Differential regulation of membrane and secretory mu chain synthesis in human beta cell lines. Regulation of membrane mu or secreted mu

Regulation of membrane and secretory mu synthesis was examined in human lymphoblastoid cell lines representing various stages of differentiation. Immunoglobulin phenotype was determined by surface and cytoplasmic staining with fluorochrome-conjugated antibodies and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of anti-mu precipitable cellular products. The thymidine analogue, 5-bromo-2'-deoxyuridine (BUdR), which inhibits differentiation-specific proteins in a variety of systems, was used to examine regulation of immunoglobulin synthesis. We found that BUdR had a differential effect on membrane (mum) and secretory (mus) type mu heavy chains. Ig production in pre-B and plasma cell-like lines, which make mus, was unaffected by BUdR. However, surface expression of IgM (mum) in B cell lines was drastically inhibited at similar doses of BUdR without diminishing total Ig or protein synthesis. Examination of labeled mu chains from control and BUdR-treated B cell lines by SDS- PAGE revealed the production of two sizes of mu (mum and mus) in control cells and only the smaller size (mus) in BUdR-treated cells. This size difference could not be attributed to alterations in glycosylation of the molecules. These data show that BUdR inhibits the production of membrane mu chains without diminishing secretory mu chain synthesis in the same cell. Our findings suggest that thymidine-rich regions of the genome are involved in the regulation of mum vs. mus during B cell differentiation.     

Helper activity for immunoglobulin synthesis of T helper type 1 (Th1) and Th2 human T cell clones: the help of Th1 clones is limited by their cytolytic capacity

A large number of CD4+ human T helper type 1 (Th1) clones specific for purified protein derivative and of Th2 clones specific for the excretory/secretory antigen of Toxocara canis, derived from the same individuals, were analyzed for both cytotoxic capacity and helper function for immunoglobulin (Ig) synthesis. The great majority of Th1, but only a minority of Th2 clones exhibited cytolytic activity. All Th2 (noncytolytic) clones induced IgM, IgG, IgA, and IgE synthesis by autologous B cells in the presence of the specific antigen, and the degree of response was proportional to the number of Th2 cells added to B cells. Under the same experimental conditions, Th1 (cytolytic) clones provided helper function for IgM, IgG, and IgA, but not IgE, synthesis with a peak response at 1:1 T/B cell ratio. At higher T/B cell ratios, a strong decrease of Ig synthesis was observed. All Th1 clones lysed Epstein-Barr virus transformed autologous B cells pulsed with the specific antigen. The decrease of Ig production at high T/B cell ratios correlated with the lytic activity of Th1 clones against autologous antigen-presenting B cell targets. These data suggest that Th1 differ from Th2 human T cell clones not only for their profile of cytokine secretion, but also for cytolytic potential and mode of help for B cell Ig synthesis.     

The 26-kD transmembrane form of tumor necrosis factor alpha on activated CD4+ T cell clones provides a costimulatory signal for human B cell activation

Interleukin 4 (IL-4) induces immunoglobulin (Ig)E and IgG4 synthesis in human B cells. In addition to IL-4, costimulatory signals provided by activated CD4+ T cells are required for productive IgG4 and IgE synthesis. Here we report that the 26-kD transmembrane form of tumor necrosis factor alpha (mTNF-alpha), which is rapidly expressed on CD4+ T cell clones after activation, contributes to the costimulatory signals resulting in IL-4-dependent Ig synthesis by B cells, including IgG4 and IgE production. mTNF-alpha expression was induced on T cell clones within 2 h after activation with concanavalin A. Peak expression was observed at 24 h, followed by a gradual decrease, but appreciable levels of mTNF-alpha were still detectable 72 h after activation. The presence of the 26-kD membrane form of TNF-alpha on activated T cell clones was confirmed by immunoprecipitation. Monoclonal antibodies (mAbs) recognizing mTNF-alpha, or the p55 TNF receptor, inhibited IgM, IgG, IgG4, and IgE synthesis induced by IL-4 and activated CD4+ T cell clones in cultures of highly purified surface IgD+ B cells. The anti- TNF-alpha mAbs also blocked Ig production in cultures in which the activated CD4+ T cell clones were replaced by their plasma membranes. Furthermore, pretreatment of the plasma membranes with anti-TNF-alpha mAbs strongly reduced their capacity to stimulate B cells to produce Ig in the presence of IL-4, indicating that the anti-TNF-alpha mAbs blocked the effects of mTNF-alpha. Anti-TNF-alpha mAbs did not affect IgM, IgG, IgG4, or IgE synthesis induced by anti-CD40 mAbs and IL-4 in the absence of CD4+ T cells, supporting the notion that the anti-TNF- alpha mAbs indeed interfered with the costimulatory, contact-mediated signal provided by T cells, or their membranes. Collectively these results indicate that mTNF-alpha, which is rapidly induced after activation of CD4+ T cells, participates in productive T-B cell interactions resulting in IL-4-induced Ig production. This is a novel property of the T cell membrane form of TNF-alpha.     

Limiting dilution analysis of Epstein-Barr virus-induced immunoglobulin production by human B cells

The Epstein-Barr virus (EBV) is a herpes virus that has the capacity to infect human B cells and to induce them to secrete immunoglobulin (Ig). In the current experiments, Poisson analysis of limiting dilution cultures has been used to study the activation of human peripheral B cells by the B95-8 strain of EBV. Under the culture conditions used, 0.2-1% of peripheral blood B cells were activated by EBV to secrete IgM or IgG. In addition, when multiple replicate cultures containing limited numbers of B cells were tested for IgM and for IgG production, the precursors for IgM and IgG segregated independently; thus, individual B cell precursors matured into cells secreting IgM or IgG but not both classes of Ig. Additional experiments using limiting dilutions of EBV were undertaken to study the viral requirements for B cell activation. These studies indicated that B cell activation by EBV to produce Ig was consistent with a "one-hit" model and inconsistent with a "two-hit" model. Taken together, these results indicate that infection by one EBV virion is sufficient to induce a precursor peripheral blood B cell to secrete Ig and that only one isotype of Ig is then secreted.     

Establishment of specific antibody producing human lines by antigen preselection and Epstein-Barr virus (EBV)-transformation.

Specific antibody producing human cell lines were established by preselecting antigen binding B-lymphocytes and subsequently transforming ("immortalizing") them with Epstein-Barr virus (EBV). NNP-binding B-cells were isolated from the blood of three donors with high anti-NNP titers. EBV-transformation led to polyclonal cell lines that had 15-18% NNP receptor positive cells. A similar fraction of the cells produced NNP-specific plaques in the Cunningham-Szenberg assay. Unconcentrated culture media agglutinated NNP-coupled erythrocytes in up to an 1/2,048 dilution and inactivated NNP-coupled T4 bacteriophage in up to an 1/10,000 dilution. EBV-transformed but not similarly NNP-preselected lines of the same donors were completely negative in the rosette, plaque and antibody secretion tests. Supernatants of the antibody producing lines gave no reaction with the non-coupled erythrocytes or with a number of other hapten coupled controls. Anti-NNP antibodies secreted by all three preselected lines were of the IgM kappa type, which was in contrast to the sera of the donors that contained both IgM and IgG antibodies, with both light chain types. Cloning of one NNP-antibody producing line yielded 9 antibody producers out of 30. The positive clones formed NNP rosettes and plaques with 31-86% of the cells and produced anti-NNP of class IgM, Kappa. The cell culture contained 5-16 micrograms IgM/ml cell culture.     

The essential role of B cell stimulatory factor 2 (BSF-2/IL-6) for the terminal differentiation of B cells

The role of recombinant B cell stimulatory factor 2 (BSF-2/IL-6) in the regulation of growth and differentiation of B cells was investigated. rBSF-2 at 200 pg/ml could induce 50% of the maximum Ig production in B lymphoblastoid cell lines, the specific activity being estimated as 5 X 10(6) U/mg. rBSF-2 augmented PWM-induced IgM, IgG, and IgA production in mononuclear cells (MNC); the effect was exerted by directly acting on PWM-induced B blast cells to induce Ig production. However, rBSF-2 did not induce any growth of activated B cells. In contrast, rBSF-2 showed a potent growth activity on a murine hybridoma clone, MH60.BSF2. The concentration required for half-maximal [3H]TdR uptake was approximately 5 pg/ml, which was 40 times less than that required for Ig induction in a B cell line. Anti-BSF-2 antibody inhibited PWM-induced Ig production in MNC, but not PWM-induced proliferation. The antibody was effective even when added on day 4 of an 8-d culture, indicating that BSF-2 is one of the essential late-acting factors in PWM-induced Ig production.     

DEVELOPMENT OF CHICKEN LYMPHOID SYSTEM : I. SYNTHESIS AND SECRETION OF IMMUNOGLOBULINS BY CHICKEN LYMPHOID CELLS

Synthesis and secretion of Ig by chicken lymphoid cells was studied. Both spleen and bursa cells synthesize and secrete IgM and IgG whereas Ig was not detected in thymus cells. In contrast to the spleen cells which synthesize H and L chains in balanced quantities, the bursa cells synthesize and secrete free L chains. In addition to the lymphoid cells which secrete IgM or IgG, the bursa appears to contain a cell population which synthesizes nonsecretory Ig. The structure of this Ig was studied by specific serological precipitation and by SDS-acrylamide gel electrophoresis. The H chains of this nonsecretory Ig are serologically related to µ-chains and exhibit a smaller molecular weight (i.e., ~50,000) in SDS-acrylamide gel electrophoresis than H chains of IgG and IgM synthesized by the spleen cells (i.e., ~70,000).     

Human B cell clones can be induced to proliferate and to switch to IgE and IgG4 synthesis by interleukin 4 and a signal provided by activated CD4+ T cell clones

In the present study, it is demonstrated that cloned surface IgM-positive human B cells can be induced to proliferate and to switch with high frequencies to IgG4 and IgE production after a contact-mediated signal provided by T cell clones and interleukin 4 (IL-4). This T cell signal is antigen nonspecific and is provided by activated CD4+ cells, whereas activated CD8+ or resting CD4+ T cell clones are ineffective. 15-35% of the B cell clones cultured with cloned CD4+ T cells and IL-4 produced antibodies; 35-45% of those wells in which antibodies were produced contained IgE and IgG4. In addition to B cell clones that produced IgG4 or IgE only, B cell clones producing multiple isotypes were observed. Simultaneous production of IgG4 and IgE, IgM, IgE, and IgM, or IgG4 and IgE was detected, suggesting that during clonal expansion switching might occur in successive steps from IgM to IgG4 and IgE. In addition, production of only IgM, IgG4, and IgE during clonal expansion indicates that this isotype switching is directed by the way a B cell is stimulated and that it is not a stochastic process.     

Detection of cell surface and intracellular antigens by human monoclonal antibodies. Hybrid cell lines derived from lymphocytes of patients with malignant melanoma

This study represents an initial attempt to analyze the humoral immune reactions of patients with malignant melanoma by hybridoma methodology. Using lymphocytes from regional lymph nodes, peripheral blood and tumor infiltrates, 158 fusions were performed with SKO-007 (human myeloma line), LICR-LON-HMy2 (LICR-2), GM 4672 (human lymphoblastoid lines), or NS-1 (mouse myeloma line). Fusion of lymph node lymphocytes with NS-1 resulted in a 3-4 times higher frequency of clones than fusion with LICR-2, and a 10 times higher frequency than fusion with SKO-007 or GM 4672. In the case of peripheral blood lymphocytes, fusion with NS-1 gave greater than 25 times higher frequency of clones than fusion with LICR-2 or SKO-007. Production of human mu, gamma, or alpha heavy chains was detected in 50-80% of wells containing growing clones, and the levels of immunoglobulin ranged from 0.3 micrograms to 40 micrograms/ml. NS-1-derived clones could be easily subcultured, while LICR-2 and SKO-007 clones grew more slowly on subculturing. In this study, Ig secretion appeared to be a more stable property of LICR-2- derived clones than NS-1-derived clones. A panel of 20 human cancer cell lines was used to screen 771 Ig-secreting cultures for antibody to cell surface or intracellular antigens. Reactivity with cell surface antigens was found infrequently (6 cultures), whereas reactivity with intracellular antigens was more common (27 cultures). A new cell surface antigen with properties of a glycolipid was defined with an IgM monoclonal antibody secreted by a tetraploid cell derived from a fusion of LICR-2 with lymphocytes from the axillary lymph node of a patient with melanoma. The hybrid cell line has been subcloned four times and secretes 5 micrograms IgM/ml. The antigen detected by this IgM antibody was found on 5 of 23 melanoma cell lines and 12 of 30 epithelial cancer cell lines. No reactions were found with 11 cultures derived from normal cells. Stable cell lines secreting human antibody that detected nuclei, nucleoli, cytoskeletal elements, Golgi complex, or other cytoplasmic components were also isolated in this study. One of these antibodies detected an intracellular antigen that is restricted to cells of neuroectodermal derivation, and a second antibody reacted primarily with cells of epithelial origin. Using these methods to isolate and analyze human monoclonal antibody, it should now be possible to define the repertoire of the humoral immune response to melanoma.     

The export of immunoglobulin D by human neoplastic B lymphocytes

An investigation has been made into the ability of human neoplastic B lymphocytes expressing surface IgM and IgD to export IgD in culture. Cells that expressed surface Ig of the lambda light chain type frequently exported IgD (10/12 patients), whereas cells expressing surface Ig of the kappa light chain type exported no IgD, although most (8/11 patients) were able to export IgM. It appears, therefore, that in most of the 23 cases studied, cells synthesizing IgD with lambda light chains can both express and export IgD, whereas those synthesizing IgD kappa can only insert it into the surface membrane. This finding and the known preponderance of lambda in plasma IgD imply that the possession of a lambda chain facilitates the IgD secretory pathway, a conclusion that implicates a control mechanism subsequent to the surface/secretory dichotomy arising from different splicings of heavy chain messenger RNA.     

Production of recombinant murine-human chimeric IgM and IgG anti-Js(b) for use in the clinical laboratory

BACKGROUND: Directly agglutinating MoAbs are more useful than IgG MoAbs of murine origin for typing RBCs from donors and patients. The molecular manipulation and conversion of a murine IgG MoAb into mouse- human chimeric IgM and IgG antibodies are described. STUDY DESIGN AND METHODS: cDNA encoding the variable heavy- and light-chain genes of a murine hybridoma anti-Jsb cell line (MIMA-8) were cloned into human IgM or IgG expression vectors, which were then separately stably transfected into SP2/0-Ag14 B-cells. The secreted antibodies were screened by ELISA and analyzed by flow cytometry and hemagglutination. RESULTS: Forty percent (16 of 40) of the stable clones secreted IgM and 66 percent (12 of 18) of the stable clones secreted IgG. The chimeric IgM from the highest expressing clone reacted 4+ in LISS at room temperature. The chimeric IgG from one clone reacted 4+ by the IAT, resembling the specificity of the original murine antibody. Both manipulated MoAbs reacted specifically with RBCs as assessed by flow cytometry. CONCLUSION: Human-mouse chimeric IgM and IgG from a murine IgG MoAb anti-Jsb has been successfully engineered for use in the clinical laboratory. This approach can potentially be used to manipulate other murine MoAbs to blood group antigens into more clinically useful human isotypes.     

Immunoglobulin VH determinants defined by monoclonal antibodies

Hybridoma clones secreting antibodies against common VH determinants were readily produced by fusion of cells from mice immunized with isolated V mu fragments of human immunoglobulins (Ig), but not with intact Ig molecules or isolated heavy chains. Four monoclonal antibodies to the V mu fragments of different IgM paraproteins were selected for analysis: MH-44 (mu kappa), GB-24 (mu kappa), NF-11 (gamma 1 kappa), and SA-44 (gamma 1 kappa). Each antibody reacted with the homologous V mu fragment, homologous mu chain, and normal gamma chains, but not with the intact IgM molecules, intact IgG, or isolated light chains, as determined by radioimmunoassay. The VH reaction spectra with a panel of myeloma heavy chains showed overlapping but distinctive patterns for the four antibodies. Each of the four monoclonal anti-VH antibodies appeared to react with a different "hidden" VH determinant that is not exposed on undenatured, intact Ig molecules and differs from conventional VH subgroup determinants. In immunofluorescence studies, the monoclonal anti-VH antibodies did not bind to surface Ig on viable B lymphocytes, but visibly stained subpopulations of fixed B lymphocytes, pre-B cells, and normal plasma cells. The mean frequencies of VH+ plasma cells were 30% (MH-44), 17% (GB-24), 13% (NF-11), and 3% (SA-44), and similar frequencies were obtained for the VH+ B cell subpopulations. While subpopulations of B cells could be identified at all stages in differentiation by immunofluorescence with the anti-VH antibodies, neither resting nor activated T cells expressed these VH determinants in detectable amounts.     

Tumor promoter phorbol myristic acetate stimulates immunoglobulin secretion correlated with growth cessation in human B lymphocyte cell lines.

Immunoglobulin production by lymphoblast cell lines was studies using protein A-red blood cell plaque formation to detect individual secreting cells. Immunoglobulin (Ig) secretion by 6 of 12 human B-cell lines tested could be stimulated up to twentyfold by phorbol myristic acetate (PMA) at subtoxic concentrations of 10-1000 ng/ml depending on the line. Stimulation was found with both IgM and IgG cell lines. No switch of Ig class synthesis was found in the cell lines as a result of PMA incubation. Increase in Ig secretion was closely associated with cessation of growth resembling induction of terminal differentiation in the cells. PMA induction of Ig secretion in B lymphocytes from normal peripheral blood requires the cooperation of T cells. PMA stimulation of certain cell lines reported here suggests that the lines are late in the differentiation pathway to plasmacyte and can be easily triggered to secrete Ig by membrane-altering agents.     

Loss of secretion in mouse-human hybrids need not be due to the loss of a structural gene

Three cloned mouse-human lines (B1-29, E2-42, and A2-31) secreting human immunoglobulin (Ig) were obtained from a fusion between the mouse myeloma line NS-1 and human tonsillar lymphocytes stimulated in vitro with pokeweed mitogen. One line, B1-29, has continued to secrete human IgG for a period of 2 yr in culture. This line was recloned three times to give a panel of secreting and nonsecreting subclones. Most of the nonsecreting subclones had also lost surface Ig. The structural genes for human Ig heavy chains have been provisionally assigned to chromosome 14, which also encodes the enzyme nucleoside phosphorylase. Human nucleoside phosphorylase was detected in all secreting and nonsecreting B1-29 subclones, indicating the presence of human chromosome 14. The retention of chromosome 14 in nonsecreting clones implied that the structural genes for human Ig were A2-31 and E2-42, which had stopped secreting, an attempt was made to restimulate the secreting of human Ig with mitogens A2-31 was unique among the cell lines examined, in that chromosome 14 could not be detected by an isoenzyme marker. Lipopolysaccharide, at an optimum dose of 10 micrograms/ml, restimulated these nonsecreting hybrid lines to secrete human IgG in levels up to 0.7 micrograms/ml. Loss of Ig secretion may not therefore be caused by loss of Ig structural genes.     

Cellular basis of hyper IgM immunodeficiency

Six patients with primary hypogammaglobulinaemia and hyper IgM were studied. All showed very low serum IgG and IgA concentrations. The in vitro pokeweed-mitogen (PWM)-induced immunoglobulin (Ig) production, including IgM, by their peripheral blood lymphocytes was low. Even when patients' B cells were cocultured with normal T cells, IgM production did not reach normal levels. These results and studies of Ig class on the surface of B lymphocytes point to a maturation arrest of these cells. T cells from all but one patient helped very little Ig production by patients' or normal B cells. Similar numbers of these T cells did not suppress Ig production by normal T plus B cells. Therefore a defect in T cell help for IgM, IgG and IgA was seen in most patients, in addition to the B cell abnormality.     

Cytokine-induced proliferation and immunoglobulin production of human B lymphocytes triggered through their CD40 antigen

Human resting B lymphocytes enter a state of sustained proliferation when incubated with both mouse fibroblastic L cells stably expressing Fc gamma RII/CDw32 and anti-CD40 antibodies. We have explored the effects of 11 recombinant human cytokines (CKs) on induced cell proliferation and immunoglobulin (Ig) production. Interleukin 4 (IL-4) was the only CK able to enhance anti-CD40-induced B cell multiplication as measured by enumeration of viable cells, and interferon gamma (IFN-gamma) further stimulated this induced proliferation. IL-4 enhanced the production of IgM and IgG by B cells and induced them to produce IgE. Combinations of IL-4 and IL-2 resulted in the production of large amounts of IgM and IgA. Interestingly, IFN-gamma did not inhibit the production of IgE by cells stimulated with anti-CD40 and IL-4. None of the tested CK combinations resulted in the production of large quantities of IgG. Therefore, this new culture system represents a unique model to study isotype regulation in highly purified human B lymphocytes, in addition to allowing the generation of long-term factor-dependent human B cell lines.     

The switch from IgM to IgG secretion in single mitogen-stimulated B- cell clones

The frequency of mitogen-reactive B cells yielding an IgG plaque-forming cell (PFC) response has been determined in vitro by limiting dilution analysis under culture conditions which allow every growth-induced B cell to grow and mature into a clone of Ig-secreting cells. The frequencies of lipopolysaccharide (LPS)-and lipoprotein-reactive precursors for IgG-secreting cells in the spleen of 6--8 wk old C3H/Tif and of C57BL/67 mice were found to be between 1 in 30 and 1 in 40 B cells and, therefore, only one tenth of the frequencies of mitogen-reactive precursors of clones secreting IgM. All IgG-secreting cells developed by switching in clones which previously contained IgM-secreting cells. This was shown in two experiments where the total number of mitogen-reactive precursor yielding IgM-secreting cell clones was limited such that 82 or 90% of all responding cultures originated from one precursor. Thus, of 480 cultures in the first and 720 cultures in the second experiment, 86 and 98 cultures were found positive, yielding IgM-secreting cells at day 5. When the same cultures were assayed at day 7 for IgG-secreting cells 9 and 10 cultures were found positive. All 19 cultures with IgG-secreting cells previously had contained IgM-secreting cells. The probability that IgG-secreting cells and IgM-secreting cells would have arisen from independent precursors can be calculated using Fisher's exact test of independence. For the two experiments those probabilities are 3.4 X 10(-7) and 4.0 X 10(-9). Since we have previously shown that each cell in a mitogen-stimulated, growing B-cell clone divides, and that each dividing cell secretes Ig, we conclude from these experiments that the large majority--in our experiments all--of the IgG-secreting cells in mitogen-stimulated B-cell clones develop by switch from IgM-secreting cells. IgG-secreting cells develop either early or late during growth of a single IgM-secreting cell clone. The switch to IgG secretion, therefore, is not fixed in the time of clonal growth after mitogenic stimulation.