Macrophage deactivation. Altered kinetic properties of superoxide-producing enzyme after exposure to tumor cell-conditioned medium

Deactivation of the respiratory burst of human and murine macrophages by lipopolysaccharide is a receptor mediated effect independent from autocrine mechanisms

Endotoxin blunts secretion of reactive oxygen intermediates by macrophages. Because transforming growth factor β (TGFβ) or interleukin 10 (IL-10) were shown to deactivate macrophages, and are secreted by macrophages in response to LPS, we sought for autocrine mechanisms of macrophage deactivation by endotoxin. TGFβ did not deactivate the respiratory burst of human blood-derived and resident or thioglycollate-induced murine peritoneal macrophages. According to previous reports, suppression of H202 secretion by TGFβ was restricted to periodate-elicited murine peritoneal macrophages.

In contrast to TGFβ, IL-10 deactivated systems producing reactive oxygen intermediates in human blood-derived human macrophages, but neither anti-TGFβ1 nor anti-IL-10 antibodies restored LPS-mediated deactivation of macrophages.

Supernatants from LPS-treated human blood-derived macrophages could not confer deactivation to homologous macrophages.

Deactivation by LPS required the presence of serum proteins and appeared to be mediated by the CD14 antigen-related LPS receptor, because anti-CD14 antibody and IL-4, which downregulates CD14, antagonized the LPS effect.

Taken together, these observations indicate that the suppressive effect of LPS on the respiratory burst of macrophages is lipid A receptor-dependent, and results in a direct deactivation response of the cell without mediation by autocrine mechanisms.

TNF-Mediated Restriction of Arginase 1 Expression in Myeloid Cells Triggers Type 2 NO Synthase Activity at the Site of Infection

Neutralization or deletion of tumor necrosis factor (TNF) causes loss of control of intracellular pathogens in mice and humans, but the underlying mechanisms are incompletely understood. Here, we found that TNF antagonized alternative activation of macrophages and dendritic cells by IL-4. TNF inhibited IL-4-induced arginase 1 (Arg1) expression by decreasing histone acetylation, without affecting STAT6 phosphorylation and nuclear translocation. In Leishmania major-infected C57BL/6 wild-type mice, type 2 nitric oxide (NO) synthase (NOS2) was detected in inflammatory dendritic cells or macrophages, some of which co-expressed Arg1. In TNF-deficient mice, Arg1 was hyperexpressed, causing an impaired production of NO in situ. A similar phenotype was seen in L. major-infected BALB/c mice. Arg1 deletion in hematopoietic cells protected these mice from an otherwise lethal disease, although their disease-mediating T cell response (Th2, Treg) was maintained. Thus, deletion or TNF-mediated restriction of Arg1 unleashes the production of NO by NOS2, which is critical for pathogen control.

Melanoma-derived conditioned media efficiently induce the differentiation of monocytes to macrophages that display a highly invasive gene signature

The presence of tumor-associated macrophages (TAMs) in melanomas is correlated with a poor clinical prognosis. However, there is limited information on the characteristics and biological activities of human TAMs in melanomas. In this study, we developed an in vitro method to differentiate human monocytes to macrophages using modified melanoma-conditioned medium (MCM). We demonstrate that factors from MCM-induced macrophages (MCMI-Mφ) express both M1-Mφ and M2-Mφ markers and inhibit melanoma-specific T-cell proliferation. Furthermore, microarray analyses reveal that the majority of genes up-regulated in MCMI-Mφ are associated with tumor invasion. The most strikingly up-regulated genes are CCL2 and MMP-9. Consistent with this, blockade of both CCL-2 and MMPs diminish MCMI-Mφ-induced melanoma invasion. Finally, we demonstrated that both MCMI-Mφ and in vivo TAMs express the pro-invasive, melanoma-associated gene, glycoprotein non-metastatic melanoma protein B. Our study provides a framework for understanding the mechanisms of cross-talk between TAMs and melanoma cells within the tumor microenvironment.

Antibodies directed to antigens secreted by murine epithelioid macrophages modulate BCG-induced granulomata

The authors have previously shown that epithelioid cells isolated from mice secrete a factor, called macrophage deactivating factor (MDF), that promptly deactivates superoxide release by activated macrophages and neutrophils. In this paper some biological properties of a polyclonal rat antiserum directed to MDF and other substances secreted by these cells are described. The immunoglobulin fraction of this antiserum reacted, by immunocytochemical methods, with epitopes in the cell membrane of macrophages adherent to coverslips subcutaneously implanted for 14 days; but not for 5 days. It also reacted with antigens within and outside cells in BCG-induced granulomas. This antiserum blocked completely the macrophage deactivating activity of epithelioid cell culture supernatants. Anti-IL-10 monoclonal antibody, did not block MDF activity. The administration of the immunoglobulin fraction from immunized rats to C₅ deficient mice bearing BCG-induced granulomatas in the footpad, significantly reduced the size of the lesions. A marked necrosis of inflammatory cells and mononuclear cells phagocyting debris of necrotic cells were observed in these lesions.

Expression of NADPH oxidases and enhanced H(2)O(2)-generating activity in human coronary artery endothelial cells upon induction with tumor necrosis factor-alpha

Tumor necrosis factor (TNF)-alpha, which potentiates reactive oxygen species (ROS) generation, is crucial for the development of coronary arteritis and aneurysm in Kawasaki disease. We hypothesized that vascular NADPH oxidase (Nox) enzymes participate in the TNF-alpha-triggered endothelial damage through elevating ROS generation. Thus, we herein examine the expression of Nox enzymes in human coronary artery endothelial cells (HCAEC) and the effects of TNF-alpha on Nox-mediated ROS generation. We show that HCAEC in culture spontaneously generate H(2)O(2) at basal level (0.53 nmol/min/mg protein). In searching for Nox components responsible for the H(2)O(2) generation, two distinct isoforms of Nox4 are found expressed in HCAEC: the prototype Nox4A and the shorter Nox4B, respectively in the postnuclear supernatant and the nuclear fractions. Other expressed Nox family components are: as mRNAs, Nox4C, Nox4D, Nox1, p51(nox), and Racs; as mRNAs and proteins, Nox2, p22(phox), p47(phox), and p67(phox). The H(2)O(2)-generating activity increases up to three-fold upon inclusion of TNF-alpha in culture, concomitantly with augmented expressions of Nox4A, p22(phox), p47(phox) and p67(phox) proteins. Together, these results suggest that Nox2 and Nox4A enzymes are induced by TNF-alpha endowing HCAEC with enhanced ROS-generating activity, which may play a role in the initial endothelial dysfunction through oxidative stress.

NADPH analog binding to constitutive nitric oxide activates electron transfer and NO synthesis

We report here that NADPH analogs such as 2'5'ADP, ATP, and 2'AMP paradoxically activate constitutive calcium/calmodulin regulated nitric oxide synthases (cNOS), including the endothelial isoform (eNOS) and the neuronal isoform (nNOS). These activators compete with NADPH by filling the binding site of the adenine moiety of NADPH, but do not occupy the entire NADPH binding domain. Effects of these analogs on cNOS's include increasing the electron transfer rate to external acceptors, as assessed by cytochrome c reductase activity in the absence of calmodulin. In addition, NO synthase activity in the presence of calmodulin (with or without added calcium) was increased by the addition of NADPH analogs. In contrast, the same NADPH analogs inhibit iNOS, the calcium insensitive inducible isoform, which lacks control elements found in constitutive isoforms. Because ATP and ADP are among the effective activators of cNOS isoforms, these effects may be physiologically relevant.

Modulation of the antilisterial activity of human blood-derived macrophages by activating and deactivating cytokines

A concept of macrophage deactivation by hormones and cytokines that opposes activation was recently proposed. Deactivation of the antilisterial activity of macrophages by IL-4, IL-10, and TGF-beta, as well as by dexamethasone, was studied here. IL-4, IL-10, and dexamethasone, but not TGF-beta, caused a complete loss of the competence of human blood-derived macrophages infected with Listeria monocytogenes to control or eliminate ingested bacteria. IL-10 and, to a lesser degree, dexamethasone lessened in parallel the capacity of macrophages to secrete H2O2. The antilisterial activity of cells simultaneously exposed to deactivating agents could be significantly augmented by IFN-gamma. Likewise, TNF-alpha and to a limited degree GM-CSF increased the antilisterial activity of cells treated with IL-10 and dexamethasone but not that of cells treated with IL-4. Suppression of TNF-alpha secretion in response to Listeria by TGF-beta, IL-10, dexamethasone, or pentoxifylline did not closely parallel antilisterial activity. Studies by transmission electron microscopy and actin staining suggested that deactivation by IL-10, IL-4, and dexamethasone of human blood-derived macrophages resulted in intraphagosomal multiplication of Listeria followed only then by an escape of bacteria into the cytoplasm. The antibacterial competence of human macrophages is lessened by IL-4 and IL-10 and augmented by IFN-gamma, TNF-alpha, and GM-CSF. The success of human macrophages in controlling intracellular pathogens appears to depend on the balance of activating and deactivating mediators modulating their activity.

Aspects of the release of superoxide by leukocytes, and a means by which this is switched off

Although great progress has been made in understanding the respiratory burst of leukocytes that produce superoxide (O2-), it is possible that a component or components, might have been overlooked. Furthermore, O2- production and its sequels, though cardinal in bactericidal action, might ultimately be damaging to the host's own cells. It is important, therefore, that a biologic mechanism exist to turn off O2- production by stimulated leukocytes. This article offers evidence that methoxatin (PQQ), a redox-cycling orthoquinone, might be involved in O2- production by leukocytes. This is based on the fact that inhibitors of O2- production, such as diphenylene iodonium (DPI) and 4,5-dimethylphenylene diamine (DIMPDA), were shown to sequester PQQ in leukocytes, i.e., to form adducts with that substance. Addition of PQQ to cells blocked with the inhibitors partially restored O2- release. With respect to turning off cellular O2- release, a factor was observed to be released to the medium by old macrophages (14 days old, but not by those less than 7 days old). Such conditioned medium, when added to stimulated neutrophils or macrophages, blocked O2- release. This factor was sensitive to proteases, exhibited molecular sizes of 3 and 11 kDa, and its action was independent of the nature of the stimulus applied to the leukocytes. It was partially purified by column (sizing) chromatography and HPLC. It seems to be a general modulator of the release of reactive oxygen species by phagocytes and is irrespective of phagocytic cellular type, or species from which the cells were derived.

Leukocyte-deactivating factor from macrophages: partial purification and biochemical characterization. A novel cytokine

A deactivating factor (MDF) is released from granuloma-like lesions of mice (giant and epithelioid macrophages) to the surrounding medium. Test cells incubated in the presence of MDF display dramatic inhibition of superoxide anion (O2-) release when stimulated. This failure to manifest O2 release is observed whether PMA, all-transretinal, or fMet-Leu-Phe is the stimulating agent. MDF acts on different cell types from different species; mouse macrophages as well as guinea pig, human, and mouse neutrophils. Such results suggest that it is a universal regulatory cytokine with high affinity for phagocytic lineages. The factor was subjected to various purification methods: ultrafiltration, gel chromatography, and reversed phase HPLC. A crude preparation that resulted from conditioning of medium by old macrophages (MCM) shows two peaks of activity when subjected to gel filtration. These correspond to molecular weights for the active principle of 3 and 11 kD. When the factor was obtained by extraction of the same cells after washing and sonication, only the former peak was seen. Fractions corresponding to a MW of 3 kD from several preparations were combined and subjected to HPLC. MDF activity then appeared in a single fraction. MDF is thus putatively a modulator of the cidal activity of phagocytic cells that utilize release of reactive oxygen species for cytocidal activity.

Immunovascular communication: activation and deactivation of murine endothelial cell nitric oxide synthase by cytokines

A murine endothelial cell line, send1, was found to produce substantial amounts of nitric oxide, particularly after activation with cytokines. The endothelial cell activation paralleled that of macrophages. Macrophage deactivation opposing activation has recently been brought into focus. We therefore studied the cytokine-mediated deactivation of endothelial cells in send1 and vascular strips. Our observations document that activation of nitric oxide synthase of endothelial cells can be counterbalanced by deactivating cytokines such as interleukin-4, interleukin-8, interleukin-10 and transforming growth factor-beta. Deactivation of nitric oxide synthase in endothelial cells might be an essential mechanism for the control of immune-mediated vasodilatation or septic shock and represents a novel mechanism of communication between the immune and the vascular systems.

Native cytokine antagonists

Cytokines orchestrate the complex homeostasis of cells and tissues by acting in both an autocrine and paracrine fashion. The processes responsible for regulation of cytokines is not well understood. This chapter has summarized what is known about antagonism and inhibition of the action of cytokines. Several concepts have emerged from work in this area. At least two cytokines (IL-1 alpha and IL-1 beta) have an endogenous receptor antagonist, the IL-1 receptor antagonist. This is the first example of one endogenous molecule directly blocking the binding of another molecule to its receptor: most forms of regulation occur through independent receptors. Several cytokines, including TNF, IFN-gamma, IL-2 and IL-4, are inhibited by soluble receptors. Several cytokines, including IL-10, TGF-beta and MDF, act to inhibit other cytokines. It is likely that these inhibitors will be found to have pleiotropic actions in vivo. Finally, we describe antibody inhibition of cytokines. Detailed studies will be required to understand the complex interplay of the aforementioned cytokine inhibitors and the processes they regulate.

Macrophage functions are regulated by murine decidual and tumor extracellular matrices

Because of their paternal antigens, the fetus and placenta may be considered an allograft in the maternal host. Understanding the mechanisms which prevent maternal immunological rejection of the fetus remains a fundamental unsolved problem in immunology. We have previously reported that macrophages are inhibited by maternal decidual stromal cells residing at the maternal-fetal interface. In view of the central role of macrophages in cell-mediated immunity, this inhibition may contribute to preventing maternal antifetal responses. We now report that it was the solid phase signals embedded in the extracellular matrix (ECM) made by decidual cells which are responsible for inhibiting macrophage-mediated lysis of TNF-alpha-resistant P815 mastocytoma cells. The latter macrophage function is acquired after stimulation by interferon gamma and endotoxin. All these macrophage functions were also inhibited by ECM isolated from the Engelberth-Holm-Swarme (EHS) tumor. This tumor ECM has a similar biochemical composition to decidual ECM. This ECM inhibited the effector, as opposed to the stimulator, phase of macrophage-mediated tumor lysis. Laminin, type IV collagen, and heparan sulfate proteoglycans, the major known components of decidual and EHS ECMs, did not inhibit the above macrophage functions. Altogether these data indicate that macrophages were inhibited by solid phase signals embedded in decidual and EHS ECMs. Whether the solid phase signals in these two ECMs are biochemically identical remains to be determined. To our knowledge, such signals are a novel pathway of inhibiting macrophage functions which may be important in understanding the maternal-fetal immunologic relationship, and the pathogenesis of perinatal infections. Furthermore, the ability of EHS tumor ECM to inhibit macrophage functions may indicate that some tumors may defend themselves against host macrophage responses using solid phase signals. This may be important in understanding some host-tumor relationships.

Avoidance, and inactivation of reactive oxygen species: novel microbial immune evasion strategies

A prominent aspect of host cell-mediated immune (CMI) reactions leading to the clearance of infections is the production of one or more reactive oxygen species (ROS) such as superoxide (O2-), hydrogen peroxide (H2O2), hydroxyl radical (OH.), and hypohalite (e.g., OC1-). These ROS are usually produced by phagocytes. A number of chemotherapeutic agents also produce ROS in the process of their curative mechanisms. In a variety of infections, these ROS constitute a formidable arsenal in the clearance of the infection. In some cases, the excess ROS could also cause tissue damage. Evidence is herewith presented that pathogenic intracellular microorganisms, in order to enhance their survival as well as effective virulence within the host, have evolved novel strategies in the nature of avoidance, or inhibition of ROS production by phagocytes, or neutralization of already produced ROS. It is advocated that more in depth studies be undertaken in these respects in order to be able to exploit these phenomena in the production of more efficacious chemotherapeutic agents and anti-pathogen vaccines.

The effect of macrophage activation state on antigen presenting capability as defined by helper T-cell function

Resident peritoneal cells were obtained from BALB/c mice and enriched for cells of the macrophage lineage by adherence onto 96 well tissue culture plates. Adherent cells were then exposed to various recombinant cytokines or supernatants from cell cultures, for 24 h. The ability of such adherent antigen presenting cells (APC) to support proliferation and development of helper function in T-lymphocyte populations, primed with sheep erythrocytes (SRBC), was examined. The addition of cytokines to the APC population did not enhance either proliferation of the T-cells nor helper function, assessed by assay of polyclonal IgG secretion in second cultures, beyond that obtained with control APC. The potent macrophage activators interferon-gamma and lipopolysaccharide caused a significant decrease in both parameters of T-cell activity. This effect was caused by a prostaglandin-mediated pathway inasmuch as indomethacin (1-5 microM) prevented it. Further analysis showed that this negative signal predominated until macrophages were diluted below 5% of the total cell population. At 0.5% macrophages, interferon-gamma stimulated APC function of these cells compared with untreated macrophages. Despite the relative difficulty in manipulating the T-cell response by attempted modulation of the APC with cytokines, the simple manoeuvre of incubation of otherwise responsive, primed T-cells with a high dose (10%) of SRBC during in vitro restimulation, caused the proliferation and helper function of these T-cells to be markedly decreased. This phenomenon was seen regardless of the cytokine used to stimulate the APC population. These studies further clarify the dual role the macrophage in regulation of T-cell responses.

Epithelial macrophages secrete a deactivating factor for superoxide release

The release of superoxide anion (O2-) by inflammatory macrophages, multinucleated giant cells, and epithelioid cells, obtained by the insertion of round glass coverslips into the subcutaneous tissue of mice, was investigated. O2- was shown to be spontaneously released by cells on the surface of glass coverslips implanted up to 7 days, but not by cells obtained 14 or 21 days after coverslip implantation. The former showed increased O2- release when stimulated by phorbol myristate acetate, whereas cells harvested after 14 or 21 days implantation did not. The induction of delayed type hypersensitivity around coverslips implanted for 5 days increased spontaneous O2- release by these cells by 40%. On the other hand, when the same protocol was used with coverslips implanted for 14 days, O2- release was not detected. These results were viewed in regard to the composition of the cell population at each time point. When coverslips were removed after 14 days of implantation and the cells incubated for 30 minutes in vitro, the medium so conditioned inhibited O2- release by cells of 5 day old preparations. This indicates the release by cells on the longer term coverslips of a substance that inhibits O2- production by cells of coverslips implanted for 5 days only. This inhibitory activity could be suppressed by treating the conditioned medium with proteases. The factor was, however, heat stable and exerted its effects even when the test cells were exposed to phorbol myristate acetate.

Macrophage functions are regulated by the substratum of murine decidual stromal cells

Because of their paternal antigens, the fetus and placenta may be considered an allograft in the maternal host. Local properties of the maternal-fetal interface, the placenta and decidua basalis, are important in preventing maternal immunologic rejection of the fetoplacental allograft. However, the exact nature of these local properties remains a fundamental unsolved problem in immunology. We now report that three macrophage functions were inhibited by the substratum formed by monolayers of decidual stromal cells via a novel pathway. Solid-phase inhibitors blocked macrophage adhesion, spreading, and lysis of tumor necrosis factor-alpha-resistant P815 mastocytoma tumor cells. Inhibition was not solely attributable to an inability of macrophages to adhere to decidual substratum because there were differences in macrophage functions on this surface versus polyhema where no adherence occurred. Because macrophages play a central role in cell-mediated immunity, including allograft rejection, inhibiting their function in the decidua basalis may help prevent maternal antifetal responses.

Purification of macrophage deactivating factor

Macrophage deactivation factor (MDF) in P815 tumor cell-conditioned medium was assayed by its suppression of the ability of activated mouse peritoneal macrophages to release hydrogen peroxide. MDF displayed properties of a soluble protein(s) associated with both low (8-25,000) and high (greater than 450,000) Mr fractions. MDF was purified 6,140-fold by a seven-step procedure: extraction with acid-ethanol; precipitation with ether; and fractionation on gel filtration, anion-exchange, diphenyl reversed-phase and C4 reversed-phase HPLC columns, the last column twice. The final preparation contained two species: (a) a approximately 13,000 Mr band on reducing or nonreducing SDS-PAGE and on autoradiograms after radioiodination with chloramine T, and (b) a 66,000 Mr species ranging from approximately 5% to approximately 50% of the protein detectable by silver strain. The 66,000 Mr species was identified as albumin from its NH2-terminal amino acid sequence. However, no amino acid sequence could be obtained for the approximately 13,000 Mr species, either in fluid phase or after electroelution of the corresponding SDS-PAGE band. Thus, approximately 13,000 Mr MDF associates tightly with albumin through a variety of separation techniques, and may have a blocked NH2 terminus. Purified MDF afforded 50% inhibition of activated macrophage H2O2 releasing capacity at a concentration of 1-10 nM. Separation of MDF from most higher Mr moieties was associated with disproportionately small increases in specific activity, suggesting MDF might be partially inactivated by purification. As purified, MDF was approximately 1,000-fold less potent at deactivating macrophages than TGF-beta. Antibodies that neutralized the macrophage-deactivating effect of TGF-beta did not inhibit deactivation by MDF.

Macrophages: current views on their differentiation, structure, and function

Macrophages are large mononuclear phagocytes that represent the major differentiated elements of the mononuclear phagocytic system. They arise from distinct progenitors in the bone marrow, and their immediate precursors, the monocytes, emigrate from the vascular compartment into many tissues and organs where they develop into mature macrophages. The latter display diverse morphological and functional characteristics, depending on the environmental stimuli that they receive. This phenotypic heterogeneity is, therefore, the final consequence of a series of down-regulation of some cellular processes and the up-regulation of others. The kinetics of the production of macrophages and their participation in various physiological and pathological phenomena is the subject of this review.

Different effects of bacterial lipopolysaccharide on superoxide anion production by macrophages from normal and tumor-bearing rats

Bacterial endotoxins or lipopolysaccharides (LPS) exhibit a wide range of modulatory activities on immunocompetent cells. Among the numerous effects of LPS on macrophages, an enhancement of superoxide anion (O2-) release has been reported. In previous studies carried out on tumor-bearing rats, it was found that several functions of peritoneal macrophages such as phagocytic, microbicidal and antiviral activities were depressed. In this paper we evaluated the spontaneous or phorbol myristate acetate (PMA)-induced production of superoxide anion by macrophages from tumor-bearing rats with respect to controls. Moreover, the effect of in vitro priming with LPS on O2- production by the same cells was studied. It was found that the pattern of superoxide release by macrophages from tumor-bearing rats is significantly different from controls. Preincubation of macrophages from normal rats with LPS enhanced the spontaneous and PMA-induced production of O2-. In contrast, the same concentrations of LPS did not prime macrophages from tumor-bearing rats.

Effects of Histoplasma capsulatum on murine macrophage functions: inhibition of macrophage priming, oxidative burst, and antifungal activities

Histoplasma capsulatum yeast cells fail to trigger an oxidative burst response in normal murine macrophages. The results of this study, in which an in vitro assay of macrophage antifungal effects was used, extend these findings. During 18 h of incubation, unprimed elicited murine macrophages inhibited H. capsulatum growth only when macrophages were present in great excess. Gamma interferon (IFN-gamma)-primed macrophages showed enhanced fungal growth inhibition but a similar requirement for an excess of phagocytes. Macrophages containing heat-killed H. capsulatum exhibited diminished antifungal effects toward viable H. capsulatum and Saccharomyces cerevisiae cells. Parallel experiments showed no comparable effect of ingested latex particles on macrophage antifungal activity. Using chemiluminescence as a measure of the oxidative burst, we found that macrophages primed in vitro with IFN-gamma alone failed to exhibit a significant response to triggering by H. capsulatum yeast cells unless a second priming agent (tumor necrosis factor alpha or bacterial lipopolysaccharide) was added to IFN-gamma. Furthermore, macrophage priming with single agents was blocked by the prior ingestion of heat-killed H. capsulatum. These studies provide evidence that ingestion of H. capsulatum yeast cells can induce a prompt and enduring deactivation of murine macrophages.

Guinea pig Kupffer cells can be activated in vitro to an enhanced superoxide response. II. Involvement of eicosanoids

In the preceding paper it was shown that Kupffer cells isolated by digestion of the liver and purified by centrifugal elutriation can be activated in vitro by lipopolysaccharide and muramyl dipeptide to an enhanced superoxide response upon zymosan phagocytosis. Lipopolysaccharide and muramyl dipeptide also led to a strongly increased prostaglandin E2 release during the phagocytosis of zymosan. This activation was accompanied by an increased production of prostaglandin E2 during the incubation with the stimuli. Prostaglandin E2 synthesis was inhibited by the cyclooxygenase inhibitor indomethacin, reduced by dexamethasone, but only slightly decreased by the lipoxygenase inhibitor nordihydroguaiaretic acid. Indomethacin and dexamethasone also reduced the superoxide response, which only in the case of indomethacin is reversed by exogenous prostaglandin E2. Dexamethasone reduced the superoxide response in unstimulated cells as well. From these results it is deduced that cyclo-oxygenase products, especially prostaglandin E2, but not lipoxygenase products, i.e. leukotrienes, play some regulatory role in the activation process of Kupffer cells; in addition, a prostaglandin-independent inhibition exerted by dexamethasone seems to exist.

Effects of assay medium composition on macrophage-mediated tumor cell binding and lysis

Activated macrophages express selective, high avidity tumor binding and cytotoxicity for tumor targets. The reported macrophage-mediated tumor binding and killing activities vary considerably among studies. Whereas, some of these studies utilized identical tumor target cells and similar sources of macrophages, the composition of the assay media used by different groups varied with respect to: type of medium (Eagle's minimal essential medium (EMEM), RPMI-1640, Dulbecco's modified Eagle's medium with 1.0 g/l glucose (DMEMLG), or with 4.5 g/l, glucose (DMEMHG)), concentration of serum (0-20%), and the addition of certain reagents (amphotericin B, pyruvate, and Hepes). The purpose of this study was to evaluate the effects of varying these parameters of medium composition on macrophage-mediated high (HA) and low avidity tumor binding and cytolysis. Tumor cytolysis was measured with an 18 h 51Cr release assay using peritoneal macrophages from C3H/HeN mice primed in vivo with pyran copolymer and further stimulated in vitro with lipopolysaccharide (10 ng/ml). P815 tumor cells were used as targets at a 10:1 effector:target ratio. Binding of targets to macrophages was determined by a method utilizing inverted centrifugation. Under optimal conditions, 2 x 10(5) macrophages bound as many as 17,600 +/- 3565 tumor cells and caused up to 50.4 +/- 3.6% cytolysis. Assays performed in DMEMHG compared with the other three media tested resulted in HA tumor binding and cytolysis which were decreased by up to 42.5% (P less than 0.05) and 64.3% (P less than 0.01), respectively, compared with the three other types of medium. The addition of pyruvate (1 mM) to EMEM with 5% fetal calf serum (FCS) stimulated 98.8% (P less than 0.01) and 50.6% (P less than 0.1) increases in tumor binding and cytolysis, respectively compared with EMEM/5% FCS alone, while Hepes (25 mM) stimulated 58.3% (P less than 0.01) and 37.5% (P less than 0.1) increases in these activities. Amphotericin B (2.5 micrograms/ml) completely abrogated tumor cytolysis, but it caused no change in tumor binding. Serum produced variable effects on macrophage-mediated tumor killing. Five of six lots of FCS inhibited tumor lysis, by 16 to 98% (32.6 +/- 28.6%; mean +/- SD). However, the same lot of FCS which inhibited cytolysis by 98% enhanced HA binding by 152% (P less than 0.05). Finally, several commercially available serumless medium preparations supported macrophage-mediated tumor binding; however, none of the serumless media tested supported macrophage-mediated tumor cytolysis. We conclude that common differences in assay medium composition can markedly alter macrophage-mediated tumor cell binding and cytolysis.

Enhanced oxygen metabolism of peritoneal macrophages in the presence of murine neuroblastoma cells is partly caused by enkephalins

A bioluminescent technique was used to show that murine neuroblastoma (NB) cells or cell-free extracts (H variant) were able to enhance the release of reactive oxygen intermediates (ROI) from peritoneal macrophages in vitro. L-variant NB cells were ineffective. Physiological concentrations of met-enkephalin produced the same effect in vitro but not leu-enkephalin. When both H- and L-variant cells, or their extracts, were incubated together with macrophages, ROI production was not increased. Similar findings were detectable when met- and leu-enkephalin were cultured together with macrophages. In vivo, preliminary studies gave the same results. The concentration rate of met- to leu-enkephalin was higher in H-variant than in L-variant NB cells. We conclude from our results that met-enkephalin can enhance the release of ROI from peritoneal macrophages. The difference in the effects produced by the H and L variants is due to differences in the concentrations of enkephalins released.

Deactivation of macrophages by transforming growth factor-beta

Macrophage activation--enhanced capacity to kill, in a cell that otherwise mostly scavenges--is essential for host survival from infection and contributes to containment of tumours. Both microbes and tumour cells, therefore, may be under pressure to inhibit or reverse the activation of macrophages. This reasoning led to the demonstration of macrophage deactivating factors from both microbes and tumour cells. In some circumstances the host itself probably requires the ability to deactivate macrophages. Macrophages are essential to the healing of wounds and repair of tissues damaged by inflammation. Yet the cytotoxic products of the activated macrophages can damage endothelium, fibroblasts, smooth muscle and parenchymal cells (reviewed in ref. 6). Thus, after an inflammatory site has been sterilized, the impact of macrophage activation on the host might shift from benefit to detriment. These concepts led us to search for macrophage deactivating effects among polypeptide growth factors that regulate angiogenesis, fibrogenesis and other aspects of tissue repair. Among 11 such factors, two proteins that are 71% similar proved to be potent macrophage deactivators: these are transforming growth factor-beta 1 (TGF-beta 1) and TGF-beta 2.

Specific activation by concanavalin A of the superoxide anion generation capacity during U937 differentiation

Phorbol myristate acetate (PMA) induces changes in the human monocyte-macrophage-like cell line U937 which reflect cellular differentiation. PMA prompted the expression of the superoxide anion (O2-) generating capacity in U937 upon appropriate stimulation. A highly specific stimulation by Concanavalin A (Con A) of O2- release was observed in PMA-differentiated U937 cells, which exceeded in 10-20 times that obtained with Con A-stimulated monocytes and neutrophils. These results indicate that a highly specific machinery required for Con A stimulation, practically absent in mature monocytes and neutrophils, is synthesized during PMA-induced U937 differentiation. A novel cytochrome b putatively involved in O2- generation was detected in U937 cells. This cytochrome b content was increased during PMA-induced cell differentiation, although no linear correlation was found between capability to produce O2- by macrophage-like U937 cells and their content of cytochrome b.

Analysis of the nonfunctional respiratory burst in murine Kupffer cells

Murine Kupffer cells (KCs), which constitute one of the largest populations of tissue macrophages, differ from most other cells of the myelomonocytic lineage in lacking the capacity for a respiratory burst. A collagenase perfusion technique followed by adherence to plastic at low temperature yielded pure cultures of KCs uniformly expressing receptors for Fc and C3bi, and containing virtually no morphologically detectable intracytoplasmic debris. Such KCs took up and oxidized glucose via the hexose monophosphate shunt about the same as peritoneal macrophages (PCs). Respiratory burst stimuli failed to enhance the hexose monophosphate shunt in KCs, probably because no H2O2 was produced. Detergent-permeabilized KCs generated no O2- in the presence of 1 mM NADPH, in striking contrast to all PC populations studied. Yet, KCs contained at least one component of the O2(-)-producing oxidase, cytochrome b559, in the same quantities as PCs and neutrophils. Cytochrome b559 was demonstrated by a novel double-reduction spectral technique that eliminated interference from hemoglobin and mitochondrial cytochromes. Consistent with the presence of the oxidase, KCs acquired normal respiratory burst capacity after prolonged incubation in vitro. The defect in triggering the respiratory burst in KCs was selective for the reduction of O2 by NADPH, in that reduction of O2 by endogenous arachidonate was readily demonstrate in response to zymosan. The percent of arachidonate released, the percent oxygenated, and the suppression of prostacyclin and leukotriene C production, as well as the pattern of LFA-1 expression, all resembled the pattern reported with PCs several days after exposure to bacteria. Indeed, exposure of PCs to low numbers of zymosan particles led gradually to complete suppression of respiratory burst capacity and refractoriness to its enhancement by rIFN-gamma, as evident in KCs both before and after their explanation. Thus, the modulation of oxidative metabolism that characterizes KCs probably arises from frequent endocytic encounters. This phenomenon may permit macrophages to act as scavengers without oxidative damage to bystander cells.

The expression of a gamma interferon-induced protein (IP-10) in delayed immune responses in human skin

Our knowledge of the induction of new molecules by IFN-gamma has led to the characterization of IP-10 and the preparation of a monospecific, polyclonal antibody. Using this reagent we have now examined inflammatory states occurring in human skin and used immunocytochemical staining for the expression of both Ia and IP-10 determinants. After evoking a delayed-type response to purified protein derivative of tuberculin (PPD), we noted the presence of IP-10 in dermal macrophages and endothelial cells. Intense staining of the basal layer of epidermal keratinocytes was prominent at 41 h, and by 1 wk the entire epidermis was staining. The comparison of the amount of IP-10 secreted by keratinocytes vs. macrophages, fibroblasts, and endothelial cells revealed that keratinocytes were by far the major producers of this molecule. The expression of Ia occurred in conjunction with IP-10. The injection of rIFN-gamma mimicked many of the features of the PPD response, including the expression of both Ia and IP-10 by epidermal keratinocytes. Coexpression was also found in the natural lesions of tuberculoid leprosy and cutaneous Leishmaniasis. However, it was absent in lepromatous leprosy, a state where activated T lymphocytes are not present. We suggest that the local production of IFN-gamma by T cells of the dermal infiltrate induces IP-10 formation in both the dermis and epidermis. IP-10 and Ia then serve as specific markers of immune IFN and its possible influence on effector cells of the cell mediated immune response.

Rat macrophage treatment with lipopolysaccharide leads to a reduction in respiratory burst product secretion and a decrease in NADPH oxidase affinity

The effect of LPS on the respiratory burst in resident rat peritoneal macrophages has been examined. Rat macrophages secreted high levels of both O2- and H2O2 in response to triggering with phorbol esters, opsonized zymosan, and immune complexes. After culture in vitro with LPS these macrophages exhibited a marked diminution in their capacity to secrete high levels of respiratory burst products. The LPS-mediated loss of secretory activity was apparent after 2 hr of exposure to LPS and was inhibitable by polymyxin B in a dose-dependent fashion. The effect was not selective for any triggering agent type as inhibition of secretory activity occurred after triggering with PMA, zymosan and immune complexes. PGE2 added at levels secreted by the macrophages in response to LPS also inhibited respiratory burst product secretion. In addition, indomethacin prevented the LPS-mediated inhibition of secretion. Because the inhibition of secretion was common to all triggering agents tested, this suggested that the basis for the impaired secretion was at a level other than the receptor for the triggering agent. Both LPS and PGE2 treatment of the macrophages increased the Km of the oxidase for NADPH (1.7- to 2.3-fold) without affecting significantly the Vmax of the enzyme. These data suggest that stimulation of rat peritoneal macrophages by LPS results in an impaired ability to secrete respiratory burst products as a result of a PGE2-mediated decrease in NADPH oxidase affinity and that this alteration is independent of alterations in tumoricidal activity.