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.

CD23 regulates monocyte activation through a novel interaction with the adhesion molecules CD11b-CD18 and CD11c-CD18.

CD23 is expressed on a variety of haemopoietic cells and displays pleiotropic activities in vitro. We report that in addition to CD21 and IgE, CD23 interacts specifically with the CD11b and CD11c, the alpha chains of the beta 2 integrin adhesion molecule complexes CD11b-CD18 and CD11c-CD18, on monocytes. Full-length recombinant CD23 incorporated into fluorescent liposomes was shown to bind to COS cells transfected with cDNA encoding either CD11b-CD18 or CD11c-CD18 but not with CD11a-CD18. The interaction was specifically inhibited by anti-CD11b or anti-CD11c, respectively, and by anti-CD23 MAbs. The functional significance of this ligand pairing was demonstrated by triggering CD11b and CD11c on monocytes with either recombinant CD23 or anti-CD11b and anti-CD11c MAbs to cause a marked increase in nitrite-oxidative products and pro-inflammatory cytokines (IL-1 beta, IL-6, and TNF alpha). These CD23-mediated activities were decreased by Fab fragments of MAbs to CD11b, CD11c, and CD23. These results demonstrate that CD11b and CD11c are receptors for CD23 and that this novel ligand pairing regulates important activities of monocytes.

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.

IL-4 induces cAMP and cGMP in human monocytic cells.

Human monocytes, preincubated with IFN-gamma respond to IL-4 by a cGMP increase through activation of an inducible NO synthase. Here, IL-4 was found to induce an accumulation of cGMP (1 - 3 min) and cAMP (20 - 25 min) in unstimulated monocytes. This was impaired with NOS inhibitors, but also with EGTA and calcium/calmodulin inhibitors. These results suggest that: (1) IL-4 may stimulate different NOS isoforms in resting and IFN-gamma activated monocytes, and (2) cAMP accumulation may be partially dependent on the NO pathway. By RT-PCR, a type III constitutive NOS mRNA was detected in U937 monocytic cells. IL-4 also increased the [Ca(2+)](i) in these cells. Different NOS may thus be expressed in monocytic cells depending on their differentiation and the signals they receive.

Role of cyclic nucleotides and nitric oxide in blood mononuclear cell IgE production stimulated by IL-4.

The involvement of cyclic nucleotides and of phosphodiesterase activities in IL-4-induced IgE production and release of the soluble form of the low affinity receptor for IgE (sCD23) by normal human peripheral blood mononuclear cells (PBMC) was evaluated. PBMC were stimulated by a suboptimal dose of IL-4 (10 ng/ml) cAMP inducers, adrenaline (ADR) and cholera toxin (CTx), which were found to potentiate IL-4-induced IgE production and sCD23 release after 12 days of culture. In the presence of an optimal dose of IL-4 (30 ng/ml), both ADR and CTx inhibited the production of both IgE and sCD23. In the presence of a chemical cGMP inducer, Sin-1, the production of IgE induced by 10 ng/ml IL-4 appeared to be potentiated whereas in the same experimental situation the sCD23 production was decreased. Sin-1 was found to inhibit the production of both IgE and sCD23 as effectively as cAMP inducers when an optimal dose of IL-4 was used. Since Sin-1 is a nitric oxide (NO) generating compound, we evaluated the possible involvement of the L-arginine metabolic pathway using a competitive inhibitor of L-arginine, NG-monomethyl-L-arginine (LNMMA). In the presence of 1 mM LNMMA both IgE and sCD23 production induced by either a sub-optimal or an optimal dose were partially inhibited (from 50 to 80% inhibition depending on the donor). The generation of cAMP and cGMP in the cells is controlled by cyclic nucleotide phosphodiesterases (CN-PDE), so we evaluated the effect of a CN-PDE inhibitor, isobutyl-methyl xanthine (IBMX), on the IL-4-induced IgE and sCD23 production.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation by interleukin-4 of cytokine release from mononuclear phagocytes in asthma.

BACKGROUND: Interleukin (IL)-4 is involved in IgE upregulation and downregulates cytokine release by mononuclear phagocytes. Mononuclear cells release greater amounts of IL-1, tumor necrosis factor-alpha, and IL-6 in patients with asthma than in control subjects, but the effect of IL-4 on cells from patients with asthma is unknown. The effects of IL-4 on the release of IL-1, tumor necrosis factor-alpha, and IL-6 by monocytes and alveolar macrophages were compared in 19 patients with asthma and 18 control subjects. METHODS: The release of IL-1, tumor necrosis factor-alpha, and IL-6 from unstimulated and lipopolysaccharide stimulated monocytes and alveolar macrophages was measured by ELISA. The effect of 30 U of IL-4 on the release of these cytokines was studied. RESULTS: Lipopolysaccharide-stimulated monocytes released significantly fewer cytokines in patients with asthma than in control subjects. IL-4 significantly inhibited cytokine release by monocytes of both groups. Unstimulated alveolar macrophages from patients with asthma released more cytokines than those of control subjects. Lipopolysaccharide induced a significantly greater increase in cytokine release in alveolar macrophages of control subjects in comparison with asthmatic subjects. IL-4 abolished the release of cytokines in alveolar macrophages from control subjects and had a minimal inhibitory effect on alveolar macrophages from patients with asthma. CONCLUSIONS: Alveolar macrophages from patients with asthma are hyperreactive but less prone to lipopolysaccharide stimulation and IL-4-downregulation than those from normal subjects.

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.

[Role of interleukin-4 in the regulation of nitric oxide production by normal human monocytes]. / Rôle de l'interleukine-4 dans la régulation de la production de monoxyde d'azote (NO) par les monocytes humains normaux.

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.

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.

Phenotypic and functional modulation of normal human alveolar macrophages by histamine.

Alveolar macrophages (AM) play a regulatory role in asthma. AM from asthmatics are activated, release increased amounts of cytokines, and express higher levels of the low affinity receptor for IgE (Fc epsilon RIIb/CD23b) and receptors for adhesion molecules. The bronchial microenvironment may modulate the phenotypic and functional characteristics of AM. On AM from normal subjects, the effects of histamine were studied on the expression of adhesion molecules (LFA-1, ICAM-1) and CD23b as well as on the release of fibronectin. The expression of LFA-1, ICAM-1, and CD23b was examined by immunocytochemistry using the alkaline phosphatase-anti-alkaline phosphatase technique. The expression of CD23b mRNA was studied by in situ hybridization. The release of fibronectin was measured by enzyme immunoassay. We found that histamine induced in a dose- and time-dependent fashion a significant increase of AM expressing the three membrane markers and a significant increase in the release of fibronectin. The maximum effect of histamine was observed after an incubation of 12 to 24 h and a dose of 1 microM. The histamine effects were specific, since they were significantly inhibited by an H1-blocker, pyrilamine, used at a concentration of 10 microM. The effect of an H2-blocker (ranitidine, concentration of 10 microM) was inconstant. Cycloheximide blocked the histamine effects, suggesting that it requires protein synthesis for its action. This study provides an in vitro model of cellular interaction between mast cells and AM, which might be relevant in the airway inflammation in asthma.

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.

Involvement of cyclic AMP and nitric oxide in immunoglobulin E-dependent activation of Fc epsilon RII/CD23+ normal human keratinocytes.

Epidermal keratinocytes (EK) are exposed to multiple inflammatory stimuli and paracrine factors secreted by various dermal cells (lymphocytes, mast cells, macrophages, fibroblasts) during wounding, cutaneous allergy, and infections. We have previously demonstrated that after stimulation with interleukin 4 or interferon-gamma, human EK express the low-affinity receptor for IgE (Fc epsilon RII/CD23) on their surface. In the present study, we showed that the ligation of CD23 by IgE/anti-IgE immune complexes or specific monoclonal antibody induces a dose-dependent release of interleukin 6 and tumor necrosis factor-alpha from EK. CD23-ligation activates the nitric oxide-dependent pathway, as demonstrated by the high levels of nitrites released in cell supernatants, and the accumulation of intracellular cyclic nucleotides in EK. These second messengers are required for IgE-dependent stimulation of cytokine production by these cells, inasmuch as this is completely abolished by the use of cAMP or nitric oxide synthase antagonists. Human epithelial keratinocytes may thus participate in IgE-mediated immune responses, through their ability to express functional CD23 antigen.

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.

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 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.

[Physiopathological role of low affinity IgE receptor (CD23) in hematopoietic cells]. / Rôle physiopathologique du récepteur de basse affinité des IgE (CD23) dans les cellules hématopoïétiques.

Ligation of the low affinity IgE receptor by specific monoclonal antibodies or multivalent IgE complexes result in the transduction of signals which differ according to the CD23 isotype expressed by the various cell types. In B lymphocytes, it elicits the early activation of phospholipase C through a mechanism involving a G-protein insensitive to Pertussis toxin, followed by a late phase of cAMP accumulation. In monocytes, which express the CD23b isoform, ligation of CD23 was also found to induce a delayed accumulation of cAMP, that was largely dependent on a prior cGMP increase through a mechanism involving the activation of a NO synthase. This pathway, which appears to be exacerbated in allergic diseases, seems to play an important role in the differentiation of cells of the monocytic lineage, their capacity to release proinflammatory mediators and their cytotoxic functions.

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.