Characterization of lipopolysaccharide from Myxococcus xanthus by use of monoclonal antibodies.

Lipopolysaccharide is a major constituent of the cell surface of the gram-negative procaryote Myxococcus xanthus. We have purified lipopolysaccharide from M. xanthus and have shown by silver staining that the lipopolysaccharide contains a heterogeneous population of molecules which migrate as a broad low-molecular-mass band (approximately 5 kilodaltons) and as a stepladder of about 30 higher-molecular-mass bands (15- to 70-kilodalton range). The broad band consists of lipopolysaccharide molecules with just lipid A and core regions. The stepladder bands contain lipopolysaccharide molecules with lipid A, core regions, and various numbers of O-antigen units. Monoclonal antibodies generated against the cell surface of developing M. xanthus cells (J. S. Gill and M. Dworkin, Proc. Natl. Acad. Sci. USA 84:4505-4508, 1987) were used to help characterize the lipopolysaccharide molecules. Five monoclonal antibodies bound to carbohydrate epitopes on the stepladder but not to the broad band, indicating that these monoclonal antibodies recognize carbohydrates on the O antigen of the lipopolysaccharide molecules. Four of these five monoclonal antibodies bound to doublet bands in the stepladder, while the other monoclonal antibody bound to singlet bands in the stepladder. One monoclonal antibody bound to a carbohydrate epitope on both the broad band and the stepladder, indicating that it bound to the core of the lipopolysaccharide.     

The epitope specificity and tissue reactivity of four murine monoclonal anti-CD22 antibodies

The CD22 antigen is expressed on the surface of normal human B cells and some neoplastic B cell lines and tumors. Previous cross-blocking studies using a panel of monoclonal anti-CD22 antibodies have defined four epitope groups, termed A-D. In the present studies, we have further dissected the epitopes recognized by four monoclonal anti-CD22 antibodies using immunoprecipitation and cross-blocking techniques, immunofluorescence analyses with a variety of cell lines, and immunoperoxidase analyses of 36 normal human tissues. Two of the antibodies, HD6 and RFB4, have been described previously, and two, UV22-1 and UV22-2, are described in this report. Our studies indicate that the four monoclonal antibodies show unexpected complexities in their reactivity with CD22+ and CD22- cells and their reactivity with solubilized CD22 molecules. The four antibodies, which recognize epitopes defined previously as CD22-A and CD22-B, further subdivide these epitope clusters into four determinants, A1, A2, B1, and B2. Furthermore, only two of the antibodies, RFB4 and UV22-2, are B cell-specific. In summary, our data indicate that RFB4 and UV22-2 would be the antibodies of choice for constructing immunotoxins to treat B cell tumors.     

Monoclonal antibodies for carcinoembryonic antigen and related antigens as a model system: a systematic approach for the determination of epitope specificities of monoclonal antibodies

A systematic approach for the determination of epitope specificities of monoclonal antibodies to a complex antigen system is described. After initial screening to identify antigen-binding monoclonal antibodies, one or more of the clones are isolated by limiting dilution cloning, grown in ascites, and the resulting antibodies secreted into the ascitic fluid are affinity purified on Sepharose-bound protein A, radiolabeled, and cross-compared with antibodies from other clones by a solid-phase competitive immunoassay. In this work, BALB/c mice were immunized with either purified carcinoembryonic antigen (CEA) or the CEA-producing cell line HC 84S. Spleen cells were fused with the mouse myeloma cell line Sp2/0-Ag14. The supernatants from 25 hybrids showed a significant binding of 125I-CEA (greater than or equal to 15%). Nine hybrids were cloned, resulting in 33 different clones. The antibodies produced by the different cloned hybrids and the remaining uncloned hybrids recognized a total of five different epitopes on CEA. All of the epitopes reside on the protein moiety of the molecule as determined by antibody binding to deglycosylated CEA. The monoclonal antibodies with five different epitope specificities were reacted with tissue sections of normal and cancerous tissues and with peripheral blood smears. Each of the five monoclonal antibodies reacted with tissue sections from colonic, gastric, lung, and mammary carcinomas, as well as from a benign colonic polyp and a resection margin from a colonic carcinoma. Four monoclonals reacted with normal liver tissue. Granulocytes in peripheral blood smears bound three antibodies strongly and one antibody weakly, and one antibody was not bound. One monoclonal antibody that reacted with normal liver tissue was not bound by granulocytes. The ability of these five monoclonal antibodies to differentially detect three different CEA-related antigens in normal and malignant tissues may have clinical utility.     

A novel CD44 antibody identifies an epitope that is aberrantly expressed on acute lymphoblastic leukaemia cells

Previous studies have shown that the antibody 7H9D6 identifies CD44, a glycoprotein receptor for hyaluronic acid. 7H9D6 recognizes an epitope of CD44 that is not always present on CD44 molecules. The 7H9D6 antibody bound to the hyaluronic acid binding domain of CD44 and inhibited cell adhesion to immobilized hyaluronic acid. However, the expression of the 7H9D6 epitope was not sufficient for hyaluronic acid binding. Immunofluorescent staining with 7H9D6 revealed a punctate surface staining pattern, suggesting that CD44 molecules recognized by 7H9D6 are located in clusters on the cell surface. In contrast, other CD44 antibodies produced a uniform staining pattern. Early bone marrow B cells were negative for 7H9D6 but reactive with other CD44 monoclonal antibodies. In contrast, leukaemic cells from 65% of patients (28 of 43) with B lineage acute lymphoblastic leukaemia bound 7H9D6. Patients expressing the 7H9D6 epitope on their leukaemic cells had an increased risk of death (HR 3.5 95% CI 1.1-10.9, P = 0.029) and of disease relapse (HR 3.2 95% CI 1.2-8.5, P = 0.017) when corrected for white cell count. This antibody may be useful for the detection of residual disease in B lineage acute lymphoblastic leukaemia and as a prognostic indicator and for the study of CD44 function.     

Model for studying virus attachment: identification and quantitation of Epstein-Barr virus-binding cells by using biotinylated virus in flow cytometry.

Epstein-Barr virus (EBV) was purified and biotinylated without significant loss of its cell-transforming activity. The use of biotinylated virus in conjunction with antibodies specific for selected cell surface molecules and flow cytometric analysis allowed for the positive identification of the virus-binding lymphocytes among a heterogeneous mononuclear cell population. Biotinylated EBV efficiently bound to all B lymphocytes, including those bearing surface mu, delta, gamma, and alpha immunoglobulin heavy chains or the surface CD5 (Leu-1) marker, but not to T lymphocytes, natural killer cells, or monocytes. By using biotinylated EBV and specific monoclonal antibodies in competitive inhibition experiments, it was also found that the virus attaches to an epitope on the CR2 molecule (the receptor for C3d and EBV), which is close to or identical with the one recognized by OKB7 monoclonal antibody, and that cell surface structures other than CR2 cannot mediate attachment of EBV. Moreover, studies on the binding of the virus to induced B lymphocytes (cells in S through G2 phase), and this was associated with the disappearance of the surface CR2 molecule and the inability of the virus to attach to these cells. The approach described here should be useful in studying the attachment of other viruses, identifying the specific cell types involved, and analyzing the effect of the cell cycle on virus binding.     

Mapping the binding of synthetic disaccharides representing epitopes of chlamydial lipopolysaccharide to antibodies with NMR

A NMR study of the binding of the synthetic disaccharides alpha-Kdo-(2-->4)-alpha-Kdo-(2-->O)-allyl 1 (Kdo, 3-deoxy-D-manno-oct-2-ulopyranosonic acid) and alpha-Kdo-(2-->8)-alpha-Kdo-(2-->O)-allyl 2, representing partial structures of the lipopolysaccharide epitope of the intracellular bacteria Chlamydia, to corresponding monoclonal antibodies (mAbs) S23-24, S25-39, and S25-2 is presented. The conformations of 1 bound to mAbs S25-39 and of 2 bound to mAbs S23-24 and S25-39 were analyzed by employing transfer-NOESY (trNOESY) and QUIET-trNOESY experiments. A quantitative analysis of QUIET-trNOESY buildup curves clearly showed that S25-39 recognized a conformation of 1 that was similar to the global energy minimum of 1, and significantly deviated from the conformation of 1 bound to mAb S25-2. For disaccharide 2, only a qualitative analysis was possible because of severe spectral overlap. Nevertheless, the analysis showed that all mAbs most likely bound to only one conformational family of 2. Saturation transfer difference (STD) NMR experiments were then employed to analyze the binding epitopes of the disaccharide ligands 1 and 2 when binding to mAbs S23-24, S25-39, and S25-2. It was found that the nonreducing pyranose unit was the major binding epitope, irrespective of the mAb and the disaccharide that were employed. Individual differences were related to the engagement of other portions of the disaccharide ligands.     

Murine polyspecific antibodies. I. Monoclonal and serum anti-DNA antibodies cross-reactive with 2,4,6-trinitrophenyl derivatives

Six anti-DNA hybridoma autoantibodies were prepared by fusing spleen cells from unimmunized MRL/MpJ/lpr/lpr female mice with BALB/c myeloma cells. The monoclonal antibodies were analyzed by solid-phase ELISA for antigen-binding specificities. Three antibodies (62A2, 85A5, and 43B2) bound ssDNA, TNP-KLH, and recognized an epitope(s) present on insolubilized proteins such as BSA, KLH, ferritin, and insulin. The antibodies bound, with a marked preference, TNP-KLH, either soluble or insoluble. The other three antibodies (35A1, 32C5, and 39D2) bound only ssDNA. However, this binding was inhibited by free flavinic acid. None of the six antibodies bound either cardiolipin or proteoglycans, indicating that they do not recognize the repeating negatively charge units common to cardiolipin, proteoglycans, and DNA. All six monoclonal antibodies were purified by affinity chromatography with TNP-Sepharose. Moreover, both anti-DNA and anti-TNP antibodies from sera of nonautoimmune and autoimmune mice were purified easily on TNP-Sepharose.     

Genetic control of immune response to staphylococcal nuclease. XII: Analysis of nuclease antigenic determinants using anti-nuclease monoclonal antibodies

Summary SJL mice, which are high responders to Staphylococcal nuclease (nuclease), were immunized and used to produce hybridoma cell lines secreting anti-nuclease monoclonal antibodies (mAb). Ten stable clones were derived from a single fusion. Seven of these produced antibodies of the IgG_1, isotype and were more precisely characterized for antigenic specificity. Only one hybridoma cell line (54-10-4) produced anti-nuclease antibodies capable of inhibiting enzymatic activity of nuclease. Binding inhibition analyses strongly suggest that the other monoclonal antibodies, which failed to inhibit nuclease activity detect two different antigenic regions, or epitopes, of the molecule: epitope cluster 1 domain is defined by hybridomas 54-2-7, 54-5-2, 54-9-8, and 54-10-8; epitope cluster 2 by 54-5-1 and 54-1-9. Because of its capacity to inhibit nuclease enzymatic activity mAb 54-10-4 was considered specific for a third epitope of the nuclease molecule called epitope 3. Binding studies of these monoclonal antibodies were extended to peptide fragments of the nuclease molecule in order to examine possible cross-reactions with such fragments, as has previously been reported for antibodies purified from polyclonal antisera. Monoclonal antibodies specific for epitope cluster 1 on the native molecule also bound to the fragments 1–126 and 49–149 but failed to bind to fragment 99–149, suggesting that the corresponding epitope(s) is determined by amino acids localized between residues 49 and 99. The epitope clusters 2 and 3 appeared to be expressed only on the native molecule. Monoclonal antibodies of different clusters exhibited very different migration patterns on isoelectric focusing while monoclonal antibodies of the same cluster were indistinguishable, which suggests that they may have originated from the same B cell precursor. Taken together these data suggest that this panel of monoclonal antibodies detects at least three distinct epitopes of the nuclease molecule, one of which could be involved in the determination of the enzymatic site.     

Isolation and chemical characterization of a melanoma-associated proteoglycan antigen

Many melanoma-associated antigens have been identified by monoclonal antibodies. One of these monoclonal antibodies, O₁-94-45, binds only to melanomas, nevus cells, some astrocytomas, and fetal epitheloid cells. There are approximately 100,000 cell surface antigens per melanoma cell with an association constant of 3 × 10⁸m^?1. The antigen is efficiently extracted from the membrane only in the presence of detergent and is, therefore, bound by hydrophobic forces. However, it is also shed into the culture supernatant during normal cell growth. The two components of the O₁-95-45 antigen are a chondroitin sulfate proteoglycan (CSP, >500,000 Da) and a glycoprotein gp260 (260,000 Da, pI 6.9). CSP contains chondroitin sulfate and N-linked and O-linked oligosaccharides. Only N-linked saccharides were associated with gp260. The antigenic site is expressed on both components and is heat-sensitive. Since the CSP was converted to gp260 by chondroitinase, the protein cores of the two molecules are the same or similar. For more detailed study the O₁-95-45 antigen was purified by immunoaffinity chromatography. The amino acid composition of the purified antigen was relatively polar with an unusually high Leu content and low Lys content. Initial attempts to sequence the antigen were unsuccessful probably due to a blocked N-terminus. CSP and gp260 were partially separated by gel filtration chromatography, and both were found to carry the O₁-95-45 antigenic determinant. Three other monoclonal antibodies were found to bind the purified antigen at a site or sites different from the O₁-95-45 epitope and one other monoclonal antibody may bind at the same site. Two of these antibodies were used for a double determinant immunoassay.     

Monoclonal antibodies to murine gamma-interferon which differentially modulate macrophage activation and antiviral activity

Four monoclonal IgG antibodies to purified, recombinant murine gamma-interferon (rIFN-gamma) have been produced by fusion of immune hamster splenocytes with HAT-sensitive murine myeloma cells. Specificity was confirmed either with an enzyme-linked immunosorbent assay (ELISA) that used immobilized rIFN-gamma or with a radioimmunoassay that employed soluble 125I-rIFN-gamma and heat-killed, fixed Staphylococcus aureus-bearing Protein A. Competition binding experiments suggested that the monoclonal antibodies (MoAb) displayed two distinct epitope specificities: one displayed by H1 and H2, and the other displayed by H21 and H22. By using murine-human recombinant IFN-gamma hybrid molecules, the H1/H2 epitope was shown to depend on the amino-terminus of IFN-gamma, whereas the H21/H22 epitope was formed by the carboxy-terminal amino acid sequence. The MoAb also reacted with natural IFN-gamma. When bound to a surface, all four MoAb, but not normal hamster IgG, removed 100% of the antiviral and MAF activities present in supernatants of cultures of the murine 24/G1 T cell hybridoma. In free solution, all four antibodies inhibited IFN-gamma dependent antiviral activity, but with different efficiencies. Soluble H21/H22 also blocked all of the 24/G1-derived activity that induces nonspecific tumoricidal activity in macrophages (MAF) while H1/H2 enhanced MAF activity. The differential inhibitory or enhancing activities of H21 or H1 reflected their ability to inhibit or enhance binding of 125I-rIFN-gamma to macrophages, respectively. Soluble H21/H22 and solid-phase H1/H2 inhibited 100% of the MAF, microbicidal, and Ia-inducing activities from lymphokine preparations produced by mitogen stimulation of normal murine splenic cells. These results help to establish definitive structure-function relationships for the IFN-gamma molecule, and indicate that IFN-gamma is the primary lymphokine responsible for inducing nonspecific tumoricidal activity and Ia antigen expression, and for enhancing microbicidal activity in macrophages.     

Epitope mapping of monoclonal antibodies to human plasma membrane Ca2-ATPase

Overlapping fragments of the fourth isoform of human plasma membrane Ca(2+)-ATPase (hPMCA4) and several fragments of hPMCA1 were expressed in bacterial cells and purified by metal affinity chromatography. Enzyme immunoassays of the fragments helped map epitopes for 4 monoclonal antibodies (2D8, 8B8, 7C8 and 5E6). The epitope for 2D8 was localized within the 222-249 site (i.e., in the putative transduction domain), the epitopes for 8B8 and 7C8 were localized within the 330-353 site, in which phospholipids are presumably bound, and the 5E6 epitope was found within the 791-843 site, where the putative hinge region is situated. 2D8 recognizes hPMCA1 and hPMCA4 isoforms, while 8B8 and 7C8 are specific for hPMCA4. The amino acid sequences of these epitopes and phage-displayed mimotopes were compared.     

Rapid analysis of protein interactions: On-chip micropurification of recombinant protein expressed in Esherichia coli

We describe a rapid analysis of interactions between antibodies and a recombinant protein present in total cell lysates. Using a surface plasmon resonance biosensor, a low concentration of glutathione-S-transferase (GST) fused protein expressed in small scale Esherichia coli culture was purified on an anti-GST antibody immobilized sensor chip. The 'on-chip purification' was verified using matrix-assisted laser desorption/ionization-time of flight mass spectrometry by measuring the molecular masses of recombinant proteins purified on the sensor chip. The specific binding of monoclonal antibodies for the on-chip micropurified recombinant proteins can then be monitored, thus enabling kinetic analysis and epitope mapping of the bound antibodies. This approach reduced time, resources and sample consumption by avoiding conventional steps related to concentration and purification.     

Monoclonal antibodies identify common and differentiation-specific antigens on the plasma membrane of guard cells of Vicia faba L.

Monoclonal antibodies were raised against the plasma membrane of Vicia faba L. guard cells by immunizing either with total membranes from purified guard-cell protoplasts or with sealed, predominantly right-side-out plasma-membrane vesicles prepared from abaxial epidermes of V. faba by aqueous two-phase partitioning. Hybridoma screening was performed by enzyme-linked immunosorbent assay using polystyrene-adsorbed plasma-membrane vesicles as solid phase and by indirect immunofluorescence analysis using unfixed, immobilized protoplasts in a microvolume Terasaki assay. A range of monoclonal antibodies was characterized and is reported here. One monoclonal antibody, G26-6-B2, is guard-cell-specific and does not react with mesophyll-cell protoplasts of the same species. It binds to a periodate-resistant but trypsin-labile epitope, probably a differentiation-specific plasma-membrane protein.Abbreviations ELISA enzyme-linked immunosorbent assay - FITC fluorescein isothiocyanate - GCP guard cell protoplast(s) - Ig immunoglobulin - MAB monoclonal antibody - MCP mesophyll-cell protoplast(s) - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis     

Comparison of Antiviral Activity between IgA and IgG Specific to Influenza Virus Hemagglutinin: Increased Potential of IgA for Heterosubtypic Immunity

Both IgA and IgG antibodies are known to play important roles in protection against influenza virus infection. While IgG is the major isotype induced systemically, IgA is predominant in mucosal tissues, including the upper respiratory tract. Although IgA antibodies are believed to have unique advantages in mucosal immunity, information on direct comparisons of the in vitro antiviral activities of IgA and IgG antibodies recognizing the same epitope is limited. In this study, we demonstrate differences in antiviral activities between these isotypes using monoclonal IgA and IgG antibodies obtained from hybridomas of the same origin. Polymeric IgA-producing hybridoma cells were successfully subcloned from those originally producing monoclonal antibody S139/1, a hemaggulutinin (HA)-specific IgG that was generated against an influenza A virus strain of the H3 subtype but had cross-neutralizing activities against the H1, H2, H13, and H16 subtypes. These monoclonal S139/1 IgA and IgG antibodies were assumed to recognize the same epitope and thus used to compare their antiviral activities. We found that both S139/1 IgA and IgG antibodies strongly bound to the homologous H3 virus in an enzyme-linked immunosorbent assay, and there were no significant differences in their hemagglutination-inhibiting and neutralizing activities against the H3 virus. In contrast, S139/1 IgA showed remarkably higher cross-binding to and antiviral activities against H1, H2, and H13 viruses than S139/1 IgG. It was also noted that S139/1 IgA, but not IgG, drastically suppressed the extracellular release of the viruses from infected cells. Electron microscopy revealed that S139/1 IgA deposited newly produced viral particles on the cell surface, most likely by tethering the particles. These results suggest that anti-HA IgA has greater potential to prevent influenza A virus infection than IgG antibodies, likely due to increased avidity conferred by its multivalency, and that this advantage may be particularly important for heterosubtypic immunity.     

Monoclonal antibodies specific for human chromosome 5 obtained with a monochromosomal hybrid can be used to sort out cells containing the chromosome with a FACS

Using a human-mouse monochromosomal hybrid, BG15-6, that contains an intact human chromosome 5, we isolated four monoclonal antibodies, 2A10, 3H9, 5G9, and 6G12, as chromosome marker antibodies recognizing cell surface antigens specific for human chromosome 5. The binding patterns of these antibodies to BG15 subclones containing fragments of human chromosome 5 indicated that 2A10, 3H9, and 6G12 recognized the antigens produced by genes located on 5pterq22, and that 5G9 recognized the antigen produced by a gene located on 5q23. Cells containing human chromosome 5 were very effectively sorted in a fluorescence-activated cell sorter (FACS) using monoclonal antibody 6G12. This method for sorting cells containing human chromosome 5 or an appropriate fragment of this chromosome from among human-rodent hybrid cells should be very useful in studies on gene expression, gene cloning and gene mapping.by M. Trendelenburg     

Multiple overlapping epitopes in the three antigenic regions of horse cytochrome c1

To gain a better understanding of the diversity of epitopes on a protein, the specificities of 103 monoclonal antibodies to a model antigen, horse cytochrome c(cyt c), were analyzed. The antibodies were generated in in vitro monoclonal, secondary antibody responses against horse cyt c coupled to hemocyanin in splenic fragment cultures. For this assay, horse cyt c-primed murine B lymphocytes were transferred to irradiated, hemocyanin-primed recipients. A panel of seven mammalian cyts c differing at one to six residues out of 104 and cyanogen bromide-cleaved fragments of horse cyt c containing residues 1-65, 1-80, and 66-104 was used to examine the specificities of the antibodies. Twenty-two distinct reactivity patterns were observed, even though the majority of the monoclonal antibodies were found to bind in the three previously identified antigenic regions of the molecule about residues 44-47, 60-62, and 89-92. The results indicate that each of the three antigenic regions consists of multiple overlapping epitopes. Few of the antibodies directed to any given antigenic region bound polypeptide fragments inclusive of the epitope sequences, demonstrating that some antibodies were more conformationally dependent than others. Only 13% of the antibodies bound to cyanogen bromide-cleaved polypeptide fragments that together encompassed the entire length of the protein. Considering the large number of antibodies analyzed and the reoccurrence of 13 of the 22 clonotypes in different lymphocyte donors, it is likely that the antibody specificities tabulated herein approach yet do not completely enumerate the total inventory of the horse cyt c-specific B cell repertoire. The remarkable diversity for epitope recognition within antigenic regions observed here is likely to pertain to protein antigens in general, and strongly supports the widely held notion that the entire surface of a protein is potentially antigenic. The restriction of the epitopes of horse cyt c to three antigenic regions where the amino acid sequences of the mammalian cyts c differ probably results from tolerance of the mice to their own cyt c.     

Availability to monoclonal antibodies of antigenic sites of the alpha and beta subunits in active, denatured or membrane-bound mitochondrial F1-ATPase

The binding of five monoclonal antibodies to mitochondrial F1-ATPase has been studied. Competition experiments between monoclonal antibodies demonstrate that these antibodies recognize four different antigenic sites and provide information on the proximity of these sites. The accessibility of the epitopes has been compared for F1 integrated in the mitochondrial membrane, for purified beta-subunit and for purified F1 maintained in its active form by the presence of nucleotides or inactivated either by dilution in the absence of ATP or by urea treatment. The three anti-beta monoclonal antibodies bound more easily to the beta-subunit than to active F1, and recognized equally active F1 and F1 integrated in the membrane, indicating that their antigenic sites are partly buried similarly in purified or membrane-bound F1 and better exposed in the isolated beta-subunit. In addition, unfolding F1 by urea strongly increased the binding of one anti-beta monoclonal antibody (14 D5) indicating that this domain is at least partly shielded inside the beta-subunit. One anti-alpha monoclonal antibody (20 D6) bound poorly to F1 integrated in the membrane, while the other (7 B3) had a higher affinity for F1 integrated in the membrane than for soluble F1. Therefore, 20 D6 recognizes an epitope of the alpha-subunit buried inside F1 integrated in the membrane, while 7 B3 binds to a domain of the alpha-subunit well exposed at the surface of the inner face of the mitochondrial membrane.     

Characterization of the Target Antigens of Phytomonas-specific Monoclonal Antibodies

ABSTRACT. Seven Phytomonas -specific monoclonal antibodies produced against Phytomonas serpens and Phytomonas françai were further characterised in order to identify and localise their target antigens. Four monoclonal antibodies recognized carbohydrate surface epitopes, in three of the cases associated with surface glycoproteins with apparent molecular weight of 80 kDa. One monoclonal antibody apparently bound to a surface/internal protein epitope, whereas the two others recognized intra-cellular proteins. The cell surface epitopes recognized by monoclonal antibodies were detected specifically in the genus Phytomonas. These epitopes, which are detected in culture, plant and insect forms, may be useful as targets for Phytomonas identification.     

Phenotypic characterization of Ewing sarcoma cell lines with monoclonal antibodies

The histogenesis of Ewing sarcoma, the second most frequent bone tumor in humans, remains controversial. Four Ewing cell lines were analyzed by immunological methods. A panel of antibodies directed to T, B, and myelomonocytic markers gave negative results. Surface antigens recognized on Ewing cells were found to be related to the neuroectoderm lineage. Ganglioside GD2, a marker of neuroectodermal tissues and tumors, was present on all lines. These were also stained by the mouse monoclonal antibody HNK-1, which detects a carbohydrate epitope present on several glycoconjugates of the nervous system, including two glycoproteins, the myelin-associated glycoprotein and the neural cell-adhesion molecule (N-CAM), and an acidic glycolipid of the peripheral nervous system. The P61 monoclonal antibody, which reacts with a peptide moiety of N-CAM, and a rabbit antiserum, raised to purified mouse N-CAM and not recognizing the HNK-1-defined epitope, were also reactive. By contrast, all antibodies specific for hematopoietic cell surface antigens were totally negative. Besides these antigenic features, Ewing sarcoma cells are characterized by a specific t(11;22)(q24;q12) translocation also observed in neuroepithelioma, a neuroectodermal tumor, suggesting a possible evolutionary related origin. The recent finding that the human N-CAM gene is located at the vicinity of the breakpoint on chromosome 11 indicates that it might be involved in genetic rearrangements occurring in this region.     

Mucin-carbohydrate directed monoclonal antibody

To raise monoclonal antibodies recognizing cancer-associated alterations of the carbohydrate structure of glycoproteins, Balb/c mice were immunized with human colonic cancer cells (LS 180 from ATCC). One of the generated hybridomas produced a monoclonal antibody that bound to the carbohydrate moiety of mucin-type glycoproteins from LS 180. The antibody did not bind to glycoproteins from another colonic cancer cell line, SW 1116, or to glycolipids from any of the colonic cancer cell lines. The antibody bound to ovine and bovine submaxillary mucins (OSM and BSM). NeuAc alpha 2----6Ga1NAc seemed to be involved in the epitope.