Development of specific receptors for N-formylated chemotactic peptides in a human monocyte cell line stimulated with lymphokines

Dynamic Evolution of Bacterial Ligand Recognition by Formyl Peptide Receptors

The detection of invasive pathogens is critical for host immune defense. Cell surface receptors play a key role in the recognition of diverse microbe-associated molecules, triggering leukocyte recruitment, phagocytosis, release of antimicrobial compounds, and cytokine production. The intense evolutionary forces acting on innate immune receptor genes have contributed to their rapid diversification across plants and animals. However, the functional consequences of immune receptor divergence are often unclear. Formyl peptide receptors (FPRs) comprise a family of animal G protein-coupled receptors which are activated in response to a variety of ligands including formylated bacterial peptides, pathogen virulence factors, and host-derived antimicrobial peptides. FPR activation in turn promotes inflammatory signaling and leukocyte migration to sites of infection. Here we investigate patterns of gene loss, diversification, and ligand recognition among FPRs in primates and carnivores. We find that FPR1, which plays a critical role in innate immune defense in humans, has been lost in New World primates. Amino acid variation in FPR1 and FPR2 among primates and carnivores is consistent with a history of repeated positive selection acting on extracellular domains involved in ligand recognition. To assess the consequences of FPR divergence on bacterial ligand interactions, we measured binding between primate FPRs and the FPR agonist Staphylococcus aureus enterotoxin B, as well as S. aureus FLIPr-like, an FPR inhibitor. We found that few rapidly evolving sites in primate FPRs are sufficient to modulate recognition of bacterial proteins, demonstrating how natural selection may serve to tune FPR activation in response to diverse microbial ligands.

Evaluation of cationic channel TRPV2 as a novel biomarker and therapeutic target in Leukemia-Implications concerning the resolution of pulmonary inflammation

Patients treated during leukemia face the risk of complications including pulmonary dysfunction that may result from infiltration of leukemic blast cells (LBCs) into lung parenchyma and interstitium. In LBCs, we demonstrated that transient receptor potential vanilloid type 2 channel (TRPV2), reputed for its role in inflammatory processes, exhibited oncogenic activity associated with alteration of its molecular expression profile. TRPV2 was overexpressed in LBCs compared to normal human peripheral blood mononuclear cells (PBMCs). Additionally, functional full length isoform and nonfunctional short form pore-less variant of TRPV2 protein were up-regulated and down-regulated respectively in LBCs. However, the opposite was found in PBMCs. TRPV2 silencing or pharmacological targeting by Tranilast (TL) or SKF96365 (SKF) triggered caspace-mediated apoptosis and cell cycle arrest. TL and SKF inhibited chemotactic peptide fMLP-induced response linked to TRPV2 Ca²⁺ activity, and down-regulated expression of surface marker CD38 involved in leukemia and lung airway inflammation. Challenging lung airway epithelial cells (AECs) with LBCs decreased (by more than 50%) transepithelial resistance (TER) denoting barrier function alteration. Importantly, TL prevented such loss in TER. Therefore, TRPV2 merits further exploration as a pharmacodynamic biomarker for leukemia patients (with pulmonary inflammation) who might be suitable for a novel [adjuvant] therapeutic strategy based on TL.

Oxidized LDL-induced JAB1 influences NF-κB independent inflammatory signaling in human macrophages during foam cell formation

Background

Oxidized low-density lipoprotein (oxLDL) mediates the transformation of macrophages (MΦ) to cholesterol-rich foam cells and the release of pro-inflammatory cytokines during atherogenesis. JAB1 (Jun activation domain binding protein-1) is present in all stages of human plaques, involved in the Toll-like receptor-mediated activation of p38 mitogen-activated protein kinase (MAPK) and controls nuclear factor-kappa B (NF-κB) activation. Thus, we were interested in the role of JAB1 during foam cell formation of MΦ after oxLDL exposition.

Methods and results

We found that JAB1 was present in CD68-immunoreactive (−ir) MΦ in atherosclerotic plaques of apolipoprotein E knockout (ApoE^−/−) mice after a high cholesterol/fat diet. Furthermore, differentiated human U937 MΦ - incubated with oxLDL (4 h) to induce foam cell formation – showed a significant increase of JAB1 (50 μg/ml: 1.39 + 0.15-fold; 100 μg/ml: 1.80 + 0.26-fold; 200 μg/ml: 2.05 + 0.30-fold; p < 0.05) on the protein level compared to the control. Independent from JAB1 silencing, we found an increase of total cholesterol (TC), free cholesterol (FC) and cholesteryl ester (CE) after oxLDL exposition. However, siJAB1-MФ showed a reduction of tumor necrosis factor-alpha (TNF-α) (36%; p < 0.05 vs. non-transfected MФ) and interleukin (IL)-6 (30%; p < 0.05 vs. non-transfected MФ) mRNA expression, as well as TNF-α (46%; p < 0.05 vs. non-transfected MФ) and IL-6 (32%; p < 0.05 vs. non-transfected MФ) protein secretion after oxLDL exposition. In parallel with an upregulation of inflammatory cytokines (TNF-α, IL-6) after oxLDL exposition, we found a significant (p < 0.05) increase of 37% in p38 MAPK activation after 4 h oxLDL-treatment, independent from NF-kB signaling. In this context, we showed regional co-localization of JAB1 with p38 MAPK in atherosclerotic plaques of ApoE^−/− mice. Moreover, we detected interaction of JAB1 with p38 MAPK in U937 cells.

Conclusion

We demonstrate that oxLDL induces JAB1 expression and influences its cellular localization, whereby the p38 MAPK signaling pathway is modified with consequences for inflammation of human MΦ in foam cells and atherosclerotic lesions.

Electronic supplementary material

The online version of this article (doi:10.1186/s12929-017-0320-5) contains supplementary material, which is available to authorized users.

Diced electrophoresis gel assay for screening enzymes with specified activities

We have established the diced electrophoresis gel (DEG) assay as a proteome-wide screening tool to identify enzymes with activities of interest using turnover-based fluorescent substrates. The method utilizes the combination of native polyacrylamide gel electrophoresis (PAGE) with a multiwell-plate-based fluorometric assay to find protein spots with the specified activity. By developing fluorescent substrates that mimic the structure of neutrophil chemoattractants, we could identify enzymes involved in metabolic inactivation of the chemoattractants.

Optimizing size and copy number for PEG-fMLF (N-formyl-methionyl-leucyl-phenylalanine) nanocarrier uptake by macrophages

Curing HIV-1 infection has remained elusive because of low and fluctuating drug levels arising from poor absorption, the development of viral reservoirs and sanctuary sites, toxicity, and patient nonadherence. The present study addresses the issue of insufficient drug exposure in macrophages. Viral reservoir sites such as macrophages are believed to be responsible for the viral rebound effect observed upon the discontinuation of anti-HIV drug therapy. In our proposed model, a drug can be covalently attached to a nanocarrier in order to facilitate the delivery of therapeutic agents to the site(s) of infection. As an initial step, we propose the covalent attachment of several copies of N-formyl-Met-Leu-Phe (fMLF), a known chemo-attractant for macrophages. In this article, one or more copies of fMLF were conjugated to multifunctional commercially available or novel, peptide-based PEG nanocarriers in which the structure was varied by appending PEGs with average molecular weights of 5, 20, and 40 kDa. U937 cell-specific binding and cellular uptake were analyzed. The results of uptake studies indicate that (i) uptake is energy dependent and mediated by a fMLF receptor, (ii) appending only 2 copies of the targeting ligand to the multifunctional nanocarrier appears sufficient for binding in vitro, and (iii) of the three configurations studied, the nanocarrier with a molecular weight of about 20 kDa, corresponding to a size of 20-60 nm, demonstrated the highest uptake. The results of the current studies demonstrate the feasibility of targeting macrophages and the suitability of using these synthetically versatile peptide--backbone PEG nanocarriers. The convenience, flexibility and possible limitations of this nanocarrier approach are discussed.

Anaphylatoxins: their role in bacterial infection and inflammation

Activation of the complement system plays a crucial role in the pathogenesis of infection and inflammation. Especially the complement activation products C3a and C5a, known as the anaphylatoxins, are potent proinflammatory mediators. In addition to their evident role in innate immunity, it is clear that the anaphylatoxins also play a role in regulation of adaptive immune responses. The anaphylatoxins play a role in a variety of infectious and inflammatory diseases like sepsis, ischemia-reperfusion injury, immune complex diseases, and hypersensitivity diseases like asthma. In this review we discuss the role of anaphylatoxins in infection and inflammation. Furthermore, we focus on bacterial complement evasion strategies that can provide tools for further research on pathogenesis of infectious diseases and a better understanding of the role of complement and anaphylatoxins in infection and inflammation.

Platelet-derived thrombospondin-1 is necessary for the vitamin D-binding protein (Gc-globulin) to function as a chemotactic cofactor for C5a

The chemotactic activity of C5a and C5a des Arg can be enhanced significantly by the vitamin D-binding protein (DBP), also known as Gc-globulin. DBP is a multifunctional 56-kDa plasma protein that binds and transports several diverse ligands. The objective of this study was to investigate the mechanisms by which DBP functions as a chemotactic cofactor for C5a using neutrophils and U937 cells transfected with the C5aR (U937-C5aR cells). The results demonstrate that U937-C5aR cells show C5a chemotactic enhancement only to DBP in serum, but, unlike mature neutrophils, this cell line cannot respond to DBP in plasma or to purified DBP. Analysis by SDS-PAGE and isoelectric focusing revealed no structural difference between DBP in serum compared with DBP in plasma. However, plasma supplemented with either serum, DBP-depleted serum, or activated platelet releasate provides a required factor and permits DBP to function as a chemotactic cofactor for C5a. Fractionation of activated platelet releasate revealed that the additional factor possessed the properties of thrombospondin-1 (TSP-1). Finally, purified TSP-1 alone could reproduce the effect of serum or platelet releasate, whereas Abs to TSP-1 could block these effects. These results provide clear evidence that TSP-1 is needed for DBP to function as a chemotactic cofactor for C5a.

Chemotaxis inhibitory protein of Staphylococcus aureus binds specifically to the C5a and formylated peptide receptor

Chemotaxis inhibitory protein of Staphylococcus aureus (CHIPS) is an exoprotein produced by several strains of S. aureus, and a potent inhibitor of neutrophil and monocyte chemotaxis toward C5a and formylated peptides like fMLP. These chemoattractants act on their target cells by binding and activating the C5aR and formylated peptide receptor (FPR), respectively. In the present report, we examined the mechanism by which CHIPS affects both of these receptors. We showed that CHIPS blocked binding of anti-C5aR mAb and formylated peptide to human neutrophils as efficiently at temperatures of 0 and 37 degrees C, implying that it is independent of signal transducing systems. This was confirmed by showing that CHIPS acts completely independently of ATP. Additionally, CHIPS was not internalized upon binding to neutrophils. Furthermore, we showed that CHIPS binds specifically to the C5aR and FPR expressed on U937 cells. This binding was functional in blocking C5a- and fMLP-induced calcium mobilization in these cell lines. These results suggest that CHIPS binds directly to the C5aR and FPR, thereby preventing the natural ligands from activating these receptors. The apparent K(d) values of CHIPS for the C5aR and FPR were 1.1 +/- 0.2 nM and 35.4 +/- 7.7 nM, respectively. Moreover, after screening a wide variety of other G protein-coupled receptors, CHIPS was found to affect exclusively the C5aR and FPR. This selectivity and high-affinity binding with potent antagonistic effects makes CHIPS a promising lead for the development of new anti-inflammatory compounds for diseases in which damage by neutrophils plays a key role.

Chemotaxis activation of peritoneal murine macrophages induced by the transplantation of free and encapsulated pancreatic rat islets

The present study concerns the influence of the transplantation of free and encapsulated (AN69 membrane, Hospal) islets on the chemotaxis of peritoneal macrophages. Fifty free or encapsulated rat islets, cultured for 24 h, were transplanted in the peritoneal cavity of mice (n = 12). Three days after transplantation, the chemotaxis of peritoneal murine macrophages was tested towards formyl-methionyl-leucyl-phenylalanine (fMLP) and a culture medium conditioned for 3 days by free rat islets isolated from the same rat donor. In response to fMLP, the chemotactic indexes of macrophages from mice transplanted with free or encapsulated islets were 8.09 +/- 2.10 and 9.45 +/- 2.76, respectively. These values were significantly higher than those obtained when macrophages from untreated mice were tested (2.42 +/- 0.23; p < 0.01). In response to culture medium conditioned by free islets, the transplanted encapsulated islets failed to enhance macrophage chemotaxis (2.41 +/- 0.53) compared to transplanted free islets (7.00 +/- 2.63; p < 0.01). Thus, encapsulation decreased the specific chemotactic activity of peritoneal macrophages induced by free islet transplantation, probably by prohibiting the diffusion of chemoattractants.

A fragment of alpha-actinin promotes monocyte/macrophage maturation in vitro

Conditioned media (CM) from cultures of HL-60 myeloid leukemia cells grown on extracellular bone marrow matrix contains a factor that induces macrophage-like maturation of HL-60 cells. This factor was purified from the CM of HL-60 cells grown on bone marrow stroma by ammonium sulfate precipitation, then sequential chromatography on DEAE, affi-gel blue affinity, gel exclusion, and wheat germ affinity columns, followed by C-4 reverse phase HPLC, and SDS-PAGE. The maturation promoting activity of the CM was identified in a single 31 kD protein. Amino acid sequence analysis of four internal tryptic peptides of this protein confirmed significant homology with amino acid residues 48-60, 138-147, 215-220, and 221-236 of human cytoskeletal alpha-actinin. An immunoaffinity purified rabbit polyclonal anti-chicken alpha-actinin inhibited the activity of HL-60 conditioned media. A 27 kD amino-terminal fragment of alpha-actinin produced by thermolysin digestion of chicken gizzard alpha-actinin, but not intact alpha-actinin, had maturation promoting activity on several cell types, including blood monocytes, as measured by lysozyme secretion and tartrate-resistant acid phosphatase staining. We conclude that an extracellular alpha-actinin fragment can promote monocyte/macrophage maturation. This represents the first example of a fragment of a cytoskeletal component, which may be released during tissue remodeling and repair, playing a role in phagocyte maturation.

Constitutive Activation of U937 Promonocytic Cell Clones Selected for Their Resistance to Parvovirus H-1 Infection

The human promonocytic cell line U937 is highly sensitive to the lytic effect of the autonomous parvovirus H-1. Rare cell variants that resisted H-1 virus infection could be isolated, of which four (RU1, RU2, RU3, and RU4) were further characterized. In contrast to parental cells, the RU clones sustained an abortive H-1 virus infection. Three of the clones showed a significant decrease in the accumulation levels of the c-Myc oncoprotein and in their capacity for forming tumors in immunodeficient mice. Surprisingly, all RU clones resisted the suppressing effect of 12-O-tetradecanoylphorbol-13-acetate (TPA) on c-myc oncogene expression and cell proliferation. In contrast, RU clones exhibited the TPA-induced changes in membrane surface antigens and nonspecific esterase activities that are characteristic of monocytic differentiation. Studies of the activation steady-state of RU cells demonstrated the constitutive production of significant amounts of nitric oxide (NO) and superoxide anion (O−2⋅ ). Inhibitors of NO and O−2⋅ . production sensitized all RU cells to the killing effect of parvovirus H-1 and increased the production of infectious viral particles. These data argue for the participation of active oxygen species in macrophage defence mechanisms against parvovirus infection. Moreover, the use of parvovirus H-1 as a selective agent in a cell-colony formation assay allowed us to show that expression of defined markers of monocytic differentiation can be uncoupled from suppression of proliferation.

Constitutive Activation of U937 Promonocytic Cell Clones Selected for Their Resistance to Parvovirus H-1 Infection

The human promonocytic cell line U937 is highly sensitive to the lytic effect of the autonomous parvovirus H-1. Rare cell variants that resisted H-1 virus infection could be isolated, of which four (RU1, RU2, RU3, and RU4) were further characterized. In contrast to parental cells, the RU clones sustained an abortive H-1 virus infection. Three of the clones showed a significant decrease in the accumulation levels of the c-Myc oncoprotein and in their capacity for forming tumors in immunodeficient mice. Surprisingly, all RU clones resisted the suppressing effect of 12-O-tetradecanoylphorbol-13-acetate (TPA) on c-myc oncogene expression and cell proliferation. In contrast, RU clones exhibited the TPA-induced changes in membrane surface antigens and nonspecific esterase activities that are characteristic of monocytic differentiation. Studies of the activation steady-state of RU cells demonstrated the constitutive production of significant amounts of nitric oxide (NO) and superoxide anion (O−2⋅ ). Inhibitors of NO and O−2⋅ . production sensitized all RU cells to the killing effect of parvovirus H-1 and increased the production of infectious viral particles. These data argue for the participation of active oxygen species in macrophage defence mechanisms against parvovirus infection. Moreover, the use of parvovirus H-1 as a selective agent in a cell-colony formation assay allowed us to show that expression of defined markers of monocytic differentiation can be uncoupled from suppression of proliferation.

A double-labelling fluorescent assay for concomitant measurements of [Ca2+]i and O2. production in human macrophages

To measure intracellular free Ca2+ concentration ([Ca2+]i) and superoxide (O2) production in human alveolar macrophages, we used the fluorescent Ca2+ indicator fura-2 and the O2-sensitive dye dihydrorhodamine-123, which becomes fluorescent in its oxidized form, rhodamine-123. We describe a new double-dye technique whereby the kinetics of both [Ca2+]i levels and O2. production can be monitored simultaneously. This technique was developed in the dimethylsulfoxide-differentiated monocytic-like U-937 cell line (not equal to U-937), validated by comparison with single dye measurements and applied to human alveolar macrophages. The chemotactic peptide N-formyl-L-Methionyl-L-Leucyl-L-Phenylalanine induced in both cell types a similar transient elevation in [Ca2+]i, followed within seconds by a sustained increase in O2 production, which was however 4-fold weaker in not equal to U-937 cells. These results indicate that O2 production is an early event following the stimulation of human alveolar macrophages. This new double-dye technique may be relevant to other O2 ion-producing cells and could help to define more precisely the kinetics of the events leading to this biological response.

Salicylates for ulcerative colitis--their mode of action

Delivery of 5-aminosalicylic acid to the colon by sulphasalazine, other azo-bonded compounds and controlled-release preparations is introduced in the context of metabolism by epithelial cells and therapeutic efficacy in ulcerative colitis. Potential modes of action are then reviewed, including actions on luminal bacteria, epithelial cell surface receptors, cellular events (such as nitric oxide release or butyrate oxidation), electrolyte transport and epithelial permeability. Evidence for an influence of salicylates on circulating and lamina propria inflammatory cells is presented, as well as actions on adhesion molecules, chemotactic peptides and inflammatory mediators, such as eicosanoids, platelet-activating factor, cytokines or reactive oxygen metabolites. The precise mechanism will remain uncertain as long as the aetiology of ulcerative colitis is unknown, but a pluripotential mode of action of salicylates is an advantage when influencing the network of events that constitute chronic inflammation.

Interaction of guanine-nucleotide-binding regulatory proteins with chemotactic peptide receptors in differentiated human leukemic HL-60 cells

Human leukemic HL-60 cells were differentiated into neutrophil-like cells by treatment with dimethylsulfoxide (Me2SO) or N6,O2'-dibutyryladenosine 3',5'-phosphate (Bt2cAMP), and membrane fractions were prepared from the differentiated cells. Receptors for fMLF (fM,N-formylmethionine) and guanine-nucleotide-binding regulatory proteins (G proteins) serving as the substrate for pertussis toxin (islet-activating protein; IAP) were extracted from cell membranes then reconstituted into phospholipid vesicles. The binding of fMLF to the reconstituted vesicles (or the membranes) was determined with 10 nM [3H] fMLF. In both cases, high-affinity binding to vesicle preparations from the Me2SO- and Bt2cAMP-induced cells was abolished following treatment with IAP, suggesting that fMLF receptors were functionally coupled to IAP-sensitive G proteins in each of the two vesicle types. However, the high-affinity fMLF binding was much higher in vesicle preparations originating from Bt2cAMP-induced cells than in those from Me2SO-induced cells, although the amount of IAP-substrate G protein reconstituted into the each phospholipid vesicles preparation was not significantly different from the other. The G proteins of the two differentiated cells were both identified as inhibitory forms (Gi-2) based on their electrophoretic mobilities and immunoblot analyses. When purified Gi-2 from rat brain was reconstituted into the two IAP-treated vesicles, high-affinity fMLF binding was restored in a similar manner in both. IAP-substrate G proteins partially purified from the two differentiated HL-60 cells were also effective in restoring high-affinity fMLF binding to the IAP-treated vesicles. However, a significant difference was observed that the reconstituted binding was higher with the G-protein-rich fraction from Bt2cAMP-induced cells than with that from Me2SO-induced cells, with each of the two IAP-treated vesicle types. These results suggest that the different high-affinity binding of fMLF observed in the two differentiated HL-60 cells are due to a difference in the property of endogenous G proteins rather than fMLF receptors, though the two G proteins are indistinguishable from each other in terms of the subtype of G protein, Gi-2.

Induction of the oxidative response and of concanavalin A-binding capacity in maturing human U937 cells

Differentiation of U937 cells with phorbol myristate acetate (PMA) induces high stimulation by concanavalin A of the respiratory burst as well as an increase in concanavalin A-binding cell capacity. New concanavalin A-binding proteins are detected as differentiated U937 cells acquire their capacity to be activated by concanavalin A. We identified several concanavalin A-binding proteins, of molecular mass 30-200 kDa, in PMA-differentiated cells, but only some of them seem to be directly related to the concanavalin A effect on the respiratory burst. One of these candidates could be a glycoprotein with an apparent molecular mass of 140 kDa which behaved as a major concanavalin A-binding protein and is expressed on differentiated cells at the time these cells respond maximally to concanavalin A.

Stimulus-response coupling in FMLP-stimulated U937 monocytes: effect of differentiation on Gi2 expression

The effect of differentiation on FMLP-stimulated InsP production and G-protein expression was investigated in U937 monocytes. FMLP (0.01-10 microM) stimulated [3H]InsP production in dimethyl sulphoxide-differentiated, but not in immature, U937 cells. Ionomycin (1 and 10 microM) stimulated [3H]InsP production equally well in both cell types. The FMLP response was blocked by pertussis toxin (100 ng/ml for 4 h) which catalysed [32P]ADP ribosylation of a 40 kDa 'Gi-like' G-protein alpha subunit in these cells. This protein was also identified immunologically using anti-peptide antibodies that detect 'Gi-like' alpha subunits (SG2) or Gi2 alpha specifically (LE2). With LE2 a 5-fold increase in Gi2 alpha levels was seen following differentiation of the cells, suggesting that FMLP receptor expression is accompanied by an increase in the G-protein with which these receptors interact.

Interactions between alveolar macrophage subpopulations modulate their migratory function

To better understand the mechanisms by which alveolar macrophages (AM) are attracted to local sites in the lung, the locomotion of AM in response to N-formyl-methionyl-leucyl-phenylalanine (FMLP) was investigated. Total bronchoalveolar cells (99% AM) obtained by a nondiscriminating bronchoalveolar lavage procedure migrated toward FMLP over a range of concentrations of 10(-12) M to 10(-6) M. Dose-response experiments showed a biphasic response with two peaks of migration obtained respectively at 5 x 10(-10) M and 10(-8) M. Analysis in the presence and absence of a positive gradient of FMLP revealed that the first peak of migration (5 x 10(-10) M FMLP) corresponded predominantly to chemotactic activity whereas the second peak of migration (10(-8) M FMLP) was associated with chemokinetic activity. To further evaluate these activities of oriented (chemotaxis) vs. random (chemokinesis) migration, AM were separated into two fractions by a two-step bronchoalveolar lavage procedure. Whereas fraction 1 displayed exclusively chemokinesis in response to higher concentrations of FMLP (10(-8) M), fraction 2 was totally unresponsive to FMLP over a wide range of concentrations (5 x 10(-11) M - 10(-7) M). When both fractions were combined, however, the chemotactic response to low concentrations of FMLP (5 x 10(-10) M) was restored. Additional analysis of these two AM fractions indicated that fraction 1 AM had a significantly lower degree of adherence and aggregation than fraction 2 AM. These data suggest that cell-cell cooperation is important for AM chemotactic response to FMLP and that such interaction may involve changes in adherence and aggregation.

Chemotactic factor-induced polarization, receptor redistribution, and locomotion of human blood monocytes

The locomotor response of human blood monocytes to chemotactic factors was studied using a polarization assay on cells in suspension and by filming locomotion on albumin-coated glass. Cells in optimal (5 x 10(-9) M) but uniform concentrations of N-formyl-methionyl-leucyl-phenylalanine (FMLP) polarized well and showed a 'persistent random walk' type of locomotion, whereas in supraoptimal concentrations (10(-7) M), the cells took erratic paths and polarized poorly, suggesting that monocytes cannot develop an anteroposterior polarity if hit by ligand molecules at many points on the cell surface simultaneously. Monocyte polarization in chemotactic factors at 37 degrees was transient and was gradually lost after 15-20 min. Likewise, the ability to form Fc rosettes after this time was gradually lost, suggesting loss of functional receptors from the cell surface with time. In optimally polarized cells, Fc rosettes were frequently localized at the head of the cell. This localization also was lost with time. Using pure chemotactic factors (FMLP, C5a, leukotriene B4) we found, as reported earlier (Cianciolo & Snyderman 1981), that polarization was restricted to a subpopulation (approximately 60% of cells) that responded to multiple attractants. However, 80-90% of monocytes polarized in response to combinations of any of the above pure attractants with candida-activated serum. This suggests that the subpopulation that lacks receptors for classical chemotactic factors nevertheless has locomotor capacity and can respond to undefined factors in activated serum, and that the great majority of blood monocytes is motile if appropriately stimulated.

Chemotactic peptides. Mechanisms, functions, and possible role in inflammatory bowel disease

An important component of host defenses is the ability of inflammatory cells to detect and respond to minute concentrations of chemoattractant substances. Chemotactic peptides elaborated by both bacteria and leukocytes are the focus of this review. These peptides induce directed migration of inflammatory cells towards their targets, and stimulate biological functions including degranulation, release of oxygen radicals, phagocytosis, and eicosanoid production. Among the released eicosanoids, leukotriene B4 potentiates the leukocyte response. As with other chemotactic factors, these functions are regulated partially through differential coupling to high- and low-affinity receptors and via calcium as the second messenger. Some chemotactic peptides are elaborated by normal colonic luminal bacteria. Recent evidence demonstrates that these peptides can produce mucosal inflammation in vivo. A possible mechanism for this effect involves abnormal colonic permeability in susceptible individuals that allows bacterial chemotactic peptides access to the mucosa where they may induce inflammation. Remaining questions include the mechanism by which the mucosal barrier is breached and the role of leukotrienes in the potentiation of colonic inflammation.

Intracellular Ca2+ mobilization in immature and more mature U937 induced to differentiate by dimethyl sulfoxide or phorbol myristate acetate

Intracellular Ca2+ mobilization in U937 cells was studied. Stimulation of immature U937 cells with leukotriene B4 (LTB4) increased intracellular Ca2+ levels, whereas stimulation with N-formyl-methionyl-leucyl-phenylalanine (fMLP) failed to increase intracellular Ca2+ levels. U937 cells cultured with 1.5% dimethyl sulfoxide (DMSO) for 4 days (DMSO-U937 cells) responded to LTB4 and possessed the ability to respond to fMLP. U937 cells cultured with 1 ng/ml phorbol myristate acetate (PMA) for 4 days (PMA-U937 cells) lost the ability to respond to LTB4, although they responded to fMLP. Treatment of DMSO-U937 cells with 100 ng/ml PMA for 3 min suppressed intracellular Ca2+ increase induced by LTB4 and fMLP. The fMLP-induced Ca2+ rise in PMA-U937 cells was not suppressed by a further treatment with 100 ng/ml PMA. DMSO-U937 cells responded to inositol 1,4,5-trisphosphate (IP3), indicating that IP3 functions as a messenger of intracellular Ca2+ mobilization from endoplasmic reticulum in U937. The magnitude and duration of the rise in Ca2+ induced by IP3 in DMSO-U937 cells treated with 100 ng/ml PMA for 3 min were similar to those of the controls. When DMSO-U937 cells were Ca2+-depleted, addition of Ca2+ resulted in a transient overshoot of Ca2+ influx. However, the transient overshoot was not observed, when PMA-U937 cells were tested. These results indicate that Ca2+ efflux in PMA-U937 cells is increased by an activated exit pump, which may be directly or indirectly related to the functional state of PMA-U937 cells.

Differentiation of a human monocytic cell line associated with increased production of Rift Valley fever virus by infected cells

Rift Valley fever (RVF) virus is a cause of significant human and animal disease in many parts of Africa. In some cases, it causes a hemorrhagic fever, which is frequently fatal. Prior studies have shown that RVF virus productively infects peritoneal macrophages from susceptible rat strains. The U937 human monocytic cell line was used to determine the effect of monocytic cell differentiation on the degree of viral production by cell cultures infected with RVF virus. Differentiation of U937 cells to more mature monocytic cells by phorbol ester resulted in production of 10 times more infectious virions in comparison with undifferentiated cells. These studies imply that monocytic cell differentiation increases permissiveness for RVF virus production.

1985 Kreshover lecture. Molecular factors influencing neutrophil defects in periodontal disease

Major advances in our understanding of the role of the neutrophil in host defense against periodontal organisms have been made through studies of localized juvenile periodontitis (LJP). Several lines of evidence suggest that LJP is an infectious process closely associated with Actinobacillus (Haemophilus) actinomycetemomitans as a causative agent, although other organisms may also participate. The immunologic profile of LJP patients suggests that a cell-associated neutrophil locomotory dysfunction is a key underlying immunodeficiency resulting in increased susceptibility to periodontal infection. In addition, LJP patients often exhibit cervical lymphadenopathy and IgG-hypergammaglobulinemia, and a markedly elevated antibody response to the infecting organism, A. actinomycetemcomitans, is found in the serum and crevicular fluid of most patients. Evaluation of the locomotory properties of LJP neutrophils shows that random migration and chemokinesis are normal; however, about 70% of the LJP patients suffer from a defect in chemotaxis, with their neutrophils responding poorly to bacterial chemotactic factors, synthetic chemotactic peptides, and complement fragments (C5a). Depressed chemotaxis of LJP neutrophils is paralleled by their reduced capacity to bind the synthetic chemotactic peptide N-formylmethionylleucylphenylalanine (FMLP), as well as C5a. Furthermore, there is a reduction in the amount of glycoprotein 110, a neutrophil membrane matrix component and differentiation antigen which is associated with FMLP- and possibly also C5a-mediated chemotaxis. Reduction of C5a and of FMLP ligand binding, decreased expression of GP-110, and reduced neutrophil chemotaxis are consistent with a stem cell maturation error in LJP patients. This is further supported by studies demonstrating increased expression of CR2, the C3d/EBV receptor, on peripheral blood neutrophils of LJP patients. CR2 receptors are normally present on immature human neutrophils but are lost during the maturation process. These alterations in neutrophil surface components and their reduced chemotaxis may result from a genetically determined abnormality. Studies demonstrating the familial nature of both the neutrophil chemotactic disorder and the clinical entity represented by localized juvenile periodontitis point to a strong role for genetic determinants in the disease which affect neutrophil surface receptors.

Conformation and dynamics of the chemotactic peptide formyl-L-methionyl-L-leucyl-L-phenylalanine in solution

Several conformational and dynamic features of the chemotactic peptide formyl-L-methionyl-L-leucyl-L-phenylalanine in solution have been delineated by investigations of NMR and IR spectroscopic parameters. Both 1D and 2D NMR experiments have been performed for detection of scalar and dipolar proton-proton connectivities, whereas 13C and 1H relaxation parameters have been interpreted in terms of molecular dynamics. The main conformation appeared to be unfolded with the three hydrophobic side chains extending in divergent directions with respect to the backbone. The existence of relatively weak intermolecular hydrogen bonds was demonstrated, involving the formamide end group, with increase in the hydrophobicity of the external surface.

A human-mouse hybrid cell line that stably expresses chemotaxis to N-formylmethionyl-leucyl-phenylalanine

Human leukocytes, which contain monocytes and neutrophils that exhibit chemotaxis to fMet-Leu-Phe, were fused with the mouse macrophage RAW264-TG3 cell line, which exhibits chemotaxis to endotoxin-activated mouse serum but not to fMet-Leu-Phe. From such fusions twelve cell lines were isolated, all of which migrated to endotoxin-activated mouse serum. Four of the cell lines also exhibited chemotaxis to fMet-Leu-Phe, and of these cell lines, only one, WBC264-9, retained the capacity to migrate to fMet-Leu-Phe after culture for 20 or more passages. Determination of the number of chromosomes and analysis of the electrofocusing patterns of human and mouse hypoxanthine-guanine phosphoribosyltransferase activity showed that WBC264-9 was derived from a human-mouse cell fusion. WBC264-9, a stable macrophage cell line that exhibits chemotaxis to fMet-Leu-Phe, provides a model system to investigate attractant-specific biochemical reactions.

Effects of gold sodium thiomalate on functional correlates of human monocyte maturation

The mechanism of action of gold salts in the treatment of rheumatoid arthritis is unknown. Effects of gold on monocyte-macrophage function could be due to inhibition of maturation and differentiation. We found that 3 markers of monocyte differentiation, loss of peroxidase activity, spontaneous synthesis of C2, and spontaneous cytotoxicity for chicken erythrocytes, were all inhibited by gold treatment. This was not a general toxic effect since phorbol myristate acetate could still induce gold-treated monocytes to lyse chicken erythrocytes. Also, phorbol myristate acetate-stimulated superoxide production, a monocyte function not requiring further differentiation, was not inhibited by incubation with gold. Lymphokine-stimulated cytotoxicity for nucleated target cells, another function of monocytes, was inhibited only partially for certain target cells and not at all for others. These data suggest that gold has the capacity to selectively inhibit some monocyte functions which are associated with macrophage differentiation.

Human monocyte and neutrophil chemotaxis in vitro employing 51Cr-labelled leukocytes

A modification of an objective technique for measuring leukocyte chemotaxis is described using 51Cr-labelled neutrophils and monocytes. Influence of cell concentration, incubation time, chemotactic factor concentration and gradient, filter pore size and incubation temperature on migrational activity of the studied cells has been investigated. The technique was rigorously standardized in order to optimize the assay conditions. The chemotactic activity is expressed as a ratio of stimulated migration and random migration (chemotactic index = CI). The method is relatively simple, sensitive, and fast. It is suitable as a screening test for abnormal leukocyte chemotaxis.

In vitro induction of cytologic and functional differentiation of the immature human monocytelike cell line U-937 with phorbol myristate acetate

The tumor-promoting ester 4 beta-phorbol 12-myristate 13-acetate (PMA) has been shown to induce the differentiation of the immature monocytelike cell line U-937 c in vitro into a heterogeneous population of cells, including small "dense" cells, large vacuolized or "foamy" cells, spindle-shaped cells, and cells with multiple filopodia ("stellate" cells). The effect of PMA was dose- and time-dependent, the optimal conditions being 40-162 nM PMA for 48 hours. The minimum time of exposure to PMA to ensure further differentiation of U-937 cells was about 5 hours. The PMA-stimulated cells acquired morphologic, ultrastructural, and functional characteristics typical of cells of the monocyte/macrophage lineage. The PMA-treated U-937 cells became adherent, ceased to proliferate, and exhibited increased expression of monocyte-specific antigens (Leu-M2, - M3, HLADr), surface receptors (FcR, C3bR), enzymes (nonspecific esterase, transglutaminase), and ability to mediate chemotaxis, phagocytosis, superoxide anion production, and antibody-dependent cytotoxicity reactions. The induced cells lost their morphologic differentiation and ability to attach to surfaces and regained proliferative capacity upon repeated subculture in PMA-free media.

Locomotion and chemotaxis of mononuclear phagocytes

The capacity for locomotion and for chemotaxis is probably very different in monocytes and macrophages from different sources. Numerous techniques have been established for studying the locomotion of these cells. Many of the factors are sparsely documented and the reports are scattered among various cell types. Heterogeneity of locomotion and chemotactic responsiveness is evident when established macrophage lines and mouse peritoneal macrophage are studied. The effects of mononuclear phagocytes and their released products on the locomotion of other cell types are reviewed.

Chemotaxis of macrophage in inflammation

Our particular attention in this article was given to natural mediators for macrophages isolated from the sites of tissue injury. A number of chemotactic factors, which may satisfy many criteria making them acceptable as inflammatory leucocyte chemotactic factors, has been separated. Among them, our laboratory has isolated three macrophage (monocyte) chemotactic factors (MCF-a, -b and -c). Their purification, characterization and functional specificity are discussed.

Chemotactic and candidacidal responses of rabbit alveolar macrophages during postnatal development and the modulating roles of surfactant in these responses

Chemotactic responses of alveolar macrophages from 1-, 7-, and 28-day-old rabbits to various concentrations of endotoxin-activated serum and n-formyl-methionyl-phenylalanine were tested utilizing both blind well and agarose plate assay systems. A dramatic increase in both the chemotactic response and responsiveness to various concentrations of chemoattractant was observed during postnatal maturation. The pattern of result was similar with both methods of assay. An age-related increase was also found to occur in the candidacidal activity of alveolar macrophages in contrast to their phagocytic uptake, which showed no age-related increases. Furthermore, the decreased function of macrophages from newborn animals correlated with a morphologically and biochemically less mature cell population which contained large amounts of phagocytosed surfactant-related material. Moreover, pretreatment of macrophages from 7- and 28-day-old animals with vesicles of surfactant-related material resulted in decreases in both chemotactic and candidacidal activity, with a paradoxical increase in their phagocytic activity. The resulting activities were similar to those of macrophages from 1-day-old animals treated with buffer alone. These data suggest that there is an age-related increase in the chemotactic and candidacidal activity of alveolar macrophages during maturation and that the decreased activity of macrophages from newborn animals is related in part to the large amount of surfactant-related material present at that time.

Chemotactic subpopulation of macrophage cell line cells (M1 cells) discerned by three macrophage chemotactic factors from delayed hypersensitivity reaction sites

The functional specificity of three types of macrophage chemotactic factors ( MCFs ), -a, -b, and -c, from purified protein derivative of tuberculin (PPD)-induced delayed hypersensitivity reaction (DHR) skin sites on guinea pigs, was analyzed using macrophage cell line cells, M1, established from myeloid leukemia cells of a SL/Am strain mouse. M1 cells yielded two subclones: Mk1 cells, which were Ia+ and migrated specifically toward MCF-c; and Mm1 cells, which were Ia- and migrated specifically toward MCF-a and -b. These differences show the heterogeneity of the biologic activities of the MCFs in the presence of cell line cells. M-1 cells, blast cells, when grown in continuous culture, migrated toward none of the MCFs . Upon differentiation to mature macrophage-like cells in conditioned medium (M+1 cells), however, they migrated to MCF-a, -b, and -c and the experimental evidence points to the possibility that M+1 cells are separated into subpopulations on the basis of their chemotactic response. Cytotoxic treatment of M+1 cells with anti-Ia antisera resulted in the specific decrease of activity toward MCF-c. Furthermore, MCF-c attracted Ia-positive M+1 cells, while MCF-a and -b attracted Ia-negative M+1 cells. Thus, our results indicate the existence of two migrating subpopulations of M+1 cells with specificities for MCF-a, and -b and for MCF-c, respectively. The data suggest that MCF-c attracts Ia-bearing accessory macrophages and MCF-a and -b attract Ia-negative macrophages in the DHR.

Appearance of chemotactic responsiveness to elastin peptides by developing fetal bovine ligament fibroblasts parallels the onset of elastin production

We studied chemotaxis to elastin peptides by bovine ligamentum nuchae fibroblasts to determine whether there is a developmental association between chemotactic responsiveness to elastin and expression of the elastin phenotype. Undifferentiated ligament cells demonstrate chemotactic responsiveness to platelet-derived growth factor and fibronectin, known chemoattractants for fibroblasts, but do not show chemotaxis to elastin peptides. After matrix-induced differentiation, however, young cells display a positive chemotactic response to elastin that persists even after the cells are removed from the matrix substratum. Matrix-induced chemotaxis to elastin could be inhibited selectively by incorporation of bromodeoxyuridine into DNA of undifferentiated cells before (but not after) contact with inducing matrix. These results show that the appearance of chemotaxis to elastin peptides parallels the onset of elastin synthesis and suggests that the acquisition of chemotactic responsiveness to elastin and expression of the elastin phenotype are affected by the same inducing elements or processes and may be closely coupled in development.

Localization of a chemotactic domain in human thrombin

The cyanogen bromide fragment CB67-129 of human prethrombin 1, corresponding to residues 54-116 of the thrombin B chain, is a potent chemotaxin for human peripheral blood monocytes and the murine macrophage like cell line, J774. Both of these cell types have been shown to respond chemotactically to alpha-thrombin and iPr2P-alpha-thrombin. Effective concentrations for stimulating directed cell movement with the fragment vary from 10(-11) to 10(-7) M. Moreover, CB67-129 and its parent protein compete for the same chemotactic receptor site. Fragment CB67-129, representing residues 54-116 of the human thrombin B chain sequence, contains a nine-residue insertion ("loop B") that is absent in homologous sequences derived from the closely related proteases chymotrypsin and trypsin. Unlike iPr2P-alpha-thrombin, iPr2P derivatives of these latter enzymes possess little or no chemotactic activity, suggesting a relationship between the insertion sequence and thrombin chemotactic activity. The loop B sequence is unique insofar as it contains all of the carbohydrate moieties known to reside in alpha-thrombin. However, chemotactic activity is only minimally reduced subsequent to hydrolysis by both neuraminidase and beta-galactosidase, indicating that receptor recognition and stimulated cell movement are mainly a function of structure of the cyanogen bromide derived fragment rather than of asparagine-linked carbohydrates.

The appearance of phospholipase activity in the human macrophage-like cell line U937 during dimethyl sulfoxide induced differentiation

The human histiocyte cell line, U937, with monocyte characteristics, can be induced to differentiate into macrophage-like cells when exposed to growth medium containing 1.5% DMSO. Following three days of exposure, DMSO-treated but not control U937 cells can be stimulated to release endogenous arachidonic acid from their phospholipids. Maximum release of the unsaturated fatty acid occurs with 10 microM calcium ionophore in the presence but not in the absence of exogenously added calcium ion. In addition, DMSO-treated but not control U937 cells exhibit phospholipase activity when exposed to human IgG and then anti-human immunoglobulin. These data suggest that with respect to arachidonic acid metabolism U937 cells differentiate into functional macrophage-like cells when exposed to DMSO.

Transductional mechanisms of chemoattractant receptors on leukocytes

Phagocytic leukocytes contain receptors for chemoattractants on their cell surface. Binding of chemotactic factors to these receptors initiates a number of coordinated cellular responses in a strict dose-dependent manner. Motility-related functions such as shape change, cytoskeletal rearrangement, and chemotaxis are stimulated by relatively low doses of chemoattractants, while microbiocidal or cytotoxic functions (i.e., secretion of lysosomal enzymes or stimulation of the respiratory burst), require approximately 10- to 50-fold higher concentrations of these agents. The receptor for oligopeptide chemotactic factors on leukocytes has provided an important model for the study of stimulus-response coupling in phagocytic cells. This receptor on human polymorphonuclear leukocytes exists in two affinity states that are partially interconvertible. Guanine nucleotides regulate the convertibility between a portion of the high- and low-affinity states, thereby suggesting that a nucleotide regulatory protein allosterically modifies receptor affinity and participates in its transduction mechanisms. A fraction of the high-affinity receptors in PMN membranes is not subject to guanine nucleotide regulation and appears to be formed by prior exposure of the receptors to specific agonists. This high-affinity form of the oligopeptide chemoattractant receptor is rapidly internalized at 37 degrees C, and its formation may be dependent on aggregation or covalent modification of the receptor. The chemotaxis and microbiocidal functions of PMNs can be divergently manipulated by pharmacological agents indicating that the transduction mechanisms for these two types of processes are independently regulated. Aliphatic alcohols at doses that induce mild fluidization of PMN membranes increase the average affinity of the chemoattractant receptor and enhance chemotactic functions but markedly depress lysosomal enzyme secretion and the respiratory burst. In contrast, polyene antibiotics that bind to membrane cholesterol lower the receptor's affinity and depress chemotactic functions but enhance secretion of specific granule enzymes. In addition, transmethylation reactions mediated by S-adenosyl-methionine appear to regulate receptor affinity. When such reactions are blocked pharmacologically, the oligopeptide receptor on macrophages reverts to a lower average affinity form and is ineffective in transducing chemotactic as well as microbicidal functions.(ABSTRACT TRUNCATED AT 400 WORDS)

Binding of 125I-insulin to the human histiocytic lymphoma cell line U-937: effect of differentiation with retinoic acid

The human histiocytic lymphoma line U-937 consists of cells having characters of immature monocytes. We have demonstrated that these cells possess highly specific insulin receptors with binding properties similar to that found for mature human blood monocytes. 125I-insulin binding increased progressively with time to reach a maximum at 90 min at 22 degrees C and was proportional to the number of cells in the incubation medium. Insulin degradation as assessed by TCA precipitation was negligible. Scatchard analysis of the binding data was curvilinear and the total number of insulin binding sites was around 13,500. The average affinity profile gave an 'unoccupied site' affinity constant of 1.34 nM-1. When the U-937 cells were induced to differentiate into morphologically and functionally monocyte-like cells, after incubation with retinoic acid, the total number of binding sites decreased significantly with no change in the affinity of the hormone for its receptor.

Effect of membrane fluidizers on the number and affinity of chemotactic factor receptors on human polymorphonuclear leukocytes

Chemotaxis by leukocytes appears to be initiated by the binding of chemo-attractants to specific cell surface receptors. In other biological systems, the affinity and functional activity of membrane receptors are regulated by the local microviscosity. The present studies were undertaken to determine if the number and/or affinity of chemotactic factor receptors expressed on human polymorphonuclear leukocytes were similarly affected. Aliphatic alcohols and cis-vaccenic acid, agents known to decrease membrane microviscosity, were studied for their effects on the binding of the radiolabeled chemoattractant f-Met-Leu-[3H]Phe to human polymorphonuclear leukocytes. Butanol and propanol increased the number of f-Met-Leu-[3H]Phe binding sites approximately 1.5 fold. More dramatically, these same agents enhanced the affinity of the receptor by ten-fold, without affecting the specificity of the receptor. Similarly, cis-vaccenic acid enhanced both the number and affinity of this chemotactic factor receptor on human polymorphonuclear leukocytes contain cryptic receptors for the N-formylated peptide chemotactic factors, but more importantly that the affinity of these receptors can exist in more than one state and can be modulated by membrane microviscosity. Alterations of membrane fluidity in leukocytes during chemotaxis may be an important mechanism for regulating their sensitivity to chemoattractants.

Induction of selective biological responses to chemoattractants in a human monocyte-like cell line

The availability of monocyte cell lines that can be induced to differentiate in a predictable fashion can provide important tools for the study of the biochemical mechanisms of specific cellular responses. The U937 human monocyte cell line was previously shown to differentiate into chemotactically responsive cells when incubated with supernatants of lectin-stimulated lymphocytes (conditioned medium). Considering the heterogeneous nature of stimulated lymphocyte supernatants, attempts were made to identify well-defined agents that could reproducibly induce U937 cell differentiation. Both dimethyl sulfoxide and dibutyryl cAMP induced expression of receptors for the N-formylated oligopeptide chemoattractants in U937 cells. Unstimulated U937 cells contained no detectable receptors. After cells were exposed to 1 mM dibutyryl cAMP, 1.3% dimethyl sulfoxide, or 5% conditioned medium for 72 h, the average number of oligopeptide chemoattractant receptors per U937 cell was 33,000, 4,000, and 3,400, respectively. Specific binding proteins for the chemoattractants were identified by covalent affinity labeling on the differentiated U937 cells as well as on normal human monocytes. Cells exposed to conditioned medium responded chemotactically, secreted lysosomal enzymes, and formed superoxide anion when incubated with the chemoattractant. Treatment of U937 cells with dibutyryl cAMP resulted in the most reproducible and rapid increase in the number of chemoattractant receptors as well as in chemotactic responsiveness. The receptors on dibutyryl cAMP-treated cells and on dimethyl sulfoxide-treated cells initiated chemotaxis and lysosomal enzyme secretion in response to chemoattractants, but not the formation of superoxide anion. These findings demonstrate that development of the chemotactic and respiratory burst functions during the differentiation of a monocyte-like cell line can occur independently.

Interferon-induced differentiation of U937 cells. Comparison with other agents that promote differentiation of human myeloid or monocytelike cell lines

Effects of human fibroblast (beta) or leukocyte (alpha) interferon (IFN) on differentiations of a human histiocytic lymphoma-derived cell line (U937) or promyelocytic leukemia-derived cell line (HL-60) were studied. When cultured with beta-IFN (400-1,000 U/ml), U937 cells showed gross morphologic and microscopic changes consisting of clumping, increased cytoplasmic-to-nuclear ratio, enhanced prominence of cytoplasmic granules, and membrane ruffling. After culture with beta-IFN, the number of U937 cells reactive with B43.4.1 monoclonal antibody, which is specific for human monocytes, natural killer cells, and neutrophils, increased from less than 10% of U937 cells to 47% beta-IFN treatment also enhanced antibody-dependent cellular cytotoxicity against chicken erythrocytes by U937 cells. The same morphologic, phenotypic, and functional changes were also observed when U937 were treated with recombinant or natural alpha-IFN. The effects of alpha-IFN were totally abolished by anti-alpha-IFN serum. In contrast, HL-60, which differentiates toward cells of the monocyte lineage in response to phorbol 12-myristate 13-acetate (based on the above criteria), and toward granulocytes in response to dimethyl sulfoxide, did not differentiate when cultured with alpha- or beta-IFN. No consistent relationship between induction of differentiation and changes in phospholipid methylation were observed.

Endocytosis by the mononuclear phagocyte system and autoimmune disease

The mononuclear phagocyte system, formerly called the reticuloendothelial system, is an important element in basic immunology, cell biology, and clinical disease. Secretory products participate in inflammation and immunoregulation. Endocytosis mediated by specific receptors for immunoglobulin and complement or by other opsonins is important in removal of damaged self or foreign particles. The ability to assess receptor-specific endocytosis has led to the recognition of Fc-receptor dysfunction in certain autoimmune diseases. This defect in membrane receptor function, whether inherited or acquired, may be important in the pathogenesis of these diseases.

Physiochemical properties of polymorphonuclear leukocyte surface structures associated with the f-Met-Leu-Phe receptor

Surface property changes of polymorphonuclear leukocytes (PMNL) as a result of development of functional receptors to f-Met-Leu-Phe and as a result of f-Met-Leu-Phe binding have been studied by aqueous biphasic partitioning of the cells in systems of dextran and polyethylene glycol (PEG) with part of the PEG exchanged for positively charged or hydrophobic PEG. The Phe was associated with increased exposure of hydrophobic surface structures as well as of negatively charged groups on the PMNL surface. Binding of f-Met-Leu-Phe to the PMNL surface receptors caused hiding of hydrophobic and charged structures, indicating that these properties are of importance in the interaction between PMNL and the chemotactic peptide.

Tissue factor-like activity of the human monocytic tumor cell line U937

Undisrupted cells of the human monocytic tumor cell line U937 have procoagulant activity that is Ca2+ dependent and is not demonstrable in Factor VII or Factor X deficient plasma. Furthermore, U937 cells when incubated with purified human Factor VII in the presence of Ca2+ and then repeatedly washed promoted coagulation of Factor VII deficient plasma in the absence of added tissue factor. Culture with endotoxin increased the procoagulant activity of U937 cells approximately 5-fold. In separate experiments, exposure to lymphokines obtained from phytohemagglutinin-stimulated lymphocytes enhanced the procoagulant activity of U937 cells 4 to 110-fold. Other cell lines (of myeloid and lymphoid origin) tested lacked the procoagulant activity found in U937 cells. These results indicate that the constitutive tissue factor-like activity of U937 cells resembles that of normal activated human monocytes.