Superinduction of the murine B cell Fc epsilon RII by T helper cell clones. Role of IL-4

Th cell clones are known to induce an IL-4 dependent polyclonal IgE synthesis. Because IL-4 can induce the expression of the low affinity FcR for IgE (Fc epsilon RII) the ability of Th cell clones to induce Fc epsilon RII on purified splenic B cells was analyzed. It was found that a TH2 clone could cause a 50- to 100-fold superinduction of Fc epsilon RII after 2 days in culture; after 3 days, the Fc epsilon RII levels had almost returned to base line. The superinduction was inhibited by an anti-IL-4 antibody, 11B11, indicating its dependence on IL-4. A TH1 clone could cause a modest (four fold) induction of Fc epsilon RII, and this induction was not influenced by 11B11. A similar Fc epsilon RII induction was seen when using the supernatant from activated TH1 cells. The component(s) causing this relatively low level Fc epsilon RII induction is not known; a variety of known lymphokines were tested, and only IL-4 demonstrated any capacity for Fc epsilon RII induction on LPS-activated B cells. Addition of rIL-4 at concentrations of 400 U/ml or greater to the TH1 culture was sufficient to cause a Fc epsilon RII superinduction similar to that seen with the TH2 clone, while 40 U/ml was not. In order to determine a potential role for the Fc epsilon RII or its soluble fragment on the IgE synthesis mediated by TH2, a monoclonal anti-Fc epsilon RII, B3B4, was added to the culture. The addition of B3B4 did not have an influence on IgE levels in this system.     

Isolation, characterization, and expression of cDNA clones encoding the mouse Fc receptor for IgE (Fc epsilon RII)1

We have isolated cDNA clones encoding a mouse low affinity receptor for IgE (Fc epsilon RII) from a cDNA library of BALB/c splenic B cells activated with LPS and IL-4. The 2.2-kb cDNA clone encodes a 331 amino acid membrane glycoprotein that is homologous to human Fc epsilon RII (CD23) and a family of carbohydrate-binding proteins. COS7 cells transfected with the cDNA clones expressed a 45,000 m.w. protein that bound IgE and the anti-Fc epsilon RII mAb, B3B4. Fc epsilon RII mRNA was up-regulated in mouse B cells by culture with IL-4, but not in B cells cultured with IgE. Fc epsilon RII mRNA was detected in IgM+/IgD+ B cell lines, but not in pre-B cell lines or in B cell lines which have undergone differentiation to secrete Ig. The monocyte line P388D1, mast cell lines MC/9 and PT18, and peritoneal macrophages stimulated with IL-4 lacked detectable Fc epsilon RII mRNA, as did Thy-1.2+, CD4+, and CD8+ normal T cells and Thy-1.2+ T cells from Nippostrongylus brasiliensis-infected mice.     

IFN-alpha and IFN-gamma have different regulatory effects on IL-4-induced membrane expression of Fc epsilon RIIb and release of soluble Fc epsilon RIIb by human monocytes

We used highly purified human monocytes to study the regulation of cell surface and secretion of the low affinity FcR for IgE (Fc epsilon RIIb). IL-4 induces Fc epsilon RIIb expression and soluble Fc epsilon RIIb release in a dose-dependent manner. Significant levels of Fc epsilon RIIb expression were obtained after 12 h of incubation with IL-4 and maximal expression was observed between 24 to 48 h after which the expression declined. Surface expression was followed by secretion of soluble Fc epsilon RIIb which reached maximal levels after 3 to 4 days of incubation and which remained constant throughout 7 days of culture. Induction of Fc epsilon RIIb expression by IL-4 was completely blocked by anti-IL-4 antibodies. Furthermore, IL-1 alpha, IL-2, IL-5, granulocyte-macrophage-CSF, IFN-alpha, IFN-gamma, low m.w. BCGF and also LPS all failed to induce Fc epsilon RIIb expression, demonstrating the specificity of the induction. Fc epsilon RIIb membrane expression induced by IL-4 was reduced in the presence of IFN-gamma and IFN-alpha. Strong inhibition of IL-4-induced Fc epsilon RIIb expression was observed at IFN-alpha concentrations of 450 U/ml (80%), and 100 U/ml of IFN-gamma reduced IL-4-induced Fc epsilon RIIb expression by 70%. Interestingly, soluble Fc epsilon RIIb release was strongly inhibited by IFN-alpha. In contrast, IFN-gamma did not affect soluble Fc epsilon RIIb release, suggesting that reduced membrane expression of Fc epsilon RIIb observed in the presence of IFN-gamma does not reflect inhibition of Fc epsilon RIIb expression but may represent enhanced cleavage or reduced anchoring in the membrane of Fc epsilon RIIb. Finally, IL-5 that has been shown to enhance IL-4-induced Fc epsilon RII on B cells does not enhance significantly IL-4-induced Fc epsilon RIIb membrane expression or subsequent soluble Fc epsilon RIIb release by monocytes. Taken together these results show that IFN-alpha and IFN-gamma have different regulatory effects on IL-4-induced Fc epsilon RIIb membrane expression and soluble Fc epsilon RIIb release by human monocytes.     

Lack of Fc epsilon RII expression by murine B cells after in vivo immunization is directly associated with Ig secretion and not Ig isotype switching.

The "low affinity" Fc receptor for IgE (Fc epsilon RII) has been reported to be absent from normal murine and human B cells that express a membrane (m)Ig isotype other than mIgM or mIgD in vivo. This would suggest that Fc epsilon RII expression is specifically lost after in vivo Ig isotype switching. We demonstrate that during a murine immune response to the bacterium Brucella abortus, to goat anti-mouse IgD (G alpha M delta) antibody, or to infection with the nematode parasites Nippostrongylus brasilienis or Heligmosomoides polygyrus, Fc epsilon RII expression is low or absent on virtually all B cells secreting IgM, IgG1, IgG2a, and IgE. However, up to 50% of B cells that express mIgG1 after G alpha M delta injection continue to express Fc epsilon RII. These mIgG1 + Fc epsilon RII+ cells secrete little, if any, IgG1 when placed in vitro, in contrast to their mIgG1 + Fc epsilon RII- counterparts. The mIgG1 + Fc epsilon RII+ cells may be a transitional cell population, because they undergo substantial loss of Fc epsilon RII in culture, unlike mIgM+ Fc epsilon RII+ cells, which maintain constant levels of Fc epsilon RII throughout a comparable culture period. Thus, low or absent expression of Fc epsilon RII after immunization in vivo is directly associated with B cell differentiation to Ig production in the presence or absence of Ig isotype switching. However, all post-switched B cells may eventually lack Fc epsilon RII expression, independently of their differentiative state.     

Mechanisms of IgE homeostasis. Sequestration of IgE by murine type II IgE Fc receptor-bearing B cell hybridomas.

Among all classes of Ig, IgE exhibits the highest rate of fractional catabolism of which the site and mechanisms is not understood. We construct a panel of murine B cell hybridomas to investigate the catabolism of IgE; one of these hybridomas, 17A11, constitutively expresses high levels of type II IgE FcR (Fc epsilon RII, CD23) (Kd:1.77 nM; B max: 1.65 x 10(5], and is capable of clearing receptor-bound IgE. Receptor-mediated endocytosis of IgE ligand ensues after binding monomeric and DNP-BSA:IgE immune complexes, and the binding is inhibited by treating 17A11 with anti-CD23. IgE ligands are sequestered and are not susceptible to acid stripping from the cell surface. The internalized IgE ligands redistributed into acid hydrolase containing high density lysosomal vesicles and were degraded; metabolic inhibitors such as chloroquine and monensin that elevate intracellular pH of 17A11 also prevent entry of IgE ligand into lysosomes. These observations raise the possibility that normal Fc epsilon RII-bearing mature B cells in the circulation and lymphoid tissues may function in sequestration and catabolic turnover of IgE molecules through IgE or IL-4 up-regulated Fc epsilon RII uptake; B cell Fc epsilon RII may perform an important role in determining the short biological half-life of IgE molecules, and contributes to IgE homeostasis.     

B cell activator. Effects on B cell expression of CD23, proliferation, and antibody secretion.

The studies herein describe a B cell hybridoma-derived, low m.w. (less than 1000 Da), hydrophilic mediator denoted B cell activator (BCA). BCA stimulates B cell expression of IgE-specific FcR (Fc epsilon RII or CD23) in a manner similar to IL-4. However, BCA can be readily distinguished from IL-4 because it does not 1) enhance B cell Ia expression; 2) bind 11B11 anti-IL-4 mAb; or 3) elicit superinduction of Fc epsilon RII expression or IgE production in cultures of LPS-activated B cells. Moreover, BCA is considerably more mitogenic than IL-4 for LPS-activated B cells and, in contrast to IL-4, lacks mitogenicity for anti-mu-activated B cells. BCA can enhance IgG2b and IgG3 production by LPS-activated B cells, responses that are suppressed by IL-4. BCA alone did not stimulate IgE and IgG1 production by LPS-activated B cells, but exerted synergistic activity when combined with IL-4 in stimulating secretion of these antibody isotypes. Finally, secondary Ag-driven IgG1, IgE, and IgA antibody responses can be stimulated by BCA in vitro. Thus, BCA appears to be a novel mediator with broad B cell activation properties.     

The binding of IgE to murine Fc epsilon RII is calcium-dependent but not inhibited by carbohydrate

Despite extensive study, little is known about the functions of the moderate affinity IgE receptors (Fc epsilon RII) on B cells. Recent cDNA and genomic cloning studies have demonstrated that, in contrast to other FcR, Fc epsilon RII is not a member of the Ig gene superfamily. Moreover, it uniquely expresses a region that is highly homologous with a membrane-associated, calcium-dependent binding lectin, the asialoglycoprotein receptor. We now report that the interaction between IgE and the Fc epsilon RII of murine B cells and macrophages requires calcium. Furthermore, as might be expected of asialoglycoprotein lectins, this binding was pH-dependent and resulted in ligand internalization. However, although 125I-Fc epsilon RII bound in a calcium-dependent manner to monosaccharide-agarose beads, high concentrations of mono- and disaccharides did not inhibit the interaction between either 125I-IgE and intact B cells or 125I-Fc epsilon RII (from surface-labeled B cells) and IgE-Sepharose. These results suggest that although murine Fc epsilon RII is a lectin, it is not strictly dependent upon IgE oligosaccharides for its binding to IgE.     

Induction of Fc epsilon RII/CD23 on phytohemagglutinin-activated human peripheral blood T lymphocytes. I. Enhancement by IL-2 and IL-4.

Despite evidence for the expression of low affinity Fc receptor for IgE (Fc epsilon RII)/CD23 in T cell lines and pathologic T cells, Fc epsilon RII/CD23 in normal human T cells is still unclear. We studied the expression of Fc epsilon RII/CD23 on T cells in short-term culture of normal human PBMC stimulated with 15 micrograms/ml PHA. PHA stimulation also resulted in the release of soluble Fc epsilon RII/CD23 (IgE binding factor). Using two-dimensional flow cytometry, more than 10% of the Fc epsilon RII/CD23+ cells were found to co-express CD3 Ag. Both CD4+ and CD8+ T cells expressed Fc epsilon RII/CD23. The induction of Fc epsilon RII/CD23 on PHA-activated T cells was enhanced by IL-2 as well as IL-4. Both IL-2 and IL-4 also augmented PHA-induced production of soluble Fc epsilon RII/CD23. The enhanced expression of Fc epsilon RII/CD23 on T cells by both lymphokines was suppressed by rabbit anti-IL-4 antiserum, suggesting the involvement of an IL-4-dependent process even in the IL-2-dependent Fc epsilon RII/CD23 expression on T cells. The expression of mRNA for Fc epsilon RII/CD23 on PHA and IL-4-stimulated PBMC was examined by Northern blot analysis. Fc epsilon RII/CD23 mRNA was detected in RNA prepared from the T cell fraction depleted of B cells and macrophages (Fc epsilon RII+CD3+ = 6.2%, Fc epsilon RII+CD3- = 0.8%). The expression of the mRNA for Fc epsilon RII/CD23 on CD3+ T cells was also confirmed by in situ hybridization with Fc epsilon RII/CD23 cDNA combined with CD3 rosette formation at the single cell level.     

Recombinant soluble Fc epsilon receptor II (Fc epsilon RII/CD23) has IgE binding activity but no B cell growth promoting activity

We have undertaken the production of recombinant soluble Fc epsilon receptor II (Fc epsilon RII) as a secretory protein, but not as a cleavage product of membrane-bound receptor. Several plasmid constructs containing soluble receptor sequence were prepared. Only a chimeric gene containing the sequences encoding IL-6 signal peptide and the soluble moiety of Fc epsilon RII could be expressed in Xenopus laevis oocytes and CHO cells, resulting in the secretion of soluble Fc epsilon RII. The recombinant soluble Fc epsilon RII was also produced in the yeast expression system. The NH2-terminal sequence analysis of the chimeric gene product generated by oocytes demonstrated the correct cleavage of IL-6 leader sequence by a signal peptidase. Moreover, most of CHO cell and all of the yeast-derived recombinant molecules were products identical with the native B cell-derived soluble Fc epsilon RII. These recombinant products as well as the natural soluble receptor derived from a human B cell line could bind both human IgE and two different anti-Fc epsilon RII mAb and could competitively inhibit the binding of IgE to Fc epsilon RII-expressing cells. However, the recombinant soluble Fc epsilon RII and highly purified native molecules did not display any B cell growth-promoting activity.     

IL-4 induces co-expression of intrinsic membrane IgG1 and IgE by murine B cells stimulated with lipopolysaccharide

IL-4 promotes IgG1 and IgE secretion by murine B cells stimulated with bacterial LPS. We show that stimulation of unprimed resting splenic B cells with LPS and 10(4) U/ml rIL-4 results in the expression of membrane (m) IgG1 and mIgE on 40 to 50% and 15 to 25% of the total B cell population, respectively, on day 4 of culture. The possibility of a significant contribution to cell surface staining by cytophilic, secreted Ig isotypes was eliminated by either the addition of anti-Fc gamma or anti-Fc epsilon R mAb during the culture or by acid treatment before staining. A similar proportion of IgE-expressing B cells are also found, after stimulation with LPS and 10(4) U/ml IL-4, by cytoplasmic staining using fluorescence microscopy. Cell sorting analysis further indicates that B cell populations that express mIgG1 and mIgE secrete these respective Ig isotypes. In addition, such cells show striking diminution in IgM secretion compared to mIgG1- or mIgE- sorted B cells. Stimulation with LPS and IL-4 (10(4) U/ml) induces co-expression of mIgG1 and mIgE on LPS-stimulated B cells; up to 75% of mIgE+ B cells co-express mIgG1 and up to 19% of mIgG1+ B cells express mIgE. This striking co-expression of mIgG1 and mIgE is mirrored by the co-expression of mIgG1 with mIgG3 and mIgG2b by B cells stimulated with LPS and 200 U/ml IL-4. Cell sorting analysis demonstrates that the B cell population that co-expresses mIgG1 and mIgE secretes both IgG1 and IgE. However, "two-color" cytoplasmic staining fails to demonstrate any B cells that simultaneously secrete both IgG1 and IgE.     

Murine follicular dendritic cells and low affinity Fc receptors for IgE (Fc epsilon RII).

The present study was undertaken to determine whether mouse follicular dendritic cells (FDC) bear Fc epsilon RII (CD23) and whether IgE-immune complexes are retained by FDC. Mouse Fc epsilon RII was localized by both L and electron microscopy using the mAb B3B4. In lymph nodes of normal mice, Fc epsilon RII was low but detectable on FDC. By 14 days after Nippostrongylus brasiliensis infection, the level of Fc epsilon RII increased on B lymphocytes located in the cortex of draining mesenteric lymph nodes. However, the Fc epsilon RII level on FDC remained low. Although numerous IgE-producing plasma cells were seen at day 14, very little IgE was associated with FDC. By 26 days after infection, Fc epsilon RII was observed on FDC in increased levels and IgE binding was clearly associated with FDC. Unexpectedly, FDC of control mice immunized with albumin in CFA to elicit an IgG response showed intense labeling for Fc epsilon RII. In contrast, the B cells exhibited very little Fc epsilon RII. IgE immune complexes were observed in association with FDC in the CFA-immunized mice. When mice were given a hapten-specific monoclonal of the IgE isotype, hapten carrier complexes were trapped and retained on Fc epsilon RII-bearing FDC. In conclusion, FDC were clearly one of the major murine cell types bearing Fc epsilon RII. IgE immune complexes were found in association with FDC and Fc epsilon RII appeared to play a major role in trapping and retaining IgE immune complexes. FDC Fc epsilon RII was subject to regulatory control, but the Fc epsilon RII level on FDC was regulated very differently from the Fc epsilon RII level on B cells.     

Recombinant human IgG1-murine IgE chimeric Ig. Construction, expression, and binding to human Fc gamma receptors

We have constructed a set of chimeric Ig by exchanging corresponding H chain C domains between human (hu) IgG1 and murine (m) IgE. We used this set of Ig to dissect the interaction of individual Ig domains with human Fc gamma receptors. Only one of the chimeras, epsilon/C gamma 2,3 (an mIgE with C epsilon 3 and C epsilon 4 replaced by C gamma 2 and C gamma 3 from huIgG1), binds tightly to the human Fc gamma RI on U937 cells. We found that epsilon/C gamma 2,3 has only twofold lower affinity for Fc gamma RI as compared to huIgG1. The gamma/C epsilon 4 (huIgG1 with C epsilon 4 replacing C gamma 3) binds weakly to Fc gamma RI. The other chimeric Ig, epsilon/C gamma 3, epsilon/C gamma 2, and gamma/C epsilon 3, as well as mIgE do not bind detectably to Fc gamma RI. From these data we conclude that the C gamma 2 domain is crucial for binding and contains the majority of the binding site for Fc gamma RI on IgG1. The C gamma 3 domain makes a smaller contribution to the binding, and the C gamma 1 domain and the hinge region have very little effect on the Fc gamma RI-IgG1 interaction. The chimeric epsilon/C gamma 2,3 and huIgG1 both mediate the formation of rosettes between K562 cells and antigen-sensitized E with similar concentration dependences. These results suggest similar ability to bind to Fc gamma RII. The other chimeric Ig do not cause rosettes in this assay system. Hence, both C gamma 2 and C gamma 3 seem to be required for binding to Fc gamma RII, but the C gamma 1-hinge region has no detectable effect.     

Leukotriene B4 potentiates the expression and release of Fc epsilon RII/CD23, and proliferation and differentiation of human B lymphocytes induced by IL-4

This study documents the influence of leukotriene (LT) B4 on human B lymphocyte responses. Incubation of freshly isolated B lymphocytes with LTB4, but not LTC4, induced a slight but significant, time- and dose-dependent increase in the surface expression of Fc epsilon RII/CD23 and class II MHC Ag and in the release of soluble CD23. These changes were maximal at 10 nM LTB4 after an incubation period of 48 h. When B lymphocytes were preactivated in vitro with Staphylococcus aureus Cowan strain I (SAC), neither LTB4 nor LTC4 was able to promote proliferation and/or IgG and IgM secretion. In contrast, when resting B lymphocytes were stimulated with a suboptimal concentration (3 U/ml) of IL-4, LTB4, but not LTC4, potentiated both the Fc epsilon RII/CD23 and the class II MHC antigen expression, and the release of soluble CD23 in a dose-dependent manner, without affecting the kinetics of these responses. Furthermore, LTB4, but not LTC4, amplified both the proliferative response and the IgG and IgM secretion induced by addition of a suboptimal dose of IL-4 (3 U/ml) to SAC-preactivated B lymphocytes. Again, LTB4 did not modify the kinetics of the proliferative response promoted by IL-4. Although LTB4 potentiated IL-4-induced IgG and IgM secretion from SAC-activated B lymphocytes, no production of IgE was observed. These data indicate that LTB4 could play a regulatory role in the modulation of IL-4-induced signaling in human B lymphocytes.     

Prostaglandin E2 and cAMP inhibit B lymphocyte activation and simultaneously promote IgE and IgG1 synthesis.

Macrophage-secreted prostaglandins of the E series inhibit numerous immunologic events, including IgM secretion by B lymphocytes. In this study, we investigated whether PGE also regulates the activation of normal quiescent murine B cells and subsequent isotype differentiation to IgE and IgG1 production. PGE2 and PGE1 were found to inhibit cellular enlargement induced by IL-4 or bacterial LPS, IL-4 and LPS, or anti-mu and IL-4 by approximately 75%, and completely inhibit enlargement in response to anti-mu antibody. PGE2 also suppresses activation-induced class II MHC up-regulation by 35% and expression of the low affinity IgE receptor, Fc epsilon RII/CD23, by 30%. Interestingly, PGE completely inhibits a fraction of cells from these activation events, while other cells fully respond to activation stimuli, even in the presence of high PGE2 concentrations. Therefore, a PGE-resistant subset of B lymphocytes may exist. A closely related PG, PGF2 alpha, had no immunoregulatory effect in these systems. Because PGE induces production of cAMP in B cells, we determined whether other agents that increase cAMP could inhibit B cell activation. Cholera toxin and dibutyryl cAMP mimicked the ability of PGE2 to inhibit B cell enlargement, and class II MHC and Fc epsilon RII induction, suggesting that PGE2 signaling occurs via cAMP. In addition, cholera toxin and dibutyryl cAMP inhibited B cell activation much more potently (90-100% inhibition) than PGE, indicating that whereas all B cells are cAMP-sensitive only some are PGE-sensitive. Although PGE inhibits activation-associated events, we previously reported that PGE enhances IL-4 and LPS-induced differentiation to IgE and IgG1 synthesis. To investigate the relationship between the cells that are activation-inhibited and those that are differentiation-enhanced by PGE, we sorted B cell subsets by FACS and determined their relative abilities to produce IgM, IgG1, and IgE in response to IL-4 and LPS in the presence of PGE. The population of lymphocytes that was unaffected by PGE in terms of class II hyperexpression was also unaffected by PGE for Ig synthesis, again indicating a PGE-resistant subpopulation of B cells. Furthermore, the PGE activation-inhibited subset of B cells was responsive to PGE enhancement of IL-4-induced class switching, reducing IgM synthesis and inducing a sevenfold increase in IgE and IgG1 synthesis compared with other sort groups. These results are consistent with the hypothesis that the B lymphocytes that are PGE activation-inhibited are the same cells that are PGE differentiation-enhanced.(ABSTRACT TRUNCATED AT 400 WORDS)     

IgE enhances Fc epsilon receptor I expression and IgE-dependent release of histamine and lipid mediators from human umbilical cord blood-derived mast cells: synergistic effect of IL-4 and IgE on human mast cell Fc epsilon receptor I expression and mediator release

We investigated the effects of IgE versus IL-4 on Fc epsilon RI surface expression in differentiated human mast cells derived in vitro from umbilical cord blood mononuclear cells. We found that IgE (at 5 micrograms/ml) much more strikingly enhanced surface expression of Fc epsilon RI than did IL-4 (at 0.1-100 ng/ml); similar results were also obtained with differentiated mouse mast cells. However, IL-4 acted synergistically with IgE to enhance Fc epsilon RI expression in these umbilical cord blood-derived human mast cells, as well as in mouse peritoneal mast cells derived from IL-4-/- or IL-4+/+ mice. We also found that: 1) IgE-dependent enhancement of Fc epsilon RI expression was associated with a significantly enhanced ability of these human mast cells to secrete histamine, PGD2, and leukotriene C4 upon subsequent passive sensitization with IgE and challenge with anti-IgE; 2) preincubation with IL-4 enhanced IgE-dependent mediator secretion in these cells even in the absence of significant effects on Fc epsilon RI surface expression; 3) when used together with IgE, IL-4 enhanced IgE-dependent mediator secretion in human mast cells to levels greater than those observed in cells that had been preincubated with IgE alone; and 4) batches of human mast cells generated in vitro from umbilical cord blood cells derived from different donors exhibited differences in the magnitude and pattern of histamine and lipid mediator release in response to anti-IgE challenge, both under baseline conditions and after preincubation with IgE and/or IL-4.     

IL-6 augments Fc IgE receptor (Fc epsilon RII/CD23) expression on human monoblastic/monocytic cell lines U937, THP-1, and Mono-Mac-6 but not on blood monocytes. Regulatory effects of IL-4 and IFN-gamma.

Human monoblastic/monocytic leukemia cell lines U937, THP-1, Mono-Mac-6, and blood monocytes were incubated with various concentrations of human rIL-6 and other cytokines and analyzed for their capacity to bind several anti-Fc epsilon RII/CD23 mAb. A marked and dose-dependent increase in the percentage of CD23+ cells, as well as in the mean channel fluorescence intensity, as demonstrated by FACS analysis, was noted after 8- to 72-h incubation of U937 cells with 1 to 1000 U/ml of human rIL-6. Furthermore, rIL-4 synergized with rIL-6 and rIFN-tau in augmenting the Fc epsilon RII expression on U937 cells, whereas rIFN-tau and rIL-6 showed rather additive effects. The enhancement of CD23 expression on IL-6-treated U937 cells was blocked by anti-IL-6 antibodies. Northern blot analysis, employing cDNA probes for Fc epsilon RII, showed that U937 cells contain Fc epsilon RII-specific mRNA. The level of Fc epsilon RII-encoding mRNA was evidently increased by treatment of U937 cells with human rIL-6, rIL-4, or with rIL-6 + rIL-4. The expression of CD23 on THP-1 and Mono-Mac-6 cells was increased slightly by rIL-6 and markedly by rIL-4, rIFN-tau, or a mixture of them. Approximately 14% of blood monocytes, isolated from apparently healthy donors, constitutively possess Fc epsilon RII. In contrast to the cell lines, the Fc epsilon RII density and the percentage of blood monocytes bearing Fc epsilon RII was not augmented by IL-6. Furthermore, rIL-6, and more evidently rIFN-tau, down-regulate rIL-4-driven Fc epsilon RII expression on monocytes but not on monocytic cell lines. Our findings point to differences in the capability of mononuclear phagocytes to respond to cytokine treatment, which may be differentiation dependent, and suggest separate regulatory pathways.     

Differential regulation of murine B cell Fc gamma RII expression by CD4+ T helper subsets

The murine B cell FcR for IgG (Fc gamma RII) is a membrane glycoprotein reported to mediate inhibition of B cell activation and differentiation. We show that IL-4 inhibits the enhanced expression of Fc gamma RII by LPS-stimulated B cells. This activity is completely reversed by anti-IL-4 mAb and is specific, in that multiple other lymphokines tested do not exert a similar effect. This effect of IL-4 is apparent by day 1 of culture, although maximal inhibition occurs on day 4 at a concentration of 500 U/ml. The IL-4-induced inhibition of enhanced Fc gamma RII expression by LPS stimulation observed on day 4 of culture is associated with a significant reduction in the steady state level of Fc gamma RII beta gene-specific mRNA. IFN-gamma which inhibits many of the effects of IL-4 on B cells, does not reverse the IL-4-induced inhibition of Fc gamma RII membrane expression nor the levels of beta gene-specific mRNA. Fc gamma RII expression is significantly increased in B cells stimulated with antigen-specific, CD4+ T cell clones of the Th1 type (i.e., IL-2 and IFN-gamma-producing). By contrast, three different Th2 clones (i.e., IL-4-producing) fail to stimulate an increase in Fc gamma RII levels. Anti-IL-4 mAb significantly enhanced Fc gamma RII expression by Th2-stimulated B cells indicating that IL-4 was the active, inhibitory, substance produced by the Th2 cells. Supernatants from stimulated Th2 clones inhibited the enhanced expression of Fc gamma RII by LPS-stimulated B cells and this activity was completely reversed by anti-IL-4 mAb. By contrast, supernatants from stimulated Th1 clones further enhanced Fc gamma RII expression by LPS-stimulated B cells. The differential regulation of B cell Fc gamma RII expression by Th subsets may play an important role in the regulation of humoral immunity by altering the sensitivity of B cells to IgG immune complex-mediated inhibition of B cell activation and differentiation in vivo.     

Human neutrophils express the high-affinity receptor for immunoglobulin E (Fc epsilon RI): role in asthma.

Polymorphonuclear neutrophils (PMNs) are important effector cells in host defense and the inflammatory response to antigen. The involvement of PMNs in inflammation is mediated mainly by the Fc receptor family, including IgE receptors. Recently, PMNs were shown to express two IgE receptors (CD23/Fc epsilon RII and galectin-3). In allergic diseases, the dominant role of IgE has been mainly ascribed to its high-affinity receptor, Fc epsilon RI. We have examined the expression of Fc epsilon RI by PMNS: mRNA and cell surface expression of Fc epsilon RI alpha chain was identified on PMNs from asthmatic subjects. Furthermore, preincubation with human IgE Fc fragment blocks completely the binding of anti-Fc epsilon RI alpha chain (mAb15--1) to human PMNS: Conversely, preincubation of PMNs with mAb15--1 inhibits significantly the binding of IgE Fc fragment to PMNs, indicating that IgE bound to the cell surface of PMNs mainly via the Fc epsilon RI. Peripheral blood and bronchoalveolar lavage (BAL) PMNs from asthmatic subjects also express intracellular Fc epsilon RI alpha and beta chain immunoreactivity. Engagement of Fc epsilon RI induces the release of IL-8 by PMNS: Collectively, these observations provide new evidence that PMNs express the Fc epsilon RI and suggest that these cells may play a role in allergic inflammation through an IgE-dependent activation mechanism.