T-cell-derived lymphokines that induce IgM and IgG secretion in activated murine B cells

T cell-replacing factor (TRF)/interleukin 5 (IL-5): molecular and functional properties

TRF has originally been defined as a T-cell-derived lymphokine that triggers activated B cells for a terminal differentiation into Ig-secreting cells. HPLC-purified TRF from Sup of a murine TRF-producing B151 cell is an acidic glycoprotein, exerts BCGF II activity and induces expression of IL-2 receptors. It does not show IL-1, IL-2, IL-3, BSF-1/IL-4, or IFN gamma activity. We prepared monoclonal TB13 and NC17 antibodies against HPLC-purified B151-TRF which are specific for and can inhibit TRF as well as BCFG II activity of B151-TRF. Moreover, TB13 as well as NC17 antibody can immunoprecipitate the 46 Kd molecule from B151 Sup which exerts TRF as well as BCGF II activity. Complementary DNA (pSP6K-mTRF23) encoding for murine TRF/IL-5 was cloned and its entire nucleotide sequences were determined. The murine TRF/IL-5 cDNA encodes 133 amino acids including N-terminal strongly hydrophobic regions. Secreted recombinant TRF/IL-5 (apparent m.w. of 46 Kd) has 113 amino acid residues and also comprises homodimers of a molecule with an apparent m.w. of 25 to 30 Kd. TRF/IL-5 mRNA is constitutively expressed in constitutively TRF-producing B151 and is inducible in some T cell lines upon stimulation with PMA or Con A. TRF/IL-5 mRNA is also expressed in Tbc-primed T cells upon the stimulation with PPD, whereas its expression is not effectively induced in non-primed spleen cells by stimulation with Con A or PMA plus calcium ionophore. The translation product of murine TRF/IL-5 cDNA triggers resting as well as activated (DNP-primed or LPS-stimulated) murine B cells for terminal differentiation into Ig-secreting cells (IgM, IgG1, or IgA) accompanied by increased mRNA expression for secreted forms of relevant Ig heavy chain (mu, gamma, or alpha). Among these, increases in the level of mu, and alpha-specific mRNA for the secreted form of IgM and IgA, respectively, are prominent. Moreover, TRF/IL-5 induces maturation of resting B cells into IgM-secreting cells. TRF/IL-5 promotes growth of activated B cells as well as BCL1 cells. TRF/IL-5 is, therefore, a growth as well as a differentiation inducing factor for B cells. Moreover, it induces functional IL-2 receptors on resting as well as activated B cells, besides TRF and BCGF II activities.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of TH-lines and clones on the growth and differentiation of B cell clones in microculture

Antibody isotype expression by B cell clones was analyzed using in vitro microcultures containing low numbers of hapten-gelatin-enriched B cells and higher numbers of hemocyanin-specific helper T cell lines or clones. Twenty-eight to sixty-three percent of clones grown in microculture with haptenated hemocyanin and T cells from established lines expressed IgG and/or IgA isotypes in random mixtures, almost always accompanied by IgM. Helper T cells from hemocyanin-specific clones also supported the expression of non-IgM isotypes by the B cell clones, suggesting that a single specificity of T cell can provide sufficient growth and differentiation factors for the display of isotype switching. A positive correlation between the antibody output of clones and the expression of non-IgM isotypes indicated that the switching process may be associated with cell division. Although memory B cells that give clones expressing IgG and/or IgA in the absence of IgM are also enriched on haptenated gelatin, they are not stimulable under conditions of this microculture assay.

Biochemical events associated with inhibition of B-cell proliferation by phorbol diesters

Phorbol myristate acelate (PMA), a potent tumor promoter, has a variety of effects on cells of the immune system resulting in altered patterns of cell proliferation and differentiation. Although PMA is mitogenic or co-mitogenic for human lymphocytes and murine T-cells, it inhibits proliferation of murine B-cells stimulated by LPS or anti-Ig. PMA, however, does not inhibit the ability of LPS or anti-Ig to activate B-cells, as evidenced by increased Ia antigen expression and RNA synthesis. In the present studies it was shown that inhibition of DNA synthesis by PMA coincided with qualitative and quantitative changes in phosphorylated proteins. In particular, PMA treatment resulted in a unique profile of phosphoproteins independent of LPS or anti-Ig treatment. Inhibition of DNA synthesis occurred over a wide range of PMA concentrations. At concentrations up to 10(-9) M, inhibition of proliferation correlated with decreased phosphatidylinositol turnover and decreased intracellular Ca2+ levels, suggesting that PMA affects the phosphoinositide signal transduction pathway. However, at PMA concentrations less than 10(-10) M, inhibition of anti-Ig- and LPS-mediated proliferation occurred without inhibition of the phosphoinositide transduction signal. At these concentrations, PMA-induced inhibition of DNA synthesis was highly sensitive to recombinant IL-2. These data suggest that the antiproliferative effects of PMA on B-cells stimulated by LPS or anti-Ig may be mediated by two mechanisms. At high concentrations, PMA causes a feedback regulation of the phosphoinositide-dependent messenger system, while at lower concentrations, PMA alters the response to specific growth factors. Since PMA induces unique phosphoproteins and both of these events can be regulated by protein phosphorylation, it is possible that these unique phosphoproteins are responsible for the antiproliferative effects of PMA.

T-independent activation of single B cells: an orderly analysis of overlapping stages in the activation pathway

This review has three chief purposes. It describes a microculture system in which single, hapten-specific B lymphocytes can be microscopically observed, cultured and assayed for antibody production in isolation and thus are the unequivocal target of ligands present in the culture fluid. It defines the respective roles of antigens and cytokines acting singly or in combination in the four discernible phases of the immunoproliferative cascade, namely activation, clonal expansion, IgM antibody secretion and isotype switching. It then argues that this precise stepwise analysis can yield useful information concerning important immunological situations, such as experimentally induced immunological tolerance or the effects of constitutive expression of the c-myc oncogene. Evidence is presented that initial activation of the resting B cell in "T-independent" triggering can be achieved either by attachment of a molecule that has B-cell stimulatory properties, such as FLU-LPS or FLU-polymerized flagellin (FLU-POL) or by the lymphokine interleukin 4 (IL-4). IL-4 + FLU-POL is somewhat more effective than either agent alone. IL-4 alone or, better, FLU-POL + IL-4 can stimulate clonal proliferation of the B cell, but FLU-POL alone does not achieve this. Moreover, IL-4 or FLU-POL + IL-4 lead to very little antibody formation. None of IL-1, IL-2 or IL-5 acting alone causes either activation or proliferation. IgM antibody formation is stimulated most strongly by FLU-POL + IL-5, somewhat less strongly by FLU-POL + IL-1 + IL-2 and rather weakly with antigen plus only one of the latter cytokines. The cloning efficiency in the single cell system, and the median clone size can be markedly enhanced by the addition of small numbers of fibroblast or other filler cells to the cultures. While filler cell-free clones do not progress to the stage of isotype switching, filler cell-supported ones can do so in up to 30% of cases. The only cloned lymphokine which has so far been found to promote such switching is IL-4, and the fact that it is at least as powerful as a T-cell supernatant may mean that it is the only agent active in this particular system. However, the detailed pattern of secreted isotypes is different from that seen when MHC-restricted, carrier-specific T cells act on hapten-specific B cells. Hapten-specific B cells from animals rendered neonatally tolerant to FLU-HGG exhibit anergy in the single cell system.(ABSTRACT TRUNCATED AT 400 WORDS)

B cell stimulatory factor-1/interleukin-4 mRNA is expressed by normal and transformed mast cells

BSF-1/interleukin-4, a product of activated T cells, has multiple biological activities that affect cells of most hematopoietic lineages. Among these is the ability of BSF-1 to costimulate the growth of mast cells and regulate the production of IgE. We demonstrate here that BSF-1 mRNA is expressed by a majority of transformed mast cell lines and by 5 IL-3-dependent non-transformed mast cell lines. BSF-1 activity, including the ability to enhance the growth of IL-3-dependent mast cells, was detected in the supernatants of transformed mast cells. The role of BSF-1 as a mast cell growth factor, its constitutive production by transformed mast cells, and the lack of IL-3 production by most of these cells raise the possibility that BSF-1 may act as an autocrine growth factor for some transformed mast cells. Furthermore, production of BSF-1 mRNA by nontransformed cells indicates that mast cells may be an important physiologic source of this factor.

Regulated progression of B lymphocyte differentiation from cultured fetal liver

Lymphoid fetal liver cultures (LFLC) are long-term, nontransformed cultures of early B lymphoid lineage cells which appear developmentally blocked at the pre-B stage in vitro. When injected into severe combined immunodeficient (SCID) mice, cells from LFLC could reconstitute splenic B lymphocytes and serum IgM. T lymphocyte reconstitution was not observed and serum IgG levels were very low. IgG3 was the predominant gamma subisotype in the serum of the LFLC-reconstituted mice, indicating impaired class switching in these B lymphocytes. When thymocytes were coinjected with LFLC, the B lymphocytes were able to class switch fully and respond to T-dependent antigens. These serological responses were heterogeneous. This experimental system allows separation of three B lymphocyte developmental stages: early differentiation in vitro, progression to IgM secretion in vivo, and late differentiation dependent upon mature T lymphocytes in vivo. The unique advantage of this system is the ability to regulate the B lymphocyte developmental pathway in a defined, stepwise manner.

Receptors for B-cell stimulatory factor-1 expressed on cells of haematopoietic lineage

B-cell stimulatory factor-1 (BSF-1) is a T-cell product of relative molecular mass 20,000 (Mr, 20K) initially described as a cofactor required for DNA synthesis by resting mouse B cells stimulated with low concentrations of anti-IgM antibodies. It acts on resting B cells to enhance the expression of class II major histocompatibility complex (MHC) molecules, to prepare these cells to respond more promptly to subsequent stimuli, such as anti-IgM antibodies, and causes the secretion of IgG1 and IgE by B cells stimulated with lipopolysaccharide (LPS). BSF-1 has been shown to stimulate T cell lines, resting T cells and some mast cell lines. Recently, the designation interleukin-4 (IL-4) has been suggested for BSF-1. We report here the existence of high-affinity cell-surface receptors specific for BSF-1 on both B and T lymphocytes, and on cells of several other haematopoietic lineages, including mast cell, macrophage and undifferentiated haematopoietic cell lines. Resting B and T lymphocytes express receptors, which increase in number upon activation of B cells with LPS or anti-IgM, and of T cells with concanavalin A. Cross-linking of 125I-labelled-BSF-1 to its receptors creates a complex of Mr approximately 80,000.

Age-dependent changes in isotype expression and down-regulation of C57BL/6 mice

Age-related changes in antibody response and tolerance inducibility are polymorphic; in this paper isotype changes in ageing C57BL/6 mice are examined. Female C57BL/6 mice of various ages were immunized with either heat-aggregated RGG (a-RGG) or phosphorylcholine conjugate of RGG (PC-RGG); other animals of the same ages were given aggregate free RGG, followed by injections with either aggregated RGG or haptenated RGG. Sera from these four groups were analysed for antibody isotype. The data presented here indicate that age-related changes in isotype predominance and magnitude are different for different determinants. The capacity to be down-regulated appeared to undergo different age-related changes with different isotypes: there is split tolerance in isotypes. Age-dependent changes in T- and B-cell tolerance could be deduced by comparing responses of animals to hapten and to carrier determinants. In 5-week-old animals tolerance to hapten was more profound than tolerance to carrier. It was concluded that T-cell regulation dominated the response at this age. With advancing age, i.e. by 95 weeks, tolerance is observed in response to hapten but not in response to carrier determinants. We concluded that suppressor cells were induced by aggregate free RGG and affected the response of 'naive' but not of 'experienced' B cells.

Development of in vitro immunization in murine and human hybridoma technology

The development of in vitro immunization in murine and human hybridoma technology is reviewed. Special consideration is given to: technical aspects of in vitro immunization of mouse B cells; quality of antibodies produced by in vitro immunization; advantages of murine in vitro immunization; technical aspects of in vitro immunization of human B cells; and the advantages of human in vitro immunization and human monoclonal antibodies. Future developments likely to be made in this area of immunotechnology are outlined.

Carrier-specific T cells sufficient for the expression of multiple isotypes in B cell cultures

A modified splenic fragment assay was used to assess the role of antigen-specific helper T cells in B cell isotype expression. Limiting numbers of carrier-specific helper T cells from lines or clones were injected along with a source of B cells into lethally irradiated unprimed recipients. The incidence of lodging of the T cell lines in recipient spleens at 18 h was determined by autoradiography to be 1.5 to 4.3% of the injected cells. These T cells were necessary and sufficient for the generation of T-dependent B cell responses within splenic fragments cultured in vitro with specific antigen. A comparison of isotypic responses from splenic and Peyer's patch B cells generated with the same T cell population revealed that a high proportion of the response from Peyer's patch B cells consisted of IgA antibody exclusively (46-57%) while the percentage of such responses from splenic B cells was much lower (7-10%). Thus, the isotype pattern of the response reflected the B cell source. Experiments in which cloned hemocyanin-specific T cells provided help to T-depleted spleen cells within splenic fragments from athymic recipients indicated that a single specificity of helper T cell is both necessary and sufficient to support the generation of antibody responses consisting of multiple isotypes. Isotype-specific T cells do not appear to be required in this system.

Human B-cell differentiation factor defined by an anti-peptide antibody and its possible role in autoantibody production

The partial amino acid sequence of the NH2 terminus of a factor named human B-cell differentiation factor or B-cell stimulatory factor 2 (BSF-2) has been determined. Antibodies raised against the synthetic peptide corresponding to residues 1-13 of the NH2-terminal sequence specifically react with BSF-2 generated by a T-cell line and by phytohemagglutinin-stimulated normal T cells. Furthermore, the antipeptide antibodies react with a BSF-2-like factor produced by cardiac myxoma as well as uterine cervical carcinoma cells. The results show that BSF-2 functions in vivo as well and suggest that the constitutive production of BSF-2 may be involved in autoantibody production, since patients with cardiac myxoma and uterine carcinoma showed autoantibody production.

B cell stimulatory factor 1 (interleukin 4) is a potent costimulant for normal resting T lymphocytes

Resting T cells proliferate in response to B cell stimulatory factor 1 (BSF-1; interleukin 4) plus phorbol myristate acetate (PMA). This response is obtained with highly purified T cells and is density independent, suggesting that accessory cells are not required. Both L3T4+ and Lyt-2+ T cells respond to BSF-1 plus PMA. Although BSF-1 alone does not cause T cell proliferation, it maintains the viability of small, dense T cells, indicating that it acts on resting T cells. Furthermore, BSF-1 is required early in the proliferative response of resting T cells to BSF-1 plus PMA, further supporting the concept that it acts on G0 or early G1 cells. However, BSF-1 is also needed late in the first round of division of T cells stimulated with BSF-1 plus PMA. Removing BSF-1 at 24 h of stimulation prevents entry into S phase. These results indicate that BSF-1 is involved in both the induction of competence and in the progression phases of T cell division.

Isolation of antigen-binding virgin and memory B cells

One major obstacle in studying the activation of antigen-specific B cells is the small number of B cells reactive with a particular antigenic epitope. In this report, we describe a method by which large numbers of highly purified antigen-binding cells can be obtained. We have shown that by varying the haptenation level of the erythrocytes used for rosetting, we can purify antigen-binding B cells which have different affinities for the antigenic epitope. Thus, memory cells (which have receptors of higher affinity) can be prepared and these cells are essentially free of contaminating virgin cells. The effects of varying the haptenation levels on the red cells used for purifying the B cells can, in turn, be related to the precursor frequency of secreting cells following their activation with T cells and antigen.

B cell stimulatory factor 1 (BSF-1) prepares resting B cells to enter S phase in response to anti-IgM and lipopolysaccharide

BSF-1 prepares resting BALB/c, DBA/2, and BDF1 B cells to enter S phase more promptly in response to subsequent culture with anti-IgM-based stimulants. It prepares DBA/2 and BDF1 B cells to respond to LPS, but its preparative effect for LPS responses of BALB/c B cells is both inconstant and meager. Preparation mediated by BSF-1 requires extended contact of B cells with the stimulant for full effect. Half-maximal preparation requires approximately 12 h of contact, as judged by delayed addition of BSF-1 or by inhibition of BSF-1 action with anti-BSF-1 mAbs. BSF-1 preparative action on resting DBA/2 B cells is mimicked by anti-Lyb-2.1 antibody. B cell blasts prepared by culture with BSF-1 and anti-IgM show modest responses to high concentrations of BSF-1; large B cells directly isolated from the spleen are not stimulated to enter S phase by BSF-1. These results lead us to conclude that BSF-1 functions principally as an activation factor for resting B cells.

Isolation and characterization of a human interleukin cDNA clone, homologous to mouse B-cell stimulatory factor 1, that expresses B-cell- and T-cell-stimulating activities

A cDNA sequence coding for a human interleukin has been isolated from a concanavalin A-activated human T-cell cDNA library based on homology with a mouse interleukin cDNA that expresses B-cell stimulatory factor 1 (BSF-1) activity and T-cell- and mast-cell-stimulating activities. The human cDNA contains a single open reading frame encoding a protein of 153 amino acid residues including a putative signal peptide. Amino acid sequences of the mouse and human polypeptides, deduced from their cDNAs, share extensive homology with the exception of about 40 amino acid residues near the middle portion, which share little homology. Supernatant of COS-7 monkey cells transfected with the human cDNA clone stimulated proliferation of human helper T-cell clones and of anti-IgM-activated human B cells, two properties of mouse BSF-1 on mouse cells. These results indicate that this human cDNA clone encodes a protein structurally and functionally homologous to mouse BSF-1.

Isotype-specific resistance against tolerance induction in SJL mice

Age-related changes in antibody response of SJL mice were examined in terms of isotype expression after treatment with immunogen or with immunogen, preceded by the molecule in normally tolerogenic form. We report here that tolerance induction and resistance to down regulation are isotype specific. Tolerance can be induced in terms of all detectable isotypes at the age of 5 weeks. In older SJL mice, tolerance to the carrier is found in IgM antibody, whereas there is resistance against down regulation in terms of IgG2a and IgG2b isotypes, and sensitization in terms of IgG3, IgG1, and IgA antibody. Furthermore, the degree of down regulation is determinant dependent. This was observed when older SJL mice, pretreated with the carrier in a normally tolerogenic form, were immunized with haptenated carrier and tested for their response to hapten and carrier determinants. In this case, IgA antibody shows tolerance to the hapten and sensitization by carrier determinants.

Regulation of B-lymphocyte activation, proliferation, and immunoglobulin secretion

Lymphocyte growth and differentiation are controlled by signals resulting from the interaction of antigen and cellular products, such as lymphokines, with specific cell membrane receptors. Resting B lymphocytes can be activated by low concentrations (1-5 micrograms/ml) of antibodies to membrane IgM, which is the B-lymphocyte receptor for antigen. The binding of anti-IgM to B cells causes a rapid increase in intracellular free calcium concentration ([Ca2+]i), in inositol phosphate concentration, and in protein kinase activity. Moreover, the effects of anti-IgM on B cells are mimicked by the combined use of calcium ionophores and phorbol esters. Since phorbol esters activate protein kinase c, this suggests that the increase in [Ca2+]i and in phosphatidylinositol metabolism stimulated by anti-IgM are critical events in B-cell activation. The entry into S phase of B cells stimulated with anti-IgM depends on the action of a T-cell-derived factor designated B-cell stimulatory factor (BSF)-1. This is a 20,000-Da protein which is a powerful inducer of class II major histocompatibility complex molecules. Although an important cofactor for B-cell proliferative responses to anti-IgM, its major locus of action is on resting B cells. B cells stimulated with anti-IgM and BSF-1 do not synthesize secretory IgM. However, if two additional T-cell-derived factors, B151-TRF and interleukin-2, are added to cultures, a substantial proportion of stimulated B cells produce secretory IgM. BSF-1 has also been shown to participate in the "switch" in Ig class expression. Resting B cells cultured with lipopolysaccharide will switch to IgG1 secretion in the presence of purified BSF-1.

Serological, biochemical, and functional identity of B cell-stimulatory factor 1 and B cell differentiation factor for IgG1

By three criteria, we have demonstrated that B cell stimulatory factor (BSF-1) and B cell differentiation factor (BCDF-gamma) are the same lymphokine. Highly purified preparations of high performance liquid chromatography-purified or affinity-purified BSF-1 had BCDF-gamma activity but not BCDF-mu activity. A monoclonal anti-BSF-1 antibody coupled to Sepharose depleted both BSF-1 and BCDF-gamma activity but not BCDF-mu activity from two different T cell supernatants. Soluble monoclonal anti-BSF-1 blocked the BSF-1 and BCDF-gamma but not the BCDF-mu responses. These results suggest that BSF-1 acts on both resting and activated B cells to induce different effects.

Antigen non-specific activities in culture supernatant of ovalbumin-specific, cloned helper T lymphoma

Antigen non-specific activities in culture supernatants from clones of a radiation leukemia virus transformed, ovalbumin-specific helper T lymphoma were studied. After stimulation with ovalbumin-pulsed macrophages, these clones release factor(s) capable of providing carrier-specific help for anti-hapten antibody responses. It was found that in addition to IL 2-like activity, one clone constitutively released a suppressive factor that could inhibit polyclonal growth and differentiation of B cells stimulated with LPS. The factor inhibited activation of both syngeneic and allogeneic B cells directly, rather than via activation of accessory suppressor T lymphocytes. However, upon dilution of the supernatant, B cell growth and differentiation activities were detected. A role for a polyclonal B cell suppressor factor in the overall helper activity of the clone is proposed.

A subset of Ly-1 inducer T cell clones activates B cell proliferation but directly inhibits subsequent IgG secretion

We find that a fraction of Ly-1+2- inducer T cell clones inhibits differentiation of memory B cells into IgG-secreting plaque-forming cells. Inhibition of secondary antibody responses was not the result of induction of Ly-2+ T suppressors. Instead, inducer cells directly inactivated B cells, requiring an antigen bridge as well as identity at the major histocompatibility complex (I-A) locus. The interaction between the inducer T cell clone and hapten-specific B memory cells results in an early proliferative response and subsequent failure of B cells to secrete antibody in response to T helper cell signals. Possible mechanisms for this novel type of B cell inactivation are explored.

The influence of Igh-1 genes on the class and subclass distribution of oxazolone-specific antibodies

Previous studies have demonstrated that the level of the oxazolone-specific antibody response induced by contact sensitization is under the control of H-2 and Igh-1-linked genes. The aim of the present study was to clarify the role of H-2 and Igh-1 genes in the regulation of antibody affinity and isotype composition of oxazolone-specific antibodies. Analysis of the antibody response to oxazolone has revealed different ratios of IgG2a and IgG2b antibodies in mice carrying the Igh-1b allele and in strains carrying alleles a, c, and e. The characteristic ratio of IgG2a and IgG2b isotypes persisted during the whole period of the primary and secondary antibody response of CBA and CBA-Igb Igh-C congenic mice. The Igh-1-linked genes influenced the isotype distribution and not the affinity of oxazolone-specific antibodies induced by contact sensitization.

Clonal analysis of B cells induced to secrete IgG by T cell-derived lymphokine(s)

To gain insight into how T cell-derived lymphokines induce the secretion of IgG in activated B cells, we performed a limiting dilution analysis, using murine splenic B cells incubated with lipopolysaccharide (LPS) and a T cell-derived B cell differentiating factor for IgG (BCDF gamma)-containing supernatant (SN). The results of this analysis indicate that such a SN induces a marked increase in the precursor frequency of IgG1-secreting cells and a modest increase in clone size. The precursors lack surface IgG and are committed to the differentiation pathway for IgG1 secretion after LPS activation, but before the addition of BCDF gamma-containing SN. The majority of IgG1-secreting clones arise independently from precursors of cells that secrete IgG3. Taken together, these results indicate that BCDF gamma directs differentiation of activated B cells to IgG1 secretion.