Mechanism of action of mouse macrophages as antitumor effector cells: role of arginase

Tumor-inhibitory effect and immunomodulatory activity of fullerol C60(OH)x

The tumor-inhibitory effect of C60(OH)x was tested on the murine H22 hepatocarcinoma model. Doses of 0.2 and 1.0 mg kg(-1) body weight both showed significant antitumor activity with tumor inhibition rates of 31.9 and 38.4%, respectively, when mice were treated for 17 consecutive days. The damnification of liver was prominently reduced. Furthermore, histological examination indicated that an envelope of fibroblasts and lymphocytes was formed surrounding tumor tissues in the C60(OH)x-treated group, which inhibited the infiltration of tumor to the neighboring normal skeleton muscle tissues. To understand the antitumor mechanism, the immunomodulatory activity of C60(OH)x was investigated. The results indicate that C60(OH)x enhances the phagocytosis of peritoneal macrophages and elevates the activity of arginase and acid phosphatase in vivo. The tumor necrosis factor alpha production of C60(OH)x-treated macrophages also increases in vitro. These results suggest that C60(OH)x can enhance the innate immunity of tumor-bearing mice, and therefore inhibits growth of the tumor.

Periodontal therapy reduces arginase activity in saliva of patients with chronic periodontitis

This present study evaluated the salivary arginase activity (SAA) in patients with chronic periodontitis and the effect of periodontal therapy on the activity of such enzyme. Thirty-six patients (mean age, 45.97 +/- 14.52), 18 chronic periodontitis subjects (test group), and 18 periodontally healthy individuals (control group) participated in the study. Clinical periodontal examinations included measurements of probing pocket depth (PD), clinical attachment level (CAL), plaque (PI), and gingival (GI) indexes. The test group received periodontal therapy according to individual needs. The saliva sample was collected from all study population at baseline (both groups) and 30 days after periodontal therapy (test group). SAA was determined by measuring the L: -ornithine formation from L-arginine and was expressed as mU/ml. The results showed that the mean values of SAA were statistically different between control and test groups. SAA was about 2.5 times higher in test than control groups. Thirty days after periodontal therapy, enzyme levels were 1.56 times lower than before periodontal therapy. We concluded that SAA is increased in chronic periodontitis subjects when compared to periodontally healthy individuals and that periodontal therapy significantly reduced SAA levels. It was suggested that in the near future, SAA may be used as a salivary marker of periodontal status.

Neurotoxicity of soluble macrophage products in vitro--influence of dexamethasone

When macrophage conditioned medium is added to neurons in vitro, there is a loss of cell membrane integrity, a loss of cell processes, and a large increase in apoptotic neurons. We tested the influence of a potent anti-inflammatory steroid on the interaction between macrophages and neurons. Dexamethasone was applied to macrophages in culture for 24 h while the culture was stimulated with lipopolysaccharide and hypoxia. Conditioned medium was collected after dexamethasone was removed. The dexamethasone pretreated medium was not toxic to hippocampal neurons in contrast to medium from stimulated macrophages not treated with steroid. The dexamethasone effect was concentration dependent. Pretreatment of macrophages with indomethacin and transforming growth factor beta had similar but less impressive effects when compared to dexamethasone. The effect of dexamethasone may have been mediated by inhibiting the synthesis or release of neurotoxic macrophage protein(s), as a combination of medium from steroid pretreated macrophages with medium from nontreated macrophages was not neuroprotective. The toxin(s) did not appear to be tumor necrosis factor alpha or arginase. A role for most neutral proteases was also excluded. We also assessed the consequence of stressing neurons with a mild hypoxic exposure immediately prior to conditioned medium application. Medium from dexamethasone-treated macrophages did not exaggerate hypoxic neuronal injury, unlike medium from non-dexamethasone-treated macrophages. It did not, however, block the exaggerating effect when coapplied in equal volume with medium from nontreated macrophages. Dexamethasone at 100 nM had no impact when applied directly to neurons while they were being exposed to conditioned medium. This in vitro protection by dexamethasone may be relevant to the demonstrated benefit of glucocorticoids in selected brain and spinal cord conditions. Suspicion of a potential link between this in vitro finding and in vivo CNS injury justifies an assessment of more specific agents acting on macrophage protein synthesis or secretion.

Phospholipase A2 in macrophage plasma membrane releases arachidonic acid from phosphatidylinositol

A high level of arachidonic acid release from [2-14C]arachidonylphosphatidylinositol (PI) was observed at neutral pH (6.0-7.0) in the presence of purified plasma membranes of guinea pig peritoneal macrophages. This activity was at least 10-fold higher than that with arachidonylphosphatidylcholine (PC) or phosphatidylethanolamine (PE) as substrate. The accumulation of [14C]diacylglycerol and [14C]phosphatidic acid was not detected at any time, and arachidonic acid release from [14C]arachidonyldiacylglycerol was not detectable either. The data suggest that arachidonic acid release from PI may not occur via the phospholipase C pathway. In this paper, we demonstrate the possibility that arachidonic acid release from PI at neutral pH in the macrophage plasma membrane is dependent on the action of phospholipase A2 (EC 3.1.1.4) -like activity. The maximum arachidonic acid release was dependent upon both pH and substrate. Particularly, the activity of arachidonic acid release from PI at neutral pH was very high compared with that from PC or PE. We suggest that phosphatidylinositol phospholipase A2 (EC 3.1.1.52) may play an important role in providing arachidonic acid for subsequent metabolic activity in the macrophages.

Cytostatic product(s) released by activated macrophages, unrelated to interleukin 1, tumor necrosis factor alpha, and interferon-alpha/beta

Murine peritoneal macrophages activated for cytotoxicity by trehalose dimycolate in vivo and lipopolysaccharide in vitro released cytostatic factor(s) against EMT6 target cells, in 8-hr conditioned medium (CM). The cytostatic factor(s) completely blocked DNA synthesis by EMT6 cells within 16 hr. Other cell lines are less sensitive (P815 and R-L929) or resistant (KB and HT29) to the cytostatic effect of CM. The anti-proliferative activity of CM had a MW greater than 10,000 Da, as judged by ultrafiltration. It was destroyed by proteases and strongly inhibited by P815 cell product(s). Conditioned media from nonactivated macrophages were not cytostatic against EMT6 cells. No relationship was found between cytostatic factor(s) in CM and interleukin 1 (IL-1), tumor necrosis factor alpha (TNF-alpha), and interferon-alpha/beta (IFN-alpha/beta): the growth of EMT6 cells was unaffected by Hu.r.IL-is and Hu.r.TNF-alpha and was only slightly inhibited by IFN-alpha/beta. Furthermore, cytostatic CM contained low levels of TNF and IFN activities. Finally, antibodies raised against murine IFN-alpha/beta had no effect on the cytostatic activity of CM.

Recognition of acidic phospholipase A2 activity in plasma membranes of resident peritoneal macrophages

Phospholipase (PLase) activities in the plasma membrane of guinea pig peritoneal macrophages were studied, as these enzymes having such activity may be candidates for the release of arachidonic acid (AA) from phosphatidylcholine (PC). An AA release system operating at acidic pH was identified in the macrophage plasma membrane and characterized. This membrane-bound acidic PLase A2 had an optimum pH at 4.5, and enzyme activation was observed in Ca++-free medium; but the maximum activity was found at 0.5 mM Ca++ concentration. The Km value for PC of acidic PLase A2 was 4.2 microM, and a Michaelis-Menten relationship was evident. Calcium might act as a cofactor at some intermediate step during the activation of acidic PLase A2 in light of the uncompetitive manner of Ca++ action. Furthermore, the release of [3H]-AA from preradiolabelled macrophage plasma membranes occurred with the addition of Ca++ at pH 4.5. These data suggest that the acid PLase A2 is a component of the plasma membrane and is not due to lysosomal contamination since membrane-bound acidic PLase A2 properties are opposite to those found for lysosomal PLase A2.

The mechanisms of inhibitory effects of liver extract on lymphocyte proliferation. I. The extracellular mechanism of the inhibition

Liver aqueous extract (LEx) can powerfully inhibit phytohaemagglutinin (PHA)-induced lymphocyte proliferation. The extracellular mechanism of inhibition by LEx was studied. There are three possibilities. (1) The possibility of extracellular inactivation of PHA by LEx was excluded by incubating cells with PHA first, followed by washing, and then incubating cells with LEx. The result was that LEx was still able to inhibit cell proliferation completely. (2) The possibility of competition for cell surface PHA receptors by LEx was excluded by the above experiments plus the use of N-acetyl-D-galactosamine to remove surface-bound PHA. Following this treatment, LEx was still able to inhibit cell proliferation completely. (3) The possibility of arginase-induced arginine depletion resulting in lymphocyte suppression was supported by the following experiments. Cells were incubated in media in which arginine was depleted either by reacting with LEx, and the media were afterwards bound with anti-arginase antibody, or by amino acid constituted media without arginine. The degrees of proliferation inhibition were similar in both treatments. These results indicate the important role of arginine-depletion by LEx, and may account for the LEx-induced lymphocyte inhibition.

Rapid procedure for preparation of macrophage plasma membrane

This report describes a simple and efficient procedure for the isolation of plasma membrane from guinea pig peritoneal macrophages. The use of polycationic beads (Affi-gel 731 beads) facilitates rapid and high-clear separation of plasma membrane within 30 min. The final plasma membrane coated beads fraction has high specific activities of marker enzymes with little contamination with mitochondrial, lysosomal or cytoplasmal markers.

Cytostatic effect of gangliosides present in the membrane of macrophages

Stimulated macrophages are known to inhibit the growth of certain tumor cells. Using mouse peritoneal exudates as a source of macrophages and the mastocytoma cell line P815 as the target, the inhibition was found to depend on direct contact between the macrophages and the growing cells. Cytostatic activities were detected in extracts of macrophages as well as in membranes of macrophages bound to substances of low molecular weight. Physical and biochemical characteristics of the cytostatic activity hint toward N-acetylneuraminic acid containing glycosphingolipids (gangliosides). The different macrophage gangliosides were separated by thin-layer chromatography. All types showed cytostatic activity, but the most effective gangliosides were identified as monosialoganglioside GM1 and disialoganglioside GD3.

Role of Bacterial Lipopolysaccharide and Lymphokine in the Regulation of Macrophage Activation: Correlates between Secretion of Plasminogen Activator and Tumor Lysis

The effects of bacterial lipopolysaccharide (LPS) and lymphokine (LK) upon the activation of murine C57BL/6 peritoneal macrophages (M phi) were studied. Enhancement of the secretion of plasminogen activator (PA) by lymphokine did not require, nor was significantly boosted by LPS. In contrast, lysis of tumor target cells required LPS in addition to lymphokine confirming prior studies (1-3). Once macrophages were induced to secrete PA, LPS suppressed its release but did not directly interfere with fibrinolysis. These findings are consistent with the concept that induction of PA secretion may represent an earlier step in activation than the acquisition of cytolytic potential (4, 5) and that LPS is important both in the regulation of macrophage proteases and mediation of tumor cell lysis (2, 6).

Characterization and sorting of mouse cytotoxic macrophages by their light scattering properties

The light scattering properties of mouse activated macrophages were analyzed by flow cytometry. Peritoneal adherent cells from B. abortus treated animals were found to segregate into two subpopulations as a function of their forward angle and 90 degrees angle light scatter. The cell subpopulations were separated by automatic sorting. The strongly scattering ones contained an elevated proportion of large volume and acid phosphatase rich cells. Their nonspecific cytotoxic activity against tumor cells was more important than that of weakly light scattering cells. Thus, flow cytometry might be helpful to characterize and isolate cytotoxic macrophage populations.

Molecular mechanisms in tumor-cell killing by activated macrophages

Macrophages kill tumor cells with and without the aid of antibody and evidence suggests that secreted cytotoxic substances are at work in each system. Here Dolph Adams and Carl Nathan discuss the likely involvement in both pathways of several such substances including cytolytic protease and hydrogen peroxide.

Potentiation of nonspecific immunotherapy of experimental lung metastases by indomethacin

Intraperitoneal treatment with the interferon inducer, maleic anhydride-divinyl ether copolymer (MVE), has previously been demonstrated to effectively reduce metastatic growth in the lungs and prolong survival times of BALB/c mice bearing the syngeneic Madison lung (M109) carcinoma. Resistance to lung metastasis formation induced by MVE appears to result from an activation of alveolar macrophage function. Since E-type prostaglandins (PGE) suppress the cytotoxic activity of activated macrophages, we sought to determine the effect of indomethacin, a prostaglandin synthetase inhibitor, on the antimetastatic activity of MVE. An artificial metastasis model was developed in which single-cell suspensions of the M109 tumor were injected i.v. into BALB/c mice. A 52,600 molecular weight fraction of MVE (MVE-5) was administered i.p. at 20 mg/kg two days prior to tumor inoculation. MVE-5 treatment produced greater than 80 percent reduction in macroscopic lung lesion formation at Day 15 and Day 19 after tumor inoculation and a resultant 45 percent increase in lifespan. Chronic administration of indomethacin in the drinking water at 10 micrograms/ml potentiated the MVE-5 antitumor induced macrophage activation in vivo. In the absence of any evidence for an interaction between indomethacin and circulating M109 cells, it was felt that the potentiating effect could be best explained in terms of interference with PGE-mediated feedback inhibition of macrophage functional activity.

Is Percoll innocuous to cells?

Peritoneal macrophages from mice, isolated rat liver Kupffer cells and rat testis Leydig cells ingested large numbers of Percoll particles, a gradient medium widely used for separation of cells and subcellular organelles by density-gradient centrifugation. A decrease in the percentage of macrophages adhering to plastic also occurred after exposure of the cells to Percoll, even at 4 degrees C, a temperature at which Percoll was not ingested. The effect of Percoll on macrophage adherence may involve a loose association between the density medium and the cell surface. Other cell-surface-related phenomena may also be affected by prior exposure of cells to Percoll.