Picolinic acid- or desferrioxamine-inducible autocrine activation of macrophages engineered to produce IFNγ: an approach for gene therapy

Macrophage (Mphi)-based vectors are highly mobile cellular shuttles designed to deliver therapeutic genes within the tissues. We engineered a mouse Mphi cell line to express the murine interferon-gamma (IFNgamma) under the control of an inducible promoter containing the hypoxia-responsive element, which can be triggered by hypoxia and other stimuli. We show that this Mphi vector can be induced to produce IFNgamma under normoxic conditions by stimulation with picolinic acid (PA), a catabolite of tryptophan, or desferrioxamine (DFX), an iron-chelating drug. The Mphi vector responds to IFNgamma with the induction of IRF-1 and of other IFNgamma-inducible genes, the expression of Ia antigens and induction of phagocytic activity. Inducible nitric oxygen synthase gene expression, nitric oxide production, as well as TNFalpha secretion were enhanced by PA or DFX as the sole stimuli. None of the above responses could be triggered individually by PA or DFX in control, normal Mphi, indicating that the Mphi vector overcame the need for costimulatory molecules derived from the immune system for its full activation. Furthermore, we demonstrate that extracellular iron can downregulate such response, thereby identifying an additional tool for the fine tuning of the Mphi vector response to stimulation.

Engineering of macrophages to produce IFN-gamma in response to hypoxia

Activation of murine macrophages (Mphi) requires the collaboration of signals derived from the immune system and the environment. In this study, we engineered a murine Mphi cell line to become activated in response to an environmental signal, hypoxia, as the sole stimulus. Hypoxia is a condition of low oxygen tension, occurring in several pathological tissues, which acts in synergy with IFN-gamma to induce full Mphi activation. We transfected the ANA-1 murine Mphi cell line with a construct containing the IFN-gamma gene controlled by a synthetic promoter inducible by hypoxia (HRE3x-Tk), and we characterized the cellular and molecular biology of the engineered Mphi under normoxia or hypoxia. Engineered Mphi in normoxia expressed basal levels of IFN-gamma mRNA and protein that were strongly augmented by shifting the cells to hypoxia. Furthermore, they responded to the synthesized IFN-gamma with induction of IFN-responsive factor-1 and 2'-5'-oligoadenylate synthase expression. Under normoxic conditions, the engineered Mphi had a significant constitutive level of Ia Ags and Fc receptors. Hypoxia induced further augmentation of Ia and Fc expression. Finally, hypoxia induced inducible NO synthase expression, and subsequent reoxygenation led to the production of NO. In conclusion, the engineered Mphi, which produce IFN-gamma in an inducible manner, express new biochemical and functional properties in response to low oxygen environment as the sole stimulus, thereby circumventing the need for costimulation by other immune system-derived signals.

Generation of high-titer retroviral vector-producing macrophages as vehicles for in vivo gene transfer

The goal of this project was to develop a novel gene transfer system based on macrophages (Mphi) as shuttles of recombinant retroviral vectors carrying therapeutic or marker genes. The murine Mphi cell line WGL5 was used as a source of Mphi for this study. We generated retrovirus-producing Mphi by transducing the WGL5 cells with a replication-defective retroviral vector carrying the enhanced green fluorescent protein (EGFP) reporter gene and the Moloney murine leukemia virus (MoMLV) as helper virus. We demonstrated stable integration of the recombinant retrovirus in the Mphi genome, efficient recombinant retrovirus production, and EGFP gene delivery to different cell lines in vitro. To evaluate Mphi-mediated EGFP gene transfer in vivo, allogeneic mice were injected s.c. with the retrovirus-producing WGL5 Mphi, that gave rise to solid tumor masses at the injection site, highly infiltrated with host leukocytes. We observed EGFP fluorescence in tumor-infiltrating CD4(+) and CD8(+) host T lymphocytes, providing direct evidence of the ability of engineered Mphi to mediate EGFP gene delivery to host cells in vivo. Moreover, we showed that retrovirus-producing Mphi could home to different organs in vivo following i.v. injection into mice. These data demonstrate that Mphi can be engineered as cellular vehicles for recombinant retroviruses carrying heterologous genes and suggest potential applications of this novel vector system for gene therapy.

IL-2 signaling in human monocytes involves the phosphorylation and activation of p59hck

The activating properties of IL-2 and the structure of the IL-2R on human monocytes are well characterized. However, relatively little is known about the biochemical mechanisms involved in IL-2 signal transduction in these cells. We investigated the role of protein tyrosine kinases (PTKs) in the activation of monocytes by IL-2. Incubation of monocytes with the PTK inhibitor herbimycin A (HA) resulted in the dose-dependent suppression of IL-2-induced monocyte tumoricidal activity. This inhibition was rather potent, as a concentration of HA as low as 0.5 microM caused a complete abrogation of cytolytic activity. Furthermore, HA markedly suppressed the ability of IL-2 to induce IL-1 beta, TNF-alpha, IL-6, and IL-8 mRNA expression and protein secretion by monocytes. Anti-phosphotyrosine immunoblotting demonstrated that IL-2 induced a rapid and time-dependent increase in tyrosine phosphorylation of several cellular proteins of molecular masses ranging from 35 to 180 kDa. Interestingly, IL-2 caused a significant up-regulation of the constitutive levels of hck PTK mRNA and protein relative to medium-treated cells as well as an increase in p59hck tyrosine phosphorylation. Finally, we demonstrated by in vitro kinase assay that the specific activity of p59hck PTK was also induced by IL-2 in monocytes. Thus, these data show that the activation of PTKs is required for the triggering of monocyte effector and secretory functions by IL-2 and strongly suggest that p59hck is a key participant in IL-2 signaling in human monocytes.

The tryptophan catabolite picolinic acid selectively induces the chemokines macrophage inflammatory protein-1 alpha and -1 beta in macrophages

We previously found that the tryptophan catabolite picolinic acid (PA) is a costimulus for the activation of macrophage effector functions. In this study, we have investigated the ability of PA to modulate the expression of chemokines in macrophages. We demonstrate that PA is a potent activator of the inflammatory chemokines MIP (macrophage inflammatory protein)-1 alpha and MIP-1 beta (MIPs) mRNA expression in mouse macrophages in a dose- and time-dependent fashion and through a de novo protein synthesis-dependent process. The induction by PA occurred within 3 h of treatment and reached a peak in 12 h. The stimulatory effects of PA were selective for MIPs because other chemokines, including monocyte chemoattractant protein-1, RANTES, IFN-gamma-inducible protein-10, MIP-2, and macrophage-derived chemokine, were not induced under the same experimental conditions and were not an epiphenomenon of macrophage activation because IFN-gamma did not affect MIPs expression. Induction of both MIP-1 alpha and MIP-1 beta by PA was associated with transcriptional activation and mRNA stabilization, suggesting a dual molecular mechanism of control. Iron chelation could be involved in MIPs induction by PA because iron sulfate inhibited the process and the iron-chelating agent, desferrioxamine, induced MIPs expression. We propose the existence of a new pathway leading to inflammation initiated by tryptophan catabolism that can communicate with the immune system through the production of PA, followed by secretion of chemokines by macrophages. These results establish the importance of PA as an activator of macrophage proinflammatory functions, providing the first evidence that this molecule can be biologically active without the need for a costimulatory agent.

Enhanced B7-2 gene expression by interferon-gamma in human monocytic cells is controlled through transcriptional and posttranscriptional mechanisms

B7-2 is a costimulatory molecule expressed on professional antigen-presenting cells that provides T cells with a critical signal resulting in T-cell activation. Interferon-gamma (IFN-gamma) enhances B7-2 protein expression in monocytic cells. However, the molecular mechanisms controlling the enhanced expression of B7-2 are poorly understood. Northern blot and flow cytometry analysis revealed that human monocytes and the human monocytic cell line MonoMac6 (MM6) constitutively expressed B7-2 mRNA and protein and IFN-gamma treatment further enhanced the expression of both molecules. The ability of IFN-gamma to enhance B7-2 mRNA was evident at the dose of 31 U/mL and reached plateau levels at 500 U/mL. The effects of IFN-gamma on B7-2 mRNA expression were time dependent and occurred within 3 hours of treatment and increased through 24 hours. In vitro transcription assays and mRNA stability experiments showed that IFN-gamma increases both transcriptional activity and the stability of B7-2 mRNA. Treatment of MM6 cells with cycloheximide showed that de novo protein synthesis was not required for the IFN-gamma-enhanced expression of B7-2 mRNA. Overall, these studies show for the first time that IFN-gamma-enhanced expression of B7-2 protein in human monocytic cells is controlled at the gene level through a dual mechanism involving transcriptional and posttranscriptional mechanisms.

Functional role for the myeloid differentiation antigen CD14 in the activation of human monocytes by IL-2

Human monocytes express functional IL-2Rs and are directly activated by IL-2 to exert effector and secretory functions. In this study, we demonstrate that the myeloid differentiation Ag CD14 participates in monocyte activation by IL-2. Engagement of CD14 by specific mAbs resulted in the selective and dose-dependent suppression of IL-2-induced, but not of IFN-gamma-induced, monocyte tumoricidal activity. Furthermore, anti-CD14 mAbs effectively inhibited the secretion of IL-8 and IL-1beta in response to IL-2. Preincubation of monocytes with mAbs directed to selected epitopes on CD14 blocked the binding of IL-2 to the cell surface, providing a possible explanation for the inhibition of IL-2-triggered responses. A critical role for CD14 in IL-2-mediated monocyte activation was further demonstrated by experiments with the human U937 promonocytic cell line. These cells are negative for CD14 and unresponsive to IL-2 despite the expression of the beta and gamma subunits of the IL-2R. U937 cells acquired the capacity to respond to IL-2 following transfection with the human CD14 cDNA (U937/CD14). Stimulation of U937/CD14 cells with IL-2 up-regulated the constitutive levels of IL-8 mRNA, whereas no change in IL-8 mRNA basal expression was observed in control cells transfected with the vector alone (U937/Neo). Accordingly, increased secretion of IL-8 by U937/CD14, but not by U937/Neo cells, was detected following exposure to IL-2. Expression of IL-1beta was also augmented by IL-2 in U937/CD14 cells. These data provide the first evidence that CD14 expression is required for the response of monocytic cells to IL-2.

Functional role for the myeloid differentiation antigen CD14 in the activation of human monocytes by IL-2

Human monocytes express functional IL-2Rs and are directly activated by IL-2 to exert effector and secretory functions. In this study, we demonstrate that the myeloid differentiation Ag CD14 participates in monocyte activation by IL-2. Engagement of CD14 by specific mAbs resulted in the selective and dose-dependent suppression of IL-2-induced, but not of IFN-gamma-induced, monocyte tumoricidal activity. Furthermore, anti-CD14 mAbs effectively inhibited the secretion of IL-8 and IL-1beta in response to IL-2. Preincubation of monocytes with mAbs directed to selected epitopes on CD14 blocked the binding of IL-2 to the cell surface, providing a possible explanation for the inhibition of IL-2-triggered responses. A critical role for CD14 in IL-2-mediated monocyte activation was further demonstrated by experiments with the human U937 promonocytic cell line. These cells are negative for CD14 and unresponsive to IL-2 despite the expression of the beta and gamma subunits of the IL-2R. U937 cells acquired the capacity to respond to IL-2 following transfection with the human CD14 cDNA (U937/CD14). Stimulation of U937/CD14 cells with IL-2 up-regulated the constitutive levels of IL-8 mRNA, whereas no change in IL-8 mRNA basal expression was observed in control cells transfected with the vector alone (U937/Neo). Accordingly, increased secretion of IL-8 by U937/CD14, but not by U937/Neo cells, was detected following exposure to IL-2. Expression of IL-1beta was also augmented by IL-2 in U937/CD14 cells. These data provide the first evidence that CD14 expression is required for the response of monocytic cells to IL-2.

Bryostatin-1 and IFN-gamma synergize for the expression of the inducible nitric oxide synthase gene and for nitric oxide production in murine macrophages

Bryostatin-1 (Bryo) is a nontumor-promoting protein kinase C modulator that has been shown to have both in vitro and in vivo activity against several murine and human tumors. In this study, we investigated the effects of Bryo on nitric oxide production, measured as accumulated nitrite (NO2-) in culture supernatant, and inducible nitric oxide synthase (iNOS) gene expression in the murine macrophage cell line ANA-1. ANA-1 macrophages did not produce NO2- or iNOS mRNA constitutively, and very little or no NO2- or iNOS mRNA were detectable upon exposure to IFN-gamma. Bryo, although ineffective alone, and IFN-gamma synergized to produce high levels of NO2- and iNOS mRNA. The activity of Bryo was evident at a concentration of 0.1 ng/ml and reached its maximum at 1 ng/ml. The effects of Bryo were time dependent because expression of iNOS mRNA was detectable as early as 6 h and increased through 24 h. Analyses of the molecular mechanisms involved indicate that Bryo and IFN-gamma mainly regulate iNOS gene expression posttranscriptionally through stabilization of iNOS mRNA. Experiments designed to investigate the role of tumor necrosis factor alpha (TNF-alpha) in NO2- production by Bryo- and IFN-gamma-activated macrophages revealed that ANA-1 macrophages expressed low levels of TNF-alpha mRNA constitutively that were not augmented in the presence of IFN-gamma. However, Bryo alone augmented the TNF-alpha mRNA expression, which was only slightly increased with the addition of IFN-gamma. A polyclonal antibody to TNF-alpha was able to completely neutralize TNF-alpha secreted in either medium or Bryo plus IFN-gamma-treated cultures. Neutralizing concentrations of anti-TNF-alpha antibody suppressed the Bryo plus IFN-gamma-induced NO2- production approximately by 50%, suggesting that NO2- produced by Bryo plus IFN-gamma-treated ANA-1 macrophages may involve both TNF-alpha-dependent and TNF-alpha-independent mechanisms. Overall, these findings provide the first evidence that Bryo and IFN-gamma can synergize for the induction of NO2- production as well as iNOS gene expression and show the involvement of posttranscriptional mechanisms in the induction of iNOS mRNA.

The antineoplastic agent bryostatin-1 induces proinflammatory cytokine production in human monocytes: synergy with interleukin-2 and modulation of interleukin-2Rgamma chain expression

The antineoplastic agent bryostatin-1 (bryo-1) possesses powerful immunomodulatory properties and can function as a biological response modifier in vivo. However, there is currently little information regarding the effects of bryo-1 on cells of the monocytic lineage. In this study, we demonstrate that bryo-1 can potently induce the production of pro-inflammatory cytokines from human peripheral blood monocytes. Stimulation of monocytes with subnanomolar concentrations of bryo-1 significantly upregulated the constitutive levels of interleukin-8 (IL-8) mRNA and induced the expression of IL-1beta, tumor necrosis factor-alpha (TNF-alpha), and IL-6 mRNA in a time and dose-dependent manner. Accordingly, secretion of all four proinflammatory cytokines was induced after monocyte exposure to bryo-1. Furthermore, we showed that bryo-1 selectively synergized with IL-2 in triggering monocyte activation, and this effect seemed to be dependent, at least in part, on the ability of bryo-1 to upregulate IL-2Rgamma chain expression. Finally, we demonstrated that the responses of monocytes to bryo-1 could be blocked by the protein kinase C (PKC) inhibitors staurosporine and UCN-01, indicating a role for PKC in monocyte activation by bryo-1. These results show for the first time that bryo-1 is a powerful activator of human monocytes and suggest that stimulation of monokine secretion by bryo-1 may represent at least one of the mechanisms responsible for the in vivo antitumor activity of this drug.

IL-6 signals inhibition of cell adhesion in melanoma A375-C6

IL-6 has been found to be a potent inhibitor of melanoma A375-C6 cell adhesion, in addition to its known action in arresting cells at G1/G0 phase of the cell cycle IL-6 treated melanoma cells were found to round up and to lose the ability to adhere to fibronectin, laminin, collagen, and tenascin over 72 to 96 hours of IL-6 treatment, a time course similar to that seen for cell cycle inhibition. Cell cycle inhibition and loss of adhesion were found, however, to be independent effects of IL-6. Analysis of cell surface integrins indicated significant changes in the expression of several integrins including downregulation of a3 and av beta 5 and upregulation of a3. However, the changes in integrin expression did not correlate with loss of adhesion to relevant ligands. Three A375 melanoma clones varying in metastatic potential also demonstrated inhibition of both cell proliferation and matrix adhesion by IL-6.

Multiple cytokines inhibit interleukin-6-dependent murine hybridoma/plasmacytoma proliferation

A panel of cytokines was tested for inhibitors of interleukin-6 (IL-6)-dependent cell proliferation. Murine type I and II interferons (mIFNs) strongly inhibited proliferation of IL-6-dependent B9 and 7TD1 cells in a dose-dependent manner. Human tumor necrosis factor-alpha (hTNF-alpha) and human transforming growth factor-beta (hTGF-beta) potently inhibited B9 and to a lesser extent 7TD1 cells, while hIL-11, human oncostatin M (hOSM), and human leukemia inhibitory factor (hLIF) had no inhibitory effects on IL-6-dependent growth. Conversely, IL-11 and OSM but not LIF stimulated B9 and 7TD1 cell growth. However, compared with IL-6, up to 1000-fold higher IL-11 and OSM concentrations were required to induce maximal cell proliferation. Increasing concentrations of IL-6 (up to 100 ng/ml) could not overcome the antiproliferative effects of mIFNs, hTNF-alpha and hTGF-beta. Supernatants from mIFN-gamma and lipopolysaccharide (LPS)-treated mouse macrophages (ANA-1 cell line) were tested in B9 cell assays to identify cytokines among stimulatory and inhibitory biological activities that can inhibit IL-6-dependent proliferation. Undiluted or relatively concentrated supernatants from ANA-1 macrophages treated with mIFN-gamma and/or LPS did not contain detectable IL-6 bioactivity. However, diluted samples contained considerable amounts of detectable IL-6 bioactivity (nanogram levels). Testing the same samples for IL-6 immunoreactivity using enzyme-linked immunoabsorbent assay revealed comparable levels of mIL-6. We conclude that IFNs, TNF-alpha, and TGF-beta and possibly other factors are potent, dominant inhibitors of IL-6-dependent plasmacytoma/hybridoma growth in vitro.

IL-4 inhibits IL-2-induced tumoricidal activity and secretory functions of human monocytes. Modulation of IL-2 binding and IL-2 receptor beta gamma chain expression

Human monocytes express functional IL-2 receptors (IL-2R) and are directly activated by IL-2 to exert effector and secretory functions. In this study, we show that IL-4 selectively suppressed, in a dose-dependent manner, IL-2-induced monocyte tumoricidal activity, without affecting IFN-gamma-dependent cytotoxicity. This effect was specific because a neutralizing anti-IL-4 mAb completely restored IL-2-activated cytolysis. Furthermore, IL-4 effectively blocked the secretion of proinflammatory cytokines by IL-2-stimulated monocytes. Binding studies with biotin-conjugated IL-2 demonstrated that monocyte stimulation with IL-2 increased IL-2 binding to the cell surface, and that treatment with IL-4 inhibited this augmentation, providing a possible explanation for the decreased responsiveness of monocytes to IL-2 in the presence of IL-4. However, IL-4 suppressive effects could not be ascribed to the down-regulation of the individual components of the IL-2R complex. In fact, co-treatment of monocytes with IL-2 and IL-4 increased the expression of IL-2R gamma chain above the levels induced by IL-2 alone, whereas it did not significantly affect the expression of IL-2R beta chain. Thus, the inhibition of IL-2 binding by IL-4 may be due to the recruitment of the gamma chain into the IL-4-IL-4R system, making it unavailable for participation in the formation of IL-2 binding sites. These findings provide the first evidence of the ability of IL-4 to suppress IL-2-mediated activation of human monocytes and suggest that IL-4 may play an important role in vivo as an inhibitory signal that controls the response of monocytes to IL-2.

IL-4 inhibits IL-2-induced tumoricidal activity and secretory functions of human monocytes. Modulation of IL-2 binding and IL-2 receptor beta gamma chain expression

Human monocytes express functional IL-2 receptors (IL-2R) and are directly activated by IL-2 to exert effector and secretory functions. In this study, we show that IL-4 selectively suppressed, in a dose-dependent manner, IL-2-induced monocyte tumoricidal activity, without affecting IFN-gamma-dependent cytotoxicity. This effect was specific because a neutralizing anti-IL-4 mAb completely restored IL-2-activated cytolysis. Furthermore, IL-4 effectively blocked the secretion of proinflammatory cytokines by IL-2-stimulated monocytes. Binding studies with biotin-conjugated IL-2 demonstrated that monocyte stimulation with IL-2 increased IL-2 binding to the cell surface, and that treatment with IL-4 inhibited this augmentation, providing a possible explanation for the decreased responsiveness of monocytes to IL-2 in the presence of IL-4. However, IL-4 suppressive effects could not be ascribed to the down-regulation of the individual components of the IL-2R complex. In fact, co-treatment of monocytes with IL-2 and IL-4 increased the expression of IL-2R gamma chain above the levels induced by IL-2 alone, whereas it did not significantly affect the expression of IL-2R beta chain. Thus, the inhibition of IL-2 binding by IL-4 may be due to the recruitment of the gamma chain into the IL-4-IL-4R system, making it unavailable for participation in the formation of IL-2 binding sites. These findings provide the first evidence of the ability of IL-4 to suppress IL-2-mediated activation of human monocytes and suggest that IL-4 may play an important role in vivo as an inhibitory signal that controls the response of monocytes to IL-2.

Interleukin-2 and human monocyte activation

The recognition of the monocyte/macrophage-activating properties of IL-2 has broadened our image of the biological effects of this lymphokine from those of a T cell growth factor to those of a molecule with pleiotropic effects. The detailed analysis of the mechanisms of action of IL-2 including its biological effects on different cell types and the regulation of its receptors has increased dramatically the spectrum of the biological responses that can be modified by IL-2. The regulation of the expression of the IL-2 receptor subunits differs in terms of response to extracellular stimuli and intracellular control, suggesting that the response to IL-2 will vary depending on the nature and extent of environmental stimulation. Furthermore, the fact that the IL-2R gamma chain can be part of the receptor for IL-4, IL-7, and perhaps other cytokines indicates that IL-2 may modulate the response of monocytes simply by binding or releasing the IL-2R gamma chain and thus modulating the responsiveness to IL-4 or IL-7. Conversely, the extent of utilization of IL-2R gamma chain by various cytokines may dictate the monocytic response to IL-2. In fact, the availability of IL-2R gamma chain seems to be the limiting factor in the response of monocytes to IL-2. Modulation of cytokine receptors is an integral part of the control of the IL-2 response. The induction of CSF-1 receptor by IL-2 and the positive effect of CSF-1 on the duration of the cytotoxic response in IL-2-stimulated monocytes are an interesting example of a synergistic interaction of potential physiological relevance. The response of monocytes to IL-2 can also be modulated by inhibitory circuits, such as those involving TGF-beta 1, IFN-gamma, and IL-4. However, IFN-gamma and IL-4 can also activate monocytes and the timing and relative concentrations of the various cytokines may be critical variables in determining the ultimate monocyte phenotype. These studies have given us a glimpse of a very complex picture composed of multiple backgrounds and several players. However, the present information is not sufficient to make meaningful predictions of the resulting monocyte phenotype in an inflammatory reaction in which multiple cytokines are involved.(ABSTRACT TRUNCATED AT 400 WORDS)

Disruption by interferon-alpha of an autocrine interleukin-6 growth loop in IL-6-dependent U266 myeloma cells by homologous and heterologous down-regulation of the IL-6 receptor alpha- and beta-chains

IL-6 is an autocrine growth factor for U266 myeloma cells and their growth is inhibited by IFN-alpha or IL-6 mAb. We asked, therefore, whether IFN-alpha-induced growth inhibition involved IL-6. IFN-alpha and mAb against IL-6, the IL-6R alpha-(gp80) or beta-chain (gp130) potently inhibited U266 cells. Remarkably, this effect occurred despite IFN-alpha-augmented secretion of endogenous IL-6. However, examining the IL-6R revealed that IFN-alpha drastically curtailed expression of the IL-6R alpha- and beta-chain. This effect occurred on two different levels (protein and mRNA) and by two different mechanisms (directly and indirectly through IL-6). First, IFN-alpha, but not IL-6, greatly decreased gp80 and, to a lesser extent, gp130 mRNA levels which resulted in a loss of IL-6 binding sites. Second, IFN-alpha-induced IL-6 predominantly down-regulated membrane-bound gp130. IFN-alpha-mediated decrease of gp80 levels was not detected on IL-6-independent myeloma (RPMI 8226) or myeloid cells (U937). We conclude that IFN-alpha inhibited IL-6-dependent myeloma cell growth by depriving U266 cells of an essential component of their autocrine growth loop, a functional IL-6R.

LPS-inducible nuclear factor in human monocytes that binds the negative regulatory element of the HIV LTR

We studied the constitutive and lipopolysaccharide (LPS)-induced expression of nuclear protein binding to the negative regulatory element (NRE) of the human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR) in fresh human monocytes. We demonstrated the existence of a constitutive factor binding to the NRE 73-bp HpaII/HpaII fragment (-216 to -143) whose expression is up-regulated by LPS treatment. Competition experiments with overlapping oligonucleotides covering the HpaII/HpaII fragment and with mutated oligonucleotides mapped the binding within the TTTCATCAC region (-171 to -163). This binding pattern is unique to human monocytes.

The gamma subunit of the interleukin-2 receptor is expressed in human monocytes and modulated by interleukin-2, interferon gamma, and transforming growth factor beta 1

The interleukin-2 receptor gamma (IL-2R gamma) chain is a newly recognized component of the IL-2R of lymphoid cells that is required for their response to IL-2. We investigated the expression of IL-2R gamma protein in human monocytes by Western blot analysis using an antiserum specific for IL-2R gamma. We found that IL-2R gamma subunit is constitutively expressed in human monocytes and upregulated by the monocyte-activating factors IL-2 and interferon gamma (IFN gamma). Furthermore, we show that transforming growth factor beta 1 (TGF beta 1) downmodulates, in a dose-dependent manner, basal and IL-2-induced, but not IFN gamma-induced, IL-2R gamma chain expression, and this effect may be responsible for TGF beta 1 suppressive activity on IL-2-activated monocytes. Overall, these results show that the expression of the IL-2R gamma subunit in human monocytes is tightly regulated by the cytokine network, suggesting a critical role played by this protein on monocyte activation.

Inhibitory cytokine circuits involving transforming growth factor-beta, interferon-gamma, and interleukin-2 in human monocyte activation

We have previously reported that transforming growth factor-beta 1 (TGF-beta 1) inhibits interleukin-6 (IL-6) induction by IL-2 and IL-1 in fresh human monocytes. We investigated the effects of TGF-beta 1 on the expression of tumoricidal activity induced by IL-2 or interferon-gamma (IFN-gamma) in human monocytes. We showed that TGF-beta 1 specifically inhibited, in a dose-dependent manner, IL-2-induced but not IFN-gamma-induced monocyte tumoricidal activity. The inhibitory effects of TGF-beta 1 on IL-2-activated monocytes were not caused by down-modulation of the IL-2 receptor beta (IL-2R beta) because the treatment of monocytes with IL-2 and TGF-beta 1 increased IL-2R beta mRNA expression. However, we found that TGF-beta 1 down-modulated IL-2-induced IL-2R gamma mRNA, which may be responsible for the TGF-beta 1 inhibition of monocyte activation by IL-2. The resistance of the IFN-gamma-induced activation to the inhibitory effects of TGF-beta 1 could be caused by the ability of IFN-gamma to decrease TGF-beta 1 receptor expression, as shown by cross-linking experiments. Overall, these results showed that TGF-beta 1 is a powerful inhibitor of IL-2- but not of IFN-gamma-induced activation of monocytes to a cytotoxic stage. This differential effect may be attributed to modulation of cytokine receptor expression.

Regulation by interleukin-2 (IL-2) and interferon gamma of IL-2 receptor gamma chain gene expression in human monocytes

The interleukin-2 receptor gamma chain (IL-2R gamma) gene codes for a subunit of the IL-2R and is expressed in human lymphoid cells. The present study was undertaken to determine whether human monocytes expressed the IL-2R gamma gene constitutively or after activation by IL-2 or interferon gamma (IFN gamma). Fresh human monocytes constitutively expressed low but significant levels of IL-2R gamma mRNA, and nuclear run-on experiments showed that IL-2R gamma gene was transcriptionally active. Stimulation with IL-2 or IFN gamma induced a major increase of IL-2R gamma mRNA in a time- and a dose-dependent manner. However, neither cytokine increased the transcriptional activity of the gene. The enhancement of IL-2R gamma mRNA expression by either IL-2 or IFN gamma was concomitant with the stabilization of the mRNA, suggesting a postranscriptional level of control. Finally, the augmented expression of IL-2R gamma in IL-2- and IFN gamma-treated monocytes was associated with an increased IL-2-binding activity, compared with that of unstimulated cells. These results provide the first evidence of the expression of the IL-2R gamma gene in nonlymphoid cells and of its modulation by IL-2 and IFN gamma through posttranscriptional mechanisms.

Nature and potential of the reactive response to mouse mammary adenocarcinoma cells engineered with interleukin-2, interleukin-4 or interferon-gamma genes

A spontaneous mammary adenocarcinoma of BALB/c mice was transduced with the murine interleukin (IL)-2, IL-4, and interferon (IFN)-gamma genes. The ability of clones releasing IL-2, IL-4 or IFN-gamma to form tumors after s.c. challenge was compared to the TS/A parental cells (TS/A-pc) and to cells transduced with the neomycin resistance gene alone. Cytokine-gene-transduced clones activated a strong inflammatory reaction. The elicited by IL-2 and IL-4-gene-transduced cells efficiently led to tumor rejection. This reaction depended on the activation of several cell mechanisms, those classed as nonspecific being predominant. The repertoire of reactive leukocytes recruited in the reaction varies as a function of the secreted cytokine. The growth of a secondary contralateral TS/A-pc challenge after clone rejection was significantly impaired.

Interferon-gamma upregulates interleukin-8 gene expression in human monocytic cells by a posttranscriptional mechanism

Interleukin-8 (IL-8) is a neutrophil chemotactic and activating cytokine that is produced in response to several stimuli. Because monocytic cells are important producers of IL-8, we investigated whether interferon-gamma (IFN-gamma), a potent inducer of activation and differentiation of mononuclear phagocytes, affected IL-8 expression in this cell lineage. We found a low constitutive level of IL-8 mRNA expression that was upregulated by IFN-gamma in a dose- and time-dependent manner and via a protein-synthesis-dependent process in the human monocytic cell line U937. IL-8 protein secretion was also stimulated by IFN-gamma. Nuclear run-on experiments showed that the IL-8 gene was transcriptionally active in control cells and that IFN-gamma did not enhance the transcriptional activity. The increase in IL-8 mRNA by IFN-gamma was concomitant with the stabilization of the mRNA and, therefore, controlled primarily at a posttranscriptional level. These results represent the first evidence that IFN-gamma upregulates IL-8 gene expression in cells of the monocytic lineage, and show the involvement of posttranscriptional mechanisms in the induction of IL-8 mRNA.

Inhibition of tumor growth and enhancement of metastasis after transfection of the gamma-interferon gene

Cells from the spontaneous metastatic TS/A mammary adenocarcinoma of a BALB/c mouse were transfected with the murine gamma-interferon (IFN-gamma) gene. Six clones (IFN-gamma clones) releasing between 2 and 6,000 international units (IU) of IFN-gamma/ml culture medium, were compared to TS/A parental cells (TS/A-pc) and to cells transfected with neomycin resistance gene only (NEO cells). Autocrine IFN-gamma up-regulated membrane expression of H-2 class-I and Ly-6 glycoproteins, but did not alter cellular proliferation in vitro. All IFN-gamma clones gave rise to progressive tumors with a growth rate significantly slower than that of tumors induced by TS/A-pc and NEO cells, and inversely correlated with the amount of IFN-gamma secreted. TS/A-pc and NEO tumors displayed a marginal reactive infiltrate, whereas those formed by IFN-gamma clones were massively infiltrated mostly by macrophages. In T- and NK-deficient mice the growth of tumors formed by IFN-gamma clones was not enhanced. In vitro tests showed that IFN-gamma clone cells were markedly more lysed by macrophages than TS/A-pc and NEO cells, while they remained poorly sensitive to NK and LAK cells. These data as a whole suggest that the development of solid tumors by IFN-gamma clones is primarily hampered by macrophages and not by T-lymphocytes or NK cells. When spontaneous metastatic ability was compared, 2 IFN-gamma clones releasing 2-4 IFN-gamma IU/ml were significantly more metastatic, while most IFN-gamma clones appeared to be as metastatic as NEO cells. By contrast, following intravenous challenge, all IFN-gamma clones produced 5-10 times more experimental metastases than NEO cells. The higher metastatic ability of IFN-gamma clones was attributed to increased resistance to NK cells since, in NK-depleted BALB/c mice, metastatic spread of IFN-gamma clones was not enhanced, whereas a 50-fold increase in the number of metastases was found upon injection of NEO cells.

IL-2 up-regulates but IFN-gamma suppresses IL-8 expression in human monocytes

IL-2 has pleiotropic properties and is a potent activator of monocytic functions. Since monocytes are an important source of the chemoattractant cytokine IL-8, we studied the effects of IL-2 on the expression of IL-8 in human monocytes. IL-8 mRNA expression was detectable in resting human monocytes. Treatment of monocytes with IL-2 increased IL-8 mRNA expression by a protein synthesis-independent process. The augmentation of IL-8 mRNA by IL-2 was associated with an increase in IL-8 secretion. The expression of IL-8 mRNA was not a nonspecific response to any stimulus of monocyte activation. In fact, IFN-gamma, which is also a potent monocyte activator, not only failed to induce IL-8 expression but inhibited the stimulation of IL-8 by IL-2. Nuclear run-on experiments demonstrated that both the enhancement of IL-8 mRNA expression and its down-regulation by IFN-gamma occurred at the transcriptional level. These results show for the first time that in fresh human monocytes, IL-8 expression is differentially regulated by IL-2 and IFN-gamma and suggest that the interactions among IL-2, IL-8, and IFN-gamma may be important for the development and control of the inflammatory response.

IL-2 up-regulates but IFN-gamma suppresses IL-8 expression in human monocytes

IL-2 has pleiotropic properties and is a potent activator of monocytic functions. Since monocytes are an important source of the chemoattractant cytokine IL-8, we studied the effects of IL-2 on the expression of IL-8 in human monocytes. IL-8 mRNA expression was detectable in resting human monocytes. Treatment of monocytes with IL-2 increased IL-8 mRNA expression by a protein synthesis-independent process. The augmentation of IL-8 mRNA by IL-2 was associated with an increase in IL-8 secretion. The expression of IL-8 mRNA was not a nonspecific response to any stimulus of monocyte activation. In fact, IFN-gamma, which is also a potent monocyte activator, not only failed to induce IL-8 expression but inhibited the stimulation of IL-8 by IL-2. Nuclear run-on experiments demonstrated that both the enhancement of IL-8 mRNA expression and its down-regulation by IFN-gamma occurred at the transcriptional level. These results show for the first time that in fresh human monocytes, IL-8 expression is differentially regulated by IL-2 and IFN-gamma and suggest that the interactions among IL-2, IL-8, and IFN-gamma may be important for the development and control of the inflammatory response.

Ultrastructural evidence of the mechanisms responsible for interleukin-4-activated rejection of a spontaneous murine adenocarcinoma

The ultrastructural pattern of the anti-tumor response elicited by interleukin-4 (IL-4) was investigated by using a spontaneous mammary adenocarcinoma (TS/A) unable to elicit protective immunity in syngeneic BALB/c mice as suggested by a variety of preimmunization-challenge experiments. A subcutaneous lethal challenge of TS/A tumor cells was inhibited in a significant number of BALB/c mice receiving recombinant murine IL-4 injected daily for 10 days around the tumor-draining lymph node. Tumor rejection was mainly the result of direct membrane and cytoplasmic damage to tumor cells by eosinophils, neutrophils and macrophages that deeply penetrated the proliferating tumor mass. Lymphocytes and fibroblasts participated in the reaction by interacting with tumor cells, granulocytes and each other. The most frequent cell interactions in the peri- and intra-tumoral areas and in the tumor-draining lymph nodes are illustrated. The efficiency with which the IL-4-activated reaction leads to tumor inhibition and induction of a T-lymphocyte-dependent tumor-specific immune memory appears to depend on interactions between distinct leukocytes.

Selective transformation of host lymphocytes in vivo by retrovirus-producing macrophages

Macrophage-mediated retroviral transformation of host cells was studied in vivo utilizing the cloned murine macrophage-line GG2EE, generated by in vitro infection of bone marrow cells from C3H/HeJ mice (H-2k) with the acute transforming retrovirus J2 bearing the v-myc and v-raf oncogenes. Because GG2EE macrophages produce the J2 retrovirus, the development of secondary, J2 virus-induced tumors after the injection of the cell line into several strains of mice was evaluated. GG2EE cells proliferated and gave rise to histiocytic tumors in syngeneic mice and in allogeneic athymic Swiss mice. The inoculum of GG2EE cells in allogeneic DBA/2 mice (H-2d) and, to a lesser extent, in BALB/c (H-2d) and BALB/k (H-2k) mice gave rise to a small, solid mass at the injection site. Although the initial tumor was slowly rejected, secondary lymphomas belonging to the B or T cell lineage developed, leading to mouse death. Extensive phenotypic, functional, and chromosomal analyses proved that lymphomas were derived from host T and B cell transformation. Southern and Northern blot studies showed that J2 virus was integrated and expressed in lymphoma cells, demonstrating that the virus was transmitted to the host lymphocytes and suggesting that it was causal in lymphoma development. The existence of close and protracted interactions between GG2EE macrophages and allogeneic host lymphocytes and the presence of viral particles in the area of macrophage-lymphocyte contact were demonstrated by histologic and ultrastructural analysis. Rejection of J2 virus-infected lymphocytes in allogeneic mice suggested that host lymphocyte transformation was dependent upon the macrophage cell type. These results demonstrate that macrophage-derived J2 retrovirus transforms host lymphocytes in vivo in allogeneic mice and that a condition of host alloreactivity is critical for such event.

Selective transformation of host lymphocytes in vivo by retrovirus-producing macrophages

Macrophage-mediated retroviral transformation of host cells was studied in vivo utilizing the cloned murine macrophage-line GG2EE, generated by in vitro infection of bone marrow cells from C3H/HeJ mice (H-2k) with the acute transforming retrovirus J2 bearing the v-myc and v-raf oncogenes. Because GG2EE macrophages produce the J2 retrovirus, the development of secondary, J2 virus-induced tumors after the injection of the cell line into several strains of mice was evaluated. GG2EE cells proliferated and gave rise to histiocytic tumors in syngeneic mice and in allogeneic athymic Swiss mice. The inoculum of GG2EE cells in allogeneic DBA/2 mice (H-2d) and, to a lesser extent, in BALB/c (H-2d) and BALB/k (H-2k) mice gave rise to a small, solid mass at the injection site. Although the initial tumor was slowly rejected, secondary lymphomas belonging to the B or T cell lineage developed, leading to mouse death. Extensive phenotypic, functional, and chromosomal analyses proved that lymphomas were derived from host T and B cell transformation. Southern and Northern blot studies showed that J2 virus was integrated and expressed in lymphoma cells, demonstrating that the virus was transmitted to the host lymphocytes and suggesting that it was causal in lymphoma development. The existence of close and protracted interactions between GG2EE macrophages and allogeneic host lymphocytes and the presence of viral particles in the area of macrophage-lymphocyte contact were demonstrated by histologic and ultrastructural analysis. Rejection of J2 virus-infected lymphocytes in allogeneic mice suggested that host lymphocyte transformation was dependent upon the macrophage cell type. These results demonstrate that macrophage-derived J2 retrovirus transforms host lymphocytes in vivo in allogeneic mice and that a condition of host alloreactivity is critical for such event.

Lymphokine-activated tumor inhibition: combinatory activity of a synthetic nonapeptide from interleukin-1, interleukin-2, interleukin-4, and interferon-gamma injected around tumor-draining lymph nodes

This report initially reviews the progressive steps of research designed to build up a new, well-defined helper system triggering both the non-specific and the tumor-specific immune reactivity of a host bearing a tumor, in order to impair tumor growth. Tumor-specific T-helper lymphocytes were first generated in vitro from the spleen of mice with evident tumors. As these lymphocytes inhibit tumor growth by recruiting host reactivity through the release of lymphokines, the peri-tumoral injection of interleukin-2 (IL-2) was then experimented. Repeated injections of 10 units of IL-2 are only weakly effective, but its triggering of an efficient anti-tumor reactivity is markedly enhanced when non-reactive lymphocytes directly obtained from tumor-bearing mice are artificially admixed with the challenge tumor cells. Lastly, in order to ascertain whether lymphocytes themselves could be dispensed with, lymphokines were injected around tumor-draining lymph nodes. Ten daily injections of 1 pg of the 163-171 synthetic nonapeptide of human IL-1 beta appeared very efficient in activating tumor inhibition, particularly when combined with IL-4 or (to a lesser extent) IL-2.

The effects of a long term dihydroergotoxine treatment on agonist and antagonist striatal dopamine binding sites are dose and age related

Chronic administration of dihydroergotoxine, at the two doses of 2.5 mg/kg and 5 mg/kg decreases the binding of dopamine 3H-agonists to striatal membranes. By contrast the binding of dopamine 3H-antagonists is decreased in the animals treated with the higher dose and increased in those treated with the lower one. In old rats, in which a partial loss of both 3H-antagonist and 3H-agonist binding sites is observed, the DHT treatment confirms to increase the binding of 3H-antagonists, without affecting that of 3H-agonists. Thus, aging and ergot alkaloids seem to discrimate between DA-agonist and DA-antagonist receptor sites suggesting that this receptors are separate entityes.