Ig production and proliferation of B cells.

HLA class-II-mediated homotypic aggregation: involvement of a protein tyrosine kinase and protein kinase C

Homotypic aggregation of B-lymphocytes, B-cell lines and class-II-positive T cells via HLA class II molecules was examined. Signaling via DR antigens induced rapid aggregation in a dose- and time-dependent manner, maximum and stable aggregation was induced within 20 minutes. On the contrary, rapid signaling via DP or DQ required prestimulation with either PMA or anti-sIg. Aggregation was temperature and energy dependent. [Ca2+] and [Mg2+] concentrations and an intact cytoskeleton were required while neither mRNA or protein synthesis were required. Furthermore, FACS analysis revealed that aggregation was not directly correlated with cell surface expression of HLA class II molecules. Our results demonstrate that aggregation was mediated through a protein tyrosine kinase (PTK)-dependent pathway that preceded activation of protein kinase C (PKC) and failure to generate either the PTK signal or the PKC signal prevented aggregation. The contribution of a tyrosine kinase was further demonstrated by the total inhibition of aggregation following treatment with an anti-CD45 mAb.

Mechanisms involved in NK resistance induced by interferon-gamma

Human tumor cell lines were treated with interferon-gamma (IFN-gamma) and then used as target cells in NK assays to measure their ability to form conjugates and stimulate the production of NK cytotoxic factors (NKCF) and to determine their susceptibility to NKCF lysis. K562 and cell lines RS1, RS3, RS7, CAC, and CAP2, obtained from solid brain tumors, were used as targets, and peripheral blood lymphocytes (PBL) from normal donors were used as effector cells. IFN-gamma-treated cell lines had a decreased susceptibility to NKCF lysis and a decreased ability to induce the release of these factors without affecting target-effector cell binding. These results were not due to changes in HLA class I antigen expression, given that the level of HLA class I antigens on the tumor cell lines was not affected, the only exception being K562. In an attempt to further clarify the possible influence of HLA class I expression on K562, IFN-gamma-pretreated K562 cells were separated into HLA class I positive and HLA class I negative subsets for the NK assays. The results showed that both populations behaved similarly upon target-effector conjugate formation, whereas the HLA class I positive population showed a reduced susceptibility to lysis by NK cells and NKCF. Thus, these results establish that NK resistance induced by IFN-gamma is mediated by blocking the target cell's ability to activate NK cell triggering and release of NKCF and by blocking its susceptibility to lysis by these factors. This analysis helps to clarify not only the NK process but also the controversial regulatory effect of IFN in NK lysis.

Natural killer susceptibility is independent of HLA class I antigen expression on cell lines obtained from human solid tumors

The susceptibility to natural killer (NK) cell-mediated cytotoxicity of 20 cell lines obtained from human solid tumors and their class I histocompatibility antigen (HLA) levels were studied in an attempt to determine whether major histocompatibility complex (MHC) products expressed on cells derived from human solid tumors influence NK susceptibility. The effect of interferon-gamma (IFN-gamma) treatment on these elements was also analyzed. The MHC class I (HLA-ABC, HLA-A and HLA-B) antigen levels and degree of NK lysis were very heterogeneous and no correlation was found on comparison. After treatment with IFN-gamma a marked decrease in NK susceptibility was observed in all the cell lines, including the control line K-562. However, the level of HLA class I expression was not modified in any of the lines with the exception of the K-562, which increased. In some cell lines the expression of HLA class I-like antigens. CDla, b and c, was also measured before and after IFN treatment; however, no correlation was found between CD1 levels and NK susceptibility. Consequently, from our results it is possible to conclude that HLA class I antigens do not play a decisive role in NK susceptibility of cell lines derived from human solid tumors and to suggest that molecules which are not HLA class I antigens but IFN-gamma inducible may confer NK resistance to these lines.

Analysis of the mechanisms involved in NK resistance induced by a new tumor factor NK-RIF

The mechanisms involved in susceptibility or resistance of neoplasic cells to lysis by NK cells are not well known. We have recently described a 12-kDa factor (NK-RIF), produced and released by different tumor cell lines, making K562 resistant to NK lysis without affecting the cytotoxic function of NK effector cells. In this paper we further study the mechanism involved in NK resistance of K562 mediated by NK-RIF and its biological implications. The results show that NK-RIF does not affect the binding capacity of target and effector cells nor the levels of HLA class I antigen expression on the target cells, as a proof that resistance to NK-mediated lysis is not always associated with a defect in target effector binding or with an increased MHC class I antigen expression. However NK-RIF-treated K562 loses its capacity to induce NK cell activation and the subsequent capacity to release NKCF and makes K562 resistant to lysis by NKCF. Therefore our results show that induction of resistance to NK cytotoxicity can be the result of the modulation of target structures responsible for inducing effector cell activation without affecting target/effector binding molecules. This indicates that the structures involved in adherence and activation of NK cells have a different nature and that molecules other than HLA participate in NK resistance.

MHC class I expression on human tumour cells and their susceptibility to NK lysis

Although natural killer (NK) activity is not restricted by the major histocompatibility complex (MHC), it has been suggested that the level of expression of MHC antigens by target cells may influence their lysis by NK cells. We have studied the NK susceptibility of 20 cell lines obtained from primitive and metastatic human tumours and the K562 cell line treated with gamma-interferon, phorbol ester TPA and tumour factor NK-RIF. When the levels of MHC class I antigen expression on the human tumour cell lines and their NK susceptibility were compared, no relationship between these two parameters was observed. Furthermore the treatment of K562 with either gamma-interferon, TPA or NK-RIF decreased its NK susceptibility independently of MHC class I expression. These results indicate that the MHC class I antigen is not the only factor directly involved in NK susceptibility and suggest that other membrane structures modulated by gamma-interferon, TPA or NK-RIF may also influence NK susceptibility.