Production of IgE-potentiating factor in man by T cell lines bearing Fc receptors for IgE

How aluminum adjuvants could promote and enhance non-target IgE synthesis in a genetically-vulnerable sub-population

Aluminum-containing adjuvants increase the effectiveness of vaccination, but their ability to augment immune responsiveness also carries the risk of eliciting non-target responses, especially in genetically susceptible individuals. This study reviews the relevant actions of aluminum adjuvants and sources of genetic risk that can combine to adversely affect a vulnerable sub-population. Aluminum adjuvants promote oxidative stress and increase inflammasome activity, leading to the release of IL-1β, IL-18, and IL-33, but not the important regulatory cytokine IL-12. In addition, they stimulate macrophages to produce PGE₂, which also has a role in regulating immune responses. This aluminum-induced cytokine context leads to a T(H)2 immune response, characterized by the further release of IL-3, IL-4, IL-5, IL-9, IL-13, and IgE-potentiating factors such as sCD23. Genetic variants in cytokine genes, such as IL-4, IL-13, IL-33, and IL-18 influence the response to vaccines in children and are also associated with atopy. These genetic factors may therefore define a genetically-vulnerable sub-population, children with a family history of atopy, who may experience an exaggerated T(H)2 immune response to aluminum-containing vaccines. IL-4, sCD23, and IgE are common factors for both atopy and the immune-stimulating properties of aluminum adjuvants. IL-4 is critical in the production of IgE and total IgE up-regulation. IL-4 has also been reported to induce the production of sCD23 and trigger resting sIgM+, sIgD+ B-cells to switch to sIgE+ B-cells, making them targets for IgE-potentiating factors. Further, the actions of IgE-potentiating factors on sIgE+ B-cells are polyclonal and unrestricted, triggering their differentiation into IgE-forming plasma cells. These actions provide a mechanism for aluminum-adjuvant promotion and enhancement of non-target IgE in a genetically vulnerable sub-population. Identification of these individuals may decrease the risk of adverse events associated with the use of aluminum-containing vaccines.

Identification of novel CD23 transcripts on human T and B lymphocytes and eosinophil cell line

The main aim of the present studies was to investigate the structure of the human low-affinity IgE Fc receptor (CD23) present on T and B lymphoid cells and eosinophil cell line. A novel finding in these studies has been the detection and sequence analysis of CD23 transcripts in human T lymphocytes. These studies have established that some of the human T-cell populations analyzed express CD23 mRNA and that its structure is quite similar to that previously described for human B lymphocytes. A second major finding in these studies is that some human T- and B-cell lines and eosinophil cell line contain multiple forms of CD23 transcripts. These appear to be generated via alternative splicing, resulting in transcripts that may encode a truncated, possibly secretory form of CD23. These findings in human T and B lymphocytes and eosinophils provide new information about the structure of lymphocyte CD23 and suggest that alternative processing of transcripts generates CD23 mRNA that encodes CD23 isoforms. These studies are the first experimental evidence showing that CD23 isoforms may occur in the human and are the first direct evidence for production of CD23 by human T lymphocytes. In addition, these studies provide the first experimental evidence that T and B lymphocytes express CD23 transcripts lacking exon 3-encoded sequences, raising the possibility that a secretory form of CD23 may be synthesized by human T and B lymphocytes, and eosinophils.

Recombinant soluble form of the human high-affinity immunoglobulin E (IgE) receptor inhibits IgE production through its specific binding to IgE-bearing B cells

A recombinant soluble form of the alpha subunit of the human high-affinity receptor for IgE (rsFc epsilon RI alpha), one of the potent IgE-binding molecules, was tested for its ability to regulate IL-4-induced IgE synthesis by human lymphocytes. Addition of rsFc epsilon RI alpha to cultures induced a dose-dependent inhibition of the T cell-dependent and independent synthesis of IgE. The suppression of IgE synthesis was observed at the protein and the mRNA levels, and it was IgE class specific. By flow cytometry, specific binding of rsFc epsilon RI alpha was detected on surface IgE-bearing B cells as well as on U266 cells, and it was completely blocked by preincubation with IgE. rsFc epsilon RI alpha bound to the cell surface IgE could be effectively dissociated not only by a large excess of IgE, but also by an anti-rsFc epsilon RI alpha mAb that competes with IgE for the binding to rsFc epsilon RI alpha. This mAb abolished the rsFc epsilon RI alpha-mediated suppression of IgE synthesis. These data suggest that rsFc epsilon RI alpha may have a function in selectively suppressing IgE synthesis through its interaction with the membrane-bound form of IgE.

Fc epsilon receptor II/CD23+ lymphocytes in atopic dermatitis. III. Aberrant control in the in vitro expression of Fc epsilon RII/CD23 on peripheral blood T cells in atopic dermatitis

In vitro Fc epsilon RII expression was examined in patients with atopic dermatitis, those with non-atopic eczematous dermatitis and normal individuals following stimulation of peripheral blood cells with recombinant IL-4 (rIL-4), phytohaemagglutinin (PHA), or PHA plus rIL-2. At various days cells were stained with MoAbs to human lymphocyte Fc epsilon RII and to lymphoid cell-surface antigens and analysed by flow cytometry. rIL-4, but not rIL-2, specifically induced Fc epsilon RII on T cells as well as B cells in atopic dermatitis, eczematous dermatitis and normal individual groups. Both atopics and non-atopics generated comparable proportions of Fc epsilon RII+ T cells (T epsilon cells), whereas the frequency of B cells bearing Fc epsilon RII(B epsilon cells) was significantly higher in patients with extensive atopic dermatitis than in those with mild atopic dermatitis and other subjects. Comparable levels of T epsilon cells were detected in both atopic and non-atopic donors following stimulation of peripheral blood cells with PHA or pre-activation of the cells with PHA plus subsequent incubation with rIL-2. Whereas both CD8+ and CD4+ subsets were present in T epsilon cell populations induced specifically by rIL-4, PHA and PHA plus rIL-2, patients with atopic dermatitis had a greater tendency for Fc epsilon RII expression on CD8+ T cells compared with patients with eczematous dermatitis and normal individuals. Recombinant interferon-gamma (rIFN-gamma), but not rIFN-alpha or prostaglandin E2 (PGE2), suppressed the generation of T epsilon cells by rIL-4 in atopics and non-atopics to the same degree. These results suggest the aberrant control of Fc epsilon RII expression on T cells, especially those bearing CD8, in atopic dermatitis.

Enhancement of IgE synthesis in the human myeloma cell line U-266 with an IgE binding factor from a human T-cell line

An IgE-binding factor(s) (IgE-BF(s] was partially purified from the supernatant of human HTLV-II carrying T-cell line MO. This IgE-BF(s) was shown to increase the IgE synthesis in the human myeloma cell line U-266, but did not affect its viability or growth. The effect of the IgE-BF(s) was dose-dependent and selective for IgE protein synthesis as beta 2-microglobulin synthesis in the U-266 and the immunoglobulin production in the U-1958 IgG-secreting human myeloma cell line were unaffected. The IgE-BF(s) increased the production of the epsilon heavy chain but not the lambda light chain production. The IgE-BF(s) was distinct from IL-1 beta, IL-3, IL-4, IL-5, IL-6, TNF-alpha, IFN-alpha, -beta, -gamma, M-CSF, and fragments of CD23.

Imbalance of CD4+CD45R+ and CD4+CD29+ T helper cell subsets in patients with atopic diseases

To evaluate the proportion of helper cell subsets we studied 18 children with atopic dermatitis, 30 patients with asthma, 27 healthy age-matched controls aged 1 to 17 years and 11 atopic controls without symptoms related to atopy, aged 9-22 years. Lymphocytes were isolated from heparinized peripheral blood and the proportion of CD4+CD29+ and CD4+CD45R+ cells was determined by double-labelling immunofluorescence. Children with atopic dermatitis yielded a significantly (P less than 0.01) higher proportion of CD4+CD45R+ (median 75%) cells compared with normal controls (median 66.6%), whereas the proportion of CD4+CD29+ cells was significantly (P less than 0.01) lower in patients with atopic dermatitis (median 20.4 versus 29.6%). Interestingly, the percentage of CD4+CD45R+ cells shows an age-dependent decline (r = -0.67, P less than 0.01) in the control group, which is not found in the patient group.

Regulation of immunoglobulin (Ig)E synthesis in the hyper-IgE syndrome

The hyper-IgE (HIE) syndrome is characterized by high IgE serum levels, chronic dermatitis, and recurrent infections. The mechanisms responsible for hyperproduction of IgE in HIE patients are presently unknown. We investigated whether spontaneous in vitro IgE synthesis by PBMC from seven HIE patients was sensitive to signals (cell adhesion, T/B cell cognate interaction and lymphokines: IL-4, IL-6, and IFN-gamma) known to regulate IgE induction in normals. Our results show that, unlike IL-4 dependent IgE synthesis induced in normals, spontaneous IgE production by PBMC from HIE patients was not blocked by monoclonal antibodies to CD2, CD4, CD3, and MHC class II antigens. Furthermore, antibodies to IL-4 and IL-6 did not significantly suppress IgE production. IFN-gamma had no significant effects on spontaneous in vitro IgE synthesis. To test whether an imbalance in lymphokine production might underlie hyperproduction of IgE in HIE patients, mitogen-induced secretion of IL-4 and IFN-gamma by PBMC was assessed. No significant difference was detected between HIE patients and normal controls. Thus, ongoing IgE synthesis in the HIE syndrome is largely independent of cell-cell interactions and endogenous lymphokines, and is due to a terminally differentiated B cell population, no longer sensitive to regulatory signals.

T- and B-cell dysregulation of IgE synthesis in cystic fibrosis patients with allergic bronchopulmonary aspergillosis

Since Aspergillus fumigatus (Af)-specific and polyclonal serum IgE levels are characteristically elevated in patients with allergic bronchopulmonary aspergillosis (ABPA), we evaluated in vitro regulation of IgE synthesis in cystic fibrosis (CF) patients with ABPA. We studied 11 CF patients with ABPA, 37 patients with positive Af prick skin tests and/or IgG precipitating antibodies (ST/PPT+), and 35 patients with no humoral or skin responses to Aspergillus (ST/PPT-). Mean serum IgE concentration was significantly elevated in CF subjects with ABPA compared to ST/PPT+ and ST/PPT- patients, 2866 vs 303 and 61 IU/ml, respectively (P less than 0.01). In vitro studies demonstrated that ABPA patients' B cells spontaneously synthesized significantly increased amounts of IgE compared to ST/PPT positive and negative subjects, 1980 vs 220 and 13 pg/ml, respectively (P less than 0.01). In addition, preformed B-cell-associated IgE was also significantly elevated in ABPA subjects (P less than 0.01), indicating prior in vivo activation. Supernatant cultures of Af-stimulated T cells from ABPA subjects significantly induced allogeneic B-cell IgE synthesis compared to ST/PPT positive and negative CF subjects, 206 vs 13 and 4 pg/ml, respectively (P less than 0.01). Thus T cells stimulated with Aspergillus antigens secrete cytokines that induce B-cell IgE synthesis in ABPA subjects. B-cell IgE hyperactivity is manifested by in vivo and in vitro increased IgE concentrations. Analyses of T-cell regulation and B-cell IgE synthesis distinguish CF subjects with ABPA from Aspergillus sensitive non-ABPA subjects.

Regulation of immunoglobulin production in hyperimmunoglobulin E recurrent-infection syndrome by interferon gamma

The hyperimmunoglobulin E recurrent-infection (Job) syndrome (HIE) is a congenital disorder characterized by high serum IgE, chronic eczematoid dermatitis, and recurrent infections. We examined the effect of interferon gamma (IFN-gamma) on excessive IgE production in HIE patients. Spontaneous in vitro production of IgE by peripheral blood mononuclear cells from HIE patients was elevated compared to normal individuals and correlated with serum IgE. In 9 of 13 patients, IgE production by peripheral blood mononuclear cells was inhibited by 50% by IFN-gamma at 100-1000 units/ml, whereas inhibition by IFN-gamma at 10(4) units/ml ranged from 67 to 93% for these 9 patients. IFN-gamma also inhibited IgG1, IgG3, and IgG4 production by B lymphocytes without inhibiting IgG2 production. IFN-gamma was administered subcutaneously to 5 HIE patients. After 2 weeks of treatment with IFN-gamma (0.05 mg/m2) at three doses per week given on alternate days, peripheral blood mononuclear cells from all 5 HIE patients decreased spontaneous in vitro IgE production (27-62% decrease) with no change in IgG and IgM. One patient had a 58% decrease in serum IgE and another patient had a 50% decrease in serum IgE after the IFN-gamma was increased to 0.1 mg/m2 for three doses per week for a month. In both patients, serum IgE returned to pre-IFN-gamma-challenge levels 1-3 months after completion of treatment, and in vivo IFN-gamma did not affect serum IgG and IgM, although serum IgG4 decreased with changes in serum IgE. Our studies demonstrate that IFN-gamma can regulate production of IgE and some IgG subclasses in humans.

Human IgE-binding factors

The production of IgE antibodies is known to be regulated by isotype-specific mechanisms that are not antigen specific. During the last decade several studies have indicated that soluble factors with affinity for IgE (IgE-binding factors, IgE-BFs) may exert such a role by interacting with IgE-bearing B lymphocytes. In the human, some of these IgE-BFs appear to be identical to soluble CD23, a B-cell surface marker thought to be involved in the control of B-cell proliferation or differentiation. In this article, Guy Delespesse and colleagues summarize several new findings regarding the cellular origin, structure and function of IgE-BFs/sCD23.

Interferon and (2'-5')oligoadenylate enhance the expression of low affinity receptors for IgE (Fc epsilon R2/CD23) on the human monoblast cell line U937

The regulation of low affinity IgE receptor (Fc epsilon R2/CD23) expression on the human monoblast cell line U937 was examined by an anti-Fc epsilon R2/CD23 monoclonal antibody (H107) and the cDNA probe for Fc epsilon R2/CD23. Alpha interferon (IFN-alpha) and its intracellular mediator, (2'-5')oligoadenylate (2, 5-A), induced Fc epsilon R2/CD23 expression on U937 with no significant increase of the Fc epsilon R2/CD23 mRNA. PMA and IFN-gamma increased both surface Fc epsilon R2/CD23 expression and the Fc epsilon R2/CD23 mRNA levels. IFN-alpha effectively induced 2, 5-A synthetase activity in U937 cells, whereas IFN-gamma induced little. The results suggest that the mechanisms of enhancement of Fc epsilon R2/CD23 expression on U937 cells by IFN-alpha and IFN-gamma are different and that 2, 5-A may play an important role in the Fc epsilon R2/CD23 expression on U937 cells induced by IFN-alpha.

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

We have followed the pathway of the IgE-committed B lymphocyte from fresh, unstimulated peripheral blood, through EBV activation, transformation, and eventual cloning. Using cell sorting in conjunction with limiting dilution culture systems, we found that: (a) cells that are selected in the cell sorter and secrete IgE in culture are sIgM+/sIgD+. They secrete all three isotypes after EBV activation and continue to do so stably in culture; (b) individual IgE+ cells in culture coproduce IgM, IgD, and IgE and cytoplasmic Ig of each isotype can be detected in single cells; (c) no rearrangement was observed of VDJ to epsilon in any of six lines tested. DNA between the rearranged VDJ-mu and -epsilon appears to be overall intact, including a region 10.5 kb upstream and 18 kb downstream of the 2-kb epsilon coding region and; (d) mRNA of mu and epsilon species is of normal and comparable size. In contrast to IgG- and IgA-producing clones, multiple isotype expression appears to be both frequent and stable in cells committed to IgE production. We propose that IgE-committed cells represent a unique B cell sublineage whose differentiation pathway may be more strictly regulated than that of other isotypes with regard to the signals required for classical, deletional switch recombination that has been observed in rare IgE-producing myeloma cell lines.

Expression and functional role of CD23 on T cells

We have found that approximately 10%-15% of tonsil, but not peripheral blood, T cells express the CD23 antigen following activation with 12-O-tetradecanoylphorbol 13-acetate (TPA), phytohemagglutinin (PHA) or recombinant interleukin 4. The proliferative response of tonsil T cells is significantly increased when CD23 monoclonal antibodies (mAb) are present in the cultures. In contrast, no such proliferative augmentation is seen when peripheral blood T cells are cultured in this way. Supernatant (SN) of Epstein-Barr Virus-transformed B lymphoblastoid cell lines (EBVLCL), is found to have a similar co-stimulatory effect on the proliferation of tonsil T cells to that seen with CD23 mAb. This effect is greatly diminished by preclearing SN with CD23 mAb. Similarly, SN from a CD23+ L cell transfectant augments the proliferative response of tonsil T cells to both TPA and PHA. The CD23 molecule expressed by TPA-driven T cell blasts appears identical in size to the 45-kDa glycoprotein present on EBVLCL and activated B cells. In contrast, a 42-kDa molecule is observed when CD23 is precipitated from T cells activated with PHA. The results presented here demonstrate that CD23 is expressed on activated tonsil, but not peripheral blood T cells and plays a role, via the binding of CD23 mAb and CD23+ material, present in EBVLCL and CD23+ transfectant SN, in the regulation of T cell proliferation in response to mitogens such as PHA and TPA.

Formation of IgE-binding factors by T cells of patients infected with human immunodeficiency virus type 1

Peripheral blood mononuclear cells of 10 out of 26 patients with human immunodeficiency virus type 1 (HIV-1) released IgE-binding factors, as determined by two independent assays. The formation of the factors by the mononuclear cells was enhanced by incubation of the cells with homologous IgE. In the presence of IgE, peripheral blood mononuclear cells from 15 of the 26 patients formed a detectable amount of IgE-binding factors, whereas those of normal individuals of allergic rhinitis patients failed to do so. The major source of IgE-binding factors was the T cells of the HIV-1-infected patients. The CD8+ T cells from a HIV-1-infected patient formed IgE-binding factors upon incubation with IgE, and type II receptors for Fc epsilon were detected on both CD4+ T cells and CD8+ T cells in one of five patients studied. It was also found that culture supernatants of mononuclear cells from HIV-1-infected patients released soluble factors that induce normal human T cells to form IgE-binding factors. The results suggest that lymphocytes of some HIV-1-infected patients are activated to produce lymphokines regulating formation of IgE-binding factors.

Functional interaction between B cell subpopulations defined by CD23 expression

Using the CD23 monoclonal antibody (mAb) MHM6 and sheep anti-mouse Ig bound to magnetic beads we have obtained highly purified populations of MHM6+ and MHM6- tonsil B cells. We have found that the increased expression of MHM6 reactivity seen on B cells after activation results from up-regulation of antigen on cells already weakly positive and not from expression of new antigen on the previously negative population. The strong proliferative responses of MHM6+ cells seen in the presence of anti-IgM (alpha mu) and interleukin 4 (IL4) or the CDw40 mAb G28-5, and with Staphylococcus aureus Cowan I (SAC), and to a lesser extent with the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA), resemble that seen among unfractionated B cells. In contrast, the MHM6- population cultured alone responds only weakly to alpha mu + G28-5 or SAC and exhibits virtually no response to alpha mu + IL4 or TPA. With all these mitogenic stimuli, tritiated thymidine uptake by the MHM6- population is augmented three- to sixfold by the addition of mitomycin C (MC)-treated MHM6+ cells. Pretreatment of cells with anti-leukocyte functional antigen 1 mAb has little effect on the subsequent proliferation of the MHM6- population but shows cell contact to be critical for the proliferation of MHM6+ cells. Such pretreatment has revealed that the functional interaction observed between MHM6+ and MHM6- cells is dependent on both cell contact and the presence of an MHM6+ cell-derived soluble component. We have found that addition of soluble CD23, purified from Epstein-Barr virus-transformed lymphoblastoid cell line supernatant, increases the proliferative response of MHM6- tonsil B cells to mitogenic stimuli in the presence of inactivated MHM6+ cells but has no effect on proliferation when MHM6+ cells are absent. By way of contrast to normal B lymphocytes, we have examined functional responses of prolymphocytic leukemia (PLL) B cells. Although these cells, when freshly isolated, show comparable levels of CD23 expression to normal B cells, this expression is not increased upon activation. In addition, in contrast to normal B cells, the PLL MHM6- population cultured alone shows a strong proliferative response to various mitogenic stimuli, comparable to that of MHM6+ or unfractionated cells, and this response is not augmented by the addition of MC-treated MHM6+ cells. Thus, a novel functional interaction is described between normal, but not leukemic, B cell populations defined by their expression of CD23.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulatory effects of human IgE-binding factors in the IgE synthesis by human and rat lymphocytes

We have previously established human T cell hybridomas which produce IgE-binding factors. Incubation of one of the T cell hybridomas, 166A2, with human IgE dimer in the presence of 1 microgram/ml bradykinin resulted in the formation of IgE-binding factors having affinity for lentil lectin. The factors selectively enhanced both IgE-forming cell responses of rat mesenteric lymph node (MLN) cells and spontaneous IgE synthesis by human peripheral blood B cells of atopic patients, without affecting the IgG response. The same factors that enhanced IgE synthesis of B cells from atopic patients also enhanced IgE synthesis induced under bystander conditions by activated alloreactive T cells. Fractionation of the affinity-purified IgE-binding factors by gel filtration revealed three molecular mass species, i.e., 60 kDa, 30 kDa and 15 kDa. The 60-kDa and 15-kDa IgE-binding factors selectively enhanced both the spontaneous IgE synthesis by B cells of atopic patients and IgE response of rat MLN cells. In contrast, the 30-kDa IgE-binding factors had only marginal enhancing effects on the IgE synthesis by both human B cells and rat MLN cells. When the 166A2 hybridoma cells were incubated with IgE dimer in the presence of glycosylation-inhibiting factor (GIF), essentially all IgE-binding factors formed by the cells had affinity for peanut agglutinin (PNA) but for neither lentil lectin nor concanavalin A. All of the 60-kDa, 30-kDa and 15-kDa species, having affinity for PNA, selectively suppressed the potentiating factor-enhanced IgE response of rat MLN cells. The factors also suppressed the IgE synthesis of human B cells from atopic patients when the synthesis was enhanced by IgE-potentiating factor. The results indicate that human IgE-binding factors regulate IgE synthesis by both human and rat lymphocytes.

IgE response and its regulation in allergic diseases

The distinguishing feature of the allergic person is his or her elevation of serum IgE. This propensity to develop a sustained IgE response is determined genetically. The biologic effects of IgE are mediated via Fc receptors (Fc epsilon R) present on mast cells and basophils (Fc epsilon R type 1) and subpopulations of monocytes, macrophages, eosinophils, and platelets (Fc epsilon R type 2). Interaction of allergen with IgE on these cells results in receptor "bridging" and the release of histamine and other inflammatory mediators. Fc epsilon R type 2 on lymphocytes and monocytes are upregulated in atopic disease and may play a role in the allergic inflammatory reaction. The activation of B cells to synthesize IgE requires several stages (see Fig. 2). T cells play an important role in the regulation of IgE synthesis. In vitro activation of resting B cells to synthesize IgE requires direct cellular interaction with T cells or the presence of IL4 for activation. The latter effect is inhibited by alpha-interferon. Preactivated B cells are influenced in an isotype-specific manner by T-cell-derived IgE binding factors (IgE-BF), which may act as IgE-potentiating or IgE-suppressive factors, depending on their degree of glycosylation. The regulation of IgE synthesis is an important area of investigation. It provides us with an understanding of the basis of the human allergic response and ultimately may provide the basis for novel strategies in the treatment of allergic diseases.

IgE production by normal human lymphocytes is induced by interleukin 4 and suppressed by interferons gamma and alpha and prostaglandin E2

The effect of human recombinant interleukin 4 (IL-4) on antibody production by normal peripheral blood mononuclear cells enriched for B cells was investigated. IL-4 preferentially induced IgE synthesis in vitro. In addition, a low induction of IgG production was observed, whereas IL-4 had no effect on IgA and IgM synthesis. The IL-4-induced IgE production by B cells required T cells and monocytes but was specifically inhibited by an anti-IL-4 antiserum indicating that, although IL-4 acts indirectly, it is responsible for the induction of IgE synthesis. IL-4-induced IgE production was blocked in a dose-dependent way by interferon gamma (IFN-gamma), interferon alpha (IFN-alpha), and prostaglandin E2. IFN-gamma also inhibited IL-4-induced IgG production. These inhibitory effects of IFN-gamma and IFN-alpha on IgE production cannot be attributed to toxic effects since IFN-alpha induced IgM production in the presence of IL-4, whereas IFN-gamma was ineffective in inhibiting IgG production induced by IL-2. IFN-gamma, IFN-alpha, and prostaglandin E2 also inhibited IL-4-induced expression of the low-affinity receptor for the Fc portion of IgE (CD23) on B cells, indicating that there is an association between CD23 expression and IL-4-induced IgE production. This theory was supported by the finding that IL-4-induced IgE production was inhibited by F(ab')2 fragments of an anti-CD23 monoclonal antibody.

Subset of natural killer cells is induced by immune complexes to display Fc receptors for IgE and IgA and demonstrates isotype regulatory function

Expression of Fc receptors for IgE (FcER) or IgA (FcAR) on purified natural killer (NK) cells was investigated. No FcER+ and a few FcAR+ NK cells were detectable on freshly separated NK (NKH-1+) cells from normal donors. Incubation of NK cells with IgE-anti-IgE immune complexes or IgA-anti-IgA immune complexes induced up to 10 and 20% FcER+ or FcAR+ cells, respectively. These FcR were induced on CD3- but not on CD3+ NKH-1+ cells. In contrast, NK cells from patients with various dysgammaglobulinemias could not be induced to express FcER or FcAR corresponding to their abnormal circulating IgE and/or IgA levels. Enriched FcER+ or FcAR+ induced NK cell supernatants from normals enhanced IgE or IgA synthesis from Ig secreting B cell lines in an isotype-specific fashion without increasing proliferation. Thus NK cells, after interaction with specific Ig isotypes in complexes, express FcR and produce differentiation factors for that isotype.

IgE-binding factors: their possible role in the regulation of IgE synthesis

B cell-derived IgE-BFs (sCD23) are cleavage fragments of surface Fc epsilon R II. Their production is increased by IL4 and suppressed by IFN-gamma and IFN-alpha. IgE-BFs are likely to play a role in the regulation of human IgE synthesis as shown by the following two observations: i. MabER specifically blocks both the spontaneous IgE by synthesis by atopic B cells and the IL4-induced IgE synthesis by normal lymphocytes, ii. purified IgE-BFs enhance the IL4-induced and the spontaneous IgE synthesis. Soluble fragments of Fc epsilon R II also display BCGF-like activity although the exact structure of these fragments is not yet identified. The cDNA coding for Fc epsilon R II has been cloned and functionally expressed. The predicted amino acid sequence reveals no homology between human and rodent IgE-BFs indicating that they are unrelated molecules.

Human recombinant interleukin 4 induces normal B cells to produce soluble CD23/IgE-binding factor analogous to that spontaneously released by lymphoblastoid B cell lines

Surface-labeled Epstein-Barr virus (EBV)-transformed lymphoblastoid RPMI 8866 cells release in their supernatant a radiolabeled 25-kDa polypeptide which reacts with the Fc epsilon RL/CD23-specific monoclonal antibody (mAb) 25 and which binds to IgE but not IgG (IgE BF/sCD23). IgE BF/sCD23 had an isoelectric point of 4.5-5.0. The reactivity of mAb 25 with IgE BF/sCD23 allowed us to set up a radioimmunoassay for detection of IgE BF/sCD23 in cell culture supernatants. Supernatants from Fc epsilon RL/CD23+ cell lines were found to contain IgE BF/sCD23. Addition of human recombinant interleukin 4 (IL 4) to normal human B cells cultures induced the production of IgE BF/sCD23. Activation of B cells with anti-IgM antibody coupled to beads enhanced the IL 4-induced production of IgE BF/sCD23 when compared to nonactivated B cells. This correlates with the finding that anti-IgM antibody-activated B cells cultured with IL 4 express more Fc epsilon RL/CD23 than B cells cultured with IL 4 alone. The biochemical characteristics of radiolabeled IgE BF/sCD23 immunoprecipitated by mAb 25 from the supernatants of normal B cells cultured with IL 4 were identical to those of the IgE BF/sCD23 isolated from EBV-transformed cell line supernatants. Addition of interferon-gamma to B cells cultured with IL 4 strongly decreased the level of IgE BF/sCD23 in culture supernatants correlating with the observed decrease of Fc epsilon RL/CD23 on B cell surface. These data demonstrate that normal human B cells cultured in the presence of IL 4 produce an IgE-binding factor (sCD23) biochemically and antigenically equivalent to that spontaneously produced by EBV-transformed lymphoblastoid cell lines.

T cell-derived B cell growth and differentiation factors

In the last few years it has been demonstrated that clonal expansion of B lymphocytes and their differentiation into antibody-producing cells are regulated by a complex series of soluble products released by T cells. The application of cloning and recombinant DNA techniques has made it possible to obtain most of these molecules in a purified form and, therefore, to study in more detail their functional properties. To date, three distinct T cell-derived B cell growth factors (BCGFs) and/or B cell differentiation factors (BCDFs), i.e., IL-2, IL-4 and IL-5, have been reported for mouse B cells. Likewise, at least five distinct molecules showing BCGF and/or BCDF activity (IL-2, IFN-gamma, IL-4, the 12 kD-BCGF and BSF-2) for human B cells have been identified. Human T cell-derived lymphokines active on B cells are functionally similar but not identical to murine lymphokines. Most T cell-derived lymphokines can exert their activity on the same B cells in different stages of activation and evoke different responses. In addition, some of them are not specific for B cells, but act as competence factors or competence cofactors for different hemopoietic cell lines. Finally, convincing evidence is accumulating to suggest that both activated and resting B cells may have receptors for BCGFs and BCDFs. This makes it clear why although the goal of a directed immune response is to generate antigen-specific antibodies, a large part of this response can actually be polyclonal and nonspecific.

Modulation of ongoing human immunoglobulin synthesis by natural killer cells

Freshly separated human NK cells (NKH-1+) inhibited IgE synthesis from IgE myeloma U266/AF-10 as much as 70% whereas they enhanced IgG and IgA synthesis 200 and 500% from the lymphoblastoid cell lines GM-1500 and GM-1056, respectively. The inhibition of IgE synthesis by NK cells was due to a direct cytolytic effect on AF-10. This could be reversed using K562 cells in a cold target competition assay. NK cells also inhibited spontaneous IgE as well as IgG and IgA synthesis from B cells of highly atopic donors. On the other hand the enhancement of Ig secretion by NKH-1+ cells was shown to be mediated by soluble factors released from NK cells. Furthermore when NK cells were preincubated with immune complexes (IgE-IC) constructed of human IgE and mouse IgG1 monoclonal anti-human IgE, inhibition of IgE synthesis was reversed, and in some cases actual enhancement of IgE synthesis was observed, while enhancement of IgG and IgA synthesis was not affected. In contrast to NK cells, T cells depleted of NK cells (T-NK), when activated by IgE-IC, suppressed IgE synthesis in an isotype specific fashion. Thus, NK and T-cell modulation of ongoing Ig synthesis involve distinct mechanisms.

Modulation of IgE synthesis by IgE-binding factors released by T cells of asthmatic patients with elevated serum IgE

The culture supernatants of unstimulated T cells (TCS) from asthmatic patients with elevated serum IgE were tested for IgE-binding factors (IgE-BFs) displaying the IgE-potentiating activity. The IgE-BFs were detected by their ability to inhibit the rosetting of RPMI 8866 cells with ox erythrocytes coupled with mouse monoclonal antibody (E-Mab) specific to Fc receptors for IgE (Fc epsilon R). TCS showing the rosette-inhibiting activity significantly enhanced the spontaneous IgE synthesis by B cells of allergic individuals. Interestingly, rosette-inhibiting factors could be removed by absorption with IgE-Sepharose from which they were subsequently eluated with acid buffer, indicating that the rosette inhibition was indeed mediated by IgE-BFs. In addition, such IgE-BFs had affinity for concanavalin A and lost their IgE-potentiating activity after treatment with trypsin and neuraminidase. In contrast, T cells treated with tunicamycin released IgE-suppressing factors capable of inhibiting the IgE-potentiating activity of TCS derived from untreated T cells. On the other hand, the culture supernatants from subpopulations depleted of Fc epsilon R+ T cells but not of Fc gamma R+ T cells contained neither rosette-inhibiting factors nor IgE-potentiating factors, suggesting that IgE-BFs were released by in vivo pre-activated Fc epsilon R+ T cells. With regard to circulating Fc epsilon R+ T cells determined by E-Mab, they were significantly higher in asthmatic patients with elevated serum IgE (0.77 +/- 0.15%) than in normal subjects (0.17 +/- 0.07%) in spite of a very small proportion of T cells bearing Fc epsilon R.

Enhancement of IgE synthesis and histamine release by T cell factors derived from atopic patients with bronchial asthma

Culture supernatants of unstimulated T cells (TCS) derived from normal donors or from atopic patients with bronchial asthma were tested for their ability to regulate the spontaneous IgE synthesis by B cells of normal and atopic subjects. The same TCS were also tested for their influence on the histamine release from leukocytes of house dust mites-sensitive patients. Addition of TCS to B cell cultures from allergic donors induced a dose-dependent increase of the spontaneous IgE production without affecting the synthesis of IgG, IgM, and IgA. The potentiating activity of TCS was observed only in B cell cultures spontaneously producing IgE; TCS were still active on irradiated B cells. The maximal IgE-enhancing activity was observed when TCS were added at the onset of B cell cultures. The supernatants of T cells lysed at day 0 did not contain IgE-potentiating factors. The antigen-induced but not the spontaneous histamine release from leukocytes of house dust mite-sensitive patients was enhanced by pretreatment with TCS from allergic donors. The enhancing activities of TCS on IgE synthesis and on histamine release could be removed by absorption with IgE-Sepharose and subsequently recovered by elution with glycine buffer. The results indicate that T cells of patients with asthma spontaneously release IgE-binding factors capable of increasing both the spontaneous IgE synthesis by B cells and the antigen-induced histamine release.

The presence of IgE on macrophages and dendritic cells infiltrating into the skin lesion of atopic dermatitis

Monoclonal antibodies reactive with human IgE were used to investigate the presence of surface IgE in situ on mononuclear cells infiltrating into the skin lesion of atopic dermatitis (A.D.) by application of the immunoperoxidase technique to tissue sections for light and electron microscopic examination. A substantial proportion of infiltrating macrophages but not of lymphocytes were found to bear IgE on their cell surfaces. These observations raise the possibility that IgE may contribute to the skin inflammation associated with A.D. via non-mast-cell-mediated immune mechanisms. We hypothesize that allergens introduced into the skin lesion of A.D. are potentially capable of interacting not only with IgE-bearing mast cells but also with IgE-bearing macrophages and dendritic cells to cause the release of inflammatory mediators.

Potentiating and suppressive IgE-binding factors are expressed by a single cloned gene

We have investigated expression of an IgE-binding factor (IgE-BF) cDNA in both COS-7 monkey kidney cells and Chinese hamster ovary cells. Transient expression of the IgE-BF clone in either cell type yielded IgE-BF, which potentiated an in vitro IgE response and had an affinity for lentil lectin. In contrast, when the transient expression experiments were carried out in the presence of tunicamycin, the factors no longer bound to lentil lectin. Moreover, IgE-BF expressed under these conditions suppressed an in vitro IgE response. IgE-BF lacking affinity for lentil lectin and suppressing the IgE response also resulted from transient expression of the IgE-BF gene in the presence of glycosylation inhibiting factor, a phospholipase inhibitory protein. Thus, IgE-BF that either potentiate or suppress the IgE response can be expressed from a single cloned gene; the difference in biological activities appears to be determined principally by the type of glycosylation of the common polypeptide chain. Previous work showed that IgE-BF bears an antigenic determinant recognized by the anti-Ia monoclonal antibody OX3. IgE-BF produced in the presence of tunicamycin, and IgE-BF expressed from a mutant cDNA lacking one of two carbohydrate-attachment sites, lacked the OX3 determinant. Thus, the OX3 determinant on IgE-BF appears to be associated with a site of N-linked glycosylation.

The expression of IgE Fc receptors on lymphocytes of allergic patients

Peripheral blood lymphocytes from nonatopic subjects and atopic patients were analyzed for cells expressing Fc receptors for IgE (Fc epsilon R). Nonatopic humans and atopic patients in remission had approximately 1 percent of Fc epsilon R+ peripheral blood lymphocytes. Usually greater than 99 percent of these cells were mIgM+/mIgD+ B cells. However, in approximately 10 percent of nonatopic and atopic subjects a transient increase of Fc epsilon R+ lymphocytes to 3-6 percent was observed in the absence of any disease manifestations and measurable changes in the serum IgE level. At times of increased numbers of peripheral blood Fc epsilon R+ lymphocytes, up to 1 percent Fc epsilon R+ positive cells were detected in isolated T cell preparations. The Fc epsilon R+ T cells reacted with the monoclonal antibody Lyt 3 to the sheep erythrocyte receptor of human T cells but not the anti-T cell antibody OKT3, and fractions also with the monoclonal antibodies OKT8 (cytotoxic and suppressor T cells) and OKM1, which binds to an antigen present on monocytes and a subpopulation of T cells and large granular lymphocytes. No OKT4+ (helper T cells) Fc epsilon R+ cells were detected. The reactivity with monoclonal antibodies to T cell subsets of the Fc epsilon R+ T cells paralleled the reactivity of the IgG Fc receptor positive T cells. In contrast to patients with allergic rhinitis and asthma, patients with severe atopic dermatitis or the Hyper IgE Syndrome always had significantly elevated percentage of Fc epsilon R+ lymphocytes (4-10 percent), which were almost entirely B cells since less than 0.1 percent Fc epsilon R+ T cells were detected in these patients. Atopic dermatitis patients receiving systemic corticosteroid treatment had only 0.2 percent Fc epsilon R+ lymphocytes which was significantly less than the 1 percent of the nonatopic control donors. Attempts to define the function of Fc epsilon R on human B and T lymphocytes have been unsuccessful thus far; however, the increase of Fc epsilon R+ cells associated with atopic disease in man and parasitic infections in rats and mice suggest that Fc epsilon R+ lymphocyte may be involved in the IgE isotype regulation.

Regulation of the human IgE antibody response

The frequent association of elevated serum IgE in patients with T cell immunodeficiencies suggest a role for T cells in the regulation of the human IgE antibody response. Unlike the situation with other isotypes the polyclonal B cells activators, pokeweed mitogen and Epstein Barr virus, do not routinely induce IgE synthesis in normal B cells. However, B cells from normal donors will synthesize immunoglobulins of all isotypes (including IgE) when cultured with T cell clones that recognize determinants expressed on the B cells (cognate stimulation). T cells with Fc receptors for IgE can be isolated from patients with hyper IgE syndrome and maintained as long term continuous T cell lines. These cells secrete IgE binding factors which enhance IgE synthesis but not IgG synthesis by preactivated IgE bearing B cells from allergic subjects but not resting B cells from normal donors. IgE binding factors isolated from sera of normal donors selectively suppress IgE synthesis. In contrast, IgE binding factors isolated from sera of patients with hyper IgE syndrome contain IgE potentiating activity as well as IgE suppressor activity. These results suggest that IgE synthesis in man is activated by T cells and isotype specific secretion of this immunoglobulin is modulated by IgE binding factors.

Fc epsilon receptor, a specific differentiation marker transiently expressed on mature B cells before isotype switching

The expression of Fc epsilon R on human lymphocytes was studied with the anti-Fc epsilon R mAbs. Fc epsilon R was expressed on most mu+,delta+ circulating B cells, whereas T cells did not express Fc epsilon R even in patients with hyper-IgE syndrome. B cells with gamma, alpha, or epsilon phenotype did not express Fc epsilon R, moreover its expression could not be induced, suggesting that the Fc epsilon R expression was correlated with isotype switching. mu+delta+ B cells in bone marrow did not express Fc epsilon R, but PHA-sup (supernatant from PHA-stimulated cell cultures) could induce its expression, and the addition of IgE augmented this induction. Recombinant IL-2, IL-1, IFN-gamma or -beta, or purified B cell differentiation factor (BSF-2 B cell-stimulatory factor 2) could not induce Fc epsilon R expression in bone marrow B cells. IFN-gamma inhibited the Fc epsilon R expression induced by PHA-sup, suggesting that the human counterpart of BSF-1 may be responsible for Fc epsilon R expression in bone marrow B cells. B cells from patients with common variable immunodeficiency and ataxia telangiectasia did not express Fc epsilon R, but PHA-sup could induce its expression, indicating that circulating B cells of these patients are at a differentiation stage similar to B cells in bone marrow. The study showed that Fc epsilon R is a B cell-specific differentiation marker, the expression of which is restricted to a defined stage of B cell differentiation.

IgE receptors on human lymphocytes. III. Expression of IgE receptors on mitogen-stimulated human mononuclear cells

Human peripheral blood mononuclear cells (PBMC) were tested for the expression of Fc epsilon-receptor (Fc epsilon R) after stimulation with various mitogens in the absence of IgE. Fc epsilon R were found on virtually all the cells from 19 Epstein-Barr virus-transformed B cell lines including those derived from cord blood, from one agamma-globulinemic patient and VDS-0 pre-B cells. Hence, the data clearly indicate that Fc epsilon R may be expressed on very immature B cells. PBMC cultures stimulated with either pokeweed mitogen (PWM), phytohemagglutinin (PHA) or concanavalin A displayed an early increase of their content in Fc epsilon R-bearing cells followed by a decrease to levels below those of control cultures. After fractionation of the PWM-stimulated cultures into T and B cell-enriched preparations, most of the Fc epsilon R+ cells were in the in the B cell fractions and the same low levels of Fc epsilon R+ cells were found in the T cell fractions isolated from the PWM-stimulated and from the control cultures. Double-labeling experiments, employing biotinylated F(ab')2 monoclonal antibody to FcR and either fluorescein isothiocyanate-conjugated B1 or Mo2 monoclonal antibodies, indicated that PWM mainly exerted its effect on B cells and on monocytes. This effect was T cell dependent and it was mediated by soluble factors of T cell origin. At the peak of the PHA or concanavalin A response, most of the Fc epsilon R-bearing cells were found in the B cell fraction but the T cells isolated from mitogen-stimulated cultures contained significant more Fc epsilon R+ cells than those from the control cultures, suggesting that T cell mitogens had increased the expression of Fc epsilon R on some T cells. This view was supported by the finding of a higher proportion of Fc epsilon R+ cells in PHA-stimulated than in control cultures of highly purified T cells with a maximum response at the end of the culture period. Double-labeling experiments at the peak (day 2) of the peripheral blood mononuclear cell response indicated that the expression of Fc epsilon R was increased on B cells (B1+) and on monocytes (Mo2+). By using the same approach at the peak of the T cell response (day 7), it was found that T cells isolated from PHA-stimulated cultures expressed more Fc epsilon R than those isolated from control cultures.(ABSTRACT TRUNCATED AT 400 WORDS)

Presence of IgE suppressor factors in human colostrum

In spite of intensive investigations, the ability of breast feeding to delay and to attenuate atopic diseases in children remains debatable. This study documents a mechanism whereby breast feeding might interfere with the synthesis of IgE by breast-fed infants. Indeed, we show that colostrum contains IgE-binding factors (IgE-BF) capable of suppressing the in vitro synthesis of human IgE. Colostrum obtained from 15 donors was successively depleted of lipids and casein, filtered through Amicon XM50 membrane (mol. mass cut-off 50 kDa) and lyophilized. IgE-BF was demonstrated in such preparations by two different approaches, i.e. a classical rosette inhibition assay and Western blot analysis. In the first instance, lyophilized preparations of colostrum inhibited the binding of IgE-coated bovine erythrocytes to IgE recovered on the surface of RPMI 8866 lymphoblastoid cells. The rosette-inhibiting activity could be absorbed on IgE- but not on IgG-Sepharose 4B and it could be recovered in the eluate of IgE-Sepharose 4B. The molecular mass of IgE-BF was comprised between 10 to 20 kDa as estimated by gel filtration through a calibrated Sephadex G-75 column. After fractionation on 12% sodium dodecyl sulfate-polyacrylamide gel electrophoresis and transfer to nitrocellulose membrane, colostrum displayed one band of 14 kDa and reacted with radiolabeled IgE but not with IgG nor IgM. This 14-kDa band could be removed by absorbing colostrum with IgE- but not with IgG-Sepharose 4B. Most importantly, the colostrum IgE-BF suppressed the spontaneous in vitro synthesis of IgE by B lymphocytes derived from allergic donors without altering the production of IgM.

Characterization of human T cell-derived IgE-potentiating factor

We have previously shown that Fc epsilon receptor-positive (Fc epsilon R+) T cell lines from patients with the hyper IgE syndrome secrete IgE-binding factors which selectively enhance IgE but not IgG synthesis in cultures of B cells obtained from patients with allergic rhinitis but not from nonatopic subject. In the present study we have tested the effect of supernatants from Fc epsilon R+ T cell lines on a large panel of B cells from atopic patients (n = 20). We found that IgE synthesis was selectively enhanced only in B cell cultures in which there was ongoing spontaneous synthesis of IgE. The target of IgE-potentiating factor(s) was a large low-density B cell present in the circulation of responding atopic donors. In addition, we further characterized IgE-potentiating factors derived from Fc epsilon R+ T cell lines. The factor(s) fractionated into 2 peaks on Sephadex G-75 with approximate molecular masses of 15,000 and 60,000 kDa, and had affinity for lentil lectin but not for peanut agglutinin. Release of IgE-potentiating factor(s) was enhanced by the addition of exogenous human IgE to Fc epsilon R+ T cell cultures and was inhibited by tunicamycin, an inhibitor of N-glycosylation. These studies suggest a close homology between the physicochemical characteristics of human and rodent IgE-potentiating factors and the immune signals which modulate production of these IgE regulatory factors.

IgE receptors on human lymphocytes. II. Detection of cells bearing IgE receptors in unstimulated mononuclear cells by means of a monoclonal antibody

A monoclonal antibody (mAb) specific for lymphocyte IgE receptors (ER) was employed in a rosette assay for the detection of cells bearing IgE receptors (Fc epsilon R). The specificity of the assay was documented by inhibition studies with soluble immunoglobulins (Ig) and anti-Ig antibodies. Moreover, similar results were obtained by employing the F(ab')2 fragment of mAbER instead of intact molecule. Circulating mononuclear cells isolated from normal or allergic adults and from umbilical cord blood contained approximately 8% of Fc epsilon R-bearing cells with values ranging from 0.3 to 17%. Tonsillar lymphocytes contained about 30% of Fc epsilon R+ cells. After the removal of adherent cells, there was a small but significant reduction of the proportion of Fc epsilon R+ cells. When mononuclear cells were separated into T and B cell fractions by two-cycle rosetting with 2-aminoethylisothiouronium bromide hydrobromide-treated sheep red blood cells, most of the Fc epsilon R+ cells were in the B cell fraction; however, a small proportion of Fc epsilon R+ was also found in the enriched T cells and double-labeling experiments confirmed that these cells were indeed T lymphocytes. Fc epsilon R+ cells were purified by rosetting with mAbER-coated erythrocytes and their phenotype was compared to that of Fc epsilon R- cells; Fc epsilon R+ cells contained about 90% of B cells (B1+) together with a small proportion of OKT3+, Leu 7+ and Mo2+ cells. The bulk of T cells, macrophages and natural killer (NK) cells was found in the Fc epsilon R- cells which contained fewer B cells than the fraction of Fc epsilon R+ cells. These data thus indicated that the great majority of Fc epsilon R-bearing cells are B cells but that a small proportion of NK cells, macrophages and T lymphocytes also express Fc epsilon R. Upon incubation at 37 degrees C, B cells lost their Fc epsilon R and this phenomenon was selectively inhibited by IgE; however, purified T cells seemed to express more Fc epsilon R after overnight incubation at 37 degrees C and this was not influenced by IgE. It is finally shown that the expression of Fc epsilon R is cyclic and that Fc epsilon R-bearing B cells do not represent a functionally distinct subpopulation of B lymphocytes.

IgE receptors on human lymphocytes. I. Identification of the molecules binding to monoclonal anti-Fc epsilon receptor antibodies

The present study indicates that the surface molecules from Fc epsilon receptor-bearing human lymphoblastoid cells binding to monoclonal antibodies to Fc epsilon receptor (mAbER) are identical to those binding to IgE. mAbER identify three components in the Nonidet-P40 cell lysate of surface-iodinated RPMI 8866 cells with approximately 65-95 kDa, 45 kDa and 37 kDa as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions and autoradiography. The same pattern is observed under nonreducing conditions, except for the low mol. wt component which displays an apparent molecular mass 31 kDa. When the labeled and solubilized membranes are adsorbed on IgE-Sepharose the 45-kDa component is always found in the eluate, whereas the 65-95-kDa component is occasionally detected and the low mol. wt component is rarely found. The binding of these molecules to IgE-Sepharose is inhibited by soluble IgE, mAbER but not by an unrelated mAb; reciprocally, the binding to mAbER-Sepharose is prevented by mAbER and to some extent by IgE. To improve the stability of IgE-Fc epsilon R complexes, biotinylated IgE was cross-linked on surface iodinated intact cells, which were then solubilized and adsorbed on avidin-Sepharose. Under these conditions, it was clearly shown that IgE binds to the same three surface molecules as mAbER. The isoelectric point of the high mol. wt component ranged from 4.2 to 4.4 as compared to 5.1-5.2 for the 45-kDa and the 37-kDa components. The observation in the Western blot assay that both the 65-95-kDa and the 45-kDa molecules react with 9 different mAbER indicates that these molecules have a polypeptide sequence in common.

Induction of IgE synthesis in normal human B cells. Sequential requirements for activation by an alloreactive T cell clone and IgE-potentiating factors

Two human alloreactive T cell clones were established from a one-way mixed lymphocyte culture involving two nonatopic donors, and were assessed for their capacity to induce IgE synthesis by B cells obtained from the original stimulator. The two alloreactive T cell clones studied induced IgG but not IgE synthesis in normal B cells. However, one of the two clones, clone 2H6, induced IgE synthesis in the presence of supernatants from T cell lines derived from patients with the hyper-IgE syndrome (HIE), and enriched for T cells bearing receptors for IgE. These supernatants by themselves caused no IgE synthesis in nonatopic B cells. The potentiating factors in these supernatants were shown to bind to IgE. Time sequence experiments indicated that interaction of the B cells with the alloreactive clone 2H6 renders them responsive to the action of the IgE-potentiating factors. These results indicate that induction of IgE synthesis in normal B cells involves at least two sequential T cell derived signals. Furthermore, T cell clones are heterogenous in their capacity to provide these signals.