Establishment and characterization of a human acute monocytic leukemia cell line (THP-1)

Activation of human monocytic cells by Treponema pallidum and Borrelia burgdorferi lipoproteins and synthetic lipopeptides proceeds via a pathway distinct from that of lipopolysaccharide but involves the transcriptional activator NF-kappa B

There is increasing evidence that lipoproteins of Treponema pallidum and Borrelia burgdorferi are key inflammatory mediators during syphilis and Lyme disease. A principal objective of the present study was to identify more precisely similarities and divergences among lipopolysaccharide (LPS)- and lipoprotein-lipopeptide-induced immune cell signaling events. Like LPS, purified native B. burgdorferi OspA and synthetic analogs of OspA, OspB, and two T. pallidum lipoproteins (Tpp47 and Tpp17) all induced NF-kappa B translocation in THP-1 human monocytoid cells. Acylation of OspA and the synthetic peptides was requisite for cell activation. Polymyxin B abrogated only the response to LPS. By using 70Z/3-derived pre-B-cell lines either lacking or expressing human CD14 (the LPS receptor), it was observed that expression of human CD14 imparted responsiveness to LPS but not to OspA or spirochetal lipopeptides (assessed by induction of NF-kappa B and expression of surface immunoglobulin M). Finally, the biological relevance of the observation that T. pallidum lipoproteins-lipopeptides induce both NF-kappa B and cytokine production in monocytes was supported by the ability of the synthetic analogs to promote human immunodeficiency virus replication in chronically infected U1 monocytoid cells; these observations also suggest a potential mechanism whereby a syphilitic chancre can serve as a cofactor for human immunodeficiency virus transmission. The combined data lend additional support to the proposal that spirochetal lipoproteins and LPS initiate monocyte activation via different cell surface events but that the signaling pathways ultimately converge to produce qualitatively similar cellular responses.

CD32 expression and signaling is down-regulated by transforming growth factor-beta 1 on human monocytes

CD32 (Fc gamma RII) is the most abundantly distributed class of IgG Fc receptors in the human body. In this study, we analyzed the effect of transforming growth factor (TGF)-beta 1, a cytokine with strong immunosuppressive function, on the expression and function of CD32 on freshly isolated peripheral blood monocytes and three human monocytic cell lines, U937, THP-1 and Mono mac-6. We found that TGF-beta 1 down-regulates CD32 expression on monocytes and all monocytic cell lines in a dose- and time-dependent fashion. A mean down-regulation of CD32 expression on THP-1 cells of 54 +/- 3.2% after 24 h was found at a concentration of 1 ng/ml TGF-beta 1. At the mRNA level, TGF-beta 1 induced a twofold down-regulation of CD32. Cross-linking of CD32 induced an increase in the concentration of intracellular Ca2+, which was reduced by 50% by TGF-beta 1, suggesting a decreased downstream signaling mediated by the receptor.

Gamma interferon induced increases in intracellular cathepsin B activity in PMA primed THP-1 cells are blocked by inhibitors of protein kinase C

Macrophage proteinases including cathepsin B (CB) are implicated in the tissue injury of inflammatory lesions. We have previously shown that interferon-gamma (IFN-gamma) increases intracellular levels of the lysosomal proteinase, CB, in THP-1 cell primed with phorbol 12-myristate 13-acetate (PMA). We have now examined the role of protein kinase C (PKC) in this effect. Following activation with PMA, the intracellular CB activity was significantly increased in the presence of 500 U/ml IFN-gamma. With the addition of protein kinase C (PKC) inhibitors bisindolylmaleimide, staurosporine, H-7, or phloretin a reversal of the effect of IFN-gamma was noted whereas the addition of the cyclic nucleotide-dependent protein kinase inhibitors HA 1004, H-8, H-89, or cAMP-Dependent Protein Kinase (PKA) Inhibitor did not block the effect. Although diacylglycerol (DAG) did not replace PMA in the study. Diacylglycerol Kinase Inhibitor induced a more pronounced augmentation and PKC depletion inhibited the effect. This suggests that a PKC-dependent pathway is involved in the response of CB in PMA primed THP-1 cells to IFN-gamma.

A cardiotonic steroid bufalin-induced differentiation of THP-1 cells. Involvement of Na+, K(+)-ATPase inhibition in the early changes in proto-oncogene expression

Human monocytic leukemia THP-1 cells were induced to differentiate into macrophage-like cells by treatment with cardiotonic steroid bufalin, which was previously shown to interact with the Na+, K+-ATPase with similar kinetics to ouabain, a specific inhibitor of the enzyme. This induction of differentiation was characterized by loss of proliferation, cell adherence, increased ability to reduce Nitro Blue tetrazolium (NBT), and increased expression of interleukin 1 beta (IL-1 beta). During this process, bufalin downregulated c-myb and c-myc expressions and induced c-fos and Egr-1 transcripts. Ouabain also caused similar changes in proto- oncogene expression and induced phenotypic markers of differentiated cells at concentrations comparable to bufalin. The 12-O-tetradecanoyl phorbol-13-acetate resistant THP-1 cell variant, which was unresponsive to this agent as to growth inhibition and proto-oncogene expression, responded to bufalin. The finding that protein kinase inhibitor H7 failed to bufalin-mediated c-fos induction further supports the theory that the signal transduction machinery caused by bufalin is separable from the phorbol ester. The cytotoxic effect of high doses of bufalin apparently disappeared in the medium where Na+ was replaced with choline ions. Furthermore, bufalin failed to induce c-fos expression and to downregulate c-myb transcripts in the low-Na+ medium. These findings indicate that an increased intracellular Na+ concentration resulting from the Na+, K(+)-ATPase inhibition possibly triggers the change in proto-oncogene expression evoked by bufalin.

beta-Amyloid induces increased release of interleukin-1 beta from lipopolysaccharide-activated human monocytes

Previous reports have demonstrated that IL-1 is elevated in the Alzheimer's disease brain. We propose that beta-amyloid (A beta) in senile plaques triggers microglial interleukin-1(IL-1) release. Since microglia and monocytes have similar lineage and functions, the human monocyte cell line, THP-1, was used to determine whether A beta peptides can stimulate release of IL-1 beta. THP-1 cells were grown in culture with LPS and incubated with various A beta peptides (0.5-10 microM). IL-1 released into the medium was measured using either an IL-1 beta ELISA or an IL-1 bioassay. Treatment of activated THP-1 cells with A beta 25-35, fibrillar A beta 1-40, or A beta 1-42 significantly elevated IL-1 beta release. A beta 25-35 with a scrambled sequence or non-fibrillar A beta 1-40 did not significantly change IL-1 beta release from activated THP-1 cells. The A beta 25-35- and fibrillar A beta 1-40 induced IL-1 beta release was dose-dependent. IL-1 released following treatment with A beta 25-35 and measured using an IL-1 bioassay gave similar results. The present report provides evidence that A beta is capable of elevating release of functional IL-1 beta, a potent pro-inflammatory cytokine, from macrophages/microglia and provides support that a chronic local inflammatory response is an ongoing phenomenon within and surrounding senile plaques.

Lipopolysaccharide induction of THP-1 cells activates binding of c-Jun, Ets, and Egr-1 to the tissue factor promoter

These studies examine the molecular basis for increased transcription of tissue factor (TF) in THP-1 cells stimulated with lipopolysaccharide (LPS). DNase I footprinting identified six sites of protein-DNA interaction between -383 and the cap site that varied between control and induced extracts. Four footprints show qualitative differences in nuclease sensitivity. Footprints I (-85 to -52) and V (-197 to -175) are induction-specific and localize to regions of the promoter that mediate serum, phorbol ester, partial LPS response (-111 to +14), and the major LPS-inducible element (-231 to -172). Electrophoretic mobility shift assays with the -231 to -172 probe demonstrate JunD and Fos binding in both control and induced nuclear extracts; however, binding of c-Jun is only detected following LPS stimulation. Antibody inhibition studies implicate binding of Ets-1 or Ets-2 to the consensus site between -192 and -177, a region that contains an induction-specific footprint. The proximal region (-85 to -52), containing the second inducible footprint, binds Egr-1 following induction. These data suggest that LPS stimulation of THP-1 cells activates binding of c-Jun, Ets, and Egr-1 to the TF promoter and implicates these factors in the transcriptional activation of TF mRNA synthesis.

Effect of recombinant human gamma interferon on intracellular activities of antibiotics against Listeria monocytogenes in the human macrophage cell line THP-1

Listeria monocytogenes is a facultative intracellular pathogen which enters cells by endocytosis and reaches phagolysosomes from where it escapes and multiplies in the cytosol of untreated cells. Exposure of macrophages to gamma interferon (IFN-gamma) restricts L. monocytogenes to phagosomes and prevents its intracellular multiplication. We have tested whether IFN-gamma also modulates the susceptibility of L. monocytogenes to antibiotics. We selected drugs from three different classes displaying marked properties concerning their cellular accumulation and subcellular distribution, namely, ampicillin (not accumulated by cells but present in cytosol), azithromycin (largely accumulated by cells but mostly restricted to lysosomes), and sparfloxacin (accumulated to a fair extent but detected only in cytosol). We used a continuous line of myelomonocytic cells (THP-1 macrophages), which display specific surface receptors for IFN-gamma, and examined the activity of these antibiotics against L. monocytogenes Hly+ (virulent variant) and L. monocytogenes Hly- (a nonvirulent variant defective in hemolysin production). Untreated THP-1 and phorbol myristate acetate-differentiated THP-1 were permissive for infection and multiplication of intracellular L. monocytogenes Hly+ (virulent variant). All three antibiotics tested were bactericidal against this Listeria strain when added to an extracellular concentration of 10x their MIC. After preexposure of THP-1 to IFN-gamma, L. monocytogenes Hly+ was still phagocytosed but no longer grew intracellularly. The activity of ampicillin became almost undetectable (antagonistic effect), and that of azithromycin was unchanged (additive effect with that of IFN-gamma), whereas that of sparfloxacin was markedly enhanced (synergy). A similar behavior (lack of bacterial growth, associated with a loss of activity of ampicillin, an enhanced activity of sparfloxacin, and unchanged activity of azithromycin) was observed in cells infected with L. monocytogenes Hly-. This modulation of antibiotic activity, which we ascribe to the change of subcellular localization of L. monocytogenes caused by IFN-gamma or by the lack of virulence factor, could result from a change in bacterial responsiveness to antibiotics, a modification of the drug activity, or differences in drug bioavailabilities between cytosol and phagosomes.

Establishment and characterization of a novel human promonocytic cell line from peripheral blood of a patient with psoriasis

Human monocyte/macrophage lineages have unique phagocytic and immune-regulatory functions. We established a promonocytic cell line from the peripheral blood of a patient with psoriasis vulgaris. The newly established cells, termed YAP cells, grew in a suspension culture. In Wright-Giemsa-stained preparations, YAP cells were round or polygonal in shape. Transmission electron microscopy showed that the cells had clear nuclei with well-defined nucleoli. There were frequent mitochondria, a relatively abundant endoplasmic reticulum profile, free ribosomes and an occasional Golgi apparatus. Cytochemical studies showed a positive reaction for alpha-naphthyl butyrate esterase, which was completely inhibited by sodium fluoride, a diffuse positive reaction for periodic acid-Schiff, and a negative result for alkaline phosphatase and peroxidase. A large population of YAP cells reacted with the CD4, CD11b, CD25 and CD33 surface markers, but not with CD2, CD3, CD8 or CD19. We also found that YAP cells produced considerable amounts of TNF alpha, which was detected in the culture supernatant when the cells were treated with 1 ng/ml 12-O-tetradecanoylphorbol-13-acetate (TPA). Chromosome analyses showed that YAP cells contained a variety of marker chromosomes. It should be stressed that YAP cells were derived from a patient with a non-neoplastic disorder, whereas most monocytic cell lines previously reported are of malignant origin. This newly established cell line might be valuable for studying the pathogenesis of psoriasis, especially the role of monocytes/macrophages in the aetiology of the disease.

Differentiation-associated toxin receptor modulation, cytokine production, and sensitivity to Shiga-like toxins in human monocytes and monocytic cell lines

Infections with Shiga toxin-producing Shigella dysenteriae type 1 or Shiga-like toxin (SLT)-producing Escherichia coli cause bloody diarrhea and are associated with an increased risk of acute renal failure and severe neurological complications. Histopathological examination of human and animal tissues suggests that the target cells for toxin action are vascular endothelial cells. Proinflammatory cytokines regulate endothelial cell membrane expression of the glycolipid globotriaosylceramide (Gb(3)) which serves as the toxin receptor, suggesting that the host response to the toxins or other bacterial products may contribute to pathogenesis by regulating target cell sensitivity to the toxins. We examined the effects of purified SLTs on human peripheral blood monocytes (PBMn) and two monocytic cell lines. Undifferentiated THP-1 cells were sensitive to SLTs. Treatment of the cells with a number of differentiation factors resulted in increased toxin resistance which was associated with decreased toxin receptor expression. U-937 cells, irrespective of maturation state, and PBMn were resistant to the toxins. U-937 cells expressed low levels of GB(3), and toxin receptor expression was not altered during differentiation. Treatment of monocytic cells with tumor necrosis factor alpha (TNF-alpha) did not markedly increase sensitivity or alter toxin receptor expression. Undifferentiated monocytic cells failed to synthesize TNF and interleukin 1beta when treated with sublethal concentrations of SLT type I (SLT-I), whereas cells treated with 12-0-tetradecanoylphorbol-13-acetate acquired the ability to produce cytokines when stimulated with SLT-I. When stimulated with SLT-I, U-937 cells produced lower levels of TNF than PBMn and THP-1 cells did.

Expression of intercellular adhesion molecules 1 (ICAM-1) via an osmotic effect in human umbilical vein endothelial cells exposed to high glucose medium

To clarify the etiology of accelerated atherosclerosis in patients with diabetes mellitus, we measured expression of intercellular adhesion molecule 1 (ICAM-1), vascular cellular adhesion molecule 1 (VCAM-1), and E-selection on the cell surface by enzyme-linked immunosorbent assay and ICAM-1 mRNA content in human umbilical vein endothelial cells exposed to 5.5 mM glucose (NG), 33 mM glucose (HG), or 27.5 mM mannitol plus 5.5 mM glucose (HM).1) Cell-surface ICAM-1 expression in HG and HM cells was maximally increased by 37% and 32% (P < 0.01), respectively. This effect was dependent on glucose concentration in the medium and was found as early as 24 h and maintained until 6 days after exposing cells of HG. However, neither VCAM-1 nor E-selection expression were affected by HG conditions. 2) Both HG and HM induced increased mRNA content between 6 and 12 h after the stimulation. 3) Adhesion of THP-1 cells to endothelial cells exposed to HG and HM was increased, when compared to NG conditions. These results indicate that osmotic effects can induce increased mRNA and cell-surface expression of ICAM-1 via an as yet unknown mechanism.

Inhibition of macrophage scavenger receptor activity by tumor necrosis factor-alpha is transcriptionally and post-transcriptionally regulated

Regulation of expression of the scavenger receptor is thought to play a critical role in the accumulation of lipid by macrophages in atherosclerosis. Tumor necrosis factor-alpha (TNF-alpha) has been shown to suppress macrophage scavenger receptor function (van Lenten, B.J., and Fogelman, A.M. (1992) J. Immunol. 148, 112-6). However, the mechanism by which it does so is unknown. We evaluated the mechanism by which TNF-alpha inhibited macrophage scavenger receptor surface expression and binding of acetylated low density lipoprotein (aLDL). Binding of aLDL to phorbol 12-myristate 13-acetate (PMA)-differentiated THP-1 macrophages was suppressed by TNF-alpha in a dose-dependent manner. Inhibition of aLDL binding was paralleled by a reduction of macrophage scavenger receptor protein as detected by the Western blot. TNF-alpha partially decreased macrophage scavenger receptor mRNA steady state levels in PMA-differentiated THP-1 macrophages, a result that was confirmed by reverse transcription-polymerase chain reaction. PMA increased the luciferase activity driven by the macrophage scavenger receptor promoter in the transfected cells, whereas TNF-alpha partially reduced luciferase activity. However, macrophage scavenger receptor mRNA half-life was dramatically reduced in cells treated with TNF-alpha relative to untreated cells. Reduction in macrophage scavenger receptor message in response to TNF-alpha was dependent on new protein synthesis because it was blocked by cycloheximide. These results indicate that TNF-alpha regulates macrophage scavenger receptor expression in PMA-differentiated THP-1 macrophages by transcriptional and post-transcriptional mechanisms but principally by destabilization of macrophage scavenger receptor mRNA.

Tumor necrosis factor alpha: posttranscriptional stabilization of WAF1 mRNA in p53-deficient human leukemic cells

The p53 protein directly regulates the expression of the WAF1 (wild-type p53-activated fragment 1) protein which is a cyclin-dependent kinase inhibitor (CDK1). DNA damaging agents such as ionizing or UV radiation, and some chemical agents induce WAF1 in wild-type p53 containing cells, thereby halting cell cycle progression. WAF1 expression is also induced through a p53-independent pathway. Tumor necrosis factor alpha (TNF alpha) is a cytotoxic/cytostatic compound for some human cancer cells. We examined a series of myeloid leukemic cell lines that expressed either no p53 (HL-60, K562) or mutant inactive p53 (KG-1, KCL22,THP-1, U937). The KG-1, HL-60, K562, and KCL22 myeloid leukemic cells increased their levels of WAF1 mRNA in the presence of TNF alpha. We focused on KG-1 cells to determine how TNF alpha modulated WAF1 expression. WAF1 mRNA increased in a dose-dependent manner in the cells after exposure to increasing concentrations of TNF alpha, and this increase occurred in the absence of new protein synthesis. An increase of WAF1 protein and a concominant decrease of cyclin-dependent kinase 2 activity also was found in KG-1 cells. Flow cytometry using 5-bromo-2'-deoxyuridine showed an increase in the proportion of TNF alpha- treated KG-1 cells in the G0/G1 phase of the cell cycle. TNF alpha enhanced the rate of WAF1 transcription only 1.4 fold in TNF alpha-treated KG-1 cells as compared to untreated cells. Notably, however, the half-life (t 1/2) of WAF1 mRNA in TNF alpha-treated cells was 2.5 hours as compared to 0.5 hours in untreated cells. These results indicate that TNF alpha increases WAF1 levels at least in part via a postttranscriptional stabilization of the mRNA; and TNF alpha may mediate its cytostatic effects through WAF1 in some cell types.

Detection of unintegrated HIV type 1 DNA in cell culture and clinical peripheral blood mononuclear cell samples: correlation to disease stage

This article reports on the development of PCR as a sensitive method of detecting both linear and circular forms of HIV-1 unintegrated viral DNA (UVD). The method was developed in a cell line study designed to follow the sequential synthesis of these forms over time. In all T lymphoid lineage cell lines, the full-length linear UVD (LUVD) was synthesized prior to both 1 and 2 LTR forms of circular UVD (CUVD), although all forms were detected by 12 hr postinoculation. Analysis of unstimulated PBMC samples from HIV-positive patients showed a significant difference in the presence of detectable CUVD forms and CDC groups II and IV (p < 0.001) and CDC groups III and IV (p < 0.001). No significance was demonstrated between CDC groups II and III (p > 0.5), linking the presence of CUVD forms to clinical disease and immunodeficiency. We propose that circular unintegrated forms of HIV-1 DNA may play a role in the development of acquired immunodeficiency syndrome.

Mycoplasma membrane lipoproteins induced proinflammatory cytokines by a mechanism distinct from that of lipopolysaccharide

To gain a clear understanding of the mechanisms by which mycoplasmas induced the expression of proinflammatory cytokines in monocytic cells, we have studied the induction of interleukin-1 beta (IL-1 beta), tumor necrosis factor alpha, and IL-6 by mycoplasmas in three distinct human myelomonocytic cell lines in comparison with induction by lipopolysaccharide (LPS). HL-60 cell line did not release cytokines when induced with either LPS or mycoplasmas. In contrast to LPS, mycoplasmas failed to increase the weak levels of tumor necrosis factor alpha secreted by phorbol myristate acetate-differentiated U937 cells. In addition, Northern (RNA) blot analysis of cytokine expression in these cells showed that the induction of IL-1 beta by mycoplasmas involves, unlike that by LPS, posttranscriptional events. Interestingly, in THP-1 cells, cytokine induction pathways triggered by mycoplasmas remained operational under conditions where LPS pathways were abolished, suggesting functional independence. The study of cytokine-inducing activity displayed by distinct fractions derived from a series of different mycoplasma species demonstrated that lipid membrane constituents were largely responsible for these effects. Finally, we have demonstrated that tyrosine phosphorylation is a crucial event in the mycoplasma-mediated induction of proinflammatory cytokines in either THP-1 cells or human monocytes.

Isolation and characterization of two monoclonal antibodies that recognize different epitopes of the human c-kit receptor

After immunizing mice with a human megakaryoblastic leukemia cell line, M-MOK, we obtained two monoclonal antibodies which recognize the human c-kit receptor. The monoclonal antibodies, designated MTK1 and MTK2, were found to specifically recognize Balb/3T3 cells transfected with human c-kit cDNA and not parent Balb/3T3 cells while showing different immunological, biochemical and biological behaviors. Both allowed visualization of the 140 kDa c-kit protein by Western blot analysis, but MTK1 detected only positive band with non-reducing conditions for sodium dodecyl sulfate-polyacrylamide gel electrophoresis. MTK1 partially inhibited the stem cell factor (SCF) induced proliferation of M-MOK cells, whereas, MTK2 was without effect. MTK1 also inhibited the bone marrow derived colony forming unit granulocyte/macrophage (CFU-GM) formed by granulocyte-macrophage colony stimulating factor (GM-CSF) and SCF. Not only anti-CD34 antibodies (HPCA-1) but also MTK1 could be shown to concentrate bone marrow CFU-GM and burst forming unit erythroid (BFU-E) effectively. The presently described monoclonal antibodies may therefore be useful for functional analysis of the ligand binding domain of the human c-kit receptor, as well as for further classification of hematopoietic stem cells in addition to the CD34 positive cells.

A decrease in glucose 6-phosphate dehydrogenase activity and mRNA is an early event in phorbol ester-induced differentiation of thp-1 promonocytic leukemia cells

Redox modification of regulatory proteins implicates the glutathione redox system (GRS) in the control of gene expression. Glucose-6-phosphate dehydrogenase (G6PD) provides reducing equivalents for the GRS, and it has been suggested that high levels of G6PD in preneoplastic lesions are directly related to neoplastic transformation. We have used THP-1 human promonocytic leukemia cells, an established model of induced macrophage differentiation, to test an important corollary of this hypothesis, viz., that a decrease in G6PD activity should accompany the loss of the transformed phenotype. Phorbol 12-myristate 13-acetate (PMA) arrests the constitutive cycling of THP-1 and induces a phenotype that approaches normalcy. We measured the specific activities of the GRS enzymes, G6PD, glutathione peroxidase, and glutathione reductase during the early stages of phorbol ester-induced differentiation of THP-1 cells. We observed an 80% decrease in G6PD activity and an increase in the apparent KM for glucose 6-phosphate. In contrast, glutathione peroxidase (GPX) activity increased, while glutathione reductase (GR) activity remained essentially constant. The reduction in G6PD activity, preceding the loss of the transformed phenotype, is accompanied by a fourfold decrease in steady-state levels of G6PD mRNA. These findings are consistent with the hypothesis that high levels of G6PD are causally related to neoplastic transformations.

19-Allylaminoherbimycin A, an analog of herbimycin A that is stable against treatment with thiol compounds or granulocyte-macrophage colony-stimulating factor in human leukemia cells

Herbimycin A, a benzoquinonoid ansamycin antibiotic, reduces intracellular phosphorylation by some protein tyrosine kinases and inhibits the proliferation of malignant cells which express high tyrosine kinase activity. Herbimycin A inhibited the proliferation of human monoblastic leukemia U937 cells, but this inhibition was abrogated by the addition of granulocyte-macrophage colony-stimulating factor (GM-CSF). On the other hand, a derivative of herbimycin A, 19-allylaminoherbimycin A, inhibited the proliferation of such cells without interference by the addition of GM-CSF. Phosphorylation of MAP kinase and c-myc expression induced by GM-CSF in U937 cells were inhibited by both herbimycin A and 19-allylaminoherbimycin A. The time courses of growth inhibition showed that the growth-inhibitory activity of herbimycin A in U937 cells was initially potent, but gradually decreased in the presence of GM-CSF. Thiol compounds, glutathione (GSH) and 2-mercaptoethanol, abrogated the inhibition of the growth of U937 cells by herbimycin A, but not by 19-allylaminoherbimycin A, like GM-CSF. Intracellular GSH content in U937 cells was increased by treatment with GM-CSF, and decreased with herbimycin A, but returned to the control level with the addition of GM-CSF to herbimycin A. In thin-layer chromatography, after in vitro incubation with herbimycin A and GSH, nothing could be detected at the position of intact herbimycin A, while 19-allylaminoherbimycin A was stably detected. These findings suggest that changes in the intracellular concentration of GSH play a role in the abrogation of the inhibition of U937 cell growth by herbimycin A. In the presence of GSH, 19-allylaminoherbimycin A inhibited the proliferation of U937 cells and Philadelphia chromosome-positive K562 cells more effectively than herbimycin A. Since GSH plays a role in detoxicating several anticancer drugs, 19-allylaminoherbimycin A may have therapeutic advantages over herbimycin A against some types of leukemia.

Quantitative cell line based bioassays for human cytokines

Research in cytokine biology is ever increasing and it is clear that cytokines are involved in a wide range of pathological and physiological processes. The validity of such research relies heavily on the appropriate measurement of levels of cytokines in various biological samples. Amongst the currently available methods for measuring cytokine levels, it is only the biological assay of samples that can directly provide estimates of biologically active cytokines present in test samples. Of the several bioassay systems available for detecting cytokines, cell line based bioassays are the easiest to perform and provide the most precise and accurate data. The suitability of any cell line for bioassaying a particular cytokine depends on several criteria such as sensitivity, ease of growth maintenance, and cytokine specificity. The design and analysis of cell line bioassays is also important in providing valid estimates of cytokine levels. We review the most useful cell lines currently available for bioassaying cytokines and discuss the design advantages and limitations of cytokine bioassays.

Interleukins and colony stimulating factors in human myeloid leukemia cell lines

The present review has summarized the expression, production and effects of the human interleukins (IL) 1-11 and myelopoietic colony stimulating factors (CSF) in the established myeloid leukemia cell lines and in cells from patients with acute myeloid leukemia as well as the oncogene expression reported in these myeloid leukemia cell lines. The genetic dissection of leukemic myelopoiesis may provide new perspectives for the control of myeloid leukemias. Based on their expression of phenotypic markers (e.g., surface antigens, cytochemical staining, etc.), myeloid cell lines can be further subdivided into myelogenous, monocytic, erythroid and megakaryoblastic leukemia cell lines. Due to the close relationship of erythroid and megakaryoblastic progenitor cells and to the existence of a probably common precursor cell giving rise to these two different cell lineages, many megakaryoblastic cell lines express erythroid markers (e.g., expression of hemoglobin or glycophorin A) and conversely cell lines with a predominant erythroid profile might display megakaryoblastic features (e.g., platelets peroxidase or glycoproteins CD41, CD42b or CD61). The recent cloning of the specific cytokine: thrombopoietin (TPO) and its receptor generated a strong interest in these particular myeloid cell lines that are discussed in more detail in the present review. Both normal and leukemic megakaryocytopoiesis are stimulated by granulocyte-macrophage colony stimulating factor (GM-CSF), IL-3, GM-CSF/IL-3 fusion protein, IL-6, IL-11 and TPO but inhibited by IL-4, interferon-alpha (IFN-alpha) and IFN-gamma. Human megakaryoblastic leukemia cell lines have common biological features: high expression of the megakaryocytic specific antigen (CD41); high expression of early myeloid antigens (CD34, CD33 and CD13); constitutive expression of IL-6 and platelet-derived growth factor; a complex karyotype picture; expression of c-kit (the stem cell factor receptor); growth-dependency or -stimulation by IL-3 and/or GM-CSF; and in vivo tumorigenicity in mice associated with marked fibrosis. Whereas numerous chemical and biologic agents induce granulocytic and/or monocytic differentiation of myeloid leukemia cell lines, only a few agents including phorbol myristate acetate, vitamin D3, IFN-alpha, IL-6 and thrombin have been reported to induce megakaryocytic differentiation in the megakaryoblastic leukemia cells.

Potentiation of tumor necrosis factor-mediated cytotoxicity on human myeloid cell lines: effects of interferons versus dimethylsulphoxide

After prolonged incubation times of 72 h IFN alpha 2a and IFN beta 1 significantly reduced cell growth in the myelomonocytic U937 and THP1 cell lines. IFN gamma showed only slight growth inhibitory activities. IFN activities were potentiated by the highly polar differentiation inducer dimethylsulphoxide, which is similar to our previous study on tumor necrosis factor (TNF). However, in contrast with TNF, none of the interferon types induced cell cytotoxicity or DNA fragmentation. Like DMSO, all interferons potentiated TNF-induced cytotoxicity, IFN beta 1 and IFN gamma being the most potent in this respect. When applied together, DMSO and IFN gamma enhanced TNF-mediated cell lysis in either an additive (in the case of U937, THP1, HL60 cells) or a synergistic (in the case of KG1) manner, suggesting that the mechanisms of the potentiating activity of DMSO and IFN gamma are different. The potential role of the simultaneous use of DMSO-related molecules, and TNF and/or IFN in leukemic cancer chemotherapy is discussed.

Growth hormone activation of human monocytes for superoxide production but not tumor necrosis factor production, cell adherence, or action against Mycobacterium tuberculosis

We have previously demonstrated that growth hormone (GH) is a human macrophage-activating factor which primes monocytes for enhanced production of H2O2 in vitro. This report extends our observations to other monocyte functions relevant to infection. We find that GH also primes monocytes for O2- production, to a degree similar to the effect of gamma interferon. Neither macrophage-activating factor alone stimulates monocytes to release bioactive tumor necrosis factor. However, GH, unlike gamma interferon, does not synergize with endotoxin for enhanced tumor necrosis factor production. In further contrast, GH does not alter monocyte adherence or morphology, while phagocytosis and killing of Mycobacterium tuberculosis by GH-treated monocytes are also unaffected. Therefore, despite the multiplicity of the effects of GH on the immune system in vivo, its effects on human monocytes in vitro appear to be limited to priming for the release of reactive oxygen intermediates.

Crystal structure of the I-domain from the CD11a/CD18 (LFA-1, alpha L beta 2) integrin

We report the 1.8-A crystal structure of the CD11a I-domain with bound manganese ion. The CD11a I-domain contains binding sites for intercellular adhesion molecules 1 and 3 and can exist in both low- and high-affinity states. The metal-bound form reported here is likely to represent a high-affinity state. The CD11a I-domain structure reveals a strained hydrophobic ridge adjacent to the bound metal ion that may serve as a ligand-binding surface and is likely to rearrange in the absence of bound metal ion. The CD11a I-domain is homologous to domains found in von Willebrand factor, and mapping of mutations found in types 2a and 2b von Willebrand disease onto this structure allows consideration of the molecular basis of these forms of the disease.

High-level expression from a cytomegalovirus promoter in macrophage cells

To identify vectors that provide optimal gene expression in human hematopoietic cells, we investigated retroviruses containing the adenosine deaminase (ADA) gene under the transcriptional control of the promoters/enhancers of Moloney murine leukemia virus and the human cytomegalovirus (CMV) immediate-early gene. ADA expression was monitored in transduced human multipotential promyelocytic leukemic HL-60 cells and human monocytic leukemic THP-1 cells. HL-60 cells can be induced by phorbol ester to differentiate into macrophage lineage cells and by retinoic acid into granulocytic cells. THP-1 cells undergo phorbol ester-induced differentiation to macrophage cells. In LNCA-transduced HL-60 derived macrophage cells, ADA controlled by the CMV promoter was expressed at 100.0 mumol/hr.mg, in contrast to 1.2 mumol/hr.mg from LN-transduced control cells. LNCA-transduced THP-1 macrophage cells showed a similar increase in ADA activity over control cells. These elevated enzyme activities were confirmed by Northern blots, which showed substantial increases in ADA mRNA derived from the CMV promoter. This suggests use of the CMV promoter for gene therapy targeted at macrophages, as, for example, in the treatment of lysosomal storage disorders such as Gaucher disease. These inducible cell lines have allowed the evaluation of transduced gene expression in proliferating and differentiating hematopoietic cells that may serve as an in vitro model of bone marrow-targeted gene therapy.

Alpha 1,4galactosyltransferase activity and Gb3Cer expression in human leukaemia/lymphoma cell lines

We have used two methods to evaluate the level of expression of Gb3Cer in several human leukaemia/lymphoma cell lines representative of the myeloid (K562, KG-1, HL-60, and lymphoid (Reh, Daudi, Raji, RPMI 8226, CCRF-CEM, MOLT-4) lineages blocked at varied stages of differentiation. TLC immunostaining of glycolipid extracts with a monoclonal antibody, 12-101, and FACS analysis with the same antibody were used to demonstrate that the expression of Gb3Cer in neoplastic myeloid and lymphoid cells is both lineage and differentiation dependent. As a possible control point in the regulated expression of Gb3Cer we have investigated the first committed step in the synthesis of globo series glycosphingolipids that involves UDP-Gal:LacCer alpha (1,4)-galactosyltransferase (alpha 1,4GalT). We present the first characterization of this enzyme in a human myeloid cell line using an ELISA-based assay, which was subsequently used to measure alpha 1,4GalT activity in the human leukaemia/lymphoma cell lines. In general, there is a positive correlation between the levels of endogenous Gb3Cer and the level of the alpha 1,4 GalT activity. However, in two cases (KG-1 and CCRF-CEM) the level of enzyme activity did not correspond to the level of Gb3Cer expression.

N-ras mRNA expression is unaffected in glutathione-depleted cells of hematopoietic origin

Glutathione (GSH) depletion in mitogen-stimulated T lymphocytes has been shown to markedly inhibit their proliferative response. This block in proliferation is associated with a significant reduction in total RNA and DNA synthesis; however, the specific mechanism involved in this inhibition of proliferation is unknown. Miller et al. have reported that lowering intracellular GSH levels by greater than 30%, in murine and human tumor cell lines of non-hematopoietic origin, leads to down-regulation of HA-, Ki- and N-ras oncogene expression [Miller. A.C., Gafner, J., Clark, E.P. and Samid, D. (1993) Mol. Cell Biol., 13, 4416-4422]. The reduction in ras transcript levels correlated with the extent of GSH depletion and was independent of the specific mode of oncogene activation. Since the activity of p21(ras) is thought to be involved in pathways of T cell activation, we set out to determine whether down-regulation of ras expression in T cells could be the mechanism by which T cell proliferation was inhibited in GSH-depleted T lymphocytes. Despite reducing the GSH level of concanavalin A-activated human peripheral blood mononuclear cells by 66%, no effect on ras mRNA expression was observed. Similarly, no reduction of ras transcript levels were detected in a human T cell line (Jurkat) or in a human monocytic cell line (THP-1) depleted of glutathione. Our results demonstrate that the mechanism by which GSH depletion inhibits T cell proliferation does not appear to involve a decrease in ras mRNA expression. In addition, our results suggest that differences in the regulation of ras mRNA expression may exist between lymphoid/monocytic cells of non-hematopoietic origin.

Cell membrane bound N-acetylneuraminic acid is involved in the infection of fibroblasts and phorbol-ester differentiated monocyte-like cells with human cytomegalovirus (HCMV)

We focused on the role of membrane bound sugar residues in the infection of fibroblasts and monocyte-like cells with human cytomegalovirus (HCMV). Treatment of phorbol 12-myristate 13-acetate (PMA) differentiated monocyte-like cells THP-1 or human fibroblasts MRC-5 with lectins specific for N-acetylneuraminic acid (NeuAc) blocked infection with HCMV. HCMV failed to infect sialidase-treated differentiated THP-1 cells or MRC-5 cells. By using NeuAc, N-glycolylneuraminic acid (NeuGl) and alpha 2-3, but not alpha 2-6, sialyl-oligosaccharide, the infection of cells was less efficient. NeuAc was more potent inhibitor than NeuGl. These observations suggest that the sialic acid specificity and the nature of the interglycosidic linkage at the end of the complex carbohydrates may play an important role. Analogous experiments indicated that HCMV binds to N-acetylglucosamine (GlcNAc) in addition to NeuAc. Human cytomegalovirus infection in differentiated THP-1 cells and in human fibroblasts was inhibited by incubation of the virus with 20 micrograms/ml of heparin before and during the adsorption period. Treatment of the cells with heparinase or heparitinase inhibited infection with HCMV. We emphasized the role of NeuAc and GlcNAc and heparan sulfate proteoglycans at the surface of the cells, in the early steps of infection of both human fibroblasts and PMA differentiated monocyte-like cells with HCMV.

THP-1 macrophage membrane-bound plasmin activity is up-regulated by transforming growth factor-beta 1 via increased expression of urokinase and the urokinase receptor

Receptors for urokinase (uPA) and plasminogen provide a mechanism to direct the cellular activation of plasminogen. The regulation of these receptors is important for several macrophage functions. In these studies, the effect of transforming growth factor-beta 1 (TGF-beta 1) on uPA, uPA receptor, and plasminogen receptor expression by human THP-1 macrophage was examined. TGF-beta 1 induction of uPA expression by THP-1 cells was differentiation dependent. Suspension and adherent cultures expressed similar constitutive levels of uPA. Exposure of adherent cells to TGF-beta 1 led to a dose- and time-dependent increase in uPA activity which was paralleled by an increase in uPA antigen and uPA mRNA. In contrast, uPA expression by suspension cultures was unresponsive to TGF-beta 1. The differential response exhibited by suspension and adherent THP-1 cells may reflect differences in their expression of TGF-beta 1 receptors, since when assayed by crosslinking techniques, suspension cells primarily expressed a 65 kDa receptor; whereas, the adherent cells expressed 65 and 100 kDa receptors. TGF-beta 1-induced alterations in uPA receptor expression by adherent THP-1 cells were examined by quantitating membrane-bound uPA activity. Membrane-bound uPA activity increased three-fold when cells were incubated with TGF-beta 1. The increase in membrane-uPA activity expressed by TGF-beta 1-treated cells was not due to increased uPA receptor occupancy since incubation of either control or TGF-beta 1 primed cells with exogenous uPA did not lead to an increase in membrane-bound uPA activity. Furthermore, immunoreactive uPA receptor was increased in TGF-beta 1-treated cells. Following incubation with plasminogen, membrane-bound plasmin activity increased three-fold in TGF-beta 1-treated cells. However, no change in immunoreactive membrane-bound plasmin(ogen) was observed. In addition, binding of 125I-Lys-plasminogen to THP-1 cells was not affected by TGF-beta 1 treatment. We conclude that TGF-beta 1 stimulates membrane-bound plasmin activity, without affecting plasminogen receptor expression, through the up-regulation of uPA and the uPA receptor expression.

Copper-induced tissue factor expression in human monocytic THP-1 cells and its inhibition by antioxidants

BACKGROUND

Transition metals such as copper are known to initiate free radical formation and lipid peroxidation. Recent reports suggest that intracellular reactive oxygen intermediates can induce the transcription of a number of important genes. The present study examines the effects of copper and iron on the ability of monocytic cells to synthesize and express tissue factor, the potent procoagulant factor.

METHODS AND RESULTS

Exposure of human monocytic THP-1 cells to 5 to 10 mumol/L Cu2+ led to cell damage and the expression of tissue factor activity to levels up to 70 times higher than control, as measured by a single-stage plasma coagulation assay. These effects were seen only in the presence of a lipophilic chelating agent, 8-hydroxyquinoline, suggesting that intracellular transport of Cu2+ was required. The effects of Cu2+ were mimicked by ceruloplasmin but not by Fe3+ or hemin. The induction of tissue factor activity by Cu2+ was slow in onset (6 hours) but sustained (24 hours) and was accompanied by increased tissue factor mRNA levels, measured by reverse transcription/polymerase chain reaction after annealing with oligomer primers. Increases in tissue factor protein, measured by a specific immunoassay, also occurred but were smaller than those in activity. Cu2+, therefore, appears to act at both the transcriptional and posttranslational levels. The effects of Cu2+ were inhibited by a number of lipophilic antioxidants, including probucol, vitamin E, butylated hydroxytoluene, and a 21-aminosteroid, U74389G.

CONCLUSIONS

Exposure of monocytes to oxidizing conditions may lead to the expression of high levels of tissue factor activity, with accompanying risk for disseminated intravascular coagulation, and this may be inhibited by lipophilic antioxidants.

Identification of macrophage and stress-induced proteins of Mycobacterium tuberculosis

Using phosphorimager technology to quantitate differences in protein expression, we have investigated the modulation of protein synthesis by Mycobacterium tuberculosis in response to intracellular residence in human macrophages and, for comparison, in response to various stress conditions during extracellular growth. Proteins of M. tuberculosis growing intracellularly in human THP-1 cells and extracellularly in broth were labeled with [35S]methionine; during intracellular growth, host cell protein synthesis was inhibited with cycloheximide. The metabolically labeled proteins were separated by two-dimensional gel electrophoresis and quantitatively analyzed. Intracellular residence in macrophages induced a profound change in the overall phenotype of M. tuberculosis. The expression of at least 16 M. tuberculosis proteins was induced (at least a twofold increase compared with growth in broth) and 28 proteins repressed (at least a twofold decrease). Many of the phenotypic changes in protein expression induced during intracellular growth occurred during extracellular growth in response to stress conditions including heat-shock, low pH, and H2O2. However, the pattern of induced and repressed proteins was unique to each stress condition. Of the 16 macrophage-induced proteins, 6 were absent during extracellular growth under both normal and stress conditions. Such proteins are potential virulence determinants and/or they may be important in the cell-mediated and protective immune response to M. tuberculosis infection.

Activation of alpha-human tumour necrosis factor (TNF-alpha) by human monocytes (THP-1) exposed to 2-chloroethyl ethyl sulphide (H-MG)

Tumour necrosis factor (TNF) is a monokine produced by monocytes and macrophages in response to different stimuli. To determine whether vesicant agents such as half-mustard gas (H-MG; chemical structure: ClCH2CH2SCH2CH3) may induce the release of TNF-alpha in human monocytes (THP-1), ELISA experiments were conducted at different post exposure times. The results indicate that: (1) Significant increases in the TNF-alpha (pg mL-1) concentration were observed as a function of time when THP-1 cells were exposed to 100 microL of 2 M H-MG. A specific serine-type protease inhibitor, N alpha-p-tosyl-L-lysine chloromethyl ketone (TLCK), led to partial but significant inhibition of TNF activation. (2) Furthermore, this laboratory detected the generation of spin adducts of 2-methyl-2-nitrosopropane (MNP) having a resemblance to MNP-adducts generated from hydrogen atom abstraction of protein constituents. The EPR/Spin Trapping data indicate the trapping of by-products of protein degradation after exposure to H-MG. TNF-alpha may play a role as a biochemical marker for pathophysiological changes induced by H-MG or related agents.

Influence of surface charges on cell adhesion: difference between static and dynamic conditions

We tested the hypothesis that nonspecific repulsion, as a result of electrostatic forces and (or) steric stabilization effects, impaired adhesion more efficiently under dynamic than under static conditions. Cells from the human monocytic line THP1 were plated on a glass surface. Spherical particles bearing monoclonal antibodies specific for antigens expressed by THP1 cells (CD11b, CD18, CD35, CD64) were then added and adhesion was quantified. The effect of neuraminidase treatment of THP1 cells was also studied. Adhesion was then measured in a flow chamber under low shear flow (wall shear rate was 11 or 22 s-1), allowing a quantitative determination of cell adhesion frequency. The following conclusions were obtained: (i) under static conditions, neuraminidase treatment had little effect on adhesion (only CD18-mediated interaction was significantly increased at 4 degrees C after enzyme treatment); (ii) under dynamic conditions, neuraminidase treatment significantly increased binding; (iii) surprisingly, there was no clear relationship between the length of adhesion molecules involved in the interaction and binding efficiency; and (iv) such parameters as cell shape and topographical distribution of adhesion molecules may strongly influence adhesion under flow. It is concluded that a dynamic reorganization of the pericellular matrix following intercellular contact may play an important role in regulating adhesion.

Induction of intracellular cAMP by a synthetic retroviral envelope peptide: a possible mechanism of immunopathogenesis in retroviral infections

A synthetic heptadecapeptide, CKS-17, represents the highly conserved amino acid sequences occurring within the transmembrane envelope protein of many animal and human retroviruses. CKS-17 has been demonstrated to exhibit suppressive properties for numerous immune functions. We have recently shown that CKS-17 acts as an immunomodulatory epitope causing an imbalance of human type 1 and type 2 cytokine production and suppression of cell-mediated immunities. cAMP, an intracellular second messenger, plays an important role in regulation of cytokine biosynthesis--i.e., elevation of intracellular cAMP levels selectively inhibits type 1 cytokine production but has no effect or enhances type 2 cytokine production. Here, we demonstrate that CKS-17 induces dramatic rises in the intracellular cAMP levels of a human monocyte cell line and of human peripheral blood mononuclear cells in a time- and dose-dependent manner. A peptide corresponding to the reverse sequence of CKS-17, used as control, has no effect on intracellular cAMP levels. The cAMP-inducing ability of CKS-17 is significantly blocked by SQ-22536, an inhibitor of adenylate cyclase. These results indicate that CKS-17, a highly conserved component of the transmembrane proteins of immunosuppressive retroviruses, induces increased intracellular levels of cAMP via activation of adenylate cyclase and suggest that this retroviral envelope peptide may differentially modulate type 1 and type 2 cytokine production through elevation of intracellular cAMP levels.

Apoptosis as a cause of death in measles virus-infected cells

To determine the mechanism of measles virus-induced cell death, we studied the infection of Vero cells and monocytic cell lines with wild-type (Chicago-1) and vaccine (Edmonston) strains of measles virus. DNA fragmentation indicative of apoptosis was apparent by flow cytometry, agarose gel electrophoresis, and electron microscopy. Within syncytia, DNA strand breaks were demonstrated by end labeling with terminal transferase and then by visualization.

Identification of a cell-type-specific and E2F-independent mechanism for repression of cdc2 transcription

Human myeloid leukemia cells, such as HL60, U937, and THP1 cells, undergo macrophage differentiation and growth arrest following treatment with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). Surprisingly, we find that growth of a significant percentage of THP1 cells is arrested in the G2 phase of the cell cycle. G2 arrest correlates with cell-specific repression of the gene encoding p34cdc2, a crucial regulator of G2/M progression. Intriguingly, TPA-mediated repression of the cdc2 promoter was independent of the transcription factor E2F, distinguishing this pathway from mechanisms responsible for repression of cdc2 transcription in response to serum starvation. The region of the cdc2 promoter required for repression was located from bp -22 to -2 from the major transcriptional start site. This sequence, which we term the R box, directs the uncoupling of the basal promoter from upstream activators following TPA treatment. Analysis of THP1 nuclear proteins revealed a 55-kDa protein that was induced by TPA and interacted with the cdc2 promoter in an R-box-dependent manner. These observations provide evidence for the existence of cell-type- and promoter-specific pathways for the assembly of stable transcriptional initiation complexes that function to differentially regulate the expression of cell cycle control genes in mammalian cells.

A peptide derived from the intercellular adhesion molecule-2 regulates the avidity of the leukocyte integrins CD11b/CD18 and CD11c/CD18

beta 2 integrin (CD11a,b,c/CD18)-mediated cell adhesion is required for many leukocyte functions. Under normal circumstances, the integrins are nonadhesive, and become adhesive for their cell surface ligands, the intercellular adhesion molecules (ICAMs), or soluble ligands such as fibrinogen and iC3b, when leukocytes are activated. Recently, we defined a peptide derived from ICAM-2, which specifically binds to purified CD11a/CD18. Furthermore, this peptide strongly induces T cell aggregation mainly mediated by CD11a/CD18-ICAM-1 interaction, and natural killer cell cytotoxicity. In the present study, we show that the same ICAM-2 peptide also avidly binds to purified CD11b/CD18, but not to CD11c/CD18. This binding can be blocked by the CD11b antibody OKM10. The peptide strongly stimulates CD11b/CD18-ICAM-1-mediated cell aggregations of the monocytic cell lines THP-1 and U937. The aggregations are energy and divalent cation-dependent. The ICAM-2 peptide also induces CD11b/CD18 and CD11c/CD18-mediated binding of THP-1 cells to fibrinogen and iC3b coated on plastic. These findings indicate that in addition to induction of CD11a/CD18-mediated cell adhesion, the ICAM-2 peptide may also serve as a "trigger" for high avidity ligand binding of other beta 2 integrins.

Enzymatically deacylated lipopolysaccharide (LPS) can antagonize LPS at multiple sites in the LPS recognition pathway

Like other tetraacyl partial structures of lipopolysaccharide (LPS) and lipid A, LPS that has been partially deacylated by acyloxyacyl hydrolase can inhibit LPS-induced responses in human cells. To identify the site(s) of inhibition in the LPS recognition pathway, we analyzed the apparent binding affinities and interactions of 3H-labeled enzymatically deacylated LPS (dLPS) and [3H]LPS with CD14, the LPS receptor, on THP-1 cells. Using (i) incubation conditions that prevented ligand internalization and (ii) defined concentrations of LPS binding protein (LBP), which facilitates LPS and dLPS binding to CD14, we found that dLPS can antagonize LPS in at least three ways. 1) When the concentration of LBP in the medium was suboptimal for promoting LPS-CD14 binding, low concentrations of dLPS were able to compete with LPS for binding CD14, suggesting competition between LPS and dLPS for engaging LBP. 2) When LBP was present in excess, dLPS could compete with LPS for binding CD14, but only at dLPS concentrations that were at or above its KD for binding CD14 (100 ng/ml). 3) In contrast, substoichiometric concentrations of dLPS (1 ng/ml) inhibited LPS-induced (3 ng/ml) interleukin-8 release without blocking LPS binding to CD14. Functional antagonism was possible without competition for cell-surface binding because both LPS-induced interleukin-8 release and dLPS inhibition occurred at concentrations that were far below their respective CD14 binding KD values. In addition to its expected ability to compete with LPS for binding LBP and CD14, dLPS thus potently antagonizes LPS at an undiscovered site that is distal to LPS-CD14 binding in the LPS recognition pathway.

Stealth Me.PEG-PLA nanoparticles avoid uptake by the mononuclear phagocytes system

Nanoparticles were prepared from methoxy poly(ethylene glycol)poly(d,l-lactic acid) block copolymers (Me.PEG-PLA) or blends of Me.PEG-PLA and PLA by the precipitation-solvent diffusion method. These nanoparticles, labeled by introducing [14C]PLA in the formulation, were shown to be more slowly captured by cultured THP-1 monocytes than F68-coated PLA nanoparticles, in a PEG chain-length-dependent manner. In vivo, the half-life in plasma of the Me.PEG-PLA nanoparticles that were intravenously administered to rats is increased by a factor 180 compared with the F68-coated PLA nanoparticles. This mononuclear phagocytes system avoidance was explained according to a conformation model in which the PEG density at the surface of the particles is a key parameter.

Analysis of Pichinde arenavirus transcription and replication in human THP-1 monocytic cells

Human promonocytic THP-1 cells were previously shown to be nonpermissive for Pichinde virus (PV) replication unless the cells were induced to differentiate to macrophages by stimulation with phorbol ester (PMA) (J. Virol. 65, 3575, 1991). The restriction did not involve receptor modulation, virus binding, nor internalization of virus but a requirement for a host cell function in PV replication was observed in that the phorbol ester effect required protein kinase C activation and was inhibited by actinomycin D. In this report we demonstrate that PV S RNA genomes, antigenomes, GPC mRNA and NP mRNA are expressed at high levels in PMA treated THP-1 cells but at significantly lower levels or not at all in untreated cells. We have also determined that degradation of input viral S RNA does not account for decreased PV RNA synthesis in the undifferentiated cells. This suggests that the restriction of PV replication in THP-1 cells is a post-penetration event which precedes transcription of viral mRNAs and replication of viral genomes and supports a role for differentiation-specific host cell factors early in PV replication.

Activation of human THP-1 cells and rat bone marrow-derived macrophages by Helicobacter pylori lipopolysaccharide

The mechanism by which Helicobacter pylori, which has little or no invasive activity, induces gastric-tissue inflammation and injury has not been well characterized. We have previously demonstrated that water-extracted proteins of H. pylori are capable of activating human monocytes by a lipopolysaccharide (LPS)-independent mechanism. We have now compared activation of macrophages by purified LPS from H. pylori and from Escherichia coli. LPS was prepared by phenol-water extraction from H. pylori 88-23 and from E. coli O55. THP-1, a human promyelomonocytic cell line, and macrophages derived from rat bone marrow each were incubated with the LPS preparations, and cell culture supernatants were assayed for production of tumor necrosis factor alpha (TNF-alpha), prostaglandin E2 (PGE2), and nitric oxide. THP-1 cells showed maximal activation by the LPS molecules after cell differentiation was induced by phorbol 12-myristate 13-acetate. Maximal TNF-alpha and PGE2 production occurred by 6 and 18 h, respectively, in both types of cells. In contrast, NO was produced by rat bone marrow-derived macrophages only and was maximal at 18 h. The minimum concentration of purified LPS required to induce TNF-alpha, PGE2, and NO responses in both types of cells was 2,000- to 30,000-fold higher for H. pylori than for E. coli. Purified LPS from three other H. pylori strains with different polysaccharide side chain lengths showed a similarly low level of activity, and polymyxin B treatment markedly reduced activity as well, suggesting that activation was a lipid A phenomenon. These results indicate the low biological activity of H. pylori LPS in mediating macrophage activation.

In vitro reverse cholesterol transport from THP-1-derived macrophage-like cells with synthetic HDL particles consisting of proapolipoprotein A1 or apolipoprotein A1 and phosphatidylcholine

The human monocytic leukaemia cell line THP-1 was induced to differentiate to macrophage-like cells by the addition of phorbol myristoyl acetate (PMA). Subsequently, the cells were enriched in cholesterol and these cholesterol laden cells were used to study the capability of reconstituted discoidal complexes (RDCs), consisting of either human apolipoprotein A1 (apo A1) or recombinant human proapolipoprotein A1 (proapo A1) and phosphatidylcholine (PC), to promote cholesterol efflux. RDCs containing apo A1 and proapo A1 were both effective in the mobilization of intracellular cholesterol, whether this was measured by intracellular cholesterol mass or by the appearance of radiolabelled cholesterol in the supernatant. Using the radiolabelling technique, the activity was saturable and followed Michaelis-Menten kinetics. For both types of complexes and for native HDL the maximum rate of cholesterol removed was approximately 0.5 nmol h-1 per 10(6) cells. For RDCs of proapo A1 and apo A1 and for native HDL the Km values were 3.7, 2.9 and 64.8 micrograms ml-1 respectively. A significant in vitro cholesterol efflux could only be achieved with protein-lipid complexes; no significant export was observed with either free proapo A1 or multilamellar PC liposomes without apolipoprotein. Both RDCs were found to be more active in the mobilization of intracellular cholesterol than HDL isolated from human plasma. The combined results demonstrate that synthetic complexes consisting either of apo A1 or proapo A1 and PC are both active in the in vitro reverse transport of cholesterol.

Isolation of cDNA clones for 42 different Krüppel-related zinc finger proteins expressed in the human monoblast cell line U-937

To study the complexity and structural characteristics of zinc finger proteins expressed during human hematopoiesis and to isolate novel regulators of blood cell development, a degenerate oligonucleotide probe specific for a consensus zinc finger peptide domain was used to isolate 63 cDNA clones for Krüppel-related zinc finger genes from the human monoblast cell line U-937. By extensive nucleotide sequence and Northern blot analysis, these cDNA clones were found to originate from approximately 42 different genes (HZF 1-42) of which only 8 have previously been described. Northern blot analysis showed that a majority of these genes were expressed at comparable levels in U-937 and HeLa cells. The large number of individual genes represented among the 63 clones and their apparent non-cell-type-specific expression suggest that the majority of the Krüppel-related zinc finger genes are likely to be expressed in most human tissues. In contrast, some of the genes displayed a restricted expression pattern, indicating that they represent potential regulators of monocyte differentiation or proliferation. Detailed structural analysis of the first 12 cDNAs (HZF 1-10) and a partial characterization of HZF 11-42 revealed that a common feature of human Krüppel-related zinc finger proteins is the presence of tandem arrays of zinc fingers ranging in number from 3 to over 20 that are preferentially located in the carboxy-terminal regions of the proteins. In addition, several novel KRAB-containing zinc finger genes and a novel conserved sequence element were identified.

Adhesion properties of Mono Mac 6, a monocytic cell line with characteristics of mature human monocytes

Progress in the understanding of blood cell--endothelial cell interactions has been achieved by the development of in-vitro model systems. We describe adhesion properties of the recently established human monocytic cell line Mono Mac 6. These cells showed increased adherence to unstimulated and tumour necrosis factor (TNF)-alpha (50 U/ml) stimulated human umbilical vein endothelial cells (HUVEC) (9.4% +/- 0.4% and 56.5% +/- 3.3%), as compared to U937 cells (2.6% +/- 0.8% and 40.0% +/- 8.4%). The values were similar to freshly isolated human blood monocytes (18.8% +/- 7.5% and 55.7% +/- 9.3%, respectively). Maximal binding was 6.2 +/- 0.6 Mono Mac 6 cells per HUVEC, which was 34% less than U937 cells (8.9 +/- 0.3). The lower number of adherent Mono Mac 6 cells per HUVEC could be due to their larger size, as assessed by flow cytometry. Blocking experiments with monoclonal antibody (mAb) directed against E-selectin, VCAM-1 and ICAM-1 on HUVEC and CD11b or CD14 on Mono Mac 6 cells demonstrated the contribution of these molecules to Mono Mac 6 adherence. Reduced binding after 24 h parallels the decline of E-selectin expression in HUVEC. Linearity of cell binding was confirmed from 0.2 x 10(6) to 1.0 x 10(6) Mono Mac 6 cells. Expression of CD11b and CD14 in Mono Mac 6 cells and in isolated human monocytes but not in U937 cells leading to interaction with ICAM-1 on HUVEC appears to be responsible for the increased adhesion of Mono Mac 6, as compared to U937 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

K+ channel blockers inhibit tissue factor expression by human monocytic cells

Human monocytes express the important procoagulant protein, tissue factor (TF), after stimulation by a variety of agents, including bacterial lipopolysaccharide (LPS). Monocyte TF expression may contribute to intravascular coagulation in a number of disease states. The present studies show that monocytic cell TF expression can be inhibited by several agents known to block cellular K+ channels. Exposure of human peripheral blood to 100 ng/mL LPS for 2 hours led to pronounced TF procoagulant activity associated with the mononuclear cell fraction. This was inhibited by 4-aminopyridine (2 mmol/L), tetraethylammonium chloride (10 mmol/L), and apamin (1 mumol/L). In contrast, charybdotoxin (100 nmol/L) was inactive. More detailed studies were carried out in cultured human monocytic tumor THP-1 cells. These cells exhibited low but detectable levels of TF mRNA, measured by reverse transcription and polymerase chain reaction; cell surface procoagulant activity, measured by a plasma clotting assay; and cell homogenate TF antigen, measured by immunoassay. Exposure of THP-1 cells to 1 microgram/mL LPS led to threefold to fivefold increases in all three parameters. Basal and LPS-induced levels of all three parameters were reduced in a dose-dependent manner by 4-aminopyridine (I50, 1 mmol/L) and tetraethylammonium chloride (I50, 20 mmol/L) but not by apamin or charybdotoxin. Expression of TF activity was also inhibited by glibenclamide, an inhibitor of ATP-dependent K+ channels (I50, 25 mumol/L). These results suggest that facilitation of TF synthesis may be an important role for K+ channels in monocytes.

Partial characterization of a low molecular weight phagocytosis inhibitory factor obtained from human erythrocyte membranes

Phagocytosis Inhibitory Factor (PIF), a small (< 3000 D) molecule, was partially purified from human red blood cell membranes. This factor inhibits latex phagocytosis by monocytic cells. PIF is not toxic under the experimental conditions employed and the phagocytosis inhibitory activity is reversible since removal of this factor restores the phagocytic capability of cells. The phagocytic activity of murine macrophages was not affected by PIF.

Influence of host cell type and V3 loop of the surface glycoprotein on susceptibility of human immunodeficiency virus type 1 to polyanion compounds

Dextran sulfate is a potent inhibitor of human immunodeficiency virus (HIV) binding and replication in lymphocytic cell lines. In this study, we demonstrate that the effect of dextran sulfate and heparin depends on the host cell type and on the V3 loop, the principal neutralizing determinant of HIV gp120. In particular, when dextran sulfate was tested on primary human macrophages infected with macrophage-tropic viruses, enhancement of infection was observed in 6 of 11 independent macrophage preparations and with 5 of 13 primary HIV isolates. Our in vitro observations might explain why enhanced HIV replication was observed in HIV-infected patients treated with dextran sulfate.

Constitutive nuclear NF-kappa B in cells of the monocyte lineage

In monocytes, the nuclear factor NF-kappa B has been invoked as an important transcription factor in the expression of cytokine genes, of cell-surface receptors and in the expression of human immunodeficiency virus. In such cells, DNA binding activity of NF-kappa B can be detected without intentional stimulation. In our studies, cells of the human monocytic line Mono Mac 6, cultured in medium containing fetal-calf serum and low levels of lipopolysaccharide (LPS), also exhibit such 'constitutive' NF-kappa B, as demonstrated by mobility-shift analysis of nuclear extracts. This nuclear NF-kappa B was still present when contaminant LPS was removed by ultrafiltration and when serum was omitted. Protein-DNA complexes of constitutive NF-kappa B are similar in mobility to the LPS-induced NF-kappa B and both are recognized by an antibody specific to the p50 subunit of NF-kappa B. By contrast, treatment of cells with pyrrolidine dithiocarbamate (PDTC) will only block LPS-induced NF-kappa B, but not the constitutive binding protein. Using LPS-free and serum-free conditions, constitutive NF-kappa B can be detected in different cell lines of the monocytic lineage (HL60, U937, THP-1, Mono Mac 1 and Mono Mac 6), but not in Molt 4 T cells or K562 stem cells. When ordered according to stage of maturation, the amount of constitutive NF-kappa B was not increased in more mature cell lines. Furthermore, when inducing differentiation in Mono Mac 6 cells, with vitamin D3, no change in constitutive or inducible NF-kappa B can be detected. Analysis of primary cells revealed substantial constitutive NF-kappa B-binding activity in blood monocytes, pleural macrophages and alveolar macrophages. The constitutive NF-kappa B appears to be functionally active, since a low level of tumour necrosis factor (TNF) transcript is detectable in monocytes, and this level can be increased by blocking transcript degradation using cycloheximide. The level of constitutive NF-kappa B in these cells is variable and is frequently found to be lower in the more mature macrophages. Constitutive NF-kappa B was not maintained by autocrine action of cytokines TNF, interleukin 6, interleukin 10, granulocyte-macrophage colony-stimulating factor or macrophage colony-stimulating factor, since neutralizing antibodies did not reduce constitutive DNA-binding activity. Furthermore, blockade of prostaglandin or leukotriene biosynthesis did not affect constitutive NF-kappa B.(ABSTRACT TRUNCATED AT 400 WORDS)