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G Tosato

Publications and source records attributed to G Tosato.

At least 91 records · Page 5Linked to original sources
PubMed1991

The role of lactic acid in autocrine B-cell growth stimulation.

Growth and survival of Epstein-Barr virus (EBV)-immortalized B lymphocytes cultured at low cell densities require autocrine soluble factors. In this study, we have purified a low molecular weight autocrine soluble factor that promotes growth of EBV-immortalized B cells in serum-free conditions and identified it as lactic acid (LA). Synthetic LA stimulated growth in EBV-immortalized B cells at 1-10 mM, a concentration of LA measured in the culture supernatant of EBV-immortalized cell lines. LA alone was found to account for greater than 70% of the autocrine growth factor activity in serum-free supernatants of EBV-immortalized B cells. Aminooxyacetate, a glutamate-oxaloacetate transaminase inhibitor, specifically inhibited B-cell growth induced by LA, suggesting that this process requires mitochondrial-cytosol transfers. Thus, LA is an autocrine stimulatory molecule that in serum-free conditions is essential for the continuous proliferation of EBV-immortalized B cells. This represents an unexpected function for LA.

Animals↗
PubMed1991

Impairment of natural killer functions by interleukin 6 increases lymphoblastoid cell tumorigenicity in athymic mice.

Expression of the human IL-6 gene in EBV-immortalized normal human B lymphocytes following retroviral-mediated transduction rendered these cells highly tumorigenic in athymic mice. The tumors were lymphomas composed of the originally inoculated human lymphoblastoid cells. Co-injection of IL-6 expressing EBV-immortalized cells with IL-6 nonexpressing control cells resulted in increased tumorigenicity of the IL-6 nonexpressing cells. The lymphoblastoid cells expressing IL-6 were indistinguishable from parental cell lines in morphology and in a variety of cell surface characteristics, and did not exhibit growth advantage over parental cell lines in vitro, such that increased tumorigenicity is unlikely to depend upon a direct oncogenic effect of IL-6 on the B cells. Rather, at high concentrations, IL-6 markedly inhibits human lymphoblastoid cell killing by IL-2-activated murine splenocytes in vitro, suggesting that IL-6-related tumorigenicity might depend upon IL-6 inhibiting cytotoxicity at the tumor site. Thus, production of IL-6 by tumor cells that results in natural killer cell dysfunctions illustrates a novel mechanism of tumor cell escape from immune surveillance.

Animals↗
PubMed1990

Induction of interleukin-6 during human immunodeficiency virus infection.

Interleukin-6 (IL-6), a multifunctional cytokine produced in monocytes, fibroblasts, and other cell types, is induced by a variety of stimuli, including bacteria, viruses, and other cytokines. When normal monocyte cultures were exposed to a monocytotropic strain of human immunodeficiency virus (HIV), HTLV-IIIBa-L, significant levels of IL-6 bioactivity were detected in the culture supernatants after 12 to 43 days of incubation, at a time when there was associated evidence of HIV production. Similarly, when normal monocyte cultures were cocultured with peripheral blood mononuclear cells from HIV-infected individuals, HIV replication in these cultures was associated with production of IL-6. In further studies, we determined that mean serum levels of IL-6 bioactivity were abnormally elevated in HIV-seropositive individuals with stage 1/2 infection (25.2 x/divided by 1.8 U/mL) and stage 3/4 infection (46.1 x/divided by 1.7 U/mL) when compared with normals (1.6 x/divided by 1.2 U/mL). In contrast mean serum IL-6 levels were not different from normal in stage 5/6 infection (2.7 x/divided by 1.6 U/mL). A selected group of 12 HIV-seropositive individuals (stages 1, 2, and 3) who harbored HIV capable of replicating in T cells but not in monocyte cultures had a mean serum IL-6 level of 5.3 U/mL (x/divided by 1.5), a value significantly lower (P less than .004) than that measured in control HIV-seropositive individuals infected with monocytropic HIV (39 x/divided by 1.9 U/mL). In addition, serum IL-6 levels in HIV-seropositive individuals (stages 1 through 6) correlated directly with serum immunoglobulin G (IgG) levels (R = .74, P less than .001). Monocytes but not T cells are capable of a high level IL-6 production in vitro, and monocyte-derived IL-6 stimulates Ig production in activated B cells. Thus, HIV-seropositive individuals who often are infected with monocytotropic HIV and often display abnormally elevated serum IgG levels may exhibit these abnormalities as a consequence of abnormally elevated IL-6 levels induced by HIV.

Cells, Cultured↗
PubMed1990

Interleukin-1 induces interleukin-6 production in peripheral blood monocytes.

Interleukin-6 (IL-6), a multifunctional cytokine produced in monocytes, fibroblasts, endothelial cells, and keratinocytes, is induced by a variety of stimulating signals, including lipopolysaccharide (LPS), poly (I), poly (C), IL-1, tumor necrosis factor (TNF), and platelet-derived growth factor. Some of these signals induce IL-6 effectively only in one cell type, and this selectivity of induction may explain selectivity of biologic effects. In the present study, we show that IL-1 beta, previously known to be a potent inducer of IL-6 in fibroblasts, endothelial cells, and keratinocytes, but not in monocytes, is also a potent inducer of IL-6 in peripheral blood monocytes. High level IL-6 activity that could be neutralized by specific antibodies to IL-6 was detected in supernatants of IL-1-stimulated monocytes. Maximal induction required IL-1 concentrations of 10 ng/mL. As judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions, IL-6 species of relative molecular mass of 19 to 26 Kd could be specifically immunoprecipitated from supernatants of IL-1-induced monocytes. Size heterogeneity is a reported feature of IL-6 produced in a variety of cell types, and monocyte-derived IL-6 induced by either IL-1 or LPS displayed similar size heterogeneity. The highly purified recombinant IL-1 beta preparation used contained little, if any, LPS. In addition, monocyte production of IL-6, induced by IL-1 beta, was specifically neutralized by anti-IL-1 beta antibodies, demonstrating that IL-1, rather than a contaminant in the IL-1 preparation, was responsible for IL-6 induction. A number of biologic activities have been ascribed both to IL-1 and IL-6. The finding that IL-1 induced IL-6 in monocytes may help in defining the spectrum of biologic activities of each of these interactive cytokines.

Cells, Cultured↗
PubMed1990

Accessory function of interleukin-1 and interleukin-6: preferential costimulation of T4 positive lymphocytes.

Two monocyte-derived cytokines, interleukin-1 (IL-1) and interleukin-6 (IL-6), have been reported to costimulate monocyte-depleted T cell populations in the presence of mitogen, and this effect has been attributed to an accessory function of these molecules. We have now examined further the accessory function potential of IL-1 plus IL-6, and examined how these cytokines promote T cell growth with mitogen. Together, IL-1 and IL-6 additively and, to a small degree, synergistically promote the proliferation of highly purified human peripheral blood T cells with phytohemagglutinin (PHA). However, maximum costimulation by IL-1 plus IL-6 over a wide range of concentrations is significantly smaller than that induced by optimal numbers of monocytes. Also, in contrast to monocytes that costimulate equally effectively T4 positive and T8 positive cells, IL-1 plus IL-6 costimulate T4 positive lymphocytes in marked preference to T8 positive cells. IL-1 plus IL-6 induces IL-2 secretion in T cell cultures costimulated with PHA, and an antibody to the IL-2 receptor, anti-Tac, markedly inhibits PHA-activated T cells costimulated by IL-1 plus IL-6. In addition, IL-1 plus IL-6 enhances the expression of surface IL-2 receptors. Because the costimulatory effect of IL-1 plus IL-6 is quantitatively smaller than that of monocytes, and it is preferentially directed toward T4 positive as opposed to T8 positive T cells, IL-1 plus IL-6, together, appear to represent a selective set of monocyte-derived accessory signals.

CD4-Positive T-Lymphocytes↗
PubMed1990

Biochemical and biological analysis of human interleukin 6 expressed in rodent and primate cells.

The cDNA for human interleukin 6 (IL 6) was stably expressed at high levels in the three mammalian cell lines COS-7, PA317, and GH3 to yield IL 6 proteins of 25 to 27, 26, 22 to 24, and 23 kDa molecular mass. Both size and relative amounts of the recombinant IL 6 (rIL 6) species produced correspond to those of natural IL 6 secreted by LPS-stimulated monocytes. Oligosaccharide analysis of recombinant IL 6 utilizing tunicamycin and endoglycosidases revealed O- and N-linked glycosylation that is comparable to that of natural IL 6 derived from human monocytes and fibroblasts. IL 6 expressed in each of the three cell lines was phosphorylated similarly to the IL 6 produced in human monocytes and fibroblasts. IL 6 secreted by the three different cell lines have marked differences in specific biological activities. COS-7 IL 6 appeared to be 12-fold more active in its hybridoma growth factor activity than that made in PA317 or GH3 cells. In contrast, PA317 and GH3 IL 6 were 230 and 6.7 times more effective than COS-7 IL 6 in inducing Ig production in CESS cells. Also, PA317 and GH3 IL 6 were more effective than COS-7 IL 6 in inducing the acute-phase protein fibrinogen in human hepatocytes. The rIL 6 species exhibited no antiviral activity.

Acute-Phase Proteins↗
PubMed1990

Identification of interleukin-6 as an autocrine growth factor for Epstein-Barr virus-immortalized B cells.

Autocrine growth factors are believed to be important for maintenance of an immortalized state by Epstein-Barr virus (EBV), because cell-free supernatants of EBV-immortalized cell lines promote the proliferation of autologous cells and permit their growth at low cell density. In this study, we provide evidence for the existence of two autocrine growth factor activities produced by EBV-immortalized lines distinguished by size and biological activities. Much of the autocrine growth factor activity in lymphoblastoid cell line supernatants resided in a low-molecular-weight (less than 5,000) fraction. However, up to 20 to 30% of the autocrine growth factor activity resided in the high-molecular-weight (greater than 5,000) fraction. While the nature of the low-molecular-weight growth factor activity remains undefined, the high-molecular-weight growth factor activity was identified as interleukin-6 (IL-6). Culture supernatants from six EBV-induced lymphoblastoid cell lines tested contained IL-6 activity, because they promoted proliferation in the IL-6-dependent hybridoma cell line B9. In addition, a rabbit antibody to human IL-6 neutralized the capacity of the high-molecular-weight (greater than 5,000) fraction of a lymphoblastoid cell line supernatant to promote growth both in autologous EBV-immortalized cells and in B9 cells. Similarly, this high-molecular-weight autocrine growth factor activity was neutralized by a monoclonal antibody to human IL-6. Furthermore, characteristic bands, attributable to IL-6, were visualized in supernatants of each of four EBV-induced lymphoblastoid cell lines after immunoprecipitation with a rabbit antiserum to human IL-6. Thus, in addition to its previously reported properties, IL-6 is an autocrine growth factor for EBV-immortalized B cells cultured under serum-free conditions.

B-Lymphocytes↗
PubMed1988

Interferon-beta 2/interleukin 6 is a co-stimulant for human T lymphocytes.

IFN-beta 2/IL-6 promotes the proliferation of human peripheral blood T cells in the presence of either PHA or Con A. This effect is observed with highly purified T cells and is masked by the addition of as few as 2% monocytes, suggesting that accessory cells are not required and that IFN-beta 2/IL-6 acts directly on the T cells. Both T4-positive and T8-positive cells respond to IFN-beta 2/IL-6 plus PHA. Studies of the time requirements of IFN-beta 2/IL-6 and of PHA in the response of T cells show that optimal co-stimulation occurs when both IFN-beta 2/IL-6 and PHA are added together at the outset of culture, suggesting that IFN-beta 2/IL-6 acts predominantly on resting T cells. Unlike T cell proliferation induced by IL-2, T cell proliferation induced by IFN-beta 2/IL-6 is not blocked by antibodies to the IL-2 R, suggesting that IFN-beta 2/IL-6 does not act by stimulating IL-2 production. Thus, in addition to its previously reported properties, IFN-beta 2/IL-6 stimulates T cells in the presence of mitogen, and may prove to be of considerable importance in the physiologic activation of T cells.

Adjuvants, Immunologic↗
PubMed1988

Stimulation of EBV-activated human B cells by monocytes and monocyte products. Role of IFN-beta 2/B cell stimulatory factor 2/IL-6.

EBV infects human B lymphocytes and induces them to proliferate, to produce Ig, and to give rise to immortal cell lines. Although the mechanisms of B cell activation by EBV are largely unknown, the continuous proliferation of EBV-immortalized B cells is dependent, at least in part, upon autocrine growth factors produced by the same EBV-infected B cells. In the present studies we have examined the influence of monocytes on B cell activation by EBV and found that unlike peripheral blood T cells and B cells, monocytes enhance by as much as 30- to 50-fold virus-induced B cell proliferation and Ig production. Upon activation with LPS, monocytes secrete a growth factor activity that promotes both proliferation and Ig secretion in EBV-infected B cells and thus reproduces the effects of monocytes in these cultures. Unlike a number of other factors, rIFN-beta 2/B cell stimulatory factor 2 (BSF-2)/IL-6 stimulates the growth of human B cells activated by EBV in a manner similar to that induced by activated monocyte supernatants. In addition, an antiserum to IFN-beta that recognizes both IFN-beta 1 and IFN-beta 2 completely neutralizes the B cell growth factor activity of activated monocyte supernatants. These findings demonstrate that IFN-beta 2/BSF-2/IL-6 is a growth factor for human B cells activated by EBV and suggest that this molecule is responsible for B cell growth stimulation induced by activated monocyte supernatants. We have examined the possibility that IFN-beta 2/BSF-2/IL-6 might also be responsible for B cell growth stimulation by supernatants of EBV-immortalized B cells and thus may function as an autocrine growth factor. However, IFN-beta 2/BSF-2/IL-6 is not detectable in supernatants of EBV-immortalized B cells by immunoprecipitation. Also, an antiserum to IFN-beta that neutralizes IFN-beta 2/BSF-2/IL-6 fails to neutralize autocrine growth factor activity. This suggests that autocrine growth factors produced by EBV-immortalized B cells are distinct from IFN-beta 2/BSF-2/IL-6. Thus, the continuous proliferation of EBV-immortalized B cells is enhanced by either autocrine or paracrine growth factors. One of the mediators with paracrine growth factor activity is IFN-beta 2/BSF-2/IL-6.

B-Lymphocytes↗
PubMed1988

The human interleukin 2 receptor beta chain (p70). Direct identification, partial purification, and patterns of expression on peripheral blood mononuclear cells.

IL-2 binds to high- and low-affinity receptors on activated T cells. The high-affinity receptor was hypothesized to consist of the noncovalent association between the alpha chain (IL-2-R-alpha, p55) and a beta chain (IL-2-R-beta, p70), whereas the low-affinity receptor consists of p55 without p70. We now directly identify p70 as a 65-77-kD glycoprotein doublet. Preparative quantities of the IL-2/p70 complex have been isolated. Further, we demonstrate that p70 is the principal IL-2 binding protein on both resting CD4+ and CD8+ T cells and that both p70 and p55 can be induced on normal B cells and monocytes.

Antigens, Surface↗
PubMed1988

Monocyte-derived human B-cell growth factor identified as interferon-beta 2 (BSF-2, IL-6).

Soluble products of either Epstein-Barr virus (EBV)-infected B cells or activated monocytes promote the proliferation of EBV-infected B cells and permit their growth at low cell densities. This suggests that growth factors are important for B-cell immortalization by EBV. In this study, a monocyte-derived factor that promotes the growth of EBV-infected b cells was purified and identified as interferon-beta 2 (IFN-beta 2), which is also known as 26-kilodalton protein, B-cell differentiation factor (BSF-2), and interleukin-6 (IL-6). The purified protein has a specific activity of approximately 4 X 10(7) units per milligram of protein in assays of B-cell growth. Thus, IFN-beta 2/BSF-2 is a B-cell growth factor that promotes the proliferation of human B cells infected with EBV.

B-Lymphocytes↗
PubMed1987

Suppressor T cell clones from patients with acute Epstein-Barr virus-induced infectious mononucleosis.

Suppression and/or cytotoxicity are believed to play an important role in the defense against Epstein-Barr virus (EBV) infection. To analyze the role of suppressor T cells in relation to EBV, we sought to clone and study these T cells. Analysis of 152 T cell clones derived from the peripheral blood of two patients with acute EBV-induced infectious mononucleosis (IM) yielded 11 highly suppressive clones that had no cytotoxic activity for the natural killer sensitive K562 cell line, an autologous EBV-infected cell line, or an allogeneic EBV-infected B cell line. Four of six suppressor T cell clones also profoundly inhibited EBV-induced immunoglobulin production, and five of five clones delayed the outgrowth of immortalized cells. These results indicate that during acute IM, suppressor T cells capable of inhibiting B cell activation in the absence of cytotoxicity can be identified, and may play a key role in the control of EBV infection.

Antibody Formation↗
PubMed1986

Epstein-Barr virus immortalization of normal cells of B cell lineage with nonproductive, rearranged immunoglobulin genes.

Most continuous cell lines derived by EBV immortalization of peripheral blood cells are composed of phenotypically mature B lymphocytes, and secrete Ig. Occasionally, EBV-immortalized cell lines have failed to secrete Ig. Expansion and characterization of one of these EBV-induced cell lines, VDS-O, showed that in addition to a lack of Ig secretion, surface and intracytoplasmic Ig were absent. Cell surface phenotyping revealed that VDS-O belongs to the B cell lineage, because it expresses the B cell restricted antigens B1 and B4, while it lacks T cell and monocyte-associated determinants. Analysis of the Ig gene organization in VDS-O revealed that the Ig genes are rearranged for both heavy (gamma) and light (kappa) chains. However, the expected gamma-heavy chain and/or kappa-light chain RNA species were not detected. These findings demonstrate the existence in normal peripheral blood of cells of B cell lineage susceptible to EBV immortalization that have Ig genes that are rearranged but are nonproductive.

Antibody Formation↗
PubMed1986

Defective regulation of Epstein-Barr virus infection in patients with acquired immunodeficiency syndrome (AIDS) or AIDS-related disorders.

Patients with the acquired immunodeficiency syndrome (AIDS) acquire undifferentiated B-cell lymphomas that are similar to African Burkitt's lymphoma and contain Epstein-Barr virus (EBV). Using an in vitro assay system that measures a complex of cellular responses to EBV-infected lymphocytes, we found that B cells from 7 patients with AIDS and from 10 patients with AIDS-related disorders produced abnormally low numbers of immunoglobulin-secreting cells (P less than 0.001 as compared with normal controls) and that T-cell suppression, which was greater than 80 percent in EBV-seropositive normal controls, was absent. Instead, the patients' T cells markedly increased immunoglobulin production induced by EBV. In further studies, we determined that the mean frequency of circulating EBV-infected B cells capable of spontaneous outgrowth in vitro was 13 per 10(6) B cells in 7 patients with AIDS and 21 per 10(6) B cells in 10 patients with AIDS-related disorders--figures that were significantly higher than the mean in normal controls (P less than 0.001). Thus, patients with AIDS or AIDS-related disorders may be predisposed to the development of EBV-containing lymphomas, because they have a profound defect of T-cell immunity to EBV and abnormally high numbers of EBV-infected B cells in the circulation.

Acquired Immunodeficiency Syndrome↗
PubMed1985

B-cell-derived interleukin 1 (IL-1)-like factor. I. Relationship of production of IL-1-like factor to accessory cell function of Epstein-Barr virus-transformed human B-lymphoblast lines.

The relationship of production of interleukin 1 (IL-1)-like factor to accessory function of Epstein-Barr virus (EBV)-transformed B lymphocytes was examined. Six of eight human EBV-B cell lines spontaneously produced and released detectable levels of thymocyte comitogenic factor in vitro, but no interleukin 2 (IL-2) activity. Eight of eight produced fibroblast proliferation activity. Culture supernatants from the two apparent nonproducers of thymocyte comitogenic activity induced the proliferation of the IL-1-dependent murine helper-T-cell clone D10G4.1 in the presence of concanavalin A (Con A). One of the EBV-B cell lines produced a potent inhibitory factor in addition to IL-1-like thymocyte comitogenic and fibroblast proliferation factors. The inhibitory factor inhibited mouse thymocyte proliferative response to Con A, and the proliferation of the IL-2-dependent CT6 cell line, but not human fibroblast growth. All but one of the eight EBV-B cell lines tested, the exception being the line that produced an inhibitory factor, were able to serve as antigen-presenting cells that enabled purified human T lymphocytes to proliferate in one-way mixed lymphocyte reactions (MLR) and in response to Con A. The supernatants of 14 of 16 clones derived from two of the EBV-B cell line cells contained thymocyte comitogenic activity and all 16 stimulated fibroblast proliferation. The phenotypic characteristics of the EBV-B cell lines were heterogeneous, but there was no clear-cut relationship between the cell surface phenotypes of either the cloned or uncloned EBV-B cells and their ability to produce these factors. These studies show that all of the EBV-B cell lines that can function as accessory cells have the capacity to produce an IL-1-like factor.

Animals↗
PubMed1985

B-cell-derived interleukin-1 (IL-1)-like factor. II. Sources, effects, and biochemical properties.

A variety of types of human B-cell lines were evaluated for their ability to produce interleukin 1 (IL-1)-like factors. All of the eight Epstein-Barr virus (EBV)-transformed B lymphocyte lines, three of four of the EBV+ lymphoma lines, only three of seven of the EBV- lymphoma lines, and none of the three tested myeloma lines secreted some IL-1 activity. The IL-1-like factor produced by the cell lines was detected on the basis of its thymocyte comitogenic and/or fibroblast proliferative activities. Injections of partially purified IL-1-like factor from one of the EBV-transformed B-lymphocyte lines also induced the appearance of an acute phase protein (haptoglobin) in the serum of C3H/HeJ mice. These biological activities are identical with those of monocyte-derived IL-1. Thymocyte comitogenic activity and fibroblast proliferation activity from one of the EBV-B cell line-derived IL-1-like activities were not dissociable by biochemical procedures, including HPLC gel filtration and HPLC anion-exchange chromatography. However, the IL-1-like factor from one of the EBV-B lymphocyte cell lines was larger in size (25 kDa) and more acidic (pI 5.5) than monocyte-derived IL-1.

Animals↗