Expression of IL-8 gene in human monocytes and lymphocytes: differential regulation by TNF and IL-1

TNF-alpha and IL-1 were reported to be the most powerful inducers of IL-8 in a multitude of cells, including leukocytes. In this study, we investigated TNF-alpha- and IL-1-mediated regulation of IL-8 gene expression in non-fractionated PBMC, and purified monocyte (MO) and lymphocyte (LY) fractions. Our analysis revealed that purified human MO did not respond to exogenous TNF-alpha with the induction of IL-8 mRNA or protein, nor require endogenous TNF-alpha for IL-8 expression. In contrast, in the presence of exogenous IL-1alpha and IL-1beta a substantial enhancement of IL-8 mRNA and protein expression in MO was observed. Nevertheless, antibodies to IL-1alpha and IL-1beta were unable to downregulate the expression of IL-8 in resting adherent or Staphylococcus aureus Cowan 1 (SAC)-stimulated MO. In contrast with MO, purified LY and non-fractionated PBMC expressed IL-8 in response to exogenous TNF-alpha, similar to exogenous IL-1alpha and IL-1beta. As was seen with MO, antibodies to TNF-alpha, IL-1alpha and IL-1beta did not inhibit the expression of IL-8 in purified LY and non-fractionated PBMC stimulated with SAC and LPS. Taken together, our data demonstrate major differences in responsiveness of MO and LY to exogenous TNF-alpha and IL-1, and suggest relative autonomy of IL-8 gene expression in these cells that does not require accessory cytokines but can be induced directly by exogenous stimuli.     

Cytolysis of tumor necrosis factor (TNF)-resistant tumor targets. Differential cytotoxicity of monocytes activated by the interferons, IL-2, and TNF

Herein we demonstrate that IFN-alpha, IFN-gamma, and IL-2 can induce human peripheral blood monocyte-mediated lysis of tumor cells that are resistant to both the direct effects of TNF and to monocytes activated by TNF. Monocytes activated by TNF kill only TNF-sensitive tumor targets, whereas those activated by IFN and IL-2 can lyse both TNF-sensitive and TNF-resistant tumor targets. Monocyte cytotoxicity against TNF-sensitive lines induced by the IFN, IL-2, or TNF can be completely abrogated by the addition of anti-TNF antibodies. In contrast, anti-TNF antibodies have no effect on IFN- or IL-2-induced monocyte cytotoxicity against TNF resistant targets, confirming non-TNF-mediated lysis induced by lymphokine-activated monocytes. Neither induction of TNF receptors by IFN-gamma nor inhibition of RNA synthesis by actinomycin D increased the susceptibility of TNF-resistant tumor targets to TNF-mediated monocyte cytotoxicity. Thus, non-TNF-mediated modes of monocyte cytotoxicity are induced by IFN and IL-2, but not by TNF, indicating that different cytotoxic mechanisms are responsible for the lysis of TNF-sensitive and TNF-resistant tumor cells. In addition, these findings also suggest that TNF-sensitive lines are susceptible only to TNF-mediated killing and apparently insensitive to non-TNF-mediated monocyte cytotoxicity.     

Tumor necrosis factor and IL-1 associated with plasma membranes of activated human monocytes lyse monokine-sensitive but not monokine-resistant tumor cells whereas viable activated monocytes lyse both

The purpose of our study was to determine some of the mechanisms involved in macrophage-mediated lysis of tumorigenic cells. A375 human melanoma cells (A375-R) resistant to lysis mediated by TNF and IL-1 were selected from the TNF- and IL-1-sensitive A375 parental melanoma cells subsequent to continuous (2 mo) exposure to rTNF. Peripheral blood monocytes isolated by centrifugal elutriation from healthy donors were incubated with rIFN-gamma and muramyl dipeptide, with a lipoprotein derived from Escherichia coli (CG-31362) or with LPS for 24 h. These activated monocytes lysed both the A375 (monokine-sensitive) and A375-R (monokine-resistant) melanoma cells. Activated tumoricidal macrophages fixed in 2% paraformaldehyde lysed only the TNF- and IL-1-sensitive A375 cells. These fixed monocytes contained both IL-1 and TNF activities as determined by D10 cell proliferation and L929 cytolysis assays, respectively. Nearly identical results were obtained with preparations of plasma membranes from activated human monocytes. Anti-IL-1 and/or anti-TNF sera neutralized the cytolysis of tumor cells mediated by free monokines, by fixed monocytes, or by plasma membrane preparations. In contrast, anti-TNF and/or anti-IL-1 sera did not inhibit tumor cell lysis by viable activated monocytes. We conclude that IL-1 and TNF molecules associated with the plasma membranes of activated monocytes mediate lysis of susceptible target cells. However, because activated monocytes lysed IL-1-and TNF-resistant target cells, molecules other than these monokines must also be involved in the antitumor activity of monocytes.     

Macrophage inflammatory protein-3 beta enhances IL-10 production by activated human peripheral blood monocytes and T cells.

We report that the addition of human macrophage inflammatory protein-3 beta (MIP-3 beta) to cultures of human PBMCs that have been activated with LPS or PHA results in a significant enhancement of IL-10 production. This effect was concentration-dependent, with optimal MIP-3 beta concentrations inducing more than a 5-fold induction of IL-10 from LPS-stimulated PBMCs and a 2- to 3-fold induction of IL-10 from PHA-stimulated PBMCs. In contrast, no significant effect on IL-10 production was observed when 6Ckine, the other reported ligand for human CCR7, or other CC chemokines such as monocyte chemoattractant protein-1, RANTES, MIP-1 alpha, and MIP-1 beta were added to LPS- or PHA-stimulated PBMCs. Similar results were observed using activated purified human peripheral blood monocytes or T cells. Addition of MIP-3 beta to nonactivated PBMCs had no effect on cytokine production. Enhancement of IL-10 production by MIP-3beta correlated with the inhibition of IL-12 p40 and TNF-alpha production by monocytes and with the impairment of IFN-gamma production by T cells, which was reversed by addition of anti-IL-10 Abs to the cultures. The ability of MIP-3 beta to augment IL-10 production correlated with CCR7 mRNA expression and stimulation of intracellular calcium mobilization in both monocytes and T cells. These data indicate that MIP-3 beta acts directly on human monocytes and T cells and suggest that this chemokine is unique among ligands binding to CC receptors due to its ability to modulate inflammatory activity via the enhanced production of the anti-inflammatory cytokine IL-10.     

Exaggerated human vascular cell prostaglandin biosynthesis mediated by monocytes: role of monokines and interleukin 1

Incubation of cultured human umbilical vein endothelial cells with factors derived from human peripheral blood mononuclear cells (MNCF) or adherent monocytes (AMF) resulted in concentration-and time-dependent increases in prostacyclin and prostaglandin E2 (PGE2) production. MNCF and AMF also stimulated prostacyclin and PGE2 biosynthesis in cultured human arterial smooth muscle cells and human dermal fibroblasts. The effect of these monokines on endothelial cells and fibroblasts was mimicked by treatment with purified human interleukin 1 (IL 1). Mononuclear cell-conditioned medium subjected to gel filtration yielded fractions (Mr 12,000 to 18,000 daltons) which simultaneously contained endothelial cell and fibroblast prostaglandin-stimulating activity and IL 1 activity. Therefore, monokines, specifically IL 1, appear to serve as chemical mediators of the interaction between monocytes and vascular cells as would occur in blood vessel injury, inflammation, and atherosclerosis.     

P48 induces tumor necrosis factor and IL-1 secretion by human monocytes

Bacterial products are potent stimulators of TNF and IL-1 release, however, the factors that regulate cytokine secretion in the absence of bacterial products are not well defined. P48 is a cytokine recently identified in the supernatant of the human null cell leukemia cell line Reh, which induces differentiation and cytolytic activity in HL-60 cells. P48 has been purified to homogeneity and is distinct from TNF-alpha TNF-beta, IFN-gamma, IL-6, and macrophage CSF. In the present study we examined the ability of P48 to stimulate cytokine release by human peripheral blood monocytes. P48 stimulated the secretion of TNF and IL-1 in a dose-dependent manner. Priming the monocytes with IFN-gamma enhanced P48-induced cytokine release but was not a requirement for secretion. Cytokine secretion was in response to P48 and was not caused by endotoxin contamination. The cytokine-inducing activity of P48 was extremely sensitive to heat treatment but could not be eliminated by using polymyxin B. Polyclonal antisera to P48 completely blocked the cytokine-inducing activity. P48 may be an important new member of the cytokine network involved in the regulation of cytokine secretion by monocytes.     

Substance P and calcitonin gene-related peptide increase IL-1 beta, IL-6 and TNF alpha secretion from human peripheral blood mononuclear cells.

We found that substance P (SP) and calcitonin gene-related peptide (CGRP) (0.3-1 microM) increased, in a concentration-dependent manner, the basal secretion of interleukin-1 beta (IL-1 beta), interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF alpha) from cultured lymphocyte-enriched mononuclear cells isolated from human peripheral blood. SP and CGRP (0.1 microM) synergistically increased basal TNF alpha secretion. Dynorphin A((1-17)) (0.1-1 microM) did not modify basal cytokine secretion. Lipopolysaccharide (10 ng/ml)-induced cytokine secretion and [(3)H]thymidine uptake were not altered by any neuropeptide (at 0.1 microM). Thus, SP and CGRP stimulate the production of pro-inflammatory cytokines from lymphocytes only at high concentrations, similar to those reached during tissue damage.     

Alveolar macrophages differ from blood monocytes in human IL-1 beta release. Quantitation by enzyme-linked immunoassay

Fresh human alveolar macrophages and blood monocytes were stimulated with LPS and assessed for their ability to produce and release antigenic IL-1 beta. Using a sensitive and specific ELISA for IL-1 beta, monocytes released 13.3 +/- 3.1 ng/10(6) cells compared to 3.5 +/- 0.8 ng/10(6) cells for alveolar macrophages (p less than 0.01). To investigate the reason for this difference in IL-1 beta release, monocytes were compared to alveolar macrophages for total IL-1 beta production (i.e., the amount released plus that detected in the lysates). Monocytes produced a total of 19.0 +/- 3.2 ng/10(6) cells whereas alveolar macrophages produced 24.8 +/- 5.6 ng/10(6) cells (p = 0.37). The relative increase in alveolar macrophage intracellular IL-1 beta was confirmed by Western blot analysis of cell lysates. Thus, the limitation in IL-1 release from alveolar macrophages appears to be due to a decrease in the processing and release of the IL-1 beta precursor. In addition, TNF production studies demonstrated that the limitation in IL-1 release was not a generalized defect. In contrast to the IL-1 beta data, when TNF was measured from monocytes and macrophages, monocytes released only 14.6 +/- 3.4 ng/10(6), whereas macrophages released 101 +/- 30 ng/10(6) (p less than 0.02). In this same context, when fresh monocytes were allowed to mature in vitro they took on monokine production characteristics similar to alveolar macrophages. In vitro matured monocytes had a greater than 20-fold decrease in their ability to release IL-1 beta and a 6- to 8-fold increase in their ability to release TNF. Taken together, these studies suggest that IL-1 beta release is limited in mature mononuclear phagocytes as compared to fresh blood monocytes, and furthermore, that IL-1 beta regulation differs significantly from that of TNF-alpha.     

Additive effects of IL-1 and TNF on induction of prostacyclin synthesis in human vascular endothelial cells

The effect of interleukin 1 (IL-1) and tumor necrosis factor (TNF) on the induction of prostacyclin (PGI2) synthesis in human vascular endothelial cells (EC) was investigated. Both IL-1 and TNF increased PGI2 production by EC in both a time- and dose-dependent manner, and a combination of the two cytokines additively enhanced PGI2 production. Metabolic inhibitors including indomethacin and cycloheximide abolished cytokine induced PGI2 synthesis. Since, the effect of TNF was not inhibited by neutralization with antibody to IL-1 alpha and IL-1 beta, it seems that the mechanism is not mediated by endogenous IL-1 induced by TNF.     

Induction of IL-1 secretion from human monocytes by Fc region subfragments of human IgG1

Peripheral blood-derived human monocytes and the murine P388D1-monocytes-like cell line are induced to secrete IL-1 when stimulated with Fc region but not F(ab) region subfragments obtained from the cleavage of human IgG1 with papain or pepsin. The portion of the Fc region of IgG1 responsible for stimulation of IL-1 secretion appears to be located within the C gamma 3 domain of the molecule. This hypothesis is supported by the observation that the biologically active pepsin-derived pFc' subfragment is located within the C gamma 3 domain and the long-term papain digests containing predominately Fc' are also active. In contrast, short term papain digests containing mostly intact Fc fragments were found to be unable to induce IL-1 secretion.     

Immunomodulatory effects of probiotic bacteria DNA: IL-1 and IL-10 response in human peripheral blood mononuclear cells

A new therapeutic approach for inflammatory bowel diseases is based on the administration of probiotic bacteria. Prokaryotic DNA contains unmethylated CpG motifs which can activate immune responses, but it is unknown whether bacterial DNA is involved in the beneficial effects obtained by probiotic treatment. Peripheral blood mononuclear cells (PBMC) from healthy donors were incubated with pure DNA of eight probiotic strains and with total bacterial DNA from human feces collected before and after probiotic ingestion. Cytokine production was analyzed in culture supernatants. Modification of human microflora after probiotic administration was proven by polymerase chain reaction analysis. Here we show that Bifidobacterium genomic DNA induced secretion of the antiinflammatory interleukin-10 by PBMC. Total bacterial DNA from feces collected after probiotic administration modulated the immune response by a decrease of interleukin-1 beta and an increase of interleukin-10.     

IL-7 up-regulates the expression of IL-8 from resting and stimulated human blood monocytes.

Blood monocytes are important cellular sources of a vast array of bioactive substances, including regulatory and chemotactic cytokines. The regulation of these cytokines is of critical importance to the expression of acute and chronic inflammatory responses. IL-7, a T and B cell-activating cytokine, has recently been shown to have stimulatory effects on the expression of several monocyte-derived proinflammatory cytokines. We now describe the induction of IL-8 mRNA and extracellular protein from human blood monocytes by IL-7. The up-regulation of IL-8 mRNA by IL-7 was not altered by concomitant treatment with cycloheximide, suggesting that the direct stimulatory effects of IL-7 were not dependent upon de novo protein synthesis. In addition, IL-7 significantly potentiated the production of IL-8 from LPS-, TNF-, and IL-1-treated peripheral blood monocytes. Our findings suggest that IL-7 may play a critical role in the modulation of macrophage-derived cytokine expression and may function in vivo as an important proinflammatory cytokine.     

Antigen presentation by human monocytes: evidence for stimulant processing and requirement for interleukin 1

We studied the role of stimulant processing and presentation and of IL 1 in monocyte-mediated activation of human lymphoproliferative responses. The effects of two lysosomotropic agents, ammonium chloride and chloroquine, on the capacity of human monocytes to activate T lymphocyte responses to the soluble antigen streptolysin O (SLO) and to the polyclonal stimulant S. aureus protein A (SpA) were investigated. These agents inhibited the presentation of SLO and SpA by human monocytes in a dose-dependent manner. The inhibition occurred if monocytes were treated with ammonium chloride and chloroquine for 1.5 hr, starting only 30 min after exposure to the stimulants, whereas only minimal inhibition occurred when monocytes were treated with the two lysosomotropic compounds 2 hr after pulsing with SLO or SpA. In contrast, cell membrane alloantigen presentation by monocytes in the MLR was not affected by ammonium chloride or chloroquine treatment. Thus, these reversible inhibitors of monocyte phagosome-lysosome functions presumably interfere with intracellular processing of the stimulants but do not seem to interfere with alloantigen presentation at the cell surface. Furthermore, we investigated whether gently fixed monocytes were still capable of passively presenting stimulant or whether active metabolic processes as well as IL 1 were required. We observed that only monocytes treated with paraformaldehyde after SLO or SpA pulsing stimulated a proliferative response by T lymphocytes, provided 50 U/ml of partially purified human IL 1 were added back to cultures. In contrast, monocytes fixed before exposure to SLO or SpA were not able to stimulate T lymphocytes even if supplemented by IL 1. Taken together these data suggest that a finite incubation period is required for human monocytes to become able to present SLO or SpA to T lymphocytes. During this time the soluble stimulants presumably undergo some metabolic process in viable macrophages perhaps at the phagosome-lysosome level, to become recognizable by T lymphocytes.     

IL-2 stimulates the production of IL-1 alpha and IL-1 beta by human peripheral blood mononuclear cells

Human PBMC were cultured in medium containing human rIL-2, and the supernatants and cell lysates were analyzed for IL-1 alpha and IL-1 beta using specific RIA. IL-2, but not the excipient detergents included in the rIL-2 preparation, induced the synthesis of both cytokines. The concentrations of IL-1 alpha and IL-1 beta in the cell lysates and supernatants depended on both the concentration of rIL-2 in the culture medium and the duration of the incubation. After 24 h of stimulation, IL-2-induced IL-1 alpha remained almost entirely cell-associated. In contrast, IL-1 beta was present in both cell lysates and supernatants and was more abundant in the latter. SDS-PAGE analysis after radioimmunoprecipitation with anti-IL-1 antibodies indicates that cell-associated IL-1 resulting from IL-2 stimulation was in the form of the 35 kDa IL-1 precursor whereas secreted IL-1 was almost entirely in the form of the mature 18 kDa product. Depletion of monocytes from the PBMC culture substantially reduced IL-2-induced IL-1 production. In addition, Leu M3+ monocytes obtained through FACS, but not CD16+ NK cells, produced both IL-1 alpha and IL-1 beta in response to IL-2. The low level of endotoxin present in the IL-2 preparation used in our studies and the selective inhibition by polymyxin B of LPS-induced, but not IL-2-induced, IL-1 production by PBMC indicate that IL-2-induced IL-1 production was not due to endotoxin contamination. Furthermore, an anti-IL-2 antiserum selectively inhibited IL-1 production in response to IL-2 stimulation. We conclude that IL-2 is a potent inducer of IL-1 synthesis and secretion in vitro and propose that IL-1 may be generated in vivo in patients undergoing IL-2 immunotherapy.     

Isolation and properties of interleukin 1 from human blood monocytes

Among different tested substances LPS-containing preparations were found to be most effective inducers of secretory interleukin-1 in human peripheral blood monocytes in vitro. IL-1 from supernatant of prodigiozan- + con A-stimulated monocytes had a MM of 18-20 KD and pI of 5.2-5.4 and 6.8 revealing an equal comitogenic activity and of 6.0 (minor peak).     

Alpha-tocopherol decreases tumor necrosis factor-alpha mRNA and protein from activated human monocytes by inhibition of 5-lipoxygenase

Cardiovascular disease is the leading cause of morbidity in Westernized populations. Low levels of alpha-tocopherol (AT) are associated with increased incidence of atherosclerosis and increased intakes appear to be protective. AT supplementation decreases interleukin 1 and 6 release from human monocytes. Thus, the aim of this study was to examine the effect of AT on an important proinflammatory cytokine, tumor necrosis factor-alpha (TNF) release from human monocytes. AT supplementation (1200 IU/day for 3 months) significantly decreased TNF release from activated human monocytes. Mechanisms that were examined included its effect as a general antioxidant, its inhibitory effect on protein kinase C (PKC), and the cycloxygenase-lipoxygenase pathway. While AT decreased TNF release from activated monocytes, other antioxidants had no effect on TNF release. Specific PKC inhibitors had no effect on TNF release from activated monocytes. The inhibition of TNF release by AT in activated monocytes was reversed by leukotriene B(4) (LTB(4)), a major product of the 5-lipoxygenase (5-LO) pathway. Similar observations were seen with inhibitors of 5-lipoxygenase. Indomethacin, a COX inhibitor, in the presence and absence of AT failed to affect TNF activity. These findings suggest that AT decreases TNF release from activated human monocytes via inhibition of 5-lipoxygenase. Also, AT as well as a 5-LO inhibitor significantly decreased TNF mRNA. Furthermore, AT and the 5-LO inhibitor decreased NFkappab-binding activity. Thus, in activated human monocytes, AT appears to inhibit TNF mRNA and protein by inhibition of 5-LO.