NS-1 Cells Research Articles

Monoclonal antibodies to hydroxyindole O-methyltransferase from bovine pineal gland

Hybridomas that produce monoclonal antibodies to bovine hydroxyindole O-methyltransferase have been established by immunizing a mouse with hydroxyindole O-methyltransferase partially purified from bovine pineal glands followed by fusion of the spleen cells with myeloma NS-1 cells. Twenty-three clones have been isolated by screening the medium by two different methods. These clones produced various antibodies with different binding properties. Most of the antibodies belonged to IgG1 subtype, while 7 clones produced IgG2α or IgG2β antibodies. Three antibodies inhibited enzymatic activity, whereas others did not. Antibodies of 7 clones recognized enzyme protein denatured with sodium dodecyl sulfate, while other antibodies reacted only with native enzyme protein. Thus a variety of monoclonal antibodies will offer us a good tool for immunohistochemical localization of the enzyme, immunoaffinity purification of hydroxyindole O-methyltransferase, and isolation of the cDNA clones encoding it. We also report here on the immunohistochemical demonstration of hydroxyindole O-methyltransferase in bovine pineal gland and a new immunoaffinity procedure to purify the enzyme to homogeneity by use of monoclonal antibodies.

Human monoclonal antibodies to thyroid antigens derived by hybridization of lymphocytes from a diabetic patient

Human monoclonal antibodies to human endocrine cells have been obtained following the generation of immunoglobulin-secreting interspecies lymphocyte hybridomas. Peripheral blood lymphocytes from an adult patient presenting with acute onset, Type I, diabetes mellitus were fused in vitro with mouse myeloma cells of the NS1 cell line. Initial selection of resulting hybridomas was made by their ability to proliferate in HAT medium. Those hybridomas secreting human immunoglobulins were identified by radioimmunoassay and, thereafter, cloned at frequent intervals to ensure continued antibody production. Human monoclonal antibodies selected in this manner are being employed to identify those epitopes which are common antigenic targets during initial stages of autoimmune-mediated diabetes mellitus and associated multiple endocrinopathies. Of these antibodies, one (HML 3.22) recognizes an epitope present on the human TSH receptor and a second (HML 3.21) identifies a component of thyroglobulin. The potential value of human monoclonal antibodies as probes for analyzing autoimmune-mediated endocrine diseases is discussed.

Studies of the role of the Escherichia coli heat shock regulatory protein sigma 32 by the use of monoclonal antibodies.

Purified Escherichia coli RNA polymerase containing the heat shock regulatory protein sigma 32 (gprpoH) was used to inject BALB/c mice, and the spleen cells of an immunized mouse were fused to NS1 cells. Three stable cell lines were isolated which produced monoclonal antibodies to sigma 32. The antibodies varied in their ability to bind sigma 32 which was bound to core polymerase. Each of the antibodies was found to inhibit transcription from the rpoD heat shock promoter to a different extent. Extensive homology at the protein level has been observed between various sigma factors. The monoclonal antibodies to sigma 32 were tested for the ability to cross-react with sigma 70 on Western blots. None of the antibodies reacted with electroblotted sigma 70. The sigma 32 content was examined in total cell extracts during heat shock Levels of sigma 32 were found to increase approximately 4-fold over pre-heat shock levels at five min after temperature upshift. These levels remained slightly elevated above pre-heat shock levels at 10 and 15 min after temperature upshift.

A phenotypically dominant regulatory mechanism suppresses major histocompatibility complex class II gene expression in a murine plasmacytoma.

The expression of major histocompatibility complex (MHC) class II antigens is down-regulated when B cells differentiate into plasma cells. We have studied the mechanism of down-regulation of MHC class II expression in a BALB/c strain-derived murine plasmacytoma cell line, NS1. NS1 cells express MHC class I antigens but not MHC class II antigens. We tested 20 uncloned hybrid cell lines obtained from the fusion of NS1 cells with MHC class II-expressing splenic B cells prepared from CBA, SJL or BALB/c mice. All the hybrid cell lines expressed MHC class I antigens of either or both parental haplotypes but did not express MHC class II. One NS1 X splenic B cell hybrid clone, K3, was used to further validate these results; K3 cells expressed MHC class I but not MHC class II antigens. K3 was fused to the MHC class II-expressing B lymphoma A20, and the seven resulting hybrid cell lines were again found to express MHC class I but not MHC class II antigens. Since NS1 is a subclone of the P3-X63Ag8 murine plasmacytoma, we also tested one P3-X63Ag8 x splenic B cell hybrid, Sp2/0, and two Sp2/0 x splenic B cell hybrids. All were found to express the appropriate MHC class I antigens but did not express MHC class II. Thus, our results suggest that the NS1 plasmacytoma suppresses MHC class II expression by a phenotypically dominant regulatory mechanism. We found that NS1 cells express correctly sized mRNA for the MHC class II genes A alpha, E alpha and the invariant chain. The co-expression of MHC class I protein and I-A and I-E region gene transcripts provides strong evidence that the MHC gene cluster is structurally intact, and that lack of class II expression is due to a genetic regulatory mechanism. The amounts of class II mRNA expressed by NS1 cells were at least equivalent to those found in splenic lymphocytes. Therefore, this regulation must operate post-transcriptionally.

Production and characterization of high affinity monoclonal antibodies to cyclic anti-depressant molecules.

A procedure is reported by which high levels of the tricyclic molecule desipramine was modified and conjugated at high density to the carrier molecules keyhole limpet hemocyanin and bovine serum albumin so that these could be used as immunogens in Balb/c mice. Such conjugates generated immune responses with high levels of antibody with specificity for the tricyclic. B cell hybridomas generated by fusion of immune Balb/c splenocytes to NS-1 cells which secreted monoclonal antibodies with specificity for the tricyclic were selected in a standard ELISA. In this report, we show that the binding constants of these monoclonal antibodies with various haptens can be assessed accurately by measuring fluorescence polarization, that a high degree of cross-reactivity between the monoclonals and various tricyclics exists, and that this procedure can be used to generate monoclonal antibodies of high binding constants.

Inhibitory effects of monoclonal sperm antibodies on the fertilization of mouse oocytes in vitro and in vivo

The inhibitory effects of monoclonal antibodies on the fertilization of mouse oocytes were evaluated in vitro and in vivo. Among the 40 sperm-specific monoclonal antibodies that had been examined, nine showed significant inhibition of the fertilization of mouse oocytes in vitro. MS 204 was shown to cause a high incidence of penetration of the zona pellucida of mouse eggs by multiple sperm, when the sperm concentration for insemination exceeds 1 × 10 5/ml. This antibody prevented further penetration of the vitelline membrane by sperm. On the other hand, sperm penetration to zona was inhibited in the presence of MS 207. However, neither MS 204 nor MS 207 caused significant inhibition of penetration of zona-free mouse or hamster eggs by sperm. MS 204 and MS 207 were also found to inhibit the fertilization of mouse oocytes in vivo and embryo development in vitro, when superovulated mice were injected intraperitoneally with given doses of antibodies prior to the mating. Further in vitro culture of the recovered 2-cell oocytes revealed little or no further embryo development beyond two- to four-cell stages. In the controls, > 80% of the retrieved oocytes were fertilized and successively developed to the blastocyst stages in vitro when the ascites fluid from NS-1 cells was administered. Two of the monoclonal antibodies generated against human sperm antigens. HS11 and HS 63, were shown to cross-react specifically with mouse sperm acrosomal antigens and also inhibited the fertilization of mouse oocytes in vitro and in vivo. The results of this study suggest that some monoclonal antibodies to sperm acrosomal antigens exhibit strongly inhibitory effects on the in vitro and in vivo fertilization of mouse oocytes as well as subsequent development of early embryos. As a comparative control, rabbit antisera against sperm-specific enzymes, lactate dehydrogenase-X and 3-phosphoglycerate kinase-2, showed little or no inhibition on the fertilization of mouse oocytes in vitro or in vivo or the subsequent embryo development.

Monoclonal antibodies to human squamous cell carcinoma of the lung and their application to tumor diagnosis

Three immunoglobulin G1 monoclonal antibodies, LuCa2, LuCa3, and LuCa4, were produced by fusing murine myeloma NS1 cells with splenocytes obtained from a BALB/c mouse immunized with SK-MES1 cells derived from human squamous cell carcinoma of the lung. These three monoclonal antibodies were shown to recognize different protein antigens on SK-MES1 cells by indirect immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. While the pattern of cell line distribution of antigens recognized by these antibodies was not tumor type specific, their reactivity with tissue and pleural effusion was much more informative than with cell lines. The presence of target antigens in vivo was analyzed by immunoperoxidase staining of frozen tissue sections and immunofluorescence staining of tumor cells in pleural effusions. LuCa2 antibody was reactive with lung squamous carcinoma and adenocarcinoma tumor tissues and pleural effusions, but only infrequently with those of small cell carcinoma. This antibody was also reactive with many tumor tissues from other organs as well as with various normal tissues, including alveoli and bronchus. LuCa3 and LuCa4 antibodies reacted with lung squamous carcinoma in tissues and pleural effusions, but not with lung adenocarcinoma nor with small cell carcinoma. These two antibodies reacted only weakly with normal squamous tissues of the esophagus, skin, and cervix uteri, but not with various other normal tissues. Moreover, LuCa3 had weak reactivity with squamous cell carcinoma tissue of tongue and esophagus, whereas LuCa4 had no reactivity with nonpulmonary tumor tissues. LuCa3 and LuCa4 antibodies should be of clinical interest, because our data suggest that these antibodies may be potentially useful for the diagnosis of the histological type of lung tumor cells in both cancer tissue and pleural effusions.

Induction of monocyte-macrophage procoagulant activity by transformed cell lines.

Human peripheral blood monocytes and mature macrophages were found to produce significant procoagulant activity (PCA), identified as tissue factor, on exposure to a variety of human (K562, HL60, Raji) and murine (TU5, NS-1) transformed cell lines. The monocyte procoagulant response was vigorous, generating PCA to a level nearly comparable to the response to endotoxin, a known stimulant for monocyte PCA. The response was rapid and could be fully elicited, in a dose-dependent fashion, within 4 hr with HL60 and Raji cell lines and within 14 hr with K562, TU5, and NS-1 cells. The monocyte PCA-inducing activity was found to reside in the membrane fraction of transformed cells. Other transformed human (Laz 509, Laz 221, Laz 156, U937, CEM) and murine (L1210, P815, TLX9, WEHI 164) cell lines had little, if any, activity. The induction of monocyte PCA by transformed cells most probably was not due to an allogeneic signal, as 1) the K562 and HL60 cell lines were potent PCA inducers despite the lack of class II histocompatibility antigen expression, whereas Laz 156, which did express HLA antigens, was ineffective; 2) mouse peritoneal macrophages responded with the production of strong PCA to the syngeneic transformed cell lines TU5 and NS-1. The monocyte-macrophage procoagulant response to transformed cell lines appeared to be independent of T lymphocytes. Indeed, monocytes purified on the basis of reactivity with monoclonal antibody Mo2 and sorting or depleted of contaminating T cells by anti-T3 antibody and complement responded similarly to conventional monocyte preparations. The production of tissue factor by monocyte-macrophages in response to exposure to some tumor cells may represent a mechanism whereby blood coagulation is activated in malignancy.

Biochemical characterization of the cholesterol-dependent growth of the NS-1 mouse myeloma cell line

The biochemical basis for the cholesterol-dependent growth phenotype of the NS-1 myeloma cell line has been investigated. In one series of experiments, the growth response of NS-1 cells to several of the intermediates of cholesterol biosynthesis was studied in serum-free medium. The cholesterol precursors, squalene and lanosterol, were totally ineffective in promoting NS-1 cell growth. In contrast, cholesterol precursors downstream from lanosterol, i.e., desmosterol and 7-dehydrocholesterol, completely replaced cholesterol in supporting NS-1 cell growth. In a second series of experiments, NS-1 cells and NS-1-503 cells (a cholesterol growth-independent variant of NS-1 cells) were labelled with [2- 14C]acetate and the distributions of radioactivity between cholesterol and its precursors were determined by thin-layer chromatography using two different solvent systems. The major labelled sterol product (>80%) in NS-1 cells after a 24-h exposure to [2- 14C]acetate was lanosterol. In contrast, the major labelled sterol product (>95%) in NS-1-503 cells after a 24-h exposure to [2- 14C]acetate was cholesterol. Taken together, these results indicate that NS-1 cells are defective in cholesterol biosynthesis and identify the site of lesion as the demethylation of lanosterol to C-29 sterol intermediates.

Production and characterization of a bovine T cell-specific monoclonal antibody identifying a mature differentiation antigen.

A monoclonal antibody (MAb), BLT-1, with specificity for bovine mature T cells was prepared by somatic cell hybridization of myeloma NS-1 and spleen cells from BALB/c mice hyperimmunized with bovine T lymphocytes. The MAb reacted with over 92% of nylon wool-nonadherent lymphocytes (T cells) but not with nylon wool-adherent EAC-positive lymphocytes (B cells) in the indirect immunofluorescence assay. It is an IgM, with kappa-light chains, which fixed complement well and killed over 95% of mature T cells in complement-mediated cytotoxicity assays. It reacted with the same proportions of peripheral lymphoid cells (peripheral blood, lymph nodes, and spleen) as the polyclonal goat anti-bovine thymocyte serum (GABTS), but only with 25% of GABTS-positive thymocytes. Immunoperoxidase staining of frozen tissue sections showed that the BLT-1-positive cells were located in the medulla of the thymus and in the T lymphocyte areas of lymph nodes. Western immunoblotting assays showed that the BLT-1-reactive membrane antigen is a 22,000 m.w. protein which was inducible in bovine thymocytes with bovine thymic hormones, thymosin fraction 5, thymosin alpha 1, and thymopentin ORF-18150, indicating that it is a mature T lymphocyte differentiation antigen. The thymosin alpha 1 and thymopentin were found to show additive effects on mature T cell antigen expression by bovine thymocytes.

Monoclonal antibody against human HLA class II antigens. I. Analysis of sero-reactive patterns

Monoclonal antibody Sa3 was obtained by fusion of the spleen cells from the BALB/c mice immunized with Epstein-Barr virus (EBV)-transformed human B lymphoblastoid cell line, EBVSA (HLA-A24; B7; C-; DR1; DQ1; DP4) with mouse myeloma NS-1 cells. In the microcytotoxicity test, this antibody reacted with EBV-transformed B lymphoblastoid cell lines, Burkitt's lymphomas, Pre-B leukemia and peripheral B cells, but not with T cell leukemias, Myelomonocytes, human spleen cells, human bone marrow cells or peripheral T cells. By SDS gel electrophoresis, the monoclonal antibody Sa3 detected on the HLA class II molecules was found to consist of two subunits of α chain (31-34k mol. wt.) and β chain (28-29k mol. wt.). These results suggest that monoclonal antibody Sa3 reacts with human HLA class II antigens.

A role for suppressor T cells in induction of self-tolerance.

The potential role of suppressor T cells (Ts) in the induction of self-tolerance was investigated by eliminating I-J+ cells during ontogeny (I-J antigens are encoded by the I-J subregion of the murine major histocompatibility complex). To achieve this, F1 mice were exposed to anti-I-J antibodies via the transplacental route by mating B10.A(3R) females, preimmunized with B10.A(5R) cells, with CBA males. At 6 weeks of age, the offspring were injected with rat erythrocytes (RRBC) to induce erythrocyte autoantibodies. By comparison with age-matched controls, Ts-depleted mice produced significantly higher titers of autoantibody, whereas there was no difference in the antibody response of the two groups to the foreign determinants on the RRBC. The selective increase in autoantibody production was mirrored at the clonal level by the appearance of self-reactive B-cell hybridomas after fusion of RRBC-immune spleen cells with the NS-1 cell line. On the other hand, when helper cell function of RRBC-primed cells was measured in a T-cell proliferative assay, Ts depletion in utero resulted in enhanced T-cell activity to nonself (RRBC) but not to self (mouse erythrocyte) determinants. Thus, helper T cells recognizing nonself determinants on RRBC appeared to be responsible for activating self-specific B cells, presumably through linked recognition of different epitopes on mouse erythrocytes. Taken together, these findings indicate that elimination of I-J+ cells during ontogeny can lead to the appearance and activation of "forbidden" B-cell clones and points to a central role for Ts in induction as well as maintenance of self-tolerance.

Monoclonal antibodies directed against human α-thrombin and the thrombin-antithrombin III complex

Human α-thrombin was poorly immunogenic in Balb/c mice. Nevertheless, following fusion of spleen cells from a responding mouse with NS-1 cells, 8 mouse monoclonal antibodies against α-thrombin were isolated, and 6 were characterised. Five of these were isotype IgG 2a, and one was IgG 1. One, EST 1, bound thrombin only minimally, and was directed against a neoantigen on the thrombin-ATIII (T-AT) complex. This antibody also recognised a site on prothrombin, though with much lower affinity. Its binding was markedly temperature-dependent, indicating a requirement for molecular mobility. A second antibody, EST 4, would not bind the T-AT complex. It inhibited both the clotting and amidase activities of thrombin, and modification of the active site histidine, but not the active site serine, reduced the affinity constant of binding to EST 4. This antibody appears to be directed against an epitope in the vicinity of the enzyme active site. The epitopes for EST 1 and EST 4 were both remote from those of the other monoclonal antibodies, EST 2, 6, 7 and 8. These four competed with each other for binding to thrombin, and all inhibited clotting but not amidase activity. Thrombin binding was not affected by modification of the active site, though formation of the T-AT complex reduced the affinity of binding to EST 6 and EST 8. These monoclonals recognise epitopes in the region of the fibrinogen binding site.

Monoclonal antibody against a genus-specific antigen of Chlamydia species: location of the epitope on chlamydial lipopolysaccharide

Monoclonal antibodies were prepared by the fusion of murine myeloma NS1 cells with spleen cells of BALB/c mice immunized with Formalin-killed elementary bodies of the Chlamydia trachomatis L2 serovar. The specificity of these monoclonal antibodies was determined with a solid-phase immunoassay in which HeLa 229 cells infected with C. trachomatis serovars D, G, H, I, L2 and the Chlamydia psittaci meningopneumonitis strain Cal-10 were used. An immunoglobulin G3 monoclonal antibody (L2I-6) was identified that reacted with both C. trachomatis- and C. psittaci-infected HeLa cells. The immunoreactivity of the genus-specific epitope was heat resistant (100 degrees C, 10 min) but was destroyed by sodium metaperiodate treatment. Further characterization of the chlamydial specificity of monoclonal antibody L2I-6 by microimmunofluorescence showed that it was reactive with all 15 C. trachomatis serovars and seven C. psittaci strains isolated from five different animal species. We undertook studies to identify the biochemical nature of the chlamydial component on which the genus-specific epitope was located. The immunoreactive component was isolated by hot phenol-water extraction of dithiothreitol-reduced chlamydial elementary bodies. The component was positive in the Limulus amoebocyte lysate test (results of Limulus amoebocyte lysate assay were identical with those of Salmonella typhimurium LT2 SAI 377 Re lipopolysaccharide [LPS]), contained 8.8% 2-keto-3-deoxyoctulosonic acid, was resistant to proteinase K, and possessed electrophoretic mobility and silver-staining characteristics in sodium dodecyl sulfate-polyacrylamide gel electrophoresis consistent with a rough LPS or glycolipid. On the basis of these findings, we conclude that the genus-specific epitope recognized by monoclonal L2I-6 is located on chlamydial LPS. We further characterized the antigenic properties of the chlamydial LPS epitope by examining the immunoreactivity of monoclonal antibody L2I-6 by immunoblotting analyses against isolated LPSs extracted from Neisseria gonorrhoeae, S. typhimurium, and Escherichia coli. Monoclonal antibody L2I-6 did not bind LPS of these organisms, demonstrating that the chlamydial genus-specific LPS epitope is apparently not shared by these gram-negative bacteria. We were able, however, to show that the chlamydial LPS does share antigenic determinants with LPS of gram-negative organisms. Polyclonal rabbit antisera raised against S. typhimurium Re LPS or lipid A showed intense immunological cross-reactivity with chlamydial LPS by immunoblotting.(ABSTRACT TRUNCATED AT 400 WORDS)

Production of a macromomycin (MCR)-monoclonal antibody conjugate and its biological activity.

Macromomycin (MCR), an unique membrane-reactive anticancer antibiotic, was incubated with murine monoclonal anti-HLA IgG1 antibody (H-1) in the presence of carbodiimide. The resulting mixture was fractionated with a Sephadex G-200 column. The first and second fractions were shown to contain MCR-(H-1) conjugate by the elution profile, as well as by the Sarcina lutea growth inhibition assay and Ouchterlony double-diffusion method. A membrane immunofluorescence test with anti-MCR and anti-mouse IgG antibodies demonstrated specific localization of MCR-(H-1) on the surface of HLA-bearing NALL -1 cells. MCR-(H-1) inhibited the growth of HLA-lacking NS-1 cells statistically less effectively than MCR alone (p less than 0.01). On the other hand, the conjugate and free MCR equally inhibited the growth and 3H-TdR incorporation of HLA-bearing NALL -1 cells. These results indicate that the antibody-bound MCR retained both MCR and antibody activities, and thus exerted antibody-targeting MCR cytotoxicity in vitro.

Malaria Parasites Do Not Contain or Synthesize Sialic Acids

The capacity of Plasmodia to synthesize sialic acids was investigated by adding radioactive acetate to short-term in vitro cultures of the intraerythrocytic asexual forms of three malaria parasites (the human malaria Plasmodium falciparum in Aotus trivirgatus erythrocytes; the simian malaria P. knowlesi in rhesus monkey erythrocytes; the rodent malaria P. berghei in mouse erythrocytes) and to cultures of extracellular zygotes of the avian malaria P. gallinaceum. Radioactive acetate was added to normal rhesus monkey erythrocytes and to cells of the murine myeloma NS-1 for comparison. Although [1-14C]-acetate labeled many proteins with each malaria parasite and the NS-1 cells, analysis of purified sialic acids revealed that only with the NS-1 cells was radioactivity incorporated into sialic acids. Furthermore, N-acetyl[6-3H]mannosamine was not incorporated into sialic acids or malarial glycoproteins when added to P. knowlesi cultures. All of the malaria parasites underwent growth or differentiation during these experiments as measured by [35S]methionine uptake into protein and by light microscopy. Extracellular parasites largely free of erythrocyte membranes were prepared to determine whether Plasmodia contain sialic acids that are not labeled by exogenous precursors. Purified merozoites of P. knowlesi and zygotes of P. gallinaceum did not contain detectable amounts of sialic acids on chemical analysis. Thus, although we could show that Plasmodia can incorporate radioactive sugars such as glucosamine, galactose and mannose into proteins, presumably glycoproteins, they do not synthesize sialic acids or sialo-glycoproteins, nor do they contain sialo-glycoconjugates of host origin.

A Mouse Monoclonal Antibody with Anti-A,(B) Specificity Which Agglutinates Ax Cells

A hybridoma (ES-15) was obtained by fusing the NS-1 cell line with spleen cells from a mouse immunised with soluble blood group A(2) substance. The cloned hybridoma culture supernatant was shown to contain an IgM class antibody which strongly agglutinates group A cells and weakly agglutinates group B cells. The serological specificity of this antibody is described as anti-A,(B) in this report. The abilities of unconcentrated monoclonal anti-A,(B), a commercial human polyclonal anti-A,B (group O serum) and a commercial monoclonal anti-A reagent to detect 15 examples of Ax cells were compared by both slide and tube techniques. Using a slide technique monoclonal anti-A,(B) agglutinated 14 examples of Ax cells, human anti-A,B 2 examples, while monoclonal anti-A failed to detect any of the Ax cells tested. Similar differences in the reactivity of the three antibodies were observed using a tube technique. Data are also presented which show that a 1:1 (v/v) mixture of monoclonal anti-A,(B) with a monoclonal anti-B reagent is an effective replacement for human anti-A,B in ABO grouping procedures.

Characterization of a monoclonal antibody directed to a T cell suppressor factor.

A monoclonal antibody raised by fusion of immune BALB/c splenocytes with NS1 cells is described. BALB/c mice were immunized with a T suppressor factor (TsF) raised in DBA/2 mice with specificity for the P815 tumor. The TsF had been purified by affinity chromatography before its use as an immunogen. The monoclonal antibody (B16G) was shown to affect the course of P815 growth in DBA/2 mice if administered i.v. on days -2 to 0 before tumor cell inoculation. Mice treated with B16G demonstrated slower tumor development and growth than controls, and a small number of animals (about 10%) did not develop tumors; all controls did. It was also shown that B16G did not exhibit total specificity for the P815 tumor in that it had similar effects on the growth of an unrelated myosarcoma (M-1) of DBA/2 mice. The general immunopotentiating effect of the B16G monoclonal was demonstrated by the fact that spleen cells of DBA/2 mice that had received B16G showed significantly higher MLC than did equivalent controls. When spleen cells of DBA/2 mice were depleted of B16G-reactive cells by panning in vitro, it was also found that cells so treated gave rise to elevated MLC reactions in comparison to appropriate controls. When an immunoadsorbent was prepared with B16G and cell lysates from splenocytes of immunosuppressed mice were passed over it, the immunosuppressive properties of the lysate in MLC were eliminated. The conclusion that the B16G recognizes a marker common to a group of regulatory T cells in DBA/2 mice is discussed.

Anti-schistosome monoclonal antibodies of different isotypes--correlation with cytotoxicity.

Five monoclonal antibodies specific towards Schistosoma mansoni antigens were prepared by fusion of spleen cells of infected and immunized mouse with the murine myeloma NS-1 cells. Three of the five antibodies belonged to the IgG1 class, one was an IgM and the fifth one was an IgE. The IgE monoclonal antibody designated 54.10, induced antigen-specific degranulation of rat basophilic cell line, a property which served as the basis for the screening assay. Its biological function was demonstrated by a specific macrophage activation that led to killing of schistosomula; no such killing was obtained with anti-schistosome antibodies of other classes or with IgE of different antigenic specificity. The second monoclonal antibody of biological significance was an IgG1, designated 27.21 which is reactive in the immunofluorescence staining of surface antigens on intact schistosomula. All three monoclonal antibodies that belonged to the IgG1 class were effective in mediating killing of schistosomula by complement, with the highest effect exerted by 27.21. It is thus apparent that the 27.21 monoclonal antibody is directed against a densely distributed surface antigen on the schistosomula membrane which is possibly involved in the protective immunity. Preliminary data showed that immunoprecipitation with the 27.21 antibodies results in the isolation of three major protein bands, of 60 kd, 50 kd, 19 kd, respectively.

Inducible Macrophage Cytotoxins. I. Biokinetics of Activation and Release In Vitro<xref ref-type="fn" rid="FN2">2</xref>

Peritoneal exudate macrophage monolayers (PEMM) from C57BL/6 and DBA/2 mice inoculated ip with tumor allografts were induced to release in vitro labile cell toxin(s), herein called "macrophage cytotoxin(s)" (MCT). Macrophages released MCT spontaneously for a short interval when initially established as monolayers, and they were reinduced to secrete MCT by exposure to allogeneic and syngeneic tumor cells (but not to normal cells) and by exposure to polyinosinic-polycytidylic acid (poly I . poly C) and lipopolysaccharide (LPS). PEMM from normal mice treated ip 3 days previously with thioglycollate were also induced to release toxins in vitro. These cells did not release MCT spontaneously before or after treatment with neoplastic cells but were induced to release MCT by exposure to poly I . poly C or LPS. Resident peritoneal macrophages did not release MCT either spontaneously or after treatment with tumor cells, poly I . poly C, or LPS. MCT released from alloimmune mice stimulated with syngeneic or allogeneic tumor cells were resolved by molecular sieving into a major peak at 140,000--160,000 daltons, called "alpha-MCT," and into a minor peak at 60,000 daltons, called "beta-MCT." However, supernatants from thioglycollate-induced PEMM, stimulated with poly I . poly C or LPS, appeared to be composed entirely of the alpha-class. alpha-MCT from poly I . poly C-stimulated PEMM caused 31--56% lysis of syngeneic EL-4 and allogeneic L-929, NS-1, and YAC-1 tumor cells in vitro but was not cytotoxic for normal cells. Secretion of the MCT by PEMM derived from thioglycollate-treated animals stimulated with poly I . poly C was inhibited by colchicine, emetine, iodoacetic acid, trypan blue, and cytochalasin B.