Antibody synthesis in vitro, a marker of B cell differentiation

Differential effect of chromium compounds on the immune response of the African mouth breeder Oreochromis mossambicus (Peters)

The objective of this study was to investigate the effect of trivalent (chromic chloride) and hexavalent (potassium dichromate) forms of chromium in the African mouth breeder Oreochromis mossambicus (Peters), with reference to the humoral immune response and lymphoid cells/organs. The 96 h LD50 for hexavalent and trivalent chromium was found to be 75 and 1,000microg fish(-1), respectively. Groups of fishes were injected intraperitoneally with 10, 1, 0.1 and 0.01% LD50 hexavalent and trivalent forms of chromium and subsequently immunised with bovine serum albumin (5 mg in 0.2 ml physiological saline). Both forms of chromium suppressed the antibody response, with hexavalent chromium being more suppressive than trivalent chromium. Reduction in spleen weight, splenocyte number and the percentage of blood lymphocytes was observed following administration of both forms of chromium. The possible immunological mechanisms behind the differential suppression of the antibody response and the reduction in spleen weight, splenocyte and lymphocyte counts are discussed.

Effects of anti-IgM suppression on polyclonally activated murine B cells: analysis of immunoglobulin mRNA, gene specific nuclear factors and cell cycle distribution

Polyclonal activation of murine B cells with bacterial lipopolysaccharide (LPS) and dextran sulfate (DxS) results in cell proliferation as well as increased immunoglobulin gene transcription and antibody secretion. When added to B cell cultures during mitogen activation, anti-mu antibody suppresses the rate of proliferation and immunoglobulin gene expression. Using this model system we show that co-cultures of B cells with LPS/DxS and anti-mu resulted in a decrease of both mu and kappa chain mRNA. Suppression did not prevent B cell entry into cycle nor a significant alteration in the distribution of cells in phases of cell cycle, although it did prolong the cycle transit time in a dose dependent fashion as determined by bromodeoxyuridine pulse labelling. Analysis of B cell specific nuclear binding factors, which previously have been shown to be important in regulating immunoglobulin gene transcription were examined. Results show that the kappa-specific enhancer binding activity of NF-kappa B was induced in activated as well as suppressed cultures. The lymphoid specific factor NF-A2, which recognizes the octamer sequence motif in the promoters of immunoglobulin genes, was induced by the polyclonal activation but was selectively lost in extracts from suppressed cells. Thus, specific regulation of the nuclear factor which plays a critical role in both heavy and light chain immunoglobulin gene expression may contribute to the transcriptional suppression observed in anti-mu treated B cells.

The Florey lecture, 1989. Self-tolerance: the key to autoimmunity

'Horor autotoxicus', as it was termed by Erhlich, is a rare clinical event despite the genetic potential of every individual to mount immune responses to self-antigens. This can be explained by the fact that the developing immune system learns to recognize self-antigens and to tolerate them. The key to autoimmunity therefore lies in unravelling the mechanisms of self-tolerance. Studies of conventional models of unresponsiveness have failed to provide a definitive answer owing to the difficulty in controlling for the large number of antigen-related variables associated with self-tolerance and in following the fate of individual clones of self-reactive lymphocytes which emerge in very low numbers from the pre-immune repertoire. These problems have now been overcome by creation of transgenic mice tolerant to endogenous antigens and containing high frequencies of autoreactive T or B lymphocytes. According to the results obtained to date, different mechanisms of tolerance induction operate for self-reactive T lymphocytes compared with B lymphocytes. Thus self-tolerance in T lymphocytes appears to depend largely on clonal deletion within the thymus. By contrast, self-reactive B lymphocytes are functionally silenced without undergoing deletion provided that the transgenic B lymphocytes express both IgM and IgD on their surfaces. This dichotomy makes good sense given that the T-lymphocyte repertoire once shaped within the thymus is not subject to further mutation whereas antigen receptors on mature B lymphocytes undergo hypermutation in the periphery.

Prospective partition analysis of independently assorted sets. Accessory elements supporting clonal lymphoid activation by mitogens

Accessory cells for mitogen-induced clonal proliferation of lymphocytes can be found after in vitro culture of murine spleen cells. Mitogenic activation of T cells (concanavalin A) depends on such accessory cells. When the cultures in which the accessory cells developed are partitioned, assortment of the accessory cells in cultures is found. When small numbers (1-10) of responder cells, T cells, are dispensed into the above cultures, clonal growth of the T cells is achieved. Neither the dose-response profile of accessory cells nor that of responding cells shows single hit kinetics. Re-categorizing the data set reveals that only cultures with over 20 adherent cells were likely to promote T cell growth and single hit kinetics for the responding cell clone and the accessory cell clone were obtained.

Clonal analysis of the synergistic mitogenic effect of lipopolysaccharide and dextran sulphate on B cell activation, growth, and differentiation into Ig-secreting cells

Splenic B cells of BALB/c mice were stimulated in vitro either with lipopolysaccharide (LPS), dextran sulphate (DxS), or with both LPS and DxS. The absolute frequency of B cells that differentiate into clones of immunoglobulin (Ig)-secreting cells upon activation with these mitogens was determined by means of limiting dilution analysis. Determination of the number of Ig-secreting cells in DxS-stimulated cultures with the protein A plaque assay proved to be difficult because of the anti-complementary activity of DxS. Therefore, we assayed the number of Ig-secreting cells with a reverse ELISA-plaque assay. This assay is complement-independent and is at least as sensitive as the protein A plaque assay. The results showed that LPS, DxS, and the combination of LPS and DxS stimulate 1 in 27, less than 1 in 500 and 1 in 15 nucleated spleen cells of BALB/c mice to proliferation and differentiation into a clone of Ig-secreting cells, respectively, indicating that these mitogens have a synergistic effect on B cells at the precursor cell level. Analysis of the clone size of the activated B cells showed that the combination of both mitogens also caused a larger clone size. Thus, the synergistic effect of LPS and DxS that was previously observed in mass cultures is due to two separate effects. Quantitatively most important, however, is that more precursors are activated by the combination of the two mitogens.

Analysis of the activation of lymphoid cells by mitogens in vitro with limiting dilution methods: adherent peritoneal cells suppress B-cell activation and synergize with WEHI-3 in the activation of T cells by Con A

Adherent peritoneal cells (APC) have often been used as a pure and effective macrophage population. Using partition analysis and small numbers of lymphoid cells activated by mitogens (concanavalin A for T cells (in the presence of TCGF) and LPS + DxS for B cells) we found that APC were accessory cells for T cell activation and growth but were not effective for B cells. Although APC were effective in assisting T-cell mitogenesis, they were not especially efficient. However, when APC were mixed with irradiated WEHI-3 cells (a tissue culture line previously shown to exhibit accessory cell activity in vitro for mitogenic activation T and B cells), the APC and WEHI-3 showed apparent synergy. One reason for failure of APC to assist B-cell mitogenesis was traced to the presence of a suppressor cell population which overcame the accessory cell help given by irradiated WEHI-3 cells to LPS-DxS stimulated murine B cells. It is thus possible to find "helper" effects (synergy of APC and WEHI-3 assisting the mitogenesis of T cells), as well as suppressor effects within the range of cells found in adherent accessory cells.

Cloning of mitogen- and antigen-reactive B lymphocytes on filter paper discs. I. A description of the technique and of methods for the analysis of colonies

A novel technique for establishing short term clones of antigen- or mitogen-activated splenic B lymphocytes is described. Spleen cells are plated onto the surface of filter paper discs and subsequently stimulated by antigen or mitogen in situ; activated B cells proliferate and differentiate into pure colonies of cells analogous to bacterial colonies growing on agar. These colonies of lymphocytes may be characterized in a series of replica hemolytic-plaque, autoradiographic, or immunoenzyme assays making possible a full characterization of the frequency of secreted idiotopes and paratopes and of the cells that produce them. Colony induction by either antigen or mitogen occurs under identical conditions, thus a rigorous comparison between the mitogen-selected and antigen-selected antibody repertoires may be made.

Peritoneal B cells differentiate without proliferation into autoantibody secretors under the influence of factors released by other cells

After 3-5 days of in vitro culture, peritoneal cells from untreated C3H mice produce autoantibodies specific for autoantigens in the membranes of mouse erythrocytes. The autoantigens are exposed in vitro by treating mouse erythrocytes with the proteolytic enzyme bromelain. Limiting-dilution cell culture techniques were used to determine the frequency of the autoreactive B cells. Cells were cultured in Terasaki trays at 10-200 cells/well. Autoantibody production was assayed with an in situ plaque-forming cell (PFC) assay. On average, one autoantibody precursor cell was detected for every 150-200 peritoneal cells cultured. This precursor frequency was increased to 1 in 50 by the addition of lipopolysaccharide (LPS) and dextran sulphate (DS) to the culture medium. The addition of a culture supernatant from an EL4 lymphoma subline also induced a high proportion of the peritoneal cells to secrete autoantibodies. However, it was not possible to determine the frequency of PFC accurately because at limiting numbers of peritoneal cells the effects of EL4 affected more than one limiting variable. Significant cell division was observed in cultures to which LPS/DS had been added, in contrast to untreated cultures to which EL4 supernatant was added. The results show that high numbers of autoreactive B cells committed to self antigens are present in the peritoneal cavity and that these cells under the influence of appropriate cytokines can differentiate in vitro, even without proliferation, into autoantibody secretors. The cell type or types releasing the cytokines remain to be identified.

Polyclonal activation of canine B lymphocytes evaluated by a protein A reverse hemolytic plaque assay

This paper describes the optimal culture and assay conditions for the polyclonal activation of canine lymphocytes with pokeweed mitogen and the quantitation of immunoglobulin secreting plaque-forming cells (PFC) using a staphylococcal protein A-reverse hemolytic plaque assay. The assay permits the quantitation of total immunoglobulin secreting PFC as well as class-specific immunoglobulin secreting PFC. On the optimal day of culture, a mean of 176 IgA PFC/10(6), 575 IgM PFC/10(6), 1276 IgG PFC/10(6), and 2158 total PFC/10(6) cells were generated following polyclonal activation. This study provides a simple and reproducible assay for the delineation of the immunoregulatory mechanisms involved in the differentiation of canine B lymphocytes.

Improved fusion technique. III. The growth promoting activity of lipopolysaccharide, dextran sulfate, and red cell lysate added to Hy-clone calf serum

A new high quality young-calf serum, Hy-clone calf serum (HcCS), was tested for use in hybridoma culture. This calf serum alone had little growth promoting activity and was much inferior to fetal calf serum (FCS). Red cell lysate (RCL) used in combination with the young-calf serum showed very good growth promoting activity. Growth was increased about threefold over that in the presence of FCS. However, HcCS and RCL could not substitute for feeder cells when hybridomas were cultured as single cells under conditions of limiting dilution. It is thought likely that the potent growth promoting factor in red cell lysate is hemoglobin.

The polyclonal lipopolysaccharide response is accessory-cell-dependent

Different concentrations of spleen cells from C57BL.10 mice were activated with lipopolysaccharide (LPS), and DNA synthesis and IgM and IgG secretion were measured. The dilution curve was sigmoid, and the response was rapidly lost below a certain cell concentration. In the presence of thymocytes or spleen cells from the LPS-non-responder strain C57BL.10/ScCr the dilution curve for the LPS response of cells from C57BL.10 mice became linear, and the overall response was increased. Irradiated cells could not restore the response at suboptimal cell concentrations. In addition, enriched T cells restored the response as well as normal spleen cells, whereas enriched B cells did not. We compared the restoring capacity of different filler cells for the LPS response with that of a plasmacytoma cell line cultured at suboptimal cell concentrations. The results are compatible with the idea that the filler cells provide growth-stimulating activity to LPS-responsive cells but growth-supporting activity to the tumour cells. Furthermore, highly enriched B-cell populations respond poorly to LPS, but the response can be partly restored by filler cells. These data suggest that the LPS response is accessory-cell-dependent.

Limiting dilution analysis of Epstein-Barr virus-induced immunoglobulin production

The major goal of this work is to establish a culture system for the growth of human B lymphocytes at the single-cell level so that the immunoglobulin secreted by the clonal progeny of that cell can be analyzed. A method which involves culturing small numbers (1-1000) of lymphocytes, which have been infected with Epstein-Barr virus (EBV) prior to plating, in round-bottom microtiter plates is described. A feeder layer of irradiated (2500 R) umbilical cord blood lymphocytes to which phytohemagglutinin has been added was found to be optimal. Culture supernatants collected from 3 to 6 weeks postinfection are assayed for the production of IgG and IgM by radioimmunoassay in order to determine the overall cloning efficiency of the system. We have shown that up to 33% of surface Ig-positive cells produce detectable clones in this system. Umbilical cord blood cells are superior to T-cell and macrophage cell lines as feeder layers. Furthermore, culture supernatants from phytohemagglutinin-stimulated umbilical cord lymphocytes do not adequately replace these cells. We also observed that while most IgM-secreting clones continued to produce immunoglobulin during the 7-week time period analyzed, the majority of IgG-secreting clones had a relatively short half-life in vitro. This culture system allows us to examine a significant proportion of the human B-cell population and carry out studies on the frequency of specific antibody- and isotype-producing clones.

Clonal anergy: inhibition of antigen-driven proliferation among single B lymphocytes from tolerant animals, and partial breakage of anergy by mitogens

Mice were injected with fluoresceinated human gamma globulin (FLU-HGG) either at 2-3 days of age or as pregnant females. At 2 weeks of age, the spleen cells of the injected suckling mice or offspring were fractionated on FLU-gelatin dishes to yield FLU-binding B cells. These B cells were then cloned in microcultures using one of two recently described systems in which single B cells grow in the absence of feeder or filler cells, namely following stimulation with FLU-polymerized flagellin (FLU-POL) and conditioned media containing B cell growth and differentiation factor(s); or mitogenic activation by a mixture of E. coli lipopolysaccharide (LPS) and dextran sulfate (DxS). As such cultures permit visualization of clonal proliferation as well as ultimate harvesting of cultures for assay of hemolytic plaque-forming cells, it was possible to ask whether the lesion in the tolerant state affected the B cell's capacity to divide, to differentiate to antibody secretion, or both. The results indicated that, when stimulated with antigen, the anergic cells could neither divide nor differentiate. However, when the strong mitogen mixture was used, clonal anergy was partially broken. The cells proliferated, and a small proportion of them differentiated into anti-FLU antibody-forming cells. A marked variation in antigen-binding avidity of the FLU-binding cells made it difficult to quantitate the degree of uncoupling of proliferation and differentiation among tolerant, LPS plus DxS-stimulated cells. Nevertheless, a partial reversibility of clonal anergy must affect views on mechanisms of self-tolerance.

A monoclonal T cell-replacing activity can act directly on B cells to enhance clonal expansion

We have used a B cell cloning system in which the response of a single isolated B cell to lipopolysaccharide and dextran sulfide can be followed. We have shown that culture supernatants from the Dennert long-term alloreactive T cell line C.C3.11.75 increase the frequency of B cells stimulated to clonal expansion by mitogens. These culture supernatants are devoid of interleukin 1 and 2 but contain the T cell-replacing factor activity (DL)TRF. These experiments provide unequivocal proof that a T cell-derived factor or factors can act directly on a B lymphocyte in the absence of any other cell.

Clonal anergy: the universally anergic B lymphocyte

The clonal anergy theory of induction of immunological tolerance states that differentiating B lymphocytes that encounter multivalent antigen at the pre-B to B cell transition stage can receive and store a negative signal, which renders them anergic to later triggering stimuli. The theory was tested by using an anti-mu chain monoclonal antibody, E4, as a model tolerogen. The fluorescence-activated cell sorter was used to select B cell-free cell populations from adult murine bone marrow or newborn spleen, and later, to analyze B cell neogenesis in vitro. The presence of E4 at greater than or equal to 1 microgram/ml was required to impede the development of normal numbers of B cells with full receptor status. The subsequent capacity of these B cells to respond in vitro to mitogens was assessed in a filter-cell free microculture system that allows single B cells to proliferate and differentiate. Concentrations of E4 far below those required to affect B cell neogenesis had profound inhibitory effects on the subsequent functional capacity of the B cells. In fact, 10(-3) micrograms/ml of E4 markedly impaired both proliferation and antibody formation, and 10(-1) micrograms/ml, which had no effect on Ig receptor development, abrogated functional capacity. Thus B cells formed in the presence of E4 at 10(-1) micrograms/ml, though possessing the receptor status typical of B cells, were functionally entirely anergic. Exposure to E4 appeared to accelerate the spontaneous death rate of newly formed B cells in vitro. Whether the anergic cell would also have a shortened life span in vivo is not known.

Antibody production by single, hapten-specific B lymphocytes: an antigen-driven cloning system free of filler or accessory cells

CBA mouse spleen cells were subjected to hapten affinity fractionation on thin layers of fluorescein (FLU)-gelatin. This procedure yields 97% B cells with varying FLU-binding avidities. One to 30 cells were placed in 10-microliter microcultures without any filler or accessory cells. the T-independent antigen polymerized flagellin coupled to FLU (FLU-POL) was ineffective in stimulating these cells to clonal proliferation or antibody production when used alone. Unpurified preparations rich in interleukins also failed to stimulate the cells. When specific antigen, but not in irrelevant hapten-POL, was combined with the interleukins, clonal proliferation was stimulated and most clones produced anti-FLU antibody-forming cells. The frequency of antibody-forming clones was only slightly lower than that in a system using antigen plus filler cells. In the absence of added interleukins, the mitogens Escherichia coli lipopolysaccharide plus dextran sulfate induced equivalent antibody production. However, a higher frequency of clonal proliferation was noted. Added interleukins did not aid these mitogen-driven responses. Such an antigen-dependent cloning system, free of filler and accessory cells, should permit more precise analysis of the respective roles of antigens and interleukins in the physiology of antibody-forming clone formation.

A synergistic polyclonal response to dextran sulphate and lipopolysaccharide: immunoglobulin secretion and cell requirements

The effects of the simultaneous addition of lipopolysaccharide (LPS) and dextran sulphate (DxS) were studied in a low-cell density culture system, which enables extensive cell proliferation and high immunoglobulin secretion. Using these two mitogens, a synergistic response was observed, with regard to both cell division and IgM secretion. However, only a very low IgG production could be detected. This was caused by the extensive cell proliferation, leading to suboptimal culture conditions. Thus, when the blasts were recultured at a lower density or when a lower initial cell concentration was used, a high IgG response was obtained. The synergistic response induced by LPS plus DxS was independent of T cells. Furthermore, no apparent need for phagocytic cells was found. Both the LPS- and the LPS plus DxS-induced activation led to a switch, preferentially to IgG2b and IgG3 secretion. This subclass pattern was not changed when the cultures were lacking functional T cells.