Baryon-Number Violation by Two Units and the Deuteron Lifetime.

We calculate the lifetime of the deuteron with dimension-nine quark operators that violate baryon number by two units. We construct an effective field theory for |ΔB|=2 interactions that give rise to neutron-antineutron (n-n[over ¯]) oscillations and dinucleon decay within a consistent power counting. We calculate the ratio of the deuteron lifetime to the square of the n-n[over ¯] oscillation time up to next-to-leading order. Our result, which is analytical and has a quantified uncertainty, is smaller by a factor ≃2.5 than earlier estimates based on nuclear models, which impacts the indirect bound on the n-n[over ¯] oscillation time and future experiments. We discuss how combined measurements of n-n[over ¯] oscillations and deuteron decay can help to identify the sources of baryon-number violation.

Heterogeneity in both cytokine production and responsiveness of a panel of monoclonal human Epstein-Barr virus-transformed B-cell lines.

To optimize growth and Ig production of in vitro-cultured Epstein-Barr virus (EBV)-transformed B cells, a panel of six monoclonal EBV B-cell lines was analyzed for autocrine growth factor production and responsiveness to various cytokines. Three cell lines produced Il-I and four produced Il-6, although differences concerning the amount of lymphokines produced were observed. Interestingly a considerable tumor necrosis factor beta (lymphotoxin) activity was found in supernatants of all cell lines. One IgM-producing cell line that did not secrete either Il-1 or Il-6 was exceptional in its ability to respond to the addition of rIl-6 with a 5- to 10-times elevated IgM production. In contrast, cell lines in the panel capable of Il-6 production showed only a minimal elevation of Ig production on addition of exogenous Il-6. Ig production was slightly less in some cell lines when Il-6 was neutralized. Antibodies against lymphotoxin or Il-6 did not influence growth rate of the cell lines significantly, implying that neither Il-6 nor lymphotoxin had an autostimulatory effect on the analyzed cell lines. This study demonstrates a heterogeneity regarding the amount and type of lymphokines produced by long-term monoclonal EBV cell lines, which may account for the diverse responses exhibited by these cells towards exogenously added lymphokines.

A human hybrid hybridoma.

Hybrid hybridomas are obtained by fusion of two cells, each producing its own antibody. Several authors have reported the construction of murine hybrid hybridomas with the aim to obtain bispecific monoclonal antibodies. We have investigated, in a model system, the feasibility of constructing a human hybrid hybridoma. We fused two monoclonal cell lines: an ouabain-sensitive and azaserine/hypoxanthine-resistant Epstein-Barr virus-transformed human cell line that produces an IgG1 kappa antibody directed against tetanus toxoid and an azaserine/hypoxanthine-sensitive and ouabain-resistant human-mouse xenohybrid cell line that produces a human IgG1 lambda antibody directed against hepatitis-B surface antigen. Hybrid hybridoma cells were selected in culture medium containing azaserine/hypoxanthine and ouabain. The hybrid nature of the secreted antibodies was analyzed by means of two antigen-specific immunoassays. Our results show that it is possible, with the combined use of transformation and xenohybridization techniques, to construct human hybrid hybridomas that produce bispecific antibodies.

Requirements for growth of Epstein-Barr virus-transformed cells at low cell densities.

We investigated the requirements for growth of Epstein-Barr virus-transformed cells at low cell densities in a homotypic system: only Epstein-Barr virus-transformed cells or their products were used to supply feeder activity. The cloning efficiency was increased markedly under conditions favouring close cell-to-cell contact: culture in round-bottomed rather than in flat-bottomed wells or the addition of irradiated Epstein-Barr virus-transformed cells. Further enhancement was obtained by the addition of the tumour promoter phorbol-myristate acetate. Part of this effect was also induced by supernatants of Epstein-Barr virus-transformed cells, in particular when the latter had been stimulated with phorbol ester. Thus, under limiting dilution conditions, Epstein-Barr virus-transformed cells were found to be dependent upon autologous cell-mediated and soluble proliferation-stimulating signals. In such a homotypic feeder system, the cloning efficiency could be enhanced up to eight-fold; a 100% cloning efficiency could not be achieved. Evidence is presented that the residual deficit in cloning efficiency is inherent to these cell lines.

Colony-forming cells in chronic granulocytic leukemia--II. Analysis of membrane markers.

Membrane markers and functional properties in vitro of blast cells from the peripheral blood of 2 patients with chronic granulocytic leukemia were studied. Buffy-coat cells were enriched for colony-forming cells by density centrifugation (d less than or equal to 1.062 g cm-3). Upon culture, a large proportion of the (cryopreserved) low-density cells from both patients formed hemopoietic colonies that were heterogeneous with respect to size and cellular composition. Expression of membrane markers on the cells, which had the morphology of undifferentiated blasts, was studied using flow cytometry with a panel of monoclonal antibodies. A striking heterogeneity was observed in that variable numbers of cells were found to express myelomonocytic, megakaryocytic and erythroid membrane markers. Antigenic properties of colony-forming cells were studied by sorting of cells with a fluorescence activated cell sorter. Low numbers of cells (10, 4 and 1, respectively) were sorted directly into the wells of Terasaki microtest plates. With this system, it was shown that myeloid colony-forming cells from patient 1 were exclusively present in HLA-DR-positive cell fractions. Colony formation from the level of a single sorted cell was documented. Sorting of cells labeled with anti-blood-group-H antibody showed that small erythroid colony-forming cells from patient 2 were blood-group-H antigen-positive. These cells did not express HLA-DR. The other colony-forming cells from this patient and essentially all colony-forming cells from patient 1 were HLA-DR-positive and blood-group-H-negative. Although only 2 patients were tested, our studies clearly demonstrate that low-density cell fractions from the blood of patients with CGL provide distinct advantages for the study of membrane properties of hemopoietic cells and of hemopoietic differentiation in general.

Xenohybridization of Epstein-Barr virus-transformed cells for the production of human monoclonal antibodies.

Transformation of human B lymphocytes, obtained from hyperimmune donors with Epstein-Barr virus, yields polyclonal cell populations in which a minority of cells produce IgG antibodies of predetermined specificity, whereas the majority of cells produce 'non-specific' immunoglobulin (mainly of the IgM class). Such lymphoblastoid cell lines can be easily propagated in high-density cultures. Because cloning at 1 cell per well is not possible, stabilization of lymphoblastoid cell lines by limiting dilution is not feasible and most newly established lines cease to produce specific antibody within a few weeks. Xenohybrids, resulting from fusion of Epstein-Barr virus-transformed cells with NS1 mouse plasmacytoma cells, can be cloned at 1 cell per well. Stable xenohybridoma subclones, producing antibody of the desired specificity, can be isolated after a series of limiting dilutions. In a model system, we have studied the efficiency of xenohybridization of human lymphoblastoid cells. Using this system, we have constructed IgG anti-tetanus-toxoid- and IgG anti-HBsAg-producing cell lines. Next, we investigated whether transformation with Epstein-Barr virus is essential in such a two-step procedure or whether a polyclonal stimulator, such as pokeweed mitogen, could also be used. It was found that antibody-producing xenohybrids can be obtained after stimulation with pokeweed mitogen. However, this latter system is subject to more variations and lacks the advantage of pre-selection of antibody-producing cells as compared to xenohybridization after transformation.

Colony-forming cells in chronic granulocytic leukemia--I. Proliferative responses to growth factors.

Peripheral blood cells from 2 patients with chronic granulocytic leukemia were separated by density centrifugation. Mononuclear cells of low density (d less than 1.062g cm-3) with blast-cell morphology were cryopreserved before culture in vitro. Upon culture in conventional colony assays, up to 20% of the cells formed hemopoietic colonies. Although the spectrum of colony types resembled that of normal bone-marrow cells, there were large differences between the patients with respect to the number, type and size of colonies that were observed. Colony formation required the addition of hemopoietic growth factors, such as colony-stimulating activity and erythropoietin to the culture medium. The cells were used to assay hemopoietic regulatory molecules. Both erythropoietin and colony-stimulating activity induced a strong proliferative response as measured by thymidine incorporation. Maximal stimulation was observed when erythropoietin and the supernatant of mixed lymphocyte cultures were added simultaneously. The difference between the cells from the 2 patients in clonal assays was reflected by the different response to individual hemopoietic regulators. The time course of maximal stimulation followed distinct patterns dependent on the source of stimulator. The stimulation was linearly dependent on the input cell number. Taken together, cryopreserved blast cells from patients with chronic granulocytic leukemia appear to be very useful for the characterization of factors regulating hemopoiesis, as well as for studies of hemopoiesis in general.

Detection of HLA antigens on blood platelets and lymphocytes by means of monoclonal antibodies in an ELISA technique.

The expression of HLA-A and -B antigens on peripheral blood lymphocytes and blood platelets was measured using monoclonal antibodies in a semi-quantitative ELISA technique. Reactively of monoclonal anti-HLA-A2 and anti-HLA-B7, with lymphocytes as well as platelets, was in agreement with the presence of these antigens as detected by conventional HLA typing of lymphocytes. When the actual amount of HLA antigens was measured, a gene-dose effect was seen: cells from HLA-B7-homozygous individuals bound more monoclonal anti-HLA-B7 antibodies compared to their HLA-B7-heterozygous siblings. At the same time, cells of different donors showed only very small differences in binding of monoclonal antibody against an HLA-"backbone" determinant. Relative to total HLA-A, -B and -C expression, the amounts of HLA-A2 on lymphocytes and platelets were similar. On the other hand, the expression of HLA-B7 on platelets was diminished compared to that on peripheral blood lymphocytes.

Human endothelial culture supernatant (HECS): a growth factor for hybridomas.

Human endothelial culture supernatant (HECS) had strong growth-promotion activity for hybridoma cells: the yield of hybridomas after fusion was increased at least 2-fold over that in the presence of feeder cells, such as mouse macrophages and spleen cells. Moreover, HECS could substitute for feeder cells when hybridomas were cultured at the single-cell level, and strongly enhanced the proliferation of hybrid cells. furthermore, the presence of human endothelial cells prolonged the stability of human-mouse hybridomas, producing human immunoglobulin, hybrids known to survive poorly during culture in vitro.

Immunoperoxidase procedures to detect monoclonal antibodies against cell surface antigens. Quantitation of binding and staining of individual cells.

An immunoperoxidase method has been developed which allows accurate and sensitive quantitation of the binding of monoclonal antibodies to cell surface antigens. Monolayers of fixed cells were prepared in wells of Terasaki micro-test plates and monoclonal antibodies bound to cell surface antigens were identified by the unlabeled antibody-enzyme method of Sternberger (1974). The cell-bound peroxidase could either be quantified per well or visualized on individual cells by the use of appropriate substrates for peroxidase. Experimental procedures are described in detail and results obtained with several monoclonal antibodies with specificity for different target cells are shown. Limitations and applications of the technique are discussed.

A simple immunofluorescence test for the detection of platelet antibodies.

Immunofluorescence tests on platelets have always been hampered by nonspecific fluorescence caused by non-immunological binding of plasma proteins to the platelet membrane. It was found that this could be easily overcome by fixation of the cells with paraformaldehyde (PFA). By using PFA-fixed platelets, a simple method for the detection of platelet antibodies, the platelet suspension immunofluorescence test (PSIFT) was developed. PFA fixation did not alter or inactivate the platelet antigens tested. Platelet-reactive antibodies detected specifically with the PSIFT included platelet-specific agglutinins of the IgM class, non-agglutinating platelet-specific antibodies of the IgG class, drug-dependent platelet antibodies, HLA antibodies, as well as anti-A and anti-B antibodies. The sensitivity of the new test was satisfactory, as was its reproducibility. Measurement of platelet immunofluorescence was possible in a continuous flow microfluorometer, making a principle, quantitation of platelet antibodies and antigens possible.

Immunofluorescence microphotometry for the detection of platelet antibodies. III. Demonstration of autoantibodies against platelets.

After a survey of the literature dealing with the demonstration of platelet autoantibodies by immunofluorescence techniques, the results are given of a study in which immunofluorescence microphotometry was used for this purpose. The serum of 58, the platelets of 34, and the megakaryocytes of 2 patients with thrombocytopenia were investigated. In 21 of 52 sera (40%) in which the presence of platelet autoantibodies could be expected, positive results were obtained that could not be due to isoantibodies, either because the patients had not been pregnant and had not received blood transfusions or because the reactivity of the serum with the patient's own platelets was demonstrated. The platelets of 28 patients with thrombocytopenia not due to a platelet defect or decreased thrombopoiesis were investigated. In the platelets of 15 (54%) of these, significant differences in fluorescence were found with anti-immunoglobulin conjugate as well as with anti-IgG, -IgA, -IgM, or -complement reagents. It was concluded that in these patients in vivo sensitization of the platelets with autoantibody was demonstrated. In two patients an indication of the in vivo sensitization of the megakaryocytes was also obtained.