Production and characterization of cytostatic protein factors released from human monocytes during exposure to lipopolysaccharide and muramyl dipeptide

Natural production and release of tumour necrosis factor

Tumour necrosis factor (TNF) was first described as an oncolytic factor found in sera of animals injected (primed) with reticuloendothelial stimulators and subsequently (days later) given lipopolysaccharide (LPS). TNF is not found in the serum of 'primed' animals but can be found in animals given LPS alone when sensitive assays are employed. TNF appears almost immediately upon LPS injection, reaches a maximum from about 1.5-2 hours and disappears rapidly thereafter, and is almost undetectable by 4-6 hours. When such mice are injected again with LPS, they are unresponsive (tolerized) and do not produce TNF again, at least for seven days. Other unrelated substances, such as muramyl dipeptide, viruses and mitogens, also induce TNF production. A high percentage of patients with some parasitic infections (but not cancers) demonstrate low levels of TNF in their sera; thus, they do not seem to be tolerized but produce it continuously. TNF can also be produced in macrophage cultures by treatment with LPS, muramyl dipeptide and other substances. Again, it appears almost immediately and synthesis is maintained for about 8-12 hours. Synthesis is dependent upon the continuous presence of LPS. After synthesis stops it cannot be reinitiated by adding more LPS; thus, the macrophages also appear to be tolerized. Macrophage cell lines eventually become sensitive again after cultivation in LPS-free conditions. Synthesis of TNF is inhibited by actinomycin D or cycloheximide, indicating that it is an inducible protein. Its production is also inhibited by glucocorticoids and prostaglandin E2, indicating that these substances play important roles in the regulation of TNF synthesis.

Gene expression of tumor necrosis factor alpha and interferon gamma in the lungs of Mycoplasma pulmonis-infected mice

ICR mice were infected intranasally with Mycoplasma pulmonis isolated freshly from the lungs of a rat with pneumonia. We demonstrated with high reproducibility the expressions of messenger RNAs of cytokines, tumor necrosis factor alpha (TNF alpha) and interferon gamma (IFN gamma) in the lung tissue of M. pulmonis-infected mice by the reverse transcriptase-polymerase chain reaction and confirmed specific mRNA of the cytokines by restriction endonuclease digestion. Both the viable population of M. pulmonis in the lung tissue and the titers of the neutralizing antibody in the serum increased between 7 and 21 days, and reached their maximum 35 days after infection. The pneumonia in mice progresses with the development of lung lesions after 7 days of infection. The early lesions are characterized primarily by neutrophils and edema in the alveolar spaces. mRNAs prepared from the lung tissue of M. pulmonis-infected and -uninfected mice were also tested for the presence of messages specific to TNF alpha and IFN gamma by the reverse transcriptase-polymerase chain reaction. The expression of the genes encoding TNF alpha and IFN gamma was constitutively demonstrated from 24 hr through 35 days after the intranasal inoculation of M. pulmonis. Furthermore, cells of two types, adherent and nonadherent cells, in bronchoalveolar lavage fluids obtained from the mice 3 weeks after inoculation of M. pulmonis were also found to express the genes of TNF alpha and IFN gamma respectively. These data suggest that these cytokines would play a role in both stimulation in the development of pathological changes in mycoplasmal infection, affecting the inflammatory responses.

Inhibitory effect of lipopolysaccharide-stimulated P388D1 macrophage-like cells on plasmacytoma cells

Culture supernatants of lipopolysaccharide-stimulated P388D1 macrophage-like tumor cells showed a growth inhibitory effect on plasmacytoma MOPC-315, MPC-11 and myeloma FO cells, but had no effect on J558 plasmacytoma cells. Based on the results of trypan blue staining and a 51Cr release assay, the supernatant had both cytotoxic and cytostatic activity for MOPC-315 plasmacytoma cells. The inhibitory activity was trypsin-sensitive, heat-stable at 100 degrees C for 20 min., but sensitive to 2-mercaptoethanol and cystein HCl. At least 6 hrs of exposure period were required for the P388D1 culture supernatant to show an inhibitory effect on plasmacytoma cells. Since the inhibitory activity could not be blocked by protease inhibitor or neutralized by antibodies to mouse IL-1 beta, IL-6 and TNF-alpha, the inhibitory factor(s) was distinct from the defined cytotoxic factors. After partial purification with DEAE-Sephacel and Sephacryl S-300 chromatography, four major active peaks with the molecular mass of 874-KDa (near the void volume), 112-KDa, 45-KDa and 18-KDa were obtained.

Conditions controlling tumor cytotoxicity of rat liver macrophages mediated by liposomal muramyl dipeptide

Activation of rat liver macrophages with free and liposome-encapsulated muramyl dipeptide (MDP) to a tumorcytotoxic state was characterized by employing various experimental conditions. Macrophage-mediated tumor cytotoxicity was determined using two standard assay systems: a [methyl-3H]thymidine release assay to measure the extent of tumor cell lysis and a [methyl-3H]thymidine incorporation assay to measure the combined effects of tumor cell lysis and stasis. The extent of cell lysis was not affected by the ratio of macrophages to tumor cells within the ratio range of 30:1 to 5:1, provided that the macrophages form a confluent monolayer. Tumor cell lysis, however, was significantly influenced by macrophage density; a low macrophage density for example resulted in a low percentage of tumor cell lysis. Tumor target cells used in this study, i.e., C26 adenocarcinoma, B16 melanoma and P815 mastocytoma, differed in their susceptibility towards macrophage-mediated cell lysis, whereas no differences were observed with respect to tumor cell stasis. Non-tumorigenic cell lines such as human fibroblastic cells and LLC monkey kidney cells were not lysed by activated macrophages, although proliferation of these cells was markedly inhibited. Additionally, the effects of liposomal lipid composition on macrophage activation were studied. With a basic composition of phospholipid/cholesterol/dicetylphosphate, we used either egg-yolk, dipalmitoyl-, distearoyl- or dihexadecylphosphatidylcholine as the bulk phospholipid constituent. Although these liposomes display a widely different susceptibility to lysosomal phospholipase activities, we could not detect any significant difference in either the extent or the duration of the tumoricidal activity induced by MDP encapsulated in these different types of liposomes.

Synergistic growth-inhibitory activity of tumour necrosis factor and alpha interferon. Contribution to the monocyte-derived cytostatic activity towards human leukaemia K562 cells

Monocyte supernatants are cytotoxic towards WEHI 164 clone 13 cells and cytostatic towards K562 cells. The cytotoxic activity towards the clone 13 cells is entirely due to tumour necrosis factor alpha (TNF alpha), since it was completely neutralized by recombinant TNF alpha (rTNF) antiserum, and identical dose-response curves were obtained with supernatants and rTNF alpha. The cytostatic activity towards the K562 cells, however, was only partly due to TNF alpha, since this activity was only partly neutralized by the rTNF alpha antiserum. Moreover, the supernatants were found to be more cytostatic towards K562 cells than rTNF alpha preparations that contained comparable amounts of TNF. Alpha interferon (IFN-alpha) also contributed to cytostasis of the K562 cells, since antibodies against IFN-alpha partially inhibited the cytostatic activity in the supernatants, and further inhibition, although not complete, was obtained in the presence of both IFN-alpha antibodies and rTNF alpha antiserum. Moreover, recombinant IFN-alpha-2c (rIFN-alpha-2c) inhibited the growth of K562 cells, acting synergistically with rTNF alpha. Upon cation exchange chromatography, natural TNF in the monocyte supernatants eluted more broadly than rTNF, and significant amounts of TNF alpha were found in all column fractions containing cytostatic activity.

Toxic shock syndrome toxin 1 as an inducer of human tumor necrosis factors and gamma interferon

We present evidence that toxic shock syndrome toxin 1 (TSST-1) induces the production of high levels of TNF by human blood monocytes. Enriched lymphocyte preparations incubated with the staphylococcal toxin produced significant levels of TNF-like activity that is not neutralized by anti-rHuTNF antibodies and is likely to be lymphotoxin (LT or TNF-beta). We demonstrate also that TSST-1 is a potent inducer of IFN-gamma. When lymphocyte preparations were costimulated with PMA, the TSST-1 effect was strongly potentiated and the levels of cytotoxic factors, IFN-gamma, and IL-2 present in supernatant fluids were comparable to those observed after treatment with PMA and PHA. Thus, TSST-1, which is also known as an inducer of IL-1 and IL-2, stimulates the production of endogenous mediators that could play a role in the physiopathological processes of toxic shock syndrome (TSS). The described results suggest that the discrepancies in the clinical features between TSS and endotoxin shock may be related to qualitative differences in cytokine production.

Quantitative histology of muramyl dipeptide-potentiated induction of tumor necrosis by endotoxins

Combinations of muramyl dipeptide (MDP) and toxic or detoxified endotoxin induced necrosis and subsequent disappearance of solid Meth A tumors in syngeneic mice. Toxic endotoxin alone was far less effective. MDP and detoxified endotoxin had negligible antitumor effects of their own. These observations were confirmed by histological examination. Neither MDP nor detoxified endotoxin induced significant changes in and around the tumor by 4, 24, and 48 h after intravenous administration when compared with saline treatment. MDP amplified various effects of toxic endotoxin such as the induction of hyperemia, mitotic arrest, mast cell depletion, non-hemorrhagic necrosis and reduction in lymphocyte infiltrates, but did not affect hemorrhagic necrosis or the influx of polymorphonuclear leukocytes. The combination of MDP and detoxified endotoxin lacked the latter two effects, but the other effects were similar to, although slightly less marked than those induced by the toxic combination. Because the degree of hyperemia was proportional to the degree of subsequent non-hemorrhagic necrosis, MDP seems to potentiate necrosis by enhancing mechanisms leading to hyperemia and mast cell mediators might be involved in the latter effect. Lymphocyte influx and the therapeutic outcome are likely to be related, since exclusively therapeutic treatments reduced the influx of these cells.

Effect of antisera against recombinant tumor necrosis factor and the monocyte-derived cytotoxin(s) on monocyte-mediated killing of various tumor cells

Antisera raised against recombinant tumor necrosis factor (TNF) and against the monocyte-derived cytotoxic/cytostatic protein factor (CF), which is related to recombinant TNF, have been compared with respect to their ability to inhibit monocyte-mediated killing of various types of cells which differ in their sensitivity to recombinant TNF. During 6 hr of coculturing monocytes and target cells, the recombinant TNF antiserum inhibited killing of the extremely TNF-sensitive WEHI 164 clone 13 cells and actinomycin D-treated WEHI 164 cells from which the clone 13 cells were derived (parental WEHI 164 cells (P-WEHI 164 cells]. The CF antiserum also inhibited monocyte-mediated killing of these cells during 6 hr of coculturing with monocytes, but on a per volume basis it was less potent than the recombinant TNF antiserum, consistent with the fact that the CF antiserum also was much less potent in inhibiting the cytotoxic activity of recombinant TNF. However, during 72 hr of coculturing with monocytes and target cells, the CF antiserum inhibited monocyte-mediated killing of P-WEHI 164 cells more efficiently than the recombinant TNF antiserum. Moreover, during 72 hr of coculturing with monocytes, only the CF antiserum was able to significantly inhibit monocyte-mediated killing of the relatively recombinant TNF-resistant K562 cells. This suggests that a factor immunologically different from recombinant TNF, perhaps a form of natural TNF differing somewhat immunologically from recombinant TNF, was involved in the killing of K562 cells, and possibly in the killing of P-WEHI 164 cells, during 72 hr of coculturing with monocytes. Although this factor was present extracellularly, it appears that it may act as a monocyte-associated factor in monocyte-mediated killing of K562 cells, since exposure to recombinant interferon-gamma (rIFN-gamma) in the absence of Escherichia coli endotoxin (lipopolysaccharide, LPS) activated the monocytes to mediate killing of K562 cells more efficiently than exposure to LPS alone, despite the fact that only little cytotoxic/cytostatic activity was released from the monocytes without the addition of LPS. The ability of rIFN-gamma and LPS to activate monocytes to produce and release CF has also been studied.

Monocyte-derived influence on growth of normal human fibroblasts. The contribution of tumour necrosis factor to growth inhibition

The current study demonstrates that whereas high concentrations of recombinant tumour necrosis factor (rTNF, 0.05 microgram/ml) induced enhanced growth of normal human fibroblasts, supernatants from human monocytes with a similar TNF concentration induced cytostasis. This cytostasis was inhibited by an antiserum against rTNF. The TNF activity, measured as cytotoxicity against TNF-sensitive WEHI 164 cells, cochromatographed with the fibroblast growth inhibitory activity upon ion-exchange chromatography of monocyte supernatants. This indicates that TNF contributes to the fibroblast growth inhibition mediated by monocyte supernatants. Alpha interferon (IFN-alpha) abolished the growth of fibroblasts induced by rTNF, whereas rTNF in combination with gamma interferon (IFN-gamma) inhibited growth of fibroblasts. The interferon activity in the supernatants was determined to find out whether the growth-inhibitory activity of natural TNF was due to interferons present in the monocyte supernatants, which might modulate the TNF activity. Cytostasis of fibroblasts was mediated by monocyte supernatants which did not contain IFN-gamma in significant amounts. All supernatants contained IFN-alpha. An antiserum against IFN-alpha partially reduced the cytostasis induced by monocyte supernatants. This cytostasis was totally abolished by rTNF antiserum, suggesting that IFN-alpha modulates the growth-inhibitory activity of TNF in the monocyte supernatants. It appeared that the different effects of recombinant and natural TNF on fibroblast growth can probably not be attributed to monocyte-derived TNF-modulating factors alone. Thus, recombinant and natural TNF may differ in a way that affects their capacity to induce cytostasis of normal fibroblasts.

Use of mannosylated liposomes for in vivo targeting of a macrophage activator and control of artificial pulmonary metastases

From a mannosylated mycobacterial phospholipid, we prepared an original type of liposome which was taken up by macrophages by means of the mannose/fucose receptor. When a lipophilic immunomodulator, MDP-L-alanyl-cholesterol (MTP-CHOL) was included in such liposomes, they were able to activate WAG rat alveolar macrophages for cytotoxicity against syngeneic tumour cells in vitro. The presence of suboptimal levels of endotoxin was essential for this activation. Cytotoxic macrophages could also be induced in vivo by injecting immunomodulator-loaded liposomes intravenously 24 h before harvesting macrophages. A decrease in experimental pulmonary colonies arising from i.v. injected tumour cells was observed following repeated administration of such liposomes.

A highly sensitive cell line, WEHI 164 clone 13, for measuring cytotoxic factor/tumor necrosis factor from human monocytes

By limiting dilution of WEHI 164 mouse fibrosarcoma cells we have isolated a cell line, WEHI 164 clone 13, which is extremely sensitive to cytotoxic factor (CF) derived from human monocytes. By using WEHI 164 clone 13 in a MTT tetrazolium cytotoxicity assay it was found that CF supernatants from activated monocytes had to be diluted 10(5)-10(6) times to reach the dose which produced 50% dead cells (LD50). By comparing the LD50 of different target cells, WEHI 164 clone 13 cells were found to be approximately 10(3) times more sensitive for CF-induced cytotoxicity as compared to WEHI 164 parental cells and approximately 10(2) times more sensitive as compared to actinomycin D-treated L929 cells. Treatment of the WEHI 164 clone 13 cells with actinomycin D did not increase their sensitivity for CF-induced cytotoxicity. Recombinant tumor necrosis factor (rTNF) also mediated high cytotoxicity towards WEHI 164 clone 13 cells, with an LD50 of 2 X 10(-3) ng/ml. Neutralizing CF antiserum completely inhibited the toxic activity of rTNF. WEHI 164 clone 13 cells were highly sensitive to monocyte-mediated cytotoxicity in that 1-2 monocytes were able to kill at least 5000 of these target cells. Neutralizing TNF antiserum completely inhibited monocyte-mediated cytotoxicity. These results indicate that the high level of cytotoxicity mediated by CF supernatants and monocytes on WEHI 164 clone 13 cells is due to TNF as the effector molecule.

Detection of tumour necrosis factor-like cytotoxicity in serum from patients with septicaemia but not from untreated cancer patients

With a bioassay sensitive for recombinant tumour necrosis factor at a concentration of 10(-4) ng/ml, we were able to detect tumour necrosis factor-like cytotoxicity in serum from three patients in the initial phase of septicaemia. The cytotoxic activity corresponded to a concentration of recombinant tumour necrosis factor of 2 X 10(-2)-3 X 10(-3) ng/ml serum. The concentration in cerebrospinal fluid was estimated to be three times higher than in serum. In 23 untreated patients with malignant disease of varying origin and stage, including two patients with severe cachexia, we were not able to detect tumour necrosis factor-like cytotoxicity.

Human monocyte cytotoxic factor mediates cytolysis of WEHI 164 cells

Human monocytes can be activated to release a 40,000-Da cytostatic protein factor (CF). In this report we have investigated the cytolytic activity of CF on WEHI 164 cells which are sensitive to monocyte-mediated cytolysis. Monocyte supernatants containing CF induced cytolysis of murine WEHI 164 sarcoma cells, as determined in a 51Cr-release assay. Preincubation of WEHI 164 cells with actinomycin D enhanced cytolysis induced by supernatants containing CF, suggesting that CF may be involved in drug-dependent cellular cytotoxicity. The cytolytic activity was profoundly inhibited by a rabbit antiserum raised against purified CF, indicating that the cytolytic activity in the supernatants was in fact mediated by CF. These results indicate that CF may be an important effector molecule in monocyte-mediated cytostatic and cytolytic reactions.

IFN-gamma-induced production of monocyte cytotoxic factor

The effect of activating human monocytes in vitro with recombinant Interferon-gamma (IFN-gamma) and lymphokines on monocyte-mediated cytotoxicity and on the production of cytotoxic protein factor(s) (CF), has been investigated. Lymphokines and IFN-gamma enhanced both cytotoxicity and CF production in a dose-dependent manner. A monoclonal antibody against human IFN-gamma abrogated the lymphokine-induced cytotoxic activity and CF production completely, indicating that the actual monocyte-activating factor in the lymphokine supernatant was IFN-gamma. At concentrations of 10(3)-10(4) U/ml, IFN-gamma induced an enhanced release of CF from the monocytes. However, IFN-gamma at concentrations (less than 100 U/ml) present in our lymphokine preparation was not sufficient to induce enhanced CF release. Since IFN-gamma at concentrations less than 100 U/ml activated monocytes for cytotoxicity, CF as an extracellular factor in the supernatant does not appear to be essential for monocyte-mediated cytotoxicity. However, using neutralizing antiserum raised against purified CF, indirect immunofluorescence microscopy revealed that IFN-gamma induced a marked accumulation of CF on the monocyte membrane. Taken together, the data shows that IFN-gamma is both necessary and sufficient at concentrations less than 100 U/ml for inducing monocyte-mediated cytotoxicity and production of CF as a membrane-associated component, but not as a released factor, suggesting that CF may function as a membrane-associated cytotoxin in monocyte-mediated cytotoxicity.