Interaction of Bacillus Calmette--Guérin-activated macrophages and neoplastic cells in vitro. I. Conditions of binding and its selectivity

Mainstream and sidestream cigarette smoke condensates suppress macrophage responsiveness to interferon gamma

Sidestream smoke evolves from the smoldering end of a cigarette while the smoker is not puffing, and contributes substantially to environmental tobacco smoke (ETS). In contrast, main stream smoke emerges from the butt end of the cigarette and is mainly inhaled by the smoker. This study was performed to compare the effects of short-term exposure to cigarette smoke condensates prepared from sidestream (CSC-SS) and mainstream cigarette smoke (CSC-MS) on macrophage basal metabolism and responsiveness to two different stimuli, bacterial lipopolysaccharide (LPS) and interferon gamma (IFNgamma). Despite their generation at different temperatures and their different chemical composition, CSC - SS and CSC - MS had similar effects on macrophages. Both enhanced macrophage basal metabolism and responsiveness to LPS. Macrophage responsiveness to IFNgamma, assessed by their expression of four functional capacities, was suppressed by both CSC-SS and CSC-MS. The four assessed IFNgamma-inducible functional capacities were: enhanced phagocytosis of immuoglobulin-opsonized sheep red blood cells, TPA-induced peroxide production, class II major histocompatibility complex expression, and nitric oxide synthesis with LPS co-stimulation. The effects of CSC - SS and CSC - MS were similar qualitatively; they differ quantitatively in some cases, with CSC-MS generally effective at lower concentrations (expressed as cigarette-equivalents) than CSC-SS. Considering dilution of sidestream smoke in room air and loss during passage through the respiratory system, we expect to deliver the maximal dose to lung macrophages in situ only in rooms dense with smokers. However, only a fraction of the maximal dose can partially suppress induction of some functions, such as nitric oxide production and MHC expression. Macrophages play critical roles in tissue modeling during development. Of particular concern are neonates, whose organs are still undergoing growth and development, and are therefore susceptible to impaired development. If involuntary exposure to ETS hinders induction of macrophage functional capacities by cytokines, then development of the lungs and perhaps other organs would be impaired. In general, since macrophages are potent effectors and regulators of immunity, impairment of their responsiveness to cytokine must disrupt the proper functioning of the immune system.

Immunotoxicology of cigarette smoke condensates: suppression of macrophage responsiveness to interferon gamma

We have investigated systematically the effects of short-term exposure to main stream cigarette smoke condensates (CSC-MS) on basal and inducible functional capacities of murine peritoneal exudate macrophages. Macrophages treated with CSC-MS form granules that fluoresce orange under blue excitation, consistent with the speculation that they are polycyclic aromatic hydrocarbons (PAH). CSC-MS selectively suppressed interferon gamma (IFN gamma) induction of four macrophage functional capacities: enhanced phagocytosis of immunoglobulin-opsonized sheep red blood cells, TPA-induced H2O2 production, class II major histocompatibility complex expression, and nitric oxide synthesis. In contrast, two macrophage functions that are not induced by IFN gamma, basal electron transport and LPS-induced TNF alpha production, were enhanced by treatment with CSC-MS. These results suggest that the suppressive effects of CSC-MS on macrophage responsiveness were selective and were not due to nonspecific inhibition of general functions such as RNA or protein synthesis. Since macrophage responsiveness to IFN gamma can result in induction of functional capacities that are fundamental to immunity, the data suggest that CSC-MS maybe deleterious to the general health of the smoker.

A possible mechanism by which dietary fat can alter tumorigenesis: lipid modulation of macrophages function

It has been known for at least 20 years that fatty acids can alter immune functions in vitro. More recently we have begun to understand the role that dietary fats play in immunity [formula: see text] and specifically how they may alter macrophage function. In the future it will be important not simply to redefine that fatty acids can alter select macrophage functions but to understand the mechanisms by which that occurs. Whether the same or different mechanisms are operational for those functions that are altered by dietary fat remains to be determined. Nevertheless, tumoricidal responses can be modified depending on the fatty acids in the diet. Hopefully, these recent observations will expand our understanding of how lipids regulate macrophage tumoricidal function and thus, might lead to new insights of how dietary fat may be manipulated to affect breast tumor regression.

Effects of fine and ultrafine sulfuric acid aerosols in guinea pigs: alterations in alveolar macrophage function and intracellular pH

Acidic sulfate is the most toxicologically important sulfur oxide which exists in the ambient air. To determine if particle size influences toxic effects of sulfuric acid, we investigated the effects of sulfuric acid aerosols of two different sizes on biochemical and cellular parameters of bronchoalveolar lavage fluid from exposed guinea pigs. Guinea pigs were exposed to fine (mass median diameter, 0.3 micron), and ultrafine (mass median diameter, 0.04 micron) sulfuric acid aerosols at 300 micrograms/m3 for 3 hr/day. The animals were euthanized immediately and 24 hr after 1 and 4 days of exposure and lungs were lavaged. Elevated beta-glucuronidase, lactate dehydrogenase activities, and total protein concentration as well as decreased cell viability were observed in the lavage after a single exposure to sulfuric acid aerosols of both sizes. These alterations were small, though statistically significant, and transient. No alteration in these parameters was observed after 4 days of exposure to acid aerosols. In contrast, sulfuric acid-induced alterations in alveolar macrophage function were more pronounced and longer lasting. Immediately after a single exposure to fine acid, there was a 2.7-fold increase in the spontaneous tumor necrosis factor (TNF) release over that in the control group while endotoxin-stimulated TNF release was increased by 2.2-fold. In addition, acid aerosols of both sizes increased the TNF release from macrophages after 4 days of exposure, although there was no clear temporal pattern of induction or recovery. Furthermore, immediately after 4 days of exposure to either fine or ultrafine acid, the amount of H2O2 that could be induced from baseline production by alveolar macrophages was 2.2-fold higher than that of the controls. The phagocytic function of macrophages was also altered by exposure to sulfuric acid aerosols. Twenty-four hours after single or multiple exposure, fine acid enhanced (as high as 78% above control) the in vitro phagocytic activity of alveolar macrophages while ultrafine acid depressed the phagocytic capacity (as much as 50% below that in the control). In addition to these biochemical parameters and cellular functions, we also measured the intracellular pH (pHi) of macrophages harvested after exposures to these acid aerosols using a pH-sensitive fluorescent dye. The resting pHi was depressed after a single exposure to both acid aerosols. The depression in pHi persisted 24 hr after ultrafine acid exposure.(ABSTRACT TRUNCATED AT 400 WORDS)

Activation of macrophages for ADCC in vitro: effects of IL-4, TNF, interferons-alpha/beta, interferon-gamma, and GM-CSF

Macrophages in varying states of activation differ in their ability to perform antibody-dependent cellular cytotoxicity (ADCC) and antibody-independent macrophage-mediated tumor cytotoxicity (MTC). To define further the activation requirements for macrophages to perform various cytolytic functions, we stimulated peptone-elicited peritoneal macrophages, which are only poorly cytolytic, with one of a panel of cytokines and then quantified three distinct cytolytic capacities. The peptone-elicited macrophages, after stimulation with IFN-alpha/beta, IL-4, or TNF, had increased ability to perform both the rapid and slow variants of ADCC but not to perform MTC. Stimulation with high doses of IFN-gamma, however, increased the macrophages' ability to perform all three cytolytic functions. GM-CSF had no effects on any cytolytic capacity. The effects of IL-4, TNF, IFN-gamma, and IFN-alpha/beta on the macrophages' capacity for both forms of ADCC were dose-dependent. IFN-gamma and IFN-alpha/beta increased the macrophages' capacity for both variants of ADCC within 4 hr of treatment, whereas IL-4 and TNF did so only after prolonged treatment. These results suggest that three forms of macrophage cytolytic capacity can be enhanced by cytokine treatment but that the requirements for enhancing each of the three forms of macrophage cytolytic capacity differ.

Cytokine activation of murine macrophages for in vitro killing of Entamoeba histolytica trophozoites

Macrophage-mediated effector mechanisms against the protozoan parasite Entamoeba histolytica were studied. Unstimulated macrophages were inefficient at killing E. histolytica trophozoites in vitro and were killed by the trophozoites. Conversely, immature cells of the mononuclear phagocyte lineage (promonocytes) were shown to display a strong spontaneous amebicidal activity. The acquisition of macrophage amebicidal activity following cytokine treatment was investigated. Gamma interferon, tumor necrosis factor alpha, and macrophage colony-stimulating factor 1, or combinations thereof, were shown to endow murine bone marrow-derived macrophages with significant amebicidal activity. Low doses of gamma interferon and tumor necrosis factor alpha and of gamma interferon and colony-stimulating factor 1 were shown to act synergistically in this phenomenon. This enhancement of amebicidal activity was shown to operate on bone marrow-derived macrophages, elicited peritoneal macrophages, and, to a much lesser extent, spleen macrophages. Although acquisition of amebicidal activity was associated with a strong respiratory burst, the addition of oxygen-free radical scavengers showed that the killing activity was approximately 45% H2O2 dependent. In addition, amebicidal activity by macrophages was shown to be contact dependent and was inhibited by 61% with the protease inhibitor tosyl lysyl chloromethyl ketone. Our results indicate that immunologic production of gamma interferon, tumor necrosis factor alpha, and colony-stimulating factor 1 could be important in the activation of macrophages for host defense against amebiasis and that promonocytes are strong effector cells against virulent amebae.

Effects of inhibitors of tumoricidal activity upon schistosomulum killing by activated macrophages

Larvae of the helminth parasite Schistosoma mansoni are efficiently killed in vitro by lymphokine-activated macrophages, leading to the hypothesis that these cells may participate in the effector mechanism of protective immunity against schistosomiasis. Larvacidal activity has also been demonstrated in the IC-21 macrophage cell line in the absence of a demonstrable respiratory burst, indicating that macrophages possess nonoxidative mechanisms of schistosomulum killing. In this study, we demonstrated that IC-21 larval killing was most effective when contact was allowed between cells and target. Nonoxidative larvacidal activity was prevented by protein synthesis inhibitors, by the inhibition of microtubule polymerization, and by tosyllysylchloromethylketone but not by other inhibitors or substrates of tryptic or chymotryptic protease activity. The addition of excess iron to the culture also prevented IC-21-mediated larval killing, suggesting that the production of an iron-binding molecule may be involved. In contrast, the addition of excess thymidine or arginine did not reverse macrophage larvacidal activity, nor did lysosomotropic agents that depress the activity of acid hydrolases. Under appropriate conditions of activation and surface membrane stimulation, IC-21 cells could be induced to release soluble cytotoxic factors retaining larvacidal activity. These observations provide insight into the mechanism of macrophage-mediated schistosome killing, in comparison to the cytotoxic mechanisms described in the better-studied tumoricidal models, and supply a basis for further biochemical investigation of macrophage function against a multicellular target.

Macrophage stimulation with some structurally related polysaccharides

The macrophage-stimulating properties of some structurally related polysaccharides were studied in vitro. When the polysaccharides were presented to the macrophages in a sterically fixed form, i.e. as microparticles, they induced the release of interleukin 1 (IL-1) from the macrophages. Microparticulate 1.3-beta-glucan (curdlan) induced nonspecific macrophage mediated tumour cell killing while 1.4-alpha-glucan (starch), 1.6-alpha-glucan (dextran), and 1.6-alpha-mannan were without effect. The corresponding soluble polysaccharides did not stimulate the macrophages. Kinetic studies showed that although IL-1 was released immediately after stimulation, the macrophages needed a time lag of several days to develop tumour cytotoxicity. The development of cytotoxicity paralleled binding of tumour cells to the macrophages. Resident and inflammatory peritoneal macrophages showed differences in their responses to the polysaccharides. Stationary, resident peritoneal macrophages stimulated by macroparticles secreted high levels of IL-1 but expressed a low cytotoxic activity, while newly recruited inflammatory macrophages released lower levels of IL-1 but readily killed the tumour cells. The influence of cyclo-oxygenase products on the IL-1 release and macrophage cytotoxicity was also investigated. When cyclo-oxygenase was blocked with indomethacin, a significantly higher release of IL-1, and then an increased cytotoxicity, were obtained with 1.3-beta-glucan stimulated macrophages. The results suggest that microparticulate polysaccharides may be useful for studies on the induction of macrophage differentiation and also for studies on nonspecific cellular immune responses in vitro and in vivo.

Quantitation of intercellular binding strength by disruptive centrifugation: application to the analysis of adhesive interactions between P815 tumour cells and activated macrophages

The cell binding assay described in the present paper provides a quantitative measurement of intercellular binding strengths between P815 mastocytoma cells and macrophages activated for cytotoxicity. Conjugates were submitted to a dislodgement force generated by centrifugation tending to remove radiolabelled probe cells from macrophages adhering to a glass support. Non-specific binding occurred between P815 cells and the glass support, but was negligible on siliconed coverslips. The adhesive interactions macrophage/glass were strong enough to resist up to about 1 X 10(-9) N, the maximal dislodgement force tested. Completion of conjugate formation was reached at 37 degrees C after 45 to 60 min and was inhibited at 4 degrees C or in Ca++-free medium. The strengths of intercellular bonds between P815 cells and macrophages varied from 7 X 10(-11) N (the minimal force applied) to more than 9 X 10(-10) N. No clear-cut separation between weak and strong interactions was observed when the centrifugation step was performed at 4 degrees C. In contrast, when centrifugation was carried out at 37 degrees C, a subpopulation of loosely bound tumour targets could be distinguished from more strongly bound P815 cells.

Disruption of oligosaccharide processing in murine tumor cells inhibits their susceptibility to lysis by activated mouse macrophages

The components of tumor cell surfaces that participate in the recognition and lysis of these cells by activated macrophages have not been identified. One plausible hypothesis is that these components are specific carbohydrate structures. As an initial test of this hypothesis, I have made use of the oligosaccharide processing inhibitors 1-deoxynojirimycin (dNM) and 1-deoxymannojirimycin (dMM). dNM is an inhibitor of the glucosidases involved in the initial steps of oligosaccharide processing. dMM inhibits mannosidase I. P815 cells incubated in the presence of 1-2 mM dNM for 24 hr synthesized mature glycoproteins that contained glucosylated high-mannose asparagine-linked oligosaccharides instead of complex forms. The glucosylated oligosaccharides were present in trypsin digests of the cell surface. The dNM treatment resulted in a diminution in the amount of surface galactose residues as evidenced by neuraminidase/galactose oxidase/NaB3H4 labeling of surface glycopeptides. It did not, however, inhibit protein synthesis or alter the surface polypeptide profile of the tumor cells. P815 and R1- cells incubated in the presence of 1-3 mM dNM for 24 hr were considerably less sensitive to lysis by interferon-gamma-activated macrophages than were cells incubated in control medium. At a dNM concentration of 3 mM, a 71% inhibition of P815 cell lysis was observed. Similarly, P815 and R1- cells incubated in the presence of 2 mM dMM were also less sensitive to macrophage-mediated lysis than were control cells. The inhibitors did not affect cell viability, growth, or gross morphology. These observations suggest that complex asparagine-linked oligosaccharides on tumor cell surfaces may participate in recognition and lysis by activated macrophages.

Activated macrophages demonstrate direct cytotoxicity, antibody-dependent cellular cytotoxicity, and enhanced binding of Naegleria fowleri amoebae

Macrophages activated in vivo by injection of Corynebacterium parvum or bacillus Calmette-Guérin caused direct cytolysis of the pathogenic free-living amoeba, Naegleria fowleri, in vitro. Amoebicidal activity was time and cell density-dependent but was not dependent on the presence of specific antibody. Antibody-dependent cellular cytotoxicity for amoebae was also expressed by activated macrophages. Resident and thioglycolate-elicited macrophages demonstrated low cytolytic activity under all conditions tested. From scanning electron microscopy it appears that the degree of target cell binding is directly related to the degree of cytolysis expressed by the macrophage populations. Cell-cell contact was required for cytolysis of amoebae by activated macrophages since cytolysis did not occur when contact was blocked by a porous filter. For each macrophage population, the levels of amoebicidal activity and tumoricidal activity were comparable.

Firm persistent binding between activated macrophages and tumor cells is not a prerequisite for the mediation of cytolysis

The present study seeks to reassess the roles of macrophage activation and persistent firm binding to tumor cells as a prerequisite for tumoricidal activity. To this end, macrophage effector populations from various tissues, expressing diverse functional activities, were made to interact in vitro with different suspension tumor cell lines. The resultant binding and cytolytic effector cell capacities were determined. Macrophage activation appears to be an absolute prerequisite for binding and for killing of tumor cells. Activated macrophages firmly bind and form clusters with D-12 rat fibrosarcoma cells, which are relatively resistant to macrophage-mediated tumoricidal action. In contrast, P-815 murine mastocytoma cells, highly susceptible to the lytic activity of macrophages, bind rather poorly with activated macrophages and do not form clusters. Since susceptible target cells are readily killed by activated rat macrophages in the absence of persistent firm contact, it appears that firm binding and killing are not causally related events.

A microassay for the rapid and selective binding of cells from solid tumors to mouse macrophages

A microassay was developed to study the rapid binding characteristics of murine macrophages activated by gamma interferon and muramyl dipeptide to adherent neoplastic or nonneoplastic target cells. The binding of tumor cells to both activated and nonactivated macrophages was time- and temperature-dependent, and independent of tumor cell type. Activated macrophages bound more tumor cells than nonactivated macrophages. The initial binding of macrophages to target cells did not necessarily lead to lysis. First, primed macrophages bound tumor cells but did not lyse them, and second, nonactivated macrophages bound nontumorigenic cells without subsequent lysis. The rapid binding assay described here could prove useful in investigating the recognition mechanism(s) between macrophages and tumor cells derived from solid primary and metastatic cancers.

A potential role for the extracellular matrix glycoprotein laminin in macrophage-tumor-cell interactions

Although cell surface molecules are thought to be involved in macrophage (MO)-tumor-cell recognition, the nature of these molecules remains unknown. In this study we have shown that the glycoprotein laminin may facilitate macrophage-tumor-cell binding. Macrophage binding to tumor cells was assessed by measuring the adherence of radiolabelled 3-MCA2 induced malignant fibrosarcoma cells to syngeneic peritoneal MOs. Addition of exogenous laminin promoted the binding of a weakly metastatic subline of these tumor cells by 31-68%. These weakly metastatic tumor cells express negligible endogenous cell-surface laminin but display specific cell-surface receptors for binding soluble laminin. Exogenous laminin promoted MO binding of these tumor cells whether it was present during the assay or whether the tumor cells were pretreated with the laminin. This increase in binding was blocked by anti-laminin antibody. In contrast, MO binding of a strongly metastatic variant of the same tumor was not enhanced by the addition of exogenous laminin. This highly malignant fibrosarcoma line already expressed endogenous cell-surface laminin. Since the MOs were found to specifically bind 125I-laminin, the interaction between laminin-bearing tumor cells and MOs may be mediated via a specific MO plasma membrane receptor. Thus, the expression of cell-surface laminin and its receptors on both tumor cells and MOs may provide a mechanism for promoting MO-tumor-cell binding.

Ultrastructural studies of the killing of schistosomula of Schistosoma mansoni by activated macrophages in vitro

Immunologically activated murine macrophages have been shown elsewhere to kill skin stage schistosomula of Schistosoma mansoni in vitro, in a manner analogous to the extracellular killing of tumour cell targets. In this study, the kinetics of the interaction between activated macrophages and larval targets and the resultant ultrastructural changes in parasite morphology that culminated in death have been analysed in detail. Unlike granulocyte-mediated schistosomular killing, macrophage-mediated cytotoxicity did not appear to be directed against the surface tissues of the parasite. Macrophages adhered only transiently following initiation of the cultures, yet changes in the subtegumental mitochondria and muscle cells of the larva were detected within the first hour of incubation. Progressive internal disorganisation followed rapidly, but the tegument and tegumental outer membrane remained intact, to form a 'shell' that maintained the general shape of the parasite. Such changes were recognised irrespective of whether the effector cell population comprised peritoneal macrophages activated by lymphokine treatment in vitro, or by infection with Mycobacterium bovis (strain BCG), or S. mansoni in vivo. That macrophages rather than contaminating granulocytes or lymphocytes, had mediated the observed damage was demonstrated by the use of a lymphokine treated macrophage cell line, IC-21. The observation that macrophage cytotoxicity is directed against internal organelles rather than the tegumental outer membrane of this multicellular target, may help to elucidate the general mechanism of extracellular killing by these cells.

Studies on the mechanism of macrophage cytotoxicity

The interactions with tumor target cells of resident and BCG-activated murine peritoneal macrophages (M phi) as well as of BCG-activated M phi additionally stimulated by a lymphokine-like factor were investigated in order to get some insight into the cytolytic process mediated by activated M phi. The lymphokine-like factor enhancing the cytotoxicity of BCG-activated M phi (MCF) was isolated and partially purified from cell-free fluid of rat Zajdela ascites hepatoma. M phi cytotoxicity was determined by a modified 51Cr release assay. Scanning and transmission electron microscopic findings suggested a two-step mechanism of target cell lysis: a first step of specific attachment of processes of M phi on the target cell surface and a second step with transport of lysosome-like vesicles to the target cells obviously with liberation of these vesicles in the immediate vicinity of target cells resulting in a local accumulation of cytolytic substances. This interpretation was supported by findings after treatment of interacting effector and target cells with amphotericin B and bestatin which substances were modifying M phi cytotoxicity. MCF caused only an augmentation of M phi cytotoxicity without qualitative differences to the cytolytic action of merely BCG-activated M phi.

Interaction of high or low metastatic related tumor lines with normal or lymphokine-activated syngeneic peritoneal macrophages: in vitro analysis of tumor cell binding and cytostasis

Peritoneal macrophages from normal DBA/2 mice were found to bind significantly more cells of a syngeneic low metastatic lymphoma line (Eb) than cells of a high metastatic variant (ESb) derived therefrom. These differences were observed in three different assays, at 4 degrees C and at 37 degrees C, and at various ratios of macrophages to tumor cells. Upon co-culture with normal macrophages, a tumor cytostatic effect was consistently observed with Eb but not with ESb tumor cells. Further experiments indicated that macrophages exerted their growth inhibitory effect via direct tumor cell contact. Pre-treatment of tumor cells with neuraminidase or pre-treatment of macrophages with lens culinaris lectin increased the numbers of macrophages binding Eb and ESb tumor cells. Addition of D-galactose or D-mannose at 50 mM concentration led to an increase of tumor cell binding and tumor cytostatic activity. Taken together, these results suggest (i) that carbohydrates play a role in tumor cell recognition by macrophages and (ii) that the differences observed between Eb and ESb tumor cells may be due to differences in the expression of carbohydrates. Pre-activation of the macrophages by lymphokine(s) led to a short increase in their tumor cell binding capacity. Lymphokine activation resulted in a strong but also short-lived increase of tumor cytostatic potential. This was effective against both the low and the high metastatic tumor line.

Extracellular cytolysis by activated macrophages: studies with macrophages on permeable membranes

Mouse peritoneal macrophages were allowed to adhere to discs cut from permeable membranes, then activated by incubation in lymphokine-rich supernates from ConA-stimulated spleen cells. Such filter-borne cultures of activated macrophages (AM) were cytotoxic for various target cells (Tc). The kinetics of the cytotoxic process could be monitored by removal of the filter-bound AM after increasing times of contact with Tc. Using 3 assay procedures to assess macrophage cytotoxicity, i.e. chromium-51 release, thymidine incorporation, and cloning inhibition, most of the damage to Tc was found to occur within 30 min to 2 h of interaction between the two cell types. The kinetics of the cytolytic effect were similar, whether Tc were in direct contact with AM or separated by the filter; thus cytotoxicity appeared to be mediated by a highly diffusible compound. Supernates of AM incubated with Tc for 1 to 4 h, but not of AM incubated alone, were toxic for Tc, suggesting that Tc provide a signal to AM, in the absence of which toxic intermediates fail to be released. Addition of catalase or peroxidase considerably reduced Tc destruction by AM, indicating that oxygen metabolites might play a role as mediators of AM cytotoxicity in the present experimental model.

Characterization of a monoclonal antibody defining a macrophage activation-specific cell surface antigen

Macrophages have been obtained from the peritoneal cavities of C57BL/6 mice following treatment with C. parvum, MVE-2, mineral oil, or thioglycollate. Cell populations were primarily composed of mononuclear phagocytes as determined by a latex bead uptake assay. Macrophages obtained from C. parvum or MVE-2 were activated as judged by enhanced cytostatic activity against two tumor cell target lines. Thioglycollate-elicited macrophages demonstrated much lower cytostatic ability. Rats were immunized with activated MVE-2 macrophages. Hybridomas were prepared by fusion with a non-secreting myeloma cell line followed by cloning. Cell supernates were selected on the basis of binding to activated but not elicited macrophages. The monoclonal antibody produced has been characterized by flow cytometry. The antibody does not react with syngeneic erythrocytes, thymocytes, or spleen cells. Reaction with thioglycollate macrophages is very low. Alternatively, intense binding is found on activated macrophages. This antigen which accompanies macrophage activation for tumor cell cytostasis is designated as macrophage activation antigen-1 (MAA-1). Several important physiological changes accompany the process of macrophage activation. For example, activated macrophages demonstrate enhanced microbicidal, phagocytic, secretory, and tumoricidal activity (for reviews see refs. 1,2). Concommitant alterations in cell surface properties have been observed. These include: (a) changes in surface morphology and spreading (3-5), (b) altered lipid and protein content (6,7), (c) decreases in 5'-nucleotidase activity and alkaline phosphodiesterase (8), increases in leucine aminopeptidase (8), decreases in mannose receptors (11,12), and antigen F4/80 (11), (d) increases in Ia antigens (11,12), and (e) increased tumor cell binding (13). These structural and functional modifications indicate that activated macrophages represent a unique class of functionally differentiated cells (9). Antigenic modifications accompanying macrophage differentiation are of special interest. Markers for specific macrophage classes might be useful in defining differentiation pathways, dissecting type-specific functional activities such as tumor cytotoxicity, and providing a means to identify macrophage subsets in heterogeneous cell populations. In the present work we have taken the first step in this direction by defining a cell surface macrophage activation antigen.

Binding and lysis of antibody-coated human erythrocytes by activated human monocytes

Human monocytes exposed to PHA-leukocyte-conditioned medium for 24 hr acquire markedly enhanced ADCC against antibody-coated human erythrocytes. Confluent monolayers of these activated monocytes were found to bind several fold the number of 51Cr-labeled antibody-coated erythrocytes as compared to monolayers formed from control monocytes (uncoated erythrocytes were not bound). The stoichiometry of this reaction indicated that activated monolayers bind approximately 3-5 erythrocyte targets per effector monocyte, whereas control monolayers bind less than 2. Bound target cells remain intact, affixed to the monocyte surface for up to 3 hr at 25 degrees C (they were not phagocytized); incubation at 37 degrees C resulted in both target cell adherence and 51Cr release suggesting that a proportion of target cells were lysed. A substantial fraction of target cells bound at 25 degrees C were lysed (activated greater than control monocytes) if the monolayers were warmed to 37 degrees C. These results indicate that target cell target cell binding can occur at both 25 and 37 degrees C, but lysis of bound targets requires incubation at 37 degrees C. Using this temperature distinction to examine binding and lysis independently, it was found that binding was abrogated by IgG Fc fragments, but could occur over a broad pH range (5-8), and in the presence of 2-deoxy-D-glucose, colchicine, and sodium azide. Lysis of bound targets, on the other hand, was blocked by inhibitors of glycolysis, microtubule/filament organization, cellular respiration, and serine esterase activity, as well as EDTA and low pH; lysis was unaffected by scavengers of extracellular H2O2 and superoxide radicals.

Antibody-dependent cytolysis (ADCC) of tumor cells by activated murine macrophages is a two-step process: quantification of target binding and subsequent target lysis

To analyze the antibody-dependent cell-mediated cytotoxicity (ADCC) reaction between tumor cells and activated murine macrophages in detail, it must be first determined if physical binding occurred between the two cell types. Over 15-20 min in vitro, antibody-coated HSB neoplastic targets became so firmly attached to the activated macrophages that they resisted removal with 4 vigorous washes. When a quantitative assay of binding was employed, attachment of tumor cells to activated macrophages was found to depend on the concentration of antibody and on the density of the macrophages. These two variables also determined the subsequent extent of cytolysis. Binding of antibody-coated targets by macrophages elicited with thioglycollate broth or activated by bacillus Calmette-Guerin (BCG) was comparable. Lysis by the activated macrophages, however, was far greater. Binding occurred at 4, 22, or 37 degrees C, while the subsequent lytic reaction occurred only at 37 degrees C. Thioglycollate broth effectively inhibited lysis but had no effect on binding. A porous filter placed between activated macrophages and targets resulted in abrogation of binding and lysis, even when antibody-coated targets were placed beneath the filters. When labeled, uncoated targets were added to cultures of macrophages in the presence of unlabeled antibody-coated targets, no lysis of the bystander (i.e., uncoated) targets was seen. The data suggest that ADCC is a multistep reaction, that vigorous physical binding of antibody-coated targets by activated macrophages is an initial and necessary step in ADCC, that such binding is not sufficient for ADCC, that such binding controls the selectivity of lysis in ADCC, and that the second step in ADCC results in target lysis.

Activation of macrophages for microbicidal and tumoricidal effector functions by soluble factors from EL-4, a continuous T cell line

Macrophages treated with culture fluids from EL-4 cells, a continuous T cell line, were activated to kill mKSA-TU-5 fibrosarcoma cells, amastigotes of Leishmania tropica, and schistosomula of Schistosoma mansoni. Active EL-4 factors eluted from Sephadex G-100 in two distinct regions: molecular weight 45,000 (activities induced killing of unrelated intracellular and extracellular targets) and molecular weight 23,000 (activities induced killing of extracellular targets only). These results confirm heterogeneity among activation signals for the induction of macrophage microbicidal and tumoricidal activities. Factors that induced cytocidal activity against extracellular tumor cells and schistosomula were distinct from those that induced destruction of intracellular amastigotes.

Role of macrophage lipids in regulating tumoricidal activity

Peritoneal macrophages (M phi) from mice became cytotoxic after incubation with lymphokine (LK); tumoricidal activity was evident with M phi treated with LK for 4 hr, became maximal after 8-12 hr of incubation, and decreased to control levels by 24-36 hr. LK induced marked changes in M phi lipid composition: cellular content of cholesterol (CHOL) and polyunsaturated fatty acid (UFA) content of cellular lipids (especially 18:3) increased two- to threefold after 8 hr when the cells showed maximal tumoricidal activity. Cellular lipid and fatty-acid content returned to control levels by 24 hr when the M phi had lost tumoricidal activity. These changes were not observed with equal numbers of M phi cultured in control supernatants. To analyze the role of CHOL and UFA in M phi tumor cytotoxicity, casein-induced peritoneal M phi were enriched in CHOL or linolenic acid (18:3) and then tested for their ability to kill 1023 tumor cells. The 18:3-enriched cells were markedly tumoricidal, whereas controls cultured in delipidized medium alone or enriched with saturated fatty acid (18:0) were not cytotoxic. CHOL-enriched M phi were not tumoricidal; indeed, these cells were inhibited in their killing after treatment with LK compared to M phi cultured in delipidized medium with LK alone. The effects of 18:3 and CHOL enrichment of the M phi on their metabolic status, inflammatory function, and tumor cell-binding capacity were tested. The 18:3-enriched M phi were depressed in their ability to synthesize protein and in phagocytic activity compared to controls; these cells showed a transient increase in superoxide release. M phi cultured with 18:3 for 48 hr were also cytotoxic for P815 tumor cells, but did not show an enhanced capacity for P815 binding compared to controls. CHOL-enriched M phi were similar to control cells in their protein synthesizing and phagocytic activities; these cells also showed an early transient increase in superoxide release. CHOL-enriched M phi were not cytotoxic for P815 cells, but bound the tumor cells more readily than did the 18:3-enriched M phi. The data suggest that endogenous levels of 18:3 and CHOL can regulate M phi tumor cytotoxicity, but not through regulation of M phi protein synthesis, oxidative metabolism, or augmented capacity for tumor target binding.

Selective inhibition by monosaccharides of tumor cell cytotoxicity mediated by mouse macrophages, macrophage-like cell lines, and natural killer cells

A series of monosaccharides were tested for their ability to inhibit the effector phase of macrophage-mediated cytolysis against two susceptible murine tumor target cells, L5178Y and RL male I. Two monosaccharides, D-mannose and N-acetyl-D-galactosamine, were found to decrease cytotoxicity consistently in a dose-dependent manner. However, D-mannose preferentially inhibited lysis of RL male I target cells with little effect on lysis of L5178Y target cells, while the reverse was found with N-acetyl-D-galactosamine. Neither monosaccharide interfered with the activation of macrophages by polyinosinic:polycytidylic acid. Natural killer cell activity was decreased by a 25 mM concentration of D-mannose but not by N-acetyl-D-galactosamine, although increasing concentrations of N-acetyl-D-galactosamine were inhibitory. Neither monosaccharide affected cytotoxicity by alloimmune T cells. Cytotoxicity of macrophage-like cell lines against tumor target cells was also decreased by monosaccharides but the pattern of inhibition was different from that seen with activated macrophage effector cells. Both D-mannose and N-acetyl-D-galactosamine inhibited glucose oxidation by activated macrophages but only D-mannose significantly decreased protein synthesis of activated macrophages. These results indicate that monosaccharides can inhibit macrophage-mediated cytotoxicity in a selective manner with the pattern dependent on the tumor target cell used in the assay.

Selective targeting of magnetic albumin microspheres to the Yoshida sarcoma: ultrastructural evaluation of microsphere disposition

Magnetic albumin microspheres (1 micron average diameter) were selectively targeted to subcutaneous solid Yoshida sarcoma tumors (average size 450 mm2) in Holtzman rats. This was accomplished by placing an external magnet adjacent to the tumor while the microspheres were infused. Microspheres contained ultra-fine particles of Fe3O4 and no drug (placebo). Placebo microspheres were used due to the previously demonstrated rapid tumoricidal effect of targeted low-dose doxorubicin microspheres. Animals were killed 10 min, 60 min, 30 min, 24 hr and 72 hr after microsphere administration and tumors were examined by transmission electron microscopy to determine the in vivo disposition of the magnetically targeted microspheres. Using placebo microspheres, we have demonstrated microspheres endocytosed in endothelial cells as early as 10 min after infusion. By 30 min microspheres can be seen in the extravascular compartment, sitting adjacent to tumor cells and occasionally in tumor cells. By 24 hr the majority of microspheres have been endocytosed by tumor cells. Microspheres were still observed within tumor cells as late as 72 hr after administration. The rapid extravasation and cellular uptake of magnetically focused microspheres explains the extremely rapid tumoricidal effect previously observed when doxorubicin-containing microspheres were targeted to the tumor.

Human monocyte mediated cytotoxicity to K-562 cells: a freeze-fracture-, scanning- and thin section electron microscopic study

The structural features of "natural"human monocyte-mediated cytotoxicity towards K-562 leukemia cells in vitro have been examined. Human monocytes bound K-562 cells firmly and mediated a slow cytolysis of the leukemia cells. Monocyte binding of target cells was shown to be trypsin sensitive. Freeze-fracture and thin section electron microscopy revealed that effector and target cells were separated by a irregular space larger than 20 nm. There was no evidence for the involvement of specialized membrane junctions or organelle transfer between monocytes and target cells. Scanning electron microscopy revealed that K-562 cells bound to monocytes progressively lost their microvilli. This process started in the membrane areas close to the effector-target cell interaction. The results suggest that binding of target cells by monocytes followed by action of short-range soluble cytotoxic mediators may be the mechanism for the monocyte-mediated cytotoxicity towards K-562 cells.

Binding of bacillus Calmette-Guérin-activated macrophages to tumor targets. Selective inhibition by membrane preparations from homologous and heterologous neoplastic cells

The binding of tumor cells by activated macrophages is an initial and necessary event in the cytolysis of these targets. The data here indicate that membrane preparations from RL sigma 1 leukemia targets, EL-4 lymphoma targets, and P815 mastocytoma targets each inhibited binding of its homologous target to bacillus Calmette-Guérin (BCG)-activated murine macrophages in a dose-dependent fashion. Similar amounts of membrane from lymphocytes did not alter binding of the three neoplastic target to BCG-macrophages. Membranes of the three targets also inhibited binding of the heterologous neoplastic targets. Inhibitory activity of membrane preparations from P815, EL-4, and RL sigma 1 targets could be adsorbed by incubation of limiting concentrations of the membrane preparations with BCG-activated macrophages but not with thioglycollate broth-elicited macrophages. Exposure of BCG macrophages to membrane preparations from RL sigma 1, FL-4, or P815 targets inhibited subsequent cytolysis of the three targets. Inhibitory activity was increased in preparations enriched for plasma membrane. The data suggest that binding of three murine, nonadherent neoplastic targets to BCG-activated murine macrophages is mediated, in part, by recognition structures present within the plasma membranes of the three targets.