Role of leukotriene B4 in the interleukin-4-induced human mononuclear phagocyte activation

Interleukin-4 (IL-4) induced a time- and dose-dependent production of leukotriene B4 (LTB4) by human resting monocytes indicating that IL-4 induced the activation of the 5-lipoxygenase pathway in resting human monocytes. Maximal effect was observed in the presence of 10 ng/ml IL-4, and in kinetics experiments LTB4 production plateaued 40 min after the onset of stimulation. When stimulated for 48 hr with IL-4, resting human monocytes expressed and released the low-affinity receptor for IgE (CD23) and were partially inhibited in the presence of a highly non-redox 5-lipoxygenase inhibitor (BW B70C), suggesting that the production of LTB4 partially contributed to the IL-4-induced CD23 expression and release. This hypothesis was strengthened by the fact that exogenous LTB4 (10 nM) was found to increase the effect of a suboptimal dose of IL-4 (1 ng/ml). In addition to these phenotypical changes, IL-4 primed the phorbol-12-myristate-13-acetate (PMA)-induced luminol-dependent chemiluminescence response (LDCL) by normal human monocytes, this priming effect being abrogated in the presence of BW B70C. Taken together, these data indicated that IL-4 induced the production of LTB4 by activation of the 5-lipoxygenase pathway in human monocytes, and that the activation of this pathway could upregulate the expression and release of CD23 and the respiratory burst of these cells.

Triggering of CD23b antigen by anti-CD23 monoclonal antibodies induces interleukin-10 production by human macrophages

The aim of this study was to evaluate the capacity of human macrophages to produce interleukin (IL)-10 upon stimulation of membrane CD23. An anti-CD23 monoclonal antibody (mAb) was found to elicit the expression of the specific mRNA for IL-10 in CD23-bearing macrophages, and to induce a time-dependent production of this cytokine with a maximal effect reached after 12 h. Inasmuch as we previously reported that CD23 ligation evoked the generation of nitric oxide and of cAMP, the effect of the Rp diastereoisomer of adenosine 3', 5'-cyclic phosphorothioate (Rp-cAMP, an inhibitor of the cAMP pathway) and of NG-monomethyl-L-arginine (L-NMMA, an inhibitor of the nitric oxide pathway) were evaluated on CD23-induced IL-10 production. In the presence of Rp-cAMP, the CD23-induced production of IL-10 and of the pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) was totally abrogated, whereas, in the presence of L-NMMA, IL-10 production was enhanced and TNF-alpha production was suppressed. In addition, neutralization of IL-10 with an anti-IL-10 mAb increased both the magnitude and duration of CD23-driven TNF-alpha production. Such an inducing effect was observed with different anti-CD23 mAb (clone 135, MHM6 and 25), indicating that the triggering of the CD23 molecule at the surface of human macrophages induced the generation of IL-10 through a cAMP-dependent mechanism. Concomitantly this generation of IL-10 was down-regulated by nitric oxide, which was also produced after triggering of the CD23 antigen. Taken together these data indicated that human macrophages produced IL-10 after triggering of the CD23 molecule and that this production could regulate the inflammatory state of these cells.

Granulocyte macrophage colony stimulating factor induces Fc epsilon RII/CD23 expression on normal human polymorphonuclear neutrophils

Three major molecules have been recognized as IgE-binding structures on hematopoietic cells: the heterotrimeric high-affinity receptor for IgE (Fc epsilon RI), the low-affinity receptor for IgE (Fc epsilon RII/CD23) and the Mac-2/IgE-binding protein (epsilon BP). The latter has been shown to be expressed on polymorphonuclear neutrophils (PMN), where it regulates IgE-dependent activation. Experiments were undertaken to determine whether the IgE-binding capacity of PMN is mediated exclusively by this molecule. No detectable binding of human myeloma IgE to unstimulated PMN from normal volunteers could be evidenced. In contrast, PMN stimulated with granulocyte macrophage colony stimulating factor (GM-CSF) (500 U/ml) for 24 h displayed positive IgE binding. This binding was significantly inhibited in the presence of mAb directed against Mac-2/epsilon BP and also in the presence of anti-CD23 mAb, but not of anti-Fc epsilon RI mAb or isotype-matched controls. By flow cytometry, CD23 expression was detected on GM-CSF-primed PMN by several anti-CD23 mAb, including EBVCS-5, BB10 or Mab135, which recognize different epitopes. CD23 was also evidenced by immunocytochemistry in GM-CSF-primed PMN. By in situ hybridization, GM-CSF-treated PMN exhibited a hybridization signal for CD23 mRNA and the presence of the CD23b isoform-specific mRNA was detected by RT-PCR. These findings indicate that PMN can synthesize CD23 molecules under GM-CSF induction. This strong CD23 expression might be of physiopathological relevance in IgE-dependent activation during allergic processes.

Nitric oxide production by human monocytes: evidence for a role of CD23

Nitric oxide (NO) appears to be an important and pleiotropic bioregulator of immune responses. The existence of the NO synthase (NOS) pathway in human monocytes/macrophages remains a subject of controversy, despite an increasing number of reports suggesting that human monocytes produce NO in vitro in response to various stimuli. Here, Bernard Dugas and colleagues consider the arguments supporting these conclusions, with particular emphasis on the results obtained by ligation of the low-affinity IgE receptor (Fcepsilon RIIb/CD23b).

Evidence for a role of Fc epsilon RII/CD23 in the IL-4-induced nitric oxide production by normal human mononuclear phagocytes

IL-4 stimulates NO production by human monocytes. After 6 days of culture with IL-4, human monocytes released detectable amounts of nitrite and L-citrulline that were inhibited in the presence of nitro-L-arginine (1 mM). Incubation with an anti-CD23 mAb Fab fragment that suppressed the biological effect of CD23 led to a strong reduction (50 to 70%) of the IL-4-induced nitrite and L-citrulline production. Ligation of membrane-associated CD23 or stimulation with recombinant soluble CD23 elicited monocytes to release nitrite and L-citrulline that was suppressed by nitro-L-arginine. Preactivation of human monocytes with IFN-gamma led to subsequent increased IL-4- and CD23-driven nitrite and L-citrulline productions that were also suppressed in the presence of either nitro-L-arginine or the anti-CD23 mAb Fab fragment. The CD23 molecule under its membrane or soluble form thus regulates NO generation by human monocytes. In addition, the IL-4-induced NO production could be mediated, at least in part, by CD23.

Involvement of CD23/Fc epsilon RII in the homotypic and heterotypic cytoadhesion of the human eosinophilic cell line Eol-3

A subclone of the EoL-3 human eosinophilic leukemia cell line (EoL-3.12) was selected for its high inducibility of CD23 (low affinity IgE receptor/Fc epsilon RII) by IL-4. Maximum membrane CD23 expression was detected after 16 h of incubation with IL-4, then gradually returned to basal level after 48 h. Membrane expression of CD23 on EoL-3.12 cells was found to parallel their homotypic aggregation. Extending the time of incubation with IL-4 to 48 h or more resulted in a de-aggregation of cells of cells with a shedding of membrane CD23 and an increase of its soluble form, sCD23. The IL-4-induced aggregation of EoL-3.12 cells was inhibited with anti-CD23 antibody or human myeloma IgE protein, indicating that it was mediated through the engagement of CD23. EoL3.12 incubated with IL-4 displayed morphological changes associated with differentiation, such as an increased number of lobulated nuclei with prominent nucleoli, increased ratio of cytoplasm and distinct cytoplasmic processes. EoL-3.12 cells incubated with IL-4 also displayed an enhanced adherence to human umbilical vein endothelial cells (HUVEC), which was reverted when the IL-4 incubation time extended. Furthermore, the transendothelial migration of EoL-3.12 cells toward a chemokinetic gradient of soluble CD23 (sCD23; 29 kDa fragment) closely paralleled the density of membrane CD23 expressed on EoL-3.12 cells. Additionally, the engagement of CD23 led to the activation of the L-arginine-dependent pathway of nitric oxide (NO) production, as detected by the increase in intracytoplasmic cGMP concentration. The capacity of EoL-3.12 cells to form homotypic as well as heterotypic adhesion appears therefore to be regulated, at least in part, by the level of CD23 expression.

Ligation of CD23 activates soluble guanylate cyclase in human monocytes via an L-arginine-dependent mechanism

Transduction through Fc epsilon R2/CD23 was analyzed in normal human monocytes using immunoglobulin E (IgE)-anti-IgE immune complexes (IgE ICs) and monoclonal antibodies (mAbs) to CD23. Anti-CD23 mAb and IgE IC triggered a time-dependent increase in cGMP and cAMP in interleukin-4-preincubated (CD23+) but not in unstimulated (CD23-) monocytes. Maximal cGMP and cAMP accumulations were observed 10 and 20 min, respectively, after the onset of CD23 ligation. The increase in cGMP was inhibited with N omega-monomethyl-L-arginine (L-NMMA), which also partially affected cAMP accumulation. Addition of an anti-CD23 mAb Fab fragment inhibited the IgE IC- and the anti-CD23 mAb-induced cGMP and cAMP accumulation, confirming the engagement of CD23. In addition, IgE IC and anti-CD23 mAb induced, at least in some donors, a production of nitrite that was inhibited in the presence of L-NMMA. Taken together, these findings suggest a possible involvement of the nitric oxide synthase pathway in IgE IC-mediated activation of CD23+ monocytes.

[Role of interleukin-4 in the regulation of nitric oxide production by normal human monocytes]

Resting normal human monocytes were found to produce small amounts of cGMP in response to IL-4. This production was inhibited in the presence of LNMMA suggesting an association with activation of the NO synthase (NOS) pathway. In addition, this cGMP generation was abrogated in the presence of either a Ca2+ chelator, EGTA, or a calcium/calmodulin inhibitor, W7, suggesting that IL-4 stimulates the constitutive NOS (cNOS). An enhanced response was observed when monocytes were preincubated with IFN-gamma and whether the cGMP accumulation was still abrogated in the presence of LNMMA it was not affected by either EGTA or W7 suggesting, in that case, the activation of an inducible NOS (iNOS). Taken together these data suggest that IL-4 could stimulate a cNOS in resting and an iNOS in the IFN-gamma-treated human monocytes, indicating that the generation of NO is highly dependent on the maturation state of these cells.

Growth arrest and terminal differentiation of leukemic myelomonocytic cells induced through ligation of surface CD23 antigen

Acute myelogenous leukemia (AML) cells express CD23 surface antigen after in vitro treatment with various cytokines, including interleukin-4 (IL-4) and interferon gamma. Subsequent ligation of CD23 by specific monoclonal antibody (MoAb) induces substantial morphologic and functional modifications in these cells. In the present study, we investigated the role of CD23 in the proliferation and the maturation of leukemic cells from AML patients or the U937 cell line. CD23+ cell treatment with CD23 MoAb inhibited the proliferation of leukemic cells. This correlated with their terminal differentiation after 7 to 9 days incubation because they (1) definitively lost their growth capacity; (2) adhered to culture flasks and became monocyte/macrophage-like; and (3) expressed mature monocyte markers including nonspecific esterases. Intracellular mechanism of this antitumoral effect was then analyzed in U937 cells. Induction of high-density surface CD23 expression by IL-4 or granulocyte-macrophage colony-stimulating factor coincided with a transient decrease of U937 cell proliferation. CD23 ligation during this low-proliferative phase induced a rapid activation of L-arginine-dependent pathway and the intracellular accumulation of cyclic guanosine monophosphate and cyclic adenosine monophosphate (cAMP). Induction of these early messengers was followed by the activation of nuclear factor-kB transcription factor and the modulation of proto-oncogene expression by U937 cells. Whereas U937 cell treatment with IL-4 decreased c-fos/c-jun expression, CD23 MoAb reinduced c-fos/c-jun and promoted the expression of cell maturation-associated proto-oncogenes junB and c-fms, during the first 24 hours. Both IL-4 and CD23 MoAb downregulated the expression of c-myb. CD23 ligation also induced the production of TNF alpha by U937 cells. Inhibitors of cAMP and nitric oxide reversed CD23-mediated modification in U937 cells. These data evidence the ability of CD23 surface antigen to mediate terminal differentiation of early leukemic myelomonocytic cells.

Regulatory role of nitric oxide in the IL-4-induced IgE production by normal human peripheral blood mononuclear cells

An in vitro study was performed in order to assess a possible regulatory role of nitric oxide (NO), a short-lived biologic mediator that displays immunoregulatory properties, in the IL-4-driven synthesis of IgE by normal human peripheral blood mononuclear cells (PBMC). In addition to induce IgE production, IL-4 was found to elicit nitrite (NO2-) release by PBMC. A marked correlation was observed between IgE secretion and nitrite release by PBMC stimulated with an optimal concentration of IL-4. The IL-4-dependent IgE production was significantly reduced (p < 0.001) in the presence of N omega-monomethyl-L-arginine (LNMMA), an inhibitor of the NO-synthase pathway; this inhibition was partially reverted with an excess of L-arginine. Addition to PBMC cultures of the chemical NO donor Sin-1, inactive alone, was found to result, depending on the concentration of IL-4, in either potentiation (suboptimal concentration of IL-4, 10 ng/ml) or inhibition (optimal concentration of IL-4, 50 ng/ml) of IgE synthesis. The potentiating effect of Sin-1 was dose dependent, with a maximal effect for 300 microM, whereas its metabolite Sin-1c was inactive. In both cases, Sin-1 markedly reduced the IL-4-induced release of the soluble form of the low affinity IgE receptor (sCD23). Together, these data strongly suggest that NO may display biphasic immunoregulatory properties on the IL-4-induced IgE production by PBMC.

Heterogenous nitrite production by IL-4-stimulated human monocytes and peripheral blood mononuclear cells

The capacity of human peripheral blood mononuclear cells and monocytes to generate nitrites, spontaneously or in response to Interleukin-4 was evaluated in vitro. Peripheral blood mononuclear cells and monocytes were found to release significant amounts of nitrites after 8 to 12 days in culture. This spontaneous production of nitrites was inhibited in the presence of 1 mM NG monomethyl-L-arginine, suggesting that this process was dependent upon the L-arginine metabolism. The present data also indicated that addition of Interleukin-4 generally resulted in an increased nitrite production, that was potentiated by IFN-gamma, inactive alone. The response of human monocytes to Interleukin-4 was more heterogenous than that observed with unfractionated peripheral blood mononuclear cells. These results suggest that cell/cell interactions could play an important role in the activation of the nitric oxide synthase pathway in human.

Heterogeneous spontaneous and interleukin-4-induced nitric oxide production by human monocytes

The generation of nitric oxide by human monocytes has long been a subject of controversy because of the difficulty of rationalizing this production. In this work we evaluated the capacity of human monocytes to produce nitric oxide (NO) as measured by nitrite (NO2-) release. Resting unstimulated monocytes (2 x 10(6) cells/ml) were found to produce significant amounts of NO2- after 8 to 12 days in culture. This production appeared to be highly heterogeneous. Indeed, approximately, 75% of monocytes from the different donors produced up to 10 microM NO2- and were considered low producers; the last 25% produced higher amounts of NO2- (from 10 to 110 microM) and were considered high producers. In any case the spontaneous production of NO2- by monocytes was overcome in the presence of 1 mM N omega-monomethyl-L-arginine (LNMMA). This inhibitory effect was reversed in the presence of an excess of L-arginine (5 mM), indicating that this process is effectively dependent on L-arginine metabolism. Because interleukin-4 (IL-4) is considered an important NO-regulatory cytokine, its regulatory effect on this spontaneous production of NO was also evaluated. In the presence of a defined dose of IL-4 (1 to 100 ng/ml) the spontaneous production of the high-producing population of monocytes was abrogated, whereas IL-4 stimulated the production by the low-producing population of monocytes, which was suppressed in the presence of LNMMA. The present data indicate that NO production by human monocytes is heterogeneous and that IL-4 can be a potent inducer or inhibitor of this production, suggesting a variability in the activation state of these cells.

Involvement of Fc epsilon RII/CD23 and L-arginine-dependent pathway in IgE-mediated stimulation of human monocyte functions

Elevated IgE levels are commonly observed during the inflammatory responses in allergy and a variety of infections. This Ig activates the release of multiple mediators from monocytes/macrophages. In the present work, we attempted to clarify the IgE-dependent events involved in the activation of monocyte functions. IgE-anti-IgE immune complexes induce the production of tumor necrosis factor-alpha, oxygen radicals, IL-6 and thromboxane B2 from normal human purified monocytes. Expression and cross-linkage of Fc epsilon RII/CD23 were essential for these IgE-mediated effects. Cytokine production following CD23 ligation depended on nitric oxide transduction pathway, as it was inhibited by NG-monomethyl-L-arginine, a competitive inhibitor of the conversion of L-arginine to L-citroline by nitric oxide synthase. Furthermore, addition of the nitric oxide chemical donator, Sin-1, enhanced IgE-induced monokine release. CD23-ligation also induced the production of nitrites by these cells. This work linked CD23 to the L-arginine-dependent transduction pathway and shows their involvement in IgE-mediated stimulation of human monocytes.

Leukotriene B4 enhances IL-4-induced IgE production from normal human lymphocytes

Interleukin 4 (IL-4)-induced IgE production by normal peripheral blood mononuclear cells (PBMC) and E- cells (PBMC partially depleted of T cells) was significantly enhanced by leukotriene B4(LTB4) in a dose-dependent manner, whereas LTB4 by itself was not effective for IgE production. The potentiating effect of LTB4 was strictly dependent on IL-4. When PBMC or E- cells were primed with IL-4 (300 U/ml) for 48 hr, then recultured with LTB4 alone (10(-10) to 10(-8) M), increased IgE production was observed. Maximum enhancement of IgE production after IL-4 priming was achieved using a combination of IL-4 and LTB4, acting additively. Moreover, the potentiating effect of LTB4 on IL-4-induced IgE production was completely dependent on the presence of a monocyte/macrophage population. This effect of LTB4 was completely abolished by depletion of monocytes and recovered by reconstitution with autologous monocytes. From the study of IL-4 receptor (IL-4R) expression determined by flow cytometry, IL-4 was found to upregulate the biotinylated-IL-4 (B-IL-4)/streptavidin binding to both T- and B-cell populations. A further increase of B-IL-4 binding was obtained when the cells were incubated with IL-4 and LTB4. Finally, LTB4 can induce soluble CD23 (sCD23) release by E- cells tested either alone or in the presence of IL-4. Taken together, these data suggest that LTB4 can influence the IL-4-induced IgE production through, at least, a bimodal action, i.e., increase of IL-4R positive cells and release of sCD23. These findings may be a specific feature of LTB4 which provides a crucial role in IL-4-linked allergic inflammatory process.

Interleukin-4 stimulates cGMP production by IFN-gamma-activated human monocytes. Involvement of the nitric oxide synthase pathway

Resting human blood monocytes from some donors were found to produce a small amount of 3'-5' guanine cyclic monophosphate (cGMP) in response to interleukin 4 (IL-4). A much higher response was observed when monocytes were preincubated with interferon (IFN-gamma), which alone was ineffective. Preincubation of monocytes with IL-4 led, in contrast, to their subsequent incapacity to generate cGMP in response to IL-4. The accumulation of cGMP induced by IL-4 in IFN-gamma preincubated monocytes was dose-dependent and peaked about 15 min after its addition. It was inhibited in the presence of NG-mono-methyl-L-arginine (L-NMMA), an inhibitor of the nitric oxide synthase pathway. This suppressive effect of L-NMMA was reverted by an excess of L- but not of D-arginine. Accumulation of cGMP was significantly reduced by addition of soluble guanylyl cyclase inhibitors, such as LY83583 [correction of LY83853] and methylene blue, but was not impaired in the presence of EGTA, suggesting that the pathway involved is calcium independent. In addition, IL-4 induced an increased secretion of nitrite by monocytes, that was potentiated by IFN-gamma and inhibited by L-NMMA. Taken together, these results suggest that the sequential exposure of monocytes to IFN-gamma and IL-4 elicits the release of NO from L-arginine, which in turn is capable to stimulate soluble guanylyl cyclase.

Purified excretory-secretory component of filarial parasite enhances Fc epsilon RII/CD23 expression on human splenic B and T cells and IgE synthesis while potentiating T-helper type 2-related cytokine generation from T cells

The CD23-bearing cells are known to be involved in multiple biological activities, including IgE synthesis and IgE-dependent cytotoxicity to parasites. The factors that regulate interleukin-4 (IL-4)-induced IgE synthesis in helminthic infection were analysed by using an excretory-secretory component (ESC) of Dirofilaria immitis (DI). Human splenic B and T cells significantly enhanced the expression of low-affinity Fc receptors for IgE (Fc epsilon RII/CD23) by stimulation with ESC, either acting alone or in synergy with IL-4. On B cells, ESC potentiated the CD23 expression in synergy with IL-4, whereas ESC alone was unable to modulate CD23 expression. In contrast, ESC directly induced CD23 expression on T cells by acting alone and no further enhancement was observed in the presence of IL-4. Furthermore, IL-4-induced IgE synthesis by splenic mononuclear cells (SMNC) was greatly enhanced in the presence of ESC. Of particular interest, T cells primed by ESC significantly produced a set of cytokines including IL-3, IL-4, IL-5 and IL-6. Inasmuch, IL-4-induced IgE synthesis in helminthic infection may be selectively modulated by parasite protein(s) acting on the generation of T-helper type 2 (Th2)-related cytokines.

Beta 2-adrenoceptor agonists regulate the IL-4-induced phenotypical changes and IgE-dependent functions in normal human monocytes

The beta 2-adrenoceptor agonists salbutamol and fenoterol were tested for their regulatory effects on human monocyte phenotype and functions, either alone or in combination with interleukin-4 (IL-4). These drugs enhanced in a dose-dependent manner the IL-4-induced membrane and mRNA expression of the low-affinity receptor for immunoglobulin E (IgE) (CD23), as well as the release of its soluble form, sCD23. Salbutamol and fenoterol alone elicited expression of the monomorphic beta 2-chain (CD18) of the leukocyte functional antigen (LFA1) family. This effect appeared to be restricted to CD11b (CR3) and CD11c (gp 150-95), because CD11a (LFA-1 alpha chain) was not modified. beta 2-Adrenoceptor stimulation was also found to potentiate the effect of IL-4 on CD11b, CD11c, and CD18 expression. In contrast, these agents alone did not alter the level of major histocompatibility complex class II and CD14 antigens or modify their respective up- and down-regulation by IL-4. Ligation of CD23 on IL-4-preincubated (CD23+) monocytes with IgE/anti-IgE immune complexes induced the release of free radicals nitric oxide and of the proinflammatory mediators IL-6 and thromboxane B2 (TxB2). Addition of salbutamol, inactive alone, potentiated the generation of superoxide anion and of nitric oxide generation, as well as the production of IL-6 and TxB2 triggered by CD23 ligation. These results indicate that beta 2-adrenoceptor stimulation potentiates in vitro the IL-4-induced phenotypical and functional changes on monocytes and suggest that such an interaction could occur in IgE-dependent immune reactions.

CD23-mediated cell signalling

Signal transduction through ligation of the CD23 (Fc epsilon RII) molecule was analysed in human B cells and monocytes. Monoclonal antibodies directed against the IgE binding site of CD23 were found to trigger phosphoinositide hydrolysis and calcium mobilization in B cells, but not in monocytes. These early events were also obtained with an IgE+anti-IgE complex, which supposedly mimicks the physiological situation of a multivalent antigen inducing the cross-linking of cell-bound IgE. Redistribution of CD23 was also found to evoke cAMP accumulation both in B lymphocytes and monocytes. Moreover, we present evidence indicating a possible cross-talk between the IL-4- and CD23-induced second messengers. We suggest that the alternative transduction pathways elicited by ligation of CD23 are linked to the CD23 isoform(s) expressed by these cells and may result from their association with different sets of molecules.

CD23 and IgE expression during the human immune response to cutaneous leishmaniasis: possible role in monocyte activation

Leishmania brasiliensis causes cutaneous leishmaniasis (CL) in humans. During this infection, a variety of inflammatory mediators are produced by T cells and monocytes/macrophages. In the present study, we analysed serum IgE levels and their correlation with in situ expression of the low affinity receptor for IgE (Fc epsilon RII/CD23) in patients infected with L. brasiliensis before and following therapy. These analyses were compared to in situ expression of tumour necrosis factor-alpha (TNF alpha), interleukin 3 (IL3), interferon-gamma (IFN gamma) and IL4. Disease-free individuals from the same endemic area sensitized with L. brasiliensis antigens were also included in this work. Our data indicate that during infection, serum levels of IgE and TNF alpha increased and correlated with elevated in situ expression of CD23, IL4 and TNF alpha mRNA. This expression disappeared following successful treatment, but persisted in patients resistant to anti-leishmania therapy. Patients resistant to therapy differed from other cases by a dramatic decrease in their in vivo expression of IFN gamma protein. Analysis of CD23 function in purified human monocytes indicated that this antigen mediates IgE/anti-IgE-dependent TNF alpha production. These data suggest a possible in vivo role of CD23 in acute immune responses in human CL.

1,1'-Ethylidenebis(tryptophan) (Peak E) induces functional activation of human eosinophils and interleukin 5 production from T lymphocytes: association of eosinophilia-myalgia syndrome with a L-tryptophan contaminant

This study was designed to clarify the important association between eosinophilia-myalgia syndrome (EMS) and the L-tryptophan contaminant, "Peak E." To determine the functional activation of eosinophils induced by Peak E, eosinophil cationic protein (ECP) release was examined. Peak E augumented the release of ECP from peripheral blood normodense eosinophils by degranulation. Proliferative analysis using the human eosinophilic leukemia cell line EoL-3 showed prominent cellular replication in the presence of Peak E. Moreover, Peak E upregulated interleukin 5 (IL-5) receptor levels on normodense eosinophils. Of particular interest, Peak E-stimulated human splenic T cells produced bioactive and immunoreactive IL-5. Marked induction of IL-5 mRNA in Peak E-stimulated T cells was also shown by reverse-transcriptase polymerase chain reaction (RT-PCR). In contrast, L-tryptophan without the contaminant showed none of these effects. Thus, these data suggest that Peak E might be involved in the pathogenesis of EMS through bimodal mechanism including IL-5 generation by T cells and potentiation of eosinophil functional activation.

Inhibitors of protein tyrosine kinases and protein tyrosine phosphatases suppress IL-4-induced CD23 expression and release by human B lymphocytes

The pleiotropic lymphokine IL-4 is a growth and differentiation factor for human B cells. IL-4 induces the expression of the CD23 (Fc epsilon RII) molecule on B lymphocytes and promotes the release of its soluble form (sCD23); the cleavage fragments of the latter have been reported to modulate IL-4-dependent IgE biosynthesis. In the present work, we have tested the effects of inhibitors of protein tyrosine kinases (PTK) and protein phosphatases (PP) on the induction by IL-4 of the membrane and soluble forms of CD23. The PTK inhibitors genistein and lavendustin A were found to suppress, in a dose-dependent way, the induction by IL-4 of CD23 membrane expression as well as CD23 release by resting and SAC-preactivated B lymphocytes. No such suppression was detected with inhibitors of serine and threonine kinases. The addition of the protein tyrosine phosphatase (PTP) inhibitor sodium orthovanadate also resulted in a marked decrease in CD23 induction by IL-4. Cell viability was little affected by these inhibitors. However, a diminution of the large activated B cell population was observed, which correlated with an inhibition of the entry in the S phase. Partial inhibition of sCD23 release was also observed with okadaic acid and calyculin A, two inhibitors of serine/threonine PP, but only at concentrations which block PP1 in addition to PP2A. These results suggest that protein tyrosine phosphorylation and dephosphorylation may play a major role in IL-4 signalling. This conclusion was strengthened by the observation that a mAb anti-CD45, a membrane tyrosine phosphatase, inhibited IL-4-induced sCD23 release by B lymphocytes.

Biochemical and functional alterations induced by CD23 ligation in the human promonocytic cell line U937

The early events triggered in interleukin-4 (IL-4)-stimulated U937 cells by ligation of CD23/Fc epsilon RII with specific monoclonal antibodies (mAb) were analysed, as a model of the action of this molecule on the differentiation of promonocytic cells. As well as IL-4-activated human monocytes, addition of anti-CD23 mAb to IL-4-treated U937 cells triggered cAMP accumulation but did not evoke significant polyphosphoinositide hydrolysis. However, by a microspectrofluorometric technique allowing single cell analysis, anti-CD23 mAb was found to elicit calcium mobilization in these cells. In addition, the treatment induced phenotypic alterations in these cells, as evidenced by the acquisition of the monocyte marker CD14 and the increase of the alpha-chain (CD11a) and of the common beta-chain (CD18) of the leucocyte function-associated antigen 1 (LFA-1) family antigens. Although weaker than in monocytes, CD23 ligation evoked a small secretion of the pro-inflammatory mediators IL-6 and thromboxane B2. These data suggest that a significant maturation of promonocytic cells towards a more mature monocytic phenotype can be achieved through successive exposure to IL-4 and CD23 ligation.

Leukotriene B4 induces interleukin 5 generation from human T lymphocytes

Leukotriene B4 (LTB4) has been shown to affect several interleukin (IL)-linked functions of human lymphocytes. In this study, we investigated whether LTB4 regulates IL-5 generation from human T cells and subsequently modulates eosinophil functions. Preincubation of T cells with very low concentrations (10(-12) to 10(-8) M) of LTB4 induced concentration-dependent IL-5 production, the event occurring after the first 24 h of cultivation. However, direct action of LTB4 to IL-5 generation is strictly dependent on a preincubation with appropriate concentration of LTB4. In contrast, the stereoisomer of LTB4, 5S,12S-dihydroxy-6,8,10,14-eicosatetraenoic acid showed no enhancement of IL-5 production. IL-5 released from LTB4-primed T cells elicited sustained viability of mature eosinophils and reduced the content of eosinophil cationic protein in their crystalloid matrix by degranulation. These data suggest that LTB4 induces bioactive IL-5 production from T cells and that the released IL-5 modulates eosinophil functions which might play a crucial role in eosinophil-linked allergic inflammatory process.