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

Assay of pyrogens by interleukin-6 release from monocytic cell lines

A novel in-vitro system has been developed for the detection and quantification of pyrogen in pharmaceutical products. The measured variable was evoked secretion of the pyrogenic cytokine interleukin-6 from MONO MAC 6 monocytic cells incubated with the product. The interleukin-6 was detected using a specific and sensitive ELISA developed for this purpose. The test system detected pyrogenic contamination in 3 batches of therapeutic human serum albumin which had caused adverse reactions in recipients. The contamination was not detected in conventional tests: the rabbit pyrogen test and the limulus amoebocyte lysate test.

Characterization of Pichinde virus infection of cells of the monocytic lineage

To establish a model of viral infection of monocytes, we examined infection of human cells and cell lines of the monocytic series with the arenavirus Pichinde virus. We demonstrate for the first time that human peripheral blood monocytes are susceptible to Pichinde virus infection, as shown by immunoprecipatation of virus-specific polypeptides from infected cells, immunofluorescence analyses, and quantitation of virus production from infected cells. The human promyelocytic leukemia cell line HL60 did not support Pichinde virus replication, even if cells were induced with the phorbol ester phorbol myristate acetate (PMA) to differentiate to monocytes. However, the human promonocytic leukemia cell line THP-1 did support Pichinde virus replication. Replication depended on exposure of the cells to PMA. We examined the nature of the effect of PMA in the induction of THP-1 cells to support Pichinde virus replication. We found that 5 min of exposure of THP-1 cells to PMA is sufficient to support virus growth and that PMA-treated THP-1 cells remain susceptible to infection up to 4 days after the initial PMA treatment. We also showed that infection of PMA-treated THP-1 cells is mediated through protein kinase C (PKC). H7, a PKC inhibitor, was able to block both PMA-induced differentiation and Pichinde virus infection of THP-1 cells. The synthetic diacylglycerol and PKC agonist, diC8, was able to stimulate THP-1 cells to support virus growth, albeit to lower levels than PMA. Dactinomycin abrogated the ability of virus to replicate and suggested a requirement for host cell transcription. The PMA effect did not appear to relate to receptor modulation. These results suggest that PMA-induced susceptibility to Pichinde virus infection occurs at a point later than the initial binding and penetration stages and that infection depends on the activation or differentiation state of the cell.

Characterization of phospholipase A2 in monocytic cell lines. Functional and biochemical aspects of membrane association

Phospholipase A2 activity was characterized in the human monocytic tumour-cell lines U937 and THP1. The enzyme showed an alkaline pH optimum and substrate specificity for arachidonoyl-phosphatidylcholine. The activation of phospholipase A2 required bivalent cations (Ca2+ greater than Mg2+ = Sr2+ greater than Ba2+). Investigation of the subcellular distribution of the enzyme revealed that the phospholipase A2 activity was shifted to the cytosol in the presence of EDTA, indicating that the association of the enzyme with the cellular membranes is Ca2+ (bivalent-cation)-dependent. Stimulation of THP1 cells for 2-4 h with the phorbol ester phorbol 12-myristate 13-acetate (PMA) activated cytosolic and membrane-bound phospholipase A2. At this time, no effect of PMA on phospholipase A2 activity was observed in the less mature U937 cells. However, when both cell lines were induced to differentiate along the monocytic pathway by a 2-3-day treatment with PMA, the cells released significant amounts of arachidonic acid and prostanoids. Compared with undifferentiated control cells, these PMA-differentiated cells showed a decrease in cytosolic phospholipase A2 activity and an increase in membrane-bound activity. Membrane-bound and cytosolic enzyme showed the same pH optimum, Ca(2+)-dependency and substrate specificity. These data indicate that membrane-bound and cytosolic phospholipase A2 activities represent one enzyme and that the membrane-bound form is the biologically active phospholipase A2.

Erythropoietin gene expression in haemopoietic cell lines

Erythropoietin (Epo) gene expression was studied in a number of different haemopoietic cell lines by in situ hybridization and Northern Blot analysis using a radioisotope-labelled monkey Epo DNA probe. A positive message was expressed by a human cell line, CM-S, derived from a patient with congenital hypoplastic anemia, and by a murine erythro-leukaemic cell line, clone 707, derived from the spleen of Friend virus-infected mice. No message was detected in two megakaryoblastic cell lines, and in a monocytic cell line, derived from a patient with acute monocytic leukaemia. These data may fit with the hypothesis of expression of Epo and other growth factors by haemopoietic cells through a mechanism of so-called autocrine secretion.

Human immunodeficiency virus infection in cells of myeloid-monocytic lineage

We established persistent infection with a strain of human immunodeficiency virus type 1, HTLV-IIIB, in a promyelomonocytic cell line, ML-1 (CD4 antigen nearly negative and CD4 mRNA negative), and a promonocytic cell line, THP-1 (CD4 antigen positive). Different reaction of giant cell formation was found after co-cultivation of infected and uninfected cells of ML-1, HL-60, THP-1 and U-937 cell lines with uninfected and infected MOLT4 (a T-lymphoma cell line).

Lipoarabinomannan, a possible virulence factor involved in persistence of Mycobacterium tuberculosis within macrophages

Mycobacterium tuberculosis and Mycobacterium leprae, the causative agents of tuberculosis and leprosy, respectively, produce large quantities of lipoarabinomannan (LAM), a highly immunogenic, cell wall-associated glycolipid. This molecule has been previously reported to be a potent inhibitor of gamma interferon-mediated activation of murine macrophages. Studies of the mechanism by which this mycobacterial glycolipid down-regulates macrophage effector functions provide evidence that LAM acts at several levels and that it can (i) scavenge potentially cytotoxic oxygen free radicals, (ii) inhibit protein kinase C activity, and (iii) block the transcriptional activation of gamma interferon-inducible genes in human macrophage-like cell lines. These results suggest that LAM can inhibit macrophage activation and triggering and cytocidal activity and that it may represent a chemically defined virulence factor contributing to the persistence of mycobacteria within mononuclear phagocytes.

The evolutionarily conserved Krüppel-associated box domain defines a subfamily of eukaryotic multifingered proteins

We have previously shown that the human genome includes hundreds of genes coding for putative factors related to the Krüppel zinc-finger protein, which regulates Drosophila segmentation. We report herein that about one-third of these genes code for proteins that share a very conserved region of about 75 amino acids in their N-terminal nonfinger portion. Homologous regions are found in a number of previously described finger proteins, including mouse Zfp-1 and Xenopus Xfin. We named this region the Krüppel-associated box (KRAB). This domain has the potential to form two amphipathic alpha-helices. Southern blot analysis of "zoo" blots suggests that the Krüppel-associated box is highly conserved during evolution. Northern blot analysis shows that these genes are expressed in most adult tissues and are down-regulated during in vitro terminal differentiation of human myeloid cells.

The cytokine-protease connection: identification of a 96-kD THP-1 gelatinase and regulation by interleukin-1 and cytokine inducers

The induction of proteolytic enzymes is an important mechanism in the migration of monocytes into tissues and body fluids. The monocytic cell line THP-1 was used as a model system to study the production of a particular gelatinase. Upon stimulation with phorbol myristate acetate (PMA) the cells differentiated to the adherent phenotype and produced significant amounts of a 96-kD gelatinase in a dose-dependent way. The secretion rate was maximal between 12 and 24 h after induction. Study of gelatinase mRNA steady state levels showed that the synthesis of THP-1 gelatinase is regulated by PMA at transcriptional or posttranscriptional levels. Stimulation of signal transduction pathways with other substances, including calcium ionophore A 23187, dibutyryl cyclic AMP, and dexamethasone, were ineffective in inducing gelatinase mRNA or enzyme activity. However, THP-1 cells were responsive to the cytokine interleukin (IL)-1 beta, to bacterial lipopolysaccharide (LPS), and the lectin concanavalin A (Con A), the kinetics of gelatinase induction being similar to those of induction by PMA. The THP-1 cells did not synthesize and/or secrete detectable levels of IL-6 after stimulation with PMA, Con A, LPS, or IL-1 beta. The 96-kD monocytic THP-1 gelatinase was shown to be a neutral metalloproteinase that cross-reacted with hepatoma-derived and neutrophil gelatinases in immunoprecipitation experiments. The active enzyme produced by THP-1 cells consistently showed, however, a molecular mass different from that of normal granulocyte-, monocyte-, and tumor cell-derived gelatinases.(ABSTRACT TRUNCATED AT 250 WORDS)

Human alpha-fetoprotein (AFP) causes a selective down regulation of monocyte MHC class II molecules without altering other induced or noninduced monocyte markers or functions in monocytoid cell lines

Human alpha-fetoprotein (AFP) purified from human amniotic fluid was investigated for its effect on human monocytoid cell lines, including U 937 cells with established subclones. The impact of AFP on the expression of surface markers (MHC class I and II, CD4, CD18, CD45, Fc receptors for IgG) was analyzed using known inducers of monocyte-macrophage differentiation such as phorbol esters and IFN-gamma. Furthermore we investigated the effect of AFP on the induction of macrophage antibody-dependent cell-mediated cytolytic activity (ADCC). AFP did selectively induce a rapid down regulation of surface MHC class II expression. No evidence of alterations was found in the endogenous or differentiation-induced expression of other markers on the surface on monocytes, nor did AFP affect the functional maturation of surface Fc receptors or the ability to express ADCC.

Coexpression of the genes for platelet-derived growth factor B-chain receptor and macrophage colony-stimulating factor 1 receptor during monocytic differentiation

Receptors for platelet-derived growth factor (PDGF) have not been identified previously to our knowledge in human myeloid cells that also produce PDGF. Here we report that phorbol ester-treated myeloid cells differentiated along the monocytic lineage express both a full-length 5.5-kilobase (kb) mRNA and a predominant, truncated 4.6-kb mRNA coding for the PDGF B-chain receptor (PDGF-BR). PDGF-BR was identified in phorbol ester-differentiated myeloid cells by indirect immunofluorescence with an antibody specific to PDGF-BR. This anti-PDGF-BR was also used in immunoprecipitation studies to demonstrate that lysates of phorbol ester-differentiated myeloid cells contain PDGF-BR molecules of 37 kDa to 130 kDa. The results also show that the tandemly linked genes for PDGF-BR and the macrophage colony-stimulating factor 1 receptor are coexpressed in the phorbol ester-differentiated myeloid cells. Expression of these two receptor genes has not been shown previously in any cell type to our knowledge.

Assay of neomycin phosphotransferase activity in cell extracts

A simple method for the measurement of neomycin phosphotransferase (NPT) activity in crude extracts of eukaryotic cells is described. This method is based on the elimination of interfering phosphorylated proteins by using phenol-chloroform extraction. This solution phase assay allows the detection of greater than or equal to 0.01 ng of NPT in the crude cell extract. Rapid screening of a large number of cell cultures generated in gene-transfer experiments, using NPT as a selective marker, is made possible by this simple technique. Further, the promoter strength of vector constructs used in gene therapy may also be estimated by this procedure.

The long terminal repeat is not a major determinant of the cellular tropism of human immunodeficiency virus type 1

The long terminal repeats (LTRs) of human immunodeficiency virus type 1 (HIV-1) strains from the central nervous systems of four patients with AIDS and of an HIV-1 isolate which is highly macrophage-tropic were isolated by using the polymerase chain reaction. In transient transfection assays, these LTRs demonstrated no significant difference in basal or stimulated levels of transcription in any of a variety of cell lines tested, compared with expression directed from the LTR of a T-lymphocyte-tropic strain of HIV-1. Chimeric viruses were created with the LTRs of the macrophage-tropic and brain-derived viruses ligated to the viral backbone from a T-lymphocyte-tropic strain. No change in cellular tropism was demonstrated with these chimeric viruses. Thus, unlike the LTRs of some murine retroviruses, the LTR of HIV-1 does not appear to play a major role in determining cellular tropism.

The human leukemia cell line, THP-1: a multifacetted model for the study of monocyte-macrophage differentiation

THP-1 is a human monocytic leukemia cell line. After treatment with phorbol esters, THP-1 cells differentiate into macrophage-like cells which mimic native monocyte-derived macrophages in several respects. Compared to other human myeloid cell lines, such as HL-60, U937, KG-1, or HEL cell lines, differentiated THP-1 cells behave more like native monocyte-derived macrophages. Because of these characteristics, the THP-1 cell line provides a valuable model for studying the mechanisms involved in macrophage differentiation, and for exploring the regulation of macrophage-specific genes as they relate to physiological functions displayed by these cells.

The HIV core protein p24 inhibits interferon-gamma-induced increase of HLA-DR and cytochrome b heavy chain mRNA levels in the human monocyte-like cell line THP1

Cells from the human monocytic cell-line THP1 were incubated prior to activation with IFN-gamma or LPS with varying amounts of p24, the main product of the HIV gag gene and the major component of the virus core. The IFN-gamma-dependent increase of mRNA for HLA-DR and for the heavy chain of cytochrome b was markedly decreased by p24 but not by gp120. This effect was abrogated by anti-p24 antibodies. On the other hand, preincubation of THP1 cells with p24 did not affect the accumulation of the LPS-dependent mRNA for TNF alpha and IL1-beta. These results indicate that p24 at concentrations similar to those found in the serum of HIV-infected individuals specifically affects IFN-gamma-induced activation markers.

Inhibition of endotoxin-induced monocytic procoagulant activity by n-alcohols and anesthetics

1. The effect of n-alcohols (methanol and ethanol) and anesthetics (lidocaine, thiopental, methohexital and thiamylal) on procoagulant activity (PCA) in human peripheral-blood monocytes and non-adherent cultured leukemia promonocytic U937 and THP-1 cells was examined herein. 2. Exposure of whole blood to ethanol showed no effect on PCA in human monocytes. However, ethanol dose-dependently inhibited LPS-induced PCA in isolated human monocytes. 3. In THP-1 cells, ethanol had no significant effect on PCA in either non-challenged or LPS-induced status. However, the induction of PCA by LPS was substantially inhibited when cells were pretreated with 1% ethanol (v/v) for 72 hr. 4. In U937 cells, n-alcohols and anesthetics resulted in dose-dependent depressions in PCA. Importantly, the percent reduction in LPS-induced PCA was much more pronounced than that in non-challenged PCA. 5. These data clearly suggest that n-alcohols and anesthetics readily inhibit the LPS-stimulatory action on monocytic PCA.

Secretion of neurotoxins by mononuclear phagocytes infected with HIV-1

Mononuclear phagocytes (microglia, macrophages, and macrophage-like giant cells) are the principal cellular targets for human immunodeficiency virus-1 (HIV-1) in the central nervous system (CNS). Since HIV-1 does not directly infect neurons, the causes for CNS dysfunction in acquired immunodeficiency syndrome (AIDS) remain uncertain. HIV-1-infected human monocytoid cells, but not infected human lymphoid cells, released toxic agents that destroy chick and rat neurons in culture. These neurotoxins were small, heat-stable, protease-resistant molecules that act by way of N-methyl-D-aspartate receptors. Macrophages and microglia infected with HIV-1 may produce neurologic disease through chronic secretion of neurotoxic factors.

Factors affecting cellular tropism of human immunodeficiency virus

To evaluate the basis of the slow growth of many human immunodeficiency virus strains in monocytes/macrophages, various stages of the virus life cycle have been studied for their possible contribution to viral tropism. Although we found that monocytic U937 cells had a higher percentage of CD4-positive cells than T-lymphoid H9 cells, the human immunodeficiency virus strain grew much less efficiently in the monocytic line. Viral tropism was primarily determined during the early stages of the virus cycle, that is, sometime between binding of the virus to the cell surface and reverse transcription of viral genomic RNA. Once the virus entered the host cell, reverse transcription, use of the long terminal repeat, RNA expression, and production of virus particles was about as efficient in monocytes as in T cells. Thus, during viral entry into the host cell cytoplasm there is a major limiting event that is particularly inefficient in U937 cells and possibly in all monocytes/macrophages.

Enhancement of interferon-gamma-induced differentiation of human monoblastic leukemia U-937 cells by cAMP-inducing agents

The effects of combinations of interferons (IFNs) and cAMP-inducing agents on the induction of differentiation of human monocytic leukemia U-937 cells were examined. IFN-gamma induced nitro blue tetrazolium (NBT) reducing activity of U-937 cells in a dose-dependent manner, while cAMP-inducing agents such as cholera toxin, prostaglandin E1, forskolin, and isoproterenol only marginally induced NBT reducing activity. However, they all synergistically increased IFN-gamma induction of NBT reducing activity. Cholera toxin was the most potent of the cAMP-inducing agents. Combination effects of IFN-gamma and cholera toxin on other differentiation-associated markers of alpha-naphthyl acetate esterase activity, morphological maturation, Fc receptors, and surface phenotype were also observed. IFN-alpha and -beta, either alone or in combination with cAMP-inducing agents, did not induce NBT reducing activity. IFN-gamma and cholera toxin also synergistically induced differentiation-associated markers in another human monocytic leukemia cell line, THP-1, and a human myeloblastic leukemia cell line, ML-1. These results suggest that cAMP/A-kinase may be an important but insufficient signal for the maturation process of myelogenous leukemia cells.

Establishment and characterization of a human CD4 positive cell bank for HIV related studies

The human CD4 positive cell lines JM, CCRF, CEM, U937, HL60 and THP-1 have been cleared of mycoplasma contamination and defined by DNA fingerprinting and cell surface phenotype marker analysis. These cells have been banked and are now available as a source of standardized cell lines for HIV related research.

Regulation of plasminogen receptor expression on human monocytes and monocytoid cell lines

The capacity of human monocytoid cell lines and peripheral blood monocytes to modulate their expression of plasminogen receptors has been assessed. After PMA stimulation, THP-1 or U937 monocytoid cells were separated into adherent and nonadherent populations. Plasminogen bound to adherent cells with similar capacity and affinity as to nonstimulated cells. In contrast, the nonadherent cells bound plasminogen with 5-17-fold higher capacity (without a change in affinity). This increase was selective as urokinase bound with similar affinity and capacity to the adherent and nonadherent populations. Upregulation of plasminogen receptors on the nonadherent monocytoid cells was rapid, detectable within 30 min, and reversible, adhesion of the nonadherent cells resulted in a sixfold decrease in plasminogen binding within 90 min. The increase in plasminogen binding to the nonadherent cells was associated with a marked increase in their capacity to generate plasmin activity from cell-bound plasminogen. PMA stimulation of human peripheral blood monocytes increased their expression of plasminogen receptors by two- to fourfold. This increase was observed in both adherent and nonadherent monocytes. Freshly isolated monocytes maximally bound 5.0 x 10(5) plasminogen molecules per cell, whereas monocytes cultured for 18 h or more maximally bound 1.7 x 10(7) molecules per cell, a 30-fold difference in receptor number. These results indicate that both monocytes and monocytoid cell lines can rapidly and markedly regulate their expression of plasminogen binding sites. As enhanced plasminogen binding is correlated with an increased capacity to generate plasmin, an enzyme with broad substrate recognition, modulation of plasminogen receptors may have profound functional consequences.

Identification of an Arg-Gly-Asp (RGD) cell adhesion site in human immunodeficiency virus type 1 transactivation protein, tat

Tat, the transactivation factor of human immunodeficiency virus type 1 (HIV-1), contains the highly conserved tripeptide sequence Arg-Gly-Asp (RGD) that characterizes sites for integrin-mediated cell adhesion. The tat protein was assayed for cell attachment activity by measuring the adhesion of monocytic, T lymphocytic, and skeletal muscle-derived cell lines to tat-coated substratum. All cell lines tested bound to tat in a dose-dependent manner and the tat cell adhesion required the RGD sequence because tat mutants constructed to contain an RGE or KGE tripeptide sequence did not mediate efficient cell adhesion. The tat-mediated cell attachment also required divalent cations and an intact cytoskeleton. In addition, cell adhesion to tat was inhibited in the presence of an RGD-containing peptide GRGDSPK or an anti-tat mAb that recognizes the RGD epitope. These results strongly suggest that cells are bound to tat through an integrin. Interestingly, myoblast cells bound to tat remained round, whereas the same cells attached through an integrin for a matrix protein typically flatten and spread. The role of this RGD-dependent cellular adhesion of tat in HIV-1 infection remains to be determined.

Platelet-derived growth factor and its receptor in blood cell differentiation and neoplasia

Platelet-derived growth factor (PDGF) is a family of dimeric protein molecules synthesized by differentiated, non-dividing and proliferating blood cells. Experimental findings indicate that PDGF is involved in development and/or maintenance of physiological functions of certain normal blood cells. Also, PDGF synthesis correlates with certain blood cell proliferative diseases caused either spontaneously or associated with viral infection. There is increasing evidence that the diverse effects of PDGF in both normal and abnormal physiological functions of blood cells may be regulated at the level of its receptor. New experimental findings are discussed relating to PDGF receptors in normal leukemic, and virally-infected human cells of myeloid and lymphocytic lineages. At specific developmental stages this regulation may take the form of PDGF and its receptor being expressed or co-expressed; the unmodified or modified form of receptor that specifically interacts with PDGF; the cellular site at which the PDGF-receptor interacts with its ligand; and co-expression of the PDGF-receptor with other receptors associated with specific cell lineage or functions. Elucidation of events involved in synthesis, processing, and interactions of PDGF isoforms and their respective receptors will enable us to develop pharmacological means that may either interfere with, or enhance these desired blood cell functions. This review focuses on PDGF and its receptor in human blood cell differentiation and neoplasia.

The receptor for urokinase type plasminogen activator polarizes expression of the protease to the leading edge of migrating monocytes and promotes degradation of enzyme inhibitor complexes

Receptor-bound urokinase-type plasminogen activator (uPA) remains associated to the surface of human monocytes for many hours. Monocytes induced to migrate in a chemotactic gradient of f-Met-Leu-Phe rapidly polarize their uPA receptors to the leading front of the cells. Receptor-bound enzyme can be inhibited by plasminogen activator inhibitor 2 (PAI-2), with a kinetics comparable to that determined for the free enzyme, and uPA/PAI-2 complexes can bind to the uPA receptor. In contrast to the active enzyme, the uPA/PAI-2 complex is rapidly cleared from the monocyte cell surface; this involves an initial cleavage of the complex at the cell surface, followed by endocytosis and degradation. These results indicate that the uPA receptor can function both to focus plasmin-mediated extracellular matrix degradation in front of migrating cells, and to target uPA/PAI-2 enzyme/inhibitor complexes for degradation; they suggest that this receptor is a key determinant in the control of uPA-catalyzed extracellular proteolysis.

Infection of the human monocytic cell line Mono Mac6 with human immunodeficiency virus types 1 and 2 results in long-term production of virus variants with increased cytopathogenicity for CD4+ T cells

The recently established human monocytic cell line Mono Mac6 expressing distinct characteristics of mature monocytes/macrophages was tested for its susceptibility to infection with human immunodeficiency virus. Inoculation of the cells with the T-cell-tropic human immunodeficiency virus strains human T-lymphotropic virus type IIIB and lymphadenopathy-associated virus type 2 led to a noncytopathic productive infection becoming apparent only after a latency period of up to 56 days. The infectibility of the Mono Mac6 cells was dependent on low levels of CD4 expression, as demonstrated by blocking experiments with various CD4-specific antibodies. Increasing with time after infection (greater than 200 days), the cultured Mono Mac6 cells released virus variants which showed shortened latency periods when passaged onto uninfected Mono Mac6 cells. Also, cytopathogenicity for several CD4+ T cells of the Mono Mac6-derived virus was drastically increased; thus, the infection of the H9 cell line with low doses of virus (less than 0.1 50% tissue culture infective dose per cell) led to giant syncytium formation within 1 day and subsequent death of all fused cells. We propose Mono Mac6 cells as a new model for the study of human immunodeficiency virus infecting the monocyte/macrophage lineage, particularly with regard to virus-host cell interaction and the influence of cell differentiation and activation on latency and development of virulence. The human immunodeficiency virus-infected Mono Mac6 cell may also serve as a valuable tool for in vitro testing of antiviral therapies.

Uptake of extracellular enzyme by a novel pathway is a major determinant of cathepsin L levels in human macrophages

The phorbol myristate acetate (PMA)-differentiated myelomonocytic cell line, THP-1, and human alveolar macrophages contain the cysteine proteinase cathepsin L. This enzyme is synthesized as a 43-kD proenzyme and processed to the active 25-kD form. Differentiation of THP-1 cells in the presence of human serum resulted in an increase in the size of the vacuolar compartment and the accumulation of more 25-kD cathepsin L antigen, as compared with THP-1 cells differentiated in the presence of fetal calf serum. Cells cultured in both types of sera have equivalent levels of cathepsin L mRNA. Metabolic labeling experiments demonstrated equivalent rates of synthesis, processing to the active form, and persistence in both culture conditions. An extracellular source of enzyme was documented by immunoblotting human serum which demonstrated 25-kD cathepsin L antigen; furthermore, we demonstrated that both THP-1 cells, differentiated in human serum, and human alveolar macrophages take up the 43-kD proenzyme and process it to the 25-kD form. Thus, human serum contains a factor(s) that induces both a marked increase in the size of the vacuolar compartment in differentiated THP-1 cells and a novel pathway that is responsible for the uptake and processing of extracellular cathepsin L. The activity of this inducible pathway is a major determinant of levels of intracellular cathepsin L. Cathepsin L is a potent elastase and the regulation of its uptake and processing may play a role in the pathogenesis of disease processes characterized by the destruction of elastin, such as pulmonary emphysema.

Lipopolysaccharide is a potent monocyte/macrophage-specific stimulator of human immunodeficiency virus type 1 expression

Lipopolysaccharide (LPS) potently stimulates human immunodeficiency virus type 1-long terminal repeat (HIV-1-LTR) CAT constructs transfected into monocyte/macrophage-like cell lines but not a T cell line. This effect appears to be mediated through the induction of nuclear factor kappa B (NF-kappa B). Electrophoretic mobility shift assays demonstrate that LPS induces a DNA binding activity indistinguishable from NF-kappa B in U937 and THP-1 cells. LPS is also shown to dramatically increase HIV-1 production from a chronically infected monocyte/macrophage-like cloned cell line, U1, which produces very low levels of HIV-1 at baseline. The stimulation of viral production from this cell line occurs only if these cells are treated with granulocyte/macrophage colony-stimulating factor (GM-CSF) before treatment with LPS. This stimulation of HIV-1 production is correlated with an increase in the level of HIV-1 RNA and and activation of NF-kappa B. LPS is not able to induce HIV-1 production in a cloned T cell line. The effect of LPS on HIV-1 replication occurs at picogram per milliliter concentrations and may be clinically significant in understanding the variability of the natural history of HIV-1 infection.

Structure and polymorphic map of human lipoprotein lipase gene

Lipoprotein lipase (LPL) catalyzes the key step for the removal of triacylglycerol-rich lipoproteins from the circulation. In this paper, we report the cloning and structure of the normal human LPL gene, which was isolated in three overlapping lambda phage clones that span about 35 kilo bases (kb) of the genetic locus. The peptide coding region of the gene is approx. 23 kb in length and contains nine exons with intron sizes ranging from 0.7 to 8.7 kb. The entire 3' untranslated region is in the tenth exon. Specific sequences in this region support the hypothesis that two mRNA species found for human LPL are generated by differential utilization of polyadenylation signals. The first exon occurs in the 5' untranslated region and the region coding for the signal peptide. The second exon includes the protein domain coding for the N-linked glycosylation site that is required for the expression of enzyme activity. The fourth exon contains the region that was proposed as a lipid binding domain, the sixth for one putative heparin binding domain, and the eighth codes for a domain containing another N-linked glycosylation site. These results suggest that the unique structural and functional domains are confined to specific exons. The PvuII polymorphic site was located within the intron between exon 6 and 7 and the HindIII polymorphic site to the 3' flanking region. The location of these polymorphic sites suggests that the PvuII restriction fragment length polymorphism (RFLP) associated with lipase deficiency in a few Japanese kindred may be a linkage marker for a functional defect of LPL, while the HindIII RFLP associated with hypertriglyceridemia may be important for gene regulation of LPL.

Induction of antigen expression of follicular dendritic cells in a monoblastic cell line. A contribution to its cellular origin

Experiments were carried out to elucidate the cellular origin of the dendritic reticulum cell (DRC). The monoblastic cell line THP-1, the histiocytic cell line U-937, and the mononuclear cell fraction from peripheral blood (PMC) were stimulated with supernatants from lectin-stimulated peripheral blood lymphocytes and from stimulated T- and B-cell lines. Differentiation towards DRC was assessed by immunocytochemical demonstration of the DRC-specific antigen Ki-M4. Supernatants from isolated peripheral T lymphocytes and from T- and B-cell lines were capable of stimulating THP-1 to Ki-M4 antigen expression, whereas U-937 and the PMC fraction remained negative for this antigen throughout the experiments. These results provide further evidence for a relationship of DRCs with the mononuclear-phagocytic cell system and hence for their bone marrow origin. Furthermore, the data suggest that soluble factors of T and/or B cells are involved in mediating the differentiation process of precursor cells to DRC.

Negative regulation of human immune deficiency virus replication in monocytes. Distinctions between restricted and latent expression in THP-1 cells

In THP-1 monocytoid cells infected with HIV, viral expression can be regulated in several ways: (a) latency (no viral expression); (b) restricted expression (chronic low-level viral expression with little or no detectable virus released); and (c) continuous production. In cells with restricted HIV expression, nuclear factor(s) were found that blocked tat-associated DNA binding complex formation, suggesting that initiation of transcription was negatively regulated. Also, viral particles were seen budding into and accumulating within intracytoplasmic vacuoles with little virus released, suggesting multiple levels of regulation. These cells with restricted expression had no detectable viral antigens on the cell surface and were not lysed by IL-2-activated large granular lymphocytes. However, they could cause viral-mediated T cell cytolysis in cell-cell assays, suggesting viral transmission through cell contact. In addition, cells with latent HIV were identified and could still produce infectious virus after 5-azacytidine exposure 10 mo later. LPS and other treatments could increase viral production in cells with restricted but not latent expression, suggesting they occur by distinct mechanisms. These infected cells provide a reservoir for viral transmission to uninfected T cells that itself is not detected by immune surveillance mechanisms.

Differentiation-inducing and growth-inhibitory activities of erythroid differentiation factor (EDF/activin A) toward mouse erythroleukemic cells in vivo

The in vivo differentiation-inducing activity of a purified human erythroid differentiation factor (EDF) toward mouse erythroleukemic cells (MEL cells) was examined. BDF1 mice with diffusion chambers implanted in the peritoneal cavity were treated with continuous i.p. administration of EDF. MEL cells within a diffusion chamber differentiated into hemoglobin-positive cells when treated with EDF, the percentage of the positive cells being 32.3 +/- 28.3 on day 5 as compared to 0.2 +/- 0.3 in the controls. The anti-tumor activity of EDF was also examined in a nude mouse MEL solid tumor model. Daily intra-tumor treatment with EDF for 10 days resulted in 73% suppression of tumor growth on day 25. A histological study revealed that EDF-treated solid tumor cells became hemoglobin-positive, indicating the anti-tumor activity of EDF through induction of differentiation in vivo. EDF could induce in vitro the differentiation of human erythroleukemic cell lines K562 and HEL, as well as the murine cell line. These results indicate the possibility of differentiation therapy for erythroleukemia using EDF.

Inducible gene expression of activin A/erythroid differentiation factor in HL-60 cells

Treatment of HL-60 cells with 12-O-tetradecanoyl-phorbol 13-acetate (TPA) for 48 h induced expression of mRNA of beta A chain of activin A/erythroid differentiation factor. Under the same condition, interferon-gamma caused a slight increase in beta A chain mRNA, whereas 1 alpha, 25-dihydroxyvitamin D3, dimethylsulfoxide and all-trans-retinoic acid failed to induce this mRNA in HL-60 cells. Furthermore, 4 h-treatment with TPA or lipopolysaccharide (LPS) induced a marked increase in beta A chain mRNA levels in interferon-gamma-pretreated HL-60 cells. In the cells pretreated with 1 alpha, 25-dihydroxyvitamin D3, TPA and LPS induced as little increase in beta A chain mRNA as in the control cells. Neither alpha nor beta B chain mRNA was detected in any sample. These results indicate that interferon-gamma has a priming effect on the activation of activin A/erythroid differentiation factor gene by TPA or LPS in HL-60 cells.

Dengue-2 virus infection of human mononuclear cell lines and establishment of persistent infections

Twenty three human mononuclear cell lines including ten myelomonocytic cell lines, eight B cell lines and five T cell lines, were examined to determine whether they could be infected with dengue-2 virus. All the cell lines were infected with dengue-2 virus as determined by immunofluorescent staining and by virus titration of culture supernatant fluids. K562, Jiyoye and Jurkat, respectively, showed the highest percentage of infected cells of these myelomonocytic, B and T cell lines. Antibody to dengue-2 virus at subneutralizing concentrations augmented dengue-2 virus infection of myelomonocytic cell lines, but not of B cell lines or of T cell lines. Persistent dengue-2 virus infection was established using a myelomonocytic cell line (K562), a B cell line (Raji), and a T cell line (HSB-2). These cell lines maintained a high percentage (more than 70%) of dengue-2 virus antigen-positive cells for at least 25 weeks. Very low titers of infectious dengue-2 virus were detected in the culture supernatant fluids of the persistently infected cells. Dengue-2 virus antigen-positive Raji cell clones were established from persistently-infected Raji cells using limiting dilutions and all of the cells in these clones were dengue-2 virus antigen-positive. These findings demonstrate that a variety of human mononuclear cell lines can be infected with dengue-2 virus and may be useful as models for the analysis of dengue virus-human cell interactions in dengue virus infections.

Interactions between the human monocytic leukaemia THP-1 cell line and Old and New World species of Leishmania

The human promyelocytic THP-1 cell line has been found to support the growth of Leishmania parasites. THP-1 cells, differentiated with retinoic acid, cease replication while remaining in suspension. 72 +/- 8% of THP-1 cells became infected after inoculation with promastigotes of several Old and New World Leishmania species. The resulting amastigotes (19 +/- 5 per infected cell) were easy to harvest, capable of reinfecting cultures of normal human cells and, in the case of L. major and L. infantum, caused specific lesions in BALB/c mice. This culture system should facilitate biochemical and immunological studies on amastigotes and be of use in screening anti-parasite drugs.

U937 and THP-1 cells do not release LTB4, LTC4, or LTD4 in response to A23187

U937 and THP-1 cells possess some characteristics of human mononuclear phagocytes, cells which synthesize and release LTB4, LTC4, and LTD4. Incubation of these cells with recombinant human interferon-gamma (IFN-gamma) or Phorbol Myristate Acetate (PMA) induces a more differentiated cell state. We hypothesized that U937 and THP-1 cells would release LTB4, LTC4, and LTD4 in response to stimulation with the non-physiologic agonist, calcium ionophore A23187 and that preincubation with IFN-gamma or PMA might alter leukotriene release by these cells. We cultured both cell lines for 48 hours in the presence and absence of IFN-gamma (1000 units/ml) and for 120 hours in the presence and absence of PMA (160 nM) and then challenged them with A23187 (5uM) for 30 minutes at 37 degrees C. The supernatants were deproteinated and assayed by RIA for LTB4 and LTC4 and by RP-HPLC for LTB4, LTC4, and LTD4. Neither U937 nor THP-1 cells released quantities of leukotrienes detectable by RIA, less than 0.3ng/5 X 10(6) cells. Peripheral blood mononuclear phagocytes from normal volunteers, cultured and challenged in vitro at under identical conditions, released 11.3 +/- 2.9 ng LTB4 and 2.0 +/- 1.5 ng LTC4/10(6) viable monocytes. The lack of leukotriene production by U937 and THP-1 cells was not altered by preincubation for 48 hours with IFN-gamma (n = 3) nor by preincubation with PMA for 120 hours (n = 3). We conclude 1) U937 and THP-1 cells do not appear to be appropriate in vitro models for the examination of leukotriene release from normal mononuclear phagocytes. 2) Pre-incubation of U937 and THP-1 cells with IFN-gamma or PMA under the conditions tested, does not induce the ability of these cell lines to release leukotrienes.

Coupled and uncoupled induction of fos and jun transcription by different second messengers in cells of hematopoietic origin

The nuclear oncoproteins fos and jun are associated as a heterodimer which binds to TPA (PMA or TPA: phorbol 12-myristate 13-acetate)- responsive promoter elements (TRE), the recognition site for the transcription factor AP-1. The fos/jun heterodimer has a higher affinity to the TRE and stimulates transcription of responsive genes more than the jun homodimer. The association of these two oncoproteins may play a central role in signal transduction and regulation of cell proliferation and differentiation. We further defined the regulation of fos and jun by studying their inducibility by second messengers in cells of hematopoietic origin. In THP-1 monocytic leukemia cells fos and jun mRNA levels are regulated in a coupled manner by second messengers activated after membrane phospholipid turnover. Addition of phospholipase C to cells, as well as stimulation of protein kinase C and release of intracellular Ca2+, caused a rapid induction of fos and jun mRNA levels, but the induction of jun mRNA showed a more persistant and less transient pattern than fos. In contrast to the phosphoinositol system, stimulation of the adenylate cyclase pathway in THP-1 cells induced only fos transcription whereas jun mRNA levels remained unchanged. A similar uncoupling of fos and jun inducibility was found after phorbol ester addition to the human erythroleukemia cell line HEL and the human promyelocytic cell line HL-60. The uncoupling of fos and jun levels might predispose cells to the formation of combinatorial transcription complexes of a different composition and activity than the fos/jun heterodimer. Indeed, nuclear extracts from THP-1 cells before or after activation of the phosphinositol or adenylate cyclase second messenger pathways revealed a correlation in fos and jun expression and specific binding of the heterocomplex to a TRE sequence.

Synergistic increases in IL-1 synthesis by the human monocytic cell line THP-1 treated with PAF and endotoxin

The capacity to stimulate cytokine release may be important to the long-term effects of platelet-activating factor (PAF), which has a very short half-life. Previous studies have shown that PAF stimulates interleukin 1 (IL-1) release by human monocytes. IL-1 and other cytokines produced in response to PAF may be important to the long-term effects of this short-lived lipid. The THP-1 human monocytic leukemia cell line, was used to study the mechanism by which PAF stimulates IL-1 release. PAF stimulates the release of IL-1 beta activity into THP-1 cell supernatants with a multiphasic dose-response curve very similar to that for monocytes. When THP-1 cells are treated with PAF and LPS in combination, these two stimuli interact synergistically to greatly increase the release of IL-1 activity. To assess the effect of PAF on IL-1 beta synthesis, THP-1 cell pellet proteins were separated by SDS-PAGE, blotted, and immunostained to detect IL-1 beta. Immunostaining revealed that PAF increases intracellular IL-1 beta precursor and that the combination of PAF and LPS increases IL-1 beta precursor synergistically. PAF increases IL-1 beta release mainly by increasing IL-1 beta synthesis.

M-CSF and M-CSF-receptor gene expression in acute myelomonocytic leukemias

The role of hematopoietic growth factors in the pathogenesis of human leukemias is still obscure. In this study, RNA from 24 human acute myelomonocytic leukemias (AML) was used to analyze the expression of the macrophage colony stimulating factor (M-CSF) and its corresponding receptor (c-fms). Fifty percent of AML cells exhibited c-fms transcripts of regular length but at a lower level than in normal monocytes/macrophages. In most cases the reduced c-fms expression of AML cells was not associated with autostimulatory M-CSF expression. Only a few cases of AML showed co-expression of M-CSF and c-fms, which by contrast was regularly observed in cultivated blood monocytes and some tissue macrophage subsets. Higher levels of c-fms expression could be found in AMLs with a more mature monocytic immunophenotype. Permanent myelomonocytic cell lines expressed c-fms only after induction of monocytic differentiation. Neither the M-CSF gene nor the c-fms gene were rearranged in AML cells. In AML cells the homozygote genotype of the c-fms gene predominated. Our results do not provide evidence for the involvement of M-CSF and c-fms genes in human myeloid leukemogenesis. c-fms expression appears to indicate monocytic differentiation within the myelomonocytic lineage. We found autostimulatory M-CSF expression to be a physiologic feature of some tissue macrophages and hence not necessarily associated with neoplastic proliferation.

Lack of a negative influence on viral growth by the nef gene of human immunodeficiency virus type 1

Human immunodeficiency virus type 1 (HIV-1) contains an open reading frame called nef at the 3' end of its genome. The nef gene product has been reported to down-regulate viral growth by suppressing viral transcription through interaction with the long terminal repeat region. We have compared two isogenic HIV-1 (HIV-1-WI3) strains, one of which lacks nef expression, and found little difference between them in in vitro growth. We tested effects on viral entry, DNA synthesis, and RNA expression by measuring HIV-specific low molecular weight DNA and RNA after infection. The qualitative and quantitative aspects of DNA and RNA synthesis were comparable between the nef+ and nef- strains. The effects on viral growth were also examined by following changes in reverse transcriptase activity during the course of infection. The presence of the nef gene product failed to slow viral growth in several different cell types tested, including the human T-lymphocyte cell lines H9 and CEM-SS, human primary T cells enriched for CD4+ cells, and human monocytic cell lines U-937 and THP-1. On the contrary, the nef+ strain grew more efficiently in some cell types than the nef- strain. The same results were obtained with nef+ and nef- strains of a different virus, HIV-1-432, whose Nef had been reported to have a negative effect on viral growth. Our data suggest that the Nef protein does not act as a negative factor, at least in the experimental systems employed in our studies.

Modulation of galactoside-binding lectins in tumor cells by differentiation-inducing agents

The effects of the differentiation-inducing agents N6, O2'-dibutyryl cyclic AMP, beta-all-trans retinoic acid, dimethylsulfoxide and butyrate on the levels of galactoside-binding proteins (lectins) in cultured human and murine tumor cells were examined by immunoblotting. Differentiation was associated with decreased levels of a 34-kDa lectin in the K-1735P and B16-F1 melanoma cells and decreased levels of a 14.5-kDa lectin in S20 neuroblastoma, MDA-MB 175 breast carcinoma, HL-60 and THP-1 leukemia cells. The level of a 14.5-kDa lectin increased during differentiation of F-9 embryonal and KM12P colon carcinoma cells. These results indicate that tumor cell differentiation along specific pathways is accompanied by distinct modulation of lectin expression. These changes may recapitulate the normal developmental regulation of lectin expression.

Growth properties of human herpesvirus-6 strain Z29

Experiments performed to optimize the growth conditions of HHV-6(Z29) revealed that the virus grows best in phytohemagglutinin-stimulated umbilical cord blood lymphocytes (CBL) cultured in media containing 32 units/ml interleukin-2 and 0.01 mg/ml hydrocortisone. The titer of maternal antibody in the plasma of the cord blood cells does not affect the ability of the cells to support virus growth. DEAE-dextran and polybrene do not increase virus growth in umbilical cord blood lymphocytes. Phorbol myristate acetate abolishes virus growth. The HHV-6(Z29) growth cycle in CBL was approximately 5 days; capsids were not seen before day 3, and mature virions were not seen before day 5.

Induction of tissue factor-like activity of human monoblastic leukemia cell line by tumor necrosis factor-alpha

Cell lysates of the human monoblastic leukemia cell line, THP-1, have procoagulant activity (PCA) that is Ca++-dependent and not demonstrable in either Factor VII-, or Factor X-deficient plasma. The PCA of THP-1 cells was enhanced by human recombinant tumor necrosis factor-alpha (TNF-alpha) up to five fold. There was a dose-dependent increase in PCA when THP-1 cells were cultured with concentrations of TNF-alpha, up to 10 U/ml. PCA of cell lysates or whole cell preparations was measured in comparison to a rabbit brain thromboplastin standard. The effect of TNF-alpha was enhanced by recombinant human interferon-gamma (IFN-gamma). Cycloheximide inhibited the induction of PCA by THP-1 cells, which shows that the protein synthesis is essential to mediate the effect of TNF-alpha. THP-1 cells and U937 cells bound 125I-labeled TNF specifically. The numbers of receptors per cell were found to be 1,890 and 1,550 for THP-1 and U937 cells, respectively. Other lymphoid and myeloblastic leukemia cell lines examined did not have TNF receptors, indicating that the effect of TNF-alpha is mediated by the receptors on the cell surface.

Involvement of second messengers in regulation of the low-density lipoprotein receptor gene

Transcription of the low-density lipoprotein receptor (LDL-R) gene in the human monocytic leukemic cell line THP-1 and in the human hepatocarcinoma cell line Hep-G2 is regulated by second messengers of the diacylglycerol-protein kinase C (DAG-PKC), inositol 1,4,5-triphosphate-Ca2+, and cyclic AMP pathways. Exogenous phospholipase C (which releases DAG and inositol 1,4,5-triphosphate), PKC activators (phorbol esters and DAG), Ca2+ ionophores, and a cyclic AMP analog all transiently induced accumulation of LDL-R mRNA. The effects of these three signal-transducing pathways were to a large extent additive. Furthermore, PKC stimulation effected an increase in LDL binding, which suggested that the increase in LDL-R mRNA resulted in an increase in functional cell surface receptor activity. These results suggest that uptake of cholesterol by these cells is under control of both intracellular cholesterol levels and external signals.

Production of tumor necrosis factor alpha and interleukin 1 beta by monocytic cells infected with human immunodeficiency virus

The production of tumor necrosis factor alpha (TNF alpha) and IL-1 beta by the monocytic cell line THP-1, productively infected with HIV-1, was investigated using specific RIA and Northern blot analysis. HIV-infected cells, like uninfected cells, did not constitutively produce any detectable amounts of protein or mRNA for TNF alpha or IL-1 beta. After stimulation with LPS or a combination of LPS plus IFN-gamma, TNF alpha and IL-1 beta were detected in tissue culture supernatants and cell lysates and transcripts for both cytokines were seen on Northern blots. No significant difference in production of these two cytokines was observed between uninfected and chronically infected cells. Acutely HIV-infected cells, however, showed phenotypic changes compatible with maturation and an increase in TNF alpha and IL-1 beta mRNA production, and released significantly higher levels of TNF alpha and IL-1 beta compared with chronically infected or uninfected cells. Furthermore, LPS stimulation of HIV-infected cells increased virus production. These results suggest that HIV-infected monocytic cells may produce increased amounts of TNF alpha and IL-1 beta in response to stimuli that could be present in vivo.

Rapidly and slowly replicating human immunodeficiency virus type 1 isolates can be distinguished according to target-cell tropism in T-cell and monocyte cell lines

Human immunodeficiency virus type 1 (HIV-1) isolates from various patients were divided into two major groups, rapid/high and slow/low, according to their replication properties in vitro. Rapid/high isolates grow well in cell lines and induce the formation of syncytia in peripheral blood mononuclear cells. In contrast, slow/low isolates do not replicate in cell lines and rarely induce syncytia in peripheral blood mononuclear cells. To understand the differences in replicative capacity of these isolates, a panel of indicator cell lines was used. These cell lines were generated for sensitive detection of HIV-1 isolates and show characteristics of T-lymphoid or monocytoid cells. As a result of infection, chloramphenicol acetyltransferase expression is activated. Rapid/high viruses activate chloramphenicol acetyltransferase expression in T-cell and monocytoid indicator cell lines, whereas slow/low isolates activate chloramphenicol acetyltransferase expression only in monocytoid cell lines. The block in infection of T-lymphoid cells by the slow/low isolates appears to occur early in the infection cycle, prior to the production of the virally encoded tat protein. HIV-1 isolates can thus be distinguished according to target-cell tropism. Monocyte-derived cells seem to be a more general target for the various HIV-1 isolates.

Neurotoxic activity in HTLV-I carrier lymphocyte culture

A close association between human T-lymphotropic virus type I (HTLV-I) infection and a group of chronic myelopathies of unknown etiology has recently been established and the name "HTLV-I associated myelopathy" (HAM) has been coined. Although the mechanism of neural tissue damage in HAM remains virtually unknown, several lines of evidence suggest the involvement of a soluble factor(s) including cytokines and viral proteins in the disease process. In this study, we examined cytopathic effects of the supernatants from 6 HTLV-I carrier human T lymphocyte cell lines on 4 human and one murine neuroblastoma cell lines, and 2 human glioma cell lines. Among 6 lymphocyte cell culture supernatants, only 1 from MT-2 cell culture repeatedly exerted cytopathic effects on human neuroblastoma cells, particularly on IMR-32 cells: marked retraction of neurites leading to cellular clumping. This activity was neither abolished by treatment of the medium at 80 degrees C for 30 min or by UV-irradiation, nor was it neutralized by anti-HTLV-I antibodies. The MT-2 supernatant also induced mild cytopathic changes in 2 other human neuroblastoma cell lines and 2 human glioma cell lines. This activity was abolished by treatment of the medium at 80 degrees C for 30 min but not at 56 degrees C for 30 min. Myelinated murine cerebellum explants and other cell lines showed no morphological changes when incubated with the MT-2 supernatant. In addition, the growth of THP-1 cells, a monocyte/macrophage lineage cell line, was remarkably suppressed when maintained in the MT-2 conditioned medium, accompanied by enhancement of phagocytic activity. The THP-1 conditioned medium, on the other hand, suppressed tumor necrosis factor (TNF) activity detected in the MT-2 culture. These observations suggest that HTLV-I induced cytokines may directly act on neural cells, but their action appears to be regulated by the intricate interactions of lymphocytic and monocytic cells.