Differential regulation of IgG1 and IgE synthesis by interleukin 4.

IL-4/B cell stimulatory factor-1 is a T cell-derived lymphokine that has been shown to enhance IgG1 and IgE and to suppress IgG3 and IgG2b secretion by B cells stimulated with bacterial LPS. We show here that the stimulation of IgG1 and IgE secretion in response to rIL-4 is differentially regulated. The dose-response curve for IgG1 production is bimodal with peaks at 100 and 10,000 U/ml. IgE production is modest at 100 U/ml and exhibits a progressive enhancement as the IL-4 concentration is increased to 10,000 U/ml, reaching approximately 1 microgram of IgE from an initial cell number of 2 X 10(4). Both of these effects are reversed by monoclonal anti-IL-4 antibody. Neither the enhancing nor suppressing effects of IL-4 can be explained by changes in viable cell yields or [3H]thymidine incorporation. The production of both IgG1 and IgE is controlled by IL-4 in a two-phase manner. During the initial 2 d of culture with LPS, IL-4 action for both IgG1 and IgE production is relatively concentration independent at doses greater than 600 U/ml. This 2-d treatment leads to maximal IgG1 production at day 6 with no further addition of IL-4. Addition of IL-4 during the final 4 d of culture has no effect at concentrations under 100 U/ml. At higher concentrations, IL-4 is strikingly suppressive for IgG1 production. By contrast, little IgE is produced unless IL-4 is present after 2 d of culture and the response is directly dependent on the concentration of IL-4 during this second phase of culture with maximal responses observed at 10,000 U/ml. These differences in IL-4 requirements for IgG1 and IgE production, respectively, may have an important role in the regulation of the synthesis of these isotypes in responses to microbial antigens.

Interleukin 5 induces S mu-S gamma 1 DNA rearrangement in B cells activated with dextran-anti-IgD antibodies and interleukin 4: a three component model for Ig class switching.

The cellular signals required for induction of immunoglobulin (Ig) class switching are only partially understood. Two processes that are considered to be necessary for such induction are DNA synthesis and germline constant heavy (CH) gene transcription. We now show that an additional signal, as mediated by interleukin 5 (IL-5), is also required. To induce proliferation of resting B cells, but not Ig secretion, we utilized anti-IgD antibodies conjugated to dextran (alpha delta-dex). The addition of IL-4, a well-established switch factor for the IgG1 subclass, to alpha delta-dex-activated cell cultures failed to induce IgG1 secretion or mIgG1+ cells unless IL-5 was also present. While IL-4 stimulated an increase in germline gamma 1 RNA in alpha delta-dex-activated cells, this effect could neither be induced nor enhanced by IL-5. By contrast, IL-5 strongly enhanced steady-state levels of productive gamma 1 RNA induced by alpha delta-dex and IL-4, suggesting that IL-5 stimulated IgG1 switch rearrangement. To test this possibility we measured switch (S) mu-S gamma 1 DNA recombination events using a newly developed assay, digestion circularization polymerase chain reaction (DC-PCR). We demonstrated that IL-5 was necessary for induction of S mu-S gamma 1 DNA rearrangement in alpha delta-dex plus IL-4-activated cells but that it had little effect on rearrangement in the absence of IL-4. Our data strongly suggest, therefore, a three-component model for induction of Ig class switching. This model includes germline CH gene transcription, DNA synthesis, and a third component that is necessary for recombination.

B cells lacking RelB are defective in proliferative responses, but undergo normal B cell maturation to Ig secretion and Ig class switching.

A number of distinct functional abnormalities have been observed in B cells derived from p50/ NF-kappa B or c-rel knockout mice. RelB, another member of the NF-kappa B/Rel family of transcription factors, is expressed during the latter stages of B cell maturation and can bind to regulatory sites within the Ig heavy chain locus. Therefore, we tested the ability of B cells from relB knockout mice (relB-/-) to proliferate, undergo maturation to IgM secretion, and switch to the expression of downstream Ig isotypes in response to distinct activators including LPS, anti-CD40 mAb or CD40 ligand, and/or dextran anti-IgD antibodies in combination with various cytokines, including IL-4, IL-5, IFN-gamma, and TGF-beta. B cells lacking RelB showed up to 4-fold reductions in DNA synthesis in response to LPS, CD40, and membrane Ig-dependent activation relative to controls. However, relB-/- B cells were comparable to control B cells in their ability to undergo maturation to IgM secretion and switch to the expression of IgG3, IgG1, IgG2b, IgG2a, IgE, and/or IgA under all activation conditions tested. Thus, RelB, like c-Rel and p50/NF-kappa B, plays a role in B cell proliferation. However, in contrast to c-Rel and p50/ NF-kappa B, it is not critically involved in maturation to Ig secretion or expression of Ig isotypes.

Induction of IgG3 secretion by interferon gamma: a model for T cell-independent class switching in response to T cell-independent type 2 antigens.

T cell-independent type 2 (TI-2), in contrast to T-dependent, antigens stimulate the production of murine IgG3. To investigate a possible role for cytokines in mediating the induction of this IgG subclass, we established an in vitro polyclonal model system for studying TI-2 antigen-mediated B cell activation by using dextran-conjugated anti-IgD antibody (alpha delta-dex). We demonstrate that interferon gamma (IFN-gamma) stimulates, and interleukin 4 inhibits, the expression of IgG3 by alpha delta-dexactivated cells. The production of IFN-gamma by non-T cells in response to bacterial products, possibly capsular polysaccharides, may provide an explanation underlying the ability of TI antigens, which are unable to directly stimulate T cell-derived cytokines to induce Ig isotype switching.

Transforming growth factor beta 1 selectivity stimulates immunoglobulin G2b secretion by lipopolysaccharide-activated murine B cells.

Bacterial lipopolysaccharide (LPS) has been reported to induce immunoglobulin (Ig)G2b class switching, yet we observed strain differences in IgG2b secretion in response to this mitogen. Specifically, BALB/c B cells, unlike those from DBA/2, synthesized relatively low amounts of IgG2b relative to IgG3, IgG1, or IgM. This report demonstrates that transforming growth factor (TGF) beta 1, previously shown to induce IgA class switching, selectively stimulates IgG2b secretion by BALB/c resting B cells activated with LPS. This activity was specifically reversed with a neutralizing anti-TGF-beta 1 antibody. The ability of TGF-beta 1 to act directly on highly purified membrane (m)IgM+ mIgG2b- cells to stimulate IgG2b production, stimulate an increase in IgG2b-secreting cells, and selectively increase the steady-state levels of germline gamma 2b RNA, suggests that it promotes IgG2b class switching. In this regard, addition of anti-TGF-beta antibody to cultures of DBA/2-derived resting B cells activated by LPS, alone, led to selective reduction in IgG2b secretion, indicating that endogenous TGF-beta 1 accounts for the high IgG2b secretory response observed in that strain. Finally, TGF-beta 1 failed to stimulate IgG2b secretion by B cells activated with dextran-conjugated anti-IgD antibody. We propose that TGF-beta 1 is a switch factor for the murine IgG2b subclass for appropriately activated B cells. In combination with other data, this would show that all six non-IgM, non-IgD isotypes in the mouse can be selectively induced by specific cytokines.

Nuclear factor (NF)-kappa B2 (p100/p52) is required for normal splenic microarchitecture and B cell-mediated immune responses.

The nfkb2 gene is a member of the Rel/NF-kappa B family of transcription factors. COOH-terminal deletions and rearrangements of this gene have been associated with the development of human cutaneous T cell lymphomas, chronic lymphocytic leukemias, and multiple myelomas. To further investigate the function of NF-kappa B2, we have generated mutant mice carrying a germline mutation of the nfkb2 gene by homologous recombination. NF-kappa B2-deficient mice showed a marked reduction in the B cell compartment in spleen, bone marrow, and lymph nodes. Moreover, spleen and lymph nodes of mutant mice presented an altered architecture, characterized by diffuse, irregular B cell areas and the absence of discrete perifollicular marginal and mantle zones; the formation of secondary germinal centers in spleen was also impaired. Proliferation of NF-kappa B2-deficient B cells was moderately reduced in response to lipopolysaccharide, anti-IgD-dextran, and CD40, but maturation and immunoglobulin switching were normal. However, nfkb2 (-/-) animals presented a deficient immunological response to T cell-dependent and -independent antigens. These findings indicate an important role of NF-kappa B2 in the maintenance of the peripheral B cell population, humoral responses, and normal spleen architecture.

Interferon-gamma and B cell stimulatory factor-1 reciprocally regulate Ig isotype production.

Gamma interferon (IFN-gamma) and B cell stimulatory factor-1 (BSF-1), also known as interleukin-4, are T cell-derived lymphokines that have potent effects on B cell proliferation and differentiation. They are often secreted by distinct T cell clones. It is now shown that IFN-gamma stimulates the expression of immunoglobulin (Ig) of the IgG2a isotype and inhibits the production of IgG3, IgG1, IgG2b, and IgE. By contrast, BSF-1 has powerful effects in promoting switching to the expression of IgG1 and IgE but markedly inhibits IgM, IgG3, IgG2a, and IgG2b. These results indicate that BSF-1 and IFN-gamma as well as the T cells that produce them may act as reciprocal regulatory agents in the determination of Ig isotype responses. The effects of IFN-gamma and BSF-1 on isotype expression are independent.

T cell independent antigens.

T cell independent antigens type 2 (TI-2), which are represented predominantly by polysaccharide antigens, stimulate humoral antibody responses in the absence of T-cell help. We and others have recently reported that natural killer cells and/or natural killer cell derived lymphokines may provide a form of 'help' that is necessary for the induction and maintenance of TI-2 responses. Two natural killer cell derived lymphokines, interferon-gamma and granulocyte-macrophage colony-stimulating factor, show synergistic stimulatory activity in inducing Ig secretion in B cells stimulated by a multivalent ligand that mimics TI-2 antigens. The recent finding that natural killer cells have receptors for various classes of polysaccharides supports a role for these cells in regulating responses to TI-2 antigens.

Influence of HLA-DR polymorphism and allergic sensitization on humoral immune responses to intact pneumococcus in a transgenic mouse model.

Asthma is independently associated with HLA-DR3 and increased risks of pneumococcal diseases. We aimed to determine whether HLA-DR polymorphism (HLA-DRB1*03), sensitization to house dust mite (HDM), or their interaction affects humoral immune responses to pneumococcal polysaccharide and protein antigens of intact pneumococci. Induction of serum titers of anti-pneumococcal polysaccharide and anti-surface protein IgM and IgG in response to immunization with intact pneumococci (Pn) serotype 14 was determined using humanized HLA-DR3 and DR2 transgenic mice. Transgenic mice were sensitized by injecting HDM and challenged with intranasal HDM. Mice were subsequently immunized with heat-killed Pn14 at day 24. Serum titers of anti-phosphorylcholine (PC) IgM and IgG, anti-pneumococcal polysaccharide, capsular type 14 (PPS14) IgM and IgG, and anti-pneumococcal surface protein A (PspA) IgG were measured. We included a total of 44 mice (22 DR3 and 22 DR2 mice) and half of mice in each group were sensitized with HDM (i.e. 22 HDM-sensitized and 22 control mice). HDM-sensitized mice, irrespective of HLA-DR polymorphism, had significantly lower humoral immune responses. HLA-DR3 mice, irrespective of HDM sensitization, elicited a significantly lower anti-PC IgG response. In contrast, the anti-PspA IgG response was higher in DR3 relative to DR2 mice. The effect of HDM sensitization on lowering humoral immune responses to Pn14 was observed in DR3 mice regardless of the nature of the antigen, whereas such decreases were observed only for the anti-PPS14 IgG and anti-PC IgM responses in DR2 mice. HDM sensitization lowered humoral immune responses to intact pneumococcus and this effect was significantly modified by the HLA-DR polymorphism.

Regulation of murine B cell Thy-1 expression by IL-4, IFN-gamma, and CD4+ T cell subsets.

Interleukin 4 (IL-4) induces the expression of membrane Thy-1 on the vast majority of lipopolysaccharide (LPS)-stimulated normal murine B cells in vitro. This induction is inhibited by interferon-gamma (IFN-gamma). IL-4 and IFN-gamma are required late in culture to effect maximal induction and inhibition of Thy-1 expression by LPS- or LPS + IL-4-stimulated B cells, respectively. IFN-gamma suppresses IL-4-induced Thy-1 expression by inhibiting the induction of steady-state levels of Thy-1-specific mRNA. Three distinct CD4+ Th2 clones, through their release of IL-4, induce B cells to express high levels of Thy-1, by 24 hr, in striking contrast to the 3 days required to induce Thy-1 expression after stimulation with LPS and IL-4. This induction is abrogated by the addition of IFN-gamma. B cells stimulated with three distinct Th1 clones (IFN-gamma- and IL-2-producing) exhibit a modest, non-IL-4-dependent, expression of Thy-1. In contrast to intrinsic expression of Thy-1 by Th2-stimulated B cells. Thy-1 expressed by Th1-stimulated B cells is acquired, having the allotype specificity of the stimulating T cell.

B cell stimulatory factor-1 (interleukin 4) prepares resting murine B cells to secrete IgG1 upon subsequent stimulation with bacterial lipopolysaccharide.

B cell stimulatory factor-1 (BSF-1)/interleukin 4 markedly enhances IgG1 and IgE secretion by B cells stimulated with bacterial lipopolysaccharide (LPS). We show that preincubation of resting B cells with BSF-1 alone prepares them to secrete IgG1, but not IgE, on subsequent stimulation with LPS. The ability of BSF-1 preincubation to increase overall viable cell yield on the subsequent addition of LPS only partially accounts for this enhancement. The degree of enhancement is dependent on the duration of preincubation, up to at least 48 hr. BSF-1 exerts this effect on resting B cells which have been selected for absence of surface IgG and in the presence of the reversible DNA synthesis inhibitor, hydroxyurea. BSF-1 can act to significantly enhance the IgG1 response when added for 48-hr periods before, at the same time as, or after the addition of LPS. These results suggest strongly that the mode of action of BSF-1 in preparing for the secretion of IgG1 is independent of that of LPS.

Rapid loss of IgM expression by normal murine B cells undergoing IgG1 and IgE class switching after in vivo immunization.

Injection of mice with polyclonal goat anti-mouse IgD antibody (G alpha M delta) stimulates a potent T cell-dependent immune response characterized by large increases in serum IgG1 and IgE concentrations and by the generation of substantial numbers of membrane (m)IgG1+ B cells. The onset of this response occurs 6 days after G alpha M delta injection and peaks by day 7 to 8. Utilizing two color fluorescence analysis and cell sorting we demonstrate that most mIgG1-expressing B cells lack mIgM during the period of onset of Ig isotype switching (day 6). Both IgG1 and IgE are produced predominantly by mIgM- cells. On day 6, IgG1 and IgE are secreted predominantly by cells expressing mIgG1 and mIgE, respectively. By day 8, a majority of the IgG1 secretion occurs among the mIgG1- cells but virtually all IgE secretion continues to come from the mIgE+ population. B cells that strongly express mIgG1 secrete little IgM or IgE. Freshly harvested B cells expressing mIgG1, 6 days after G alpha M delta injection, have undergone substantial deletion of CH mu-specific DNA in contrast to their mIgG1- counterparts. Hence, the great majority of B cells that switch to the IgG1 or IgE isotypes in vivo rapidly lose their expression of IgM.

A model for induction of T cell-independent humoral immunity in response to polysaccharide antigens.

We provide a model for induction of T cell-independent, polysaccharide-specific Ig secretion in response to bacterial challenge. Two predominant pathways are defined that require the concerted action of multivalent membrane Ig cross-linking by the polysaccharide Ag with 1) various B cell-activating moieties contained within the bacterial pathogen and/or 2) cytokines, such as IFN-gamma and granulocyte-macrophage colony-stimulating factor produced by NK cells and macrophages, that become activated in a T cell-independent manner during bacterial infection.

Towards a comprehensive view of immunoglobulin class switching.

While it is well established that T cells play a prominent role in regulating Ig isotype switching in response to T-cell-dependent (TD) antigens, the events which control this process in response to antigens that do not recruit antigen-specific T cells (T-cell-independent (TI) antigens) is less clear. In this article, Clifford Snapper and James Mond suggest that the nature of the B-cell activator, in combination with cytokines produced by antigen non-specific cells, including macrophages, NK cells, and polyclonally activated B cells, may play an important role in the process leading to Ig isotype switching in response to TI antigens.

IFN-gamma stimulates IgG2a secretion by murine B cells stimulated with bacterial lipopolysaccharide.

rIFN-gamma strikingly enhances the secretion of IgG2a by murine splenic B cells stimulated with bacterial LPS in vitro and concomitantly suppresses the production of IgG3, IgG1, IgG2b, and IgE while sparing IgM secretion. IFN-gamma stimulates highly purified B cell populations to secrete IgG2a, strongly suggesting that it acts directly on B cells. It increases the frequency of precursors of IgG2a-expressing soft agar colonies and enhances the number of IgG2a+ cells in colonies indicating that it both increases the frequency of precursors of IgG2a+ cells and enhances the number of IgG2a+ daughter cells emerging from each precursor. IFN-gamma completes its action within the first 24 to 48 h of a 6-day culture with LPS and its addition cannot be delayed beyond the first 48 h. Preincubation of resting B cells in the presence of IFN-gamma leads to a time dependent increase, up to 42 h, in IgG2a secretion upon subsequent addition of LPS. IFN-gamma can exert this action on resting B cells that have been selected for absence of membrane IgG expression by cell sorting. The promotion of IgG2a secretion appears to be a specific property of IFN-gamma in that IFN-alpha, IFN-beta, IL-1, IL-2, IL-3, IL-4, IL-5, granulocyte-macrophage-CSF, granulocyte-CSF, and CSF-1 fail to enhance IgG2a secretion by LPS-stimulated B cells.

Heterogeneity in the ability of cytotoxic murine NK cell clones to enhance Ig secretion in vitro.

We recently described a panel of cytotoxic murine NK cell clones that also enhanced Ig secretion by B cells activated in an in vitro model of T cell-independent type 2 (TI-2) responses. We employed dextran-conjugated anti-IgD (alphadelta-dex) as a model antigen. Here we study the mechanism of Ig induction by these clones. Addition of the various NK clones to sort-purified B cells stimulated with alphadelta-dex and IL-2 resulted in a markedly heterogeneous increase in Ig secretion, which varied from 3-fold, as mediated by clone PKO 56, to 15-fold, as induced by clone PKO 101. The other NK cells showed intermediate levels of Ig induction. Furthermore, while addition of as few as 0.04% of PKO 101 cells stimulated significant increases and 1% induced near maximum Ig production, a 3% addition of PKO 56 cells was required for significant enhancement of Ig secretion. Supernatant material collected from the NK clones mediated Ig production at levels that mirrored the induction by the corresponding cells. Cytokine analysis showed that while all members of the NK panel produced IFN-gamma only two secreted granulocyte macrophage colony stimulating factor and that the levels of Ig induction mediated by the NK clones correlated only with their levels of IFN-gamma secretion. Culture of B and NK cells in the presence of anti-IFN-gamma demonstrated that IFN-gamma was the critical cytokine in NK-induced Ig production. These findings establish heterogeneity in the ability of NK cells to increase Ig secretion in vitro and show that NK-produced IFN-gamma is an important factor in determining this heterogeneity.

T cell-independent antigens type 2.

In this review we have attempted to define the characteristics of TI-2 antigens that enable them to stimulate antibody production in the absence of T cell help. One of the most critical properties of this group of antigens is their ability to deliver prolonged and persistent signaling to the B cell. This by itself is not however sufficient to stimulate Ig synthesis, and they must therefore stimulate non-T cells to interact with the B cells either directly or indirectly via cytokine production. There is evidence implicating the NK cell and T cell as playing this important role in response to TI antigens. Furthermore, we discuss the importance of cytokines such as IL-3, GMCSF, and IFN-gamma, which significantly enhance antibody production by these antigens. Finally, we present evidence demonstrating that B cell activation via TI stimuli does not play merely a permissive role in allowing for cell cycle entry and enhanced responsiveness to other stimuli. Rather, the nature of the B cell activating signal is critical in determining the quantitative and qualitative profile of Ig isotype production.

NF-kappaB/p50 and NF-kappaB/c-Rel differentially regulate the activity of the 3'alphaE-hsl,2 enhancer in normal murine B cells in an activation-dependent manner.

The enhancer complex located 3' to the C(H)alpha gene in the IgH locus (3alphaE) may regulate B cell function through its ability to act as a locus control region. Multiple, functionally relevant NF-kappaB binding sites are located within the 3'alphaE. NF-kappaB subunits, especially p50 and c-Rel, have also been shown to play critical and differential roles in regulating B cell proliferation, Ig secretion, germline C(H) transcription and Ig class switching. Thus, NF-kappaB could regulate B cell function in part through modulation of 3'alphaE activity. In this study we determined whether p50 and/or c-Rel regulate 3'alphaE activity in normal murine B cells and whether this depends on the nature of the B cell activator. For this purpose, we crossed p50- and c-Rel-deficient mice with mice that are transgenic for a 3'alphaE-hsl,2-human beta-globin reporter gene, and established p50(-/-) or c-Rel(-/-) mice homozygous for the enhancer transgene. We show, using optimal stimulating conditions, that p50 selectively augments 3'alpha E-hsl,2 activity in lipopolysaccharide-activated B cells, whereas c-Rel is required for optimal 3'alphaE-hs1,2 induction in B cells activated through CD40.

T(h)1 versus T(h)2 cytokine profile determines the modulation of in vitro T cell-independent type 2 responses by IL-4.

We have previously demonstrated that stimulation of B cells by multivalent membrane Ig cross-linking, using dextran-conjugated anti-IgD mAb (alpha delta-dex), in the presence of cytokines, is an in vitro model for T cell-independent type 2 (TI-2) Ig secretory responses. Earlier studies have shown that IL-4 enhances IgM secretion upon stimulation with alpha delta-dex plus IL-5 and induces IgG1 isotype-switching, without altering the proliferative response to alpha delta-dex. Here we show that IL-4 can have both stimulatory and inhibitory effects on alpha delta-dex-induced Ig secretion. Both the kinetics and time of exposure to IL-4, and the nature of the cytokine additions, T(h)1 versus T(h)2, determine whether stimulation or inhibition is observed. Preincubation of sort-purified B cells with IL-4 caused a 6- to 8-fold increase in Ig secretory responses to subsequent stimulation with alpha delta-dex plus IL-1, IL-2 or a combination of both. However, the continued presence of IL-4 during B cell stimulation suppressed responses to all cytokine combinations tested, except for those which included IL-5. Of 11 cytokines tested, only IL-4 showed this dual effect of enhancement and suppression. The stimulatory effect of IL-4 required a minimum of 4 h of preincubation and could be inhibited by the addition of IFN-gamma. Thus stimulation of non-MHC class II-dependent T or non-T cells by multivalent antigens to secrete IL-4 may regulate the response to these antigens, such that early and brief exposure of B cells to IL-4 will enhance a subsequent TI-2 response in the presence of T(h)1-dependent cytokines, while continuous exposure will result in inhibition of the response.

Novel in vitro model for high-rate IgA class switching.

The parameters necessary for induction of high-rate IgA class switching are unknown. Thus, although TGF-beta is switch factor for the IgA class, the percentage of membrane (m)IgA+ cells generated in vitro in response to TGF-beta and various individual modes of B cell activation is limited to 1 to 2% of the total B cell population, a percentage far below that observed within Peyer's patches. In this report we determined a set of parameters that act synergistically to generate up to 15 to 20% mIgA+ cells in vitro. A dual mode of B cell activation is required whereby signaling through CD40 or in response to LPS stimulation must occur in concert with multivalent Ag receptor crosslinking. A complex cytokine requirement is also revealed in that both IL-4 and IL-5 must be present with TGF-beta for high-rate IgA class switching to occur. By contrast, IFN-gamma, a known antagonist of IL-4, strongly suppresses the induction of mIgA+ cells in response to these stimuli. This novel cellular system should serve as a powerful tool for studying the molecular mechanisms that underly the IgA class switch and may provide insight into the physiologic parameters that induce it.