Activation of human monocyte and natural killer cell-mediated tumour cell killing by two dialysable thymic factors

The human Clara cell protein: biochemical and biological characterisation of a natural immunosuppressor

The Clara cell protein, the human counterpart of rabbit uteroglobin, exerts an anti-inflammatory action by interfering in different ways with the cytokine-network. Firstly, CC16 behaves like an anti-cytokine by downregulating the production of IFN-gamma, IL-1 and TNF-alpha by stimulated leukocytes. The extent of inhibition depends on the inducing agent (being maximal when IL-2 is used as inducer) and varies with the applied concentration of CC16. Secondly, the protein reduces the antiviral activity and the augmentation of phagocytosis induced by IFN-gamma. In both cases (inhibition of production and biologic activity) there is a 50% reduction in the presence of 10 ng/ml CC16. The natural and IFN-gamma-enduced cytotoxicity of NK-cells however, are enhanced by the presence of CC16, indicating a more complex interaction of CC16 with the immune-system. The immunosuppressive properties make CC16 a promising agent for the treatment of inflammatory reactions and auto-immune diseases.

Enhancement of human NK and LAK cytotoxicity against HCMV-infected cells by rhamnogalacturonan: specificity of reaction

Human peripheral blood mononuclear cells (PBMC) and their subpopulations obtained from healthy donors were used to study improvement of MHC-unrestricted cytotoxic reactions against cells infected with human cytomegalovirus (HCMV) at different multiplicities of infection. Natural killer (NK) and lymphokine-activated killer (LAK) cytotoxicity against HCMV-infected cells was greatly enhanced in the presence of rhamnogalacturonan (500 ng/ml). The increase of the multiplicity of infection from MOI 0.1 to 1.0 had only a slight effect on cytotoxicity enhancement by rhamnogalacturonan. The chemical specificity of interaction of rhamnogalacturonan with effector cells and virus-infected cells was found to be analogous to the interaction with tumor cells, i.e., both types of target cells must express a receptor for rhamnogalacturonan since rhamnogalacturonan-mediated enhancement of NK and LAK cytotoxicity against HCMV-infected cells was similarly inhibited by preincubation of CD56+ effector cells with 60% deacetylated D-mannose pentaacetate.

Comparison of hexose acetate-specific receptors isolated from human leukocytes showing competitive inhibition of human CD56+NK and LAK cytotoxicity

Specific cytotoxicity of human CD56+NK and LAK cells was quantitatively inhibited by acetylated mannose, galactose and glucose (Scand. J. Immunol., in press). The respective NK cell receptors were isolated from human leukocyte lysates by affinity chromatography based on 60% deacetylated penta-acetates of mannose, galactose and glucose. All three affinity isolates contained a main component with +/- 87 kDa molecular mass exhibiting about the same patterns of isoforms at pI 4.90, 4.75, 4.60 and 4.50 in isoelectric focusing. Moreover, preincubation of tumor target cells with the three 87-kDa receptors revealed very similar inhibitory potentials for human NK and LAK cytotoxicity showing dose-dependent inhibition between 20 (no inhibition) and 700 pmol/ml (100% inhibition) receptor concentration. The data support the assumption that the three affinity isolates contain the same type of receptor directed against a unique epitope common to acetylated mannose, galactose and glucose.

Anti-(transforming growth factor beta) antibodies with predefined specificity inhibit metastasis of highly tumorigenic human xenotransplants in nu/nu mice

Monoclonal antibodies (mAb) were prepared against conjugated transforming growth factor beta 1 (TGF beta 1) peptides: amino acid positions 48-60 and positions 86-101. Two antibodies, mAb 16-3G1 [anti-(48-60)] and mAb 5-2G6 [anti-(86-101)] cross-reacted with native TGF beta 1, -beta 2 and -beta 3 (16-3G1) or only with native TGF beta 1 (5-2G6). Both mAb were used to characterize TGF beta-mediated effects on the metastatic potential in nude mice of human carcinoma cell line SLU-1 and its metastatic subline SLU-M1. Autocrine TGF beta 1-mediated up-regulation of cell proliferation and its suppression by anti-TGF beta antibodies in vitro was recorded for SLU-M1 cells whereas SLU-1 cell proliferation in vitro appeared to be refractory to anti-TGF beta antibodies and exogenous TGF-beta 1. However, the potential of s.c. tumours to develop distant metastases in nude mice was about the same for both cell lines. Development of primary tumours and distant metastases could be suppressed by treatment of mice with anti-TGF beta antibodies. Thus we assume that the metastatic potential of tumour cells is independent of TGF beta-mediated growth-regulation effects in vitro. The anti-TGF beta-induced suppression of tumour progression and metastasis in nude mice might rather result from stimulation of the immune surveillance. TGF beta-mediated autocrine down-regulation of MHC-unrestricted cytotoxicity of activated human monocytes and CD56+ LAK cells and its reversion by anti-TGF beta antibodies could be readily demonstrated. In all our experimental series, the neutralizing potential of both anti-TGF beta antibodies, though directed against opposite sites of the TGF beta 1 molecule, was very similar.

Chemospecificity and cross-reactivity of target cell recognition by human CD56+ NK and LAK cells

Inhibition of specific cytotoxicity of highly purified (> 95%) human CD56+ NK and LAK cells against K562 tumour cells was studied with various sugar acetates. Maximum inhibitory specificity was obtained with 60%-deacetylated penta-acetates of mannose, galactose, glucose, or 80%-deacetylated penta-O-acetate of N-acetyl neuraminic acid. The inhibition was strictly dosedependent and 100% inhibition was achieved in the concentration range of 500-1000 nmoles/ml with all four sugar acetate samples. Enhancement of specific cytotoxicity in the presence of rhamnogalacturonan (RG; 500 ng/ml), acting as a bridging molecule, was also inhibited in a dose-dependent manner with the same inhibitory specificity and within the same concentration range indicating involvement of the same number of sugar acetate-specific receptors. Moreover, formation of lytic CD56+ effector cell/tumour cell (E/T) conjugates was equally well inhibited whereas formation of total E/T conjugates was only partially inhibited (NK: 44-73%; LAK: 46-50%). E/T conjugate formation in the presence of RG was enhanced. Inhibition of the enhancement of formation of lytic E/T conjugates in the presence of RG was again completely accomplished with the same inhibitory specificity and within the same concentration ranges as recorded for E/T conjugate formation in the absence of RG. However, inhibition of total E/T conjugate formation was again only partially achieved at the given concentrations. The data support the assumption of an NK cell receptor with specificity for acetylated carbohydrate moieties on target cells or on bridging molecules such as RG.

Bone marrow-derived T-cell clones obtained from untreated acute myelocytic leukemia exhibit blast directed autologous cytotoxicity

The eradication of minimal residual blast populations by activation of autologous cytotoxic cells with interleukin 2 (IL-2) is a new promising tool in the treatment of acute myelocytic leukemia (AML). However, the immunological effector cells are not yet clearly defined. The present study was designed to investigate the presence of cytotoxic precursor cells in active AML and to identify phenotypical and functional characteristics of autologous anti-leukemic cytotoxic effector cells. For this purpose, mononuclear cells (MNC) containing at least 70% leukemic blasts were isolated from bone marrow of untreated AML and cultured in the presence of 3000 IU/ml recombinant IL-2 (rIL-2) for 6-8 weeks. Under these conditions, T-cells were selected in the bone marrow cultures and overgrew the leukemic blasts. The resulting T-cell populations were cloned by limiting dilution and the clones obtained were characterized for their phenotypical and functional patterns. Totally, cloning resulted in 68 clones and a few cell lines. The clonality was verified by RT PCR analysis of TCR V beta gene expression. All clones obtained stained positive for CD2, CD3, DR and CD56. The vast majority (68%) of T-cell clones/lines was CD4+, a few clones expressed CD8 (19%) or CD4 and CD8, and four clones were of TCR gamma delta origin. Seven of 15 clones tested, including three CD4+, two CD8+ and two TCR gamma delta(+)-clones were found to be cytotoxic against autologous leukemic blast cells. All except one clone expressed oncolytic activities against allogeneic blasts too. One of the TCR gamma delta(+)-clones demonstrated NK activity by lysis of K562 targets. The majority of the T-cell-clones released IL-2, IL-8, TNF-alpha, GM-CSF but only a few IFN gamma and expressed high levels of mRNA for IL-2, TGF-beta and IL-10. None of the clones was found to produce IL-3, IL-4, IL-7 and TNF-beta. The data provide evidence of the existence of T-cell precursors in untreated AML bone marrow differentiating to cytotoxic cells with activity against autologous and allogeneic AML blast cells.

Identification of a mannose-acetate-specific 87-kDa receptor responsible for human NK and LAK activity

Target cell recognition and cytotoxicity of human CD56+ NK and LAK cells is readily inhibited by acetylated mannose. Two respective NK cell receptor candidates were isolated from human leukocyte lysates by mannose acetate affinity chromatography. The 87-kDa receptor showed sequence homologies with lactoferrin and the 59-kDa receptor represented a complex of two Ca-binding proteins MRP-8 and MRP-14 reportedly expressed only by cells of myeloid origin. The 87-kDa receptor exhibited heterogeneity in isoelectric focusing and behaved entirely differently from lactoferrin. Preincubation of tumor target cells with the 87-kDa receptor inhibited competitively target cell recognition and cytotoxicity of human CD56+ NK and LAK cells.

Enhancement of MHC-unrestricted cytotoxic activity of human CD56+ CD3- natural killer (NK) cells and CD3+ T cells by rhamnogalacturonan: target cell specificity and activity against NK-insensitive targets

Rhamnogalacturonan-mediated enhancement of MHC-unrestricted cytotoxicity was studied with freshly isolated CD56+CD3- natural killer (NK) cells, interleukin-2 (IL-2)-activated CD56+ lymphokine-activated killer (LAK) cells und IL-2/anti-CD3-activated T cells as effector cells using NK-sensitive and NK-insensitive tumor cells as targets. The rhamnogalacturonan fractions IM, IP, and IQ were prepared from commercially available extracts of Viscum album. The dose/response relation of IM, IP, and IQ demonstrated the presence of various concentrations of cytotoxicity-enhancing compounds in all three fractions that were identified as rhamnogalacturonans by degradation studies with poly-alpha-D-galacturonidase (EC 3.2.1.15) and alpha-1,6-rhamnosidase (EC 3.2.1.40). Specific cytotoxicity of all three effector cell populations as well as the respective rhamnoagalacturonan-mediated cytotoxicity enhancement was readily inhibited in a dose-dependent manner by 60%-deacetylated mannose pentaacetate. Rhamnogalacturonan-mediated enhancement of cytotoxicity of fresh CD56+ NK cells was also observed with four of five NK-insensitive tumor cells as targets, indicating that the effector-cell/tumor-cell bridging activity of rhamnogalacturonans renders NK-insensitive targets susceptible to NK-mediated lysis. Moreover, the rhamnogalacturonan-mediated cytotoxicity enhancement became even more prominent when lymphokine-activated CD56+ LAK and CD3+ T cells were assayed with the NK-insensitive tumor cell targets.

Activation of human monocyte/macrophage cytotoxicity by IL-2/IFN gamma is linked to increased expression of an antitumor receptor with specificity for acetylated mannose

Spontaneous cytotoxicity of human monocytes (purity: 92-95%) against K562 tumor cells was only observed in 31% healthy donors but, in the presence of rhamnogalacturonan (500 ng/ml), enhanced cytotoxicity was recorded for 79% (n = 14) of the donors. Monocytes activated by culturing with interleukin-2 and/or IFN gamma showed increased antitumor cytotoxicity against K562 tumor cells in 86% (n = 21) of the donors exhibiting additional increases in specific cytotoxicity when the cytotoxicity assays were carried out in the presence of rhamnogalacturonan. Increases of monocyte cytotoxicity achieved by activation with cytokines coincided with increased formation of monocyte/tumor cell conjugates. Similarly, increased monocyte cytotoxicity mediated by rhamnogalacturonan also correlated with increased monocyte/tumor cell conjugate formation most likely due to effector cell/target cell bridging as was originally described for rhamnogalacturonan interacting with CD56+ natural killer or lymphokine-activated killer cells and tumor cells. The chemospecificity of the monocyte-based receptors responsible for cytotoxicity and for monocyte/tumor cell conjugate formation, as well as for their rhamnogalacturonan-mediated enhancements, appears to be identical since all these effects could be inhibited in a dose-dependent manner by partially deacetylated (60%) mannose pentaacetate.

Mechanism of stimulation of human natural killer cytotoxicity by arabinogalactan from Larix occidentalis

Cultures of human peripheral blood mononuclear cells (PBMC) as well as cultures of preseparated peripheral non-adherent cells (PNAC) and monocytes showed enhancement of natural killer (NK) cytotoxicity against K562 tumor cells when pretreated with arabinogalactan from Larix occidentalis for 48-72 h. Lack of enhanced responses of PBMC (37% of donors) did not necessarily mean that PNAC and monocyte cultures were also non-responsive to arabinogalactan treatment. Moreover, PBMC, PNAC and monocytes of individual donors could exhibit various responses to arabinogalactan when cultures derived from bleedings after intervals of several months were assayed. Arabinogalactan-mediated enhancement of NK cytotoxicity was not initiated directly but was found to be governed by the cytokine network. Generally, arabinogalactan pretreatment induced an increased release of interferon gamma (IFN gamma), tumor necrosis factor alpha, interleukin-1 beta (IL-1 beta) and IL-6 but only IFN gamma was involved in enhancement of NK cytotoxicity since cytotoxicity enhancement of PBMC and PNAC but not that of monocytes could be blocked when anti-IFN gamma antibodies were present during pretreatment. The presence of anti-IL-2 antibodies completely blocked NK cytotoxicity enhancement of PBMC and only moderately that of PNAC and monocytes. This blocking effect was also observed when no detectable increase of IL-2 release could be recorded. The receptor specificity of arabinogalactan is not well characterized. Initial information obtained from comparative studies indicated that arabinogalactan presumably interacts with a receptor that showed specificity for a NK-cytotoxicity-enhancing oligo-saccharide from Viscum album extracts since the action of both components was not synergistic but rather competitive.

The CySF-L2 factor from dialysable human leucocyte extract activates natural killer cytotoxicity by induction of interferon gamma

The mechanism of natural killer (NK) cytotoxicity activation of human peripheral blood mononuclear cells (PBMC) by CySF-L2 was elucidated. CySF-L2 is a cytotoxicity-stimulating factor isolated from dialysable human leucocyte extract, which activates NK cytotoxicity against NK-sensitive and insensitive tumour cells (K562; Daudi; Raji; MOLT4) when preincubated with effector cells for 72 h. CySF-L2-mediated activation was synergistic to interleukin-2(IL-2)-mediated activation of NK cytotoxicity. Induction of interferon gamma (IFN gamma) release was the crucial step during CySF-L2-mediated NK cytotoxicity activation since enhancement of NK activity was completely blocked when anti-IFN gamma antibodies were present during treatment of PBMC. Anti-IFN alpha, anti-TNF alpha (tumour necrosis factor alpha) anti-IL-1 and anti-IL-2 antibodies showed no blocking effect. Analysis of the supernatant culture medium after 72 h incubation of PBMC and their highly purified subpopulations demonstrated that CySF-L2 induced release of IFN gamma from CD3+T cells and CD56+CD3- NK cells and of TNF alpha and prostaglandin E2 from monocytes. CySF-L2 was also capable of activating NK cytotoxicity of highly purified (98%) CD56+CD3- NK cells as well as of monocytes (94% pure). Cell cooperation studies connected with analysis of cytokine release and enhancement of NK cytotoxicity indicated that CySF-L2 might play an essential role in the up and down regulation of NK cytotoxicity by the cytokine network.

Chemical specificity of effector cell/tumor cell bridging by a Viscum album rhamnogalacturonan enhancing cytotoxicity of human NK cells

The component in Viscum album extract Iscador-M enhancing the NK cytotoxicity of human CD56+CD3- NK cells (87-95% enrichment) in cocultures with K562 tumor cells and increasing the formation of NK cell/tumor cell conjugates was identified as a rhamnogalacturonan. Both activities were abolished by treatment of V. album extract with poly-alpha-D-galacturonidase and alpha-rhamnosidase and both activities were inhibited in the presence of galacturonic acid and acetylated rhamnose (6-deoxymannose). Inhibition was also observed in the presence of structurally related derivatives such as acetylated mannose or acetylated mannonic acid gamma-lactone, the latter exhibiting a 5-10-fold higher inhibitory potential. The rapid formation of NK cell/tumor cell conjugates in the presence of V. album extract was based on the bridging of NK cells with tumor cells by rhamnogalacturonan. Using a specifically adapted agglutination assay, the saccharide residues of the rhamnogalacturonan interacting with NK cells and tumor cells could be identified by the formation of homologous cell conjugates induced by acetylated rhamnose or acetylated mannose conjugated to dextran and by polygalacturonic acid: terminal acetylated rhamnose or acetylated mannose bound only to NK cells in a dose-dependent manner but not to K562 tumor cells, and terminal galacturonic acid only to K562 tumor cells but not to NK cells. This type of bridging represents a novel mechanism of enhancement of NK cytotoxicity.

A Viscum album oligosaccharide activating human natural cytotoxicity is an interferon gamma inducer

Commercial Viscum album extract Helixor-M contains a dialysable oligosaccharide (HM-BP) that activates natural killer (NK) cytotoxicity against K562 tumour cells when preincubated with human peripheral blood mononuclear cells (PBMC) for 72 h. The activated effector cells were exclusively found in the monocyte/macrophage subpopulation. However, when peripheral non-adherent cells (PNAC) were preincubated with HM-BP for 72 h the NK cytotoxicity of CD56+CD3- NK cells was activated. This discrepancy was found to be due to the release of prostaglandin E2 from activated monocytes/macrophages, which blocked activation of the cytotoxicity of NK cells. Analysis of the supernatant culture medium after 72 h preincubation demonstrated that HM-BP induced release of interferon gamma (IFN gamma) from T cells (preferentially from CD3+CD4+ cells) and of tumour necrosis factor alpha (TNF alpha) from monocytes/macrophages. Release of IFN gamma was the crucial step for activation of NK cytotoxicity since enhancement of NK cytotoxicity during pretreatment of PBMC or PNAC with HM-BP was completely blocked in the presence of anti-IFN gamma antibodies. Anti-interleukin-2, anti-TNF alpha or anti-IFN alpha antibodies had no effect on the HM-BP-induced enhancement of NK cytotoxicity. The activation of the NK cytotoxicity of nonadherent cells by interleukin-2 treatment was found to be synergistic to the enhancement of NK cytotoxicity by treatment with HM-BP.

Interleukin 2-induced protein phosphorylation/dephosphorylation in human non-adherent peripheral blood mononuclear cells: initial phosphorylation of two 75-kDa proteins

The kinetics of protein phosphorylation/dephosphorylation induced by IL-2 in cells of the non-adherent subpopulation of human peripheral blood mononuclear cells after pretreatment with and without phytohaemagglutinin (PHA) was analyzed by two-dimensional gel electrophoresis. In cells not pretreated with PHA, IL-2 induced the phosphorylation of two 75-kDa proteins with pI values 6.6 and 6.9, detectable 30 min after addition of IL-2, and the dephosphorylation of a 94-kDa (pI 4.0) protein, two 85-kDa (pI 5.2 and 5.4) proteins and a 65-kDa (pI 4.9) protein. The latter three phosphoproteins were found to be unlabelled after PHA pretreatment, but upon IL-2 stimulation the 94-kDa and the 85-kDa proteins became labelled simultaneously with two minor phosphoproteins of 68 kDa (pI 5.7) and 37 kDa (pI 4.8). Moreover, PHA pretreatment of cells induced a drastic phosphorylation of a 48-kDa (pI 6.5) and a 46-kDa (pI 6.7) protein, which were gradually dephosphorylated after IL-2 addition. Phosphorylation of the 75-kDa proteins could not be detected when the cells were pretreated with PHA prior to labelling. These results suggest that IL-2-induced phosphorylation of the 75-kDa proteins is one of the early events in IL-2 stimulation, an event already completed in PHA-pretreated cells since PHA is known to induce release of IL-2. Furthermore, the retarded appearance of the labelled 75-kDa proteins suggests an IL-2-induced de novo synthesis, possibly reflecting the expression of the 75-kDa alpha chain of the IL-2 receptor.

Biochemical characterization of a component in extracts of Viscum album enhancing human NK cytotoxicity

Enhancement of human NK cytotoxicity in the presence of fresh Viscum album extract and some commercial V. album extracts Iscador correlated strictly with an increased formation of lytic effector cell/K562 tumor cell conjugates in the single-cell assay. Both activities were completely destroyed by pretreatment of V. album extracts with pectinase, hemicellulase, amyloglucosidase and alpha-glucosidase, but not with proteases and RNase, i.e., the activities are linked to a polysaccharide. The active component in V. album extract was non-dialysable at a molecular weight cutoff of 10,000. Inhibition of both activities was observed with D-galacturonic acid, poly-galacturonic acid and pectins. The site of galacturonic acid-specific interaction could be identified on the effector cells. The rate of effector cell/tumor cell conjugate formation in the presence of V. album extracts, as well as the abrogation of both activities by pretreatment of V. album extracts with exoglycosidases specific for sugars other than galacturonic acid indicated an action of the NK cytotoxicity-enhancing component on the basis of a bridging mechanism. However, no conclusive results could be obtained for the structural specificity of the site interacting with the target cells.