Lysis of Human Leukemic Cells by Monocyte-derived Macrophages Activated with Interferon-γ and Interleukin-2

Cytolysis of leukemic cells by peripheral blood-derived macrophages was examined by means of an in vitro ¹¹¹In release assay. Monocytes prepared on culture dishes lyse YK-M2. However, when monocytes were cultured in vitro and transformed into macrophages, they lost most of their lytic activity. The addition of human recombinant interleukin-2 (rIL-2) on day 5 in culture enhanced the lytic activity significantly. Similarly, treatment of macrophages with human recombinant interferon gamma (rIFN-γ) promoted the lysis of YK-M2 and K-562, although the extent of lysis was smaller than that by rIL-2. Macrophages activated with rIL-2 and rIFN-γ also Iysed human leukemic cells. Activated macrophages lysed leukemic cells of acute myelocytic leukemia more than acute lymphocytic leukemia cells. Macrophages derived from the peripheral blood of patients with leukemia were examined for their lytic activity against YK-M2. The patient's macrophages lysed more YK-M2 than did control macrophages when they were activated with rIL-2 and rIFN-γ. The macrophages of two patients also demonstrated autologous leukemic cell lysis.     

Lysis of human leukemic cells by monocyte-derived macrophages activated with interferon-gamma and interleukin-2

Cytolysis of leukemic cells by peripheral blood-derived macrophages was examined by means of an in vitro 111In release assay. Monocytes prepared on culture dishes lyse YK-M2. However, when monocytes were cultured in vitro and transformed into macrophages, they lost most of their lytic activity. The addition of human recombinant interleukin-2 (rIL-2) on day 5 in culture enhanced the lytic activity significantly. Similarly, treatment of macrophages with human recombinant interferon gamma (rIFN-gamma) promoted the lysis of YK-M2 and K-562, although the extent of lysis was smaller than that by rIL-2. Macrophages activated with rIL-2 and rIFN-gamma also lysed human leukemic cells. Activated macrophages lysed leukemic cells of acute myelocytic leukemia more than acute lymphocytic leukemia cells. Macrophages derived from the peripheral blood of patients with leukemia were examined for their lytic activity against YK-M2. The patient's macrophages lysed more YK-M2 than did control macrophages when they were activated with rIL-2 and rIFN-gamma. The macrophages of two patients also demonstrated autologous leukemic cell lysis.     

Tumor necrosis factor as effector molecule in monocyte mediated cytotoxicity

A newly developed assay system which uses actinomycin D (Act D) pretreated Wehi 164 target cells allows for the measurement of human monocyte cytotoxicity in a 7-h 51Cr release assay. Using the monocyte specific monoclonal antibody M42 in a direct rosetting procedure we confirm herein that among human peripheral blood mononuclear cells cytotoxicity is restricted to monocytes. When applying stringent conditions that exclude exogenous lipopolysaccharide (LPS) we could demonstrate that as little as 0.1 ng of LPS per ml triggers this cytotoxicity. Further, a factor can be detected in supernatants of mononuclear cells which is also cytotoxic against Act D treated Wehi 164 cells. This cytotoxic factor can be triggered by LPS within 4 h, but at as low a LPS concentration as 0.001 ng/ml. Since one of the LPS triggered monocyte products is tumor necrosis factor (TNF), we tested the effect of recombinant TNF cloned from the U937 cell line and we could show potent lytic activity against Act D pretreated but not, or only minimally, against untreated Wehi 164 target cells. Recombinant TNF rapidly lysed the target with significant specific release occurring as early as after 3 h in the assay. By contrast, recombinant interleukin 1 gave no lysis while lymphotoxin derived from the RPMI 1788 cell line was effective. An affinity purified antiserum directed against TNF neutralized the lytic activity of recombinant TNF and also the cytotoxic factor produced by LPS triggered mononuclear cells, while the antiserum was ineffective against lymphotoxin. Further, the antiserum when added to the assay of effector cells and Act D treated Wehi 164 cells also completely ablated cytotoxic activity. Size fractionation of cytotoxic factor and recombinant TNF by high pressure liquid chromatography led to a superimposable peak of cytotoxicity in the molecular weight range of 9,500-17,000. Further, immunoblotting with the anti-TNF antibody revealed the same Mr 15,500-16,500 band for the recombinant TNF and LPS triggered cytotoxic factor. Taken together, our data demonstrate that the cytotoxic activity of human monocytes against Act D treated Wehi 164 is mediated entirely by a LPS triggered molecule that is very similar or identical to the human tumor necrosis factor. The assay system thus provides a powerful tool to analyze the biology of TNF in humans.     

Production of Tumor Necrosis Factor-α by Alveolar Macrophages of Lung Cancer Patients

The abilities of human alveolar macrophages (AM) obtained from healthy donors and patients with lung cancer to produce tumor necrosis factor (TNF) were compared with those of their blood monocytes after activation with lipopolysaccharide (LPS). TNF activity was assayed by measuring cytotoxicity against actinomycin D-treated L929 cells and TNF was determined quantitatively by sandwich enzyme-linked immnnosorbent assay (ELISA) with polyclonal and monoclonal antibodies against TNF-α. Unstimulated AM from healthy donors released variable amounts of TNF spontaneously, whereas blood monocytes did not. When treated with LPS for 24 h, AM and monocytes produced TNF dose-dependently, but TNF production by AM was significantly more than that by blood monocytes. This TNF activity was inhibited completely by monoclonal anti-TNF-α antibody. Macrophages generated by in vitro maturation of monocytes induced by granulocyte-macrophage colony-stimulating factor (GM-CSF) produced more TNF than freshly isolated monocytes. No difference was found in the abilities of AM from healthy donors and patients with lung cancer to produce TNF after activation stimuli. These observations suggest that human AM may be important in in vivo antitumor defense of the lung through TNF-α production.     

Enhancing Effect of an Inhibitor of Nitric Oxide Synthesis on Bacillus Calmette-Guérin-induced Macrophage Cytotoxicity against Murine Bladder Cancer Cell Line MBT-2 in vitro

We studied the effect of an inhibitor of nitric oxide (NO) synthesis, N^G-monomethyl-L-arginine (LNMMA), on the Bacillus Calmette-Guérin (BCG)-induced antitumor activity of murine peritoneal exudate cells (PEC) against murine bladder cancer cell line MBT-2 in vitro. L-NMMA enhanced BCG-induced cytotoxic activity of PEC, as well as interferon (IFN)-γ and tumor necrosis factor (TNF)-α production. The L-NMMA-induced enhancement was due to the prolonged survival of BCG in macrophages, because no enhancement of cytotoxicity was observed and neither IFN-γ nor TNF-α production was significantly enhanced by killed BCG. Anti-TNF-α antibody (Ab) and anti-IFN-γAb reduced the L-NMMA-induced enhancement of the cytotoxicity. The depletion of T cells from PEC reduced the production of both IFN-γ and TNF-α, as well as the enhancement of cytotoxicity induced by viable BCG plus L-NMMA. These results suggest that L-NMMA has an enhancing effect on BCG-induced macrophage cytotoxicity and the enhancement is partially mediated by T cells and their soluble products. Accordingly, NO inhibitor should be a valuable adjunct to BCG immunotherapy for bladder cancer.     

Role of tumor necrosis factor in macrophage activation and tumoricidal activity

Tumor necrosis factor (TNF)-sensitive (LM) and -insensitive (P815) target cell lines were used to examine the role of TNF in both the activation and lytic phases of macrophage-mediated lysis. LM cells were lysed spontaneously by thioglycolate-elicited macrophages in an 18-h assay (media or activating agents added with targets) or 36-h assay (macrophages cultured with media or activating agents for 18 h, washed, and targets added for a subsequent 18 h). In contrast, P815 cells were lysed only in the 36-h assay by macrophages exposed to appropriate activation signals. Using antibody to murine TNF, it was shown that lysis of LM cells but not P815 cells was TNF mediated. The addition of lipopolysaccharide (LPS) to the 18-h assay resulted in augmented LM killing. This was probably due to the fact that LPS stimulates macrophages to produce TNF. Conversely, when macrophages were pretreated with LPS for 18 h, washed, and assessed for lytic activity during the subsequent 18 h, lysis of LM cells was reduced relative to the endogenous level. Although macrophage lysis of P815 was not mediated by TNF, the addition of TNF to macrophage activation cultures facilitated LPS triggering of cytolytic activity against P815. Similarly, the addition of TNF to the activation cultures partially prevented the LPS-induced reduction in macrophage-mediated LM cell lysis. Taken together, these data suggest that TNF may act as an autocrine signal during macrophage activation, in addition to being directly lytic to a select number of sensitive target cell lines.     

Study of the dependence of human monocytes and macrophages antitumoral properties upon TNF-alpha expression or release

This study compares the antitumoral properties of isolated circulating human blood monocytes (Mo) and of mature macrophages (MO) obtained by 7 days differentiation of Mo or isolated from alveolar washing. These cells were activated to cytotoxicity in the presence of recombinant human interferon-gamma (rHuIFN-gamma). This antitumoral effect was measured at a low (1/1) effector/target ratio without pretreatment of the tumor cells. Activated Mo released tumor necrosis factor-alpha (TNF-alpha) in the culture medium where their antitumoral activity could be totally neutralized by specific anti-rHuTNF-alpha antibodies. In contrast, blood monocytes derived macrophages differentiated and activated in vitro expressed TNF-alpha on their membrane where it could be labelled and partially neutralized by anti-rHuTNF-alpha antibodies. Direct effector/target contact was required for the activity of macrophages differentiated in culture or collected from the lung cavity of healthy subjects. When these macrophages were obtained from infected patients or subjected to LPS treatment, they directly released cytotoxic amounts of TNF in the extracellular fluid after activation with IFN-gamma. Monocytes act mainly by soluble mediators (TNF-alpha being a key factor), while differentiated macrophages in the absence of endotoxin act by close cell to cell contact involving the lytic action of membranous TNF-alpha as well as some release of soluble TNF-alpha. We also present evidences (based on the use of various protease inhibitors) that the role of proteases is much less crucial in the cytotoxic action of monocytes and macrophages.     

EFFECTS OF PHYTOLACCA ACINOSA POLYSACCHARIDES I ON CYTOTOXICITY OF MACROPHAGES AND ITS PRODUCTION OF TUMOR NECROSIS FACTOR AND INTERLEUKIN 1

The in vivo effects of Phytolacca acinosa poly-saccharides I (PEP-I) on immunologic cytotoxicity of mouse peritoneal macrophages and its production of tumor necrosis factor (TNF) and interleukin 1 (IL-1) were studied. PEP-I 80 or 160 mg kg was given ip twice every 4 day. Both doses were found to have significant enhancing activity on macrophages cytotoxicity against S180 sarcoma cells and malignant transformed fibroblast L929 cells. Peritoneal activated macrophages were incubated with LPS for 2 and 24 hrs to induce TNF and IL-1, respectively. The TNF and IL-1 activities were tested from cytotoxicity against L929 cells in an absorbence assay of enzymatic reaction and proliferation of thymocytes co-stimulated assay separately. The optimal time for TNF production was found on day 8. Significant increases in TNF and IL-1 were observed. In comparison of the effect of PEP-I on TNF with that of known priming agent BCG, there was no difference between them, but PEP-I had a high effect on IL-1. These results sug     

Tumoricidal activation of murine resident peritoneal macrophages by interleukin 2 and tumor necrosis factor alpha.

The capacity of recombinant human interleukin 2 (rH-IL2), alone or in combination with recombinant tumor necrosis factor (r-TNF alpha), to activate murine resident peritoneal macrophages to a tumoricidal state was examined. Resident peritoneal exudate cells from C57BL/6 mice were cultured for 18 h with activating agents and washed and the adherent cells (macrophages) were assessed for cytolytic activity against radiolabeled target tumor cells (EL4, P815). Under these conditions, rH-IL2 alone activated macrophages to a tumoricidal state in a concentration dependent fashion. Neither murine nor human r-TNF alpha alone had any activating effect but, when combined with rH-IL2, further stimulated rH-IL2-inducible responses. Using polymyxin B, it was shown that macrophage activation was not due to an inadvertent lipopolysaccharide contamination of the r-TNF alpha or rH-IL2 preparations. It was also unlikely that target cell lysis was a direct result of increased TNF alpha production by rH-IL2 stimulated macrophages since P815 is totally resistant to lysis by r-TNF alpha. Although the lytic effector function was mediated by adherent cells, nonadherent peritoneal exudate cells were required for activation to occur. Furthermore, antisera against murine gamma-interferon, when added to activation cultures, reduced the level of cytolytic activity which developed. These data suggest that rH-IL2-induced peritoneal macrophage activation requires stimulation of nonadherent cells and is dependent upon gamma-interferon mediated mechanisms.     

Comparison of recombinant tumor necrosis factor and the monocyte-derived cytotoxic factor involved in monocyte-mediated cytotoxicity

A direct comparison of recombinant tumor necrosis factor (rTNF) and the monocyte-derived cytotoxic factor (CF) which is involved in monocyte-mediated cytotoxicity revealed immunological, physiochemical, and biological similarities, indicating that TNF is an effector molecule in monocyte-mediated cytotoxicity. Neutralizing antiserum raised against rTNF completely inhibited the ability of CF-containing monocyte supernatants to induce cytolysis and cell death of sensitive target cells and, conversely, antiserum raised against purified CF completely inhibited the cytotoxic activity of rTNF. Both CF and rTNF have an apparent isoelectric point of 5.8-5.9 as determined by chromatofocusing, and a molecular weight of about 40,000 as determined by gel filtration. Moreover, when present in monocyte supernatants with a total protein concentration of about 1 mg/ml and 0.1% sodium dodecyl sulfate, both CF and rTNF migrated with a molecular weight of about 35,000 upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Pure rTNF, however, migrated with a molecular weight of 17,000, suggesting that the relative amount of sodium dodecyl sulfate to protein is critical for dissociating the apparent dimeric structure of TNF. CF and rTNF were also similar with respect to their ability to kill various types of target cells the sensitivity of which to TNF differ, and the dose-response curves of cytotoxicity obtained with CF-containing monocyte supernatants and rTNF were similar. As is the case with anti-CF serum, anti-rTNF serum inhibited drug-dependent cellular cytotoxicity and cytolysis mediated by both freshly isolated monocytes and in vitro cultured unactivated and lymphokine-lipopolysaccharide activated monocytes, indicating that TNF is an effector molecule in both drug-dependent cellular cytotoxicity and "classical" monocyte-mediated cytotoxicity.     

In vitro and in vivo susceptibility of human leukemic cells to lymphokine activated killer activity

The susceptibility of human myeloid and lymphoid leukemic blasts to the lytic action of recombinant interleukin-2 (rIL-2)-generated lymphokine activated killer (LAK) cells was analyzed. With the exception of the K562 cell line, all 9 leukemic cell lines tested were resistant to the natural killer activity of freshly isolated peripheral blood lymphocytes (PBL) from healthy donors but were susceptible to the lytic action of PBL cultured for 3 days in the presence of rIL-2. Of the 32 primary myeloid and lymphoid acute leukemia samples investigated, the great majority were natural killer cell-resistant but were variably sensitive to LAK effectors. Variations in LAK activity were observed according to the donor of PBL, while little or no difference was documented in the capacity to elicit LAK activity of PBL cultured with 100 or 1,000 U of rIL-2/ml. Pretreatment of the leukemic target cells with neuraminidase did not increase substantially their sensitivity to LAK activity. LAK cells generated from the PBL of patients at the onset of the disease or in complete clinicohematological remission lysed Raji cells as efficiently as normal LAK effectors. Finally, LAK cells were capable of abrogating the tumor growth in nude mice of a human leukemic T cell line. These findings demonstrate the susceptibility in vitro and in vivo of human leukemic blasts to the lytic effect of LAK cells and point to a possible clinical exploitment of this new form of adoptive immunotherapy in the management of acute leukemia.     

体外实验中巨噬细胞对肿瘤细胞的作用

利用小鼠肺腺癌细胞母系与巨噬细胞混合培养，通过扫描电镜及３Ｈ－ＴｄＲ掺入，观察巨噬细胞对肿瘤细胞的作用。结果显示：在共培养１２小时时，巨噬细胞呈活跃状态包绕瘤细胞，瘤细胞的细胞溶解率在共培养１２及２４小时时分别为７２．５％和９３．８％，表明，巨噬细胞对肿瘤细胞有抑制和细胞毒作用。     

In vivo Effects of Recombinant Interferon Alpha A/D Incorporated in Gelatin Microspheres on Murine Tumor Cell Growth

Intraperitoneal (ip) injections of gelatin microspheres containing a very small amount of recombinant human interferon alpha A/D (A/D-IFN) (IFN-microspheres) plus free A/D-IFN improved the survival of mice bearing ascitic Meth A-R1 cells which we had isolated as IFN-resistant cells under in vitro conditions. The dose of free A/D-IFN in one injection was 10,000 IU, which was insufficient by itself for manifesting in vivo antitumor activity. In these mice, in vivo Rl cell growth was suppressed and macrophage recruitment was enhanced in comparison with mice receiving other control agents. Administration of IFN-microspheres alone was also effective but less than that of IFN-microspheres plus free A/D-IFN. Peritoneal macrophages obtained from normal or R1-bearing mice receiving ip injection of IFN-microspheres with or without free A/D-IFN were activated to inhibit the in vitro growth of R1 cells. The intratumoral injection of IFN-microspheres strongly inhibited the growth of solid R1 tumors. Intravenous injection of IFN-microspheres was effective in preventing the pulmonary metastasis of B16 melanoma cells. These results indicate that the IFN-microsphere is much more effective against tumors than free A/D-IFN.     

Induction of tumor immunity and natural killer cell cytotoxicity in mice by 5-halo-6-phenyl pyrimidinone

We have investigated the effect of pyrimidinone molecule 2-amino-5-iodo-6-phenyl-4 pyrimidinone (AIPP) on natural killer (NK) cell lytic potential and on the growth of ascitic mammary adenocarcinoma, ACA-755, in B6D2F1 mice. Our studies demonstrated that AIPP was effective in both the prophylaxis and the therapy of this tumor and that the antitumor effect was mediated via induction of NK cell lytic activity. In vitro characterization studies showed that the AIPP-induced cytotoxic cells were not macrophages and exhibited characteristics of NK cells such as morphology of the large granular lymphocytes and sensitivity to asialo GM-1 antibody. Analysis of the mechanism of potentiation of NK cell cytotoxic function by AIPP indicated that the enhancement of cytotoxicity was accomplished by recruitment of NK cell tumor-binding potential (primarily those with large granular lymphocytic morphology) as well as by increased frequency of lytic NK cells. These studies implicate NK cells in the defense against malignant tumors and suggest that regional therapy with AIPP may represent a new therapeutic modality for treatment of cancer.     

Production of tumor necrosis factor-alpha by alveolar macrophages of lung cancer patients

The abilities of human alveolar macrophages (AM) obtained from healthy donors and patients with lung cancer to produce tumor necrosis factor (TNF) were compared with those of their blood monocytes after activation with lipopolysaccharide (LPS). TNF activity was assayed by measuring cytotoxicity against actinomycin D-treated L929 cells and TNF was determined quantitatively by sandwich enzyme-linked immunosorbent assay (ELISA) with polyclonal and monoclonal antibodies against TNF-alpha. Unstimulated AM from healthy donors released variable amounts of TNF spontaneously, whereas blood monocytes did not. When treated with LPS for 24 h, AM and monocytes produced TNF dose-dependently, but TNF production by AM was significantly more than that by blood monocytes. This TNF activity was inhibited completely by monoclonal anti-TNF-alpha antibody. Macrophages generated by in vitro maturation of monocytes induced by granulocyte-macrophage colony-stimulating factor (GM-CSF) produced more TNF than freshly isolated monocytes. No difference was found in the abilities of AM from healthy donors and patients with lung cancer to produce TNF after activation stimuli. These observations suggest that human AM may be important in in vivo antitumor defense of the lung through TNF-alpha production.     

Lymphokine-activated killer cell cytotoxicity against human colon carcinomas enhanced by monoclonal antibody D612

The antibody-dependent cellular cytotoxicity (ADCC) properties of a murine monoclonal antibody (MAb), designated D612 (IgG2a), which reacts with human colon carcinomas, was studied using normal human peripheral blood lymphocytes (PBMNC). Although the level of ADCC of PBMNC with D612 varied among different donors, it was 20 to 30 times higher than the lytic activity of control cultures containing isotype-matched control MAb. Incubation of PBMNC with recombinant interleukin-2 (IL-2) resulted in a 2- to 5-fold augmentation in the cytotoxicity of effector cells exposed to MAb. This augmentation was apparent after subtracting nonspecific cellular cytotoxicity from the total cytotoxicity mediated by activated effector cells in the presence of D612. Optimal stimulation of specific ADCC with IL-2 appeared after 24 hr of culture in 500 U/ml of IL-2, resulting in a 3.8 +/- 1.7 fold increase in lytic units. However, stimulation of ADCC was also evident at 10 U/ml of IL-2. Furthermore, antibody dose titrations with untreated and IL-2 activated effectors showed that the threshold dose of MAb needed for efficient ADCC was reduced by 200-fold with IL-2. Depletion of FcR gamma III-positive lymphoid cells markedly reduced D612 ADCC, demonstrating the participation of NK/LAK cells in D612-mediated ADCC. Low levels of ADCC activity were found associated with adherent cells, either untreated or following their activation with gamma-interferon, while D612 was most active with non-adherent effectors. The specificity and ADCC properties of the D612 MAb suggest that it should be considered as a candidate for immunotherapy of colon cancer, particularly when used in combination with IL-2 plus LAK cell treatment.     

Lymphokine-activated killer cells: lysis of fresh syngeneic natural killer-resistant murine tumor cells by lymphocytes cultured in interleukin 2

Normal splenocytes that are cultured in the lymphokine, interleukin 2 (IL-2), for as short as 2 days develop lytic activity for fresh syngeneic natural killer-resistant tumor cells as well as natural killer-sensitive YAC cells in a 4-hr 51Cr release assay. Lymphokine-activated killer (LAK) cells do not lyse syngeneic fresh lymphocytes but do lyse syngeneic concanavalin A-induced lymphocyte blasts. Lysis is not due to the presence of lectin or xenogeneic serum and appears to be an intrinsic property of lymphocytes activated in IL-2. The activation appears universal in that lymphocytes from all strains of mice activated in this manner exhibited similar patterns of lysis for fresh tumor target cells. To characterize the cells responsible for this lysis, we analyzed the phenotypic expression of surface markers on these cells with depletion techniques using monoclonal antibody and complement. These studies indicate that the precursor of the LAK cell is Thy-1+ and nonadherent to plastic or nylon wool. Lysis of syngeneic tumor was inhibited when LAK cells were treated with an anti-Thy-1.2, or anti-Lyt-2.2 monoclonal antibody and complement but not with anti-Lyt-1.2 monoclonal antibody and complement, indicating that the observed lytic activity was due to a Thy-1+ Lyt-1-2+ cell. Furthermore, LAK cell-mediated lysis could be inhibited by the addition of anti-Lyt-2 or LFA-1 monoclonal antibody to cytotoxicity assays. Cold target inhibition analysis revealed that the syngeneic tumor cells were lysed by recognition of a determinant not present on normal lymphocytes or lymphocyte blasts. This lysis of fresh solid tumor cells by lymphoid cells grown in IL-2 may be of value in the study of tumor-host immunological interactions. The biological significance of tumor lysis by IL-2-activated cells requires further study.     

Serum protease inhibitor abrogation of Newcastle disease virus enhancement of cytolysis by recombinant tumor necrosis factors alpha and beta

Newcastle disease virus (NDV) has been used to induce regression of tumors in human cancer patients. We recently demonstrated that human malignant melanoma cells resistant to the lytic effects of tumor necrosis factor-alpha (TNF-alpha) become susceptible after treatment with NDV. We examined the effects of a serine protease inhibitor, N-1-tosylamide-2-phenyl-ethyl-chloromethyl ketone (TPCK), on viral enhancement of TNF cytotoxicity. Virulent NDV (but neither heat- nor UV-inactivated NDV) induced a 100-fold increase in the sensitivity of murine fibroblast L929 cells to recombinant human TNF-alpha (rHuTNF-alpha), rHuTNF-beta, and recombinant murine TNF-alpha (rMuTNF-alpha). TPCK, which is an inhibitor of chymotrypsin-like proteases, blocked between 42% and 93% of the cytolytic activity of rMuTNF-alpha, rHuTNF-alpha, and rHuTNF-beta toward NDV-treated L929 cells. Similarly, TPCK abrogated 62% of the cytotoxicity of rMuTNF-alpha toward dactinomycin-treated L929 cells. In contrast, TPCK had no effect on WEHI 164 clone 13 cells, a murine fibrosarcoma cell line that is much more sensitive to the lytic effects of TNF and does not show enhanced sensitivity to TNF after treatment with either NDV or dactinomycin. These results suggest a role for a cellular protease in the mechanism by which some viruses sensitize tumor cells to the cytolytic activity of TNF.     

Dual Function of Macrophage Galactose/N-Acetylgalactosamine-specific Lectins: Glycoprotein Uptake and Tumoricidal Cellular Recognition

We investigated whether the interaction of peritoneal macrophages with extracellular ligands is mediated by C-type lectins specific for galactose and N-acetylgalactosamine. The carbohydrate-binding domain of mouse galactose/N-acetylgalactosamine-specific lectin was prepared in a recombinant form. The purified recombinant lectins were tested for competitive inhibition against glycoprotein uptake and against tumoricidal effect. Thioglycolate-elicited macrophages internalized galactosylated bovine serum albumin in vitro . The internalization was blocked by recombinant macrophage lectins. Activated macrophages obtained after intraperitoneal injection of a nonspecific immune potentiator, OK432, did not internalize galactosylated bovine serum albumin. These cells elicited a cytotoxic effect against P815 murine mastocytoma cells, and the effect was blocked by recombinant macrophage lectins. These results indicated that galactose/N-acetylgalactosamine-specific C-type lectins expressed on the surface of inflammatory macrophages and on activated tumoricidal macrophages mediate two distinct functions, i.e. glycoprotein uptake and tumoricidal effector mechanisms.