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

Human immunodeficiency virus Vpx is required for the early phase of replication in peripheral blood mononuclear cells

Functional importance of Vpx protein of human immunodeficiency virus type 2 was evaluated in various types of cells. In 8 lymphocytic or monocytic cell lines tested, vpx mutant virus grew as well as wild-type virus. Only in primary peripheral blood mononuclear cell cultures, severely retarded growth of mutant virus was observed. No replication of vpx-minus virus was detected in primary macrophage cells. A highly sensitive single-round replication assay system was used to determine the defective replication phase in primary mononuclear cells of vpx mutant virus. In all cell lines examined, vpx mutant displayed no abnormality. In contrast, the vpx mutant was demonstrated to be defective at an early stage of the infection cycle in primary cell cultures. No evidence of a replication-defect at a late phase in primary cells of the vpx mutant was obtained by a transfection-coculture method. These results indicate that the virion-associated Vpx protein is essential for early viral replication process in natural target cells such as primary macrophages.

Abrogation of gamma interferon-induced inhibition of Ehrlichia chaffeensis infection in human monocytes with iron-transferrin

Ehrlichia chaffeensis is an obligate intracellular bacterium which infects cells of the macrophage/monocyte lineage. To test whether gamma interferon (IFN-gamma) inhibits infection of monocytes with E. chaffeensis, human peripheral blood monocytes were incubated with recombinant human IFN-gamma for 3 h and then exposed to E. chaffeensis. With 2,000 U of IFN-gamma per ml, maximal inhibition of infection by E. chaffeensis was observed. THP-1 cells, a human monocyte cell line, pretreated with phorbol myristic acetate or not pretreated, were incubated with various concentrations of IFN-gamma. Maximum inhibition was obtained at 1,000 U of IFN-gamma per ml with phorbol myristic acetate-treated THP-1 cells. However, nontreated cells did not achieve a similar level of anti-ehrlichial activity even with 10,000 U of IFN-gamma per ml. IFN-gamma given within 6 h postinfection was effective in inhibiting E. chaffeensis. Nitric oxide production was not demonstrated in the monocyte medium incubated with IFN-gamma and E. chaffeensis. None of the reactive oxygen intermediate scavengers tested blocked the IFN-gamma-induced anti-ehrlichial activity. Deferoxamine, an intracellular iron chelator, at 15 microM completely inhibited the survival of E. chaffeensis. Iron-saturated transferrin at 1.67 mg/ml completely reversed the IFN-gamma-induced ehrlichial killing. These results indicate that (i) E. chaffeensis is sensitive to intracytoplasmic iron depletion, (ii) E. chaffeensis is sensitive to IFN-gamma-induced killing, and (iii) the anti-ehrlichial activity induced in human monocytes by IFN-gamma is mediated by limitation of available cytoplasmic iron and is not due to the generation of reactive oxygen intermediates or nitric oxide.

Cloning and characterization of the human osteopontin gene and its promoter

We isolated the human osteopontin (hOP) gene and the 5' upstream region, and analysed its exon-intron structure and potential regulatory sequences of the promoter region in comparison with those of the mouse and porcine gene. The coding sequence is split into 7 exons which are similar to those of the mouse gene, although the hOP gene is longer than the mouse gene. The difference in length is mainly due to variations in intron 3, which is approximately 2.7-fold longer than that of the mouse OP gene. The 5' upstream region of the hOP, which is highly conserved up to nucleotide -250, contains a number of potential cis regulatory consensus sequences. A series of sequentially 5'-deleted chimeric clones was tested for the ability to stimulate chloramphenicol acetyltransferase (CAT). Initial CAT analysis demonstrated that nucleotides at positions -474 to -270, -124 to -80, and -55 to -39 contained cis-acting enhancing sequences in a human monocyte cell line, SCC-3, although the -124 to -80 region was much more active than other regions. Deletion of the sequences between -474 and -270 localized this cis region to the sequence at positions -439 to -410, whereas the deletion between -124 to -80 localized the regions to -124 to -115, and -94 to -80. Gel-shift analysis using as probes synthesized double-stranded DNA corresponding to the 10 and 15 bp region at positions -124 to -115 and -94 to -80 respectively revealed that each probe formed a major band complexed with nuclear proteins prepared from SCC-3 cells.

A tetrazolium-based colorimetric MTT assay to quantitate human monocyte mediated cytotoxicity against leukemic cells from cell lines and patients with acute myeloid leukemia

The MTT-colorimetric monocyte mediated cytotoxicity assay, based upon the ability of living cells to reduce 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyltetrazolium bromide (MTT) into formazan, was evaluated using leukemic cells from five representative human leukemic cell lines and from 28 patients with acute myeloid leukemia (AML). An excellent linearity between absorbance and leukemic cell number was observed up to 5 x 10(4) cells/well and 50 x 10(4) cells/well for all cell lines and patients samples tested, respectively, in a 96-wells microtiter culture system. A huge variability in the susceptibility of leukemic cells to purified and IFN-gamma-activated human monocytes could be observed at effector-to-target cell (E:T) ratios of 1. The mean signal-to-noise ratio of the MTT assay for monocyte-leukemic cell mixtures from patients was 2.69 +/- 0.39 at E:T 1. In conclusion, the MTT based monocyte mediated cytotoxicity assay should be useful for studying the susceptibility of a variety of leukemic cells from cell lines and from patients with AML to monocytes in a rapid, sensitive and semi-automated manner.

Establishment of mononuclear phagocyte cell lines

Macrophage cell lines have been derived from cells residing in a number of tissues from a variety of species. In this report, the methods used to obtain these cell lines are reviewed and a simple and efficient method for generating nonvirus-transformed lines from individual cloned progenitors located in mouse tissues is described.

Correlation of heat resistance and HSP-70A mRNA levels in human tumor cells measured by competitive quantitative polymerase chain reaction

PURPOSE

Several HSP-70 genes have been cloned and sequenced in human cells. Among these genes, the HSP-70A mRNA and protein levels correlate best with the development and decay of thermotolerance and intrinsic thermal sensitivity. Leukemic and nonleukemic human tumor cells express low levels of the normally heat inducible HSP-70A mRNA in control nonheated cells. Using a competitive quantitative polymerase chain reaction, we have measured the levels of mRNA for this gene and have correlated it with both transient and intrinsic thermal sensitivity of tumor cells. Such studies were also extended to tumor samples obtained from patients.

METHODS AND MATERIALS

In these studies, the plasmid phHSP-70 which contains the entire human HSP-70A gene was modified by the insertion of the T7 promoter at the 5'-end untranslated region as well as the insertion of a 23 bp synthetic linker at the BamH1 site in the promoter region of the HSP-70A gene. The PCR primers were located such that the amplified fragment contained the linker. Using the T7 polymerase, the HSP-70A mRNA was transcribed from this plasmid (phHSP-70L) in vitro. A known amount of HSP-70A mRNA was then added to the total RNA prepared from the cell samples or from the tumor tissues obtained from patients. Using the components of the PCR reaction plus known amounts of HSP-70A mRNA synthesized from phHSP-70L and unknown amounts of total cellular RNA, the samples were amplified and analysed on a denaturing acrylamide gel. The PCR products obtained from phHSP-70L were 23 bp larger than the PCR products obtained from the cell samples due to the addition of the synthetic linker to the HSP-70A gene in phHSP-70L and therefore, the two products could be easily distinguished from each other and quantitated. The alpha-32P-dCTP incorporated in each sample was quantitated by AMBIS Scanner. When the 32P-counts were equal in the known and the unknown samples, the amount of the HSP-70A mRNA was taken to be equal in the known and the unknown sample.

RESULTS

The results show that HSP-70A mRNA levels can be used to predict the survival levels during the development and decay of thermotolerance. In nonleukemic human tumor cell lines, there are as much as 40-50-fold induction of HSP-70A mRNA levels during the peak of thermotolerance. In leukemic cell lines, however, HSP-70A mRNA levels are induced only by three-fold during the same time period. These differences between the levels of HSP-70A mRNA positively correlate with the amount of tolerance development in leukemic and nonleukemic tumor cells. HSP-70A mRNA levels also vary in different tumor cells under nonheated conditions and there is a positive correlation between HSP-70A mRNA levels in nonleukemic human tumor cells and the level of their intrinsic thermal resistance.

CONCLUSION

HSP-70A mRNA levels can be used to predict the intrinsic thermal sensitivity of nonleukemic human tumor cells.

Subtypes of inositol 1,4,5-trisphosphate receptor in human hematopoietic cell lines: dynamic aspects of their cell-type specific expression

Inositol 1,4,5-trisphosphate (IP3)-mediated Ca2+ signaling plays important roles in cellular responses to extracellular stimuli. We recently succeeded in cloning human counterparts of the three subtypes derived from separate genes. Using the cDNA sequences type-specific to these subtype receptors, we here analyzed the expression profile of IP3R subtypes in stimulated and unstimulated human hematopoietic cell lines representing T cells, B cells, neutrophils, macrophages, erythrocytes and megakaryocytes. Northern and dot blot analysis showed that each IP3R subtype is expressed differently in these cells and that the expression profile in each cell is dynamically changed upon stimuli which induce differentiation. Moreover, most of these cells were found to simultaneously express at least two different subtype receptors.

Two independent sets of monoclonal antibodies define neoepitopes linked to soluble ligand binding and leukocyte adhesion functions of activated alpha M beta 2

The integrin alpha M beta 2 mediates a variety of events, adhesive, phagocytic, and inflammatory. Evidence has suggested that the functional events may be mediated by the "activated" conformational forms of alpha M beta 2 produced by appropriate stimulation of myeloid and monocytic lineage. The activation of alpha M beta 2 may be associated with new epitopes on alpha M beta 2, sites that may be related to the acquired receptor functions. Monoclonal antibodies were produced that preferentially bind neoepitopes expressed by activated alpha M beta 2. These anti-neo antibodies each inhibited three activation-associated specific receptor alpha M beta 2 functions, though to different extents. One set of anti-neo antibodies inhibited in a concordant manner the binding of factor X and of fibrinogen by > 90%, abolished the alpha M beta 2-initiated cellular coagulant response, and inhibited monocyte adhesion to unstimulated endothelial monolayers. A second set of anti-neo antibodies only diminished factor X and fibrinogen binding by approximately 40% to 50% but markedly suppressed Xa generation and only partially inhibited monocyte adherence to unstimulated endothelium. Concordance was observed between binding of factor X or fibrinogen and competence for leukocyte adhesion to unstimulated endothelium. Antibody competition assays segregated the anti-neo antibodies into the same two distinct sets, consistent with recognition of separate neoepitopes that are linked to alpha M beta 2 function. These data support the conclusion that the activated conformer of alpha M beta 2 that binds fibrinogen and factor X also mediates monocyte-endothelial interactions as well as the alternative cellular coagulation pathway.

Activation of adult human derived microglia by myelin phagocytosis in vitro

The present study was designed to determine the extent to which cultured glial cells phagocytose normal central nervous system (CNS) myelin and CNS myelin opsonized with serum or purified antibody against myelin basic protein (MBP). Glial cells studied were mixed cultures (consisting of astrocytes, microglia, and oligodendrocytes) and enriched microglia established from adult human brain specimens and enriched astrocytes from fetal human brain. A human monocytic cell line, THP-1, was included as a control. Uptake of 125I-labelled myelin was followed over a 24 hr time period. An assay of oxidative burst (30 min) and cytokine bioassays measuring IL-1, IL-6, and tumor necrosis factor (TNF) production (6-48 hr) were used to investigate short- and long-term activation of phagocytosing cells. Maximum myelin uptake by phagocytosing glial cells occurred within 12-24 hr following myelin incubation. Opsonization of myelin prior to the phagocytosis assay resulted in greater myelin uptake by mixed glial cell cultures, microglia, and THP-1 cells over that of nontreated myelin. The magnitude of myelin phagocytosis by astrocytes was considerably lower than microglia and THP-1, and was not affected by myelin opsonization. Within 30 min of myelin phagocytosis, microglia and THP-1 cells underwent oxidative burst; opsonization of myelin by purified anti-MBP IgG and heat-inactivated serum enhanced the microglial oxidative burst activity. Production of IL-1, TNF, and most markedly IL-6 by microglia was increased following 12-24 hr of myelin ingestion. Our data demonstrate that myelin phagocytosis by adult human-derived microglia occurs in vitro, is augmented when myelin is opsonized, and results in the activation of microglia as assessed by oxidative burst and cytokine production.

Lipopolysaccharide induction of tissue factor gene expression in monocytic cells is mediated by binding of c-Rel/p65 heterodimers to a kappa B-like site

Exposure of monocytic cells to bacterial lipopolysaccharide (LPS) activates the NF-kappa B/Rel family of proteins and leads to the rapid induction of inflammatory gene products, including tissue factor (TF). TF is the primary cellular initiator of the coagulation protease cascades. Here we report the characterization of a nuclear complex from human monocytic cells that bound to a kappa B-like site, 5'-CGGAGTTTCC-3', in the 5'-flanking region of the human TF gene. This nuclear complex was activated by LPS with kinetics that preceded induction of the TF gene. In vitro binding studies demonstrated that the TF site bound translated c-Rel and p65 homodimers but not p50/p65 heterodimers or p50 homodimers. Base-pair substitutions in the TF site indicated that the presence of a cytosine at position 1 precluded binding of NF-kappa B. In fact, under low-ionic-strength conditions, the TF complex did not migrate with translated p50/p65 dimers but instead comigrated with c-Rel/p65 dimers. Antibodies against the NF-kappa B and Rel proteins and UV cross-linking studies revealed the presence of c-Rel and p65 and the absence of p50 in the TF complex and further showed that c-Rel/p65 heterodimers selectively bound to the TF kappa B-like site. Functional studies indicated that the TF site conferred LPS inducibility on a heterologous promoter and was transactivated by c-Rel or p65. Taken together, our results demonstrated that binding of c-Rel/p65 heterodimers to a novel kappa B-like site mediated LPS induction of TF gene expression in monocytic cells.

Lipopolysaccharide-mediated signal transduction through phospholipase D activation in monocytic cell lines

Lipopolysaccharide (LPS)-induced phospholipase D (PLD) activation was investigated in undifferentiated monocytic leukemic cell lines THP-1 and U-937. Treatment of THP-1 or U-937 cells labelled with [32P]orthophosphate, [32P]acyl GPC or [3H]alkyl GPC with LPS, in the presence of 0.5% ethanol, resulted in the accumulation of labelled phosphatidylethanol (PEt) through PLD activation. LPS-mediated PLD activation of THP-1 or U-937 was inhibited by staurosporine (2 microM) and by protein kinase C (PKC) down-regulation with 12-O-tetradecanoylphorbol 13-acetate (TPA) suggesting a role for PKC. In addition to LPS, TPA, ionomycin and cell-permeant analogs of diacylglycerol also stimulated [3H]PEt accumulation. The TPA-induced PEt accumulation was also completely abolished by staurosporine or down-regulation of PKC (> 95% inhibition). Furthermore, the LPS-mediated [32P]PEt formation was attenuated by either depletion of extracellular Ca2+ with EGTA (5 mM) or chelation of intracellular Ca2+ by BAPTA (30 microM). These results indicate that an increase in intracellular Ca2+ is necessary for LPS-mediated PLD activation. Further support for PKC activation by LPS was obtained by determining PKC activity in an in vitro assay of histone H1 phosphorylation using [gamma-32P]ATP. In untreated THP-1 cells, approximately 64% of the PKC activity was localized in the cytosol and 36% in the membrane fraction. Treatment of the cells with LPS (10 micrograms/ml, for 2 h) resulted in an increase of 10% of the membrane-associated PKC activity and a corresponding decrease in the cytosol fraction. These data provide evidence that one of the mechanisms of LPS-mediated signal transduction in human monocytic cell lines involves activation of PLD.

Lipopolysaccharide induction of tissue factor gene expression in monocytic cells is mediated by binding of c-Rel/p65 heterodimers to a kappa B-like site

Exposure of monocytic cells to bacterial lipopolysaccharide (LPS) activates the NF-kappa B/Rel family of proteins and leads to the rapid induction of inflammatory gene products, including tissue factor (TF). TF is the primary cellular initiator of the coagulation protease cascades. Here we report the characterization of a nuclear complex from human monocytic cells that bound to a kappa B-like site, 5'-CGGAGTTTCC-3', in the 5'-flanking region of the human TF gene. This nuclear complex was activated by LPS with kinetics that preceded induction of the TF gene. In vitro binding studies demonstrated that the TF site bound translated c-Rel and p65 homodimers but not p50/p65 heterodimers or p50 homodimers. Base-pair substitutions in the TF site indicated that the presence of a cytosine at position 1 precluded binding of NF-kappa B. In fact, under low-ionic-strength conditions, the TF complex did not migrate with translated p50/p65 dimers but instead comigrated with c-Rel/p65 dimers. Antibodies against the NF-kappa B and Rel proteins and UV cross-linking studies revealed the presence of c-Rel and p65 and the absence of p50 in the TF complex and further showed that c-Rel/p65 heterodimers selectively bound to the TF kappa B-like site. Functional studies indicated that the TF site conferred LPS inducibility on a heterologous promoter and was transactivated by c-Rel or p65. Taken together, our results demonstrated that binding of c-Rel/p65 heterodimers to a novel kappa B-like site mediated LPS induction of TF gene expression in monocytic cells.

Comparison of enhanced chemiluminescence and colorimetric techniques for the immuno-detection of alpha 1-antitrypsin

In order to detect, characterize and quantify blotted proteins, such as human alpha 1-antitrypsin (AAT), there is a need for a specific, extremely sensitive, non-radioactive and uniform revelation system applicable to diluted biological fluids and to culture supernatants of cells isolated from such fluids. We compared two immunochemical revelation systems, enhanced chemiluminescence (ECL) and colorimetric procedures, applied to human ATT, after determining their optimal conditions of performance. ECL was the most sensitive method (down to 50 pg blotted AAT), but could not be used to quantify AAT. In contrast, the colorimetric method enables quantification of blotted AAT, either simply dotted or transferred after SDS-polyacrylamide gel electrophoresis, but is not as sensitive as ECL. Using these two complementary procedures, we have been able to detect AAT in the culture supernatant of a monocytic cell line (THP-1), to characterize the different forms of AAT present in the culture supernatant of blood monocytes and to quantify both.

Effect of corticosteroids, cyclosporin A, and methotrexate on cytokine release from monocytes and T-cell subsets

Corticosteroids are the most effective drugs in the management of asthma. However, because of their known side effects and the existence of corticosteroid-resistant patients, there is a need for substitute medications in asthma therapy. Using cell lines, in the present study, the two corticosteroids dexamethasone (Dex), and beclomethasone (Bec), as well as the immunosuppressant cyclosporin A (CsA), and the antimetabolic drug methotrexate (Mtx) were examined in their effect on release of immunoreactive IL-1 beta, IL-2, IL-4, IL-5, and IL-8. THP-1 cells served as a test model for monocytes secreting IL-1 beta and IL-8 upon stimulation by lipopolysaccharide. Jurkat cells were used as a test model for TH1-type T-cells and were stimulated for IL-2 release with a combination of phytohemagglutinin and phorbol myristate acetate. Representing TH2-type T-cells, D10.G4.1 cells challenged by anti-CD3-mAb produced IL-4, and IL-5. Considerable qualitative and quantitative differences in the relative efficacy of the test compounds were found. Following IC50 values (nmol/l) of the test compounds were estimated (IL-1 beta/IL-8/IL-2/IL-4/IL-5): Dex (10.8/35.7/ > 10,000.0/5.1/4.1), Bec (30.9/102.2/8591.4/0.6/0.4), and CsA (318.7/6211.2/2.3/68.2/237.9). Mtx in concentrations up to 10,000.0 nmol/l was completely inactive. It can be concluded that corticosteroids show another inhibition pattern than CsA: corticosteroids affect mainly TH2-type T-cells, while CsA primarily inhibits the TH1-type T-cell response.

Induction of proto-oncogene and cytokine expression in human peripheral blood monocytes and the monocytic cell line THP-1 after stimulation with mycoplasma-derived material MDHM

Mycoplasma fermentans-derived high-molecular-weight material (MDHM) was originally described to induce differentiation of murine thymocytes to cytolytic effector T-cells by stimulating IL-6 release from adherent cells. This study shows that human peripheral blood monocytes (PBMo) also respond to MDHM with increases in IL-1 beta, IL-6 and TNF alpha expression, both at the mRNA and protein level. The induced expression of IL-1 beta and TNF alpha mRNA in the monocytic THP-1 cell line increased as quickly as in primary cells. In contrast to PBMo, THP-1 and 14 other monocytic/myeloid leukemia-derived cell lines did not secrete measurable amounts of the cytokines upon treatment with MDHM. IL-1 beta and IL-6 genes contain AP-1 binding sites as regulatory elements, the AP-1 protein being composed of c-jun and c-fos gene products. In THP-1 cells c-jun mRNA expression increased after incubation with MDHM while positive c-fos expression remained unaffected. Although these data suggest AP-1 regulated cytokine mRNA expression, results from PBMo are not in accordance with this notion. In the primary cells MDHM-induced elevation of cytokine mRNA levels was preceded by a downregulation of c-fos expression while positive c-jun expression was not modulated. c-myc mRNA expression, constitutively high in THP-1 cells, was induced in MDHM-stimulated PBMo. In conclusion, MDHM-stimulated induction of cytokine mRNA expression was accompanied by different proto-oncogene responses in PBMo and THP-1 cells. These differences may represent different regulatory pathways of the two cell systems. Alternatively, these data support the notion that neither AP-1 nor the c-myc protein are involved in the MDHM-induced increase in IL-1 beta, IL-6 or TNF alpha mRNA levels. Furthermore, the present results demonstrate clearly that mycoplasma products can have a profound impact on the activation status of eukaryotic cells.

Cellular adherence enhances HIV replication in monocytic cells

Cellular adherence is important for monocyte migration and function and is known to induce monocyte activation, leading to the production of mRNA for several proto-oncogenes and cytokines. In addition, since cellular adherence has important intracellular signalling function, it has the potential to enhance human immunodeficiency virus (HIV) replication in monocytic cells. We have investigated the effects of adhesion of the monocytic cell line THP-1 transfected with HIV1 or HIV2 long terminal repeat chloramphenicol acetyltransferase (LTR CAT) constructs. These studies have shown that adherence to tissue culture plastic or confluent endothelial cells is essential for enhanced HIV LTR CAT expression in lipopolysaccharide-stimulated cells. In addition, we have investigated the effects of engagement of specific adhesion molecules, using immobilized antibodies, on HIV replication in the promonocytic cell line OM101, which contains a single latent proviral copy of HIV. Such studies have demonstrated that engagement of CD18, the beta subunit of the lymphocyte function-related antigen-1 (LFA-1) and major histocompatibility complex class II (MHC II) enhanced HIV replication. LFA-1 is involved in both monocyte-endothelial cell interactions and monocyte-T-cell interactions, and MHC II is involved in monocyte interaction with antigen-specific T cells. These data suggest that such interactions of membrane adhesion molecules with their appropriate ligand enhance HIV replication in vivo. Thus, this study has demonstrated that cellular adherence is a key regulatory factor of HIV replication in monocytic cells.

Stimulation of integrin-mediated adhesion of T lymphocytes and monocytes: two mechanisms with divergent biological consequences

We show that the adhesion of T lymphoid cells to immobilized fibronectin can be increased by two distinct mechanisms. The first is by increasing the affinity of the fibronectin receptor/ligand interaction using the anti-beta 1 integrin monoclonal antibody 8A2. The second is by treating the cells with phorbol 12-myristate 13-acetate (PMA), which alters events that occur after receptor occupancy (e.g., cell spreading) without affecting receptor affinity. The effects of these two mechanisms on adhesion in the presence of physiological concentrations of soluble fibronectin suggest that they have different biological consequences. Under these conditions, the net effect of increasing the affinity of the fibronectin receptors is to decrease cell adhesion, whereas the increase in adhesion induced by PMA is unaffected. This suggests that the high affinity receptors are not primarily available for cell adhesion under these circumstances, and that they have an alternative function. We further show that high affinity binding of soluble fibronectin can be induced by either differentiation of the monocytic cell line THP-1 or by cross-linking the T cell receptor complexes on the T lymphoid cell line HUT-78. The differentiated monocytic cells express two populations of fibronectin receptors: a minority in a high affinity state, and the majority in a low affinity state. Thus they will both continue to adhere in the presence of physiological concentrations of soluble fibronectin and bind significant amounts of soluble fibronectin at the cell surface.

Flow cytometric measurement of non-specific esterase activity

alpha-Naphthyl acetate esterase (alpha-NAE) is primarily found in mononuclear phagocytes and may be used to distinguish them from other leucocytes. Conventional cytochemical techniques are subjective and may be difficult to interpret, especially with cells which express only low levels of activity. This has caused difficulties in the classification of non-lymphoblastic leukaemias. This paper describes the adaptation of a cytochemical assay for use with the flow cytometer. The alpha-NAE activity of peripheral blood mononuclear cells was examined and found to be associated with the expression of the surface antigen CD14. The reaction could be inhibited by sodium fluoride. A series of human cell lines were also compared for alpha-NAE activity. Distinct differences in staining observed between the cell lines correlated with the number of cell-associated granules observed under the microscope.

Identification of a cis-regulatory element and putative trans-acting factors responsible for 12-O-tetradecanoylphorbol-13-acetate (TPA)-mediated induction of heme oxygenase expression in myelomonocytic cell lines

The human monocytic leukemia cell line THP-1 differentiates into macrophage-like cells when treated with a variety of agents, including 12-O-tetradecanoylphorbol-13-acetate (TPA). We show here that during this process, the expression of heme oxygenase, a rate-limiting enzyme in heme catabolism, is induced. Treatment with TPA increases heme oxygenase mRNA in other myelomonocytic cell lines also, but not in cell lines of other lineages, such as HeLa cells. Increased heme oxygenase activity may represent one of the functions of activated macrophages, which sequestrate senescent erythrocytes and degrade heme derived from hemoglobin. This cell-type-specific induction by TPA treatment further investigated with respect to transcriptional regulation. We defined a cis-regulatory element, 5'-GTCATATGAC-3', located in the 5'-flanking region (positions -156 to -147) of the human heme oxygenase gene, which confers inducibility by TPA in THP-1 cells but not in HeLa cells. Nuclear proteins that bind to this element, which may be responsible for the cell specificity, were identified in THP-1 nuclear extracts. This element contains the consensus motif CANNTG, to which a large family of basic helix-loop-helix proteins binds. Our results suggest a novel mechanism of TPA-mediated transcriptional regulation in myelomonocytic cell lines.

delta 9-Tetrahydrocannabinol (THC) modulates IL-1 bioactivity in human monocyte/macrophage cell lines

We have previously observed that delta 9-tetrahydrocannabinol (THC), the major psychoactive component of marijuana, increased supernatant interleukin-1 (IL-1) bioactivity in cultures of mouse resident peritoneal macrophages stimulated with lipopolysaccharide (LPS). In this study, experiments were performed to determine whether THC treatment similarly affected phagocytes of human origin. The results showed that THC increased the levels of supernatant IL-1 bioactivity of two human monocytic cell lines, but only if the cells were differentiated with phorbol myristate acetate. Undifferentiated cells displayed decreased IL-1 bioactivity in response to THC. However, under conditions in which THC augmented supernatant IL-1 bioactivity from THP-1 cells, ELISA studies showed that the levels of IL-1 alpha and IL-1 beta were unchanged and decreased, respectively. Furthermore, supernatant interleukin-6 (IL-6) levels were decreased, but tumor necrosis factor (TNF-alpha) levels were increased by THC treatment. These results show that THC treatment modulates cytokine production and/or release by mouse and human macrophages and the drug effects on IL-1-like bioactivity in the supernatants of the human THP-1 cells are due to increased levels of other cytokines, such as TNF-alpha, rather than IL-1 itself.

Stimulation with a monoclonal antibody (mAb4E4) of scavenger receptor-mediated uptake of chemically modified low density lipoproteins by THP-1-derived macrophages enhances foam cell generation

mAb4E4, a murine monoclonal antibody that is specific for acetylated LDL and malondialdehyde-treated LDL, binds specifically to modified LDL present in human atherosclerotic lesions. It is directed against an epitope that is poorly exposed in delipidated and solubilized apolipoprotein B-100 from modified LDL. mAb4E4, as well as its F(ab')2 and Fab fragments, enhanced the uptake of both acetylated LDL and malondialdehyde-treated LDL by THP-1-derived macrophages resulting in a sixfold increase of cytoplasmic cholesteryl ester levels. The increased uptake of modified LDL/mAb4E4 complexes did not occur via the Fc receptor and did not depend on aggregation of modified LDL particles. However, their uptake was inhibited by blocking the scavenger receptors with fucoidin or by downregulation of receptor expression with endotoxins or interferon-gamma, indicating that their uptake is mediated via these receptors. Thus, generation of autoimmune antibodies against modified LDL and subsequent endocytosis of soluble modified LDL/antibody complexes via scavenger receptors may enhance foam cell generation. This mechanism may contribute to the progression of atherosclerotic lesions.

Phagocytosis of a fluorescently labeled perflubron emulsion by a human monocyte cell line

We hypothesized that fluorocarbon-based lipid emulsions are phagocytosed by monocytes and that many of the in vivo side effects related to the infusion of these particulate emulsions are due to release of cytokines by these monocytes. To clarify whether these emulsions are actually phagocytosed we attempted to measure by flow cytometry the apparent uptake of a fluorescently labeled high-concentration (90%, w/v) perflubron (perfluorooctyl bromide [PFOB]) emulsion by a differentiated human monocyte cell line. A fluorescent chromophore (Zynaxis Cell Science) was used to label the egg yolk phospholipid in a perflubron emulsion. This phospholipid label was used to track the perflubron emulsion during overnight incubation with the human monocyte (THP-1) cell line which had been differentiated, by exposure to PMA, into macrophage-like cells. Our results indicate that after 24 hours of incubation with the labeled perflubron emulsion, 64.9% (+/- 11.0) of differentiated THP-1 cells had cell-associated emulsion (ingested and/or membrane bound) whereas 24.4 (+/- 6.8%) of the control cells had cell-associated emulsion. We speculate that this technique may be a useful method to track the intravascular persistence and extravascular distribution of such emulsions, and that the degree of uptake of the emulsion by macrophages in this assay may correlate with its in vivo half life.

Identification of a cis-regulatory element and putative trans-acting factors responsible for 12-O-tetradecanoylphorbol-13-acetate (TPA)-mediated induction of heme oxygenase expression in myelomonocytic cell lines

The human monocytic leukemia cell line THP-1 differentiates into macrophage-like cells when treated with a variety of agents, including 12-O-tetradecanoylphorbol-13-acetate (TPA). We show here that during this process, the expression of heme oxygenase, a rate-limiting enzyme in heme catabolism, is induced. Treatment with TPA increases heme oxygenase mRNA in other myelomonocytic cell lines also, but not in cell lines of other lineages, such as HeLa cells. Increased heme oxygenase activity may represent one of the functions of activated macrophages, which sequestrate senescent erythrocytes and degrade heme derived from hemoglobin. This cell-type-specific induction by TPA treatment further investigated with respect to transcriptional regulation. We defined a cis-regulatory element, 5'-GTCATATGAC-3', located in the 5'-flanking region (positions -156 to -147) of the human heme oxygenase gene, which confers inducibility by TPA in THP-1 cells but not in HeLa cells. Nuclear proteins that bind to this element, which may be responsible for the cell specificity, were identified in THP-1 nuclear extracts. This element contains the consensus motif CANNTG, to which a large family of basic helix-loop-helix proteins binds. Our results suggest a novel mechanism of TPA-mediated transcriptional regulation in myelomonocytic cell lines.

Neither CD14 nor serum is absolutely necessary for activation of mononuclear phagocytes by bacterial lipopolysaccharide

The stimulation of mononuclear phagocytes by lipopolysaccharide (LPS) is facilitated by the binding of complexes of LPS and LPS-binding protein to CD14. Although it is clear that CD14 is involved in LPS-induced signaling, other investigators have hypothesized the existence of additional signaling pathways in macrophages. We sought to determine whether CD14-independent pathways of monocyte activation might exist. Washed human mononuclear cells responded with reduced sensitivity to LPS in the absence of serum. Anti-CD14 monoclonal antibody (MAb) inhibited the response to LPS in serum-free conditions, but this was easily reversed at higher concentrations of LPS. We established a human monocytic cell line, designated SFM (derived from THP-1), in serum-free medium to examine LPS responses under defined conditions. Differentiation of SFM cells with 1,25-dihydroxycholecalciferol promoted the expression of abundant cell surface CD14. Differentiated SFM cells responded to LPS despite the complete absence of serum proteins for > 20 generations of growth. LPS stimulation of differentiated SFM cells was inhibited by anti-CD14 MAbs only when serum was present. In contrast to anti-CD14 MAb, the LPS antagonists lipid IVa and Rhodobacter sphaeroides lipid A inhibited monocyte activation under serum-free conditions, implying that these compounds compete with LPS at a site distinct from CD14. Undifferentiated SFM cells (expressing minimal CD14) still responded to LPS in serum-free conditions, and anti-CD14 MAb had little inhibitory effect. The addition of purified LPS-binding protein or human serum promoted a CD14-dependent pathway of monocyte activation by LPS in these cells. We conclude that monocytes do not absolutely require serum proteins to be stimulated by LPS and that CD14-independent LPS signaling pathways exist which are inhibitable by lipid IVa and R. sphaeroides lipid A.

n-6 and n-3 fatty acid accumulation in thp-1 cell phospholipids

The human monocytic leukemia cell line THP-1 is depleted of the long-chain n-6, AA, when compared to human monocytes. This reflects the low availability of this FA in the growth medium generally used for cultured cells. The effects of AA, as well as EPA, supplementation of THP-1 cells on the incorporation of these FA in cell PL, especially in PC and PE, was investigated. In addition the incorporation of labeled AA in PL from THP-1 cells was compared to that in human monocytes. Measurements were done through HPLC separation of PL, detected by UV absorption and radioactivity, FA analysis by GC and characterization of PC subclasses by FAB-MS. Marked differences were observed in the incorporation of the two FA in cell PL, particularly two PC subclasses, and in the accumulation in individual PL after supplementation of THP-1 cells. Accumulation of AA and EPA in THP-1 cells appeared to be mutually independent. The incorporation of AA was also quite different in THP-1 from that in monocytes. Thus, characterization of the FA content in lipids of cultured cells is an essential requirement for optimal utilization of these cells.

Peripheral benzodiazepine receptor modulation with phagocyte differentiation

Peripheral benzodiazepine receptor (PBR) was found to be less expressed in the immature phagocytic HL-60 and U-937 cell lines than in the more mature monocytic THP-1 cell line. Cell differentiation by several agents induced a strong enhancement of PBR density on these three phagocytic cell lines but not on the lymphocytic CEM cell line. Detailed analysis of phorbol 12-myristate 13-acetate-treated THP-1 cells showed an increased PBR expression and the rise came along with an increase of CD11a and CD11b antigens and a secretion of macrophagic cytokines tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-1 beta and IL-8. Quantitation of mRNA using polymerase chain reaction (PCR)-based technique showed that overexpression of PBR did not parallel mRNA expression, indicating a gene-independent regulation. These results suggest that PBR predominance on phagocytic cells could be related to maturation process.

Immunoreactive fucosylceramide as a B-cell differentiation marker

The reactivity of PC47H, a monoclonal antibody (mAb) directed against fucosylceramide, with cells of lymphoid lineage was examined. Immunoreactive fucosylceramide (FC) was recognized only in pokeweed mitogen (PWM)-stimulated B blasts, plasma cells and germinal center cells. mAb PC47H did not react with T cells at different stages or with peripheral blood B cells. Furthermore, FC was expressed abundantly in blastic cells of B-cell lymphoma, multiple lymphoma and myeloma cell lines KMS-12-BM and KMS-12-PE. In other words, FC was expressed more strongly in mature than in immature B cells. Immunoelectron microscopy showed that FC was located in the plasma membrane and rough endoplasmic reticulum. mAb PC47H can therefore be used as a unique B-cell differentiation marker for study of B-cell activation and differentiation and clonal analysis of lymphoid malignancies.

Fibrinogen mediates leukocyte adhesion to vascular endothelium through an ICAM-1-dependent pathway

Leukocyte traffic in immune-inflammatory responses requires regulated adhesion of leukocyte subsets to vascular endothelium. We show that fibrinogen or normal human plasma enhances by 2- to 5-fold the adhesion of cells of myeloid and lymphoid lineage to endothelium. This mechanism is mediated by fibrinogen binding to complementary membrane receptors on leukocytes and endothelial cells. Using an affinity chromatography purification strategy, genetically engineered transfectants, and direct binding studies to the isolated recombinant protein, we identified a novel hematopoietic fibrinogen receptor participating in this adhesion pathway as intercellular adhesion molecule 1 (ICAM-1). Accordingly, a new model can be proposed, in which fibrinogen binding to a variety of vascular cell receptors mediates a specific pathway of cell to cell adhesion by bridging together leukocytes and endothelial cells.

Effects of prostacyclin analogues on human endothelial cell tissue factor expression

Prostacyclin analogues have been reported to inhibit the expression of tissue factor procoagulant activity in human monocytes, primarily by elevating intracellular levels of adenosine 3',5'-cyclic monophosphate (cAMP). The present studies have investigated whether prostacyclins can also inhibit tissue factor expression in endothelial cells. Iloprost, carbacyclin, and ciprostene had no effect on human umbilical vein endothelial tissue factor activity induced by lipopolysaccharide (LPS), tumor necrosis factor-alpha (TNF-alpha), or interleukin-1 beta (IL-1 beta). Iloprost failed to elevate intracellular levels of cAMP, even when combined with a phosphodiesterase inhibitor. In contrast, forskolin increased endothelial cAMP and inhibited tissue factor expression. Conditioned medium from LPS-challenged monocytic THP-1 cells, which contained both TNF-alpha and IL-1 beta, induced endothelial cell procoagulant activity to levels 20-fold higher than those achieved in response to LPS alone. Iloprost abolished LPS-induced TNF-alpha secretion by THP-1 cells and inhibited IL-1 beta secretion by 45%. In keeping with this, iloprost reduced levels of TNF-alpha and IL-1 beta mRNA in LPS-challenged cells. Treatment of THP-1 cells with iloprost strongly inhibited the ability of conditioned medium to induce endothelial tissue factor expression, an effect that was mimicked by treating the medium with blocking antibodies to the cytokines. We conclude that although prostacyclin analogues do not directly suppress endothelial tissue factor expression due to their failure to elevate cAMP, they may do so indirectly by inhibiting the amplification produced by monocyte-derived cytokines.

Differential regulation of the human immunodeficiency virus type 2 enhancer in monocytes at various stages of differentiation

We have demonstrated that stimulation of the human immunodeficiency virus type 2 (HIV-2) enhancer in T cells is dependent upon at least four cis-acting elements, including two purine-rich binding sites, PuB1 and PuB2, which are capable of binding members of the ets family of proto-oncogenes, the pets (peri-ets) site, which lies just upstream of the PuB2 site, and a single kappa B site (D. M. Markovitz, M. Smith, J. M. Hilfinger, M. C. Hannibal, B. Petryniak, and G. J. Nabel, J. Virol. 66:5479-5484, 1992). In this study, we examined the regulation of the HIV-2 enhancer in cells of monocytic lineage. We found that in immature monocytic cell lines, the HIV-2 enhancer is markedly induced by phorbol esters and that all four cis-acting elements are required for activation. In mature monocytic cells, constitutive activity is high, with only modest stimulation following phorbol ester treatment. Mutation of any of the four cis-acting elements resulted in greatly reduced basal expression in mature monocytes. This is in contrast to HIV-1, in which developmentally controlled expression of the enhancer in monocytes is mediated largely through the kappa B sites alone [G. E. Griffin, K. Leung, T. M. Folks, S. Kunkel, and G. J. Nabel, Nature (London) 339:70-73, 1989]. Further, we demonstrated that although both Elf-1, an ets family member with significant similarity to the drosophila developmental regulatory protein E74, and Pu.1, a monocyte- and B-cell-specific member of the ets family, bind the purine-rich enhancer region, Elf-1 is the protein which binds predominantly in vivo. A nuclear factor(s) which binds the pets site, an element which has been described only in HIV-2, was detected in extracts of all of the monocytic cells tested. These findings indicate that the mechanism by which cellular factors regulate HIV-2 enhancer function in monocytic cells differs significantly from that of HIV-1 and may offer a partial explanation for the differences in the biological and clinical characteristics of the two viruses.

Identification and target-size analysis of the leukotriene D4 receptor in the human THP-1 cell line

The human acute monocytic leukemia cell line THP-1 has been identified, by radioligand binding, as expressing the leukotriene D4 receptor at a high level (4000 binding sites per cell), without the need for further cell differentiation. [3H]Leukotriene D4-specific binding to THP-1 cell membranes was of high affinity (KD = 0.47 nM) and saturable, enhanced by divalent cations but inhibited by both monovalent cations and non-hydrolyzable GTP analogs. The cysteinyl leukotrienes competed for [3H]leukotriene D4-specific binding with the following rank order of potency: leukotriene D4 >> leukotriene E4 > leukotriene C4. In addition, leukotriene D4-receptor antagonists from two structural classes, the quinolines MK-571 and L-697,008, and the indole ICI 204,219, displayed nanomolar potency in [3H]leukotriene D4 competition assays. These data show that [3H]leukotriene D4-specific binding to THP-1 cell membranes fulfils the criteria for binding to a leukotriene D4 receptor regulated through interaction with a G protein. Several novel features of the THP-1 leukotriene D4 receptor were investigated. Culture of THP-1 cells in the presence of tunicamycin, an inhibitor of N-glycosylation, resulted in a 6-fold decrease in the number of detectable [3H]leukotriene D4-specific binding sites. Target-size analysis by radiation inactivation estimated a molecular mass of 65 kDa for the [3H]leukotriene D4 specific binding site(s) present in THP-1 cell membranes. Together, these results suggest that the human THP-1 cell leukotriene D4 receptor is a glycosylated protein with a molecular mass of approx. 65 kDa within the membrane environment.

Processing of complex between urokinase and its type-2 inhibitor on the cell surface. A possible regulatory mechanism of urokinase activity

Complexes between the urokinase-type plasminogen activator (uPA) and its type-2 inhibitor (PAI-2) are bound by a cell-surface receptor for uPA and rapidly cleaved into two fragments of 70 and 22 kDa. The 70-kDa fragment contains the active site of uPA and PAI-2, while the 22-kDa species was identified as the amino terminal fragment of uPA, that binds specifically to the receptor. When the experiment is performed at 4 degrees C, both fragments remain bound to the cell surface and can be eluted by acid treatment. We therefore postulate that after the binding of the uPA-PAI-2 complex, a new binding site for the 70-kDa species becomes available. This additional binding favours the cleavage of the complex into the 70-and 22-kDa fragments; the 70-kDa species is endocytosed or released, while the 22-kDa fragment remains on the cell surface to prevent the binding of intact uPA.

Hepatitis B virus differentially suppresses myelopoiesis and displays tropism for immature hematopoietic cells

The hematopoietic cell lines HL-60 and THP-1 were challenged with hepatitis B virus (HBV) in vitro to study interactions between the virus and host cell. Exposure to HBV suppressed the ability of HL-60 cells to differentiate into granulocytes after treatment with retinoic acid (RA) or dimethyl sulfoxide (DMSO), and RA-induced activation of the monocytic cell line THP-1 was also suppressed. Terminal differentiation of both cell lines by phorbol 12-myristate 13-acetate (PMA) was not affected by HBV. The suppressive effect on RA- or DMSO-induced differentiation was unique to HBV, since cell exposure to human cytomegalovirus, another virus that inhibits hematopoiesis, failed to block cellular differentiation. At 5 days postinfection, extracellular viral DNA was detected in immature but not in differentiated cultures and higher levels of core antigen (HBcAg) and surface antigen (HBsAg) were seen in undifferentiated cells than in RA- or PMA-treated cells. In addition, release of HBsAg into the medium was 2 to 12 times greater in untreated cultures than for RA- or PMA-treated cells. Thus, HBV suppresses hematopoiesis by blocking the maturational development of progenitors and selectively infects immature myeloid cells compared with mature end-stage cells.

Release of human immunodeficiency virus by THP-1 cells and human macrophages is regulated by cellular adherence and activation

Macrophage adherence, an important regulatory signal, has the potential to affect human immunodeficiency virus (HIV) production either directly or by priming monocytes to respond to other activating signals. We have investigated the role of adherence as an activator of HIV-1 transcription and release. The effects of adherence on HIV-1 transcription were examined by using THP-1 cells, a human monocytic cell line, transfected with HIV long terminal repeat (LTR)-chloramphenicol acetyltransferase (CAT) constructs. The effects of adherence on release of HIV-1 were investigated in both HIV-1-infected THP-1 cells and human peripheral blood monocyte-derived macrophages (MDM). Adherence of lipopolysaccharide (LPS)-stimulated THP-1 cells to either tissue culture plastic or endothelial cells was crucial for enhanced HIV-1 transcription as measured by LTR-CAT expression. Such increased LTR-CAT expression did not occur with an HIV LTR construct containing mutated NF-kappa B binding sites. In contrast, release of whole HIV, measured by reverse transcriptase (RT) activity in tissue culture medium, was reduced upon adherence of stimulated HIV-1-infected THP-1 cells without suppression of HIV LTR-CAT transcription or p24 release. This finding suggested that activation of adherent monocytic cells interfered with HIV assembly and release. Although the reduction of RT activity following activation of HIV-1-infected MDM was independent of adhesion, adherence alone of nonstimulated HIV-infected MDM to endothelial cells was sufficient to induce a reduction in RT release. This study demonstrates that LPS stimulation of monocytic cells enhances HIV LTR transcription under adherent conditions. In contrast, activation of adherent monocytic cells infected with HIV reduced viral release.

Post-transcriptional regulation of apolipoprotein E expression in mouse macrophages by phorbol ester

Phorbol ester-mediated differentiation of THP-1 cells (a human monocytic cell line) into mature macrophages is associated with a transcriptional induction of apolipoprotein E (apoE) expression [Auwerx, Deeb, Brunzell, Peng and Chait (1988) Biochemistry 27, 2651-2655]. Endotoxin, on the other hand, which may also act through activation of protein kinase C, is a potent inhibitor of apoE expression in mouse macrophages [Werb and Chin (1983) J. Biol. Chem. 258, 10642-10648]. The present experiments examine the effect of phorbol ester, an activator of protein kinase C, on the apoE expression in mouse thioglycollate-elicited peritoneal macrophages. Phorbol ester inhibits apoE expression in a specific, time- and dose-dependent manner. A 75% inhibition in the rate of apoE secretion, but not that of total protein, was observed following a 4.5 h incubation with 160 nM phorbol ester, although nearly full inhibition was obtained with 40 nM. The changes in apoE secretion were paralleled by similar changes in apoE synthesis, indicating synthesis as the primary site of action. The decreased rates of apoE synthesis are shown not to be due to increased apoE degradation. The profound inhibition of apoE synthesis was not accompanied by significant changes in apoE mRNA levels at any concentration of phorbol ester (up to 16 microM), or length of treatment (up to 24 h), suggesting a post-transcriptional locus of regulation of apoE expression. Although the early changes in apoE synthesis correlate with increased microsomal protein kinase C activity, the suppression of apoE expression persists even during conditions of nearly complete (> 95%) loss of protein kinase C activity, suggesting that the direct or indirect effect of protein kinase C on apoE expression is mediated by a stable phosphorylated protein, or that the observed effects are mediated through a protein kinase C species that is not readily downregulated by phorbol esters. The presented studies clearly demonstrate the potential importance of the translational regulation of apoE expression through the protein kinase C signal transduction pathway.

Fc gamma receptor-mediated biological activities of human leukemic cell lines and their modulation by transforming growth factor-beta 1 and interleukin 6

Previously we reported that transforming growth factor-beta 1 (TGF-beta 1) remarkably enhanced the differentiation of human leukemic cell lines, HL-60 and THP-1, in the presence of 1 alpha,25-dihydroxyvitamin D3 (VD3) and also that it induced Fc receptor for immunoglobulin G (Fc gamma R), type IIIB, in the presence of retinoic acid (RA). The present study revealed that TGF-beta 1 enhanced the Fc gamma RI- and Fc gamma RII-mediated antibody-dependent cellular cytotoxicity (ADCC) of the cells differentiated in the presence of VD3 and RA. However, production of active oxygen molecules was suppressed by TGF-beta 1. On the other hand, IL-6 stimulated production of active oxygen molecules and ADCC of the cells treated with VD3 and tumor necrosis factor-alpha (TNF-alpha). Furthermore, the levels of cell surface Fc gamma RI and Fc gamma RII were not clearly correlated with the ADCC. The TGF-beta 1/VD3-treated HL-60 cells were able to synthesize mRNAs for TGF-beta 1 and TNF-alpha, although TNF-alpha protein was not detectable. These results suggest that TGF-beta 1 has a bifunctional role, either stimulatory or inhibitory, in the modulation of macrophage activities through Fc gamma Rs and that IL-6 stimulates certain macrophage activities in mature cells.

Interferon-gamma inhibits macrophage apolipoprotein E production by posttranslational mechanisms

Macrophage-derived apolipoprotein (apo) E and multimers of a synthetic apo E-peptide display monokine-like functions by inhibiting mitogen- or antigen-driven lymphocyte proliferation. This study demonstrated how the target lymphocyte itself can modulate macrophage apo E production. The lymphokine interferon-gamma (IFN) dramatically inhibited the accumulation of apo E in the supernatant of human monocytic THP-1 cells when present during phorbol myristate acetate-induced differentiation. A similar effect was observed when IFN was added to differentiated THP-1 cells. Treatment with IFN did not change the steady-state levels of apo E mRNA. Furthermore, in the presence of IFN no increased degradation or increased uptake of extracellular apo E was detected. Pulse-chase experiments indicated that IFN reduced the accumulation of extracellular apo E and increased the degradation of intracellular apo E. The inhibitory effect of IFN on apo E production also was observed in human monocyte-derived macrophages. Thus, our data demonstrated that IFN inhibited macrophage apo E production by posttranslational mechanisms. This represents a previously uncharacterized immunoregulatory interaction and lends further support to a relationship between lipid metabolism and the immune system.

Modulation of secretory processes of phagocytes by IX 207-887

In chronic inflammation, the mediators released by phagocytes are in part responsible for the initiation and perpetuation of the disease. IX 207-887, which is a novel antiarthritic drug, inhibits the release of cytokines from mononuclear cells at concentrations which are achieved therapeutically in human rheumatoid arthritis and in animal models of arthritis. Furthermore, the production of superoxide and release of azurophil and specific granules by N-formyl-Met-Leu-Phe-stimulated neutrophils are significantly reduced. As a consequence, IX 207-887 may break the vicious circle which is manifest in chronic inflammation. In a recent double-blind placebo controlled study IX 207-887 has been shown to be an effective slow-acting drug for use in rheumatoid arthritis.

Detection of recombinational mutations in cultured human cells by Southern blot analysis with minisatellite DNA probes

Using the human acute monocytic leukemia cell line, THP-1, a hypermutability of minisatellite loci was demonstrated in cell culture by Southern blot analysis with minisatellite DNA probes. DNA was isolated from 98 subclones and hybridized to a panel of minisatellite probes consisting of three multilocus minisatellite probes (ML probes) and seven locus-specific minisatellite probes (LS probes). The Southern blot patterns of the hybridized subclones were compared with those of the parental THP-1. Four mutated bands with two ML probes and two mutated bands with two LS probes were detected. The mutation frequency was estimated roughly at 0.1% based on the total number of bands analyzed, and it was much higher than that expected for other DNA regions. Four of these mutations were thought to be alterations of repetitions caused by insertion or deletion of tandem repeats, and one mutant lost a complete minisatellite allele. The nature of the sixth mutant was unclear. Because of the hypermutability of minisatellite DNA, Southern blot analysis using minisatellite DNA probes can be used as a mutation assay system directly based on the DNA.

Synergism between protein-kinase C and cAMP-dependent pathways in the expression of the interleukin-1 beta gene is mediated via the activator-protein-1 (AP-1) enhancer activity

In many different cell types treatment with phorbol esters (e.g. 4 beta-phorbol 12-myristate 13-acetate, PMA) leads to the activation of protein-kinase C (PKC) and subsequently to the activation of the activator-protein-1(AP-1)-responsive gene expression. We have previously reported that a structural analog of cAMP (dibutyryl cAMP, Bt2cAMP) or agents elevating the endogenous cAMP levels strongly enhanced the PMA-induced interleukin-1 beta(IL-1 beta)-gene expression in human myeloid leukemia cells (THP-1, HL-60). We have now examined the role of AP-1 in the regulation of the IL-1 beta gene expression by PKC and cAMP in THP-1 cells. AP-1 is a complex composed of products of the jun and fos gene families. Our studies show that Bt2cAMP enhances the PMA-induced c-fos and jun-B expression, but inhibits c-jun expression. Electrophoretic mobility-shift assay revealed that Bt2cAMP also increased the PMA-induced AP-1 DNA-binding activity. The functional role of the increased AP-1 DNA-binding activity was studied by transfecting THP-1 cells with reporter constructs containing AP-1 sites [Col-TREx5/TK-CAT and IL-1 beta-X-CAT, which contains the putative 12-O-tetradecanoyl-phorbol-13-acetate(TPA)-responsive element of the IL-1 beta gene]. Transient transfection assay demonstrated that Bt2cAMP similarly increased the PMA-induced transcription from both of these reporter constructs. Taken together, these results suggest that cAMP increases the PMA-induced AP-1 activity which then leads to increased IL-1 beta expression.

Interaction between human immunodeficiency virus and Toxoplasma gondii replication in dually infected monocytoid cells

THP-1 monocytoid cells, either not infected or chronically infected with human immunodeficiency virus type 1 (HIV-1), were challenged with Toxoplasma gondii. Parasitic growth, as assessed by trophozoite counting and measurement of supernatant p30 membrane antigen, was similar in HIV-infected and noninfected THP-1 cells. Also, T. gondii did not affect HIV replication. These experiments therefore failed to demonstrate any interaction between HIV-1 and T. gondii replication in concurrently infected monocytoid cells.

Aleutian mink disease parvovirus infection of mink peritoneal macrophages and human macrophage cell lines

Aleutian mink disease parvovirus (ADV) mRNAs are found in macrophages in lymph nodes and peritoneal exudate cells from ADV-infected mink. Therefore, we developed an in vitro infection system for ADV by using primary cultures of mink macrophages or macrophage cell lines. In peritoneal macrophage cultures from adult mink, virulent ADV-Utah I strain showed nuclear expression of viral antigens with fluorescein isothiocyanate-labeled ADV-infected mink serum, but delineation of specific viral proteins could not be confirmed by immunoblot analysis. Amplification of ADV DNA and production of replicative-form DNA were observed in mink macrophages by Southern blot analysis; however, virus could not be serially propagated. The human macrophage cell line U937 exhibited clear nuclear expression of viral antigens after infection with ADV-Utah I but not with tissue culture-adapted ADV-G. In U937 cells, ADV-Utah I produced mRNA, replicative-form DNA, virion DNA, and structural and nonstructural proteins; however, virus could not be serially passaged nor could [3H]thymidine-labeled virions be observed by density gradient analysis. These findings indicated that ADV-Utah I infection in U937 cells was not fully permissive and that there is another restricted step between gene amplification and/or viral protein expression and production of infectious virions. Treatment with the macrophage activator phorbol 12-myristate 13-acetate after adsorption of virus reduced the frequency of ADV-positive U937 cells but clearly increased that of human macrophage line THP-1 cells. These results suggested that ADV replication may depend on conditions influenced by the differentiation state of macrophages. U937 cells may be useful as an in vitro model system for the analysis of the immune disorder caused by ADV infection of macrophages.

The envelope glycoprotein of human immunodeficiency virus type 1 stimulates release of neurotoxins from monocytes

Mononuclear phagocytes infected with human immunodeficiency virus 1 (HIV-1) produce soluble factors that kill neurons in culture. To define the molecular events that lead to neuron killing, HIV-1 proteins were tested for the ability to trigger release of neurotoxins from human monocytes and lymphocytes. None of the recombinant-derived HIV-1 proteins examined (reverse transcriptase, protease, gag, nef, or gp120) were directly neurotoxic at concentrations from 100 pM to 10 nM. The envelope glycoprotein gp120 did, however, stimulate both isolated human blood monocytes and the monocytoid line THP-1 (but not lymphocytes or the lymphoid cell line H9) to discharge neurotoxic factors. These toxins consisted of heat-stable, protease-resistant molecules (< 500 Da) that copurified with neurotoxins from HIV-1-infected THP-1 cells and were blocked by antagonists to N-methyl-D-aspartate receptors. Release of neurotoxins through gp120 stimulation involved monocytoid CD4 receptors because toxin production could be inhibited either by a monoclonal antibody to the CD4-binding region of gp120 or by soluble CD4 receptors. Alternatively, production of neuron-killing factors could be induced with a peptide from the CD4-binding region of gp120. These data show that the HIV-1 envelope glycoprotein alone can stimulate neurotoxin release by binding to CD4 receptors of mononuclear phagocytes. Such neurotoxic factors may, in turn, contribute to the central nervous system dysfunction associated with HIV-1 by acting on neurons through N-methyl-D-aspartate receptors.

Interaction of VIP, PACAP and related peptides in normal and leukemic human monocytes and macrophages

The activation of the cAMP signaling pathway by vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating peptide (PACAP) and related peptides was studied (i) in normal peripheral human monocytes and THP-1 leukemic human monocytes, (ii) in their derived macrophage counterparts respectively obtained after spontaneous differentiation or retinoic acid (RA) treatment, and (iii) in human bronchoalveolar macrophages. In THP-1 monocytes, PACAP increased basal adenylate cyclase activity 5.3-fold, with an affinity 50-times greater than that of VIP or helodermin (Ka = 3.2 x 10(-11) M VIP), whereas in normal peripheral monocytes, PACAP and VIP exhibited similar affinities and only increased cAMP generation 2-fold (EC50 = 10(-9) M). Spontaneous and RA-induced differentiation into normal and leukemic macrophages induced a progressive loss of cAMP production and regulation of superoxide anion production by VIP and related peptides. The neoplastic transformation in THP-1 monocytes and the deficiencies in the cAMP cascade observed during the terminal differentiation of normal and leukemic human macrophages may relate to a differential genetic expression of the VIP/PACAP receptor subtypes, and alterations in the functional activity of the stimulatory and inhibitory Gs/Gi subunits of adenylate cyclase.