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A rat anti-recombinant mouse tumour necrosis factor-alpha (rmTNF-α) monoclonal IgM antibody (1F3F3) with high specific binding activity for rmTNF-α was generated. The 1F3F3 monoclonal antibody (mAb) neutralizes the cytotoxic activity in vitro of rmTN F-α on L929 cells and inhibits the binding of radiolabelled rmTNF-α to its putative receptor on L929 cells. The 1F3F3 mAb binds to monomeric, dimeric and trimeric rmTNF-α and does not bind to reduced rmTNF-α, indicating that the recognized epitope is sensitive to denaturation. Using the 1F3F3 mAb as a capturing antibody and a biotinylated anti-rTNF-α as a detecting antibody, we have developed a sandwich ELISA that can specifically detect biologically active mTNF-α with a detection limit of 10 pg mTNF-α/well. This assay correlates well with the classical L929 cristal violet assay for the detection of bioactive rmTNF- in biological fluids. The 1F3F3 mAb inhibits various in vitro biological activities of the rmTNF-α, such as the TNF-α-mediated tumouricidal activity of activated macrophages, the rmTNF-αdependent stimulation of neutrophil degranulation and the growth-promoting effect of rmTN F-α. In vivo the 1F3F3 mAb inhibits lipopolysaccharide (LPS)-induced endotoxic shock. In conclusion, the 1F3F3 mAb is a useful tool to probe rmTNF-α activity both in vitro and in vivo. [ABSTRACT FROM AUTHOR]

Recently we reported the expression of the human natural killer cell associated antigen CD56 (Leu 19/NKH1) in plasma cells of a majority of multiple myeloma (MM) patients. CD56 is known to be an isoform of the human neural adhesion molecule N-CAM which is involved in homotypic adhesive interactions. By immunophenotyping using four CD56 specific monoclonal antibodies and immunoprecipitation analysis we here confirm that the Leu 19 antigen expressed by myeloma plasma cells is identical to N-CAM and corresponds to the 145 kDa isoform. Because of the possible biological role of adhesion molecules on myeloma cells, we compared the expression of N-CAM with the intercellular adhesion molecule 1 (ICAM-1) and the beta 1 and beta 2 integrins. By immunogold-silver staining of cytospin preparations of mononuclear cell suspensions, bone marrow plasma cells of 17 MM patients were analysed. Plasma cells expressed N-CAM (CD56) in 14 patients. ICAM-1 (CD54) in 16 patients, and beta 2 integrins (CD18) in eight patients. beta 1 integrins (CD29) were expressed in all patients. The expression of beta 2 integrins was always very weak while N-CAM, ICAM-1 and the beta 1 integrins showed a moderate to strong positivity. The plasma cells of five haematological normal individuals lacked significant N-CAM expression but were positive for ICAM-1 and both integrin subgroups. One plasma cell leukaemia patient and two out of four end-stage MM patients showed no expression of N-CAM or beta 2 integrins on their circulating plasma cells. Among 11 previously established myeloma cell lines, surface expression of ICAM-1 and the integrins was detected in most cases, while N-CAM was present in only four lines. Most cell lines showed coexpression of the fibronectin receptors (VLA-4 and VLA-5) and the laminin receptor (VLA-6). The collagen receptor (VLA-2) was not expressed. The N-CAM negative cell lines included four cell lines that were derived from plasma cell leukaemia patients. These results indicate that the expression of adhesion molecules is an intrinsic part of the biology of multiple myeloma.

In vitro macrophage- or TNF-alpha-mediated selection procedures on 3LL tumor cells have led to the selection of 3LL variants manifesting a highly reduced sensitivity towards the cytotoxic effects of both TNF-alpha and tumoricidal macrophages, while retaining the parental sensitivity to the cytolytic activity of (i) H2O2, (ii) macrophage-ADCC reactions and (iii) NK cells. A correlation was observed between the TNF-alpha binding capacity of the 3LL cell lines and their susceptibility towards macrophage- and TNF-alpha-mediated cytotoxicity, indicating that macrophage and TNF-alpha sensitivity may partially be regulated at the TNF-alpha receptor level. Further, the selected 3LL variants are gene-regulatory variants rather than cellular mutants, as upregulation of the TNF-alpha receptor by interferon-gamma (IFN-gamma) or 5'-azacytidine treatment resulted in an increased vulnerability of the selected 3LL variants to the killing activity of macrophages and TNF-alpha. The resistance of the 3LL variants to macrophage- and TNF-alpha-mediated cytotoxicity in vitro was reflected by a higher tumorigenic and metastatic potential in vivo. Therefore, the generation of TNF-alpha- and macrophage-resistant variants through immunoselection may contribute to the basic mechanisms of tumor progression and metastasis.

Following sequential interactions between activated syngeneic M phi s and 3LL tumor cells, stable M phi-resistant 3LL variants were isolated. Unlike the unselected 3LL cells, these M phi-selected variants were relatively resistant to the cytostatic and cytolytic activity of activated effector M phi s. Such M phi-resistant 3LL variants evade the M phi tumoricidal activity by at least two mechanisms. Firstly, they manifest a reduced susceptibility towards M phi-related cytotoxins such as TNF. Secondly, they actively suppress the cytotoxic potential of M phi s through secretion of M phi-inhibitory factors. The resistance of the 3LL variants to M phi effector cells in vitro was reflected in vivo by a higher tumorigenic and metastatic potential. No strict correlation was found between the NK sensitivity of M phi-resistant and M phi-sensitive 3LL cells and their metastatic ability. Hence, activated tumoricidal M phi s may play a central role in either the elimination or selection of neoplastic cells.

Considerable numbers of large granular lymphocytes (LGL) were isolated from rat liver by a simple method consisting of sinusoidal lavage at elevated (50 cm water column) perfusion pressure. This method gave a yield comparable with the enzymatic dissociation method commonly used for the isolation of nonparenchymal liver cells, but was shorter in time and had the advantage of avoiding the potentially harmful effects of the dissociating enzymes. The isolated LGL were highly cytotoxic against YAC-1 lymphoma cells and this cytolytic activity was blocked by treatment of the effector cells with an antibody against natural killer cells (anti-asialo GM1). We characterized the hepatic LGL as nonphagocytic, nonadherent, peroxidase-negative and acid phosphatase-positive cells which could be enriched in the low-density fraction of a Percoll gradient. At the light microscopic level, they showed characteristic azurophilic granules which corresponded to strongly osmiophilic granules with a specific morphology in electron microscopy. It is concluded that these LGL are identical to the "pit cells" which were formerly described by electron microscopy in situ as normal components of the liver sinusoids and which are easily recognized by their fine structure. It is also proposed that the liver may represent one of the major natural killer organs.

Lymph node cell populations derived from Trypanosoma brucei-infected mice failed to produce interleukin 2 (IL 2) in response to a potent mitogenic trigger and suppress the potential of normal lymph node cells to secrete IL 2 in co-culture assays. This suppression is promptly restored by the addition of indomethacin, which blocks prostaglandin synthesis, but is not markedly affected by the addition of catalase, which degrades H2O2. The suppression of the IL 2 receptor expression, on the other hand, is not restored by the addition of indomethacin, nor by the simultaneous supply of both indomethacin and catalase. This discrepancy is not caused by an extreme susceptibility of the receptor expression to low prostaglandin (PG) concentrations, but rather by the presence of suppressive cells that operate through a PG-independent mechanism. This suppressive mechanism accounts for the loss of the IL 2 receptors on both the Ly-2+ and the L3T4+ T cell compartment. The indomethacin-treated co-cultures, which manifest a normal IL 2 production but lack the IL 2 receptors, manifest an impaired DNA synthesis and contain a decreased number of T cell blasts.

The in vitro cytotoxic activity of two types of hepatic sinusoidal cells, i.e., natural killer (NK) cells and macrophages (Kupffer cells), was tested against a syngeneic rat colon adenocarcinoma cell line (DHD-K12). Purified hepatic NK cells (85% cells with large granular lymphocyte morphology) were spontaneously cytolytic, whereas Kupffer cells (90% pure) were not able to kill the DHD-K12 cells. This carcinoma cell line was found to be resistant to the action of mouse recombinant tumor necrosis factor which is considered as the major cytolytic molecule secreted by macrophages. However, colon carcinoma cells were readily lysed by soluble factors present in the culture supernatant of NK cells. It is postulated that hepatic NK cells, which are strategically located within the lumen of the sinusoids, may form a first line of defense to metastasizing colon carcinoma cells.

Intravenous inoculation of the AKR mouse-strain-derived BW lymphoma into CBA recipients resulted in a case of liver metastasis; cells derived from this metastatic nodule were termed BW-Li cells. BW-Li cells, upon reinoculation, generated metastases in the spleen, liver, kidney and ovaries in 100% of CBA recipients. Furthermore, BW-Li cells, in contrast to BW cells, were found to infiltrate in vitro monolayers of hepatocytes, thus confirming their inherent invasive potential. Analysis of the alloantigenic phenotype of BW-Li cells revealed that such cells were Thy 1.1+, Thy 1.2+, Lyt 1.2+, Lyt 1.1-, Lyt 2- and H-2Dk+, as compared to BW cells which exhibited the membrane phenotype Thy 1.1+, Thy 1.2-, Lyt 1.2-, Lyt 1.1-, Lyt 2-, H-2Dk-. BW-Li cells also differed functionally from BW cells since these cells secreted IL-2 upon stimulation with Concanavalin A. BW tumor transplantation experiments were repeated in a semi-allogeneic F1 strain combination, i.e. (AKR X CBA)F1, and again a case of massive liver metastasis was observed. Cells derived from these liver metastases (termed BW-O-Li) manifested an invasive and metastatic potential similar to that of BW-Li cells. Furthermore, BW-O-Li cells secreted IL-2 upon stimulation with Con A and manifested the following alloantigenic phenotype: Thy 1.1+, Thy 1.2+, Lyt 1.2+, Lyt 1.1-, Lyt 2-, H-2Dk+ and H-2Kk+. These results indicate that BW-Li and BW-O-Li cells are functional T-cell hybrids which express T-cell markers derived from BW cells and Thy 1.2+ CBA host cells. The acquisition of host-derived T-cell properties may have led to the expression of metastatic and invasive capabilities. From these results we conclude that the acquisition of metastatic properties following somatic cell fusion with normal lymphoreticular cells may represent a mechanism for tumor progression in vivo.