Modulating mesenchymal stromal cell function with cholesterol synthesis inhibitors

There is increasing evidence that statins, inhibitors of 3-hydroxyl-3-methylglutaryl coenzyme A reductase, can effectively be used not only in the treatment of hypercholesterolemia, but also in other human disorders; indeed, statins have strong anti-inflammatory and immunomodulatory effects, so that they can influence the onset and outcome of inflammation and autoimmunity. On the other hand, it has been shown that statins can affect growth and survival of solid tumour and leukemic cells, thus they have been proposed in the treatment of neoplasias as multiple myeloma, in association with drugs, as thalidomide, known to act on the cancer microenvironment. In the current view, tumor microenvironment include many cell types that interact with tumor cells: among them, stromal and endothelial cells, macrophages and dendritic cells, the various types of lymphocytes such as NK cells, B and T cells. The interplay between all these cell populations, and the balance between these, determines whether there is a tumour cell growth promotion or inhibition. In haematological malignancies, such as multiple myeloma, chronic lymphocytic and myeloid leukemias and follicular lymphomas, the survival, drug-resistance and proliferation of leukemic cells have been shown to be largely dependent on a supportive microenvironment, so that some cellular components of it, mainly mesenchymal stromal cells, cancer associated fibroblasts and macrophages, are now proposed as targets of new therapies. Herein, we analyze the effects that statins can exert on cancer cells, stromal cells and human natural killer cells, to discuss whether they can be proposed as anti-cancer drugs.

MF-59 adjuvant influence on the functions of gammadelta T cells in HIV-1+ adults immunized with influenza seasonal vaccine

INTRODUCTION

We previously reported that in HIV-1 infected patients circulating Vdelta1 T lymphocytes (Vdelta1) increase and proliferate in vitro in response to Candida albicans (Ca). Herein, we analysed the effects of MF59 adjuvant on the Vdelta1 T cell responses to hemagglutinin (HA) and Ca in HIV-1 seropositive and seronegative adults after influenzal vaccine, to clarify th molecular mechanisms triggered in vivo by an adjuvanted vaccine against influenza virus.

MATERIALS AND METHODS

58 seropositive (HIV-1+) and 48 seronegative (HIV-1-) subjects received influenzal vaccines containing or not the MF59 adjuvant. The follow-up of in vitro T cell proliferation and cytokine production (IL-17A, IL-22, IL-23, IL-6) to HA and Ca antigens were performed at different time points (at basal time and after 30 and 90 days from vaccination) by cytofluorimetric approaches.

RESULTS

We confirmed that in HIV-1 infected individuals the Vdelta1 T cell subset is expanded in HIV-1 infected individuals and moreover the number of circulating Vdelta1 Tcells significantly enhanced in all HIV-1+ subjects on day 90 after influenza vaccination. Regard the follow-up of proliferative responses, the increments of CD3+ response to HA and Vdelta1 T cells to Ca in HIV-1+ individuals were detectable earlier on day 30 for MF59-vaccinated patients, instead on day 90 post-vaccination in HIV(+)-vaccinated without MF59 adjuvant. Of note, production of lL-17A and IL-22, two cytokines with anti-fungal activity, in response to Ca was enhanced (for IL-17A) or restored (for IL-22) by vaccination in HIV-1+ donors, mainly using the MF59-adjuvanted vaccine. Moreover, after vaccination IL-23 and IL-6 production increased in response to HA in the HIV+ and HIV- groups vaccinated with MF59 adjuvant.

CONCLUSIONS

We suggest that in HIV-1 infected patients the circulating Vdelta1 T lymphocytes reactive to Ca upon challenge with influenza virus vaccine receive an activating/enhancing signal mediated by cytokines triggered by the boost with HA antigen particularly in presence of MF59 adjuvant.

Gammadelta T lymphocytes producing IFNgamma and IL-17 in response to Candida albicans or mycobacterial antigens: possible implications for acute and chronic inflammation

T lymphocytes bearing the gammadelta T cell receptor are known to play an important role in the first-line defense against viral, bacterial and fungal pathogens. Two main subsets of gammadelta T cells are known, showing distinct functional behaviour: Vdelta2 T lymphocytes, circulating in the peripheral blood, are involved in the response to mycobacterial infections and certain viruses, including coxsakie virus B3 and herpes simplex virus type 2. Vdelta1 T cells are resident in the mucosal-associated lymphoid tissue and are reported to participate in the immunity against Listeria monocytogenes and cytomegalovirus. Vdelta2 T lymphocytes recognize non-peptidic phosphorylated metabolites of isoprenoid biosynthesis, expressed by mycobacteria, while Vdelta1 T cells mainly interact with MHC-related antigens (MIC-A and MIC-B) and with receptors, called UL-16 binding proteins, for the UL-16 protein produced by cytomegalovirus-infected cells. Both Vdelta1 and Vdelta2 T cells can produce interferon-gamma in response to MIC-A(+) cells or non-peptide antigens, respectively. Moreover, production of TNF-alpha by human Vgamma9/Vdelta2 T cells has been demonstrated in response to bacterial products and non-peptidic molecules. Recently, it has been reported that gammadelta T lymphocytes can produce IL-17 during Escherichia coli or Mycobacterium tuberculosis infections in mice. This is of interest as IL-17 is emerging as a cytokine crucial in the control of intracellular pathogens and fungi. In this review, we will discuss the possible role of IL-17 producing gammadelta T cells in the regulation of acute and chronic inflammation, focusing on the different response of the two subsets to mycobacterial, viral or fungal antigens.

Migratory Pathways of T Cells and Response to CXCR3 and CXCR4 Ligands: Adhesion Molecules Involved and Implications for Multiple Sclerosis Pathogenesis

Gammadelta T lymphocytes are thought to be involved in multiple sclerosis (MS) pathogenesis. In this work, we discuss the characteristics of these cells and possible implications in the pathogenesis of MS, focusing on the mechanism(s) underlying extravasation and tissue localization. Phenotype and transendothelial migration of gammadelta T cells from healthy donors and patients with relapsing-remitting MS were studied. In MS patients the V delta 2 T cell subset, expressing NKRP1A/CD161 adhesion molecule, is expanded and capable of transendothelial migration. V delta 1/V delta 2 subsets use distinct signal transduction pathways: V delta 1 cells lack NKRP1A and express PECAM-1/CD31, which drives transmigration, while V delta 2 cells are PECAM-1 negative and use NKRP1A. V delta 2 migration is coupled with CAMKII, whereas V delta 1 depend on PI-3K. NKRP1A and PECAM-1 selectively activate the two pathways: indeed, oligomerization of NKRP1A on V delta 2 T cells leads to CAMKII activation, occupancy of PECAM-1 on V delta 1 cells triggers the PI-3K-dependent Akt/PKB pathway. Moreover, V delta 2 T cells are CXCR3(bright)CXCR4(dull), while V delta 1 are mostly CXCR4(+). V delta 1 and V delta 2 cells transmigrate in response to IP-10/CXCL10 and SDF-1/CXCL12 according to the expression of their specific receptors. In a fraction of V delta 1 T cells coexpressing CXCR3 and CXCR4, the homeostatic chemokine 6Ckine/SLC/CCL21 is more effective. IP-10/CXCL10 or 6Ckine/SLC/CCL21 and SDF-1/CXCL12-induced transmigration is coupled to PI-3K/Akt/PKB, but only CXCR3 is capable of inducing CAMKII activation. We suggest that both subsets of gammadelta T lymphocytes may migrate to the site of lesion in MS using two different signaling pathways to extravasate and responding to different chemokines.

In vivo apoptosis of CD8(+) lymphocytes in acute myeloid leukemia patients: involvement of soluble HLA-I and Fas ligand

In this study, we show that high serum levels of soluble human leukocyte antigens (HLA) class I molecules (sHLA-I, range: 0.7-1.7 micro g/ml) and soluble Fas ligand (FasL, range: 0.4-1.9 ng/ml) are detected in patients with acute myeloid leukemia (AML) at diagnosis, compared with healthy donors (HD) (sHLA-I, range: 0.1-0.6 micro g/ml; sFasL, range: 0.1-0.4 ng/ml). Patients' sera were able to induce transcription and secretion of FasL in CD8(+) T cells, followed by apoptosis in vitro; this apoptosis was inhibited by anti-HLA-I-specific monoclonal antibodies, suggesting that sHLA-I is responsible for cell death. These findings closely relate to the in vivo upregulation of FasL transcription observed in peripheral blood (PB) lymphocytes from AML patients; in the same cells, mRNA for the antiapoptotic proteins Bcl-2 and Bcl-x(L) was downregulated. Interestingly, caspase-8 and caspase-3, both downstream mediators of death receptor-induced apoptosis, were activated in CD8(+) cells of AML patients; one-third of these cells were already apoptotic in vivo, at variance with lymphocytes of HD. These data strongly suggest that in AML, increased levels of sHLA-I molecules may contribute to the elimination of potentially anti-tumor effector cells through a FasL/Fas interaction.

ZAP-70 is expressed by normal and malignant human B-cell subsets of different maturational stage

ZAP-70 tyrosine kinase is involved in signalling pathways following T-cell receptor stimulation and was originally described only in T cells and natural killer cells. ZAP-70 expression has been reported in normal mouse B lineage cells and in human malignant B lymphocytes, mainly in chronic lymphocytic leukemia (CLL) where it correlates with clinical outcome. We analyzed several B-cell lines and ex vivo malignant B cells, ranging from acute lymphoblastic leukemia to multiple myeloma and reflecting different stages of B-cell differentiation, and they showed ZAP-70 expression regardless their maturation stage. We then analyzed by Western blot and flow cytometry different human normal B-lymphocyte subpopulations: naïve, germinal center and memory B cells from tonsils, CD19+ CD5+ cells from cord blood and CD19+ lymphocytes from peripheral blood. All expressed ZAP-70 protein, though at different levels depending on their differentiation, activation and tissue localization. In addition, ZAP-70 expression levels could be modulated following stimulation via the B-cell receptor. These findings implicate a potential role of ZAP-70 in the signalling pathway of B lymphocytes at different maturational stages, indicate that ZAP-70 expression is not a CLL-specific feature among B-cell malignancies and suggest that the absence of ZAP-70 rather than its presence should be considered abnormal for malignant B lymphocytes.

Leukocyte-associated Ig-like receptor-1 prevents granulocyte-monocyte colony stimulating factor-dependent proliferation and Akt1/PKB alpha activation in primary acute myeloid leukemia cells

The leukocyte-associated Ig-like receptor-1 (LAIR-1), a surface leukocyte receptor containing two immune receptor tyrosine-based inhibitory motif (ITIM) is expressed on acute myeloid leukemia (AML) blasts isolated from peripheral blood or bone marrow of 17 patients (2 M0, 3 M1, 5 M2, 2 M4 and 5 M5 according to French, American and British classification). Further, we provide evidence thatLAIR-1 engagement inhibits granulocyte-monocyte colony-stimulating factor (GM-CSF)-induced proliferation of AML blasts. Indeed, leukemia cells stimulated with GM-CSF were blocked in the G0/G1 phase of the cell cycle and underwent apoptosis within 4 days after the engagement of LAIR-1. Remarkably, LAIR-1 was functional also in AML blasts which do not express CD33, mainly M4 and M5. Importantly, the LAIR-1 ligation led to a strong inhibition of both GM-CSF receptor-mediated intracellular calcium increases, phosphorylation and activation of Akt1/protein kinase B alpha, a substrate of the phosphatidylinositol-3 kinase. This last inhibitory effect was prevented by a synthetic peptide spanning the ITIM portion of LAIR-1, suggesting the involvement of SHP-1 phosphatase in LAIR-1-mediated inhibitory signal. Altogether, these findings indicate that the engagement of LAIR-1 can down-regulate GM-CSF-mediated survival and proliferation of AML blasts, suggesting an additional therapeutic approach to the treatment of AML patients.

CD8(+) T lymphocytes induce polarized exocytosis of secretory lysosomes by dendritic cells with release of interleukin-1beta and cathepsin D

We recently reported that human dendritic cells release the leaderless secretory protein interleukin-1beta (IL-1beta) following specific interaction with alloreactive T lymphocytes. To clarify the molecular mechanism underlying this secretion, this study investigated the intracellular trafficking of IL-1beta in dendritic cells and the signal(s) regulating its release. Results show that a fraction of the intracellular IL-1beta precursor colocalizes with the hydrolase cathepsin D in endolysosomes of dendritic cells; secretion of both proteins is elicited by stimuli that induce intracellular calcium increases. Alloreactive CD8(+) T lymphocytes generate a Ca(++) influx in dendritic cells followed by enrichment in endolysosomes containing IL-1beta and cathepsin D beneath the membrane in contact with T cells. These events result in polarized exocytosis of secretory lysosomes, mediated by microtubules, with release of IL-1beta and cathepsin D toward the interacting CD8(+) T cell.

Roles of tumor necrosis factor p55 and p75 receptors in TNF-alpha-induced vascular permeability

We have investigated the role of p55 and p75 tumor necrosis factor receptors 1 and 2 (TNFR1 and TNFR2, respectively) in TNF-induced alteration of endothelial permeability in vitro and in vivo. Stimulation of TNFR1 with an agonist antibody or a receptor-selective TNF mutein increased the flux of (125)I-albumin through endothelial cell monolayers. An antagonist anti-TNFR1 antibody, but not antagonist anti-TNFR2 antibodies, blocked the activity of TNF in vitro. Stimulation of TNFR1, but not TNFR2, induced cytoskeletal reorganization associated with increased permeability. SB-203580, a p38 mitogen-activated protein kinase inhibitor, blocked TNFR1-induced cytoskeletal reorganization and permeability. A selective mouse TNFR1 agonist and human TNF, which binds to murine TNFR1, increased the leakage of trypan blue-albumin from liver vessels in mice. These results indicate that stimulation of TNFR1 is necessary and sufficient to increase endothelial permeability in vitro and in vivo. However, an antagonist anti-murine TNFR2 antibody partially inhibited the effect of murine TNF on liver vessels, suggesting that TNFR2 also plays a role in the regulation of TNF-induced vascular permeability in vivo.

NK cell-mediated lysis of autologous antigen-presenting cells is triggered by the engagement of the phosphatidylinositol 3-kinase upon ligation of the natural cytotoxicity receptors NKp30 and NKp46

Interleukin-2 (IL-2)-activated polyclonal or clonal NK cells lysed autologous antigen presenting cells (APC) through the engagement of the natural cytotoxicity receptors (NCR) NKp30 and NKp46. NK cell-mediated cytolysis of APC correlated with the surface density of these NCR. Indeed, NK cell clones bearing low amounts of NKp30 and NKp46 did not lyse autologous APC, whereas NK cell clones with bright expression of these NCR efficiently killed autologous APC. Upon masking of NKp30 or NKp46 by specific monoclonal antibodies a strong reduction (by 50%) of APC lysis could be detected and the complete inhibition was achieved by the simultaneous masking of these NCR. Interestingly, NK cell-mediated APC lysis was impaired by the phosphatidylinositol 3-kinase (PI-3 K) inhibitors LY294002 or wortmannin. Similarly, these drugs strongly reduced NK cell activation triggered by NKp30 or NKp46 in a re-directed killing assay as well as the activation of Akt/PKB, substrate of PI-3 K, induced by the engagement of these receptors. Altogether, these findings strongly suggest that NCR are responsible for the killing of autologous APC through the activation of PI-3 K.

Engagement of the leukocyte-associated Ig-like receptor-1 induces programmed cell death and prevents NF-kappaB nuclear translocation in human myeloid leukemias

Leukocyte-associated Ig-like receptor-1 (LAIR-1) is a surface molecule that functions as an inhibitory receptor on natural killer cells, T lymphocytes and monocytes. Here, we provide evidence that occupancy of LAIR-1 on human myelomonocytic leukemic cell lines inhibits proliferation and leads to programmed cell death (PCD), evaluated by propidium iodide staining and transmission electron microscopy. Interestingly, PCD elicited via LAIR-1 was not blocked by different caspase inhibitors, at variance with apoptosis induced via CD95/Fas, which was prevented by the caspase-1 and caspase-8 specific inhibitors. In addition, we show that the p65 subunit of the nuclear factor kappaB (NF-kappaB), constitutively expressed in the nucleus of these cell lines, was retained in the cytoplasm upon engagement of LAIR-1. This was evident already 8 h after LAIR-1 occupancy, when apoptosis was not yet detectable by fluorometric or ultrastructural analysis. Moreover, a reduction in inhibitor kappaBalpha phosphorylation was observed after LAIR-1 engagement. As blocking of NF-kappaB activation has been shown to rescue sensitivity to anti-cancer drugs in solid tumors, we suggest that LAIR-1 may represent a possible target for pharmacological approaches aimed to potentiate anti-leukemic therapy.

Control of interleukin-18 secretion by dendritic cells: role of calcium influxes

Here we show that dendritic cells accumulate the precursor form of the leaderless secretory protein interleukin-18 (pro-interleukin-18) in the cell cytosol and in organelles co-fractionating with endolysosomes. Upon antigen specific contact with T lymphocytes, particulated pro-interleukin-18 decreases rapidly, and the cytokine appears extracellularly, suggesting that exocytosis of pro-interleukin-18-containing organelles is induced. Exocytosis of secretory lysosomes is modulated by calcium: in agreement with this, calcium influx results in secretion of pro-interleukin-18. In turn, pro-interleukin-18 secretion induced by T cells is prevented by the calcium channel blocker nifedipine. Our results demonstrate a novel, calcium-mediated mechanism of post-translational regulation of secretion for interleukin-18, that allows a fast release of the cytokine.

Secretion of bioactive interleukin-1beta by dendritic cells is modulated by interaction with antigen specific T cells

The role of interleukin-1beta (IL-1beta) as a regulator of the immune response, although extensively investigated, is still debated. We then studied the expression of IL-1beta by human dendritic cells (DCs), the professional antigen presenting cells, and its modulation during immune reactions in vitro. Our results show that, on maturation or tetanus toxoid presentation to specific CD4(+) CD40L(+) T lymphocytes, DCs begin to accumulate IL-1beta precursor (pro-IL-1beta) but do not secrete bioactive IL-1beta. In contrast, interaction with alloreactive T cells results in both stimulation of pro-IL-1beta synthesis and secretion of processed isoforms of the cytokine, that display biologic activity. Both CD4(+) and CD8(+) subsets of allospecific T lymphocytes are required: CD4(+) T cells drive the synthesis of pro-IL-1beta through CD40 engagement but have no effects on pro-IL-1beta processing; CD8(+) T cells, unable to induce synthesis of pro-IL-1beta per se, are responsible for the generation of mature IL-1beta by pro-IL-1beta-producing DCs. Interleukin-1beta-converting enzyme (ICE) inhibitors do not prevent the recovery of IL-1beta bioactivity after allorecognition, indicating that allospecific CD8(+) T cells may induce the release of bioactive IL-1beta via mechanism(s) other than ICE activation. Altogether, these findings suggest that CD4(+) and CD8(+) T-lymphocyte subsets have distinct roles in the induction of IL-1beta secretion by DCs and support the hypothesis that IL-1beta plays a role in cell-mediated immune responses. (Blood. 2000;95:3809-3815)

uPA/uPAR system is active in immature dendritic cells derived from CD14+CD34+ precursors and is down-regulated upon maturation

We recently described a subset of peripheral CD14+CD34+ cells able to migrate across endothelial cell monolayers and differentiate into immunostimulatory dendritic cells (DC). In this paper we show that immature DC derived from CD14+CD34+ precursors are also capable of reverse transendothelial migration and extracellular matrix (ECM) invasion using the urokinase plasminogen activator receptor (uPAR). We found that these cells respond to macrophage-inflammatory protein (MIP)-1alpha, enhancing their ability to invade ECM and supporting the idea that immature DC are selectively recruited at the site of inflammation to expand the pool of APCs. Interestingly, MIP-1alpha was also capable of preventing the decreased matrix invasion observed by blocking uPAR, suggesting that the uPA/uPAR system and MIP-1alpha cooperate in driving immature DC migration through the subendothelial matrix. Upon exposure to maturating stimuli, such as TNF-alpha, CD14+CD34+-derived DC enhance their APC function and decrease the capacity of invading ECM; these changes are accompanied by altered expression and function of uPAR. Moreover, mature DC shift their sensitivity from MIP-1alpha to MIP-3beta, enhancing their transendothelial migration capability in response to the latter chemokine. Our data support the hypothesis that bloodborne DC can move through ECM toward the site of pathogen entry where they differentiate into fully mature APCs with their motility and function regulated by microenvironmental stimuli, including MIP-1alpha, MIP-3beta, and TNF-alpha.

Interleukin-18 synthesis and secretion by dendritic cells are modulated by interaction with antigen-specific T cells

We show that interleukin-18 is constitutively produced by dendritic cells; synthesis and secretion are poorly affected by maturative stimuli. Challenge of dendritic cells with autologous anti-tetanus toxoid T lymphocytes results in a secretory switch, with induction of secretion of biologically active interleukin-18 and decrease of its intracellular content. Similarly, when dendritic cells are challenged with allospecific T cells a dramatic decrease of intracellular interleukin-18 content occurs, whereas no effects are observed after co-culture with autologous activated T cells. The induction of secretion call be mediated by engagement of CD40 on dendritic cells, as indicated by the increased amount of interleukin-18 in dendritic cell supernatants after CD40 triggering by anti-CD40 antibodies. However, CD40 engagement, unlike from antigen-specific T cells, does not result in reduced intracellular interleukin-18 content, suggesting that this decrease may be mediated by structure(s) involved in antigen recognition.

IL-12-mediated NKRP1A up-regulation and consequent enhancement of endothelial transmigration of V delta 2+ TCR gamma delta+ T lymphocytes from healthy donors and multiple sclerosis patients

Gamma delta T lymphocytes are thought to play a role in the pathogenesis of multiple sclerosis (MS) contributing to demyelinization and fibrosis in the central nervous system. In this study, we show that, in MS patients with active disease, the percentage of circulating V delta 2+ gamma delta T cells coexpressing NKRP1A is significantly increased compared with healthy donors. V delta 2+ and V delta 1+ T cells were sorted from MS patients and healthy volunteers and cloned. At variance with V delta 1+ clones, all V delta 2+ clones expressed NKRP1A, which was strongly up-regulated upon culture with IL-12; this effect was neutralized by specific anti-IL-12 Abs. No up-regulation of NKRP1A by IL-12 was noted on V delta 1+ clones. RNase protection assay showed that IL-12R beta 2 subunit transcript was significantly less represented in V delta 1+ than V delta 2+ clones. This finding may explain the different effect exerted by IL-12 on these clones. In transendothelial migration assays, V delta 2+ NKRP1A+ clones migrated more effectively than V delta 1+ clones, and this migratory potential was enhanced following culture with IL-12. Migration was strongly inhibited by the F(ab')2 of an anti-NKRP1A Ab, suggesting that this lectin is involved in the migration process. We also show that, in freshly isolated PBMC from MS patients, the migrated population was enriched for V delta 2+ NKRP1A+ cells. We conclude that the expression of NKRP1A on V delta 2+ cells is associated with increased ability to migrate across the vascular endothelium and that this phenomenon may be regulated by IL-12 present in the microenvironment.

Functional association of platelet endothelial cell adhesion molecule-1 and phosphoinositide 3-kinase in human neutrophils

In this paper we show that the engagement of the platelet-endothelial cell adhesion molecule-1 (PECAM-1/CD31) up-regulates the adhesion of human neutrophils to the EA.hy926 endothelial cell line through a phosphoinositide 3-kinase (PI3K)-dependent pathway. Indeed, LY294002 and wortmannin prevented the effect of PECAM-1/CD31 cross-linking on cell adhesion, at concentrations known to inhibit PI3K without affecting other kinases. Both compounds blocked neutrophil binding to murine fibroblasts transfected with human ICAM-1, to purified ICAM-1 protein, or to fibronectin, suggesting that PECAM-1/CD31-mediated up-regulation of beta2 and beta1 integrin-mediated adhesion is PI3K-sensitive. We also provide evidence for the association of PECAM-1/CD31 to PI3K, because PI3K was detectable in neutrophil lysates after PECAM-1/CD31 cross-linking and immunoprecipitation. PECAM-1/CD31-dependent recruitment of PI3K was suggested by the finding that the serine/threonine kinase p70 S6 kinase (S6K), a signaling protein downstream of PI3K, is activated in neutrophils upon PECAM-1/CD31 cross-linking, based on the appearance of serine phosphorylation in S6K immunoprecipitates. In turn, S6K is not directly involved in the up-regulation of integrin function because rapamycin, which can inhibit S6K independent of PI3K, did not block PECAM-1/CD31-induced adhesion of neutrophils to beta1 and beta2 integrin substrates. In conclusion, PECAM-1/CD31 appears to be one of the molecules functionally coupled to PI3K, suggesting that this enzyme may represent a common pathway of integrin and adhesiveness regulation in leukocytes.

HIV-1 Tat inhibits human natural killer cell function by blocking L-type calcium channels

Herein we show that functional phenylalkylamine-sensitive L-type calcium channels are expressed by human NK cells and are involved in the killing of tumor targets. Blocking of these channels by phenylalkylamine drugs does not affect effector/target cell binding but inhibits the release of serine esterases responsible for cytotoxicity. Interestingly, treatment of NK cells with HIV-1 Tat, which is known to affect several calcium-mediated events in immune cells, impairs their cytotoxic activity. In addition, Tat inhibits the rise in intracellular free calcium concentration upon cross-linking of the adhesion molecule CD11a, engaged during effector/target cell interaction, and the activation molecule CD16. Exogenous Tat does not influence NK-target cell binding but prevents NK cell degranulation. We propose that the molecular structure(s) on NK cells mediating the inhibitory effects HIV-1 Tat belong to L-type calcium channels, based on three lines of evidence: 1) binding of phenylalkylamine derivatives to these channels is cross-inhibited by Tat; 2) L-type calcium channels from NK cell lysates bind to Tat linked to Sepharose columns; 3) the inhibitory effect of HIV-1 Tat on NK cell function is prevented by the agonist of L-type calcium channels, Bay K 8644. Altogether, these results suggest that exogenous Tat is deeply involved in the impairment of NK cell function during HIV-1 infection.

Tumor-driven matrix invasion by infiltrating lymphocytes: involvement of the alpha1 integrin I-domain

Here we show that tumor cells (TC) from renal cancers regulate the migratory properties of autologous tumor-infiltrating lymphocytes (TIL), enhancing their ability to invade the extracellular matrix. A similar effect is exerted by human recombinant macrophage chemotactic protein 1 (MCP-1) and IL-8, chemokines known to increase T lymphocyte migration both across vascular endothelium and subendothelial matrix. We found that TC freshly derived from renal cell carcinoma surgical specimens constitutively secrete both IL-8 and MCP-1 and that TIL express both specific receptors. TIL matrix invasion elicited by TC is inhibited by the addition of neutralizing antisera specific for IL-8 and MCP-1, demonstrating the direct relationship between chemokine release by TC and TIL invasion. Of note, TIL invasion of the extracellular matrix requires the alpha1 integrin, which acts through its I-domain that is upregulated upon culture with MCP-1 and IL-8. Collectively, these findings suggest that TC may actively recruit TIL via the release of chemotactic factors that enhance an alpha1 integrin-mediated pathway of matrix invasion.

p40/LAIR-1 regulates the differentiation of peripheral blood precursors to dendritic cells induced by granulocyte-monocyte colony-stimulating factor

p40/LAIR-1, a member of the immunoglobulin superfamily, is a surface molecule broadly distributed among leukocytes which has been shown to down-regulate T and NK cell activation. In this study, we show that p40/LAIR-1 is highly expressed in CD14+ peripheral blood mononuclear cells (PBMC). When cultured in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) for 10-14 days, CD14+ cells acquired morphologic and phenotypic features (i.e. loss of CD14 and expression of CD80bright and CD86bright) typical of dendritic cells (DC) and lost the expression of p40/LAIR-1. Engagement of p40/LAIR-1 (but not of CD58) by specific monoclonal antibodies prevented CD14+ PBMC differentiation into DC; when cultured in the presence of GM- CSF upon p40/LAIR-1 cross-linking, the resulting cells were CD14+CD80(dull)CD86(dull) and displayed a macrophage-like morphology. We have recently demonstrated that peripheral blood CD14+ cells co-expressing the CD34 progenitor marker represent the circulating precursors of CD83+ DC. Herein we show that cross-linking of p40/LAIR-1 prevented the maturation of CD14+CD34+ cells into CD83+ DC. This effect appears to be consequent to the impairment of GM-CSF receptor-mediated activation signaling. Indeed, triggering of GM-CSF receptors in both CD14+ and CD14+CD34+ cells led to increases in the intracellular free calcium concentrations which were inhibited by p40/LAIR-1 engagement. Taken together, these data suggest a possible regulating role played by p40/LAIR-1 in the process of differentiation from peripheral blood precursors into DC induced by GM-CSF.

Involvement of dihydropyridine-sensitive calcium channels in human dendritic cell function. Competition by HIV-1 Tat

The entry of extracellular calcium in leukocytes mediates several cellular processes; however, unlike in excitable tissues, the underlying molecular mechanisms are poorly defined. In this paper we provide phenotypical and biochemical evidence that peripheral blood-derived human dendritic cells express dihydropyridine-sensitive calcium channels. Exposure to the dihydropyridine drug nifedipine, which binds L-type calcium channels blocking calcium influx, prevents two dendritic cell functions that are dependent on extracellular calcium entry: apoptotic body engulfment and interleukin-12 production induced by cross-linking of the surface lectin NKRP1A. It is known that exogenous human immunodeficiency virus, type 1 Tat affects several Ca2+-dependent immune cell responses. Here we demonstrate that Tat inhibits apoptotic body engulfment and interleukin-12 production by blocking extracellular calcium influx. This inhibition is prevented by the calcium channel agonist dihydropyridine derivative Bay K 8644, suggesting the involvement of L-type calcium channels. This hypothesis is further supported by the observation that Tat and dihydropyridine drugs compete for binding to dendritic cells. Taken together, these findings indicate that exogenous Tat exerts its inhibitory effects on dendritic cells by blocking dihydropyridine-sensitive L-type calcium channels.

CD14+ CD34+ peripheral blood mononuclear cells migrate across endothelium and give rise to immunostimulatory dendritic cells

We describe a subset of peripheral CD14+ cells, coexpressing the CD34 progenitor marker and able to migrate across endothelial cell monolayers. On culture with granulocyte-macrophage-CSF, this population differentiated into dendritic cells expressing CD83, CD80, HLA-DR(bright), CD86, and CD54. These dendritic cells were immunostimulatory, in that they induced proliferation of allogenic and tetanus toxoid-specific T lymphocytes. The CD14+ CD34+ population expressed higher levels of platelet endothelial cell adhesion molecule-1 (PECAM-1) and alpha4beta1 integrin than the CD14+ CD34- counterpart, being dull positive for other integrins. Using stably transfected PECAM-1+, VCAM-1+, or ICAM-1+ cells, we found that PECAM-1 and, to a lesser extent, VCAM-1, could support transmigration of CD14+ CD34+ cells, whereas the alphaL-ICAM-1 interaction was involved in cell adhesion. PECAM-1-driven transmigration was conceivably dependent on a haptotactic gradient, as it was reduced by 80% across NIH3T3 cells transfected with the PECAM-1-delta cyto deletion mutant. This mutant lacks the cytoplasmic tail and displays a reduced tendency to localize at the intercellular junctions, thus failing to form a molecular junctional gradient. Once differentiated, dendritic cells derived from CD14+ CD34+ precursors retained their transendothelial migratory capability, using both PECAM-1 and ICAM-1 for transmigration. We suggest that a subset of CD14+ CD34+ circulating leukocytes can localize to peripheral tissues and differentiate into functional dendritic cells, thus representing a functional reservoir of potential APC. PECAM-1, constitutively expressed on vascular endothelium, is likely to play a relevant role in the egress of this population from the bloodstream.

Expression and function of NKRP1A molecule on human monocytes and dendritic cells

In this study, we analyzed the expression and function of the lymphocyte surface lectin NKRP1A on peripheral blood monocytes (Mo) or Mo and dendritic cells (DC) derived from thymic and bone marrow precursors. De novo expression of NKRP1A and CD14 molecules was detected upon culture of CD2- CD3- CD14- CD16- CD1a- NKRP1A- immature thymic precursors for 7 days in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF). Under these culture conditions, by day 21, a fraction of cells had lost CD14 and acquired both CD80 (B7.1) and CD86 (B7.2) molecules. These cells displayed a DC-like morphology and were surface NKRP1A positive. CD34+ NKRP1A- CD14- precursors, isolated from bone marrow and cultured in the presence of GM-CSF, also expressed both NKRP1A and CD14: these antigens were newly expressed on about one third of cells which had lost the CD34 precursor marker. In addition, NKRP1A was constitutively present on resting CD14+ peripheral blood Mo. When these cells were cultured in the presence of GM-CSF, the resulting DC population retained the expression of NKRP1A and acquired CD80, while they lost the CD14 antigen. Functional analysis revealed that the engagement of NKRP1A molecule leads to a strong intracellular calcium ([Ca2+]i) increase both in resting peripheral blood Mo and in vitro-derived DC. [Ca2+]i increase was mainly due to extracellular calcium influx, as it was completely abrogated by the addition of EGTA. More importantly, the engagement of the NKRP1A molecule induced interleukin (IL)-1 beta and IL-12 production by resting Mo and DC, respectively. Altogether these data indicate that NKRP1A lectin is present at the surface of Mo and DC and may play a relevant role in the activation and function of both cell types.

Phenotypic and functional analysis of CD4+ NKRP1A+ human T lymphocytes. Direct evidence that the NKRP1A molecule is involved in transendothelial migration

In this report, we show that among human CD4+ T lymphocytes 5-20% express the C-type lectin molecule NKRP1A. This lymphocyte subset displays a slightly more limited T cell receptor V beta repertoire than the CD4+ NKRP1A- counterpart. CD4+ NKRP1A+ T lymphocytes are characterized by a high expression of beta 1 and beta 2 integrins, thus representing a T lymphocyte subset that can possibly adhere and migrate through vascular endothelium. Indeed, resting CD4+ NKRP1A+ lymphocytes, differently from the CD4+ NKRP1A- subset, migrated across endothelial cell monolayers in a Transwell chamber system. Pretreatment of CD4+ NKRP1A+ T lymphocytes with an anti-NKRP1A monoclonal antibody (mAb) strongly reduced transendothelial migration, suggesting the involvement of the NKRP1A molecule in the transmigration process. Furthermore, cells of the NKRP1A- Jurkat CD4+ T cell line stably transfected with NKRP1A cDNA migrated more rapidly and efficiently than either untransfected or mock-transfected Jurkat cells. Finally, mAb-mediated cross-linking of NKRP1A molecules in CD4+ T lymphocytes induced the up-regulation of the lymphocyte function-associated antigen 1 Mg(2+)-binding site as well as beta 1 and beta 2 integrin chains. Altogether, these findings suggest that the NKRP1A molecule is involved in transendothelial migration of resting CD4+ T lymphocytes.

The selective engulfment of apoptotic bodies by dendritic cells is mediated by the alpha(v)beta3 integrin and requires intracellular and extracellular calcium

Dendritic cells derived in vitro from monocytes are known to be poor phagocytes. Here we show that, unlike macrophages, monocyte-derived dendritic cells indeed fail to take up opsonized particles or necrotic cells; however, apoptotic bodies are efficiently engulfed by dendritic cells. The temperature dependence and the sensitivity to cytochalasin D indicate that the apoptotic body engulfment is representative of early stages of phagocytosis. Inhibition studies with ligands for surface molecules involved in recognition of apoptotic bodies, such as vitronectin receptor, CD36 and phosphatidylserine receptor, revealed that apoptotic body engulfment by dendritic cells is mediated preferentially by the vitronectin receptor alpha(v)beta3, while all the receptors, with different efficiency, are engaged in phagocytosis of apoptotic bodies by macrophages. The interaction between apoptotic bodies and dendritic cells elicits a rise in intracellular free calcium concentration ([Ca2+]i) which is essential for the process of engulfment. Either intra- or extracellular Ca2+ buffering inhibits apoptotic body engulfment by dendritic cells and [Ca2+]i increases, indicating the involvement of both intra- and extracellular Ca2+. In contrast, Ca2+ mobilization is dispensable for macrophage phagocytosis of apoptotic bodies. The different requirements of Ca2+ in macrophages and dendritic cells is possibly due to the differential usage of phagocytic receptors (CD36 vs. alpha(v)beta3) and might reflect different fates of apoptotic bodies in the two cell types.

The RGD-containing domain of exogenous HIV-1 Tat inhibits the engulfment of apoptotic bodies by dendritic cells

OBJECTIVE

HIV-1 Tat can be released by infected cells and exert various extracellular functions on bystander cells, possibly contributing to immunodeficiency. In order to investigate whether exogenous Tat can affect antigen presentation, the effects of synthetic Tat on the function of dendritic cells displaying antigen presenting cell phenotype were studied.

DESIGN

Cultured dendritic cells were challenged with apoptotic bodies and monitored for cell engulfment and free intracellular calcium ([Ca2+]i) increase. The effect of synthetic HIV-1 Tat and its RGD-containing domain (peptide 65-80) or basic domain (peptide 46-60) on both functions was investigated.

METHODS

Dendritic cells were obtained by culture of monocytes with granulocyte-macrophage colony-stimulating factor. Apoptosis was induced in Jurkat cells by sub-lethal irradiation. Engulfment of radiolabelled apoptotic bodies by dendritic cells was obtained by a 45 min co-incubation at 37 degrees C. Non-ingested apoptotic bodies were removed and cell-associated radioactivity evaluated in a gamma-counter after cell lysis. Single cell analysis of calcium fluxes was performed by video-microscopy and ratio-imaging, after cell staining with the fluorescent calcium chelator FURA-2.

RESULTS

Apoptotic bodies were engulfed by dendritic cells: this process was accompanied by [Ca2+]i rise. Synthetic HIV-1 Tat inhibited both apoptotic body engulfment and [Ca2+]i increase. The same inhibition was obtained with the RGD-containing domain (peptide 65-80), but not with the basic domain (peptide 46-60) of Tat, suggesting the involvement of an integrin. This integrin is likely to be alpha v beta 3, since RGD-containing peptides from vitronectin, but not from fibronectin, inhibited apoptotic body engulfment. Furthermore, both HIV-1 Tat and its 65-80 peptide blocked [Ca2+]i increase due to beta 3-integrin cross-linking.

CONCLUSIONS

Our results support a role for HIV-1 Tat in decreasing the function of dendritic cells, possibly impairing antigen presentation.

NKRP1A molecule is involved in transendothelial migration of CD4+ human T lymphocytes

Among human CD4+ T lymphocytes, 5-20% express the C-type lectin molecule NKRP1A. Interestingly, CD4+ NKRP1A+ T lymphocytes express high levels of beta 1 and beta 2 integrins, thus representing a T lymphocyte subset that can possibly adhere and migrate through vascular endothelium. Indeed, resting CD4+ NKRP1A+ lymphocytes, differently from the CD4+ NKRP1A- subset, migrated across endothelial cell monolayers in a Transwell chamber system. This transendothelial migration was strongly reduced after pre-treatment with an anti-NKRP1A monoclonal antibody (mAb). In addition, the NKRP1A negative Jurkatt CD4+ T-cell line that had been stably transfected with NKRP1A cDNA, migrated more rapidly and efficiently than untransfected Jurkatt cells. Finally, mAb-mediated cross-linking of NKRP1A molecule in CD4+ T lymphocytes induced the upregulation of the LFA1 Mg2+ binding site as well as beta 1 and beta 2 integrin chains. Altogether, these findings indicate that NKRP1A molecule is involved in transendothelial migration of resting CD4+ T lymphocytes.

Physical and functional association of CD45 and CD3-TCR complex on CD1+ human thymocytes. Evidence that the engagement of CD45 molecules can prevent CD1+ thymocytes from apoptosis

In this study the effects of CD45 engagement on CD3-TCR-driven stimulation of CD1+ human immature thymocytes have been analyzed. Simultaneous cross-linking of CD45 and CD3 antigens on highly purified CD1+ thymocytes reduced the number of cells undergoing apoptosis after 16 h of in vitro culture. This cell population might represent immature thymocytes committed in vivo to die by programmed cell death (PCD). CD45 engagement could also increase the number of cycling CD1+ thymocytes; of note, the large majority (> 95%) of dividing cells expressed the CD1 molecule at the cell surface, indicating that proliferating cells were actually represented by immature thymocytes. These data suggest that the CD45 molecule might play a role in the rescue of immature thymocytes from PCD during differentiation. Along this line, we found that activation of CD1+ thymocytes via the CD3-TCR complex could be enhanced by CD45, both in terms of transcription and surface expression of IL-2R. These effects might be explained by the finding that the CD45 molecule (but not its isoforms CD45RO and RA) was physically associated with the CD3-TCR complex at the cell surface of CD1+ human thymocytes, as shown by co-precipitation and co-capping experiments. Finally, cross-linking of CD45 and CD3 antigens led to the expansion of CD3+ thymocytes co-expressing CD4 and CD8, indicating that simultaneous engagement of CD45 and CD3 molecules can block CD1+ cells at the double-positive (CD3+CD4+CD8+) differentiation stage. On the other hand, stimulation through CD3 resulted in the expansion of thymocytes showing a mature phenotype (CD3+CD4+ or CD3+CD8+). Altogether, these findings suggest that the CD45 molecule is involved both in early activation and in the regulation of CD1+ thymocyte differentiation.

Tumor necrosis factor alpha-induced vascular leakage involves PECAM1 phosphorylation

Herein we show that exposure of human umbilical vein endothelial cells to tumor necrosis factor alpha (TNFalpha) led to platelet endothelial cell adhesion molecule-1 (PECAM1) surface redistribution, disruption of cytoskeleton connections, and increased PECAM1 phosphorylation, accompanied by increased permeability to macromolecules. The in vitro use of inhibitors of tyrosine or serine-threonine kinases could prevent both PECAM1 surface redistribution and the increase in permeability induced by the cytokine. In vivo administration of lavendustin A, a natural tyrosine kinase inhibitor, protected endothelial cells from TNFalpha-dependent vascular leakage in mouse liver. We propose that the involvement of PECAM1 in TNFalpha-mediated effects on vascular permeability may depend on a dynamically regulated cytoskeletal association, related to the degree of PECAM1 phosphorylation.

A functional monoclonal antibody recognizing the human alpha 1-integrin I-domain

Alpha 1 beta 1 heterodimer is a member of the integrin receptor superfamily that has been described to be involved in cell-matrix binding through its interaction with collagens, fibronectin and laminin. The alpha 1 integrin belongs to a subset of I-domain containing integrins that includes alpha M, alpha L, alpha X and alpha 2. In this study we describe an anti-alpha 1 mAb (FB12) that recognizes an epitope located in the human alpha 1 I-domain, since the mAb can bind to human, but not to rat, recombinant I-domain GST fusion protein. FB12 mAb efficiently and specifically inhibits the binding of activated human lymphocytes to laminin, collagen and fibronectin. These data support the notion that the alpha 1 I-domain itself has an important role in receptor-ligand binding. In particular, we show that alpha 1 integrin-dependent lymphocyte adhesion to fibronectin is I-domain mediated, at variance with the RGD-dependent adhesion which seems to be mediated by the beta 1 rather than the alpha 1 integrin chain. Lastly, the overexpression of the alpha 1-integrin by stromal cells and blood vessels of solid tumors may suggest a role for this integrin in tumor biology.

Drug-induced in vitro inhibition of neutrophil-endothelial cell adhesion

1. Leukocyte-endothelial cell interactions play an important role during ischaemia-reperfusion events. Adhesion molecules are specifically implicated in this interaction process. 2. Since defibrotide has been shown to be an efficient drug in reducing damage due to ischaemia-reperfusion in many experimental models, we analysed the effect of defibrotide in vitro on leukocyte adhesion to endothelial cells in basal conditions and after their stimulation. 3. In basal conditions, defibrotide (1000 micrograms ml-1) partially inhibited leukocyte adhesion to endothelial cells by 17.3% +/- 3.6 (P < 0.05), and after endothelial cell stimulation (TNF-alpha, 500 u ml-1) or after leukocyte stimulation (fMLP, 10(-7) M), it inhibited leukocyte adhesion by 26.5% +/- 3.4 and 32.4% +/- 1.8, respectively (P < 0.05). 4. In adhesion blockage experiments, the use of the monoclonal antibody anti-CD31 (5 micrograms ml-1) did not demonstrate a significant inhibitory effect whereas use of the monoclonal antibody anti-LFA-1 (5 micrograms ml-1) significantly interfered with the effect of defibrotide. 5. This result was confirmed in NIH/3T3-ICAM-1 transfected cells. 6. We conclude that defibrotide is able to interfere with leukocyte adhesion to endothelial cells mainly in activated conditions and that the ICAM-1/LFA-1 adhesion system is involved in the defibrotide mechanism of action.

Dissection of lymphocyte function-associated antigen 1-dependent adhesion and signal transduction in human natural killer cells shown by the use of cholera or pertussis toxin

The effect of the guanosine triphosphate-binding protein (G-protein) inhibitors cholera toxin (Ctx) and pertussis toxin (Ptx) has been analyzed on lymphocyte function-associated antigen 1 (LFA-1)-dependent adhesion and signal transduction in human natural killer (NK) cells. Ctx, but not Ptx, inhibited the LFA-1-dependent adhesion of NK cells to tumor target cells which constitutively express the intercellular cell adhesion molecule-1 (ICAM-1) and to NIH/3T3 mouse fibroblasts stably transfected with human ICAM-1. This effect was detectable only by the use of the entire Ctx but not of the Ctx B subunit. In addition, Ctx could inhibit both NK cell binding and spreading to purified ICAM-1 protein. NK cell treatment with Ctx modified neither the surface expression of LFA-1 nor its Mg2+ binding site. These findings, together with the absence of any detectable effect of Ctx on the constitutive phosphorylation of LFA-1 alpha, suggests that this toxin modifies the avidity of LFA-1 for ICAM-1 by acting on LFA-1-cytoskeletal protein association. Unlike Ctx, Ptx did not affect NK cell adhesion. The effects of Ctx and Ptx are unlikely to depend on intracellular levels of cyclic adenosine 3',5'-monophosphate (cAMP), since a strong increase of cAMP was induced by both toxins. Moreover, this was confirmed by the observation that the LFA-1-dependent adhesion was not inhibited by the adenylate cyclase activator forskolin (FSK), the phosphodiesterase inhibitor isobutyl-1-methylxanthine (IBMX), or both, which increase intracellular cAMP levels. Unlike the differential effect on cell adhesion, both the intracellular calcium [Ca2+]i increase and phosphoinositide breakdown mediated via LFA-1 were consistently inhibited in a dose-dependent manner by both Ctx and Ptx. Also in this case, the inhibitory effect did not depend on an increase of intracellular cAMP as indicated by NK cell treatment with FSK, IBMX, or both. Further evidence of the involvement of G-proteins in LFA-1-mediated signal transduction was the inhibitory effect of the GDP analog guanosine-5'-O-2-thiodiphosphate (GDP beta S) on LFA-1-mediated calcium mobilization. Taken together, our data provide evidence that the LFA-1-mediated NK cell adhesion and signal transduction are partially independent phenomena which may be regulated by different G-proteins.

CD31/PECAM-1-driven chemokine-independent transmigration of human T lymphocytes

We assessed the relative contribution of CD31/PECAM-1 (platelet-endothelial cell adhesion molecule-1) to T lymphocyte transmigration by the use of transfected murine fibroblasts stably expressing either the human CD31/PECAM-1 or the intercellular adhesion molecule-1 (CD54/ICAM-1). Unlike CD54/ICAM-1, CD31/PECAM-1 supported migration of activated T cells in the absence of chemokines: most of the migrating lymphocytes were CD31+ and displayed a phenotype corresponding to the naive subpopulation (LFA-1 dull and CD45RA+). Migration of activated T lymphocytes through CD54/ICAM-1+ transfected monolayers could be induced by creating a chemotactic gradient with the chemokine monocyte chemotactic protein-1, and the migrating cells mainly displayed a memory phenotype (LFA-1 bright CD45RO+) under these conditions. Furthermore, we found that in transfected cells CD54/ICAM-1 is uniformly distributed along the apical surface of the cells, while CD31/PECAM-1 is concentrated at the intercellular junctions, suggesting the existence of a haptotactic gradient (i.e. a gradient of substrate- or cell-bound molecules) responsible for T cell migration. This was also confirmed by the finding that monolayers of murine fibroblasts transfected with a CD31/PECAM-1 mutant lacking the cytoplasmic domain (CD31/PECAM-1-delta cyto), which has a reduced tendency to localize at cell-cell contact areas, supported efficient adhesion but were unable to induce migration of activated T cells unless a chemotactic gradient was created. We propose that in lymphocytes, homophilic CD31/PECAM-1 adhesion may be primarily involved in transmigration of naive T cells and that its role is complementary to that of CD54/ICAM-1.

CD31-triggered rearrangement of the actin cytoskeleton in human natural killer cells

In this report, we analyze whether CD31, also known as platelet-endothelial cell adhesion molecule-1 (PECAM-1), can transduce an outside-in signal in human natural killer (NK) lymphocytes in vitro. We show that CD31, but not HLA class-I cross-linking triggers an outside-in transmembrane signal in NK lymphocytes, mediating cell spreading and cytoskeletal rearrangement. These phenomena are Mg2+, but not Ca2+ dependent, suggesting that signal transduction elicited by CD31 cross-linking may involve an associated integrin. Two possible candidates would be alpha v and alpha L, whose function is known to depend on Mg2+. However, the CD31-induced cytoskeletal rearrangement was not reduced by the use of alpha v- or alpha L-specific F(ab')2, suggesting that CD31 could transduce a signal by itself or by association with a still-undefined integrin. Moreover, talin, but not vinculin or tubulin, appears to co-localize with actin microfilaments in the membrane ruffles of NK cells that undergo cytoskeleton rearrangement following CD31 cross-linking. Both spreading and cytoskeletal rearrangement appear to be regulated by intracellular cyclic-3',5'-adenosine monophosphate (cAMP). Indeed, the activator of the adenylyl cyclase, forskolin, inhibited cell spreading and cytoskeletal rearrangement induced by CD31 cross-linking. This phenomenon was also observed using the membrane-permeants cAMP analog Sp adenosine-3', 5' -cyclic monophosphothioate (Sp-cAMPS), but not its inactive isomer Rp-cAMPS. Likewise, adhesion of NK lymphocytes to NIH/3T3 murine fibroblasts transfected with the cDNA encoding human CD31 was blocked by increasing intracellular cAMPS levels. We suggest that intracellular cAMP may be involved in CD31-mediated signal transduction, and may regulate NK-endothelial cell adhesion and possibly, the tissue localization of NK cells.

The platelet endothelial cell adhesion molecule-1 (PECAM1) contributes to endothelial barrier function

In this study we have analyzed the role of the platelet-endothelial cell adhesion molecule-1 (PECAM1) in vascular barrier function. PECAM1 is an immunoglobulin gene superfamily member expressed by endothelial cells at the cell boundaries. Macromolecule permeability assays performed on cell monolayers that express native or transfected PECAM1, indicated that the molecule participates in the establishment and maintenance of vascular barrier function in vitro. This hypothesis was confirmed by the finding that in vivo injection of the specific monoclonal antibody directed against the murine vascular PECAM1 led to a detectable leakage of hepatic and renal blood vessels.

Inducible nitric oxide synthase modulates fibronectin production in the EA.hy926 cell line and cultured human umbilical vein endothelial cells

We wished to test the hypothesis of a connection existing between inducible nitric oxide (NO) synthesis and production of extracellular matrix proteins in endothelial cells (EC). We recently reported that the inducible-NO pathway contributes to cytokine-induced enhancement of tumor cell (TC) adhesion to cultured vascular endothelium, independent of changes in E-selectin expression on endothelial cells (EC). We now show that inducible NO-synthase is involved in enhancing fibronectin production by EC. Indeed, fibronectin synthesis and secretion increased both in the EA.hy926 EC line and in human umbilical vein EC (HUVEC) after prolonged exposure to tumor necrosis factor-alpha (TNF-alpha) or interferon-gamma (IFN-gamma). This effect was reversed by the reported inhibitor of NO synthase N omega-nitro-L-arginine methyl ester (L-NAME 10(-5) M). The two cytokines exerted no additive effect, suggesting that they trigger a common metabolic pathway. NO production by cytokine-stimulated EC was dependent on the inducible NO-pathway, as demonstrated by studies of EC-dependent inhibition of platelet aggregation. This inhibition was also evident in calcium-free medium and was reversed by L-NAME and by two inhibitors of protein synthesis that are reported to block the inducible-NO synthase, such as dexamethasone (Dex 10(-7) M) and cycloheximide (Chx 10(-6) M). We conclude that modulation of the inducible NO-synthase may regulate matrix protein production by vascular endothelium during inflammation.

Expression of N-CAM by human renal cell carcinomas correlates with growth rate and adhesive properties

In the present study we provide evidence for the involvement of N-CAM in the spreading of human renal cell carcinomas (RCC) through the interaction with the subendothelial matrix. We found that in tumor cell lines derived from human RCC the increase of growth rate and the loss of adhesiveness to inert substrate were accompanied by N-CAM expression and by the appearance of specific binding to endothelial heparan sulfate. Indeed, the adhesion of tumor cells to human endothelial cells and heparan sulfate in vitro was inhibited by monoclonal antibodies able to bind and inactivate N-CAM and was abrogated by endothelial cell treatment with heparitinase. Furthermore, when the renal epithelial cell line COS7 was transfected with a cDNA coding for N-CAM a significant increase in the ability to bind both endothelium and heparan sulfate in vitro was observed. Of note, HS complexed with epithelial growth factor could enhance the proliferation of RCC-derived tumor cells; this effect was also achieved by cross-linking of N-CAM at the surface of tumor cells, suggesting that N-CAM could transduce an activation signal across the cell membrane. This was also supported by the finding that N-CAM cross-linking induced a strong calcium mobilization from internal stores and opening of surface calcium channels in such tumor cells. N-CAM was detectable in vivo at the tumor site in the areas of active proliferation, as judged by the coexpression of Ki67 nuclear antigen, and heparan sulfate was present in the wall of blood vessels in the proximity of the tumor. These findings would suggest that growing kidney tumors might use N-CAM to bind the subendothelial matrix and complexed growth factors during tissue invasion and spreading.

Distinct pattern of HSP72 and monomeric laminin receptor expression in human lung cancers infiltrated by gamma/delta T lymphocytes

We have previously demonstrated that gamma/delta T lymphocytes may participate in the host immune response against lung adenocarcinomas. Here we show that, in about one-fourth of human lung cancers, gamma/delta T cells represented a significant proportion of freshly isolated tumor-infiltrating lymphocytes. Moreover, these cells selectively expand in vitro upon culture in the presence of IL-2, thus suggesting a prior activation in vivo. Finally, when we evaluated the expression of heat shock proteins and of a panel of tumor-associated antigens in lung cancers infiltrated by gamma/delta vs. alpha/beta T cells, we found that the former displayed a distinct antigenic pattern, characterized by over-expression of HSP72 and of the 67-kDa high-affinity laminin receptor, which might account for gamma/delta T-cell recognition.

T-cell receptor V delta gene usage by tumour reactive gamma delta T lymphocytes infiltrating human lung cancer

In seven human adenocarcinomas and a non-neoplastic granulomatous disease of the lung, gamma delta+ infiltrating lymphocytes (TIL) could be isolated and selectively expanded in vitro upon culture in interleukin-2 (IL-2), without any additional stimuli, indicating a prior activation in vivo. In most cases gamma delta TIL were predominantly V delta 1+, despite a normal V delta 2:V delta 1 ratio in paired peripheral blood lymphocytes, suggesting a possible expansion of this subset in response to localized antigens/superantigens. Moreover, in five patients it was possible to identify a V delta 1- V delta 2- TIL population which by polymerase chain reaction (PCR) analysis was shown to be heterogeneous as V delta gene usage, inclusive of V delta 3,4,5,6,7 and 8. Of note, these V delta regions have not been found in peripheral blood so far. Finally, in all cases, gamma delta TIL displayed killing activity of the autologous tumour, which appeared to be more restricted in the case of V delta 1+ cells. Altogether, these findings suggest a preferential expansion, at the tumour site, of V delta 1+ cells and of cells expressing V delta genes other than V delta 2.

Involvement of CD56/N-CAM molecule in the adhesion of human solid tumor cell lines to endothelial cells

Tumor-endothelial cell adhesion has been investigated, as this event might represent one of the first steps in the generation of tumor metastasis. We focused our attention on the N-CAM homologous CD56 (besides the CD44, CD15, and CDw49d antigens), as we have recently reported that it can mediate lymphocyte-endothelial cell adhesion [11]. Herein we show that CD56 is involved in tumor cell-endothelial cell binding. This phenomenon is independent of Ca2+ and unlikely to be influenced by the degree of CD56 sialylation.

Unusual expression and localization of heat-shock proteins in human tumor cells

It has been suggested that members of HSP families represent the surface target of immune responses leading to tumor rejection in mice. Here we report that tumor cells, compared with normal cells, constitutively expressed 2- to 10-fold higher levels of intracellular HSP90. Moreover, in the absence of environmental stress, 2 lines (out of 6) expressed the "inducible" HSP72, which was also detectable in fresh tumor cells. HSP72 expression was not regulated during the cell cycle, in contrast with what has been observed with normal cells. Both HSP90 and HSP72 proteins exhibited a heterogeneous pattern of intracellular distribution in most cells, HSP72 being confined mainly to the nuclear compartment. Finally, we could detect both HSP90 and, to a lesser extent, HSP72 (that are generally believed to be located intracellularly) at the surface of some tumor cell lines. We conclude that tumor cells differ from normal cells in their pattern of HSP expression; this might imply a role of HSPs in eliciting an immune response against cancer.

Antigen-independent pathways of T-cell activation are functional in human immature thymocytes

The signal requirements for proliferation of CD1+CD3- immature thymocytes have been studied in order to define whether this immature cell population could function despite the lack of the CD3/T-cell receptor complex. We found that CD1+CD3- cells proliferate upon stimulation with anti-CD28 monoclonal antibody as well as with a pair of anti-CD2 monoclonal antibodies in the presence of low doses (0.5 ng/ml) of phorbol-13-myristate-12-acetate and/or recombinant interleukin-2. A minor fraction of CD3+ cells (15%-20%) was also present in the proliferating cell population originating from CD1+CD3- thymocytes stimulated with phorbol-13-myristate-12-acetate and recombinant interleukin-2, either in the presence or in the absence of specific monoclonal antibodies. We further observed that the anti-CD3 monoclonal antibody did not induce the proliferation of CD1+CD3- cells, as expected, and efficiently triggered unfractionated or CD1+CD3+ thymocytes only if exogenous recombinant interleukin-2 was provided. Unexpectedly, we noted that highly purified (greater than 99%), CD1+CD3- immature thymocytes could mobilize calcium via CD3, besides CD2 and CD28 surface molecules, suggesting that a minor undetectable fraction (less than 1%) of CD3+ cells was still present in the purified CD3- population. Nevertheless, the preferential expansion of CD3-CD8+ cells (about one-third of proliferating cells) after triggering via CD28, and to a lesser extent via CD2, support the notion that the alternative pathways of T-cell activation are actually functional in CD1+CD3- immature thymocytes.

Cultured human thymocytes lacking CD2 and CD11a/CD18 antigens are functional and adhere to endothelial cells via CD56 or CDw49d molecules

The preferential growth of CD3-CD2-CD11a/CD18- thymocytes was obtained by stimulation of CD2-CD3- thymic cells with low doses of PMA (0.5 ng/ml) and subsequent culture in the presence of recombinant interleukin-2 (100 U/ml). After 2-3 weeks, CD3-CD2-CD11a/CD18- thymocytes represented 40-60% of the total proliferating cells. Highly purified CD3-CD2-CD11a/CD18- cell populations were obtained by depletion of the CD11a/CD18+ thymocytes by immunomagnetic beads. Moreover, these populations proliferated for 2-5 weeks and did not change their surface phenotype. It is of note that these cells, despite the lack of CD2 and CD11a/CD18 adhesion molecules, could bind to umbilical vein endothelial cells as efficiently as did CD3+CD2+CD11a/CD18+ thymocytes. Furthermore we demonstrate that (a) CD56 molecule is involved in the adhesion of CD3-CD2-CD11a/CD18- thymic cells, but not of peripheral CD3-CD56+ lymphocytes, to untreated or IFN-gamma- and/or TNF-alpha-treated endothelium, (b) anti-CDw49d mAb could inhibit the adhesion of this thymus-derived population to either IFN-gamma- or TNF-alpha-treated endothelial cells but not to untreated endothelium, and (c) CD56 antigen expressed by these cultured thymocytes has a sialic acid content different from that of peripheral lymphocytes. Indeed, isoelectrofocusing analysis showed that CD56 molecule expressed on CD3-CD2-CD11a/CD18- thymocytes displayed an isoelectric point (pI 5.0) different from that of CD56 antigen expressed by peripheral NK cells (pI 4.7 and 5.4). Further, we noted that CD56 antigen showed the same pI 5.8 after desialylation obtained using neuraminidase treatment. Finally, CD3-CD2-CD11a/CD18- thymocytes mobilized Ca2+ and released TNF-alpha and IFN-gamma after treatment with lectins.

Signalling in human tumour infiltrating lymphocytes: The CD28 molecule is functional and is physically associated with the CD45R0 molecule

The CD28 T cell activation pathway was functional in human tumour infiltrating lymphocytes (TIL) and can induce strong proliferation, lymphokine release and calcium mobilisation. Conversely, TIL responded poorly to stimulation via CD2, and CD28 did not synergise with CD2, which is at variance with that observed using peripheral lymphocytes from the same patients. On stimulation with anti-CD28 the monoclonal antibody, most TILs, which were CD3+, CD28+ and CD45R0+ at the beginning of culture, co-expressed both high (CD45RA) and low (CD45R0) molecular weight isoforms of CD45. CD28 was associated with the CD45R0 isoform at the cell surface of activated TIL, as demonstrated by immunoprecipitation and immunoenzymatic assay. Thus CD28 can substitute for CD3 in TIL leading to the expansion of functional lymphocytes and to the amplification of antitumour immune response.

Involvement of nitric oxide in tumor cell adhesion to cytokine-activated endothelial cells

The aim of the present experiments was to test the possible involvement of nitric oxide (NO) in cytokine-induced enhancement of tumor cell (TC) adhesion to endothelial cells (ECs). Exposure of EA hyb 926 cells to TNF (500 U/ml) plus IFN (100 U/ml) for 24 h significantly enhanced their adhesivity for the 51Cr-labeled GLC1 (small cell lung carcinoma) TCs. Conversely, exposure of TCs to cytokines did not result in an increased adhesion of these cells to ECs. TC-stimulated adhesion to EA hyb 926 was abrogated by the glucocorticoid dexamethasone (Dex, 10(-7) M), the NO synthase inhibitors N omega-nitro-L-arginine methyl ester (L-NAME, 10(-5) M) and NG-monomethyl-L-arginine (L-NMMA, 10(-5) M) and the protein synthesis inhibitor cycloheximide (Cex, 10(-6) M). Furthermore, GLC1-stimulated adhesion to EA hyb 926 was reversed following removal of L-arginine from the medium or pretreatment with the guanylate cyclase inhibitor methylene blue. TC-stimulated adhesion was also prevented when TCs were pretreated with the monoclonal antibody CD15 directed against the endothelial-leukocyte adhesion molecule (ELAM-1) ligand or following exposure of ECs to anti-ELAM-1 monoclonal antibody. Although suppressing TC-stimulated adhesion, L-NMMA failed to modify significantly cytokine-induced ELAM-1 expression in EA hyb 926. These results (a) provide evidence for the NO-inducible pathway contributing to cytokine-induced enhancement of tumor cell adhesion to the vascular endothelium and (b) demonstrate the involvement of the ELAM-1/CD15 adhesion system in tumor cell-stimulated adhesion to ECs.