Clonal and molecular characteristics of the human IgE-committed B cell subset

The who, where, and when of IgE in allergic airway disease

Allergic asthma and allergic rhinitis/conjunctivitis are characterized by a T(H)2-dominated immune response associated with increased serum IgE levels in response to inhaled allergens. Because IgE is a key player in the induction and maintenance of allergic inflammation, it represents a prime target for therapeutic intervention. However, our understanding of IgE biology remains fragmentary. This article puts together our current knowledge on IgE in allergic airway diseases with a special focus on the identity of IgE-secreting cells ("who"), their location ("where"), and the circumstances in which they are induced ("when"). We further consider the therapeutic implications of the insights gained.

Exploiting the avian immunoglobulin system to simplify the generation of recombinant antibodies to allergenic proteins

BACKGROUND

Monoclonal antibodies are a valuable tool in the study of allergens, but the technology used in their generation can be slow and labour-intensive. Therefore, we have examined recombinant antibody development by phage-display against single allergens and protein mixtures.

OBJECTIVE

We used the avian immunoglobulin system (generated from single V(H) and V(L) genes) to provide a rapid method for generating highly specific recombinant antibody fragments from a minimal number of animals.

METHODS

A single-chain antibody fragment (scFv) library was generated from a single chicken immunized with model allergens. ScFvs were isolated by phage-display and their properties investigated by ELISA and Western blot.

RESULTS

Mono-specific scFvs were generated against recombinant Fel d 1 and native Amb a 1. Pannings against yellow jacket venom extracts only yielded clones that reacted with multiple proteins in the venom extract. The scFvs from each panning type were effectively expressed in Escherichia coli and readily purified. Highly specific and sensitive recognition of Fel d 1 and Amb a 1 was demonstrated in ELISA, with scFvs displaying antibody-concentration-dependent absorbance curves down to picogram levels of antibody. The specificity of selected antibodies for their cognate antigen was further confirmed in Western blot analysis, with scFvs directed to either Fel d 1 or Amb a 1 showing no reactivity for the other antigens used in immunization. Anti-Amb a 1 scFvs also mapped Amb a 1-isoform location in Western blot of ragweed extracts separated by 2D SDS-PAGE. DNA sequence analysis of scFvs showed that multiple different clones had been generated against Fel d 1 and Amb a 1. Using two anti-Fel d 1 scFv for ELISA analysis of Fel d 1 content in crude cat pelt extracts, we could produce data which were highly similar (P=0.33 and 0.89 by paired t-test analysis) to those obtained using conventional assays (radial immunodiffusion).

CONCLUSION

Phage-display technology may generate multiple allergen-specific recombinant antibody fragments from a single chicken, to allergens from mammalian, plant and insect sources. The resulting antibody fragments are of demonstrable use in allergen identification and quantification, in comparison with standard immunoassays.

Cytotoxic T-cells specific for natural IgE peptides downregulate IgE production

Immunoglobulin E (IgE) plays a central role in IgE-mediated immediate type hypersensitivity. Since production of IgE depends on Th2, efforts to block IgE production and control allergic reactions include tolerization of Th2 or deviating development of Th2. We hypothesized that cytotoxic T lymphocytes targeting natural IgE peptides/MHC I complexes can eliminate IgE-producing cells and inhibit centrally IgE production. CTL to self-IgE peptides were elicited in mice immunized with nonameric p109-117, p113-121, and p103-141 (CHepsilon2 domain), which encompass both peptides with an OVA helper peptide (OVAp restricted for H-2d/b) in liposomes and presented by dendritic cells (DC). CTL from BALB/c lysed IgE peptide-pulsed P815 target as well as IgE-producing 26.82 hybridomas (H-2d). Natural tolerance to self-IgE peptides was tested in IgE sufficient (IgE +/+) as well as IgE-deficient (IgE -/-) 129/SvEv mice (H-2b). Comparable magnitude of CTL responses was observed in both strains immunized with p109-117 or p103-141 concomitantly with CD4 T-cell costimulation. CTL from 129/SvEv lysed not only IgE peptide-pulsed EL-4 but also IgE-producing B4 hybridomas (H-2b). This observation strongly suggests a correspondence of epitope of immunogenic peptide to that of physiologically processed IgE peptides presented on IgE-producing cells. Moreover, CTL were generated in 129/SvEv, immunized with the recombinant antigenized antibody in liposomes encompassing p107-123, p109-117, and p113-121 expressed in CDR3 of VH62/human gamma1. Polyclonal IgE production was inhibited by coincubation with MHC I-restricted CTL in vitro. Furthermore, antigen-specific IgE responses were inhibited in mice, immunized with p109-117 and p103-141 while IgG responses were not suppressed. Since IgE peptide sequences of CHepsilon2 are ubiquitous to all murine IgE heavy chain, peptides made as such can serve as a universal IgE vaccine to prevent allergy for a myriad of allergens in rodents. This observation suggests that similar human IgE peptides should be identified and employed to downregulate human IgE production.

Detection and characterization of plasma cells in peripheral blood: correlation of IgE+ plasma cell frequency with IgE serum titre

In atopic patients and patients with hyper-IgE syndrome (HIE) highly elevated IgE serum levels can be detected. Due to their very low frequency little is known about IgE-producing plasma cells (PC) in peripheral blood. We used CD138 MACS microbeads to enrich plasma cells from peripheral blood of normal donors, atopic patients and one HIE patient. CD138+ cells were mainly CD45+, CD44++, CD19dim, CD38++, CD27++, CD86+, HLA-DR+/++, CD71dim, VLA-4+, VLA-5-, CD28-, CD25-, CD69-, CLA-, CD20-, CD21- and CD22-. They show weak expression of surface Ig but high levels of intracellular Ig and they secrete Ig in culture. Thus CD138+ cells from peripheral blood show characteristics of early plasma cells. IgE+ CD138+ plasma cells could be detected in 19 of 24 normal donors with an average frequency of 0.06% IgE+ cells among CD138+ cells. Higher frequencies were detected in atopic patients, atopic patients with markedly elevated serum IgE levels and the hyper-IgE patient with an average of 0.32%, 7.21% and 6.54%, respectively. Additionally, using the recently developed cellular affinity matrix technology, we were able to detect IgE secreting plasma cells and thereby could demonstrate that most of the IgE secreting cells express CD138. The frequency of IgE+ CD138+ cells among PBMC correlated highly significantly with serum IgE titres (r = 0.8532***), indicating that IgE secreting CD138+ cells in peripheral blood are directly related to the plasma cell pool contributing to the IgE titre.

Staphylococcal toxins augment specific IgE responses by atopic patients exposed to allergen

Microbial agents are known to play a significant role in aggravating allergic diseases. Recently described viral and bacterial superantigens represent one important strategy by which infectious agents can stimulate the immune response. In previous work, we reported that the staphylococcal toxin toxic shock toxin-1 (TSST-1), a prototypic superantigen, induces in vitro total IgE synthesis after cross-linking T and B cells. This study was carried out to establish a potential link between superantigens and the enhanced IgE response to specific allergens in allergic patients. Peripheral blood mononuclear cells from atopic patients were isolated during and outside the pollen allergen season and stimulated with TSST-1, a prototypic superantigen. Total IgE and interferon-gamma production were measured in supernatants of these cultures. Outside the pollen season, TSST-1 significantly increased total IgE production only in the presence of exogenous interleukin-4, whereas during the pollen season IgE production was significantly enhanced without the need of exogenous interleukin-4. This increase in the absence of exogenous interleukin-4 was associated with significantly lower interferon-gamma production by peripheral blood mononuclear cells stimulated by TSST-1 during the pollen season. Moreover, TSST-1 stimulation of peripheral blood mononuclear cells from inhalant allergic patients was followed by an increased production of allergen-specific IgE that was restricted to the allergen to which the patient was allergic and recently exposed. In addition, TSST-1 induced on B cells the expression of B7.2, a molecule that has recently been demonstrated to enhance T helper 2 responses and to be involved in IgE regulation. This study, by demonstrating that superantigens can augment allergen-specific IgE synthesis and B7.2 expression, provides a mechanism by which microbial superantigens may modulate allergic responses.

The two membrane isoforms of human IgE assemble into functionally distinct B cell antigen receptors

The human C epsilon gene expresses two membrane IgE heavy chain mRNAs which differ in the sequence that encodes their extracellular membrane-proximal domain. In the long IgE isoform (mLIgE), this domain contains a stretch of 52 amino acids which are absent in the short variant (mSIgE). We have now generated B cell transfectoma cell lines that express these two isoforms and show that both types of mIgE form functional B cell antigen receptors (BCR). Both receptors associate with the Ig-alpha/Ig-beta heterodimer, as well as with protein kinases that are capable of phosphorylating this complex. Upon their cross-linking, both receptors can activate protein tyrosine kinases that phosphorylate the same substrate proteins. Both IgE receptors also associate with two novel proteins that do not bind to mIgM. Apart from these similarities, the two IgE-BCRs show several differences of which some are analogous to the differences between the IgM- and IgD-BCRs. First, the mSIgE is transported to the cell surface at a higher rate than the mLIgE. Second, the two IgE-BCRs associate with differently glycosylated Ig-alpha proteins, the mLIgE associates with the completely glycosylated form, whereas the mSIgE associates with an Ig-alpha glycoform that is partially sensitive to endoglycosidase H. Third, the kinetics of protein tyrosine phosphorylation induced by receptor cross-linking is significantly different for the two IgE-BCRs. Finally, cross-linking of the mSIgE-BCR leads to growth inhibition of the B cell transfectoma, whereas signaling through the mLIgE-BCR does not affect the cellular proliferation. These data show that the two human membrane IgE isoforms assemble into functionally distinct antigen receptors which can induce different cellular responses.

Interleukin (IL)-4-independent immunoglobulin class switch to immunoglobulin (Ig)E in the mouse

Immunoglobulin (Ig) class switching in B cells is regulated by stimuli transduced by cytokines and cell-cell contact. Among these stimuli, interleukin (IL)-4 has been considered an absolute prerequisite for class switching to IgE in the mouse. Here we report that IL-4-deficient (IL-4-/-) and wildtype mice had comparably elevated serum IgE levels during the course of a murine retrovirus-induced immunodeficiency syndrome, MAIDS. IgE switching in IL-4-/- mice was also induced by injection of anti-IgD antibody. Treatment with anti-IgD induced germline epsilon (g epsilon) transcripts with comparable efficiency in IL-4-/- mice and controls, but the levels of productive epsilon transcripts (p epsilon) were lower by a factor of 200 and serum IgE levels were lower by a factor of 300 in IL-4-/- mice as compared with controls. Induction of g epsilon after anti-IgD treatment of IL-4-/- mice was unaffected by simultaneous treatment with monoclonal antibodies to IL-4 and IL-4 receptor alpha chain. Infection of IL-4-/- mice with Nippostrongylus brasiliensis, a potent stimulus for IgE production, resulted in induction of g epsilon transcripts; however, p epsilon transcripts were barely detectable and serum IgE was not detected. These findings establish a novel IL-4-independent pathway for IgE switching in the mouse that is strongly activated in retroviral infection but weakly in nematode infection. This pathway appears to be dependent on distinct factors that separately control induction of g epsilon transcription and switch recombination to p epsilon.

Construction of a combinatorial IgE library from an allergic patient. Isolation and characterization of human IgE Fabs with specificity for the major timothy grass pollen allergen, Phl p 5

To characterize human IgE antibodies with specificity for a major allergen at the molecular level, we have constructed an IgE combinatorial library from a grass pollen allergic patient. cDNAs coding for IgE heavy chain fragments and for light chains were reverse-transcribed and polymerase chain reaction-amplified from RNA of peripheral blood lymphocytes and randomly combined in plasmid pComb3H to yield a combinatorial library of 5 x 10(7) primary clones. IgE Fabs with specificity for Phl p 5, a major timothy grass pollen allergen, were isolated by panning. Sequence analysis showed that the 4 of the Fabs used the same heavy chain fragments which had combined with different kappa light chains. Soluble recombinant IgE Fabs were purified by affinity chromatography to Phl p 5 and, like natural IgE antibodies, cross-reacted with group 5 allergens from different grass species. The described approach should facilitate studies on the molecular interaction between IgE antibodies and allergens and encourages the consideration of specific IgE Fabs that are capable of interfering with allergen-IgE binding as potential therapeutic tools.

An increased frequency of IgE-producing B cell precursors contributes to the elevated levels of plasma IgE in atopic subjects

BACKGROUND

The production of specific IgE, which underlies the allergic response, may be a normal correlate of the immune response to a certain class of antigen (allergens), or could represent a unique response driven by regulatory signals that are absent in non-allergic individuals. If atopic subjects do possess a regulatory environment favoring IgE production, they may display not only allergen-specific IgE, but also higher levels of total IgE and higher frequencies of IgE-producing B lymphocytes.

OBJECTIVE

To address the contribution of antibody-producing cell number to the circulating IgE titre in atopic vs non-atopic subjects.

METHODS

Frequency determination by limiting dilution of EBV transformants and Poisson distribution analysis. Titres of total and allergen-specific IgM, IgG, and IgE by specific ELISA.

RESULTS

In contrast to findings reported by others, the atopic subjects had a significantly higher frequency of IgE-producing B cells than non-atopics (0.79% of total Ig-producing cells, as compared with 0.17% for the control group; P < 0.01), suggesting that one factor contributing to the high plasma IgE titres in atopic subjects is the high frequency of B lymphocytes with the potential to produce IgE. Although only the atopic subjects produced allergen-specific IgE, the frequency of specific IgE-producing B cells was undetectable in both groups.

CONCLUSION

Atopic subjects have higher frequencies of IgE-producing B cell precursors than non-atopics. A correlation exists between IgE-producing B cell frequency and levels of circulating IgE.

Germ-line human epsilon heavy chain gene RNA transcripts utilize the full range of alternative 3' splicing seen in productive epsilon mRNA

An early step in immunoglobulin isotype switching involves the initiation of active transcription of downstream heavy chain loci while they are still in germ-line configuration. This results in the production of 'sterile' germ-line RNA transcripts that do not contain VDJ sequences, the role of which in isotype switching is under intense scrutiny. We investigated whether such human epsilon germ-line transcripts employ the full complement of complex alternative 3' RNA splicing, splicing we have recently reported occurring with productive epsilon mRNA transcripts. Using a reverse transcriptase polymerase chain reaction (RT-PCR) strategy, in which the 5' primer was located in the I region of the epsilon gene, a region expressed in germ-line but not productive (VDJ containing) epsilon transcripts, we showed that the full range of alternative 3' epsilon splices occur with germ-line transcripts. These results demonstrate that epsilon 3' splicing events are independent of 5' isotype DNA switching. Additionally, we showed that, just as with mature epsilon mRNA, the relative production of the various epsilon germ-line mRNA isoforms was responsive to modulation by stimuli such as interleukin-10 (IL-10). Thus B cells, when stimulated to produce epsilon germ-line transcripts, generate a family of germ-line mRNA that differ not only in their initiation sites but, more importantly, also differ in their 3' sequences, sequences that could be important in regulation of the parent gene itself. Furthermore, by discontinuous or trans-splicing, cells could utilize these various epsilon germ-line transcripts to produce the full range of mature IgE proteins prior to undergoing deletional recombination of isotype switching.

IgE+ cells in the peripheral blood of atopic, nonatopic, and bee venom-hypersensitive individuals exhibit the phenotype of highly differentiated B cells

We have analyzed IgE+ cells in peripheral blood of atopic donors, donors hypersensitive to bee venom, and nonatopic control donors with two- and three-color flow cytometry. Although the percentage of IgE+ cells varied among these groups, the overall phenotypic patterns were similar. Most IgE+ cells do not display typical B-cell markers, such as CD19, CD20, and CD21. A significant proportion of these cells stain for CD38, indicating that they are more differentiated. IgE+ cells express Fc gamma RII and CD45RO, an isoform associated with an advanced level of differentiation. The majority of IgE+ cells do not coexpress other surface immunoglobulin isotypes. In the case of bee venom-hypersensitive donors, we have been able to identify a small population of IgE+ cells with a specificity for phospholipase A2, a major immunogenic component of bee venom. The phospholipase A2+ cells display a phenotype similar to that of the IgE+ cells.

Self and non-self antigen in diabetic autoimmunity: molecules and mechanisms

In this article, we have summarized current facts, models and views of the autoimmunity that leads to destruction of insulin-producing beta-cells and consequent Type 1 (insulin-dependent) diabetes mellitus. The presence of strong susceptibility and resistance gene loci distinguishes this condition from other autoimmune disorders, but environmental disease factors must conspire to produce disease. The mapping of most of the genetic risk (or disease resistance) to specific alleles in the major histocompatibility locus (MHC class II) has direct functional implications for our understanding of autoimmunity in diabetes and directly implies that presentation of a likely narrow set of peptides is critical to the development of diabetic autoimmunity. While many core scientific questions remain to be answered, current insight into the disease process is beginning to have direct clinical impact with concerted efforts towards disease prevention or intervention by immunological means. In this process, identification of the critical antigenic epitopes recognized by diabetes-associated T cells has achieved highest priority.

Failure of IgG production due to a defect in the opening of the chromatin structure of I gamma 1 region in a patient with IgG and IgA deficiency

Patients with common variable immunodeficiency (CVID) display reduced levels of two or all three of the major immunoglobulin isotypes, and the deficiency is characterized by failure of B cells to differentiate into plasma cells in many cases. A patient (14 years old, female) showed normal serum IgM levels and low serum IgG and IgA levels, including low levels of all IgG subclasses. Northern blot analysis suggested that the patient's B cells may be defective at the immunoglobulin heavy chain isotype switch. The germ-line C gamma 1 transcript was amplified from cDNA of healthy controls by the addition of recombinant IL-2 (rIL-2) to pokeweed mitogen-stimulated peripheral mononuclear cells or Staphylococcus aureus Cowan I (SAC)-stimulated IgM-producing lymphoblastoid cell lines (LCL) transformed by Epstein-Barr virus, while it was not amplified from cDNA of the patient. In the I gamma 1 region of LCL cultured with SAC plus rIL-2, the inner cytosine in the 5' C-C-G-G 3' sequence nearest the 3' site of the I gamma 1 region, at least, was not completely unmethylated in the patient. Moreover, the DNase I hypersensitive site was not induced in the patient's LCL by SAC plus rIL-2. These results indicate that the defects of the immunoglobulin heavy chain isotype switch in the patient's B cells are due to failure in the synthesis of germ-line C gamma transcripts, and this may be caused by defects in opening of the chromatin structures of specific switch regions.

T cells from children with IDDM are sensitized to bovine serum albumin

Epidemiological and experimental evidence suggested that denial of dietary cow milk protein early in life protects genetically susceptible children and animals from insulin-dependent diabetes (IDDM). Bovine serum albumin (BSA) was proposed as a candidate milk-borne mimicry antigen responsible for the diabetogenic cow milk effect. Elevated anti-BSA antibodies have been observed in patients and diabetic rodents, and these antibodies precipitate p69 from islet cell lysates. IDDM is a T cell mediated disorder but efforts to detect BSA-specific T cells in diabetic children have so far failed. We describe here a culture system which allowed the detection of BSA-specific T cells and we mapped this response to the ABBOS peptide (pre-BSA position 152-169) previously identified as a possible mimicry epitope. ABBOS-sensitized T cells were found in 28/31 children with recent onset IDDM but not in non-diabetic controls nor in children with SLE or JRA. T cell proliferative responses declined within the first few years of diabetes diagnosis. Although no effector cell role for BSA/ABBOS specific T lymphocytes has been demonstrated, the presence of BSA peptide-specific T cells strengthens the postulated link between a cow milk protein and IDDM.

Switch recombination in normal IgA1+ B lymphocytes

Most B lymphocytes in normal individuals express two classes of cell-surface immunoglobulins, IgM and IgD. The specificity of the two antigen receptors is identical since they are produced by transcription and differential splicing of the same variable region gene segment to the heavy-chain constant region gene segments for both mu and delta heavy chains. B lymphocytes expressing other immunoglobulin isotypes, IgG, IgA, or IgE, are rare and not well characterized. Particularly controversial is the molecular mechanism of their isotype switch. Here we use high-gradient magnetic cell sorting and fluorescence-activated cell sorting to purify surface IgA1-bearing B lymphocytes from human blood for cellular and molecular analysis. These cells express no immunoglobulin class other than IgA1 and are a relatively uniform population with regard to expression of other cell-surface molecules. They are resting cells in terms of cell cycle and activation marker analysis. The molecular basis for class switching in the IgA1+ cells is not differential transcription or splicing. Rather, switch recombination involving deletion of DNA has occurred on both immunoglobulin heavy-chain gene loci, including the allelically excluded one, and appears to have been directed to IgA1 under normal physiological conditions.

Stimulation of human IgE production by a subset of anti-CD21 monoclonal antibodies: requirement of a co-signal to modulate epsilon transcripts

CD21, the receptor for Epstein-Barr virus (EBV) and the complement receptor-2 (CR2), was recently found to interact specifically with CD23, a low-affinity receptor for IgE, and to regulate IgE production. Therefore, the effect of different anti-CD21 monoclonal antibodies (mAb) on IgE synthesis by blood mononuclear cells was investigated. One anti-CD21 mAb, BU-33, was able to increase significantly (more than threefold) interleukin-4 (IL-4)-induced IgE synthesis, whereas HB-5, OKB-7 and B2 anti-CD21 mAb had no effect. BU-33 had no effect on IgG and IgA production and produced only a moderate increase in IgM production. Recombinant, 29,000 MW, soluble CD23 (sCD23) expressed in COS cells exhibited the same IgE-enhancing activity. BU-33 was the best inhibitor of CD23-liposome binding to the CD21-positive cell line RPMI-8226 when compared to the other anti-CD21 mAb tested. BU-33 identified a different epitope on CD21. The effect of BU-33 on IgE production by purified tonsillar B cells and highly purified germinal centre B cells, was dependent on the presence of T cells or anti-CD40 mAb stimulation. Molecular analysis revealed that BU-33 alone failed to induce germline epsilon mRNA but increased the IL-4-induced germline epsilon transcription levels. Moreover, BU-33 had a synergistic effect on anti-CD40 mAb or T-cell-induced productive epsilon transcript expression. These results therefore indicate that the CD23-CD21 interaction needs a co-signal for B-cell differentiation towards IgE production.

DNA rearrangement can account for in vitro switching to IgG1

During immune responses, B lymphocytes may switch from the expression of immunoglobulin M (IgM) to the expression of another isotype (e.g., IgG, IgE, IgA). In stable hybridomas and myelomas expressing a "switched" (S) isotype, DNA deletions between S mu and a "downstream" S region (S region recombination) have been found. In primary B cells, studies of the molecular basis of switching have been limited by the ability to sensitively quantitate the amount of DNA deletion; such studies would be of interest because other nondeletional mechanisms (trans-splicing, alternative processing of a long transcript) have been proposed to account for isotype switching in certain circumstances. We have applied the digestion-circularization polymerase chain reaction (DC-PCR) technique to measure the amount of S region recombination that occurs in the course of class switching in primary B lymphocytes. Resting B cells were cultured in lipopolysaccharide (LPS) and interleukin 4 (IL-4) to stimulate switching to IgG1. These cells begin to express membrane IgG1 at day 2.5 of culture and reach maximum expression by day 4.5. DNA was prepared from cultured cells and analyzed for S mu-S gamma 1 rearrangement by DC-PCR. Chimeric switch regions, indicating S mu-S gamma 1 recombination, were detected in amounts that, in most cases, correlated with surface expression. Furthermore, when cells were sorted on the basis of surface IgG1 expression, a mean of at least one S mu-S gamma 1 rearrangement per cell was seen in five out of seven experiments. In general, the IgG1+ cells obtained at 4.5 and 5.5 d of culture had close to 2 S mu-S gamma 1 rearrangements per cell. In IgG1- cells, S mu-S gamma 1 rearrangements were detectable, but at frequencies substantially lower that in IgG1+ cells. Thus, these results indicate that DNA deletion accompanies class switching in normal B cells stimulated with LPS and IL-4.

Differential sensitivity of human myeloma cell lines and normal bone marrow colony forming cells to a recombinant diphtheria toxin-interleukin 6 fusion protein

The cytotoxicity of a recombinant interleukin 6 (IL-6)-diphtheria toxin (DT) fusion protein towards human myeloma cell lines was investigated. DAB389-IL-6 inhibited protein synthesis and methylcellulose colony formation by U266 myeloma cells. In the clonogenic assay, the fusion protein approached the level of cytotoxicity achieved by native DT. The specificity of killing by DAB389-IL-6 was demonstrated by inhibition of cytotoxicity by a molar excess of free rhIL-6. The effect of DAB389-IL-6 on colony formation by six OCI-My cell lines was assessed. Similar to U266 cells, colony growth by the OCI-My 5 and -My 2 cell lines was inhibited in a simple dose dependent manner. However, a biphasic effect was observed for the IL-6 dependent OCI-My 4 cells; DAB389-IL-6 stimulated colony formation at low (< or = 10(-11) M) concentrations, yet was inhibitory at higher doses. Three other cell lines whose growth was not altered by IL-6 were relatively unaffected by DAB389-IL-6, despite their sensitivity to native DT. Flow cytometric analysis for IL-6 receptor expression using phycoerythrin-conjugated IL-6 demonstrated specific binding sites on both DAB389-IL-6 sensitive and certain insensitive cell lines, suggesting that other factors in addition to the expression of IL-6 receptors are involved in killing by the fusion toxin. Despite evidence for a role of IL-6 in myeloid cell development, normal bone marrow was insensitive to the IL-6 fusion toxin. In cultures containing both normal bone marrow and U266 cells DAB389-IL-6 effectively inhibited the growth of U266 myeloma colonies but had little effect on normal bone marrow erythroid, granulocyte and mixed erythroid/granulocyte colony growth. From these experiments we conclude that DAB389-IL-6 is specifically cytotoxic towards a subset of IL-6-responsive human myeloma cell lines and may be useful, in some cases, in the selective elimination of tumour cells from mixed populations of normal and malignant cells.

Differentiation of membrane IgE+ rat B cells into IgE-secreting cells

Rat spleen cells were stimulated with pokeweed mitogen (PWM) and the IgM and IgE responses were assessed. An enrichment of the cell suspension with IgE-bearing cells before stimulation resulted in an increase in the number of IgE-secreting cells. A decrease of the number of IgE-secreting cells was found after depletion of IgE- or IgM-bearing cells, but not those bearing IgD molecules on their membranes, before stimulation. Moreover, the stimulation of membrane IgE on B cells with anti-IgE antibodies was shown to increase the number of IgE-secreting cells after PWM-induced differentiation in vitro. In vivo, it was also observed that a single injection of anti-IgE antibodies can induce the differentiation of IgE-secreting cells. These results demonstrate the presence of IgE(+)-IgM (+)-IgD- B cells in the rat that are responsive to PWM-induced differentiation into IgE-secreting cells. They indicate a pre-commitment of these cells at a stage where they still express IgM on their surface. IgE molecules on the cell membranes play a role in their differentiation.

T cell dependent differentiation of human B cells: direct switch from IgM to IgE, and sequential switch from IgM via IgG to IgA production

Ig production by splenic human B cells that express different surface Ig isotypes were analysed in limiting dilution cultures. Therefore, FACS sorted IgM+, IgG+ and IgA1+ B cells were stimulated with PMA-activated EL4 thymoma cells as helper cells in the presence of IL-2 and IL-4. We found that at least every second B cell responded in vitro and secreted the antibody corresponding to its surface Ig isotype. IgE secreting cells developed from surface IgM+ D+ cells (1/31 to 1/167), but not from IgG+ or IgA1+ cells (much less than 1/5000). Negative signalling of the IgM+ B cells by addition of anti-IgM antibodies into the cultures reduced the number of single IgM producing cells by greater than 85%, and completely inhibited IgE switch. In contrast, anti-IgG and anti-IgA antibodies did not reduce the IgE response. The results indicate a direct switch from IgM to IgE secretion in vitro. In contrast to IgE, IgA secreting cells developed from IgM+D+ (1/30 to 1/51) and from IgG+ B cells (1/14 to 1/25). Negative signalling of the IgG+ B cell subset within total B cells by anti-IgG antibodies suppressed the development of IgG as well as IgA producing cells, but did not inhibit IgM and IgE responses. This indicates a sequential switch from IgM via IgG to IgA. Taken together, this study indicates that IgE secreting cells are derived directly from IgM+D+ B cells by non-sequential switching, whereas IgA producing cells preferentially develop by sequential switching via IgG+ B cells.

Quantitation of immunoglobulin mu-gamma 1 heavy chain switch region recombination by a digestion-circularization polymerase chain reaction method

B lymphocytes expressing surface IgM with or without IgD may switch to the expression of other isotypes (IgG, IgA, or IgE) in the course of immune responses. Analyses of genomic DNA from cloned myelomas and hybridomas have shown that the isotype switch is accompanied by a rearrangement characterized by deletion of DNA between the switch (S) region of the mu gene and that associated with the new isotype, resulting in the formation of a composite S region. Measurement of this deletional rearrangement has been difficult in populations of normal B cells but would be useful for investigating the mechanism of the rearrangement and determining whether deletional rearrangement is responsible for all instances of class switching. We have developed a sensitive assay for deletional rearrangement that we designate the digestion-circularization polymerase chain reaction (PCR). In this assay, genomic DNA is digested with a restriction enzyme that recognizes sites that flank the recombined composite S region. The digested DNA is then ligated at low concentrations to favor the formation of circles. The ligation joins the 5' and 3' ends of each restriction fragment, making it possible to amplify by PCR across the ligated restriction site by using appropriate primers. From DNA that has undergone deletional rearrangement, a single-sized PCR product is produced and can be quantitated. We demonstrate here that the digestion-circularization PCR assay can detect S mu-S gamma 1 rearrangements in B cells cultured with lipopolysaccharide and interleukin 4. The assay is sensitive enough to quantitate switched cells constituting only 1-2% of the population.

A bovine albumin peptide as a possible trigger of insulin-dependent diabetes mellitus

BACKGROUND

Cow's milk has been implicated as a possible trigger of the autoimmune response that destroys pancreatic beta cells in genetically susceptible hosts, thus causing diabetes mellitus. Studies in animals have suggested that bovine serum albumin (BSA) is the milk protein responsible, and an albumin peptide containing 17 amino acids (ABBOS) may be the reactive epitope. Antibodies to this peptide react with p69, a beta-cell surface protein that may represent the target antigen for milk-induced beta-cell--specific immunity.

METHODS

We used immunoassays and Western blot analysis to analyze anti-BSA antibodies in the serum of 142 children with insulin-dependent diabetes mellitus, 79 healthy children, and 300 adult blood donors. Anti-ABBOS antibodies were measured in 44 diabetic patients at the time of diagnosis, three to four months later, and one to two years later.

RESULTS

All the diabetic patients had elevated serum concentrations of IgG anti-BSA antibodies (but not of antibodies to other milk proteins), the bulk of which were specific for ABBOS: The mean (+/- SE) concentration was 8.5 +/- 0.2 kilofluorescence units (kfU) per microliter, as compared with 1.3 +/- 0.1 kfU per microliter in the healthy children. IgA antibodies were elevated as well, but not IgM antibodies. The antibody concentrations declined after diagnosis, reaching normal levels in most patients within one to two years. The initial decline involved anti-ABBOS--specific antibodies almost exclusively. Much lower serum concentrations of anti-BSA antibodies were found in all 379 control subjects, but only 2.5 percent of them had small amounts of ABBOS-specific IgG.

CONCLUSIONS

Patients with insulin-dependent diabetes mellitus have immunity to cow's-milk albumin, with antibodies to an albumin peptide that are capable of reacting with a beta-cell--specific surface protein. Such antibodies could participate in the development of islet dysfunction.

Molecular analysis of the induction of immunoglobulin E synthesis in human B cells by interleukin 4 and engagement of CD40 antigen

The molecular events leading to immunoglobulin E (IgE) synthesis in human sIgE- B cells stimulated with interleukin 4 (IL-4) and anti-CD40 monoclonal antibody (mAb) 626.1 were analyzed. Anti-CD40 mAb increased the levels of IL-4-induced germline C epsilon transcripts and induced the production of mature C epsilon mRNA. These effects were dependent on the presence of IL-4. Nested primer PCR revealed deletional switch recombination occurring only in B cell stimulated with both IL-4 and anti-CD40 mAb. DNA sequence analysis of switch fragments showed direct S mu/S epsilon joining, without the deletions or duplications within S mu often found in B cells stimulated with IL-4 and Epstein-Barr virus. Analysis of the switch junction map sites showed "hot spots" for recombination within S mu, but not within S epsilon. These findings indicate that IL-4 provides a signal to B cells to induce germline C epsilon transcription and concurrent CD40 engagement induces S mu/S epsilon deletional switch recombination, production of mature C epsilon mRNA, and IgE synthesis.

IgG2b or IgE molecules can be co-expressed with those of the IgM and IgD isotypes of the membrane of normal rat B cells

Expression of Ig isotypes other than IgD together with IgM on the membranes of single B cells has been reported in different experimental models. This paper describes the co-expression of IgG2b or IgE with IgM-IgD on the surface of single B cell subpopulations from normal rats. Their expression was demonstrated with anti-IgE or IgG2b monoclonal antibodies and their F(ab')2 fragments. After pronase digestion, the re-expression of these isotypes together with IgM-IgD was observed in vitro and was inhibited by cycloheximide. These observations imply that mechanisms other than class switching may participate in the expression of membrane isotypes in vivo. The role of these membrane isotypes is still to be established, but could be important as IgG2b molecules are found on a large B cell subpopulation.

Regulation of IgE synthesis by cytokines

Considerable progress has been made in our understanding of the mechanisms underlying regulation of human IgE synthesis. Interleukin-4 induces IgE production specifically, but costimulatory signals provided by T cells are required. Other cytokines modulate interleukin-4-induced IgE synthesis. The roles of T cells and cytokines in regulating IgE switching are discussed.

Comparison of IgE expression at the mRNA and protein levels in vitro

The regulating effects of IL-4 and pokeweed mitogen on IgE synthesis in vitro by human peripheral blood leucocytes has been compared with the corresponding effect of these regulators on the expression of IgE mRNA. The latter was measured by dot blot hybridization with an oligonucleotide coding for a unique six amino acid region of the CH epsilon 2 domain. Specificity of the oligonucleotide probe was established by its inability to hybridize with RNA extracted from HMY-2 (IgG) and XQ-15 (IgM) secreting cell lines whilst producing intense signals with RNA extracted from the IgE secreting cell line U266. Whilst IgE mRNA was detected in RNA extracted from PBL of both atopic and control subjects, spontaneous IgE synthesis was restricted to atopic PBL. IL-4 increased both IgE mRNA and IgE synthesis in all PBL samples but PWM, while significantly increasing IgE mRNA expression either failed to modify IgE synthesis or actively suppressed it. The assay system employed to quantitate IgE synthesis in vitro was shown to be inhibited by both IgE binding factors and IgG anti-IgE autoantibodies which are produced in PBL cultures. IgE mRNA levels might therefore more accurately monitor the regulatory effects of IL-4 and PWM on IgE synthesis than quantitation of the IgE by radioimmunoassay.

What determines an antigen-specific IgE isotypic response? A hypothesis

Two models to account for an antigen-specific IgE isotypic response are proposed. Both models assume a first-tiered IgE production induced by antigen and IL-4; however, the processed IgE or Ag-IgE immune complexes stimulate T epsilon cells differently in the two models. In Model I, we propose that T epsilon cells express conventional T-cell receptors which recognize IgE isotypic determinants. Model IA proposes that IgE fragments are processed and recognized along with class II MHC molecules, and T epsilon cell preferentially act on antigen-activated IgE-committed B epsilon cells via recognition of processed membrane IgE determinants but not antigens; thus T epsilon cells are in principle capable of modulating non-antigen-specific polyclonal IgE responses. Model IB proposes that IgE function as a class-restriction determinant for nominal antigens analogous to that of class II molecules, and T epsilon cells exert stringent antigen-specific IgE isotypic responses by recognizing nominal antigens restricted to IgE. T epsilon cells thus exert antigen-specific and IgE concerted immunoregulation, and do not participate in modulating polyclonal IgE production. Model II proposes a heterotypic interaction of IgE with a cell interaction receptor (or IgE Fc receptor) on T cells. T epsilon cells modulate antigen-specific IgE isotypic responses via ligation with IgE-antigen immune complexes on B-cell surface; thus, T epsilon cells in principle contribute to polyclonal IgE responses.

Deletional switch recombination occurs in interleukin-4-induced isotype switching to IgE expression by human B cells

There is controversy as to whether deletional rearrangement occurs between the IgM and IgE switch regions (S mu and S epsilon, respectively) during switching to the IgE isotype. We have addressed the issue by stimulating normal human B cells, sorted for lack of expression of surface IgE, to produce IgE by infection with Epstein-Barr virus (EBV) in the presence of interleukin 4 (IL-4). Genomic DNA was amplified for S mu/S epsilon switch junction fragments by utilizing the nested-primer polymerase chain reaction. Switch junction fragments were amplified from B cells infected with EBV in the presence of IL-4 but not from B cells infected with EBV alone. The DNA sequence of these "switch fragments" revealed direct joining of S mu to S epsilon in each case. The recombination sites within S mu were clustered within 900 base pairs at the 5' end of the switch region, suggesting that there are "hot spots" for recombination within S mu. The S epsilon recombination sites were scattered throughout the S epsilon region. These findings indicate that IL-4-induced isotype switching to IgE production in human B cells is accompanied by DNA rearrangements with joining of S mu to S epsilon.

A deletion map of the human immunoglobulin heavy chain variable region

Analysis of VH gene segments deleted in the process of immunoglobulin heavy chain (IGH) variable region assembly in three series of monoclonal B cell lines has been used to determine the human VH region organization. A deletion map of the relative positions of 21 different VH gene segments has been determined. The characterization of B cell lines from three unrelated adults of two racial groups yielded the same relative VH gene segment order, suggesting that the overall order of VH genes in the normal population is constant. This VH gene segment order was consistent with what we had previously generated from physical mapping techniques. DH segments from the second DH cluster, distinct from the major DH locus 3' of the VH region, were not observed to be used in 32 different rearrangements. Approximately 77% of the VH-(D)JH rearrangements involved VH gene segments within 500 kb of the JH region, indicating that human B cell lines preferentially rearrange JH-proximal VH gene segments. The switch, observed in mice, from the fetal use of JH-proximal VH gene segments to an adult VH use dependent upon VH family size may therefore not occur in humans. This detailed map of the VH gene segments is a necessary prerequisite for understanding VH usage in development and disease.

Isotype switching in anti-immunoglobulin-activated B lymphoblasts: differential requirements for interleukin 4 and other lymphokines to elicit membrane vs. secreted IgG1

Anti-immunoglobulin (Ig)-activated B lymphoblasts, prepared by culturing high-density B cells with anti-Ig-Sepharose for 48 h, can be induced to secrete IgM and IgG1 by a mixture of T cell-derived lymphokines containing interleukin (IL) 4. In this study we have examined the conditions required for lymphokine-mediated induction of IgG1 secretion and membrane (m)IgG1 expression in B lymphoblasts. Resting B cells exposed to IL 4 (10-100 U/ml) during anti-Ig-mediated blast transformation did not secrete IgG1 upon subsequent culture with lipopolysaccharide (LPS) regardless of whether IL 4 was present or absent during the secondary culture. In contrast, B lymphoblasts previously exposed to IL 4 did secrete IgG1 in response to T cell-derived lymphokines [EL 4 supernatant depleted of IL 4; (D)EL 4 SN]. However, optimal IgG1 secretion was obtained when B lymphoblasts were simultaneously exposed to IL 4 and other lymphokines. Pre-exposure to (D)EL 4 SN, which contains IL 5 and IL 2, failed to prepare anti-Ig blasts to secrete IgG1 in response to LPS and IL 4. Inhibition of IL 5 and IL 2 activity in EL 4 SN suppressed IL 4-mediated IgG1 secretion. Together, these data indicate that B lymphoblasts require IL 5 and IL 2 in addition to IL 4 to secrete IgG1, and that the IL 4 signal(s) must precede or accompany those provided by the other lymphokines. As a measure of the fraction of cells capable of switching to IgG1, we assessed expression of mIgG1 on B lymphoblasts by fluorescence flow cytometry. B lymphoblasts cultured for 3 days with (D)EL 4 SN and IL 4 (10-100 U/ml) were 8% to 20% mIgG1+; in the absence of IL 4 blasts did not express detectable mIgG1. Although anti-Ig blasts treated with LPS and IL 4 did not secrete appreciable IgG1, a substantial fraction of B lymphoblasts (4% - 19%) cultured with LPS and IL 4, but not LPS alone, expressed mIgG1. These results suggest that LPS and IL 4 are sufficient to commit B lymphoblasts to mIgG1 expression, but that additional signals provided by T cell-derived lymphokines are required to elicit IgG1 secretion.

Murine memory B cells are multi-isotype expressors

Flow cytometric analyses of the surface immunoglobulins of murine memory B cells revealed the existence of populations expressing multiple isotypes, including an IgM+/IgG+ population that could be stimulated in vitro with antigen to secrete both IgM and IgG. Female BALB/c mice were immunized with R-phycoerythrin (RPE), a fluorescent photosynthetic accessory protein from red algae. Pooled splenocytes from these mice at different stages of immunization were stained with RPE as well as with allophycocyanin- and fluorescein-conjugated anti-isotype antibodies and analysed on a two-laser FACS. RPE-binding cell sub-populations were defined and selectively sorted to verify their phenotype and to demonstrate that the various subpopulations (IgM+/IgG+, IgM+/IgG-, IgM-/IgG+) had different isotype-secretion patterns when challenged with RPE in vitro. These results re-affirm the notion that a transcriptional processing mechanism may be responsible for the simultaneous expression of multiple isotypes in memory cells.

CD40 and IgE: synergism between anti-CD40 monoclonal antibody and interleukin 4 in the induction of IgE synthesis by highly purified human B cells

A novel pathway of IgE-B cell differentiation has been identified. Engagement of the B cell antigen CD40 by F(ab')2 fragments of monoclonal antibody (mAb) 626.1 in the presence of recombinant interleukin 4 (rIL-4) induced intense IgE synthesis, but modest IgG synthesis, by highly purified human B cells. Surface IgE- B cells isolated by cell sorting were induced to produce IgE by mAb 626.1 and IL-4. Thus, IgE synthesis is unlikely to result from expansion of a B cell population precommitted to IgE in vivo. A neutralizing anti-IL-6 antibody strongly, but not completely, inhibited the IgE response. This indicates that autocrine production of IL-6 plays an important amplification role in IgE synthesis triggered by anti-CD40 mAb and IL-4. Although the exact role played by CD40 in IgE responses in vivo remains to be established, this T cell-independent system represents a useful model to characterize the biochemical and molecular events leading to IgE synthesis in human B cells.

Expression of the alpha-chain gene in heterogeneous IgA immunodeficiency

Five heterogeneous IgA-immunodeficient patients were analysed for expression of the alpha-chain gene. The number of surface IgA-bearing B cells was low in four patients. Southern blot analysis indicated no deletion of immunoglobulin structural genes coding for C alpha or alpha switching-region genes. The number of surface IgM and IgA double-bearing B cells increased in some patients. Addition of recombinant interleukin 4 (rIL-4), rIL-5, and rIL-6 to the normal B cells enhanced IgA production. However, B cells of the patients showed no or one-third lower IgA production in response to these lymphokines, even though there was proliferation. rIL-4, rIL-5, and rIL-6 induced low or no expression of alpha mRNA of the patients' B cells. These results suggested that the patients lacked B cells able to produce transcripts for the IgA heavy chain, and that some patients' B cells might be defective at the switch-recombination process from mu to alpha or from mu and alpha to alpha.

Human IgE mRNA expression by peripheral blood lymphocytes stimulated with interleukin 4 and pokeweed mitogen

Expression of human IgE mRNA by peripheral blood lymphocytes (PBL) and an IgE-producing myeloma cell line, U-266, was examined by Northern blot hybridization and compared with IgE levels in culture supernatants. A 2.35-kb IgE mRNA was detected in unstimulated atopic PBL and U-266 cells but not in normal PBL, and its levels correlated with IgE protein levels in the supernatant. Upon stimulation with interleukin 4, a new 1.75-kb transcript was revealed in both atopic and normal PBL but not in U-266 cells. Its expression did not correlate with IgE levels in the supernatant. Pokeweed mitogen also induced the expression of the 1.75-kb transcript without concomitant induction of IgE synthesis by normal PBL and even suppressed the spontaneous expression of the 2.35-kb transcript and IgE protein synthesis by atopic PBL. Interferon-gamma, which suppressed both the 2.35-kb transcript and IgE protein production, had no inhibitory effect on the 1.75-kb transcript. Expression of the 1.75-kb transcript was already high after 2 days of stimulation and peaked around day 4. The length of the transcript is smaller than that of mRNA coding for secreted human IgG and IgA and contains all four C epsilon exon sequences, suggesting it might be a truncated transcript without v region and might be a human counterpart of the murine germ-line C epsilon transcript.

Enumeration of IgE secreting B cells. A filter spot-ELISA

To assess the frequency of IgE producing cells in humans a filter immunoplaque assay has been developed to detect IgE secretion from individual B lymphocytes in unfractionated peripheral blood mononuclear cells (PBMC). PBMC were incubated in microfilter plates containing nitrocellulose membranes coated with polyclonal anti-human IgE antibody, and the IgE production by a single cell was detected using a specific anti-human IgE monoclonal antibody followed by enzymatic development. The products of the enzymatic reaction were visualized as blue plaques on the membranes. The assay was both sensitive and specific as determined by: (1) a near 1:1 correlation between direct cell counts of an IgE producing myeloma cell line (U266) and the number of plaques in the filter immunoassay; and (2) the absence of detectable plaques generated by human B cells transformed by Epstein-Barr Virus (EBV) and producing only IgG or IgM. The presence of other cell types in PBMC did not affect the ability to detect IgE secreting cells. Replicate cultures of highly purified B lymphocytes, first transformed with EBV and then stimulated with recombinant human interleukin-4, produced IgE levels in culture supernatants that correlated closely with the number of IgE producing cells (r = 0.93; P less than 0.001). Furthermore, using the same transformed cells, the number of IgE secreting cells assessed by the immunoplaque assay was significantly correlated (r = 0.94; P = 0.002) with the number of IgE producing cells assessed by immunofluorescence staining of intracytoplasmic IgE. This assay provides a simple and direct method to assess the frequency of IgE producing lymphocytes in humans.

Structure and expression of germline epsilon transcripts in human B cells induced by interleukin 4 to switch to IgE production

Interleukin 4 (IL-4)-induced IgE production coincides with the appearance of the 2.2-kb productive epsilon-mRNA, but is preceded by synthesis of a 1.7-kb epsilon-RNA. Analysis of cDNA copies of the 5' end of this RNA indicated that the 1.7-kb epsilon-RNA is a germline epsilon immunoglobulin heavy chain transcript with an exon mapping 5' to the switch region. Transcription through switch regions has been implicated in the control of class switching. However, IL-4 or cloned CD4+ T cells were able to induce germline epsilon transcripts without inducing IgE synthesis, for which both signals were required. These results indicate that induction of human germline epsilon-RNA does not necessarily result in IgE synthesis, and that additional regulatory mechanisms are involved in class switching.

Monoclonal antibodies specific for human IgE-producing B cells: a potential therapeutic for IgE-mediated allergic diseases

Monoclonal antibodies (MAbs) specific for surface antigens of lymphocytes are being used to target and deplete tumorous or normal lymphocytes in vivo. Here, we report evidence for the existence of antigenic epitopes on IgE that are accessible on IgE-secreting B cells but not on other cells bearing IgE. Among 42 murine MAbs specific for human IgE, two were shown by fluorescence flow cytometric analyses to bind to IgE-secreting cell lines but not to IgE bound to high-affinity IgE.Fc receptors (Fc epsilon RI) on basophils or low-affinity IgE receptors (Fc epsilon RII) on other cell types. Neither could they induce histamine release from basophils of various donors even under very permissive conditions. These antibodies may be useful for targeting IgE-secreting B cells in patients suffering from IgE-mediated allergies.

IgE synthesis by chronic lymphocytic leukemia cells

The present results indicate that B cells isolated from chronic lymphocytic leukemia (B-CLL) from 11 of 14 patients are capable of specifically producing IgE upon costimulation with IL-4 and hydrocortisone (HC). IgE is detected by intracytoplasmic fluorescence staining and by RIA. Clinical, hematological, and immunological parameters (including Rai stage, WBC, Lc, sIg kappa/lambda, CD5, and CD23 expression) cannot distinguish the IgE responder from the nonresponder patients. IL-4 alone is a potent inducer of human IgE synthesis by normal PBMC and we show here that its effect is strikingly enhanced by HC. The IgE produced by B-CLLs are monoclonal since they display the same L chain type as the freshly isolated CD5+ B-CLLs. We, therefore, conclude that the combination of IL-4 and HC can abrogate the maturation arrest of CD5+ B-CLLs by inducing their differentiation into IgE-producing cells. The present data provide a unique model to study the isotype switching to IgE and the regulation of human IgE synthesis by monoclonal human B cells.

IgE secretion by Epstein-Barr virus-infected purified human B lymphocytes is stimulated by interleukin 4 and suppressed by interferon gamma

The cytokine interleukin 4 (IL-4) has been shown to induce lipopolysaccharide-activated murine B cells to differentiate into IgE-secreting cells and to stimulate IgE secretion by cultured human peripheral blood lymphoid cells. It is unclear, however, whether this effect of IL-4 on human peripheral blood lymphoid cells is a direct effect on the B cell because IL-4 can stimulate T cells and monocytes as well as B cells and does not induce purified human B cells to secrete immunoglobulin. To investigate this issue we studied the ability of IL-4 to induce IgE secretion by purified human B cells (93-96% CD20+, less than 1% CD3+) that were cultured with Epstein-Barr virus (EBV). Although B cells cultured with IL-4 alone did not secrete Ig and B cells cultured with EBV alone secreted IgM, IgG, and IgA but less than 150 pg of IgE per ml, the combination of EBV and IL-4 induced an IgE response that ranged from 11.4 to 40.3 ng/ml of culture supernatant after 26 days of culture. While IL-4 also enhanced IgM, IgG, and IgA secretion, as well as proliferation by EBV-infected B cells, these effects were less pronounced, occurred earlier during culture, and required a lower concentration of IL-4 than did the stimulation of IgE secretion. Furthermore, interferon gamma at 10 units per ml was found to inhibit IL-4/EBV-induced IgE secretion without inhibiting the other stimulatory effects of IL-4. We conclude that (i) IL-4 and interferon gamma can act directly on polyclonally activated human B cells to respectively stimulate and suppress IgE secretion and (ii) IL-4, in addition to its specific effect on IgE secretion, has a general stimulatory effect on the growth and differentiation of EBV-infected human B cells.